Angiotensin II receptor binding associated with nigrostriatal dopaminergic neurons in human basal ganglia

In the human brain, receptor binding sites for angiotensin are found in the striatum and in the substantia nigra pars compacta overlying dopamine-containing cell bodies. In contrast, angiotensin-converting enzyme occurs in the substantia nigra pars reticulata and is enriched in the striosomes of the striatum. In this study, using quantitative in vitro autoradiography, we demonstrate decreased angiotensin receptor binding in the substantia nigra and striatum of postmortem brains from patients with Parkinson's disease. In the same brains the density of binding to angiotensin-converting enzyme shows no consistent change. We propose, from these results, that angiotensin receptors in the striatum are located presynaptically on dopaminergic terminals projecting from the substantia nigra. In contrast, the results support previous studies in rats demonstrating that angiotensin-converting enzyme is associated with striatal neurons projecting to the substantia nigra pars reticulata. These findings raise the possibility that newly emerging drugs that interact with the angiotensin system, particularly converting enzyme inhibitors and new nonpeptide angiotensin receptor blockers, may modulate the brain dopamine system.     

Effects of neonatal dopamine depletion on sensory inhibition in the rat

Central dopamine systems appear to play an important role in sensory information processing. In particular, the filtering (or gating) of repetitive auditory stimuli is modulated by pharmacological manipulations that affect dopaminergic neurotransmission. The present study further addressed the role of dopamine in auditory gating. Three-day-old male Sprague-Dawley rats, pretreated with desipramine, received intracisternal injections of 6-hydroxydopamine (6-OHDA; 75 micrograms in 10 microliters) or the vehicle. At 4 months of age the rats were implanted for evoked potential recording and auditory gating was assessed using a paired click paradigm. Neonatally administered 6-OHDA did not alter gating in the adult rats. However, unlike for the control group, systemic amphetamine (1.83 mg/kg, IP) failed to disrupt gating in the treated rats. Apomorphine (1.0 mg/kg, SC) disrupted gating in both groups. Neonatal 6-OHDA treatment caused significant reductions in dopamine levels in the striatum, nucleus accumbens, and substantia nigra/ventral tegmental regions. There was an inverse relationship between substantia nigra/ ventral tegmental area dopamine levels and auditory gating. Overall, the results suggest that amphetamine-induced auditory gating loss requires presynaptic dopamine release, but that the deficiency occurs through postsynaptic dopamine receptor activation.     

Rapid tolerance and crosstolerance to motor impairment effects of benzodiazepines, barbiturates, and ethanol

Susceptibility to develop Parkinson's disease has been linked to abnormalities of P450 enzyme function. Multiple P450 enzymes are expressed in brain but the relationship of these to Parkinson's disease is unknown. We have investigated the expression of P450 enzymes in the rat substantia nigra and their co-localization in tyrosine hydroxylase-positive neurons and astrocytes. Immunohistochemistry was performed using anti-peptide antisera against the following P450 enzymes: CYP1A1, CYP1A2, CYP2B1/2, CYP2C12, CYP2C13/2C6, CYP2D1, CYP2D4, CYP2E1, CYP3A1, CYP3A2 and NADPH-P450 oxidoreductase. Immunoreactivity in nigral cells was found only for CYP2E1 and CYP2C13/2C6. CYP2E1 immunoreactivity was localized to many midbrain nuclei including the substantia nigra pars compacta but not the substantia nigra pars reticulata while immunoreactivity to CYP2C13/2C6 was found in the substantia nigra pars compacta, substantia nigra pars reticulata and many other midbrain nuclei. Sections of rat midbrain double labelled for either CYP2E1 or CYP2C13/2C6 and tyrosine hydroxylase or glial fibrillary acidic protein were examined for co-localization by confocal laser scanning microscopy. CYP2E1 and CYP2C13/2C6 immunoreactivity was found in tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta but not in glial cells. CYP2C13/2C6, but not CYP2E1, was also found in non-glial, non-tyrosine hydroxylase-expressing cells in the substantia nigra pars reticulata. Isoniazid induction increased CYP2E1 fluorescence signal intensity from nigral dopaminergic neurons. At least two P450 enzymes are found in nigral dopamine containing cells and one, namely CYP2E1, is selectively localized to this cell population. CYP2E1 is a potent generator of free radicals which may contribute to nigral pathology in Parkinson's disease. The expression of CYP2E1 in dopaminergic neurons in substantia nigra raises the possibility of a causal association with Parkinson's disease.     

Co-expression of dopamine transporter mRNA and tyrosine hydroxylase mRNA in ventral mesencephalic neurones

Radioactive in situ hybridization was used to map the cellular localization of dopamine (DA) transporter mRNA-containing cells in the adult rat central nervous system. The distribution of DA transporter mRNA-containing cells was compared to adjacent sections processed to visualize tyrosine hydroxylase (TH) mRNA, a marker of catecholamine containing neurones. TH mRNA-containing cells, visualized using an alkaline phosphatase labelled probe, were detected in the hypothalamus, midbrain and pons; the strongest hybridization signals being detected in the substantia nigra, ventral tegmental area and locus coeruleus. The distribution of DA transporter mRNA-containing cells was more restricted; a strong signal being detected in the substantia nigra pars compacta and ventral tegmental area only. No hybridization signal was detected in the locus coeruleus. By simultaneously hybridizing mesencephalic tissue with both the alkaline phosphatase-labelled TH probe and the 35S-labelled DA transporter probe we were able to demonstrate that both DA transporter and TH mRNAs are expressed by the same cells in the substantia nigra and ventral tegmental area. The restricted anatomical localization of DA transporter mRNA-containing cells and the lack of expression in the locus coeruleus and other adrenergic and noradrenergic cell groups confirms the DA transporter as a presynaptic marker of DA containing nerve cells in the rat brain.     

Dopamine receptors status after unilateral nigral 6-OHDA lesion. Autoradiographic and in situ hybridization study in the rat brain

The physiological effects of dopamine (DA) are mediated by several distinct receptor subtypes. The effects of unilateral nigral 6-hydroxydopamine (6-OHDA) lesions on DA receptors were investigated by receptor autoradiography using the D1 selective ligand [3H]SCH 23390 as well as the D2 ligand [3H]spiroperidol. mRNA distribution was studied by in situ hybridization. Lesioned rats were sacrificed at different time intervals. Receptor binding studies were performed on tissue sections using selective ligands. [35S]UTP labeled RNA probes were prepared from the different cDNA (D1, D2, D3) and used for in situ hybridization. A specific loss of receptor binding sites and mRNA hybridization was found in the lesioned substantia nigra pars compacta (SNc) at all times examined. Receptor binding studies revealed a different time-dependent increase in both D1 and D2 receptors. In situ hybridization showed that only D2 receptor mRNA increased in the caudate-putamen (CPu) of the lesioned side 15 d after 6-OHDA. No changes were observed in D1 and D3 receptor mRNA during the entire time-course.     

Electrophysiological studies of rat substantia nigra neurons in an in vitro slice preparation after middle cerebral artery occlusion

We studied sequential changes in electrophysiological profiles of the ipsilateral substantia nigra neurons in an in vitro slice preparation obtained from the middle cerebral artery-occluded rats. Histological examination revealed marked atrophy and neurodegeneration in the ipsilateral substantia nigra pars reticulata at 14 days after middle cerebral artery occlusion. Compared with the control group, there was no significant change in electrical membrane properties and synaptic responses of substantia nigra pars reticulata neurons examined at one to two weeks after middle cerebral artery occlusion. On the other hand, there was a significant increase in the input resistance and spontaneous firing rate of substantia nigra pars compacta neurons at 13-16 days after middle cerebral artery occlusion. Furthermore, inhibitory postsynaptic potentials evoked by stimulation of the subthalamus in substantia nigra pars compacta neurons was suppressed at five to eight days after middle cerebral artery occlusion. At the same time excitatory postsynaptic potentials evoked by the subthalamic stimulation was increased. Bath application of bicuculline methiodide (50 microM), a GABA(A) receptor antagonist, significantly increased the firing rate of substantia nigra pars compacta neurons from intact rats. These results strongly suggest that changes in electrophysiological responses observed in substantia nigra pars compacta neurons is caused by degeneration of GABAergic afferents from the substantia nigra pars reticulata following middle cerebral artery occlusion. While previous studies indirectly suggested that hyperexcitation due to deafferentation from the neostriatum may be a major underlying mechanism in delayed degeneration of substantia nigra pars reticulata neurons after middle cerebral artery occlusion, the present electrophysiological experiments provide evidence of hyperexcitation in substantia nigra pars compacta neurons but not in pars reticulata neurons at the chronic phase of striatal infarction.     

NMDA-NR1 receptor subunit mRNA expression in rat brain after 6-OH-dopamine induced lesions: a non-isotopic in situ hybridization study

Antisense digoxigenin-labeled deoxyoligonucleotides probes and non-isotopic in situ hybridization (HIS) techniques have been used to explore the NMDA-NR1 receptor subunit mRNA distribution in different brain areas of rats which had their dopaminergic nigrostriatal pathway previously lesioned with intracerebral administration of 6-OH-dopamine (6-OH-DA). Intense and significant hybridization signals for NR1 mRNA were found in dentate gyrus and regions CA1-CA2-CA3 of the hippocampus, in layers II-III and V-VI of the cerebral cortex, and in the cerebellum of sham-treated rats. Basal ganglia structures such as the striatum exhibited few NR1 mRNA hybridization signals as compared to the hippocampus and cerebral cortex. In contrast, both zona compacta and reticulata of substantia nigra (SN) showed a reduced number of cells with nevertheless intense NR1 mRNA HIS signals. The NR1 mRNA distribution in the brain was affected in a brain regional selective manner by 6-OH-DA induced lesions of DA neuronal systems. A striking increase in NR1 mRNA HIS signals was observed in both striata after unilateral lesioning with 6-OH-DA. Instead, in SN compacta but not in reticulata, a moderate but significant bilateral reduction of NR1 mRNA was observed after unilateral 6-OH-DA injection. No significant changes in NR1 mRNA were detected in cerebral cortex and other brain regions after 6-OH-DA treatment. These studies, and others reported in the literature, support the view that extensive lesions of nigrostriatal DA-containing neurons in the brain may trigger compensatory or adaptative responses in basal ganglia structures such as striatum and substantia nigra which involve glutamateric neurons and the genic expression of NMDA receptors.     

Occurrence of heat shock response in deafferented neurons in the substantia nigra of rats

The substantia nigra is innervated by massive inhibitory GABAergic projections from the striatum and globus pallidus, deafferentation of which is supposed to lead to anterograde trans-synaptic degeneration of the nigral neurons. An immunohistochemical method was used to examine the induction of 72,000 mol. wt heat shock protein in the substantia nigra following cerebral hemitransection or transient middle cerebral artery occlusion. At three and four days post-transection, strong immunoreactivity for 72,000 mol. wt heat shock protein was found in the ipsilateral substantia nigra pars reticulata. Light microscopic observation revealed a number of pars reticulata neurons showing strong immunoreactivity for 72,000 mol. wt heat shock protein in their perikarya and proximal processes. In addition, Golgi-like stained neurons with dystrophic features were occasionally observed in the ipsilateral substantia nigra pars reticulata. The immunoreactivity for 72,000 mol. wt heat shock protein in the ipsilateral pars reticulata gradually declined and almost disappeared by 15 days after transection. No apparent induction of 72,000 mol. wt heat shock protein was found in the substantia nigra pars compacta throughout the time period examined. Massive striatal ischemic injury produced by transient middle cerebral artery occlusion also induced expression of 72,000 mol. wt heat shock protein in the pars reticulata neurons three and four days postoperatively. These findings suggest that deafferentation of the striatal or striatopallidal inputs per se is a harmful stress for the substantia nigra pars reticulata neurons, inducing 72,000 mol. wt heat shock protein synthesis. The present data may contribute to our understanding of the molecular basis of the pathomechanism of the transneuronal regression of substantia nigra pars reticulata neurons, which may occur after removal of inhibitory GABAergic inputs.     

Expression of metabotropic glutamate receptor 1 isoforms in the substantia nigra pars compacta of the rat

Metabotropic glutamate receptors, which are linked via G-proteins to second messenger systems, have been implicated in the physiological regulation of dopaminergic neurons of the substantia nigra pars compacta as well as in neurodegeneration. Of the eight known metabotropic glutamate receptors, metabotropic glutamate receptor 1 is the most abundant subtype in the substantia nigra pars compacta. Metabotropic glutamate receptor 1 is alternatively spliced at the carboxy terminal region to yield five variants: 1a, 1b, 1c, 1d and a form recently identified in human brain, 1g. We used an antibody recognizing metabotropic glutamate receptor 1, and another recognizing the splice form la only, to study the localization of these receptors in dopaminergic neurons identified by the presence of tyrosine hydroxylase. Metabotropic glutamate receptor immunoreactivity was present within the somata, axons, and dendrites of substantia nigra pars compacta neurons. The 1a splice form specific antibody, however, did not label these cells, suggesting that they express a metabotropic glutamate receptor 1 splice form different from 1a. In situ hybridization with splice form-specific oligonucleotide probes was used to determine which of the other known metabotropic glutamate receptor 1 splice forms might be present in the substantia nigra pars compacta. Each probe produced a very distinct labelling pattern in the rat brain with the exception of the 1g specific probe which produced only background signal. Substantia nigra pars compacta neurons were most intensely labelled by the metabotropic glutamate receptor 1d splice form specific probe. Metabotropic glutamate receptor 1a was expressed weakly whereas there was no detectable 1b, c, or g signal in the substantia nigra pars compacta. These data demonstrate that metabotropic glutamate receptor 1 protein is present within the perikarya and processes of dopaminergic neurons in the substantia nigra pars compacta. The majority of this protein is not the 1a splice form, which is abundant in other brain regions, and may be the 1d isoform. Since splicing alters the carboxy terminus of the receptor, it is likely to affect the interaction of the receptor with intracellular signalling systems.     

The relationship between striatal and mesolimbic dopamine dysfunction and the nature of circling responses following 6-hydroxydopamine and electrolytic lesions of the ascending dopamine systems of rat brain

The importance of extrapyramidal and mesolimbic function for circling behaviour was investigated by placing 6-hydroxydopamine (6-OHDA) and electrolesions in the cell bodies, axons and terminals of each system. Circling behaviour was weak when 6-OHDA was placed at the centre of the substantia nigra (SN), but the characteristic contralateral/ipsilateral turning to apomorphine/amphetamine were recorded. Circling was more marked when 6-OHDA was placed anterior to the SN but was generally absent following injections posterior to the SN. However, 6-OHDA placed in the medial forebrain bundle in the lateral hypothalamus resulted in intense contralateral/ipsilateral turning to apomorphine/amphetamine. Generally, the intensity of circling responses was related to the degree of striatal dopamine (DA) depletion but the more effective lesions also caused reductions in mesolimbic DA content. However, circling was not observed following any 6-OHDA injection into the mesolimbic DA system and it is concluded that mesolimbic DA function is not essential for the initiation of circling. In contrast to the 6-OHDA lesions, rats circled ipsilateral to both apomorphine and amphetamine when the SN was damaged by electrocoagulation to cause marked depletion of striatal dopamine. Lesser depletions of striatal dopamine after electrocoagulation in different regions of the medial forebrain bundle were associated with a lower intensity of ipsilateral circling to both drugs. In general, the differences between 6-OHDA and electrolesions could not be explained by additional damage to ascending noradrenaline or 5-hydroxytryptamine pathways. Lower doses of apomorphine were effective in the 6-OHDA circling rats, and the ipsilateral striatum of such rats was more sensitive to directly applied DA. Higher doses of apomorphine were required to produce circling after chronic electrolesions which rendered the ipsilateral striatum insensitive to DA. The contralateral circling to apomorphine after 6-OHDA lesions was abolished by chronic but not by acute electrolesion of the SN. It is suggested that electrolesions of the SN cause different effects to 6-OHDA because they destroy neuronal pathways in addition to the dopaminergic nigrostriatal tract. These appear to be required for the expression of circling behaviour caused by stimulation of the denervated striatum. Whereas 6-OHDA lesions result in super-sensitivity of the denervated strital DA receptors, electrolesions may cause a hypo-sensitivity of the same receptor sites.     

Effects of repeated administration of l-DOPA and apomorphine on circling behavior and striatal dopamine formation

We tested the circling response to l-DOPA and apomorphine administration in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra. Rats demonstrated a progressively diminished circling response when l-DOPA-carbidopa was repeatedly administered at 120 min intervals. This decreasing response was not present when apomorphine was administered under the same conditions. We also perfused l-DOPA directly into the striatum in vivo of rats with an ipsilateral 6-OHDA nigrotomy at 60 min intervals and monitored striatal dopamine levels with the technique of brain microdialysis. Dopamine formation increased from the first to the fifth trial. This may be secondary to the decrease in uptake sites which accompanies the loss of striatal dopamine nerve terminals. We postulate that the continued presence of dopamine at striatal receptor sites conditions a short-term loss of dopamine receptor sensitivity and a consequent decreased circling response. The observation that desensitization (as measured by decreasing circling) was not present following repeated apomorphine administration may be attributable to its shorter duration of action. We also perfused l-DOPA into the striatum of normal rats and noted a progressive decrease in striatal dopamine levels from the first to the fifth trial. Since this occurred following direct administration of l-DOPA into the striatum, the decrease could not be accounted for by peripheral pharmacodynamics or bioavailability of l-DOPA in the striatum. Since this decrease in dopamine formation was seen only in the normal striatum, its relevance to the diminished behavioral response is unclear.     

Intranigral or intrastriatal injections of GDNF: effects on monoamine levels and behavior in rats

The present studies were designed to determine whether administration of recombinant human glial cell line-derived neurotrophic factor (rhGDNF) into either the substantia nigra or striatum is capable of augmenting dopamine function of the nigrostriatal pathway in normal rats. Single bolus intracranial injections of rhGDNF at either site increased locomotor activity and decreased food and water consumption and body weight in a dose-dependent manner when compared to vehicle-treated animals. These behavioral responses returned to pre-control levels within 3 weeks post rhGDNF administration. Administration of rhGDNF intranigrally increased dopamine, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels of the ipsilateral substantia nigra at 2 and 6 weeks post injection but had no augmenting effects on dopamine or its metabolites in the striatum. Administration of rhGDNF intrastriatally increased DOPAC and HVA levels of the ipsilateral striatum, although striatal dopamine levels were unchanged. Ipsilateral nigral dopamine levels were increased after intrastriatal injection of rhGDNF. The effects of intracranial rhGDNF were not specific to the nigrostriatal dopamine system, since nigrostriatal serotonin, 5-hydroxyindoleacetic acid (5-HIAA), epinephrine and norepinephrine transmitter levels were altered depending on administration route for rhGDNF and dose. Taken together, these data demonstrate long-lasting neurochemical and behavioral changes which suggest that rhGDNF can augment function in adult rat dopamine neurons. Therefore, rhGDNF may have therapeutic potential for Parkinson's disease.     

Regional distribution of monoamine vesicular uptake sites in the mesencephalon of control subjects and patients with Parkinson's disease: a postmortem study using tritiated tetrabenazine

The distribution of the vesicular monoamine transporter was investigated post mortem in the human ventral mesencephalon of control subjects (n = 7) and patients with Parkinson's disease (n = 4) using tritiated dihydrotetrabenzine binding and autoradiography. Tritiated dihydrotetrabenazine binding was characterized by a single class of sites with a Kd of 7 nM and a Bmax of 180 fmol/mg of protein in the substantia nigra. Tritiated dihydrotetrabenazine binding sites were heterogeneously distributed in the mesencephalon of control subjects: the density of tritiated dihydrotetrabenazine binding sites was high in the substantia nigra pars compacta, locus coeruleus and nucleus raphe dorsalis, moderate in the ventral tegmental area and low in the substantia nigra pars reticulata and catecholaminergic cell group A8. Within the substantia nigra, a zone with maximal density of tritiated dihydrotetrabenazine binding, two times higher than the mean estimate for the whole substantia nigra pars compacta, was detected in the medial part of the structure. The anatomical organization of the human ventral mesencephalon was analyzed on adjacent sections stained for acetylcholinesterase histochemistry and tyrosine hydroxylase immunohistochemistry. Tritiated dihydrotetrabenazine binding displayed the same characteristic regional pattern of distribution as that observed with tyrosine hydroxylase immunohistochemistry except in the nucleus raphe dorsalis, where no tyrosine hydroxylase immunoreactivity was detected. In parkinsonian brains, the level of tritiated dihydrotetrabenazine binding was dramatically decreased in all regions of the ventral mesencephalon analyzed except in the substantia nigra pars reticulata. In the substantia nigra pars compacta, the reduction was by 55% for the whole structure and by 65% in its medial zone, where binding site density was maximal. In most nigral subsectors analyzed, the decrease in density of tritiated dihydrotetrabenazine binding sites reached the level expected given the loss of tyrosine hydroxylase-positive cells observed. By contrast, the ratio of [3H]dihydrotetrabenazine binding to the number of tyrosine hydroxylase positive neurons was significantly increased in the zone of high [3H]dihydrotetrabenazine binding sites. This relative sparing of tritiated dihydrotetrabenazine binding sites may be due either to the contribution of other monoaminergic neurons such as serotoninergic neurons or more likely to hyperactivity of the still surviving dopaminergic neurons.     

Neuroprotective effects of growth/differentiation factor 5 depend on the site of administration

Growth/differentiation factor 5 (GDF5) is a neurotrophin which protects the rat nigrostriatal dopaminergic pathway from 6-hydroxydopamine-induced damage. Here we used amphetamine-induced rotational testing, high-performance liquid chromatography and immunocytochemistry to investigate the minimum effective dose of GDF5. We also compared the effectiveness of injecting GDF5 into either the substantia nigra pars compacta (SNpc), the lateral ventricle (LV) or the striatum (or combinations of these sites).     

Constructing a new nigrostriatal pathway in the Parkinsonian model with bridged neural transplantation in substantia nigra

The physical repair and restoration of a completely damaged pathway in the brain has not been achieved previously. In a previous study, using excitatory amino acid bridging and fetal neural transplantation, we demonstrated that a bridged mesencephalic transplant in the substantia nigra generated an artificial nerve pathway that reinnervated the striatum of 6-hydroxydopamine (6-OHDA)-lesioned rats. In the current study, we report that a bridged mesencephalic transplant can anatomically, neurochemically, and functionally reinstate the 6-OHDA-eradicated nigro-striatal pathway. An excitatory amino acid, kainic acid, laid down in a track during the transplant generated a trophic environment that effectively guided the robust growth of transplanted neuronal fibers in a bundle to innervate the distal striatum. Growth occurred at the remarkable speed of approximately 200 microm/d. Two separate and distinct types of dopamine (DA) innervation from the transplant have been achieved for the first time: (1) DA innervation of the striatum, and (2) DA innervation of the pars reticularis of the substantia nigra. In addition, neuronal tracing revealed that reciprocal connections were achieved. The grafted DA neurons in the SNr innervated the host's striatum, whereas the host's striatal neurons, in turn, innervated the graft within 3-8 weeks. Electrochemical volt- ammetry recording revealed the restoration of DA release and clearance in a broad striatal area associated with the DA reinnervation. Furthermore, the amphetamine-induced rotation was attenuated, which indicates that the artificial pathways were motor functional. This study provides additional evidences that our bridged transplantation technique is a potential means for the repair of a completely damaged neuronal pathway.     

Vasopressin receptors in the mouse (Mus musculus) brain: sex-related expression in the medial preoptic area and hypothalamus

We have investigated the distribution of vasopressin binding sites in the brain of male and female adult mice using a radio-iodinated ligand and film autoradiography. Vasopressin receptors were uncovered in various regions of the brain including the basal nucleus of Meynert, the substantia innominata, the hypothalamic paraventricular nucleus, the substantia nigra pars compacta and the hypoglossal nucleus. A sex-related difference in the expression of vasopressin receptors was seen in the medial preoptic area/anterior hypothalamus corresponding to the rat sexually dimorphic nucleus in the rat and in the hypothalamic mammillary nuclei. In both structures the autoradiographic labeling is more intense in females than in males. These observations confirm that vasopressin binding sites are present in the hypothalamic preoptic area of most species examined so far and that sex-related expression of neuropeptide receptors could trigger sex-related behavioral differences.     

Higher plants light harvesting proteins. Structure and function as revealed by mutation analysis of either protein or chromophore moieties

In vivo microdialysis was used to examine the effects of dopaminergic transplants on extracellular concentrations of dopamine (DA), serotonin (5-HT), and their precursors and major metabolites in the denervated rat striatum. Dialysis perfusates were collected from intact 6-hydroxydopamine (6-OHDA) lesion plus sham grafted, and lesion plus fetal substantia nigra (SN) grafted striata. The SN transplants ameliorated the reduction of striatal DA and dihydroxyphenylacetic acid (DOPAC) levels in rats with unilateral 6-OHDA lesions of the mesostriatal pathway. The transplants also increased extracellular levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the denervated striatum. In response to NSD-1015 (an inhibitor of aromatic L-amino acid decarboxylase, AADC), 5-hydroxytryptophan (5-HTP) levels were substantially elevated in the SN grafted striata as compared with those in the sham grafted controls, which continued even after subsequent administration of L-3,4-dihydroxyphenylalanine (L-DOPA, 100 mg/kg i.p.). Immunohistochemical analysis showed hyperinnervation of 5-HT fibers in the grafted striatum, which was consistent with the results of microdialysis experiments. These results indicated that implantation of SN grafts into the 6-OHDA-lesioned striatum of rats induces hyperactivity of 5-HT synthesis, release and metabolism.     

Partial striatal dopamine depletion differentially affects striatal substance P and enkephalin messenger RNA expression

Near total striatal dopamine denervation results in a decrease in substance P and an increase in enkephalin messenger RNA expression in the striatum. It is unknown whether partial depletions of striatal dopamine content produce similar changes in these peptide messenger RNAs. To test whether compensations in dopamine synthesis and release following partial dopamine denervation prevent the lesion-induced alterations in substance P and enkephalin messenger RNAs, varying concentrations of 6-hydroxydopamine were injected unilaterally into the substantia nigra. Seven days after injection of 6-hydroxydopamine (2-16 micrograms) or vehicle, in situ hybridization histochemistry was used to examine tyrosine hydroxylase messenger RNA in the substantia nigra and substance P and enkephalin messenger RNAs in the striatum. The extent of the dopamine depletion was determined by measuring striatal dopamine tissue content. The decrease in tyrosine hydroxylase messenger RNA paralleled the change in striatal tissue dopamine content. Substance P messenger RNA was decreased in all lesioned rats. In contrast, a significant increase in enkephalin messenger RNA was not detected until striatal dopamine was reduced to 10% of control levels. These results suggest that compensations within the residual dopamine system are not sufficient to maintain normal striatal substance P messenger RNA levels in partially denervated animals, but are sufficient to maintain normal striatal enkephalin messenger RNA expression.     

Correlation of apomorphine- and amphetamine-induced turning with nigrostriatal dopamine content in unilateral 6-hydroxydopamine lesioned rats

In the unilateral 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease, controversy exists concerning the use of apomorphine- or D-amphetamine-induced rotations as reliable indicators of nigrostriatal dopamine depletion. Our objective was to evaluate which, if either, drug-induced behavior is more predictive of the extent of nigrostriatal dopamine depletion. Fischer 344 and Sprague-Dawley rats were unilaterally injected with 9 micrograms/4 microliters/4 min 6-hydroxydopamine into the medial forebrain bundle. The animals were behaviorally tested with apomorphine (0.05 mg/kg, s.c.) and D-amphetamine (5.0 mg/kg, s.c.). Following testing, the brains were removed and the right and left striata, substantia nigra and ventral tegmental area were dissected free and quickly frozen at -70 degrees C for analysis of catecholamine content by high performance liquid chromatography coupled with electrochemical detection. Our results indicate that an animal which has greater than a 90% depletion of dopamine in the striatum might not rotate substantially on apomorphine, without a concomitant depletion of > 50% of the DA content in the corresponding substantia nigra. No correlations were seen involving depletions of the ventral tegmental area and the extent of the lesions to the striatum. Submaximally lesioned (75-90% depleted) rats were found to rotate on D-amphetamine but not on apomorphine. In addition, control rats that did not receive lesions were often seen to rotate extensively on D-amphetamine. We therefore conclude that maximal lesions of the striatum and substantia nigra are required to generate rotations demonstrable with low dose apomorphine but not with D-amphetamine.(ABSTRACT TRUNCATED AT 250 WORDS)