Habituation to Repeated Stress is Stressor Specific

Rats were exposed to 15 min of restraint or footshock or forced running in an activity wheel once a day for 10 days. Control groups were handled only. On the 11th day, rats from each stressor group and controls were exposed to 15 min of one stressor in a crossed design such that all combinations of one chronic stressor and one acute stressor were performed. Rats were sacrificed immediately following removal from their home cage or after 15 min stressor exposure on the 11th day and plasma corticosterone and prolactin and pituitary cyclic AMP levels were determined. There were no measured differences in these stress indices among groups of rats sacrificed immediately upon removal from their home cage on day 11 regardless of previous history on days 1 through 10. Plasma corticosterone and plasma prolactin and pituitary cyclic AMP levels were elevated in all rats exposed to any of the three stressors immediately prior to sacrifice as compared to all rats not exposed to stress immediately before sacrifice. However, plasma prolactin and pituitary cyclic AMP responses to each of the 3 stressors were attenuated in rats which had previous exposure to that specific stressor as compared to rats which had previous experience with a different or no stressor. We conclude that habituation results from behavioral experience with a particular stressor rather than biochemical adaptation resulting from repeated challenge to hormonal and neurochemical systems responsive to stress.