Wheel running reinforces behavior that precedes it. Also, wheel running can produce activity anorexia, a marked suppression of feeding in food-restricted rats. Some authors propose that the activity anorexia effect is produced by activation of the same reward system that mediates the reinforcing effect. One hypothesis is that such activation persists after wheel running stops and results in a rewarding aftereffect that suppresses feeding. Alternatively, such activation may give rise to an opponent process, an aversive aftereffect that suppresses feeding. The method of place conditioning was used to test whether the aftereffect of wheel running is rewarding or aversive. Food-deprived rats received pairings of a distinctive chamber with the aftereffect of wheel running. In Experiment 1, 2 h in a running wheel followed by 30 min in a distinctive chamber produced conditioned place preference. In Experiment 2, 22-22.5 h in a running wheel was followed by 30 min in the chamber and then a 60-min feeding test. Wheel running suppressed feeding and produced conditioned place preference. The conditioned place preference indicates that the aftereffect of wheel running is reinforcing rather than aversive. This finding supports the idea that the activation of the reward system persists after wheel running stops, thereby suppressing food intake.
Copyright 2000 Academic Press.