Striatal glutamic acid decarboxylase immunoreactivity is increased after dopaminergic deafferentation: densitometric analysis

Developmental exposure to methylmercury alters GAD67 immunoreactivity and morphology of endothelial cells and capillaries of midbrain and hindbrain regions of adult rat offspring

INTRODUCTION

Methylmercury (MeHg) is an environmental contaminant that is of particular concern in Northern Arctic Canadian populations. Specifically, organic mercury compounds such as MeHg are potent toxicants that affect multiple bodily systems including the nervous system. Developmental exposure to MeHg is a major concern, as the developing fetus and neonate are thought to be especially vulnerable to the toxic effects of MeHg. The objective of this study was to examine developmental exposure to low doses of MeHg and effects upon the adult central nervous system (CNS). The doses of MeHg chosen were scaled to be proportional to the concentrations of MeHg that have been reported in human maternal blood samples in Northern Arctic Canadian populations.

METHOD

Offspring were exposed to MeHg maternally where pregnant Sprague Dawley rats were fed cookies that contained MeHg or vehicle (vehicle corn oil; MeHg 0.02 mg/kg/body weight or 2.0 mg/kg/body weight) daily, throughout gestation (21 days) and lactation (21 days). Offspring were not exposed to MeHg after the lactation period and were euthanized on postnatal day 450. Brains were extracted, fixed, frozen, and sectioned for immunohistochemical analysis. A battery of markers of brain structure and function were selected including neuronal GABAergic enzymatic marker glutamic acid decarboxylase-67 (GAD67), apoptotic/necrotic marker cleaved caspase-3 (CC3), catecholamine marker tyrosine hydroxylase (TH), immune inflammatory marker microglia (Cd11b), endothelial cell marker rat endothelial cell antigen-1 (RECA-1), doublecortin (DCX), Bergmann glia (glial fibrillary acidic protein (GFAP)), and general nucleic acid and cellular stains Hoechst, and cresyl violet, respectively. Oxidative stress marker lipofuscin (autofluorescence) was also assessed. Both male and female offspring were included in analysis. Two-way analysis of variance (ANOVA) was utilized where sex and treatment were considered as between-subject factors (p* <0.05). ImageJ was used to assess immunohistochemical results.

RESULTS

In comparison with controls, adult rat offspring exposed to both doses of MeHg were observed to have (1) increased GAD67 in the cerebellum; (2) decreased lipofuscin in the locus coeruleus; and (3) decreased GAD67 in the anterior CA1 region. Furthermore, in the substantia nigra and periaqueductal gray, adult male offspring consistently had a larger endothelial cell and capillary perimeter in comparison to females. The maternal high dose of MeHg influenced RECA-1 immunoreactivity in both the substantia nigra and periaqueductal gray of adult rat offspring, where the latter neuronal region also showed statistically significant decreases in RECA-1 immunoreactivity at the maternal low dose exposure level. Lastly, males exposed to high doses of MeHg during development exhibited a statistically significant increase in the perimeter of endothelial cells and capillaries (RECA-1) in the cerebellum, in comparison to male controls.

CONCLUSION

Findings suggest that in utero and early postnatal exposure to MeHg at environmentally relevant doses leads to long-lasting and selective changes in the CNS. Exposure to MeHg at low doses may affect GABAergic homeostasis and vascular integrity of the CNS. Such changes may contribute to neurological disturbances in learning, cognition, and memory that have been reported in epidemiological studies.

Involvement of lateral habenula α1 subunit-containing GABAA receptor-mediated inhibitory transmission in the regulation of depression-related behaviors in experimental Parkinson's disease

The lateral habenula (LHb) plays an important role in the regulation of depression. At present, it is not clear whether GABA_A receptor-mediated inhibitory transmission in the LHb is involved in Parkinson's disease (PD)-associated depression. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra in rats induced depressive-like behaviors and led to hyperactivity of LHb neurons compared to sham-operated rats, which attribute to depletion of dopamine, and decreased synthesis and release of GABA and increased release of glutamate in the LHb. Intra-LHb injection of GABA_A receptor agonist muscimol produced antidepressant-like effects, while the injection of GABA_A receptor antagonist picrotoxin induced or increased the expression of depressive-like behaviors in sham-operated and the lesioned rats. However, the doses producing these behavioral effects in the lesioned rats were lower than those in sham-operated rats. Intra-LHb injection of muscimol decreased the firing rate of LHb neurons and increased the medial prefrontal cortex serotonin (5-HT) release; conversely, picrotoxin increased the firing rate of the neurons and decreased 5-HT release in two groups of rats. Compared to sham-operated rats, the duration of muscimol and picrotoxin action on the firing rate of the neurons and 5-HT release was prolonged in the lesioned rats. These changes in the lesioned rats were associated with up-regulation of the expression of α1 subunit-containing GABA_A receptors and reduction of GABA release in the LHb. Collectively, our findings suggest that degeneration of the nigrostriatal pathway impairs GABA_A receptor-mediated inhibitory transmission in the LHb, and the transmission is important for regulating PD-associated depression.

L-DOPA Reverses the Increased Free Amino Acids Tissue Levels Induced by Dopamine Depletion and Rises GABA and Tyrosine in the Striatum

Perturbations in the cerebral levels of various amino acids are associated with neurological disorders, and previous studies have suggested that such alterations have a role in the motor and non-motor symptoms of Parkinson's disease. However, the direct effects of chronic L-DOPA treatment, that produces dyskinesia, on neural tissue amino acid concentrations have not been explored in detail. To evaluate whether striatal amino acid concentrations are altered in peak dose dyskinesia, 6-hydroxydopamine (6-OHDA)-lesioned hemiparkinsonian mice were treated chronically with L-DOPA and tissue amino acid concentrations were assessed by HPLC analysis. These experiments revealed that neither 6-OHDA nor L-DOPA treatment are able to alter glutamate in the striatum. However, glutamine increases after 6-OHDA and returns back to normal levels with L-DOPA treatment, suggesting increased striatal glutamatergic transmission with lack of dopamine. In addition, glycine and taurine levels are increased following dopamine denervation and restored to normal levels by L-DOPA. Interestingly, dyskinetic animals showed increased levels of GABA and tyrosine, while aspartate striatal tissue levels are not altered. Overall, our results indicate that chronic L-DOPA treatment, besides normalizing the altered levels of some amino acids after 6-OHDA, robustly increases striatal GABA and tyrosine levels which may in turn contribute to the development of L-DOPA-induced dyskinesia.

Neurosteroid and neurotransmitter alterations in Parkinson's disease

Parkinson's disease (PD) is associated with a massive loss of dopaminergic cells in the substantia nigra leading to dopamine hypofunction and alteration of the basal ganglia circuitry. These neurons, are under the control, among others, of the excitatory glutamatergic and inhibitory γ-aminobutyric acid (GABA) systems. An imbalance between these systems may contribute to excitotoxicity and dopaminergic cell death. Neurosteroids, a group of steroid hormones synthesized in the brain, modulate the function of several neurotransmitter systems. The substantia nigra of the human brain expresses high concentrations of allopregnanolone (3α, 5αtetrahydroprogesterone), a neurosteroid that positively modulates the action of GABA at GABAA receptors and of 5α-dihydroprogesterone, a neurosteroid acting at the genomic level. This article reviews the roles of NS acting as neuroprotectants and as GABAA receptor agonists in the physiology and pathophysiology of the basal ganglia, their impact on dopaminergic cell activity and survival, and potential therapeutic application in PD.

Dopamine depletion alters responses to glutamate and GABA in the rat subthalamic nucleus

We used whole-cell recordings to compare currents evoked by glutamate and GABA receptor agonists in subthalamic nucleus neurons located ipsilateral and contralateral to unilateral 6-hydroxydopamine (6-OHDA) injections into the substantia nigra zona compacta. The ratio of currents evoked by AMPA (0.6 microM) and NMDA (20 microM) was significantly greater in neurons recorded ipsilateral to 6-OHDA lesions compared with the ratio of currents recorded in control (contralateral) neurons. Both the GABA(A) agonist isoguvacine (20 microM) and the GABA(B) agonist baclofen (10 microM) evoked significantly greater outward currents in subthalamic nucleus neurons ipsilateral to the lesion compared to contralateral neurons. We conclude that chronic dopamine depletion up-regulates expression of GABA receptors and shifts the functional expression of ionotropic glutamate receptor subtype from NMDA to AMPA receptors in subthalamic nucleus.

Glutamic acid decarboxylase 67 mRNA regulation in two globus pallidus neuron populations by dopamine and the subthalamic nucleus

The globus pallidus (GP) consists of two neuron populations, distinguished according to their immunoreactivity for parvalbumin (PV). The PV-immunoreactive (PV+) neurons project preferentially to "downstream" targets such as the subthalamic and entopeduncular nuclei, whereas neurons lacking PV (PV- neurons) project preferentially to the striatum, suggesting a role for PV- cells in feedback to striatal neurons. Although dopamine D2 antagonist administration induces immediate early gene expression preferentially in PV- GP neurons, little is known about long-term regulation of PV- versus PV+ GP neurons. Nigral 6-hydroxydopamine (6-OHDA) lesions or repeated D2-class antagonist injections have been shown to increase pallidal expression of glutamate decarboxylase (GAD(67) isoform) mRNA. This increase in GAD(67) is believed to be secondary to activation of excitatory subthalamopallidal projections. The current study examined the effects of subthalamic nucleus (STN) lesion on 6-OHDA- or repeated D2 antagonist-induced changes in GP GAD(67) mRNA expression in PV+ and PV- neurons. Five or 21 d after nigral 6-OHDA injections or after 3, 7, or 21 d of D2 antagonist administration, GAD(67) mRNA increased in both the PV- and PV+ GP neurons, but the magnitude of the increase was significantly greater in PV- neurons. By contrast, STN lesion resulted in declines in GAD(67) mRNA in both cell populations, with the decreases in PV+ neurons exceeding those in PV- neurons. Furthermore, STN lesion completely blocked 6-OHDA- or D2 antagonist-induced GAD(67) mRNA increases in PV+ cells but only partly offset the GAD(67) mRNA increase in PV- pallidal neurons. Thus, the PV+ and PV- neurons are influenced in qualitatively similar ways by dopamine and the STN, but these cell types exhibit contrasting degrees of regulation by the dopaminergic and STN perturbations. This pattern of results has implications for pallidal control of striatal versus downstream basal ganglia nuclei.

Gene therapy in a rodent model of Parkinson's disease using differentiated C6 cells expressing a GFAP-tyrosine hydroxylase transgene

Cells expressing a tyrosine hydroxylase (TH) cDNA under control of the promoter of the human glial fibrillary acidic protein (GFAP) gene were tested for therapeutic efficacy in a rat model of Parkinson's disease. The GFAP gene encodes an intermediate filament protein found almost exclusively in astrocytes. Its promoter is of interest for gene therapy as it is expressed in astrocytes throughout postnatal life and is upregulated in response to almost any damage to the central nervous system, including Parkinson's disease. We previously showed that a line of C6 rat glioma cells that expresses a GFAP-TH transgene, C6-THA, displays increased transgene activity when differentiated by forskolin treatment. Accordingly, the effects were investigated of implantation of both undifferentiated and differentiated C6-THA cells into the striatum of rats that had been lesioned with 6-hydroxydopamine. Implantation of either cell type produced significant behavioral recovery one week after transplantation, as judged by the turning response to apomorphine. At two and three weeks after transplantation, the behavioral effect of the undifferentiated cells was no longer statistically significant, whereas that for the forskolin-differentiated cells remained robust. Transgenic TH mRNA and protein could be detected in implants of both cell types, and in agreement with the behavioral results, levels were higher for the differentiated C6-THA cells than for the undifferentiated cells. These results indicate that the GFAP promoter is sufficiently active to enable production of therapeutic levels of dopamine from a GFAP-TH transgene, and suggest the use of astrocytes for gene therapy for Parkinson's disease. They also show that beneficial modifications of cells produced by treatment while in culture may be maintained following implantation.

Unilateral 6-hydroxydopamine lesions of meso-striatal dopamine neurons and their physiological sequelae

One of the primary approaches in experimental brain research is to investigate the effects of specific destruction of its parts. Here, several neurotoxins are available which can be used to eliminate neurons of a certain neurochemical type or family. With respect to the study of dopamine neurons in the brain, especially within the basal ganglia, the neurotoxin 6-hydroxydopamine (6-OHDA) provides an important tool. The most common version of lesion induced with this toxin is the unilateral lesion placed in the area of mesencephalic dopamine somata or their ascending fibers, which leads to a lateralized loss of striatal dopamine. This approach has contributed to neuroscientific knowledge at the basic and clinical levels, since it has been used to clarify the neuroanatomy, neurochemistry, and electrophysiology of mesencephalic dopamine neurons and their relationships with the basal ganglia. Furthermore, unilateral 6-OHDA lesions have been used to investigate the role of these dopamine neurons with respect to behavior, and to examine the brain's capacity to recover from or compensate for specific neurochemical depletions. Finally, in clinically-oriented research, the lesion has been used to model aspects of Parkinson's disease, a human neurodegenerative disease which is neuronally characterized by a severe loss of the meso-striatal dopamine neurons. In the present review, which is the first of two, the lesion's effects on physiological parameters are being dealt with, including histological manifestations, effects on dopaminergic measures, other neurotransmitters (e.g. GABA, acetylcholine, glutamate), neuromodulators (e.g. neuropeptides, neurotrophins), electrophysiological activity, and measures of energy consumption. The findings are being discussed especially in relation to time after lesion and in relation to lesion severeness, that is, the differential role of total versus partial depletions of dopamine and the possible mechanisms of compensation. Finally, the advantages and possible drawbacks of such a lateralized lesion model are discussed.

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic denervation potentiates gabaergic inhibition in the mouse neostriatum in vitro

Using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease, we investigated the long-term effects of dopaminergic denervation on synaptic transmission in an in vitro slice preparation of the mouse neostriatum. In control mice, electrical stimulation elicited an antidromic potential (N1) followed by a synaptically mediated field potential (N2). In many slices, a third component (N3) was observed. Determination of the maximum stimulus intensities unveiled that in 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine-pretreated animals, the stimulus strength necessary to evoke a maximum N2 response was significantly higher compared to control mice. Furthermore, 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine-pretreatment led to a less frequent appearance and/or to a reduction in the amplitude of the N3 component. Application of glutamate receptor agonists and antagonists revealed two additional differences between normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-pretreated mice. (1) Comparison of the efficacy of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist 6-cyano-7-nitroquinoxaline-2, 3-dione demonstrated an increase in the inhibitory effect of 6-cyano-7-nitroquinoxaline-2,3-dione in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-pretreated mice. (2) In normal mice, removal of magnesium ions from the bathing solution invariably led to the appearance of late N-methyl-D-aspartate receptor-dependent synaptic components. There components were only slightly expressed or virtually absent in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-pretreated mice. The described differences between the electrophysiological and pharmacological properties of evoked field potentials in slices from normal and 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine-pretreated mice disappeared following blockade of GABAA receptor-dependent inhibition by bicuculline. In normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-pretreated mice, bicuculline did not influence the amplitude of the N2 component, but invariably unmasked late synaptic components mediated by glutamate receptors. However, the potentiating effect of bicuculline was significantly stronger in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-pretreated mice compared to the controls. In the presence of bicuculline, the frequency of occurrence of the N3 component was identical in both groups. Furthermore, the apparent efficiency of 6-cyano-7-nitroquinoxaline-2,3-dione was no longer different. Application of bicuculline in the absence of magnesium ions resulted in a similar disinhibition of N-methyl-D-aspartate receptor-dependent late components as observed in the controls in the absence of bicuculline. The data demonstrate that chronic dopaminergic denervation reduces glutamate receptor-dependent synaptic excitation in the mouse neostriatum. Since differences between normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-pretreated mice disappear in the presence of bicuculline, we conclude that this reduction in excitability is due to a potentiation of GABAA receptor-dependent inhibition.

Intrathalamic striatal grafts survive and affect circling behaviour in adult rats with excitotoxically lesioned striatum

Current models of basal ganglia disorders suggest that choreoathetosis is the end result of reduced GABAergic inhibition of the motor thalamus. Graft-derived release of GABA from intrastriatal striatal grafts has also been reported. In the present work, cell suspension grafts from embryonic day 14-15 rat striatal primordia were implanted close to the ventromedial thalamic nucleus to investigate whether they can develop and survive in this ectopic location, and whether they induce changes in the circling behaviour of the host. The grafts were implanted either in normal rats or in rats whose striatum had been lesioned with ibotenic acid. These grafts were implanted either ipsilateral or contralateral to the lesioned striatum. Additionally, some rats received intrastriatal grafts, and lesioned but non-grafted rats and lesioned rats that had received injections of saline or of cell suspensions from fetal spinal cord in the thalamus were used as control. Four to eight months after transplantation, circling behaviour after amphetamine or apomorphine injection was evaluated. Serial sections were stained with Cresyl Violet and studied immunohistochemically with antibodies against DARPP-32 (dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein, as striatal marker), Fos protein, glutamate decarboxylase (67,000 mol. wt), glutamate decarboxylase (65,000 mol. wt) and GABA. Cresyl Violet sections showed that the intrathalamic striatal grafts developed into tissue masses resembling those observed in intrastriatal striatal grafts. DARPP-32 immunohistochemistry revealed that the grafts were composed of DARPP-32 immunoreactive (striatum-like) and DARPP-32-negative patches. The intrathalamic grafts of rats which had received a low dose of apomorphine (0.25 mg/kg) 2 h before perfusion showed clusters of intensely Fos-immunoreactive nuclei throughout the transplant, indicating that these cells had developed dopamine receptors and supersensitivity to dopamine agonists. Double Fos and DARPP-32 immunohistochemistry revealed that the Fos-positive nuclei were located in the striatum-like areas. Finally, the intrathalamic grafts also contained neurons immunoreactive to GABA and glutamate decarboxylase (65,000 and 67,000 mol. wt). Rats that had received intrathalamic grafts contralateral to the lesioned striatum (i.e. contralateral to the lesion-induced turning direction) showed a significant reduction of circling both after amphetamine (78% reduction) or apomorphine (77% reduction) injection. Rats that had received grafts ipsilateral to the lesioned striatum showed a 75% decrease in amphetamine-induced circling, but no significant change in apomorphine-induced circling. No significant drug-induced circling was observed in non-lesioned and grafted rats. Sham grafting (saline) or grafting of weakly GABAergic tissue (fetal spinal cord) had no significant effects on lesion-induced circling behaviour.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiovascular neurons in cat caudal ventrolateral medulla: location and characterization of GABAergic input

The purposes of the present study were to: (1) characterize the GABAergic input to vasodepressor neurons in the caudal ventrolateral medulla of the cat, and (2) define more precisely the anatomical localization of these neurons in this species. This was done by microinjecting GABA receptor antagonists and agonists, and a negative allosteric modulator of the GABA receptor, namely, ethyl-beta-carboline-3-carboxylate, into the caudal ventrolateral medulla of alpha-chloralose-anesthetized animals while monitoring arterial blood pressure and heart rate. Localization studies where performed relating injection sites in the caudal ventrolateral medulla where cardiovascular responses were elicited, to neurons exhibiting immunoreactivity to tyrosine hydroxylase (TH) and phenethyl-N-methyl-transferase (PNMT). Microinjection of 1 and 10 ng of bicuculline into the caudal ventrolateral medulla produced decreases in mean blood pressure and heart rate of -34 +/- 6.4 and -49 +/- 9.2 mmHg, and -22 +/- 4.3 and -35 +/- 8.2 beats/min, respectively. Hypotension and bradycardia were also observed with picrotoxin microinjection (120 ng). Microinjection of muscimol (100-200 ng) and GABA (12 microgram) had no effect on mean blood pressure and heart rate. Microinjection of ethyl-beta-carboline-3-carboxylate also decreased mean blood pressure (-39 +/- 7.0 mmHg). The location of the micropipette tip after bicuculline microinjection in relation to TH and PNMT immunoreactive cells was as follows: (1) TH-immunoreactive cells of the A1 cell group were visible in the same relative location as the micropipette tip, and (2) no PNMT-positive cells were noted at the sites where bicuculline elicited hypotension. These results indicate that there is a tonic GABAergic input to neurons in the caudal ventrolateral medulla. The location of these neurons overlaps with the A1 cells.

Intracellular increases of cAMP induce opposite effects in glutamic acid decarboxylase (GAD67) and glial fibrillary acidic protein immunoreactivities in C6 cells

C6 is a cell line that expresses glial and neuronal markers. Treatments that increase intracellular cAMP levels induce the differentiation of these cells. We had previously demonstrated that forskolin, an agent that activates adenylate cyclase, produced changes in gene expression in C6 cells. As a consequence of this treatment, glutamic acid decarboxylase (GAD) activity and the mRNA for GAD67, one of the isoforms of the enzyme, decreased. In contrast, this treatment increased the transcription of the glial fibrillary acidic protein (GFAP) gene. We now show, by immunocytochemistry, that the changes in gene expression are phenotypically reflected by corresponding changes in the levels of the proteins encoded by the GAD67 and GFAP genes. Computer-assisted image analysis demonstrated that both the increase in GFAP immunofluorescence, and the decrease in GAD67 immunofluorescence are statistically significant. The changes in gene expression and in protein immunoreactivity are part of the differentiation process of the C6 cells towards a more mature glial phenotype.

Synaptic reorganisation in the rat striatum after dopaminergic deafferentation: an ultrastructural study using glutamate decarboxylase immunocytochemistry

The ultrastructure of GABAergic and non-GABAergic synapses in the adult rat neostriatum was examined 6-8 months after unilateral removal of the nigrostriatal dopaminergic pathway by 6-hydroxydopamine injection into the medial forebrain bundle. GABAergic profiles were identified by preembedding glutamate decarboxylase (GAD) immunocytochemistry performed on parasagittal vibratome sections. In three representative fields of the striatum, the nature and number of boutons and their postsynaptic partners were determined and the differences between the striata ipsi- and contralateral to the lesion analyzed. The percentage of GAD-immunoreactive boutons was increased from 23% on the intact side to 28% on the lesioned side. In addition, the GABAergic boutons underwent significantly more multiple contacts with several independent postsynaptic profiles, preferentially with dendritic spines. This could reflect a lesion-induced sprouting of local GABAergic axon terminals. On the other hand, although the vast majority of GABAergic boutons underwent synaptic contacts with dendrites (77% vs. 80%), the number of boutons per dendrite or per dendritic circumference remained unchanged. Thus, the higher frequency of GABAergic boutons may simply reflect the loss of the dopaminergic nerve endings, without a heterosynaptic replacement by GABAergic boutons. The deafferentation also induced structural changes of the postsynaptic profiles. Some dendritic spines had a shortened neck; others were completely integrated in the dendrite which now contained a spine apparatus and was contacted by boutons with the features of axospinous synapses. The spine retraction resulted in a quantitative decrease in the number of spines. Analysis of the synaptic curvature revealed that only spines with a flat contact zone were lost. Concurrently, the number of dendrites was increased, of the GAD-containing in particular, suggesting that the denrites of GABAergic interneurons tend to elongate and/or arborize. Taken together, the results of the present study show that the dopaminergic denervation caused a remodeling of the postsynaptic neurons. The relative increase of the number of GABAergic boutons and their synaptic contacts suggests that an altered wiring of the intrinsic GABAergic system contributes to the changes in the striatal output activity.

Dorsal striatal mechanisms involved in the dopamine D2 receptor-mediated potentiation of apomorphine-induced jaw movements

The role of dorsal striatal mechanisms in the regulation of apomorphine-induced jaw movements was studied. Jaw movements induced by apomorphine (0.2 mg/kg i.v.) were potentiated by quinpirole (10 micrograms/0.2 microliter) injected into the dorsal part of the striatum 10 min before apomorphine. Quinpirole injection into the ventral part of the striatum did not affect the effects of apomorphine. the quinpirole-induced potentiation in the dorsal striatum was prevented by l-sulpiride (25 ng), nemonapride (1 microgram), SCH23390 (1 microgram) or methylscopolamine (1 microgram), but not muscimol (50 ng), co-administered with quinpirole. Injection of these drugs alone 10 min before apomorphine failed to alter the effects of apomorphine. l-Sulpiride (25 ng) injected into the dorsal striatum 60 min before apomorphine increased the frequency of jaw movements induced by apomorphine (0.2 mg/kg). The l-sulpiride-induced potentiation was prevented by methylscopolamine (0.1 microgram) or l-sulpiride (25 ng) injected into the dorsal striatum 10 min before apomorphine; we had already found that this potentiation was also blocked by SCH23390. It is suggested that a synergistic dopamine D1/D2 receptor interaction underlies both the quick-onset potentiation by quinpirole and the delayed-onset potentiation by l-sulpiride.

Further evidence for a functional dorsal-ventral division of the rat striatum: GABAergic involvement in oral movements

Interactions between the gamma-aminobutyric acid (GABA)ergic system and the dopaminergic and cholinergic systems in the control of jaw movements, measured with a phototransducer system, were investigated in both dorsal and ventral regions of the rat striatum. Muscimol (25 and 50 ng/0.2 microliters) injected into the dorsal striatum did not affect jaw movements induced by apomorphine (0.2 mg/kg i.v.) or pilocarpine (4 mg/kg i.v.), but when injected into the ventral striatum it inhibited these jaw movements and those induced by carbachol (1 micrograms/0.2 microliters) injected into the ventral striatum. Picrotoxin (250 and 500 ng/0.2 microliters) injected into the dorsal striatum enhanced the effects of apomorphine (0.2 mg/kg) but not those of pilocarpine. When injected into the ventral striatum, picrotoxin did not affect apomorphine-induced oral movements but enhanced the effects of pilocarpine and carbachol. The benzodiazepine, flunitrazepam (100 ng/0.2 microliters), had no effect when injected in the dorsal striatum, and showed some inhibitory effects on dopaminergic and cholinergic oral movements when injected in the ventral striatum. The results suggest that the striatal GABAergic inhibitory effect on dopaminergic and cholinergic function is regionally specific, supporting a dorsal/ventral functional division of the rat striatum. The results also suggest that oral movements induced by dopaminergic and cholinergic drugs are distinct forms of repetitive oral behaviour.

Sex differences in densities of dopaminergic fibers and GABAergic neurons in the prenatal rat striatum

On the basis of observations on dopaminergic neurons developing in gender-specific cultures of embryonic rat mesencephalon, we have hypothesized that as yet unknown sexual dimorphisms might be found in projection areas of dopaminergic neurons. Therefore we searched for possible sex differences in the striatum during the period when massive ingrowth of mesencephalic afferents occurs and the striatal gamma-aminobutyric acid (GABA)ergic neurons differentiate. Male and female rats of embryonic days (E) 16, 18, 20, and 21 were fixed by perfusion through the heart. Vibratome sections were cut from the striatal anlage and sequentially immunostained for GABA by the immunogold-silver technique and tyrosine hydroxylase (TH) by the avidin-biotin-peroxidase method. Ultrathin sections were scanned for numbers of GABA- and TH-immunoreactive (IR) elements. Densities of TH-IR axons as well as of GABA-IR cell body profiles progressed with time. Contacts between TH-IR axons and GABA-IR and immunonegative cells were observed as early as E-16, increasing in numbers toward later stages. Throughout prenatal development, female striata displayed higher densities of both TH-IR axon and GABA-IR cell body profiles than male ones. This is the first report of a distinct anatomical sex difference regarding two major components of a key center of motor control. Prenatal sexual differentiation of the striatum may lead to a sexually dimorphic extrapyramidal circuitry, the existence of which, in the adult, is suggested by experimental and clinical data.