Schedule-induced polydipsia: attenuating effects of decreased size of food granulations.

The effect of food texture on the development of schedule-induced polydipsia was examined in six groups of rats (n = 8), each receiving one of six grades of food granulation. A seventh group received pellets. By the end of 15 sessions of FT 60-sec food delivery, rats receiving pellets and the coarser granulations had developed polydipsia. The volume of water drunk at asymptote by the remaining groups declined with decreased coarseness of the food. Ethological analyses of the behavioral repertoire of the rats during the fifteenth session showed that the polydipsic groups sustained their drinking throughout the session, rather than turning from ingestive to exploratory behaviors near the end of the session, as was the case with animals receiving finer granulations. The enhanced drinking induced by the coarser food texture was reciprocally related to the amount of time the animal spent with its head in the feeder hole during the period of maximum drinking. The results support the conclusion that the schedule-induced polydipsia traditionally demonstrated with pellets as the reinforcer is critically dependent on the fact that pellets are coarse in texture.