Development and reacquisition of tolerance to ethanol administered pre- and post trial to rats.

The development of tolerance to the disruptive effects of ethanol on bar-pressing behavior was studied in rats by exposing them to four cycles of drug administration intercalated by 34-day drug-free periods. A negative correlation was obtained between the successive cycles and the number of sessions required for the rats to reach the criterion of tolerance. Also studied was the possible difference in the rate of development of tolerance in the four cycles when ethanol was administered before or after the task. One group of rats was required to perform the response under the influence of ethanol, while other group received the drug 90 min after the bar-pressing sessions. At the first cycle the group which performed under drug action developed tolerance more rapidly than the group which received ethanol after the task.