Depression And Microbiota: Intestinal Bacteria May Influence Mental Health

New findings published in the journal Nature Communications reveal that intestinal microbiota may play a role in inducing anxiety and depression.

"We have shown for the first time in an established mouse model of anxiety and depression that bacteria play a crucial role in inducing this abnormal behaviour," said Premysl Bercik, senior author of the paper and an associate professor of medicine with McMaster's Michael G. DeGroote School of Medicine, in a news release. "But it's not only bacteria, it's the altered bi-directional communication between the stressed host -- mice subjected to early life stress -- and its microbiota, that leads to anxiety and depression."

In the study, researchers subjected mice to early life stress with a procedure of maternal separation, meaning that from day three to 21, newborn mice were separated for three hours each day from their mothers and then put back with them.

First, researchers confirmed that mice with complex microbiota which had been maternally separated displayed anxiety and depression-like behavior via abnormal levels of the stress hormone corticosterone. They also showed gut dysfunction based on the release of a major neurotransmitter, acetylcholine.

Next, they found that when the maternally separated germ-free mice were colonized with bacteria from control mice, the bacterial composition and metabolic activity changed within several weeks and the mice began exhibiting anxiety and depression.

"However, if we transfer the bacteria from stressed mice into non stressed germ-free mice, no abnormalities are observed. This suggests that in this model, both host and microbial factors are required for the development of anxiety and depression-like behavior. Neonatal stress leads to increased stress reactivity and gut dysfunction that changes the gut microbiota which, in turn, alters brain function," said Bercik.

He also noted the following, courtesy of the release: "We are starting to explain the complex mechanisms of interaction and dynamics between the gut microbiota and its host. Our data show that relatively minor changes in microbiota profiles or its metabolic activity induced by neonatal stress can have profound effects on host behaviour in adulthood."

Bercik concluded that it would be important to understand how microbiota can shape host behavior and how it might help researchers one day better understand certain psychiatric disorders.

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