DELAYED STARTLE SENSITIZATION DISTINGUISHES RATS EXPOSED TO ONE OR 3 STRESS SESSIONS - FURTHER EVIDENCE TOWARD AN ANIMAL-MODEL OF PTSD

Posttraumatic stress disorder (PTSD) may occur in humans exposed chron ically to stressors or after a single exposure to a traumatic event. A distinguishing feature of patients with PTSD is an exaggerated startl e response, evident long after the traumatic event. We have observed s imilar abnormalities in our animal model of a chronic stress state. Ra ts exposed to 3 days (3DS) of our stress regimen (2-hr sessions of 40, 2 mA tailshocks) have exhibited a consistent pattern of persistent ph ysiological and behavioral abnormalities including an exaggerated star tle response several days after stressor cessation. In contrast, rats exposed to a single stress session (1DS) have exhibited many, but not all, of the persistent abnormalities displayed by 3DS rats. The presen t experiment compared the startle responding of 3DS and 1DS rats 4, 7, and 10 days after stressor cessation. Consistent with previous work, stressed rats exhibited elevated basal plasma corticosterone (CORT) le vels the first day poststressor. These CORT levels were sensitive to t he number of stressor exposures with higher CORT levels in 3DS rats th an in 1DS rats. As for startle responding, the 1DS rats exhibited an e xaggerated startle response 7 days poststressor, whereas startle sensi tization was apparent 10 days poststressor in 3DS rats. Thus, the appe arance of an exaggerated startle response after stressor cessation app ears to be related to the number of stress session exposures. These an imal models, the 3DS and 1DS rats, may be useful to gain insight into the neurobehavioral changes associated with PTSD.