Summary: A recent study uncovers the brain mechanism that drives female mice to kill their young.
The research identifies a mid-brain region, the principal nucleus of the bed nucleus of stria terminalis (BNSTpr), as a trigger for infanticide in females. Blocking this region chemically prevented infanticide almost completely, while artificially activating it led to killings in nearly all instances.
The study also revealed the BNSTpr’s antagonistic relationship with the medial preoptic area (MPOA), a brain region known to promote maternal behavior.
Key Facts:
- The study revealed that chemically blocking the BNSTpr region in female mice almost entirely prevented infanticide.
- When the BNSTpr region was artificially activated, both mothers and females without offspring attacked and killed pups nearly every time, suggesting this structure specifically controls aggression towards young animals.
- The research also uncovered an antagonistic relationship between the BNSTpr and the MPOA, a region known to promote mothering behavior. This dynamic helps in shifting the behavior from infanticidal to maternal after giving birth.
Source: NYU Langone
A middle-brain region tied to the control of emotions likely prompts females to kill their young, a new study in mice shows. With the region also present in humans, the study authors say the findings could play a similar role in better understanding infanticide by women.
Before giving birth for the first time, female mice are known to often kill others’ pups. This behavior may have evolved to preserve scarce food supplies for their own future offspring, according to experts.
However, most studies have focused on infanticide by adult males, and the brain mechanism behind this behavior in females has until now remained poorly understood.
Led by researchers at NYU Grossman School of Medicine, the study showed that chemically blocking the region, called the principal nucleus of the bed nucleus of stria terminalis (BNSTpr), prevented infanticide nearly 100% of the time.
By contrast, when the study team artificially activated the brain region, both mothers and females without offspring killed pups in nearly all trials, attacking within a second of the stimulation. The mice rarely attacked other adults, the authors say, suggesting that the structure specifically controls aggression toward young animals.
The investigation also revealed that the BNSTpr appears to work in opposition to a brain region called the medial preoptic area (MPOA), itself known to promote mothering behavior.
According to the findings, mice that had not yet reached motherhood showed high BNSTpr activity, which dampened activity in the MPOA. After the mice gave birth, however, MPOA activity ramped up, likely suppressing the infanticidal system in the process. The new mothers tended to avoid infanticide regardless of whether the pup was theirs.
“Our investigation pinpoints for the first time the brain mechanisms that we believe encourage and discourage infanticide in females,” said study lead author Long Mei, PhD, a Leon Levy Foundation postdoctoral fellow in NYU Langone Health’s Neuroscience Institute.
The new study, publishing online June 7 in the journal Nature, also demonstrates that the switch to maternal behaviors can be reversed by extra pressure to the BNSTpr, notes Mei.
According to the U.S. Centers for Disease Control and Prevention, child abuse is the fourth leading cause of death among preschool children in the United States. Mei notes that while early studies had largely focused on potential problems in the parenting centers of the brain, experts have more recently begun to search for a separate system dedicated to infanticide and aggression against children.
For the investigation, researchers first narrowed down the most likely brain regions behind infanticidal behavior by tracking which structures were connected to the MPOA. Next, they artificially stimulated each of the resulting seven areas in live mice to determine which, if any, caused the animals to attack pups. Then, the team blocked activity in the BNSTpr, the most promising candidate remaining, to see if this would prevent infanticide.
To demonstrate that the BNSTpr and MPOA counteract each other, the study authors prepared brain slices from female rodents and activated one region while at the same time recording cell activity in the other. They also traced how activity in these structures changed as rodents reached motherhood.
“Since these two connecting regions in the middle of the brain can be found in both rodents and humans alike, our findings hint at a possible target for understanding, and perhaps even treating, mothers who abuse their children,” said study senior author and neuroscientist Dayu Lin, PhD.
“Maybe these cells normally remain dormant, but stress, postpartum depression, and other known triggers for child abuse may prompt them to become more active,” added Lin, a professor in the Departments of Psychiatry and Neuroscience and Physiology at NYU Langone.
That said, Lin, also a member of NYU Langone’s Neuroscience Institute, cautions that it remains unclear if the two brain regions perform the same roles in humans as they do in rodents.
She adds that the study team next plans to examine the BNSTpr and MPOA in male mice and to explore ways of turning off activity in the former region without invasive surgery.
Funding: Funding for the study 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 Mei and Lin, other NYU study investigators involved in the study were Rongzhen Yan, PhD; Luping Yin, PhD; and Regina Sullivan, PhD.
About this neuroscience research news
Author: Shira Polan
Source: NYU Langone
Contact: Shira Polan – NYU Langone
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Antagonistic circuits mediating infanticide and maternal care in female mice” by Long Mei et al. Nature
Abstract
Antagonistic circuits mediating infanticide and maternal care in female mice
In many species, including mice, female animals show markedly different pup-directed behaviours based on their reproductive state. Naive wild female mice often kill pups, while lactating female mice are dedicated to pup caring.
The neural mechanisms that mediate infanticide and its switch to maternal behaviours during motherhood remain unclear.
Here, on the basis of the hypothesis that maternal and infanticidal behaviours are supported by distinct and competing neural circuits, we use the medial preoptic area (MPOA), a key site for maternal behaviours, as a starting point and identify three MPOA-connected brain regions that drive differential negative pup-directed behaviours.
Functional manipulation and in vivo recording reveal that oestrogen receptor α (ESR1)-expressing cells in the principal nucleus of the bed nucleus of stria terminalis (BNSTprESR1) are necessary, sufficient and naturally activated during infanticide in female mice.
MPOAESR1 and BNSTprESR1 neurons form reciprocal inhibition to control the balance between positive and negative infant-directed behaviours.
During motherhood, MPOAESR1 and BNSTprESR1 cells change their excitability in opposite directions, supporting a marked switch of female behaviours towards the young.
