Abstract

The primary objective of this investigation was to explore the effects of prior exposure to amphetamine on subsequent stress-induced and free feeding of regular chow or palatable cereal. After treatment with 5 injections of either d-amphetamine (3 mg/kg IP) or saline, administered on alternate days, animals in Experiments 1 and 3 were permanently moved to computer-controlled test cages, whereas animals in Experiment 2 remained in the colony room and were transported to the test cages for testing only. After 14 drug-free days, animals were either briefly handled or restrained for 20 min, on 10 consecutive days, 6 hours into the light cycle. Consumption of regular chow or palatable cereal was monitored for 1 hour following the return of animals to the cages. Amphetamine preexposure enhanced stress-induced consumption of regular chow (Experiment 1) and, to some extent, of palatable cereal (Experiment 2), despite the stress-induced suppression of palatable food intake. Stress-induced feeding of regular chow increased progressively over initial stress sessions, indicating sensitization of the response to stress. Amphetamine preexposure also enhanced free consumption of palatable cereal, which similarly sensitized over repeated tests. The effects of amphetamine preexposure on stress-induced and free intake of palatable food were more pronounced in females than in males. When testing was conducted in home cage environment (Experiment 3), amphetamine preexposure had no effect on palatable food consumption, however, it enhanced regular chow intake during the light cycle. Thus, prior exposure to sensitizing regimen of amphetamine exerts long-lasting effects on subsequent response of animals to motivationally significant stimuli.