EFFECTS OF FOOD-DEPRIVATION AND SATIATION ON SENSITIVITY TO THE DISCRIMINATIVE-STIMULUS EFFECTS OF PENTOBARBITAL IN PIGEONS AND MORPHINE INRATS

Food deprivation can produce a substantial increase in the self-admini stration of drugs of abuse, suggesting that food deprivation increases their reinforcing properties. This finding has been replicated with a wide variety of reinforcing drugs. The present experiments examined t he effects of food deprivation and satiation on the discriminative sti mulus properties of drugs, to determine whether food deprivation affec ts the discriminative-stimulus effects of drugs in a similar manner. U sing pigeons that were trained to discriminate 5 mg/kg i.m. pentobarbi tal from saline, dose-effect curves were determined under both food-de privation conditions (80% free-feeding body weight) and partial food-s atiation conditions (25% and 50% of the amount of full satiation). It was found that generalization curves for both pentobarbital and saline were similar at all levels of food deprivation. In a second set of ex periments, rats were trained to discriminate 10 mg/kg i.p. morphine fr om saline, and the discriminative properties of morphine were then tes ted when the animals were either food-deprived or after a 15 min suppl emental feeding. The ED(50) value for the food-deprived condition was comparable to that the food-satiated condition (3.6 vs. 4.8 mg/kg, res pectively). Thus, in both pigeons and rats, there was little evidence that food deprivation increased sensitivity to the discriminative stim ulus properties of drugs. Thus, food deprivation must increase drug se lf-administration by a mechanism other than by increasing the discrimi native stimulus properties of self-administered drugs.