Showing papers on "GABAergic published in 1983"

First visualization of glutamate and GABA in neurones by immunocytochemistry

Abstract: Immunocytochemical methods for peptides and serotonin have greatly advanced the study of neurones in which these substances are likely to be transmitters1,2. Such direct techniques have not so far been available for the amino acid transmitter candidates. We report here the selective immunocytochemical visualization of the putative transmitters glutamate (Glu) and γ-aminobutyrate (GABA) by the use of antibodies raised against the amino acids coupled to bovine serum albumin (BSA) with glutaraldehyde (GA). The tissue localizations of Glu-like and GABA-like immunoreactivities (Glu-LI and GABA-LI) matched those of specific uptake sites for Glu and GABA, and, in the case of GABA-LI, also that of the specific marker enzyme glutamic acid decarboxylase (GAD). Thus, GABA-LI was located in what are believed to be GABAergic inhibitory neurones, whereas Glu-LI was concentrated in excitatory, possibly glutamatergic neurones. Preliminary electron microscopic observations suggest that the transmitter amino acids are significantly concentrated in synaptic vesicles.

GABAergic cells in the dentate gyrus appear to be local circuit and projection neurons.

Abstract: Immunocytochemical results indicate that GAD-positive neurons are found in the molecular and granule cell layers of the dentate gyrus as well as in the hilar region. GAD-positive cells in the molecular and granule cell layers are identified as various types of local circuit neurons. Most of the GAD-positive puncta found throughout the molecular layer and within the granule cell layer are interpreted as axon terminals of these neurons, including five types of basket cells. This interpretation is based on data that indicate the axons of basket cells form synapses with the somata and proximal dendrites of granule cells. The results in the hilus show that 60% of the hilar neurons are GAD-positive. Since previous studies have indicated that 80% of hilar neurons give rise to both associational and commissural pathways, many GABAergic neurons in the hilus are probably projection neurons. This finding is consistent with recent physiological data which suggest that commissural pathway stimulation directly inhibits granule cells. Therefore, GABAergic cells in the dentate gyrus appear to be both projection and local circuit neurons.

Distribution of GABA‐T‐Intensive neurons in the hat forebrain and midbrain

Abstract: The neuronal distribution of gamma-aminobutyric acid (GABA) transaminase (GABA-T), the enzyme which metabolizes GABA, has been mapped in rat brain. The method involves staining for newly synthesized GABA-T by the previously established nitro blue tetrazolium technique in animals killed 8-48 hours after administration of gabaculine, an irreversible inhibitor of GABA-T. Neuronal staining is obscured by staining of other elements if initial suppression is inadequate or survival times postgabaculine are too long. With appropriate conditions, GABA-T-positive neuronal somata can be widely detected. The stained cells include neuronal groups previously reported to be GABAergic on the basis of glutamate decarboxylase (GAD)-colchicine immunocytochemistry and other methods, i.e.: Purkinje, basket, Golgi, and stellate neurons of the cerebellum; basket and stellate neurons of the hippocampus; granule and periglomerular cells of the olfactory bulb; magnocellular neurons of the hypothalamus; and neurons of the striatum, pallidum, entopeduncular nucleus, cortex, medial septal area, diagonal band, substantia innominata, reticular nucleus of the thalamus, substantia nigra, and dorsal raphe. Other cells that stain intensely for GABA-T and may be GABAergic include neurons in the midlateral septal area, accumbens, the central medial and basal nuclei of the amygdala, zona incerta, the brainstem reticular formation, central gray, interstitial nucleus of Cajal, and various thalamic nuclei including the periventricular, intralaminar, rhomboid, and subparafascicular. Known non-GABA neuronal groups are negative for GABA-T staining under these conditions, reinforcing the hypothesis that GABA neurons are far more GABA-T intensive than other neurons.

Changes in [3H]muscimol binding in substantia nigra, entopeduncular nucleus, globus pallidus, and thalamus after striatal lesions as demonstrated by quantitative receptor autoradiography

Abstract: A quantitative autoradiographic technique for measuring the binding of [3H]muscimol to central nervous system GABA receptors is described using tritium-sensitive film [3H]Muscimol binding was studied in primary and secondary striatal projection areas of rat brain following kainic acid lesions of the striatum Seven days after the lesion, binding affinities in the striatum and its projection areas were not altered significantly There was a loss of [3H]muscimol receptors in the striatum Receptors increased in numbers in the ipsilateral globus pallidus (19%), entopeduncular nucleus (22%), and substantia nigra pars reticulata (38%) [3H]Muscimol binding was decreased in the ipsilateral anteroventrolateral and ventromedial (8%) thalamic nuclei [3H]Muscimol binding in other brain areas (layer IV of the cerebral cortex, central gray, superior colliculus, and stratum moleculare of hippocampus) was not affected The findings suggest that a loss of striatal innervation resulted in increased numbers of GABA receptors in striatal projection sites It is further suggested that loss of inhibitory striatal inputs to neurons in the entopeduncular nucleus and substantia nigra pars reticulata may activate GABAergic projections to thalamus and thus result in decreased numbers of thalamic GABA receptors

Light and electron microscopic immunocytochemical localization of glutamic acid decarboxylase in monkey geniculate complex: evidence for gabaergic neurons and synapses

Abstract: The morphology and distribution of neuronal cell bodies and synapses that utilize y-aminobutyric acid (GABA) as a transmitter have been studied in Mczcaca dorsal lateral geniculate nucleus (dLGN), ventral lateral geniculate nucleus (vLGN), and reticular nucleus of the thalamus (RNT). These cells are identified by immunocytochemical staining for the antiserum to the enzyme that synthesizes GABA, glutamic acid decarboxylase (GAD) and visualized by the peroxidase-antiperoxidase method for light and electron microscopy. In the dLGN, GAD-positive (GAD+) cell bodies are found in all layers and in the interlaminar zones. The neuropil is more heavily labeled in the laminar than the interlaminar zones, with the magnocellular layers being most densely labeled. In the vLGN no stained cell bodies are seen, but the neuropil is intensely GAD+, especially in the retinal input layer. The RNT is just the opposite, with many GAD+ neurons but sparsely labeled neuropil. The GAD+ neurons in dLGN have small cell bodies with a large infolded, unlabeled nucleus. GAD reactivity is found in the thin rim of cytoplasm and in the two to four thick, straight dendrites, and on the cytoplasmic surfaces of mitochondria, Golgi and membraneous cisternae, and vesicles. GAD+ synaptic profiles are found in both preand postsynaptic relationships in the dLGN. Some GAD+ profiles are both preand postsynaptic in the same section, suggesting that these are presynaptic dendrites. In the laminae, GAD+ presynaptic profiles are very commonly found within synaptic glomeruli where they lie postsynaptic to a retinal axon terminal and presynaptic to an unlabeled dendrite, which also receives input from the retinal terminal. Outside of glomeruli, individual GAD+ profiles are presynaptic to either labeled or unlabeled cell bodies and dendrites. Other GAD+ profiles are postsynaptic to unlabeled F or RSD-type terminals. Individual GAD+ profiles ending on unlabeled or labeled dendrites are found in the interlaminar zones. These data, when combined with previously published work on dLGN circuitry, suggest that GAD+ glomerular profiles are the presynaptic dendrites of the dLGN interneuron, whereas the individual GAD+ contacts arise from axons of RNT neurons. The primate dorsal lateral geniculate nucleus (dLGN) whose processes remain within the dLGN (reviewed by has been the subject of numerous studies that have Guillery, 1971; Wilson and Hendrickson, 1981). In monresulted in a substantial amount of information concernkey, more than 90% of the neurons are labeled after ing its structural organization. It appears to have two horseradish peroxidase injections into striate cortex, inmain neuronal types: projection cells that send their dicating that interneurons are present but scarce (Ogren axons to visual cortex, and intrinsic or interneurons and Hendrickson, 1976; Norden and Kaas, 1978). Several ’ This study was supported by National Institutes of Health Reinvestigators have described a candidate for interneurons search Grants EY-01208, NS18858, EY-03909, NS13224, and in part by in Golgi preparations of monkey dLGN (Polyak, 1957; EY-01730, RRO0166, and HD02274. A. E. H. is the recipient of the Campos-Ortega et al., 1968; Pasik et al., 1973; Saini and Dolly Green Scholar Award from Research to Prevent Blindness, Inc., Carey, 1981; Wilson and Hendrickson, 1981). These cells and a travel grant from the Burroughs WeIIcome Fund. are small with relatively few, straight, long primary den* To whom correspondence should be addressed. drites that branch into elaborate processes with multiple

GABA acts directly on cells of pituitary pars intermedia to alter hormone output

Abstract: Recent immunohistochemical evidence from the rat, indicating that γ-aminobutyric acid (GABA)-containing fibres of central nervous origin project to the pars intermedia of the pituitary1,2, prompts inquiry into the function of this innervation. There is electrophysiological evidence that GABA acts directly on melanotrophs isolated from rat, through bicuculline-blockable receptors, to increase Cl− conductance and thereby drive the membrane potential towards the Cl− equilibrium potential in these cells, resulting in depolarization at rest or reduction of the depolarization caused by excess K+ (ref. 3). As voltage-dependent Ca channels can participate in the regulation of secretion in these cells4, we have now examined the effect of GABA on hormone output and find that it first stimulates and then inhibits spontaneous secretion of melanocyte-stimulating hormone (MSH) and inhibits K+-evoked secretion. Moreover, our pharmacological evidence suggests that similar receptors are involved in the secretory and the electrophysiological responses. A function of the GABAergic innervation may therefore be to regulate hormone output by acting directly on the melanotrophs, and this regulation may be affected by the changes in electrical properties induced by GABA.

Involvement of preoptic-anterior hypothalamic GABA neurons in the regulation of pituitary LH and prolactin release

Abstract: The effects of intraventricular injections of the highly specific gamma-amino-butyric acid (GABA) agonist muscimol (5 nmol/animal) on blood LH and prolactin levels were measured in ovariectomized (ovx) and in ovx estrogen-progesterone (OEP) primed rats. While the drug stimulated pituitary prolactin release in both experimental groups, pituitary LH release was significantly inhibited in the ovx animals. Muscimol was without any effect on LH levels in ovx-OEP primed rats. Bilateral implantation of tubes containing a muscimol-mannitol mixture into the medial preoptic/ anterior hypothalamic (MPO/AH) area abolished pulsatile LH release whereas blood prolactin values were elevated. The intraventricular injection of GABA (8 μmol) also reduced LH and increased prolactin levels in the blood. Measurements of catecholamine turnover rates in the MPO/AH and in the mediobasal hypothalamus (MBH) yielded reduced preoptic but unchanged hypothalamic norepinephrine (NE) and stimulated hypothalamic dopamine (DA) turnover. In view of the well known stimulatory involvement of the NE system in the mechanism of pulsatile LH release and the inhibitory effect of GABA and its agonist muscimol on pulsatile LH release, it is suggested that GABA inhibits NE release in the MPO/AH by the mechanism of presynaptic inhibition. The observation that muscimol is unable to suppress LH release in vox OEP-primed rats may indicate that those estrogen receptive neurons in the MPO/AH which mediate the negative feedback action of the steroid may use GABA as neurotransmitter and that they are the neurons which inhibit NE release. The inhibitory effect of locally implanted muscimol into the MPO/AH also supports this hypothesis. The facilitatory action of this implanted GABAergic drug on prolactin release points to the involvement of control mechanisms for the regulation of prolactin secretion which reside in the MPO/ AH. The stimulatory effect of intraventricularly injected GABA on hypothalamic DA turnover makes it likely that other than dopaminergic mechanisms are involved in mediating the stimulatory effect of GABA on prolactin release.

Glutamic acid decarboxylase-immunoreactive neurons and horseradish peroxidase-labeled projection neurons in the ventral posterior nucleus of the cat and Galago senegalensis

Abstract: Immunocytochemical methods were used to identify neurons in the ventral posterior nucleus of the cat and Galago senegalensis that contain glutamic acid decarboxylase (GAD), the synthetic enzyme for the inhibitory neurotransmitter, GABA. In both species GAD-immunoreactive neurons make up about 30% of the total neurons in the ventral posterior nucleus and form a distinct class of small cells. After cortical injections of horseradish peroxidase (HRP), GAD-immunoreactive cells are not labeled with HRP and may, therefore, be GABAergic local circuit neurons. Comparison of the dendritic morphology of GAD-immunoreactive neurons with that of HRP-filled projection neurons reveals that the morphology of the GAD-containing neurons is distinct and, in particular, that the GAD-immunoreactive neurons display fewer primary dendrites. The relay neurons, in turn, can be divided into classes based on dendritic morphology and cell body size.

Effect of acute and chronic cholinesterase inhibition with diisopropylfluorophosphate on muscarinic, dopamine, and GABA receptors of the rat striatum.

Abstract: The effects of acute and chronic administration of diisopropylfluorophosphate (DFP) to rats on acetylcholinesterase (AChE) activity (in striatum, medulla, diencephalon, cortex, and medulla) and muscarinic, dopamine (DA), and gamma-aminobutyric acid (GABA) receptor characteristics (in striatum) were investigated. After a single injection of (acute exposure to) DFP, striatal region was found to have the highest degree of AChE inhibition. After daily DFP injections (chronic treatment), all brain regions had the same degree of AChE inhibition, which remained at a steady level despite the regression of the DFP-induced cholinergic overactivity. Acute administration of DFP increased the number of DA and GABA receptors without affecting the muscarinic receptor characteristics. Whereas chronic administration of DFP for either 4 or 14 days reduced the number of muscarinic sites without affecting their affinity, the DFP treatment caused increase in the number of DA and GABA receptors only after 14 days of treatment; however, the increase was considerably lower than that observed after the acute treatment. The in vitro addition of DFP to striatal membranes did not affect DA, GABA, or muscarinic receptors. The results indicate an involvement of GABAergic and dopaminergic systems in the actions of DFP. It is suggested that the GABAergic and dopaminergic involvement may be a part of a compensatory inhibitory process to counteract the excessive cholinergic activity produced by DFP.

Anatomical relationships of dopaminergic and GABAergic systems with the GnRH-systems in the septo-hypothalamic area. Immunohistochemical studies.

Abstract: Immunohistochemical double staining for gonadotropin releasing hormone (GnRH) and tyrosine hydroxylase (TH) or glutamic acid decarboxylase (GAD) reveals in the septo-preopticdiagonal band complex of the rat brain close spatial associations between GnRH-immunoreactive perikarya and TH and GAD immunoreactive fibers. In the organum vasculosum laminae terminalis, no close spatial relationships could be observed between TH-or GAD-positive fibers and the GnRH-containing system. In contrast, in the median eminence substantial overlap exists in the distribution of GnRH with TH and GAD containing nerve fibers. This overlap is most intense for TH throughout the lateral palisade zone, while for GAD it is more restricted to the outermost portion of the external palisade zone. The results suggest that dopamine and GABA influence GnRH secretion via axosomatic contacts in the septo-preoptic-diagonal band complex, as well as via axo-axonic interactions in the median eminence, while no such interactions seem to exist in the organum vasculosum laminae terminalis. Since dopaminergic cell bodies in the ventral hypothalamus are closely apposed by GnRH and GAD containing fibers, the existence of feedback circuits among GnRH, dopamine and GABA systems is proposed.

Effect of gamma-aminobutyric acid agonists, glycine, taurine and neuropeptides on acetylcholine release from the rabbit retina.

Abstract: The light-evoked release of [3H]acetylcholine (ACh) from the rabbit retina in vivo was measured and taken as an index of cholinergic amacrine cell activity. The light-evoked release of [3H]ACh was reduced by locally applied gamma-aminobutyric acid (GABA), muscimol and 3-aminopropanesulphonic acid (3-APS). The concentrations of these drugs which reduced the light-evoked release of [3H]ACh by 50% (EC50) were 900, 0.3 and 5 microM respectively. In contrast, (-)-baclofen (5 mM), but not (+)-baclofen, significantly increased the light-evoked release of [3H]ACh. The GABA antagonist, bicuculline increased the resting release of [3H]ACh but abolished the inhibitory action of muscimol on the light-evoked release of [3H]ACh. Glycine and taurine also reduced the light-evoked release of [3H]ACh from the retina, their EC50 values being 1.5 and 0.3 mM respectively. This action was blocked by strychnine, but not by bicuculline. In contrast to the GABA antagonist, strychnine did not affect the spontaneous resting release of [3H]ACh. Retinal [3H]ACh release was not affected by dopamine, 5-hydroxytryptamine (5-HT) morphine, substance P, somatostatin, cholecystokinin sulphate, thyrotropin releasing hormone, luteinizing hormone releasing hormone or angiotensin. Electroretinographic changes produced by amino acids and GABA agonists involved mainly the b-wave and were not correlated with their effects on ACh release. Thus, GABA increased the b-wave amplitude, 3-APS had no effect, whilst muscimol, taurine and glycine either had no effect, or reduced the b-wave amplitude. No obvious changes in the e.r.g. were produced by baclofen, dopamine, 5-HT, morphine or any of the peptides studied with the exception of somatostatin, which reduced the amplitude of the b-wave. It is concluded that cholinergic amacrine cell activity in the rabbit retina may be affected by inputs from other amacrines using GABA or glycine (taurine) as their transmitters, but probably not by inputs from peptidergic or dopaminergic amacrine cells. Our experiments do not provide evidence on the sites of action of GABA, glycine or taurine but the action of bicuculline on the resting release of ACh implies that the activity of the cholinergic amacrine cells is affected by a tonically active GABAergic input.

GABA affects the release of gastrin and somatostatin from rat antral mucosa.

Abstract: gamma-Aminobutyric acid (GABA) is regarded as the major inhibitory neurotransmitter in the central nervous system of vertebrates. GABA exerts its inhibitory actions by interacting with specific receptors on pre- and postsynaptic membranes and has been shown to inhibit somatostatin release from hypothalamic neurones in vitro. Concepts of innervation of the gastrointestinal tract have been expanded by recent studies which suggest that GABAergic neurones are not confined solely to the central nervous system but may also exist in the vertebrate peripheral autonomic nervous system. Jessen and coworkers have demonstrated the presence, synthesis and uptake of GABA by the myenteric plexus of the guinea pig taenia coli, and have documented the presence of glutamic acid decarboxylase (GAD) in isolated myenteric plexus. This enzyme is responsible for the conversion of glutamic acid to GABA in GABAergic neurones. The possibility that GABA may have a role in neurotransmission or neuromodulation in the enteric nervous system of the vertebrate gut has been suggested by several investigators. Furthermore, GABA receptors have been demonstrated on elements of the enteric nervous system. The effects of GABA on gastrointestinal endocrine cell function have not been examined. We report here the effects of GABA on gastrin and somatostatin release from isolated rat antral mucosa in short-term in vitro incubations.

Amino acids in the substantia nigra of rats with striatal lesions produced by kainic acid.

Abstract: In an attempt to estimate the pool size of glutamate and other amino acids in gamma-aminobutyric acid (GABA)-containing neurons, we determined the content of 12 amino acids in the bilateral substantia nigra of rats, in which unilateral striatal lesions had been made with kainic acid two weeks earlier. The assay of the amino acids (including glutamate, aspartate, glutamine, asparagine, glycine, and GABA) and ethanolamine was based on HPLC and fluorimetric detection after precolumn derivatization with omicron-phthaldialdehyde. The levels of all measured amino acids (except those of tyrosine, threonine, and ethanolamine) were decreased in the affected striatum, but only the levels of aspartate, taurine, and GABA were lowered in the ipsilateral substantia nigra. These results indicate that the pool size of the various amino acids in the striatonigral GABAergic pathway is small compared to their nigral content, and that in addition to GABA a significant fraction of aspartate and taurine may be confined to nerve terminals in the substantia nigra.

Differential localization of type I and type II benzodiazepine binding sites in substantia nigra

Abstract: A number of studies have suggested the existence of multiple benzodiazepine binding sites in the brain1–20 We have recently reported the physical separation of two apparent benzodiazepine binding site subtypes21, the pharmacological properties, and distribution in tissue sections of which correspond to the putative type I and type II sites20,22 Benzodiazepine and γ-aminobutyric acid (GABA) receptors have been shown to interact23, and lesions of the GABAergic striatonigral pathway, which lead to GABA supersensitivity24,25, both increase the numbers of GABA binding sites24,26 and enhance GABA-stimulated benzodiazepine binding27 We demonstrate here that degeneration of striatonigral fibres increases the density of putative type I benzodiazepine binding sites in the substantia nigra and decreases the density of the putative type II sites This suggests that type I sites that increase after denervation are postsynaptic, whereas the type II sites reduced by the lesion may be localized to axons or terminals of the striatonigral pathways

Modulation of cortical acetylcholine and gamma-aminobutyric acid release in freely moving guinea pigs: effects of clonidine and other adrenergic drugs.

Abstract: The effects of various doses of clonidine and norepinephrine (NE) on the release of acetylcholine (ACh) and gamma-aminobutyric acid (GABA) from the brain surface of freely moving guinea pigs have been investigated in order to study the role of alpha adrenoceptors on the function of cortical cholinergic and GABAergic neurons. Clonidine administration at doses of 7.5 and 18.7 nmol/kg inhibits by 40% the release of ACh; larger doses (112 nmol/kg) are inactive. On the other hand, the largest dose of clonidine used in this study (112 nmol/kg) increases the release of GABA by 45%, whereas lower doses are inactive. Norepinephrine (0.9 mumol i.c.v.) decreases by 40% the release of ACh and increases by 80% that of GABA. The inhibitory effects of clonidine and of NE on cortical ACh output are completely antagonized by yohimbine (0.28 mumol/kg), a selective alpha-2 antagonist, thus suggesting an involvement of the alpha-2 adrenoceptors in the neurochemical action of the drug. However, yohimbine releases GABA and does not prevent the action of clonidine or of NE on the cortical GABA system. On the other hand, prazosin (35.8 nmol/kg), a selective alpha-1 antagonist, completely antagonizes the stimulating effects of clonidine and of NE on the release of GABA, suggesting that alpha-1 receptors modulate this release. The present experiments indicate that the neurochemical and neuropharmacological profile of activity of clonidine is strictly dependent upon the dose of the drug. In addition, they support the concept that cortical alpha adrenoceptors modulate the function of neurons releasing ACh or GABA.