Critical Periods During Development: Hormonal Influences on Neurobehavioral Transitions Across the Life Span

Abstract

Hormones exert powerful influences on mammalian nervous system development, particularly during developmental transitions associated with a change in reproductive state, including the perinatal period of sexual differentiation, puberty, pregnancy and lactation, and reproductive aging. This chapter focuses on the influences of gonadal steroid hormones, their sites and mechanisms of action, and behavioral outcomes during these reproductive transitions in mammals. The major emphasis of this chapter is on organizational influences of gonadal steroid hormones – that is, how early life exposures to hormones program neural and behavioral phenotypes expressed later in life. Organizational hormones, both endogenous and exogenous (such as endocrine disrupting chemicals), alter developmental trajectory, often irreversibly, and they program sensitivity and responsiveness of the nervous system to hormones during subsequent developmental transitions. Because hormonal influences during later periods of development depend to a large extent on hormonal events that occurred during earlier periods of development, the organizational effects of hormones are compounded over the lifespan. Thus, the overarching premise of this chapter is that hormonal life history underlies much of the complexity that characterizes individual differences in neural, behavioral, and other physiological responses, not only to endogenous hormones, but also to endocrine disruptors and hormonal therapies.