Persistent stress-induced sensitization of adrenocortical and startle responses

Abstract

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 suprathreshold (96 dB) stimuli was assessed in rats given 3 daily sessions (3DS) of 40, 2-mA tailshocks. The 3DS rats showed an exaggerated startle response to the threshold auditory stimulus 4 days poststressor compared to nonshocked controls (CON). An exaggerated startle response in stressed rats was not evident either 1 day or 10 days poststressor. In Experiment 2, adrenocortical sensitization and behavioral reacivity were assessed in rats exposed to 1 day (1DS) or 3 days of our stress regimen. Stressed rats exhibited elevated basal plasma corticosterone (CORT) levels 1 day poststressor which recovered by 9 days poststressor. Stressed rats also exhibited suppressed open-field activity 4 days poststressor. On the 10th day poststressor, rats were exposed to a single tailshock. The 1DS and 3DS rats showed both a sensitized and prolonged CORT response to stressor reexposure compared to control rats which received only the single tailshock. In addition, on the 11th day poststressor 3DS rats exhibited a moderate recapitulation of the elevated basal CORT levels seen after the initial stressor exposures. Thus, exposure to our stress regimen produces a chronic stress state in rats characterized 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 as posttraumatic stress disorder.