Neuroendocrine Suppression of Female Courtship in a Wild Passerine: Corticotropin‐Releasing Factor and Endogenous Opioids

Abstract

During emergencies in their natural environments, vertebrates initiate coping mechanisms that redirect behavior away from nonessential activities and towards survival. Reproductive behaviors are suppressed. Evidence from field studies on passerine birds shows that this inhibition may not depend on the suppression of gonadal sex steroids, since during the breeding season they remain elevated despite activation of the stress response. We hypothesize that an alternate, central mechanism mediates the inhibition of reproductive behavior during stress in passerines. In this study, we tested the intracerebroventricular effects of endogenous opioids and corticotropin‐releasing factor (CRF), neuropeptides implicated in the stress response, on courtship behavior in wild‐caught female white‐crowned sparrows. β‐endorphin (β‐EN) significantly inhibited copulation solicitation, an estrogen‐dependent courtship display, 30 min after treatment. Naloxone, an opioid antagonist, enhanced the behavior. CRF caused a suppression of solicitation that was reversible by pretreatment with naloxone, suggesting an intermediary role for endogenous opioids in CRF‐induced suppression of courtship. The effects of β‐EN and CRF on solicitation appear to be independent of any general effects on locomotor activity. These results support our hypothesis that stress neuropeptides orchestrate coping behaviors in wild birds.