Gonadotropins and Progestogens: Obligatory Developmental Functions during Early Embryogenesis and their Role in Adult Neurogenesis, Neuroregeneration and Neurodegeneration

Abstract

IntroductionHormones of the hypothalamic-pituitary-gonadal (HPG) axis are well known for their roles in reproduction. However, sex hormones have roles far beyond the regulation and coordination of reproduction; they also control the entire molecular process of life from the conception of the embryo through its development into an adult and finally its demise during senescence [1]. This recent understanding of the ''big picture,'' that is, of how HPG hormones regulate life processes, has gathered support from studies identifying the function of reproductive hormones in embryonic development [2][3][4][5], as well as from studies into the extrareproductive functions of HPG hormones in the postreproductive physiology of mammals (reviewed in [6]).This chapter describes our current, albeit incomprehensively small, knowledge of how reproductive (pregnancy) hormones direct growth and development during embryogenesis. It also describes the requirement for these reproductive hormones during adult life, and how the age-related dysregulation in the signaling of these hormones drives neurodegeneration and cognitive decline during senescence. Hormonal Regulation of Human Embryogenesis The Missing LinksEmbryogenesis is a complex coordinated series of molecular and cellular changes that takes place within a well-defined internal environment. Human embryogenesis is orchestrated by a complex array of endocrine signals that commences with conception, is followed by the growth and development of the zygote into a blastocyst, its implantation into the endometrium, and the subsequent growth and development of the blastocyst into the neonate. Following conception, the Hormones in Neurodegeneration, Neuroprotection, and Neurogenesis.