Water-intake volume regulation in the rat: schedule-induced drinking compared with water-deprivation-induced drinking

Hungry rats drink extremely large amounts of water when they are intermittently fed small amount of food (schedule-induced polydipsia). Are such animals motivated to drink for long durations, to ingest large amounts of fluid, or to do both? When drinking-tube apertures were decreased to slow the rate of water ingestion, each of eight rats spent more time drinking (M = 11.5 min) than when larger apertures were used (M = 7.8 min). The mean volumes ingested were not different. These equal volumes were generated by adjustment of each drink duration in accordance with ingestion rate even during the first few drinks of the sessioons, even when the drinking tubes were frequently switched (every 1-3 min) during the sessions. During drinking induced by water deprivation when food was concurrently available, restriction of the driking-tube apertures reduced intake volumes by 18%-19%. However, when food was not concurrently available during water-deprivation-induced driking, regulation of intake volumes was comparable with that found during schedule-induced polydipsia. These data pose difficulties for theories that ascribe a crucial role to the motor aspects of schedule-induced drinking.