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LONDON — Scientists in the United Kingdom have discovered that hormones produced during pregnancy can “rewire” the brain to prepare for motherhood, even before they give birth. Francis Crick Institute researchers found that the hormones estrogen and progesterone stimulate specific neurons in the brain to activate maternal instincts. The findings challenge the previous belief that hormones released during childbirth primarily trigger these maternal behaviors.
It was observed previously that virgin female rodents didn't engage much with offspring. However, mothers would dedicate a significant portion of their time to caring for their young. Some past studies have shown that even rats that have given birth through Caesarean section, and virgin mice exposed to pregnancy hormones, displayed maternal behaviors. This hinted that the hormonal shifts during pregnancy, not just after childbirth, play a pivotal role in igniting these instincts.
In this new study, researchers found that female mice started demonstrating increased parental behaviors during the late stages of their pregnancies, irrespective of their exposure to pups.
The study identified a specific group of nerve cells, known as galanin-expressing neurons, located in the medial preoptic area (MPOA) of the hypothalamus, a brain region linked to parenting. Estrogen was found to reduce the activity of these neurons while also making them more reactive. Progesterone, on the other hand, modified the connections, or synapses, between these neurons.
By making these neurons unresponsive to hormones, the mice didn't display any maternal behaviors during pregnancy and even after giving birth. This observation indicates that there's a vital phase during pregnancy when these hormones kick into action.
Some of these neurological changes persisted for a month post-childbirth, while others appeared to be lasting alterations, suggesting that pregnancy can permanently reshape certain aspects of the female brain.
“We know that the female body changes during pregnancy to prepare for bringing up young. One example is the production of milk, which starts long before giving birth. Our research shows that such preparations are taking place in the brain, too,” says Jonny Kohl, group leader of the State-Dependent Neural Processing Laboratory at the Francis Crick Institute, in a media release.
“We think that these changes, often referred to as ‘baby brain’, cause a change in priority – virgin mice focus on mating, so don’t need to respond to other females’ pups, whereas mothers need to perform robust parental behavior to ensure pup survival. What’s fascinating is that this switch doesn’t happen at birth – the brain is preparing much earlier for this big life change.”
Researchers speculate that similar brain alterations could occur in pregnant humans, given that identical hormonal changes likely affect the same brain regions, possibly influencing parental behavior alongside other cues from the environment and society.
“We’ve demonstrated that there’s a window of plasticity in the brain to prepare for future behavioral challenges,” says study first author Rachida Ammari, a postdoctoral fellow at Francis Crick. “These neurons receive a large number of inputs from elsewhere in the brain, so now we’re hoping to understand where this new information comes from.”
The study is published in the journal Science.
