Stress-induced increases in avoidance responding: an animal model of post-traumatic stress disorder behavior?

One prominent symptom of post-traumatic stress disorder (PTSD) is avoidance of stimuli reminiscent of the traumatic event. We attempted to study this aspect of PTSD in two experiments. Groups of rats received forty 3-s tailshocks, or served as home cage controls (HCC). Twenty-four hours later, all subjects received a 4-h session of leverpress escape/avoidance conditioning. In Experiment 1, shock periods in the absence of a response were 1 s; in Experiment 2 they were 30 s. No group differences were observed in Experiment 1. In Experiment 2, previously shocked animals made more avoidance responses and had a higher percent avoidance during the fourth hour of the session than controls. Further, previously shocked animals had a higher efficiency ratio (the percent of responses that were avoidances). No group differences were observed in leverpresses during the safety period (an index of anxiety) in either study. Results are discussed in terms of the effects of stress on avoidance behavior as a potential model for this important feature of PTSD.