Low Alcohol Sensitivity Research Articles

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

The effects of lorazepam and sodium barbital on GABA A 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°C, GABA decreased [ 3H]Ro 15-4513 binding in the presence of diazepam only in ANT rats. Similarly, GABA decreased this binding at 37°C in ANT rats having a high affinity for diazepam, whereas it enhanced the binding in all AT samples and 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. This enhanced interaction between GABA and a benzodiazepine agonist suggests that the altered DZ-IS binding sites might be involved in the augmented sensitivity of the ANT rats to sedative drugs.

Hormone responses to sedative drugs and cold exposure in two rat lines with high and low alcohol sensitivity

Two rat lines bred for differences in motor impairment in the tilting plane test after a moderate dose of ethanol were compared for peripheral hormone responses. The alcohol-sensitive ANT rats had significantly lower plasma corticosterone concentrations than the alcohol-insensitive AT rats 30 min after an IP saline injection. Ethanol (2 g/kg, IP) and lorazepam (3 mg/kg, IP) injections increased the corticosterone concentration in ANT rats. Sodium barbital (160 mg/kg, IP) did not produce any increase in these rats; instead, it prevented any increase caused by a tilting plane test procedure 10 min before decapitation. Three trials on the tilting plane significantly elevated the corticosterone concentration in saline-treated ANT rats, but produced no additional increase in drug-treated ANT rats. In AT rats, drug injections caused no significant corticosterone increase but the tilting plane test procedure after barbital (lorazepam) treatment(s) elevated the corticosterone concentration. Cold exposure (+4°C for 30 min) of the drug-naive animals elevated their concentrations of serum and adrenal corticosterone, thyrotropin, and growth hormone, but not of prolactin and luteinizing hormone. The increase in serum corticosterone was greater in AT than ANT rats, whereas the increase in serum thyrotropin was slightly greater in ANT rats. No differences between the rat lines were found in the growth hormone, prolactin, and luteinizing hormone levels. The results confirm and extend our earlier findings of the inability of ANT rats to produce additional stress responses to behavioral challenges when being intoxicated by sedative drugs, which may at least partly account for their increased sensitivity to sedative drugs.

Ethanol-produced interoceptive stimuli are time dependent in selectively bred HAS and LAS rats

Fourteenth generation high alcohol-sensitive (HAS) and low alcohol-sensitive (LAS) rats were trained to discriminate the effects of 600 mg/kg intraperitoneally administered ethanol from its vehicle at 6 and 30 min postadministration. Each of the earlier- and later-trained animals were given lower doses of ethanol and ED 50 values at their trained postadministration interval were found to be nonsignificantly different. Thus, there was no difference between HAS and LAS animals as to their sensitivity to the discriminative effects of ethanol. Phase-generalization studies, where rats trained at 6 min postadministration were tested with the drug at 30 min postadministration were shown not to generalize, whereas the animals trained at 30 min postadministration and tested at 6 min postinjection were shown to readily discriminate the discriminative stimuli. This asymmetrical generalization lends evidence to the biphasic action of ethanol, and suggests that the earlier phase is quantitatively different than the latter phase. The similarity in sensitivity of the LAS and HAS animals, furthermore, suggests that the discrimination of ethanol is not based on its hypnotic effects.

HAS and LAS rats respond differentially to behavioral effects of ethanol, pentobarbital, chlorpromazine and chlordiazepoxide

The drug discrimination paradigm (DD) was used to evaluate differences in performance of rats selectively bred for differential sensitivity to the hypnotic effects of ethanol. Tenth generation high-alcohol sensitive (HAS) and low-alcohol sensitive (LAS) rats were trained to discriminate between ethanol (1.0 g/kg, IP) and saline vehicle on a VR-5 schedule of reinforcement. The HAS strain was more sensitive to the discriminative effects of ethanol than the LAS strain, but the magnitude of difference was much smaller than the differential sleep-time differences. The biphasic action of ethanol was differentially seen when the LAS animals exhibited increased activity during both DD and spontaneous motor activity measures and the HAS exhibited decreases activity during DD only. Pentobarbital and chlordiazepoxide but not chlorpromazine elicited the ethanol discriminative choice in both HAS and LAS strains. Response rates during DD indicated a dissociation of rate depressant effects and discriminative performance following ethanol. These findings are discussed in relationship to some current and future uses of selectively bred animal strains and DD for studying the effects of alcohol.

Responses to Cholinergic Agonists of Rats Selectively Bred for Differential Sensitivity to Ethanol

Alcoholics are almost invariably heavy users of tobacco. Both alcoholism and smoking appear to be influenced by genetic factors but it is not known whether the same or different genes regulate the abuse of ethanol and nicotine. Recent studies have demonstrated that the long-sleep (LS) and short-sleep (SS) mouse lines, which were selectively bred for differences in ethanol-induced anesthesia ("sleep-time"), also differ in several effects of nicotine and the muscarinic agonist, oxotremorine. In order to determine whether or not these differences are due to chance, the relative sensitivities of rat lines which were selectively bred for differences in ethanol-induced sleep-time were determined. The high alcohol sensitivity (HAS) rat line was more sensitive to the locomotor and body temperature depressant effects of nicotine than was the low alcohol sensitivity (LAS) rat line. The control line (CAS) was intermediate in sensitivity. The rat lines did not differ in sensitivity to oxotremorine's hypothermia-producing effects. The numbers and affinities of two classes of brain nicotinic receptors were measured in eight brain regions. No differences among the rat lines were detected. These results suggest that ethanol elicits some of its depressant actions via an effect on brain nicotinic systems, but the differences in sensitivity to ethanol and nicotine are probably not due to differences in the number of brain nicotinic receptors. Perhaps this interaction explains the high correlation between alcoholism and smoking in humans.

Ethanol interoceptive cue and sleep-time duration in HAS and LAS selectively bred rats

The drug discrimination paradigm was used to evaluate the effects of selective breeding for differential sensitivity to the hypnotic effects of ethanol. Tenth generation high alcohol sensitive (HAS) and low alcohol sensitive (LAS) rats were trained to discriminate between ethanol (0.6 g/kg, IP) and saline vehicle on a VR-5 schedule of reinforcement. The animals were tested with 0.15, 0.3, and 0.9 g/kg ethanol following 40, 50, and 60 training sessions. Sleep-time, tested before and following discrimination training, did not change for the HAS and LAS animals. Dose-response functions showed differences between the HAS and LAS phenotypes after 40 training sessions but not after 50 sessions or after 60 sessions.

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 result 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 behavioral 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-senstive ANT rats.

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.