Acquisition of schedule-induced polydipsia in rats with no prior drinking experience.

Three litters of 10 rat pups each were reared on Purina laboratory chow and either (1) continuous access to water, (2) access to both water and lettuce until weaning at 21 days and then only lettuce, or (3) continuous access to lettuce. At 100 days all rats were reduced to 80% free feeding weight and tested for polydipsia. During 15 sessions of polydipsia testing, excessive postpellet drinking developed in all groups to 45 mg Noyes pellets delivered on a fixed-time 1 min schedule. No significant differences in water intake over sessions were found among groups. It was concluded that schedule-induced polydipsia does not represent an exaggeration of a learned prandial drinking pattern, but rather an exaggeration of an inborn prandial drinking reflex.