ABSTRACT
Sexually dimorphic regulation of pituitary gonadotropin secretion was postulated in the early 1900s. G. W. Harris and D. Jacobsohn found that male pituitaries could support estrous cycle, mating, pregnancy, and milk production when transplanted into the median eminence region in hypophysectomized adult female rats. They established that the pituitary was not sexually differentiated, but sex differences existed in the brain. N. Takasugi reported that neonatal treatment of female rats with estrogen induced persistent vaginal estrus. He was of the opinion that the neural substrates for the estrogen feedback system were highly sensitive to estrogen in neonatal females, and the development of the estrogen feedback system was irreversibly disturbed by estrogen given neonatally. The concept of sexual differentiation can be applied as well to the organization of the neural substrates for sexual behavior. The presence or absence of androgen during a critical period induces behavioral sexual differentiation.
