ABSTRACT
The interaction between sex hormones and the brain, in development, may be the basis not only for sex differences in reproduction (menstrual cycle), gender identity (feeling of being male or female) and sexual orientation (heterosexuality, homosexuality), but later in life also for sex differences in the prevalence of psychiatric and neurological diseases in adulthood, changes in central functions in postmenopausal women and age-related neurodegeneration such as Alzheimer’s disease. The proportions of cases are more than 75% women in Rett syndrome, lymphocytic hypophysitis, anorexia and bulimia nervosa and hypnic headache syndrome, and more than 75% men in dyslexia, attention deficit hyperactivity disorder (ADHD), autism, sleep apnea, Gilles de la Tourette syndrome, rabies, Kallman syndrome and Kleine-Levin syndrome (Table 1). Whether sex differences in the brain that arise in development (‘organizing effect’) are indeed the basis for the sex difference in neurological or psychiatric diseases has yet to be established. An alternative mechanism for sex differences in the prevalence of brain disorders is the immediate effect of circulating sex hormone levels (‘activating effect’) as shown in, for example, sleep apnea. Both effects may be mediated by sex hormone receptors. This chapter focuses on the hypothalamus.
