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

Abstract

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.

Male‐induced early puberty correlates with the maturation of arcuate nucleus kisspeptin neurons in does

“…However, no such difference was found during pubertal development in E2‐treated ovariectomized ewes (OVX + E2), both at the level of Kiss1 transcripts 48,49 and kisspeptin immunoreactivity 49 . The choice of conditions (ovary‐intact vs. OVX + E2 females) could explain the divergence of these outcomes 49 . Our results in ovary‐intact pubescent does during the luteal phase are consistent with the observations of Nestor et al 33 Although in female goats the number of kisspeptin‐immunoreactive neurons seems to be greater during the follicular phase than during the luteal phase, 50 the kisspeptin neuronal network may be sufficiently developed to maintain cyclic ovarian activity in pubescent females exposed to sexually active males.…”

“…In sheep, the number of kisspeptin neurons was higher in the ARC of ovary‐intact pubescent ewes during the early follicular phase (>9 months) compared to prepubescent ewes (5–6 months) 33 . However, no such difference was found during pubertal development in E2‐treated ovariectomized ewes (OVX + E2), both at the level of Kiss1 transcripts 48,49 and kisspeptin immunoreactivity 49 . The choice of conditions (ovary‐intact vs. OVX + E2 females) could explain the divergence of these outcomes 49 .…”

“…In goats, some studies show that NKB is colocalized with most of ARC kisspeptin neurons (97%–99.5%) 31,38 . In sheep, NKB‐immunoreactive fiber density is greater in the ARC of ovary‐intact pubescent ewes during the early follicular phase (>9 months) compared to prepubescent ewes (5–6 months), 33 but not in OVX + E2 females 49 . Nonetheless, NKB could also have a key role during puberty onset.…”

“…49 The choice of conditions (ovary-intact vs. OVX + E2 females) could explain the divergence of these outcomes. 49 Our results in ovary-intact pubescent does during the luteal phase are consistent with the observations of Nestor et al 33 Although in female goats the number of kisspeptin-immunoreactive neurons seems to be greater during the follicular phase than during the luteal phase, 50 the kisspeptin neuronal network may be sufficiently developed to maintain cyclic ovarian activity in pubescent females exposed to sexually active males. Thus, our results support the hypothesis of a key role for ARC kisspeptin in the caprine female pubertal transition.…”

Opioidergic pathways and kisspeptin in the regulation of female reproduction in mammals

“…Our previous study showed that chronic food restriction (negative energy balance) during the pre-pubertal phase caused suppression of ARC Pdyn and Kiss1 expression and subsequent pubertal failure in growth-retarded female rats and that ad libitum feeding (positive energy cues) caused an acute increase in the number of Pdyn-and Kiss1-expressing cells in the ARC, triggering puberty onset in growth-retarded female rats (Majarune et al, 2019). Similarly, Aerts et al (2021) showed pubertal increases in Pdyn and Kiss1, but not Tac3, expression in the ARC of lambs. These findings suggest that dynorphin-KOR signaling and Kiss1 (as components of KNDy neurons) serve as critical regulators of GnRH pulse generation at the onset of puberty in female mammals.…”