How female sex hormones 'rewire' brain during pregnancy, prepare for motherhood

New Delhi: How female sex hormones 'rewire' the brain during pregnancy and prepare it for motherhood, scientists reveal by studying mice.

The hormones, oestrogen and progesterone, acted on certain specific neurons in the brain region associated with parenting by making them more sensitive and enriching their network, the researchers at the Francis Crick Institute, UK, observed. The hormones are majorly produced in the ovary and responsible for typical female sexual characteristics, including fertility.

In this brain region, called the medial preoptic area (MPOA) and located in the hypothalamus, oestrogen made the neurons or nerve cells more excitable, whereas progesterone enhanced the communication by adding more connections between these neurons, called synapses, the researchers found by analysing brain recordings.

Further, the mice did not display maternal behaviour both during pregnancy and after giving birth, when the researchers prevented the sex hormones from impacting the MPOA neurons by desensitising the neurons.

This led the researchers to conclude that there is a critical period during pregnancy when these hormones take effect. They have published their findings of their study in the journal Science.

These changes in the brain effected by the sex hormones resulted in stronger and more selective responses to pups, the researchers said. They added that while some changes lasted for a month following birth, others seemed permanent, suggesting that pregnancy can lead to long-term rewiring of the female brain.

Previously, it was thought that hormones released at the time of giving birth were most crucial for the onset of maternal behaviour.

However, earlier research also showed that rats giving birth by Caesarean section and virgin mice exposed to pregnancy hormones still displayed maternal behaviour, suggesting that hormonal changes during pregnancy may be more important, the researchers said.

"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 behaviour 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," said Jonny Kohl, study author and Group Leader of the State-Dependent Neural Processing Laboratory at the Crick.

"We've demonstrated that there's a window of plasticity in the brain to prepare for future behavioural challenges. 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," said Rachida Ammari, postdoctoral fellow at the Crick, and co-first author.

In humans too, the brain may be rewired similarly during pregnancy, as the same hormonal changes are expected to effect the same brain regions, which could influence parental behaviour along with environmental and social cues, the researchers said.