Amphetamine induces hypermotility in MPTP-lesioned mice

Two strains of mice (NMRI and C57B1/ 6) were treated with MPTP (within 8 h 4 x 30 mg/kg MPTP, IP) and motility was monitored 10 days later. An acute administration of amphetamine (2.5 mg/kg or 10.0 mg/kg) or apomorphine (0.5 mg/kg or 5.0 mg/kg) led to hypermotility and a dose-dependent increase of stereotyped behavior. Immunocytochemical investigations indicated a substantial loss of tyrosine-hydroxylase immunoreactivity in the basal ganglia which was accompanied by a 15% increase of 3H-spiroperidol binding to a striatal membrane preparation. No difference was found in biochemical and behavioral measures between both mice strains. Thus, MPTP-induced lesions in mice are probably followed by a denervation-like supersensitivity of the dopaminergic system, which might account for the finding that despite a severe degeneration of dopaminergic terminals amphetamine induces hypermotility.

Consequences of nigrostriatal denervation on the functioning of the basal ganglia in human and nonhuman primates: an in situ hybridization study of cytochrome oxidase subunit I mRNA

To examine the consequences of nigrostriatal denervation and chronic levodopa (L-DOPA) treatment on functional activity of the basal ganglia, we analyzed, using in situ hybridization, the cellular expression of the mRNA encoding for cytochrome oxidase subunit I (COI mRNA), a molecular marker for functional neuronal activity, in the basal ganglia. This analysis was performed in monkeys rendered parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) Intoxication, some of which had been receiving L-DOPA, and in patients with Parkinson's disease (PD). In MPTP-intoxicated monkeys compared with control animals, COI mRNA expression was increased in the subthalamic nucleus (STN) and in the output nuclei of the basal ganglia, i.e., the internal segment of the globus pallidus and the substantia nigra pars reticulata. This increase was partially reversed by L-DOPA treatment. COI mRNA expression remained unchanged in the external segment of the globus pallidus (GPe). In PD patients, all of whom had been treated chronically by L-DOPA, COI mRNA expression in the analyzed basal ganglia structures was similar to that in control subjects. These results are in agreement with the accepted model of basal ganglia organization, to the extent that the output nuclei of the basal ganglia are considered to be overactive after nigrostriatal denervation, partly because of increased activity of excitatory afferents from the STN. Yet, our results would also seem to contradict this model, because the overactivity of the STN does not seem to be attributable to a hypoactivation of the GPe.

Defects of cytochrome c oxidase in the substantia nigra of Parkinson's disease: and immunohistochemical and morphometric study

Defects of respiratory chain complexes were considered as possible pathogenetic mechanisms in Parkinson's disease (PD). Changes of cytochrome c oxidase (COX) in four different nuclei of the substantia nigra of 8 PD cases and 10 age-matched controls were investigated by means of morphometry and immunohistochemistry. Pigmented neurons with COX defects were randomly distributed within the the four nuclei of PD cases, but only in the posterolateral nucleus was the numerical density of pigmented neurons with COX defects significantly increased compared with controls. The numerical density of pigmented neurons without COX defects was significantly reduced in the anteromedial, anterointermediolateral, and posterolateral nuclei in PD. The cell size of pigmented neurons with and without COX defects was significantly diminished in the anteromedial and posterolateral nuclei of PD cases. It is suggested that complex IV defects in nigral neurons are most probably a result of accelerated aging, but are least likely to be a primary aspect of the pathogenetic processes occurring in PD.

Chronic inhibition of the high-affinity dopamine uptake system increases oxidative damage to proteins in the aged rat substantia nigra

The effect of chronic treatment of aged rats with nomifensine has been studied in the rat nigrostriatal dopaminergic system. The rat substantia nigra suffers an oxidative damage during aging that results in both an increase in carbonyl groups of its total proteins and the oxidative inactivation of tyrosine hydroxylase (TH) enzyme, which are partially reversed by chronic treatment with deprenyl. Different mechanisms may account for this effect, including inhibition of the high-affinity dopamine uptake system. We treated aged rats chronically with nomifensine for 2 months and found some significant effects. Nomifensine treatment significantly increased TH enzyme amount in substantia nigra (39.2%), which was accompanied by a significant increase in TH enzyme activity (47.8%). However, these effects were not observed in the terminal field (striatum). As a further step we quantified the oxidative level of proteins by measuring the number of carbonyl groups coupled either to total proteins or specifically to TH enzyme. The proteins of aged rat substantia nigra showed a significant increase of carbonyl groups following nomifensine treatment. The number of carbonyl groups coupled to nigral TH enzyme also increased in the nomifensine-treated animals. However, this increase was lower than that found in the total homogenate proteins. All these results show that the oxidative damage produced during aging in tyrosine hydroxylase enzyme and total proteins is not reduced by nomifensine treatment. On the contrary, the nomifensine treatment increased the oxidative damage to proteins. These results suggest the capability of deprenyl to induce TH enzyme could be due to inhibition of the high-affinity dopamine uptake system, but its ability to protect against oxidative damage is not produced by this mechanism.

Minor immunoreactivity in GDNF-, BDNF-, or NT-3-treated substantia nigra allografts

Glial-cell-line-derived neurotrophic factor (GDNF) stimulates the survival of dopaminergic neurons. Little is known, however, about the possible immune sequelae of GDNF exposure or of exposure to other putative trophic factors. To address these questions, pieces of mesencephalic tissue, substantia nigra, from 15-day-old donor embryos were transplanted into the anterior chamber of the eye of adult male Sprague-Dawley recipient rats. At 5-day intervals, an aliquot (0.5 microgram) of GDNF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or cytochrome-C (CC) was injected into the anterior chamber of the eye of the recipients, and the sizes of the transplants were measured. GDNF increased transplant survival and growth. On day 42, all rats were sacrificed, and the grafts were evaluated by cresyl-violet staining and by immunohistochemistry using antibodies raised against neurofilament (NF), tyrosine hydroxylase, or glial fibrillary acidic protein (GFAP), as well as the following monoclonal antibodies: OX-38 anti-CD4, OX-8 anti-CD8, OX-18 anti-MHC class I, OX-6 anti-MHC class II, OX-42 anti-CD11b, R-73 anti-alpha and anti-beta T-cell receptor, and ED1 raised against monocytes/macrophages. BDNF-treated grafts showed only weak immunoreactivity, and even weaker reactions were seen in grafts treated with NT-3, GDNF, or CC. No single immune system marker was significantly elevated in grafts from any treatment group. We used OX-42 and ED1 to study possible alterations of microglial components. Ramified microglial cells were found in GDNF-treated grafts and to a lesser extent in NT-3 and BDNF-treated grafts. ED1-labeled reactive microglial components were found in NT-3- and BDNF-treated grafts. Additionally, large and rounded OX-42-positive phagocytic cells were found in NT-3-treated grafts. Together with our previous finding that GDNF treatment of spinal cord transplants activates immune responses and leads to microglial activation, our data demonstrate that although treatment with GDNF and to some degree with BDNF can enhance immune responses to immunogenic grafts, such as fetal spinal cord grafts, but the trophic factors per se do not elicit any marked response in non-immunogenic grafts like substantia nigra.

Depletion of nigrostriatal and forebrain tyrosine hydroxylase by S-adenosylmethionine: a model that may explain the occurrence of depression in Parkinson's disease

The loss of nigrostriatal tyrosine hydroxylase (TH), dopamine and dopaminergic neurons are the major pathology of Parkinson's disease (PD). These catecholaminergic changes are responsible for the symptoms of tremor, hypokinesia and rigidity. Depression is also a major symptom in PD, but the cause is unknown. The impairments of catecholaminergic fibers in the frontal lobe may be involved, because the frontal lobe of the cerebrum is involved in the regulation of mood, and decreased catecholaminergic activity in the frontal lobe is related to behavioral depression. The changes that damage the nigrostriatal dopamine system and induce motor impairments may also damage the forebrain catecholamine fibers and induce depression. It means that manipulations that damage the nigrostriatum (NS) and induce parkinsonism may also deplete TH in the frontal cortex. Such an effect would suggests a basis for the depression seen in PD. The injection of S-adenosyl-L-methionine (SAM), the biological methyl donor, into the brain of rats damaged the NS, depleted TH and caused tremor and hypokinesia. SAM may interfere also with the forebrain TH, which may help to explain the occurrence of depression in PD. Experiments were designed to test such a hypothesis. The results showed that SAM caused a loss of immunoreactive nerve fibers and it decreased the intensity of TH-immunoreactivity (IR) in the frontal cortex. These changes were accompanied with the loss of cells and the depletion of TH-IR from nerve fibers in the SN and the caudate nucleus. Other studies showed that SAM depletes DA and since SAM induces PD-like changes the results may be relevant to the co-occurrence of PD symptoms and depression. A single biological manipulation may impair the nigrostriatal dopaminergic neurons as well as the frontal cortex catecholaminergic fibers.

Efferent connections of the caudal part of the globus pallidus in the rat

The efferent connections of the caudal pole of the globus pallidus (GP) were examined in the rat by employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L), and the retrograde transport of fluorescent tracers combined with choline acetyltransferase (ChAT) or parvalbumin (PV) immunofluorescence histochemistry. Labeled fibers from the caudal GP distribute to the caudate-putamen, nucleus of the ansa lenticularis, reuniens, reticular thalamic nucleus (mainly its posterior extent), and along a thin strip of the zona incerta adjacent to the cerebral peduncle. The entopeduncular and subthalamic nuclei do not appear to receive input from the caudal GP. Descending fibers from the caudal GP course in the cerebral peduncle and project to posterior thalamic nuclei (the subparafascicular and suprageniculate nuclei, medial division of the medial geniculate nucleus, and posterior intralaminar nucleus/peripeduncular area) and to extensive brainstem territories, including the pars lateralis of the substantia nigra, lateral terminal nucleus of the accessory optic system, nucleus of the brachium of the inferior colliculus, nucleus sagulum, external cortical nucleus of the inferior colliculus, cuneiform nucleus, and periaqueductal gray. In cases with deposits of PHA-L in the ventral part of the caudal GP, labeled fibers in addition distribute to the lateral amygdaloid nucleus, amygdalostriatal transition area, cerebral cortex (mainly perirhinal, temporal, and somatosensory areas) and rostroventral part of the lateral hypothalamus. Following injections of fluorescent tracer centered in the lateral hypothalamus, posterior intralaminar nucleus, substantia nigra, pars lateralis, or lateral terminal nucleus, a substantial number of retrogradely labeled cells is observed in the caudal GP. None of these cells express ChAT immunoreactivity, but, except for the ones projecting to the lateral hypothalamus, a significant proportion is immunoreactive to PV. Our results indicate that caudal GP efferents differ from those of the rostral GP in that they project to extensive brainstem territories and appear to be less intimately related to intrinsic basal ganglia circuits. Moreover, our data suggest a possible participation of the caudal GP in feedback loops involving posterior cortical areas, posterior striatopallidal districts, and posterior thalamic nuclei. Taken as a whole, the projections of the caudal GP suggest a potential role of this pallidal district in visuomotor and auditory processes.

The spontaneous release of acetylcholinesterase in rat substantia nigra is altered by local changes in extracellular levels of dopamine

Acetylcholinesterase release in the guinea-pig substantia nigra has been previously investigated 'on-line', using a sensitive chemiluminescent system. Since histological observations suggest that there is a difference in acetylcholinesterase distribution in the rat substantia nigra compared to that of the guinea-pig, the first aim of the present study was to use this chemiluminescent method to characterise acetylcholinesterase release in this brain region of the freely moving rat, and the second was explore the relationship between acetylcholinesterase release and dopamine systems in this region. Accordingly, acetylcholinesterase release in the rat substantia nigra was studied under basal conditions of spontaneous release and following the local administration of (a) elevated potassium ions (30, 45, 60'mM), (b) a stimulator of dopamine/acetylcholinesterase release-D-amphetamine (10(-7), 10(-6) and 10(-5) M), (c) an inhibitor of dopamine uptake-GBR12909 (10(-7), 10(-6) and 10(-5) M). Spontaneous release of acetylcholinesterase in this brain region of the rat appears to be comparable with that observed in the guinea-pig, despite the smaller number of acetylcholinesterase-containing neurones. Furthermore, not only elevated potassium ions, but D-amphetamine as well as GBR12909, all produced significant increases in the percentage spontaneous release of acetylcholinesterase. Thus, the release of acetylcholinesterase in this region may be triggered by levels of dopamine outside of the neurone.

Cytochrome c oxidase defects of the human substantia nigra in normal aging

Based on morphological, biochemical, and molecular biologic analyses, degeneration of the dopaminergic nigrostriatal system has been reported to occur with normal aging. In the present study, the substantia nigra of 36 human brains with normal aging was investigated by means of morphometry and immunohistochemistry. The anteromedial (Am), anterointermediolateral (Ail), posteromedial (Pm), and posterolateral (Pl) nuclei of the substantia nigra were analyzed using antibodies directed against the subunits II/III of cytochrome c oxidase (COX), the complex IV of the respiratory chain. The numerical density of melanin-positive neurons with COX defects was significantly increased in the four investigated nuclei, namely Am, Ail, Pm, and Pl. These cells did not show any histologic signs of degeneration. The numerical density of melanin-positive neurons without COX defects was decreased with aging. The data of the present study indicate that complex IV defects of neurons in the substantia nigra might be one cause of neuronal dysfunction occurring during aging.

Glycoxidation and oxidative stress in Parkinson disease and diffuse Lewy body disease

Oxidative stress is well accepted as an important pathogenic factor in Parkinson disease, based largely on indirect evidence. Recently, we have developed antibodies that recognize specific advanced glycation end-products (anti-pentosidine and anti-pyrraline), protein modifications that are potentiated by oxidative stress in a process termed glycoxidation. We applied these antibodies immunocytochemically to affected regions in Parkinson disease and diffuse Lewy body disease brains. Additionally, we used antibodies to heme oxygenase-1, a putative marker of oxidative stress response. Immunoreactivity to pentosidine, pyrraline, and heme oxygenase-1 was seen in the substantia nigra of Parkinson disease and the neocortex of diffuse Lewy body disease. Heme oxygenase-1 was further demonstrated by immunoelectron microscopy in intimate association with filaments of cortical Lewy bodies. Immunolocalization of advanced glycation end-products and a marker of oxidative stress response induction provides evidence that glycoxidation and oxidative stress may be an important pathogenic factor in diseases characterized by Lewy body formation, and furthers the evidence that cytoskeletal proteins and their inclusions are susceptible to oxidative stress.

Inhibition of neuronal nitric oxide synthase prevents MPTP-induced parkinsonism in baboons

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces clinical, biochemical and neuropathologic changes reminiscent of those which occur in idiopathic Parkinson's disease. 7-Nitroindazole (7-NI) is a relatively selective inhibitor of the neuronal isoform of nitric oxide synthase (NOS) that blocks MPTP neurotoxicity in mice. We now show that 7-NI protects against profound striatal dopamine depletions and loss of tyrosine hydroxylase-positive neurons in the substantia nigra in MPTP-treated baboons. Furthermore, 7-NI protected against MPTP-induced motor and frontal-type cognitive deficits. These results strongly implicate a role of nitric oxide in MPTP neurotoxicity and suggest that inhibitors of neuronal NOS might be useful in treating Parkinson's disease.

Dopamine neurons from transgenic mice with a knockout of the p53 gene resist MPTP neurotoxicity

We have examined MPTP toxicity to dopamine neurons of mice homozygous for a transgenic knockout of the p53 growth control gene (p53-/-). MPTP at a total dose of 96 mg/kg administered in four doses over two days produced a non-homogeneous loss of striatal dopamine transport sites and quantitatively reduced 3H-mazindol binding to similar degrees in p53-/- and wild type controls 2 and 3 weeks after starting MPTP. Nigral DA neurons stained immunohistochemically for tyrosine hydroxylase were counted using both manual and automated methods and found to be reduced 29-34% in wild type controls but were not reduced in p53-/-. Mean DA neuronal surface areas were reduced 63-68% by MPTP in controls and 35-50% in p53-/-. We conclude that p53 protein appears necessary for complete expression of MPTP neurotoxicity to dopamine neurons. Our findings suggest that the p53 gene and other growth control genes may regulate dopamine neuronal death in PD.

A transgenic mouse model to study transsynaptic regulation of tyrosine hydroxylase gene expression

Previous studies demonstrated that 9 kb of the rat tyrosine hydroxylase (TH) 5' flanking sequence directed appropriate spatiotemporal expression of a lacZ reporter gene to catecholaminergic cells in the CNS of transgenic mice. In the present study, specificity of transgene expression was further extended to demonstrate cell type-specific functional regulation of lacZ expression using manipulations known to alter endogenous TH expression. Alterations in lacZ reporter expression should parallel changes in endogenous TH levels if the DNA elements mediating these functional changes of TH expression in vivo reside within the 9 kb of the TH promoter region. Naris closure induced an activity-dependent decrease of TH expression in dopaminergic periglomerular cells in the olfactory bulb that was paralleled by down-regulation of lacZ expression in the transgenic mice. Densitometry and image analysis were used to quantify lacZ expression following acute reserpine administration (5 mg/kg s.c.), which up-regulates endogenous TH. At 48 h postinjection, analysis of OD values indicated a significant increase of X-gal staining in the locus coeruleus and ventral tegmental area but not in the substantia nigra or olfactory bulb of reserpine-treated transgenic animals. These data showed that the 9-kb sequence also mediates cell type-specific transsynaptic regulation of reporter gene expression. Analysis of this transgenic animal offers a useful model system to study in vivo regulation of TH gene expression.

Coexistence of NADPH-diaphorase and tyrosine hydroxylase in the mesencephalic catecholaminergic system of the Japanese quail

Previous studies have shown the presence of a large number of tyrosine hydroxylase immunoreactive neurons and nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase positive elements within the mesencephalic and pontine regions of the Japanese quail. In the present study histochemical and immunohistochemical procedures reveal that cells expressing at least one of these two neurochemical markers coexist throughout a large part of the substantia nigra and of the area ventralis of Tsai. Also about 40% of the neurons in these two regions that contain immunoreactive tyrosine hydroxylase also exhibit NADPH-diaphorase activity. This is not a general property of the quail catecholaminergic system: in the locus coeruleus (the main noradrenergic group) there is a complete separation between these two neuronal populations. The number of neurons expressing either neurochemical marker is not different between males and females in any of the regions that have been investigated. NADPH-diaphorase is known to be an indicator of the enzyme nitric oxide synthase; these results therefore suggest that nitric oxide may play an important role in the regulation of the activity of a significant part of the avian mesencephalic dopaminergic system.

Does monoamine oxidase type B play a role in dopaminergic nerve cell death in Parkinson's disease?

Evidence supports the role of hyperoxidation phenomena in the mechanism of nerve cell death in Parkinson's disease (PD). The oxidative degradation of dopamine, catalyzed by monoamine oxidase type B (MAO-B), produces free radicals and thus could be implicated in the degenerative process. For this reason, we investigated by immunohistochemistry the distribution of MAO-B-containing cells in the midbrain of five patients with PD and five matched control subjects. MAO-B-like immunoreactivity was detected in glial cells, fibers, and neurons. Although most of the MAO-B-positive neurons probably belonged to the raphe dorsalis, we demonstrated by double-labeling immunohistochemistry that some of them were also dopaminergic. MAO-B-positive dopaminergic neurons were present in all dopaminergic groups of the control midbrain. Within the substantia nigra pars compacta, most dopaminergic neurons were located in the dorsal part of the structure. MAO-B-positive dopaminergic neurons were still detected in PD midbrains. Compared with control subjects, the loss of dopaminergic neurons containing MAO-B (-45%) was no higher than that of MAO-B-negative dopaminergic neurons (-59%). The density of MAO-B-positive glial cells varied in the control midbrains: high in the least affected dopaminergic group (the central gray substance) and low in the most affected region (the substantia nigra pars compacta). The density of MAO-B-positive glial cells within dopaminergic cell subgroups in control midbrains were negatively correlated (r = -0.94; p < 0.02) to the estimated neuronal loss in PD. We conclude that the presence of MAO-B in dopamine-containing neurons does not contribute to vulnerability in PD. Moreover, its presence in some glial cells might have a protective effect against oxidative stress induced by dopamine metabolism.

Intrastriatal and intraventricular infusion of brain-derived neurotrophic factor in the cynomologous monkey: distribution, retrograde transport and co-localization with substantia nigra dopamine-containing neurons

The distribution and retrograde transport of brain-derived neurotrophic factor was examined using magnetic resonance imaging guided stereotaxic intracerebroventricular and intrastriatal infusion in the cynomologous monkey. Two intracerebroventricular animals were infused with brain-derived neurotrophic factor at a dose of 3 micrograms/h for 21 and 28 days. A third intracerebroventricular animal received sequential infusions of 15, 30 and 60 micrograms/h brain-derived neurotrophic factor each for seven days using an Alzet 2002 minipump. For the multiple intrastriatal animals (n = 5) a dose of 3 micrograms/h was infused into each site. One intrastriatal monkey was infused with vehicle solution of 10 mM phosphate-buffered saline pH 7.4 for 14 days resulting in no brain-derived neurotrophic factor immunoreactivity. Following the lower dose intracerebroventricular infusion, brain-derived neurotrophic factor immunoreactivity was confined to the ventricular ependymal layer. In the sequential higher dose intracerebroventricular case, the cannula was located mainly within the lateral ventricle, although there was damage to the ependymal wall and adjacent caudate nucleus. Brain-derived neurotrophic factor immunoreactivity revealed spread of injectate within the ipsilateral and to a lesser extent the contralateral caudate nucleus, septum, orbital cortex and ventricular ependymal wall. In this case, retrogradely labelled brain-derived neurotrophic factor neurons were found within the parafascicular thalamus and substantia nigra, pars compacta, as well as within cortex, vertical limb of the diagonal band and nucleus basalis. Brain-derived neurotrophic factor intrastriatal infusion retrogradely labelled perikarya within sensory motor cortex, parafascicular thelamus and substantia nigra, pars compacta. Sections from these cases dual-immunoreacted for brain-derived neurotrophic factor and tyrosine hydroxylase, the synthesizing enzyme for dopamine, revealed a subpopulation of pars compacta dopaminergic neurons which contained retrogradely transported brain-derived neurotrophic factor. These findings indicate that a select subgroup of nigral dopamine neurons retrogradely transport brain-derived neurotrophic factor in the primate. Furthermore it remains to be determined whether select nigral cells are responsive to the trophic influences of brain-derived neurotrophic factor in the normal and neuropathologic condition.

Influence of the thyroid hormone status on tyrosine hydroxylase in central and peripheral catecholaminergic structures

We investigated the effect of hyper- and hypothyroidism on tyrosine hydroxylase protein concentration in the locus coeruleus (divided into anterior and posterior parts), the substantia nigra and the adrenals of adult rats. Rats were made hypothyroid with propylthiouracile (PTU, 0.02% in drinking water for 21 days) or hyperthyroid by thyroxine injection (100 or 250 micrograms/kg/day), for 3 or 17 days. PTU treatment resulted in statistically significant decrease of tyrosine hydroxylase in the anterior locus coeruleus (-13%) and the adrenals (-14%). After thyroxine treatment, in the anterior locus coeruleus, tyrosine hydroxylase was significantly higher (2 way ANOVA) after the 3 day treatment than after the 17 day treatment: tyrosine hydroxylase showed a trend to increase the 3 day treatment (+20% with the 250 micrograms/kg dose) and to decrease after the 17 day treatment (-15% with the 250 micrograms/kg dose). In the adrenals, tyrosine hydroxylase was increased by the 3 day treatment (+42% after the 250 micrograms/kg dose), but this increase was not observed after 17 days of treatment. Tyrosine hydroxylase was not altered in the posterior locus coeruleus and the substantia nigra, whatever the treatment. Together, our results support the hypothesis that in the anterior locus coeruleus and in the adrenals tyrosine hydroxylase level is positively modulated by thyroid hormones. After long-term treatment (17 days) this effect is not observed.

Dopaminergic sprouting in the rat striatum after partial lesion of the substantia nigra

The capacity of the dopaminergic nerve system to reinnervate the denervated adult striatum was analyzed in a model of partial 6-hydroxydopamine-induced unilateral lesion of rat substantia nigra pars compacta. Sprouting of dopaminergic fibers entering the ventrolateral part of the striatum from a narrow zone of the external capsule was detected on the lesioned side 4 and 7 months, but not 10 days, after lesioning. Ultrastructural examination of the zone of sprouting revealed hypertrophic dopaminergic fibers and growth-cone-like structures, confirming the existence of an ongoing process of spontaneous regrowth of dopaminergic fibers. The identification of the factors involved in the regrowth of dopaminergic fibers may help to orientate molecular research into new treatments for Parkinson's disease.

Immunohistochemical studies of mesolimbic dopaminergic neurons in Fischer 344 and Lewis rats

Previous work has shown that the inbred Lewis and Fischer 344 rat strains differ in several behavioral measures related to mesolimbic dopamine function. Moreover, the ventral tegmental area (VTA) of the Lewis rat has been shown to contain higher levels of tyrosine hydroxylase compared to that of the Fischer rat by blot immunolabeling procedures. To investigate structural correlates of this biochemical difference, an immunohistochemical study of VTA dopaminergic neurons in these two strains was undertaken. Results show that the density and total number of tyrosine hydroxylase-positive neurons in the VT 4 of the Lewis rat is about 50% of that found in the Fischer rat. In contrast, examination of the substantia nigra in the same sections revealed no differences in the density and number of tyrosine hydroxylase-positive cells between these strains. Fischer-Lewis strain differences were also evident for cholecystokinin immunoreactivity in the VTA, with much lower levels seen in the Lewis rat, consistent with the known colocalization of this neuropeptide in many VTA dopamine neurons. The finding of 50% fewer tyrosine hydroxylase-positive neurons in the VTA of the Lewis rat, along with our earlier results showing 45% higher levels of tyrosine hydroxylase by blot immunolabeling, would suggest much higher levels of tyrosine hydroxylase per VTA neuron in this strain. However, no obvious strain difference in the cellular intensity of tyrosine hydroxylase immunoreactivity could be detected by immunohistochemistry. Finally, the density of VTA dopamine neurons was assessed in 1-week-old Fischer and Lewis rats. In contrast to the results obtained for adult animals, no difference in the number of tyrosine hydroxylase-positive neurons was apparent in these young animals, indicating that the Fischer-Lewis strain difference in VTA dopamine neurons appears later in postnatal development. These anatomical findings shed new light on the differences in the mesolimbic dopamine system between Fischer and Lewis rats that may contribute to the behavioral differences exhibited by these animals.

Oxidative inactivation of tyrosine hydroxylase in substantia nigra of aged rat

Study of the tyrosine hydroxylase enzyme from substantia nigra and striatum during the aging period of the rat has discovered a significant decrease (55%) of TH activity in substantia nigra between 12 and 24 mo of age. The amount of TH in substantia nigra also decreased (30%) during aging. This loss in TH activity of substantia nigra appears to be produced by the decrease in TH content along with an inactivation process. Our finding showed a significant increase of carbonyl groups in the proteins of rat substantia nigra with aging. A statistically significant increase of carbonyl groups in TH enzyme was found in aged rat brain substantia nigra, indicating that oxidative damage could be the inactivation process that explains the decrease in TH activity found during aging. This hypothesis was corroborated by the fact that when rat striatal homogenate was incubated with hydrogen peroxide, there was a time-dependent decrease in TH activity, which highly correlated with measurements of carbonyl groups content of TH enzyme. The importance of these results may be in their relationship, considering that substantia nigra is preferentially affected in many neurodegenerative disorders.

The influence of target and non-target brain regions on the development of mid-brain dopaminergic neurons in organotypic slice culture

The development and regeneration of rat dopaminergic neurons of the ventral mesencephalon was studied in organotypic slice cultures. Single ventral mesencephalon cultures and co-cultures of ventral mesencephalon with striatum (a target region) or cerebellum (a non-target region) were prepared from postnatal day 1 Wistar rats. Cultures were processed for tyrosine hydroxylase and glial fibrillary acidic protein immunoreactivity, at two day intervals, for an overall incubation period of 20 days. Analysis of these cultures revealed that the striatal target tissue, exerted neither a trophic nor a tropic influence on the tyrosine hydroxylase immunoreactive neurons. In both single and co-cultures, tyrosine hydroxylase immunoreactive neurites projected radially from the ventral mesencephalon slice. However, in striatal co-cultures, tyrosine hydroxylase immunoreactive neurites were seen penetrating the striatal slice, whereas in cerebellar co-cultures no tyrosine hydroxylase immunoreactive neurites entered the cerebellar tissue. Glial fibrillary acidic protein positive cells actively migrated from the tissue sections, however tyrosine hydroxylase immunoreactive neurite outgrowth was not guided by these glial cells. Tyrosine hydroxylase immunoreactive neurites terminated once they had penetrated the striatal slice. This retardation of neurite growth by a target region could be important in establishing and reinforcing synaptic connections in the developing nigro-striatal pathway.

Time of neuron origin and gradients of neurogenesis in midbrain dopaminergic neurons in the mouse

Previous [3H]thymidine studies in Nissl-stained sections in rats established that the substantia nigra pars compacta and the ventral tegmental area originate sequentially according to an anterolateral to posteromedial neurogenetic gradient. We investigated whether that same pattern is found in mice in the dopaminergic neurons in each of these structures. Using tyrosine hydroxylase immunostaining combined with [3H]thymidine autoradiography, the time of origin of dopaminergic midbrain neurons in the retrorubral field, the substantia nigra pars compacta, the ventral tegmental area, and the interfascicular nucleus was determined in postnatal day 20 mice. The dams of the experimental animals were injected with [3H]thymidine on embryonic days (E) 11-E12, E12-E13, E13-E14, and E14-E15. The time of origin profiles for each group indicated significant differences between populations. The retrorubral field and the substantia nigra pars compacta arose nearly simultaneously and contained the highest proportion of neurons, 49 to 37%, generated on or before E11. Progressively fewer early-generated neurons were found in the ventral tegmental area (20%), and the interfascicular nucleus (8.5%). In addition, anterior dorsolateral neurons in the substantia nigra and ventral tegmental area were more likely to be generated early than the posterior ventromedial neurons. These findings indicate that mouse and rat brains have nearly identical developmental patterns in the midbrain, and neurogenetic gradients in dopaminergic neurons are similar to those found in Nissl studies in rats.

Changes in steady-state levels of tryptophan hydroxylase protein in adult rat brain after neonatal 6-hydroxydopamine lesion

A recently developed technique of immunoautoradiography on nitrocellulose transfers of serial frozen sections was used to determine tryptophan hydroxylase concentration in selected areas of the adult rat brain following neonatal 6-hydroxydopamine destruction of nigrostriatal dopamine neurons. Particular attention was paid to the neostriatum, known to be serotonin-hyperinnervated under these conditions, and to the nucleus raphe dorsalis, containing the cell bodies of origin for these nerve terminals. The hippocampus was also investigated as a territory of structurally intact serotonin innervation arising primarily from the nucleus raphe medianus. Tryptophan hydroxylase protein was measured at successive transverse levels across the entire caudorostral extent of all these regions. Similar measurements of tyrosine hydroxylase protein across the substantia nigra and the neostriatum verified the disappearance of the nigrostriatal dopamine neurons. The average tryptophan hydroxylase tissue concentration in the dorsal third of the serotonin-hyperinnervated neostriatum was up by 36% above control, i.e. significantly less than the number of its serotonin axon terminals or varicosities. This was therefore indicative of a lowering of the tryptophan hydroxylase protein content per serotonin ending. Interestingly, a tight correlation between the respective level-by-level concentrations of tryptophan hydroxylase and tyrosine hydroxylase protein in the control neostriatum allowed the prediction the tryptophan hydroxylase concentration after dopamine denervation with a serotonin hyperinnervation. Tryptophan hydroxylase concentration was also significantly reduced in both the nucleus raphe dorsalis and nucleus raphe medianus, notably at those raphe dorsalis levels known to give rise to the serotonin hyperinnervation of neostriatum. It is hypothesized that the lower steady-state level of tryptophan hydroxylase inside the terminals and cell bodies of hyperinnervating serotonin neurons was the result of a feedback inhibition of the synthesis of the enzyme by its end-product, presumably because of the increased amount of serotonin in these terminals.

Absence of the mitochondrial A7237T mutation in Parkinson's disease

In recent years much has been speculated about a pathogenic role of mitochondrial defects in Parkinson's disease. Ozawa et al. (BBRC 176, 938-946, 1991) have described an A/T transversion at nucleotide 7237 of mitochondrial DNA affecting cytochrome-c-oxidase (complex IV) of the respiratory chain that could contribute to the pathogenesis of PD. Employing PCR based genomic sequencing and restriction enzyme analysis on 19 cases of Lewy-body parkinsonism, we exclude this mutation as a common cause of Parkinson's disease. This demonstrates the need for systematic sequencing of the mitochondrial genome in a large number of histologically verified cases of Parkinson's disease.

Excitotoxic action of NMDA agonists on nigrostriatal dopaminergic neurons: modulation by inhibition of nitric oxide synthesis

Focal infusions of N-methyl-D-aspartate (NMDA) or an endogenous NMDA agonist, quinolinic acid (QUIN), into the substantia nigra pars compacta (SNc) of adult Sprague-Dawley rats resulted in a dose-dependent depletion of ipsilateral striatal tyrosine hydroxylase (TH) activity, a biochemical marker for dopaminergic neurons. To assess the intermediary role of nitric oxide in the neurotoxicity elicited by these toxins, their action was tested in animals treated with N omega-nitro-L-arginine methyl ester (L-NAME). Systemic injections (2 injections; 8 h apart) of L-NAME (100, 150 and 250 mg/kg) produced a dose-related inhibition of cerebellar nitric oxide synthase (NOS) activity. The time-course of cerebellar NOS inhibition following L-NAME (250 mg/kg) was rapid in onset and lasted for at least 24 h following the second injection. An L-NAME treatment regimen of 250 mg/kg, with the second injection given 24 h prior to assessment of NOS activity, produced an 87 and 91% inhibition of cerebellar and nigral NOS activity, respectively. Intranigral infusion of 40 and 60 nmol QUIN reduced ipsilateral striatal TH activity by 62 and 75%, respectively. However, 40 and 60 nmol QUIN infusions into animals pretreated with L-NAME (250 mg/kg) reduced striatal TH activity by 83 and 96%, respectively. Intranigral infusion of 15 and 30 nmol NMDA produced a 48 and 77% decrease in striatal TH activity, respectively, whereas the same doses of NMDA given to animals pretreated with L-NAME (250 mg/kg) resulted in a 59 and 88% decrease in TH activity.(ABSTRACT TRUNCATED AT 250 WORDS)