GERLACH, N.M.**; KETTERSON, E.D.; Indiana University, Bloomington; Indiana University, Bloomington: Behavioral responses to a GnRH challenge in captive male dark-eyed juncos (Junco hyemalis)

This study examined the role of Gonadotropin-releasing hormone (GnRH) in eliciting courtship behavior in a male songbird. GnRH is a peptide produced by the hypothalamus that stimulates secretion of gonadotropins from the pituitary. In dark-eyed juncos, an intramuscular injection of 50 �L of cGnRH1 (500ng/20�l PBS) leads to a temporary spike in plasma testosterone (T) ca. 30 minutes post-injection; levels of T return to baseline levels by 60 minutes post-injection. We investigated male juncos in reproductive condition and asked if a GnRH-induced peak in T leads to detectable changes in behavior. We observed the behavior of males before and after they received injections of GnRH or an equivalent amount of buffer (PBS). We quantified activity, feeding, maintenance, and song for 15 minutes prior to each bird receiving an injection. We then observed behavior for 15-minute intervals at 30 and 60 minutes post-injection while the males were visually isolated from other juncos and at 90 minutes post-injection in the presence of a female. To assess plasma levels of T, we collected blood samples two days later, prior to and 30 minutes after a second injection of the same type (GnRH or buffer) given previously. Plasma testosterone levels were significantly higher in males given GnRH injections. However, there were no observable differences in behavior between GnRH- or control-injected birds at any time period, nor was there any correlation within treatment groups between plasma T and rates of behavior. This may be because hormonally-induced behavioral changes occur later than the peak in T-levels, because the pulse in T is not sufficient to effect a change in behavior, or because the stimulus environment was not appropriate to elicit a differential change in behavior.