RP3V kisspeptin neurons mediate neuroprogesterone induction of the luteinizing hormone surge in female rat

To induce ovulation, neural circuits are sequentially activated by estradiol and progesterone. In female rodents, estradiol-induced neuroprogesterone, synthesized in astrocytes, is essential for the luteinizing hormone (LH) surge and subsequently, ovulation. However, the gonadotropin-releasing hormone (GnRH) neurons do not express the steroid receptors necessary for reproduction: progesterone receptors (PGR) or estrogen receptor- (ER). Steroid information is transduced by rostral periventricular (RP3V) kisspeptin neurons that express ER and PGR and innervate GnRH neurons in the diagonal band of Broca (DBB) and the medial septum. In this study, we tested the hypothesis that estradiol induced neuroprogesterone needed for the LH surge is mediated by kisspeptin. Neuroprogesterone synthesis was inhibited with aminoglutethimide (AGT; s.c.) in 17{beta}-estradiol benzoate (EB)-primed, ovariectomized (ovx) and adrenalectomized (adx) rats. Kisspeptin-10 (20 nmol/{micro}l) was infused into the DBB, trunk blood was collected 53 hours post-EB injection, and serum LH levels were analyzed by ELISA. AGT inhibition of neuroprogesterone synthesis blocked the EB-induced LH surge. Subsequent treatment with either progesterone or DBB kisspeptin-10 infusion restored the LH surge. Kisspeptin restored the LH surge, which was blocked by DBB infusion of kisspeptin receptor (GPR54) antagonist (kisspeptin-234). Finally, knockdown of kisspeptin protein levels in the RP3V with kisspeptin antisense oligodeoxynucleotide (ODN) significantly lowered LH levels in EB-primed rats compared to scrambled ODN, demonstrating the importance of endogenous RP3V kisspeptin for the LH surge. These results support the hypothesis that neuroprogesterone induces both kisspeptin release from RP3V neurons impacting the LH surge.