The effects of the GABA(B) agonist baclofen on the temporal and structural characteristics of ethanol intake.

The present study examined the behavioral processes mediating the influence of the GABA(B) agonist baclofen on the maintenance of voluntary ethanol intake. Long-Evans rats were randomly assigned to two groups, one receiving baclofen (10 mg/kg, IP) and the other an equal volume of saline. Subjects were presented with a free choice of ethanol (10% v/v) and water immediately following drug injections, which occurred every other day. The results demonstrated that baclofen treatment resulted in an overall increase in the intake of absolute ethanol but failed to influence the intake of water. In contrast, food intake was substantially attenuated as evidenced by a decrease in the number of pellets consumed in subjects treated with baclofen. A microanalysis of the patterns of food and fluid bouts indicated that the enhanced ethanol intake was primarily a function of an increase in the frequency of ethanol bouts. In contrast, the decrease in food intake appeared to be a reflection of a decrease in the size of the food meals but not their frequency. An analysis of the temporal pattern of intake over the 23-h test sessions indicated that baclofen treatment produced a biphasic effect on ethanol intake with a slight decrease in intake during the first hour following treatment. Baclofen-treated animals then were observed to consume greater amounts of ethanol than did saline controls throughout the remainder of the dark cycle as well as into the light cycle. Although ethanol intake gradually decreased in controls throughout the light cycle, baclofen-treated subjects maintained a consistent level of intake throughout this period. Furthermore, there was a clear dissociation between the temporal pattern of ethanol intake and that of food and water, as intake of the latter substances was shown to decrease during the first hour following injection, but unlike with ethanol, no increase in intake was observed during the remainder of the test session. The nature of the effects of baclofen observed in the present study would suggest that the GABA(B) receptor system may not play a central role in the mediation of voluntary ethanol intake.