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Mental health disorders might start in the gut, not in the brain

Kathleen Blanchard's picture
Changes in gut bacteria and mental health

Disruption of normal gut microbes changes brain chemistry.

Researchers from McMasters University say they now have evidence showing bacteria in the gut can alter behavior and brain chemistry , potentially making mental health disorders treatable with probiotics.

The scientists found behavior and brain chemistry changes in mice when they manipulated bacteria in the gut with antibiotics.

When gut flora changed, the mice had an increase in brain derived neurotrophic factor (BDNF), which has been associated with depression and anxiety.

Some of the mice in the experiment were bred to be germ free. Without normal gut flora, the scientists noted the mice were passive. When they colonized them with bacteria from mice bred to be more active, their behavior became more daring and exploratory.

Conversely, when the researchers altered gut bacteria in active mice, they became more passive.

Behavior changes when gut microbes altered

Stephen Collins, professor of medicine and associate dean research, Michael G. DeGroote School of Medicine said, “The exciting results provide stimulus for further investigating a microbial component to the causation of behavioral illnesses.”

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The study is the first to link mental health disorders to intestinal bacteria and is published in the journal Gastroenterology.

The scientists note irritable bowel syndrome and other intestinal disorders are frequently accompanied by anxiety and depression, leading them to explore whether disruption of gut microbes might alter brain chemistry that could lead to mental health disorders.

Collins said when bacteria in the gut returned to normal in the mice, their behavior changed. The mice became less anxious and cautious and brain chemistry returned to normal.

He notes past studies have focused on the role intestinal bacteria play in early brain development.

Premysl Bercik, assistant professor of medicine, who conducted research in the Farncombe Family Digestive Health Research Institute said the findings might indicate probiotics could have a role for treating anxiety, depression and other mental health disorders, especially those associated with gastrointestinal conditions like irritable bowel syndrome.

The authors say the finding show a variety of factors can influence behavior. Disruption of gut bacteria was shown to alter brain chemicals. They speculate any change in intestinal bacteria could also influence behavior and potentially lead to anxiety, depression and other mental health disorders.

"The Intestinal Microbiota Affect Central Levels of Brain-Derived Neurotropic Factor and Behavior in Mice"
P. Bercik et al

Image credit: Morguefile