GERLACH, N.M.*; KETTERSON, E.D.; Indiana University, Bloomington; Indiana University, Bloomington: Behavioral responses to a GnRH challenge in 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 (Junco hyemalis), an exogenous dose of GnRH 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 whether a GnRH-induced peak in T leads to detectable changes in behavior. We observed behavior before and after a GnRH challenge, then repeated the challenge 48 hours later to assess its impact on plasma levels of T. For the behavior trial we quantified activity levels, feeding, maintenance (preening), and song for 15 minutes prior to each bird�s receiving an intramuscular injection of either 50 μL of cGnRH1 (500ng/20μL PBS, Sigma L-0637) or a control injection of 50 μL of buffer (PBS). 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 following a second injection of the same type (GnRH or buffer) given previously. There were no observable differences in behavior between GnRH- or control-injected birds at any time period, perhaps because (1) hormonally induced behavioral changes occur later than the peak in T-levels, (2) the brief pulse in T is not sufficient to effect a change in behavior, or (3) the stimulus environment was not appropriate to elicit a difference in behavior.