MICE STUDIES
Brain mechanism teaches mice to avoid bullies
Findings may offer insight into social disorders like autism
Peer-Reviewed PublicationLike humans, mice live in complex social groups, fight over territory and mates, and learn when it is safer to avoid certain opponents. After losing even a brief fight, the defeated animals will flee from the mice that hurt them for weeks afterward, a new study shows.
Led by researchers at NYU Grossman School of Medicine, the study reveals that such “retreating behavior” is influenced by a distinct area on the underside of the hypothalamus, a part of the brain that controls hunger, sleep, and levels of many hormones. The team had previously found that this special region, called the anterior ventrolateral part of the ventromedial hypothalamus (aVMHvl), helps rodents defend themselves against bullies’ attacks. Here, the authors further identified a central role of the area to drive longer-lasting avoidance after being defeated.
The study showed that when rival mice first meet, scent information about opponents is not strong enough to activate aVMHvl cells to prompt a retreat. Once a fight begins, however, pain (such as from getting bitten) triggers the release of the “cuddle hormone” oxytocin. While this signal has long been linked with parenting and attraction, in this case it binds to oxytocin receptors on aVMHvl cells and signals danger. This process links pain signals to the opponent’s scent so the next time the aggressor approaches, its smell alone encourages the bullied mouse to stay away, say the study authors.
“Our findings provide new insight into how oxytocin within the hypothalamus drives learning from traumatic social experiences,” said study lead author Takuya Osakada, PhD. “While the hormone is often associated with positive behaviors like caregiving, our study highlights its key role in social conflict,” adds Osakada, a postdoctoral fellow in the Departments of Psychiatry and Neuroscience and Physiology at NYU Langone Health.
The study team, while cautioning that mice share a lot of brain chemistry with people but are not the same, says previous research has shown similar “retreat” behavior following social defeat in many species including humans. In addition, past studies in children have linked the experience of being bullied to increased social isolation and school absences.
Osakada notes that while previous research had examined rodent behavior over time after experiencing repeated defeats, the new study, publishing online Jan. 24 in the journal Nature, is the first to explore rapid social learning that occurs immediately after losing a fight.
For the research, the study team observed hundreds of mice that were exposed to a rival for 10 minutes before being separated. They also measured the animals’ brain activity before and after a conflict. The results showed that 24 hours after losing a single fight, social interaction dropped down to just 20% of pre-defeat levels. In addition, the findings revealed that pain prompted the immediate activation of oxytocin-releasing brain cells located right next to the aVMHvl.
To further examine the role of the aVMHvl in social avoidance, the researchers prevented receptors on these cells from binding to oxytocin. They found that rodents with blocked oxytocin receptors were less likely to retreat from their aggressor in later encounters. Meanwhile, when the team instead artificially activated aVMHvl cells, animals kept to themselves even if they had not lost a fight.
“Now that we have a better understanding of critical forces behind social avoidance, researchers can start exploring ways to harness oxytocin to treat disorders that affect social skills, such as autism, social anxiety, and attention-deficit hyperactivity disorder,” said study senior author Dayu Lin, PhD. Lin is a professor in the Departments of Psychiatry and Neuroscience and Physiology at NYU Langone, as well as a member of its Neuroscience Institute.
That said, Lin cautions that while the team connected the aVMHvl to social avoidance, they found no such link to another behavior exhibited by defeated mice — freezing up in the face of conflict. As a result, researchers say additional brain systems are likely involved in defeat behavior, and understanding such systems is essential before developing oxytocin-based therapies for human social disorders.
The study team next plans to examine whether the newly uncovered aVMHvl mechanism may also be involved in behaviors that rodents use to establish their social hierarchy under more natural conditions, instead of during the contrived scenario from the initial experiment.
Funding for the study was provided by National Institutes of Health grants U19NS107616, R01MH101377, R01MH124927, and R01HD092596. Further funding was provided by the Mathers Foundation, the Vulnerable Brain Project, the Uehara Memorial Foundation, the JSPS Overseas Research Fellowship, and the Osamu Hayaishi Memorial Scholarship.
In addition to Osakada and Lin, other NYU Langone researchers involved in the study were Rongzhen Yan, PhD; Yiwen Jiang, MS; Dongyu Wei, PhD; Rina Tabuchi; Bing Dai, BS; Xiaohan Wang, PhD; Richard Tsien, PhD; and Adam Mar, PhD.
JOURNAL
Nature
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
A dedicated hypothalamic oxytocin circuit controls aversive social learning
ARTICLE PUBLICATION DATE
24-Jan-2024
Study in mice uncovers new protective benefit of breast milk
Immune system proteins in breast milk protect offspring by shaping gut microbiota
Peer-Reviewed PublicationAn immune component of breast milk known as the complement system shapes the gut environment of infant mice in ways that make them less susceptible to certain disease-causing bacteria, according to a study led by researchers at the Johns Hopkins Bloomberg School of Public Health.
The researchers found that mouse pups that nursed from lactating mice whose breast milk lacked a key complement protein had different gut microbe populations than pups that nursed on standard mouse breast milk, making them highly vulnerable to Citrobacter rodentium, a bacterium that infects the guts of mice. Citrobacter rodentium is similar to certain types of diarrhea-causing E. coli that can infect humans but not mice.
The researchers’ experiments suggest that mouse breast milk’s complement components boost mouse infant health by directly eliminating some types of gut-dwelling bacteria. This reshaping of the gut microbiota leaves the infant mice far less susceptible to Citrobacter rodentium infection, thus protecting the young from certain infectious threats. The reshaping activity is not dependent on antibodies, in contrast to the way complement components are thought to typically work.
The researchers also confirmed in separate in vitro analyses that human breast milk contains these complement components, which demonstrated similar activity in targeting specific bacteria.
Taken together, these findings shed light on the mechanisms of how breast milk functions to provide protection from certain bacterial infections.
The study was published online January 18 in the journal Cell.
”These findings reveal a critical role for breast milk complement proteins in shaping offspring’s gut microbe compositions and protecting against bacterial infection in the gut in early life,” says study senior author Fengyi Wan, PhD, a professor in the Bloomberg School’s Department of Biochemistry and Molecular Biology. “This represents an important expansion of our understanding of breast milk’s protective mechanisms.”
The study’s first author is Dongqing Xu, PhD, an assistant scientist in Wan’s research group.
Breastfeeding has many known and suspected benefits. It provides excellent nutrition to infants and appears to protect against some short-term or long-term illnesses. Breast milk is also known to help protect against common infections by sharing antibodies and white blood cells from the mother.
Breast milk also contains complement proteins that can work with, or “complement,” antibodies in attacking bacteria. While complement proteins that circulate in the blood have been the focus of much research, complement proteins in breast milk have been far less studied, and until now their role has been unclear.
In the new study, Wan and his team used engineered mice that lacked critical complement genes. They found that milk from female mice of this type left several-weeks-old mouse pups—even those with normal complement genes—highly susceptible to colitis, often lethal, from Citrobacter rodentium infections. By contrast, pups feeding on normal, complement-containing milk showed only minor and transient signs of gut infection.
The team discovered that this protective effect of breast milk complement proteins depends on their capacity in shaping infant gut microbiota. The complement proteins kill certain gut bacterial species, and this culling of microbes creates an overall gut environment in which harmful inflammation is much less likely in the presence of Citrobacter rodentium.
“Gut microbiota is of great importance to health,” says Wan. “Breast milk complement proteins contribute crucially to the establishment of a ‘protective’ gut microbiota during the early stages of development, promoting infant health and defending against pathogens.”
The study also appears to mark an advance in basic immunology. Complement proteins in blood, although known to be capable of causing direct damage to bacterial cells, have been thought to typically work in partnership with antibodies in a specific immune response. However, Wan and his team showed that this breast milk complement activity against bacteria does not require antibodies and is a nonspecific immune response.
“This opens the door to a lot of new investigations, for example, elucidating the specific complement biology in breast milk and comparing that to complement biology in the blood, and assessing the role of complement beyond the antibody-dependent specific immune system,” Wan says.
“Complement in breast milk modifies offspring gut microbiota to promote infant health” was co-authored by Dongqing Xu, Siyu Zhou, Yue Liu, Alan L. Scott, Jian Yang, and Fengyi Wan.
Support for the research was provided by the National Institutes of Health (GM111682, AI137719, CA244350); the U.S. Department of Defense (W81XWH-19-1-0479); the American Association of Immunologists; and the American Heart Association (19PRE34380234).
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JOURNAL
Cell
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Complement in breast milk modifies offspring gut microbiota to promote infant health
ARTICLE PUBLICATION DATE
24-Jan-2024
UW researchers uncover news clues about the cause of common birth defects
IMAGE:
THIS IMAGE OF A SECTION THROUGH THE MIDFACE OF A MOUSE EMBRYO ILLUSTRATES FUSION OF THE TISSUES THAT FORM THE SECONDARY PALATE ABOVE THE TONGUE. GREEN STAINING ILLUSTRATES CELLS EXPRESSING A KEY ENZYME THAT MEDIATES DNA METHYLATION, BLUE INDICATES NUCLEI OF ALL CELLS, RED INDICATES EPITHELIAL CELLS.
view moreCREDIT: UNIVERSITY OF WISCONSIN–MADISON
MADISON, WI.-- Cleft lip and palate are the most common craniofacial birth defects in humans, affecting more than 175,000 newborns around the world each year. Yet despite decades of research, it’s still not known what causes most cases or what can be done to prevent them. But a recent study from the University of Wisconsin School of Veterinary Medicine (SVM) has uncovered new information about orofacial development in mice that researchers believe could one day help reduce the risk of these birth defects in humans.
Published this week in the Proceedings of the National Academy of Sciences (PNAS) the study provides the first direct evidence of a mechanism called DNA methylation being required for craniofacial development. DNA methylation is a process where a group of molecules are added to DNA that change the expression of genes without actually altering the DNA sequence. It's also affected by various environmental factors. The researchers discovered that disruption to DNA methylation interferes with development of the lip and palate and causes these birth defects in mice.
Led by Robert Lipinski, associate professor of comparative biosciences at the UW School of Veterinary Medicine, the research is an important step toward developing preventive strategies that could one day lessen the risk of cleft lip and palate, known collectively as orofacial clefts (OFCs), in both animals and humans.
“We knew from past research that genetics and the environment interact to cause these types of birth defects, but our understanding of the environmental component lagged far behind that of genetics.” says Lipinski. “Unlike genetics, we don’t have a permanent record of the prenatal environment that can be examined retrospectively, but connecting OFCs to DNA methylation helps narrow our focus on the particular environmental influences that modify the risk for these types of birth defects.”
His team’s work confirmed the essential role of DNA methylation in regulating orofacial development during embryonic development and demonstrates how disruptions to that process alter the ability of stem cells to form the connective tissue of craniofacial bone and cartilage, resulting in OFCs.
Lipinski and his team arrived at these results by first genetically manipulating DNA methylation in two separate groups of mouse embryos. The experiments resulted in seemingly contradictory results, with OFCs developing in one group of mice, but not the other. To understand why there was a difference between the groups, the team conducted another round of experiments in which they inhibited DNA methylation in mouse embryos at different stages of development. The timing of when DNA methylation occurs, was critical to the development of orofacial clefts.
They found that exposure on the 10th gestational day resulted in OFCs but administering the same inhibitor just 48 hours later resulted in normal orofacial development.
Identifying this narrow window of gestational sensitivity is important, Lipinski says, because it not only helps narrow the focus of the next stage of his team’s research but it will also help design future public education initiatives once more is known about the modifiable environmental and behavioral risk factors that impact OFC risk in humans. The 10th gestational day in mouse embryos corresponds with the beginning of the 5th week of embryonic development in humans–a stage at which many pregnancies may not yet be recognized.
“We know DNA methylation can be influenced by a variety of environmental factors, including maternal stress, diet, and exposure to drugs, toxins and environmental pollutants, and having a better understanding how orofacial development is regulated by environmentally sensitive mechanisms could directly inform birth defect prevention strategies,” he says. “This next phase of our team’s research is focused on identifying specific factors that influence DNA methylation during orofacial development and which could therefore alter OFC risk.”
Lipinski and his team are uniquely positioned to pursue this next stage of research because of another important outcome of the study: a new in vitro model the team developed. The model will allow them to rapidly screen thousands of dietary and environmental factors in a laboratory dish before testing the impact of specific factors on cleft susceptibility in mouse models.
The results in cell and animal models will help the researchers more quickly and accurately identify factors likely to be of consequence to human development[ETM1] .
Orofacial clefts of the upper lip and palate affect approximately 1 in 700 newborns, and individuals with OFCs navigate feeding difficulties as infants that require multiple surgeries, dental procedures, and speech therapy during childhood and adolescence. Studies have shown higher mortality rates at all stages of life for individuals with OFCs.
This study was supported by funding from the National Institutes of Health under award numbers R03DE027162, R56DE030917, RO1DE032710, U01 DK11807, and R01DK099328, and T32ES007015. Additional support was also provided by the University of Wisconsin Hilldale Undergraduate Research Award.
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Founded in 1983, the UW School of Veterinary Medicine provides outstanding programs in veterinary medical education, research, clinical practice, and service that enhance the health and welfare of both animals and people and contribute to the economic and environmental well-being of the state of Wisconsin, the nation and the world.
JOURNAL
Proceedings of the National Academy of Sciences
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Animals
