Choice between cocaine and food by rhesus monkeys: effects of conditions of food availability.

The present experiment was designed to examine the effects of the conditions of food availability on choice between cocaine and food in rhesus monkeys. Monkeys (n = 3), maintained at approximately 90% of their free-feeding weights, were trained in a discrete-trials choice procedure and allowed to choose between intravenous injections of cocaine (0.03-1.0mg/kg/injection) and food delivery (4 pellets; 1g/pellet) during daily 7-h sessions. When food was available both within the session and by supplemental post-session feeding, the frequency of cocaine choice increased in a dose-related manner for all monkeys. When supplemental post-session feeding was eliminated (i.e. food was only available within the session) the cocaine dose-response function was shifted to the right and down relative to that found initially. However, changes in the frequency of cocaine choice did not vary consistently with changes in body weight. Thus, these results suggest that the reinforcing efficacy of cocaine can be modified by changing the conditions of availability of an alternative non-drug reinforcer.