Food granules elicit heavy drinking in polydipsic rats independently of meal duration

Excessive drinking, in rats made polydipsic on intermittent delivery of food pellets, is inversely related to the time the rat spends with its head in the feeder, early in the interfood interval. In a sensitization model, this explains why food textures that induce more oral activity, e.g., powder, do not elicit drinking. This hypothesis was examined by coding the behavior of polydipsic rats and varying the duration of the meal delivered in each interval, while holding texture constant. Polydipsic rats were presented with pellets, food granules, or food powder. The food granules were dispensed over periods lasting 1, 14, 21, and 28 s. All food deliveries were of the same mass. The food was delivered periodically at 60-s intervals in each condition. The 14 rats in the experiment served as their own controls by experiencing every condition. The food granule conditions induced the expected increases in feeding early in the interval. However, instead of progressively reducing drinking, the excessive drinking simply occurred later in the interval. By contrast, the powder condition resulted in the immediate elimination of polydipsia. The results suggest that food texture elicits excessive drinking independently of temporal factors and that elicitation of the sensitized drinking response must depend on other factors.