Functional sex differences ('sexual diergism') of central nervous system cholinergic systems, vasopressin, and hypothalamic-pituitary-adrenal axis activity in mammals: a selective review

Sexual dimorphism of the mammalian central nervous system (CNS) has been wi dely documented. Morphological sex differences in brain areas underlie sex differences in function. To distinguish sex differences in physiological fu nction from underlying sexual dimorphisms, we use the term, sexual diergism , to encompass differences in function between males and females. Whereas t he influence of sex hormones on CNS morphological characteristics and funct ion of the hypothalamic-pituitary-gonadal axis has been well-documented, li ttle is known about sexual diergism of CNS control of the hypothalamic-pitu itary-adrenal (HPA) axis. Many studies have been conducted on both men and women but have not reported comparisons between them, and many animal studi es have used males or females, but not both. From a diergic standpoint, the CNS cholinergic system appears to be more responsive to stress and other s timuli in female than in male mammals; but from a dimorphic standpoint, it is anatomically larger, higher in cell density, and more stable with age in males than in females. Dimorphism often produces diergism, but age, hormon es, environment and genetics contribute differentially. This review focuses on the sexual diergism of CNS cholinergic and vasopressinergic systems and their relationship to the HPA axis, with resulting implications for the st udy of behavior, disease, and therapeutics. (C) 1999 Elsevier Science B.V. All rights reserved.