Central Administration of Chicken Gonadotropin-Releasing Hormone-II Enhances Courtship Behavior in a Female Sparrow

Abstract

Like most vertebrates, birds have two forms of gonadotropin-releasing hormone (GnRH). Chicken GnRH-I (cGnRH-I) is released at the median eminence to elicit gonadotropin release; chicken GnRH-II (cGnRH-II) is thought to be non-hypophysiotropic and its function is unclear. Both forms are hypothesized to act as neurotransmitters in the control of reproductive behavior. In the present study, we implanted chronic cannulae aimed at the third ventricle in female white-crowned sparrows (Zonotrichia leucophrys gambelii) to test the effects of both forms of GnRH on copulation solicitation, a female courtship behavior. This behavior can be elicited in captive, estrogen-primed females by playing a recording of male song. We quantified the behavioral response to recorded song 30, 60, and 90 min after intracerebroventricular infusion of cGnRH-I, -II, or saline. cGnRH-II, but not cGnRH-I, increased solicitation behavior compared with saline 30 min after infusion. Under control conditions, responses to the playback diminish from the 30-min to the 90-min time point. Responses after cGnRH-II infusion followed a similar pattern, whereas after cGnRH-I, there was no significant response decrement. cGnRH-I appears to maintain the level of solicitation seen at 30 min after infusion. Our results suggest a behavioral role for cGnRH-II that may be independent of cGnRH-I.