Control of drinking-bout magnitude in schedule-induced polydipsia by interpellet-interval duration

Schedule-induced polydipsia (SIP) is a function of interpellet-interval (IPI) durations: intermediate (40-180-sec) IPIs are most effective in producing SIP, while longer and shorter IPIs are increasingly less effective. In order to determine whether each IPI exerts its influence on SIP by regulating drinking during that IPI itself or during the immediately succeeding IPI, rats were presented with systematic sequences of IPI durations during individual sessions of SIP testing. It was found that a very brief (20-sec) IPI tended to reduce the duration of drinking during the ongoing IPI, but that a very long (4-min) IPI reduced the probability that any drinking would occur during subsequent IPIs. It was suggested that the motivation to drink is reduced following long IPIs, while feeding, or behaviors anticipatory to feeding, compete with drinking when IPI lengths are very short.