Self-Maintenance of Intoxication in the Rat

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Abstract
Training food-deprived rats to press a bar for the delivery of food pellets at irregular intervals established a behavior resembling compulsive drinking of a 5.6% alcohol solution. All 9 rats tested developed this response. The average amount of solution consumed was 9.9 g/hour. Intoxication was produced in 3-hour test sessions with blood alcohol levels reaching 0.2%. With variable food delivery and without bar pressing, the average consumption of alcohol solution was 2.0 gAour. With bar pressing but with food delivered at a fixed interval, the average consumption was 2.5 g/hour. With no fluid present during training, the average consumption was 3.2 g/hour. By means of this method, a rat has maintained itself at blood alcohol levels of 0.11 to 0.19% for a period of 70 hours. When intoxication was thus maintained, increased alcohol intake on the third day was paralleled by a lower blood-alcohol level, indicating the development of a metabolic tolerance. The method offers a simple approach to the study of metabolic and functional tolerance and other effects of prolonged intoxication, such as the withdrawal syndrome. The factors of bar pressing, presence of fluid during training, and predictability of the reward, are discussed as responsible and modifying elements in the development of the compulsive drinking and as potential elucidators of addictive processes.