Corticotropin-releasing factor antagonist attenuates defensive-withdrawal behavior elicited by odors of stressed conspecifics.

This study examined the hypothesis that defensive responsiveness induced by threatening stimuli of biological origin is mediated by the action of endogenous corticotropin-releasing factor (CRF). Rats were exposed for 15 min to a large open field containing a small chamber. Twenty-four hours later, rats received intracerebroventricular injections of either vehicle or 20 micrograms of alpha-helical CRF(9-41), a CRF receptor antagonist. After 20 min, rats were reexposed to the open field, which now contained odors of urine and feces from a stressed conspecific. In the reexposure test, vehicle- and antagonist-treated rats withdrew rapidly into the chamber. Antagonist-treated rats, however, emerged subsequently from the chamber to explore the open field as indicated by a significant increase in the number of passages made between the chamber and the open field. Results suggest that central injection of alpha-helical CRF(9-41) reduces the level of fear induced by odors associated with threat. In addition, CRF receptors are implicated in mediating the species-typical display of defensive-withdrawal behavior.