skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Benzodiazepine agonist and inverse agonist actions on GABAA receptor-operated chloride channels. II. Chronic effects of ethanol

Abstract

Mice were made tolerant to and dependent on ethanol by administration of a liquid diet. Gamma-aminobutyric acid (GABA) receptor-dependent uptake of 36Cl- by mouse cortical microsacs was used to study the actions of benzodiazepine (BZ) agonists and inverse agonists. Chronic exposure to ethanol attenuated the ability of a BZ agonist, flunitrazepam, to augment muscimol-stimulated uptake of 36Cl- and enhanced the actions of BZ inverse agonists, Ro15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo(1,4)-benzodiazepine - 3-carboxylate) and DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate), to inhibit GABAA receptor-operated chloride channels. Augmentation of chloride flux by pentobarbital was not reduced by chronic ethanol exposure. Attenuation of flunitrazepam efficacy was transient and returned to control levels within 6 to 24 hr after withdrawal from ethanol, but increased sensitivity to Ro15-4513 was observed as long as 8 days after withdrawal. Chronic exposure to ethanol did not alter (3H)SR 95531 (2-(3'-carbethoxy-2'propyl)-3-amino-6-p-methoxyphenylpyridazinium bromide) binding to low-affinity GABAA receptors or muscimol stimulation of chloride flux; and did not alter (3H)Ro15-4513 or (3H)flunitrazepam binding to central BZ receptors or allosteric modulation of this binding by muscimol (i.e., muscimol-shift). These results suggest that chronic exposure to ethanol reduces coupling between BZ agonist sites and the chloride channel, and may be responsible for the development of cross-tolerance between ethanol and BZmore » agonists. In contrast, coupling between BZ inverse agonist sites and the chloride channel is increased.« less

Authors:
;  [1]
  1. (Univ. of Colorado Health Sciences Center, Denver (USA))
Publication Date:
OSTI Identifier:
6721290
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Pharmacology and Experimental Therapeutics; (USA); Journal Volume: 253:2
Country of Publication:
United States
Language:
English
Subject:
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.; 59 BASIC BIOLOGICAL SCIENCES; AMINOBUTYRIC ACID; RECEPTORS; CHLORIDES; MEMBRANE TRANSPORT; ETHANOL; BIOLOGICAL EFFECTS; SYMPATHOLYTICS; BIOCHEMICAL REACTION KINETICS; CHLORINE 36; CHRONIC EXPOSURE; MICE; TRACER TECHNIQUES; TRITIUM COMPOUNDS; ALCOHOLS; AMINO ACIDS; ANIMALS; AUTONOMIC NERVOUS SYSTEM AGENTS; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; CARBOXYLIC ACIDS; CHLORINE COMPOUNDS; CHLORINE ISOTOPES; DRUGS; ELECTRON CAPTURE RADIOISOTOPES; HALIDES; HALOGEN COMPOUNDS; HYDROGEN COMPOUNDS; HYDROXY COMPOUNDS; ISOTOPE APPLICATIONS; ISOTOPES; KINETICS; LIGHT NUCLEI; MAMMALS; MEMBRANE PROTEINS; NEUROREGULATORS; NUCLEI; ODD-ODD NUCLEI; ORGANIC ACIDS; ORGANIC COMPOUNDS; PROTEINS; RADIOISOTOPES; REACTION KINETICS; RODENTS; VERTEBRATES; YEARS LIVING RADIOISOTOPES 560300* -- Chemicals Metabolism & Toxicology; 550201 -- Biochemistry-- Tracer Techniques

Citation Formats

Buck, K.J., and Harris, R.A. Benzodiazepine agonist and inverse agonist actions on GABAA receptor-operated chloride channels. II. Chronic effects of ethanol. United States: N. p., 1990. Web.
Buck, K.J., & Harris, R.A. Benzodiazepine agonist and inverse agonist actions on GABAA receptor-operated chloride channels. II. Chronic effects of ethanol. United States.
Buck, K.J., and Harris, R.A. 1990. "Benzodiazepine agonist and inverse agonist actions on GABAA receptor-operated chloride channels. II. Chronic effects of ethanol". United States. doi:.
@article{osti_6721290,
title = {Benzodiazepine agonist and inverse agonist actions on GABAA receptor-operated chloride channels. II. Chronic effects of ethanol},
author = {Buck, K.J. and Harris, R.A.},
abstractNote = {Mice were made tolerant to and dependent on ethanol by administration of a liquid diet. Gamma-aminobutyric acid (GABA) receptor-dependent uptake of 36Cl- by mouse cortical microsacs was used to study the actions of benzodiazepine (BZ) agonists and inverse agonists. Chronic exposure to ethanol attenuated the ability of a BZ agonist, flunitrazepam, to augment muscimol-stimulated uptake of 36Cl- and enhanced the actions of BZ inverse agonists, Ro15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo(1,4)-benzodiazepine - 3-carboxylate) and DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate), to inhibit GABAA receptor-operated chloride channels. Augmentation of chloride flux by pentobarbital was not reduced by chronic ethanol exposure. Attenuation of flunitrazepam efficacy was transient and returned to control levels within 6 to 24 hr after withdrawal from ethanol, but increased sensitivity to Ro15-4513 was observed as long as 8 days after withdrawal. Chronic exposure to ethanol did not alter (3H)SR 95531 (2-(3'-carbethoxy-2'propyl)-3-amino-6-p-methoxyphenylpyridazinium bromide) binding to low-affinity GABAA receptors or muscimol stimulation of chloride flux; and did not alter (3H)Ro15-4513 or (3H)flunitrazepam binding to central BZ receptors or allosteric modulation of this binding by muscimol (i.e., muscimol-shift). These results suggest that chronic exposure to ethanol reduces coupling between BZ agonist sites and the chloride channel, and may be responsible for the development of cross-tolerance between ethanol and BZ agonists. In contrast, coupling between BZ inverse agonist sites and the chloride channel is increased.},
doi = {},
journal = {Journal of Pharmacology and Experimental Therapeutics; (USA)},
number = ,
volume = 253:2,
place = {United States},
year = 1990,
month = 5
}
  • Acute exposure to ethanol was found to enhance the ability of a benzodiazepine (BZ) inverse agonist, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), to reduce muscimol-activated 36Cl- uptake by membranes isolated from mouse cerebral cortex. Pretreatment in vivo with a hypnotic dose of ethanol (but not a subhypnotic dose), or exposure to a corresponding concentration in vitro, was effective. This increase in sensitivity of gamma-aminobutyric acid receptor-operated chloride channels to the actions of DMCM was due to an increase in both the potency and efficacy of DMCM. Sensitization to DMCM was reversible and was not observed 24 hr after a single injection of ethanol. Pretreatmentmore » with ethanol (10, 50 and 100 mM) in vitro produced sensitization to DMCM in a concentration-dependent manner, similar to that produced by in vivo exposure; this increase in sensitivity did not develop if the membranes were pretreated with ethanol at 0 degrees C. Similarly, in vitro exposure to pentobarbital (200 microM) or flunitrazepam (1 microM) enhanced the actions of the inverse agonist Ro15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo(1,5a)(1,4)BZ-3- carboxylate). Acute ethanol exposure did not alter low-affinity gamma-aminobutyric acidA receptor binding or muscimol action, or the ability of a BZ agonist, flunitrazepam, to augment muscimol-activated chloride flux. Ethanol exposure did not alter (3H)flumazenil (Ro15-1788) binding to central BZ receptors, its displacement by DMCM or allosteric modulation of DMCM binding by muscimol (muscimol-shift).« less
  • This study focuses on how ethanol exposure affects biochemical processes associated with the GABA[sub A] complex in the mammalian CNS, and examines the role of these changes in the development of alcohol tolerance and withdrawal. In vitro studies of control mice and those acutely or chronically exposed to alcohol were conducted. Radioligand binding using the low-affinity GABA[sub A] receptor-selective antagonist [[sup 3]H]SR95531 showed no changes in saturation binding analysis of receptor affinity or density. Muscimol-activated [sup 36]Cl[sup [minus]] flux in isolated brain membrane vesicles was not reduced by ethanol exposure. Radioligand binding, using the central BZ-selective agonist [[sup 3]H]flunitrazepam, antagonistmore » [[sup 3]H]flumazenil, and inverse agonist [[sup 3]H]Ro15-4513, was used to measure cortical receptors; saturation binding analysis revealed no affect of ethanol on BZ receptor density or affinity and no change in allosteric modulation of BZ receptor binding by muscimol. [sup 36]Cl[sup [minus]] flux studies, used to measure BZ agonist enhancement or inverse agonist inhibition of muscimol-activated channel activity, showed attenuation of the former and increase of the latter in ethanol exposure. These results support the hypothesis that ethanol exposure results in subsensitivity of the GABA[sub A] receptor complex to BZ agonists and increased sensitivity to BZ inverse agonists. Ethanol-induced changes in the GABAergic system were examined in mice genetically selected for being resistant (WSR) or prone (WSP) to the developemnt of seizures associated with ethanol withdrawal. Ethanol-induced sensitization to BZ inverse agonist inhibition of channel activity was greater in WSP than in WSR mice. This supports the hypothesis that hypersensitivity to BZ inverse agonists is functionally related to ethanol withdrawal severity.« less
  • Withdrawal seizure prone (WSP) and withdrawal seizure resistant (WSR) mice were treated with 5 mg/kg lorazepam for 7 days via implanted osmotic mini pumps. Following chronic drug treatment, brains were assayed for GABA-mediated chloride flux (GABA-Cl[sup [minus]]). Under control conditions, brain membranes prepared from WSP and WSR lines did not differ in flunitrazepam or ethanol stimulation of GABA-mediated [sup 36]Cl[sup [minus]]uptake, but the WSP lines were more sensitive to inhibition of [sup 36]Cl[sup [minus]] flux by the inverse agonist, FG-7142.. Withdrawal from chronic treatment, by an acute injection with the benzodiazepine antagonist RO15-1788, returned flunitrazepam stimulation of GABA-CL[sup [minus]] tomore » near control levels in WSR membranes but not in WSP membranes and restored ethanol modulation of the channel to control levels in both lines. Inhibition of chloride flux by the benzodiazepine partial inverse agonist, FG-1742 was greater in membranes from WSP mice compared with WSR mice. Tolerance to lorazepam increased sensitivity of the WSR membranes to FG-7142 without altering the response in the WSP line. Again, withdrawal restored the Cl[sup [minus]] flux response to FG-7142 back to near control levels. Lorazepam tolerance lowered [[sup 3]H]-flunitrazepam binding affinity slightly only in the WSR strain with no change in binding number.« less
  • The antagonistic effects of the benzodiazepine receptor inverse agonist ..beta..-CCM and of the partial inverse agonist RO 15-3505 on the anxiolytic properties of ethanol in mice confronted with a light/dark choice procedure and with the staircase test were investigated. Both drugs reversed the effects of ethanol on some of the behavioral parameters, but ..beta..-CCM alone elicited anxiogenic intrinsic effects. RO-3505 induced seizures in mice treated with a subconvulsant dose of pentylenetetrazole, the most efficient doses being 3 and 6 mg/kg. These data indicate that ..beta..-CCM and RO 15-3505 can reverse some of the anxiolytic effects of ethanol, acting probably tomore » oppose GABA function via the benzodiazepine receptor.« less
  • The intrinsic effects of the benzodiazepine receptor inverse agonists RO 15-4513 and FG 7142 on the behavior of mice in a holeboard were investigated. Both drugs caused dose-related decreases in exploratory head-dipping. The highest dose of FG 7142 (40 mg/kg) also reduced locomotor activity. RO 15-4513 (1.5 and 3.0 mg/kg) and FG 7142 (10 and 20 mg/kg) reversed the reductions in the number of head-dips caused by ethanol (2 g/kg). The higher doses of these two drugs also partially reversed the locomotor stimulant action of ethanol. Animals that received ethanol in combination with either inverse agonist spent less time head-dippingmore » than vehicle-treated controls. These data indicate that FG 7142 and RO 15-4513 can reverse, at least in part, some of the behavioral effects of ethanol. Neither drug significantly altered blood alcohol concentrations suggesting that the antagonism does not result from pharmacokinetic changes. 26 references, 5 figures, 2 tables.« less