Effects of ethanol concentration and fixed-ratio requirement on ethanol self-administration by P rats in a continuous access situation.

Rats, from the alcohol preferring (P) line, were placed in operant chambers in which food pellets, water, and 10% ethanol (v/v) were available continuously for 23 hr/day. During Experiment 1, the effects of changing ethanol concentration and response requirement for ethanol were examined. Ten percent and 20% ethanol (v/v) were available on two fixed ratio (FR) schedules, FR 1 and FR 4, for 2 weeks each. During Experiment 2, the effects of increasing the response requirement for ethanol were investigated. Starting with FR 4, the FR requirement for ethanol doubled during 2-week intervals until FR 32 was in effect. For the final phase of these studies, water was placed in the dipper for 1 week followed by a return to 10% ethanol in the dipper. The results from Experiment 1 indicated that when the FR requirement was decreased from FR 4 to FR 1, ethanol-reinforced responding decreased but total daily intake increased. Lowering the FR requirement did not affect the number of ethanol bouts per day but bout size increased. Ethanol concentration had no effect on bout size but the number of bouts per day decreased when the concentration was increased to 20%. Since bout size was unchanged by increasing the ethanol concentration, intake per bout increased at 20% ethanol. The results from Experiment 2 indicated that increasing the response requirement for ethanol decreases ethanol intake. When water was placed in the dipper, responding decreased to the lowest levels observed in the experiment. When ethanol was returned to the dipper, responding returned to baseline levels.(ABSTRACT TRUNCATED AT 250 WORDS)