Chronic gastrointestinal conditions, such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), are often associated with anxiety and depression. The intestinal bacterial content of these patients is less diverse than that found in healthy individuals and its composition can become unstable over time.1

In a small study recently published in the online edition of the journal, Gastroenterology, researchers at McMaster University have shown that bacteria in the gut of mice have an effect on brain chemistry that is independent of the autonomic nervous system, gastrointestinal-specific neurotransmitters, and inflammation.

When the researchers disrupted the normal bacterial content in the gut of healthy adult mice with antibiotics, the mice became less cautious or anxious. There was also a measurable associated change in the amount of a brain chemical that has been linked to depression and anxiety. When oral antibiotics were discontinued, bacteria in the gut returned to normal, as did the behaviour and brain chemistry of the mice.

In addition, when the digestive tracts of mice that had a genetic predisposition to passive behaviour were colonized with bacteria from mice that had higher exploratory behaviour, they became more active and daring.2 Similarly, normally active mice became more passive after receiving bacteria from mice with a known genetically passive behaviour.

The researchers say this small study will contribute to future investigations of a microbial role in behavioural illnesses, as well as the potential of using probiotics as a treatment for behavioural disorders, especially those associated with gastrointestinal conditions.

First published in the Inside Tract® newsletter issue 178 – 2011
1. Bercik P et al. The Intestinal Microbiota Determines Mouse Behavior and Brain BDNF Levels. Gastroenterology. 2011;140(5).
2. McMaster University. Press release: That anxiety may be in your gut, not in your head. 2011-05-17. Available at Accessed 2011-06-23.