Synchronous activation of gonadotropin-reeleasing hormoneGnRH gene transcription and secretion by pulsatile kisspeptin stimulation

Abstract

Pulsatile secretion of hypothalamic gonadotropin-releasing hormone(GnRH) is pivotal for pituitary gonadotrope function. The physiological importance of pulsatile GnRH secretion has been well recognized, but the mechanism underlying GnRH pulse generation remains elusive. We demonstrated rhythmic GnRH gene transcription in single GnRH neurons in coronal slices of the hypothalamic tissue prepared from transgenic mice (postnatal 5-7 days) expressing a GnRH promoter-driven destabilized luciferase reporter (GnRHp-dsLuc). GnRH promoter activity was monitored by a real-time bioluminescence device and GnRH secretion was determined in media collected at 15 min intervals by radioimmunoassay. The basal GnRH promoter activity in each GnRH neuron exhibited irregular and episodic, oscillation, but GnRH neuronal population showed partially synchronized bursts of GnRH transcriptional activity with ~2 hr intervals under the basal condition. Intermittent administration of kisspeptin (10nM, 15 min-on, 45 min-off), a potent GnRH secretagogue, evoked dramatic synchronous activation of GnRH gene transcription together with robust stimulation of pulsatile GnRH secretion. Kisspeptin-evoked GnRH transcription was attenuated in the presence of 15a (GPR54 antagonist) or Go6983 (protein kinase C inhibitor). In summary, synchronous burst of kisspeptin-evoked GnRH transcription in hypothalamic neuronal networks appear to be important for GnRH pulse generation.