Gonadotropin-releasing hormone (GnRH) is produced by neurons of the basal hypothalamus and is essential for the regulation of reproductive function. GnRH containing neurons sit at the top of the hypothalamic-pituitary-gonadal axis and therefore mediate the effects of a number of environmental and homeostatic cues on reproduction. For example, nutritional deprivation has been shown in both experimental paradigms and clinical observations to decrease reproductive function via an inhibition of GnRH release. In addition, some models ascribe a role for a permissive level of nutritional growth needed to trigger the onset of puberty. It is unclear, however, how GnRH neurons acquire a sensitivity to nutritional signals. Our studies are focused on identifiying and characterizing the nutritional and metabolic regulators of reproductive hormone function. Previous studies from our laboratory have indicated that GnRH neurons, in vitro, respond to treatment with IGF-1 with an increase in GnRH mRNA expression that is mediated by the IGF-I receptor. The IGF-1 receptor mediated effects on GnRH promoter activity are mediated by a Ras/Raf/Mek signaling cascade. Erk1/2 activation of AP-1 activates human GnRH promoter activity and is thought to activate mouse GnRH (mGnRH) promoter activity, albeit via a non-classical AP-1 element, in the murine promoter. Recently it has been reported that a neuronal conditional knock out mouse lacking the insulin receptor in the brain resulted in hypothalamic hypogonadotropic hypogonadism suggesting a critical role for the insulin receptors in the brain for the regulation of central reproductive function in vivo. Preliminary results from transient transfections indicating that insulin treatment (30nM) increased GnRH promoter activity in a GnRH neuronal cell line nearly 3-fold when compared to insulin?s effects on a minimal GnRH promoter and that this response was blocked by the MEK inhibitor PD98059. In a fasted mouse paradigm using the mGnRH-LUC reporter mouse, insulin! treatment induced a 2.5 fold activation of mouse GnRH promoter activity. These results in conjunction with the previous reports describe above suggest that insulin plays a regulatory role in GnRH gene expression in vitro and in vivo.