Ingestion after stress: Evidence for a regulatory shift in food-rewarded operant performance

Stress usually decreases food consumption and body weight in rats. According to the regulatory shift hypothesis, these effects reflect orderly changes in how animals meet their metabolic needs in dangerous circumstances. This interpretation was tested by examining food-rewarded operant performance before and after stress. Six fixed-ratio (FR) schedules were used in a within-subject design in Experiment 1, and a between-subject design (FR2 versus FR32) was used in Experiment 2. In both experiments, exposure to 100 inescapable tailshocks reduced response rate on smaller schedules, whereas responding on larger schedules was unchanged or increased. This pattern can be interpreted as a decrease in preferred eating rate and an improvement in the behavioral regulation of food intake. Milder stressors generally had less impact but did increase preferred feeding rate, an effect potentially related to stress-induced eating in other paradigms. This study provides evidence that strong stressors reorganize ingestive behavior, as predicted by the regulatory shift hypothesis. (C) 1997 Academic Press.