Habituation of gastric function suppression in monkeys after repeated free-operant avoidance sessions

Gastric fluid and hydrogen ion secretory rates as well as concurrent fractional emptying rates were determined in monkeys subjected to repeated sessions of free operant avoidance. During the first avoidance session, fractional emptying rate and fluid and hydrogen ion secretory rates were all reduced as compared to preavoidance control rates. By the time the monkeys were performing avoidance stably, fluid and hydrogen ion secretory rates had returned to control levels while fractional emptying tended to return to control levels. Our interpretation that this represented habituation of the stomach to the stressor was buttressed by another experiment in which response-contingent shock was superimposed upon the baseline avoidance schedule. Gastric fractional emptying and fluid and hydrogen ion secretory rates remained at control levels despite the increase in shock frequency related to this new paradigm.