Endocrine Abstracts

JOINT3133

Gonadotropin-releasing hormone (GnRH) is the master regulator of the hypothalamic-pituitary-gonadal (HPG) axis, orchestrating reproductive function through its pulsatile and surge release patterns. While kisspeptin has been extensively studied as a primary excitatory input to GnRH neurons, the precise mechanisms regulating GnRH pulsatility remain debated. We have previously proposed a theoretical model of the Kisspeptin/nNOS/GnRH (KiNG) network as a critical regulatory circuit, in which neuronal nitric oxide (NO) acts as a dynamic modulator of GnRH secretion—opposing kisspeptin’s excitatory drive and providing an essential “OFF” signal for pulse generation. This study aimed to experimentally validate the KiNG network, examining the interplay between kisspeptin, NO, and GnRH neurons in the preoptic hypothalamic area, in shaping the pulsatile and surge release of GnRH/lH. By employing a combination of neuroanatomical, genetic, chemogenetic, and pharmacological approaches, including a novel viral tool for highly sensitive NO/cGMP detection, we extensively assessed the functional role of NO signaling in GnRH pulse generation. Our study reveals the existence of a functional network formed between the nNOS-expressing neurons of organum vasculosum of the lamina terminalis (OV) and the median preoptic nucleus (MePO), and the kisspeptin and GnRH neurons. Kisspeptin directly stimulates GnRH neurons while simultaneously engaging nNOS neurons to induce NO release. NO, in turn, is necessary to fine-tune the kisspeptin response, shaping both the GnRH pulse and surge. Our findings reveal that NO production from nNOS neurons is not merely a modulatory factor but an essential component of the network, acting as a gatekeeper for the dynamic regulation of GnRH secretion in a cycle- and sex-dependent manner. This study provides experimental validation of the KiNG network as a fundamental mechanism governing GnRH/lH pulsatility. By acting as the Yin to kisspeptin’s Yang, NO ensures the proper balance between excitation and inhibition, allowing for the precise control of reproductive hormone release. Understanding this interplay offers new perspectives on the neuroendocrine control of fertility and potential targets for reproductive disorders.