The Two Populations of Kisspeptin Neurons Are Involved in the Ram-Induced LH Pulsatile Secretion and LH Surge in Anestrous Ewes

Abstract

Exposure to a ram during spring stimulates luteinizing hormone (LH) secretion and can induce ovulation in sexually quiescent ewes ("ram effect"). Kisspeptin (Kiss) present in the arcuate nucleus (ARC) and the preoptic area (POA) is a potent stimulators of LH secretion. Our aim was to investigate whether Kiss neurons mediate the increase in LH secretion during the ram effect. With double immunofluorescent detection, we identified Kiss neurons (Kiss IR) activated (Fos IR) by exposure to a ram for 2 hours (M2) or 12 hours (M12) or to ewes for 2 hours (C). The density of cells Kiss + Fos IR and the proportion of Kiss IR cells that were also Fos IR cells were higher in M2 and M12 than in C in ARC (P < 0.002) and POA (P < 0.02). In ARC, these parameters were also higher in M12 than in M2 (P < 0.02 and P < 0.05). Kiss antagonist (P234 10-6M) administered by retrodialysis in POA for 3 hours at the time of introduction of the ram reduced the amplitude of the male-induced increase in LH concentration compared with solvent (P < 0.02). In ARC, P234 had a more limited effect (P < 0.038 1 hour after P234) but pulse frequency increased less than after solvent (P = 0.07). In contrast, Kiss antagonist (P271 10-4M) infused in ARC but not POA 6 to 18 hours after introduction of the ram prevented the LH surge in the ewe (0/6 vs 4/5 and 4/6 in C). These results suggest that both populations of Kiss neurons are involved in the ram-induced pulsatile LH secretion and in the LH surge.

Arcuate nucleus kisspeptin response to increased nutrition in rams

“…Our study showed a response potentially within 2 hours with mean LH significantly greater in supplemented animals at this time. Importantly, supplemented feed effects in male sheep are far more subtle and variable between animals -consistent with our relatively small changes in KNDy neurons -than other stimuli, such as the ram effect (De Bond et al 2013;Fabre-Nys et al 2017). This variability is evident in our kisspeptin-fos data, which only represents a single point in time and unfortunately cannot be directed paired to the overall LH activity during each period.…”

“…Evidence further suggests that kisspeptin neurons may be the 'missing link' between HPG activity and nutritional cues. KNDy neurons are known to mediate environmental effects on reproductionthey are involved in the 'ram effect', a phenomenon where ewes show a surge in HPG activity when presented with a novel ram (De Bond et al 2013;Fabre-Nys et al 2017). Importantly, kisspeptin also seems to be involved in responses to nutritional signals, particularly in rodents, where several lines of evidence have been published: i) fasting decreases Kiss mRNA and central administration of kisspeptin reverses fasting-induced inhibition of GnRH secretion (Castellano et al 2005); ii) kisspeptin neurons apposite to GnRH neurons possess insulin, leptin and ghrelin receptors (Qiu et al 2011;Cravo et al 2013;Frazao et al 2014;Qiu et al 2015); iii) leptin-deficient ob/ob mice have lower levels of Kiss1 mRNA in the ARC, compared to wild-type controls, and the peripheral administration of leptin reduces this effect (Smith et al 2006); iv) kisspeptin also interacts with the insulin signalling pathway in the hypothalamus, as evidenced by diabetic rats having diminished expression of Kiss1 mRNA, an effect that can be reversed with insulin therapy (Castellano et al 2006); and v) impairment of kisspeptin signalling decreases metabolism and increases obesity and glucose intolerance (Tolson et al 2014).…”

Optogenetic stimulation of kisspeptin neurones within the posterodorsal medial amygdala increases luteinising hormone pulse frequency in female mice

“…Kisspeptin and the amygdala have been shown to be critically involved in the integration of olfactory cues with the promotion of sexual behaviour. Lesioning of the MePD results in a diminution of sexual partner preference in rodents and, in the “ram effect”, where the introduction of a sexually active ram can overcome reproductive inactivity in anoestrous ewes, the resurgence of functional LH pulsatility coincides with an increase in Kiss1 neurone activity (FOS) in the ARC, POA and MeA . Our previous study using pharmacological activation of MePD Kiss1 neurones with the DREADD (Designer Receptors Exclusively Activated by Designer Drugs) methodology built upon previous understanding of the facilitatory role of the MePD in sexual behaviour.…”

Facing the Challenges of Neuropeptide Gene Knockouts: Why Do They Not Inhibit Reproduction in Adult Teleost Fish?

“…Since the discovery of the link between mutations in the human gpr54 and isolated hypogonadotropic hypogonadism (de Roux et al, 2003 ; de Roux, 2006 ), the kisspeptins have become a key to the central dogma of neuroendocrine regulation of mammalian reproduction (Figure 1 ). Critical work in several mammalian species has now established that specific kisspeptin neuronal populations directly control Gnrh neurons to regulate Lh release (Clarkson and Herbison, 2009 ; Fabre-Nys et al, 2017 ). In vivo and in vitro studies in fish showed that exogenous kisspeptin peptides could variably enhance Lh release, depending on form and species (Espigares et al, 2015 ; Zmora et al, 2015 ).…”