The effect of repeated withdrawal episodes on acquisition and loss of tolerance to ethanol in ethanol-treated rats.

Male rats were administered ethanol via an intragastric catheter (8.0-12.0 g/kg/day) either continuously for 8 weeks or on a binge schedule with four 2 week cycles of drug administration separated from each successive cycle by a 2 week period of no drug treatment. Older rats were administered ethanol for 2 weeks, to provide an age control for the binge-treated animals as age can alter an animal's sensitivity to ethanol. Acquisition and loss of tolerance to ethanol-induced motor impairment were measured on a dowel task while acquisition and loss of tolerance to ethanol-induced hypothermia were assessed by measuring rectal temperature. Acceleration of tolerance development to both ethanol-induced motor impairment and hypothermia was observed in animals subjected to repeated withdrawal episodes (binge-Study 1) but not in the controls for total dose and duration of drug treatment who experienced withdrawal only once (continuous-Study 2). Persistence of tolerance to ethanol-induced motor impairment occurred in both binge and continuously treated animals while persistence of tolerance to ethanol-induced hypothermia was seen only in the binge treated animals. Age (3 to 7 months) did not affect tolerance development or decay. After three cycles of drug treatment (three withdrawal episodes), binge treated animals showed an impairment in motor ability when blood ethanol levels were near zero. This impairment disappeared when the animals were administered ethanol, indicating a normalizing effect of ethanol on motor behavior in animals subjected to repeated episodes of withdrawal. A similar, but not significant, effect was seen in continuously treated animals. Thus, in an animal exposed to prolonged ethanol treatment, persistent changes in responding to the drug were found. The persistence of these changes was enhanced by the experience of withdrawal from ethanol.