Researchers have shown that pregnancy hormones “rewire” the brains of mice to prepare them for motherhood, and the same could happen in women too
It is known that although virgin female rodents show little interaction with their offspring, mothers spend most of their time caring for them. The hormones released during birth were thought to be paramount in triggering maternal behavior.
However, previous research also showed that rats that delivered their child via cesarean section and virgin mice exposed to pregnancy hormones still exhibited these maternal behaviors, suggesting that hormonal changes may be more important early in pregnancy.
The findings, published today in Science, show that both estrogen and progesterone act on a small population of neurons in the brain to activate parental behavior even before offspring arrive. These adaptations produce stronger and more selective responses toward offspring.
In the current study, researchers found that female mice actually exhibited increased parenting behavior in late pregnancy and that this behavioral change did not require exposure to offspring. They found that estrogen and progesterone affected a population of nerve cells (galanin-expressing neurons) in an area of the brain called the medial preoptic area (MPOA) in the hypothalamus, which is associated with parenting.
Brain recordings showed that estrogen simultaneously reduced the basal activity of these neurons and made them more excitable, while progesterone reconfigured their inputs and recruited more synapses (communication sites between neurons). The insensitivity of these neurons to hormones completely prevented the occurrence of parental behavior during pregnancy. The mice showed no paternal behavior even after birth, suggesting that there is a critical period during pregnancy when these hormones take effect.
Although some of these changes lasted at least a month after birth, others appear to be permanent, suggesting that pregnancy may result in long-term rewiring of the female brain.
Jonny Kohl, group leader at Crick’s State-Dependent Neural Processing Laboratory, said: “We know that a woman’s body changes during pregnancy to prepare for raising her children.” One example is milk production, which occurs long before Birth begins. Our research shows that these preparations also take place in the brain.
“We believe these changes, often referred to as ‘baby brain,’ lead to a change in priorities: young mice focus on mating so they don’t have to respond to other females’ offspring, while mothers exhibit robust parenting behavior to ensure this.” survival of the offspring. The fascinating thing is that this change doesn’t happen at birth: the brain prepares for this major vital change much earlier.
Rachida Ammari, postdoctoral researcher at the Crick and first author along with PhD student Francesco Monaca, said: “We have shown that there is a window of plasticity in the brain to prepare for future behavioral challenges.” “These neurons receive a large number of inputs from other parts of the brain, so we now hope to understand where this new information comes from.”
Researchers believe that the brain may also change in similar ways during pregnancy in humans, as the same hormonal changes are expected to affect the same areas of the brain. This could influence parental behavior as well as environmental and social cues.
REFERENCE
Hormone-mediated neuronal remodeling orchestrates the onset of parenthood during pregnancy