A study in mice reveals how pregnancy hormones influence the brain’s reward system, helping explain why newborns become a mother’s priority.
Using studies in mice, we identified part of the brain circuitry that drives a mother’s urge to interact with her newborn. We found an essential pathway linking a hormone-sensing region of the brain to its reward network.
Activated by the pregnancy hormone placental lactogen and the milk-production hormone prolactin, this pathway helps make caring for a newborn rewarding rather than simply necessary. Remarkably, we were even able to switch that drive on and off experimentally.
We focused on a brain region called the medial preoptic area, known for decades to be a key controller of parenting behaviours. Many of its neurons carry receptors for placental lactogen and prolactin.
In earlier studies, we showed that mice without these receptors in this region were unable to care for their offspring after birth. What remained unclear was exactly how these neurons helped drive parenting behaviour.
Using specialised neuroscience techniques to observe these neurons in living mice, we found they became highly active when females came into close contact with pups. The response was much stronger in mothers than in females that had never given birth, with the biggest surge occurring at the very first meeting.
We then traced where these neurons send their signals. A subset of these neurons connect directly to the brain’s reward system, triggering the release of dopamine – the neurochemical that helps make experiences feel rewarding. Recent advances in neuroscience allowed us to watch dopamine being released in real time as mice interacted with their pups.
When we artificially activated this pathway, female mice that had never given birth behaved much more like new mothers. Faced with a barrier separating them from newborn pups, they climbed over it more quickly and repeatedly returned to the pups.
Interestingly, when we blocked the pathway, the opposite happened. Mice no longer showed the normal dopamine surge when meeting the pups and were slower to engage with them. Removing prolactin receptors from the pathway also reduced mother–pup interactions, while leaving other aspects of maternal care largely unchanged.
These new insights help explain why caring for a newborn becomes such a powerful priority after birth. Prolactin acts through this pathway to tune the brain’s reward system, making time with offspring rewarding rather than simply another task.
Although our work was conducted in mice, the same reward pathways are found in human mothers, with prolactin serving as the key milk-production hormone in all mammals.
Source: The brain rewires itself for motherhood. We now know more about how