Regulation of the Hypothalamo-Pituitary-Adrenal Axis in Pregnancy and Lactation

Physiological and behavioural responses to stress are critical to ensure individual survival in all species. This is even more important when the survival of the offspring depends on parental protection from predators and other environmental challenges. However, exaggerated maternal stress responses and enhanced glucocorticoid secretion can be deleterious to the development of the offspring, with negative impacts on the developing brain, as well as on the provision of maternal care and nourishment. Thus, in both late gestation and lactation, mothers exhibit a period of stress hyporesponsiveness that is regulated by both common and divergent mechanisms that are appropriate for the physiological, hormonal, and behavioural environment of pregnancy and lactation. This chapter will describe our current understanding of the mechanisms in the peripartum period that underlie adaptations of the neuroendocrine stress system—the hypothalamo-pituitary-adrenal (HPA) axis. Changes in central brain structures regulating HPA axis activity and the role of steroid and peptide hormones in maintaining blunted responses to stress will be discussed. The importance of the offspring’s presence and suckling stimulation on the maintenance of reduced stress responses in lactation will also be considered. Finally, implications of this research for postpartum depression and other mood disorders characterized by dysregulated stress responses in human mothers will be examined.