Fos expression following regimens of predator stress versus footshock that differentially affect prepulse inhibition in rats.

Stress is suggested to exacerbate symptoms and contribute to relapse in patients with schizophrenia and several other psychiatric disorders. A prominent feature of many of these illnesses is an impaired ability to filter information through sensorimotor gating processes. Prepulse inhibition (PPI) is a functional measure of sensorimotor gating, and known to be deficient in schizophrenia and sometimes in post-traumatic stress disorder (PTSD), both of which are also sensitive to stress-induced symptom deterioration. We previously found that a psychological stressor (exposure to a ferret without physical contact), but not footshock, disrupted PPI in rats, suggesting that intense psychological stress/trauma may uniquely model stress-induced sensorimotor gating abnormalities. In the present experiment, we sought to recreate the conditions where we found this behavioral difference, and to explore possible underlying neural substrates. Rats were exposed acutely to ferret stress, footshock, or no stress (control). 90 min later, tissue was obtained for Fos immunohistochemistry to assess neuronal activation. Several brain regions (prelimbic, infralimbic, and cingulate cortices, the paraventricular hypothalamic nucleus, the paraventricular thalamic nucleus, and the lateral periaqueductal gray) were equally activated following exposure to either stressor. Interestingly, the medial amygdala and dorsomedial periaqueductal gray had nearly twice as much Fos activation in the ferret-exposed rats as in the footshock-exposed rats, suggesting that higher activation within these structures may contribute to the unique behavioral effects induced by predator stress. These results may have implications for understanding the neural substrates that could participate in sensorimotor gating abnormalities seen in several psychiatric disorders after psychogenic stress.