Meeting Abstract
Hypothalamic neurohormones involved in vertebrate reproduction, gonadotropin releasing hormone (GnRH-I) and gonadotropin-inhibitory hormone (GnIH), can vary in peptide cell abundance in accordance with reproductive stage, and concerning GnIH, nest box status in European starlings. Using cell abundance as a proxy for neurohormone activity is informative, but incorporating other information gathered from visualizing these cells may yield a heightened understanding of hormonal dynamics associated with environmental change. We hypothesized that, along with previously reported cell abundance, soma sizes and a proxy for peptide concentrations of cells immunoreactive for GnRH-I and GnIH increased during the beginning and middle of their breeding season as compared to the non-breeding season. We report that the direction of increase follows the same seasonal patterns of previously reported GnRH-I and GnIH cell abundance. Additionally, we hypothesized that, like cell abundance, only GnIH (and not GnRH-I) soma size and peptide concentration would respond to a change in nest box status. However, we found only GnIH peptide concentration and not soma size followed this pattern, and only during the mid-breeding season. Finally, we examined the relationship of the gonadal sex steroid testosterone with GnRH-I and GnIH soma size and peptide concentration. In males, but not females, testosterone was positively correlated with GnRH-I and GnIH factors. In sum, GnRH-I and GnIH soma size and peptide concentration change in accordance with breeding period and, in males, with testosterone, and GnIH peptide concentration changes with nest box status. These details have the potential to offer a more in-depth snapshot of how GnRH-I and GnIH may be functioning.
