FOOD-DEPRIVATION AFFECTS EXTINCTION AND REINSTATEMENT OF RESPONDING IN RATS

Food deprivation has been shown to increase the self-administration of a wide variety of drugs in a number of different species. However, th e effects of food deprivation of other phases of drug taking have not been established. The purpose of the present study was to evaluate the effects of food deprivation of reinstatement of responding cocaine. R ats trained to self-administer 0.2, 0.4, or 1.0 mg/kg cocaine intraven ously (IV) under a fixed-ratio 1 schedule for the first 2 h during dai ly 7-h sessions were fed either before or after the experimental sessi on. During hours 3-7, rats self-administered saline. Saline replaced c ocaine in the infusion pumps at the beginning of hour 4. The number of infusions that was self-administered was measured throughout the 7-h session. During hours 1 and 2 when cocaine was available, the number o f infusion was inversely related to cocaine dose. During hour 3, rats typically self-administered several infusions of saline, which gradual ly decreased to near-zero levels by hours 4-7 (extinction responding). A priming injection of cocaine administered at the beginning of hour 4 reinstated responding in a dose-related manner. The magnitude of ext inction responding during hour 3 and reinstatement of responding durin g hour 4 were similar regardless of cocaine maintenance dose. However, responding during hour 4 did increase in all cocain maintenance dose groups when rats were fed before versus after the session. The effects of food deprivation level (8-12 g, 20 g, unlimited food) and time of feeding (before versus after the session) were also assessed in rats m aintained at 0.4 mg/kg cocaine. While the magnitude of reinstatement o f responding during hour 4 did not vary as a function of food level, e xtinction responding during hour 3 hour was significantly increased in rats maintained at the lowest food level (8-12) g when feeding occurr ed after the session. These results suggest that food deprivation leve l and time of feeding, but not cocaine maintenance dose, are important variables in altering extinction and reinstatement of responding.