Pituitary-adrenal correlates of schedule-induced polydipsia and wheel running in rats.

To investigate the pituitary-adrenal correlates of schedule-induced behaviours, rats were submitted to a fixed-time 60-s schedule of food reinforcement, with free access to either a water spout or a running wheel. Schedule-induced water drinking (polydipsia) was accompanied by an important drop in plasma corticosterone levels, while wheel running resulted in a significant increase in plasma corticosterone concentrations. This contrast between the pituitary-adrenal consequences of schedule-induced drinking and wheel running was not due to functional differences between the two activities since wheel running was shown to display all the characteristics of schedule-induced activities, mainly excessiveness, differential time distribution and dependance on deprivation level and reinforcement rate.