Substantia Nigra Area Research Articles

Transcranial Sonography in Parkinson’s Disease

Transcranial sonography (TCS) is able to image in B-mode infratentorial and supratentorial structures, and can be used for the diagnosis and differential diagnosis of various intracranial pathologies. The authors review the contribution of TCS in the diagnosis and differential diagnosis of Parkinson’s disease (PD). TCS can be used to evaluate changes of echogenicity and in the area of substantia nigra in PD. Hyperechogenic enlarged substantia nigra can be detected in approximately 90% of PD patients and also in approximately 10% of the healthy population as a marker of subclinical injury of the nigrostriatal system. Hypoechogenic nucleus raphe could be detected in PD patients with unipolar depression and this finding also correlates with incontinency. Evaluations of echogenicity of the thalamus, nucleus lentiformis, nucleus caudatus, nucleus dentatus and the cerebellum, and measurement of enlargement of the ventricular system, could be used for differential diagnosis of movement disorders. TCS is a quick, safe and noninvasive method and can be used for early diagnosis of PD.

Structural Changes in Mesocorticolimbic Dopaminergic System of the Brain during Long-Term Alcoholization in Rats

We studied morphofunctional changes in structures of the mesocorticolimbic system of rat brain upon long-term (5 months) ethanol intoxication. Alcoholization reduced the volume and specific density of neurons in the substantia nigra and ventral tegmental area. The density of neurogliocytes in the substantia nigra and ventral tegmental area increased. Neuronal density in the nucleus accumbens and anterior cingulate cortex significantly decreased, the volume of viable neurons slightly increased. One month after alcohol cessation, the volume of neurons in the substantia nigra and ventral tegmental area remained elevated against the background of their reduced density. The density of neuroglia in the nucleus accumbens and anterior cingulate cortex remained at the level observed during alcoholization. Significant decrease in the density and decrease in the volume of neurons in structures of the mesocorticolimbic system accompanied by the increase in neuroglyocyte density in these structures can be considered as morphological signs of long-term alcoholic intoxication, which persist after alcohol cessation.

Immunocytochemical expression of dopamine‐related transcription factors Pitx3 and Nurr1 in prenatally stressed adult rats

Rats exposed to different types of stress during the last week of pregnancy produce offspring that show severe anomalies in neural development and brain morphology. We have previously reported that prenatal stress (PS) induced by immobilization increases D2-type dopamine (DA) receptor levels in the adult offspring, with a concomitant reduction in DA release in prefrontal cortex after amphetamine stimulation. Recently, two transcription factors, Nurr1 and Pitx3, have been identified that are expressed at critical moments of DA neuron differentiation. Their genetic expression is activated immediately after these neuron determinations and maintained through adult life. Nurr1 regulates several proteins that are required for dopamine synthesis and regulation, and Pitx3 is specifically involved in the terminal differentiation and maintenance of dopamine neurons. By means of an immunocytochemistry approach, we studied the expression of Nurr1 and found an ubiquitous distribution in cerebral cortex, hippocampus, thalamus, amygdala, and midbrain, whereas Pitx3 remains restricted to the mesencephalic DA neurons such as substantia nigra and ventral tegmental area. Our results show that the expression of both Nurr1 and Pitx3 increased in prenatally stressed adult offspring in the ventral tegmental area, whereas no changes were observed in the substantia nigra area. It might be hypothesized that the increase of the specific dopaminergic transcription factors might be a compensatory mechanism to counteract the reduction in dopamine levels previously observed as a consequence of prenatal stress.

Marked microglial reaction in normal aging human substantia nigra: correlation with extraneuronal neuromelanin pigment deposits

Multiple reports have documented an age-related loss, estimated at about 10% per decade, of the pigmented neurons in the substantia nigra. This is associated with motor dysfunction, including bradykinesia, stooped posture and gait disturbance. As microglia are activated by cell death and neuromelanin pigment, we hypothesized that there should be a significant microglial reaction in normal aging human substantia nigra. Sections of substantia nigra from elderly subjects (N = 15; mean 81.3; SD 7.0) and younger subjects (N = 7; mean 30.3; SD = 8.7), all of which had no specific neurologically or neuropathologically defined disorders, were stained immunohistochemically for MHC Class II and the area occupied by microglia was quantified in substantia nigra pars compacta. All elderly subjects showed a pronounced microglial reaction in the substantia nigra, with frequent, intensely stained hypertrophic microglia, while immunoreactive nigral microglia were much less frequent in the younger subjects. Quantification showed that in older subjects, the percentage of substantia nigra area occupied by microglial bodies and processes was significantly greater than for younger subjects (mean 19.6 vs. 3.6; P = 0.005). Extraneuronal neuromelanin deposits were present in all the older subjects but were absent or rare in the younger subjects. The neuromelanin deposit abundance score in the older subjects correlated significantly with the area occupied by immunoreactive microglia. The marked microglial reaction in normal aging human substantia nigra, together with the previously reported 35-80% pigmented neuron loss, indicates the presence of a powerful pathologic process that may be additive with specific age-related neurodegenerative diseases, including Parkinson's disease.

Quetiapine reverses altered locomotor activity and tyrosine hydroxylase immunoreactivity in rat caudate putamen following long-term haloperidol treatment

Haloperidol (HAL) is a typical antipsychotic drug and known to cause extrapyramidal symptoms (EPS) that may be associated with the blockade of dopamine D2-receptors in nigrostriatal pathway by the drug. In contrast, quetiapine (QTP) is an atypical antipsychotic drug that has the lowest incidence of producing EPS in patients with schizophrenia, while improving psychosis symptoms. In the present study, we investigated the possibility of reversing the HAL-induced changes in locomotor activity and in striatal tyrosine hydroxylase (TH) of rats. Rats were administered HAL (2mg/kg/day, p.o.) for 3 months, followed by vehicle (VEH), QTP (10mg/kg/day), HAL, or HAL+QTP for another 5 weeks. The locomotor activity and TH immunoreactivity of the rats were measured. Chronic administration of HAL caused significant increase in locomotor activity and lower levels of TH immunoreactivity in the caudate putamen of the striatum. When the long-term haloperidol treatment was removed, the change in TH immunoreactivity was normalized, while the HAL induced high level of locomotor activity was returned to normal level only in the rats that stopped HAL consumption and received QTP treatment. In the substantia nigra and ventral tegmental areas, all rats showed comparable numbers of TH-positive cell bodies, which had no shrinkage. These results support a previously proposed relationship between EPS and TH levels in the striatum and provide valuable preclinical information towards understanding why QTP produces a lowest incidence of EPS among antipsychotics and has been used to treat EPS caused by other antipsychotics, and eventually establish a principle of treating EPS.

The mammalian transcriptome and the cellular complexity of the brain

The mammalian transcriptome and the cellular complexity of the brain

KDI tripeptide of γ1 laminin protects rat dopaminergic neurons from 6‐OHDA induced toxicity

Our previous studies indicate that the KDI (Lys-Asp-Ile) tripeptide of gamma1 laminin protects central neurons from mechanical trauma and excitotoxicity. At least part of the neuroprotective effect of the KDI tripeptide may be mediated by its inhibitory function on ionotropic glutamate receptors. We studied the protective effect of the KDI tripeptide against 6-hydroxy-dopamine (6-OHDA) induced neurotoxicity in a rat experimental model of Parkinson's disease (PD). We found that a single unilateral injection of the KDI tripeptide into the substantia nigra before an injection of 6-OHDA protected the dopaminergic neurons from the neurotoxicity of 6-OHDA. Compared to rats treated with 6-OHDA alone, the KDI + 6-OHDA-treated substantia nigra was relatively intact with large numbers of dopaminergic neurons present at the injection side. In the rats treated with 6-OHDA alone, no dopaminergic neurons were detected, and the substantia nigra-area at the injection side was filled with blood-containing cavities. Quantification of the rescue effect of the KDI tripeptide indicated that, in animals receiving KDI before 6-OHDA, 33% of tyrosine hydroxylase-positive dopaminergic neurons of the substantia nigra were present as compared to the contralateral non-injected side. In animals receiving 6-OHDA alone, only 1.4% of the tyrosine hydroxylase expressing dopaminergic neurons could be verified. If this much protection were achieved in humans, it would be sufficient to diminish or greatly alleviate the clinical symptoms of PD. We propose that the KDI tripeptide or its derivatives might offer a neuroprotective biological alternative for treatment of PD.

K ATP Channels Determine Which Dopaminergic Neurons Will Die

Liss et al. set out to understand why the dopaminergic (DA) neurons of the substantia nigra were selectively vulnerable to toxins that produce Parkinson's disease-like symptoms and dopaminergic cell death in mice. DA neurons of the substantia nigra or ventral tegmental area (VTA) were selectively labeled in brain slices from 3-month-old mice. All midbrain DA neurons exhibited ATP-regulated K + current such that activation of the K ATP channel in the brain slices with ATP-free solution hyperpolarized the membrane. This response was absent in slices from mice lacking the pore-forming subunit Kir6.2. All midbrain DA neurons expressed the mRNA for the SUR1 subunit of the K ATP channel, so differences in susceptibility were not the result of either lack of the channel or differential expression of channel subunits. However, substantia nigra DA neurons exhibited greater magnitude K ATP currents, which may be due to the increased abundance of the SUR1 mRNA relative to that present in the VTA DA neurons. Rotenone and 1-methyl-4-phenylpyridinium (MPP + ) are mitochondrial respiratory complex I inhibitors that cause selective DA degeneration and increased reactive oxygen species (ROS) production. When applied with glucose, these agents alter ROS production without altering cellular metabolism. Application to brain slices of either of these complex I inhibitors in the presence of glucose resulted in the cessation of spontaneous activity and, ultimately, hyperpolarization of the membrane of striatal DA neurons, selectively. This response was absent in the slices from Kir6.2 —/— mice. The difference in activation of the K ATP channels in response to complex I inhibition appeared to involve the degree of mitochondrial uncoupling present in the different DA neurons. VTA DA neurons, which have greater abundance of the mRNA for the uncoupling protein UCP-2 than do the substantia nigra DA neurons, showed loss of firing and hyperpolarization in response to rotenone when the cells were pretreated with a low concentration of an uncoupling agent to cause a drop in ROS production. In contrast, pretreatment of substantia nigra DA neurons to cause mild uncoupling prevented hyperpolarization and loss of spontaneous activity in response to rotenone. The authors suggest that VTA DA neurons exist in a state of partial mitochondrial uncoupling and decreased ROS production that protects them by preventing activation of the K ATP channel and loss of activity. B. Liss, O. Haeckel, J. Wildmann, T. Miki, S. Seino, J. Roeper, K-ATP channels promote the differential degeneration of dopaminergic midbrain neurons. Nat. Neurosci. 8 , 1742-1751 (2005). [PubMed]

Differential expression of the homeobox gene Pitx3 in midbrain dopaminergic neurons

The transcription factor Pitx3 is expressed selectively in the midbrain and regulates the differentiation and survival of dopaminergic neurons. Lack of this factor results in a degeneration similar to that seen in Parkinson's disease. We have studied the pattern and the level of expression of Pitx3 in dopaminergic neurons of 3- to 4-week-old Wistar rats. We report Pitx3 expression in almost all dopaminergic substantia nigra (SN) and ventral tegmental area (VTA) neurons. It is coexpressed with the neuroprotective marker calbindin (CB) in a larger population of VTA (43%) than SN (16%) dopaminergic neurons. The level of Pitx3 mRNA, determined by semiquantitative RT-PCR, is approximately 6x higher in VTA than in SN single neurons. In the VTA but not in SN the level of Pitx3 is associated with the presence of CB: in CB-positive neurons the expression of Pitx3 mRNA is 3.6x higher than in CB-negative cells. CB is expressed in a larger population of VTA than SN neurons and the relative level of CB expression is 4x higher in VTA than in SN. A higher Pitx3 expression level and higher coexpression of Pitx3 and CB in VTA than in SN neurons may contribute to the different vulnerability of these dopaminergic nuclei to neurodegeneration.

DOPAMINE CELL MORPHOLOGY AND GLIAL CELL HYPERTROPHY AND PROCESS BRANCHING IN THE NIGROSTRIATAL SYSTEM AFTER STRIATAL 6-OHDA ANALYZED BY SPECIFIC STEROLOGICAL TOOLS

Morphological changes in the dopamine neurons and glial cells of the rat midbrain ascending dopamine pathways were investigated after a partial lesion induced by unilateral striatal injection of a small dose of 6-hydroxydopamine (6-OHDA). Fourteen days after lesion, animals showed contralateral rotation induced by apomorphine injection. After behavioral analysis, rats were killed and their brains processed for the immunohistochemistry tyrosine hydroxylase (TH), a marker for dopamine cells, as well as glial fibrillary acidic protein (GFAP) and OX-42, markers for astrocyte and microglia, respectively. Stereological tools were employed in the quantifications. The volumes of the regions of the striatal TH immunoreactive disappearance, as well as the astroglial and microglial activation were several folds increased compared to control saline-injected rats. The optical disector detected decreases in the estimated total number of dopamine cells in the entire ipsilateral pars compacta of the substantia nigra (SNc) and ventral tegmental area (VTA) as well as in the estimated total number of varicosity profiles in the entire ipsilateral neostriatum. The stereological tool rotator showed no changes either in the mean or in the histogram distribution of the cytoplasmic volume of the nigral and VTA dopamine cells of 6-OHDA lesioned rats. Increases in the estimated total number of GFAP positive astrocytes were found in the entire neostriatum bilaterally as well as in the ipsilateral entire SNc and VTA of 6-OHDA lesioned rats. The estimated total number of OX-42 immunoreactive microglial profiles was elevated only in the ipsilateral entire neostriatum of the lesioned rats. The rotator detected cytoplasmic hypertrophy in the astrocytes, and also a shift to the right of the gaussian curves of the normal distribution of the logarithmic plotted values of the astroglial cell body volumes,of the neostriatum bilaterally as well as in the ipsilateral SNc and VTA of the striatal 6-OHDA injected rats. Cytoplasmic hypertrophy of microglia, and also a shift to the right of the gaussian curves of the values of microglia cell body volumes were seen only in the ipsilateral neostriatum; however, the point intercepts revealed an increased amount of microglial processes in the ipsilateral SNc and VTA of the lesioned rats. Specific stereological methods can be applied on detection of regionally different forms of cellular astroglial and microglial reaction after a partial lesion of dopamine pathway.

GLIAL bFGF AND S100 IMMUNOREACTIVITIES INCREASE IN ASCENDING DOPAMINE PATHWAYS FOLLOWING STRIATAL 6-OHDA-INDUCED PARTIAL LESION OF THE NIGROSTRIATAL SYSTEM: A STEROLOGICAL ANALYSIS

S100, a calcium-binding protein, and basic fibroblast growth factor (bFGF, FGF-2) are found predominantly in astrocytes in the central nervous system. Those molecules show trophic properties to neurons and are upregulated after brain lesions. The present study investigated the changes in the S100b and bFGF immunoreactivities after a partial lesion of the rat midbrain ascending dopamine pathways induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA). Stereological method revealed increases in the estimated total number and density of bFGF immunoreactive astroglial profiles in the ipsilateral pars compacta of the substantia nigra (SNc) and ventral tegmental area (VTA). Increases in the counts of astroglial S100b immunoreactive profiles were found in the striatum, SNc, and VTA mainly ipsilateral but also in the contralateral nuclei. These results open up the possibility that interactions between astroglial S100b and bFGF may be relevant to paracrine events related to repair and maintenance of remaining dopamine neurons following striatal 6-OHDA induced partial lesion of ascending midbrain dopamine pathway.

Postnatal Inorganic Lead Exposure Reduces Midbrain Dopaminergic Impulse Flow and Decreases Dopamine D1 Receptor Sensitivity in Nucleus Accumbens Neurons

Lead treatment via drinking water for 3 to 6 weeks at 250 ppm was found to significantly decrease the number of spontaneously active dopamine (DA) neurons in both the substantia nigra and ventral tegmental area that were recorded using standard extracellular electrophysiological recording techniques. Lead exposure did not affect the discharge rate or discharge pattern of these DA neurons. No significant decrease in the number of tyrosine hydroxylase immunopositive cells was detected in lead-treated animals relative to controls even though the length of lead exposure was extended beyond that of the electrophysiological studies. The significant lead-induced decrease in spontaneously active cells observed in the electrophysiological studies was, therefore, not due to cell death. An acute drug challenge with the DA receptor agonist apomorphine at a dose known to hyperpolarize midbrain DA neurons (50 mug/kg i.v.) was used to determine whether hyperpolarization would normalize the number of spontaneously active DA neurons. The results suggest that depolarization inactivation was most likely not the cause for this lead effect. The D(1) receptor agonist SKF-38393 [1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol] was iontophoretically applied to type I nucleus accumbens (Nacb) neurons. The results demonstrated that type I Nacb neurons have a significantly lower basal discharge rate in lead-treated animals relative to controls and that the Nacb DA D(1) receptors were significantly less sensitive to SKF-38393 in the lead-treated animals. Therefore, lead exposure decreases DA neuron impulse flow presynaptically and decreases DA D(1) receptor sensitivity postsynaptically in the nucleus accumbens.

Chronic nicotine and smoking treatment increases dopamine transporter mRNA expression in the rat midbrain

Previous pharmacokinetics and electrophysiological results indicated an important role of nicotine in the modulation of dopamine transporter (DAT). To elucidate the expression changes of DAT on chronic nicotine and smoke administration, the effects of nicotine and passive cigarette smoke on DAT mRNA expression in the ventral tegmental area (VTA) and the substantia nigra (SN) area were examined using in situ hybridization and RNase protection assay. The results showed that chronic nicotine and smoke exposure highly unregulated DAT mRNA in the VTA and SN areas, including the dorsal part of substantia nigra pars compacta. Smoke for 30 min showed the highest increasing effect, whereas nicotine and smoke for 10 min only had slightly increasing effects. However, smoke for 1 h showed an increasing effect to a lesser extent than 30 min. These results revealed a new aspect of nicotine's modulation on the DAT, and may have important roles in neuropsychological disorders related to the midbrain abnormalities such as drugs addiction.

Chronic nicotine and smoking treatment increases dopamine transporter mRNA expression in the rat midbrain

Previous pharmacokinetics and electrophysiological results indicated an important role of nicotine in the modulation of dopamine transporter (DAT). To elucidate the expression changes of DAT on chronic nicotine and smoke administration, the effects of nicotine and passive cigarette smoke on DAT mRNA expression in the ventral tegmental area (VTA) and the substantia nigra (SN) area were examined using in situ hybridization and RNase protection assay. The results showed that chronic nicotine and smoke exposure highly unregulated DAT mRNA in the VTA and SN areas, including the dorsal part of substantia nigra pars compacta. Smoke for 30 min showed the highest increasing effect, whereas nicotine and smoke for 10 min only had slightly increasing effects. However, smoke for 1 h showed an increasing effect to a lesser extent than 30 min. These results revealed a new aspect of nicotine's modulation on the DAT, and may have important roles in neuropsychological disorders related to the midbrain abnormalities such as drugs addiction.

Destruction of midbrain dopaminergic neurons by using immunotoxin to dopamine transporter.

1. The ability to target specific neurons can be used to produce selective neural lesions and potentially to deliver therapeutically useful moieties for treatment of disease. In the present study, we sought to determine if a monoclonal antibody to the dopamine transporter (anti-DAT) could be used to target midbrain dopaminergic neurons. 2. The monoclonal antibody recognizes the second, large extracellular loop of DAT. The antibody was conjugated to the "ribosome-inactivating protein"; saporin, and stereotactically pressure microinjected into either the center of the striatum or the left lateral ventricle of adult, male Sprague-Dawley rats. 3. Local intrastriatal injections produced destruction of dopaminergic neurons in the ipsilateral substantia nigra consistent with suicide transport of the immunotoxin. Intraventricular injections (i.c.v.) produced significant loss of dopaminergic neurons in the substantia nigra and ventral tegmental area bilaterally without evident damage to any other aminergic structures such as the locus coeruleus and raphe nuclei. To confirm the anatomic findings, binding of [3-H]mazindol to DAT in the striatum and midbrain was assessed using densitometric analysis of autoradiograms. Anti-DAT-saporin injected i.c.v. at a dose of 21 microg, but not 8 microg, produced highly significant decreases in mazindol binding consistent with loss of the dopaminergic neurons. 4. These results show that anti-DAT can be used to target midbrain dopaminergic neurons and that anti-DAT-saporin may be useful for producing a lesion very similar to the naturally occurring neural degeneration seen in Parkinson's disease. Anti-DAT-saporin joins the growing list of neural lesioning agents based on targeted cytotoxins.

Effect of repeated treatment with high doses of selegiline on behaviour, striatal dopaminergic transmission and tyrosine hydroxylase mRNA levels.

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.

Increases in [3H]FK-506 and [3H]L-N(G)-nitro-arginine binding in the rat brain after nigrostriatal dopaminergic denervation.

Receptor autoradiographic technique was studied to investigate sequential changes in FK-506 binding proteins, nitric oxide synthase and dopamine uptake sites in the brain 1 week to 8 weeks after unilateral 6-hydroxydopamine injection of the medial forebrain bundle in rats. [3H]FK-506, [3H]L-N(G)-nitro-arginine and [3H]mazindol were used to label FK-506 binding proteins (immunophilin), nitric oxide synthase and dopamine uptake sites, respectively. [3H]FK-506 binding showed about 13-25% increase in the ipsilateral striatum from 2 to 8 weeks after degeneration of nigrostriatal pathway. However, no significant change in [3H]FK-506 binding was observed in the ipsilateral substantia nigra during the postlesion periods. In the contralateral side, [3H]FK-506 binding also showed about 13-25% increase in the striatum from 2 to 8 weeks postlesion. The substantia nigra showed a 21% increase in [3H]FK-506 binding only 2 weeks after the lesioning. On the other hand, [3H]L-N(G)-nitro-arginine binding showed about 21-31% increase in the parietal cortex and striatum 1 week or 2 weeks postlesion. In the contralateral side, a 21% increase in [3H]L-N(G)-nitro-arginine binding was found in the dorsolateral striatum only 1 week postlesion. In contrast, degeneration of nigrostriatal pathway caused a conspicuous loss of [3H]mazindol binding in the ipsilateral striatum (87-96%), substantia nigra (36-73%) and ventral tegmental area (91-100%) during the postlesion periods. In the contralateral side, no significant changes in [3H]mazindol binding were observed in these areas up to 8 weeks after the postlesion. The present study demonstrates that unilateral injection of 6-hydroxydopamine into the medial forebrain bundle of rats can cause a significant increase in [3H]FK-506 and [3H]L-N(G)-nitro-arginine bindings in the brains. In contrast, a marked reduction in [3H]mazindol binding is observed in the brains after the lesioning, indicating severe damage to nigrostriatal dopaminergic pathway. These results suggest that immunophilin and nitric oxide synthase may play some role in the pathogenesis of neurodegenerative disorders such as Parkinson's disease.

Sequential changes of dopaminergic receptors in the rat brain after 6-hydroxydopamine lesions of the medial forebrain bundle.

We investigated the sequential patterns of changes in dopamine uptake sites, D1 and D2 receptors in the brain of animals lesioned with 6-hydroxydopamine using quantitative receptor autoradiography. The rats were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. Degeneration of the nigrostriatal pathway caused a significant loss of dopamine uptake sites in the ipsilateral striatum, substantia nigra (SN) and ventral tegmental area (VTA) in the lesioned animals. Dopamine D1 receptors were significantly increased in the ventromedial part of striatum of the ipsilateral side from 2 to 4 weeks postlesion. In the ipsilateral SN, a transient increase in dopamine D1 receptors was observed only 1 week after lesioning. However, the frontal cortex, parietal cortex and dorsolateral part of the striatum showed no significant change in dopamine D1 receptors throughout the experiments. On the other hand, dopamine D2 receptors were decreased increased in the ipsilateral SN and VTA from 1 week to 8 weeks postlesion. In the ipsilateral striatum, dopamine D2 receptors were increased in the dorsolateral part from 2 weeks to 8 weeks and in the ventromedial part from 2 weeks to 4 weeks. However, the frontal cortex and parietal cortex showed no significant change in dopamine D2 receptors during postlesion. In the contralateral side, most of regions examined showed no significant change in dopamine uptake sites, dopamine D1 receptors and dopamine D2 receptors during postlesion except for a transient change in a few regions. These results demonstrate that 6-hydroxydopamine can cause a severe functional damage in dopamine uptake sites in the striatum, SN and VTA. Our findings also suggest that the up-regulation in dopamine D2 receptors is more pronounced than that in dopamine D1 receptors in the brain after 6-hydroxydopamine treatment. Furthermore, our results support the existence of dopamine D2 receptors on the neurons of SN and VTA. Thus, our findings provide insights into the pathogenesis of Parkinson's disease.

Understanding the Development of Dopamine Neurons

Alterations in dopamine-containing neurons of the substantia nigra and ventral tegmental areas of the midbrain have long been implicated in the

Nicotine withdrawal leads to increased firing rates of midbrain dopamine neurons

In order to explore the neurophysiology of nicotine withdrawal, we examined the activity of substantia nigra (A9) and ventral tegmental area (A10) dopamine cells in rats undergoing withdrawal from chronic exposure to nicotine. Animals were exposed to nicotine (6 mg kg-1 day-1 base) via s.c. implanted osmotic minipumps. After 12 days the pumps were removed and the animals allowed to go through spontaneous withdrawal. Rats were anesthetized on various days of the procedure and single-unit recordings were made from A9 and A10 dopamine cells. Chronic administration of nicotine led to a decreased firing rate of A10, but not A9, dopamine cells. Upon withdrawal from the chronic exposure to nicotine, the firing rates of A10 dopamine cells returned to control levels, while the firing rate of A9 dopamine cells significantly increased above control levels. This increased dopamine neuronal activity may play a role in some behavioural symptoms of nicotine withdrawal.