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Dopamine and neurodegeneration

(140 References)

(2002). "Dopamine transporter brain imaging to assess the effects of pramipexole vs levodopa on Parkinson disease progression." Jama 287(13): 1653-61.

            CONTEXT: Pramipexole and levodopa are effective medications to treat motor symptoms of early Parkinson disease (PD). In vitro and animal studies suggest that pramipexole may protect and that levodopa may either protect or damage dopamine neurons. Neuroimaging offers the potential of an objective biomarker of dopamine neuron degeneration in PD patients. OBJECTIVE: To compare rates of dopamine neuron degeneration after initial treatment with pramipexole or levodopa in early PD by means of dopamine transporter imaging using single-photon emission computed tomography (SPECT) with 2beta-carboxymethoxy-3beta(4-iodophenyl)tropane (beta-CIT) labeled with iodine 123. DESIGN: Substudy of a parallel-group, double-blind randomized clinical trial. SETTING AND PATIENTS: Eighty-two patients with early PD who were recruited at 17 clinical sites in the United States and Canada and required dopaminergic therapy to treat emerging disability, enrolled between November 1996 and August 1997. INTERVENTIONS: Patients were randomly assigned to receive pramipexole, 0.5 mg 3 times per day with levodopa placebo (n = 42), or carbidopa/levodopa, 25/100 mg 3 times per day with pramipexole placebo (n = 40). For patients with residual disability, the dosage was escalated during the first 10 weeks, and subsequently, open-label levodopa could be added. After 24 months of follow-up, the dosage of study drug could be further modified. MAIN OUTCOME MEASURES: The primary outcome variable was the percentage change from baseline in striatal [(123)I]beta-CIT uptake after 46 months. The percentage changes and absolute changes in striatal, putamen, and caudate [(123)I]beta-CIT uptake after 22 and 34 months were also assessed. Clinical severity of PD was assessed using the Unified Parkinson Disease Rating Scale (UPDRS) 12 hours off anti-PD medications. RESULTS: Sequential SPECT imaging showed a decline in mean (SD) [(123)I]beta-CIT striatal uptake from baseline of 10.3% (9.8%) at 22 months, 15.3% (12.8%) at 34 months, and 20.7% (14.4%) at 46 months-approximately 5.2% per year. The mean (SD) percentage loss in striatal [(123)I]beta-CIT uptake from baseline was significantly reduced in the pramipexole group compared with the levodopa group: 7.1% (9.0%) vs 13.5% (9.6%) at 22 months (P =.004); 10.9% (11.8%) vs 19.6% (12.4%) at 34 months (P =.009); and 16.0% (13.3%) vs 25.5% (14.1%) at 46 months (P =.01). The percentage loss from baseline in striatal [(123)I]beta-CIT uptake was correlated with the change from baseline in UPDRS at the 46-month evaluation (r = - 0.40; P =.001). CONCLUSIONS: Patients initially treated with pramipexole demonstrated a reduction in loss of striatal [(123)I]beta-CIT uptake, a marker of dopamine neuron degeneration, compared with those initially treated with levodopa, during a 46-month period. These imaging data highlight the need to further compare imaging and clinical end points of PD progression in long-term studies.

 

Ahn, Y. H., M. Emgard, et al. (2003). "Ultrastructural characterization of dissociated embryonic ventral mesencephalic tissue treated with neuroprotectants." Cell Transplant 12(3): 235-41.

            Poor survival and differentiation of grafted dopamine neurons limits the application of clinical transplantation in Parkinson's disease. The survival of grafted dopamine neurons is only improved by a factor of 2-3 by adding neuroprotectants during tissue preparation. We used dye exclusion cell viability and electron microscopy to investigate the effects of the caspase inhibitor ac-YVAD-cmk and the lazaroid tirilazad mesylate on ultrastructural changes in dissociated embryonic mesencephalic cells. In addition, we examined whether the neuroprotectants selectively counteracted specific signs of neurodegeneration. Cell viability decreased significantly over time in both control and treated cell suspensions, but the number of viable cells remaining was significantly higher in tirilazad mesylate-treated cell suspensions. In control samples, the proportion of cells with an ultrastructure consistent with healthy cells decreased from 70%, immediately after dissociation, to 30% after 8 h of incubation. Similar changes were also observed in cell suspensions treated with neuroprotectants. Thus, the neuroprotectants examined did not block the development of specific morphological signs of neurodegeneration. However, when also taking into account that dead cells lysed and disappeared from each cell suspension with time, we found that the total number of remaining viable cells with healthy nuclear chromatin or intact membrane integrity was significantly higher in the tirilazad mesylate-treated group. The results indicate that tirilazad mesylate protects only a small subpopulation of embryonic mesencephalic cells from degeneration induced by mechanical trauma during tissue dissection and dissociation.

 

Akerud, P., P. C. Holm, et al. (2002). "Persephin-overexpressing neural stem cells regulate the function of nigral dopaminergic neurons and prevent their degeneration in a model of Parkinson's disease." Mol Cell Neurosci 21(2): 205-22.

            Persephin (PSP) is a neurotrophic factor of the GDNF family that has been found to promote the survival of multiple populations of neurons. In the present study we have examined: (1) the mechanism of action and the function of PSP on nigrostriatal dopamine neurons and (2) the therapeutic potential of PSP, delivered by neural stem cells (NSCs) in a model of Parkinson's disease. Interestingly we found that the prenatal ventral mesencephalon and the newborn striatum express high levels of PSP mRNA. Moreover, midbrain dopamine neurons express its preferred receptor GFRalpha4, allowing a cis type of action of PSP on dopamine neurons. Primary culture studies showed that PSP is as potent and efficacious as GDNF at promoting both survival and neuritogenesis of midbrain dopamine neurons. To study the function and therapeutic potential of PSP in vivo we engineered NSCs to overexpress PSP. PSP-c17.2 cells were found to stably express PSP mRNA and protein for at least 3 months in vivo, to disperse within the striatum, and to give rise to neurons, astrocytes, and a large proportion of oligodendrocytes that integrated within white matter tracts in the striatum. Moreover, PSP-c17.2 cells enhanced dopamine-dependent behavioral parameters in unlesioned mice and prevented the loss of dopamine neurons and the behavioral impairment of mice receiving intrastriatal 6-OHDA injections. Thus, our findings are consistent with a direct action of PSP on developing and adult midbrain dopamine neurons and suggest that the delivery of PSP by NSCs may constitute a very useful strategy in the treatment of Parkinson's disease.

 

Antonelli, T., M. C. Tomasini, et al. (2002). "Neurotensin enhances glutamate excitotoxicity in mesencephalic neurons in primary culture." J Neurosci Res 70(6): 766-73.

            The tridecapeptide neurotensin has been demonstrated to increase glutamate release in discrete rat brain regions, leading to the hypothesis of a possible involvement of the peptide in neurodegenerative pathologies. The role of neurotensin in modulating glutamate excitotoxicity and the possible neuroprotective action of the neurotensin receptor antagonist SR48692 were investigated in primary cultures of mesencephalic neurons by measuring [(3)H]dopamine uptake and tyrosine hydroxylase immunocytochemistry 24 hr after glutamate treatment. The exposure to glutamate (30 and 100 microM, 10 min) decreased [(3)H]dopamine uptake into mesencephalic neurons. Neurotensin (10 and 100 nM), added before glutamate (30 microM) exposure, significantly enhanced the glutamate-induced reduction of [(3)H]dopamine uptake. In addition, the peptide (10 nM) also significantly enhanced the effect of 100 microM glutamate. The effects of neurotensin were counteracted by the neurotensin receptor antagonist SR48692 (100 nM) and by the protein kinase C inhibitor calphostin C. The exposure to 100 microM, but not 30 microM, glutamate significantly reduced the number of tyrosine hydroxylase-immunoreactive cells, and neurotensin (10 nM) significantly enhanced this effect. SR48692 (100 nM) prevented the neurotensin-induced action. These findings support the view of a possible pathophysiological role of neurotensin in mesencephalic dopamine neuronal function. Furthermore, selective neurotensin antagonists in combination with conventional drug treatments could provide a novel therapeutic approach for the treatment of neurodegenerative disorders, such as Parkinson's disease.

 

Arimoto, T. and G. Bing (2003). "Up-regulation of inducible nitric oxide synthase in the substantia nigra by lipopolysaccharide causes microglial activation and neurodegeneration." Neurobiol Dis 12(1): 35-45.

            The present study was designed to examine whether expression of iNOS was involved in LPS-induced neurodegeneration in rat substantia nigra (SN) and to study the role of NO in the loss of the SN dopaminergic neurons. In Western blot analysis, iNOS was induced in the SN after injection of LPS in a time- and dose-dependent manner. Immunofluorescence and immunohistochemical analyses revealed that the iNOS is located in a fully activated microglia with the characteristic amoeboid morphology. Furthermore, LPS-induced loss of dopaminergic neurons was significantly inhibited by the administration of L-N(G)-nitroarginine, a selective inhibitor of NOS, and the glucocorticoid dexamethasone. These inhibiting agents for iNOS reduced LPS-induced microglial activation, suggesting that NO has a role in inflammatory-mediated microglial activation. These results demonstrate that LPS induces the expression of iNOS in activated microglia in the SN, and that NO and/or its metabolites may play a crucial role in inflammation-mediated degeneration of dopaminergic neurons.

 

Auluck, P. K., H. Y. Chan, et al. (2002). "Chaperone suppression of alpha-synuclein toxicity in a Drosophila model for Parkinson's disease." Science 295(5556): 865-8.

            Parkinson's disease is a movement disorder characterized by degeneration of dopaminergic neurons in the substantia nigra pars compacta. Dopaminergic neuronal loss also occurs in Drosophila melanogaster upon directed expression of alpha-synuclein, a protein implicated in the pathogenesis of Parkinson's disease and a major component of proteinaceous Lewy bodies. We report that directed expression of the molecular chaperone Hsp70 prevented dopaminergic neuronal loss associated with alpha-synuclein in Drosophila and that interference with endogenous chaperone activity accelerated alpha-synuclein toxicity. Furthermore, Lewy bodies in human postmortem tissue immunostained for molecular chaperones, also suggesting that chaperones may play a role in Parkinson's disease progression.

 

Bernert, G., H. Hoeger, et al. (2003). "Neurodegeneration, Neuronal Loss, and Neurotransmitter Changes in the Adult Guinea Pig with Perinatal Asphyxia." Pediatr Res.

            There is only limited morphologic information on long-term alterations and neurotransmitter changes after perinatal asphyxia, and no long-term study showing neurodegeneration has been reported so far. We used an animal model for perinatal asphyxia well documented in the rat to investigate the guinea pig as a species highly mature at birth. Cesarean section was performed on full-term pregnant guinea pigs, and pups, still in membranes, were placed into a water bath at 37 degrees C for asphyxia periods from 2 to 4 min. Thereafter pups were given to surrogate mothers and examined at 3 mo of age. We studied brain areas reported to be hypoxia-sensitive. Neurodegeneration was evaluated by fluoro-jade, neuronal loss by Nissl, reactive gliosis by glial fibrillary acidic protein staining, and differentiation by neuroendocrine-specific protein C immunoreactivity. We tested tyrosine hydroxylase, the vesicular monoamine transporter, and dopamine beta-hydroxylase, representing the monoaminergic system; the vesicular acetylcholine transporter; and the excitatory amino acid carrier 1. Neurodegeneration was evident in cerebellum, hippocampal area CA1, and hypothalamus, and neuronal loss could be observed in cerebellum and hypothalamus; gliosis was observed in cerebellum, hippocampus, hypothalamus, and parietal cortex; dedifferentiation was found in hypothalamus and striatum; and monoaminergic, cholinergic, and amino acidergic deficits were shown in several brain regions. The major finding of the present study was that neurodegeneration and dedifferentiation evolved in the guinea pig, a species highly mature at birth. The relevance of this contribution is that a simple animal model of perinatal asphyxia resembling the clinical situation of intrauterine hypoxia-ischemia and presenting with neurodegeneration was characterized.

 

Bozzi, Y. and E. Borrelli (2002). "Dopamine D2 receptor signaling controls neuronal cell death induced by muscarinic and glutamatergic drugs." Mol Cell Neurosci 19(2): 263-71.

            Dopamine (DA), through D1/D2 receptor-mediated signaling, plays a major role in the control of epileptic seizures arising in the limbic system. Excitotoxicity leading to neuronal cell death in the affected areas is a major consequence of seizures at the cellular level. In this respect, little is known about the role of DA receptors in the occurrence of epilepsy-induced neuronal cell death. Here we analyze the occurrence of seizures and neurotoxicity in D2R -/- mice treated with the cholinergic agonist pilocarpine. We compared these results with those previously obtained with kainic acid (KA), a potent glutamate agonist. Importantly, D2R -/- mice develop seizures at doses of both drugs that are not epileptogenic for WT littermates and show greater neurotoxicity. However, pilocarpine-induced seizures result in a more widespread neuronal death in both WT and D2R -/- brains in comparison to KA. Thus, the absence of D2R lowers the threshold for seizures induced by both glutamate and acetylcholine. Moreover, the dopaminergic control of epilepsy-induced neurodegeneration seems to be mediated by distinct interactions of D2R signaling with these two neurotransmitters.

 

Callier, S., M. Le Saux, et al. (2002). "Evaluation of the protective effect of oestradiol against toxicity induced by 6-hydroxydopamine and 1-methyl-4-phenylpyridinium ion (Mpp+) towards dopaminergic mesencephalic neurones in primary culture." J Neurochem 80(2): 307-16.

            Recent findings suggest that gonadal steroid hormones are neuroprotective and may provide clinical benefits in delaying the development of Parkinson's disease. In this report we investigated the ability of oestradiol to protect mesencephalic dopaminergic neurones cultured in serum-free or serum-supplemented medium from toxicity induced by 6-hydroxydopamine or 1-methyl-4-phenylpyridinium ion (MPP+). The efficiency of both toxins and oestradiol was evaluated by tyrosine hydroxylase (TH) immunocytochemistry, [3H]dopamine ([3H]DA) uptake, length of dopaminergic processes and lactate dehydrogenase (LDH) release measurement. In cultures grown in serum-supplemented medium, a 2-h pre-treatment with high concentrations (10-100 microM) of 17beta-oestradiol or 17alpha-oestradiol, the stereoisomer with weak oestrogenic activity, protected both dopaminergic and non-dopaminergic neurones from toxicity induced by 6-hydroxydopamine (6-OHDA; 40 or 100 microM) and by the high MPP+ concentrations (50 microM) necessary to obtain significant neuronal death under those culture conditions. At these concentrations, MPP+ was no longer selective for dopaminergic neurones but affected all cells present in the culture. In contrast, the hormonal treatments did not protect against selective degeneration of dopaminergic neurones induced by lower MPP+ concentrations (below 10 microM), related to inhibition of complex I of respiratory chain. In cultures grown in serum-free medium, oestradiol concentrations higher than 1 microM induced neuronal degeneration and no protection against 6-OHDA or MPP+ toxicity was observed at lower concentrations of the steroid. The neuroprotective effects of 17alpha- or 17beta-oestradiol evidenced in this model might be due to the antioxidant properties of these compounds. However, other non-genomic effects of the steroids cannot be excluded.

 

Cantuti-Castelvetri, I., B. Shukitt-Hale, et al. (2003). "Dopamine neurotoxicity: age-dependent behavioral and histological effects." Neurobiol Aging 24(5): 697-706.

            The oxidative stress (OS) theory has implicated the involvement of reactive oxygen species (ROS) in both aging and age-dependent neurodegenerative diseases. The dopaminergic system is particularly vulnerable to ROS, and dopamine (DA) itself can be an endogenous source of ROS. The present study evaluated the hypothesis that DA-induced toxicity is age-dependent, and tested the behavioral and histological correlates of DA neurotoxicity in aging. Young (6 months) and middle-aged (15 months) rats were chronically treated with DA in the substantia nigra (SN, 1micromol/2microlvehicleperside/day/5 days) and were subsequently examined for changes in motor function and histology. The neurotoxic effect of DA treatment was an age-dependent effect, as middle-aged animals that received DA infusions in the SN were more impaired than their age-matched controls, especially on tasks that involved greater sensory-motor coordination, whereas young animals that received DA behaved similarly to their age-matched controls. The behavioral effects noted were accompanied by a loss of the tyrosine hydroxylase phenotype in substantia nigra. However, selective neurodegeneration was not noted in the SN of the treated animals, nor was a selective iron deposition noted at the site of injection. These results suggest that a neurochemical deficit and not cell loss per se within the nigrostriatal system underlies the motor behavioral deficits observed in the middle-aged rats.

 

Castano, A., A. J. Herrera, et al. (2002). "The degenerative effect of a single intranigral injection of LPS on the dopaminergic system is prevented by dexamethasone, and not mimicked by rh-TNF-alpha, IL-1beta and IFN-gamma." J Neurochem 81(1): 150-7.

            It is becoming widely accepted that the inflammatory response is involved in neurodegenerative disease. In this context, we have developed an animal model of dopaminergic system degeneration by the intranigral injection of lipopolysaccharide (LPS), a potent inductor of inflammation. To address the importance of the inflammatory response in the LPS-induced degeneration of nigral dopaminergic neurones, we carried out two different kinds of studies: (i) the possible protective effect of an anti-inflammatory compound, and (ii) the effect of the intranigral injection of inflammatory cytokines (TNF-alpha, IL-1beta and IFN-gamma) on dopaminergic neurones viability. Present results show that dexamethasone, a potent anti-inflammatory drug that interferes with many of the features characterizing pro-inflammatory glial activation, prevented the loss of catecholamine content, Tyrosine hydroxylase (TH) activity and TH immunostaining induced by LPS-injection and also the bulk activation of microglia/macrophages. Surprisingly, injection of the pro-inflammatory cytokines failed to reproduce the LPS effect. Taken together, our results suggest that inflammatory response is implicated in LPS-induced neurodegeneration. This damage may be due, at least in part, to a cascade of events independent of that described for TNF-alpha/IL-1 beta/IFN-gamma.

 

Chen, J., C. Wersinger, et al. (2003). "Chronic stimulation of D1 dopamine receptors in human SK-N-MC neuroblastoma cells induces nitric-oxide synthase activation and cytotoxicity." J Biol Chem 278(30): 28089-100.

            Elevated synaptic levels of dopamine may induce striatal neurodegeneration in l-DOPA-unresponsive parkinsonism subtype of multiple system atrophy (MSA-P subtype), multiple system atrophy, and methamphetamine addiction. We examined the participation of dopamine and D1 dopamine receptors in the genesis of postsynaptic neurodegeneration. Chronic treatment of human SK-N-MC neuroblastoma cells with dopamine or H2O2 increased NO production and accelerated cytotoxicity, as indexed by enhanced nitrite levels and cell death. The antioxidant sodium metabisulfite or SCH 23390, a D1 dopamine receptor-selective antagonist, partially blocked dopamine effects but together ablated dopamine-mediated cytotoxicity, indicating the participation of both autoxidation and D1 receptor stimulation. Direct activation of D1 dopamine receptors with SKF R-38393 caused cytotoxicity, which was refractory to sodium metabisulfite. Dopamine and SKF R-38393 induced overexpression of the nitric-oxide synthase (NOS) isoforms neuronal NOS, inducible NOS (iNOS), and endothelial NOS in a protein kinase A-dependent manner. Functional studies showed that approximately 60% of total NOS activity was due to activation of iNOS. The NOS inhibitor N(G)-nitro-l-arginine methyl ester and genistein, wortmannin, or NF-kappaB SN50, inhibitors of protein tyrosine kinases phosphatidylinositol 3-kinase and NF-kappaB, respectively, reduced nitrite production by dopamine and SKF R-38393 but were less effective in attenuating H2O2-mediated effects. In rat striatal neurons, dopamine and SKF R-38393, but not H2O2, accelerated cell death through increased expression of neuronal NOS and iNOS but not endothelial NOS. These data demonstrate a novel pathway of dopamine-mediated postsynaptic oxidative stress and cell death through direct activation of NOS enzymes by D1 dopamine receptors and its associated signaling pathways.

 

Chen, S. T., J. I. Chuang, et al. (2002). "Melatonin attenuates MPP+-induced neurodegeneration and glutathione impairment in the nigrostriatal dopaminergic pathway." J Pineal Res 32(4): 262-9.

            In this study we selected a rat model of Parkinson's disease (PD) by using intrastriatal infusion of the 1-methyl-4-phenyl-pyridinium ion (MPP+) to investigate the neuroprotective action of melatonin and its inhibitory activity on MPP+-impaired glutathione (GSH) system in the nigrostriatal system. Results show that MPP+ caused not only a severe neuronal injury in the striatum and in the ipsilateral substantia nigra (SN), but it also induced a significant decrease in GSH levels and an increase in the GSSG/GSH ratio 3 days after intrastriatal MPP+ infusion. Intraperitoneal co-administration of melatonin (10 mg/kg, five times) significantly attenuated MPP+-induced nigrostriatal neurotoxicity and GSH impairment. Depletion of cytosolic GSH by L-buthionine sulfoximine (BSO) did not cause neuronal damage by itself. It, however, when co-administrated with MPP+, potentiated the GSH reduction in the striatum, without aggravating nigrostriatal neurodegeneration induced by MPP+. Moreover, the MPP+-caused neuronal damage was positively correlated with a rising ratio of GSSG/GSH, but not with a drop of GSH. These results suggest that the MPP+-triggered oxidative stress may play a more important role than the loss of the antioxidant GSH in determining neuronal injury. Interestingly, the neuronal damage and oxidative stress elicited by co-treatment of BSO with MPP+ were effectively reduced by melatonin. Our results hence provide direct evidence showing that melatonin attenuates MPP+-induced nigrostriatal dopaminergic injury by its ability to impede the increase of GSSG/GSH ratio; therefore melatonin may have therapeutic implications in PD.

 

Choi, H. J., S. W. Kim, et al. (2003). "Dopamine-dependent cytotoxicity of tetrahydrobiopterin: a possible mechanism for selective neurodegeneration in Parkinson's disease." J Neurochem 86(1): 143-52.

            Parkinson's disease is a neurodegenerative disorder associated with selective loss of dopaminergic neurons in the substantia nigra. While the underlying cause of this cell death is poorly understood, oxidative stress is thought to play a role. We have previously shown that tetrahydrobiopterin (BH4), an obligatory co-factor for tyrosine hydroxylase (TH), exerts selective toxicity on dopamine-producing cells and that this is prevented by antioxidants. This study shows that BH4-induced dopaminergic cell death is primarily mediated by dopamine, evidenced by findings that (i) BH4 toxicity is increased in proportion to cellular dopamine content; (ii) non-dopaminergic cells become susceptible to BH4 upon exposure to dopamine; and (iii) depletion of dopamine attenuates BH4 toxicity in dopamine-producing cells. BH4 causes lipid peroxidation, suggesting involvement of oxidative stress but the toxicity does not require enzymatic oxidation of dopamine. Instead, it seems to involve formation of quinone product(s) because (i) the cell death is attenuated by exposure to or induction of quinone reductase and (ii) BH4-treated cells show increased formation of protein-bound quinones, which is inhibited by thiol antioxidants. These data taken together suggest that the presence of both BH4 and dopamine is important in rendering dopaminergic cells vulnerable and that this involves formation of reactive dopamine quinone products.

 

Cossu, G., M. Melis, et al. (2002). "Hallervorden Spatz syndrome (pantothenate kinase associated neurodegeneration) in two Sardinian brother with homozygous mutation in PANK 2 gene." J Neurol 249(11): 1599-600.

           

Crocker, S. J., P. Liston, et al. (2003). "Attenuation of MPTP-induced neurotoxicity and behavioural impairment in NSE-XIAP transgenic mice." Neurobiol Dis 12(2): 150-61.

            X-linked IAP protein is a potent inhibitor of cell death. Here, we describe a novel transgenic mouse in which the human XIAP gene is expressed under the control of the neuron-specific enolase promoter (NSE-xiap). We demonstrate that nigrostriatal dopamine neurons of NSE-xiap mice were resistant to the damaging effects of the dopaminergic neurotoxin MPTP. MPTP-induced reduction of striatal dopamine metabolism was also attenuated in NSE-xiap mice. Furthermore, NSE-xiap mice treated with MPTP did not exhibit deficits in exploratory behaviour in an open-field test. Taken together, these findings suggest that strategies to enhance neuronal expression of XIAP may provide therapeutic benefit for the treatment of neurodegeneration in Parkinson's disease.

 

Dauer, W., N. Kholodilov, et al. (2002). "Resistance of alpha -synuclein null mice to the parkinsonian neurotoxin MPTP." Proc Natl Acad Sci U S A 99(22): 14524-9.

            Parkinson's disease (PD) is most commonly a sporadic illness, and is characterized by degeneration of substantia nigra dopamine (DA) neurons and abnormal cytoplasmic aggregates of alpha-synuclein. Rarely, PD may be caused by missense mutations in alpha-synuclein. MPTP, a neurotoxin that inhibits mitochondrial complex I, is a prototype for an environmental cause of PD because it produces a pattern of DA neurodegeneration that closely resembles the neuropathology of PD. Here we show that alpha-synuclein null mice display striking resistance to MPTP-induced degeneration of DA neurons and DA release, and this resistance appears to result from an inability of the toxin to inhibit complex I. Contrary to predictions from in vitro data, this resistance is not due to abnormalities of the DA transporter, which appears to function normally in alpha-synuclein null mice. Our results suggest that some genetic and environmental factors that increase susceptibility to PD may interact with a common molecular pathway, and represent the first demonstration that normal alpha-synuclein function may be important to DA neuron viability.

 

DeGiorgio, L. A., Y. Shimizu, et al. (2002). "APP knockout attenuates microglial activation and enhances neuron survival in substantia nigra compacta after axotomy." Glia 38(2): 174-8.

            Focal microglial activation and progressive dopaminergic neurodegeneration in substantia nigra compacta (SNc) have characterized Parkinson's disease (PD). We have hypothesized that the microglial response may be provoked by molecular signals from chronically stressed SNc neurons. To test whether amyloid precursor protein (APP) could serve as such a signal, we evaluated microglial activation in SN after unilateral transection of the medial forebrain bundle (MFB) in mice either wild-type (WT) or null (KO) for APP. WT and KO mice displayed comparable microglial response at the MFB transection site. In WT mice microglial activation was first apparent in the ipsilateral SN at 3 days postlesion (dpl), marked by morphological change and increased isolectin immunoreactivity. The microglial response intensified at 7 dpl and persisted in the medial nigra through 14 dpl. In contrast, in KO mice activated microglia appeared predominantly at 7 dpl, with little activation at 3 dpl and none at 14 dpl. Neuron number in affected WT SNc at 14 dpl was significantly reduced compared with loss in affected KO SNc. The delayed and limited local microglial activation and increased neuron survival in response to distal axotomy of SNc neurons in APP KO mice are consistent with the important role APP in neuronal stress responses in vivo.

 

Delgado, M. and D. Ganea (2003). "Neuroprotective effect of vasoactive intestinal peptide (VIP) in a mouse model of Parkinson's disease by blocking microglial activation." Faseb J 17(8): 944-6.

            Parkinson's disease (PD) is a common neurodegenerative disorder with no effective protective treatment, characterized by a massive degeneration of dopaminergic neurons in the substantia nigra (SNpc) and the subsequent loss of their projecting nerve fibers in the striatum. To elucidate PD pathogenic factors, and thus to develop therapeutic strategies, a murine PD model based on the administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been used extensively. It has been demonstrated that activated microglia cells actively participate in the pathogenesis of MPTP-induced PD through the release of cytotoxic factors. Because current treatments for PD are not effective, considerable research focused lately on a number of regulatory molecules termed microglia-deactivating factors. Vasoactive intestinal peptide (VIP), a neuropeptide with a potent anti-inflammatory effect, has been found to be protective in several inflammatory disorders. This study investigates the putative protective effect of VIP in the MPTP model for PD. VIP treatment significantly decreases MPTP-induced dopaminergic neuronal loss in SNpc and nigrostriatal nerve-fiber loss. VIP prevents MPTP-induced activation of microglia in SNpc and striatum and the expression of the cytotoxic mediators, iNOS, interleukin 1beta, and numor necrosis factor alpha. VIP emerges as a potential valuable neuroprotective agent for the treatment of pathologic conditions in the central nervous system, such as PD, where inflammation-induced neurodegeneration occurs.

 

Di Monte, D. A., M. Lavasani, et al. (2002). "Environmental factors in Parkinson's disease." Neurotoxicology 23(4-5): 487-502.

            Evidence discussed in this review article lends strong support in favor of an etiologic role of environmentalfactors in Parkinson's disease. First, thanks to the discovery of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), it is now clear that, by targeting the nigrostriatal system, neurotoxicants can reproduce the neurochemical and pathological features of idiopathic parkinsonism. The sequence of toxic events triggered by MPTP has also provided us with intriguing clues concerning mechanisms of toxicant selectivity and nigrostriatal vulnerability. Relevant examples are (i) the role of the plasma membrane dopamine transporter in facilitating the access of potentially toxic species into dopaminergic neurons; (ii) the vulnerability of the nigrostriatal system to failure of mitochondrial energy metabolism; and (iii) the contribution of inflammatory processes to tissue lesioning. Epidemiological and experimental data suggest the potential involvement of specific agents as neurotoxicants (e.g. pesticides) or neuroprotective compounds (e.g. tobacco products) in the pathogenesis of nigrostriatal degeneration, further supporting a relationship between the environment and Parkinson's disease. A likely scenario that emerges from our current knowledge is that neurodegeneration results from multiple events and interactive mechanisms. These may include (i) the synergistic action of endogenous and exogenous toxins (e.g. the ability of the pesticide diethyldithiocarbamate to promote the toxicity of other compounds); (ii) the interactions of toxic agents with endogenous elements (e.g. the protein alpha-synuclein); (iii) the tissue response to an initial toxic insult; and, last but not least, (iv) the effects of environmental factors on the background of genetic predisposition and aging.

 

Diaz, M. R., P. Barroso-Chinea, et al. (2003). "Effects of dopaminergic cell degeneration on electrophysiological characteristics and GAD65/GAD67 expression in the substantia nigra: different action on GABA cell subpopulations." Mov Disord 18(3): 254-66.

            The motor disturbances occurring in Parkinson's disease have been partially attributed to a hyperactivity of gamma-aminobutyric acid (GABA)-ergic nigral cells largely in the substantia nigra pars reticulata (SNr) secondary to the degeneration of dopaminergic nigrostriatal neurons. However, some aspects of this response remain unclear. In this work, different electrophysiological and neurochemical parameters were studied in GABAergic cells of the SN after unilateral nigrostriatal dopaminergic lesion using 6-hydroxydopamine injection in rats. Our data showed that 1) the SN under normal conditions contains different subsets of GABAergic cells according to their firing pattern and glutamic acid decarboxylase mRNA levels, and 2) the response of these GABAergic cell subgroups was different after the ipsi- and contralateral dopaminergic cell degeneration. These findings indicate a complex regulation of nigral GABAergic activity after nigrostriatal dopaminergic degeneration that probably involves local mechanisms, the nigro-striato-nigral loop, as well as interhemispheric mechanisms whose anatomical basis remains unstudied.

 

Dluzen, D. E., C. Tweed, et al. (2003). "Gender differences in methamphetamine-induced mRNA associated with neurodegeneration in the mouse nigrostriatal dopaminergic system." Neuroendocrinology 77(4): 232-8.

            In this report female and male CD-1 mice were treated with a neurotoxic regimen of methamphetamine (MA) to compare gender differences in striatal dopamine depletion and concordant changes in mRNA markers of the transforming growth factor-beta injury response associated with neurodegeneration. Striatal dopamine concentrations of MA-treated female mice were less depleted and significantly greater than that of identically treated males. Associated with this gender difference in striatal dopamine depletion were significantly decreased mRNA levels of plasminogen activator inhibitor-1 and a trend for increased (p = 0.06) mRNA levels of glial fibrillary acidic protein within females. No statistically significant differences between MA-treated female and male mice were obtained in mRNA levels for transforming growth factor-beta, transforming growth factor-beta type 2 receptor, activin-like kinase-5 or fibronectin. These data demonstrate the presence of changes in two specific molecular markers of the transforming growth factor-beta injury response which are in accordance with gender differences in MA-induced striatal dopamine depletion. The results suggest that the neuroprotective advantage displayed by females may in part be related to reductions in the transforming growth factor-beta injury response as indicated by decreased mRNA plasminogen activator inhibitor-1 and an increased response of reactive astrocytes which promote neuronal survival as indicated by augmented glial fibrillary acidic protein mRNA levels.

 

Ebadi, M. and S. K. Sharma (2003). "Peroxynitrite and mitochondrial dysfunction in the pathogenesis of Parkinson's disease." Antioxid Redox Signal 5(3): 319-35.

            Nitric oxide (NO), in excess, behaves as a cytotoxic substance mediating the pathological processes that cause neurodegeneration. The NO-induced dopaminergic cell loss causing Parkinson's disease (PD) has been postulated to include the following: an inhibition of cytochrome oxidase, ribonucleotide reductase, mitochondrial complexes I, II, and IV in the respiratory chain, superoxide dismutase, glyceraldehyde-3-phosphate dehydrogenase; activation or initiation of DNA strand breakage, poly(ADP-ribose) synthase, lipid peroxidation, and protein oxidation; release of iron; and increased generation of toxic radicals such as hydroxyl radicals and peroxynitrite. NO is formed by the conversion of L-arginine to L-citrulline by NO synthase (NOS). At least three NOS isoforms have been identified by molecular cloning and biochemical studies: a neuronal NOS or type 1 NOS (nNOS), an immunologic NOS or type 2 NOS (iNOS), and an endothelial NOS or type 3 NOS (eNOS). The enzymatic activities of eNOS or nNOS are induced by phosphorylation triggered by Ca(2+) entering cells and binding to calmodulin. In contrast, the regulation of iNOS seems to depend on de novo synthesis of the enzyme in response to a variety of cytokines, such as interferon-gamma and lipopolysaccharide. The evidence that NO is associated with neurotoxic processes underlying PD comes from studies using experimental models of this disease NOS inhibitors can prevent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity. Furthermore, NO fosters dopamine depletion, and the said neurotoxicity is averted by nNOS inhibitors such as 7-nitroindazole working on tyrosine hydroxylase-immunoreactive neurons in substantia nigra pars compacta. Moreover, mutant mice lacking the nNOS gene are more resistant to MPTP neurotoxicity when compared with wild-type littermates. Selegiline, an irreversible inhibitor of monoamine oxidase B, is used in PD as a dopaminergic function-enhancing substance. Selegiline and its metabolite, desmethylselegiline, reduce apoptosis by altering the expression of a number of genes, for instance, superoxide dismutase, Bcl-2, Bcl-xl, NOS, c-Jun, and nicotinamide adenine nucleotide dehydrogenase. The selegiline-induced antiapoptotic activity is associated with prevention of a progressive reduction of mitochondrial membrane potential in preapoptotic neurons. As apoptosis is critical to the progression of neurodegenerative disease, including PD, selegiline or selegiline-like compounds to be discovered in the future may be efficacious in treating PD.

 

El-Khodor, B. F. and R. E. Burke (2002). "Medial forebrain bundle axotomy during development induces apoptosis in dopamine neurons of the substantia nigra and activation of caspases in their degenerating axons." J Comp Neurol 452(1): 65-79.

            There is growing evidence that programmed cell death may play a role in degenerative neurologic disease. The caspases are a family of cell death proteins that mediate proteolytic cascades in the death process. Although there is clear evidence that caspases play a role in the destruction of the components of the neuronal soma, it has been controversial whether they play a role in the degeneration of axons that accompanies the death of the cell body. It is important to define the molecular mechanisms of axonal degeneration, because terminal degeneration may occur early in neurodegenerative disease. We have therefore investigated whether caspases play a role in axonal degeneration in the dopaminergic nigrostriatal system following axotomy of the median forebrain bundle during development. We find that this lesion induces apoptosis in midbrain dopaminergic neurons at the level of the cell soma. Concomitantly with this induction of apoptosis, degeneration of dopaminergic axons occurs and is characterized by the formation of axonal swellings and spheroids. Immunohistochemical analysis reveals that the activated form of caspase-3 and a caspase cleavage product of beta-actin are abundantly expressed in these degenerating fibers. We conclude that caspases are activated in degenerating dopaminergic axons as the somata undergo programmed cell death in this model. These results raise the possibility that caspase activation may occur in other programmed cell death contexts for these neurons, and, if this is so, then their inhibition may be a useful therapeutic target.

 

Ellison, G. (2002). "Neural degeneration following chronic stimulant abuse reveals a weak link in brain, fasciculus retroflexus, implying the loss of forebrain control circuitry." Eur Neuropsychopharmacol 12(4): 287-97.

            There is increasing evidence that the fasciculus retroflexus (FR) represents a 'weak link' following the continuous administration of drugs of abuse. A variety of drugs which predominantly potentiate dopamine, including D-amphetamine, methamphetamine, MDMA, cocaine, and cathinone, all induce degeneration in axons from lateral habenula, through the sheath of FR, to midbrain cells such as SN, VTA, and raphe. For some drugs, such as cocaine, this is virtually the only degeneration induced in brain. Continuous nicotine also selectively induces degeneration in FR, but in the other half of the tract, i.e. in axons from medial habenula through the core of the tract to interpeduncular nucleus. This phylogenetically primitive tract carries much of the negative feedback from forebrain back onto midbrain reward cells, and the finding that these descending control pathways are compromised following simulated drug binges has implications for theories of drug addiction but also psychosis in general.

 

Emgard, M., K. Blomgren, et al. (2002). "Characterisation of cell damage and death in embryonic mesencephalic tissue: a study on ultrastructure, vital stains and protease activity." Neuroscience 115(4): 1177-87.

            Dissociated embryonic ventral mesencephalic tissue is a source of dopaminergic neurones in both cell culture and neural transplantation studies. Around 90% of grafted dopaminergic neurones die within 1 week after transplantation. Little is known about when the cell death is triggered and what forms of cell death predominate. Using electron microscopy, we characterised ultrastructural changes in dissected embryonic day 14 rat mesencephalic tissue before and after tissue dissociation. In addition, cell viability was evaluated using Trypan Blue and Hoechst/Ethidium Homodimer. Several cells exhibited leaky outer membranes (permitting entry of vital stains) and ultrastructural degeneration already immediately after the mesencephalon was dissected, and before it was mechanically disrupted. After 2 h at room temperature, 90% of the remaining cells had intact outer membranes. However, when estimating cells lost acutely in the tissue dissociation, in addition to cells exhibiting condensed chromatin and organellar changes, we suggest that only around 14% of the cells initially dissected in the mesencephalic tissue pieces remained healthy after 2 h. There was a peak in calpain activity (specific cleavage of fodrin) immediately following tissue dissociation, and it subsided during the next few hours. Caspase-3 activity was initially low, but increased almost 20-fold 4 h after tissue disruption. Interestingly, extensive degradation of caspase-3 occurred already directly after dissection and was at least partly calpain-dependent. Our data suggest that, in addition to cells undergoing primary necrosis, some cells undergo apoptotic or related changes soon after tissue harvesting, and eventually undergo a secondary necrosis. In summary, embryonic mesencephalic cells exhibit multiple degenerative changes very early on in the neural transplant/tissue culture preparation protocol.

 

Fattore, L., M. C. Puddu, et al. (2002). "Astroglial in vivo response to cocaine in mouse dentate gyrus: a quantitative and qualitative analysis by confocal microscopy." Neuroscience 110(1): 1-6.

            Astrocytes have been proved to play a critical role in neuromodulation, neuroprotection, pH maintenance, axon guidance control during development, homeostasis preservation and blood brain barrier maintenance in the CNS (Kimmelberg and Norenberg, 1989). Quantitative changes in the expression of glial fibrillary acidic protein (GFAP), a cytoskeletal intermediate filament protein exclusively expressed in astrocytes (Bignami et al, 1972), have been observed after administration of alcohol (Framke, 1995), morphine (Beitner-Johnson et al., 1993), amphetamine and its derivates (Aguirre et al., 1999), cannabinoids (Suarez et al., 2000), nicotine (Janson and Moller, 1993), caffeine (Marret et al., 1993) and prenatal exposure to cocaine (Clarke et al., 1996; Nassogne et al., 1998). However, the general astrocytic response to drugs of abuse is still far from being defined. In the present study we examined the in vivo astroglial response to cocaine in mouse dentate gyrus, the hippocampus being a common target of neurotoxic agents (Walsh and Emerich, 1988) which has a prominent effect on learning and memory processes (Eichenbaum et al., 1992). Quantitative changes in immunoreactivity of GFAP were investigated 24 h after acute and repeated daily administration of intraperitoneal cocaine (20 mg/kg). Drug-induced morphological alterations and spatial distribution of astrocytes were evaluated by means of confocal microscope. The results show that, compared to control animals, GFAP expression is two-fold enhanced after a single cocaine injection, still significantly higher after seven consecutive daily administrations, but not statistically different after prolonged (14 days) drug treatment. Moreover, morphological and morphometric analyses reveal significant modifications in astrocytic numbers, cell size and shape complexity. These data demonstrate that in mouse dentate gyrus, cocaine exposure differently affects the expression of GFAP and induces strong changes in astrocytes proliferation rate and cell morphology. Taken together, our findings provide the first in vivo quantitative and qualitative evaluation of astrocytic response to several regimens of cocaine in adult animals brain.

 

Fernagut, P. O., E. Diguet, et al. (2002). "Dopamine transporter knock-out mice are hypersensitive to 3-nitropropionic acid-induced striatal damage." Eur J Neurosci 15(12): 2053-6.

            Evidence suggests that dopamine is involved in the modulation of striatal excitotoxic processes. To further investigate this issue, we studied the effects of systemic 'low-dose' (total dose, 340 mg/kg in 7 days) 3-nitropropionic acid (3-NP) intoxication in dopamine transporter knock-out mice (DAT-/-) compared to wildtype (DAT+/+) mice. Systemic 'low-dose' 3-NP induced a significant impairment in a rotarod task only in DAT-/- mice. Histopathology also demonstrated a significant reduction of the striatal volume (-7%, P < 0.05), neuronal density (-12.5%, P < 0.001) and absolute number estimates of striatal neurons (-11.5%, P < 0.001) in DAT-/- compared to DAT+/+ mice, with increased glial activation, independent of the degree of succinate dehydrogenase inhibition. These findings strengthen the hypothesis for dopamine modulation of excitotoxicity within the nigrostriatal system.

 

Fitsanakis, V. A., V. Amarnath, et al. (2002). "Catalysis of catechol oxidation by metal-dithiocarbamate complexes in pesticides." Free Radic Biol Med 33(12): 1714-23.

            Dithiocarbamate (DTC)-based pesticides have been implicated in Parkinson's disease (PD) through epidemiological links to increased risk of PD, clinical reports of parkinsonism following occupational exposure to the DTC-based pesticide maneb, and experimental studies showing dopaminergic neurodegeneration with combined exposure of rats to maneb and paraquat. We hypothesize that the manganese-ethylene-bis-dithiocarbamate (MnEBDC) complex in maneb may produce oxidative stress by catalyzing catechol oxidation. We tested this hypothesis by performing a structure-function analysis of metal-EBDC and metal-diethyldithiocarbamate (DEDC) complexes of Mn(2+), Zn(2+), and Cu(2+) to catalyze oxidation of N-acetyldopamine (NA-DA) and 3,4-dihydroxyphenylacetic acid (DP) in the presence and absence of N-acetylcysteine (NAC), a model of glutathione. Both Mn-DTCs retained the capacity of the parent ion to catalyze one-electron oxidation of NA-DA, but lost the ability to catalyze DP oxidation. Strikingly, while Zn(2+) did not catalyze catechol oxidation, both Zn-DTCs catalyzed one-electron oxidation of NA-DA but not DP. While Cu(2+) catalyzed oxidation of both catechols, Cu-DTCs were inert. Similar results were obtained with MnEBDC and dopamine or norepinephrine; however, zinc-ethylene-bis-dithiocarbamate was less efficient at catalyzing oxidation of these catechols. Our results point to the potential for manganese- and zinc-containing EBDC pesticides to promote oxidative stress in catecholaminergic regions of the brain.

 

Fornaguera, J. and R. K. Schwarting (2002). "Time course of deficits in open field behavior after unilateral neostriatal 6-hydroxydopamine lesions." Neurotox Res 4(1): 41-9.

            In this study, the degree and time course of deficits in open field behavior was analyzed in male Wistar rats (aged 1 year) which had received unilateral neostriatal lesions with 6-OHDA. The post-mortem neurochemical analysis showed that dopamine was partly depleted in the lateral (to 45%) and in the medial neostriatum (65%). In spontaneous (i.e. undrugged open field behavior, lesion-dependent asymmetries were observed in turning and scanning. The time courses of asymmetry differed between the two measures, since pronounced ipsiversive asymmetries in turning were observed within the first days after lesion placement and persisted throughout the postoperative testing period of 30 days, whereas the ipsilateral asymmetry in scanning appeared during the first week and remained stable thereafter. Systemic treatment with the dopamine receptor agonist apomorphine reversed the asymmetry in turning, indicating supersensitivity of postsynaptic neostriatal dopamine receptors. Furthermore, an enhanced grooming response to apomorphine was measured; however, only in those animals with the more severe 6-OHDA lesions. These findings are discussed in comparison to those obtained with 6-OHDA lesions placed at the level of dopamine cell bodies or fibers, the role of neostriatal dopamine depletion, and the possible relationships with progressive neurodegeneration.

 

Freiman, R. N. and R. Tjian (2002). "Neurodegeneration. A glutamine-rich trail leads to transcription factors." Science 296(5576): 2149-50.

           

Gao, H. M., J. S. Hong, et al. (2002). "Distinct role for microglia in rotenone-induced degeneration of dopaminergic neurons." J Neurosci 22(3): 782-90.

            Increasing evidence has suggested an important role for environmental factors such as exposure to pesticides in the pathogenesis of Parkinson's disease. In experimental animals the exposure to a common herbicide, rotenone, induces features of parkinsonism; mechanistically, rotenone-induced destruction of dopaminergic neurons has been attributed to its inhibition of the activity of neuronal mitochondrial complex I. However, the role of microglia, the resident brain immune cells in rotenone-induced neurodegeneration, has not been reported. Using primary neuron-enriched and neuron/glia cultures from the rat mesencephalon, we discovered an extraordinary feature for rotenone-induced degeneration of cultured dopaminergic neurons. Although little neurotoxicity was detected in neuron-enriched cultures after treatment for 8 d with up to 20 nm rotenone, significant and selective dopaminergic neurodegeneration was observed in neuron/glia cultures 2 d after treatment with 20 nm rotenone or 8 d after treatment with 1 nm rotenone. The greatly enhanced neurodegenerative ability of rotenone was attributed to the presence of glia, especially microglia, because the addition of microglia to neuron-enriched cultures markedly increased their susceptibility to rotenone. Mechanistically, rotenone stimulated the release of superoxide from microglia that was attenuated by inhibitors of NADPH oxidase. Furthermore, inhibition of NADPH oxidase or scavenging of superoxide significantly reduced the rotenone-induced neurotoxicity. This is the first report demonstrating that microglia play a pivotal role in rotenone-induced degeneration of dopaminergic neurons. The results of this study should advance our understanding of the mechanism of action for pesticides in the pathogenesis of Parkinson's disease.

 

Gao, H. M., J. S. Hong, et al. (2003). "Synergistic dopaminergic neurotoxicity of the pesticide rotenone and inflammogen lipopolysaccharide: relevance to the etiology of Parkinson's disease." J Neurosci 23(4): 1228-36.

            Parkinson's disease (PD) is characterized by a progressive degeneration of the nigrostriatal dopaminergic pathway resulting in movement disorders. Although its etiology remains unknown, PD may be the final outcome of interactions among multiple factors, including exposure to environmental toxins and the occurrence of inflammation in the brain. In this study, using primary mesencephalic cultures, we observed that nontoxic or minimally toxic concentrations of the pesticide rotenone (0.5 nm) and the inflammogen lipopolysaccharide (LPS) (0.5 ng/ml) synergistically induced dopaminergic neurodegeneration. The synergistic neurotoxicity of rotenone and LPS was observed when the two agents were applied either simultaneously or in tandem. Mechanistically, microglial NADPH oxidase-mediated generation of reactive oxygen species appeared to be a key contributor to the synergistic dopaminergic neurotoxicity. This conclusion was based on the following observations. First, inhibition of NADPH oxidase or scavenging of free radicals afforded significant neuroprotection. Second, rotenone and LPS synergistically stimulated the NADPH oxidase-mediated release of the superoxide free radical. Third and most importantly, rotenone and LPS failed to induce the synergistic neurotoxicity as well as the production of superoxide in cultures from NADPH oxidase-deficient animals. This is the first demonstration that low concentrations of a pesticide and an inflammogen work in synergy to induce a selective degeneration of dopaminergic neurons. Findings from this study may be highly relevant to the elucidation of the multifactorial etiology of PD and the discovery of effective therapeutic agents for the treatment of the disease.

 

Gao, H. M., J. Jiang, et al. (2002). "Microglial activation-mediated delayed and progressive degeneration of rat nigral dopaminergic neurons: relevance to Parkinson's disease." J Neurochem 81(6): 1285-97.

            The etiology of sporadic Parkinson's disease (PD) remains unknown. Increasing evidence has suggested a role for inflammation in the brain in the pathogenesis of PD. However, it has not been clearly demonstrated whether microglial activation, the most integral part of the brain inflammatory process, will result in a delayed and progressive degeneration of dopaminergic neurons in substantia nigra, a hallmark of PD. We report here that chronic infusion of an inflammagen lipopolysaccharide at 5 ng/h for 2 weeks into rat brain triggered a rapid activation of microglia that reached a plateau in 2 weeks, followed by a delayed and gradual loss of nigral dopaminergic neurons that began at between 4 and 6 weeks and reached 70% by 10 weeks. Further investigation of the underlying mechanism of action of microglia-mediated neurotoxicity using rat mesencephalic neuron-glia cultures demonstrated that low concentrations of lipopolysaccharide (0.1-10 ng/mL)-induced microglial activation and production of neurotoxic factors preceded the progressive and selective degeneration of dopaminergic neurons. Among the factors produced by activated microglia, the NADPH oxidase-mediated release of superoxide appeared to be a predominant effector of neurodegeneration, consistent with the notion that dopaminergic neurons are particularly vulnerable to oxidative insults. This is the first report that microglial activation induced by chronic exposure to inflammagen was capable of inducing a delayed and selective degeneration of nigral dopaminergic neurons and that microglia-originated free radicals play a pivotal role in dopaminergic neurotoxicity in this inflammation-mediated model of PD.

 

Gassen, M., I. Lamensdorf, et al. (2003). "Attenuation of methamphetamine induced dopaminergic neurotoxicity by flupirtine: microdialysis study on dopamine release and free radical generation." J Neural Transm 110(2): 171-82.

            Flupirtine is a triaminopyridine derived centrally acting analgetic, which has been found to display neuroprotective effects in models of excitotoxic cell damage, global, and focal ischemia, but no direct interaction with any component of the N-methyl-D-aspartate (NMDA) and glutamate triggered Ca(2+)-channel. Additionally flupirtine shows potent antioxidant effects in isolated mitochondria and cell culture. Work in models of monoamine depletion and neuroleptic induced catalepsy in rats suggests a interaction of flupirtine with the dopaminergic neurotransmitter system as well. This prompted us to examine the effect of flupirtine on methamphetamine toxicity in mice and to investigate the influence on dopamine release and free radical formation in the rat striatum by microdialysis that may explain methamphetamine neurotoxicity. Pretreatment of C57-BL mice with flupirtine (4 x 10 mg/kg) significantly attenuated the striatal dopamine loss after methamphetamine application (4 x 5 mg/kg). In rats, a single injection of 10 mg/kg flupirtine reduced the methamphetamine induced striatal dopamine release by almost 50%, as measured by in vivo microdialysis. Flupirtine, however, did not influence the increase of free radical formation after methamphetamine infusion, which was assayed after infusion of salicylic acid by quantification of 2,3- and 2,5-dihydroxybenzoic acid. This suggests that other mechanisms rather than dopamine metabolism and autoxidation, may contribute to methamphetamine neurotoxicity.

 

Gavrilin, M. A., L. E. Mathes, et al. (2002). "Methamphetamine enhances cell-associated feline immunodeficiency virus replication in astrocytes." J Neurovirol 8(3): 240-9.

            Human immunodeficiency virus (HIV) infection among substance abusers is on the rise worldwide. Psychostimulants, and in particular methamphetamine (METH), have detrimental effects on the immune system as well as causing a progressive neurodegeneration, similar to HIV infection. Many Lentivirinae, including feline immunodeficiency virus (FIV), penetrate into the central nervous system early in the course of infection with astrocytes serving as a reservoir of chronic brain infection. We demonstrate that the FIV-Maryland isolate infects feline primary and cell line (G355-5)-cultured astrocytes only under cell-associated conditions. Infected astrocytes yielded a new astrocytotropic isolate, capable of cell-free infection (termed FIV-MD-A). This isolate contained four amino acid substitutions in the envelope polyprotein resulting in a change in net charge as compared to FIV-MD. Infection for both isolates was dependent upon a functional astrocyte CXCR4 receptor. Methamphetamine increased significantly FIV replication in feline astrocytes for cell-associated infection only, with no effect on peripheral blood mononuclear cells or astrocytes infected with FIV-MD-A. This viral replication was related to proviral copy number, suggesting the effect of METH is at the viral entry or integration into host genome levels, but not at the translational level. Thus, lentiviral infection of the brain in the presence of the psychostimulant METH may result in enhanced astrocyte viral replication, producing a more rapid and increased brain viral load.

 

Gerschlager, W., G. Bencsits, et al. (2002). "[123I]beta-CIT SPECT distinguishes vascular parkinsonism from Parkinson's disease." Mov Disord 17(3): 518-23.

            We investigated whether [(123)I]-beta-CIT and single-photon emission computed tomography (SPECT) imaging distinguishes patients with clinically suspected vascular parkinsonism (VP) from patients with idiopathic Parkinson's disease (PD). [(123)I]beta-CIT SPECT is a sensitive marker of dopaminergic degeneration, and the degree of striatal binding reduction in PD correlates with disease severity. Thirteen patients who fulfilled rigid clinical criteria for VP (mean +/- S.D.: age, 76.5 +/- 5.3 years; disease duration, 3.6 +/- 2.8 years), 20 PD patients (age, 66.2 +/- 9.5 years; disease duration, 4.3 +/- 2.7 years), and 30 healthy persons (age, 44.6 +/- 19.2 years) underwent [(123)I]beta-CIT SPECT imaging. Age-corrected striatal beta-CIT binding was reduced on average by 40.8% in PD but was near normal in the VP group (mean reduction, 1.2%). This difference was statistically significant (Z = 4.68; P < 0.001). The left-right asymmetry of striatal beta-CIT binding was significantly increased in the PD group compared with normal controls and the VP group (F(2) = 17.4, P <0.001). Moreover, putamen-caudate nucleus ratios were significantly reduced in PD compared with both VP patients and healthy controls (F(2) = 65.5, P < 0.001). Whole striatal beta-CIT binding was more than one standard deviation above the mean PD values in all but one of the individual VP patients. Our findings suggest that the presynaptic dopaminergic deficits seen in PD are absent in most patients with VP. [(123)I]beta-CIT SPECT imaging may be useful to help distinguish between PD and VP patients during life.

 

Gonzalez-Hernandez, T., P. Barroso-Chinea, et al. (2002). "Response of GABAergic cells in the deep mesencephalic nucleus to dopaminergic cell degeneration: an electrophysiological and in situ hybridization study." Neuroscience 113(2): 311-21.

            The deep mesencephalic nucleus (DMN) is a large midbrain reticular region located between the substantia nigra compacta and the superior colliculus. It contains GABAergic cells that share striatal afferents, thalamic and collicular efferents, as well as neurochemical and electrophysiological similarities, with those of the substantia nigra reticulata. In the present paper we used electrophysiological (firing rate and firing pattern) and morphological (densitometric analysis of in situ hybridization histochemical labeling for glutamic acid decarboxylase (GAD)65 and GAD67 mRNA) techniques, to study the response of DMN GABAergic cells to the degeneration of nigral dopaminergic cells. Our results showed that unilateral dopaminergic cell loss (after injection of 6-hydroxydopamine in the medial forebrain bundle) induces a bilateral and symmetrical increase in both firing rate and GAD67 mRNA levels and a decrease in GAD65 mRNA levels. These findings support the involvement of DMN GABAergic cells in the basal ganglia modifications that follow dopaminergic cell loss, also suggesting its participation in the pathophysiology of Parkinson's disease. The symmetry of effects, together with its recently reported bilateral projections to the thalamus and superior colliculus, suggest that unlike substantia nigra reticulata, DMN is involved in the interhemispheric regulation of basal ganglia, probably keeping their functional symmetry even after asymmetric lesions.

 

Gotz, M. E., E. Koutsilieri, et al. (2002). "Methylmercury induces neurite degeneration in primary culture of mouse dopaminergic mesencephalic cells." J Neural Transm 109(5-6): 597-605.

            Methylmercury cation (MeHg) is an hazardous environmental pollutant with neurotoxic action. Little is known about the effects of MeHg on catecholaminergic neurons. In the present study we have used epifluorescence microscopy and confocal microscopy to investigate the alterations induced by MeHg in primary DA (dopaminergic) cells isolated from the ventral mesencephalon of CD-1 embryonic mice and cultured for six days in vitro. DA cells were identified in the multi-culture by immunocytochemistry using a tyrosine-hydroxylase antibody. The morphometric analysis of DA neurons exposed to 1 microM MeHg demonstrated a striking decrease in the number of neurites, indicative of cytoskeletal alteration. In addition, DA neurons displayed cell shrinkage and a significant increase of nuclei with chromatin condensation. Based on these results it is concluded that MeHg is highly toxic to primary DA neurons.

 

Grant, R. J. and P. B. Clarke (2002). "Susceptibility of ascending dopamine projections to 6-hydroxydopamine in rats: effect of hypothermia." Neuroscience 115(4): 1281-94.

            The aims of this study were to determine (1) whether mesolimbic and nigrostriatal DA cell bodies degenerate to different extents after 6-hydroxydopamine (6-OHDA) is administered into their respective terminal fields and (2) whether hypothermia, associated with sodium pentobarbital anesthesia, protects DA neurons from the toxic effects of 6-OHDA. To address these questions, 6-OHDA or vehicle was infused into either the ventral or dorsal striatum or into the medial forebrain bundle, under conditions of brain normothermia or hypothermia. Two weeks post-surgery, tyrosine hydroxylase-positive cell bodies were counted in the ventral tegmental area (VTA) and substantia nigra. In addition, autoradiographic labeling of tyrosine hydroxylase protein and dopamine transporter was quantified in dopamine terminal fields and cell body areas. Overall, DA cell bodies in the VTA were substantially less susceptible than those in the substantia nigra to depletion of dopaminergic markers. Hypothermia provided two types of neuroprotection. The first occurred when 6-OHDA was administered into the dorsal striatum, and was associated with a 30-50% increase in residual dopaminergic markers in the lateral portion of the VTA. The second neuroprotective effect of hypothermia occurred when 6-OHDA was given into the medial forebrain bundle. This was associated with a 200-300% increase in residual dopaminergic markers in the mesolimbic and nigrostriatal terminal fields; no significant protection occurred in the cell body regions.Collectively, these findings show that (1) the dopaminergic somata in the substantia nigra are more susceptible than those in the VTA to 6-OHDA-induced denervation, and (2) hypothermia can provide anatomically selective neuroprotection within the substantia nigra-VTA cell population. The continued survival of mesolimbic dopamine cell bodies after a 6-OHDA lesion may have functional implications relating to drugs of abuse, as somatodendritic release of dopamine in the VTA has been shown to play a role in the effectiveness of cocaine reward.

 

Graumann, R., I. Paris, et al. (2002). "Oxidation of dopamine to aminochrome as a mechanism for neurodegeneration of dopaminergic systems in Parkinson's disease. possible neuroprotective role of DT-diaphorase." Pol J Pharmacol 54(6): 573-9.

            Although it is generally accepted that free radicals are involved in the neurodegenerative process occurring in the dopaminergic neurons of the nigro-striatal system in Parkinson's disease, the exact mechanism of neurodegeneration in vivo is still unknown. We propose that the degeneration of dopaminergic nigrostriatal system in this condition may depend on: (a) existence of free dopamine which oxidizes to aminochrome as a consequence of: (i) overproduction of dopamine; (ii) inhibition and/or low expression of synaptic vesicle catecholamine transporter; (iii) inhibition or low expression of monoamine oxidases; (b) one-electron reduction of aminochrome to leukoaminochrome o-semiquinone radical, which induces neurotoxicity, due to inhibition of DT-diaphorase or the existence of a polymorphism with a point mutation (C --> T) in the cDNA 609 expressing an inactive DT-diaphorase. We suggest that DT-diaphorase plays a neuroprotective role in dopaminergic neurons, which is supported by the following observations: (i) Cu-toxicity is dependent on DT-diaphorase inhibition with dicoumarol in RCSN-3 cells derived from the rat substantia nigra; (ii) the cytotoxic effect of monoamine oxidase-A inhibitor amiflamine in RCSN-3 cells is increased by 2.4-fold (p < 0.001) in the presence of the inhibitor of DT-diaphorase, dicoumarol; (iii) concomitant intracerebral administration of manganese (Mn3+) together with the DT-diaphorase inhibitor dicoumarol into the left medial forebrain bundle produced a behavioral pattern characterized by contralateral rotational behavior when the rats were stimulated with apomorphine, in a manner similar to that observed in animals injected unilaterally with 6-hydroxydopamine; (iv) incubation of RCSN-3 cells with salsolinol in the presence of DT-diaphorase inhibitor significantly decreased cell survival by 2.5-fold (p < 0.001).

 

Green, A. R., A. O. Mechan, et al. (2003). "The Pharmacology and Clinical Pharmacology of 3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy")." Pharmacol Rev.

            The amphetamine derivative (+/-)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a popular recreational drug among young people, particularly those involved in the dance culture. MDMA produces an acute, rapid enhancement in the release of both serotonin (5-HT) and dopamine from nerve endings in the brains of experimental animals. It produces increased locomotor activity and the serotonin behavioral syndrome in rats. Crucially, it produces dose-dependent hyperthermia that is potentially fatal in rodents, primates, and humans. Some recovery of 5-HT stores can be seen within 24 h of MDMA administration. However, cerebral 5-HT concentrations then decline due to specific neurotoxic damage to 5-HT nerve endings in the forebrain. This neurodegeneration, which has been demonstrated both biochemically and histologically, lasts for months in rats and years in primates. In general, other neurotransmitters appear unaffected. In contrast, MDMA produces a selective long-term loss of dopamine nerve endings in mice. Studies on the mechanisms involved in the neurotoxicity in both rats and mice implicate the formation of tissue-damaging free radicals. Increased free radical formation may result from the further breakdown of MDMA metabolic products. Evidence for the occurrence of MDMA-induced neurotoxic damage in human users remains equivocal, although some biochemical and functional data suggest that damage may occur in the brains of heavy users. There is also some evidence for long-term physiological and psychological changes occurring in human recreational users. However, such evidence is complicated by the lack of knowledge of doses ingested and the fact that many subjects studied are or have been poly-drug users.

 

Gu, G., A. Y. Deutch, et al. (2003). "Profiling genes related to mitochondrial function in mice treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine." Biochem Biophys Res Commun 308(1): 197-205.

            Since mitochondrial dysfunction plays an important role in the pathogenesis of dopaminergic neurodegeneration in Parkinson's disease, we determined the expression of genes related to mitochondrial function in the substantia nigra of mice treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) using a cDNA array. MPTP treatment significantly depleted striatal dopamine, but did not result in apparent neuronal loss in the substantia nigra at 3 and 18 days post-treatment. We also examined changes in genes in the hypothalamus, a region containing dopaminergic neurons that are relatively resistant to MPTP. Finally, we confirmed those genes identified by microarrays as differentially expressed in the substantia nigra but not in the hypothalamus using in situ hybridization. Our results demonstrated that MPTP significantly changed the expressions of six genes in nigral neurons, four of which were related to the mitochondrial electron transport chain: the NADH-ubiquinone oxidoreductase 13kDa B subunit, the NADH-ubiquinone oxidoreductase MNLL subunit, cytochrome c, and the cytochrome c oxidase Va subunit. Two other differentially expressed genes were the dihydropyridine-sensitive L-type calcium channel alpha-2 subunit precursor and type III alpha-1 procollagen. None of these six genes are encoded by mitochondrial DNA. The potential significance of these gene alterations in the context of Parkinson's disease is discussed.

 

Gwiazda, R. H., D. Lee, et al. (2002). "Low cumulative manganese exposure affects striatal GABA but not dopamine." Neurotoxicology 23(1): 69-76.

            The introduction of the anti-knock methylcyclopentadienyl manganese (Mn) tricarbonyl (MMT) in gasoline has raised concerns about the potential for manganese neurotoxicity. Because subpopulations such as the elderly in the early stages of neurodegenerative disease may be at increased risk for manganese toxicity, a pre-Parkinsonism rat model was used to evaluate whether sub-chronic manganese exposure can aggravate the neurochemical and behavioral dysfunctions characteristic of Parkinsonism. Sub-threshold levels of dopamine depletion of 3.5, 53 and 68% were generated via intrastriatal unilateral 6-hydroxydopamine (6-OHDA) doses. A sub-chronic dosing regimen of low cumulative manganese exposure (4.8 mg Mn/kg body weight, 3 i.p. injections per week x 5 weeks) was started 4 weeks after 6-OHDA treatments. Neurochemical and neuromotor (functional observational battery (FOB)) measures were evaluated. Manganese produced significant (P < 0.05) reductions of 30-60% in motor function. This effect was exacerbated in the presence of a pre-Parkinsonism condition [Neurotox. Teratol. 22 (2000) 851]. Manganese did not affect striatal dopamine, but resulted in significant increases in striatal y-aminobutyric acid (GABA) of 16 and 22% (P < 0.01) in both striati and a borderline non-significant 4% increase in frontal cortex (P = 0.076). Manganese treatment produced increased aspartate (P < 0.01) in the manganese and 6-OHDA treated striatum. In light of previous studies predominantly showing dopamine depletion with elevated manganese exposures, the significant effects of manganese on striatal GABA but not on striatal dopamine at the low cumulative exposure administered here suggest a progression in manganese toxicity with increasing cumulative dose, whereby GABA levels are adversely affected before striatal dopamine levels. Because these neurochemical disruptions were accompanied by motor dysfunction that was exacerbated in the presence of a pre-Parkinsonism condition, an increased environmental burden of manganese may have deleterious effects on populations with sub-threshold neurodegeneration in the basal ganglia (e.g. pre-Parkinsonism).

 

Heilig, M. (2003). "[Ecstasy is a dangerous drug the society chooses to ignore]." Lakartidningen 100(9): 688-90.

           

Helfand, S. L. (2002). "Neurobiology. Chaperones take flight." Science 295(5556): 809-10.

           

Hunot, S. and E. C. Hirsch (2003). "Neuroinflammatory processes in Parkinson's disease." Ann Neurol 53 Suppl 3: S49-58; discussion S58-60.

            Parkinson's disease (PD) is a movement disorder characterized by the progressive degeneration of dopaminergic neurons in the midbrain. To date, its cause remains unknown and the mechanism of nerve cell death uncertain. Apart from the massive loss of dopaminergic neurons, PD brains also show a conspicuous glial reaction together with signs of a neuroinflammatory reaction manifested by elevated cytokine levels and upregulation of inflammatory-associated factors such as cyclooxygenase-2 and inducible nitric oxide synthase. Mounting evidence also suggests a possible deleterious effect of these neuroinflammatory processes in experimental models of the disease. We propose that, in PD, neuroinflammation plays a role in the cascade of events leading to nerve cell death, thus propagating the neurodegenerative process. In this review, we summarize and discuss the latest findings regarding neuroinflammatory aspects in PD.

 

Ikeda, K., M. Kurokawa, et al. (2002). "Neuroprotection by adenosine A2A receptor blockade in experimental models of Parkinson's disease." J Neurochem 80(2): 262-70.

            Adenosine A2A receptors are abundant in the caudate-putamen and involved in the motor control in several species. In MPTP-treated monkeys, A2A receptor-blockade with an antagonist alleviates parkinsonian symptoms without provoking dyskinesia, suggesting this receptor may offer a new target for the antisymptomatic therapy of Parkinson's disease. In the present study, a significant neuroprotective effect of A2A receptor antagonists is shown in experimental models of Parkinson's disease. Oral administration of A2A receptor antagonists protected against the loss of nigral dopaminergic neuronal cells induced by 6-hydroxydopamine in rats. A2A antagonists also prevented the functional loss of dopaminergic nerve terminals in the striatum and the ensuing gliosis caused by MPTP in mice. The neuroprotective property of A2A receptor antagonists may be exerted by altering the packaging of these neurotoxins into vesicles, thus reducing their effective intracellular concentration. We therefore conclude that the adenosine A2A receptor may provide a novel target for the long-term medication of Parkinson's disease, because blockade of this receptor exerts both acutely antisymptomatic and chronically neuroprotective activities.

 

Iravani, M. M., K. Kashefi, et al. (2002). "Involvement of inducible nitric oxide synthase in inflammation-induced dopaminergic neurodegeneration." Neuroscience 110(1): 49-58.

            The loss of dopaminergic neurones in the substantia nigra with Parkinson's disease may result from inflammation-induced proliferation of microglia and reactive macrophages expressing inducible nitric oxide synthase (iNOS). We have investigated the effects of the supranigral administration of lipopolysaccharide on iNOS-immunoreactivity, 3-nitrotyrosine formation and tyrosine hydroxylase-immunoreactive neuronal number, and retrogradely labelled fluorogold-positive neurones in the ventral mesencephalon in male Wistar rats. Following supranigral lipopolysaccharide injection, 16-18 h previously, there was intense expression of NADPH-diaphorase and iNOS-immunoreactivity in non-neuronal, macrophage-like cells. This was accompanied by intense expression of glial fibrillary acidic protein-immunoreactive astrocytosis in the substantia nigra. There were also significant reductions in the number of tyrosine hydroxylase(50-60%)- and fluorogold (65-75%)-positive neurones in the substantia nigra. In contrast, tyrosine hydroxylase-immunoreactivity in the ventral tegmental area was not altered. Pre-treatment of animals with the iNOS inhibitor, S-methylisothiourea (10 mg kg(-1), i.p.), led to a significant reduction of lipopolysaccharide-induced cell death. Similar reduction of tyrosine hydroxylase-immunoreactivity and fluorogold-labelled neurones in the substantia nigra following lipopolysaccharide administration suggests dopaminergic cell death rather than down-regulation of tyrosine hydroxylase. We conclude that the expression of iNOS- and 3-nitrotyrosine-immunoreactivity and reduction of cell death by S-methylisothiourea suggest the effects of lipopolysaccharide may be nitric oxide-mediated, although other actions of lipopolysaccharide (independent of iNOS induction) cannot be ruled out.

 

Isacson, O., L. M. Bjorklund, et al. (2003). "Toward full restoration of synaptic and terminal function of the dopaminergic system in Parkinson's disease by stem cells." Ann Neurol 53 Suppl 3: S135-46; discussion S146-8.

            New therapeutic nonpharmacological methodology in Parkinson's disease (PD) involves cell and synaptic renewal or replacement to restore function of neuronal systems, including the dopaminergic (DA) system. Using fetal DA cell therapy in PD patients and laboratory models, it has been demonstrated that functional motor deficits associated with parkinsonism can be reduced. Similar results have been observed in animal models with stem cell-derived DA neurons. Evidence obtained from transplanted PD patients further shows that the underlying disease process does not destroy transplanted fetal DA cells, although degeneration of the host nigrostriatal system continues. The optimal DA cell regeneration system would reconstitute a normal neuronal network capable of restoring feedback-controlled release of DA in the nigrostriatal system. The success of cell therapy for PD is limited by access to preparation and development of highly specialized dopaminergic neurons found in the A9 and A10 region of the substantia nigra pars compacta as well as the technical and surgical steps associated with the transplantation procedure. Recent laboratory work has focused on using stem cells as a starting point for deriving the optimal DA cells to restore the nigrostriatal system. Ultimately, understanding the cell biological principles necessary for generating functional DA neurons can provide many new avenues for better treatment of patients with PD.

 

Ishihara, K., A. Nonaka, et al. (2002). "Lewy body-free nigral degeneration--a case report." J Neurol Sci 198(1-2): 97-100.

            A 70-year-old Japanese woman developed progressive, dopa-responsive parkinsonism consisting of akinesia, resting tremor, rigidity, and postural instability. Neuropathological examination revealed a marked loss of nigral neurons, but no Lewy bodies (LBs) were observed. Lewy bodies were also absent from their usual site, with the exception of a small number seen in the dorsal motor nucleus of the vagus nerve (DVN) and sympathetic ganglion. We propose that our case and several similar reported cases represent Lewy body-free nigral degeneration.

 

Jakab, R. L. and J. F. Bowyer (2002). "Parvalbumin neuron circuits and microglia in three dopamine-poor cortical regions remain sensitive to amphetamine exposure in the absence of hyperthermia, seizure and stroke." Brain Res 958(1): 52-69.

            The dopamine-releasing and depleting substance amphetamine (AMPH) can make cortical neurons susceptible to damage, and the prevention of hyperthermia, seizures and stroke is thought to block these effects. Here we report a 2-day AMPH treatment paradigm which affected only interneurons in three cortical regions with average or below-average dopamine input. AMPH (six escalating doses/day ranging from 5 to 30 mg/kg for 2 days) was given at 17-18 degrees C ambient temperature (T) to adult male rats. During the 2-day AMPH treatment, peak body T stayed below 38.9 degrees C in 40% of the AMPH treated rats. In 60% of the rats, deliberate cooling suppressed (<39.5 degrees C) or minimized (<40.0 degrees C) hyperthermia. Escalation of stereotypes to seizure-like behaviors was rare and post-mortem morphological signs of stroke were absent. Neurons labeled with the anionic, neurodegeneration-marker dye Fluoro-Jade (F-J) were seen 1 day after dosing, peaked 3 days later, but were barely detectable 14 days after dosing. Only nonpyramidal neurons in layer IV of the somatosensory barrel cortex and in layer II of the piriform cortex and posterolateral cortical amygdaloid nucleus were labeled with Fluoro-Jade. Isolectin B-labeled activated microglia were only detected in their neighborhood. F-J labeled neurons were extremely rare in cortical regions rich in dopamine (e.g. cingulate cortex), and were absent in cortical regions with no dopamine (e.g. visual cortex). Parvalbumin was seen in some Fluoro-Jade-labeled neurons and parvalbumin immunostaining in local axon plexuses intensified. This AMPH paradigm affected fewer cortical regions, and caused smaller reduction in striatal tyrosine hydroxylase (TH) immunoreactivity than previous 1-day AMPH regimens generating seizures or severe (above 40 degrees C) hyperthermia. Correlation between peak or mean body T and the extent of neurodegeneration or microgliosis was below statistical significance. Astrogliosis (elevated levels of the astroglia-marker, glial fibrillary acidic protein (GFAP)) was detected in many brain regions. In the striatum and midbrain, F-J labeled neurons and activated microglia were absent, but astrogliosis, decreased TH immunolabel, and swollen TH fibers were detected. In sum, after this AMPH treatment, cortical pyramidal neurons were spared, but astrogliosis was brain-wide and some interneurons and microglia in three cortical regions with average or below-average dopamine input remained sensitive to AMPH exposure.

 

Jellinger, K. A. (2002). "Recent developments in the pathology of Parkinson's disease." J Neural Transm Suppl(62): 347-76.

            Parkinson's disease (PD) is morphologically characterized by progressive loss of neurons in the substantia nigra pars compacta (SNpc) and other subcortical nuclei associated with intracytoplasmic Lewy bodies and dystrophic (Lewy) neurites mainly in subcortical nuclei and hippocampus und, less frequently in cerebral cortex. SN cell loss is significantly related to striatal dopamine (DA) deficiency as well as to both the duration and clinical severity of disease, The two major clinical subtypes of PD show different morphologic lesion patterns: the akinetic-rigid form has more severe cell loss in the ventrolateral part of SN with negative correlation to DA loss in the posterior putamen, and motor symptoms related to overacitivty of the GABAergic "indirect" motor loop, which causes inhibition of the glutamatergic thalamocortical pathway and reduced cortical activation. The tremor-dominant type shows more severe cell loss in the medial SNpc and retrorubal field A 8, which project to the matrix of the dorsolateral striatum and ventromedial thalamus, thus causing hyperactivity of thalamomotor and cerebellar projections. These and experimental data suggesting different pathophysiological mechanisms for the major clinical subtypes of PD may have important therapeutic implications. Lewy bodies, the morphologic markers of PD, are composed of hyperphosphorylated neurofilament proteins, lipids, redox-active iron, ubiquitin, and alpha-synuclein, showing a continuous accumulation in the periphery and of ubiquitin in the central core. Alpha-synuclein, is usually unfolded in alpha-helical form. By gene mutation, environmental stress or other factors it can be transformed to beta-folding which is sensible to self-aggregation in filamentous fibrils and formation of insoluble intracellular inclusions that may lead to functional disturbances and, finally, to death of involved neurons. While experimental and tissue culture studies suggest that apoptosis, a genetically determined form of programmed cell death, represents the most common pathway in neurodegeneration, DNA fragmentation, overexpression of proapoptotic proteins and activated caspase-3, the effector enzyme of the terminal apopoptic cascade, have only extremely rarely been detected in SN of PD brains. This is in accordance with the rapid course of apoptotis and the extremely slow progression of the neurodegenerative process in PD. The biological role of Lewy bodies and other intracellular inclusions, the mechanisms of the intracellular aggregation of insoluble protein deposits, and their implication for cellular dysfunction resulting in neurodegeneration and cell demise are still unresolved. Further elucidation of the basic molecular mechanisms of cytoskeletal lesions will provide better insight into the pathogenesis of neurodegeneration in PD and related disorders.

 

Jenner, P. (2003). "Oxidative stress in Parkinson's disease." Ann Neurol 53 Suppl 3: S26-36; discussion S36-8.

            Oxidative stress contributes to the cascade leading to dopamine cell degeneration in Parkinson's disease (PD). However, oxidative stress is intimately linked to other components of the degenerative process, such as mitochondrial dysfunction, excitotoxicity, nitric oxide toxicity and inflammation. It is therefore difficult to determine whether oxidative stress leads to, or is a consequence of, these events. Oxidative damage to lipids, proteins, and DNA occurs in PD, and toxic products of oxidative damage, such as 4-hydroxynonenal (HNE), can react with proteins to impair cell viability. There is convincing evidence for the involvement of nitric oxide that reacts with superoxide to produce peroxynitrite and ultimately hydroxyl radical production. Recently, altered ubiquitination and degradation of proteins have been implicated as key to dopaminergic cell death in PD. Oxidative stress can impair these processes directly, and products of oxidative damage, such as HNE, can damage the 26S proteasome. Furthermore, impairment of proteasomal function leads to free radical generation and oxidative stress. Oxidative stress occurs in idiopathic PD and products of oxidative damage interfere with cellular function, but these form only part of a cascade, and it is not possible to separate them from other events involved in dopaminergic cell death.

 

Jeohn, G. H., C. L. Cooper, et al. (2002). "p38 MAP kinase is involved in lipopolysaccharide-induced dopaminergic neuronal cell death in rat mesencephalic neuron-glia cultures." Ann N Y Acad Sci 962: 332-46.

            Immune stimulants, such as the bacterial endotoxin, lipopolysaccharide (LPS), the human immunodeficiency virus-1 coat protein gp120, or beta-amyloid peptides, lead to glial activation and production of various immune mediators, such as nitric oxide (NO) and proinflammatory cytokines in the brain. These mediators appear to contribute to neuronal cell death in neurodegenerative diseases. However, the signaling pathways, which mediate the neurotoxic effect by the endotoxin, are not understood. The purpose of this study was to determine the role of mitogen-activated protein kinase (MAPK) in LPS-induced neurodegeneration using mesencephalic dopaminergic neuron/glia cultures. We have found that the p38 MAPK is important in LPS-induced death of mesencephalic neurons in rat neuron-glia mixed cultures. Upon treatment with 10 ng/ml LPS, the number of dopaminergic neurons decreased by 80% within 48 h, preceded by a significant production of NO by glia. Neuroprotection by selective inhibition of p38 MAPK activity paralleled a decrease in LPS-induced inducible nitric oxide synthase (iNOS) expression. These events were significantly reduced by the selective p38 MAPK inhibitor, SB202190, but not by the inactive analogue SB202474. Inhibition of iNOS activity and NO production by treatment with GW274150 was also neuroprotective. Although the p38 MAPK inhibitor afforded significant neuroprotection from LPS toxicity in the neuron-glia mixed culture, it failed to protect dopaminergic neurons from 6-hydroxy-dopamine-induced toxicity, which acts directly on dopaminergic neurons by inducing hydroxyl radical formation from the mitochondria. The results suggest that p38 MAPK in glia plays a significant role in the LPS-induced death of mesencephalic neurons through induction of nitric oxide synthase and resulting NO production.

 

Kanthasamy, A., J. E. Sprague, et al. (2002). "Unilateral infusion of a dopamine transporter antisense into the substantia nigra protects against MDMA-induced serotonergic deficits in the ipsilateral striatum." Neuroscience 114(4): 917-24.

            The present study was designed to elucidate the consequences of antisense oligonucleotide-mediated knockdown of striatal dopamine reuptake transporters on 3,4-methylenedioxymethamphetamine (MDMA)-induced neurotoxicity. Antisense oligonucleotide complementary to the mRNA translational start site of the rat dopamine transporter was delivered by constant (7 days) intranigral infusion with an osmotic minipump. Delivery of the antisense oligonucleotide by this method resulted in a 70% reduction in the density of the dopamine transporter in the ipsilateral striatum, as measured by [(3)H]mazindol binding. The effect of this transporter knockdown on MDMA-induced serotonergic neurotoxicity was then examined. MDMA (2x20 mg/kg, s.c., given 12 h apart) administered to control rats produced hyperthermia following the first dose and led to a 45-50% reduction in striatal serotonin, 5-hydroxyindoleacetic acid, and serotonin reuptake transporter density 1 week after the second dose. Conversely, in antisense-, but not missense-treated rats, a significant attenuation of MDMA-induced neurotoxicity was observed only in the ipsilateral striatum. The hyperthermic response elicited by MDMA was not altered by prior administration of antisense. In vivo microdialysis revealed that the antisense treatment attenuated MDMA-induced dopamine release in the ipsilateral striatum.These results suggest that the dopamine transporter plays an essential role in the neurodegeneration induced by MDMA, and provides additional support for the hypothesis that extracellular dopamine is involved in the neurotoxic process, at least in the striatum.

 

Kirik, D., C. Rosenblad, et al. (2002). "Parkinson-like neurodegeneration induced by targeted overexpression of alpha-synuclein in the nigrostriatal system." J Neurosci 22(7): 2780-91.

            Recombinant adeno-associated viral vectors display efficient tropism for transduction of the dopamine neurons of the substantia nigra. Taking advantage of this unique property of recombinant adeno-associated viral vectors, we expressed wild-type and A53T mutated human alpha-synuclein in the nigrostriatal dopamine neurons of adult rats for up to 6 months. Cellular and axonal pathology, including alpha-synuclein-positive cytoplasmic inclusions and swollen, dystrophic neurites similar to those seen in brains from patients with Parkinson's disease, developed progressively over time. These pathological alterations occurred preferentially in the nigral dopamine neurons and were not observed in other nondopaminergic neurons transduced by the same vectors. The degenerative changes were accompanied by a loss of 30-80% of the nigral dopamine neurons, a 40-50% reduction of striatal dopamine, and tyrosine hydroxylase levels that was fully developed by 8 weeks. Significant motor impairment developed in those animals in which dopamine neuron cell loss exceeded a critical threshold of 50-60%. At 6 months, signs of cell body and axonal pathology had subsided, suggesting that the surviving neurons had recovered from the initial insult, despite the fact that alpha-synuclein expression was maintained at a high level. These results show that nigral dopamine neurons are selectively vulnerable to high levels of either wild-type or mutant alpha-synuclein, pointing to a key role for alpha-synuclein in the pathogenesis of Parkinson's disease. Targeted overexpression of alpha-synuclein in the nigrostriatal system may provide a new animal model of Parkinson's disease that reproduces some of the cardinal pathological, neurochemical, and behavioral features of the human disease.

 

Krasnova, I. N., M. T. McCoy, et al. (2002). "cDNA array analysis of gene expression profiles in the striata of wild-type and Cu/Zn superoxide dismutase transgenic mice treated with neurotoxic doses of amphetamine." Faseb J 16(11): 1379-88.

            Amphetamine (AMPH) is a drug of abuse that causes the degeneration of striatal dopamine terminals in mammals. Superoxide radicals seem to participate in AMPH-induced damage because its toxicity is attenuated in Cu/Zn superoxide dismutase transgenic (SOD-tg) mice. To provide a detailed analysis of molecular changes associated with AMPH toxicity, we used cDNA arrays consisting of 1176 genes to detect differential changes in gene expression in the striata of wild-type and SOD-tg mice treated with neurotoxic doses of the drug. We found 42 genes that showed >1.8-fold changes in at least two consecutive time points during the course of the study and were differentially affected by AMPH in the two genotypes. Specifically, more transcription factors and genes involved in responses to injury/inflammation were affected in wild-type mice after AMPH administration. Some of these stimulant-induced superoxide-dependent alterations in gene expression might affect neuronal functions and promote neuronal damage. Other changes might help to provide some degree of protection against AMPH toxicity. These results support the view that the use of global array analysis of gene expression will help to identify novel molecular mediators of AMPH-induced neurodegeneration.

 

Kuhn, K., J. Wellen, et al. (2003). "The mouse MPTP model: gene expression changes in dopaminergic neurons." Eur J Neurosci 17(1): 1-12.

            Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Although valuable animal models have been developed, our knowledge of the aetiology and pathogenic factors implicated in PD is still insufficient to develop causal therapeutic strategies aimed at halting its progression. The neurotoxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is one of the most valuable models for analysing pathological aspects of PD. In this paper we studied the gene expression patterns underlying the pathogenesis of MPTP-induced neurodegeneration. We treated young and old C57BL/6 mice with different schedules of MPTP to induce degenerative processes that vary in intensity and time-course. During the first week after intoxication we used nonradioactive in situ-hybridization to investigate the expression patterns of genes associated with (i) dopamine metabolism and signalling; (ii) familial forms of PD; (iii) protein folding and (iv) energy metabolism. MPTP injections induced different severities of neuronal injury depending on the age of the animals and the schedule of administration as well as a significant degeneration in the striatum. In situ hybridization showed that MPTP intoxication initiated a number of gene expression changes that (i) were restricted to the neurons of the substantia nigra pars compacta; (ii) were correlated in intensity and number of changes with the age of the animals and the severity of histopathological disturbances; (iii) displayed in each a significant down-regulation by the end of one week after the last MPTP injection, but (iv) varied within one MPTP regimen in expression levels during the observation period. The subacute injection of MPTP into one-year-old mice induced the most severe changes in gene expression. All genes investigated were affected. However, alpha-synuclein was the only gene that was exclusively up-regulated in MPTP-treated animals displaying cell death.

 

Kupina, N. C., M. R. Detloff, et al. (2002). "Neuroimmunophilin ligand V-10,367 is neuroprotective after 24-hour delayed administration in a mouse model of diffuse traumatic brain injury." J Cereb Blood Flow Metab 22(10): 1212-21.

            The authors present two studies that investigate the biochemical and histologic effects of the nonimmunosuppressive neuroimmunophilin (NIMM) ligand V-10,367 in a mouse model of traumatic brain injury (TBI). In study 1, the authors examined the effect of V-10,367 (50 mg/kg x 2 per day, by mouth) on neurofilament M (NFM) protein levels and on alpha-spectrin breakdown products (SBDPs) when dosed for 2 days, starting 24 hours after TBI and killed on day 3. In study 2, V-10,367 was given for 10 days, starting 24 hours after TBI and the mice killed 6 weeks after TBI, to measure the extent of neurodegeneration (amino CuAg stain). The results in study 1 revealed that V-10,367-treatment significantly increased NFM protein levels in both sham and TBI mice. In addition, V-10,367 attenuated SBDP 150 levels in the cortex, striatum, and hippocampus. The results of study 2 indicated that TBI mice treated with V-10,367 demonstrated significantly less neurodegeneration compared to injured, vehicle-treated mice. In summary, these results suggest that NIMMs may be neuroprotective indirectly through inhibition of calpain-mediated cytoskeletal damage and perhaps via maintenance of neuronal plasticity. In the context of this mouse model of TBI, the therapeutic window for V-10,367's positive effects is at least 24 hours after injury, which, in the case of TBI models, is largely unprecedented for a neuroprotective compound.

 

Kurosaki, R., Y. Muramatsu, et al. (2003). "Role of dopamine transporter against MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in mice." Metab Brain Dis 18(2): 139-46.

            We investigated the alterations of dopamine transporter (DAT)-immunopositive cells against MPTP neurotoxicity, in comparison with tyrosine hydroxylase (TH)-immunopositive neurons and glial fibrillary acidic protein (GFAP)-immunopositive cells. This study showed that DAT and TH immunoreactivity was decreased gradually in the striatum and substantia nigra of mice after MPTP treatment. The patterns of the intense TH-immunoreactive fibers and cell bodies were similar to those of DAT-immunoreactive fibers and cell bodies in the striatum and substantia nigra of mice after MPTP treatment. In contrast, GFAP immunoreactivity was increased gradually in the striatum and substantia nigra after MPTP treatment. In our double-labeled immunostaining with anti-DAT and anti-GFAP antibodies, DAT immunoreactivity was observed only in the nigral dopaminergic neurons, but not in the reactive astrocytes. The present results provide further evidence that the functional damage of DAT may precede dopaminergic neuronal death after MPTP treatment, although the decrease in the number of TH-immunopositive neurons was more pronounced than that in the number of DAT-immunopositive neurons. Furthermore, our findings demonstrate that MPTP can selectively injure the dopaminergic neurons which DAT proteins are predominantly distributed on the striatum and substantia nigra. The results provide beneficial information for MPTP-induced neurodegeneration of the nigrostriatal dopaminergic neuronal pathway.

 

Lannuzel, A., P. P. Michel, et al. (2002). "Toxicity of Annonaceae for dopaminergic neurons: potential role in atypical parkinsonism in Guadeloupe." Mov Disord 17(1): 84-90.

            In the French West Indies there is an abnormally high frequency of levodopa-resistant parkinsonism, suggested to be caused by consumption of fruit and infusions of tropical plants, especially Annona muricata (corossol, soursop). To determine whether toxic substances from this plant can cause the neuronal degeneration or dysfunction underlying the syndrome, we exposed mesencephalic dopaminergic neurons in culture to the total extract (totum) of alkaloids from Annona muricata root bark and to two of the most abundant subfractions, coreximine and reticuline. After 24 hours, 50% of dopaminergic neurons degenerated with 18 microg/ml totum, 4.3 microg/ml (13 microM) coreximine, or 100 microg/ml (304 microM) reticuline. The effects of the alkaloid totum were not restricted to the population of dopaminergic cells since GABAergic neurons were also affected by the treatment. Nuclei in dying neurons showed DNA condensation or fragmentation, suggesting that neuronal death occurred by apoptosis. Cell death was not excitotoxic and did not require toxin uptake by the dopamine transporter. Neurodegeneration was attenuated by increasing the concentration of glucose in the culture medium, which also reduced the effect of the dopaminergic neurotoxin MPP+, a mitochondrial respiratory chain inhibitor. Toxin withdrawal after short-term exposure arrested cell death. Acute treatment with totum, coreximine, or reticuline reversibly inhibited dopamine uptake by a mechanism that was distinct from that causing neuronal death. GABA uptake was not reduced under the same conditions. This study suggests that alkaloids from A. muricata can modulate the function and the survival of dopaminergic nerve cells in vitro. It is therefore conceivable that repeated consumption could cause the neuronal dysfunction and degeneration underlying the West Indian parkinsonian syndrome.

 

Lee, E. N., S. Y. Lee, et al. (2003). "Lipid interaction of alpha-synuclein during the metal-catalyzed oxidation in the presence of Cu2+ and H2O2." J Neurochem 84(5): 1128-42.

            Alpha-synuclein co-exists with lipids in the Lewy bodies, a pathological hallmark of Parkinson's disease. Molecular interaction between alpha-synuclein and lipids has been examined by observing lipid-induced protein self-oligomerization in the presence of a chemical coupling reagent of N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline. Lipids such as phosphatidic acid, phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, and even arachidonic acid induced the self-oligomerization whereas phosphatidylcholine did not affect the protein. Because the oligomerizations occurred from critical micelle concentrations of the lipids, the self interaction of alpha-synuclein was shown to be a lipid-surface dependent phenomenon with head group specificity. By employing beta-synuclein and a C-terminally truncated alpha-synuclein (alpha-syn97), the head-group dependent self-oligomerization was demonstrated to occur preferentially at the N-terminal region while the fatty acid interaction leading to the protein self-association required the presence of the acidic C-terminus of alpha-synuclein. In the presence of Cu2+ and H2O2, phosphatidylinositol (PI), along with other acidic lipids, actually enhanced the metal-catalyzed oxidative self-oligomerization of alpha-synuclein. The dityrosine crosslink formation responsible for the PI-enhanced covalent self-oligomerization was more sensitive to variation of copper concentrations than that of H2O2 during the metal-catalyzed oxidation. The enhancement by PI was shown to be due to facilitation of copper localization to the protein because actual binding affinity between copper and alpha-synuclein increased from Kd of 44.7 microm to 5.9 microm in the presence of the lipid. Taken together, PI not only affects alpha-synuclein to be more self-interactive by providing the lipid surface, but also enhances the metal-catalyzed oxidative protein self-oligomerization by facilitating copper localization to the protein when the metal and H2O2 are provided. This observation therefore could be implicated in the formation of Lewy bodies as lipids and metal-catalyzed oxidative stress have been considered to be a part of pathological causes leading to the neurodegeneration.

 

Lehtonen, E., F. Bonnaud, et al. (2002). "AAV2 vectors mediate efficient and sustained transduction of rat embryonic ventral mesencephalon." Neuroreport 13(12): 1503-7.

            The success of transplantation of human embryonic mesencephalic tissue to treat parkinsonian patients is limited by the poor survival of the transplant. We show that an AAV2 vector mediates efficient expression of the egfp reporter gene in organotypic cultures of freshly explanted solid fragments of rat embryonic ventral mesencephalon (VM). We observed early and sustained transgene expression (4 days to > or = 6 weeks). Furthermore, rAAV-infected rat embryonic VM transplanted in the adult striatum continued to express EGFP for > or = 3 months. More than 95% of the transduced cells were neurons. Dopaminergic neurons were transduced at low frequency at earlier time points. This method of gene delivery could prove useful to achieve local, continuous secretion of neurotrophic factors at physiologically relevant doses to treat Parkinson's disease.

 

Liu, B. and J. S. Hong (2003). "Neuroprotective effect of naloxone in inflammation-mediated dopaminergic neurodegeneration. Dissociation from the involvement of opioid receptors." Methods Mol Med 79: 43-54.

           

Liu, B. and J. S. Hong (2003). "Role of microglia in inflammation-mediated neurodegenerative diseases: mechanisms and strategies for therapeutic intervention." J Pharmacol Exp Ther 304(1): 1-7.

            Evidence from postmortem analysis implicates the involvement of microglia in the neurodegenerative process of several degenerative neurological diseases, including Alzheimer's disease and Parkinson's disease. It remains to be determined, however, whether microglial activation plays a role in the initiation stage of disease progression or occurs merely as a response to neuronal death. Activated microglia secrete a variety of proinflammatory and neurotoxic factors that are believed to induce and/or exacerbate neurodegeneration. In this article, we summarize recent advances on the study of the role of microglia based on findings from animal and cell culture models in the pathogenesis of neurodegenerative diseases, with particular emphasis on Parkinson's disease. In addition, we also discuss novel approaches to potential therapeutic strategies.

 

Liu, Y., L. Qin, et al. (2003). "Dextromethorphan protects dopaminergic neurons against inflammation-mediated degeneration through inhibition of microglial activation." J Pharmacol Exp Ther 305(1): 212-8.

            Inflammation in the brain has increasingly been recognized to play an important role in the pathogenesis of several neurodegenerative disorders, including Parkinson's disease and Alzheimer's disease. Inflammation-mediated neurodegeneration involves activation of the brain's resident immune cells, the microglia, which produce proinflammatory and neurotoxic factors, including cytokines, reactive oxygen intermediates, nitric oxide, and eicosanoids that impact on neurons to induce neurodegeneration. Hence, identification of compounds that prevent microglial activation may be highly desirable in the search for therapeutic agents for inflammation-mediated neurodegenerative diseases. In this study, we report that dextromethorphan (DM), an ingredient widely used in antitussive remedies, reduced the inflammation-mediated degeneration of dopaminergic neurons through inhibition of microglial activation. Pretreatment (30 min) of rat mesencephalic neuron-glia cultures with DM (1-10 micro M) reduced, in a dose-dependent manner, the microglia-mediated degeneration of dopaminergic neurons induced by lipopolysaccharide (LPS, 10 ng/ml). Significant neuroprotection by DM was also evident when DM was applied to cultures up to 60 min after the addition of LPS. The neuroprotective effect of DM was attributed to inhibition of LPS-stimulated microglial activation because DM significantly inhibited the LPS-induced production of tumor necrosis factor-alpha, nitric oxide, and superoxide free radicals. This conclusion was further supported by the finding that DM failed to prevent 1-methyl-4-phenylpyridinium- or beta-amyloid peptide (1-42)-induced dopaminergic neurotoxicity in neuron-enriched cultures. In addition, because LPS did not produce any significant increase in the release of excitatory amino acids from neuron-glia cultures and N-methyl-D-aspartate antagonist dizocilpine maleate failed to afford significant neuroprotection, it is unlikely that the neuroprotective effect of DM is mediated through N-methyl-D-aspartate receptors. These results suggest that DM may be a promising therapeutic agent for the treatment of Parkinson's disease.

 

Liu, Y., L. Qin, et al. (2002). "Inhibition by naloxone stereoisomers of beta-amyloid peptide (1-42)-induced superoxide production in microglia and degeneration of cortical and mesencephalic neurons." J Pharmacol Exp Ther 302(3): 1212-9.

            Previously we reported that naloxone stereoisomers, in an opioid receptor-independent manner, attenuated the inflammation-mediated degeneration of dopaminergic neurons by inhibition of the activation of microglia, the resident immune cells in the brain. Recently we discovered that beta-amyloid peptide Abeta (1-42) exhibited enhanced neurotoxicity toward both cortical and mesencephalic neurons through the activation of microglia and production of superoxide. The purpose of this study was to determine whether naloxone isomers had any effect on Abeta (1-42)-induced neurodegeneration. Pretreatment of either cortical or mesencephalic neuron-glia cultures with 1 to 10 microM (-)-naloxone, prior to treatment for up to 11 days with 0.1 to 3 microM Abeta (1-42), afforded significant neuroprotection as judged by neurotransmitter uptake, immunocytochemical analysis, and cell counting. More importantly, (+)-naloxone, the ineffective enantiomer of (-)-naloxone in binding opioid receptors, was equally effective in affording neuroprotection. Mechanistically, inhibition of Abeta (1-42)-induced production of superoxide in microglia underlay the neuroprotective effect of naloxone stereoisomers. Moreover, neuroprotection and inhibition of Abeta (1-42)-induced superoxide production was also achieved with naloxone methiodide, a charged analog with quaternary amine, suggesting that the site of action for naloxone isomers is at the cell surface of microglia. These results demonstrated that naloxone isomers, through mechanisms unrelated to the opioid receptors, were capable of inhibiting Abeta (1-42)-induced microglial activation and degeneration of both cortical and mesencephalic neurons. Combined with our previous observations with inflammagen-induced neurodegeneration, naloxone analogs, especially (+)-naloxone, may have potential therapeutic efficacy for the treatment of Alzheimer's and Parkinson's disease.

 

Lo Bianco, C., J. L. Ridet, et al. (2002). "alpha -Synucleinopathy and selective dopaminergic neuron loss in a rat lentiviral-based model of Parkinson's disease." Proc Natl Acad Sci U S A 99(16): 10813-8.

            Parkinson's disease (PD) is characterized by the progressive loss of substantia nigra dopaminergic neurons and the presence of cytoplasmic inclusions named Lewy bodies. Two missense mutations of the alpha-synuclein (alpha-syn; A30P and A53T) have been described in several families with an autosomal dominant form of PD. alpha-Syn also constitutes one of the main components of Lewy bodies in sporadic cases of PD. To develop an animal model of PD, lentiviral vectors expressing different human or rat forms of alpha-syn were injected into the substantia nigra of rats. In contrast to transgenic mice models, a selective loss of nigral dopaminergic neurons associated with a dopaminergic denervation of the striatum was observed in animals expressing either wild-type or mutant forms of human alpha-syn. This neuronal degeneration correlates with the appearance of abundant alpha-syn-positive inclusions and extensive neuritic pathology detected with both alpha-syn and silver staining. Lentiviral-mediated expression of wild-type or mutated forms of human alpha-syn recapitulates the essential neuropathological features of PD. Rat alpha-syn similarly leads to protein aggregation but without cell loss, suggesting that inclusions are not the primary cause of cell degeneration in PD. Viral-mediated genetic models may contribute to elucidate the mechanism of alpha-syn-induced cell death and allow the screening of candidate therapeutic molecules.

 

Luo, J., M. G. Kaplitt, et al. (2002). "Subthalamic GAD gene therapy in a Parkinson's disease rat model." Science 298(5592): 425-9.

            The motor abnormalities of Parkinson's disease (PD) are caused by alterations in basal ganglia network activity, including disinhibition of the subthalamic nucleus (STN), and excessive activity of the major output nuclei. Using adeno-associated viral vector-mediated somatic cell gene transfer, we expressed glutamic acid decarboxylase (GAD), the enzyme that catalyzes synthesis of the neurotransmitter GABA, in excitatory glutamatergic neurons of the STN in rats. The transduced neurons, when driven by electrical stimulation, produced mixed inhibitory responses associated with GABA release. This phenotypic shift resulted in strong neuroprotection of nigral dopamine neurons and rescue of the parkinsonian behavioral phenotype. This strategy suggests that there is plasticity between excitatory and inhibitory neurotransmission in the mammalian brain that could be exploited for therapeutic benefit.

 

Lutz, P. L., H. M. Prentice, et al. (2003). "Is turtle longevity linked to enhanced mechanisms for surviving brain anoxia and reoxygenation?" Exp Gerontol 38(7): 797-800.

            We suggest that the processes that protect the turtle brain against anoxia and subsequent reoxygenation might also contribute to turtle longevity since many of them are linked to age related neurodegeneration. In the turtle the mechanisms for conserving ion channel function are particularly robust. The anoxic turtle brain avoids excitatory neurotransmitter toxicity by maintaining a balance between dopamine and glutamate-release and still active uptake mechanisms. In the anoxic turtle brain the inhibitory tone is strengthened through a sustained rise in extracellular GABA, and a corresponding increase in the density of GABA(A) receptors. The turtle has enhanced mechanisms that protect against the formation of ROS and mechanisms to protect from ROS damage. As many of these may be selectively activated during anoxia and recovery, the turtle could serve as a useful model to identify and investigate mechanisms for activating key protection and rescue mechanisms implicated in aging.

 

MacDonald, V. and G. M. Halliday (2002). "Selective loss of pyramidal neurons in the pre-supplementary motor cortex in Parkinson's disease." Mov Disord 17(6): 1166-73.

            The nonprimary motor cortices have not previously been studied in Parkinson's disease, despite the selective pattern of dysfunction observed in these regions. In particular, the pre-supplementary motor region is consistently underactive, with successful treatments correlating with increased excitatory drive to nonprimary motor regions. This finding could suggest a primary cortical abnormality in the pre-supplementary motor area (pre-SMA) in Parkinson's disease. We analysed and compared neuronal number in the pre-SMA and dorsolateral premotor cortical regions in 5 cases of Parkinson's disease and 5 controls. For each cortical region, the total neuronal number as well as the estimated numbers of subpopulations of interneurons and pyramidal neurons was quantified using previously published unbiased techniques. The results showed a significant loss of cortico-cortical projecting pyramidal neurons in the pre-SMA with no loss of other pyramidal neurons or interneurons either in this region or in the dorsolateral premotor region. These findings indicate a highly selective loss of pyramidal cells in the pre-SMA in Parkinson's disease, consistent with previous imaging findings in this disease. Our results implicate the degeneration of the premotor projection from the pre-SMA, along with dopaminergic basal ganglia dysfunction, in the pathogenesis of Parkinson's disease.

 

Mandel, S., E. Grunblatt, et al. (2003). "Neuroprotective strategies in Parkinson's disease : an update on progress." CNS Drugs 17(10): 729-62.

            In spite of the extensive studies performed on postmortem substantia nigra from Parkinson's disease patients, the aetiology of the disease has not yet been established. Nevertheless, these studies have demonstrated that, at the time of death, a cascade of events had been initiated that may contribute to the demise of the melanin-containing nigro-striatal dopamine neurons. These events include increased levels of iron and monoamine oxidase (MAO)-B activity, oxidative stress, inflammatory processes, glutamatergic excitotoxicity, nitric oxide synthesis, abnormal protein folding and aggregation, reduced expression of trophic factors, depletion of endogenous antioxidants such as reduced glutathione, and altered calcium homeostasis. To a large extent, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA) animal models of Parkinson's disease confirm these findings. Furthermore, neuroprotection can be afforded in these models with iron chelators, radical scavenger antioxidants, MAO-B inhibitors, glutamate antagonists, nitric oxide synthase inhibitors, calcium channel antagonists and trophic factors.Despite the success obtained with animal models, clinical neuroprotection is much more difficult to accomplish. Although the negative studies obtained with the MAO-B inhibitor selegiline (deprenyl) and the antioxidant tocopherol (vitamin E) may have resulted from an inappropriate choice of drug (selegiline) or an inadequate dose (tocopherol), the niggling problem that still remains is why these drugs, and others, do work in animals while they fail in the clinic. One reason for this may be related to the fact that in normal human brains the number of dopaminergic neurons falls by around 3-5% every decade, while in Parkinson's disease this decline is greater. Brain autopsy studies have shown that by the time the disease is identified, some 70-75% of the dopamine-containing neurons have been lost. More sensitive reliable methods and clinical correlative markers are required to discern between confoundable symptomatic effects versus a possible neuroprotective action of drugs, namely, the ability to delay or forestall disease progression by protecting or rescuing the remaining dopamine neurons or even restoring those that have been lost.A number of other possibilities for the clinical failure of potential neuroprotectants also exist. First, the animal models of Parkinson's disease may not be totally reflective of the disease and, therefore, the chemical pathologies established in the animal models may not cause, or contribute to, the progression of the disease clinically. Second, because of the series of events occurring in neurodegeneration and our ignorance about which of these factors constitutes the primary event in the pathogenic process, a single drug may not be adequate to induce neuroprotection and, as a consequence, use of a cocktail of drugs may be more appropriate. The latter concept receives support from recent complementary DNA (cDNA) microarray gene expression studies, which show the existence of a gene cascade of events occurring in the nigrostriatal pathway of MPTP, 6-OHDA and methamphetamine animal models of Parkinson's disease.Even with the advent of powerful new tools such as genomics, proteomics, brain imaging, gene replacement therapy and knockout animal models, the desired end result of neuroprotection is still beyond our current capability.

 

Marchese, G., M. A. Casu, et al. (2002). "Sub-chronic treatment with classical but not atypical antipsychotics produces morphological changes in rat nigro-striatal dopaminergic neurons directly related to "early onset" vacuous chewing." Eur J Neurosci 15(7): 1187-96.

            In the present work, we investigated if an impairment of dopaminergic neurons after subchronic haloperidol treatment might be a possible physiopathologic substrate of the "early onset" vacuous chewing movements (VCMs) in rats. For this purpose, different antipsychotics were used to analyse a possible relationship between VCMs development and morphological alterations of tyrosine-hydroxylase-immunostained (TH-IM) neurons. Rats treated twice a day with haloperidol displayed a significant increase of VCMs that was both time- (2-4 weeks) and dose (0.1-1 mg/kg) dependent. Immunocytochemical analysis showed a shrinkage of TH-IM cell bodies in substantia nigra pars compacta and reticulata and a reduction of TH-immunostaining in the striatum of haloperidol treated rats with the arising of VCMs. No differences were observed in TH-IM neurons of ventral tegmental area and nucleus accumbens vs. control rats. The atypical antipsychotics risperidone (2 mg/kg, twice a day), amisulpride (20 mg/kg, twice a day) and clozapine (10 mg/kg, twice a day) did not produce any nigro-striatal morphological changes or VCMs. TH-IM nigro-striatal neuron morphological alterations and VCMs were still present after three days of withdrawal in rats treated for four weeks with haloperidol (1 mg/kg). Both the main morphological changes and the behavioural correlate disappeared after three weeks of withdrawal. These results suggest that haloperidol induces a morphological impairment of the dopaminergic nigro-striatal neurons which is directly associated with the arising, permanency and disappearance of VCMs in rats.

 

Mathias, C. J. (2002). "Neurodegeneration, parkinsonian syndromes and autonomic failure." Auton Neurosci 96(1): 50-8.

           

McCormack, A. L., M. Thiruchelvam, et al. (2002). "Environmental risk factors and Parkinson's disease: selective degeneration of nigral dopaminergic neurons caused by the herbicide paraquat." Neurobiol Dis 10(2): 119-27.

            Environmental toxicants and, in particular, pesticides have been implicated as risk factors in Parkinson's disease (PD). The purpose of this study was to determine if selective nigrostriatal degeneration could be reproduced by systemic exposure of mice to the widely used herbicide paraquat. Repeated intraperitoneal paraquat injections killed dopaminergic neurons in the substantia nigra (SN) pars compacta, as assessed by stereological counting of tyrosine hydroxylase (TH)-immunoreactive and Nissl-stained neurons. This cell loss was dose- and age-dependent. Several lines of evidence indicated selective vulnerability of dopaminergic neurons to paraquat. The number of GABAergic cells was not decreased in the SN pars reticulata, and counting of Nissl-stained neurons in the hippocampus did not reveal any change in paraquat-treated mice. Degenerating cell bodies were observed by silver staining, but only in the SN pars compacta, and glial response was present in the ventral mesencephalon but not in the frontal cortex and cerebellum. No significant depletion of striatal dopamine followed paraquat administration. On the other hand, enhanced dopamine synthesis was suggested by an increase in TH activity. These findings unequivocally show that selective dopaminergic degeneration, one of the pathological hallmarks of PD, is also a characteristic of paraquat neurotoxicity. The apparent discrepancy between pathological (i.e., neurodegeneration) and neurochemical (i.e., lack of significant dopamine loss) effects represents another important feature of this paraquat model and is probably a reflection of compensatory mechanisms by which neurons that survive damage are capable of restoring neurotransmitter tissue levels.

 

McGorum, B. C., R. Wilson, et al. (2003). "Systemic concentrations of antioxidants and biomarkers of macromolecular oxidative damage in horses with grass sickness." Equine Vet J 35(2): 121-6.

            REASONS FOR PERFORMING STUDY: The aetiopathogenesis of equine grass sickness (EGS) is unknown. The role of free radical-mediated neuronal damage has not previously been investigated in this condition. OBJECTIVES: To investigate the potential contribution of oxidative damage and antioxidant status to neurodegeneration in EGS. METHODS: Systemic levels of surrogate biomarkers were determined in 10 horses with acute EGS and in 2 control populations; 10 healthy horses co-grazing with the 10 EGS horses at the onset of clinical disease, and 10 healthy mares grazing where EGS has not been reported. RESULTS: EGS horses had alterations in levels of several antioxidants, consistent with oxidative stress, the acute phase response and/or the secondary metabolic complications of EGS. EGS horses had elevated plasma dihydroxyphenylalanine (DOPA) levels. CONCLUSIONS: The elevated DOPA levels probably reflected a generalised disturbance of catecholamine metabolism rather than increased DOPA production via free radical-mediated oxidation of tyrosine. However, there was no evidence of systemic macromolecular oxidative damage. POTENTIAL CLINICAL RELEVANCE: Further work is required to determine whether macromolecular oxidative damage occurring at the neuronal level contributes to EGS.

 

McNaught, K. S., R. Belizaire, et al. (2003). "Altered proteasomal function in sporadic Parkinson's disease." Exp Neurol 179(1): 38-46.

            Parkinson's disease (PD) is characterized pathologically by preferential degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNc). Nigral cell death is accompanied by the accumulation of a wide range of poorly degraded proteins and the formation of proteinaceous inclusions (Lewy bodies) in dopaminergic neurons. Mutations in the genes encoding alpha-synuclein and two enzymes of the ubiquitin-proteasome system, parkin and ubiquitin C-terminal hydrolase L1, are associated with neurodegeneration in some familial forms of PD. We now show that, in comparison to age-matched controls, alpha-subunits (but not beta-subunits) of 26/20S proteasomes are lost within dopaminergic neurons and 20S proteasomal enzymatic activities are impaired in the SNc in sporadic PD. In addition, while the levels of the PA700 proteasome activator are reduced in the SNc in PD, PA700 expression is increased in other brain regions such as the frontal cortex and striatum. We also found that levels of the PA28 proteasome activator are very low to almost undetectable in the SNc compared to other brain areas in both normal and PD subjects. These findings suggest that failure of the ubiquitin-proteasome system to adequately clear unwanted proteins may underlie vulnerability and degeneration of the SNc in both sporadic and familial PD.

 

Miguel-Hidalgo, J. J., X. A. Alvarez, et al. (2002). "Neuroprotection by memantine against neurodegeneration induced by beta-amyloid(1-40)." Brain Res 958(1): 210-21.

            Progressive neuronal loss and cognitive decline in Alzheimer's disease (AD) might be aggravated by beta-amyloid-enhanced excitotoxicity. Memantine is an uncompetitive NMDA receptor antagonist under clinical development for the treatment of AD. Memantine has neuroprotective actions in several in vitro and in vivo models. In the present study, we determined whether memantine protected against beta-amyloid induced neurotoxicity and learning impairment in rats. Twenty Sprague-Dawley rats received vehicle or vehicle plus memantine (steady-state plasma concentrations of 2.34+/-0.23 microM, n=10) s.c. by osmotic pump for 9 days. After 2 days of treatment, 2 microl of water containing beta-amyloid 1-40 [Abeta(1-40)] were injected into the hippocampal fissure. On the ninth day of treatment, animals were sacrificed, and morphological and immunohistochemical techniques were used to determine the extent of neuronal degeneration and astrocytic and microglial activation in the hippocampus. Psychomotor activity and spatial discrimination were tested on the eighth day of treatment. Abeta(1-40), but not water, injections into hippocampus led to neuronal loss in the CA1 subfield, evidence of widespread apoptosis, and astrocytic and microglial activation and hypertrophy. Memantine treated animals had significant reductions in the amount of neuronal degeneration, pyknotic nuclei, and GFAP immunostaining as compared with vehicle treated animals. These data suggest that memantine, at therapeutically relevant concentrations, can protect against neuronal degeneration induced by beta-amyloid.

 

Miller, J. W. (2002). "Homocysteine, folate deficiency, and Parkinson's disease." Nutr Rev 60(12): 410-3.

            Folate deficiency sensitizes mice to dopaminergic neurodegeneration and motor dysfunction caused by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Additional experiments indicate that this effect of folate deficiency may be mediated by homocysteine. These findings suggest that folate deficiency and hyperhomocysteinemia are risk factors for Parkinson's disease.

 

Misu, Y., N. Furukawa, et al. (2002). "DOPA causes glutamate release and delayed neuron death by brain ischemia in rats." Neurotoxicol Teratol 24(5): 629-38.

            DOPA seems to be a neuromodulator in striata and hippocampal CA1 and a neurotransmitter of the primary baroreceptor afferents terminating in the nucleus tractus solitarii (NTS) and baroreflex pathways in the caudal ventrolateral medulla and rostral ventrolateral medulla in the brainstem of rats. DOPA recognition sites differ from dopamine (DA) D(1) and D(2) and ionotropic glutamate receptors. Via DOPA sites, DOPA stereoselectively releases by itself neuronal glutamate from in vitro and in vivo striata. In the cultured neurons, DOPA and DA cause neuron death via autoxidation. In addition, DOPA causes autoxidation-irrelevant neuron death via glutamate release. Furthermore, DOPA released by four-vessel occlusion seems to be an upstream causal factor for glutamate release and resultant delayed neuron death by brain ischemia in striata and hippocampal CA1. Glutamate has been regarded as a neurotransmitter of baroreflex pathways. Herein, we propose a new pathway that DOPA is a neurotransmitter of the primary aortic depressor nerve and glutamate is that of secondary neurons in neuronal microcircuits of depressor sites in the NTS. DOPA seems to release unmeasurable, but functioning, endogenous glutamate from the secondary neurons via DOPA sites. A common following pathway may be ionotropic glutamate receptors-nNOS activation-NO production-baroreflex neurotransmission and delayed neuron death. However, we are concerned that DOPA therapy may accelerate neuronal degeneration process especially at progressive stages of Parkinson's disease.

 

Mitchell, I. J., A. C. Cooper, et al. (2002). "Acute administration of haloperidol induces apoptosis of neurones in the striatum and substantia nigra in the rat." Neuroscience 109(1): 89-99.

            Chronic administration of typical neuroleptics is associated with tardive dyskinesia in some patients. This dyskinetic syndrome has been associated with loss of GABAergic markers in the basal ganglia but the cause of these GABAergic depletions remains uncertain. Haloperidol, a commonly prescribed typical neuroleptic, is known to be toxic in vitro, possibly as a consequence of its conversion to pyridinium-based metabolites and potentially by raising glutamate-mediated transmission. We report here that the in vivo, acute administration of a large dose of haloperidol resulted in a microglial response indicative of neuronal damage. This was accompanied by an increase in the number of apoptotic cells in the striatum (especially in the dorsomedial caudate putamen) and in the substantia nigra pars reticulata. These apoptotic cells were characterised by the stereotaxic injection of a retrograde neuroanatomical tracer into the projection targets of the striatum and substantia nigra pars reticulata prior to the systemic injection of haloperidol. This procedure confirmed that the dying cells were neurones and demonstrated that within the striatum the majority were striatopallidal neurones though relatively high levels of apoptotic striatoentopeduncular neurones were also seen.The possibility that chronic administration of haloperidol could induce cumulative neuronal loss in the substantia nigra pars reticulata and thereby induce the pathological changes which lead to tardive dyskinesia is discussed.

 

Montine, K. S., K. R. Sidell, et al. (2002). "Dopamine thioethers: formation in brain and neurotoxicity." Neurotox Res 4(7-8): 663-669.

            Dopamine (DA) oxidation is proposed to be a significant contributor to some forms of neurodegeneration, although the mechanisms are not fully resolved. Recent results from in vitro and in vivo models have suggested that some products of oxidized DA metabolized along the mercapturic acid pathway (MAP) may contribute to dopaminergic neurodegeneration. Here we review recent findings on the localization of MAP enzymes in human brain, as well as the concentration and neurotoxicity of their DA thioether products.

 

Mori, I., B. Liu, et al. (2002). "Successful protection by amantadine hydrochloride against lethal encephalitis caused by a highly neurovirulent recombinant influenza A virus in mice." Virology 303(2): 287-96.

            A mouse model system for a lethal encephalitis due to influenza has been established by stereotaxic microinjection with the recombinant R404BP strain of influenza A virus into the olfactory bulb of C57BL/6 mice. The virus infection spread selectively to neurons in nuclei of the broad areas of the brain parenchyma that have anatomical connections to the olfactory bulb, leading to apoptotic neurodegeneration. The inflammatory reaction at the extended stage of viral infection involved the vascular structures affected by induction of inducible nitric oxide synthase and protein nitration; those were related to the etiology of fatal brain edema. The intraperitoneal administration of amantadine inhibited the viral growth in the brain and saved mice from the lethal encephalitis. The severity of neuronal loss paralleled the time lag between the virus challenge and the start of amantadine treatment. Thus, early pharmacological intervention is essential to minimize neurological deficits due to influenza virus-induced neurodegeneration.

 

Mouradian, M. M. (2002). "Recent advances in the genetics and pathogenesis of Parkinson disease." Neurology 58(2): 179-85.

            The identification of three genes and several additional loci associated with inherited forms of levodopa-responsive PD has confirmed that this is not a single disorder. Yet, analyses of the structure and function of these gene products point to the critical role of protein aggregation in dopaminergic neurons of the substantia nigra as the common mechanism leading to neurodegeneration in all known forms of this disease. The three specific genes identified to date--alpha-synuclein, Parkin, and ubiquitin C terminal hydrolase L1--are either closely involved in the proper functioning of the ubiquitin-proteasome pathway or are degraded by this protein-clearing machinery of cells. Knowledge gained from genetically transmitted PD also has clear implications for nonfamilial forms of the disease. Lewy bodies, even in sporadic PD, contain these three gene products, particularly abundant amounts of fibrillar alpha-synuclein. Increased aggregation of alpha-synuclein by oxidative stress, as well as oxidant-induced proteasomal dysfunction, link genetic and potential environmental factors in the onset and progression of the disease. The biochemical and molecular cascades elucidated from genetic studies in PD can provide novel targets for curative therapies.

 

Muramatsu, Y., R. Kurosaki, et al. (2003). "Expression of S-100 protein is related to neuronal damage in MPTP-treated mice." Glia 42(3): 307-13.

            S-100beta is a calcium-binding protein expressed at high levels in brain and is known as a marker of brain damage. However, little is known about the role of S-100beta protein during neuronal damage caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To determine whether S-100beta protein is induced in glial cells after MPTP treatment, we investigated the expression of S-100 protein immunohistochemically, using MPTP-treated mice. We also examined the change of neurons and glial cells in mice after MPTP treatment. The present study shows that tyrosine hydroxylase (TH) immunoreactivity decreased gradually in the striatum and substantia nigra from 1 day after MPTP treatment. Thereafter, TH-immunopositive cells and fibers decreased in the striatum and substantia nigra at 3 days after MPTP treatment. In contrast, S-100-immunopositive cells and glial fibrillary acidic protein (GFAP)-immunopositive cells increased markedly in the striatum and substantia nigra at 3 days after MPTP treatment. Seven days after MPTP treatment, S-100-immunopositive cells decreased in the striatum and substantia nigra. However, the number of GFAP-immunopositive cells increased in these regions. In double-labeled immunostaining with anti-S-100 and anti-GFAP antibodies, S-100 immunoreactivity was observed only in the GFAP-positive astrocytes. These results provide evidence that astrocytic activation may play a role in the pathogenesis of MPTP-induced degeneration of dopaminergic neurons. Furthermore, the present study demonstrates that S-100 protein is expressed selectively by astrocytes, but not by microglia, after MPTP treatment. These results provide valuable information for the pathogenesis of the acute stage of Parkinson's disease.

 

Murray, H. E., A. V. Pillai, et al. (2003). "Dose- and sex-dependent effects of the neurotoxin 6-hydroxydopamine on the nigrostriatal dopaminergic pathway of adult rats: differential actions of estrogen in males and females." Neuroscience 116(1): 213-22.

            Epidemiological and clinical studies provide growing evidence for marked sex differences in the incidence of certain neurological disorders that are largely attributed to the neuroprotective effects of estrogen. Thus there is a keen interest in the clinical potential of estrogen-related compounds to act as novel therapeutic agents in conditions of neuronal injury and neurodegeneration such as Parkinson's disease. Studies employing animal models of neurodegeneration in ovariectomised female rats treated with estrogen support this hypothesis, yet experimental evidence for sex differences in the CNS response to direct neurotoxic insult is limited and, as yet, few studies have addressed the role played by endogenously produced hormones in neuroprotection. Therefore, in this study we aimed to determine (1) whether the prevailing levels of sex steroid hormones in the intact rat provide a degree of protection against neuronal assault in females compared with males and (2) whether sex differences depend solely on male/female differences in circulating estrogen levels or whether androgens could also play a role. Using the selective, centrally administered neurotoxin 6-hydroxydopamine, which induces a lesion in the nigrostriatal dopaminergic pathway similar to that seen in Parkinson's disease, we have demonstrated a sexually dimorphic (male-dominant), dose-dependent susceptibility in rats. Furthermore, following gonadectomy, dopamine depletion resulting from a submaximal dose of 6-hydroxydopamine (1 microg) was reduced in male rats, whereas in females, ovariectomy enhanced dopamine depletion. Administration of the nonaromatizable androgen dihydrotestosterone to gonadectomized animals had no significant effect on 6-hydroxydopamine toxicity in either males or females, whereas treatment of gonadectomized males and females with physiological levels of estrogen restored the extent of striatal dopamine loss to that seen in intact rats, viz, estrogen therapy reduced lesion size in females but increased it in males. Taken together, our findings strongly suggest that there are sex differences in the mechanisms whereby nigrostriatal dopaminergic neurones respond to injury. They also reveal that the reported clinically beneficial effects of estrogen in females may not be universally adopted for males. While the reasons for this gender-determined difference in response to the activational action of estrogen are unknown, we hypothesize that they may well be related to the early organizational events mediated by sex steroid hormones, which ultimately result in the sexual differentiation of the brain.

 

Nakai, M., A. Mori, et al. (2003). "1-methyl-4-phenylpyridinium (MPP+) decreases mitochondrial oxidation-reduction (REDOX) activity and membrane potential (Deltapsi(m)) in rat striatum." Exp Neurol 179(1): 103-10.

            Mitochondrial dysfunction has long been implicated in the death of nigrostriatal dopaminergic neurons in Parkinson's disease (PD) and its experimental models. Here we further analyzed changes in the mitochondrial oxidation-reduction (REDOX) activity and membrane potential (Deltapsi(m)) of striatal synaptosomes after the infusion of 1-methyl-4-phenylpyridinium (MPP+) into rat striatum. MPP+ (40 nmol) treatment produced decreases in mitochondrial REDOX activity and Deltapsi(m) at 18 h, as measured by fluorometric analysis with both Alamar blue and JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide) dyes. At this time point, tyrosine hydroxylase (TH) and dopamine transporter (DAT) protein levels were not altered, but both decreased at 7 days after MPP+ (40 nmol) infusion. Both measures of mitochondrial dysfunction induced by MPP+ (40 nmol) at 18 h were attenuated, at least in part, by pretreatment with a selective dopamine uptake inhibitor GBR-12909 (1-(2-(bis(4-fluorophenyl)methoxy)ethyl)-4-(3-phenylpropyl) piperazine). In addition, GBR-12909 partially attenuated MPP+ (40 nmol)-caused a loss of striatal nerve terminal as indicated by decreases in TH and DAT immunoreactivities as well as dopamine and its metabolites levels. The present study indicates that decreases in mitochondrial REDOX activity and Deltapsi(m) may play a role in MPP+ -induced dopaminergic neurotoxicity, and further provides that improvement of mitochondrial dysfunction may be a better way to slow progressive dopaminergic neurodegeneration commonly associated with PD.

 

Nass, R. and R. D. Blakely (2003). "THE CAENORHABDITIS ELEGANS DOPAMINERGIC SYSTEM: Opportunities for Insights into Dopamine Transport and Neurodegeneration." Annu Rev Pharmacol Toxicol 43: 521-44.

            The neurotransmitter dopamine (DA) plays a central role in the coordination of movement, attention, and the recognition of reward. Loss of DA from the basal ganglia, as a consequence of degeneration of neurons in the substantia nigra, triggers postural instability and Parkinson's disease (PD). DA transporters (DATs) regulate synaptic DA availability and provide a conduit for the uptake of DA mimetic neurotoxins, which can be used to evoke neuronal death and Parkinson-like syndrome. Recently, we have explored the sensitivity of DA neurons in the nematode Caenorhabditis elegans to the Parkinsonian-inducing neurotoxin 6-hydroxydopamine (6-OHDA) and found striking similarities, including DAT dependence, to neurodegeneration observed in mammalian models. In this review, we present our findings in the context of molecular and behavioral dimensions of DA signaling in C. elegans with an eye toward opportunities for uncovering DAT mutants, DAT regulators, and components of toxin-mediated cell death.

 

Nass, R., D. H. Hall, et al. (2002). "Neurotoxin-induced degeneration of dopamine neurons in Caenorhabditis elegans." Proc Natl Acad Sci U S A 99(5): 3264-9.

            Parkinson's disease is a complex neurodegenerative disorder characterized by the death of brain dopamine neurons. In mammals, dopamine neuronal degeneration can be triggered through exposure to neurotoxins accumulated by the presynaptic dopamine transporter (DAT), including 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenylpyridinium. We have established a system for the pharmacological and genetic evaluation of neurotoxin-induced dopamine neuronal death in Caenorhabditis elegans. Brief (1 h) exposure of green fluorescent protein-tagged, living worms to 6-OHDA causes selective degeneration of dopamine neurons. We demonstrate that agents that interfere with DAT function protect against 6-OHDA toxicity. 6-OHDA-triggered neural degeneration does not require the CED-3/CED-4 cell death pathway, but is abolished by the genetic disruption of the C. elegans DAT.

 

Nath, A., K. F. Hauser, et al. (2002). "Molecular basis for interactions of HIV and drugs of abuse." J Acquir Immune Defic Syndr 31 Suppl 2: S62-9.

            In certain populations around the world, the HIV pandemic is being driven by drug-abusing populations. Mounting evidence suggests that these patient populations have accelerated and more severe neurocognitive dysfunction compared with non-drug-abusing HIV-infected populations. Because most drugs of abuse are central nervous system stimulants, it stands to reason that these drugs may synergize with neurotoxic substances released during the course of HIV infection. Clinical and laboratory evidence suggests that the dopaminergic systems are most vulnerable to such combined neurotoxicity. Identifying common mechanisms of neuronal injury is critical to developing therapeutic strategies for drug-abusing HIV-infected populations. This article reviews 1) the current evidence for neurodegeneration in the setting of combined HIV infection and use of methamphetamine, cocaine, heroin or alcohol; 2) the proposed underlying mechanisms involved in this combined neurotoxicity; and 3) future directions for research. This article also suggests therapeutic approaches based on our current understanding of the neuropathogenesis of dementia due to HIV infection and drugs of abuse.

 

O'Dell, S. J. and J. F. Marshall (2002). "Effects of vibrissae removal on methamphetamine-induced damage to rat somatosensory cortical neurons." Synapse 43(2): 122-30.

            Repeated methamphetamine (mAMPH) damages forebrain monoamine terminals and causes degeneration of nonmonoaminergic cell bodies in rat primary somatosensory cortex (S1). These degenerating cortical neurons can be labeled with the fluorochrome dye Fluoro-Jade (FJ) and are found almost exclusively in layers II/III and IV of the vibrissae representation in S1. Within S1, layer IV is organized into discrete, anatomically identifiable units termed barrels, each of which receives information from a single whisker. We previously reported that mAMPH-damaged neurons in S1 were located within the whisker barrels, suggesting that the prolonged mAMPH-induced whisking contributes to S1 neuronal injury. Here, we investigate effects of vibrissae removal on mAMPH-induced damage to S1 neurons. Rats were anesthetized and vibrissae were trimmed from either the left, right, or neither side of the snout. The next day they were given four injections of either saline (1 ml/kg, s.c.) or mAMPH (4 mg/kg, s.c.) at 2-h intervals. Three days later, cortical sections were processed for FJ histochemistry. The hemivibrissotomy produces a hemispheric asymmetry in FJ-positive neurons in barrel cortex, with fewer damaged neurons contralateral than ipsilateral to whisker removal. Taken together with the demonstration that acute injection of this dose of mAMPH induces the immediate early gene zif/268 and Fos protein in barrel cortex, these data suggest that the prolonged behavioral activity involving the vibrissae contributes to the mAMPH-induced damage to S1 neurons. Thus, some of the injurious effects of drugs may depend on afferent activity occurring as a result of the abnormal behaviors evoked by their administration.

 

Oiwa, Y., R. Sanchez-Pernaute, et al. (2003). "Progressive and extensive dopaminergic degeneration induced by convection-enhanced delivery of 6-hydroxydopamine into the rat striatum: a novel rodent model of Parkinson disease." J Neurosurg 98(1): 136-44.

            OBJECT: A striatal dopamine lesion induces progressive nigral degeneration in rodents; however, intrastriatal injection of 6-hydroxydopamine (6-OHDA) causes only limited lesions due to spontaneous regeneration of the neurons that survive. To make an extensive lesion, the authors used a convection-enhanced delivery (CED) method for intrastriatal infusion of 6-OHDA and evaluated the animals for a model of Parkinson disease (PD). METHODS: Different doses of 6-OHDA were infused into the unilateral striatum in rats by using the CED method. The dopaminergic neuronal degeneration was evaluated based on morphological, biochemical, and behavioral measurements until 8 weeks postlesion. Due to the wide distribution of the drug, CED of 20 microg of 6-OHDA into the striatum was sufficient to obtain a progressive and extensive nigrostriatal lesion as defined by morphological (> 80% cell loss in the substantia nigra [SN]) and biochemical (> 95% decrease in striatal dopamine) criteria. The extent of the lesion manifested as a stable turning behavior with amphetamine (> 6 turns/minute) and apomorphine (> 4 turns/minute). It also appeared that at I week postlesion the apoptotic markers were maximal in neurons of the SN. CONCLUSIONS: A rat model of PD with a progressive and extensive dopamine lesion was successfully made by intrastriatal CED of 6-OHDA. In this model, the therapeutic value can be assessed using behavioral, biochemical, and histochemical measurements. The delay of nigral neuronal death with respect to the time of 6-OHDA administration may provide a therapeutic window for testing neuroprotective strategies.

 

Oliveira, M. T., A. C. Rego, et al. (2002). "Toxic effects of opioid and stimulant drugs on undifferentiated PC12 cells." Ann N Y Acad Sci 965: 487-96.

            Cell death and reactive oxygen species production have been suggested to be involved in neurodegeneration induced by the drugs of abuse. In this study we analyze the toxicity of the following drugs of abuse: heroin, morphine, d-amphetamine, and cocaine in undifferentiated PC12 cells, used as dopaminergic neuronal models. Our data show that opioid drugs (heroin and morphine) are more toxic than stimulant drugs (d-amphetamine and cocaine). Toxic effects induced by heroin are associated with a decrease in intracellular dopamine, an increase in DOPAC levels, and the formation of ROS, whereas toxic effects induced by amphetamine are associated with a decrease in intracellular dopamine and in ATP/ADP levels. In contrast with cocaine, both amphetamine and heroin induced features of apoptosis. The data suggest that the death of cultured PC12 cells induced by the drugs of abuse is correlated with a decrease in intracellular dopamine levels, which can be associated with an increased dopamine turnover and oxidative cell injury.

 

Pang, Z. P., G. Y. Ling, et al. (2002). "Asymmetrical changes of excitatory synaptic transmission in dopamine-denervated striatum after transient forebrain ischemia." Neuroscience 114(2): 317-26.

            Spiny neurons in the neostriatum are highly vulnerable to cerebral ischemia. Recent studies have shown that the postischemic cell death in the right striatum was reduced after ipsilateral dopamine denervation whereas no protection was observed in the left striatum after dopamine denervation in the left side. In order to reveal the mechanisms of such asymmetrical protection, electrophysiological changes of dopamine-denervated striatal neurons were compared after ischemia between the left and right striatum using intracellular recording and staining techniques in vivo. No difference in cortically evoked initial excitatory postsynaptic potentials was found between the left and right striatum in intact animals after ipsilateral dopamine denervation. The initial excitatory postsynaptic potentials in the dopamine-denervated right striatum were suppressed after transient forebrain ischemia while no significant changes were found in the dopamine-denervated left striatum. Paired-pulse tests suggested that these changes involved presynaptic mechanisms. Although the incidence of a late depolarizing postsynaptic potential elicited by cortical stimulation increased after ischemia in both sides, the increase was greater in the left side. The analysis of current-voltage relationship of spiny neurons indicated that inward rectification in the left striatum transiently disappeared shortly after ischemia whereas that in the right side remained unchanged. The intrinsic excitability of spiny neurons in both sides were suppressed after ischemia, however, the suppression in the right side was stronger than in the left side. The above results demonstrate that after ipsilateral dopamine denervation, the depression of excitatory synaptic transmission and neuronal excitability in the right striatum is more severe than that in the left striatum following ischemia. The depression of excitatory synaptic transmission and neuronal excitability, therefore, might play an important role in neural protection after ischemic insult.

 

Pardini, C., F. Vaglini, et al. (2003). "Dose-dependent induction of apoptosis by R-apomorphine in CHO-K1 cell line in culture." Neuropharmacology 45(2): 182-189.

            A variety of mechanisms have been proposed as explanations for the distinctive neuropathology of Parkinson's disease, such as increased iron levels, increased oxidant stress or decreased antioxidant defences. The vulnerability of dopamine-containing neurons towards cell death has attracted much attention to the dopamine molecule itself as one of the probable neurotoxic factors leading to neurodegeneration. The similarity between apomorphine and dopamine with regards to their chemical, pharmacological and toxicological properties provided a basis for investigating the nature of the toxicity of the former agent. In this study the CHO-K1 cell line was exposed to different concentrations of apomorphine, and markers of cell death and apoptosis were studied. Apomorphine reduced cell proliferation in a dose-dependent fashion after 72 h incubation. Furthermore, apomorphine induced dose-dependent cell death at concentrations of 10-50 microM. The CHO-K1 line showed specific markers of apoptosis such as the typical DNA laddering phenomenon on agarose gel, morphological changes of apoptotic nuclei as described by in situ end labelling, and annexin binding.These data strongly suggest that apomorphine, like dopamine, elicits its cytotoxic effect with an apoptotic mechanism.

 

Pirker, W., S. Djamshidian, et al. (2002). "Progression of dopaminergic degeneration in Parkinson's disease and atypical parkinsonism: a longitudinal beta-CIT SPECT study." Mov Disord 17(1): 45-53.

            Atypical parkinsonian syndromes (APS) such as multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration are characterized by poor response to antiparkinsonian medication and rapid clinical deterioration. We used SPECT and [123I]beta-CIT as a label of dopamine transporters to study the progression of presynaptic dopaminergic degeneration in Parkinson's disease (PD) and APS. Twenty-four PD patients with short disease duration (2.4 +/- 1.5 years), 12 PD patients with long disease duration (9.2 +/- 2.6 years), 10 patients with APS (disease duration 2.1 +/- 1.5 years), and nine patients with essential tremor (ET) underwent sequential [123I]beta-CIT SPECT imaging with an interval of 25.5 +/- 10.3 (13-63) months. The age-related decline of striatal beta-CIT binding was studied cross-sectionally in 30 healthy subjects. The ratio of striatum/cerebellum -1 at 20 hours after tracer injection, reflecting specific-to-nondisplaceable binding, was used as the primary SPECT outcome measure. At scan 1, striatal beta-CIT binding was reduced in PD patients with short disease duration (-42% compared with age-corrected normal values) and long disease duration (-51%), and APS (-36%), but normal in ET. During the observation period striatal beta-CIT binding significantly declined in patients with APS (14.9% per year) and short duration PD (7.1% per year), whereas PD patients with long disease duration and patients with ET showed no significant change of striatal beta-CIT binding between scans 1 and 2. The relative annual reduction from age-corrected normal values at the time of scan 1 was significantly higher in patients with APS than in PD patients with short disease duration (9.6 vs. 4.3%, P = 0.004). These results demonstrate a rapid decline of striatal beta-CIT binding in patients with atypical parkinsonian syndromes, exceeding the reduction in PD. The dopaminergic degeneration in PD appears to slow down during the course of the disease. SPECT with [123I]beta-CIT is a sensitive marker of disease progression in parkinsonian disorders.

 

Ricaurte, G. A., J. Yuan, et al. (2002). "Severe dopaminergic neurotoxicity in primates after a common recreational dose regimen of MDMA ("ecstasy")." Science 297(5590): 2260-3.

            The prevailing view is that the popular recreational drug (+/-)3,4-methylenedioxymethamphetamine (MDMA, or "ecstasy") is a selective serotonin neurotoxin in animals and possibly in humans. Nonhuman primates exposed to several sequential doses of MDMA, a regimen modeled after one used by humans, developed severe brain dopaminergic neurotoxicity, in addition to less pronounced serotonergic neurotoxicity. MDMA neurotoxicity was associated with increased vulnerability to motor dysfunction secondary to dopamine depletion. These results have implications for mechanisms of MDMA neurotoxicity and suggest that recreational MDMA users may unwittingly be putting themselves at risk, either as young adults or later in life, for developing neuropsychiatric disorders related to brain dopamine and/or serotonin deficiency.

 

Ruprecht-Dorfler, P., D. Berg, et al. (2003). "Echogenicity of the substantia nigra in relatives of patients with sporadic Parkinson's disease." Neuroimage 18(2): 416-22.

            Increased echogenicity of the substantia nigra (SN) on ultrasound is a typical sonographic finding in Parkinson's disease (PD). Sonographic signal intensity of the SN is related to tissue iron content with higher iron level being associated with increased echogenicity. Recent findings indicate that hyperechogenicity of the SN represents an important susceptibility factor for nigrostriatal degeneration. In this study we determined the prevalence of a characteristic ultrasound sign of Parkinson's disease in first-degree relatives of PD patients. Fourteen patients with sporadic PD and 58 of their relatives underwent neurological, neuropsychological, and ultrasound examination. In addition, four pairs of relatives (one member of each pair exhibiting increased echogenicity of the SN and the other with regular SN echogenicity) underwent (18)F-Dopa PET examination. On transcranial sonography, 26 of the 58 relatives exhibited SN hyperechogenicity. Twenty-four relatives showed minor signs of motor slowing. Relatives with SN hyperechogenicity more often showed signs of hypokinesia (16 v 8 relatives; U test, P = 0.01) and impaired executive functions (Tower of London task, problems solved with the minimum number of moves; U test, P = 0.012) than relatives without this echo pattern. In addition, (18)F-Dopa uptake (influx constants) at the putamen was reduced in subjects with SN hyperechogenicity compared to their relatives without this ultrasound sign (Wilcoxon, P = 0.03). In conclusion, approximately 45% of relatives of PD patients exhibited an increased echogenicity of the SN. This sign is associated with clinical findings and objective measurements, indicating some degree of impaired nigrostriatal function.

 

Ryan, R. W., J. I. Post, et al. (2002). "Catecholaminergic neuronal degeneration in rainbow trout assessed by skin color change: a model system for identification of environmental risk factors." Neurotoxicology 23(4-5): 545-51.

            Genetic, neurochemical, and environmental factors have been implicated in neurodegenerative disease, and a combination of these factors is likely responsible for disease onset and progression. Environmental toxicants implicated in Parkinson's disease include organic compounds, reactive oxygen species, metal ions and others. Exposure to a combination of environmental toxicants may produce a synergistic insult leading to neuronal death, even though levels of individual toxicants may be below detection by conventional methods. Rodent models of toxicant-induced neurodegeneration are hampered by the high resistance of these animals to many environmental toxicants. Extensive literature on aquatic toxicology and the high homology between many human and fish neurotrophic factors makefish a useful model for investigating environmental toxicants and neurodegeneration. Skin color in salmonids is under catecholaminergic control; pigment-containing melanophores aggregate when stimulated, resulting in paling. We demonstrate that lesions to nerves innervating melanophores prevent aggregation and produce dark skin color. The time course for return of skin color corresponds to neuronal regeneration, a neurotrophin-dependent event. Observations from this model system may be useful for predicting risks associated with environmental toxicants and nervous system integrity, and may have important implications for the identification of risk factors.

 

Saji, H., Y. Iida, et al. (2003). "In vivo imaging of brain dopaminergic neurotransmission system in small animals with high-resolution single photon emission computed tomography." Anal Sci 19(1): 67-71.

            High-resolution single photon emission computed tomography (SPECT) provides a unique capability to image the biodistribution of radiolabeled molecules in small laboratory animals. Thus, we applied the high-resolution SPECT to in vivo imaging of the brain dopaminergic neurotransmission system in common marmosets using two radiolabeled ligands, [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane (beta-CIT) as a dopamine transporter (DAT) ligand and [123I]iodobenzamide (IBZM) as a dopamine D2 receptor (D2R) ligand. Specific images of the striatum, a region with a high density of dopaminergic synapses, were obtained at 240 min and 60 min after injection of [123I]beta-CIT and [123I]IBZM, respectively. Furthermore, a significantly low accumulation of [123I]beta-CIT in the striatum was observed in MPTP-treated animals compared with results for a control group, and a similar accumulation in the control group was observed with the pretreatment of deprenyl in the MPTP-treated animals. However, the striatal accumulation of [123I]IBZM showed no changes among the control, MPTP-treated, and deprenyl-MPTP-treated groups. These SPECT imaging results agreed well with those of DA concentration and motor behavior. Since MPTP destroys nigrostriatal dopamine nerves and produces irreversible neurodegeneration associated with Parkinsonian syndrome, SPECT imaging data in this study demonstrated that deprenyl shows its neuroprotective effect on Parkinsonism by protecting against the destruction of presynaptic dopamine neurons.

 

Schmidt, R. E. (2002). "Age-related sympathetic ganglionic neuropathology: human pathology and animal models." Auton Neurosci 96(1): 63-72.

            Systematic studies of the autonomic nervous system of human subjects and development of well-defined animal models have begun to substantially improve our understanding of the pathogenesis of autonomic dysfunction in aging and may eventually provide strategies for intervention. Neuropathological studies of the sympathetic ganglia of aged human subjects and rodent models have demonstrated that neuroaxonal dystrophy involving intraganglionic terminal axons and synapses is a robust, unequivocal and consistent neuropathological finding in the aged sympathetic nervous system of man and animals. Quantitative studies have demonstrated that markedly swollen argyrophilic dystrophic axon terminals develop in the prevertebral superior mesenteric (SMG) and coeliac, but to a much lesser degree in the superior cervical ganglia (SCG) as a function of age, sex (males more than females) and diabetes. Dystrophic axons were immunoreactive for neuropeptide Y, tyrosine hydroxylase, dopamine-beta-hydroxylase, trkA and p75NTR, an immunophenotype consistent with their origin from postganglionic sympathetic neurons, and contained large numbers of highly phosphorylated neurofilaments or tubulovesicular elements. The sympathetic ganglia of aged rodents also showed the hallmark changes of neuroaxonal dystrophy as a function of age and location (many more in the SMG than in the SCG). Plasticity-related synaptic remodeling could represent a highly vulnerable target of the aging process. The fidelity of animal models to the neuropathology of aged humans suggests that similar pathogenetic mechanisms may be involved in both and that therapeutic advances in animal studies may have human application.

 

Sharan, N., V. Z. Chong, et al. (2003). "Cocaine treatment increases expression of a 40 kDa catecholamine-regulated protein in discrete brain regions." Synapse 47(1): 33-44.

            Previous reports from our laboratory have described brain-specific catecholamine-regulated proteins, which bind dopamine and related catecholamines. Evidence from the molecular cloning of a 40 kDa catecholamine-regulated protein (CRP40) revealed that CRP40 is dopamine-inducible and has properties similar to those of the 70 kDa heat shock protein (HSP70) family. The present study investigates the effects of acute and chronic cocaine treatment on CRP40 expression in the striatum, nucleus accumbens, prefrontal cortex, and medulla. Acute treatment with cocaine increased CRP40 expression in the nucleus accumbens and striatum, whereas chronic treatment with cocaine increased CRP40 expression in the nucleus accumbens only. Neither of these treatments affected CRP40 levels in the prefrontal cortex or medulla. In addition, pretreatment with the spin-trapping agent alpha-phenyl-tert-butylnitrone did not attenuate cocaine-induced expression of CRP40, suggesting that the observed increases in CRP40 levels were not caused by free radicals. On the other hand, pretreatment with anisomycin, a protein synthesis inhibitor, blocked the cocaine-induced expression of CRP40. Thus, protein synthesis may be involved in the observed CRP40 level increases. Furthermore, neither acute nor chronic cocaine treatment affected levels of inducible or constitutively expressed HSP70, which indicates a specificity of cocaine's effects on CRP40. Since cocaine has been shown to increase extracellular dopamine levels, these findings suggest that increased expression of CRP40 is associated with high extracellular levels of dopamine (or its metabolites). Elevated levels of CRP40 could play a protective role for dopamine neurons in response to increased oxidative stress that has been shown to be induced by cocaine and that can lead to apoptosis and neurodegeneration.

 

Sharma, S. K. and M. Ebadi (2003). "Metallothionein attenuates 3-morpholinosydnonimine (SIN-1)-induced oxidative stress in dopaminergic neurons." Antioxid Redox Signal 5(3): 251-64.

            Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the substantia nigra zona compacta, and in other subcortical nuclei associated with a widespread occurrence of Lewy bodies. The causes of cell death in Parkinson's disease are still poorly understood, but a defect in mitochondrial oxidative phosphorylation and enhanced oxidative stress have been proposed. We have examined 3-morpholinosydnonimine (SIN-1)-induced apoptosis in control and metallothionein-overexpressing dopaminergic neurons, with a primary objective to determine the neuroprotective potential of metallothionein against peroxynitrite-induced neurodegeneration in Parkinson's disease. SIN-1 induced lipid peroxidation and triggered plasma membrane blebbing. In addition, it caused DNA fragmentation, alpha-synuclein induction, and intramitochondrial accumulation of metal ions (copper, iron, zinc, and calcium), and enhanced the synthesis of 8-hydroxy-2-deoxyguanosine. Furthermore, it down-regulated the expression of Bcl-2 and poly(ADP-ribose) polymerase, but up-regulated the expression of caspase-3 and Bax in dopaminergic (SK-N-SH) neurons. SIN-1 induced apoptosis in aging mitochondrial genome knockout cells, alpha-synuclein-transfected cells, metallothionein double-knockout cells, and caspase-3-overexpressed dopaminergic neurons. SIN-1-induced changes were attenuated with selegiline or in metallothionein-transgenic striatal fetal stem cells. SIN-1-induced oxidation of dopamine to dihydroxyphenylacetaldehyde was attenuated in metallothionein-transgenic fetal stem cells and in cells transfected with a mitochondrial genome, and enhanced in aging mitochondrial genome knockout cells, in metallothionein double-knockout cells and caspase-3 gene-overexpressing dopaminergic neurons. Selegiline, melatonin, ubiquinone, and metallothionein suppressed SIN-1-induced down-regulation of a mitochondrial genome and up-regulation of caspase-3 as determined by reverse transcription-polymerase chain reaction. The synthesis of mitochondrial 8-hydroxy-2-deoxyguanosine and apoptosis-inducing factors were increased following exposure to 1-methyl-4-phenylpyridinium ion or rotenone. Pretreatment with selegiline or metallothionein suppressed 1-methyl-4-phenylpyridinium ion-, 6-hydroxydopamine-, and rotenone-induced increases in mitochondrial 8-hydroxy-2-deoxyguanosine accumulation. Transfection of aging mitochondrial genome knockout neurons with mitochondrial genome encoding complex-1 or melanin attenuated the SIN-1-induced increase in lipid peroxidation. SIN-1 induced the expression of alpha-synuclein, caspase-3, and 8-hydroxy-2-deoxyguanosine, and augmented protein nitration. These effects were attenuated by metallothionein gene overexpression. These studies provide evidence that nitric oxide synthase activation and peroxynitrite ion overproduction may be involved in the etiopathogenesis of Parkinson's disease, and that metallothionein gene induction may provide neuroprotection.

 

Shim, H. and Z. L. Harris (2003). "Genetic defects in copper metabolism." J Nutr 133(5 Suppl 1): 1527S-31S.

            Genetic defects in copper metabolism highlight the delicate balance mammalian systems have developed to maintain normal copper homeostasis. Menkes disease, the mottled mouse, the Atox-1-deficient mouse and the ctr1 knockout mouse reveal the importance of adequate copper intake during embryogenesis and early development, especially in the central nervous system. The toxicity associated with excess copper as manifest in Wilson disease, the toxic milk mouse, the LEC rat and copper toxicosis in the Bedlington terrier demonstrate the profound cellular susceptibility to copper overload, in particular, in the brain and liver. Ceruloplasmin (Cp) contains 95% of the copper found in human serum, and inherited loss of this protein results in diabetes, retinal degeneration and neurodegeneration. Despite normal copper metabolism, aceruloplasminemic patients and the Cp knockout mouse have disturbed iron homeostasis and mild hepatic copper retention. These genetic disorders of copper metabolism provide valuable insight into the mechanisms regulating copper homeostasis and models to further dissect the role of this essential metal in health and disease.

 

Shimizu, K., K. Matsubara, et al. (2003). "Paraquat induces long-lasting dopamine overflow through the excitotoxic pathway in the striatum of freely moving rats." Brain Res 976(2): 243-52.

            The herbicide paraquat is an environmental factor that could be involved in the etiology of Parkinson's disease. We have previously shown that paraquat penetrates through the blood-brain barrier and is taken up by neural cells. In this study, we examined the in vivo toxic mechanism of paraquat to dopamine neurons. GBR-12909, a selective dopamine transporter inhibitor, reduced paraquat uptake into the striatal tissue including dopaminergic terminals. The subchronic treatment with systemic paraquat significantly decreased brain dopamine content in the striatum and slightly in the midbrain and cortex, and was accompanied by the diminished level of its acidic metabolites in rats. When paraquat was administered through a microdialysis probe, a transitory increase in the extracellular levels of glutamate, followed by long-lasting elevations of the extracellular levels of NO(x)(-) (NO(2)(-) plus NO(3)(-)) and dopamine were detected in the striatum of freely moving rats. This dopamine overflow lasted for more than 24 h after the paraquat treatment. Dopamine overflow was inhibited by N(G)-nitro-L-arginine methyl ester, dizocilpine, 6,7-dinitroquinoxaline-2,3-dione and L-deprenyl. The toxic mechanism of paraquat involves glutamate induced activation of non-NMDA receptors, resulting in activation of NMDA receptor-channels. The influx of Ca(2+) into cells stimulates nitric oxide synthase. Released NO would diffuse to dopaminergic terminals and further induce mitochondrial dysfunction by the formation of peroxynitrite, resulting in continuous and long-lasting dopamine overflow. The constant exposure to low levels of paraquat may lead to the vulnerability of dopaminergic terminals in humans, and might potentiate neurodegeneration caused by the exposure of other substances, such as endogenous dopaminergic toxins.

 

Shimizu, K., K. Matsubara, et al. (2003). "Paraquat leads to dopaminergic neural vulnerability in organotypic midbrain culture." Neurosci Res 46(4): 523-32.

            Paraquat (1,1'-dimethyl-4,4'-bipyridinium, PQ) is a herbicide to possibly induce Parkinson's disease (PD), since a strong correlation has been found between the incidence of the disease and the amount of PQ used. In this study, we examined PQ toxicity in rat organotypic midbrain slice cultures. PQ dose dependently reduced the number of dopaminergic neurons in cultured slices. Since this damage was prevented by GBR-12909, the dopamine transporter could be an initial step of the PQ induced dopaminergic neurotoxicity. The sequential treatments with lower PQ and 1-methyl-4-phenyl pyridinium (MPP(+)) doses, where each dose alone was not lethal, markedly killed dopamine neurons, suggesting that the exposure of a lower dose of PQ could lead to the vulnerability of dopaminergic neurons. This cell death was prevented by the inhibitors of NMDA, nitric oxide synthase (NOS), cycloheximide and caspase cascade. Neurons expressing NOS were identified inside and around the regions where dopamine neurons were packed. The cell death induced by the sequential treatments with PQ and MPP(+) was also rescued by L-deprenyl and dopamine D2/3 agonists. These results strongly support that the constant exposure to low levels of PQ would lead to the vulnerability of dopaminergic neurons in the nigrostriatal system by the excitotoxic pathway, and might potentiate neurodegeneration caused by the exposure of other substances and aging.

 

Snow, B. (2003). "Objective measures for the progression of Parkinson's disease." J Neurol Neurosurg Psychiatry 74(3): 287.

           

Speciale, S. G. (2002). "MPTP: insights into parkinsonian neurodegeneration." Neurotoxicol Teratol 24(5): 607-20.

            MPTP burst upon the medical landscape two decades ago, first as a mysterious parkinsonian epidemic, triggering an unparalleled quest for the toxin's identity, and closely followed by an intense pursuit of its cellular mechanisms of action. MPTP treatment created an animal model of many features of Parkinson's disease (PD), used primarily in primates and later in mice. The critical role of oxidative stress damage to vulnerable dopamine neurons, as well as for neurodegenerative diseases in general, emerged from MPTP neurotoxicity. A remarkable cross-fertilization of basic and clinical findings, including genetic and epidemiologic studies, has greatly advanced our understanding of PD and revealed multiple factors contributing to the parkinsonian phenotypes. Brain imaging localizes sites of action and provides potential presymptomatic diagnostic testing. Epidemiologic reports linking PD with pesticide exposure were complimented by supportive evidence from biochemical studies of MPTP and structurally related compounds, especially after low-level, long-term exposure. Genetic studies on the role of risk genes, such as alpha-synuclein or parkin, have been validated by biochemical, anatomical and neurochemical investigations showing factors interacting to produce pathophysiology in the animal model. Focusing on the pivotal role of mitochondria, subcellular pathways participating in cell death have been clarified by unraveling similar sites of action of MPTP. Along the way, compounds antagonizing or potentiating MPTP effects indicated new PD therapies, some of the former achieving clinical trials. The future is encouraging for combating PD and will continue to benefit from the MPTP neurotoxicity model.

 

Srinivasan, J. and W. J. Schmidt (2003). "Potentiation of parkinsonian symptoms by depletion of locus coeruleus noradrenaline in 6-hydroxydopamine-induced partial degeneration of substantia nigra in rats." Eur J Neurosci 17(12): 2586-92.

            Parkinson's disease is characterized not only by a progressive loss of dopaminergic neurons in the substantia nigra but also by a degeneration of locus coeruleus noradrenergic neurons. The present study addresses the question of whether a partial neurodegeneration of dopaminergic neurons using 6-hydroxydopamine in rat, not sufficient to produce motor disturbances, is potentiated by prior selective denervation of locus coeruleus noradrenergic terminal fields using N-ethyl-2-bromobenzylamine. Two types of denervations, one causing dopamine deficiency alone and the other causing noradrenaline and dopamine deficiency, were performed. Noradrenaline, 5-hydroxytryptamine, 5-hydroxyindole acetic acid, dopamine and its metabolites were analysed in various brain regions. Behaviour was evaluated by catalepsy tests and activity box. N-ethyl-2-bromobenzylamine selectively depleted noradrenaline from neurons of locus coeruleus origin. Decreased dopamine content in the striatum, substantia nigra and pre-frontal cortex was observed after dopaminergic lesion with 6-hydroxydopamine (42.9%). Additional locus coeruleus noradrenaline depletion with N-ethyl-2-bromobenzylamine aggravated the dopamine depletion (61.2%). The lesion in the noradrenergic and dopaminergic neurodegenerated group was not sufficient to induce consistent catalepsy and akinesia. However, after a subthreshold dose of haloperidol (0.1 mg/kg), the expression of catalepsy and akinesia was strong in the dual-lesioned group and less in the 6-hydroxydopamine-lesioned group. These results indicate that denervation of locus coeruleus noradrenergic terminals with N-ethyl-2-bromobenzylamine potentiates the 6-hydroxydopamine-induced partial dopaminergic neurodegeneration and parkinsonian symptoms. Based on the present findings and existing reports, it can be concluded that noradrenergic neurons of locus coeruleus have neuromodulatory and neuroprotective properties on the dopaminergic neurons of basal ganglia and that noradrenergic degeneration may contribute to the aetiology and pathophysiology of Parkinson's disease.

 

Sriram, K., S. A. Benkovic, et al. (2002). "Obesity exacerbates chemically induced neurodegeneration." Neuroscience 115(4): 1335-46.

            Obesity is a major risk factor associated with a variety of human disorders. While its involvement in disorders such as diabetes, coronary heart disease and cancer have been well characterized, it remains to be determined if obesity has a detrimental effect on the nervous system. To address this issue we determined whether obesity serves as a risk factor for neurotoxicity. Model neurotoxicants, methamphetamine (METH) and kainic acid (KA), which are known to cause selective neurodegeneration of anatomically distinct areas of the brain, were evaluated using an animal model of obesity, the ob/ob mouse. Administration of METH and KA resulted in mortality among ob/ob mice but not among their lean littermates. While METH caused dopaminergic nerve terminal degeneration as indicated by decreased striatal dopamine (49%) and tyrosine hydroxylase protein (68%), as well as an increase in glial fibrillary acidic protein by 313% in the lean mice, these effects were exacerbated under the obese condition (96%, 86% and 602%, respectively). Similarly, a dosage of KA that did not increase glial fibrillary acidic protein in lean mice increased the hippocampal content of this protein (93%) in ob/ob mice. KA treatment resulted in extensive neuronal degeneration as determined by Fluoro-Jade B staining, decreased hippocampal microtubule-associated protein-2 immunoreactivity and increased reactive gliosis in ob/ob mice. The neurotoxic outcome in ob/ob mice remained exacerbated even when lean and ob/ob mice were dosed with METH or KA based only on a lean body mass. Administration of METH or KA resulted in up-regulation of the mitochondrial uncoupling protein-2 to a greater extent in the ob/ob mice, an effect known to reduce ATP yield and facilitate oxidative stress and mitochondrial dysfunction. These events may underlie the enhanced neurotoxicity seen in the obese mice.In summary, our results implicate obesity as a risk factor associated with chemical- and possibly disease-induced neurodegeneration.

 

Sriram, K., J. M. Matheson, et al. (2002). "Mice deficient in TNF receptors are protected against dopaminergic neurotoxicity: implications for Parkinson's disease." Faseb J 16(11): 1474-6.

            The pathogenic mechanisms underlying idiopathic Parkinson's disease (PD) remain enigmatic. Recent findings suggest that inflammatory processes are associated with several neurodegenerative disorders, including PD. Enhanced expression of the proinflammatory cytokine, tumor necrosis factor (TNF)-alpha, has been found in association with glial cells in the substantia nigra of patients with PD. To determine the potential role for TNF-alpha in PD, we examined the effects of the 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP), a dopaminergic neurotoxin that mimics some of the key features associated with PD, using transgenic mice lacking TNF receptors. Administration of MPTP to wild-type (+/+) mice resulted in a time-dependent expression of TNF-alpha in striatum, which preceded the loss of dopaminergic markers and reactive gliosis. In contrast, transgenic mice carrying homozygous mutant alleles for both the TNF receptors (TNFR-DKO), but not the individual receptors, were completely protected against the dopaminergic neurotoxicity of MPTP. The data indicate that the proinflammatory cytokine TNF-alpha is an obligatory component of dopaminergic neurodegeneration. Moreover, because TNF-alpha is synthesized predominantly by microglia and astrocytes, our findings implicate the participation of glial cells in MPTP-induced neurotoxicity. Similar mechanisms may underlie the etiopathogenesis of PD.

 

Steindler, D. A. (2002). "Neural stem cells, scaffolds, and chaperones." Nat Biotechnol 20(11): 1091-3.

           

Stevenson, C. W., R. M. Sullivan, et al. (2003). "Effects of basolateral amygdala dopamine depletion on the nucleus accumbens and medial prefrontal cortical dopamine responses to stress." Neuroscience 116(1): 285-93.

            In vivo voltammetry was used to study the effects of basolateral amygdala dopamine depletion on stress-induced dopamine release in the nucleus accumbens and medial prefrontal cortex. Male Long-Evans rats received bilateral microinjections of 6-hydroxydopamine or vehicle into the basolateral amygdala. Changes in dopamine signal were monitored in the nucleus accumbens and in the right and left hemispheres of medial prefrontal cortex, in lesioned animals and shams. Animals were subjected to a physical stressor (tail pinch) and a species-typical threat (fox odour); each stressor was presented twice over four consecutive daily sessions. The results indicate that the nucleus accumbens dopamine responses to both stressors are significantly potentiated by dopamine-depleting lesions to basolateral amygdala. In contrast, while the dopamine stress response in the left medial prefrontal cortex did not differ between lesioned animals and shams, the right medial prefrontal cortical dopamine response to tail pinch, but not fox odour stress, was significantly attenuated in lesioned animals. Therefore, basolateral amygdala dopamine depletion had opposite effects on the nucleus accumbens and medial prefrontal cortical dopamine responses to stress, although the effect on the latter is lateralized to the right hemisphere in a stressor-specific manner. These data indicate that stress-induced activation of meso-amygdaloid dopamine exerts an inhibitory influence on the nucleus accumbens dopamine response to stress. They also suggest the possibility that meso-amygdaloid dopamine influences the nucleus accumbens dopamine response to stress indirectly by modulating stress-induced dopamine release in medial prefrontal cortex. These findings add to a growing body of evidence of a preferential involvement of right medial prefrontal cortical dopamine in a wide range of physiological responses to stress.

 

Stokes, A. H., W. M. Freeman, et al. (2002). "Induction of GADD45 and GADD153 in neuroblastoma cells by dopamine-induced toxicity." Neurotoxicology 23(6): 675-84.

            Dopamine (DA) metabolism and oxidation produce both reactive oxygen species (ROS) and reactive quinones. These chemical species are implicated in dopamine neurotoxicity and neurodegeneration. In the present studies, human neuroblastoma (SK-N-SH) cells were exposed to toxic concentrations of dopamine (333 microM) in order to investigate molecular pathways involved in dopamine toxicity. cDNA hybridization array (microarray) technology demonstrated that GADD45 and GADD153 (growth arrest and DNA-damage inducible) gene expression was increased in dopamine-treated cells (333 microM for 18 h). Subsequent Northern and Western blot analysis confirmed these changes in GADD45 and GADD153 gene expression. The antioxidant, ascorbic acid, significantly reduced the increase in GADD45 gene expression but did not significantly reduce GADD153 gene expression. Currently, the precise function of the GADD gene products is not known. It is known, however, that these genes are upregulated in response to stress to allow cells time to repair macromolecular damage. In the present case, GADD gene expression (manifested as increased mRNA and protein levels) preceded dopamine-induced cytotoxicity. It appears that dopamine, through the formation of reactive oxygen species and quinones, may damage cellular macromolecules to the point of inducing GADD gene expression. Other genes that displayed changes, but that have not been subjected to post-hoc confirmation, include clusterin (increased), ubiquitin (increased), CD27 ligand (increased), CD27BP (increased), and rac-PK-beta (decreased).

 

Storch, A., S. Ott, et al. (2002). "Selective dopaminergic neurotoxicity of isoquinoline derivatives related to Parkinson's disease: studies using heterologous expression systems of the dopamine transporter." Biochem Pharmacol 63(5): 909-20.

            Endogenous isoquinoline (IQ) derivatives structurally related to the selective dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its active metabolite 1-methyl-4-phenylpyridine (MPP(+)) may contribute to dopaminergic neurodegeneration in Parkinson's disease. We addressed the importance of the DAT molecule for selective dopaminergic toxicity by testing the differential cytotoxicity of 22 neutral and quaternary compounds from three classes of isoquinoline derivatives (3, IQs; 4,3,4-dihydroisoquinolines and 15, 1,2,3,4-tetrahydroisoquinolines) as well as MPP(+) in non-neuronal and neuronal heterologous expression systems of the DAT gene (human embryonic kidney HEK-293 and mouse neuroblastoma Neuro-2A cells, respectively). Cell death was estimated using the MTT assay and the Trypan blue exclusion method. Nine isoquinolines and MPP(+) showed general cytotoxicity in both parental cell lines after 72hr with half-maximal toxic concentrations (TC(50) values) in the micromolar range. The rank order of toxic potency was: papaverine>salsolinol=tetrahydropapaveroline=1-benzyl-TIQ=norsalsolinol>te trahydropapaverine>2[N]-methyl-salsolinol>2[N]-methyl-norsalsolinol>2[N]-M e-IQ(+)=MPP(+). Besides MPP(+), only the 2[N]-methylated compounds 2[N]-methyl-IQ(+), 2[N]-methyl-norsalsolinol and 2[N]-methyl-salsolinol showed enhanced cytotoxicity in both DAT expressing cell lines with 2- to 14-fold reduction of TC(50) values compared to parental cell lines. The rank order of selectivity in both cell systems was: MPP(+)>>2[N]-Me-IQ(+)>2[N]-methyl-norsalsolinol=2[N]-methyl-salsolinol. Our results suggest that 2[N]-methylated isoquinoline derivatives structurally related to MPTP/MPP(+) are selectively toxic to dopaminergic cells via uptake by the DAT, and therefore may play a role in the pathogenesis of Parkinson's disease.

 

Sugama, S., L. Yang, et al. (2003). "Age-related microglial activation in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration in C57BL/6 mice." Brain Res 964(2): 288-94.

            Microglial activation was investigated in the brains of young (3 months old) and older (9-12 months old) mice following administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Tyrosine hydroxylase (TH)-positive neuronal loss differed significantly between young and older mice. Importantly, the two groups clearly demonstrated a distinct microglial activation pattern. In young mice which showed TH neuronal loss at 1 day (33.4%), 3 days (45.1%), 7 days (47.1%) and 14 days (46.9%), microglial activation was first observed at 1 day, with lesser activation at 3 days and none shown later than 7 days. In contrast, in older mice which showed TH neuronal loss at 1 day (49.6%), 3 days (56.1%), 7 days (71.7%) and 14 days (72.1%), microglial activation occurred at 1 day, further intensified at 3-7 days, and was largely abated by 14 days. The double immunohistochemistry further demonstrated that the activated microglia surrounded dopaminergic neurons in older mice at 7 days, which was sharply in contrast to the young mice which were devoid of massive microglial activation in the SN later than 3 days after MPTP treatment. The present study suggests that age-related microglial activation in the SN may be relevant to the higher susceptibility to MPTP neurotoxicity in older mice.

 

Teismann, P., K. Tieu, et al. (2003). "Cyclooxygenase-2 is instrumental in Parkinson's disease neurodegeneration." Proc Natl Acad Sci U S A 100(9): 5473-8.

            Parkinson's disease (PD) is a neurodegenerative disorder of uncertain pathogenesis characterized by the loss of the nigrostriatal dopaminergic neurons, which can be modeled by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Increased expression of cyclooxygenase type 2 (COX-2) and production of prostaglandin E(2) have been implicated in neurodegeneration in several pathological settings. Here we show that COX-2, the rate-limiting enzyme in prostaglandin E(2) synthesis, is up-regulated in brain dopaminergic neurons of both PD and MPTP mice. COX-2 induction occurs through a JNKc-Jun-dependent mechanism after MPTP administration. We demonstrate that targeting COX-2 does not protect against MPTP-induced dopaminergic neurodegeneration by mitigating inflammation. Instead, we provide evidence that COX-2 inhibition prevents the formation of the oxidant species dopamine-quinone, which has been implicated in the pathogenesis of PD. This study supports a critical role for COX-2 in both the pathogenesis and selectivity of the PD neurodegenerative process. Because of the safety record of the COX-2 inhibitors, and their ability to penetrate the blood-brain barrier, these drugs may be therapies for PD.

 

Todtenkopf, M. S., J. R. Stellar, et al. (2002). "Neither ibotenic acid nor volkensin lesions of the nucleus accumbens shell affect the expression of cocaine sensitization." Eur J Neurosci 16(3): 541-6.

            Studies have shown that the nucleus accumbens shell plays an integral role in the expression of psychostimulant-induced behavioural sensitization. Dopaminergic regulation of excitatory amino acid inputs in this region of the brain could be a key factor in the neural influence of this phenomenon. Alterations in the dopaminergic innervation patterns in the shell have been demonstrated in rats that received repeated cocaine injections. Furthermore, lesions of brain regions that send projections to the shell alter psychostimulant-induced locomotion, both acutely and in sensitization paradigms. A previous study from our laboratory demonstrated that lesions of the shell before repeated cocaine treatment decrease the locomotor response to cocaine during the induction phase of behavioural sensitization. To better understand the role of this brain region during the expression phase of behavioural sensitization, the present study examined the effects of two forms of cytotoxic lesions of the shell. Rats received a sensitization-inducing regimen of cocaine (bi-daily injections of 15 mg/kg i.p. for 5 consecutive days). Two days after the last injection, rats demonstrating behavioural sensitization received one of three bilateral microinjections into the shell: (i) 0.5 micro L 0.9% saline; (ii) 2.5 micro g/0.5 micro L ibotenic acid (which lesions the cell bodies at the injection site); or (iii), 0.5 ng/0.2 micro L of volkensin (a retrograde suicide transport lectin). Upon challenge with cocaine (15 mg/kg) 12 days after surgery, neither ibotenic acid- nor volkensin-lesioned rats showed any difference in their locomotor response compared with sham controls. These data indicate that bilateral shell lesions do not affect the long-term expression of behavioural sensitization in cocaine-sensitized rats.

 

Tsuboi, Y., M. Baker, et al. (2002). "Clinical and genetic studies of families with the tau N279K mutation (FTDP-17)." Neurology 59(11): 1791-3.

            The tau N279K mutation was identified in four separately ascertained families in the United States, Japan, and France and in another recently discovered affected individual in Japan. The authors analyzed genealogical and clinical records and DNA samples. Average age at onset was 43 years; survival time was 7 years. All families exhibited similar clinical features, with parkinsonism, dementia, and supranuclear palsy uniformly seen. A founder effect indicated by a shared disease haplotype was seen only in two Japanese families. The N279K mutation can develop independently in different parts of the world.

 

Uberti, D., L. Piccioni, et al. (2002). "Pergolide protects SH-SY5Y cells against neurodegeneration induced by H(2)O(2)." Eur J Pharmacol 434(1-2): 17-20.

            We found that pergolide, a dopamine D1/D2 receptor agonist used in the clinical therapy of Parkinson's disease, protects SH-SY5Y neuroblastoma cells from cell death induced by a brief pulse (15 min) of 1 mM H(2)O(2). Neuroprotection was found when pergolide was added to the culture medium either simultaneously with (EC(50)=60 nM) or 2 h before (EC(50)=40 nM) H(2)O(2) treatment. These effects were not blocked by different dopamine receptor antagonists. Our data suggest that pergolide, independently of dopamine receptor stimulation, may interfere with the early phases of the oxidative stress-induced neurotoxic process.

 

Vaglini, F., C. Pardini, et al. (2003). "Dextromethorphan prevents the diethyldithiocarbamate enhancement of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in mice." Brain Res 973(2): 298-302.

            In this report we show that dextromethorphan, a non-opioid cough suppressant, prevents the neurodegeneration of dopaminergic neurons in the substantia nigra of mice treated with diethyldithiocarbamate (DDC) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). This effect is further substantiated by the assessment of dopamine (DA) content in the striatum of these animals. Dextromethorphan does not attenuate the striatal DA fall induced by MPTP alone but completely prevents DDC-induced enhancement after the combined treatment. Moreover, a study of DA metabolites has confirmed this neuroprotective property. The striatal levels of serotonin, which were studied as a control neuronal marker, did not change with any of the treatments administered. Furthermore, we show that dextromethorphan reduces the toxicity of glutamate against dopamine neurons in mesencephalic cell cultures. In line with previous data suggesting that dextromethorphan can prevent neuronal damage, our observations supply new evidence regarding the possibility of this compound being of therapeutic use in neurodegenerative diseases.

 

van den Munckhof, P., K. C. Luk, et al. (2003). "Pitx3 is required for motor activity and for survival of a subset of midbrain dopaminergic neurons." Development 130(11): 2535-42.

            Mesencephalic dopaminergic (MesDA) neurons play crucial roles in motor and behavioral processes; their loss in Parkinson's disease (PD) results in striatal dopamine (DA) deficiency and hypokinetic movement disorder. The Pitx3 homeobox gene is expressed in the MesDA system. We now show that only a subset of MesDA neurons express Pitx3 and that in Pitx3-deficient aphakia mice, this subset is progressively lost by apoptosis during fetal (substantia nigra, SN) and postnatal (ventral tegmental area) development, resulting in very low striatal DA and akinesia. Similar to human PD, dorsal SN neurons (which are Pitx3 negative) are spared in mutant mice. Thus, Pitx3 defines a pathway for survival of neurons that are implicated in PD and that are required for spontaneous locomotor activity.

 

van Dyck, C. H., J. P. Seibyl, et al. (2002). "Age-related decline in dopamine transporters: analysis of striatal subregions, nonlinear effects, and hemispheric asymmetries." Am J Geriatr Psychiatry 10(1): 36-43.

            Neuroimaging studies have documented an age-related decline in striatal dopamine transporters (DATs) as a marker of dopaminergic neurodegeneration. The authors further elucidated the effects on this neural system in healthy aging, in contrast to Parkinson disease (PD). The effects of age on striatal DAT availability were examined in a large, healthy subject sample (N=126) with [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([123I]beta-CIT) and single photon emission computed tomography (SPECT). Striatal DAT availability (V3") showed a significant inverse correlation with age, declining in a nearly linear manner by 46% over the age range 18 to 88 years, or 6.6% per decade. Rates of decline were comparable for caudate (48%) and putamen (45%), with only minimal increase in left-right asymmetry with age. Hemispheric asymmetries were unrelated to the handedness of subjects. These results demonstrate that aging is associated with a relatively symmetric loss of DATs in the caudate and putamen in both hemispheres. These findings have implications not only for healthy aging but also for neurodegenerative disorders such as PD.

 

Venero, J. L., H. Absi el, et al. (2002). "Melatonin induces tyrosine hydroxylase mRNA expression in the ventral mesencephalon but not in the hypothalamus." J Pineal Res 32(1): 6-14.

            We have evaluated the effect of chronic administration of melatonin in terms of mRNA expression for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, and in the terms of dopamine (DA) transporter (DAT) by means of in situ hybridization. Experimental rats received daily late afternoon injections of 1.5 mg/kg melatonin for 30 days and analysis were performed in the ventral mesencephalon including the substantia nigra (SN) and ventral tegmental area (VTA), and hypothalamus. In the ventral mesencephalon, melatonin treatment significantly induced TH mRNA levels in individual dopaminergic neurons in SN and VTA. In contrast, DAT mRNA levels remained at control levels. Striatal synaptosomal DA uptake was not modified by melatonin treatment as compared with controls. Analysis of glutamic acid decarboxylase (GAD) mRNA in SN, the biosynthetic enzyme for GABAergic neurons, revealed no effect of melatonin treatment on mRNA levels for this marker. In the hypothalamus, we performed mRNA quantitation for TH in arcuate nucleus (Arc) and supraoptic nucleus (SO). Melatonin treatment failed to alter mRNA levels in either area. We detected weak but significant mRNA levels for DAT in Arc, SO, zona incerta (ZI) and periventricular hypothalamic nucleus (Pe). However, because of the low levels of mRNA in hypothalamic areas we were unable to perform a reliable measurement of DAT mRNA levels in response to melatonin treatment. We conclude that melatonin administration, that combines antioxidant capacity and a tissue-specific TH inducing effect, may be useful as a pharmacological agent to protect dopaminergic neurons from degeneration.

 

Venero, J. L., M. Revuelta, et al. (2003). "Evidence for dopamine-derived hydroxyl radical formation in the nigrostriatal system in response to axotomy." Free Radic Biol Med 34(1): 111-23.

            We have evaluated the ability of the injured nigrostriatal dopaminergic system to produce highly reactive hydroxyl radicals ((*)OH) by the electrochemical detection of salicylate hydroxylation. Unilateral transection of the medial forebrain bundle transiently increased the formation of (*)OH in substantia nigra (SN) but not in striatum during the first 48 h postlesion, when most relevant changes in terms of oxidatively modified proteins take place. Short-term adaptive axotomy-induced changes in substantia nigra included downregulation of nigral tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA expression and more intense TH immunoreactivity. Maintained inhibition of monoamine oxidase activity with deprenyl totally prevented the axotomy-induced formation of (*)OH, thus demonstrating the dopaminergic nature of these radicals. In contrast, deprenyl treatment, which is associated with a diminution in free radical production, failed to delay the onset of dopaminergic degeneration. This observation highlights the importance of being extremely cautious when analyzing parameters of oxidative stress and extrapolating them as a primary cause of cell death in the context of neurodegeneration. Long-term adaptive changes included a dramatic downregulation of DAT mRNA expression along with a moderate decrease in TH mRNA levels in SN. We anticipate a key regulatory role of the DAT to maximally optimize dopaminergic transmission in the synaptic cleft under conditions of degeneration.

 

Vetulani, J., L. Antkiewicz-Michaluk, et al. (2003). "A possible physiological role for cerebral tetrahydroisoquinolines." Neurotox Res 5(1-2): 147-55.

            Tetrahydroisoquinolines present in the mammalian brain, 1,2,3,4-tetrahydroisoquinoline (TIQ) and salsolinol, suspected to cause neurodegeneration leading to Parkinson's disease, were investigated to find their possible physiological role. To this aim their behavioral and receptor effects induced after a single dose were tested in mice and rats. Both compounds do not affect significantly the basal locomotor activity, very effectively block hyperactivity induced by apomorphine (rats) and amphetamine (mice), only partially block hyperactivity induced by scopolamine, do not affect locomotor stimulation induced by cocaine, and strongly augment the running fit induced by morphine (mice). They do not produce extrapyramidal symptoms and do not potentiate haloperidol-induced catalepsy (rats). TIQ and salsolinol do not displace antagonists of several receptors (including D(1) and D(2)) from their binding sites, but displace the agonists of Alpha(2)-adrenoceptors, [(3)H]clonidine and of dopamine receptors, [(3)H]apomorphine. The results indicate that salsolinol and TIQ act as specific antagonists of agonistic conformation of dopamine receptors, and owing to that may play a role of endogenous feed-back regulators of the dopaminergic system. Those properties make tetrahydroisoquinolines potential antidopaminergic drugs devoid of extrapyramidal effects, with possible application in substance addiction disorder as anti-craving agents.

 

Vizi, E. S. and I. J. Elenkov (2002). "Nonsynaptic noradrenaline release in neuro-immune responses." Acta Biol Hung 53(1-2): 229-44.

            Evidence has recently been obtained that the branches of the autonomic nervous system, mainly, the sympathetic [25], regulate cytokine production. Not only the primary (thymus, bone marrow) and secondary (spleen, tonsils, and lymph nodes) lymphoid organs, but also many other tissues are involved in immune responses and are heavily influenced by noradrenaline (NA) derived from varicose axon terminals of the sympathetic nervous system [25, 100]. Besides NA released from nonsynaptic varicosities of noradrenergic terminals [92], circulating catecholamines (adrenaline, dopamine, NA) are also able to influence immune responses, the production of pro- and anti-inflammatory cytokines by different immune cells. The sympathetic nervous system (catecholamines) and the hypothalamic-pituitary-adrenal (HPA) axis (cortisol) are the major integrative and regulatory components of different immune responses. In our laboratory convincing evidence has been obtained that NA released non-synaptically [90, 92] from sympathetic axon terminals and enhanced in concentration in the close proximity of immune cells is able to inhibit production of proinflammatory (TNF-alpha, IFN-gamma, IL-12, IL-1) and increase antiinflammatory cytokines (IL-10) in response to LPS [25, 91], indicating a fine-tuning control of the production of TNF-alpha and other cytokines by sympathetic innervation under stressful conditions. This effects are mediated via beta2-adrenoceptors expressed on immune cells and coupled to cAMP levels.

 

Wang, L., S. Muramatsu, et al. (2002). "Delayed delivery of AAV-GDNF prevents nigral neurodegeneration and promotes functional recovery in a rat model of Parkinson's disease." Gene Ther 9(6): 381-9.

            Glial cell line-derived neurotrophic factor (GDNF) is a strong candidate agent in the neuroprotective treatment of Parkinson's disease (PD). We investigated whether adeno-associated viral (AAV) vector-mediated delivery of a GDNF gene in a delayed manner could prevent progressive degeneration of dopaminergic (DA) neurons, while preserving a functional nigrostriatal pathway. Four weeks after a unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA), rats received injection of AAV vectors expressing GDNF tagged with FLAG peptide (AAV-GDNFflag) or beta-galactosidase (AAV-LacZ) into the lesioned striatum. Immunostaining for FLAG demonstrated retrograde transport of GDNFflag to the substantia nigra (SN). The density of tyrosine hydroxylase (TH)-positive DA fibers in the striatum and the number of TH-positive or cholera toxin subunit B (CTB, neuronal tracer)-labeled neurons in the SN were significantly greater in the AAV-GDNFflag group than in the AAV-LacZ group. Dopamine levels and those of its metabolites in the striatum were remarkably higher in the AAV-GDNFflag group compared with the control group. Consistent with anatomical and biochemical changes, significant behavioral recovery was observed from 4-20 weeks following AAV-GDNFflag injection. These data indicate that a delayed delivery of GDNF gene using AAV vector is efficacious even 4 weeks after the onset of progressive degeneration in a rat model of PD.

 

Wersinger, C. and A. Sidhu (2003). "Attenuation of dopamine transporter activity by alpha-synuclein." Neurosci Lett 340(3): 189-92.

            Alpha-synuclein accumulates in Lewy bodies in idiopathic Parkinson's disease. Neither the normal function nor contribution of alpha-synuclein to the pathophysiology of neurodegeneration is known. Here we show that a normal function of alpha-synuclein is the negative modulation of human dopamine transporter (hDAT) activity. In cotransfected Ltk(-) cells, alpha-synuclein attenuated the reuptake of dopamine by hDAT, in a manner dependent on expression levels of alpha-synuclein. Alpha-synuclein-mediated inhibition of hDAT activity was independent of expression vectors, cell types and methods of transfection. The alpha-synuclein-mediated decrease in DAT activity occurred through diminished uptake velocity of dopamine, without changes in the affinity of hDAT for dopamine. Co-immunoprecipitation studies confirmed the formation of a stable complex between alpha-synuclein and DAT, through direct protein:protein interactions. Thus, under normal (non-toxic) expression conditions, alpha-synuclein negatively modulates dopamine uptake by DAT.

 

Winogrodzka, A., P. Bergmans, et al. (2003). "[(123)I]beta-CIT SPECT is a useful method for monitoring dopaminergic degeneration in early stage Parkinson's disease." J Neurol Neurosurg Psychiatry 74(3): 294-8.

            OBJECTIVES: To examine the validity of [(123)I]beta-CIT SPECT for monitoring the progression of dopaminergic degeneration in Parkinson's disease; to investigate the influence of short term treatment with D(2)receptor agonists on striatal [(123)I]beta-CIT binding; and to determine the sample size and frequency of SPECT imaging required to demonstrate a significant effect of a putative neuroprotective agent. METHODS: A group of 50 early stage Parkinson's disease patients was examined. Two SPECT imaging series were obtained, 12 months apart. The mean annual change in the ratio of specific to non-specific [(123)I]beta-CIT binding to the striatum, putamen, and caudate nucleus was used as the outcome measure. RESULTS: A decrease in [(123)I]beta-CIT binding ratios between the two images was found in all regions of interest. The average decrease in [(123)I]beta-CIT binding ratios was about 8% in the whole striatum, 8% in the putaminal region, and 4% in the caudate region. Comparison of scans done in nine patients under two different conditions-in the off state and while on drug treatment-showed no significant alterations in the expression of striatal dopamine transporters as measured using [(123)I]beta-CIT SPECT. Power analysis indicated that to detect a significant (p < 0.05) effect of a neuroprotective agent with 0.80 power and 30% of predicted protection within two years, 216 patients are required in each group when the effects are measured in the whole putamen. CONCLUSIONS: [(123)I]beta-CIT SPECT seems to be a useful tool to investigate the progression of dopaminergic degeneration in Parkinson's disease and may provide an objective method of measuring the effectiveness of neuroprotective treatments. Short term treatment with a D(2)agonist does not have a significant influence on [(123)I]beta-CIT binding to dopamine transporters. If the latter finding is replicated in larger groups of patients, it supports the suitability of [(123)I]beta-CIT SPECT for examining the progression of neurodegeneration in patients being treated with D(2)receptor agonists.

 

Wu, D. C., V. Jackson-Lewis, et al. (2002). "Blockade of microglial activation is neuroprotective in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of Parkinson disease." J Neurosci 22(5): 1763-71.

            1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) damages the nigrostriatal dopaminergic pathway as seen in Parkinson's disease (PD), a common neurodegenerative disorder with no effective protective treatment. Consistent with a role of glial cells in PD neurodegeneration, here we show that minocycline, an approved tetracycline derivative that inhibits microglial activation independently of its antimicrobial properties, mitigates both the demise of nigrostriatal dopaminergic neurons and the formation of nitrotyrosine produced by MPTP. In addition, we show that minocycline not only prevents MPTP-induced activation of microglia but also the formation of mature interleukin-1beta and the activation of NADPH-oxidase and inducible nitric oxide synthase (iNOS), three key microglial-derived cytotoxic mediators. Previously, we demonstrated that ablation of iNOS attenuates MPTP-induced neurotoxicity. Now, we demonstrate that iNOS is not the only microglial-related culprit implicated in MPTP-induced toxicity because mutant iNOS-deficient mice treated with minocycline are more resistant to this neurotoxin than iNOS-deficient mice not treated with minocycline. This study demonstrates that microglial-related inflammatory events play a significant role in the MPTP neurotoxic process and suggests that minocycline may be a valuable neuroprotective agent for the treatment of PD.

 

Wu, D. C., P. Teismann, et al. (2003). "NADPH oxidase mediates oxidative stress in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease." Proc Natl Acad Sci U S A 100(10): 6145-50.

            Parkinson's disease (PD) is a neurodegenerative disorder of uncertain pathogenesis characterized by a loss of substantia nigra pars compacta (SNpc) dopaminergic (DA) neurons, and can be modeled by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Both inflammatory processes and oxidative stress may contribute to MPTP- and PD-related neurodegeneration. However, whether inflammation may cause oxidative damage in MPTP and PD is unknown. Here we show that NADPH-oxidase, the main reactive oxygen species (ROS)-producing enzyme during inflammation, is up-regulated in SNpc of human PD and MPTP mice. These changes coincide with the local production of ROS, microglial activation, and DA neuronal loss seen after MPTP injections. Mutant mice defective in NADPH-oxidase exhibit less SNpc DA neuronal loss and protein oxidation than their WT littermates after MPTP injections. We show that extracellular ROS are a main determinant in inflammation-mediated DA neurotoxicity in the MPTP model of PD. This study supports a critical role for NADPH-oxidase in the pathogenesis of PD and suggests that targeting this enzyme or enhancing extracellular antioxidants may provide novel therapies for PD.

 

Xu, J., S. Y. Kao, et al. (2002). "Dopamine-dependent neurotoxicity of alpha-synuclein: a mechanism for selective neurodegeneration in Parkinson disease." Nat Med 8(6): 600-6.

            The mechanism by which dopaminergic neurons are selectively lost in Parkinson disease (PD) is unknown. Here we show that accumulation of alpha-synuclein in cultured human dopaminergic neurons results in apoptosis that requires endogenous dopamine production and is mediated by reactive oxygen species. In contrast, alpha-synuclein is not toxic in non-dopaminergic human cortical neurons, but rather exhibits neuroprotective activity. Dopamine-dependent neurotoxicity is mediated by 54 83-kD soluble protein complexes that contain alpha-synuclein and 14-3-3 protein, which are elevated selectively in the substantia nigra in PD. Thus, accumulation of soluble alpha-synuclein protein complexes can render endogenous dopamine toxic, suggesting a potential mechanism for the selectivity of neuronal loss in PD.

 

Yan, H. Q., A. E. Kline, et al. (2002). "Traumatic brain injury reduces dopamine transporter protein expression in the rat frontal cortex." Neuroreport 13(15): 1899-901.

            Disturbances in dopamine neurotransmission contribute to frontal lobe dysfunction after traumatic brain injury. The changes in dopamine neurotransmission may be mediated by alterations in the dopamine transporter, which plays a key role in maintaining dopamine homeostasis. To determine whether the dopamine transporter system is altered after traumatic brain injury, dopamine transporter protein was examined bilaterally in the rat frontal cortex by Western blot at 1, 7, and 28 days after controlled cortical impact or sham injury ( = 6/group). Dopamine transporter protein expression was decreased in the injured (ipsilateral) cortex at 7 days and bilaterally at 28 days in injured sham control rats. The decrease in dopamine transporter protein levels may reflect a traumatic brain-injury-induced down-regulation of dopamine transporter and/or a loss of dopaminergic fibers.

 

Yang, H. W., Y. W. Lin, et al. (2002). "Change in bi-directional plasticity at CA1 synapses in hippocampal slices taken from 6-hydroxydopamine-treated rats: the role of endogenous norepinephrine." Eur J Neurosci 16(6): 1117-28.

            The object of the present study is to investigate the role of endogenous adrenergic innervation in regulating bi-directional synaptic plasticity in rat hippocampal CA1 synapses. The endogenous adrenergic system was eliminated by giving subcutaneous injection of 6-hydroxydopamine (6-OHDA) to rats immediately after birth, and the animals were killed for experiments at postnatal ages of 25-35 days. In hippocampal slices taken from 6-OHDA-treated animals, theta-burst stimulation at 100 Hz failed to induce long-term potentiation (LTP) at CA1 synapses. However, the induction of long-term depression (LTD) by prolonged low frequency stimulation at 1 Hz was unaffected in slices from 6-OHDA-treated animals. Bath application of norepinephrine (NE) restored LTP to control levels and blocked LTD. This effect was mimicked by beta- but not alpha-adrenergic receptor agonists, i.e. by isoproterenol but not phenylephrine. The activators of adenylyl cyclase and protein kinase A (PKA), i.e. forskolin and 8-bromoadenosine-3', 5'-cyclic monophosphate, respectively, restored LTP in slices from 6-OHDA-treated animals. In addition, application of the D1/D5 receptor agonist, dihydrexidine, also restored LTP in slices from 6-OHDA-treated animals. These results suggest that physiologically the recruitment of catecholamine innervation may be important for induction of LTP at hippocampal CA1 synapses during tetanic stimulation, while it may not be essential for LTD induction by prolonged 1 Hz stimulation. The released NE and dopamine exert their role in modulating synaptic plasticity via activation of beta-adrenergic and D1/D5 receptors, respectively, which in turn increase the levels of cytoplasm adenosine-3',5'-cyclic monophosphate and PKA.

 

Yarlagadda, A. (2002). "Role of calcium regulation in pathophysiology model of schizophrenia and possible interventions." Med Hypotheses 58(2): 182-6.

            Recent advances into the neuroscience research related to pathophysiology of schizophrenia have been impressive. While some are based on pre-existing theories and models, others have explored on a molecular level attempting to integrate the concepts of the past and present. However, given the complex multifactorial etiology of schizophrenia attempts to improve the current treatment modalities raise more questions than answers. In the cascade model of the hypotheses, the focus will be on a common factor/marker for the disease, to address the possible stepwise correlation between the various theories. Homeostasis of calcium, its relation to the release of glutamate, dopamine and nitric oxide will be discussed in detail with the potential for interventions aimed at every stage. Although this hypothesis emphasizes the role of calcium as a common factor, other potential causes such as autoantibodies to the receptors, such as NMDA (and GABA) cannot be ruled out.

 

Youdim, M. B., E. Grunblatt, et al. (2002). "Early and late molecular events in neurodegeneration and neuroprotection in Parkinson's disease MPTP model as assessed by cDNA microarray; the role of iron." Neurotox Res 4(7-8): 679-689.

            Possible cell death mechanisms for pars compacta nigro-striatal dopamine neurons in Parkinson's disease include oxidative stress, inflammatory processes, nitric oxide iron accumulation, glutamate toxicity and diminished neurotrophic factor responses. There is a notion that Parkinson's disease is not a single disorder but a syndrome that can be initiated by several factors. Because of limitations of biochemical methods in the global analysis of neuronal death, a full picture of events has not been established. However, recently developed cDNA microarray or microchips, in which the global expression of thousands of genes can be assessed simultaneously, is changing the prospect for understanding the disease process, its progression, response to drugs, etc. The neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is considered the most valid model of Parkinson's disease. We employed the technique of cDNA microarray gene expression to determine the mechanism of action of MPTP in mouse substantia nigra. Also, we studied neuroprotective processes induced by several compounds, including R-apomorphine and the green tea polyphenol epigallo-catechin-3-gallate (EGCG). This was done in two ways: (1) the time-dependent acute effect of MPTP, for determining which of the initial genes might lead to dopamine neuron death and (2) gene expression at the time of MPTP-induced dopamine neuron death. We observed that early (acute MPTP) gene expression differs from effects seen at the time of death (chronic MPTP), and that early gene changes are crucial for setting into action genes that eventually cause dopamine neuron death. Furthermore, this process is a cascade of "domino" effects, some of which were previously established by biochemical means. However, our findings show an additional large number of events previously unknown. The neuroprotective drugs reversed some but not all of the gene expression, suggesting involvement of these genes in the neurodegenerative process. Because of the profound complexity of "domino" effect it is now reasonable to understand why a single neuroprotective drug has not shown clinical neuroprotective efficacy. Future multi neuroprotective drugs may be necessary for treatment of not only Parkinson's disease, but other neurodegenerative diseases (e.g. Alzheimer's disease) and detrimental states (e.g. ischaemia).

 

Zafar, K. S., A. Siddiqui, et al. (2003). "Dose-dependent protective effect of selenium in rat model of Parkinson's disease: neurobehavioral and neurochemical evidences." J Neurochem 84(3): 438-46.

            Normal cellular metabolism produces oxidants that are neutralized within cells by antioxidant enzymes and other antioxidants. An imbalance between oxidant and antioxidant has been postulated to lead the degeneration of dopaminergic neurons in Parkinson's disease. In this study, we examined whether selenium, an antioxidant, can prevent or slowdown neuronal injury in a 6-hydroxydopamine (6-OHDA) model of Parkinsonism. Rats were pre-treated with sodium selenite (0.1, 0.2 and 0.3 mg/kg body weight) for 7 days. On day 8, 2 micro L 6-OHDA (12.5 micro g in 0.2% ascorbic acid in normal saline) was infused in the right striatum. Two weeks after 6-OHDA infusion, rats were tested for neurobehavioral activity, and were killed after 3 weeks of 6-OHDA infusion for the estimation of glutathione peroxidase, glutathione-S-transferase, glutathione reductase, glutathione content, lipid peroxidation, and dopamine and its metabolites. Selenium was found to be successful in upregulating the antioxidant status and lowering the dopamine loss, and functional recovery returned close to the baseline dose-dependently. This study revealed that selenium, which is an essential part of our diet, may be helpful in slowing down the progression of neurodegeneration in parkinsonism.

 

Zhang, J., V. A. Fitsanakis, et al. (2003). "Manganese ethylene-bis-dithiocarbamate and selective dopaminergic neurodegeneration in rat: a link through mitochondrial dysfunction." J Neurochem 84(2): 336-46.

            Manganese ethylene-bis-dithiocarbamate (Mn-EBDC) is the major active element of maneb, a pesticide linked to parkinsonism in certain individuals upon chronic exposure. Additionally, it has been shown to produce dopaminergic neurodegeneration in mice systemically coexposed to another pesticide, 1,1'-dimethyl-4,4'-bipyridinium (paraquat). Here, we described a rat model in which selective dopaminergic neurodegeneration was produced by delivering Mn-EBDC directly to the lateral ventricles. After establishing this model, we tested whether Mn-EBDC provoked dopamine efflux in the striatum, a well-known phenomenon produced by the mitochondrial inhibitor 1-methyl-4-phenylpyridinium (MPP+), the active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) that causes parkinsonism in humans, as well as in some animals. Finally, we investigated whether Mn-EBDC directly inhibited mitochondrial function in vitro using isolated brain mitochondria. Our data demonstrated that Mn-EBDC induced extensive striatal dopamine efflux that was comparable with that induced by MPP+, and that Mn-EBDC preferentially inhibited mitochondrial complex III. As mitochondrial dysfunction is pivotal in the pathogenesis of Parkinson's disease (PD), our results support the proposal that exposure to pesticides such as maneb, or other naturally occurring compounds that inhibit mitochondrial function, may contribute to PD development.

 

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