The gamma-aminobutyric acid (GABA) system in brain during acute and chronic ethanol intoxication

Neuronal-specific methylome and hydroxymethylome analysis reveal significant loci associated with alcohol use disorder

Background: Alcohol use disorder (AUD) is a complex condition associated with adverse health consequences that affect millions of individuals worldwide. Epigenetic modifications, including DNA methylation (5 mC), have been associated with AUD and other alcohol-related traits. Epigenome-wide association studies (EWAS) have identified differentially methylated genes associated with AUD in human peripheral and brain tissue. More recently, epigenetic studies of AUD have also evaluated DNA hydroxymethylation (5 hmC) in the human brain. However, most of the epigenetic work in postmortem brain tissue has examined bulk tissue. In this study, we investigated neuronal-specific 5 mC and 5 hmC alterations at CpG sites associated with AUD in the human orbitofrontal cortex (OFC). Methods: Neuronal nuclei from the OFC were evaluated in 34 human postmortem brain samples (10 AUD, 24 non-AUD). Reduced representation oxidative bisulfite sequencing was used to assess 5 mC and 5 hmC at the genome-wide level. Differential 5 mC and 5 hmC were evaluated using the methylKit R package and significance was set at false discovery rate < 0.05 and differential methylation > 2. Functional enrichment analyses were performed, and gene-level convergence was evaluated in an independent dataset that assessed 5 mC and 5 hmC of AUD in bulk cortical tissue. Results: We identified 417 5 mC and 363 5hmC significant differential CpG sites associated with AUD, with 59% in gene promoters. Some of the identified genes have been previously implicated in alcohol consumption, including SYK, DNMT3A for 5 mC, GAD1, DLX1, DLX2, for 5 hmC and GATA4 in both. Convergence with a previous AUD 5 mC and 5 hmC study was observed for 28 genes. We also identified 5 and 35 differential regions for 5 mC and 5 hmC, respectively. Lastly, GWAS enrichment analysis showed an association with AUD for differential 5 mC genes. Discussion: This study reveals neuronal-specific methylome and hydroxymethylome dysregulation associated with AUD, identifying both previously reported and potentially novel gene associations with AUD. Our findings provide new insights into the epigenomic dysregulation of AUD in the human brain.

GABAergic mechanisms in alcohol dependence

The target of alcohol's effect on the central nervous system has been sought for more than 50 years in the brain's GABA system. The behavioral and emotional effects of alcohol in humans and rodents are very similar to those of barbiturates and benzodiazepines, and GABAA receptors have been shown to be one of the sites of alcohol action. The mechanisms of GABAergic inhibition have been a hotspot of research but have turned out to be complex and controversial. Genetics support the involvement of some GABAA receptor subunits in the development of alcohol dependence and in alcohol use disorders (AUD). Since the effect of alcohol on the GABAA system resembles that of a GABAergic positive modulator, it may be possible to develop GABAergic drug treatments that could substitute for alcohol. The adaptation mechanisms of the GABA system and the plasticity of the brain are a big challenge for drug development: the drugs that act on GABAA receptors developed so far also may cause adaptation and development of additional addiction. Human polymorphisms should be studied further to get insight about how they affect receptor function, expression or other factors to make reasonable predictions/hypotheses about what non-addictive interventions would help in alcohol dependence and AUD.

Neuronal-specific methylome and hydroxymethylome analysis reveal replicated and novel loci associated with alcohol use disorder

Alcohol use disorder (AUD) is a complex condition associated with adverse health consequences that affect millions of individuals worldwide. Epigenetic modifications, including DNA methylation (5mC), have been associated with AUD and other alcohol-related traits. Epigenome-wide association studies (EWAS) have identified differentially methylated genes associated with AUD in human peripheral and brain tissue. More recently, epigenetic studies of AUD have also evaluated DNA hydroxymethylation (5hmC) in the human brain. However, most of the epigenetic work in postmortem brain tissue has examined bulk tissue. In this study, we investigated neuronal-specific 5mC and 5hmC alterations at CpG sites associated with AUD in the human orbitofrontal cortex (OFC). Neuronal nuclei from the OFC were evaluated in 34 human postmortem brain samples (10 AUD, 24 non-AUD). Reduced representation oxidative bisulfite sequencing was used to assess 5mC and 5hmC at the genome-wide level. Differential 5mC and 5hmC were evaluated using the methylKit R package and significance was set at false discovery rate <0.05 and differential methylation >2. Functional enrichment analyses were performed and replication was evaluated replication in an independent dataset that assessed 5mC and 5hmC of AUD in bulk cortical tissue. We identified 417 5mC and 363 5hmC genome-wide significant differential CpG sites associated with AUD, with 59% in gene promoters. We also identified genes previously implicated in alcohol consumption, such as SYK, CHRM2, DNMT3A, and GATA4, for 5mC and GATA4, and GAD1, GATA4, DLX1 for 5hmC. Replication was observed for 28 CpG sites from a previous AUD 5mC and 5hmC study, including FOXP1. Lastly, GWAS enrichment analysis showed an association with AUD for differential 5mC genes. This study reveals neuronal-specific methylome and hydroxymethylome dysregulation associated with AUD. We replicated previous findings and identified novel associations with AUD for both 5mC and 5hmC marks within the OFC. Our findings provide new insights into the epigenomic dysregulation of AUD in the human brain.

D-ribose-L-cysteine exhibits neuroprotective activity through inhibition of oxido-behavioral dysfunctions and modulated activities of neurotransmitters in the cerebellum of Juvenile mice exposed to ethanol

Alcohol exposure to the cerebellum has been known to trigger cerebellar dysfunctions through several mechanisms. This present study was designed to evaluate the repealing effect of D-ribose-L-cysteine (DRLC) on alcohol-induced cerebellar dysfunctions in juvenile BALB/c mice. The animals were randomly divided into 4 groups (n = 10 per group). Mice were given oral administration of normal saline (control), DRLC (100 mg/kg, p.o), ethanol (0.2 mL of 10% w/v), or DRLC (100 mg/kg, p.o) + ethanol (0.2 mL of 10% w/v). On day 29 of the study (i.e., 24 h after the administration of the last respective doses), neurochemical quantification of the respective levels of serotonin and dopamine, lipid peroxidation, total antioxidant, superoxide dismutase, and glutathione peroxidase in the cerebellar tissues of the mice were analyzed. Compared with the saline-treated group, the studied neurochemical indices were modulated across the various experimental groups. The administration of ethanol significantly modulates the levels of monoamine neurotransmitters (serotonin and dopamine) as well as contents of total antioxidants, activities of superoxide dismutase, and glutathione peroxidase, with a concurrently increased level of lipid peroxidase in the cerebellar tissue of the mice. DRLC significantly reverses these effects in the DRLC + ethanol co-treated group. Combined exposure to DRLC + ethanol counteracts the deleterious effect of ethanol in the cerebellum of juvenile BALB/c mice via monoamine neurotransmitter, lipid peroxidation, total antioxidant status, superoxide dismutase, and glutathione peroxidase action pathways. Therefore, DRLC could be a pharmacologic or therapeutic agent in attenuating the deleterious effects of alcohol on the cerebellum.

Ameliorative effects of Albizia adianthifolia aqueous extract against pentylenetetrazole-induced epilepsy and associated memory loss in mice: Role of GABAergic, antioxidant defense and anti-inflammatory systems

Albizia adianthifolia (Schumach.) (Fabaceae) is a medicinal herb used for the treatment of epilepsy and memory impairment. This study aims to investigate the anticonvulsant effects of Albizia adianthifolia aqueous extract against pentylenetetrazole (PTZ)-induced spontaneous convulsions in mice; and determine whether the extract could mitigate memory impairment, oxidative/nitrergic stress, GABA depletion and neuroinflammation. Ultra-high performance liquid chromatography/mass spectrometry analysis was done to identify active compounds from the extract. Mice were injected with PTZ once every 48 h until kindling was developed. Animals received distilled water for the normal group and negative control groups, doses of extract (40, 80, or 160 mg/kg) for the test groups and sodium valproate (300 mg/kg) for the positive control group. Memory was measured using Y maze, novel object recognition (NOR) and open field paradigms, while the oxidative/nitrosative stresses (MDA, GSH, CAT, SOD and NO), GABAergic transmission (GABA, GABA-T and GAD) and neuro-inflammation (TNF-α, IFN-γ, IL- 1β, and IL-6) were determined. Brain photomicrograph was also studied. Apigenin, murrayanine and safranal were identified in the extract. The extract (80-160 mg/kg) significantly protected mice against seizures and mortality induced by PTZ. The extract significantly increased the spontaneous alternation and the discrimination index in the Y maze and NOR tests, respectively. PTZ kindling induced oxidative/nitrosative stress, GABA depletion, neuroinflammation and neuronal cells death was strongly reversed by the extract. The results suggest that the anticonvulsant activity of Albizia adianthifolia extract is accompanied by its anti-amnesic property, and may be supported by the amelioration of oxidative stress, GABAergic transmission and neuroinflammation.

Pergularia daemia hydro-ethanolic extract protects against pentylenetetrazole kindling-induced seizures, oxidative stress, and neuroinflammation in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Current antiepileptic drugs fail to control approximately 30% of epilepsies. Therefore, there is a need to develop more effective antiepileptic drugs, and medicinal plants provide an attractive source for new compounds. Pergularia daemia (Asclepiadaceae) is used in Cameroon traditional medicine to treat stroke, anemia, inflammation, and epilepsy. Recently, traditional healers claim that an hydro-ethanolic extract of the roots of P. daemia is more effective than an aqueous extract on refractory seizures.

AIM OF THE STUDY

The antiepileptic effect of P. daemia hydro-ethanolic extract was investigated on the pentylenetetrazole kindling model of temporal lobe epilepsy in mice and possible mechanisms of action.

MATERIALS AND METHODS

Mice were divided into 8 groups treated as follows: normal group received distilled water (10 ml/kg, p.o.), control group received distilled water (10 ml/kg, p.o.), ethanol group received ethanol (5%, p.o.), positive control received sodium valproate (300 mg/kg, p.o.), and test groups received P. daemia hydro-ethanolic (HE) extract (1.6, 4, 8 and 16 mg/kg, p.o.). All groups were kindled by 11 injections of pentylenetetrazole (PTZ) (35 mg/kg, i.p.), once every alternate day (48 ± 2 h), until the development of kindling, i.e., the occurrence of stage 5 seizures for two consecutive trials. One week later, i.e., 29^th day, mice were challenged with a single and lower dose of PTZ (25 mg/kg, i.p.) that does not induce seizures in normal mice but causes seizures in mice prone to seizures and behavioral alterations. After completion of the kindling procedure, Morris water maze, passive avoidance, and open field tests were performed. Afterward, animals were euthanized, and hippocampi were removed for the estimation of the levels of GABA-transaminase (GABA-T), L-glutamate decarboxylase (L-GAD), and γ-aminobutyric acid (GABA). Oxidative stress and neuroinflammation markers also were quantified. Finally, histological analysis of the hippocampus was carried out.

RESULTS

PTZ-kindling induced myoclonic jerks and generalized tonic-clonic seizures in control mice. However, the HE extract of P. daemia (4-16 mg/kg), compared to sodium valproate, significantly protected mice against myoclonic jerks and generalized tonic-clonic seizures. Also, the HE extract (1.6-16 mg/kg) significantly increased the seizure score. Furthermore, the HE extract of P. daemia significantly reduced seizure-induced cognitive impairments. PTZ-kindling induced significant alterations in GABA, GABA-T, and L-GAD contents as well as oxidative stress, and neuroinflammation, and the HE extract significantly reversed these effects, suggesting possible mechanisms. All these activities of the HE extract were confirmed by its protective effect against neuronal loss in the hippocampus.

CONCLUSIONS

The HE extract of P. daemia protected mice against kindled seizures and cognitive impairments, and these effects were greater than those of sodium valproate, a widely used antiepileptic drug. These effects may be mediated by neuromodulatory, anti-oxidant, and anti-inflammatory activities, thus suggesting a neuroprotective effect. These findings help to explain the beneficial use of these HE extracts of P.daemia in traditional medicine to treat epilepsy in Cameroon.

Protective Effects of Anthocleista djalonensis Extracts against Pentylenetetrazole-Induced Epileptic Seizures and Neuronal Cell Loss: Role of Antioxidant Defense System

Oxidative stress and neurodegeneration are involved in the initiation of epileptogenesis and progression of epileptic seizures. This study was aimed at investigating the anticonvulsant, antioxidant, and neuroprotective properties of active fractions isolated from Anthocleista djalonensis root barks in pentylenetetrazole mouse models of epileptic seizures. Bioactive-guided fractionation of Anthocleista djalonensis (AFAD) extracts using acute pentylenetetrazole (90 mg/kg) induced generalised tonic-clonic seizures, which afforded a potent anticonvulsant fraction (FPool 5). Further fractionation of AFAD was performed by high-performance liquid chromatography, which yielded fifteen subfractions, which were chemically characterised. In addition, AFAD was tested against convulsions or spontaneous kindled seizures induced, respectively, by acute (50 mg/kg) or subchronic (30 mg/kg) injection of pentylenetetrazole. Finally, oxidative stress markers, brain GABA content, and neuronal cell loss were evaluated in AFAD-treated pentylenetetrazole-kindled mice. Administration of AFAD significantly protected mice against acute pentylenetetrazole (90 mg/kg)-induced convulsions. In acute pentylenetetrazole (50 mg/kg)-induced hippocampal and cortical paroxysmal discharges, AFAD significantly decreased the number of crisis, the cumulative duration of crisis, and the mean duration of crisis. Additionally, AFAD significantly decreased the number of myoclonic jerks and improved the seizure score in subchronic pentylenetetrazole-induced kindled seizures. The pentylenetetrazole-induced alteration of oxidant-antioxidant balance, GABA concentration, and neuronal cells in the brain were attenuated by AFAD treatment. This study showed that AFAD protected mice against pentylenetetrazole-induced epileptic seizures possibly through the enhancement of antioxidant defence and GABAergic signalling. These events might be correlated with the amelioration of neuronal cell loss; hence, AFAD could be a potential candidate for the treatment of epilepsy.

An aqueous extract of Canarium schweinfurthii attenuates seizures and potentiates sleep in mice: Evidence for involvement of GABA Pathway

About 30% of epileptic patients continue to have seizures. The present study investigates the anticonvulsant and sedative effects of an aqueous extract of C. schweinfurthii in mice. Anticonvulsant effects of C. schweinfurthii aqueous extract (0.01-300 mg/kg, p.o.) were tested against 4-aminopyridine (4-AP, 15 mg/kg, i.p.) -, pilocarpine (PILO, 380 mg/kg, i.p.) - and pentylenetetrazole (PTZ, 75 mg/kg, i.p.) -induced seizures, while sedative effects were tested on diazepam (35 mg/kg, i.p.)-induced sleep. Afterward, the most effective dose of the extract (11.9 mg/kg) was antagonized with N-methyl-β-carboline-3-carboxamide or flumazenil. In another set of experiments, mice were sacrificed for the estimation of GABA content and GABA-T activity in the cerebral cortex. The dose of the extract that protected 50% of mice (ED₅₀) against 4-AP, PILO, and PTZ was respectively 4.43 mg/kg (versus 12.01 for phenobarbital), 9.59 mg/kg (vs 8.67 for diazepam), and 2.12 mg/kg (vs 0.20 for clonazepam). Further, the ED₅₀ of the extract that increased the duration of sleep was 0.24 mg/kg (vs 0.84 for phenobarbital). N-methyl-β-carboline-3-carboxamide or flumazenil antagonized (p < 0.001) the anticonvulsant effect of C. schweinfurthii in PTZ-induced seizures and diazepam-induced sleep when compared to the negative control group. The extract at all doses increased (p < 0.001) the GABA content and decreased (p < 0.001) GABA-T activity. These findings suggest that C. schweinfurthii possesses anticonvulsant and sedative effects. These effects seem to be mediated via the modulation of the GABA neurotransmission. These data explain the use of this plant to treat epilepsy in Cameroon traditional medicine.

Calorie restriction improves aging-induced impairment of cognitive function in relation to deregulation of corticosterone status and brain regional GABA system

Aging is known to affect adversely the corticosterone status and the brain function including cognition. Calorie restricted (CR) diet has been found to improve brain aging. The objective of the present investigation is to study the effect of short-term CR diet without any food deprivation on aging-induced impairment of cognitive function in relation to the corticosterone status and the brain regional GABA system. The result showed that aging-induced deregulation of the brain regional GABA system, increase in plasma and adrenal corticosterone levels and cognitive impairment were attenuated with short-term CR diet supplementation for consecutive 1 and 2 months to the aged (18 and 24 months) rats. But in young rats (4 months) consumption of the same CR diet under similar conditions reversibly affected those above-mentioned parameters. These results, thus suggest that (a) aging down-regulates brain regional GABA system with an up-regulation of corticosterone status and impairment of cognitive function, (b) CR diet consumption improves this aging-induced deregulation of brain regional GABA system, corticosterone status, and cognitive function, (c) these attenuating effects of CR diet are greater with a longer period of consumption but (d) CR diet consumption is harmful to young rats as observed in those parameters.

Attenuation of γ-aminobutyric acid (GABA) transaminase activity contributes to GABA increase in the cerebral cortex of mice exposed to β-cypermethrin

The current study investigated the γ-aminobutyric acid (GABA) levels and GABA metabolic enzymes (GABA transaminase (GABAT) and glutamate decarboxylase (GAD)) activities at 2 and 4 h after treatment, using a high-performance liquid chromatography with ultraviolet detectors and colorimetric assay, in the cerebral cortex of mice treated with 20, 40 or 80 mg/kg β-cypermethrin by a single oral gavage, with corn oil as vehicle control. In addition, GABA protein (4 h after treatment), GABAT protein (2 h after treatment) and GABA receptors messenger RNA (mRNA) expression were detected by immunohistochemistry, Western blot and real-time quantitative reverse transcriptase polymerase chain reaction, respectively. β-Cypermethrin (80 mg/kg) significantly increased GABA levels in the cerebral cortex of mice, at both 2 and 4 h after treatment, compared with the control. Also, GABA immunohistochemistry results suggested that the number of positive granules was increased in the cerebral cortex of mice 4 h after exposure to 80 mg/kg β-cypermethrin when compared with the control. Furthermore, the results also showed that GABAT activity detected was significantly decreased in the cerebral cortex of mice 2 h after β-cypermethrin administration (40 or 80 mg/kg). No significant changes were found in GAD activity, or the expression of GABAT protein and GABAB receptors mRNA, in the cerebral cortex of mice, except that 80 mg/kg β-cypermethrin caused a significant decrease, compared with the vehicle control, in GABAA receptors mRNA expression 4 h after administration. These results suggested that attenuated GABAT activity induced by β-cypermethrin contributed to increased GABA levels in the mouse brain. The downregulated GABAA receptors mRNA expression is most likely a downstream event.

Dietary variation of protein–carbohydrate: Effect on hypothalamic and hippocampal GABA–glutamate in relation to aging

Dietary protein variation has been found to alter brain regional neurochemistry with aging. In the present investigation, we studied the effect of short-term treatment of protein-carbohydrate variable diet to rat on hypothalamic and hippocampal gamma-amino butyric acid (GABA)-glutamate metabolism with increase of age. Exposure of male albino rats with diet containing normal protein (20%)-normal carbohydrate (68%) increased GABA metabolism and decreased glutamate metabolism in both hypothalamus and hippocampus with the increase of age. GABA-glutamate metabolism of rats having low protein (8%)-high carbohydrate (80%) diet for short-term period (STP), was activated in young age (3 months) and decreased in old age (18 months) in both the brain regions. On the contrary, intake of high protein (50%)-low carbohydrate (38%) diet under similar condition decreased GABA-glutamate metabolism in both hypothalamus and hippocampus of young brain and increased only in hypothalamus of aged brain. In hippocampus of aged brain the same diet decreased glutamate metabolism without changing its GABA metabolism. These results suggest that an age-associated change in GABA-glutamate metabolism depends on the amount of dietary protein and carbohydrate and also on the brain region.

Long-term exposure of variable dietary protein-to-carbohydrate ratio: effect on brain regional glutamatergic activity with age

Glutamatergic activity of hypothalamus and hippocampus of young (3 months) male albino rats having normal diet [protein (20%)-carbohydrate (68%)] was increased with the increase of age. Long-term (60 consecutive days) feeding of low protein (8%)-high carbohydrate (80%) diet (LP-HC) increased glutamatergic activity in these brain regions of young rats and decreased that in aged (18 months). On the contrary, supplementation of high protein (50%)-low carbohydrate (38%) diet (HP-LC) under similar condition decreased glutamatergic activity in those brain regions of young and increased that in aged brain regions. Thus, prolonged exposure of LP-HC diet may damage young brain; whereas, HP-LC diet under similar condition causes excitotoxicity to aged brain. Therefore, considering the present scenario in relation to metabolism and receptor activity of glutamatergic system, it may be suggested that long-term consumption of LP-HC and HP-LC diets modulate the brain regional glutamatergic activity reversibly with age.

Effects of MK-801 and ethanol combinations on memory consolidation in CD1 mice: involvement of GABAergic mechanisms

In the present research the effect of the noncompetitive N-methyl-d-aspartate receptor antagonist MK-801 and ethanol combinations on memory consolidation and the involvement of GABAergic mechanisms in this effect were investigated in CD1 mice injected intraperitoneally with the drugs immediately or 120 min after training in a one-trial inhibitory avoidance apparatus and tested for retention 24 h later. The results showed that (a) the retention performances of mice were impaired in a dose-dependent manner by immediate posttraining MK-801 (0.2 and 0.3, but not 0.1 mg/kg) and ethanol (1 and 2, but not 0.5 g/kg) administrations; (b) an otherwise ineffective dose of MK-801 (0.1 mg/kg) enhanced the deleterious effect exerted by ethanol (1 and 2 g/kg); (c) an otherwise ineffective dose of muscimol (0.5 mg/kg) enhanced, while otherwise ineffective doses of picrotoxin (0.25 mg/kg) or bicuculline (0.1 mg/kg) antagonized, this effect; and (d) no effect was observed when the treatments were carried out 120 min after training, suggesting that the effects observed following immediate posttraining administrations were due to the influence on the consolidation of memory. From these experiments it is evident that (a) MK-801 enhances ethanol's effects on memory consolidation and (b) GABAergic mechanisms are involved in this effect.

Effects of aluminium exposure on brain glutamate and GABA systems: an experimental study in rats

It has been postulated that the neurotoxic effects of aluminium could be mediated through glutamate, an excitatory amino acid. Hence the effects of aluminium administration (at a dose of 4.2mg/kg body weight daily as aluminium chloride, hexahydrate, intraperitoneally, for 4 weeks) on glutamate and gamma-amino butyrate (GABA), an inhibitory amino acid, and related enzyme activities in different regions of the brain were studied in albino rats. The glutamate level increased significantly in the cerebrum, thalamic area, midbrain-hippocampal region and cerebellum in response to in vivo aluminium exposure. The aluminium insult also caused significant increases in glutamate alpha-decarboxylase activity in all the brain regions. However, on aluminium insult, the GABA content was not significantly changed except in the thalamic area, where it was elevated. On the contrary, the GABA-T activities of all the regions were reduced significantly in all regions except the midbrain-hippocampal region. However, the succinic semi-aldehyde content of all brain regions increased, often significantly. The aluminium-induced modification of the enzyme activities may be either due to the direct impact of aluminium or due to aluminium-induced changes in the cellular environment. The aluminium-induced differential regional accumulation of glutamate or other alterations in enzymes of the glutamate-GABA system may be one of the causes of aluminium-induced neurotoxicity.

Long-term exposures to higher environmental temperature and body temperature: effect of chlorpromazine in relation to hypothalamic GABA

Treatment with a single dose of chlorpromazine (CPZ; 1 mg/kg, ip) at room temperature (28 degrees +/-0.5 degrees C) significantly reduced body temperature by its anticholinergic action. Long-term exposures to higher environmental temperature (40 degrees +/-0.5 degrees C, 2 h/day, for 30 consecutive days) increased body temperature significantly by reduction of hypothalamic GABAergic activity, but this increase in body temperature was attenuated from that observed with a single exposure to higher environmental temperature (40 degrees C for 2 h). Treatment with a single dose of CPZ on the last day of 30 consecutive days of exposures to higher environmental temperature increased body temperature of rats more than that observed with long-term exposures to higher environmental temperature possibly due to (i) reduction of hypothalamic GABAergic activity, (ii) heat dissipation and (iii) reverse-anticholinergic action of CPZ at higher environmental temperature.

Dietary protein alters age-induced change in hypothalamic GABA and immune response

The effect of dietary protein on hypothalamic GABAergic activity and immune response of rats in relation to age was studied. The age-induced (due to increase of age from three to 18 months) decrease in hypothalamic GABAergic activity and immune response were potentiated with the supplementation of protein rich diet under both short- and long-term conditions. Long-term consumption of protein-poor diet, in contrast, produced activation of hypothalamic GABAergic activity with an immunopotentiation with the increase of age from three to 18 months; whereas, short-term supplementation of low protein diet did not show any effect. The results of the present study may indicate that the activation or inhibition of hypothalamic GABAergic activity by immunopotentiation or immunosuppression during aging depends on the variation of the amount of dietary protein as well as the duration of its supplementation.

Chronic exposure to ethanol alters GABA(A) receptor-mediated responses of layer II pyramidal cells in adult rat piriform cortex

This study examined the effect of chronic exposure to ethanol on gamma-aminobutyric acid type-A (GABA(A)) receptor-mediated responses of layer II pyramidal neurons of the piriform cortex. Slices containing the piriform cortex were derived from pair-fed adult rats maintained on ethanol-supplemented or control liquid diet for 30 days. Responses of identified layer II pyramidal neurons to exogenously applied GABA were monitored by whole-cell patch-clamp recording. Chronic exposure to ethanol resulted in a rightward shift in the EC(50) of GABA and a decrease in the amplitude of maximal GABA response. GABA-induced responses were modulated by acutely applied ethanol (10-100 mM) in both chronic ethanol-treated and control groups. No significant difference was found in the average change in GABA response, suggesting that tolerance to acute ethanol exposure did not develop. When the modulatory responses of individual cells were classified and grouped as either being attenuating, potentiating, or having no effect, the incidence of potentiation in the ethanol-treated group was significantly higher. Consistent with the absence of tolerance to acute ethanol, cross-tolerance to diazepam was not observed following 30 days of treatment with ethanol. These results are discussed in light of regionally specific effects of chronic ethanol treatment on GABA(A) receptor-mediated responses of layer II piriform cortical neurons.

Hypothalamic GABA-ergic activity and T-cell proliferation in aged mammal: effect of dietary protein

Short-term supplementation of low protein diet (LPD) or high protein diet (HPD) to the aged (18 months old) rats did not change the hypothalamic GABAergic activity and immune response. Long-term supplementation of LPD on the other hand, enhanced hypothalamic GABAergic activity with an immunopotentiation by increasing the T-cell proliferating activity and peripheral blood lymphocyte count in the same age group of rats. Unlike LPD, HPD under long-term supplementation to the aged rats reduced the hypothalamic GABAergic activity with immunosuppression. These results thus suggest that (i) hypothalamic GABAergic activity is a regulatory index of immune response in aged mammals and (ii) long-term consumption of protein-poor or protein-rich diet may be an exogenous modulator of neuroimmune regulation in relation to central GABAergic activity and immune response.

Distribution of GABAA receptors in the limbic system of alcohol-preferring and non-preferring rats: in situ hybridisation histochemistry and receptor autoradiography

The present study has employed quantitative receptor autoradiography and in situ hybridisation histochemistry to compare the expression of the mRNA encoding the alpha 1 and alpha 2 subunits of the GABAA receptor and the binding density of mature GABAA receptors in the limbic system of alcohol-preferring Fawn-Hooded rats (FH) with Wistar-Kyoto rats (WKY). Quantifiable levels of mRNA encoding the alpha 1 subunit were found in cortical regions, ventral pallidum, substantia nigra, horizontal limb of the diagonal band and the hippocampus of both rat strains. Interestingly, expression of the alpha 1 subunit mRNA was decreased by approximately 30% in the hippocampus of FH compared to WKY rats. Following a 28-day period with free access to 10% ethanol, expression of the alpha 1 subunit transcript, was significantly increased in the piriform cortex and horizontal limb of the diagonal band, unaltered in the hippocampus but decreased in the substantia nigra of FH rats. Quantifiable levels of mRNA encoding the alpha 2 subunit were found in nucleus accumbens, amygdala, cortical regions, lateral septal nucleus, hippocampus, medial habenula and ventral pallidum of both strains. Expression of the alpha 2 subunit mRNA was decreased by approximately 35% in both the hippocampus and occipital cortex of FH compared to WKY rats. However, consumption of 10% ethanol in FH rats had no impact upon expression of the mRNA encoding the alpha 2 subunit in any region examined. Mature GABAA receptors were studied by autoradiography utilising the antagonist radioligand [3H]SR95531 and the agonist radioligand [3H]muscimol. Topographic binding throughout the limbic system of both strains was observed for both radioligands. Specifically, [3H]SR95531 binding was higher in the occipital cortex, hippocampus, lateral septal nucleus, superior colliculus and ventral pallidum of the FH rats compared to WKY rats; however, in the nucleus accumbens [3H]SR95531 binding was lower in FH compared to WKY. Ethanol consumption had no measurable effect on the binding of [3H]SR95531 in FH rats. In the case of [3H]muscimol, binding was higher in the cortex, lateral septum and ventral pallidum of FH compared to WKY. Furthermore, ethanol consumption resulted in a 25-30% increase in [3H]muscimol binding in the lateral septum and striatum of FH rats. These data provide evidence for differential expression of GABAA receptor subunits in FH and WKY rats, and additionally indicate anatomically defined variations in GABAA receptor binding between the two rat strains.

Is GABA involved in the development of caffeine tolerance?

Caffeine (10 or 20 mg/kg per day, po)-induced stimulation of locomotor activity (LA) reached its peak following 4 consecutive days of caffeine administration. Caffeine-induced stimulation of LA was restored to the control values following caffeine tolerance after 16 or 12 consecutive days of caffeine treatment at a dose of 10 or 20 mg/kg per day, po. Biochemical studies showed that caffeine in the nontolerant condition reduced GABAergic activity in cerebral cortex, corpus striatum, cerebellum, hypothalamus and pons-medulla; but tolerance to caffeine (10 or 20 mg/kg per day, po) pushed up the GABAergic activity to the control value in all these regions of brain. Further, it was found that muscimol reduced the LA while bicuculline stimulated LA in the caffeine tolerant condition. Thus, from the present study it may be concluded that: (a) caffeine-induced stimulation of LA is dependent on dose and duration of caffeine treatment, (b) development of tolerance to caffeine is dependent on the dosage of caffeine, and (c) the reduction of central GABAergic activity in the caffeine-nontolerant condition pushed up and restored the LA to the control level on the development of tolerance to caffeine.

Is hypothalamic GABA involved in immune function in relation to dietary protein during aging?

Hypothalamic GABAergic activity and immune response in spleen were not significantly changed with the increase of age from 3 to 6 months in adult male albino rats. Further increase of age from 6 to 9 months increase the GABAergic activity and decreased the cell viability in spleen without any change in its T-lymphocyte cytotoxicity. Consumption of low protein diet (LPD) for a short-term period (STP; 7 consecutive days) increased the hypothalamic GABAergic activity without changing the immune response in 3 months old rats. When supplemented for a long-term period (LTP; 30 consecutive days) to 3 months old rats, a reduction of hypothalamic GABAergic activity and the immune response was observed. Intake of high protein diet (HPD) for both STP and LTP increased the GABAergic activity and immune response, but the increase of GABAergic activity in hypothalamus under STP was greater than that observed under LTP. In 6 months old rats consumption of LPD for STP reduced the GABAergic activity without any alteration of its immune response. Long-term supplementation of this LPD to the same age group increased GABAergic activity and the mitotic activity of spleen cells without any alteration of the functional activity of the T-cells in spleen. Consumption of HPD for STP failed to produce any change in hypothalamic GABAergic activity and the immune response of 6 months old rats. Supplementation of HPD for LTP reduced the hypothalamic GABAergic activity and the immune response of the same age group. The reduction in hypothalamic GABAergic activity without any change in the immune response was observed following the supplementation of low protein diet to 9 months old rat for STP. Intake of the LPD for LTP also reduced the hypothalamic GABAergic activity and the mitotic activity of the spleen cells without any alteration of the functional activity of the T-cells in spleen of 9 months old rats. Supplementation of HPD for STP to this aged rat, on the other hand, failed to produced any change in hypothalamic GABAergic activity and the immune response. Intake of HPD for LTP by this aged rats increased the hypothalamic GABAergic activity along with the immune response. The results of this study, thus, suggest that hypothalamic GABAergic activity during aging is an index of immune response and it is modulated following the short- and long-term consumption of protein poor and protein rich diet.

Basic aspects of GABA-transmission in alcoholism, with particular reference to GABA-transaminase

Neuronal dysfunction is the neurobiological basis for alcoholic behaviour, and ethanol craving seems related to hypofunction of the GABA-ergic activity. Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). In several studies, GABA has been shown to be an important target of ethanol in the CNS, partly, as a consequence of damage to membrane-bound enzymes and receptors. GABA is involved in mediating pre- and post-synaptic inhibition of neuronal activity. It is speculated that the initial excitatory effects of ethanol may be due to inhibition of GABA-ergic activity whereas the sedative effects of the higher doses may be mediated by the activation of this inhibitory system. In the CNS, GABA is synthesised from glutamic acid by the enzyme glutamate decarboxylase (GAD) and catabolized into succinic semialdehyde by the enzyme GABA-transaminase (GABA-T), which are pyridoxal phosphate (PLP) dependent enzymes. Platelet GABA-T was characterized as being similar to central GABA-T. Inhibition of GABA-T with certain potent and selective compounds markedly increases the levels of brain GABA. Experimentally, acute ethanol treatment does not alter GABA-T activity whereas chronic treatment produces an increase in the activity, though, with some reservations since a bimodal effect has been found in chronically ethanol-treated rats. Thus, as it will be discussed below, it may be suggested that GABA-T inhibitors (e.g. vigabatrin) could have a potential role in the treatment of alcoholism and in some of the problems of ethanol withdrawal and of other drugs of abuse. Related studies on metabolism and concentrations of GABA are also promising and show a greater increase in our understanding of the aetiology and treatment of ethanol dependence and withdrawal. In general, this article also reviews both the animal and clinical observations in the field of alcoholism with regard to the GABA system.

Effects of systemic and local ethanol on responses of rat cerebellar Purkinje neurons to iontophoretically applied gamma-aminobutyric acid

The goals of this study were: (1) to determine the effects of acute systemic or local application of ethanol (ETOH) on the response of cerebellar Purkinje cells (P-cells) to iontophoretically applied gamma-aminobutyric acid (GABA) and (2) to characterize the effects of Ro15-4513, a putative antagonist of ETOH-GABA interactions, on ETOH-induced changes in GABA responsiveness. Male Sprague-Dawley rats (230-370 g) were anesthetized with halothane and implanted with intraperitoneal catheters for administration of ETOH (1.0-2.0 g/kg), before the recording session. Extracellular activity of single P-cells was recorded with the central barrel of a five-barrel micropipette, the other barrels of which were used for microiontophoresis of GABA and electro-osmosis of ETOH at the recording site. Spontaneous discharge and response of P-cells to GABA were monitored during a pre-ETOH control and for 1-1.5 h after systemic or electro-osmotic administration of ETOH. Transient suppression of spontaneous P-cell discharge was usually observed within 4-8 min of systemic ETOH injection. This effect lasted 2-4 min in 10 out of 19 rats tested. GABA-mediated inhibitory responses of cerebellar P-cells were increased by 45-50% relative to pre-ETOH values at 10 and 90 min post-ETOH injection. Prior administration of the imidazobenzodiazepine Ro15-4513 (4-6 mg/kg) failed to antagonize either the ETOH-induced enhancement of GABA-mediated inhibition or the transient inhibition of spontaneous P-cell activity rat cerebellar P-cell produced by ETOH. In these studies, electro-osmotically applied ETOH produced a potent suppression of spontaneous P-cell activity which precluded further augmentation of unit responses to GABA. These results show that doses of systemically administered ETOH which are mildly intoxicating in the awake, behaving animal, enhance the inhibitory action of GABA on cerebellar P-cell discharge.

Basic aspects of GABA-transaminase in neuropsychiatric disorders

Over the last two decades, there have been several studies suggesting the major inhibitory amino acid neurotransmitter gamma-aminobutyric acid (GABA) is involved directly and/or indirectly in the pathogenesis of many neurologic diseases and psychiatric disorders. GABA is mainly degradated to succinic semialdehyde in a reaction catalyzed by the enzyme GABA-transaminase (GABA-T). Inhibition of this enzyme produces considerable elevation of GABA contents in the brain, and such elevation has been found to correlate with pharmacologic and behavioral effects. We focus attention, from the basic aspects, on brain and platelet GABA-T activities in various species, with a special reference to neuropsychiatric disorders. It seems that the activity of GABA-T in the brain and/or in the blood platelets is correlated to certain neuropsychiatric disorders such as alcoholism, epilepsy, and Alzheimer's disease. In animal and human studies, platelet GABA-T was identified with similar kinetic and inhibitor characteristics to those of the brain. Therefore, in this way, studies of the activity of the enzyme GABA-T in relation to neuropsychiatric disorders could be undertaken to understand, diagnose, and treat GABA-related disorders of the central nervous system.

GABA-transaminase in brain and blood platelets: basic and clinical aspects

Several lines of evidence suggest that the major inhibitory neuro-transmitter, gamma-aminobutyric acid (GABA) is involved, both directly and indirectly, in the pathogenesis of certain neurological and psychiatric disorders. The main enzyme responsible for GABA catabolism is gamma-aminobutyrate aminotransferase (GABA-T). Inhibition of this enzyme produces a considerable elevation of brain GABA concentrations, and such elevation has been correlated with many pharmacological effects. There seems to be that, as is discussed below, GABA-T activity in the brain and/or blood platelets is related to some neuro-psychiatric disorders such as alcoholism, epilepsy and Alzheimer's disease. GABA-T has been identified in the blood platelets with similar characteristics to those of brain GABA-T. In this way, studies on GABA-T activity in neuro-psychiatric disorders could be performed to understand, diagnosis and treat GABA-related disorders of the central nervous system (CNS).

Increase in brain GABA-transaminase activity after chronic ethanol treatment in rats

The activity of gamma-aminobutyrate aminotransferase (GABA-T) was measured in the brains of rats treated both acutely and sub-chronically with ethanol. Previously, chronic treatment with ethanol for 90 weeks was found to increase the mean brain GABA-T activity by 20-45%. In the present study acute ethanol treatment (4 g/kg, i.p.) did not induce and change in the activity of brain GABA-T with the exception of a small increase in the cerebellum (8%) and, after repeated treatment with ethanol (4 g/kg/day, i.p.) for one and two weeks, no change in the activity of GABA-T was also found in any of the brain regions examined. Subchronic treatment with ethanol for 14 weeks, performed according to two different schedules involving a voluntary intake of ethanol in the drinking water, resulted in approximately a two-fold difference in ethanol intake. A mean increase of 50-85% in the activity of GABA-T was found in all the brain regions of rats with higher ethanol intake in comparison with the group of rats with lower ethanol intake. A bimodal distribution of brain GABA-T activity, however, was found in the ethanol-treated rats, with 60% of the rats having a two-fold increase and the remaining 40% having unchanged activities. The addition of pyridoxal phosphate to the incubation media increased the activity of brain mitochondria from ethanol-treated rats with high brain GABA-T, whereas there was a decrease in the activity in control rats and in ethanol-treated rats in which no increase in brain GABA-T had occurred. These results show firstly, that in a subpopulation of rats, subchronically treated with ethanol for 14 weeks, there was a two-fold increase in brain GABA-T activity, while in another subgroup no change occurred, and, secondly, that this increase in GABA-T activity was a consequence of a change in the response of the apoprotein to the addition of the cofactor pyridoxal phosphate.

Higher environmental temperature-induced increase in body temperature: involvement of serotonin in GABA mediated interaction of opioidergic system

Exposure (2 h) of adult male albino rats to higher environmental temperature (HET, 40 degrees C) significantly increased body temperature (BT). Administration of (a) 5-HTP (5 mg/kg, i.p.) or morphine (1 mg/kg, i.p.) or physostigmine (0.2 mg/kg, i.p.) alone significantly increased and (b) methysergide (1 mg/kg, i.p.) or naloxone (1 mg/kg, i.p.) or atropine (5 mg/kg, i.p.) reduced the BT of both normal and HET exposed rats. Further, it was observed that morphine prevented the methysergide-induced hypothermia and 5-HTP potentiated the morphine-induced hyperthermia in both normal and HET exposed conditions. Biochemical study also indicates that serotonin metabolism was increased but GABA utilization was reduced following exposure to HET.5-HTP or bicuculline-induced hyperthermia in control and HET exposed rat was potentiated with the coadministration of bicuculline and 5-HTP. The cotreatment of bicuculline with methysergide prevented the methysergide-induced attenuation of BT of heat exposed rat, rather BT was significantly enhanced indicating that inhibition of GABA system under heat exposed condition may activate the serotonergic activity. Further (a) enhancement of (i) morphine-induced hyperthermia with physostigmine (ii) physostigmine- or morphine+physostigmine-induced increase of BT with 5-HTP and (b) reduction of (i) morphine- or morphine + 5-HTP-induced hyperthermia with atropine and (ii) atropine-induced hypothermia with 5-HTP in both normal and HET exposed conditions suggest that HET exposure activates the cholinergic system through the activation of opioidergic and serotonergic system and hence increased the BT. Thus, it may be concluded that there is an involvement of serotonergic regulation in the opioidergic-cholinergic interaction via GABA system in HET-induced increase in BT.

Neurotoxic effects of gasoline and gasoline constituents

This overview was developed as part of a symposium on noncancer end points of gasoline and key gasoline components. The specific components included are methyl tertiary butyl ether, ethyl tertiary butyl ether, tertiary amyl methyl ether, butadiene, benzene, xylene, toluene, methyl alcohol, and ethyl alcohol. The overview focuses on neurotoxic effects related to chronic low-level exposures. A few general conclusions and recommendations can be made based on the results of the studies to date. a) All the compounds reviewed are neuroactive and, as such, should be examined for their neurotoxicity. b) For most of the compounds, there is a substantial margin of safety between the current permissible exposure levels and levels that would be expected to cause overt signs of neurotoxicity in humans. This is not the case for xylene, toluene, and methanol, however, where neurologic effects are observed at or below the current Threshold Limit Value. c) For most of the compounds, the relationship between chronic low-level exposure and subtle neurotoxic effects has not been studied. Studies therefore should focus on examining the dose-response relationship between chronic low-level exposure and subtle changes in central nervous system function.

Brain GABA-transaminase and monoamine oxidase after chronic ethanol treatment in rats

The activities of gamma-aminobutyrate aminotransferase (GABA-T) and monoamine oxidase (MAO-A and -B) were estimated in various brain regions of rats exposed to ethanol for 90 weeks. During the first period (weeks 1-58), the rats had access to both ethanol (10% w/v) and water during a 24-hr interval at the end of each week. At this point, the animals were given either a saline injection (intraperitoneally, group 1) or an ethanol injection (2.0 g/kg ip, group 2). During the second period (weeks 59-90), the rats in groups 1 and 2 had continuous access to both ethanol and water. The third group was composed of untreated control rats. Compared with controls, there was an increase of 20-45% in the mean brain GABA-T activity in both groups of ethanol-treated rats. However, analysis of the data for the individual ethanol-treated rats revealed a considerable difference in brain GABA-T activity. Thus, approximately 30% of the ethanol-treated rats showed approximately twice the activity of rats in the exposed groups and in the control group. There was no connection between ethanol intake, water intake, or body weight and GABA-T activity in any of the brain regions examined. There was no effect of ethanol in vitro on the activity of GABA-T in the brain cortex in concentrations of 20-100 mM, whereas acetaldehyde inhibited the activity by 15% at these concentrations. The present results suggest that there is a bimodal distribution with respect to the effect of ethanol on rat brain GABA-T activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic ethanol administration on acetylcholinesterase activity in the somatosensory cortex and basal forebrain of the rat

A chronic diet of ethanol has detrimental effects on the cholinergic system in adult humans and rats. This study examined the effects of chronic exposure to dietary ethanol on the anatomical organization of true acetylcholinesterase (AChE) active elements in rat cerebral cortex. We focused on the somatosensory cortex because of its highly organized chemical and cellular structure. Following 42 days of exposure to an ethanol diet (6.7% v/v), there were marked changes in the cortical plexus of AChE-positive fibers. The AChE-positive plexus in ethanol-treated rats was reduced in all cortical layers, in comparison to age-matched pair-fed control and chow-fed rats. The most marked reduction was evident in layers II/III, IV, and VIa. Moreover, the density of AChE-positive cell bodies was significantly reduced in the cortices of ethanol-fed rats, particularly in the deep laminae. These alterations in the chemoarchitecture of somatosensory cortex occurred in the absence of changes in the cytoarchitectonic organization of neocortex. There was no detectable ethanol-induced change in the density of Cresyl violet-stained neurons either in the horizontal limb of the diagonal band of Broca or in the nucleus basalis. The density of AChE-positive neurons in the nucleus basalis, however, was significantly lower in ethanol-fed rats than in controls. Thus, it appears that a mere 6 weeks of ethanol exposure is sufficient to alter the cholinergic innervation of the cerebral cortex. These cortical alterations occur despite the lack of an ethanol-induced death of neurons in the basal forebrain. Such changes may contribute to the memory loss associated with alcohol dementia.

Transport and metabolism of glutamate by rat cerebellar mitochondria during ammonia toxicity

Pathophysiological concentrations of ammonia, both in vivo and in vitro, suppressed the oxidation of glutamate by rat cerebellar mitochondria. The transport of glutamate into mitochondria was either unaltered or enhanced during hyperammonemic states. Activities of mitochondrial enzymes, aspartate aminotransferase, alanine aminotransferase, glutamate dehydrogenase, glutaminase, and GABA-transaminase were suppressed during hyperammonemic states. Suppression of 14CO2 production with (aminooxy)acetic acid but not with glutamic acid diethyl ester indicated that transamination but not oxidative deamination of glutamate plays a major role in glutamate oxidation during normal and hyperammonemic states.

Uptake and metabolism of glutamate and aspartate by astroglial and neuronal preparations of rat cerebellum

Astrocytes, neuronal perikarya and synaptosomes were prepared from rat cerebellum. Kinetics of high and low affinity uptake systems of glutamate and aspartate, nominal rates of 14CO2 production from [U-14C]glutamate, [U-14C]aspartate and [1-14C]glutamate and activities of enzymes of glutamate metabolism were studied in these preparations. The rate of uptake and the nomial rate of production of 14CO2 from these amino acids was higher in the astroglia than neuronal perikarya and synaptosomes. Activities of glutamine synthetase and glutamate dehydrogenase were higher in astrocytes than in neuronal perikarya and synaptosomes. Activities of glutaminase and glutamic acid decarboxylase were observed to be highest in neuronal perikarya and synaptosomes respectively. These results are in agreement with the postulates of theory of metabolic compartmentation of glutamate while others (presence of glutaminase in astrocytes and glutamine synthetase in synaptosomes) are not. Results of this study also indicated that (i) at high extracellular concentrations, glutamate/aspartate uptake may be predominantly into astrocytes while at low extracellular concentrations, it would be into neurons (ii) production of alpha-ketoglutarate from glutamate is chiefly by way of transamination but not by oxidative deamination in these three preparations and (iii) there are topographical differences glutamate metabolism within the neurons.

Low platelet gamma-aminobutyrate aminotransferase and monoamine oxidase activities in chronic alcoholic patients

The activities of gamma-aminobutyrate aminotransferase (GABA-T) and monoamine oxidase (MAO) were estimated in blood platelets from 25 male chronic alcoholics and from 27 healthy male volunteers without histories of alcohol abuse. Based on clinical criteria, the alcoholics were classified into type 1 or type 2 alcoholism. The activity of GABA-T was found to be lower both in type 1 and type 2 alcoholics than in healthy volunteers. With regard to MAO, the platelet activity was found to be significantly lower only in type 2 alcoholics in concordance with previous reports. No significant correlation was found between the activities of GABA-T and MAO in the blood platelets of healthy volunteers. The inhibitory effect of 400 mM ethanol on the platelet MAO activity increased with decreasing concentrations of the substrate phenylethylamine. The degree of inhibition of ethanol on the platelet MAO activity, however, did not differ significantly between alcoholics and controls.

Ethanol alters monoamines in specific mouse brain regions

Ethanol (3.5 g/kg 60 min post-IP injection) produced the following changes in regional brain monoamine levels and in the respective metabolite/neurotransmitter ratios: for the noradrenergic system, MHPG was decreased in the amygdala and increased in the hypothalamus, while the MHPG/NE ratio was increased in the prefrontal cortex and the hypothalamus. For the dopaminergic system, DA was decreased in the olfactory tubercle, DOPAC was increased in the prefrontal cortex and septum, and DOPAC/DA was increased in the prefrontal cortex, septum, striatum, and hypothalamus. HVA was increased in the prefrontal cortex and septum, while HVA/DA was increased in the same regions plus the olfactory bulb. 3MT was decreased in the olfactory tubercle and striatum. The serotonergic system was not altered. The results demonstrate that ETOH produces selective regional changes in the concentration and utilization of monoamines in mouse brain with a predominant influence on dopaminergic systems and a lesser effect on noradrenergic activity.

Effects of nitrendipine, chlordiazepoxide, flumazenil and baclofen on the increased anxiety resulting from alcohol withdrawal

1. Male hooded Lister rats were fed a liquid diet containing 10% absolute ethanol for 4-5 weeks. Control rats received the liquid diet in amounts controlled to produce equal weight gain. 2. The rats were tested 7.5 h after withdrawal of ethanol and 30 min after i.p. injection with nitrendipine, chlordiazepoxide or baclofen or 20 min after i.p. injection with flumazenil. 3. Nitrendipine (25-100 mg/kg) was unable to reverse the anxiogenic responses detected on withdrawal from ethanol, but the highest dose did reduce withdrawal tremor. 4. Chlordiazepoxide (10 mg/kg), flumazenil (4 mg/kg) and baclofen (1.25 mg/kg) significantly reversed the anxiogenic response detected on withdrawal from ethanol. 5. These reversals of ethanol withdrawal responses are similar to the reversal of the increased anxiety detected on withdrawal from chronic treatment with benzodiazepines. 6. The mechanisms and clinical implications of these drug-induced reversals are discussed.

Increased number of GABAergic terminals in the nucleus accumbens is associated with alcohol preference in rats

Ethanol is known to be anxiolytic and this effect may be mediated through GABA transmission acting on the GABAA-benzodiazepine-Cl- ionophore complex. Recent studies from our laboratory have suggested that GABA transmission and the GABAA-benzodiazepine-Cl- ionophore complex might be involved in the rewarding action of ethanol in alcohol-preferring rats. We report here immunocytochemical and morphometric studies analyzing the GABAergic terminal density in the nucleus accumbens (NA), corpus striatum, nucleus tractus solitarius, and lateral septum of the selectively bred P (alcohol-preferring) and the NP (alcohol-nonpreferring) lines of rats, as well as of the high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) lines of rats. The NA was included for analysis because this structure has been implicated as an important component of the brain reward system. An increase of GABAergic terminal density was found in the NA of the P rats, when compared with the NP rats. Similarly, there were more GABAergic terminals in the NA of HAD rats than of the LAD rats. No differences between the lines were seen in the other brain regions examined. The results suggest that alcohol preference in P and HAD rats may be related to increased GABA terminals and enhanced GABAergic inhibition within the NA.

Effect of short- and long-term exposure to low environmental temperature on brain regional GABA metabolism

Single exposure of adult male rats to low environmental temperature (LET, 12 +/- 0.5 degrees C) for 2 h significantly increased the hypothalamic and striatal GABA levels without affecting those in other regions of brain. The activity of glutamate decarboxylase (GAD) was elevated in hypothalamus (H) and corpus striatum (CS) under these conditions. GABA accumulation rate (measured with ethanolamine-O-sulfate, an inhibitor of GABA-transaminase) was also increased in both H and CS of rats exposed to LET for 2 h. Unlike after a single exposure, the repeated exposure (2 h/day) for 7, 15, and 30 consecutive days did not change the hypothalamic GABA metabolism. No change in GABA metabolism was observed in CS when rats were repeatedly exposed to LET for 7 consecutive days. Prolongation of repeated exposure to LET (2 h/day) for 15 and 30 consecutive days decreased the striatal GABA level and increased the activity of GABA-transaminase, although GAD activity was not altered under these conditions. These results suggest that single exposure to LET accelerates GABA synthesis and may reduce the GABAergic activity in both H and CS; whereas repeated exposure to LET for 15 or 30 consecutive days enhances GABAergic activity with the stimulation of GABA utilization only in CS without affecting its synthesizing process. Thus, it may be suggested that the hypothalamic and striatal GABA system may play a characteristic role in response to short- and long-term exposure to LET.

The role of bicuculline, aminooxyacetic acid and gabaculine in the modulation of ethanol-induced motor impairment

Ethanol's intoxicating effects may result from ethanol-induced changes in central gamma-aminobutyric acid (GABA) mechanisms. To further test this hypothesis, mice were pretreated with bicuculline (1 mg/kg s.c.), aminooxyacetic acid (15, 20, 25 or 30 mg/kg i.p.) or gabaculine (20 or 40 mg/kg i.p.). Following pretreatment, 20% ethanol (2.25 g/kg i.p.) was administered and rolling roller performance evaluated. All ethanol-treated control animals showed lack of rolling roller performance at 5 min post ethanol but regained rolling roller performance by 35 min. Only 42% of the bicuculline pretreated mice demonstrated lack of rolling roller performance at 5 min post ethanol and all regained rolling roller performance by 15 min. Impairment of rolling roller performance by ethanol was potentiated by aminooxyacetic acid in a dose-dependent manner. Aminooxyacetic acid (25 and 30 mg/kg doses) slowed blood ethanol disappearance although analysis of blood ethanol disappearance and motor impairment curves indicated that aminooxyacetic acid potentiation of ethanol-induced rolling roller performance impairment cannot be attributed solely to aminooxyacetic acid's effect on blood ethanol levels. Gabaculine also potentiated ethanol's impairment of rolling roller performance but was more effective than aminooxyacetic acid in slowing ethanol disappearance, suggesting that in comparison to aminooxyacetic acid, alteration of ethanol metabolism plays a greater role in gabaculine's potentiation of ethanol-induced motor impairment.

Effects of acute barbiturate administration, tolerance and dependence on brain GABA system: comparison to alcohol and benzodiazepines

Central nervous system depressants, e.g., barbiturates, alcohol and benzodiazepines, have a wide spectrum of activity in humans and animals. Evidence accumulated suggests that some of the pharmacological actions exerted by these agents may be mediated through GABA system by mimicking GABAergic transmission. This review attempts to summarize the evidence available as to how the GABA system plays a part in the barbiturate actions and the development of tolerance to and physical dependence on barbiturates. The comparisons of the effects of alcohol, barbiturates and benzodiazepines at different steps of GABA synapse are also presented. Furthermore, the results which have been reported in the literature are inconsistent. This may be due to differences in: (a) animal models used; (b) brain regions used; (c) protocols (dose, duration, form and route of administration, etc.) used in treating animals and/or (d) techniques (pharmacological, biochemical, physiological, etc.) used.

Effect of diazepam on electroacupuncture-induced changes in regional gamma-aminobutyric acid of the rat central nervous system

Electroacupuncture-induced analgesia (EAA), as assessed in terms of tail flick latency in adult male albino rats, was reduced or completely withdrawn by co-treatment of diazepam with electroacupuncture (EA) (10 Hz, 1 volt), although diazepam (5-20 mg/kg, i.p.) alone had no analgesic effect. Further, it was found that only the gamma-aminobutyric acid (GABA) system of thalamus and pons-medulla regions were involved in EAA. The EA-induced inhibition of GABAergic activity in the thalamus and pons-medulla was disinhibited when diazepam was pre-administered to rats treated with a single EA and reduced the EAA.

Reduced behavioral responses to intranigral muscimol following chronic ethanol

Increased biochemical measures of GABA activity are observed after acute administration of ethanol and decreased activity has sometimes been observed after chronic ethanol exposure. Since chronic alterations in neurotransmitter activity may result in changes in receptor function, it is possible that changes in GABA-receptive neurons may accompany chronic ethanol treatment. In the present study we examined the incidence of muscimol-induced motor behaviors in ethanol-naive and chronic ethanol-treated animals. Male Sprague-Dawley rats received bilateral cannula implants into substantia nigra pars reticulata for subsequent administration of muscimol or saline. After recovery from surgery, rats received chronic treatment in ethanol-vapor inhalation chambers for 15 days. Animals were then removed from the chambers and examined 10 hours after removal. Muscimol resulted in a general increase in motility in both control and ethanol-treated animals. Animals withdrawn from chronic ethanol exposure, however, exhibited significantly less muscimol-stimulated, repetitive 9 Hz movements. These results suggest that GABA receptive cells within the substantia nigra or its vicinity may be functionally less responsive to GABAergic stimulation after chronic ethanol administration.

Antagonism of ethanol effects by Ro 15-4513: an electrophysiological analysis

Ethanol (ETH) and general anesthetics have been reported to facilitate the chloride channel opening, possibly, or at least partly, through an interaction with the GABA-benzodiazepine (BZ) receptor-gated chloride ionophore "supramolecular complex". Recently Ro 15-4513, a novel BZ ligand, has been indicated as a potent and selective antagonist of various ETH-induced behavioral and biochemical effects. However, since its precise characterization is still a matter of debate, we have tested and compared the effect of Ro 15-4513, as well as its antagonism against ETH, in two objective electrophysiological parameters, i.e., the electroencephalograph (EEG) pattern in freely moving rats and single unit activity of reticulata neurons. Ro 15-4513 produced an EEG state of alertness and antagonized the behavioral impairment and the EEG deterioration by ETH. However, while its protective action was consistent against moderate doses (2 g/kg) of ETH, it was much less evident versus higher doses (4 and 8 g/kg). On reticulata cells, Ro 15-4513 potently stimulated their spontaneous firing and reversed the depression by both ETH and Na-pentobarbital. Moreover, the beta-carboline DMCM also had similar effects. The "pure" BZ antagonist Ro 15-1788 was completely inefective against ETH, yet fully cancelled the reversing actions of Ro 15-4513 and DMCM upon ETH or Na-pentobarbital effects. It is concluded that Ro 15-4513 behaves as a BZ inverse agonist, so that its opposition to ETH and Na-pentobarbital is probably the result of its "negative" coupling with the BZ recognition site that triggers the closing of chloride channels. It suggests that BZ inverse agonists might constitute, in the near future, a new class of analeptic drugs.

Release of endogenous glutamate from rat cerebellar synaptosomes: interactions with adenosine and ethanol

The effects of ethanol and adenosine receptor agonist R-PIA and antagonist theophylline on release of endogenous glutamate were tested in rat cerebellar synaptosomal preparation. Release was carried out for 5 to 60 sec after which time the released glutamate was separated from the synaptosomal membranes by rapid filtration. The amount of released glutamate in the filtrate was measured by an enzyme-linked fluorometric assay. Basal endogenous glutamate release was estimated as 3.7 +/- 0.3 nmol/mg protein/5 sec and was stimulated by high K+. Glutamate release consisted of an initial rapid phase for the first 10 sec that was followed by a relatively slower phase. Both Ca2+-dependent and Ca2+-independent glutamate release were observed which suggested the involvement of both neuronal and glial constituents of the synaptosomal preparation, respectively. Pharmacologically relevant concentrations of ethanol (25-100 mM) caused a trend toward a dose-dependent inhibition of glutamate release. R-PIA and theophylline inhibited and stimulated, respectively, basal release of glutamate and R-PIA-inhibited release was blocked by theophylline. Ethanol (25 mM) blocked the stimulatory effect of theophylline and the results of experiments following the inclusion of adenosine deaminase suggested the involvement of adenosine in this effect of ethanol. The results support our previous findings that suggest an involvement of cerebellar adenosine in the motor disturbing effects of acute ethanol and extend those findings by indicating that ethanol inhibits glutamate release from granule cells of the cerebellar cortex through an adenosine-sensitive mechanism.