The expectant brain: adapting for motherhood

Key Points The expectant brain undergoes many changes to maximize the likelihood of a successful outcome of the pregnancy. These adaptations are driven by pregnancy hormones and ensure adequate nutrient supply to the fetus, protection from maternal stress hormones, appropriate organization of parturition and the delivery of maternal care. Exposure to stress or glucocorticoids during pregnancy can adversely programme the fetuses, making them more susceptible to disease in adulthood. One protective mechanism against this effect involves endogenous-opioid inhibition of the mother's responses to stress in pregnancy, which reduces the exposure of the fetus to maternal glucocorticoids. Increased food intake in pregnancy is permitted by the resetting of central appetite control mechanisms, for example, the emergence of central leptin resistance. This resetting ensures sufficient nutrients for the fetus(es), extra energy for the mother, and a surplus of energy for storage as fat in preparation for lactation. Inhibitory-opioid mechanisms prevent the premature activation of oxytocin neurons (and hence preterm birth) and aid the accumulation of neurohypophysial oxytocin stores. Allopregnanolone, a neuroactive metabolite of progesterone, restrains oxytocin neurons by enhancing the effectiveness of GABA synapses, but also induces opioid inhibition. Dopamine neurons in the hypothalamus inhibit prolactin secretion. Before term, the stimulatory action of prolactin on these neurons is switched off, permitting increased prolactin secretion for the stimulation of lactation and maternal behaviour. Maternal behaviour emerges rapidly after birth. This depends on 'priming' of the neural circuitry that organizes the components of maternal behaviour and the motivation to perform it. Priming involves the action of oestrogen, progesterone and lactogens, particularly in the medial preoptic area. The offspring are protected from harm by a marked increase in maternal aggressiveness soon after birth. This element of maternal behaviour involves multiple neurochemical changes, in particular, increased oxytocin release and decreased activity of serotonin neurons. In humans, withdrawal of the hormones of pregnancy might predispose women to the 'blues' soon after birth, and in vulnerable women might later trigger major puerperal depression. The pregnant female's brain undergoes multiple adaptations that ensure a successful pregnancy, birth and lactation. Brunton and Russell review the mechan