Showing papers on "GABAergic published in 1984"

Different populations of GABAergic neurons in the visual cortex and hippocampus of cat contain somatostatin- or cholecystokinin- immunoreactive material

Abstract: The coexistence of gamma-aminobutyric acid (GABA), glutamate decarboxylase (GAD), and cholecystokinin (CCK)- or somatostatin- immunoreactive material in the same neurons was studied in the hippocampus and visual cortex of the cat. One-micrometer-thick serial sections of the same neuron were reacted to reveal different antigens by the unlabeled antibody enzyme method. All CCK- and somatostatin- immunoreactive neurons in the cortex and all CCK-immunoreactive and the majority of somatostatin-immunoreactive neurons in the hippocampus that could be examined in serial sections were also immunoreactive for GABA. In neurons that were immunoreactive for GAD it was often possible to demonstrate immunoreactivity for one of the peptides as well as for GABA. GABA-immunoreactive neurons, as revealed by an antiserum to GABA, were present in all layers of the cortex and hippocampus, and their shape, size, and distribution were similar to GAD-immunoreactive neurons. All GAD-immunoreactive neurons were also positive for GABA, but the latter staining revealed additional neurons. CCK/GABA- and somatostatin/GABA-immunoreactive neurons were present mainly in layers II and upper III and in layers V and VI in the visual cortex. CCK/GABA- immunoreactive neurons were most frequently present in the strata oriens, pyramidale, and moleculare of the hippocampus and in the polymorph cell layer of the dentate gyrus. Somatostatin/GABA- immunoreactive neurons were localized mainly in the stratum oriens and in the hilus of the fascia dentata. The two peptides could not be found in the same neuron. The majority of neurons that were GABA immunoreactive did not stain for either peptide. The presence of CCK- and somatostatin-immunoreactive material in GABAergic cortical neurons raises the possibility that neuroactive peptides affect GABAergic neurotransmission.

Chronic benzodiazepine treatment decreases postsynaptic GABA sensitivity

Abstract: Benzodiazepines exert most of their pharmacological effects by a selective facilitation of the postsynaptic actions of GABA. Clinical, behavioural and electrophysiological studies have shown reduced drug response following chronic benzodiazepine administration. We present here electrophysiological evidence for decreased postsynaptic sensitivity to GABA following chronic benzodiazepine administration as measured by the direct iontophoretic application of GABA and serotonin onto serotonergic cells in the midbrain dorsal raphe nucleus (DRN), known to receive GABAergic input. The subsensitivity to GABA was found to be dose dependent and was seen when diazepam administration was three weeks or longer. Further, acute injection of the specific benzodiazepine antagonist, Ro15-1788, was found to reverse rapidly the decrease in GABA sensitivity observed in chronically diazepam-treated animals without altering GABA sensitivity in vehicle-treated rats. Decreased response to chronic benzodiazepines does not appear to be consistently related to alterations in the number or affinity of receptors for benzodiazepines. Our studies of radioligand-binding showed a decrease in the ability of GABA to enhance benzodiazepine binding in cerebral cortical membranes from chronic diazepam-treated animals without significant changes in benzodiazepine binding site density or affinity.

Development of hyperpolarizing inhibitory postsynaptic potentials and hyperpolarizing response to gamma-aminobutyric acid in rabbit hippocampus studied in vitro.

Abstract: The postnatal development of IPSPs and response to locally applied GABA were examined using intracellular recording techniques in region CA1 of rabbit hippocampal slices maintained in vitro. Pyramidal neurons in slices from mature rabbits demonstrated an EPSP-IPSP sequence following stimulation of stratum radiatum. In these same slices, pressure application of GABA into stratum pyramidale and stratum radiatum produced membrane hyperpolarization and depolarization, respectively. Pyramidal neurons in slices from immature rabbits (age 6 to 10 days) responded differently. Stimulation of stratum radiatum produced a prolonged depolarizing postsynaptic potential; few IPSPs were observed. Ejection of GABA into either stratum pyramidale or stratum radiatum evoked a depolarizing response. The GABA agonist, 4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridine-3-ol (THIP), which has been reported to activate "hyperpolarizing" GABA receptors selectively, primarily produced membrane hyperpolarization when applied to the somata of mature neurons, but it evoked a depolarization when applied to immature neurons. Bicuculline, a GABA antagonist which may have a preferential selectivity for "depolarizing" GABA receptors, was somewhat more efficacious (at 50 microM concentration) at antagonizing GABA-evoked depolarization in immature cells than GABA-evoked hyperpolarization in mature cells. This same concentration of bicuculline partially antagonized IPSPs in mature cells, and it markedly potentiated depolarizing PSPs in immature cells. Taken together, these results suggest that the late development of synaptic inhibition in rabbit hippocampus is due, at least in part, to an immaturity in the GABAergic system.

An immunohistochemical study on the location of GABAergic neurons in rat septum

Abstract: Antisera against L-glutamate decarboxylase (GAD), the synthesizing enzyme of γ-aminobutyric acid (GABA) were used to locate GABAergic neurons and nerve terminals in the septal complex of the rat by using the peroxidase-antiperoxidase method. Varying densities of immunoreactive terminals were observed in saline-treated rats but nerve cell bodies were only demonstrated after intraventricular or intraseptal injections of colchicine. Small and medium-sized GAD-positive neurons were found in lateral septal nuclei, the largest number of these cells being in the pars dorsalis, and in the bed nucleus of the stria terminalis. Several GAD-immunoreactive neurons were located in the medial septal nucleus and the nucleus of the diagonal band of Broca (DB), where the cells were larger in the ventral than dorsal parts of the region. In the medial septal nucleus and in DB the GAD-positive cell bodies were distributed similarly to cholinergic neurons. Large GAD-positive neurons were also found in the septofimbrial nucleus. Intense immunoreactivity in nerve terminals was observed in the lateral septal nucleus, around the island of Calleja magna, between the DB and nucleus accumbens, and in the septofimbrial and triangular septal nuclei. In contrast, the medial septal nucleus, the DB, and the bed nucleus of the stria terminalis only showed weak to moderate immunoreactivity. These results provide direct morphological evidence for the presence of neurons capable of synthesizing GABA in septal nuclei. We suggest that there are two different GABAergic neuronal systems operating in the septum: a population of small cells in the lateral septal nucleus and a group of large cells in the medial septum and DB.

Amino Acid Neurotransmitters and New Approaches to Anticonvulsant Drug Action

Abstract: Amino acids provide the most universal and important inhibitory (gamma-aminobutyric acid (GABA), glycine) and excitatory (glutamate, aspartate, cysteic acid, cysteine sulphinic acid) neurotransmitters in the brain. An anticonvulsant action may be produced (1) by enhancing inhibitory (GABAergic) processes, and (2) by diminishing excitatory transmission. Possible pharmacological mechanisms for enhancing GABA-mediated inhibition include (1) GABA agonist action, (2) GABA prodrugs, (3) drugs facilitating GABA release from terminals, (4) inhibition of GABA-transaminase, (5) allosteric enhancement of the efficacy of GABA at the receptor complex, (6) direction action on the chloride ionophore, and (7) inhibition of GABA reuptake. Examples of these approaches include the use of irreversible GABA-transaminase inhibitors, such as gamma-vinyl GABA, and the development of anticonvulsant beta-carbolines that interact with the "benzodiazepine receptor." Pharmacological mechanisms for diminishing excitatory transmission include (1) enzyme inhibitors that decrease the maximal rate of synthesis of glutamate or aspartate, (2) drugs that decrease the synaptic release of glutamate or aspartate, and (3) drugs that block the post-synaptic action of excitatory amino acids. Compounds that selectively antagonise excitation due to dicarboxylic amino acids have recently been developed. Those that selectively block excitation produced by N-methyl-D-aspartate (and aspartate) have proved to be potent anticonvulsants in many animal models of epilepsy. This provides a novel approach to the design of anticonvulsant drugs.

Brain stem catecholamine mechanisms in tonic and reflex control of blood pressure.

Abstract: Neurons of the lower brain stem maintain resting levels of arterial pressure (AP), mediate reflex responses from cardiopulmonary receptors, and are an important site of the hypotensive actions of alpha 2-adrenergic agonists. Details of the pathways and transmitters that mediate tonic and reflex control of AP are emerging. Afferent fibers of cardiopulmonary receptors in the ninth and tenth nerves terminate bilaterally in the nucleus of the tractus solitarius (NTS). Although some neurons contain substance P, the primary neurotransmitter appears to be the excitatory amino acid L-glutamate (L-glu). Neurons in rostral ventrolateral medulla, which most probably comprise the C1 group of epinephrine neurons, are also critical in AP control. C1 neurons project to innervate cholinergic preganglionic sympathetic neurons in the spinal cord. Stimulation of the C1 area electrically or with L-glu increases AP, while lesions or local injection of the inhibitory amino acid gamma-aminobutyric acid (GABA) lowers AP to levels comparable to spinal cord transection. Lesions of C1 neurons or their pathways abolish vasodepressor reflexes from baroreceptors and vagal afferents. In contrast, noradrenergic neurons of the caudal ventrolateral medulla, the A1 group, project rostrally to innervate, in part, vasopressin neurons of the hypothalamus. Stimulation of A1 neurons lowers AP, while lesions or GABA elevates it. We propose that C1 neurons comprise the so-called tonic vasomotor center of the brain stem and also mediate, via a projection from the NTS, the vasodepressor limb of baroreflexes. The NTS-C1 projection may be GABAergic.

Alterations in uptake and release rates for GABA, glutamate, and glutamine during biochemical maturation of highly purified cultures of cerebral cortical neurons, a GABAergic preparation.

Abstract: This study demonstrates that virtually homogenous cultures of mouse cerebral neurons, obtained from 15-day-old embryos, differentiate at least as well as cultures which in addition contain astrocytes This was indicated by glutamate decarboxylase activity which within 2 weeks rose from a negligible value to twice the level in the adult mouse cerebral cortex, and by a gamma-aminobutyric acid (GABA) uptake rate which quadrupled during the second week in culture and reached higher values than in brain slices Within the same period, the GABA content increased four to five times to 75 nmol/mg protein, and a potassium-induced increase in [14C]GABA efflux became apparent Although the development was faster than in vivo, optimum differentiation required maintenance of the cultures beyond the age of 1 week Uptake and release rates for glutamate and glutamine underwent much less developmental alteration At no time was there any potassium-induced release of radioactivity after exposure to [14C]glutamate, and the glutamate uptake was only slightly increased during the period of GABAergic development This indicates that exogenous glutamate is not an important GABA precursor Similarly, glutamine uptake was unaltered between days 7 and 14, although a small potassium-induced release of radioactivity after loading with glutamine suggests a partial conversion to GABA

Intrinsic GABAergic system of adrenal chromaffin cells.

Abstract: Histochemical and biochemical studies demonstrate that gamma-aminobutyric acid (GABA), glutamic acid decarboxylase (EC 4.1.1.15), and GABA aminotransferase (EC 2.6.1.19) are present in bovine adrenal chromaffin cells. Moreover, [3H]GABA can be taken up and stored by primary cultures of adrenal chromaffin cells. Nicotinic receptor stimulation or KCl depolarization releases the [3H]GABA taken up by these cell cultures. GABA and benzodiazepine recognition sites located in chromaffin cells interact with each other with modalities similar to those described for GABA and benzodiazepine recognition sites located in synaptic membranes prepared from brain tissue. Bicuculline facilitates the release of catecholamine from chromaffin cells induced by nicotinic receptor stimulation but it fails to influence the release of catecholamine evoked by K+ depolarization. Since the GABA-benzodiazepine receptor system appears to modulate nicotinic receptor function, it is suggested that GABA transmission might participate in modulating responsiveness of chromaffin cells to incoming cholinergic stimuli.

Involvement of catecholamines and glutamate in GABAergic mechanism regulatory to luteinizing hormone and prolactin secretion.

Abstract: There is some evidence that a population of estrogen-receptive neurons exists in the preoptic/anterior hypothalamic area which uses gamma-aminobutyric acid (GABA) as neurotransmitter and which is involved in mediating the negative feedback of estrogens on pituitary luteinizing hormone (LH) secretion. These neurons are proposed to be presynaptic inhibitors to norepinephrine (NE) release thereby inhibiting the stimulatory effect of NE on LHRH neurons. Muscimol, a potent GABA agonist, inhibits pituitary LH release in ovariectomized rats after intraventricular injection of 5 nmol. This treatment significantly increased prolactin levels. Catecholamine turnover rates in micropunches of various hypothalamic and mesolimbic structures following intraventricular treatment with muscimol were determined using the method of blocking the activity of tyrosine hydroxylase by alpha-methyl-p-tyrosine. Muscimol did not affect catecholamine, GABA and glutamate concentrations. Turnover rates of NE were significantly reduced in the medial preoptic/anterior hypothalamic area. In this structure as well as in the nucleus accumbens and in the anterior mediobasal hypothalamus turnover rates of dopamine (DA) were also reduced whereas DA turnover in mediocortical amygdalae was increased by muscimol. The selective reduction of NE turnover following muscimol may be explained by a direct or indirect action of the GABA-eric drug on NE axon terminals. The reduced NE and DA turnover in the medial preoptic area may be causally related to reduced serum LH levels whereas the reduced hypothalamic DA turnover may explain increased blood prolactin levels.

Stress-induced enhancement of suppression of [3H]GABA release from striatal slices by presynaptic autoreceptor.

Abstract: The effect of cold and immobilization stress on presynaptic GABAergic autoreceptors was examined using the release of [3H]GABA (gamma-aminobutyric acid) from slices of rat striatum. It was found that in vitro addition of delta-aminolevulinic acid, as well as GABA agonists such as muscimol and imidazoleacetic acid, exhibited a significant suppression of the striatal release of [3H]GABA evoked by the addition of high potassium, whereas delta-aminovaleric acid had no significant effects on the evoked release. These suppressive actions were antagonized invariably by the GABA antagonists, bicuculline and picrotoxin, but not by the glycine antagonist, strychnine. Cholinergic agonists, such as pilocarpine and tetramethylammonium, also attenuated significantly the evoked release of [3H]GABA from striatal slices, while none of its antagonists, including atropine, hexamethonium and d-tubocurarine, affected the release. On the other hand, in vitro addition of dopamine receptor agents such as dopamine, apomorphine, and haloperidol, or the inhibitory amino acids, glycine, beta-alanine, and taurine failed to influence the evoked release of [3H]GABA from striatal slices. Application of a cold and immobilization stress for 3 h was found to induce a significant enhancement of the suppressive effects by muscimol and delta-aminolevulinic acid on the evoked release of [3H]GABA, without affecting that by pilocarpine and tetramethylammonium. These results suggest that the release of GABA from striatal GABA neurons may be regulated by presynaptic autoreceptors for this neuroactive amino acid, and may play a significant functional role in the exhibition of various symptoms induced by stress.

Gabaergic mechanisms in antinociception

Abstract: GABAergic mechanisms appear to be involved in antinociceptive processes. Generally, peripheral administration of GABAergic agents increases the antinociceptive effect of morphine, but central administration inhibits this effect, suggesting that multiple interactions may occur. GABAergic agents also can produce antinociception directly. Muscimol and THIP (GABA A agonists) act at supraspinal sites to produce antinociception, but do not appear to interact with bicueulline sensitive receptors. Baclofen (a GABA B agonist) acts at both supraspinal and spinal sites. Supraspinal mechanisms Include inhibition of ascending noradrenergic and dopaminergic pathways but activation of descending noradrenergic pathways. The spinal mechanism may involve postsynaptic inhibition of the effect of substance P. D-Baclofen is an antagonist at spinal baclofen receptors. Antinociception produced by inhibitors of GABA-transaminase is not reduced by bicuculline in most studies, while manipulations which increase the antinociceptive effect of baclofen do not alter or block the effect of GABA-transaminase inhibitors. An understanding of the role of GABA A and GABA B receptors in antinociception will require clarification of some curious pharmacological actions of bicuculline and the use of a specific GABA B receptor antagonist.

A new type of anticonvulsant, stiripentol. Pharmacological profile and neurochemical study.

Abstract: 4,4-Dimethyl-1-[3,4-(methylenedioxy)-phenyl]-1-penten-3-ol (stiripentol), selected from a series of alpha-ethylene alcohols, demonstrated anticonvulsant activity in studies in the rat and rabbit in which convulsions were induced electrically and chemically using pentetrazol, bicuculline and strychnine. Neurochemical studies showed that stiripentol in vitro did not act as a GABA receptor agonist, instead it inhibited the synaptosomal uptake of 3H-labelled GABA. Stiripentol has been shown elsewhere to inhibit GABA transaminase. These findings suggest that the anticonvulsant activity of stiripentol involves two aspects of the GABAergic mechanism in which the metabolic transamination and synaptosomal uptake of this neurotransmitter are inhibited.

GABA-related phenomena, models of nervous system function, and seizures.

Abstract: Models of nervous system function are presented that place particular emphasis on the roles in nervous system function of inhibitory neurons that liberate gamma-aminobutyric acid (GABA) as neurotransmitter. The nervous system is considered to be highly restrained, with inhibitory neurons acting like reins that serve to keep the neuronal "horses" from running away. In behavioral sequences, whether innate or learned, preprogrammed circuits are released to function at varying rates and in various combinations. This release is accomplished largely by the disinhibition of pacemaker neurons whose activities are under the control of tonically active inhibitory command neurons, many of which may use GABA as a transmitter. In addition to their restraining function, local circuit GABAergic neurons participate in feed-forward, feedback, surround, and presynaptic inhibition and in presynaptic facilitation. Information arriving from several sources is integrated in specialized analyzing regions, such as the cerebellar cortex, basal ganglia, and reticular nucleus of the thalamus. Monosynaptic inhibitory GABAergic outputs reflecting this analysis then play upon neural elements in the direct channels, making their activity optimally compatible temporally and spatially with that of neural elements elsewhere in the central nervous system. Seizures are prototypical of incoordination between inhibition and excitation. Major causes of seizures may be the loss of inhibitory GABAergic terminals at the site of focal cortical epilepsy or a disturbance in various aspects of GABAergic function.

Catecholaminergic and GABAergic anatomical relationship in the rat substantia nigra, locus coeruleus, and hypothalamic median eminence: immunocytochemical visualization of biosynthetic enzymes on serial semithin plastic-embedded sections.

Abstract: The visualization of protein antigens has been performed on semithin sections embedded in Araldite. After partial removal of the resin and a light proteolytic treatment of the tissue we were able to localize several biosynthetic enzymes: tyrosine hydroxylase (TH), phenylethanolamine N-methyltransferase (PNMT), and glutamic acid decarboxylase (GAD), which are, respectively, markers of catecholaminergic, adrenergic, gamma-aminobutyric acid (GABA)ergic systems. This technique afforded a high resolution of light microscopy details and immunostaining of TH, GAD, and PNMT on serial sections enabled us to compare with great precision GABAergic and adrenergic innervations in the rat locus coeruleus. In addition, it allows us to study the possible relationship between these terminals and the noradrenergic neurons. We also compared the general pattern of distribution of TH- and GAD-positive endings in the hypothalamic median eminence. The preliminary results obtained with this technique revealed some interesting fa...

Neurotransmitter abnormalities in genetically epileptic rodents.

Abstract: A growing body of evidence supports a pathophysiological role for norepinephrine (NE) and serotonin in the regulation of seizures in the genetically epilepsy-prone rat (GEPR). Other evidence indicates that gamma-aminobutyric acid (GABA) and taurine may also participate in the seizure regulation process. Innate deficits in NE and serotonin appear to be causes of the genetically determined seizure-prone states of the GEPR, whereas abnormalities in GABAergic systems and taurine metabolism may represent inadequate attempts of the central nervous system to compensate for the seizure-prone state in these rats. In audiogenic seizure-susceptible (AGS) mice, evidence suggests a role for dopamine as well as GABA and possibly serotonin. NE may contribute to the regulation of seizures in AGS mice, but consistent evidence for a primary role for this monoamine is lacking. It is suggested that there is no single common neurotransmitter abnormality underlying genetic seizure disorders in humans or other animals and that the GEPR and the AGS mouse may both serve as good models for study of the neurochemical abnormalities that underlie the different human epilepsies.

Decreased Uptake and Release of D‐Aspartate in the Guinea Pig Spinal Cord After Dorsal Root Section

Abstract: This study attempts to determine if L-glutamate and/or L-aspartate may be transmitters of dorsal sensory neurons. The uptake and the electrically evoked release of D-[3H]aspartate, a putative marker for L-glutamate and L-aspartate, were measured in the cervical enlargement (segments C4-T1) of the guinea pig spinal cord before and after cutting dorsal roots C5-T1 on the right side. The uptake and the release of gamma-aminobutyric acid (GABA) also were measured as indices of the integrity of GABAergic neurons in the spinal cord. The cervical enlargement was excised and divided into left and right halves, then into dorsal and ventral quadrants. Quadrants from unlesioned animals took up D-aspartate and GABA, achieving concentrations in the tissues which were 14-25 times that in the medium. Subsequently, electrical stimulation evoked a Ca2+-dependent release of D-aspartate and of GABA. The uptake and release of D-aspartate and GABA were similar in tissues taken from intact and sham-operated animals. However, dorsal rhizotomy, without damage to dorsal radicular or spinal blood vessels, depressed the uptake (by 22-29%) and the release (by 50%) of D-aspartate only in quadrants ipsilateral to the lesion. The uptake and the release of GABA were unchanged. In transverse sections of the cervical enlargement, stained to reveal degenerating fibers, by far the heaviest loss of axons occurred in the cuneate fasciculus and in the gray matter ipsilateral to the cut dorsal roots. These findings suggest that the synaptic endings of dorsal sensory neurons probably mediate the uptake and the release of D-aspartate and, therefore, may use L-glutamate or L-aspartate as a transmitter. When spinal blood vessels were damaged during dorsal rhizotomy, the deficits in D-aspartate uptake and release were larger than those in the absence of vascular damage and were accompanied by deficits in GABA uptake and release. These findings imply that vascular damage results in the loss of intraspinal neurons, some of which probably mediate the uptake and release of D-aspartate and, therefore, may use L-glutamate and/or L-aspartate as a transmitter.