THE PRENATAL AND POSTNATAL INFLUENCE OF HORMONES AND NEUROTRANSMITTERS ON SEXUAL-DIFFERENTIATION OF THE MAMMALIAN HYPOTHALAMUS

This chapter discusses brain structures and functions, which have developed differently in male and female animals. It describes some of the biological causes thatinduce such developmental disparities. A number of functions which are controlled by the brain are expressed differently in male and female mammalian organisms. These functions include the release of gonadotropic hormones from the pituitary gland, male and female sexual behavior, play and social behavior, agonistic behavior, learning behavior, gender-role behavior, and posture during urination. The most obvious functional differences between male and female animals are those involved in reproductive physiology and reproductive behavior. There is a sensitive developmental period in the brain during which sexual differentiation of neural substrates proceeds irreversibly under the influence of gonadal hormones. In the rat this period starts a few days before birth and ends approximately 10 days after birth. Female rats, treated during this sensitive period with androgens or estrogens, will permanently lose the capacity to release gonadotropin-releasing hormone (GnRH) in response to estrogenic stimulation, and will lose the capacity to show female lordosis behavior. The loss of female characteristics is termed “defeminization.” Female rats which are treated postnatally with androgens will develop the capacity to show the complete masculine sexual behavior pattern following administration of testosterone in adulthood. The acquisition of male characteristics is termed “masculinization.” © 1991 Academic Press Inc.