Oxytocin and neuroscience of lactation: Insights from the molecular genetic approach

In mammals, lactation is essential for the health and growth of infants and supports the formation of the mother-infant bond. Breastfeeding is mediated by the neurohormone oxytocin (OT), which is released into the bloodstream in a pulsatile manner from OT neurons in the hypothalamus to promote milk ejection into mammary ducts. While classical studies using anesthetized rats have illuminated the activity patterns of putative OT neurons during breastfeeding, the molecular, cellular, and neural circuit mechanisms driving the synchronous pulsatile bursts of OT neurons in response to nipple stimulation remain largely elusive. Only recently have molecular neuroscience techniques for imaging and manipulating specific genetically defined cells been applied to lactating mice. For instance, fiber photometry has revealed the temporal dynamics of the population pulsatile activity of OT neurons in freely moving dams across various lactation stages, while microendoscopy has provided single-cell level insights. In this review, we introduce the neuroscience of lactation with respect to OT neuron activity, discuss findings from molecular neuroscience approaches, and highlight key unresolved questions.