Effects of number of pellets per food delivery and pellet sucrose composition on schedule-induced drinking

Abstract

Four groups of four rats were tested on a fixed-time (FT 60-sec) schedule in which one, three, or five pellets per food delivery and 0%, 8%, 16%, and 32% sucrose pellets were factorially combined. The results showed no ststistically significant differences in water intake associated with sucrose content of the pellets, but did show a significant inverse relationship between water intake and number of pellets given per reinforcement. This latter finding was interpreted as a result of the direct relationship in the rat between total number of reinforcement opportunities and probability of drinking. This relationship was suggested to be an important dependent variable in studies that measure and attempt to account for collateral fluid ingestion.Schedule-induced polydipsia (SIP) denotes excessive fluid intakes produced in animals through concurrent placement under a regimen of food deprivation and exposure to fluids and certain schedules of intermittent food delivery (e.g., Falk, 1969Falk, , 1971 . The development and maintenance of SIP are responsive, in part, to quantitative (e.g., Falk , 1967 ; Flory, 1971) and qualitative (e.g., Christian & Schaeffer, 1973b ; Colotla & Keehn , 1975) variations in food composition . Recently , the influence on SIP of manipulating the sugar concentration of the dry-food pellets typ ically employed in SIP studies has received attention ; nonetheless, the nature, degree , and directionality of the influence of pellet sugar content on SIP remain enigmatic. For example, though both Christian and Schaeffer (1973b) and Colotla and Keehn (1975) reported an inverse, ordered relationship between the level of SIP and the percent sugar concentration of Noyes food pellets, Christian and Schaeffer (1973b) found greater water intakes for sugarless pellets than for sugared pellets, whereas Colotla and Keehn (1975) reported exactly the opposite'results.The present experiment was designed, first , to reexamine the effects of food-pellet sucrose concentration on SIP by systematically replicating Christian and Schaeffer 's (1973b) study and, second , to determine any possible interaction between food-pellet sucrose content and number of pellets delivered per reinforcement opportunity .

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

“…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 composition in the same subjects .…”