7441 KNDy Neurons and the Control of the Gonadotropic Axis in Midgestation Fetal Sheep

Abstract Disclosure: R. Amodei: None. S.S. Jonker: None. K. Gribbin: None. E. Lazen: None. C.T. Estill: None. C.E. Roselli: None. Recent evidence suggests that the neuropeptide kisspeptin (Kiss) plays a role to activate and regulate the male reproductive axis to secrete LH and testosterone during a time in gestation critical for brain sexual differentiation. KNDy neurons, an acronym for Kiss neurons that co-express neurokinin B (NKB) and dynorphin (Dyn), regulate pulsatile GnRH/LH secretion and are present in the hypothalamic arcuate nucleus of midgestation sheep fetuses. Notably, KNDy neurons are more abundant in female than in male fetuses. We hypothesize that KNDy-GnRH signaling is established during midgestation and that negative feedback mediated through KNDy neurons serves to regulate levels of testosterone needed for brain masculinization. In the current study, we used immunofluorescence histochemistry to assess the effect of testosterone manipulations on the number of arcuate Kiss neurons in male and female fetuses. In addition, we employed unanesthetized cannulated midgestation fetal sheep to test the effects of KNDy peptides on LH secretion and characterize receptor specificity in a real-time physiological context. We found that biweekly administration of testosterone propionate to the dam from Day 30–58 of gestation significantly increased (P < 0.05) plasma testosterone concentrations, which resulted in a significant decrease (P < 0.05) in both mean plasma LH concentrations and the number of arcuate Kiss neurons in female lamb fetuses. Conversely, chemical castration of midgestation male fetuses by treatment with the GnRH antagonist degarelix from day 60 – 90 of gestation resulted in a significant decrease (P < 0.05) in mean plasma LH and testosterone concentrations that was accompanied by a significant increase (P < 0.05) in the number of arcuate Kiss neurons. In unanesthetized fetuses, we found that bolus administration of both KP-10 (Kiss agonist) and senktide (NKB agonist) elicited a robust release of LH within 15 min. Treatment with the NK3 receptor antagonist SB222200 effectively blocked the senktide response, whereas the Kiss1 receptor antagonist P271 appeared to have an effect in males only. Blocking κ-opiate receptor (KOR) with a bolus injection of the KOR antagonist PF4455242 resulted in a significant increase in LH release and enhanced the stimulatory effect of senktide. These results support the hypothesis that KNDy neurons play a regulatory role in GnRH and hence gonadotropin secretion in sheep fetuses and serve as targets for negative feedback in males for maintaining a stable androgen environment crucial for brain masculinization. Supported by NIH Grant OD11047 to CER. Presentation: 6/1/2024