UC Berkeley

Stress is a known inhibitor of reproductive function and its associated behaviors. How and why stress acts to influence reproduction have been intensely studied and appear to be extremely varied, though we do not fully understand how these processes operate at the level of the brain. My dissertation work examined the role of the novel neurohormone gonadotropin inhibitory hormone (GnIH) in response to stress and social environment in reproductively active birds. To review the actions of GnIH in brief, GnIH inhibits the activity of gonadotropin releasing hormone (GnRH) neurons in the brain in addition to reducing the release of the gonadotropins luteinizing hormone and follicle-stimulating hormone from the pituitary gland. GnIH also reduces testosterone release from the gonads. Central administration of GnIH can decrease both copulation solicitations in birds and sexual behaviors in rodents. However, how GnIH fluctuates naturally in response to stress and social environment is not well understood. My questions were as follows:

1) Does capture-handling stress affect GnIH, and is there a seasonal effect?

2) Does social environment affect GnIH, and does this vary with breeding stage?

3) Is there a mechanism in place for the stress response to affect reproduction via GnIH? Specifically, are receptors for glucocorticoids expressed in avian GnIH cells? And what are the conservation implications of such neuroendocrine research?

My work is the first to demonstrate the effects of stress (in birds) and social environment (in any organism) on GnIH. My work is also the first to report the co-localization of glucocorticoid receptors in avian GnIH cells, providing a mechanism by which the stress response can influence reproduction at the level of the brain. Because GnIH presence and function are conserved throughout all vertebrates studied, these findings can create new avenues into studies of vertebrate stress and reproductive physiology.