DISTRIBUTION OF CHOLINE ACETYLTRANSFERASE AND GLUTAMATE DECARBOXYLASE WITHIN THE SUBSTANTIA NIGRA AND IN OTHER BRAIN REGIONS FROM CONTROL AND PARKINSONIAN PATIENTS

—The distribution of choline acetyltransferase (ChAc, EC 2.3.1.6) and l -glutamate 1-carboxylyase (glutamate decarboxylase, GAD, EC 4.1.1.15) was studied in serial frontal slices of the substantia nigra (SN) (pars compacta, PC; pars reticulata, PR; an intermediate region, IR) as well as in other brain areas from post mortem tissue of control and Parkinsonian patients. Within the SN from control brain ChAc and GAD activities showed a distinctive distribution: ChAc activity in PC was higher than in PR and IR by 427% and 253% respectively and within PC the enzyme activity in the rostral part exceeded that in the control part by 353%. The GAD activity in PC was higher by 41% than that in PR and within PC seemed to be higher in the caudal than in the rostral part. For both enzyme activities there were no significant differences between PR and IR or within these regions. In Parkinsonian brain both ChAc and GAD activities were reduced to 15-25% of controls in all 3 regions of the SN. The distinctive distribution of ChAc and GAD activity found in the SN of control brain was abolished: no difference was observed between the 3 regions. However, within PC the ChAc activity was lower in the medial than in the rostral part. Since nigral ChAc is possibly located in interneurons, the decrease in enzyme activity may be connected with the cell loss observed in the SN of Parkinsonian brain. By contrast, nigral GAD is probably contained in terminals of strio-nigral neurons and the decrease in enzyme activity in Parkinson's disease in the absence of striatal cell loss, may reflect a change in the functional state of these GABA neurons. Among various areas of control brains ChAc activity was highest in caudate nucleus and putamen while GAD was highest in SN. caudate nucleus, putamen and cerebral cortex. In Parkinsonian brain the most severe reduction in ChAc and GAD activities was found in the SN.     

In vivo release of transmitters in the cat basal ganglia

The release of transmitters was studied in various structures of the basal ganglia in cats implanted with several push-pull cannulas. Local depolarization enhanced Met-enkephalin release in the globus pallidus. Activation of striatonigral substance P(SP) neutrons stimulated the transmitter release from terminals. Unilateral electrical stimulation of the caudate nucleus evoked GABA release in both substantia nigrae and pallidoentopeduncular nuclei. The unilateral facilitation or interruption of nigral SP transmission modified dopamine (DA) release in the ipsilateral caudate nucleus in contrast, modifications of GABAergic or glycinergic nigral transmissions induced bilateral symmetrical effects, whereas bilateral asymmetrical changes in DA release in the two caudate nuclei were seen during the unilateral modification of nigral DA transmission. Changes in the dendritic release of DA induced changes in serotonin release both in the substantia nigra and in the ipsilateral caudate nucleus. Finally, it will be shown that acetylcholinesterase can be released from the substantia nigra and the caudate nucleus through processes dependent on nerve activity.     

The effect of bicuculline on behavior and on the neuronal activity of the caudate nucleus and of the thalamic VA-VL nuclei in the cat brain]

In chronic cat experiments, bicucullin-induced GABA receptor blockade in the dorsal and ventral parts of the rostral caudate nucleus resulted in complicated changes in spontaneous activity of 19 of 55 neurons, primarily in the cells with low spike frequency. Changes were observed also in 8 to 31 neurons of VA-VL nuclei of the thalamus. The blockade of striatal GABA receptors was accompanied by changes in motor behavior and emotional motivational state of the animals. The character and latency of unit activity rearrangements in the caudate nucleus and modifications of cat's behavior depended on the localization of bicucullin injection point within different parts of the caudate nucleus.     

Gamma-aminobutyric acid-immunoreactive neurons in the rat trigeminal nuclei

The distribution of GABAergic neurons in the rat trigeminal nuclei was studied using a highly specific monoclonal antibody (mAb3A12) to gamma-aminobutyric acid (GABA). Immunopositive cells were relatively abundant in the marginal and gelatinosa beds of the caudal part of the trigeminal spinal tract nucleus, and in the dorsomedial areas of the oral subnucleus and the principal nucleus. A high density of GABA-immunoreactive somata was also found in the rostral part of the oral subnucleus and in the adjacent parvicellular reticular formation as well as in the supratrigeminal and intertrigeminal regions. Thus, the distribution of the GABAergic cells showed a relatively high density in areas related to the convergence of sensory stimuli, and in zones that contain interneurons inhibiting masticatory motorneurons. The results suggest, therefore, that GABA might play an important role both in discriminative sensory processing and in reflex modulation of the orofacial region.Abbreviations RF reticular formation - FRp parvicellular reticular formation - Vc trigeminal nucleus of the spinal tract, subnucleus caudalis - Vmes mesencephalic nucleus - Vmo trigeminal motor nucleus - Vo trigeminal nucleus of the spinal tract, subnucleus oralis - Vp principal trigeminal nucleus - Vsp spinal trigeminal nucleus - Vsup supratrigeminal nucleus     

Effects of Lead In Vivo and In Vitro on GABAergic Neurochemistry

Abstract: Alterations in aspects of neurotransmission utilizing -γ-aminobutyric acid (GABA) are associated with in vivo exposure of rats to lead at doses that do not produce convulsions, but sensitize animals to convulsant agents. These effects are observed regionally and include: decreased GABA levels in cerebellum; increased activity of glutamate decarboxylase (GAD) in caudate; and decreased GABA release (both resting and K⁺-stimulated) in cortex, caudate, cerebellum and substantia nigra. Sodium-dependent uptake of GABA by synaptosomes of cerebellum, substantia nigra and caudate was also affected: in these regions, affinity (K_m) was increased and maximal velocity (V_max) was reduced. Sodium-independent binding of GABA to synaptic membranes was increased in cerebellum, but was observed only when tissue was Tritonized and prepared without freezing and washing. No effects on GAD or on GABA uptake, release, or binding were observed when lead was added to brain tissue in vitro in concentrations as high as 100 μM. The results suggest that lead may produce chronic inhibition of presynaptic GABAergic function, notably in the cerebellum, which is associated with supersensitivity of postsynaptic GABA receptors. Failure of lead to affect GABAergic function in vitro may indicate that these effects are secondary to another neurotoxic action of lead in the CNS or are consequent to a nonneuronal metabolic action of lead.     

Evoked Release of Proteins from Central Neurons In Vivo

Push-pull cannulae were implanted in both substantiae nigrae and caudate nuclei of the halothane-anesthetized cat. The release of total protein, acetylcho-linesterase, and nonspecific cholinesterases was examined. Following direct application of potassium to one substantia nigra, changes occurred in the local release of total protein and acetylcholinesterase, but not nonspecific cholinesterases; changes also were observed in both caudate nuclei and the contralatera/ substantia nigra. The local evoked release of acetylcholinesterase and of total protein differed in the extent to which they were calcium-dependent. Control studies suggest that release of these compounds, both spontaneous and evoked, is related, at least in part, to neuronal activity. The significance of the neuronal release of proteins is discussed.     

Effects of Repeated Administration of Estradiol Benzoate on Tubero-Infundibular GABAergic Activity in Male Rats

Repeated (once a day for 8 days) but not single administration of estradiol benzoate (10 micrograms/kg, s.c.) induced a sevenfold increase in anterior pituitary gamma-aminobutyric acid (GABA) concentration in male rats. GABA concentration also increased in the median eminence whereas no changes or decreases were observed in other brain regions including hypothalamic arcuate nucleus, lateral septum, hippocampus, caudate nucleus, and substantia nigra. Eight-day estradiol benzoate injection also enhanced the Vmax of median eminence glutamate decarboxylase activity without affecting the Km of the enzyme for glutamic acid. Taken together, these results suggest that repeated administration of estradiol benzoate increases the activity of the tubero-infundibular GABAergic system in male rats.     

Bidirectional Modulation of Substantia Nigra Activity by Motivational State

A major output nucleus of the basal ganglia is the substantia nigra pars reticulata, which sends GABAergic projections to brainstem and thalamic nuclei. The GABAergic (GABA) neurons are reciprocally connected with nearby dopaminergic neurons, which project mainly to the basal ganglia, a set of subcortical nuclei critical for goal-directed behaviors. Here we examined the impact of motivational states on the activity of GABA neurons in the substantia nigra pars reticulata and the neighboring dopaminergic (DA) neurons in the pars compacta. Both types of neurons show short-latency bursts to a cue predicting a food reward. As mice became sated by repeated consumption of food pellets, one class of neurons reduced cue-elicited firing, whereas another class of neurons progressively increased firing. Extinction or pre-feeding just before the test session dramatically reduced the phasic responses and their motivational modulation. These results suggest that signals related to the current motivational state bidirectionally modulate behavior and the magnitude of phasic response of both DA and GABA neurons in the substantia nigra.     

EFFECTS OF AMINOOXYACETIC ACID AND l-GLUTAMIC ACID-γ-HYDRAZIDE ON GABA METABOLISM IN SPECIFIC BRAIN REGIONS

Abstract— Aminooxyacetic acid (AOAA) administration produced an increase in γ-aminobutyric acid (GABA) levels in regions of cerebral cortex, subcortex and cerebellum. In some cortical areas studied, the maximal effect was observed with 25 mg/kg AOAA; in other regions GABA levels were increased further with 50 and 75 mg/kg AOAA. Pretreatment with 25 mg/kg AOAA effectively inhibited GABA:2-oxoglutarate aminotransferase (GABA-T) and partially inhibited glutamic acid decarboxylase (GAD) activity in regions of cerebral cortex. However, this dose did not affect GAD activity in substantia nigra while GABA-T in the nigra and in the cerebellum was only partially inhibited. In both cortical and subcortical areas, the increase in GABA produced by 25 mg/kg of AOAA was linear. In contrast, l -glutamic acid-hydrazide (GAH) had no effect in the pyriform and cingulate cortex for the first 60 min after injection, and produced a biphasic GABA increase in caudate and substantia nigra over a 4 h period. Results suggest that GAH and AOAA affect regional GABA metabolism differentially and that there are several problems associated with estimating absolute GABA synthesis rates by measuring the rate or GABA accumulation after inhibition of GABA catabolism with these agents. This approach, however, may provide an easily obtainable indication of whether drugs or other manipulations are altering GABA synthesis in a given region.     

尾核P物质对胃运动的抑制效应系通过黑质,迷走背核经迷走神经所介导

本工作观察损毁下丘脑外侧区,黑质,迷走背核及其传出神经对尾核微量注射Ｐ物质引起的胃肌电快波和胃运动抑制效应的影响。实验结果：该抑制效应不依赖于下丘脑外侧区的完整但可被损毁黑质,迷走背核或迷走上所消除。用利血平耗竭交感神经递质则不影响该效应。这些结果表明：尾核ＳＰ的抑胃效应系通过黑质、迷走背核经迷走神经所传出。     

A light and electron microscopic study of GAT-1 in the monkey basal ganglia

The distribution of the GABA transporter GAT-1 was studied by immunocytochemistry and electron microscopy in the monkey basal ganglia. Dense staining was observed in the globus pallidus externa and interna, intermediate in the subthalamic nucleus, and substantia nigra, and light staining in the caudate nucleus and putamen. Staining was observed in axon terminals, but not cell bodies. Electron microscopy showed that the GAT-1 positive axon terminals formed symmetrical synapses, suggesting that they were the terminals of GABAergic neurons. Comparison of areas high in GAT-1 protein with that of GABA showed a good correlation between the density in neuropil staining for GAT-1, and that of GABA.     

Micro topography of Tyrosine Hydroxylase, Glutamic Acid Decarboxylase, and Choline Acetyltransferase in the Substantia Nigra and Ventral Tegmental Area of Control and Parkinsonian Brains

Tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD), and choline acetyl transferase (CAT) were used as markers for catecholamine, gamma-aminobutyric acid, and acetylcholine containing neurons in human mesencephalon. Their rostrocaudal, mediolateral, and dorsoventral distribution was investigated within the substantia nigra pars compacta (SNC) and pars reticulata (SNR) and in the ventral tegmental area (VTA). TH activity was highest in the caudal, medial, and ventral SNC and in the middle of VTA medio-ventrally. The enzyme activity in SNR was low and uniformly distributed. In SNC as well as SNR, GAD activity was high and greater laterally and in the middle of the rostro-caudal extent. No particular pattern of distribution was observed in VTA. an area with low GAD content. In the substantia nigra, CAT activity was low. A characteristic medio-ventral distribution with a peak of high enzyme activity in the middle of the rostrocaudal extent was observed. In VTA, enzyme levels were high and also concentrated medio-ventrally and in the middle of the area. In parkinsonian brains, the distribution of TH was uniformly affected throughout the rostro-caudal extent. In VTA the enzyme activity was not as reduced as in SNC and SNR; the CAT pattern was only disrupted in a very localized part of SNC but not in SNR and VTA. In all three areas, GAD activity was reduced to a uniformly low distribution.     

GABA receptor binding in the parkinsonian brain

The binding of GABA to postsynaptic receptors was studied in the cerebral and cerebellar cortex, caudate nucleus, putamen, pallidum and substantia nigra from autopsy brains of 12 parkinsonian patients and 11 controls. GABA receptor binding in the substantia nigra was significantly decreased in the parkinsonian brain. In the other brain regions, however, GABA binding was unchanged. There was no correlation between GABA binding and sex, age, duration or severity of the disease. The results suggest the involvement of nigral GABA receptor in Parkinson's disease.     

Comparative studies on the GABA-transaminase immunoreactivity in rat and gerbil brains.

Gamma-aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the central nervous system (CNS). Degradation of GABA in the CNS is catalyzed by the action of GABA transaminase (GABA-T). However, the neuroanatomical characteristics of GABA-T in the gerbil, which is a useful experimental animal in neuroscience, are still unknown. Therefore, we performed a comparative analysis of the distribution of GABA-T in rat and gerbil brains using immunohistochemistry. GABA-T immunoreactive neurons were observed in the regions which contained GABAergic neurons of both animals: corpus striatum; substantia nigra, pars reticulata; septal nucleus; and accumbens nucleus. GABA-T + neurons were restricted to layers III and V in the rat. Unlike the rat GABA-T + neurons were observed in layers II, III, and V of the gerbil cerebral cortex. These results suggest that the expression of GABA-T in the gerbil brain may be similar to that in the rat brain, except in the cerebral cortex.     

Chronic nicotine modifies the effects of morphine on extracellular striatal dopamine and ventral tegmental GABA

Previously, we have shown that 7-week oral nicotine treatment enhances morphine-induced behaviors and dopaminergic activity in the mouse brain. In this study, we further characterized the nicotine-morphine interaction in the mesolimbic and nigrostriatal dopaminergic systems, as well as in the GABAergic control of these systems. In nicotine-pretreated mice, morphine-induced dopamine release in the caudate putamen and nucleus accumbens was significantly augmented, as measured by microdialysis. Chronic nicotine treatment did not change basal extracellular concentrations of dopamine and its metabolites in the caudate putamen and nucleus accumbens, nor did it affect the rate of dopamine synthesis, as assessed by 3-hydroxybenzylhydrazine dihydrochloride-induced DOPA accumulation. GABAergic control of dopaminergic activity was studied by measuring extracellular GABA in the presence of nipecotic acid, an inhibitor of GABA uptake. Acute (0.3 mg/kg or 0.5 mg/kg i.p.) and chronic nicotine, as well as morphine (15 mg/kg s.c.) in control mice decreased nipecotic acid-induced increase in extracellular GABA in the ventral tegmental area/substantia nigra (VTA/SN). In contrast, in nicotine-treated mice, morphine increased GABA levels in the presence of nipecotic acid. We did not find any alterations in GABA(B)-receptor function after chronic nicotine treatment. Thus, our data show that chronic nicotine treatment sensitizes dopaminergic systems to morphine and affects GABAergic systems in the VTA/SN.     

Choline acetyltransferase, glutamic acid decarboxylase and somatostatin in the kainic acid model for chronic temporal lobe epilepsy

The aim of the study was to investigate neurochemical changes in a kainic acid (KA; 10 mg/kg, s.c.)-induced spontaneous recurrent seizure model of epilepsy, 6 months after the initial KA-induced seizures. The neuronal markers of cholinergic and gamma-aminobutyric acid (GABA)ergic systems, i.e. choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities, and a marker for neuropeptide, i.e. level of somatostatin, have been investigated. The brain regions investigated were the hippocampus, amygdala/piriform cortex, caudate nucleus, substantia nigra and the frontal, parietal, temporal and occipital cortices. Six months after KA injection, reduced ChAT activity was observed in the amygdala/piriform cortex (47% of control; p<0.001), increased ChAT activity in the hippocampus (119% of control; p<0.01) and normal ChAT activity in the other brain regions. The activity of GAD was significantly increased in all analysed cortical regions (between 146 and 171% of control), in the caudate nucleus (144% of control; p<0.01) and in the substantia nigra (126% of control; p<0.01), whereas in the amygdala/piriform cortex, the GAD activity was moderately lowered. The somatostatin level was significantly increased in all cortical regions (between 162 and 221% of control) as well as in the hippocampus (119% of control), but reduced in the amygdala/piriform cortex (45% of control; p<0.01). Six months after KA injection, the somatostatin:GAD ratio was lowered in the amygdala/piriform cortex (49% of control) and in the caudate nucleus (41% of control), whereas it was normal in the hippocampus and moderately increased in the cortical brain regions. A positive correlation was found between seizure severity and the reduction of both ChAT activities and somatostatin levels in the amygdala/piriform cortex. The results show a specific pattern of changes for cholinergic, GABAergic and somatostatinergic activities in the chronic KA model for epilepsy. The revealed data suggest a functional role for them in the new network that follows spontaneous repetitive seizures.     

Distribution of tyrosine hydroxylase in human and animal brain

The activity of tyrosine hydroxylase (EC 1.10.3.1) when assayed under ideal conditions in young human brains, was comparable to that in brains of other species in level of activity and distribution. The highest levels of activity were in the putamen, caudate nucleus and substantia nigra, in keeping with data on other species. The caudate activity in human brain appeared to decrease substantially with increasing age. In both humans and baboons, the enzyme in the neostriatum was particle-bound and inhibited by the 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine cofactor system. In the substantia nigra it was soluble and stimulated by the 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine cofactor system. The data suggest that tyrosine hydroxylase may be produced in a soluble form in the cell bodies of the substantia nigra but become bound as it moves toward the nerve endings in the putamen and caudate nucleus. The bound form of the enzyme was unstable but the soluble form exhibited considerable stability.     

Immunohistochemical distribution of calbindin D-28k and parvalbumin in the head of the caudate nucleus and substantia nigra of the cat

The heterogeneous anatomy of both the dorsal striatum at the level of the head of the caudate nucleus and of the substantia nigra of cats was analyzed immunohistochemically using two calcium-binding proteins, namely, calbindin D-28k and parvalbumin. The striatal histochemical markers nicotinamide-adenine dinucleotide phosphate diaphorase and acetylcholinesterase were revealed in sections adjacent to those used for the immunohistochemical procedure. The distribution of both the calbindin D-28k and the parvalbumin immunoreactivities is heterogeneous in dorsal, ventral, lateral, and medial areas of the head of the caudate nucleus and is in register with the striosome/matrix pattern displayed by the histochemical markers. These calcium-binding proteins preferentially are located in the matrix compartment of the rostral caudate nucleus. Moreover, in some areas of the rostral two-thirds of the substantia nigra, calbindin D-28k and parvalbumin immunoreactivities appear to follow a complementary pattern that is quite different from the mesencephalic distribution of these two calcium-binding proteins. © 1994 Wiley-Liss, Inc.     

Regional Variation in γ-Aminobutyric Acid Turnover: Effect of Castration on γ-Aminobutyric Acid Turnover in Microdissected Brain Regions of the Male Rat

Abstract: This study compared the turnover of GABA neurons in different brain areas of the male rat and examined the effect of castration on GABA turnover in regions of the brain associated with the control of gonadotropin secretion. To estimate GABA turnover, GABA was quantified by HPLC in microdissected brain regions 0,30,60,90, and 120 min after inhibition of GABA degradation by aminooxyacetic acid (100 mg/kg, i.p.). GABA accumulation was linear in all areas for 90 min ( p < 0.01), and GABA turnover was estimated as the slope of the line formed by increased GABA concentration versus time, determined by linear regression. There was considerable regional variation both in the initial steady-state concentrations of GABA and in the rates of GABA turnover. Of 10 discrete brain structures, GABA turnover was highest in the medial preoptic nucleus and lowest in the caudate nucleus. Turnover times in the terminal fields of known GABAergic projection neurons ranged sevenfold, from 2.6 h in the substantia nigra to 0.4 h in the lateral vestibular nucleus. The effect of castration on GABA turnover in 13 microdissected brain regions was investigated by measuring regional GABA concentrations before and 30 min after injection of aminooxyacetic acid in intact rats or 2 or 6 days postcastration. Following castration, steady-state GABA concentrations were increased, and GABA turnover decreased in the diagonal band of Broca, the medial preoptic area, and the median eminence. GABA turnover increased in the medial septal nucleus and was unaffected in the cortex, striatum, and hindbrain. These results are consistent with the hypothesis that testosterone negative-feedback control of luteinizing hormone-releasing hormone involves steroid-sensitive GABAergic neurons in the rostral and medial basal hypothalamus.     

Effect of stimulation of GABA-ergic structures of the substantia nigra and caudate nucleus on food-getting behavior in the cat

A study was made of the functional significance of GABA-ergic structures of the substantia nigra (SN) and the caudate nucleus (CN) and their role in food-procuring behaviour of cats. Analysis was made of behavioral and EEG-effects of local GABA and the GABA antagonist, picrotoxin, microinjections into the studied brain structures. Stimulation of the GABA-ergic structures of the SN produced a sedative effect and depression of the cat food-procuring behaviour. Effects of stimulation of the CN GABA-ergic structures were to a great degree reverse. The conclusion has been made that GABA-ergic structures of the SN and the CN play different roles in controlling the CN inhibitory influence upon food-procuring behaviour.