Increased sensitivity to the stimulus properties of morphine in food deprived rats

Recent research has shown that food deprivation increases opiate self-administration; in this line a first purpose of the present experiments was to determine whether the food deprivation effect could be replicated by the use of place conditioning, an alternative procedure for the study of drug reinforcement. It was found that the conditioned reinforcing properties of morphine (2.5 mg/kg IP) paired cues are greater in food deprived rats both after 1 and 3 conditioning sessions. A second objective of the work was to examine the possibility that food deprivation could also influence the discriminative stimulus properties of opiates. To this end rats trained to discriminate 10 mg/kg IP of morphine from saline were submitted to morphine generalization tests when food deprived or after 15 min supplemental feeding in the home cages. The ED50 value was significantly lower for food deprived (6.09 mg/kg) than for partially satiated (7.79 mg/kg) rats. It was concluded that food deprived rats are mores sensitive to both the reinforcing and the discriminative stimulus properties of morphine.