Intoxicating effects of lorazepam and barbital in rat lines selected for differential sensitivity to ethanol

Effects of dopamine antagonists on methamphetamine-induced dopamine release in high and low alcohol preference rats

The authors have previously shown that high alcohol preference rats (HAP) have a significantly higher sensitivity than low alcohol preference rats (LAP) for methamphetamine (MAP). In this study, changes in dopamine and serotonin release induced by MAP (1 mg/kg, intraperitoneally) after pre-treatment with D1 and D2 receptor antagonists were examined in the striatum of rats with different alcohol preferences to elucidate differences in receptor levels between the two rat strains. D1 receptor antagonist SCH23390 or D2 receptor antagonist haloperidol were administrated intracerebroventricularly 10 min before MAP stimulation. This study investigated the effect of methamphetamine-induced dopamine and serotonin release in striatum using microdialysis of freely moving rats coupled to ECD-HPLC. With haloperidol treatment both strains of rats showed a significantly greater maximum increase on MAP-induced dopamine release compared with respective control rats. However, after SCH23390 treatment only HAP rats showed a significantly greater increase in dopamine release compared with controls. SCH23390 blocks mainly D1 receptors only in the post-synaptic membrane, whereas haloperidol blocks D2 receptors in both the pre-synaptic and post-synaptic membranes. The MAP-induced increase in dopamine release following haloperidol pre-treatment was greater than SCH23390 pre-treatment in both strains. This result indicates that D2 receptors (autoreceptors) in the pre-synaptic membrane were blocked, leading to the elimination of the feedback function that regulates dopamine release. These data suggested that alcohol preference is associated with the action of MAP, and the dopaminergic mechanism, specifically the D1 system in the striatum, might have a different pathway dependent on alcohol preference.

Effects of ethanol on the accumbal output of dopamine, GABA and glutamate in alcohol-tolerant and alcohol-nontolerant rats

Effects of ethanol on the accumbal extracellular concentrations of dopamine, as well as of the amino acid transmitters gamma-amino butyric acid (GABA), glutamate and taurine, were studied in the alcohol-insensitive (alcohol-tolerant, AT) and alcohol-sensitive (alcohol-nontolerant, ANT) rats selected for low and high sensitivity to ethanol-induced motor impairment. Ethanol (2 or 3 g/kg ip) enhanced the output of dopamine and its metabolites in freely moving rats of both lines as measured by in vivo microdialysis. The effect of ethanol on the metabolites of dopamine tended to be stronger in the ANT rats. The smaller dose of ethanol decreased the output of GABA only in the AT rats, whereas the larger dose of ethanol decreased the output of GABA in rats of both lines to a similar degree. Ethanol at the dose of 2 g/kg slightly, but statistically, significantly decreased the output of glutamate in rats of both lines, but the larger dose of ethanol decreased the output of glutamate only in the AT rats. Ethanol at the dose of 2 g/kg induced a small transient increase in the output of taurine within 2 h after its administration in rats of both lines, but the larger dose of ethanol was without significant effect. These results confirm the previous findings that ethanol suppresses the release of GABA more in the AT than ANT rats. Thus, among the neurotransmitter systems we studied, the effects of ethanol might be the most relevant on GABAergic transmission regarding the sensitivity towards ethanol. However, our findings suggest that glutamate is also involved in this respect.

Low brain histamine content affects ethanol-induced motor impairment

The effect of ethanol on motor performance in humans is well established but how neural mechanisms are affected by ethanol action remains largely unknown. To investigate whether the brain histaminergic system is important in it, we used a genetic model consisting of rat lines selectively outbred for differential ethanol sensitivity. Ethanol-sensitive rats had lower levels of brain histamine and lower densities of histamine-immunoreactive fibers than ethanol-insensitive rats, although both rat lines showed no changes in histamine synthesizing neurons. Lowering the high brain histamine content of the ethanol-insensitive rats with alpha-fluoromethylhistidine before ethanol administration increased their ethanol sensitivity in a behavioral motor function test. Higher H3 receptor ligand binding and histamine-induced G-protein activation was detected in several brain regions of ethanol-naive ethanol-sensitive rats. Brain histamine levels and possibly signaling via H3 receptors may thus correlate with genetic differences in ethanol-induced motor impairment.

Halothane and desflurane requirements in alcohol-tolerant and -nontolerant rats

On the basis of data implicating GABAA receptors in the effects of volatile general anaesthetics, we hypothesized that alcohol-, barbiturate-, and benzodiazepine-sensitive alcohol-nontolerant (ANT) rats would also be more sensitive than alcohol-tolerant (AT) rats to two clinical general anaesthetics with differing potencies, halothane and desflurane. The obtunding effect of halothane and desflurane on mature ANT (n = 17) and AT (n = 16) rats was assessed by the loss-of-righting reflex endpoint. ANT rats were significantly (P < 0.0001) more sensitive to the obtunding effects of both halothane and desflurane (ED50 = 0.45 +/- 0.03% atm for ANT vs 0.95 +/- 0.04% atm for AT and 2.16 +/- 0.17 vs 3.69 +/- 0.13% atm, respectively). The immobilization effect of halothane and desflurane was assessed with the tail clamp/withdrawal endpoint. ANT rats were more sensitive to the effects of halothane (ED50 = 1.10 +/- 0.08% atm for ANT vs 1.72 +/- 0.09% atm for AT; P < 0.0001) but not desflurane (ED50 = 6.25 +/- 0.25% atm for ANT vs 5.85 +/- 0.21% atm for AT). The data presented support the hypothesis that volatile anaesthetics interact with specific neuronal proteins (possibly GABAA receptors) and agree with recent hypotheses that different elements of the anaesthetic state are produced by separate sites or mechanisms.

New insights into the mechanism of action of hypnotics

Between 1987 and 1989, the different protein subunits that make up the receptor for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) were identified. These make up the alpha, beta, gamma and delta families, for each of which exist several subtypes. This receptor is the molecular target of modern hypnotic drugs (i.e. benzodiazepines, zopiclone, zolpidem and zaleplon). In the 10 years that have followed this milestone, significant progress has been made in exploring the molecular mechanisms of hypnotic drug action. Receptor subtype specificity of hypnotics has been explained in terms of differential affinity for receptors containing different alpha subunits, which are expressed in different brain regions. Zolpidem and zaleplon bind preferentially to alpha1-containing receptors, whereas benzodiazepines and zopiclone are aspecific. Different sets of subunits are encoded in contiguous 'cassettes' on the genome, and the transcription of each set appears to be regulated coherently. The predominant GABA(A) receptor composition found in the brain is alpha1beta2gamma2, which are all encoded on human chromosome 5. Targeted gene disruption has provided clues to the physiological functions served by GABA(A) receptors containing different subunits. Receptors containing gamma2 appear to have a vital role in maintaining appropriate central inhibition, beta3-containing receptors may also be important determinants of excitability in certain brain regions, whereas a clear role for alpha5-, alpha6- and gamma3-containing receptors has not yet been established by these techniques. Site-directed mutagenesis has indicated that benzodiazepines bind to a cleft on the GABA(A) receptor surface at the interface between the alpha and gamma subunits. Other drugs (flumazenil, zopiclone, zolpidem) also bind to the a subunit, but interact with amino acids in different binding domains to the benzodiazepines. The molecular mechanism of hypnotic dependence has been explored, and seems to involve downregulation of transcription of the normally prevalent alpha1, beta2 and gamma2 subunits, and the reciprocal upregulation of the expression of rarer subunits. Chronic treatment with hypnotic drugs that may have less dependence potential, such as zopiclone and zolpidem, appears to produce more limited change in GABA(A) receptor subunit expression. These ideas will be important both for designing new hypnotic drugs with a better safety/efficacy profile, and for evaluating more appropriate ways of using the drugs available today.

Characterization of chloride efflux from GT1-7 neurons: lack of effect of ethanol on GABAA response

The purpose of this study of GT1-7 neurons was to partially characterize basal Cl- transport and GABAA mediated Cl- efflux and to test the effect of ethanol on a GABAA receptor that lacks a gamma subunit. We measured GABAA function and Cl- transport with 36Cl-. Our results show that basal 36Cl- efflux varied with temperature at 4 degrees C, 23 degrees C, and 37 degrees C. At 23 degrees C, DIDS, an inhibitor of anion exchange, reduced basal 36Cl- efflux maximally by 79.6% with an IC50 of 42.1 microM, whereas bumetanide, an inhibitor of (Na-K-Cl) cotransport, had no effect on basal 36Cl- efflux at concentrations up to 150 microM. At 4 degrees C, muscimol, a GABAA receptor agonist, stimulated 36Cl- efflux with an EC50 of 1.47 microM. Bicuculline, a GABAA receptor antagonist, completely reversed the effect of 20 microM muscimol with an IC50 of 6.08 microM. Ethanol, at concentrations up to 87 mM (0.4% (w/v)), had no effect on muscimol-induced 36Cl- efflux at 4 degrees C or at 32 degrees C. Our results indicate that stimulation of GABAA receptors causes an efflux of Cl- from GT1-7 neurons. This finding is consistent with the concept that stimulation of GABAA receptors produces depolarization of the plasma membrane, increase in cytosolic [Ca2+], and GnRH release. Our results represent the first description of chloride transport in GT1-7 neurons and suggest the presence of a Cl- exchange, but not (Na-K-Cl), transporter mechanism. Furthermore, the lack of an effect of ethanol observed in this study is consistent with the idea that a gamma 2L subunit may be necessary for the effects of low concentrations of ethanol at GABAA receptors.

Anaesthetic concentrations of alcohols potentiate GABAA receptor-mediated currents: lack of subunit specificity

Anaesthetic concentrations of ethanol (50-400 mM) and butanol (1-20 mM) were tested for their effects on GABAA receptor-mediated chloride currents in Xenopus oocytes expressing human GABAA receptor cDNAs. Significant potentiation of the currents was seen in all receptor constructs tested. Substituting the alpha 5 subunit for the alpha 1, or the beta 2 for the beta 1, did not affect the degree of ethanol potentiation. The effects of 200 mM ethanol and 20 mM butanol were also tested using a variety of GABA concentrations (0.3-1000 microM) on oocytes expressing alpha 1 beta 1 vs. alpha 1 beta 1 gamma 2S or alpha 1 beta 2 vs. alpha 1 beta 2 gamma 2S receptor constructs. The presence of the gamma 2S subunit generally did not appear to affect the degree of potentiation, except that butanol potentiation was greater in alpha 1 beta 1 than in alpha 1 beta 1 gamma 2S receptors. This phenomenon of anaesthetic concentrations of alcohols potentiating GABAA receptor responses appears to be distinct from the low (20 mM) ethanol potentiation previously reported in the literature.

Eye movement effects of diazepam in sons of alcoholic fathers and male control subjects

Both animal and human studies suggest that the GABA-benzodiazepine receptor complex may be involved in the acute effects of ethanol, as well as the development of tolerance and dependence with chronic ethanol use. The current study was performed to assess sensitivity to benzodiazepines, and thus the functional sensitivity of the GABA-benzodiazepine receptor system, in subjects at high risk for alcoholism. Sons of alcoholic fathers (SOAs; n = 27) were compared with male controls without a family history of alcoholism (n = 23) in response to diazepam versus placebo. SOAs and controls received four logarithmically increasing doses of intravenous diazepam or placebo in randomized order on 2 days at least 1 week apart. Effects of diazepam were assessed using two eye movement tasks, peak saccadic eye movement velocity, and average smooth pursuit eye movement gain, which provide reliable, quantitative measures of benzodiazepine effects. In addition, memory, self-rated sedation, and pleasurable drug effects were measured. In comparison with control subjects, SOAs displayed significantly less diazepam effects on peak saccade velocity, average smooth pursuit gain, memory, and self-rated sedation, but significantly greater pleasurable drug effects. Differences in response to diazepam between SOAs and male controls may reflect altered functional sensitivity of the central GABA-benzodiazepine receptor system or a more general difference between groups in the effects of CNS active or sedating drugs.

Functional properties of GABAA receptors in two rat lines selected for high and low alcohol sensitivity

The effects of lorazepam and sodium barbital on GABAA receptor function were evaluated in rat lines selected for differential sensitivity to the motor-impairing effects of ethanol [alcohol-insensitive (AT) and alcohol-sensitive (ANT) lines]. The effect of GABA on [3H]flunitrazepam and [3H]Ro 15-4513 binding and the effects of lorazepam and sodium barbital on [3H]muscimol binding were measured in cerebellar, cerebrocortical, and hippocampal membrane preparations. The effects of lorazepam and sodium barbital on muscimol-stimulated 36Cl- influx were measured using membrane vesicle suspensions from the same brain areas. No differences were found between the rat lines in the GABA-induced stimulation of [3H]flunitrazepam binding or in the lorazepam and sodium barbital-induced enhancement of either [3]muscimol binding or muscimol-stimulated 36Cl- flux. Neither was desensitization of the 36Cl- flux affected differently by ethanol, lorazepam, and barbital in vitro between the lines. The affinity of cerebellar diazepam-insensitive (DZ-IS) [3H]Ro 15-4513-binding sites for benzodiazepine agonists has been shown to be much greater in the ANT than the AT rats. In the present study, at 0 degrees C, GABA decreased [3H]Ro 15-4513 binding in the presence of diazepam only in ANT rats. Similarly, GABA decreased this binding at 37 degrees C in ANT rats having a high affinity for diazepam, whereas it enhanced the binding in all AT samples in those ANT samples where diazepam had a poor AT-like affinity. The decrease in binding in ANT samples is apparently caused by the enhancing effect of GABA on diazepam binding to DZ-IS [3H]Ro 15-4513-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of aging and lifelong ethanol ingestion on ethanol-related behaviors and longevity

The interactions of aging and long-term voluntary ethanol consumption were studied in the alcohol-preferring AA (Alko Alcohol) rats. The mean daily ethanol intake was 6.45 +/- 0.31 g/kg/day (mean +/- SE) at the beginning of the exposure at 3 months of age. The control animals were given only food and water ad libitum. There was no difference in survival or weight gain between the control and ethanol groups. When tested for voluntary ethanol intake at the age of 24 months, the rats in the ethanol group consumed significantly more ethanol than the controls. The two groups did not differ in ethanol-induced motor impairment, sleep-time, or hypothermia, nor in the rate of ethanol elimination. The 24-month-old animals, however, showed higher sensitivity to ethanol than the 3-4-month-old rats in the sleep-time test. It is concluded that the feeding regimen used in this study did not produce any detectable interactions between ethanol and the aging processes in the AA rats.

Specific alterations in the cerebellar GABA(A) receptors of an alcohol-sensitive ANT rat line

The AT (alcohol-tolerant) and ANT (alcohol-nontolerant) rat lines, selected for differential sensitivity to the acute motor-impairing effects of ethanol, have been shown to differ in the ligand binding characteristics of their cerebellar GABAA receptors. In the present study, we characterized these binding differences further and determined whether similar differences are present in other rodent line pairs produced by selective breeding for differences in ethanol sensitivity. The alcohol-insensitive AT rats had more high-affinity [3H]muscimol binding sites in the cerebellum than the alcohol-sensitive ANT rats. The cerebellar "diazepam-insensitive" [3H]Ro 15-4513 binding sites were displaced by several benzodiazepine agonists (diazepam, lorazepam, clonazepam, and midazolam) at micromolar concentrations with greater efficacy in the ANT than the AT rats. Analyses of the displacement curves indicated that the "diazepam-insensitive" [3H]Ro 15-4513 binding sites have 30 to 300 times higher affinity to benzodiazepine agonists in the ANT than AT rats. There was no difference between the rat lines in the displacing potency of Ro 15-1788, a weak partial agonist; Ro 15-4513, a partial inverse agonist; or Ro 5-4864, a peripheral-type benzodiazepine receptor ligand. Thus, the affinity difference seen in the cerebellar [3H]Ro 15-4513 binding sites seems to be specific for benzodiazepine agonists. This difference in affinity may explain the behavioral difference in sensitivity to lorazepam between the rat lines. No differences in [3H]muscimol binding or in the sensitivity of [3H]Ro 15-4513 binding to micromolar diazepam concentrations were found between other rodent line pairs tested (LS/SS, HAS/LAS, HOT/COLD, FAST/SLOW, AA/ANA).(ABSTRACT TRUNCATED AT 250 WORDS)

Diazepam sensitivity of the binding of an imidazobenzodiazepine, [3H]Ro 15-4513, in cerebellar membranes from two rat lines developed for high and low alcohol sensitivity

Ro 15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a] [1,4]benzodiazepine-3-carboxylate), a partial inverse agonist of brain benzodiazepine receptors, has been shown to antagonize some actions of ethanol. In addition to conventional benzodiazepine binding sites, Ro 15-4513 binds to a specific cerebellar protein, the binding of which has been shown to be insensitive to diazepam. The binding of [3H]Ro 15-4513 was studied in washed membranes of the cerebellum, hippocampus, and cerebral cortex of two rat lines developed for differences in their sensitivity to ethanol-induced motor impairment. Only minor differences were found in the estimated parameters (KD and Bmax) for the total specific binding between the rat lines. The main difference between the rat lines was, however, observed in the characteristics of the cerebellar binding, all of which was displaced by diazepam in most of the alcohol-sensitive [alcohol-nontolerant (ANT)] rats, in contrast to only approximately 75% displacement in most of the alcohol-insensitive [alcohol-tolerant (AT)] ones. The following cerebellar results were obtained with the major subgroups of both lines, i.e., with the AT rats chosen for the presence of the diazepam-insensitive binding and with the ANT rats chosen for its absence. The KD for the total specific [3H]Ro 15-4513 binding in the ANT animals was about half of that in the AT animals. No line difference was found in the Bmax of the binding in these rats. Photolabeling with [3H]Ro 15-4513 showed that the diazepam-insensitive binding was in a protein with a molecular weight of 55,000.(ABSTRACT TRUNCATED AT 250 WORDS)

Plus-maze behavior and susceptibility to 3-mercaptopropionate-induced seizures in rat lines selected for high and low alcohol sensitivity

Selective outbreeding for high and low acute alcohol sensitivity has produced two rat lines (alcohol-sensitive ANT and alcohol-insensitive AT lines) that also differ in their sensitivity to GABAergic drugs, benzodiazepines and barbiturates. These rats were now compared in two behavioral tests believed to involve central GABAergic mechanisms, in elevated plus-maze test and in 3-mercaptopropionate-induced seizure test. The AT animals spent more time in the open arms of the plus-maze than the ANT rats, suggesting that the AT's behave less anxiously. The ANT's were more susceptible to seizures induced by 3-mercaptopropionate (50 mg/kg, IP) than the AT's, suggesting the ANT's having greater sensitivity to a decrease in brain GABA concentration. At the time of the first seizure signs, there was a tendency, though a nonsignificant one, to greater decreases in brain GABA in the ANT's than AT's. These results suggest that there are differences in GABA-related behaviors between ethanol-naive rats of the lines produced by selective outbreeding for differences in alcohol sensitivity. In theory, these behavioral line differences might physiologically counteract alcohol effects in the ANT's and enhance them in the AT's. In elevated plus-maze test, however, an acute dose of ethanol (1 g/kg, IP) significantly changed the behavior of the ANT animals, but only up to level of the AT rats. The apparent sensitivity to ethanol may thus be dependent on the naive behavior of the alcohol-insensitive AT and alcohol-sensitive ANT rats.

The alcohol tolerant and alcohol nontolerant rat lines selected for differential sensitivity to ethanol: a tool to study mechanisms of the actions of ethanol

Genetic selection work conducted in the Research Laboratories of State Alcohol Company (Alko Ltd), Helsinki, Finland, has resulted in the establishment of the ethanol sensitive Alcohol Nontolerant (ANT) and ethanol insensitive Alcohol Tolerant (AT) rat lines which differ in their sensitivity to ethanol induced motor impairment. These lines have been used in attempts to identify the mechanisms controlling ethanol induced motor impairment. The Alcohol Tolerant rats show a lower sensitivity to ethanol induced motor impairment on a tilting plane over a wide range of doses, but the lines do not differ in all behavioral measures of ethanol sensitivity. Furthermore, the Alcohol Tolerant line shows a higher capacity to develop acute tolerance and less calm behaviour, which may contribute to the line difference. Neurochemical work has shown differences in the functioning and sensitivity to ethanol of the catecholaminergic and GABAergic systems in the two lines, suggesting a role for both of these systems in the control of ethanol induced motor impairment.

Role of initial sensitivity and genetic factors in the development of tolerance to ethanol in AT and ANT rats

The role of initial sensitivity and genetic factors in the development of tolerance to ethanol were examined in rats selected for low (AT) and high (ANT) sensitivity to the motor impairment effect of ethanol. Following chronic ethanol treatment (5 g/kg PO, daily for 20 days), the AT and ANT rats acquired tolerance to the motor impairment effect of ethanol at a similar rate. The AT rats, however, acquired tolerance to the hypothermic effect of ethanol at a higher rate than the ANT rats. Such ethanol treatment did not produce any metabolic tolerance to ethanol in these animals. Since there is no difference in the initial response to the hypothermic effect of ethanol between the AT and ANT rats, the observed differences in the rate of tolerance development might be related to a direct genetic factor. The similar rate of tolerance development to the motor impairment effect of ethanol between the two lines was attributed to an interaction between an indirect (initial sensitivity) and a genetic factor in tolerance development.

Genetics of responses to drugs of abuse

Genetic differences in drug metabolism, in the number of drug receptors in the brain, and in drug-seeking behavior may contribute to the variability of individual responses to drugs of abuse. Genetic models include inbred strains, mutants, sublines, and selectively bred mice and rats. They have been used to examine acute and chronic effects of narcotics, stimulants, and alcohol as well as drug-seeking behavior, withdrawal syndromes, and the stress-induced release of endogenous opioids. These genetic models should prove helpful in defining individual differences in susceptibility to addiction.

GABA turnover in the brain of rat lines developed for differential ethanol-induced motor impairment

The role of GABAergic neurons in the differential sensitivity to ethanol between the AT (Alcohol Tolerant) and ANT (Alcohol Nontolerant) rat lines developed for low and high degree of motor impairment from ethanol, was studied by comparing the effect of ethanol (2 or 4 g/kg, IP) on GABA turnover in different regions of the brain in these rat lines. GABA turnover was estimated from the accumulation of GABA after inhibition of GABA aminotransferase with aminooxyacetic acid (AOAA, 50 mg/kg, IP) given 10 min after administration of ethanol. The rats were killed two hours after the AOAA treatment with focused microwaves. The concentrations of GABA, aspartate, glutamate, glutamine and taurine were analyzed with HPLC. The saline-treated ANT rats were found to have a higher concentration of GABA in the striatum and a higher rate of GABA accumulation in the cerebellum than the AT rats. Ethanol suppressed the accumulation of GABA in both lines, but the suppression was significantly greater in the AT rats than in the ANT rats. In specific regions, this line difference was significant in the cerebral cortex and cerebellum with the higher ethanol dose. No line differences were found in the brain or tail blood ethanol concentration. AOAA increased the concentration of glutamine, decreased that of aspartate and glutamate, and did not modify that of taurine. The AOAA-induced changes in the concentrations of these amino acids were, however, minor relative to those found in the concentrations of GABA. The results that GABAergic mechanisms are involved in the differential sensitivity to the motor-impairing effects of ethanol between the AT and ANT rats.

Effect of GABAergic drugs on motor impairment from ethanol, barbital and lorazepam in rat lines selected for differential sensitivity to ethanol

The effect of GABAergic drugs on the motor-impairing effects of ethanol, barbital, and lorazepam were studied in the ethanol-sensitive ANT (Alcohol Nontolerant) and ethanol-insensitive AT (Alcohol Tolerant) rat lines, selected for differential ethanol-induced motor impairment on the tilting plane. The basic population from which these rat lines were derived, the mixed (M) line, was also included in the study. The ANT rats were more sensitive to the intoxicating effects of ethanol, barbital, and lorazepam than the AT and M rats at the dose ranges tested. Picrotoxin antagonized motor impairment from all three drugs. Flumazenil (Ro 15-1788) antagonized only the effects of lorazepam, and isoniazid did not modify motor impairment induced by any of the three drugs. These results confirm that the selection of AT and ANT lines has not been specific to ethanol, and that it has increased sensitivity to ethanol, barbital, and lorazepam in the ANT rats rather than decreasing it in the AT rats relative to the M rats. The finding that picrotoxin counteracted motor impairment from ethanol, barbital, and lorazepam support the view that the GABAA receptor complex is important in mediating the intoxicating effects of these drugs. These results also suggest that the genetically-determined difference in sensitivity to ethanol between the rat lines involves GABAergic mechanisms, but it remains to be determined whether any part of the GABAA receptor itself has been affected by the selection program.

Cerebellar GABAA receptor binding and function in vitro in two rat lines developed for high and low alcohol sensitivity

The Bmax of the [3H]muscimol binding in the cerebellum of ethanol-naive alcohol-sensitive ANT (Alcohol Non-Tolerant) rats was only about 70% of that in the alcohol-insensitive AT (Alcohol Tolerant) rats. There were no line differences in the muscimol binding to cerebrocortical and hippocampal membranes. In the alcohol-sensitive rats, the cerebellar [3H]muscimol binding (5 nM) negatively correlated with the ethanol-induced motor-impairment measured in the tilting plane test. Muscimol stimulated the flux of 36Cl- in cerebellar synaptoneurosomes and non-filtered microsacs to the same extent in both rat lines. Ethanol produced only a small, although statistically significant, enhancement of the muscimol-stimulated chloride flux in both rat lines. The present data confirms our earlier finding of a low level of muscimol binding in the cerebellar membranes of alcohol-sensitive rats as compared to alcohol-insensitive rats. Further studies are needed to determine the relationship between the Cl- flux stimulation by muscimol and the differential muscimol binding in the cerebellum of these rat lines, and its importance for alcohol sensitivity.

Sensitivity to ethanol hypnosis and modulation of chloride channels does not cosegregate with pentobarbital sensitivity in HS mice

Several findings suggest that barbiturates and alcohol produce their sedative effects through a common neural and possibly a common genetic mechanism. We tested this hypothesis by examining the correlation between ethanol and pentobarbital sedative effects in individual animals from a genetically heterogeneous population. The duration of pentobarbital-induced hypnosis (sleep-time) was unrelated to the sleep-time produced by ethanol in heterogeneous stock (HS) mice. Therefore, the present study also examined the effect of ethanol, pentobarbital, and flunitrazepam on muscimol-stimulated chloride flux into brain membranes prepared from HS mice selected for differences in pentobarbital- and ethanol-induced sleep-time. Brain membranes from mice selected for differences in ethanol sleep-time were differentially responsive to ethanol- and flunitrazepam-, but not to pentobarbital-induced augmentation of muscimol-stimulated chloride flux. No differences in augmentation of chloride flux by ethanol, pentobarbital, or flunitrazepam were found in membranes prepared from mice differentially sensitive to pentobarbital hypnosis. The ability of muscimol to stimulate chloride uptake was not related to ethanol or pentobarbital sensitivity. These findings suggest that sensitivity to ethanol is not likely to be genetically linked to pentobarbital sensitivity.

Patterns of convulsive susceptibility in the long-sleep and short-sleep selected mouse lines

It has been hypothesized that the Long-Sleep and Short-Sleep mouse lines were bidirectionally selected for high and low brain excitability, and further, that these differences are mediated by the benzodiazepine/gamma-aminobutyric acid (GABA) receptor-chloride channel complex. Hence, mice from both lines were administered seven convulsants (bicuculline, pentylenetetrazol, 3-carbomethoxy-beta-carboline, picrotoxin, caffeine, flurothyl and strychnine) and myoclonic and clonic seizure latencies recorded. Supporting the original hypothesis, the results show that the two lines were differentiated by all of the convulsants and that in response to the drugs, three distinct convulsive patterns were found. Nevertheless, a simple genetic model accounting for these results was not evident. To further clarify these susceptibility patterns, a convulsant representing each of these patterns (bicuculline, pentylenetetrazol or caffeine) was administered in conjunction with the anticonvulsant-barbiturate phenobarbital or the benzodiazepine antagonist Ro 15-1788. Irrespective of the convulsant given, phenobarbital attenuated both myoclonus and clonus subsequent to all convulsants, while Ro 15-1788 had a more discrete anticonvulsant profile.

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.

GABAA receptor-mediated chloride flux in brain homogenates from rat lines with differing innate alcohol sensitivities

Muscimol stimulation of 36Cl- flux through GABAA receptor-associated ion channels was compared in combined cerebral cortical and cerebellar homogenates from two lines of rats produced by selective outbreeding for high and low alcohol sensitivities. There was no difference in the muscimol effects between ethanol-naive alcohol-sensitive and alcohol-insensitive rats. Acute administration of ethanol (2 g/kg, i.p.) and lorazepam (3 mg/kg, i.p.) significantly reduced the percentage stimulation by muscimol in the alcohol-sensitive animals. The results suggest that genetic selection towards differences in the sensitivity to motor-impairing effects of moderate ethanol doses does not produce alterations in the direct agonist-induced GABAA receptor function. This receptor function was, however, down-regulated in the alcohol-sensitive rats by acute ethanol and benzodiazepine treatments, indicating the involvement of GABAergic activity in the mechanisms of, or in the neural adaptations to, acute intoxication in genetically sensitive animals.

Hippocampal rhythmic slow activity in rat lines selected for differences in ethanol-induced motor impairment

Hippocampal rhythmic slow activity (RSA) was recorded during rotation and vibration stimulation after saline and ethanol (2 g/kg) administration in restrained alcohol-sensitive (ANT) and alcohol-insensitive (AT) rats implanted with chronic bipolar electrodes in the dorsal hippocampus. The saline-treated ANT rats had more high-frequency RSA than the AT rats, especially during the rotational stimulation of the optovestibular mechanisms. The difference was not found during ethanol sessions. Plasma corticosterone levels were significantly higher in the AT than the ANT rats after the recording sessions. This first electrophysiological demonstration of an alcohol-sensitivity difference in the brain between these rat lines is discussed in relation to behavioral tilting plane test used in the development of the lines, to the different innate responses of the lines to acute stress, and to the plausible line differences in brain GABAergic and serotonergic mechanisms that are known to modulate hippocampal EEG in rodents.

GABA/benzodiazepine receptor/chloride ionophore complex in brains of rat lines selectively bred for differences in ethanol-induced motor impairment

In vitro ligand binding studies were used to compare GABA/benzodiazepine receptor/chloride ionophore complexes in various brain regions of ethanol-sensitive ANT and ethanol-insensitive AT rats. In naive rats, there were several, but fairly small line differences in the binding parameters of [3H]muscimol and [3H]flunitrazepam to cerebral cortical, cerebellar or hippocampal membranes washed with or without a detergent. GABA-stimulation of flunitrazepam binding in the cerebral cortex membranes was slightly greater in the AT than ANT rats. In detergent solubilized receptors, the GABA-stimulation of flunitrazepam binding emerged only in the presence of ethanol in most AT samples, whereas the GABA-stimulation was always observed in ANT samples and ethanol had no further effect. Pharmacological characteristics of [3H]t-butylbicycloorthobenzoate binding displaceable by picrotoxin were similar in both lines. Chronic ethanol administration tended to increase the number of these binding sites in the cerebral cortex of AT rats and to decrease them in the ANT rats. Although many differences between the lines were observed, our results indicate that the ethanol-sensitivity difference between the AT and ANT rat lines cannot be explained by enhanced function of the GABA/benzodiazepine receptor/chloride ionophore complex as far as this is revealed by in vitro binding studies. It remains to be studied whether these lines differ in presynaptic GABAergic mechanisms or in the actual function of the postsynaptic chloride channels before the role of GABA can be more accurately assessed in this genetic model for ethanol-induced motor impairment.

Failure of Ro 15-4513 to antagonize ethanol in rat lines selected for differential sensitivity to ethanol and in Wistar rats

An imidazobenzodiazepine, Ro 15-4513, acting as a partial inverse agonist at the central benzodiazepine receptors has been recently reported to reverse efficiently the intoxicating effects of ethanol. In studies designed to delineate the role of benzodiazepine receptors in the ethanol-induced motor impairment difference between two rat lines selectively bred for high and low sensitivity to ethanol, however, we could not antagonize the effects of ethanol by Ro 15-4513 in the tilting plane and horizontal wire tests. Neither could we observe any consistent antagonism of ethanol actions in Han:Wistar rats, although we used a wide range of Ro 15-4513 doses, injected the drug intraperitoneally or intragastrically and before or after ethanol administration, and carried out the tests for motor impairment (rotarod, horizontal wire test and intoxication rating) at various times after the drug administration. The ex vivo assay of flunitrazepam binding in brain homogenates revealed the presence of compound(s) inhibiting the binding after administration of Ro 15-4513. Ro 15-4513 antagonized the motor impairing effects of lorazepam. In conclusion, Ro 15-4513 failed to function as a specific antagonist of moderate doses of ethanol in several tests for motor impairment in different rat lines.

Effects of ethanol, barbital, and lorazepam on brain monoamines in rat lines selectively outbred for differential sensitivity to ethanol

The acute effects of ethanol, barbital, and lorazepam on the synthesis and metabolism of brain monoamines were studied in the AT (Alcohol Tolerant) and ANT (Alcohol Nontolerant) lines of rats, which have been selected for differential motor impairment after ethanol administration. The ethanol-sensitive ANT rats are also more sensitive than the ethanol-insensitive AT rats to the motor impairment caused by barbital and lorazepam. Ethanol increased, whereas barbital and lorazepam decreased, the synthesis of catecholamines in several regions of the brain. Ethanol did not affect the formation of DOPAC, whereas barbital and lorazepam reduced it. Similarly, the accumulation of 5-HTP was increased after administration of ethanol, but was decreased after administration of barbital or lorazepam. Ethanol, barbital and lorazepam decreased the formation of 5-HIAA. The rat lines did not differ in any of these responses. Some differences could, however, be demonstrated between the AT and ANT rats in the effects of the three drugs on the levels of the brain monoamines. Although the importance of these differences in the differential sensitivity to these drugs between the two lines is difficult to determine, the role of central monoaminergic mechanisms cannot be excluded. These findings also suggest that the motor impairment induced by ethanol, barbiturates, and benzodiazepines is probably not primarily based on the monoaminergic systems.

Dopamine D2 receptor binding in striatal membranes of rat lines selected for differences in alcohol-related behaviours

The specific binding of 3H-spiperone to striatal membranes was compared within two pairs of rat lines produced by selective breeding for either differences in voluntary alcohol consumption or for differences in acute ethanol-induced motor impairment. Although a significant difference was found between the alcohol-preferring rats and alcohol-avoiding rat lines, the estimate for the Bmax value was only slightly lower in naive alcohol-preferring rats. The small magnitude of the difference suggests it is unimportant for the genetically-determined differences in alcohol preference. No significant differences were found in the estimates for their Kd values. There were no significant differences for either the Bmax and Kd values between the alcohol-sensitive and alcohol-insensitive rat lines, which suggests that striatal dopaminergic D2 receptors are not involved in the genetically-determined factors influencing sensitivity to alcohol (and also barbital and lorazepam).