Predator threat induces behavioral inhibition, pituitary-adrenal activation and changes in amygdala CRF-binding protein gene expression.

Behavioral inhibition (BI) is an adaptive defensive response to threat; however, extreme BI is associated with anxiety-related psychopathology. When rats are exposed to a natural predator they display stress- and anxiety-related behavioral alterations and physiological activation. To develop a preclinical rodent model to study mechanisms underlying human BI and anxiety, we examined the extent to which ferret exposure elicits anxiety-related BI and HPA and amygdala activation of the CRF system. In the first experiment, BI and other behaviors were assessed in the presence or absence of a ferret. In the second experiment, ferret-induced corticosterone release and changes in brain c-fos expression were assessed. In the final experiment, gene chip and quantitative real time-PCR analyses were performed on amygdala tissue from control and ferret-exposed rats. Ferret exposure increased BI and submissive posturing, as well as plasma corticosterone and the number of Fos-positive cells in several brain regions including the amygdala. Gene expression analysis revealed increased amygdalar mRNA for CRF-binding protein, but not the CRF1 receptor, CRF2 receptor or CRF. In rodents, ferret exposure can be used to elicit anxiety-related BI, which is associated with HPA and amygdala activation. Since the amygdala and the CRF system have been implicated in adaptive and maladaptive anxiety responses in humans, these data support use of our rodent model to further investigate mechanisms underlying anxiety-related psychopathology in humans.