329. IS THERE VARIATION IN THE LEVEL OF INPUT OF KISSPEPTIN TERMINALS ONTO GnRH NEURONS ACROSS THE EQUINE OESTROUS CYCLE?

Abstract

Kisspeptin (KP) plays a key role in reproductive function including the regulation of gonadotrophin releasing hormone (GnRH) and luteinising hormone (LH) secretion in many species but little is known about its role in the mare. In this study, we examined the location of KP-producing neurons in the brain of the mare, their potential interactions with GnRH neurons, and temporal changes in their expression across the oestrous cycle. Mares (n = 3/group) were killed at oestrus (just prior to ovulation), mid-dioestrus, and late dioestrus and the head was perfusion fixed with paraformaldehyde, and hypothalamus collected. Coronal sections (40 μm) were used for dual-label immuno-stained for KP & GnRH. The majority of KP-immunoreactive (-ir) neurons were located in the arcuate nucleus/median eminence (especially mid and caudal regions), and periventricular nucleus. There was a trend (P = 0.09) towards increasing numbers of KP-ir neurons across the cycle. GnRH-ir neurons, located primarily in the arcuate nucleus (especially mid arcuate), as well as the preoptic area, did not change in number across the cycle. Numerous interactions between KP and GnRH neurons were observed, primarily in the arcuate nucleus; KP fibres interacting with GnRH cell bodies, fibre-fibre interactions between KP and GnRH, and GnRH fibres interacting with KP cell bodies. Overall we found KP inputs to 32% of GnRH-ir cells, but the number of these interactions did not vary across the oestrous cycle. This study has confirmed the reciprocal innervation between KP & GnRH neurons in the mare. Although we did not detect variation in the degree across the oestrous cycle this may reflect the sample size issues inherent to equine research.