UC Berkeley

Gonadotropin-inhibitory hormone (GnIH) is a neuropeptide that typically acts in the hypothalamic-pituitary-gonadal (HPG) axis to inhibit reproductive activity and sociosexual behaviors. GnIH is synthesized in the brain and in the gonads, where it can act via its cognate receptor. However, immunohistological evidence in songbirds also shows GnIH projections towards the brainstem1. I propose that GnIH can act within the spinal cord and possibly on a variety of organs to induce rapid behavioral and physiological changes in response to environmental cues. I hypothesize that the hypothalamus directly innervates the gonads via the spinal cord to rapidly regulate steroid synthesis. I first used immunohistochemistry and PCR to provide a description of GnIH and its receptor in the zebra finch (Taeniopygia guttata) spinal cord. I then investigated potential roles and mechanisms of action of GnIH in the spinal cord of European starlings (Sturnus vulgaris) and zebra finches. I found that seasonal changes in daylength correlated with immunoreactive GnIH and its counterpart, gonadotropin-releasing hormone (GnRH), quantity in wild-caught European starling spinal cord. Food restriction and a sickness challenge caused significant behavioral changes but did not correlate with GnIH-immunoreactive quantity nor measured gene expression levels in zebra finches. These results hint at a novel pathway for neuropeptide action in vertebrates. The mechanisms of action of GnIH in the avian spinal cord are still unclear. However, these three chapters provide the first evidence of reproductive neuropeptides in the avian spinal cord and open exciting new paths for research.