Meeting Abstract

59.8  Wednesday, Jan. 6  Age-related differences in HPG axis responsiveness to GnRH challenge in Florida Scrub-Jays WILCOXEN, T. E.*; SCHOECH, S. J.; University of Memphis; University of Memphis twilcoxn@memphis.edu

Baseline concentrations of testosterone vary with age in male Florida Scrub-Jays (Aphelocoma coerulescens). Levels are relatively low in young and old male breeders and reach their highest average levels in birds aged 5 to 8 years. To determine which component of the hypothalamo-pituitary-gonadal (HPG) axis is responsible for these age-based differences, we used gonadotropin-releasing hormone (GnRH) challenges, delivered via intramuscular injection, of 27 male breeders during the 2009 breeding season. We collected an initial blood sample prior to injection, and subsequent samples at 15 and 30 minutes post-injection; thereby allowing assessment of pituitary and gonadal responsiveness by measuring plasma concentrations of luteinizing hormone (LH) and testosterone, respectively. Young birds had the greatest testosterone response to GnRH challenge and the middle-aged birds responded with a lesser, but significant, increase in T relative to the young birds. GnRH challenge did not significantly elevate testosterone in the oldest males. However, illumination of whether this evidence of reproductive senescence reflects a diminished capacity of the gonads or the pituitary awaits assay for LH in the near future.