- The hypothalamic neuropeptide kisspeptin (Kiss-1) acts as a central component of the reproductive axis. A critical factor in pubertal progression and normal reproduction, this peptide is an afferent stimulator of gonadotropin-releasing hormone (GnRH), and is responsive to gonadal steroids, integrating steroid hormone signals and modulating GnRH secretion accordingly. Kiss-1 exhibits a sexually dimorphic expression pattern, found in neurons of the arcuate (Arc) nuclei in both male and female rodents, and in the anteroventricular periventricular (AVPV) nuclei in females. In females, estradiol (E2) differentially regulates kiss1 expression in arcuate and AVPV Kiss-1 neurons, inhibiting kiss1 expression in the arcuate, while inducing it in the AVPV. Both characterized nuclear receptor subfamily isoforms, ER-α (esr1) and ER-β (esr2), have been localized to Kiss-1 neurons, and additional evidence suggests that rapid, non-genomic estrogen actions may also exert effects on these cells. Previous in vivo studies implicate ERα as crucial for the stimulatory effect of E2 in the AVPV, while multiple mechanisms may act to inhibit kiss1 expression in the arcuate. To explore in more detail the respective contribution of ER-α and ER-β on expression of kiss1, our laboratory has generated two immortalized cell lines, KTaR-1 and KTaV-3, representative models of the arcuate and AVPV Kiss-1 populations, respectively. Preliminary results indicate that that basal expression of esr1 is higher in KTaR-1 cells relative to KTaV-3, whereas esr2 basal expression is not different between the two lines. Quantitative PCR reveals that both the ER –β selective agonist (2,3-bis(4-Hydroxyphenyl)propionitrile (DPN)) and the ER-α selective agonist (propylpyrazole triol (PPT)) in KTaR-1 cells suppress kiss1 expression after 4 hours, with a return to baseline after 24 hours, with a far more potent repression by the ER-α ligand. Both DPN and PPT exhibited stimulatory effects on the kiss1 expression of KTaV-3 cells after 4 hours, however, the ER –β selective agonist, DPN, influenced a more prominent increase in expression. These results implicate ER-α as the predominant nuclear receptor isoform responsible for the repressive effects of E2 in Kiss-1 arcuate neurons, and ER –β as the predominant isoform responsible for the stimulatory effect of E2 in Kiss-1 AVPV neurons.