7934 Tac1-expressing cells in the central premammillary nucleus are essential for induction of the pre-ovulatory LH surge

Abstract Disclosure: S. Leon: None. M. Navarro: None. C. Perdices-Lopez: None. I. Velasco Aguayo: None. E. Torres Jimenez: None. D. Garcia-Galiano: None. V.M. Navarro: None. M. Tena-Sempere: None. Infertility/subfertility is a growing challenge in reproductive medicine. The most common cause of subfertility in females is ovulatory dysfunction. Conditions linked with oligo-/anovulation include polycystic ovary syndrome, hypothalamic amenorrhea and premature ovarian insufficiency. However, the central neuro-endocrine defects affecting the pre-ovulatory LH surge that drives ovulation remain ill defined. While hypothalamic GnRH neurons are the major output pathway for the brain control of ovulation, upstream Kiss1 neurons, particularly in the anteroventral periventricular area (AVPV) of the hypothalamus in rodents, are thought to be crucial for the timed activation of GnRH neurons and generation of the preovulatory surge of gonadotropins. Yet, the major upstream regulators of this Kiss1/GnRH pathway are largely unknown. Substance P (SP, encoded by Tac1), a member of the tachykinin (TAC) family that acts via the receptor, NK1R (encoded by Tacr1), has been shown to centrally regulate gonadotropin release, and, according to our initial data, might modulate the pre-ovulatory surge in mice through its direct action on AVPV Kiss1 neurons. We report herein that Tac1-expressing cells in the ventral premammillary nucleus (PMV) become activated during the preovulatory surge, as denoted by co-expression of c-Fos. Moreover, we document here that these neurons project to key reproductive areas, including the rostral preoptic area (rPOA), AVPV, arcuate nucleus (ARC), and the medial posterodorsal amygdala (MePD). Furthermore, the chemogenetic inhibition of Tac1-expressing neurons in the PMV dramatically decreases the magnitude of the pre-ovulatory LH surge, but has no influence on tonic LH pulsatility. Overall, our findings strongly support a relevant stimulatory role of SP originating from Tac1 neurons at the PMV in the generation of the pre-ovulatory surge of gonadotropins, responsible for ovulation. Presentation: 6/1/2024