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At least 37 records · Page 2Linked to original sources
PubMed1978

Baclofen (beta-p-chlorophenyl-gamma-aminobutyric acid) enhances [3H]gamma-aminobutyric acid (3H-GABA) release from rat globus pallidus in vitro.

The rat globus pallidus has been investigated as a possible model in which to study pre-synaptic GABA mechanisms in vitro. (+/-)-Baclofen (300 micrometer-1 mM) significantly enhanced the release of radioactivity from superfused slices of rat globus pallidus prelabelled with 3H-GABA in vitro. This releasing action was specific to the (+)-isomer of baclofen: neither the (-)-isomer nor another neuronal depressant dl-alpha-epsilon-diaminopimelic acid had any significant effect. The releasing effect of baclofen appeared unrelated to the phenethylamine moiety of its structure as neither beta-phenethylamine nor dopamine evoked release of 3H-GABA from pallidal slices. Baclofen increased the efflux of radioactivity from pallidal slices prelabelled with either [3H]-beta-alanine or [3H]diaminobutyric acid in vitro. The use of specific glial and neuronal GABA uptake blocking compounds (beta-alanine and (+/-)-cis-1,3-amino-cyclohexanecarboxylic acid) did not permit resolution of the elements from which baclofen was evoking [3H]GABA release. Baclofen also inhibited uptake of [3H]GABA into pallidal slices with an IC50 value of 6 x 10(-4) m. The GABA-like properties of baclofen may be related to the (+)-isomer while non-specific neuronal depressant actions are an effect of the (-)-isomer. The potential of the (+)-isomer as an antipsychotic agent while (-)-baclofen remains the effective antispastic drug free from unwanted side-effects, is discussed.

Alanine↗
PubMed2001

Upregulation of gamma-aminobutyric acid transporter expression: role of alkylated gamma-aminobutyric acid derivatives.

Pregabalin [(S)-(+)-3-isobutylgaba] and gabapentin [1-(aminomethyl)cyclohexane acetic acid] are gamma-aminobutyric acid (GABA) derivatives that are effective in the treatment of behavioural disorders, convulsions, epilepsy and hyperalgesia. The mechanisms underlying the diverse actions of these compounds in the brain have not been well elucidated. To test the hypothesis that these compounds exert some of their effects on GABAergic systems in the brain, we examined their role in regulating the rat brain GABA transporter GAT1, a plasma membrane protein involved in regulating synaptic transmitter levels. Prolonged incubation of hippocampal cultures, which endogenously express GAT1, with gabapentin and pregabalin caused a 2-fold increase in subsequent GABA uptake, which was concentration- and time-dependent. This increase in uptake was correlated with a redistribution of GAT1 protein from intracellular locations to the plasma membrane. Further experiments also suggested that the signal transduction cascade that modulates pregabalin-mediated GAT1 redistribution may involve pathways activated by specific GAT1 substrates and antagonists but does not involve protein kinase C and tyrosine kinases, two other pathways known to regulate GAT1 redistribution. These data suggest that pregabalin and gabapentin may exert some of their actions in the brain by altering GABAergic signalling.

Animals↗
PubMed1986

Effect of ethosuximide alone and in combination with gamma-aminobutyric acid receptor agonists on brain gamma-aminobutyric acid concentration, anticonvulsant activity and neurotoxicity in mice.

The acute administration of an anticonvulsant dose of ethosuximide (150 mg/kg) had no effect on brain gamma-aminobutyric acid (GABA) concentration, whereas a toxic dose (400 mg/kg) increased significantly the concentration of brain GABA (1.23 +/- 0.05 vs. 1.92 +/- 0.14 mumol/g of wet tissue). The administration of 500 mg/kg/day of ethosuximide for 1, 2, 4, 6, 8 and 11 days induced neurotoxicity in 100, 100, 67, 0, 0 and 0% of animals, respectively, and increased brain GABA concentration 46, 38, 25, 14, 9 and 0%, respectively. These results imply that the tolerance that develops in response to the chronic administration of toxic doses of ethosuximide correlates well with the concentration of brain GABA. 4,5,6,7-Tetrahydroisoxazolo [5,4-c]pyridin-3-ol even in toxic doses had no effect on the anticonvulsant activity of ethosuximide. Combination studies with ethosuximide and progabide demonstrated that the antipentylenetetrazol activity of the individual components interacts additively. Likewise, combinations of either ethosuximide and 4,5,6-tetrahydroisoxazolo [5,4-c]pyridin-3-ol or ethosuximide and progabide showed an additive effect by the rotorod test. These results indicate that the antipentylenetetrazol activity of ethosuximide is unrelated to GABA function and that the increase in brain GABA concentration induced by toxic doses of ethosuximide contributes to its neurotoxicity.

Animals↗
PubMed1987

Evidence for gamma-aminobutyric acid as the inhibitor of gamma-aminobutyric acid binding in the plasma of humans with liver disease and hepatic encephalopathy.

1. Gas-liquid chromatography and a radioreceptor assay were used to measure plasma gamma-aminobutyric acid (GABA) in patients with liver disease and hepatic encephalopathy. 2. There was a significant correlation between the results obtained by the two methods, and compared with controls plasma GABA was elevated. 3. These findings suggest that the increased GABA binding inhibitory activity of plasma of these patients is probably due to GABA itself.

Chromatography, Gas↗
PubMed1994

Synthesis and photochemistry of photolabile derivatives of gamma-aminobutyric acid for chemical kinetic investigations of the gamma-aminobutyric acid receptor in the millisecond time region.

The gamma-aminobutyric acid (GABA) receptor is an abundant neuronal receptor in the mammalian and invertebrate nervous systems and is associated with an inhibitory chloride ion channel. GABA is the endogenous neurotransmitter for the receptor and can trigger both fast activation and a reversible desensitization of the receptor. A series of photolabile amine-linked o-nitrobenzyl derivatives of GABA were synthesized that photolyze rapidly to release free GABA. The photochemical properties of the GABA precursors were determined; the compounds undergo rapid photolysis, initiated with UV irradiation at 308 nm, and release free GABA on a millisecond time scale. The pH of the photolysis medium affects both the quantum yield and the rate of photolysis. For example, the quantum yield observed for N-(alpha-carboxy-2-nitrobenzyl)-gamma-aminobutyric acid increases from 0.06 at pH 5.0 to 0.1 at pH 10.5, and the half-life for the photolytic reaction decreases from 1.0 to 2.5 ms in the same pH range. Photolysis of the compounds induces rapid onset of transmembrane ion currents in mouse cortical neurons. The potential of the new compounds for use in rapid chemical kinetic investigations of the neuronal GABA receptor is demonstrated.

Animals↗
PubMed1977

Antiseizure activity of gamma-acetylenic gamma-aminobutyric acid: a catalytic irreversible inhibitor of gamma-aminobutyric acid transaminase.

gamma-Acetylenic gamma-aminobutyric acid (gamma-acetylenic GABA) produces several-fold sustained elevations of brain GABA concentrations when administered intraperitoneally to mice. It protects mice against seizures induced by audiogenic stimuli, electroshock, thiosemicarbazide, isoniazid and strychnine. The duration and degree of audiogenic seizure protection appears to correlate with elevations in whole brain GABA levels. gamma-Acetylenic GABA does not protect against seizures induced by pentylenetetrazol or picrotoxin even at doses that increase brain GABA concentrations approximately 6-fold. This differential antiseizure activity suggests that the GABA system may play a role in some, but not all experimentally produced seizures.

4-Aminobutyrate Transaminase↗
PubMed1985

gamma-Aminobutyric acid, benzodiazepine binding sites and gamma-aminobutyric acid concentrations in epileptic E1 mouse brain.

All E1 mice provoked by postural stimulation since the age of 4 weeks had convulsions between 22 and 24 weeks of age, the refractory period ranging from 20 to 30 min. As compared to ddY mice, the maximal number of high-affinity [3H]muscimol binding sites was larger and the affinity was lower in the brains of the E1 mice, which had or had not experienced repeated seizures caused by postural stimuli. The basal and gamma-aminobutyric acid (GABA)-stimulated [3H]flunitrazepam binding sites, and GABA concentration in the brains of the E1 mice did not differ from those of the ddY mice. In E1 mice following provoked convulsions, there were no temporary changes in [3H]muscimol binding, or [3H]flunitrazepam binding with or without exogenous GABA stimulation. The GABA concentration in the brains of the E1 mice increased immediately after seizures, and returned to the control values within 60 min.

Animals↗
PubMed1984

Presumptive gamma-aminobutyric acid pathways from the midbrain to the superior colliculus studied by a combined horseradish peroxidase-gamma-aminobutyric acid transaminase pharmacohistochemical method.

A pharmacohistochemical method for gamma-aminobutyric acid transaminase, the key enzyme for gamma-aminobutyric acid metabolism, has been combined with retrograde tracing by horseradish peroxidase, to a study of projections from the midbrain to the superior colliculus. The results indicate projections from the substantia nigra zona reticulata, the zona incerta and the reticular formation of the mesencephalon which are exclusively from neurons staining intensely for gamma-aminobutyric acid transaminase and presumptively gamma-aminobutyric acid as their transmitter. The projection from the ventral lateral geniculate body to the superior colliculus, on the other hand, comes from cells which do not stain for gamma-aminobutyric acid transaminase and therefore do probably not use gamma-aminobutyric acid as their transmitter.

4-Aminobutyrate Transaminase↗
PubMed1998

Painful and non-painful effects of low doses of morphine in migraine sufferers partly depend on excitatory amino acids and gamma-aminobutyric acid.

Having a differential sensitivity to morphine can distinguish migraine suffers from healthy people who are headache-exempt. The aim of the present study was to investigate whether such an abnormal response to morphine challenge is entirely dependent on opioid receptor activation. A role for excitatory amino acids and gamma-aminobutyric acid has been proposed on the basis of the effect of diazepam. As opposed to naloxone, this gamma-aminobutyric acid agonist was found to inhibit the adverse effects of low doses of morphine in migraine sufferers, while at the same time being able to almost abolish morphine-induced miosis in subjects who underwent a short-lasting chronic pretreatment. The capacity of diazepam either to control the adverse effects of morphine or to induce well-being in subjects known to suffer from a central neurogenic pain such as migraine, is noteworthy even regarding the clinical treatment of other painful conditions, such as deafferentation pain, which is known to be not satisfactorily treated by using morphine.

Adult↗
PubMed1991

Calcium-independent gamma-aminobutyric acid release from growth cones: role of gamma-aminobutyric acid transport.

Neuronal growth cones isolated in bulk from neonatal rat forebrain have uptake and K(+)-stimulated release mechanisms for gamma-aminobutyric acid (GABA). Up to and including postnatal day 5, the K(+)-stimulated release of [3H]GABA and endogenous GABA is Ca2+ independent. At these ages, isolated growth cones neither contain synaptic vesicles nor stain for synaptic vesicle antigens. Here we examined the possibility that the release mechanism underlying Ca2(+)-independent GABA release from isolated growth cones is by reversal of the plasma membrane GABA transporter. The effects of two GABA transporter inhibitors, nipecotic acid and an analogue of nipecotic acid, SKF 89976-A, on K(+)-stimulated release of [3H]GABA from superfused growth cones were examined. Nipecotic acid both stimulated basal [3H]GABA release and enhanced K(+)-stimulated release of [3H]GABA, which indicates that this agent can stimulate GABA release and is, therefore, not a useful inhibitor with which to test the role of the GABA transporter in K(+)-stimulated GABA release from growth cones. In contrast, SKF 89976-A profoundly depressed both basal and K(+)-stimulated [3H]GABA release. This occurred at similar concentrations at which uptake was blocked. These observations provide evidence for a major role of the GABA transporter in GABA release from neuronal growth cones.

Animals↗
PubMed1999

Neuronal, glial, and epithelial localization of gamma-aminobutyric acid transporter 2, a high-affinity gamma-aminobutyric acid plasma membrane transporter, in the cerebral cortex and neighboring structures.

Neuronal and glial high-affinity Na+/Cl(-)-dependent plasma membrane gamma-aminobutyric acid (GABA) transporters (GATs) contribute to regulating neuronal function. We investigated in the cerebral cortex and neighboring regions of adult rats the distribution and cellular localization of the GABA transporter GAT-2 by immunocytochemistry with affinity-purified polyclonal antibodies that react monospecifically with a protein of 82 kDa. Conventional and confocal laser-scanning light microscopic studies revealed intense GAT-2 immunoreactivity (ir) in the leptomeninges, choroid plexus, and ependyma. Weak GAT-2 immunoreactivity also was observed in the cortical parenchyma, where it was localized to puncta of different sizes scattered throughout the radial extension of the neocortex and to few cell bodies. In sections double-labeled with GAT-2 and glial fibrillary acidic protein (GFAP) antibodies, some GAT-2-positive profiles also were GFAP positive. Ultrastructural studies showed GAT-2 immunoreactivity mostly in patches of varying sizes scattered in the cytoplasm of neuronal and nonneuronal elements: GAT-2-positive neuronal elements included perikarya, dendrites, and axon terminals forming both symmetric and asymmetric synapses; nonneuronal elements expressing GAT-2 were cells forming the pia and arachnoid mater; astrocytic processes, including glia limitans and perivascular end feet; ependymal cells; and epithelial cells of the choroid plexuses. The widespread cellular expression of GAT-2 suggests that it may have several functional roles in the overall regulation of GABA levels in the brain.

Animals↗
PubMed2000

Gamma-aminobutyric acid agonists for neuroleptic-induced tardive dyskinesia.

BACKGROUND: Chronic antipsychotic drug treatment may cause tardive dyskinesia (TD), a long-term movement disorder. The gamma-aminobutyric acid (GABA) agonist drugs have been trialed as a treatment for TD, but these drugs have intense sedative properties and can possibly exacerbate psychotic symptoms. OBJECTIVES: To determine the effects of GABA agonist drugs (baclofen, gamma-vinyl-GABA, gamma-acetylenic-GABA, progabide, muscimol, sodium valproate and tetrahydroisoxazolopyridine (THIP)) in people with neuroleptic-induced tardive dyskinesia (TD) and schizophrenia or other chronic mental illnesses. SEARCH STRATEGY: Electronic searches of Biological Abstracts (1982-1998), The Cochrane Library CENTRAL (1998), Cochrane Schizophrenia Group's Register of Trials (1998), EMBASE (1980-1998), LILACS (1982-1996), MEDLINE (1966-1998), PsycLIT (1974-1998), and SCISEARCH were undertaken. References of all identified studies were searched for further trial citations. First authors of each included trial were contacted. SELECTION CRITERIA: The inclusion criteria for all relevant randomised studies were that they should focus on people with schizophrenia or other chronic mental illnesses, with neuroleptic-induced TD and compare the use of GABA agonist drugs to placebo or no intervention. DATA COLLECTION AND ANALYSIS: The reviewers extracted the data independently and the odds ratio (OR) and its 95% confidence interval (CI) or the weighted mean difference with 95% CI were estimated. The reviewers assumed that people who dropped out had no improvement. MAIN RESULTS: Eight studies were able to be included. Results were equivocal, showing only a tendency for clinical improvement for those using GABA agonist drugs but, when analysis of any improvement (rather than clinical improvement) was performed, a significant reduction was noted in the GABA group (OR 0.36 CI 0.15-0.85). This suggests that for every 10 people treated with GABA drugs one person would benefit with a reduction in TD symptoms. People using the interventions had more confusion (OR 7.4 CI 1.3-40.9) and sedation (OR 3.0 CI 1.2-7.6). The numbers of people needed to treat to cause one extra person to experience these side effects were three and six, respectively. Tendency for more deterioration of the TD symptoms (OR 1.72 CI 0. 54-5.5), deterioration of the mental state (OR 3.07 CI 0.78-12.05), and to drop out before the end of the trial (OR 2.05 CI 0.8-5.21) were also observed in those using GABA agonists. REVIEWER'S CONCLUSIONS: No clear statement about the efficacy of GABA agonist drugs could be provided. From the combined data, GABA agonist drugs tend to be associated with some degree of improvement in TD symptoms, but also with side effects such as confusion and sedation and a deterioration of the person's mental state.

Antipsychotic Agents↗
PubMed2002

Point mutation in the first transmembrane region of the beta 2 subunit of the gamma--aminobutyric acid type A receptor alters desensitization kinetics of gamma--aminobutyric acid- and anesthetic-induced channel gating.

A conserved glycine residue in the first transmembrane (TM1) domain of the beta2 subunit has been identified to be involved with desensitization induced by gamma-aminobutyric acid (GABA) and anesthetics. Recombinant GABA(A) receptors expressed in Sf9 cells were recorded using semi-fast agonist application. Upon direct activation by GABA or anesthetics, the main effect of the TM1 point mutation on the beta2 subunit (G219F) was to slow the time constant (tau) of desensitization. At GABA concentrations eliciting maximum currents, the corresponding median tau values were 0.87 s (25-75% interval (0.76; 1.04 s)), 0.93 s (0.76; 1.23 s), and 1.36 s (1.17; 1.57 s) for alpha1beta2gamma2, alpha1(G223F)beta2gamma2, and alpha1beta2(G219F)gamma2, respectively. The tau value for the beta2-mutant receptor was significantly longer than alpha1beta2gamma2 (p < 0.01) and alpha1(G223F)beta2gamma2 (p < 0.05). For pentobarbital-induced currents (500 microm), the corresponding median tau values were 1.36 s (0.81; 1.41 s), 1.47 s (1.31; 2.38 s), and 2.82 s (2.21; 5.56 s) for alpha1beta2gamma2, alpha1(G223F)beta2gamma2, and alpha1beta2(G219F)gamma2, respectively. The tau value for the beta2-mutant receptor was significantly longer than that for alpha1beta2gamma2 (p < 0.01). The present findings suggest that this TM1 glycine residue is critical for the rate at which desensitization occurs and that both GABA and intravenous anesthetics implement an analogous pathway for generating desensitization.

Amino Acid Sequence↗