Behavioral factors in development of tolerance to ethanol's effects.

Dose-effect analyses were used to monitor the development of tolerance for ethanol's effects on FR30 operant performance in rats under different conditions of chronic ethanol exposure: (a) pre-session ethanol injections (PRE) vs. post-session ethanol injections (POST) in Experiment 1; and (b) an ethanol liquid diet (ED) vs. a control diet (CD) in Experiment 2. The PRE and ED groups developed tolerance at the conclusion of the chronic regimens, which declined by six months but not to baseline levels. These data suggest that tolerance results from learned compensatory adjustments (through intoxicated practice) to ethanol's disruptive effects. The POST, but not the CD, group developed a progressively increasing degree of tolerance after several ethanol challenge tests. These results suggest that some threshold level of passive ethanol exposure in the POST group interacted with their limited intoxicated practice. Finally, the tolerance developed under intoxicated practice conditions did not appear to reflect a generalized tolerance to rate-reducing properties of drugs, changes in ethanol kinetics, or age-related changes.