Meeting Abstract
At the termination of the breeding season, many bird species abandon exclusive territories and join winter flocks. This seasonal shift in behavior has profound fitness implications, but the neuroendocrine mechanisms that promote seasonal flocking are not well understood. Immunocytochemical data suggest that two peptides, Ile8-oxytocin (OT; or mesotocin) and corticotropin-releasing hormone (CRH) may be important modulators of seasonal flocking. In sparrows, seasonal flocking is associated with increased OT and CRH-immunoreactive fiber density in multiple forebrain areas and in the winter, flocking species have a greater number of hypothalamic cells that colocalize both peptides. To experimentally evaluate how these neuropeptide systems mediate seasonal flocking, we conducted peripheral peptide manipulations in the dark-eyed junco, a winter-flocking sparrow. Wintering juncos were peripherally injected with saline or an OT receptor antagonist (OTA) and were then exposed to either a familiar flock or empty aviary. We labeled tissue for OT, CRH, and c-Fos. Exposure to a flock significantly increases the neural activity of hypothalamic OT neurons in both males and females, irrespective of drug treatment. There was a significant effect of sex and a significant interaction of sex*drug on the activity of hypothalamic CRH neurons. Females have greater CRH neuron activity overall, and there is a female-specific increase in CRH neuron activity in OTA-treated animals. Our date support the hypothesis that OT and CRH may act in concert to promote winter flocking – we find that OT cells are socially responsive and that CRH neuron activity is modulated by OT receptor activation.
