Kisspeptin, Neurokinin B, and Dynorphin Expression during Pubertal Development in Female Sheep.

Abstract

Simple SummaryMistiming of puberty onset has negative consequences for humans and livestock. Puberty depends on increased brain secretion of gonadotrophin-releasing hormone (GnRH), which causes pituitary luteinizing hormone (LH) release. Luteinizing hormone then stimulates estrogen release from the ovary and, eventually, the first ovulation. The brain neural systems that control the pubertal increase in GnRH and LH are not completely known. Neurons co-expressing kisspeptin, neurokinin B (NKB), and dynorphin (called KNDy neurons) are critical for puberty, with kisspeptin and NKB stimulating and dynorphin inhibiting LH secretion. Herein, we used female sheep at prepubertal, peripubertal, and postpubertal ages and hypothesized that kisspeptin and NKB would increase, and dynorphin decrease, during the pubertal increase in LH secretion. We observed that kisspeptin and NKB protein and mRNA expression were evident well before the pubertal increase in LH secretion and did not change with age. We saw no change in numbers of dynorphin neurons, but actually saw an increase in the amount of mRNA per neuron at a postpubertal age. We conclude that puberty-associated increases in GnRH and LH secretion occur without significant changes in KNDy peptide expression and suggest that, while critical, KNDy neurons await inputs from other neural systems to trigger puberty onset.The neural mechanisms underlying increases in gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion that drive puberty onset are unknown. Neurons coexpressing kisspeptin, neurokinin B (NKB), and dynorphin, i.e., KNDy neurons, are important as kisspeptin and NKB are stimulatory, and dynorphin inhibitory, to GnRH secretion. Given this, we hypothesized that kisspeptin and NKB expression would increase, but that dynorphin expression would decrease, with puberty. We collected blood and hypothalamic tissue from ovariectomized lambs implanted with estradiol at five, six, seven, eight (puberty), and ten months of age. Mean LH values and LH pulse frequency were the lowest at five to seven months, intermediate at eight months, and highest at ten months. Kisspeptin and NKB immunopositive cell numbers did not change with age. Numbers of cells expressing mRNA for kisspeptin, NKB, or dynorphin were similar at five, eight, and ten months of age. Age did not affect mRNA expression per cell for kisspeptin or NKB, but dynorphin mRNA expression per cell was elevated at ten months versus five months. Thus, neither KNDy protein nor mRNA expression changed in a predictable manner during pubertal development. These data raise the possibility that KNDy neurons, while critical, may await other inputs for the initiation of puberty.