Sexual differentiation of hypothalamic Kiss1 neurons
The status of the neuroendocrine reproductive axis differs between various stages of development and adulthood, and also differs between the sexes, including earlier onset of sexual maturation in females than males and the ability to generate a preovulatory gonadotropin surge in adult females but not adult males. The reproductive axis is controlled by various hormonal and neural pathways that converge upon forebrain GnRH neurons, and many of the developmental and sex differences in the reproductive axis likely reflect differences in the afferent circuits and factors that regulate GnRH neurons. Recently, the neuropeptide kisspeptin, encoded by the Kiss1 gene, has been implicated as an important regulator of GnRH neurons. Accumulating evidence supports a critical role of kisspeptin signaling in the brain at different stages of life, including puberty and adulthood. It was also recently determined that Kiss1 neurons in the hypothalamus are sexually dimorphic, and that sexual differentiation and development of the Kiss1 system is regulated by sex steroid signaling at critical periods of development. Moreover, I recently found that sex differences in at least one Kiss1 population is age-dependent, being present at only certain developmental stages. Although the exact function(s) of sexual dimorphisms in Kiss1 neurons is not entirely known, it is likely that sex differences in hypothalamic kisspeptin signaling relate to known sex differences in puberty onset and/or the ability to display a gonadotropin surge in adulthood.