Beyond lactation: Central oxytocin in maternal mental health and disease

This review summarizes the literature on the bursting of oxytocin (OT) neurons during lactation, their downstream mechanisms of action in the brain, and potential implications for this neuropeptide on maternal mental health. We describe how OT bursts likely affect various brain areas, each containing unique compositions of OT fibers, OT receptors (OTRs), and OTR-expressing cell types. Burst firing of OT neurons leads to non-linear OT secretion and, in turn, downstream molecular pathways following OTR activation also appear non-linear. Such a nested, switch-like relationship suggests that OT bursts mediate profound changes in maternal brain function. In line with this hypothesis, most human studies report that breastfeeding and the associated OT response to suckling have protective effects against postpartum depression (PPD). Conversely, PPD can negatively affect breastfeeding success. We scrutinize mechanistic pathways that may contribute to these interactions and propose direct pathways for interactions between the OT and the stress system, which may play a role in PPD pathophysiology. We also speculate about indirect pathways involving sensorimotor areas, which are optimized by the OT system to prevent frustration and subsequent negative stress effects on caregiving. Finally, we analyze publication trends and study types, identifying a surge in breastfeeding research in recent years that is not reflected in the animal literature. Most studies examine OT, breastfeeding, and related pathologies in isolation, which highlights the need for more holistic approaches in both human and animal research.