Exposure to chronic pregnancy stress reverses peripartum-associated adaptations: implications for postpartum anxiety...

Maternal adaptations, such as decreased anxiety and attenuated stress responsiveness, are necessary to enable successful postnatal development of the offspring. However, there is growing evidence that they are also required to protect the mental health of the mother and that exposure to chronic stress during pregnancy may prevent such adaptations. Overcrowding stress (24 h) and restraint stress (2 × 1 h) were employed on alternate days between pregnancy d 4-16 to examine the impact of chronic pregnancy stress on relevant behavioral, neuroendocrine, and neuronal peripartum adaptations. To determine whether the chronic stress-induced alterations were specific to the peripartum period, we included virgins as controls. Validating the stress procedure, we demonstrated decreased body-weight gain and increased adrenal weight in stressed dams, relative to their nonstressed controls. Chronic stress prevented a number of peripartum adaptations, including basal plasma hypercorticosterone levels, increased oxytocin mRNA expression in the hypothalamic paraventricular nucleus, and anxiolysis. However, chronic stress did not prevent the peripartum-associated decrease in CRH mRNA expression or attenuate corticosterone response to an acute stressor, nor did it affect hypothalamic vasopressin mRNA expression. Illustrating the specificity of these stress-induced changes to the peripartum period, none of these parameters were affected in stressed virgins. Although chronic stress did not alter depression-related behavior, it reversed the response to acute imipramine treatment and increased active maternal behavior in lactation. Thus, prevention of the peripartum-associated increases in basal corticosterone and oxytocin system activity by pregnancy stress reveal two alterations that may increase the risk of postpartum psychiatric disorders, particularly anxiety.