Endogenous opioid signalling in the brain during pregnancy and lactation.

During pregnancy, the regulation of several neuroendocrine systems is altered to support the pregnancy and facilitate the transition to motherhood. These adaptations are organised by the mother's brain and include those that serve to optimise foetal growth, protect the foetus(es) from adverse prenatal programming by maternal stress, facilitate timely parturition and ensure the offspring are nourished and cared for after birth. Although pregnancy hormones are important in inducing and maintaining many of these adaptations, their effects are often mediated via interactions with neuropeptide systems in the brain. In particular, endogenous opioids in the maternal brain play key roles in altered regulation of the stress axis, the oxytocin system, the prolactin system and the neural circuits controlling maternal behaviour. Together, these adaptations maximise the likelihood of a successful pregnancy outcome.