Ingestion rate as an independent variable in the behavioral analysis of satiation

A novel intake testing paradigm, allowing explicit adjustment of the rate of sucrose ingestion via intraoral delivery, was used to investigate the effects of ingestion rate on ingestion duration and amount consumed. In experiment I, 12 rats were tested under each of three sucrose concentrations (0.1, 0.3, and 1.0 M) delivered at each of four rates (0.5, 1.0, 1.5, and 2.0 ml/min). For each stimulus concentration, intraoral intake varied as a decreasing linear function of ingestion rate (infusion rate). In experiment II, a second (part B) infusion (0.5, 1.0, or 1.5 ml/min) was initiated 30 s after an initial (part A) infusion (0.5, 1.0, or 1.5 ml/min) of the same stimulus was rejected. Amount consumed during the part B infusion was substantial only when the part B infusion rate was lower than that of part A. Quantitative analysis of experiment II indicated that across sessions with common part B infusion rates, total session intake remained stable regardless of 1) whether the part A ingestion rate was greater than or equal to that of part B, 2) systematic differences in part A intake and duration, 3) differences in total session duration, and 4) differences in average ingestion rate for the session (total session intake/total session duration). The behavioral results are discussed in relation to the analysis of satiety under traditional intake testing paradigms and to gastric and postgastric theories of satiety.