TrkB and TrkC Are Differentially Regulated by Excitotoxicity during Development of the Basal Ganglia

During development neurons are protected against various insults by intrinsic properties. Here we evaluate trkB (both full-length and truncated forms) and trkC expression in the striatum, cortex, and substantia nigra after intrastriatal injection of quinolinic acid (QUIN) at different stages of postnatal (P) development, by RNase protection assay and in situ hybridization. During normal development, a region-specific regulation of trkB and trkC was observed, showing the maximal mRNA levels at P5. Excitotoxic lesion did not modify striatal trkB mRNA levels at any age examined. However, trkC decreased after QUIN injection at P5 in the striatum (52 +/- 2% of control levels). On the other hand, regulation of trkB and trkC expression was observed in cortex and substantia nigra after striatal excitotoxic lesion. Both full-length and truncated receptor isoforms of trkB were enhanced in the cortex when striatal injury was produced at P21 (268 +/- 38 and 206 +/- 35%) or P30 (174 +/- 35 and 157 +/- 13%). In situ hybridization studies localized this increase in trkB expression in layers II/III and V along the cerebral cortex. Within the substantia nigra, striatal excitotoxicity at P5 selectively decreased the truncated form of trkB (70 +/- 7%), whereas the full-length form was up-regulated at P30 (130 +/- 2%). A biphasic increase in trkC mRNA levels was observed at P5 (151 +/- 3%) and P21 (168 +/- 4%). These changes were localized in the substantia nigra pars compacta. Triple-labeling studies disclosed that all these changes were mainly located in neurons. These results demonstrate that the endogenous response to excitotoxicity includes transneuronal regulation of neurotrophin receptors, which is specific for each nucleus and depends on the developmental stage.     

Developmental regulation of BDNF and NT-3 expression by quinolinic acid in the striatum and its main connections

Interactions between neurotrophic factors and neurotransmitters participate in the formation and maintenance of appropriate connections, as well as in neurodegenerative processes. Here we have measured changes in the developmental expression pattern of BDNF and NT-3 in the striatum, cortex, and substantia nigra induced by intrastriatal injection of the N-methyl-d-aspartate glutamate receptor agonist quinolinic acid (QUIN). Animals were injected at different postnatal ages, and BDNF and NT-3 mRNA levels were determined 6 h after lesion using a ribonuclease protection assay. Our results show a biphasic increase in BDNF mRNA levels in striatum and in the ipsilateral cortex at postnatal day (P)5 and P21. In contrast, although NT-3 expression did not change in the striatum, it was down-regulated in the ipsilateral cortex at P5 and P30. Intrastriatal QUIN injection did not induce changes in either BDNF or NT-3 expression in the ipsilateral substantia nigra. These findings show that neurotrophin expression is developmentally regulated after excitotoxic injury, which suggests that this endogenous response may be involved in different neuronal maturation and vulnerability during development.     

The effects of anesthetics on the concentrations of cholecystokinin octapeptide sulfate-like immunoreactivity in rat brain regions

Cholecystokinin octapeptide sulfate-like immunoreactivity (CCK-8S-LI) was determined by radioimmunoassay in rat brain areas following injections of pentobarbital, halothane and chloral hydrate. Time-dependent changes in the concentrations of CCK-8S-LI were different between pentobarbital and chloral hydrate in all brain regions studied. After pentobarbital injection, CCK-8S-Li peaked at 30-60 min in the frontal cortex, nucleus accumbens, striatum and substantia nigra; after chloral hydrate injection, CCK-8S-LI peaked at 120 min in the hypothalamus, nucleus accumbens and substantia nigra. Both anesthetics induced almost the same sleeping times. Halothane inhalation caused increases in the concentrations of CCK-8S-LI in the amygdala and hippocampus. In addition, following intracardial perfusion of saline for 30 min after pentobarbital anesthesia, the concentrations of CCK-8S-LI increased in the nucleus accumbens, and decreased in the frontal cortex. These results suggest that since different anesthetics cause different changes in CCK levels, anesthetics affect studies of these neurons.     

The neostriatal mosaic. I. Compartmental organization of projections from the striatum to the substantia nigra in the rat

Combined neuroanatomical techniques were used to examine the organization of the striatal projection to the substantia nigra in the rat. Both double anterograde axonal tracing methods (Phaseolus vulgaris leuco-agglutinin (PHA-L) and 3H-amino acid tract tracing) and double fluorescent retrograde axonal transport tracing methods were used to examine the relationship among striatal neurons projecting to separate areas of the substantia nigra. Additionally, the distributions of retrogradely labeled striatonigral projection neurons were charted relative to the neurochemically distinct striatal "patch" compartment, identified by substance P- or leu-enkephalin-like immunoreactivity, and the complementary "matrix" compartment, identified by somatostatin-like immunoreactive fibers. These studies show two distinct types of organization in the striatonigral projections. One type is topographic in that the mediolateral relationships among these striatal efferent neurons are roughly maintained by their termination patterns in the substantia nigra, while the dorsoventral relationships are inverted. Projections from any part of the striatum, however, are distributed throughout the rostrocaudal axis of the substantia nigra. Despite their general topographic organization, the variable and dispersed nature of such projections from individual striatal loci results in partial overlap of afferent fields from separate striatal areas. The second type of organization is nontopographic and provides a different system for convergence of inputs from separated striatal areas that is superimposed on the rough topographic system. In this other projection system the mediolateral and dorsoventral relationships typical of the topographically ordered system are not maintained and are sometimes reversed. For example, PHA-L injected into the dorsal striatum labels a topographic (inverted relationship) projection to the ventral substantia nigra pars reticulata but also a smaller and separate projection to the dorsal pars reticulata and adjacent pars compacta. Retrograde tracer deposits in the pars compacta label neurons in the ventral striatum (the inverted relationship) but also clusters of neurons in the dorsal striatum. These clusters are in the neurochemically defined patch compartment whereas neurons in the matrix are labeled by injections into the pars reticulata. The dendrites of both retrogradely filled patch and matrix neurons are confined to the compartment containing their cell bodies, suggesting a restriction that would functionally segregate extrinsic striatal afferents shown in other studies to be confined to either patches or matrix.(ABSTRACT TRUNCATED AT 400 WORDS)     

Intracerebral quinolinic acid injection in the rat: Effects on dopaminergic neurons

Intrastriatal infusion of the endogenous excitotoxin quinolinic acid (QUIN) leads to the degeneration of neuronal cell bodies around the injection site. Dopaminergic afferents not only survive the toxic insult but react by increasing their activity in the acute and suba-cute phases following the injection of QUIN. Measurements of the tissue concentrations of acidic dopamine metabolites, and determinations ofl-DOPA accumulation after DOPA-decar☐ylase inhibition, indicate an increased dopamine turnover within 90 min after the administration of 50 μg QUIN. At the later timepoints examined (6 h, 4 and 11 days after QUIN), dopaminergic parameters are increased in the injected striatum only while no changes can be detected in the homolateral substantia nigra. Local norepinephrine levels are elevated 4 and 11 days after an intrastriatal QUIN injection but remain unchanged at distant sites or earlier postinjection periods. The acute increase in nigrostriatal activity may be mediated by an excessively stimulated, yet functional striatonigral feedback loop whereas subsequent changes represent local reactions of dopaminergic nerve terminals secondary to neuronal degeneration in the striatum. In accordance with this interpretation, no monoaminergic changes can be observed in the hypothalamus 4 days following the local injection of 50 μg QUIN, a dose which does not cause neuronal nercosis in this brain area. These data are concordant with, and are discussed in the context of, a possible involvement of QUIN in the pathogenesis of Huntington's disease.     

In vivo labelling and axonal transport of monoamine oxidase in the rat basal ganglia using radioactive pargyline

Summary The enzyme monoamine oxidase was labelled in the rat striatum or substantia nigra with locally injected radioactive pargyline. The binding was prevented by a pretreatment with non-radioactive pargyline, or with a combination of clorgyline and deprenyl. Most of the MAO labelled with³H-pargyline was of the B-type, but also some MAO-A was labelled, as shown in rats pretreated with clorgyline or deprenyl separately.Seven days after the injection of (³H)-pargyline into the striatum a significant labelling was observed in the substantia nigra. This labelling was clorgyline sensitive, indicating type A MAO, and was not present when striatal neurons were destroyed with kainic acid. Labelling of the striatum following³H-pargyline injection into the substantia nigra was also less in kainate intoxicated striata. Damage of nigral dopamine neurons with 6-hydroxydopamine did not influence the distribution of the label.Thus by using³H-pargyline, specific labelling and axonal transport of type A MAO in striatal neurons projecting to the substantia nigra was demonstrated.     

Does cholecystokinin colocalize with dopamine in the human substantia nigra?

In situ hybridization was used to examine the distribution of neurons containing cholecystokinin (CCK) mRNA in human, monkey and rat brain. In rat and monkey brain CCK mRNA was visualized in the substantia nigra pars compacta and in the ventral tegmental area. The dopaminergic cell bodies in the human substantia nigra did not however show detectable amounts of CCK mRNA. Low levels of CCK mRNA were observed in the nucleus paranigralis, the human equivalent of the rodent ventral tegmental area. High levels of CCK mRNA were seen in other regions of the same brains including the cortex and the hippocampus. Thus, the adult human substantia nigra dopaminergic cells, in contrast to primate and rodent substantia nigra, do not express CCK. These results question the hypothesis of an involvement of CCK in the regulation of dopaminergic neurons and help to explain the absence of decreased CCK levels in the caudate and putamen of Parkinson's disease victims.     

In vivo synthesis of substance P in the corpus striatum of the rat and its transport to the substantia nigra

Incorporation of [³⁵S]methionine into substance P in the striatum of the rat and the subsequent transport of the labelled peptide to the substantia nigra has been demonstrated in vivo. After a 4-h infusion of [³⁵S]methionine into the corpus striatum and an additional interval of 4 h radiolabelled substance P was found in the striatum and the substantia nigra of the animals. The criteria for concluding that the labelled product was substance P were: (a) gel chromatography and subsequent ion exchange chromatography of an acetic acid extract of the infused striatum or the ipsilateral substantia nigra yielded a peak of radioactivity co-eluting with endogenous immunoreactive substance P or a sample of synthetic substance P; (b) the radioactive material from this peak also co-chromatographed with synthetic substance P on high-voltage paper electrophoresis or high-pressure liquid chromatography; and (c) bound specifically to the substance P antibody. Intracisternal injection of colchicine (70 μg, i.c.) completely suppressed the appearance of radiolabelled substance P immunoreactive material in the substantia nigra.The data indicate that synthesis of substance P occurs in nerve cell bodies located in the corpus striatum and that substance P is transported to the substantia nigra by a colchicine sensitive mechanism.     

Cobalt injections into the substantia nigra of the rat: effects on behavior and dopamine metabolism in the striatum

Small amounts of cobalt unilaterally injected into the substantia nigra of rats caused a strong, spontaneous contralateral turning which was suppressed by haloperidol. One to 2 days after intranigral cobalt microinjection, d-amphetamine decreased the intensity of the contralateral turning; 5 days after cobalt application, d-amphetamine changed the direction of the turning to the ipsilateral side. Intranigral cobalt microinjection initially caused a significant increase in the concentration of dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid in the ipsilateral striatum. Thereafter, dopamine and its metabolites declined progressively to values significantly below control values. Similar biochemical changes in the striatum were also seen after partial electrolytic lesions of the substantia nigra. However, such lesions produced only mild contralateral turning. Frontal hemisection did not result in any increase of striatal metabolite values, and produced mild ipsilateral turning. Thus, there was no parallelism between the intensity and time course of the turning behavior induced by the different techniques and the changes in dopamine metabolism in the striatum. Within the cobalt-injected substantia nigra, γ-aminobutyric acid (GABA) and glutamic acid decarboxylase were decreased to less than 60% of the contralateral control values. The possibility is considered that the depression of a GABA-mediated inhibitory influence on the nigrostriatal or mesolimbic dopamine neurons may play a role in the cobalt-induced contralateral turning and altered striatal dopamine metabolism.     

Pattern formation in the striatum: developmental changes in the distribution of striatonigral neurons

The striatum of the mammalian forebrain can be divided into 2 compartments, the patches and the matrix. We have investigated embryonic events involved in the formation of these compartments in rats. Early in development, dopamine fibers from the substantia nigra selectively innervate the patches. In the perinatal striatum, we observed a close match between the distributions of striatal cell bodies with axonal projections to the substantia nigra and patches of afferent dopamine fibers. Striatal cells projecting to the nigra are first seen in the ventrolateral striatum at embryonic day (E) 17. Striatonigral cell bodies are distributed homogeneously through the striatum from E18 to 19. At E20 and until postnatal day 4, these cell bodies are organized into discrete patches. After this time, striatonigral cell bodies assume the dense and homogeneous distribution characteristic of the adult striatum. A retrograde tracer injection in the nigra at E18 (during the early period of homogeneous striatonigral distribution) produces a patchy striatonigral distribution if the embryo is not sacrificed until E21. The number of retrogradely labeled striatonigral cell bodies in a midstriatal section, at times immediately before and after the early homogeneous to patchy changeover did not differ significantly. We suggest that the neurons of the patch compartment of the striatum are born first and project to the substantia nigra first. The patch neurons only become restricted to "patchy" areas as the later-born matrix neurons migrate out into the striatum.     

Inhibition of striatal energy metabolism produces cell loss in the ipsilateral substantia nigra

This study examined whether damage to dopamine (DA) nerve terminals via inhibition of energy metabolism in the striatum would result in the retrograde loss of cell bodies in the substantia nigra. Infusion of 2 μmol malonate into the left striatum of rats resulted in a 67% loss of striatal DA and a 40% loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra. No change in the number of Nissl-positive-TH-negative neurons was observed. These findings demonstrate the retrograde destruction of DA cell bodies in the substantia nigra resulting from energy impairment at their terminal projection site.     

Effects of intranigral administration of dopamine agonists and antagonists and baclofen on concentrations of dopac and dopamine in the striatum and substantia nigra of the rat

Summary Systemic administration of haloperidol to rats failed to alter the concentration of dopamine but increased the concentration of 3, 4-dihydroxy-phenylacetic acid (DOPAC), the major metabolite of dopamine, in both the striatum and substantia nigra. These haloperidol-induced changes in DOPAC were prevented by an intranigral microinjection of baclofen, a drug which reduces nigrostriatal dopaminergic neuronal activity.It has been proposed that nigrostriatal neurons are regulated, in part, by the activation of autoreceptors in substantia nigra. However, intranigral microinjections of high concentrations of several dopaminergic antagonists failed to mimic the biochemical effects resulting from systemic administration of these drugs; instead, they slightly increased the concentrations of both dopamine and DOPAC in the striatum and decreased dopamine in substantia nigra. Intranigral microinjections of the dopamine agonist, apomorphine, failed to alter the concentration of DOPAC in the striatum, but reduced both dopamine and DOPAC in the nigra. If DOPAC concentrations reflect nigrostriatal dopaminergic neuronal activity, the present results suggest that dopaminergic agonists and antagonists acting in substantia nigra do not exert a major influence on the activity of these neurons.     

Cobalt infections into the substantia nigra of the rat: Effects on behavior and dopamine metabolism in the striatum

Small amounts of cobalt unilaterally injected into the substantia nigra of rats caused a strong, spontaneous contralateral turning which was suppressed by haloperidol. One to 2 days after intranigral cobalt microinjection, d-amphetamine decreased the intensity of the contralateral turning; 5 days after cobalt application, d-amphetamine changed the direction of the turning to the ipsilateral side. Intranigral cobalt microinjection initially caused a significant increase in the concentration of dopamine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid in the ipsilateral striatum. Thereafter, dopamine and its metabolites declined progressively to values significantly below control values. Similar biochemical changes in the striatum were also seen after partial electrolytic lesions of the substantia nigra. However, such lesions produced only mild contralateral turning. Frontal hemisection did not result in any increase of striatal metabolite values, and produced mild ipsilateral turning. Thus, there was no parallelism between the intensity and time course of the turning behavior induced by the different techniques and the changes in dopamine metabolism in the striatum. Within the cobalt-injected substantia nigra, γ-aminobutyric acid (GABA) and glutamic acid decarboxylase were decreased to less than 60% of the contralateral control values. The possibility is considered that the depression of a GABA-mediated inhibitory influence on the nigrostriatal or mesolimbic dopamine neurons may play a role in the cobalt-induced contralateral turning and altered striatal dopamine metabolism.     

Lateralization of aminopeptidase A activity in substantia nigra, striatum and frontal cortex of rats

Several brain aminopeptidase activities have been reported to be asymmetrical, but no direct correlation with lateralized functions has been proposed. Cholecystokinin (CCK) coexists with dopamine (DA) in the nigrostriatal system, which is involved in lateralized motor behaviors. Because aminopeptidase A activity is probably responsible for the hydrolysis of CCK, we studied the left-right distribution of glutamate- (GluAP) and aspartate-aminopeptidase (AspAP) activities in their soluble (Sol) and membrane-bound (M-B) forms in the substantia nigra, striatum and cortex of rats. Although there was a highly significant predominance of the left side in the substantia nigra and striatum for Sol GluAP and M-B AspAP respectively, in the frontal cortex predominance was on the right side for M-B AspAP. These results suggest a relationship between aminopeptidase A activity and lateralized nigro-striato-cortical functions involving CCK.     

偏侧帕金森病猴模型黑质和纹状体一氧化氮合酶表达的变化

目的探讨偏侧帕金森病（PD）猴模型黑质和纹状体一氧化氮合酶（NOS）表达的变化。方法对3只恒河猴经单侧颈内动脉注射1-甲基4-苯基1，2，3，6-四氢吡啶（MPTP）制备成偏侧PD猴模型后，应用还原型尼克酰胺腺嘌呤二核苷酸-黄递酶（NADPH．d）组化染色方法观察偏侧PD猴黑质和纹状体NOS阳性神经元表达的变化，并与正常猴比较。结果偏侧PD猴MPTP毁损侧的黑质和纹状体的NOS阳性神经元数目较毁损对侧和正常猴明显增加（均P〈0．01），毁损对侧的黑质和纹状体NOS阳性神经元数目与正常猴比较差异无统计学意义。结论偏侧PD猴黑质和纹状体NOS阳性神经元增多，由此引起一氧化氮（NO）合成和释放增多，可能对黑质和纹状体神经元的变性和死亡起重要作用。     

Sprouting of dopaminergic fibers from spared mesencephalic dopamine neurons in the unilateral partial lesioned rat

A unilateral partially lesioned rat model of Parkinson's disease was developed following selective lesioning of the dopamine neurons of the substantia nigra pars compacta by stereotactic injection of the neurotoxin 6-hydroxydopamine. In this animal model the dopamine neurons of the ventral tegmental area and medial substantia nigra are spared. The neuronal loss in such partial lesioned models mimics more closely that seen in human mid-stage parkinsonism. Cografts of adrenal medullary cells and sciatic nerve to the partially lesioned striatum induced a sprouting response in grafted animals that was confirmed by immunocytochemical staining with antibodies to tyrosine hydroxylase (TH) and by quantification of the high affinity dopamine uptake complex using [³H]GBR 12935 binding. Enhanced TH fiber immunostaining was evident even in the presence of poor cograft survival. The origin of the TH-like immunostained fibers in the striatum was determined using Lucifer yellow retrograde axonal transport. Following discrete tracer injections into the striatum adjacent to a cograft, neurons in the medial substantia nigra and ventral tegmental area (areas A9 and A10, respectively) were labelled with Lucifer yellow. These labelled neurons displayed a morphology characteristics of dopamine neurons and, in double-labelling experiements, also immunostained for TH. These results support the utility of unilateral partially lesioned rat models of Parkinson's disease for studies investigating a host sprouting or upregulation response and confirm that the immunostained striatal fibers originate from spared dopamine neurons in the ventromedial midbrain.     

Dopamine-derived endogenous 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-(R)-salsolinol, induced parkinsonism in rat: biochemical, pathological and behavioral studies

Dopamine-derived 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol, Sal) and related compounds were examined for their selective neurotoxicity to dopamine neurons by injection into the rat striatum. Among salsolinol analogs examined, only N-methyl-(R)-salsolinol (NM(R)Sal) induced behavioral changes very similar to those in Parkinson's disease: hypokinesia, stiff tail, limb twitching at rest and postural abnormality. Biochemical analysis showed that after NM(R)Sal injection, NM(R)Sal itself and its oxidation product, 1,2-dimethyl-6,7-dihydroxyisoquinolinium ion (DMDHIQ⁺) accumulated in the striatum, and also in the substantia nigra definite amount of DMDHIQ⁺ was detected. Dopamine and noradrenaline were reduced in the striatum and more markedly in the substantia nigra, whereas serotonin and its metabolite were not affected. Morphological analysis revealed selective reduction of tyrosine hydroxylase (TH)-containing neurons in the substantia nigra after continuous NM(R)Sal administration in the striatum. These results demonstrate the selective cytotoxicity of NM(R)Sal to the dopamine neurons in the substantia nigra, and the possible involvement of this 6,7-dihydroxyisoquinoline in the pathogenesis of Parkinson's disease is discussed.     

The acute histopathology of MPTP in the mouse CNS

We found that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rapidly induced cytopathological changes in the brain, involving some neurons selectively, as well as astrocytes and blood vessels. Dopaminergic neurons in the midbrain, as identified by immunostaining for tyrosine hydroxylase, were damaged as early as 2.5 hr after MPTP administration. Ultrastructurally, there was disruption of the endoplasmic reticulum and cytoplasmic condensation and vacuolation of the tyrosine hydroxylase reactive neurons in the substantia nigra as well as their axon terminals in the striatum. Perivascular edema was associated with vacuolation and swelling of astrocytic cytoplasm and rupture of perivascular foot processes. There was also capillary and arteriolar endothelial damage. Surprisingly, there was no clear correlation of MPTP-induced pathology with mitochondrial damage in any cell type. Biochemically, dopamine was depleted in the substantia nigra and the striatum within a few hours following MPTP administration. However, in the substantia nigra, homovanillic acid (HVA), one of the metabolites of dopamine, showed relatively less depletion than did dopamine by MPTP. These results may indicate that the turnover of dopamine was stimulated in the brain as a homeostatic mechanism.     

Comparative distribution of mRNAs for glutamic acid decarboxylase, tyrosine hydroxylase, and tachykinins in the basal ganglia: an in situ hybridization study in the rodent brain

Neurotransmitter-related messenger RNAs were detected by in situ hybridization in sections of rat and mouse brains by using 35S-radiolabelled RNA probes transcribed from cDNAs cloned in SP6 promoter-containing vectors. The distribution of messenger RNAs for glutamic acid decarboxylase, tachykinins (substance P and K), and tyrosine hydroxylase was examined in the striatum, pallidum, and substantia nigra. Dense clusters of silver grains were observed with the RNA probe complementary of the cellular messenger RNA for glutamic acid decarboxylase (antisense RNA) over most large neurons in the substantia nigra pars reticulata and medium-sized to large neurons in all pallidal subdivisions. A few very densely and numerous lightly labelled medium-sized neurons were present in the striatum. Among the areas examined, only the striatum contained neurons labelled with the antisense tachykinin RNA. Most of these neurons were of medium size, and a few were large. With the antisense tyrosine hydroxylase RNA, silver grains were found over neurons of the substantia nigra pars compacta and adjacent A10 and A8 dopaminergic cell groups. No signal was observed with RNAs identical to the cellular messenger RNA for glutamic acid decarboxylase or tachykinin (sense RNA). These results show a good correlation with immunohistochemical studies, suggesting that documented differences in the distribution and the level of glutamic acid decarboxylase, tyrosine hydroxylase, and substance P immunoreactivities in neurons of the basal ganglia are related to differences in the level of expression of the corresponding genes rather than to translation accessibility, stability, or transport of the gene products.     

Iron concentration reduced in ventral pallidum, globus pallidus, and substantia nigra by GABA-transaminase inhibitor, gamma-vinyl GABA

Recent histochemical studies indicate that there is considerable overlap of brain areas accumulating iron in oligodendrocytes with those in which GABA neurons terminate. The ventral pallidum, globus pallidus, substantia nigra and cerebellar nuclei are iron-rich areas, receive GABA-containing efferents, and have high concentrations of gamma-aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD). The present study examines the effect of disruption of the metabolism of GABA on the accumulation of iron in GABAergic projection sites. Gamma-vinyl GABA, an enzyme activated inhibitor of GABA-transaminase, was injected unilaterally into the globus pallidus and adjacent striatum or into the substantia nigra of the rat brain. Additional animals received unilateral injections of saline into the same areas or an electrocoagulation lesion of the globus pallidus and surrounding striatum. Two days after injection or lesion all animals were perfused and 40 micron sections of the brain were processed with the Perls' + diaminobenzidine (DAB) histochemical method for iron. The intensity of iron stain was measured with densitometry. Gamma-vinyl GABA injection into the striatum/pallidum resulted in a significant reduction in iron concentration in the ipsilateral ventral pallidum, globus pallidus and substantia nigra. Gamma-vinyl GABA injected into the substantia nigra reduced iron in the injection site. This study provides evidence that the presence of iron in the brain is related to the utilization of GABA.