UNC researchers link gut bacteria to infant brain development

Preliminary research at UNC-Chapel Hill Medical School shows a relationship between how the brains of infants develop and the type of bacteria living in their stomachs.

The communities of bacteria, viruses and small fungi that make their homes inside larger animals are known as the “microbiome.” Studying these critters has become a new way for scientists to understand the complex ways messages travel in the human body.

Scientists like Dr. Andrea Azacarate, head of the microbiome core research group at UNC-Chapel Hill, study how the bacteria function and interact with their hosts. Researchers have found, for example, that small changes in the proportions of different bacteria in our stomachs are found in people with health problems.

An abnormal gut microbiome has been linked to irritable bowel syndrome and Crohn’s disease, but as Azacarate says it’s a “chicken or egg situation.” Microbiologists do not know if an abnormal microbiome causes diseases or if the diseases allow the communities of bacteria in the human stomach to change. Environmental factors like diet are important to how our microbiome develops, but that is another push-and-pull relationship.

“We are affecting our microbiome, which in turn affects us,” Azacarate said.

The infant microbiome study was inspired by research that found anxious lab rats have a different gut microbiome than other lab rats. Dr. Rebecca Santelli, an assistant professor of psychiatry at UNC who specializes in the brain development of infants, says she was curious to see whether there is a relationship between the gut microbiome and how the brain develops in infants.

Bacteria in a human stomach affecting the brain might be difficult to imagine, but the gut microbiome takes advantage of the channels our bodies use to send messages between different organs. The bacteria’s normal life functions produce byproducts called metabolites that move through the stomach lining, enter the bloodstream and are transported throughout the human body. Depending on the type and number of bacteria in a gut microbiome, different types and numbers of metabolites are delivered to the brain and other parts of the host’s body.

Azacarate analyzed the genetic material of bacteria found in the infants’ diapers – those bacteria were in the babies’ stomachs. And though the infants included in the study were all breastfed and were not delivered by Caesarian section, their microbiomes were very different. Some even had “adult microbiomes,” bacteria more commonly found in adults.

Santelli conjectured that the variation was not unexpected because there “could be other environmental factors that can’t be controlled for,” such as the diets of the mothers. The variation could be intrinsic to the baby’s family history as well. Azacarate says researchers do not yet agree on how the microbiome could be passed from mother to child. In addition to breast milk, the placenta also has its own community of bacteria.

Despite the variation in the group of infants, Santelli and Azacarate identified three distinct configurations in the gut microbiomes. These configurations are generally made up of the same bacteria, but in different proportions.

Santelli and other child developmental specialists tested the infants on their personalities and ability to express themselves. Infants were observed in how they interacted with their mothers compared to how they interacted with a researcher they had not previously seen. They found that 2-year-olds who were more withdrawn around strangers and less expressive had a different microbiome community than 2-year-olds who were more expressive.

The research is funded for another three years starting in August, when more complex aspects of brain development will be tested.

“Now we know how to get samples; we worked out the kinks,” Santelli said. “So now we can answer the questions.”

Santelli hopes to identify the microbiome configurations that relate to the development of anxiety and depression in young children. The bacterial communities in infants’ guts affect their expressiveness at a young age, but Santelli said being more expressive is not itself linked to anxiety and depression. So entirely different bacteria will likely be affecting different aspects of how the brain develops.

Once researchers identify the makeup of the microbiome that promotes healthy brain development, there are a couple of ways that information can be used to treat anxiety, depression or other disorders.

“If we know we need specific metabolites introduced to the brain in a specific window (of time), we can develop a treatment that provides the correct metabolite,” Azacarte said.

Research in how the microbiome affects autism hopes to identify a metabolite that is not produced in the microbiome of people on the autism spectrum. Then, pharmaceutical companies can engineer a medicine to introduce this metabolite to the brain of a child or fetus before they develop autism.

Microbiome research is vital to the discovery of prebiotics. As opposed to anitibiotics which fight bacteria, prebiotics are a type of medicine that is basically food for a type of “good” bacteria. The microbiome researchers at UNC are developing prebiotics that can grow a type of bacteria whose metabolite will signal the brain to produce serotonin, one of the “feel-good” chemicals produced by the brain.

Stephen Ginley: 919-829-4520