Maternal brain alterations based on neurotransmitter and hormone receptor distributions over six months postpartum

The long-term impact of pregnancy and post-childbirth hormonal changes on the maternal brain is yet to be fully understood. Here, we monitored 24 postpartum women longitudinally across six time points over the first 24 weeks following childbirth. By means of structural MRI, we investigated how maternal brain volume, over time and compared to nulliparous women, is associated with receptor distribution maps. While appearing to slow down toward the later time points, the voxel-wise gray matter volumes (GMV) continued to increase for at least 24 postpartum weeks, showing, from the start, a significant association with GABA_A and glutamate receptor distributions. The most pronounced increase was observed at three weeks postpartum, compared to childbirth, when the changes were also strongly co-localized with the cortisol, estradiol, and progesterone receptor systems. The volumetric increase from 12 to 24 weeks co-localized with areas of higher oxytocin receptor density. Compared to nulliparous controls, the maternal brains exhibited persistently smaller GMV in the amygdala, the hippocampus, the putamen and the SMA across the entire observation period. In the later postpartum phase, smaller volumes in the left hippocampus, the parahippocampal gyrus and the amygdala were found to be linked to reduced hostility toward the infant. The sustained, receptor-specific brain adaptation throughout the postpartum period was found to be complemented by the experience of maternity, likely mediated by oxytocin release. Given the robust link between these brain alterations and the GABA_A and glutamate receptor distributions, our findings indicate a possible role of the excitation-inhibition balance in postpartum mood regulation.