Polydipsia in adult mice and rats given corticosterone in infancy: accentuation by variable interval food reinforcement.

Abstract

Mice and rats were given crystalline corticosterone subcutaneously at 2 days of age, and water intake was measured when the animals were adult. In both species, corticosterone-treated animals consistently drank more water than their littermate controls when at rest in their home cages. In rats, there was no difference in food consumption relative to body weight, and urine volume responded equally well to withdrawal of water. The polydipsia of steroid-treated rats was greatly accentuated when the animals were working for food on a variable-interval schedule (VI 60-sec.) with free access to water. The findings are compatible with other evidence suggesting lasting alterations in the emotional disposition of rodents after hypercorticism in infancy. When mice or rats are given intensive corticosterone treatment during infancy and then allowed to grow to maturity without further manipulation, they show evidence of lasting alterations in certain behavioral patterns, such as exploration of an open field (Howard & Granoff, 1968), performance on various food-reinforced operant schedules (Howard, 1973), and acquisition of 2-way conditioned active avoidance (Olton, Johnson, & Howard, in press). The present paper extends these observations to include drinking behavior and reports the existence of increased water intake in adult mice and rats given an implant of crystalline corticosterone at 2 days of age. Water intake was measured both when the animals were at rest in their home cages and during bar pressing for food with water freely available. The latter condition is of interest in view of the observations of Falk (1961, 1969), who found polydipsia in normal rats bar pressing for food on a variable interval schedule of 60 sec. (VI 60-sec.). The polydipsia induced by operant schedules has been considered to be psychogenic be