A new study in mice shows that the midbrain region involved in controlling emotions drives mothers to kill their young. Because this region also exists in humans, the study authors say these findings may play a role in better understanding female infanticide.
It is known that female mice often kill the pups of others before their first birth. According to experts, this behavior may have evolved to preserve scarce food supplies for future generations. However, most research has focused on adult male infanticide, and the brain mechanisms behind this behavior in females are still poorly understood.
A study led by researchers at New York University’s Grossman School of Medicine found that chemically blocking a region called the nucleus accumbens bed nucleus of the stria terminalis (BNSTpr) prevented infanticide by nearly 100 percent. In contrast, when the research team artificially activated the brain region, mothers and littermates attacked within one second of stimulation, killing the pups in almost all trials. The mice rarely attacked other adults, the authors said, suggesting that the structure controls aggression in young animals.
The investigation also revealed that the BNSTpr appears to work opposite a region of the brain called the medial preoptic area (MPOA), which is known to stimulate maternal behavior. According to the results, immature mice showed higher BNSTpr activity, which reduced MPOA activity. After the mice were born, MPOA activity increased, possibly suppressing the infanticide system in the process. New mothers avoided infanticide whether the pup was theirs or not.
Our study identifies for the first time the brain mechanisms that promote and prevent female infanticide.”
Long May, PhD, lead author of the study, is a Leon Levy Foundation Postdoctoral Fellow at the NYU Langone Health Neuroscience Institute.
The new study, published online June 7 in the journal Naturealso shows that the shift to maternal behavior can be reversed by additional pressure on the BNSTpr, Dr. May noted.
According to the US Centers for Disease Control and Prevention, child maltreatment is the fourth leading cause of death among preschool children in the United States. Dr. May noted that while early research focused primarily on potential problems in the brain’s parenting centers, experts have recently begun looking for a separate system for infanticide and child aggression.
For the study, the researchers first narrowed down the most likely brain regions behind infanticide behavior by looking at which structures were connected to the MPOA. They then artificially stimulated each of the seven regions in live mice, causing the animals to attack the pups, if present. The team then blocked activity in BNSTpr, the most promising remaining candidate, to see if this would prevent infant mortality.
To show that the BNSTpr and MPOA interact, the study authors prepared brain slices from female rodents and activated one region while recording cell activity in the other. They also looked at how activity in these structures changed as the rodents reached puberty.
“Because these two connecting areas in the midbrain are found in both rodents and humans, our research points to a potential target for understanding and even treating mothers who abuse their children,” said the study’s senior author and neuroscientist. Dayu Lin, PhD. “It is possible that these cells normally remain quiescent, but stress, postpartum depression, and other known triggers of child abuse can trigger them to become active,” added Dr. Lin, the NYU Langone Professor of Psychiatry, Neurology, and Physiology. .
Additionally, Dr. Lin, a member of NYU’s Langone Neuroscience Institute, cautions that it is unclear whether the two brain regions play the same role in humans as they do in rodents.
He said the research team next plans to study the BNSTpr and MPOA in male mice and explore ways to turn off activity in the former region without invasive surgery.
Research funding was provided by National Institutes of Health grants R01HD092596, R21HD090563, R01MH101377, and U19NS107616. Additional funding was provided by the Leon Levy Foundation.
In addition to Dr. Mei and Dr. Lin, other NYU Langone researchers involved in the study were Rongzhen Yang, PhD; Lupin Yin, PhD; and Regina M. Sullivan, Ph.D.
May, L., etc. (2023). Antagonistic circuits mediating infant and maternal care in female mice. Nature. doi.org/10.1038/s41586-023-06147-9.
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