In mammals, puberty onset typically occurs earlier in females than in males, but the explanation for sexual differentiation in the
tempo of pubertal development is unknown. Puberty in both sexes is a brain-dependent phenomenon and involves alterations in the sensitivity of neuronal circuits to gonadal
steroid feedback as well as
gonadal hormone-independent changes in neuronal circuitry.
Kisspeptin, encoded by the Kiss1 gene, plays an essential but ill-defined role in pubertal maturation.
Neurokinin B (NKB) is coexpressed with Kiss1 in the arcuate nucleus (
ARC) and is also important for puberty. We tested whether sex differences in the timing of pubertal development are attributable to sexual differentiation of
gonadal hormone-independent mechanisms regulating hypothalamic Kiss1/NKB gene expression. We found that, in juvenile females,
gonadotropin secretion and expression of Kiss1 and NKB in the
ARC increased immediately following
ovariectomy, suggesting that prepubertal females have negligible
gonadal hormone-independent restraint on their reproductive axis. In contrast, in similarly aged juvenile males, no changes occurred in LH levels or Kiss1 or NKB expression following
castration, suggesting that
gonadal hormone-independent mechanisms restrain
kisspeptin/NKB-dependent activation of the male reproductive axis before puberty. Notably, adult mice of both sexes showed comparable rapid increases in Kiss1/NKB expression and LH secretion following
gonadectomy, signifying that sex differences in the regulation of
ARC Kiss1/NKB neurons are manifest only during peripubertal development. Our findings demonstrate that the mechanisms controlling pubertal activation of reproduction in mice are different between the sexes and suggest that
gonadal hormone-independent central restraint on pubertal timing involves Kiss1/NKB neurons in the
ARC.