Differential effects of two corticotropin-releasing factor antagonists on conditioned defeat in male Syrian hamsters (Mesocricetus auratus).

The purpose of the present study was to determine whether corticotropin-releasing factor (CRF) is involved in mediating the expression of conditioned defeat in male Syrian hamsters. The present study examined the effects of two different competitive CRF receptor antagonists on the expression of conditioned defeat. Specifically, Experiment 1 examined whether peripheral administration of CP-154,526, a specific non-peptide CRF1 receptor antagonist, would reduce the expression of conditioned defeat. Experiment 2 examined whether D-Phe CRF(12-41), a nonspecific CRF1/CRF2 receptor antagonist, infused directly into the brain, would reduce the expression of conditioned defeat. The results revealed that i.p. injections of CP-154,526 did not reduce the expression of conditioned defeat, whereas i.c.v. injections of D-Phe CRF(12-41) successfully reduced the expression of conditioned defeat. The duration of submissive/defensive behaviors in hamsters that received the high dose of D-Phe CRF(12-41) was significantly less than that exhibited by animals that received a vehicle control. The present data suggest that central CRF may be involved in mediating the expression of conditioned defeat and other behavioral responses to stressful stimuli.