Researchers have made a discovery, showing that pregnancy hormones have the ability to rewire the brain in order to prepare mice for motherhood. The study reveals that both estrogen and progesterone target a specific group of neurons in the brain, triggering parental behavior even before the arrival of offspring.
Previously, it was believed that the hormones released during childbirth were responsible for initiating maternal behavior. However, the researchers at the Francis Crick Institute found that rats who underwent Caesarean sections and virgin mice exposed to pregnancy hormones still exhibited maternal behavior, suggesting that hormone changes occurring during pregnancy play a more significant role.
The study, published in the journal Science, further demonstrated that female mice displayed increased parental behavior during late pregnancy, even in the absence of pups. The researchers identified a population of neurons known as galanin-expressing neurons in a region of the brain called the medial preoptic area (MPOA) in the hypothalamus, which is associated with parenting. Estrogen reduced the baseline activity of these neurons while simultaneously increasing their excitability. On the other hand, progesterone rewired the neuron's inputs by recruiting more synapses, which are sites of communication between neurons.
Interestingly, when these neurons were made insensitive to hormones, the onset of parental behavior during pregnancy was completely abolished. The mice failed to exhibit parental behavior even after giving birth, suggesting that there is a critical period during pregnancy when these hormones have their effect.
While some changes in the brain lasted for at least a month after giving birth, others appeared to be permanent, indicating that pregnancy can lead to long-term rewiring of the female brain.
Jonny Kohl, the Group Leader of the State-Dependent Neural Processing Laboratory at the Crick, explains, "We know that the female body changes during pregnancy to prepare for bringing up young. Our research shows that such preparations are taking place in the brain, too. What's fascinating is that this switch doesn't happen at birth -- the brain is preparing much earlier for this big life change."
The researchers believe that similar rewiring of the brain may occur during pregnancy in humans, as the same hormonal changes are expected to impact the same brain areas. This could potentially influence parental behavior, in conjunction with environmental and social cues.
Rachida Ammari, a postdoctoral fellow at the Crick and the study's first author, alongside PhD student Francesco Monaca, adds, "We've demonstrated that there's a window of plasticity in the brain to prepare for future behavioral 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."
