The effects of estradiol on gonadotropin-releasing hormone neurons in the developing mouse brain.

The hypothalamic-pituitary-gonadal (HPG) axis plays a critical role in the control of reproduction. Two key hormonal components of the HPG axis are gonadal steroids and gonadotropin-releasing hormone (GnRH). Gonadal steroids are known to organize the development of neural substrates which control adult reproductive behavior; GnRH is required for normal reproductive structure and function. The possibility that gonadal steroids may produce organizational changes in the pattern of GnRH staining observed in the brain is investigated through the use of injections of estradiol to neonatal mice and subsequent GnRH immunocytochemistry at 2 months of age. Our results indicate that the number of GnRH-immunoreactive (GnRH-ir) cells is normally lower in females than males. Estradiol did not affect the number of GnRH-ir cells in females, but significantly increased the number of GnRH-ir cells in males, suggesting that early exposure to estradiol results in masculinization of the GnRH axis of males.