Gut Bacteria Plays a Key Role in Inducing Early Life Anxiety and Depression

Neonatal stress leads to increased stress reactivity and gut dysfunction that changes the gut microbiota which, in turn, alters brain function.

Gut flora consists of a complex community of microorganism species that live in the digestive tracts of animals. Adding to the importance of these intestinal bacteria, scientists from McMaster University in Canada have discovered that it also plays a key role in inducing anxiety and depression that can lead to early life stress.

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

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For the study, researchers subjected mice to early life stress. Newborn mice were separated for three hours each day from their mothers and then they were put back with them. Rodents with complex microbiota, which had been maternally separated, displayed anxiety and depression-like behavior, with abnormal levels of the stress hormone corticosterone. These animals also showed gut dysfunction based on the release of a major neurotransmitter called acetylcholine.

Then, the researchers repeated the same experiment in germ-free conditions and found that in the absence of bacteria, mice which were maternally separated still have altered stress hormone levels and gut dysfunction. The study findings suggest that relatively minor changes in microbiota profiles or its metabolic activity induced by neonatal stress can have profound effects on host behavior in adulthood. Bercik said, "Neonatal stress leads to increased stress reactivity and gut dysfunction that changes the gut microbiota which, in turn, alters brain function."

The study is published in Nature Communications.

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