PERSISTENT STRESS-INDUCED SENSITIZATION OF ADRENOCORTICAL AND STARTLERESPONSES

We assessed the functional adrenocortical and behavioral state of rats previously exposed to repeated stressor presentations. In Experiment 1, the whole-body startle response to threshold (91 dB) and suprathres hold (96 dB) stimuli was assessed in rats given 3 daily sessions (3DS) of 40, 2-mA tailshocks. The 3DS rats showed an exaggerated startle re sponse to the threshold auditory stimulus 4 days poststressor compared to nonshocked controls (CON). An exaggerated startle response in stre ssed rats was not evident either 1 day or 10 days poststressor. In Exp eriment 2, adrenocortical sensitization and behavioral reactivity were assessed in rats exposed to 1 day (1DS) or 3 days of our stress regim en. Stressed rats exhibited elevated basal plasma corticosterone (CORT ) levels 1 day poststressor which recovered by 9 days poststressor. St ressed rats also exhibited suppressed open-field activity 4 days posts tressor. On the 10th day poststressor, rats were exposed to a single t ailshock. The 1DS and 3DS rats showed both a sensitized and prolonged CORT response to stressor reexposure compared to control rats which re ceived only the single tailshock. In addition, on the 11th day poststr essor 3DS rats exhibited a moderate recapitulation of the elevated bas al CORT levels seen after the initial stressor exposures. Thus, exposu re to our stress regimen produces a chronic stress state in rats chara cterized by persistent behavioral and adrenocortical sensitization, as well as suppressed open-field activity and elevated basal CORT levels . Rats exhibiting a chronic stress state may be appropriate as a model for the study of stress-related psychophysiological illnesses, such a s posttraumatic stress disorder.