KNDy Neurons and the Control of the Gonadotropic Axis in the Midgestation Fetal Sheep.

KNDy neurons, located in the hypothalamic arcuate nucleus, coexpress kisspeptin (Kiss), neurokinin B, and dynorphin and play a crucial role in regulating GnRH/LH secretion in midgestation sheep fetuses. We hypothesize that KNDy-GnRH signaling is established during midgestation, with negative feedback acting through KNDy neurons regulating testosterone levels needed for brain masculinization in male fetuses. We used immunofluorescence histochemistry to assess the effect of chemical castration with the GnRH antagonist degarelix on arcuate KNDy neurons in fetal sheep. Fluorescent in situ hybridization demonstrated the presence of steroid receptors in untreated midgestation fetal kisspeptin neurons. Additionally, unanesthetized cannulated midgestation fetal sheep were used to examine the effects of KNDy peptides on LH secretion and characterize receptor specificity. Treatment of male lamb fetuses with degarelix on day 62 of gestation resulted in significantly decreased plasma LH and testosterone concentrations (P < .05), accompanied by a significant increase in arcuate Kiss neurons (P < .05). In unanesthetized cannulated fetuses, bolus administration of KP-10 (a Kiss receptor agonist) and senktide (NK3 receptor agonist) elicited robust LH release within 15 minutes. Pretreatment with the NK3 receptor antagonist SB222200 blocked the LH response to senktide, whereas P271 (Kiss receptor antagonist) did not affect basal LH or block the LH response to KP-10. Blocking κ-opiate receptor with PF4455242 significantly increased LH release. These results support the hypothesis that KNDy neurons regulate GnRH and gonadotropin secretion in midgestation sheep fetuses, acting as targets for negative feedback to maintain a stable androgen environment crucial for brain masculinization.