Meeting Abstract

S6-1.3  Saturday, Jan. 5  Gonadotropin-inhibitory hormone: A synopsis BENTLEY, GE*; MCGUIRE, N; CALISI, RM; PERFITO, N; UBUKA, T; UC Berkeley gb7@berkeley.edu

Gonadotropin inhibitory hormone (GnIH) was discovered 8 years ago in birds. Its identification raised the possibility that gonadotropin releasing hormone (GnRH) is not the sole hypothalamic neuropeptide that directly influences pituitary gonadotropin release. Our initial studies on GnIH focused on the avian anterior pituitary as the only physiological target of GnIH, and we now have several lines of evidence that GnIH directly inhibits pituitary gonadotropin synthesis and release. Our histological studies on projections from hypothalamic GnIH neurons subsequently implied direct actions of GnIH within the brain and in the periphery. In addition to actions on the pars distalis via the median eminence, GnIH axons and terminals are present in the pars nervosa and multiple brain areas in birds. GnIH receptor is strongly expressed in the avian brain as well as in the pituitary. Furthermore, we have demonstrated the presence of GnIH and its receptor in avian gonads. Thus, GnIH can act directly at multiple levels: within the brain, on the pituitary and in the gonads. This synopsis will provide an overview of the known levels of GnIH action. In addition, GnIH effects upon physiology and behavior will be discussed, with an emphasis on the regulation of the timing of breeding in avian species. Environmental and physiological factors that are involved in GnIH regulation will be examined. Finally, we present data on our analyses of the apparent conserved properties of GnIH:GnRH interactions in multiple vertebrate species.