Regulatory drinking in rats with permanent access to a bitter fluid source.

Male rats were given a quinine adulterated fluid as their sole source of liquid for over 60 days. After a latency of a few days, fluid intake stabilised at about 20 ml/day, with the water to food ratio close to 1.0 ml/g. Bodyweights fell to 90 percent of control levels (rats drinking unadulterated water). A battery of dipsogenic challenges was administered. Compared to controls, the ingestive responses during elevated ambient temperature, hyperosmotic salty food, after fluid deprivation, and to extracellular fluid depletion, were all attentuated. Drinking to acute NaCl injections was totally abolished. The intake of the adulterated fluid was near zero during food deprivation, and when a vegetable and fruit diet was available. Body fluid changes were suggestive of a net dehydration in the quinine drinking rats. Parallels with self intravenous drinking rats and rats recovered from lateral hypothalamic lesions were considered, and possible fundamental differences between natural and nonatural thirst stimuli.