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Rats sacrificed after 4 days in the activity-stress paradigm or after 4 days of food restriction had significantly elevated levels of plasma corticosterone as compared to control rats. The approximately 5 fold increase in corticosterone in the stressed treatment groups was consistently found in all experiments. ACTH levels were elevated in activity-stress and food-restricted groups in some experiments but these increases were not statistically significant. Prolactin levels were significantly elevated in food-restricted group rats as compared to controls or activity-stress group animals in one experiment but this finding was not repeated in further experiments. In a second series of experiments, rats from activity-stressed and food-restricted treatment groups and controls were exposed to an acute stressor for 15 min prior to sacrifice to assess the effects of prior sustained stress on hormonal responses to an acute stressor. Exposure to 15 min of immobilization or intermittent footshock immediately prior to sacrifice increased plasma levels of corticosterone, ACTH and prolactin in control, foodrestricted and activity-stressed rats. Generally, hormonal responses to the acute stress were similar in all treatment groups. However, in two experiments where the resting levels of corticosterone were especially elevated in the activity-stress group, the acute stress-induced rise in corticosterone was less than that seen for the other two treatment groups. In another experiment, administration of dexamethasone suppressed acute stress-evoked levels of ACTH and corticosterone in control, activity-stressed and food-restricted rats. Thus, rats exposed to 4 days of sustained stress were found to have consistently elevated resting levels of corticosterone. Hormonal responses to acute stress or dexamethasone administration, however, were generally similar in activity-stressed, food-restricted and control rats.

The behavioral animal models of stress ulcer in the rat include immobilization, conflict, predictability, coping and avoidance responding. Research with these ulcer techniques is briefly reviewed. The activity-stress ulcer model is described and recent findings summarized. Physiological investigations of stress ulcer have produced considerable information regarding the proximal causes of ulcer disease. Behavioral scientists can make significant contributions to the study of stress ulcer by evaluating predisposing variables and by observing the relevant precipitating environmental events which lead to ulcer development.