Effect of chronic treatment of ethanol on benzodiazepine and picrotoxin sites on the GABA receptor complex in regions of the brain of the rat

Transmitter amino acid neurochemistry in chronic alcoholism with and without cirrhosis of the liver

Neurotransmitter receptor studies are beginning to be applied more widely to human brain tissue obtained at autopsy. By taking tissue from well-documented cases which have been extensively characterized on histological and morphometric criteria, it is becoming possible to make clinicopathological correlations in studies of the effects of chronic alcohol abuse. Recent findings of alterations in the nature and amounts of amino acid neurotransmitter receptors in alcoholism are summarized, with special emphasis on the effects of chronic severe liver disease. There are selective changes in receptors in the superior frontal cortex of alcoholics. There is a marked increase in the density of the GABA binding site, and a lesser change in the density of the 'central-type' benzodiazepine site, on the GABAA-benzodiazepine receptor complex. In contrast, glutamate receptors may be much less affected. Together with morphological and cognitive studies, the results suggest that the superior frontal cortex is preferentially damaged in chronic alcoholism. An increase in 'central-type' benzodiazepine sites in both superior frontal cortex and motor cortex in cirrhotic alcoholics may reflect a more global brain damage, as observed in morphological studies. However, it should be noted the changes in [3H]GABA/muscimol binding were less pronounced in cirrhotic alcoholics than in non-cirrhotic alcoholics.

Rotarod studies in the rat of the GABAA receptor agonist gaboxadol: lack of ethanol potentiation and benzodiazepine cross-tolerance

All benzodiazepines and benzodiazepine site agonists impair motor performance dose-dependently and potentiate the effects of ethanol. In order to evaluate the risk of benzodiazepine and ethanol interaction with the direct acting GABA(A) receptor agonist 4,5,6,7-tetrahydroisoxazolo (5,4-c) pyridin-3-ol (gaboxadol), we studied impairment of motor coordination for combinations of gaboxadol, ethanol and a series of benzodiazepines (flunitrazepam, zolpidem and indiplon) in a rat rotarod model. All compounds produced a dose-dependent motor impairment and, in agreement with earlier data, a supra-additive effect of the benzodiazepine ligands and ethanol 1 g/kg was seen. In contrast, no significant potentiation of the effects of gaboxadol by ethanol was detected, and furthermore, no synergistic interaction between gaboxadol and any of the benzodiazepines was seen. A 30-day tolerance study was conducted with daily injections of gaboxadol (7.9 mg/kg) and zolpidem (1.25 mg/kg), respectively. A time-dependent tolerance developed to the motor impairment produced by both compounds. On day 31, cross-tolerance studies between zolpidem/gaboxadol and gaboxadol/zolpidem were conducted. No cross-tolerance was observed, indicating that the motor coordination effects observed with gaboxadol and zolpidem may arise from interaction with different receptor populations.

Chronic ethanol consumption enhances internalization of alpha1 subunit-containing GABAA receptors in cerebral cortex

The molecular mechanisms that underlie ethanol dependence involve alterations in the functional properties and subunit expression of GABAA receptors. Chronic ethanol exposure decreases GABAA receptor alpha1 subunits and increases alpha4 subunit levels in cerebral cortical membranes. This study explored the effect of chronic ethanol exposure on internalization of GABAA/benzodiazepine receptors. Chronic ethanol exposure increased alpha1 subunit levels by 46 +/- 12% and [3H]flunitrazepam binding by 35 +/- 9% in the clathrin-coated vesicle (CCV) fraction. There was a corresponding 34 +/- 8% decrease in alpha1 peptide expression and 37 +/- 6% decrease in [3H]flunitrazepam binding in the synaptic fraction. Chronic ethanol consumption also increased the alpha1 subunit immunoprecipitate in the cytosolic fraction (77 +/- 22%), measured by western blot analysis. Moreover, co-immunoprecipitation of both clathrin and adaptin-alpha with alpha1 subunits was increased in the cytosolic fraction, suggesting that alpha1 subunit endocytosis is enhanced by chronic ethanol consumption. In contrast, alpha4 subunit peptide levels were not altered in the CCV fraction despite a 39 +/- 13% increase in peptide levels in the synaptic fraction of cortex. Moreover, acute ethanol exposure did not alter alpha1 subunit peptide expression or [3H]flunitrazepam binding in the synaptic or CCV fractions. These results suggest that chronic ethanol consumption selectively increases internalization of alpha1 subunit-containing GABAA receptors in cerebral cortex.

Unsulfated and sulfated neurosteroids differentially modulate the binding characteristics of various radioligands of GABA(A) receptors following chronic ethanol administration

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) inhibited the binding of [(3)H]flunitrazepam (2 nM), [(3)H]muscimol (5 nM) and 4 nM [(35)S]t-butylbicyclophosphorothionate [(35)S]TBPS in the rat cerebellum as well as cerebral cortex. DHEAS-induced inhibition of binding of these radioligands (62% to 100%) was more pronounced as compared to that in the case of DHEA (5% to 31%). DHEAS, unlike DHEA, inhibited [(3)H]flunitrazepam binding significantly to a lesser extent in the cerebellum of ethanol-dependent rats as compared to the control group (I(max):82+/-1vs.92+/-2%, p<0.005). However, DHEA, unlike DHEAS, inhibited [(35)S]TBPS binding to a greater extent in the ethanol-dependent rat cerebellum as compared to the control group (I(max):31+/-2vs.19+/-2%, p<0.005). Furthermore, DHEA was more potent in inhibiting [(35)S]TBPS binding in the cerebellum (IC(50):55+/-5 vs. 74+/-7 microM, p<0.05) and cerebral cortex (IC(50):26+/-4vs.64+/-9 microM, p<0.05) of ethanol-dependent rats as compared to the control group. These observations indicate that unsulfated and sulfated androstane-steroids modulate the GABA(A) receptors in the control as well as the ethanol-dependent rats differentially, and also suggest that the androstane-steroid binding sites associated with the GABA(A) receptors play an important role during ethanol dependence.

Regional variations in the effects of chronic ethanol administration on GABA(A) receptor expression: potential mechanisms

Gamma-aminobutyric acid type A (GABA(A)) receptors in brain adapt to chronic ethanol exposure via changes in receptor function and subunit expression. The present review summarizes currently available data regarding changes in GABA(A) receptor subunit mRNA and peptide expression. Data are presented from various different brain regions and the variations between specific brain regions used to draw conclusions about mechanisms that may underlie GABA(A) receptor adaptations during chronic ethanol exposure. In the whole cerebral cortex, chronic ethanol exposure leads to a reduction of GABA(A) receptor alpha1 subunit mRNA and peptide levels and a near equivalent increase in alpha4 subunit mRNA and peptide levels. This observation is the primary support for the hypothesis that altered receptor composition is a mechanism for GABA(A) receptor adaptation produced by chronic ethanol exposure. However, other brain regions do not display similar patterns of subunit changes. Moreover, subregions within cortex (prefrontal, cingulate, parietal, motor, and piriform) exhibit patterns of changes in subunit expression that differ from whole cortex. Therefore, regional differences in GABA(A) receptor subunit expression are evident following chronic ethanol administration, thus suggesting that multiple mechanisms contribute to the regulation of GABA(A) receptor expression. These mechanisms may include the involvement of other neurotransmitter systems, endogenous steroids and second or third messenger cross-talk.

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.

Effects of acute and chronic ethanol exposure on spatial cognitive processing and hippocampal function in the rat

Animals, including rats, have a predisposition to process and use spatial information to organize and guide behavior. The hippocampus and related structures are critically involved in this function, and, consequently, it has been proposed that one function of the hippocampus is to construct "spatial cognitive maps" of environments. Lesions to the hippocampus or its connections produce a pattern of alterations in behavior which include shifts from the use of spatial information to guide behavior to the use of cue- or taxon-based information to guide behavior. Recently it was demonstrated that ethanol interacts with a specific group of neurotransmitter systems, i.e., N-methyl-D-aspartate receptors and GABA(A) receptors that exist in high proportions in the hippocampus and related structures. In this review, we seek to summarize the literature demonstrating that one effect of acute and chronic ethanol exposure is to produce behavioral alterations that are strikingly similar to those found following lesions to the hippocampal system. Furthermore, cellular and anatomical alterations resulting from similar ethanol exposure paradigms will be reviewed and offered as possible mechanisms for producing the alterations in behavior. Finally, several unanswered questions concerning the interaction between ethanol and spatial cognitive processing will be identified.

Neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one modulates electrophysiological and behavioral actions of ethanol

Neuroactive steroids are synthesized de novo in brain, yet their physiological significance remains elusive. We provide biochemical, electrophysiological, and behavioral evidence that several specific actions of alcohol (ethanol) are mediated by the neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP; allopregnanolone). Systemic alcohol administration elevates 3alpha, 5alpha-THP levels in the cerebral cortex to pharmacologically relevant concentrations. The elevation of 3alpha,5alpha-THP is dose- and time-dependent. Furthermore, there is a significant correlation between 3alpha,5alpha-THP levels in cerebral cortex and the hypnotic effect of ethanol. Blockade of de novo biosynthesis of 5alpha-reduced steroids using the 5alpha-reductase inhibitor finasteride prevents several effects of ethanol. Pretreatment with finasteride causes no changes in baseline bicuculline-induced seizure threshold but reverses the anticonvulsant effect of ethanol. Finasteride pretreatment also reverses ethanol inhibition of spontaneous neural activity in medial septal/diagonal band of Broca neurons while having no direct effect on spontaneous firing rates. Thus, elevation of 3alpha,5alpha-THP levels by acute ethanol administration represents a novel mechanism of ethanol action as well as an important modulatory role for neurosteroids in the CNS.

Effect of repeated ethanol withdrawal on glutamate microdialysate in the hippocampus

BACKGROUND

Our previous studies, which identified that ethanol withdrawal is associated with increases in glutamate microdialysate in the nucleus accumbens and reaches a maximum at 12 hr, have now been extended in order to assess whether repeated cycles of chronic ethanol intoxication followed by 12 hr withdrawal periods on three occasions alters glutamate release in the hippocampus of male rats.

METHODS

In this study, the microdialysis technique has been used with the HPLC and electrochemical detection.

RESULTS

During the first cycle of ethanol withdrawal, glutamate content increased significantly 8 hr after withdrawal (198.4% +/- 89.14%) by comparison with control rats. During the second period of ethanol withdrawal, 1 week after the initial withdrawal episode, glutamate microdialysate content increased significantly 10 hr after withdrawal, but to a much lower degree than in the first episode (179.08 +/- 25.68%), by comparison with control rats. During the third cycle of ethanol withdrawal, the concentration of glutamate in the hippocampus microdialysate did not significantly change at either of these time points except at 12 hr when glutamate was significantly decreased by comparison with control rats (52.09 +/- 14.38%). Apart from arginine, which was significantly decreased both at the cessation of alcoholization and during the 12 hr of the three withdrawal episodes, none of the other neurotransmitters assayed, aspartate, taurine, alanine, or GABA, showed any significant alteration.

CONCLUSION

These results clearly indicate that elevated glutamate release during the first withdrawal episode is not paralleled in subsequent withdrawal episodes.

Ethanol tolerance and synaptic plasticity

Current concepts of the mechanisms underlying many of the pharmacological effects of ethanol on the CNS involve disruption of ion channel function via the interaction of ethanol with specific hydrophobic sites on channel subunit proteins. Of particular clinical importance is the development of tolerance and dependence to ethanol, and it is likely that adaptive changes in synaptic function in response to ethanol's actions on ion channels play a role in this process. In this article, Judson Chandler, Adron Harris and Fulton Crews discuss potential mechanisms of ethanol-induced changes in synaptic function that might provide a cellular basis for ethanol tolerance and dependence. It is proposed that multiple mechanisms are involved that include both transcriptional and post-translational modifications in NMDA and GABAA receptors.

Chronic ethanol administration alters the modulatory effect of 5alpha-pregnan-3alpha-ol-20-one on the binding characteristics of various radioligands of GABAA receptors

In this study, we investigated the modulatory effect of 5alpha-pregnan-3alpha-ol-20-one, a neurosteroid, on the binding characteristics of [3H]flunitrazepam (2 nM), [3H]muscimol (5 nM), and 4 nM [35S]t-butylbicyclophosphorothionate (TBPS) in cerebral cortex, cerebellum, and hippocampus of control, ethanol-dependent, and ethanol-withdrawn rats. 5alpha-Pregnan-3alpha-ol-20-one potentiated the binding of [3H]flunitrazepam and [3H]muscimol in all the rat brain regions investigated in this study. There was a significant increase in the maximal potentiation of [3H]flunitrazepam as well as [3H]muscimol binding (Emax) in the ethanol-dependent rat cerebellum as compared to control group (p<0. 025). Furthermore, 5alpha-pregnan-3alpha-ol-20-one elicited a biphasic response, i.e., it potentiated the binding of [35S]TBPS at lower concentrations (<=100 nM) and inhibited the binding at higher concentrations (>100 nM). There was a significant higher inhibition of [35S]TBPS binding (-Emax) by 5alpha-pregnan-3alpha-ol-20-one in the hippocampus of ethanol-dependent as well as ethanol-withdrawn rats (p<0.025). These observations suggest that the neurosteroid binding site associated with the gamma-aminobutyric acidA (GABAA) receptors in cerebellum and hippocampus plays an important role during ethanol-dependence and ethanol-withdrawal, and some of the changes following ethanol dependence and its withdrawal may be mediated through the neurosteroid binding site.

The influence of alcoholism and cirrhosis on benzodiazepine receptor function

In a previous study we reported that the affinity of the platelet benzodiazepine receptor was greater in alcoholic cirrhotic patients compared with normal controls and that there were detectable ligands for the neuronal benzodiazepine receptor in plasma from both alcoholic and nonalcoholic cirrhotic patients. The aim of the present study was to assess the separate contributions of alcoholism and cirrhosis to the presence of ligands in plasma for the neuronal and peripheral benzodiazepine receptors and to changes in peripheral benzodiazepine receptor binding in platelets. These parameters were measured in 10 alcoholic cirrhotics, 9 nonalcoholic cirrhotics, 7 alcoholics with a normal liver function, and 15 nonalcoholic subjects and normal liver function. Both groups of alcoholics had been abstinent for several months and the nonalcoholic groups had abstained for 24 h before the study. The concentration of ligands for the peripheral benzodiazepine receptor were significantly higher in both cirrhotic groups compared with the other two groups, suggesting that cirrhosis was responsible for this accumulation. Furthermore, the cirrhotic patients with detectable concentrations of these ligands had significantly poorer episodic memory than those without ligands. However, the presence of ligands for the peripheral benzodiazepine receptor did not correlate with the change in receptor affinity, which was increased in the alcoholic cirrhotic group compared with all other groups. Neither cirrhosis nor alcoholism altered the peripheral benzodiazepine receptor number. The cirrhotic patients with detectable ligands for the neuronal benzodiazepine receptor showed psychomotor slowing and executive dysfunction. The results suggest that the ligands for the peripheral benzodiazepine receptor may contribute to some of the cognitive deficits seen in hepatic encephalopathy, but are not responsible for the receptor affinity change seen in the alcoholic cirrhotics. This affinity change is not solely due to the effects of alcohol and could possibly serve as a marker for those at risk for developing alcoholic cirrhosis.

Caloric restriction retards the aging associated changes in gamma-aminobutyric acidA receptor gene expression in rat cerebellum

It is widely accepted that calorie restriction is an effective way of delaying the aging process. Also, there is an indication that the beneficial effects exerted by dietary manipulation may be due to a direct effect at the molecular level like gene expression. The studies were conducted to determine whether calorie restriction prevents any age-related changes in the structural and molecular aspects of the GABAA-BZ receptor. In aged (24-month old diet ad libitum) rats, the binding of [35S]t-butyl-bicyclophosphorothionate (TBPS) was significantly reduced in the cerebellum. In contrast, [35S]TBPS binding remained unchanged in the cerebellum of calorie restricted old rats. In order to evaluate the molecular basis of these changes, the alpha sub-unit mRNA levels were measured. The GABAA receptor alpha1 sub-unit mRNA level remained unchanged in both the old groups of rats. The alpha2 subunit mRNA level was significantly decreased in the cerebellum of aged rats (24-month old ad libitum), whereas it remained unchanged in the cerebellum of calorie restricted old animals. These findings indicate a selective age and diet related modulation in the stoichiometry of the GABAA receptor in aging.

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.

Quantitative Autoradiography on [(35)S]TBPS Binding Sites of Gamma- Aminobutyric Acid(A) Receptors in Discrete Brain Regions of High- Alcohol-Drinking and Low-Alcohol- Drinking Rats Selectively Bred forHigh- and Low-Alcohol Preference

It has been documented that ethanol can potentiate brain gamma-aminobutyric acid (GABA)ergic function, and there is a close link between the GABA(A) receptor complex and effects of ethanol, including reinforcement of alcohol which is a fundamental element of alcohol preference. However, it is unknown in what discrete brain regions GABA(A) receptors might be associated with alcohol preference. In the present study, [(35)S]t-butylbicyclophosphorothionate ([(35)S]TBPS) was used to localize GABA(A) receptors in high-alcohol-drinking (HAD) rats and low-alcohol-drinking (LAD) rats which were selectively bred for high and low alcohol preference, respectively. Initial qualitative observations indicated that [(35)S]TBPS binding sites were abundant in many brain areas including the cerebral cortex, hypothalamus and amygdala of HAD and LAD rats. Furthermore, the quantitative autoradiographic analysis revealed fewer [(35)S]TBPS binding sites of GABA(A) receptors in the amygdaloid complex, central medial thalamic nucleus, lateral hypothalamic nucleus and anterior hypothalamic nucleus of HAD rats than LAD rats. Collectively, this study has indicated that HAD rats selectively bred for high alcohol preference possess lower [(35)S]TBPS binding in the brain. Since lower TBPS binding has been proposed to reflect enhanced GABAergic function, as evidenced in rats with seizure or under alcohol withdrawal, the results from the present study suggest that HAD rats might have an enhanced GABAergic function. It is thus likely that enhanced GABAergic function in the brain might be related to high alcohol preference which is characteristic in HAD rats. In addition, the present result showing no difference of [(35)S]TBPS binding in the nucleus accumbens is also in agreement with a notion that [(35)S]TBPS binding may represent only a small spectrum of the GABA(A) receptor complex which is constituted of a sophisticated subunit combination whose functional compositions are still unknown. In conclusion, the present study supports the working hypothesis that GABA(A) receptors are involved in alcohol preference in HAD rats.

Molecular pathogenesis of alcohol withdrawal seizures: the modified lipid-protein interaction mechanism

The phrase alcohol withdrawal seizures (AWS) refers to seizures that result from the withdrawal of alcohol after a period of chronic alcohol administration. A mechanism of AWS is postulated, namely the modified lipid-protein interaction (MLPI) mechanism. This hypothesis is based upon an evaluation of the mechanisms of membrane fluidity, calcium channels, gamma-aminobutyric acid (GABA) and glutamate in the molecular pathogenesis of AWS. The mechanism hypothesizes that acute ethanol treatment alters the neuronal membrane lipids which then perturbs protein events, such as affecting the GABAA receptors, NMDA receptors and voltage-dependent Ca2+ channels synergistically or in combination. Subsequent adaptations in these systems occur after prolonged administration of ethanol. A sudden withdrawal of ethanol then leads to hyperexcitability which results in AWS.

Intra-amygdala muscimol decreases operant ethanol self-administration in dependent rats

Dependence is an important factor motivating continued alcohol use in human alcoholics. Development of a model of ethanol (EtOH) consumption in dependent animals would advance the understanding of reinforcement after chronic EtOH exposure and allow for the investigation of the neuropharmacological mechanisms mediating reinforcement in dependent versus nondependent animals. In the present study, rats were trained to lever press for 10% EtOH, surgically implanted with bilateral guide cannulae in the amygdala, and either made dependent on EtOH by exposure for 2 weeks to EtOH or exposed to air in identical vapor chambers. Upon removal, the rats were placed in operant boxes and allowed to respond on levers for 10% EtOH or water during a 12-hr period. Rats were removed briefly at approximately 6.5 hr for intra-amygdala injections of saline or the GABAA receptor agonist muscimol. After the test period, rats were returned to the vapor chambers for 4 days before retest. EtOH-dependent animals responded more for EtOH across the 12-hr test period than did air control nondependent rats; this difference became more pronounced with repeated test sessions. Intra-amygdala muscimol significantly decreased responding for EtOH in EtOH-dependent rats, but had no effect in nondependent controls. These data suggest that the reinforcing effects of EtOH and neurotransmitter pathways mediating reward are altered after the development of dependence, and they support the use of this paradigm for further investigations into the neuropharmacology of EtOH dependence.

Glutamate and benzodiazepine receptor autoradiography in rat brain after repetition of alcohol dependence

During repeated alcohol withdrawal, convulsive withdrawal behavior has been shown to be increased in a kindling-like manner in both clinical and experimental studies. In the present experiment, quantitative autoradiography was used to investigate binding of tritiated ligands to glutamate receptor subtypes and the benzodiazepine/GABA (BZ/GABA) receptor complex in rats exposed to 14 episodes of alcohol withdrawal. Seizures were detected in 25% of the animals during withdrawal episode 10-13. Repeated alcohol withdrawal resulted in a decrease in the number of [3H]-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]-AMPA) binding sites in striatum and sub-regions of the entorhinal cortex, the cerebellum and the hippocampus, while the [3H]-flunitrazepam binding was down-regulated in the frontal cortex. There was no differences between the controls and the multiple withdrawal animals regarding the [3H]-dizocilpine ([3H]-MK801) binding and the [3H]-kainic acid binding. However, within the latter group, those animals in which withdrawal seizures were observed had increased [3H]-MK801 binding sites in focal regions of entorhinal cortex and hippocampus, compared to those in which seizures were not observed. The decreased AMPA binding suggested impaired glutamate neurotransmission. As such, this receptor probably did not contribute to alcohol withdrawal kindling, but rather was involved in seizure protective mechanisms during this process.

Effects of ethanol on ion channels

Ion channels play critical roles in nervous system function, from initiating rapid synaptic activity to propagation of action potentials. Studies have indicated that many of the effects of ethanol on the nervous system are likely caused by the actions of ethanol on ion channels. Ion channels are multimeric structures that gate ions through subtle changes in tertiary structure. Ethanol readily enters molecular sites within multimeric ion channels, modifying intermolecular forces and bonds that are important for the open-close-inactivation kinetic properties of channels. The diversity of channel composition caused by the multimeric structure results in subtypes of channels that have a spectrum of sensitivity to ethanol that translates into brain regional differences in ethanol sensitivity, in part caused by differences in ion channel subunit composition. Ethanol has been shown to affect both receptor-activated ion channels and voltage-gated ion channels. The acute intoxicating and incoordinating effects of ethanol are probably related to inhibition of subtypes of NMDA-glutamate receptor ion channels and potentiation of certain subtypes of GABAA receptor ion channels. Effects on these channels, as well as glycine, nicotinic cholinergic, serotonergic, and other ion channels, likely contribute to the euphoric, sedative, and other acute actions of ethanol. Changes in ion channel subunit composition, density, and properties probably also contribute to ethanol tolerance, dependence, withdrawal hyperexcitability, and neurotoxicity. A substantial number of studies have implicated glutamate NMDA receptor, GABAA, and L-type voltage-gated calcium channels in the adaptive changes in the brain during chronic ethanol exposure. The diversity of ion channels subunits, their prominent role in brain function, and ethanol action are likely to make them important contributors to alcoholism and alcohol abuse.

Regulation of GABAA receptor structure and function by chronic drug treatments in vivo and with stably transfected cells

In this article, we review the use of stably transfected cells to study the regulation of receptor structure and function by chronic drug treatments and compare results from these cells to results obtained from other systems, including neuronal cultures and intact animals. We focus on the gamma-aminobutyric acid type A (GABAA) receptor complex. Sedative/hypnotic drugs such as benzodiazepines, barbiturates and alcohol that potentiate GABAA receptor function produce tolerance and dependence. Chronic treatment of GABAA receptor preparations from brain and neuronal cultures with GABAA agonists, as well as these other three classes of drugs, results in regulation of several properties of the receptor. Drug treatments may regulate levels of binding sites, allosteric binding interactions, receptor function, levels of receptor subunit mRNA and levels of receptor subunit protein. Some or all of these effects may comprise the molecular mechanisms of tolerance to these GABAA-modulatory drugs. The use of cells stably transfected with neurotransmitter receptors provides a homogeneous population that can be cultured under controlled conditions. As most preparations contain mixed populations of GABAA receptor subunits, stably transfected cells offer the advantage of the expression of receptors with a defined subunit composition. We conclude that chronic drug treatments regulate allosteric coupling and function of GABAA receptors in stably transfected cells. This regulation does not appear to be due to decreases in the expression of alpha 1- or beta 1-receptor subunits or to expression of subunits other than alpha 1, beta 1, gamma 2L. Therefore, it is unlikely to be due to changes in receptor subunit composition and probably represents post-translational changes. The rapid regulation of allosteric coupling and function by drug treatment of the stably transfected cells should provide insights to the mechanisms of coupling between GABAA and benzodiazepine receptors as well as tolerance and dependence of benzodiazepines and ethanol.

Neurochemical bases of locomotion and ethanol stimulant effects

The locomotor stimulant effect produced by alcohol (ethanol) is one of a large number of measurable ethanol effects. Ethanol-induced euphoria in humans and locomotor stimulation in rodents, a potential animal model of human euphoria, have long been recognized and the latter has been extensively characterized. Since the euphoria produced by ethanol may influence the development of uncontrolled or excessive alcohol use, a solid understanding of the neurochemical substrates underlying such effects is important. Such an understanding for spontaneous locomotion and for ethanol's stimulant effects is beginning to emerge. Herein we review what is known about three neurochemical substrates of locomotion and of ethanol's locomotor stimulant effects. Several lines of research have implicated dopaminergic, GABAergic, and glutamatergic neurotransmitter systems in determining these behaviors. A large collection of work is cited, which strongly implicates the above-mentioned neurotransmitter substances in the control of spontaneous locomotion. A smaller, but persuasive, body of evidence suggests that central nervous system processes utilizing these transmitters are involved in determining the effects of ethanol on locomotion. Particular emphasis has been placed on the mesolimbic ventral tegmental area to nucleus accumbens dopaminergic pathway, and on the ventral pallidum/substantia innominata, where GABA and glutamate have been found to play a role in altering the activity of this dopaminergic pathway. Research on ethanol and drug locomotor sensitization, increased responsiveness to the substance with repeated administration, is also reviewed as a process that may be important in the development of drug addiction.

Ethanol stimulates diazepam binding inhibitor (DBI) mRNA expression in primary cultured neurons

Changes in expression of diazepam binding inhibitor (DBI) mRNA in cerebral cortical neurons following long-term ethanol (EtOH) exposure were examined. A significant increase in DBI mRNA expression was observed by the exposure of neurons to 50 mM EtOH for up to 5 days and to EtOH (1-100 mM) for 3 days. These EtOH-induced increases in DBI mRNA expression were further elevated after the additional cultivation of neurons under EtOH-free condition. beta-Actin mRNA expression was not altered by similar EtOH treatments. These results indicate that EtOH possesses the activity to increase the expression of DBI mRNA in cerebral cortical neurons.

GABAA receptor function and binding in stably transfected cells: chronic ethanol treatment

Effects of chronic ethanol exposure on GABAA receptors may contribute to tolerance and dependence to alcohol. Ethanol treatment of mice and rats can produce alterations of GABAA receptor binding, function, and subunit mRNA and protein levels. We treated a cell line (PA3 cells) that stably expresses GABAA receptors chronically with ethanol. Expression of bovine alpha 1, beta 1, and gamma 2L GABAA receptor subunits genes in these cells is controlled by a dexamethasone-sensitive promoter, and this provides an excellent system to study the regulation by chronic ethanol treatment of receptors with a defined subunit composition. The actions of the GABA agonist muscimol on receptor function (36Cl- uptake) were not affected by 100 mM ethanol treatment for 4 days, but the actions of flunitrazepam (1 microM) were decreased in cells treated with ethanol. The functional coupling between benzodiazepine and GABA sites on the receptors was affected by chronic ethanol treatment in a manner consistent with results from mice. Ethanol treatments (50 or 100 mM) for 4 days did not affect the affinity (Kd) or receptor density (Bmax) of [3H]flunitrazepam binding, or the levels of alpha 1 subunit mRNA, or alpha 1 or beta 1 subunit proteins. These results demonstrate that the regulation of the stably expressed GABAA receptors by chronic ethanol, in the absence of neuronal receptor gene promoters, is posttranscriptional and likely posttranslational.

Regional differences in the effects of chronic ethanol administration on [3H]zolpidem binding in rat brain

A strong association has been observed between [3H]zolpidem binding and the presence of gamma-aminobutyric acid (GABAA) receptor mRNA for alpha 1-, beta 2-, and gamma 2-subunits in specific brain regions. This correlates with observed sensitivity of individual neurons to zolpidem and ethanol in these same regions. Previous studies using homogenate binding approaches showed small alterations in [3H]zolpidem binding levels after chronic ethanol exposure. This study was undertaken to ascertain if there is regional specificity of the effects of chronic ethanol administration on [3H]zolpidem binding levels. Chronic ethanol administration induced small, but significant alterations in [3H]zolpidem (5 nM) binding in the inferior colliculus, substantia nigra, and the medial septum. [3H]Zolpidem binding was increased in the inferior colliculus and substantia nigra, and decreased in the medial septum. No significant differences in [3H]zolpidem binding were noted in any other brain area analyzed, including the cortex and cerebellum. These findings show that chronic ethanol administration has small effects on [3H]zolpidem binding, although they occur in a site-specific and bidirectional manner. Moreover, there is no correlation between changes in [3H]zolpidem binding and alterations in GABAA receptor subunit expression.

Chronic ethanol treatment differentially regulates NMDA receptor subunit mRNA expression in rat brain

Previous studies have implicated the N-methyl-D-aspartate receptor (NMDAR) complex in the physical dependence and withdrawal effects of chronic ethanol administration. In this study, we examined the effect of chronic ethanol administration and ethanol withdrawal on the NMDAR subunit R1, R2A, R2B, and R2C mRNA levels in rat hippocampus, cerebral cortex, and cerebellum. Using the RNase protection assay, we compared the levels of the NMDAR subunits mRNAs in ethanol-treated and control rats. Our results indicate that chronic ethanol administration and ethanol withdrawal do not change the NMDAR R1 subunit mRNA levels in cerebral cortex, hippocampus, or cerebellum at any time point. In contrast, 9 h after the last ethanol administration the R2A and R2B mRNA subunits were elevated by approximately 40% in cerebral cortex, and approximately 30% in hippocampus with respect to the levels in control animals. At 48 h the mRNA levels returned to the control levels. The chronic ethanol treatment did not alter R1, R2A, and R2C subunit mRNA levels in cerebellum. Our results demonstrate that chronic ethanol administration produces a differential regulation of the genes encoding the various subunits of the NMDAR.

Chronic GABA treatment downregulates the GABAA receptor alpha 2 and alpha 3 subunit mRNAS as well as polypeptide expression in primary cultured cerebral cortical neurons

Chronic GABA exposure of mammalian primary cultured cortical neurons results in a downregulation of the GABA-benzodiazepine receptor complex. In the present study, the mRNA levels, as well as polypeptide expression, for the GABAA receptor alpha 2 and alpha 3 subunits in cultured embryonic mouse cerebral cortical neurons (7 day old) were examined using northern analysis and immunoblotting techniques following chronic GABA treatment. The alpha 1 subunit mRNA or polypeptide could not be detected in these neurons. The steady state levels of mRNA for the GABAA receptor alpha 2 and alpha 3 subunits showed a decrease in comparison with untreated neurons. There was no change in the level of the beta actin or poly(A)+ RNA under the same experimental conditions. This agonist-induced reduction in the GABAA receptor alpha 2 and alpha 3 subunit mRNA was blocked by the concomitant exposure of neurons to R 5135, an antagonist of GABAA receptor. The polypeptide expression for the GABAA receptor alpha 2 and alpha 3 subunits in chronically GABA-treated neurons also showed a decline and this change was also blocked by the concomitant exposure of cells to GABA and R 5135. These results indicate that the chronic exposure of the GABAA receptor complex to agonist downregulates the expression of the alpha subunits of the receptor complex, which may be related to an observed decreases in the number of binding sites and GABA-induced 36Cl-influx in the cortical neurons.

Chronic ethanol treatment upregulates the GABA receptor beta subunit expression

The molecular mechanisms associated with ethanol-induced tolerance and physical dependence have yet to be elucidated. In previous studies we have demonstrated that chronic ethanol administration produced a decrease in the GABAA receptor mRNA level of alpha 1, alpha 2, alpha 5 subunits, and a decrease in the polypeptide (alpha 1, alpha 2, and alpha 3) expression in the rat cerebral cortex. In this study we examined the effect of chronic ethanol treatment on the mRNA levels and the expressions of the beta-subunits of the GABAA receptors in rat cerebral cortex. The results indicate that chronic ethanol administration produced an upregulation of the beta 1 subunit mRNA (12 kb) by 29 +/- 10%, beta 2 mRNA (8 kb) by 55 +/- 6% and the beta 3-subunit (6 kb) mRNA by 72 +/- 9% in cerebral cortex. The levels of the beta 2 and beta 3 subunit mRNAs remains elevated at 24 hr withdrawal. We also investigated the effect of chronic ethanol administration on the beta-subunit polypeptide expression using monoclonal antibody BD17, which recognizes the beta 2 (P56) and beta 3 (P58) polypeptides. Chronic ethanol treatment increased the levels of both of these polypeptides in cerebral cortex. Taken together, chronic ethanol administration produced an upregulation of the beta-subunit mRNA and the polypeptide expression of these subunits in rat cerebral cortex. In contrast, chronic ethanol treatment decreased the expression of various alpha-subunits in the cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies specific for GABAA receptor alpha subunits reveal that chronic alcohol treatment down-regulates alpha-subunit expression in rat brain regions

Chronic administration of ethanol results in the development of tolerance and dependence. The molecular mechanism underlying these behavioral actions of ethanol is poorly understood. Several lines of evidence have suggested that some of the pharmacological actions of ethanol are mediated via a potentiation of GABAergic transmission. Chronic ethanol administration results in a reduction in the GABAA receptor-mediated 36Cl- uptake in cortical synaptoneurosomes and primary cultured neurons. We and others have shown that it also results in a 40-50% reduction in GABAA receptor alpha-subunit mRNA levels in the rat cerebral cortex. In the present study, we investigated the expression of alpha 1, alpha 2, and alpha 3 subunits of the GABAA receptor in the cerebral cortex and the alpha 1 subunit in the cerebellum by immunoblotting using polyclonal antibodies raised against alpha 1-, alpha 2-, and alpha 3-subunit polypeptides following chronic ethanol treatment. These results reveal that chronic ethanol administration to rats results in a 61 +/- 4% reduction in level of the GABAA receptor alpha 1 subunit (51 kDa), 47 +/- 8% reduction in level of the alpha 2 subunit (53 kDa), and 30 +/- 7% reduction in level of the alpha 3 subunit (59 kDa) in the cerebral cortex and a 56 +/- 5% reduction in content of the alpha 1 subunit in the cerebellum. In summary, this ethanol-induced reduction in content of the GABAA receptor alpha subunits may underlie alterations in the GABAA receptor function and could be related to cellular adaptation to the functional disturbance caused by ethanol.

Chronic ethanol produces a decreased sensitivity to the response-disruptive effects of GABA receptor complex antagonists

Disruption of responding for food reinforcement may reflect the motivational state subsequent to the onset of an aversive event and has previously been shown to be sensitive to spontaneous withdrawal from ethanol and precipitated opiate withdrawal. The purpose of this study was to attempt to precipitate ethanol withdrawal with bicuculline methiodide, a competitive GABAA receptor antagonist, and Ro 15-4513, a benzodiazepine inverse agonist. A quantitative operant measure of food-motivated behavior was used to evaluate the reactivity of the GABAA-benzodiazepine receptor complex during chronic ethanol treatment in rats. In the present study, rats were trained to lever-press for food reinforcement on a fixed ratio 15 schedule and then maintained for 2 weeks on a liquid diet containing 35% ethanol-derived calories or a control liquid diet that was prepared isocalorically with sucrose. Chronic ethanol treatment attenuated the disruptive effects on operant responding that were produced by bicuculline methiodide (100 ng ICV) and Ro 15-4513 (3 and 6 mg/kg). The inability of these drugs to "precipitate" EtOH withdrawal may reflect the noncompetitive interaction of ethanol with the GABA-benzodiazepine-ionophore receptor complex. These data are consistent with recent biochemical studies indicating that chronic ethanol treatment modulates the GABAA-benzodiazepine-ionophore receptor complex by altering the expression of specific molecular components and inhibiting the activity of the receptor complex.

Chronic ethanol intoxication induces differential effects on GABAA and NMDA receptor function in the rat brain

The effect of long-term treatment with ethanol was investigated on the function of gamma-aminobutyric acid A (GABAA) and N-methyl-d-aspartic acid (NMDA) receptors. Rats were rendered ethanol-dependent by repeated forced administration of a 20% ethanol solution (12 to 18 g/kg/day po) for 6 days and tested while still intoxicated or at different time intervals after withdrawal. t-[35S]Butylbicyclophosphorothionate (35S-TBPS) binding was increased by 30% in cortical homogenates of rats killed 1 to 3 hr after last ethanol administration, when compared with saline-treated animals. However, GABA-stimulated 36Cl- uptake and its enhancement by flunitrazepam was decreased in the ethanol-treated animals. 35S-TBPS binding and 36Cl- influx measured 9 to 24 hr following the last ethanol injection, when withdrawal signs were present, were unmodified with respect to saline-treated rats. Moreover, the effects of both isoniazid and FG 7142 on 35S-TBPS binding were unchanged in ethanol-dependent rats tested at 1 to 3 and 9 to 24 hr, compared with controls. In contrast, ethanol-withdrawn rats tested at 9 to 24 hr showed a dramatic enhancement in their sensitivity to the convulsant action of isoniazid (50 to 250 mg/kg, sc). The same animals were also more susceptible to the convulsant action of NMDA (0.5 to 5 micrograms/5 microliters/rat intracerebroventricularly) and kainic acid (12 mg/kg, ip), and this effect was paralleled by an enhancement (+25%) in the density of 3H-MK 801 recognition sites in the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic ethanol consumption and withdrawal affects mitochondrial benzodiazepine receptors in rat brain and peripheral organs

Ethanol administration to rats for 30 days resulted in a significant decrease (-28%; P < 0.05) in the density of mitochondrial benzodiazepine receptors (MBR) in the olfactory bulb. The reduction in [3H]PK 11195 binding persisted 24 hr after cessation of alcohol and had returned to normal values when measured 4 days later. Alterations were confined to this brain region and were not detected in the cerebral cortex, cerebellum or hippocampus. [3H]PK 11195 binding was elevated in the liver (100%; P < 0.01), heart (43%; P < 0.01) and testis (27%; P < 0.05) 30 days following ethanol consumption and this persisted for 1 and 4 days after abrupt withdrawal. A transitory decrease (-20%; P < 0.05) in MBR density was observed in the adrenal gland following 30 days of alcohol ingestion, but disappeared during withdrawal. The alterations in these receptors may be relevant to the cellular damage or dysfunction induced by chronic exposure to ethanol.

Amino acid neurotransmitter receptor changes in cerebral cortex in alcoholism: effect of cirrhosis of the liver

Gamma-aminobutyric acidA/benzodiazepine receptor binding sites and the N-methyl-D-aspartate subclass of glutamate receptor sites were assessed in synaptic plasma membrane homogenates of cerebral cortex tissue obtained at autopsy from cirrhotic and noncirrhotic alcoholic patients and matched control subjects. The alcoholic patients consumed an average of greater than 80 g of ethanol/day, the control subjects less than 20 g/day. Postmortem delays up to approximately 100 h caused no significant loss of any of the binding sites; the patient and subject groups were closely matched for age. The affinities (KD) of the receptor sites did not differ between the patient and subject groups, nor between cortical regions. Using three different radioligands ([3H]muscimol, [3H]flunitrazepam, and [3H]diazepam), the gamma-aminobutyric acidA/benzodiazepine receptor complex was found to have greater density (Bmax) in superior frontal gyrus in alcoholic patients (which selectively shows morphological change in alcoholic patients), but was unchanged in motor cortex. Alcoholic patients with cirrhosis had much less pronounced changes. The density of the N-methyl-D-aspartate subclass of glutamate receptors, assessed with [3H]MK-801, did not vary across patient and subject groups.

Aging related alterations in GABAA receptor subunit mRNA levels in Fischer rats

The influence of aging on the binding of ligands to picrotoxin binding sites as well as steady state levels of mRNA for various alpha subunits of gamma-aminobutyric acid (GABA) receptor complex was investigated in male Fischer F-344 rats. In aged rats, the binding of [35S]t-butyl-bicyclophosphorothionate (TBPS) was significantly reduced. This decrease in TBPS binding derived from a reduced density of binding sites, rather than from affinity changes, in both cerebral cortex and cerebellum. In aged rats, alpha 1 mRNA level decreased approximately 70% between age 6 months and 24 months in the cerebral cortex (P less than 0.005). In contrast, alpha 1 mRNA remained unchanged in the cerebellum of old rats. The association of a decrease in picrotoxin binding sites in the cerebral cortex with a decline in alpha 1 mRNA level in the cerebral cortex and in alpha 2 mRNA level in the cerebellum is indicated. alpha 6 mRNA level increased with age in the cerebellum. These findings indicate a selective age related modulation in the stoichiometry of GABAA receptor in aging.

Cerebellar and frontal cortical benzodiazepine receptors in human alcoholics and chronically alcohol-drinking rats

Postmortem cerebellar and frontal cortical membrane homogenates from human alcoholics, control subjects without neurological or psychiatric illnesses, and rats that chronically drank alcohol were studied to determine the binding characteristics of an imidazobenzodiazepine, [3H]Ro 15-4513. This ligand binds to classical gamma-aminobutyric acidA (GABAA)/benzodiazepine receptors, as well as to a "diazepam-insensitive" site associated with the GABAA receptor complex in the cerebellar granule cell layer. There were no differences in the density of the binding sites between alcoholics and their controls, between alcohol-drinking AA rats that had a choice between 10% alcohol or water for about 10 weeks and their controls, or between Wistar rats that had been given 20% alcohol as their only fluid for 4 months and their controls, which were pair-fed isocalorically with sucrose. The affinity for the cerebellar binding of [3H]Ro 15-4513 was higher in the alcoholics than the controls. No differences were observed in the frontocortical binding. No affinity differences were observed in the rat models. There were no differences between the groups in the characteristics of [3H]Ro 15-4513 binding to human cerebellum in the presence of micromolar diazepam, thus revealing the diazepam-insensitive binding. When this component was subtracted from the total cerebellar binding, to reveal the diazepam sensitive binding, both the KD and Bmax were lower in the alcoholic than the control group. The binding of [3H]muscimol, a GABAA agonist, tended to be higher in the frontal cortices of alcoholics; a similar trend for greater effects was observed in the alcoholics for the GABA inhibition of [3H]Ro 15-4513 binding. These results suggest that no drastic changes occur through chronic alcohol abuse in the numbers of cerebellar and frontocortical benzodiazepine receptors in humans and rodent models; however, the data indicate that the alcoholics have either acquired or innate differences in classical benzodiazepine recognition sites of the cerebellum and in the coupling of these sites to GABAA sites in the frontal cortex, without any differences in cerebellar granule cell-specific diazepam-insensitive [3H]Ro 15-4513 binding sites.

Aging reduces the mRNA of alpha 1 GABAA receptor subunit in rat cerebral cortex

The effect of aging on the binding of ligands to the GABA, benzodiazepine and picrotoxin binding sites as well as alpha subunit mRNA level of GABAA receptor was investigated in cerebral cortex of male Fischer F-344 rats. In aged (730- to 770-day-old) rats, the binding of [35S]t-butylbicyclophosphorothionate (TBPS) was significantly reduced. Also, alpha 1 mRNA level was markedly decreased (86% suppression). In contrast, alpha 1 mRNA remained unchanged in cerebellum. These findings indicate a selective age-related structural change in GABAA receptor in rat cerebral cortex.

Neuroadaptive responses to chronic ethanol

Cellular responses of neuronal tissue to chronic ethanol exposure are reviewed. Evidence for adaptive responses to the acute actions of ethanol is available for five systems: GABA-activated chloride channels, voltage-sensitive calcium channels, NMDA-activated cation channels, receptors coupled through stimulatory guanine nucleotide binding proteins, and membrane lipid order. We suggest that at least some of these adaptive responses occur because of ethanol actions at the level of gene expression.

Modulation of benzodiazepine agonist and inverse-agonist receptor binding by GABA during ethanol withdrawal

1. The present study examined the capacity of GABA to modulate flunitrazepam and Ro15-4513 binding to putative GABAA receptors. Binding was measured in distinct brain regions both before and during selected periods of withdrawal from ethanol. 2. Rats were fed a nutritionally complete liquid ethanol (4.5% w/v) diet for 4 days and at various times after the last dose of ethanol (0, 12, 24, & 72 hr), rats were sacrificed and extensively washed brain membrane fractions were prepared. 3. Competitive inhibition of 3H-flunitrazepam binding by either flunitrazepam or Ro15-4513 (10(-10)M to 10(-7)M) was performed in the absence and presence of GABA (10(-5)M). In the presence of GABA, the apparent affinity for flunitrazepam was increased approximately 1.7 fold and the apparent affinity for Ro15-4513 was decreased by 1.7 fold. 4. No alteration in the capacity of GABA to modulate flunitrazepam or Ro15-4513 affinity (e.g. GABA-shift) was observed in cortical membrane preparations either 12 or 72 hr following ethanol cessation. 5. Further, no changes in GABA-modulation of flunitrazepam binding was evident 0, 12, 24, or 72 hr after the last ethanol dose in membranes prepared from cortex, hippocampus or cerebellum. 6. Therefore, results from the present study indicate that the capacity of GABA to modulate receptor affinity for benzodiazepine agonists and inverse-agonists in rat cortex, hippocampus or cerebellum is not altered during withdrawal from chronic ethanol.

Overexcitement and disinhibition. Dynamic neurotransmitter interactions in alcohol withdrawal

In alcohol withdrawal, abnormalities occur in a number of neurotransmitter systems: there is reduced inhibitory function, and increased activity of excitatory systems. The former, indicated by reduced GABA and alpha-2-adrenoceptor activity, acts in conjunction with, and is exacerbated by, the latter, which itself may be due to the potentiation of NMDA activity by depletion of magnesium, and overactivity of catecholaminergic and CRF neurones. These dysfunctions produce immediate effects and may also contribute to the long-term changes in brain excitability by a kindling-like process. It is possible that early and active treatment may oppose this process. Present strategies for treatment of alcohol withdrawal enhance GABA and alpha-2 inhibitory, or reduce excitatory, mechanisms. Future possibilities include the use of CRF and/or NMDA antagonists.

Valproate potentiates and picrotoxin antagonizes the anxiolytic action of ethanol in a nonshock conflict task

The purpose of this study was to examine the effects of the indirect GABA agonist valproate and the indirect GABA antagonist picrotoxin on the anxiolytic (anti-conflict) activity of ethanol in a behavioral conflict task that does not employ electroshock. This task (negative contrast) quantifies how animals respond to an abrupt, unexpected reduction in reward. Treatment with valproate alone did not elevated depressed behavior engendered by abrupt reduction in reward. However, when administered together with a sub-effective dose of ethanol (0.5 g/kg), valproate (50-200 mg/kg) dose-dependently potentiated the anxiolytic action of ethanol. Picrotoxin (2 mg/kg) antagonized the anxiolytic effects of a larger dose of ethanol (1.0 g/kg) given alone, as well as the ability of valproate to enhance the anxiolytic effects of smaller dose of ethanol (0.5 g/kg). As such, these data support a role for GABA in mediating the anxiolytic activity of ethanol.

Are GABAB receptors involved in the pharmacological effects of ethanol?

The interaction of ethanol with GABAB-receptor system and the selectivity of phaclofen for GABA-receptor subtypes were investigated by employing an in vitro model of 36Cl-influx assay in mammalian cultured neurons and also in vivo models of picrotoxin- and NMDA-induced convulsions in rats. Ethanol (20 mM), without having any effect per se, potentiated the effect of GABA on 36Cl-influx, whereas at concentration 50 mM, ethanol activated Cl(-)-channels directly in mice spinal cord cultured neurons. In contrast, (-)baclofen (100 microM) did not modify the effects of GABA or ethanol on 36Cl-influx. Similarly, phaclofen (500 microM), as well as pertussis toxin (140 ng/ml, overnight incubation) did not modify these effects. Interestingly, phaclofen (200 micrograms i.c.v.) reversed the anticonvulsant effect of ethanol, but not that of pentobarbital or diazepam or progabide, against picrotoxin-induced convulsions in rats. However, phaclofen failed to modify the anticonvulsant effect of ethanol against NMDA-induced convulsions. These observations indicate that phaclofen is devoid of GABAA-receptor blockade property, and the anticonvulsant effect of ethanol against picrotoxin may be mediated through the activation of both GABA-receptor subtypes.

Chronic ethanol and pentobarbital administration in the rat: effects on GABAA receptor function and expression in brain

Chronic exposure of rats to ethanol significantly decrease GABAA receptor-mediated 36Cl- uptake in cerebral cortical synaptoneurosomes. Muscimol and pentobarbital stimulation as well as ethanol enhancement of muscimol-stimulated 36Cl- flux are significantly decreased following chronic ethanol inhalation. Repeated pentobarbital administration has a similar effect on muscimol and pentobarbital-stimulated 36Cl- uptake in cerebral cortical synaptoneurosomes. We have postulated that these adaptive response may be associated with an alteration of GABAA receptor gene expression. Chronic ethanol exposure resulted in a significant reduction in the levels of GABAA receptor alpha-subunit mRNA's. The most abundant mRNA species in the rat cerebral cortex were reduced 40-50% (4.4 Kb mRNA, 43%, 4.8 Kb mRNA, 47%). beta-Actin mRNA and poly(A)+ RNA levels were not significantly reduced following chronic ethanol exposure. Repeated pentobarbital administration had no effect on the level of the 4.4 and 4.8 Kb transcripts of alpha-subunit mRNAs in rat cerebral cortex. These data suggest that chronic ethanol exposure alters the level of mRNA's coding for the alpha-subunit of the GABAA receptor. This decrease may reflect an alteration of mRNA processing in the cell or an alteration in GABAA receptor gene expression.

Neuropharmacological and clinical aspects of alcohol withdrawal

Abnormalities in the function or activity of several neurotransmitter systems have been demonstrated after acute and chronic, exposure to alcohol, and in alcohol withdrawal. The changes can be divided into alterations in function of inhibitory and excitatory systems. Inhibitory dysfunction is indicated by reduced gamma-aminobutyric acid and alpha-2-adrenoceptor activity. In conjunction with, and exacerbating this, is increased activity of excitatory systems, perhaps the most significant of which is the probable potentiation of N-methyl-D-aspartate activity by depletion of magnesium. There is additional, and possibly secondary, overactivity of catecholamine and corticotropin releasing factor neuronal systems. Other, less specific changes include increased numbers of calcium channels, which would increase neuronal excitability. The evidence for these changes is presented, and the implications for new treatment regimes for alcohol withdrawal are discussed.

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.

Chronic ethanol treatment alters the behavioral effects of Ro 15-4513, a partially negative ligand for benzodiazepine binding sites

Pentylenetetrazol (PTZ)-induced convulsion were studied in control, chronic ethanol-maintained, and ethanol-withdrawal rats. The convulsive doses of PTZ varied among the different groups of rats. Ethanol-maintained rats required higher doses of PTZ to produce convulsions, compared to control and ethanol-withdrawal rats. The partially negative ligands for benzodiazepine binding sites, Ro 15-4513 (2 mg/kg, i.p.) and FG 7142 (20 mg/kg, i.p.) produced proconvulsant effect in saline (control) and ethanol-withdrawal rats as they potentiated the effect of subconvulsive dose of PTZ. A higher dose of Ro 15-4513 (4 mg/kg, i.p.), but not FG 7142 (up to 80 mg/kg, i.p.), also produced proconvulsant effect in ethanol-maintained rats. Furthermore, Ro 15-4513 (5, 10 mg/kg, i.p.), but not FG 7142 (up to 80 mg/kg, i.p.), produced clonic-tonic seizures of short duration in ethanol-withdrawal rats. These effects of Ro 15-4513 and FG 7142 were reversed by diazepam (2 mg/kg, i.p.), as well as by the GABA-neutral Ro 15-1788 (10 mg/kg, i.p.), thereby, indicating the involvement of central benzodiazepine receptors in the action of Ro 15-4513 and FG 7142. These observations suggest that chronic ethanol treatment selectively alters the receptor sensitivity to Ro 15-4513, an ethanol antagonist and partially negative ligand for BZ sites, and this observation supports the notion that ethanol effects are more susceptible to reversal by the imidazobenzodiazepine as compared to other negative ligand for BZ binding sites.

Ethanol and the benzodiazepine-GABA receptor-ionophore complex

Ethanol has a pharmacological profile similar to that of classes of drugs like benzodiazepines and barbiturates, which enhance GABAergic transmission in the mammalian CNS. Several lines of behavioral, electrophysiological and biochemical studies suggest that ethanol may bring about most of its effects by enhancing GABAergic transmission. Recently, ethanol at relevant pharmacological concentrations has been shown to enhance GABA-induced 36Cl-fluxes in cultured spinal cord neurons, synaptoneurosomes and microsacs. These enhancing effects of ethanol were blocked by GABA antagonists. Ro15-4513, an azido analogue of classical BZ antagonist Ro15-1788, reversed most of the behavioral effects of ethanol and other effects involving 36Cl-flux studies. The studies summarized below indicate that most of the pharmacological effects of ethanol can be related to its effects on GABAergic transmission.

Benzodiazepines in the treatment of alcoholism

This chapter comprises three sections that cover the main aspects of benzodiazepines and alcohol: (1) the basic pharmacology of benzodiazepines; (2) use of benzodiazepines in the treatment of withdrawal; and (3) the use of benzodiazepines in treating alcoholics. The basic studies suggest that a major site of action of alcohol may be the GABA/benzodiazepine receptor complex and that compensatory alterations in this complex may underly withdrawal. In the section on alcohol withdrawal, interactions between the GABA/benzodiazepine receptor complex, sympathetic nervous system, and hypothalamic-pituitary-adrenal axis are discussed. Use of benzodiazepines in the treatment of the alcohol withdrawal syndrome are reviewed, including the possibility that the benzodiazepines may prevent withdrawal-induced "kindling." Lastly, we review indications for, and efficacy of, benzodiazepines in long-term treatment of patients with alcoholism. Benzodiazepines are not indicated for the treatment of alcoholism. Furthermore, they have very few indications in alcoholics and their dependency-producing potency has to be appreciated when they are used in patients with alcoholism.