Failure of a schedule-induction procedure to increase ethanol intake in an established limited-access self-administration condition.

Determining mechanisms that can increase ethanol consumption during a single drinking bout is central to understanding alcohol abuse. When rodents are used as models to study excessive drinking, most often limited and transient increases in bout size are found with various manipulations. In a variety of studies, investigators have reported that schedule-induced drinking can result in excessive consumption of either water or alcohol (ethanol) during a single drinking period in food-restricted rats. The question examined in this experiment was, Could a schedule-induction paradigm increase bout size in nondeprived rats already self-administering ethanol? After the rats were trained to self-administer a 10% (volume/volume) ethanol solution in a fixed daily drinking session, non-response-contingent presentation of a 10% (weight/volume) sucrose solution, on a fixed-time, 120-s schedule, was used to determine whether additional ethanol consumption could be induced. This was followed by the use of a fixed-time, 300-s schedule and then, by using the fixed-time, 120-s schedule, with the presentation of a 2% (weight/volume) sucrose solution. None of these conditions induced an increase in ethanol self-administration. The results indicate that factors that control ethanol bout size in the nondeprived rat are such that the standard schedule-induction condition seems to be ineffective if an ethanol bout has occurred in the recent past.