Evaluation of a polydipsia technique to induce alcohol consumption in monkeys.

Abstract

The observation that the intermittent delivery of dry food pellets is accompanied by consumption of large quantities of water in the rat was first described by Falk in 1961 (4) and this phenomenon was subsequently termed psychogenic or schedule-induced polydipsia. Falk (4) reported that rats maintained at 80 per cent of their free feeding weight, would consume approximately one half of their total weight in water within a few hours when food pellets were presented intermittently. Variations of thirst explanations for this phenomena proved untenable since pre-session water loading did not eliminate polydipsic drinking (8) and dry food was neither necessary or sufficient for the induction of polydipsia. Intermittent delivery of small portions of a standard liquid monkey diet were equally effective in producing excessive drinking (7). Superstitious chaining, i.e. the adventitious reinforcement of drinking within the inter-pellet interval also fails to account for polydipsia (5,33). A number of factors have been identified that contribute to the magnitude of the effect such as an inter-pellet interval of more than 45 sec (6), small food portions (7) and weight reduction (8). However, Falk (9) has emphasized that reinforcement schedules do not elicit polydipsic drinking, but rather the behavior develops gradually and can be attenuated by weight increase even when response rates and food intake stay the same. The power of the procedure is illustrated by the fact that comparable levels of fluid ingestion are not achieved by other experimental manipulations such as water deprivation, heat stress or osmotic loading in rat (8). Falk describes schedule-induced polydipsia as a form of adjunctive behavior and concludes that no adequate physiological or behavioral explanation for the phenomena has yet been advanced (8,9).