A within-subjects study of variations in food pellet sucrose concentrations and steady state schedule-induced polydipsia

Abstract

Two food-deprived female albino rats received 16% sucrose pellets under a fixed-time (FTl 60-sec food-reinforcement schedule, with water freely available in the test chamber. After water intake stabilized for each animal, subjects received either 6% or 32% sucrose pellets under the same FT 60-sec reinforcement schedule. This phase was followed by a replication of the initial 16% sucrose pellet condition for each animal. Water intake was found to decrease for each animal following an initial shift from 16% sucrose pellets to 0% or 32% sucrose pellets, but not following shifts from 0% or 32% sucrose pellets to 16% sucrose pellets. Adjunctive behaviors and shift-related elation-suppression effects were compared and discussed.Food-deprived rats exposed to intermittent schedules of food reinforcement ingest varying amounts of freely available water in the absence of experimenter-programmed contingencies between drinking and the delivery of food (Fairbank & Schaeffer, 1978;Schaeffer , 1977). As previously noted by Christian, Schaeffer , and King (1977), most research on schedule-induced drinking behavior of rats exposed to intermittent food reinforcement schedules has focused upon those subjects that, relative to individual baseline levels of consumption , quaff voluminous amounts of water . Because this phenomenon has not been shown to be a direct behavioral product of specific reinforcement contingencies, it is typically referred to as schedule-induced polydipsia (SIP).Although the precise experimental parameters that are both necessary and sufficient for the development and maintenance of SIP have yet to be identified, quantitative and qualitative variations in environmental variables necessary for the development of SIP, such as degree of food deprivation (Falk, 1969;Keehn , 1979), type of fluid proferred (Ten Eyck & Schaeffer, 1969) , and schedule of reinforcement employed (Falk, 1966 ;Schaeffer & Diehl, 1966), have been observed to dramatically affect total amounts drunk. Recently, a number of investigations into the determinants of SIP have focused upon the relationship between qualitative properties of dry-food reinforcers , pellet sugar in particular , and SIP (Christian, Reister , & Schaeffer, 1973 ;Christian & Schaeffer, 1973;Colotla & Keehn, 1975 ;Hart & Schaeffer, 1978 ;McCoy, Christian, & Tolan , 1979;Schaeffer & Brush, 1978; Schaeffer & Fairbank , Note I) . Studies employing between-group experimental designs, in which independent groups of subjects differ in the sucrose content of dry food pellets to which they are exposed, have reported modest , inverse ordinal, long-term steady state relationships between pellet sucrose content and SIP (Christian et aI., 1973 ;Christian & Schaeffer , 1973 ;Fairbank & Schaeffer, 1978;Schaeffer & Brush, 1978). As a direct procedural contrast with the between-groups experimental design, other investigators have employed within-sessions probe (Colotla & Keehn, 1975 ; Falk, 1967) procedures to examine the immediate effects upon SIP of manipulating pellet sugar compositio...