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, the effects of food deprivation on other phases of drug taking have not been established. The purpose of the present study was to evaluate the effects of food deprivation on reinstatement of responding for cocaine. Rats trained to self-administer 0.2, 0.4, or 1.0 mg/kg cocaine intravenously (IV) under a fixed-ratio 1 schedule for the first 2 h during daily 7-h sessions were fed either before or after the experimental session. During hours 3-7, rats self-administered saline. Saline replaced cocaine in the infusion pumps at the beginning of hour 3 and a priming injection of either saline or cocaine (0.32, 1.0, or 3.2 mg/kg IV) was administered 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 of infusions was inversely related to cocaine dose. During hour 3, rats typically self-administered several infusions of saline, which gradually 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 extinction responding during hour 3 and reinstatement of responding during hour 4 were similar regardless of cocaine maintenance dose. However, responding during hour 4 did increase in all cocaine 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 maintained at 0.4 mg/kg cocaine. While the magnitude of reinstatement of responding during hour 4 did not vary as a function of food level, extinction responding during hour 3 was significantly increased in rats maintained at the lowest food level (8-12 g) when feeding occurred after the session. These results suggest that food deprivation level and time of feeding, but not cocaine maintenance dose, are important variables in altering extinction and reinstatement of responding.