Schedule-induced and water-deprivation-induced drinking in rats: Effects of hypertonic saline challenges to homeostatic thirst mechanisms

Abstract

Previous studies have produced conflicting results regarding whether or not schedule-induced polydipsia (SIP) drinking is sensitive to homeostatic thirst mechanisms. Prior to SIP test sessions, 10 rats were given hypertonic saline (8.0% NaCI), isotonic saline, or sham intraperitoneal preloads. Rats preloaded with hypertonic saline drank significantly more water during SIP test sessions than those given isotonic saline or sham preloads. A second group of 9 rats on a 2S.5-h water-deprivation schedule was given the same three injection test conditions prior to SO-min water-access periods. Water-deprived rats given preloads of hypertonic saline drank significantly more water than they did when given preloads of isotonic saline, but not significantly more than when given sham preloads. The present results support the contention that scheduleinduced polydipsia is a nonhomeostatic form of drinking that nevertheless may be sensitive to the state of homeostatic thirst mechanisms (Le., cellular dehydration).