Hormonal differentiation of the developing central nervous system with respect to patterns of endocrine function

Abstract

Three types of sexual cycles are found in mammals. First, the life-cycle—puberty, adulthood, senility; secondly, the breeding season; and thirdly, the oestrous or menstrual cycles. The first two types of cycle are to be found in both male and female mammals, while the third type is found in females alone . Since the early embryo is sexually undifferentiated, it is of interest to see what factors are responsible for bringing about the development of the short and rhythmic oestrous and menstrual cycles in the female mammal, but the steady-state, arhythmic pattern of activity in the male mammal. Relatively recent work has shown that: ( a ) the oestrous and menstrual rhythm is essentially dependent on some neural mechanism in the brain, probably situated in the hypothalamic-preoptic region, and ( b ) that the factors responsible for the development of this neural mechanism in the brain of the female, but not in the male, are basically similar to the factors that bring about the development of the Müllerian duct system in the genetic female and the Wolffian duct system in the genetic male.