Towards a better understanding of maternal mental health: the effect of chronic stress on peripartum adaptations

Abstract

Maternal adaptations, such as decreased anxiety and attenuated stress-responsiveness, are necessary to enable successful post-natal protection and nurturance 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 stress during pregnancy may attenuate such adaptations. Therefore, we developed a chronic pregnancy stress paradigm, combining social instability with restraint stress, and examined its impact on numerous peripartum adaptations under basal or chronic imipramine (10mg/kg/d) conditions. To determine whether the alterations where specific to the peripartum period we included virgins as an additional control. We validated the stress procedure by demonstrating decreased body weight gain and increased adrenal weight in stressed dams, and virgins, relative to their respective unstressed controls. Stress exposure prevented a number of peripartum adaptations, including basal plasma hyper-corticosterone levels, increased oxytocin mRNA expression in the hypothalamic paraventricular nucleus (PVN) and anxiolysis. However, none of these parameters were affected in virgins. Maternal behaviour was also elevated in the stressed group compared with controls. While stress exposure did not alter depression-related behaviour in virgins, it reversed the response to acute imipramine treatment in lactation. Interestingly, while the behavioural consequences of stress exposure could be reversed by chronic imipramine treatment, the physiological parameters persisted. Thus, this chronic psychosocial stress paradigm has revealed important consequences of pregnancy stress, which represent novel systems to explore in a clinical environment.