Evidence of kisspeptin receptor expression in GnRH neurons in the preoptic area and arcuate hypothalamic nuclei in cycling buffaloes

Our previous study reported the expression of kisspeptin in the preoptic area (POA) and arcuate nucleus (ARC) of the hypothalamus of cycling buffalo cows. In ruminants, POA and ARC are the main hypothalamic nuclei through which kisspeptin acts on the hypothalamic-pituitary-gonadal axis, due to their stimulation of gonadotropin releasing hormone (GnRH) secretion. In many species, kisspeptin activates GnRH neurons via its receptors (KISS1R or GPR54). The present study was designed to explore the expression of KISS1R by GnRH neurons in the POA and ARC hypothalamic nuclei in buffalo cow brains by double-labeling immunohistochemistry. In both the POA and ARC areas, KISS1R immunoreactivity (ir) was detected in the nucleus and cytoplasm of neuronal soma and some glia. GnRH-ir was found as granular formations in the cytoplasm of neuronal soma. The KISS1R-ir neuron population in the POA was the same as in the ARC (93%), however, the GnRH-ir neuron population in the POA (64%) trended lower than in the ARC (73%) (P>0.05). The double-labeling immunohistochemistry showed that all observed GnRH-ir neurons were co-localized with KISS1R-ir. These findings present evidence of kisspeptin receptors in the GnRH neurons in buffalo POA and ARC areas and suggest that kisspeptin has a functional role in GnRH release in buffalo.