EFFECTS OF FOOD-DEPRIVATION ON COCAINE BASE SMOKING IN RHESUS-MONKEYS

Studies have shown that both food deprivation and response cost have i mportant influences on the magnitude of self-administration of a wide variety of psychoactive drugs. In an attempt to extend these findings to the smoked route of drug self-administration, the effects of food a llotment and fixed-ratio (FR) value were evaluated in four male rhesus monkeys trained to smoke cocaine base. In the first phase of the expe riment, monkeys were trained to self-administer smoked cocaine base un der a chained progressive-ratio (PR), fixed-ratio (FR) schedule during daily experimental sessions. Monkeys were required to make 20 lever-p ress responses and then five inhalations on a smoking spout to obtain the first smoke delivery. The lever ratio then increased to 60, 140, 3 00, 620, 1260, 2540, and 4940 for each successive smoke delivery. The initial lever ratio value was reset to 20 at the beginning of each dai ly session. The body weights of three monkeys were-determined under fr ee-feeding conditions. Monkeys were then restricted to 100 g food and, when body weights had stabilized, the daily food allotment was increa sed to 150 g, approximately 210 g, or greater than 400 g (satiation). As the daily food allotment and body weight increased, the mean number of smoke deliveries decreased in two of three monkeys. In the second phase of the experiment, three monkeys were maintained under either fo od-satiated or food-restricted conditions. Body weights were maintaine d at approximately 90% of their free-feeding weights under food-restri cted conditions. The cost of the drug (lever FR value) was constant wi thin each experimental session, but was increased after 3 consecutive days of stable responding. Fixed-ratio values were increased from 128 to 256, 512, 1024, and 2048. Monkeys were required to complete the lev er FR value and then to make five inhalations on the smoking spout to gain access to 1.0 mg/kg per delivery cocaine base. The mean number of smoke deliveries increased at FR 256, 512, and 1024 when monkeys were food-restricted as opposed to food-satiated. Correspondingly, the mea n number of responses increased under food-restricted conditions. Resp onding continued to increase over a wider range of FR values, and the peak number of responses was higher under food-restricted, as opposed to food-satiated conditions. These results, using the smoking route of administration, are consistent with the hypothesis that food deprivat ion increases the self-administration of reinforcing drugs.