O’BRIEN, Sara; BENTLEY, George E; UKENA, Kazuyoshi; TSUTSUI, Kazuyoshi; WINGFIELD, John C; Univ. of Washington, Seattle; Univ. of Washington, Seattle; Hiroshima Univ., Japan; Hiroshima Univ., Japan; Univ. of Washington, Seattle: Does Testosterone Influence Gonadotropin-Inhibitory Hormone in the Avian Hypothalamus?

Gonadotropin-inhibitory hormone (GnIH) is a recently discovered hypothalamic neuropeptide that influences gonadotropin release. In vitro, GnIH inhibits anterior pituitary release of luteinizing hormone (LH) in a dose-dependent manner. In vivo, GnIH rapidly inhibits GnRH-induced LH release. GnIH neuron size is larger at the end of the breeding season than at other times during the annual cycle. Thus, we have hypothesized a central role for GnIH in the control of seasonal breeding. Little is known about the interaction of GnIH with other reproductive hormones, however. Given the seasonal changes in GnIH neuron size and the large fluctuations in reproductive hormones over the annual cycle, this study focused on testosterone as a possible candidate for the influence of GnIH release. Ten Gambel�s white-crowned sparrows (Zonotrichia leucophrys gambelii) were castrated and then divided into two groups: those that received 2 �10 mm silastic implants of testosterone (T) and those that received blank implants (B). After 20 days on natural spring photoperiod, birds were perfused and brain tissue was collected. GnIH neuron number, size and optical density were assessed via immunocytochemistry (ICC) for GnIH. None of the parameters measured differed between the two groups. These results suggest that testosterone does not feed back to the GnIH system. However, ICC does not provide us with information on the dynamics of GnIH protein production and release. Investigation of GnIH mRNA induction via in situ hybridization will elucidate these dynamics.