The arcuate nucleus of the hypothalamus (ARC) is central in the neuronal regulation of fertility and reproduction through translating gonadal steroid hormone cues into the GnRH signaling pathway in the brain. Evidence suggests that circulating gonadal steroids play an important role in modulating female reproduction via kisspeptin and gamma-aminobutyric acid (GABA) neurons in the ARC in both development and adulthood. However, the temporal onset of these ARC neurons' sensitivity to gonadal steroids is unknown. Using RNAscope (R) in situ hybridization, we localized androgen receptor (Ar), estrogen receptor alpha (Esr1), and progesterone receptor (Pgr) expression in ARC kisspeptin or GABA neurons of female mice at postnatal day (P)4, P8, P12, P20, and P60. A probe that binds to kiss1 mRNA or vGat mRNA was used to produce signal in kisspeptin or GABA neurons, respectively. In adult, we identified that the vast majority of kisspeptin neurons coexpressed Esr1 (95%) and Pgr (93%), while a smaller proportion coexpressed Ar (66%). Similar proportions of Ar- or Esr1-positive kisspeptin neurons were seen from P4, suggesting that kisspeptin neurons develop adult-like sensitivity to androgen and estrogen in early postnatal life. In contrast, the proportion of Pgr-positive kisspeptin cells in early life was significantly lower than in adulthood, suggesting that progesterone sensitivity develops over time in the ARC kisspeptin population. ARC GABA neurons also colocalized with Ar (70%), Esr1 (64%), or Pgr (85%) in adulthood. GABA neurons continuously expressed Esr1 or Pgr from the postnatal stages to adulthood, while the proportion of Ar-positive GABA neurons gradually increased from P4 (24%) to P20 (59%). These results suggest that while ARC GABA neurons can respond to circulating estrogen and progesterone from early postnatal ages, this same population may become more sensitive to androgens during later postnatal life. Our findings identified the expression patterns of Ar, Esr1, and Pgr by ARC kisspeptin and GABA neurons during early postnatal life. These data provide the understanding for the hormone sensitivity of these populations during early postnatal life, the critical time for the formation and regulation of female reproductive physiology.Esr1 (95%) and Pgr (93%), while a smaller proportion coexpressed Ar (66%). Similar proportions of Ar- or Esr1-positive kisspeptin neurons were seen from P4, suggesting that kisspeptin neurons develop adult-like sensitivity to androgen and estrogen in early postnatal life. In contrast, the proportion of Pgr-positive kisspeptin cells in early life was significantly lower than in adulthood, suggesting that progesterone sensitivity develops over time in the ARC kisspeptin population. ARC GABA neurons also colocalized with Ar (70%), Esr1 (64%), or Pgr (85%) in adulthood. GABA neurons continuously expressed Esr1 or Pgr from the postnatal stages to adulthood, while the proportion of Ar-positive GABA neurons gradually increased from P4 (24%) to P20 (59%). These results suggest that while ARC GABA neurons can respond to circulating estrogen and progesterone from early postnatal ages, this same population may become more sensitive to androgens during later postnatal life. Our findings identified the expression patterns of Ar, Esr1, and Pgr by ARC kisspeptin and GABA neurons during early postnatal life. These data provide the understanding for the hormone sensitivity of these populations during early postnatal life, the critical time for the formation and regulation of female reproductive physiology.
