(2002). "[In Process Citation]." Ross Fiziol Zh Im I M Sechenova 88(2): 144-57.
A possible mechanism of cannabinoid-mediated akinesia is suggested. This effect is proposed to be the consequence of a decrease in LTD/LTP in cortical inputs to striatopallidal/striatonigral cells in the matrix due to CB1 receptor activation. In addition, cannabinoids can attenuate locomotor activity due to a reducing of glutamate/GABA release from axon terminals of subthalamic nucleus/striatonigral cells of matrix and subsequent decrease/increase in the activity of neurons of globus pallidus/substantia nigra pars reticulata. Cannabinoid-mediated rise of dopamine release might be a result of a decrease of dopamine neuron inhibition by striatonigral cells of striosomes. It follows from the suggested mechanism that an inactivation (activation) of CB1 receptors leading to rise (lowering) of the motor activity can be useful for treatment of Parkinson (Huntington) disease.

Akaike, A., H. Katsuki, et al. (2002). "[Role of nitric oxide in survival and death of neurons]." Nippon Yakurigaku Zasshi 119(1): 15-20.
The prominent pathological feature of the brain in Parkinson's disease is selective degeneration of dopaminergic neurons in the substantia nigra of the midbrain. Glutamate and nitric oxide (NO) are the major effectors of the radical stress that may induce selective loss of dopaminergic neurons. It has been postulated that neurotoxicity induced by glutamate and NO in dopaminergic neurons is regulated by certain endogenous factors. We have reported that estradiol protects dopaminergic neurons against NO-mediated glutamate neurotoxicity by reducing intracellular reactive oxygen species (ROS) levels. We further searched for a candidate for neuroprotective substances with unique structure. From the ether extract of fetal calf serum (FCS), we isolated a novel substance possessing protective activity against neurotoxicity induced by glutamate NO. The compound was a sulfur-containing diterpenoid and showed hydroxyl radical scavenging activity. We further analyzed the change of resistance to excitotoxicity in midbrain dopaminergic neurons in co-culture with the striatum by using a slice culture technique. The results suggested that the generation of NO is involved in NMDA cytotoxicity on dopaminergic neurons and that increased activity of SOD in co-culture renders dopaminergic neurons resistant to NMDA cytotoxicity by preventing peroxynitrite formation. Those findings suggest that regulation of intracellular ROS levels plays a critical role in protecting neurons against NO-mediated radical stress in neurodegenerative disorders.

Araki, T., M. Matsubara, et al. (2002). "Gamma-aminobutyric acidA and benzodiazepine receptor alterations in the rat brain after unilateral 6-hydroxydopamine lesions of the medial forebrain bundle." Neurol Res 24(1): 107-12.
Gamma-aminobutyric acidA (GABA(A)) and benzodiazepine (BZ) receptors and dopamine uptake sites in 6-hydroxydopamine-treated rat brains were studied by receptor autoradiography using [3H]muscimol, [3H]flunitrazepam and [3H]mazindol binding, respectively. The rats were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks post-lesion. Degeneration of the nigrostriatal pathway after 6-hydroxydopamine treatment caused a significant loss of dopamine uptake sites in the ipsilateral striatum and substantia nigra (SN) in the lesioned animals. In the contralateral side, however, dopamine uptake sites showed no significant changes in the brain throughout the experiments. On the other hand, no significant changes in GABA(A) receptors were observed in the brain of both the ipsilateral and contralateral sides during post-lesion. In contrast, BZ receptors were observed significantly increased in the ventromedial part of striatum of the ipsilateral side from 2 to 4 weeks post-lesion. Furthermore, a transient increase in BZ receptors was found in the ipsilateral SN only at 2 weeks post-lesion. In contralateral side, most regions examined showed no significant changes in BZ receptors throughout the experiments except for a transient increase in the SN at 1 week post-lesion. These results demonstrate that 6-hydroxydopamine can cause severe functional damage in dopamine uptake sites in the nigrostriatal pathway. Our results also suggest that the change in BZ receptors is more pronounced than that in GABA(A) receptors in the brain after 6-hydroxydopamine treatment. Furthermore, our findings suggest that the increase in BZ receptors in the brain of 6-hydroxydopamine-treated model may be due to the additional disruption of the nigrostriatal dopamine system. Thus, investigations into possible changes in neurotransmitter receptors other than dopaminergic receptors appear to be important for the elucidation of pathogenesis of Parkinsons disease.

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.

Azam, L., U. H. Winzer-Serhan, et al. (2002). "Expression of neuronal nicotinic acetylcholine receptor subunit mRNAs within midbrain dopamine neurons." J Comp Neurol 444(3): 260-74.
Many behavioral effects of nicotine result from activation of nigrostriatal and mesolimbic dopaminergic systems. Nicotine regulates dopamine release not only by stimulation of nicotinic acetylcholine receptors (nAChRs) on dopamine cell bodies within the substantia nigra and ventral tegmental area (SN/VTA), but also on presynaptic nAChRs located on striatal terminals. The nAChR subtype(s) present on both cell bodies and terminals is still a matter of controversy. The purpose of this study was to use double-labeling in situ hybridization to identify nAChR subunit mRNAs expressed within dopamine neurons of the SN/VTA, by using a digoxigenin-labeled riboprobe for tyrosine hydroxylase as the dopamine cell marker and (35)S-labeled riboprobes for nAChR subunits. The results reveal a heterogeneous population of nAChR subunit mRNAs within midbrain dopamine neurons. Within the SN, almost all dopamine neurons express alpha2, alpha4, alpha5, alpha6, beta2, and beta3 nAChR mRNAs, with more than half also expressing alpha3 and alpha7 mRNAs. In contrast, less than 10% express beta4 mRNA. Within the VTA, a similar pattern of nAChR subunit mRNA expression is observed except that most subunits are expressed in a slightly lower percentage of dopamine neurons than in the SN. Within the SN, alpha4, beta2, alpha7, and beta4 mRNAs are also expressed in a significant number of nondopaminergic neurons, whereas within the VTA this only occurs for beta4. The heterogeneity in the expression of nAChR subunits within the SN/VTA may indicate the formation of a variety of different nAChR subtypes on cell bodies and terminals of the nigrostriatal and mesolimbic pathways.

Ballmaier, M., M. Zoli, et al. (2002). "Preferential alterations in the mesolimbic dopamine pathway of heterozygous reeler mice: an emerging animal-based model of schizophrenia." Eur J Neurosci 15(7): 1197-1205.
Based on a number of neuroanatomical and behavioural similarities, recent evidence suggests that heterozygous reeler mice, haploinsufficient for reelin expression, represent a useful model of psychosis vulnerability. As brain mesolimbic dopamine pathways have been proposed to be associated with the pathophysiology of psychotic disorders, we thought it would be of interest to examine whether these animals present disturbances in the mesolimbic dopamine system. To this end we studied by immunocytochemical, in situ hybridization procedures and receptor autoradiography, several markers of the mesotelencephalic dopamine pathway in heterozygous reeler mice and controls. We report that heterozygous reeler mice exhibit a reduction in the number of tyrosine hydroxylase-immunoreactive cell bodies and tyrosine hydroxylase mRNA levels in the ventral tegmental area, as well as a reduction of tyrosine hydroxylase and dopamine transporter immunoreactivity in the dopamine terminal fields of the limbic striatum. In these areas we also observed a reduction of dopamine D2 receptor mRNA. Finally, a marked increase in D3 receptor mRNA levels was observed concomitant with a significant increase in D3 binding sites. On the contrary, the nigrostriatal pathway did not show any significant alteration in heterozygous reeler mice with regards to the dopaminergic markers examined in substantia nigra cell bodies and dorsal striatum dopamine terminal fields. These results suggest a specific link between reelin-related neuronal pathology and dopamine involvement in the pathophysiology of psychotic disorders.

Barc, S., G. Page, et al. (2002). "Relevance of different striatal markers in assessment of the MPP+-induced dopaminergic nigrostriatal injury in rat." J Neurochem 80(3): 365-74.
Many striatal dopaminergic markers are available for estimating the degree of the nigrostriatal lesion by MPTP/MPP+, but the changes of these markers are not perfectly matched. In this study we investigated different striatal markers and determined which ones closely reflected the nigrostriatal alteration. The in vivo binding of (E)-N-(3-iodoprop-2-enyl)-2-beta-carbomethoxy-3beta-(4'-methylphenyl)nortr opane (PE2I), a selective and potent inhibitor of the neuronal dopamine transporter (DAT) was considered as the reference index of injury of striatal dopaminergic nerve-endings. Rats received a 10-microg MPP+ injection in the right substantia nigra and were killed at 7 days after lesion. The results were as follows: (i) a decrease (66%) of the biodistribution of [125I]PE2I; (ii) a great reduction of the DAT expression measured by the binding of [125I]PE2I in striatal membranes (Bmax decreased by 54%) and in cerebral slices (88%); (iii) an 80% inhibition of the vesicular monoamine transporter expression revealed by the binding of [3H]dihydrotetrabenazine in cerebral slices; (iv) a robust decrease in the quantity of DA and its metabolites (about 50-60%); (v) a slight modification of the DAT activity with a decreased number of functional sites (Vmax decreased by 12%, p < 0.05) without change of the affinity in striatal synaptosomes. Among these markers the binding of [125I]PE2I in membrane homogenates and the content of DA, and its metabolites, in striatum could be the most relevant in vitro indexes of the degenerative state of the nigrostriatal pathway after MPP+ lesion.

Bata-Garcia, J. L., F. J. Heredia-Lopez, et al. (2002). "Circling behavior induced by microinjection of serotonin reuptake inhibitors in the substantia nigra." Pharmacol Biochem Behav 71(1-2): 353-63.
The nigrostriatal dopaminergic neurons of the substantia nigra pars compacta (SNc) and the nondopaminergic neurons of the substantia nigra pars reticulata (SNr) receive a dense synaptic input from the serotonergic neurons of the raphe nuclei. To assess whether serotonin [5-hydroxytryptamine (5-HT)] spontaneously released at the substantia nigra could modulate motor activity, the 5-HT reuptake inhibitors (SRIs), duloxetine (6-12 nmol) and clomipramine (12 nmol), were unilaterally microinjected either into the SNc or the SNr of freely moving rats, and the circling behavior was counted with an automated rotometer. In the SNc, the main effect of the SRIs was a contraversive circling behavior that was not observed when applied at distances > or = 0.2 mm above the SNc. The circling induced by clomipramine was blocked by microinjection of haloperidol (53 nmol) into the ipsilateral neostriatum, suggesting that the circling elicited by microinjection of the SRIs into the SNc depends on an intact striatal dopaminergic transmission. Microinjection of 5-HT (21 nmol) only produced a significant contraversive circling response when it was coinjected with the SRIs. Pretreatment with methysergide (1 mg/kg ip), a nonselective 5-HT(2) antagonist, did not block the circling elicited by microinjection of clomipramine into the SNc, either alone or in combination with 5-HT. However, microinjection of the 5-HT(2) antagonist mianserin (2 nmol) into the SNc partially inhibited the circling induced by duloxetine (6 nmol), alone or coinjected with 5-HT. Since current theories of circling behavior hypothesize that the animal turns away from the cerebral hemisphere where dopamine neurotransmission predominates, these results suggest that the contraversive circling induced by the unilateral microinjection of SRIs into the SNc could be mediated by a 5-HT-induced increase of firing frequency of nigrostriatal dopaminergic neurons. When applied into the SNr, clomipramine and duloxetine also elicited a contraversive circling behavior and enhanced the circling induced by 5-HT. Systemic methysergide (1 mg/kg i.p.), but not intranigral mianserin (2 nmol), blocked the circling elicited by microinjection of clomipramine into the SNr, either alone or in combination with 5-HT. These results suggest that 5-HT(2)-like receptors are involved in the contraversive circling induced by enhancement of serotonergic transmission in the SNr.

Betarbet, R., T. B. Sherer, et al. (2002). "Animal models of Parkinson's disease." Bioessays 24(4): 308-18.
Animal models are important tools in experimental medical science to better understand pathogenesis of human diseases. Once developed, these models can be exploited to test therapeutic approaches for treating functional disturbances observed in the disease of interest. On the basis of experimental and clinical findings, Parkinson's disease (PD) was the first neurological disease to be modeled and, subsequently, to be treated by neurotransmitter replacement therapy. Agents that selectively disrupt or destroy catecholaminergic systems, such as reserpine, methamphetamine, 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine have been used to develop PD models. Recently, it has been found that agricultural chemicals, such as rotenone and paraquat, when administered systemically, can reproduce specific features of PD in rodents, apparently via oxidative damage. Transgenic animals that over-express alpha-synuclein are used to study the role of this protein in dopaminergic degeneration. This review critically discusses animal models of PD and compares them with characteristics of the human disease.

Biglan, K. M. and R. G. Holloway (2002). "A review of pramipexole and its clinical utility in Parkinson's disease." Expert Opin Pharmacother 3(2): 197-210.
Parkinson's disease (PD) is a common neurodegenerative disorder characterised by selective loss of dopaminergic neurones in the substantia nigra and resulting in progressive disability. Therapy has focused on replacing depleted dopamine (DA) via supplementation with levodopa or DA agonists. Pramipexole (Mirapex((R)), Pharmacia Corp.) has recently been approved for the treatment of PD. Evidence from preclinical studies and clinical trials have proven the effectiveness of this agent in ameliorating the symptoms of PD. There is also non-human evidence that pramipexole may be neuroprotective and could therefore possibly slow disease progression; however, this has yet to be proven in humans. The use of pramipexole may be limited by its side effect profile compared to standard therapies and its relatively higher cost compared to levodopa. Despite these concerns, pramipexole does have a role in the treatment of PD in all stages of the illness and may arguably be the treatment of choice in early disease. In addition to its use in PD, pramipexole has shown some utility in the treatment of restless legs syndrome (RLS), depression and schizophrenia.

Campusano, J. M., J. Abarca, et al. (2002). "Modulation of dendritic release of dopamine by metabotropic glutamate receptors in rat substantia nigra." Biochem Pharmacol 63(7): 1343-1352.
A superfusion system was used to study the effects of metabotropic glutamate receptor (mGluR) ligands upon the release of [3H]dopamine ([3H]DA) previously taken up by rat substantia nigra (SN) slices. trans-(+/-)-1-Amino-(1S,3R)-cyclopentane dicarboxylic acid (trans-ACPD; 100 and 600&mgr;M), a group I and II mGluR agonist, evoked the release of [3H]DA from nigral slices. This last effect was reduced significantly by (2S,3S,4S)-2-methyl-2-(carboxycyclopropyl)-glycine (MCCG; 300&mgr;M), an antagonist of group II mGluR, or by the addition of tetrodotoxin (D-APV; 1&mgr;M) to the superfusion medium. D-(-)-2-Amino-5-phosphono-valeric acid (100&mgr;M), an N-methyl-D-aspartate receptor antagonist, or the presence of Mg(2+) (1.2mM) in the superfusion medium did not modify trans-ACPD-induced [3H]DA release. In addition, a group II mGluR agonist such as (2S,1'R,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)-glycine (DCG-IV; 100&mgr;M) significantly induced the release of [3H]DA from nigral slices, whereas a group I mGluR agonist such as (RS)-3,5-dihydroxyphenylglycine (DHPG; 50 and 100&mgr;M) did not modify the release of the [3H]-amine. Further experiments showed that the NMDA (100&mgr;M)-evoked release of [3H]DA was decreased significantly by prior exposure of SN slices to trans-ACPD. Finally, partial denervation of the DA nigro-striatal pathway with 6-hydroxydopamine (6-OH-DA) increased trans-ACPD-induced release of [3H]DA, whereas it decreased trans-ACPD inhibitory effects on NMDA-evoked release of [3H]DA from nigral slices. The present results suggest that the dendritic release of DA in the SN is regulated by mGluR activation. Such nigral mGluR activation may produce opposite effects upon basal and NMDA-evoked release of DA in the SN. In addition, such mGluR-induced effects in the SN are modified in response to partial denervation of the DA nigro-striatal pathway.

Casu, M. A., G. Colombo, et al. (2002). "Reduced TH-immunoreactive fibers in the limbic system of Sardinian alcohol-preferring rats." Brain Res 924(2): 242-51.
The mesolimbic dopamine (DA) system has long been known to be involved in reward behaviors. As with other substances of abuse, it has been extensively reported that ethanol influences the dopaminergic system. The present study examined whether selectively bred Sardinian-alcohol-preferring (sP) and Sardinian alcohol non-preferring rats (sNP), differ in the DA innervation in structures of the forebrain that are related to rewarding behaviors. To this aim, we performed an immunohistochemistry study with an antibody raised against tyrosine hydroxylase (TH), the rate-limited step enzyme in the biosynthesis of monoamines. The TH-positive innervation density was found to be significantly lower in the cingulate cortex and in the shell of the nucleus accumbens of the sP when compared with the sNP and unselected Wistar rats. These anatomical structures both cluster in the medial aspect of the mesolimbic system. No differences in other major DA brain regions, such as the nigro-striatal pathway were found. The analysis of cell-body area revealed no differences between sP, sNP and Wistar rats in the ventral tegmental area and substantia nigra (pars compacta and reticulata) and the density of the TH-positive fibers was not different in the caudate-putamen. These results indicate a selective reduction of terminal innervation in the medial portion of the mesocorticolimbic DA system in sP rats and suggest that the latter may consume larger amounts of ethanol, when compared with sNP rats, to compensate for the deficiency of dopamine to produce an adequate level of reward.

Chen, B. T., M. V. Avshalumov, et al. (2002). "Modulation of somatodendritic dopamine release by endogenous H(2)O(2): susceptibility in substantia nigra but resistance in VTA." J Neurophysiol 87(2): 1155-8.
We showed previously that dopamine (DA) release in dorsal striatum is inhibited by endogenously generated hydrogen peroxide (H(2)O(2)). Here, we examined whether endogenous H(2)O(2) can also modulate somatodendritic DA release in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA), with companion measurements in DA terminal regions. Evoked DA release was monitored in brain slices using carbon-fiber microelectrodes with fast-scan cyclic voltammetry. Exogenous H(2)O(2) decreased DA release by 50-60% in SNc and VTA but only by 35% in nucleus accumbens. Whether endogenous H(2)O(2) also modulated somatodendritic release was examined using the glutathione peroxidase inhibitor, mercaptosuccinate (MCS), which should increase stimulation-evoked H(2)O(2) levels. In the presence of MCS, DA release was suppressed by 30-40% in SNc as well as in dorsal striatum and nucleus accumbens. In striking contrast, DA release in the VTA was unaffected by MCS. These data are consistent with stronger H(2)O(2) regulation or lower H(2)O(2) generation in VTA than in the other regions. Importantly, oxidative stress has been linked causally to Parkinson's disease, in which DA cells in SNc degenerate, but VTA cells are spared. The present data suggest that differences in oxidant regulation or generation between SNc and VTA could contribute to this.

Chen, L. W., L. C. Wei, et al. (2002). "Significant up-regulation of nestin protein in the neostriatum of MPTP-treated mice. Are the striatal astrocytes regionally activated after systemic MPTP administration?" Brain Res 925(1): 9-17.
We are interested in the possible role of central glial cells in pathogenesis of Parkinson's disease of mammals. Parkinsonism model was induced by systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, and the reactive glial cells were examined by immunocytochemical visualization of nestin protein in the brains and spinal cords of C57 mice. Abundant nestin-like immunoreactivity was predominately found in the caudate putamen of MPTP-treated mice and about 481-fold of nestin-like immunoreactive cells increased compared with that of control animals, indicating that significant up-regulation of nestin protein occurred in these regions. Majority of nestin-like immunoreactive cells characterized with astrocytic profiles of multiple, radical and hypotrophic processes, and showed a distribution and dynamic patterns similar to that of glial fibrillary acid protein (GFAP)-immunoreactive cells in the caudate putamen. Double immunofluorescence confirmed that 100% of nestin-like immunoreactive cells exhibited GFAP-immunoreactivity while nestin/GFAP double-labeled cells constituted about 84% of total GFAP-immunoreactive cells in the caudate putamen, indicating these nestin-like immunoreactive cells belong to a reactive population of the astrocytes. On the other hand, no obvious changes of nestin- or GFAP-like immunoreactivities were detected in the globus pallidus, the substantia nigra and the ventral tegmental area after MPTP-treatment. The results have provided morphological evidence for the regional activation of astrocytic glial cells following systemic MPTP administration, suggesting that a large population of reactive striatal astrocytes might play an important role in initial pathogenesis or acute stage of Parkinson's disease in mammals.

Chun, H. S., M. S. Yoo, et al. (2002). "Marked dopaminergic cell loss subsequent to developmental, intranigral expression of glial cell line-derived neurotrophic factor." Exp Neurol 173(2): 235-44.
Glial cell line-derived neurotrophic factor (GDNF) shows potent neuroprotective as well as neurorestorative actions on the adult neurons impacted in animal models of Parkinson's disease (PD). Long-term pharmaco-physiological effects of GDNF on developing dopaminergic (DA) neurons have not yet been explored because of technical difficulties in producing prolonged cell type-specific delivery of this neurotrophic factor in mammalian embryonic brain. The current studies used our previously characterized 9.0-kb tyrosine hydroxylase promoter to produce transgenic mice with neuronal cell type-specific expression of GDNF in substantia nigra pars compacta (SNc) and locus coeruleus (LC). These mice were used to test the parsimonious hypothesis that increased developmental expression of GDNF in SNc and LC would significantly enhance the number of postmitotic adult neurons. To our surprise, adult transgenic mice carrying the TH9.0kb-GDNF hybrid gene showed dramatic reductions in both the numbers and the volumes of SNc-DA and LC-noradrenergic (NA) neurons by quantitative morphometric analysis. The decrease in the number of DA neurons was apparent as early as postnatal day 2, the period before the major naturally occurring apoptotic cell death in midbrain. Aged transgenic mice exhibited no further significant deficits in motor behaviors. These data suggest that continuous, early developmental GDNF expression exerts physiological effects on newly differentiated, immature dopamine neurons that differ from those observed on more mature and adult DA neurons. Further elucidation of the mechanisms underlying differential GDNF actions will greatly improve the pharmacological efficacy of GDNF in fetal neural transplantation as well as adult neuronal gene therapy in PD patients.

Cicchetti, F., A. L. Brownell, et al. (2002). "Neuroinflammation of the nigrostriatal pathway during progressive 6-OHDA dopamine degeneration in rats monitored by immunohistochemistry and PET imaging." Eur J Neurosci 15(6): 991-8.
We investigated the microglial response to progressive dopamine neuron degeneration using in vivo positron emission tomography (PET) imaging and postmortem analyses in a Parkinson's disease (PD) rat model induced by unilateral (right side) intrastriatal administration of 6-hydroxydopamine (6-OHDA). Degeneration of the dopamine system was monitored by PET imaging of presynaptic dopamine transporters using a specific ligand (11)C-CFT (2beta-carbomethoxy-3beta-(4-fluorophenyl) tropane). Binding of (11)C-CFT was markedly reduced in the striatum indicating dopaminergic degeneration. Parallel PET studies of (11)C-PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3 isoquinoline carboxamide) (specific ligand for activated microglia) showed increased binding in the striatum and substantia nigra indicative of a microglial response. Postmortem immunohistochemical analyses were performed with antibodies against CR3 for microglia/macrophage activation. Using a qualitative postmortem index for microglial activation we found an initially focal, then widespread microglial response at striatal and nigral levels at 4 weeks postlesion. These data support the hypothesis that inflammation is a significant component of progressive dopaminergic degeneration that can be monitored by PET imaging.

Cobb, W. S. and E. D. Abercrombie (2002). "Distinct roles for nigral GABA and glutamate receptors in the regulation of dendritic dopamine release under normal conditions and in response to systemic haloperidol." J Neurosci 22(4): 1407-13.
The regulation of dendritic dopamine release in the substantia nigra (SN) likely involves multiple mechanisms. GABA and glutamate inputs to nigrostriatal dopamine neurons exert powerful influences on dopamine neuron physiology; therefore, it is probable that GABA and glutamate likewise influence dendritic dopamine release, at least under some conditions. The present studies used in vivo microdialysis to determine the potential roles of nigral GABA and glutamate receptors in the regulation of dendritic dopamine release under normal conditions and when dopamine signaling in the basal ganglia is compromised after systemic haloperidol administration. Nigral application of the GABA(A) receptor antagonist bicuculline by reverse dialysis significantly increased spontaneous dopamine efflux in the SN. However, spontaneous dopamine efflux in the SN was not significantly affected by local application of the glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione or (+/-)-3-[2-carboxypiperazine-4-yl]-propyl-1-phosphonic acid. Systemic haloperidol administration significantly increased the extracellular dopamine measured in the SN. Blockade of nigral GABA(A) receptors by local bicuculline application did not alter this effect of systemic haloperidol, despite the bicuculline-induced increase in spontaneous dendritic dopamine efflux. In contrast, nigral application of either glutamate receptor antagonist significantly attenuated the increases in dendritic dopamine efflux elicited by systemic haloperidol. These data suggest that under normal conditions, activity of GABA afferents to SN dopamine neurons is an important determinant of the spontaneous level of dendritic dopamine release. Circuit-level changes in the basal ganglia involving an increased glutamatergic drive to the SN appear to underlie the increase in dendritic dopamine release that occurs in response to systemic haloperidol administration.

Collier, T. J., C. E. Sortwell, et al. (2002). "Embryonic ventral mesencephalic grafts to the substantia nigra of MPTP-treated monkeys: feasibility relevant to multiple-target grafting as a therapy for Parkinson's disease." J Comp Neurol 442(4): 320-30.
Transplantation of embryonic dopamine (DA) neurons is being studied as an experimental replacement therapy for the DA-deficiency characteristic of Parkinson's disease. Some studies suggest that one of the limitations of this approach is that intrastriatal placement of implants fails to consistently restore completely normal movement. One potential cause of this suboptimal therapeutic outcome is that changes in the neural activity of several structures in the basal ganglia circuitry resulting from striatal DA depletion is not adequately normalized by graft-derived DA replacement in striatum alone. In the present study, we assessed the feasibility of grafting embryonic DA neurons into the substantia nigra (SN) of adult parkinsonian monkeys as an approach to restoration of the DA modulation of striatal-nigral afferents that is lost after degeneration of SN neurons. Sixteen St. Kitts African green monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) received implants of embryonic monkey ventral mesencephalon (VM), or sham implants, aimed at the rostral SN. At 6 months after grafting, staining for tyrosine hydroxylase (TH) indicated that grafted DA neurons survived at this site, albeit often in reduced numbers compared with VM grafts to striatum. Grafted neurons extended neurites into the parenchyma of the SN, but there was no evidence of lengthy extension of graft-derived neurites rostrally along the trajectory of the mesostriatal fiber system. A region-specific, modest increase in DA levels and TH-positive fiber density in the ventral-medial putamen was detected, accompanied by modest but significant decreases in parkinsonian behaviors at 5-6 months after grafting. Our findings support the view that grafting embryonic tissue to the SN is a feasible procedure in nonhuman primates that provides a modest but detectable benefit of its own. These results encourage the further development of multiple-target grafting strategies as a means of restoring modulation of anatomically widespread basal ganglia structures relevant to treatment of Parkinson's disease.

Creutz, L. M. and M. F. Kritzer (2002). "Estrogen receptor-beta immunoreactivity in the midbrain of adult rats: regional, subregional, and cellular localization in the A10, A9, and A8 dopamine cell groups." J Comp Neurol 446(3): 288-300.
Estrogen modulates dopamine synthesis, release, and metabolism in corticolimbic and striatal targets of midbrain dopamine neurons. The relevant sites of receptor-mediated action, however, had been elusive, because all available evidence suggested a paucity of intracellular estrogen receptors in the A8, A9, and A10 dopamine regions and their afferent targets. More recent evidence of a relative abundance of the beta isoform of the estrogen receptor (ER) in the substantia nigra and ventral tegmental area (VTA), however, suggests that this newly described receptor may be important in estrogen's stimulation of midbrain DA systems. It is unknown, however, precisely how ERbeta is distributed with respect to the functionally and neurochemically diverse cell populations of the ventral midbrain. To address these issues, this study used single- and double-label immunocytochemistry to detail the regional, subregional, and cellular distributions of ERbeta immunoreactivity in and around midbrain dopamine-containing cell groups in hormonally intact adult male and female rats. These analyses revealed that ERbeta-immunoreactive nuclei were found only in neurons, more specifically, within subsets of both dopaminergic and nondopaminergic neurons in the dorsal VTA, the parabrachial pigmented nucleus, the substantia nigra pars lateralis, the retrorubral fields, and to a lesser extent the linear midline nuclei. These regional and cellular receptor distributions thus place the ERbeta isoform in anatomical register with midbrain dopamine systems known to participate in a spectrum of motor, cognitive, and affective functions.

Cunningham, L. A. and C. Su (2002). "Astrocyte delivery of glial cell line-derived neurotrophic factor in a mouse model of Parkinson's disease." Exp Neurol 174(2): 230-42.
Primary astrocytes were genetically modified ex vivo to express recombinant glial cell line-derived neurotrophic factor (GDNF) and subsequently were tested for their ability to provide neuroprotection to dopaminergic neurons in a 6-hydroxydopamine (6-OHDA) mouse model of Parkinson's disease. A replication-defective retrovirus was constructed, which contained the rat GDNF sequence and a sequence encoding a beta-galactosidase (beta-gal)/neomycin phosphotransferase fusion protein, linked via an internal ribosomal entry site. Murine astrocytes transduced with this vector secreted GDNF into the culture media at the rate of 115 +/- 34 pg/24 h/10(5) cells and expressed cytoplasmic beta-gal, whereas control nontransduced astrocytes were negative for GDNF production and cytoplasmic beta-gal expression. Mice that received implants of GDNF-producing astrocytes into the striatum or nigra displayed elevated levels of GDNF compared to mice that received control nontransduced astrocytes. In addition, tissue content of GDNF was increased bilaterally and in brain regions both proximal and distal to the graft, even though astrocyte migration away from the graft site did not occur. Importantly, GDNF-producing astrocytes provided marked neuroprotection of nigral dopaminergic perikarya, and partial protection of striatal dopaminergic fibers, when implanted into the midbrain 6 days prior to a retrograde 6-OHDA lesion, as assessed by tyrosine hydroxylase immunohistochemistry. Similarly, GDNF-producing astrocytes prevented the acquisition of amphetamine-induced rotational behavior in 6-OHDA-treated mice and completely prevented dopamine depletion within the substantia nigra, as assessed by high-performance liquid chromatography. These results indicate that continuous exposure to low levels of GDNF provided by transgenic astrocytes provides marked neuroprotection of nigral dopaminergic neurons. (c)2002 Elsevier Science (USA).

Dluzen, D. E., L. I. Anderson, et al. (2002). "Striatal dopamine output is compromised within +/- BDNF mice." Synapse 43(2): 112-7.
We reported previously that mice lacking one brain-derived neurotrophic factor (BDNF) allele demonstrate elevated striatal dopamine (DA) concentrations but impaired behavioral responses involving the nigrostriatal dopaminergic (NSDA) system. To test the hypothesis that these elevated striatal DA concentrations are associated with perturbed NSDA functioning, we compared striatal DA output between heterozygous mutant (+/-) and wild-type littermate control (+/+) BDNF mice under conditions of an intact NSDA system, as well as following methamphetamine (MA)-induced neurotoxicity. Basal DA output from superfused CS tissue fragments did not differ between +/+ and +/- BDNF mice. Potassium (K+) stimulated DA outputs from intact striatal fragments of +/+ mice were significantly greater than that of +/- BDNF mice. Following MA treatment, K+ stimulated DA output of +/+ mice was statistically equivalent to +/- BDNF mice. Striatal DA concentrations of +/- BDNF mice were elevated, albeit not significantly, in both intact and MA-treated mice relative to +/+ mice. Following MA treatment, striatal DA concentrations were significantly decreased for both genotypes; however, the degree of DA depletion was significantly greater in +/+ mice. Analyzed collectively, these data show the differential effects exerted by a BDNF mutation upon striatal DA concentrations and output. Notably, lower striatal DA concentrations of +/+ vs. +/- BDNF mice can be contrasted with the significantly greater K+ stimulated DA output from the former. This difference was abolished following MA treatment. These results suggest that processes involved with the dynamics of DA release within the NSDA system may be compromised in +/- BDNF mutant mice.

Duan, W., B. Ladenheim, et al. (2002). "Dietary folate deficiency and elevated homocysteine levels endanger dopaminergic neurons in models of Parkinson's disease." J Neurochem 80(1): 101-10.
Although the cause of Parkinson's disease (PD) is unknown, data suggest roles for environmental factors that may sensitize dopaminergic neurons to age-related dysfunction and death. Based upon epidemiological data suggesting roles for dietary factors in PD and other age-related neurodegenerative disorders, we tested the hypothesis that dietary folate can modify vulnerability of dopaminergic neurons to dysfunction and death in a mouse model of PD. We report that dietary folate deficiency sensitizes mice to MPTP-induced PD-like pathology and motor dysfunction. Mice on a folate-deficient diet exhibit elevated levels of plasma homocysteine. When infused directly into either the substantia nigra or striatum, homocysteine exacerbates MPTP-induced dopamine depletion, neuronal degeneration and motor dysfunction. Homocysteine exacerbates oxidative stress, mitochondrial dysfunction and apoptosis in human dopaminergic cells exposed to the pesticide rotenone or the pro-oxidant Fe(2+). The adverse effects of homocysteine on dopaminergic cells is ameliorated by administration of the antioxidant uric acid and by an inhibitor of poly (ADP-ribose) polymerase. The ability of folate deficiency and elevated homocysteine levels to sensitize dopaminergic neurons to environmental toxins suggests a mechanism whereby dietary folate may influence risk for PD.

Erhardt, S., J. M. Mathe, et al. (2002). "GABA(B) receptor-mediated modulation of the firing pattern of ventral tegmental area dopamine neurons in vivo." Naunyn Schmiedebergs Arch Pharmacol 365(3): 173-80.
Previous work demonstrates the fundamental role of the firing pattern, specifically the burst firing mode of midbrain dopamine (DA) neurons in the regulation of DA release. Spontaneous burst firing has been shown to be dependent upon NMDA receptor activation of the DA cells. In addition to NMDA receptors, previous studies have reported that also GABA(B) receptors modulate the firing pattern of DA neurons in the substantia nigra. In the present electrophysiological study the role of GABA(B) receptors in the modulation of the firing pattern of DA neurons in the ventral tegmental area (VTA) in anaesthetised Sprague-Dawley rats was analysed. Systemic administration of the selective and potent GABA(B) receptor agonist baclofen dose-dependently reduced firing rate and burst firing in VTA DA neurons. An increase in the regularity of DA cell firing was also observed. All these effects were effectively antagonized by administration of the selective GABA(B) antagonist CGP 35348 (100 mg/kg or 200 mg/kg, i.v.). Administration of CGP 35348 (400 mg/kg, i.v.) per se was associated with a long-lasting increase in burst firing activity. The effects of systemic administration of baclofen, alone or in combination with CGP 35348, on the firing rate were largely mimicked by local microiontophoretic application of the drugs onto the DA neurons.Our findings indicate that central GABA(B) receptors may contribute to control of the burst firing mode of VTA DA neurons. Physiologically, activation of GABA(B) receptors may subserve a dampening function on VTA DA cell excitability which may counterbalance NMDA receptor-mediated excitation.

Fernagut, P. O., E. Diguet, et al. (2002). "A simple method to measure stride length as an index of nigrostriatal dysfunction in mice." J Neurosci Methods 113(2): 123-30.
Reduced stride length characterizes Parkinsonian gait. We aimed to demonstrate that it could be measured simply and reliably in mice by pawprints and used as an index of basal ganglia dysfunction. In C57BL/6 mice, stride length measurements proved to be consistent across measurements and experimenters. It was slightly lower in the hindlimbs and was correlated to femur size and animal velocity. Dopamine depletion by reserpine and striatal dopamine receptor blockade by haloperidol resulted in reduced mean stride length in four limbs. Significant forelimb/hindlimb difference was also observed both in mice with 3-nitropropionic acid (3-NP) induced striatal lesions and in those with MPTP-induced nigral cell loss. Reduction of hindlimb stride length was correlated significantly with the magnitude of cell loss, either in the substantia nigra or in the lateral mid-striatum. Stride length is, therefore, a simple method to obtain an index of motor disorders due to basal ganglia dysfunction in mice.

Fredduzzi, S., R. Moratalla, et al. (2002). "Persistent behavioral sensitization to chronic L-DOPA requires A2A adenosine receptors." J Neurosci 22(3): 1054-62.
To investigate the role of A(2A) adenosine receptors in adaptive responses to chronic intermittent dopamine receptor stimulation, we compared the behavioral sensitization elicited by repeated l-DOPA treatment in hemiparkinsonian wild-type (WT) and A(2A) adenosine receptor knock-out (A(2A) KO) mice. Although the unilateral nigrostriatal lesion produced by intrastriatal injection of 6-hydroxydopamine was indistinguishable between WT and A(2A) KO mice, they developed strikingly different patterns of behavioral sensitization after daily treatment with low doses of l-DOPA for 3 weeks. WT mice initially displayed modest contralateral rotational responses and then developed progressively greater responses that reached a maximum within 1 week and persisted for the duration of the treatment. In contrast, any rotational behavioral sensitization in A(2A) KO mice was transient and completely reversed within 2 weeks. Similarly, the time to reach the peak rotation was progressively shortened in WT mice but remained unchanged in A(2A) KO mice. Furthermore, daily l-DOPA treatment produced gradually sensitized grooming in WT mice but failed to induce any sensitized grooming in A(2A) KO mice. Finally, repeated l-DOPA treatment reversed the 6-OHDA-induced reduction of striatal dynorphin mRNA in WT but not A(2A) KO mice, raising the possibility that the A(2A) receptor may contribute to l-DOPA-induced behavioral sensitization by facilitating adaptations within the dynorphin-expressing striatonigral pathway. Together these results demonstrate that the A(2A) receptor plays a critical role in the development and particularly the persistence of behavioral sensitization to repeated l-DOPA treatment. Furthermore, they raise the possibility that the maladaptive dyskinetic responses to chronic l-DOPA treatment in Parkinson's disease may be attenuated by A(2A) receptor inactivation.

Fukushima, T., A. Kaetsu, et al. (2002). "Possible role of 1-methylnicotinamide in the pathogenesis of Parkinson's disease." Exp Toxicol Pathol 53(6): 469-73.
This study tested the hypothesis, that nicotinamide N-methyltransferase (NAMT) activity in the brain could convert nicotinamide to 1-methylnicotinamide (MNA) and by that means damage the nigro-neostriatal dopaminergic neurons. The NAMT activities of rat brain and liver were assayed with gas chromatographic-mass spectrometric analysis in a selected ion monitoring system. They amounted to 0.30 nmol/mg x h and 0.51 nmol/mg x h, respectively. The MNA injection in rat substantia nigra pars compacta significantly decreased dopamine content in the striatum. NADH oxidation and lipid peroxidation by MNA via rat brain submitochondrial particles (SMP) under the condition of pH ranging from pH 6.0 to 10.0 were verified. The pH optimum for the NADH oxidation was 9.0. The pH optimum for the peroxidation of the lipid composing SMP by MNA was also 9.0. The lipid peroxidation in this assay was suppressed by superoxide dismutase. The superoxide anion formed by MNA via mitochondria might be involved in the etiology of Parkinson's disease.

Gayle, D. A., Z. Ling, et al. (2002). "Lipopolysaccharide (LPS)-induced dopamine cell loss in culture: roles of tumor necrosis factor-alpha, interleukin-1beta, and nitric oxide." Brain Res Dev Brain Res 133(1): 27-35.
Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopamine (DA) neurons of the substantia nigra pars compacta (SNc). Although the exact mechanisms responsible for this cell loss are unclear, emerging evidence suggests the involvement of inflammatory events. In the present study, we characterized the effects of the proinflammatory bacteriotoxin lipopolysaccharide (LPS) on the number of tyrosine hydroxylase immunoreactive (THir) cells (used as an index for DA neurons) in primary mesencephalic cultures. LPS (10-80 microg/ml) selectively decreased THir cells and increased culture media levels of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) as well as nitrite (an index of nitric oxide (NO) production). Cultures exposed to both LPS and neutralizing antibodies to IL-1beta or TNF-alpha showed an attenuation of the LPS-induced THir cell loss by at least 50% in both cases. Inhibition of the inducible form of nitric oxide synthase (iNOS) by L-NIL did not affect LPS toxicity, but increased the LPS-induced levels of both TNF-alpha and IL-1beta. These findings suggest that neuroinflammatory stimuli which lead to elevations in cytokines may induce DA neuron cell loss in a NO-independent manner and contribute to PD pathogenesis.

Georgievska, B., D. Kirik, et al. (2002). "Neuroprotection in the rat Parkinson model by intrastriatal GDNF gene transfer using a lentiviral vector." Neuroreport 13(1): 75-82.
We used a recombinant lentiviral vector (rLV) for gene delivery of GDNF to the striatum, and assessed its neuroprotective effects in the intrastriatal 6-hydroxydopamine (6-OHDA) lesion model.The level of GDNF expression obtained with the rLV-GDNF vector was dose-related and ranged between 0.9-9.3 ng/mg tissue in the transduced striatum, as determined by ELISA, and 0.2-3.0 ng/mg tissue were detected in the ipsilateral substantia nigra (SN), due to anterograde transport of the GDNF protein. GDNF expression was apparent at 4 days and maintained for > 8 months after injection. Striatal delivery of rLV-GDNF efficiently protected the nigral dopamine (DA) neurons and their projection, against the 6-OHDA lesion (65-77% of intact side). Sprouting of the lesioned axons was observed along the nigrostriatal pathway, precisely corresponding to the areas containing anterogradely transported GDNF.

Gerhardt, G. A., W. A. Cass, et al. (2002). "Changes in somatodendritic but not terminal dopamine regulation in aged rhesus monkeys." J Neurochem 80(1): 168-77.
For these studies, young (8-9 years), middle-aged (14-17 years) and aged (23-28 years) rhesus monkeys were used as a model of normal aging in humans to investigate changes in dopamine (DA)-containing neurons in senescence. Aged monkeys exhibited significant age-related motoric declines as compared to the young animals. In vivo microdialysis studies showed that basal levels of the DA metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were diminished by 44% and 79%, respectively, in the substantia nigra (SN) of aged monkeys. In addition, d-amphetamine-evoked overflow of DA in the SN was diminished by 30% in the middle-aged animals and 67% in the aged monkeys. Post-mortem measures of DA and DA metabolites showed significant decreases in DA (20%), DOPAC (47%) and HVA (22%) levels in the putamen and a 25% decline in HVA tissue levels in the SN of the aged monkeys as compared to the young animals. Unbiased stereological cell counting of tyrosine hydroxylase (TH)-immunoreactive neurons in the SN showed a small (15-20%) but significant age-related decline in TH-positive neurons. In addition, there was a small (15-20%) but significant decline in TH-positive fiber density and TH-positive cell size. In comparison to the massive loss of DA neurons responsible for the movement dysfunctions seen in Parkinson's disease, pronounced functional changes in DA release in the SN and putamen may significantly contribute to the motoric dysfunctions characterizing normal aging in rhesus monkeys.

Grillner, P. and N. B. Mercuri (2002). "Intrinsic membrane properties and synaptic inputs regulating the firing activity of the dopamine neurons." Behav Brain Res 130(1-2): 149-69.
Dopamine (DA) neurones of the ventral mesencephalon are involved in the control of reward related behaviour, cognitive functions and motor performances, and provide a critical site of action for major categories of neuropsychiatric drugs, such as antipsychotic agents, dependence producing drugs and anti-Parkinson medication. The midbrain DA neurones are mainly located in the substantia nigra pars compacta (SNPC) and the ventral tegmental area (VTA). Intrinsic membrane properties regulate the activity of these neurones. In fact, they possess several conductances that allow them to fire in a slow pacemaker-like mode. The internal set of membrane currents interact with afferent synaptic inputs which, especially in in vivo conditions, contribute to accelerate or decelerate the firing activity of the cells in accordance with the necessity to optimise the release of dopamine in the terminal fields. In particular, discrete excitatory and inhibitory inputs transform the firing from a low regular into a bursting pattern. The bursting activity promotes dopamine release being very important in cognition and motor performances. In the present paper we review electrophysiological data regarding the role of glutamatergic and cholinergic and GABAergic afferent inputs in regulating the midbrain DAergic neuronal activity.

Hartmann, A., A. Mouatt-Prigent, et al. (2002). "FADD: A link between TNF family receptors and caspases in Parkinson's disease." Neurology 58(2): 308-10.
Fas-associating protein with a death domain (FADD) is a proximal adaptor protein of the tumor necrosis factor (TNF) receptor family death pathway. This human postmortem study showed a significant decrease in the percentage of FADD-immunoreactive dopaminergic (DA) neurons in the substantia nigra pars compacta of patients with PD compared with controls (-24.8%). This decrease correlated with the known selective vulnerability of nigral DA neurons in PD, suggesting that this pathway contributes to the susceptibility of DA neurons in PD to TNF-mediated apoptosis.

Hemsley, K. M. and A. D. Crocker (2002). "Atropine reduces raclopride-induced muscle rigidity by acting in the ventral region of the striatum." Eur J Pharmacol 434(3): 117-23.
Parkinson-like extrapyramidal motor side effects associated with the use of antipsychotic drugs, such as increased muscle rigidity, are thought to result from blockade of striatal dopamine D2 receptors. While anticholinergic medications (muscarinic receptor antagonists) ameliorate extrapyramidal side effects, the mechanisms underlying their effectiveness remain unclear. We investigated the site of action of atropine, a non-selective muscarinic receptor antagonist, in reducing increased muscle rigidity, assessed as increases in tonic electromyographic (EMG) activity, induced by the selective dopamine D2 receptor antagonist, raclopride. Atropine significantly reduced raclopride-induced EMG increases in rat hindlimb muscles, when injected into the ventral striatum, but not the dorsal striatum or the substantia nigra. Atropine's site of action was localised to a small area of muscarinic receptors within the ventral part of the striatum, using quantitative autoradiography. These findings provide new information about the regulation of motor control by muscarinic receptor antagonists and additional evidence about the functional heterogeneity of the striatum.

Hoover, B. R. and J. F. Marshall (2002). "Further characterization of preproenkephalin mRNA-containing cells in the rodent globus pallidus." Neuroscience 111(1): 111-25.
The globus pallidus (external pallidum of primates) is an essential nucleus within basal ganglia circuitry, in part because it receives at least one-half of striatal efferent projections. Neurons of the globus pallidus can be divided into subpopulations based on anatomical, physiological, and chemical features. Globus pallidus neurons project to several structures (the striatum, subthalamic nucleus, entopeduncular nucleus, and substantia nigra pars reticulata), have one of two alternative waveforms (positive/negative versus negative/positive), contain either the calcium binding protein parvalbumin or the neuropeptide precursor preproenkephalin mRNA and show differential immediate early gene responses to dopamine receptor agonists and antagonists. The objective of the present study was to characterize in greater detail the preproenkephalin mRNA-containing pallidal neurons using Sprague-Dawley rats. In situ hybridization for preproenkephalin mRNA was combined with immunocytochemical detection of: (i) the neuron-specific nuclear protein, NeuN, (ii) FluoroGold-labeled pallidostriatal and pallidosubthalamic cells, or (iii) Fos induced by either systemic combined D1-class/D2-class dopamine receptor agonists or a D2-class receptor antagonist. These experiments demonstrated that a substantial population (42%) of globus pallidus neurons contains preproenkephalin mRNA, and that globus pallidus neurons retrogradely labeled after FluoroGold injections into the striatum are more frequently preproenkephalinergic, compared to the population of pallidosubthalamic neurons. Furthermore, systemic administration of a D2 receptor antagonist, eticlopride, induced Fos immunoreactivity predominantly in globus pallidus neurons expressing preproenkephalin mRNA, while combined administration of D1 and D2 receptor agonists induced Fos predominantly in pallidal neurons lacking preproenkephalin mRNA.These results support the conclusion that preproenkephalin mRNA identifies one of the two major subpopulations of pallidal neurons. This preproenkephalin mRNA-expressing pallidal subpopulation preferentially targets the striatum and is more readily activated in its immediate early gene expression by D2 receptor antagonists than by dopamine receptor agonists. This projection provides a pallidal substrate for the dopaminergic regulation of striatal information processing.

Hsieh, P. F., L. G. Chia, et al. (2002). "Behavior, neurochemistry and histology after intranigral lipopolysaccharide injection." Neuroreport 13(3): 277-80.
Inflammation and neuronal degeneration of the substantia nigra (SN) occur in Parkinson's disease (PD). We studied the effects of intranigral lipopolysaccharide (LPS) injection on adult Sprague-Dawley rats. Locomotor activity measurement, neurotransmitter determination and perfusion fixation for immunohistochemistry were done on the 7th day. Bilateral LPS injection increased locomotor activity 2- to 3-fold. In the SN, dopamine (DA) and serotonin (5-HT) decreased but the ratios dihydroxyphenylacetic acid (DOPAC)/DA, homovanillic acid (HVA)/DA and 5-hydroxyindole-acetic acid (5-HIAA)/5-HT increased. In the striatum, DA, DOPAC, HVA, 3-methoxytyramine and epinephrine decreased but HVA/DA and 5-HIAA/5HT ratios increased. Unilateral LPS decreased dopamineric neurons ipsilaterally but increased contralaterally. This study provides the first evidence of behavioral hyperactivity, epinephrine suppression and neuronal plasticity in the LPS model of PD.

Ishihara, K. and M. Sasa (2002). "[Modulation of neuronal activities in the central nervous system via sigma receptors]." Nihon Shinkei Seishin Yakurigaku Zasshi 22(1): 23-30.
Sigma receptors have recently been the target of drug development related to psychiatric disorders, including schizophrenia and depression, as well as cognitive enhancers. This paper focused on the sigma-receptor-mediated modulation of neuronal activity, especially the effects on aminergic neuron and hippocampal neuron activity. Dopaminergic neuron activities in the substantia nigra and ventral tegmental area (VTA) are variously modified by the systemic administration of sigma ligands. When applied with microiontophoresis, they are reported to increase dopaminergic neuron activity in the VTA. This activity may be involved in the psychotropic or antipsychotic effects of these ligands. Moreover, serotonergic neurons in the raphe nucleus and noradrenergic neurons in the locus coeruleus were activated by sigma ligands. These effects are probably related to the antidepressant activity of sigma receptor ligands. In the hippocampus, sigma ligands suppressed CA1 neuronal activity in vitro. The effects were suggested to be due to an increase in the threshold of action potential and decreased synaptic transmission efficacy. NMDA receptor function was modified in biphasic fashion related to doses of sigma ligands, that is, a lower dose facilitated the NMDA receptor functions, and a higher dose inhibited them. These effects on the hippocampal neurons may contribute to their neuroprotective and antiamnesic actions. Further studies are needed to elucidate the relation between the physiological function of sigma receptor and psychiatric diseases by the use of sigma receptor ligands and molecular techniques.

Jenkins, T. A., M. P. Latimer, et al. (2002). "Determination of acetylcholine and dopamine content in thalamus and striatum after excitotoxic lesions of the pedunculopontine tegmental nucleus in rats." Neurosci Lett 322(1): 45-8.
The pedunculopontine tegmental nucleus (PPTg) contains cholinergic neurons whose principal ascending connections are with thalamic nuclei and structures associated with the striatum. It has been hypothesized that PPTg neurons are more closely associated with the substantia nigra (and therefore striatal motor systems) than with the ventral tegmental area (and therefore limbic striatal functions). In the present experiments we have examined the hypothesis that the PPTg is similarly associated with motor nuclei in the thalamus. Rats received unilateral ibotenate lesions of PPTg and were sacrificed 1, 2, 4 or 7 days later. Discrete thalamic nuclei, and samples of caudate-putamen and nucleus accumbens, were punched out and thalamic acetylcholine (ACh) and striatal ACh and dopamine (DA) content examined. Anteroventral nucleus had decreased ACh content after PPTg lesion, but a time dependent increase was found in mediodorsal nucleus; ACh concentration was unchanged in thalamic reticular nucleus or medial geniculate. No long-term lesion-dependent changes in striatal ACh or DA content were found. The effects of PPTg lesion on thalamic ACh content are consistent with the hypothesis that it has effects on motor nuclei, but also indicate that PPTg lesions have complex and dynamic effects on thalamic ACh content.

Jeyarasasingam, G., L. Tompkins, et al. (2002). "Stimulation of non-alpha7 nicotinic receptors partially protects dopaminergic neurons from 1-methyl-4-phenylpyridinium-induced toxicity in culture." Neuroscience 109(2): 275-85.
Previous work has shown that nicotine treatment protects against nigrostriatal degeneration in rodents, findings that may be of relevance to the decreased incidence of Parkinson's disease in cigarette smokers. In the present studies, we investigated the effect of nicotine against 1-methyl-4-phenylpyridinium-induced toxicity in dopaminergic ventral mesencephalic cultures to identify the nicotinic receptor population that may be involved. [3H]Epibatidine, a ligand that binds to receptors containing alpha2-alpha6 subunits, bound to at least two populations of sites that were up-regulated by nicotine in a time and dose dependent manner. We next examined the effect of nicotine on cultures treated with 1-methyl-4-phenylpyridinium, a neurotoxin that selectively damages nigrostriatal dopaminergic neurons. Pre-treatment with nicotine, at 10(-7)-10(-4) M, partially prevented the toxin-induced decline in dopaminergic cells. Pre-exposure to nicotine for 24 h resulted in optimal protection, suggesting that receptor up-regulation may contribute to the observed neuroprotective effect. Nicotine-mediated protection was blocked by pre-incubation with the nicotinic receptor antagonist d-tubocurarine (10(-4) M), but not the alpha7 receptor-selective antagonist alpha-bungarotoxin (10(-7) M).Our results show that nicotinic receptor activation partially protects nigral dopaminergic neurons from 1-methyl-4-phenylpyridinium-induced toxicity in culture and that this appears to occur through an interaction at non-alpha7 containing receptors.

Junn, E. and M. M. Mouradian (2002). "Human alpha-synuclein over-expression increases intracellular reactive oxygen species levels and susceptibility to dopamine." Neurosci Lett 320(3): 146-50.
alpha-Synuclein is a major component of Lewy bodies found in the brains of patients with Parkinson's disease (PD). Two point mutations in alpha-synuclein (A53T and A30P) are identified in few families with dominantly inherited PD. Yet the mechanism by which this protein is involved in nigral cell death remains poorly understood. Mounting evidence suggests the importance of oxidative stress in the pathogenesis of PD. Here we investigated the effects of wild-type and two mutant forms of alpha-synuclein on intracellular reactive oxygen species (ROS) levels using clonal SH-SY5Y cells engineered to over-express these proteins. All three cell lines, and particularly mutant alpha-synuclein-expressing cells, had increased ROS levels relative to control LacZ-engineered cells. In addition, cell viability was significantly curtailed following the exposure of all three alpha-synuclein-engineered cells to dopamine, but more so with mutant alpha-synuclein. These results suggest that over-expression of alpha-synuclein, and especially its mutant forms, exaggerates the vulnerability of neurons to dopamine-induced cell death through excess intracellular ROS generation. Thus, these findings provide a link between mutations or over-expression of alpha-synuclein and apoptosis of dopaminergic neurons by lowering the threshold of these cells to oxidative damage.

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.

Kitamura, Y., J. Kakimura, et al. (2002). "Antiparkinsonian drugs and their neuroprotective effects." Biol Pharm Bull 25(3): 284-90.
In Parkinson's disease, while dopamine (DA) replacement therapy, such as with L-DOPA (levodopa), improves the symptoms, it does not inhibit the degeneration of DA neurons in the substantia nigra. Numerous studies have suggested that both endogenous and environmental neurotoxins and oxidative stress may participate in this disease, but the detailed mechanisms are still unclear. Recent genetic studies in familial Parkinson's disease and parkinsonism have shown several gene mutations. This new information regarding its pathogenesis offers novel prospects for effective strategies involving the neuroprotection of vulnerable DA neurons. This review summarizes current findings regarding the pathogenesis and antiparkinsonian drugs, and discusses their possibilities of targets to develop novel neuroprotective drugs.

Klein, R. L., M. A. King, et al. (2002). "Dopaminergic Cell Loss Induced by Human A30P alpha-Synuclein Gene Transfer to the Rat Substantia Nigra." Hum Gene Ther 13(5): 605-12.
Somatic cell gene transfer was used to express a mutant form of alpha-synuclein (alpha-syn) that is associated with Parkinson's disease (PD) in the rat substantia nigra (SN), a brain region that, in humans, degenerates during PD. DNA encoding the A30P mutant of human alpha-syn linked to familial PD was incorporated into an adeno-associated virus vector, which was injected into the adult rat midbrain. The cytomegalovirus/chicken beta-actin promoter was used to drive transgene expression. Over a 1-year time course, this treatment produced three significant features relevant to PD: (1) accumulation of alpha-syn in SN neuron perikarya, (2) Lewy-like dystrophic neurites in the SN and the striatum, and (3) a 53% loss of SN dopamine neurons. However, motor dysfunction was not found in either rotational or rotating rod testing. The lack of behavioral deficits, despite the significant cell loss, may reflect pathogenesis similar to that of PD, where greater than 50% losses occur before motor behavior is affected.

Korotkova, T. M., H. L. Haas, et al. (2002). "Histamine excites GABAergic cells in the rat substantia nigra and ventral tegmental area in vitro." Neurosci Lett 320(3): 133-6.
We have investigated the effect of histamine (HA) on spontaneous firing of dopaminergic (DA) and GABAergic neurons in the substantia nigra (SN) and the ventral tegmental area (VTA) of the rat in vitro. Single-unit extracellular recordings were obtained and drugs were bath applied. In both regions application of HA (10 and 100 microM) did not affect the firing frequency of DAergic cells, but increased the firing of GABAergic neurons. The histamine-induced excitation was blocked by the H(1) receptor antagonist mepyramine (1 microM), but was unaffected by application of the H(2) antagonist cimetidine (50 microM) or the H(3) antagonist thioperamide (10 microM). Our results suggest that histamine does not directly inhibit dopaminergic neurons in SN and VTA, but rather that this inhibition is mediated through histamine-induced excitation of GABAergic neurons.

Lastres-Becker, I., H. H. Hansen, et al. (2002). "Alleviation of motor hyperactivity and neurochemical deficits by endocannabinoid uptake inhibition in a rat model of Huntington's disease." Synapse 44(1): 23-35.
Recent studies have demonstrated a loss of cannabinoid CB1 receptors in the postmortem basal ganglia of patients affected by Huntington's disease (HD) and in transgenic mouse models for this disease. These studies have led to the notion that substances that increase the endocannabinoid activity, such as receptor agonists or inhibitors of endocannabinoid uptake and/or metabolism, might be useful in the treatment of hyperkinetic symptoms of this disease. In the present study, we employed a rat model of HD generated by bilateral intrastriatal injections of 3-nitropropionic acid (3-NP), a toxin that selectively damages striatal GABAergic efferent neurons. These rats exhibited biphasic motor disturbances, with an early (1-2 weeks) hyperactivity followed by a late (3-4 weeks) motor depression. Analysis of GABA, dopamine, and their related enzymes, glutamic acid decarboxylase and tyrosine hydroxylase, in the basal ganglia proved marked decreases compatible with the motor hyperkinesia. In addition, mRNA levels for CB1 receptor, neuronal-specific enolase, proenkephalin, and substance P decreased in the caudate-putamen of 3-NP-injected rats. There were also reductions in CB1 receptor binding in the caudate putamen, the globus pallidus, and, to a lesser extent, the substantia nigra. By contrast, mRNA levels for tyrosine hydroxylase in the substantia nigra remained unaffected. Interestingly, the administration of AM404, an inhibitor of endocannabinoid uptake, to 3-NP-injected rats attenuated motor disturbances observed in the early phase of hyperactivity. Administration of AM404 also tended to induce recovery from the neurochemical deficits caused by the toxin in GABA and dopamine indices in the basal ganglia. In summary, morphological, behavioral, and biochemical changes observed in rats intrastriatally lesioned with 3-NP acid were compatible with a profound degeneration of striatal efferent GABAergic neurons, similar to that occurring in the brain of HD patients. As expected, a loss of CB1 receptors was evident in the basal ganglia of these rats. However, the administration of substances that increase endocannabinoid activity, by inhibiting the uptake process, allowed an activation of the remaining population of CB1 receptors, resulting in a significant improvement of motor disturbances and neurochemical deficits. These observations might be relevant to the treatment of hyperkinetic symptoms in HD, a human disorder with unsatisfactory symptomatic treatment for most patients.

Lindblom, J., A. Kask, et al. (2002). "Chronic infusion of a melanocortin receptor agonist modulates dopamine receptor binding in the rat brain." Pharmacol Res 45(2): 119-24.
Previous studies have shown that melanocortin peptides have facilitatory effects on dopaminergic neurotransmission. In the present study we tested the hypothesis that chronic exposure to melanocortin receptor agonists causes a prolonged release of dopamine resulting in changes in the expression of dopamine receptor subtypes. Using an autoradiographic approach we found that a 2 week intracerebroventricular infusion of the melanocortin receptor agonist melanotan-II induced changes in dopamine D(1)-like and D(2)-like receptor binding in several regions of the rat brain. D(1)-like receptor binding was increased in the nucleus accumbens and the caudate putamen, but reduced in the substantia nigra (reticular part), whereas D(2)-like receptor binding was reduced in the caudate putamen, but increased in the periaqueductal grey, substantia nigra (compact part) and the ventral tegmental area. These data suggest that chronic infusion of a melanocortin receptor agonist alters the activity of dopaminergic neurons in the ventral tegmental area and substantia nigra, and support the hypothesis that melanocortin peptides may regulate the activity of central dopamine neurons.

Lu, W., L. M. Monteggia, et al. (2002). "Repeated administration of amphetamine or cocaine does not alter AMPA receptor subunit expression in the rat midbrain." Neuropsychopharmacology 26(1): 1-13.
We previously reported that ventral tegmental area (VTA) dopamine neurons are supersensitive to AMPA when recorded three days after discontinuing repeated amphetamine or cocaine administration. By increasing dopamine cell activity, this may contribute to the induction of behavioral sensitization. The goal of this study was to determine if increased sensitivity to AMPA reflects increased AMPA receptor expression in the midbrain. Immunolabeling for GluR1, GluR2, GluR2/3, and GluR4 was quantified by immunohistochemistry with 35S-labeled secondary antibodies in VTA, substantia nigra, and a transitional area. First, rats were treated for five days with saline or amphetamine (5 mg/kg) and killed three or 14 days after the last injection. No significant changes in immunolabeling were observed for any subunit at either withdrawal time. GluR1 immunolabeling was further examined in rats killed 16-18 hrs or 24 hrs after a single injection of amphetamine or repeated injections of saline, amphetamine (5 mg/kg x 5 days) or cocaine (20 mg/kg x 7 days). No significant differences were observed in any region. Finally, neither repeated amphetamine or cocaine administration significantly altered GluR1 mRNA levels as quantified by reverse transcriptase-polymerase chain reaction. Our results suggest that enhanced responsiveness of VTA dopamine neurons to AMPA after withdrawal from repeated stimulant administration involves mechanisms more complex than increased expression of AMPA receptor subunits.

Maloney, K. J., L. Mainville, et al. (2002). "c-Fos expression in dopaminergic and GABAergic neurons of the ventral mesencephalic tegmentum after paradoxical sleep deprivation and recovery." Eur J Neurosci 15(4): 774-8.
Evidence suggests that dopaminergic neurons of the ventral mesencephalic tegmentum (VMT) could be important for paradoxical sleep (PS). Here, we examined whether dopamine (DA) and adjacent gamma-aminobutyric acid (GABA)-synthesizing neurons are active in association with PS recovery as compared to PS deprivation or control conditions in different groups of rats by using c-Fos expression as a reflection of neural activity, combined with dual immunostaining for tyrosine hydroxylase (TH) or glutamic acid decarboxylase (GAD). Numbers of TH+/c-Fos+ neurons in the substantia nigra (SN) were not significantly different across groups, whereas those in the ventral tegmental area (VTA) were significantly different and greatest in PS recovery. Numbers of GAD+/c-Fos+ neurons in both VTA and SN were greatest in PS recovery. Thus, DA neuronal activity does not appear to be suppressed by local GABAergic neuronal activity during PS but might be altered in pattern by this inhibitory as well as other excitatory, particularly cholinergic, inputs such as to allow DA VTA neurons to become maximally active during PS and thereby contribute to the unique physiological and cognitive aspects of that state.

Mendez, I., A. Dagher, et al. (2002). "Simultaneous intrastriatal and intranigral fetal dopaminergic grafts in patients with Parkinson disease: a pilot study. Report of three cases." J Neurosurg 96(3): 589-96.
The main neural transplantation strategy in Parkinson disease (PD) has been focused on reinnervating the striatum. The clinical results reported in patients who receive transplants have been limited and do not justify the use of neural transplantation as a routine therapeutic procedure for PD. Identifying the optimal target for transplantation may be one of the critical factors for optimizing clinical outcomes. Evidence from preclinical studies indicates that simultaneous intrastriatal and intranigral grafts (double grafts) may produce a more complete functional recovery. The authors report the clinical and positron emission tomography (PET) scanning results in three patients enrolled in a safety and feasibility pilot study who received double grafts and who have been followed for up to 13 months posttransplantation. Patients included in the study had idiopathic PD. All patients underwent detailed assessments before and after surgery, in accordance with the Core Assessment Program for Intracerebral Transplantation. The patients received implants of fetal mesencephalic cell suspensions in the putamen and substantia nigra (SN) bilaterally. There were no intraoperative or perioperative complications. Follow-up PET scans demonstrated an increase in the mean fluorodopa uptake constant values in the putamen and SN 12 months postsurgery. Improvements were also noted in the total Unified Parkinson's Disease Rating Scale, Hoehn and Yahr, Schwab and England, and pronation/supination scores after transplantation. The authors demonstrate the feasibility of reinnervating the SN and striatum by using a double transplant strategy in humans.

Miller, G. M. and B. K. Madras (2002). "Polymorphisms in the 3'-untranslated region of human and monkey dopamine transporter genes affect reporter gene expression." Mol Psychiatry 7(1): 44-55.
Dopamine transporter (DAT) levels vary in normal subjects and deviate from the normal range in pathological states. We investigated mechanisms by which the DAT gene may influence DAT protein expression. As the 3'-untranslated region (3'-UTR) of the DAT gene varies with regard to length and single nucleotide polymorphisms (SNPs), we addressed whether the 3'-UTR of sequence-defined DAT alleles can differentially affect the level of reporter gene expression in vitro. We first established that within individual rhesus monkeys, two alleles of the DAT gene were expressed in the substantia nigra. We then transfected HEK-293 cells with HSV-TK- and SV40-driven luciferase expression vectors harboring downstream DAT 3'-UTR segments of alleles containing polymorphisms of length (human: 9 or 10 repeat units) or SNPs within alleles of fixed length (human: DraI-sensitive (DraI+) vs. DraI-insensitive (DraI-) 10-repeat alleles; rhesus monkey: Bst1107I-sensitive (Bst+) vs. Bst1107I-insensitive (Bst-) 12-repeat alleles). Vectors containing the 3'-UTR segment of a human DAT allele containing nine tandem repeat units resulted in significantly higher levels of luciferase production than analogous vectors containing 10 tandem repeat units. Depending on the promoter used, vectors containing the human or monkey 3'-UTR segments that differed on the basis of an SNP resulted in increases or decreases in luciferase gene expression. This report provides experimental evidence that variability in the length or the sequence of the 3'-UTR of the DAT gene may influence levels of DAT protein in the brain.

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.

Moon, L. D., R. A. Asher, et al. (2002). "Relationship between sprouting axons, proteoglycans and glial cells following unilateral nigrostriatal axotomy in the adult rat." Neuroscience 109(1): 101-17.
Proteoglycans may modulate axon growth in the intact and injured adult mammalian CNS. Here we investigate the distribution and time course of deposition of a range of proteoglycans between 4 and 14 days following unilateral axotomy of the nigrostriatal tract in anaesthetised adult rats. Immunolabelling using a variety of antibodies was used to examine the response of heparan sulphate proteoglycans, chondroitin sulphate proteoglycans and keratan sulphate proteoglycans. We observed that many proteoglycans became abundant between 1 and 2 weeks post-axotomy. Heparan sulphate proteoglycans were predominantly found within the lesion core (populated by blood vessels, amoeboid macrophages and meningeal fibroblasts) whereas chondroitin sulphate proteoglycans and keratan sulphate proteoglycans were predominantly found in the lesion surround (populated by reactive astrocytes, activated microglia and adult precursor cells). Immunolabelling indicated that cut dopaminergic nigral axons sprouted prolifically within the lesion core but rarely grew into the lesion surround. We conclude that sprouting of cut dopaminergic nigral axons may be supported by heparan sulphate proteoglycans but restricted by chondroitin sulphate proteoglycans and keratan sulphate proteoglycans.

Narayanan, S., K. Lutfy, et al. (2002). "Sensitization to cocaine after a single intra-cerebral injection of orphanin FQ/nociceptin." Behav Brain Res 131(1-2): 97-103.
Orphanin FQ/nociceptin (OFQ/N) has been shown to modulate mesolimbic dopaminergic neurotransmission. Repeated administration of OFQ/N into the ventral tegmental area results in a sensitized locomotor response to subsequent peripheral cocaine administration. The aim of the present study was to examine the potential for OFQ/N to produce a sensitized locomotor response to cocaine after a single intra-VTA administration and to determine if this effect of OFQ/N extrapolates to other points along the mesolimbic or nigrostriatal dopaminergic axes. Bilateral administration of OFQ/N (30 microg/side) into the VTA on day 1 to male Sprague--Dawley rats resulted in an enhanced locomotor response to cocaine (10 mg/kg i.p) administered on day 2. However, OFQ/N (3, 10 and 30 microg per side) administered on day 2, 5 mins prior to the administration of cocaine (10 mg/kg i.p), in animals treated with aCSF or OFQ/N on day 1, similarly blocked the action of cocaine, suggesting that the sensitized response was not due to tolerance to the effect of endogenously released OFQ/N. The administration of OFQ/N into the substantia nigra or nucleus accumbens failed to produce a significant sensitized response to a cocaine challenge 24 h later. A significant increase in cocaine stimulated locomotor response on day 2 was observed after injection of OFQ/N into the striatum on day 1. These results demonstrate the ability of a single intra-VTA or intra-striatal administration of OFQ/N to produce increases in the sensitivity to cocaine and may indicate a role for endogenous OFQ/N systems in regulating responses to psychostimulant drugs.

Neuhoff, H., A. Neu, et al. (2002). "I(h) channels contribute to the different functional properties of identified dopaminergic subpopulations in the midbrain." J Neurosci 22(4): 1290-302.
Dopaminergic (DA) midbrain neurons in the substantia nigra (SN) and ventral tegmental area (VTA) are involved in various brain functions such as voluntary movement and reward and are targets in disorders such as Parkinson's disease and schizophrenia. To study the functional properties of identified DA neurons in mouse midbrain slices, we combined patch-clamp recordings with either neurobiotin cell-filling and triple labeling confocal immunohistochemistry, or single-cell RT-PCR. We discriminated four DA subpopulations based on anatomical and neurochemical differences: two calbindin D28-k (CB)-expressing DA populations in the substantia nigra (SN/CB+) or ventral tegmental area (VTA/CB+), and respectively, two calbindin D28-k negative DA populations (SN/CB-, VTA/CB-). VTA/CB+ DA neurons displayed significantly faster pacemaker frequencies with smaller afterhyperpolarizations compared with other DA neurons. In contrast, all four DA populations possessed significant differences in I(h) channel densities and I(h) channel-mediated functional properties like sag amplitudes and rebound delays in the following order: SN/CB- --> VTA/CB- --> SN/CB+ --> VTA/CB+. Single-cell RT-multiplex PCR experiments demonstrated that differential calbindin but not calretinin expression is associated with differential I(h) channel densities. Only in SN/CB- DA neurons, however, I(h) channels were actively involved in pacemaker frequency control. In conclusion, diversity within the DA system is not restricted to distinct axonal projections and differences in synaptic connectivity, but also involves differences in postsynaptic conductances between neurochemically and topographically distinct DA neurons.

Norton, C. S., C. R. Neal, et al. (2002). "Nociceptin/orphanin FQ and opioid receptor-like receptor mRNA expression in dopamine systems." J Comp Neurol 444(4): 358-68.
Although nociceptin/orphanin FQ (N/OFQ) influences dopamine (DA) neuronal activity, it is not known whether N/OFQ acts directly on DA neurons, indirectly by means of local circuitry, or both. We used two parallel approaches, dual in situ hybridization (ISH) and neurotoxic lesions of DA neurons by using 6-hydroxydopamine (6-OHDA), to ascertain whether N/OFQ and the N/OFQ receptor (NOP) mRNA are expressed in DA neurons in the ventral tegmental area (VTA) and substantia nigra compacta (SNc). In the VTA and SNc, small populations (approximately 6-10%) of N/OFQ-containing neurons coexpressed mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme for DA synthesis. Similarly, very few (1-2%) TH-positive neurons contained N/OFQ mRNA signal. A majority of NOP-positive neurons (approximately 75%) expressed TH mRNA and roughly half of the TH-containing neurons expressed NOP mRNA. Many N/OFQ neurons (approximately 50-60%) expressed glutamic acid decarboxylase 65 and 67 mRNAs, markers for gamma-aminobutyric acid (GABA) neurons. In the 6-OHDA lesion studies, NOP mRNA levels were nearly 80 and 85% lower in the VTA and SNc, respectively, on the lesioned side. These lesions appear to lead to compensatory changes, with N/OFQ mRNA levels approximately 60% and 300% higher in the VTA and SNc, respectively, after 6-OHDA lesions. Finally, N/OFQ-stimulated [(35)S]guanylyl-5'-O-(gamma-thio)-triphosphate levels were decreased in the VTA and SNc but not the prefrontal cortex after 6-OHDA lesions. Accordingly, it appears that N/OFQ mRNA was found largely on nondopaminergic (i.e., GABA) neurons, whereas NOP mRNA was located on DA neurons. N/OFQ is in a position to influence DA neuronal activity by means of the NOP located on DA neurons.

Paletzki, R. F. (2002). "Cloning and characterization of guanine deaminase from mouse and rat brain." Neuroscience 109(1): 15-26.
A search for genes differentially expressed in the rat striatum revealed a gene fragment with a ventral to dorsal striatal expression pattern. The sequence of the fragment was used to isolate mouse and rat clones that upon sequencing were identified as homologous to human guanine deaminase. Here we report the distribution of guanine deaminase in the rodent brain. In situ hybridization localization of the encoding mRNA showed a distribution primarily in forebrain areas including cortical pyramidal neurons, ventral striatal medium spiny neurons, hippocampal pyramidal neurons in CA3-CA1 and granule cells in the dentate gyrus, and neurons of the amygdala. Immunohistochemistry using antibodies raised against peptide fragments derived from the guanine deaminase protein sequence showed localization of guanine deaminase in areas predicted by the mRNA distribution. In addition to immunolabeling of neurons in the cerebral cortex, hippocampus, striatum and amygdala there was also labeling in the terminal fields of these neurons including the thalamus, globus pallidum and substantia nigra. A functional histochemical assay that demonstrates the site of guanine deamination shows guanine deaminase activity in a pattern that matched the immunohistochemical localization. The cellular distribution of guanine deaminase to distal areas of the cell including terminals and dendrites was additionally demonstrated by the expression of recombinant guanine deaminase in transformed cortical neurons in culture.In summary we have described the isolation and characterization of mouse and rat guanine deaminase. The expression of guanine deaminase is primarily restricted to forebrain neurons. A histochemical assay was used to localize guanine deaminase activity to the dendrites and axons of neurons expressing guanine deaminase.

Pi, X., J. L. Voogt, et al. (2002). "Detection of prolactin receptor mRNA in the corpus striatum and substantia nigra of the rat." J Neurosci Res 67(4): 551-8.
The observation of prolactin modulation of the nigrostriatal dopaminergic system suggests the expression of prolactin receptor in the corpus striatum or substantia nigra. The present study investigated expression of prolactin receptor mRNA in tissues microdissected from the corpus striatum and substantia nigra of the rat. By using reverse transcription PCR combined with Southern hybridization, the long form of prolactin receptor mRNA was detected in the substantia nigra, caudate putamen, globus pallidus, and ventral pallidum in ovariectomized rats, whereas the short form was not detectable in any of these areas. Estrogen had no effect on expression of the long-form mRNA in the substantia nigra and corpus striatum. By using the RNase protection assay, the expression of both short and long forms of prolactin receptor mRNA was observed in the corpus striatum in ovariectomized rats. Again, levels of expression were not significantly altered by estrogen treatment. Both forms of prolactin receptor mRNA were clearly expressed in the choroid plexus and were up-regulated by estrogen treatment. The expression of both forms of prolactin receptor mRNA in nigrostriatal areas may help to support the hypothesis that prolactin has direct actions on these brain regions.

Porras, G., V. Di Matteo, et al. (2002). "5-HT2A and 5-HT2C/2B receptor subtypes modulate dopamine release induced in vivo by amphetamine and morphine in both the rat nucleus accumbens and striatum." Neuropsychopharmacology 26(3): 311-24.
In vivo microdialysis and single-cell extracellular recordings were used to assess the involvement of serotonin(2A) (5-HT(2A)) and serotonin(2C/2B) (5-HT(2C/2B)) receptors in the effects induced by amphetamine and morphine on dopaminergic (DA) activity within the mesoaccumbal and nigrostriatal pathways. The increase in DA release induced by amphetamine (2 mg/kg i.p.) in the nucleus accumbens and striatum was significantly reduced by the selective 5-HT(2A) antagonist SR 46349B (0.5 mg/kg s.c.), but not affected by the 5-HT(2C/2B) antagonist SB 206553 (5 mg/kg i.p.). In contrast, the enhancement of accumbal and striatal DA output induced by morphine (2.5 mg/kg s.c.), while insensitive to SR 46349B, was significantly increased by SB 206553. Furthermore, morphine (0.1-10 mg/kg i.v.)-induced increase in DA neuron firing rate in both the ventral tegmental area and the substantia nigra pars compacta was unaffected by SR 46349B (0.1 mg/kg i.v.) but significantly potentiated by SB 206553 (0.1 mg/kg i.v.). These results show that 5-HT(2A) and 5-HT(2C) receptors regulate specifically the activation of midbrain DA neurons induced by amphetamine and morphine, respectively. This differential contribution may be related to the specific mechanism of action of the drug considered and to the neuronal circuitry involved in their effect on DA neurons. Furthermore, these results suggest that 5-HT(2C) receptors selectively modulate the impulse flow-dependent release of DA.

Russell, V. A. (2002). "Hypodopaminergic and hypernoradrenergic activity in prefrontal cortex slices of an animal model for attention-deficit hyperactivity disorder --- the spontaneously hypertensive rat." Behav Brain Res 130(1-2): 191-6.
Evidence supports dysfunction of dopaminergic and noradrenergic systems in patients with attention-deficit hyperactivity disorder (ADHD). Noradrenergic and dopaminergic systems exert distinct modulatory actions on the transfer of information through neural circuits that connect functionally distinct cortical areas with separate striatal regions and remain segregated in parallel striato--pallidal--thalamic and striato--substantia nigra pars reticulata--thalamic pathways. Prefrontal cortex performance is maximal at moderate stimulation of postsynaptic dopaminergic and noradrenergic receptors, and is reduced by either higher or lower levels of receptor stimulation. Spontaneously hypertensive rats (SHR) are generally considered to be a suitable genetic model for ADHD, since they display hyperactivity, impulsivity, poor stability of performance, impaired ability to withhold responses and poorly sustained attention, when compared with their normotensive Wistar--Kyoto (WKY) control rats. Evidence suggests that terminals of mesocortical, mesolimbic and nigrostriatal dopaminergic neurons of SHR release less dopamine in response to electrical stimulation and/or depolarization as a result of exposure to high extracellular K(+) concentrations, than WKY. Vesicular storage of dopamine was suggested to be impaired in SHR, causing leakage of dopamine into the cytoplasm and increased d-amphetamine-induced transporter-mediated release. While electrically stimulated release of dopamine appears to be decreased in prefrontal cortex of SHR suggesting hypodopaminergic function, autoreceptor-mediated inhibition of norepinephrine release appears to be impaired in SHR, suggesting that noradrenergic function may be poorly regulated in the prefrontal cortex of the SHR. These findings are consistent with the hypothesis that the behavioral disturbances of ADHD are the result of an imbalance between noradrenergic and dopaminergic systems in the prefrontal cortex, with inhibitory dopaminergic activity being decreased and noradrenergic activity increased relative to controls.

Schad, C. A., J. B. Justice, Jr., et al. (2002). "Endogenous opioids in dopaminergic cell body regions modulate amphetamine-induced increases in extracellular dopamine levels in the terminal regions." J Pharmacol Exp Ther 300(3): 932-8.
Opioid antagonists attenuate behavioral effects of amphetamine and amphetamine-induced increases in extracellular dopamine levels in nucleus accumbens and striatum of rats but do not alter those effects of cocaine. This study was performed to determine 1) if the effect of opioid antagonists on the dopamine response to amphetamine is mediated in either the terminal or cell body region of the nigrostriatal and mesolimbic pathways, and 2) if the enkephalinase inhibitor thiorphan, which slows degradation of endogenous opioid peptides, increases the dopamine response to amphetamine but not to cocaine. Microdialysis probes were placed either into a dopaminergic terminal region or into both a terminal and cell body region of rats. Naloxone methiodide (1.0 microM), a lipophobic opioid antagonist, was administered into either the terminal or cell body region by reverse dialysis, whereas extracellular dopamine was collected in the terminal region. Increases in extracellular dopamine in nucleus accumbens and striatum caused by amphetamine (0.1-6.4 mg/kg, s.c.) were reduced significantly (28-39%) by naloxone methiodide administered into either substantia nigra or ventral tegmentum but not into terminal regions. Thiorphan (10 microM) administered into substantia nigra increased significantly the dopamine response to amphetamine in the ipsilateral striatum by as much as 42% but did not affect the dopamine response to cocaine (3.0-56 mg/kg, i.p.). These results suggest that amphetamine promotes release of endogenous opioids, which, through actions in the ventral tegmentum and substantia nigra, contribute to amphetamine-induced increases in extracellular dopamine in the nucleus accumbens and striatum.

Schapira, A. H. (2002). "Neuroprotection and dopamine agonists." Neurology 58(4 Suppl 1): S9-S18.
Several factors are known to be capable of inducing relatively selective dopaminergic cell death in the substantia nigra and inducing the clinical features that characterize Parkinson's disease (PD). Neuronal toxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can induce parkinsonism in human and animal models, and rotenone, another specific mitochondrial complex I inhibitor, can induce similar effects in rodents to produce a model for PD. Studies in twins suggest a significant genetic component to young-onset PD, and several gene mutations have now been identified as causing familial autosomal dominant or autosomal recessive PD. Etiologic factors including free radical-mediated damage (including excitotoxicity), mitochondrial dysfunction, and inflammation-mediated cell damage can contribute to pathogenesis. In addition, the recent interest in protein misfolding, aggregation, and proteosomal activity has provided further insight into potential pathogenetic pathways in PD. Against this background there has been increasing interest in the development of drugs to modify these biochemical abnormalities and thus alter the course of PD, either by retarding the rate of cell death or by restoring function to neurons that are likely to be damaged but not dead. In this context, dopamine agonists have shown significant promise. Not only do these drugs provide symptomatic relief of PD but they also appear to be associated with a significant decrease in the rate of motor complications and to be capable of protecting against some of the adverse consequences of levodopa use. However, evidence is now emerging that dopamine agonists may have additional neuroprotective properties. As a group, they have antioxidant actions in vitro and in vivo. More specifically, the D(2)/D(3) dopamine agonist pramipexole may have neuroprotective activity that is, at least in part, unrelated to its dopamine agonist action. Protection in cell and animal models against a variety of toxins, including MPTP and 6-hydroxydopamine, confirms that this agonist has in vitro and in vivo neuroprotective action. Evidence is now emerging that some of this may be mediated by direct action on mitochondrial membrane potential and the inhibition of apoptosis. If the neuroprotective action of this drug is confirmed in patients with PD, this will have important implications for its early use in patients.

Stefani, A., F. Spadoni, et al. (2002). "D2-mediated modulation of N-type calcium currents in rat globus pallidus neurons following dopamine denervation." Eur J Neurosci 15(5): 815-25.
We have studied the effects of dopamine and the D2-like agonist quinpirole on calcium currents of neurons isolated from the striatum and the globus pallidus (GP). Experiments were performed in young adult rats, either in control conditions or following lesion of the nigrostriatal pathway by the unilateral injection of 6-hydroxydopamine (6-OHDA) in the substantia nigra. Apomorphine-driven contralateral turning, 15 days after lesioning, assessed the severity of the dopamine denervation. In addition, the loss of tyrosine hydroxylase immunohistochemistry confirmed the extent of the toxin-induced damage. In both striatal medium spiny (MS) and GP neurons of control animals dopamine and quinpirole promoted a very modest inhibition of calcium conductance. Following 6-OHDA, the inhibition was unaltered in MS (from 10 to 12%), but significantly augmented in GP neurons (21% vs. 9%). Interestingly, analogous inhibition was observed in GP neurons dissociated 20 h after reserpine treatment. Further features of the D2 response were thus studied only in neurons isolated from 6-OHDA-lesioned GP. The D2 modulation was G-protein-mediated but not strictly voltage-dependent. omega-Conotoxin-GVIA occluded the response implying the involvement of N-type calcium channels. The effect of quinpirole developed fast and was insensitive to alterations of cytosolic cAMP. The incubation in phorbol esters or OAG blocked the D2 effect, supporting the involvement of PKC. These findings suggest that postsynaptic D2-like receptors are functionally expressed on GP cell bodies and may supersensitize following dopamine-denervation. A direct D2 modulation of calcium conductance in GP may alter GP firing properties and GABA release onto pallidofugal targets.

Stefanski, R., S. H. Lee, et al. (2002). "Lack of persistent changes in the dopaminergic system of rats withdrawn from methamphetamine self-administration." Eur J Pharmacol 439(1-3): 59-68.
A continuing challenge for studies in the neurobiology of drug abuse is to identify and characterize long-lived neuroadaptations that can trigger craving and relapse. We previously reported that rats that had actively self-administered methamphetamine for 5 weeks and were then withdrawn from methamphetamine for 24 h showed marked decreases in somatodendritic dopamine D(2) autoreceptor levels in the ventral tegmental area and median and dorsal part of the substantia nigra zona compacta with a corresponding down-regulation of dopamine D(1) receptors in the shell of the nucleus accumbens. The purpose of the present study was to determine whether neuroadaptive changes in dopamine receptors or transporters in the brains of rats withdrawn for 24 h from chronic methamphetamine self-administration are persistent changes that can be demonstrated long after withdrawal. A "yoked" procedure was used in which rats were tested simultaneously in groups of three, with only one rat actively self-administering methamphetamine while the other two received yoked injections of either methamphetamine or saline. In vitro quantitative autoradiography was used to determine densities of dopamine uptake sites and dopamine D(1) and D(2) receptors in different brain regions following 7- and 30-day periods of withdrawal from chronic methamphetamine self-administration. No changes in dopamine transporter and dopamine receptor numbers were detected in any brain region examined in rats self-administering methamphetamine compared with littermates receiving yoked infusions of either methamphetamine or saline. Thus, neuroadaptive changes in densities of dopamine receptors or transporters in certain brain areas may contribute to the reinforcing effects of methamphetamine during the acquisition and maintenance phases of self-administration, but do not appear to contribute to the long-lasting neuroadaptive effects of chronic methamphetamine self-administration, which may trigger craving and relapse.

Svenningsson, P. and C. Le Moine (2002). "Dopamine D1/5 receptor stimulation induces c-fos expression in the subthalamic nucleus: possible involvement of local D5 receptors." Eur J Neurosci 15(1): 133-42.
The activity of neurons in the subthalamic nucleus controls various aspects of movement. The present study examined the action of dopamine receptor agonists on c-fos gene expression in the subthalamic nucleus in normal rats. We found that systemic administration of the dopamine D1/5 receptor agonist, SKF 82958 (1 mg/kg), induces c-fos expression in the subthalamic nucleus. In contrast, systemic administration of the dopamine D2/3 receptor agonist, quinelorane (2 mg/kg) had no effect. When combined, SKF 82958 and quinelorane induced c-fos expression in subthalamic neurons that was similar to that found following administration of SKF 82958 alone. We also examined c-fos expression in the substantia nigra pars reticulata, the major projection area for subthalamic neurons, and found that SKF 82958, but not quinelorane, caused an induction of c-fos expression in this area. In order to clarify the mechanisms underlying the SKF 82958-mediated induction of c-fos expression in the subthalamic nucleus and substantia nigra pars reticulata, in situ hybridization for the dopamine D1, D2, D3 and D5 receptor mRNAs was performed. The only significant observation was that D5 receptor mRNA is expressed in subthalamic neurons.The present data show that dopamine, via D1/D5 receptors, upregulates c-fos expression in subthalamic neurons, and that the high expression of D5 receptors in this area might be involved. Taken together, these data suggest that dopamine D1/5 receptors are more important for the action of dopamine in the so-called indirect pathway of the basal ganglia circuitry than what is recognized in current models of basal ganglia organization.

Themann, C., D. Alvarez Fischer, et al. (2002). "Effect of repeated treatment with high doses of selegiline on behaviour, striatal dopaminergic transmission and tyrosine hydroxylase mRNA levels." Naunyn Schmiedebergs Arch Pharmacol 365(1): 22-8.
The anti-parkinsonian drug selegiline is a monoamine oxidase B (MAO-B) inhibitor and a potential neuroprotective agent which facilitates dopaminergic transmission. Its metabolites (-)-amphetamine and (-)-metamphetamine might contribute to the pharmacological effects as they are also able to increase dopaminergic transmission and in addition might lead to behavioural sensitization after repeated administration. We investigated the effects of acute and repeated treatment with a high dose of selegiline on dopamine overflow in the striatum as well as on behaviour and on tyrosine hydroxylase (TH) mRNA levels in midbrain. Two experiments were performed. In the first one, rats were implanted with microdialysis probes into the striatum and received daily injections of selegiline (10 mg/kg, i.p.) for 1 or 8 days or a single dose of saline. In vivo microdialysis was carried out on days 1, 8 or 17 (after withdrawal of 9 days) to measure dopamine overflow. Motility was measured at the same time. In the second experiment, rats were injected daily with selegiline (10 mg/kg, i.p.) or saline over a time period of 6 weeks or only once before the brains were processed for in situ hybridization with a (35)S-radiolabelled probe for TH.Repeated treatment led to higher levels in motility scores than acute administration after administration of the same dose, indicating behavioural sensitization, which was still manifest after an interruption of 9 days in the supply of selegiline. In contrast, acute administration of selegiline increased dopamine levels to a similar degree as the same dose after subchronic treatment, with or without interruption of 9 days. The dopamine metabolite DOPAC was reduced by more than 50% after acute administration of selegiline and even more so on day 8 by the same dose, after repeated administration. The basal concentrations of dopamine (before challenge with selegiline) were not altered by the repeated administration, whereas the basal concentrations of DOPAC were decreased by more than 80% by the repeated administration of selegiline, suggesting a decrease in dopamine turnover. Acute administration did not have any influence on TH mRNA levels, whereas chronic treatment significantly reduced TH mRNA levels in substantia nigra and ventral tegmental area.In conclusion, repeated administration of selegiline leads to behavioural sensitization independent of altered dopamine levels. In addition, it leads to a decrease, probably due to a down-regulation, of dopamine turnover and tyrosine hydroxylase.

Tornqvist, N., E. Hermanson, et al. (2002). "Generation of tyrosine hydroxylase-immunoreactive neurons in ventral mesencephalic tissue of Nurr1 deficient mice." Brain Res Dev Brain Res 133(1): 37-47.
Nurr1 is an orphan nuclear receptor belonging to the family of evolutionary conserved steroid/thyroid hormone receptors. It has been shown that Nurr1 is required for development of ventral mesencephalic dopaminergic cells in vivo and that Nurr1 regulates the tyrosine hydroxylase (TH) gene. The aim of this study was to investigate the possibility of finding ventral mesencephalic TH-positive neurons in Nurr1 deficient tissue when developed in the presence of wild type (WT) striatum. Therefore, fetal ventral mesencephalic tissue from embryonic day (E) 9.5-10.5 fetuses from Nurr1 mutant mice was co-cultured with lateral ganglionic eminence (LGE) from WT fetuses using the 'roller-drum' culture technique. TH-immunohistochemistry revealed similar number of positive neurons in WT, heterozygous, and Nurr1 deficient tissue, respectively. When ventral mesencephalon, dissected from E10.5 fetuses, was cultured alone without the presence of LGE, significantly more TH-immunoreactive neurons were found in WT and Nurr1 +/- than that seen in Nurr1 -/- cultures. In single ventral mesencephalic cultures dissected from E15.5, TH-positive neurons were found in all tissue cultures derived from knockout animals. Interestingly, the formation of TH-positive nerve fiber bundles was obvious in WT cultures while not observed in cultures of knockout tissue. When ventral mesencephalon was cultured alone in serum-free medium, almost no TH-positive neurons were found in cultures of knockout tissue. The addition of the growth factors epidermal growth factor and fibroblast growth factor-8 did not induce TH-immunoreactivity in serum-free Nurr1 -/- tissue cultures. In conclusion, TH-positive neurons may be generated in ventral mesencephalic tissue of Nurr1 deficient mice, suggesting that Nurr1 is not required for TH gene expression in ventral midbrain in vitro.

Trevitt, T., B. Carlson, et al. (2002). "Interactions between dopamine D1 receptors and gamma-aminobutyric acid mechanisms in substantia nigra pars reticulata of the rat: neurochemical and behavioral studies." Psychopharmacology (Berl) 159(3): 229-37.
RATIONALE: Several studies have shown that dopamine D1 agonists act on forebrain dopamine terminal regions to exert many of their behavioral effects. Yet, there is also a large number of D1 receptors in the substantia nigra pars reticulata (SNr), and these receptors are located mainly on terminals of gamma-aminobutyric acid (GABA)-ergic striatonigral neurons. OBJECTIVE: The present studies were undertaken to determine the behavioral and neurochemical effects of local administration of the D1 agonist SKF 82958 and to study the interactions between D1 and GABA mechanisms in SNr. METHODS: Microdialysis methods were used to characterize the effect of SKF 82958 on extracellular GABA, and several experiments studied the effects of nigral D1 stimulation on motor activity and investigated the behavioral significance of D1/GABA interactions in SNr. RESULTS: Local infusion of 10(-6) M SKF 82958 increased extracellular levels of SNr GABA, and this effect was blocked by co-infusion of the D1 antagonist SCH 23390. Bilateral SNr injections of SKF 82958 increased locomotor activity, and this effect was blocked by the GABA-A antagonist bicuculline. Intranigral bicuculline reduced motor activity, while the GABA-A agonist muscimol increased various motor activities in a manner similar to SKF 82958. CONCLUSIONS: The present results suggest that the D1 agonist SKF 82958 acts on D1 receptors in SNr to increase extracellular levels of GABA, and the increase in motor activity produced by nigral D1 stimulation is dependent on stimulation of GABA-A receptors. D1/GABA interactions in SNr are important for the modulation of basal ganglia output, which may have important implications for Parkinson's disease.

Turner, M. S., L. Mignon, et al. (2002). "Alterations in responses of ventral pallidal neurons to excitatory amino acids after long-term dopamine depletion." J Pharmacol Exp Ther 301(1): 371-81.
The present study explored the possibility that excitatory amino acid (EAA) sensitivity within the ventral pallidum (VP) is altered by long-term removal of dopamine (DA). Electrophysiological experiments were conducted in chloral hydrate-anesthetized rats 21 to 28 days after they received unilateral substantia nigra injections of the dopaminergic toxin 6-hydroxydopamine (6-OHDA). VP neurons increased firing at low microiontophoretic ejection currents of the EAA agonists N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA); however, high currents decreased action potential amplitude and rapidly caused cessation of neuronal firing. These responses likely reflected the induction of depolarization block for they were reversed by coiontophoresis of the hyperpolarizing transmitter gamma-aminobutyric acid (GABA) at ejection current levels that normally suppressed firing. The ability of NMDA and AMPA to induce such inactivation was greater in the VP of 6-OHDA-lesioned hemispheres, but unchanged in reserpinized rats, verifying that the alterations in responding to NMDA were the result of chronic, rather than acute, DA removal. The adaptations do not appear to be the consequence of a diminished GABAergic tone for the ability of bicuculline to increase firing (due to blocking a tonic GABAergic input) was not changed. However, low ejection currents of GABA that were insufficient to alter firing rate greatly attenuated the ability of NMDA to induce an apparent depolarization inactivation when coiontophoresed with NMDA onto VP neurons of the lesioned, but not the unlesioned, hemisphere. These studies show that chronic DA removal altered the EAA-induced amplitude-decreasing (i.e., the apparent depolarization inactivation) effects in VP neurons in the absence of a decrease in GABAergic tone.

van Oosten, R. V. and A. R. Cools (2002). "Differential effects of a small, unilateral, 6-hydroxydopamine-induced nigral lesion on behavior in high and low responders to novelty." Exp Neurol 173(2): 245-55.
The goal of this study was to develop an animal model that evaluates striatal-specific behavior after partial, unilateral destruction of nigrostriatal neurons. 6-OHDA (1 microg) was injected intranigrally (day 0) to reduce dopaminergic innervation of the dorsal striatum (DS); 6-OHDA (5 microg) was injected to reduce innervation of DS and nucleus accumbens (ACC). We analyzed changes in (a) behavior regulated by dopamine (DA) release in the DS (hindpaw preference from day 5 to day 19, every other day) and the ACC (novelty-induced locomotion on day 16) and (b) apomorphine-induced rotation (on day 21). We used two types of rat that show differences in structure and function of the dopaminergic neurons, namely high (HR) and low (LR) responders to novelty. 6-OHDA (1 microg) significantly decreased TH immunoreactivity (TH-ir) in the DS and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. Only in LRs was the significant increase of novelty-induced locomotion accompanied by a significant increase in TH-ir density in the ACC: this suggests a lesion-induced shift in nigrostriatal/mesolimbic balance toward a dominance of the mesolimbic system. The higher 6-OHDA dose significantly decreased TH-ir in the DS and the ACC and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. However, this increase occurred significantly earlier in LRs than in HRs. Apomorphine elicited contralateral rotations solely in LRs, and not in HRs, indicating development of supersensitive dopamine receptors in the DS of LRs, but not HRs. The data show that LRs are more susceptible to 6-OHDA than HRs. The relevance of the present data for Parkinson's disease is discussed.

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.

Viggiano, D., G. Grammatikopoulos, et al. (2002). "A morphometric evidence for a hyperfunctioning mesolimbic system in an animal model of ADHD." Behav Brain Res 130(1-2): 181-9.
The hyperfunctioning dopamine hypothesis in the mesocorticolimbic (MCL) system has been addressed by a neurogenetic approach in model systems. Thus, a morphometric analysis was carried out on neurons of origin of Substantia Nigra (SN) and Ventral Tegmental Area (VTA) dopamine systems of the Naples High-Excitability (NHE), Low-Excitability (NLE) and control lines. Male adult rats were tested in a spatial novelty for indices of activity and non-selective attention. Mesencephalic coronal sections were processed for tyrosine hydroxylase (TH) immunohistochemistry and cytochromoxidase (C.O.) histochemistry. Image analysis in the rostro-caudal plane showed (i) a higher neuron size of TH+ elements in the VTA of NHE and NLE, across the entire structure in the NHE, and only in the middle portion in the NLE; (ii) a higher expression of TH in the neuropil of the VTA in NHE; (iii) a lower C.O. activity in both NLE and NHE; (iv) no differences in the SN. The larger neuron size in both NHE and NLE rats as compared with control rats, along with higher TH expression mainly in the NHE, in absence of any relevant alteration in the SN, reveals an unbalance between the two dopamine systems and a subsequent alteration in limbic (reward, motivation, sustained attention) functions. The decreased C.O. activity might be due to reduced feedback inhibition by striatal GABA neurons and interneurons leading to increased DA neuron firing. In conclusion, the increased behavioral activity and impaired attention observed in the NHE rats are associated to hyperfunctioning MCL system in this genetic model of Attention-Deficit Hyperactivity Disorder (ADHD).

Vitalis, T., C. Fouquet, et al. (2002). "Developmental expression of monoamine oxidases A and B in the central and peripheral nervous systems of the mouse." J Comp Neurol 442(4): 331-47.
Monoamine oxidases A (MAOA) and B (MAOB) are key players in the inactivation pathway of biogenic amines. Their cellular localization has been well established in the mature brain, but nothing is known concerning the localization of both enzymes during development. We have combined in situ hybridization and histochemistry to localize MAOA and MAOB in the developing nervous system of mice. Our observations can be summarized as five key features. (1) MAOA is tightly