Effects of manipulating food availability on ethanol self-administration by P rats in a continuous access situation.

Male rats from the alcohol-preferring (P) line were housed in operant chambers in which food, water, and ethanol (10% v/v) were available continuously 23 hr per day. Over a period of weeks, the fixed ratio (FR) requirement for food reinforcement was gradually increased from FR 1 to FR 64. The response requirements for water and ethanol remained constant throughout the experiment. As the FR requirement for food reinforcement increased, the total number of food-reinforced responses increased significantly, whereas the total number of food pellets delivered per day and total calories per day decreased significantly. Conversely, ethanol intake (g/kg) and the percentage of total calories from ethanol increased significantly as the response requirement for food reinforcement increased. The increase in ethanol intake was accounted for largely by an increase in the number of ethanol drinking bouts per day rather than an increase in the number of dippers presented per bout. The results support the hypothesis that the manipulation of environmental variables, such as FR requirement for food reinforcement, can influence the ethanol self-administration of P rats; an effect observed previously with nonselected Long-Evans rats.