Researchers at Stockholm University and the Karolinska Institute have discovered a system in the brain that can explain why normally non-aggressive female mice suddenly and dramatically develop this behavior after gestation and birth (so-called maternal aggression). The study shows that a group of neurons that control aggression in normally aggressive males is switched off in non-pregnant females but switches to active mode as soon as they become mothers. When the researchers silenced the neurons, the mother stopped attacking intruders in the cage. The study also shows that oxytocin and prolactin, the hormones that control maternal bodily functions such as milk production, can strongly activate these neurons.
The study was conducted on animals and should be interpreted with caution in the human context. However, the findings touch upon a broader conceptual question: How can an individual gain access to a behavior that is outside its normal repertoire during a limited period of its life? The example of a brain circuit examined here, which can be switched on and off depending on whether an animal (regardless of sex) needs access to a particular behavior for its (or its offspring’s) survival, could have general significance for how the plastic brain functions, also in humans.
“Surprisingly, it turned out that the same neural network that triggers aggression in male mice is dormant in female mice – until motherhood flips the switch on this hormone-sensitive system,” says the first author of the article, Stefanos Stagkourakis, who now leads his own research group at SciLifeLab and the Karolinska Institute.
“This is a study in laboratory mice, and we currently do not know if the results are transferable to humans. But the mechanism we identify here – how a behavior that is not normally part of an individual’s repertoire can become available for a limited period of its life – could reflect a principle of brain flexibility that is relevant beyond maternal aggression,” says Christian Broberger, Professor of Neurochemistry at Stockholm University.
The study was led by Christian Broberger, Professor of Neurochemistry at Stockholm University. The experiments were conducted at the Karolinska Institute, where his lab was previously located.
https://www.nature.com/articles/s41467-025-64043-4
