Operant Performance by Rats for Alcohol Reinforcement; A Comparison of Alcohol-Preferring and Nonpreferring Animals

Abstract

After 75 days of observation of the home cage drinking patterns in 4 hooded rats given a free choice between ethanol and water, an alcohol-preferring and a non-preferring animal were selected from the 5% ethanol group and from the 15% ethanol group. These animals were reduced to 85% of their free-feeding weight and were taught to press a lever for evaporated milk reinforcement on a multiple fixed ration of 25, fixed interval of 5 minutes schedule. After 40 sessions, 5% ethanol was substituted for milk as a reinforcement. Animals continued to lever press for ethanol and there were only small differences between the alcohol-preferring and non-preferring animals in the 5% ethanol group with respect to decline of over-all response rate through time (40 sessions). The lever-pressing behavior of the 15% ethanol preferring and non-preferring animals showed a comparable decrease in rate when 5% ethanol was substituted for milk reinforcement. However, when 15% ethanol was substituted for 5% ethanol after 10 sessions, the preferring animal showed an increase in rate of response comparable to the rate observed with milk reinforcement and the average response output over the first and second blocks of 5 sessions was higher than that for 5% ethanol reinforcement over the same length of time. The nonpreferring animal showed a small initial increase in rate when 15% ethanol was introduced and showed a consistent low rate of response thereafter. These data demonstrate that rats will press a lever to obtain ethanol concentrations as high as 15% without any motivating stressor such as aversive electric shock. These data further suggest that at high concentrations, marked differences in preference may be reflected in rate of response to obtain alcohol. The relationship of preferential drinking to addiction is discussed and it is concluded that the demonstrated behavior does not represent addiction.