How gut bacteria influence brain chemistry & mood – for better or worse

“The nature and stability of bacteria in the gut appear to influence behavior – and any disruption, from antibiotics or infection, might produce changes in behavior.”

For the first time, researchers at Canada’s McMaster University have conclusive evidence that bacteria residing in the gut influence brain chemistry and behavior.

The findings are important because:

• Several common types of gastrointestinal disease, including irritable bowel syndrome, are frequently associated with anxiety or depression.

• In addition there has been speculation that some psychiatric disorders, such as late onset autism, may be associated with an abnormal bacterial content in the gut.

“The exciting results (published online by the journal Gastroenterology) provide stimulus for further investigating a microbial component to the causation of behavioral illnesses,” according to McMaster gastroenterologists Stephen Collins and Premysl Bercik.

For each person, the gut is home to about 1,000 trillion bacteria with which we live in harmony. These bacteria perform a number of functions vital to health. They:

• Harvest energy from the diet,

• Protect against infections,

• And provide nutrition to cells in the gut.

Any disruption of the gut bacteria can result in life-threatening conditions, such as antibiotic-induced colitis from infection with the “superbug” Clostridium difficile.

Working with healthy adult mice, the researchers showed that disrupting the normal bacterial content of the gut with antibiotics produced changes in behavior; the mice became less cautious or anxious.

This change was accompanied by an increase in brain derived neurotrophic factor (BDNF), which has been linked to depression and anxiety.

When oral antibiotics were discontinued, bacteria in the gut returned to normal. “This was accompanied by restoration of normal behavior and brain chemistry,” says Collins.

To confirm that bacteria can influence behavior, the researchers colonized germ-free mice with bacteria taken from mice with a different behavioral pattern. They found that:

• When germ-free mice with a genetic background associated with passive behavior were colonized with bacteria from mice with higher exploratory behavior, they became more active and daring.

• Similarly, normally active mice became more passive after receiving bacteria from mice whose genetic background is associated with passive behavior.

While previous research has focused on the role bacteria play in brain development early in life, Collins says this latest research indicates that while many factors determine behavior, the nature and stability of bacteria in the gut appear to influence behavior – and any disruption, from antibiotics or infection, might produce changes in behavior.

Bercik adds that these results lay the foundation for investigating the therapeutic potential of
probiotic bacteria and their products in the treatment of behavioral disorders, particularly those associated with gastrointestinal conditions such as irritable bowel syndrome.

The research was funded by grants from the Canadian Institutes of Health Research and the Crohn’s and Colitis Foundation of Canada.

Source: McMaster University news release, May 17, 2011

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One thought on “How gut bacteria influence brain chemistry & mood – for better or worse”

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