That anxiety may be in your gut, not in your head
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For the first time, researchers at McMaster University have conclusive evidence that
bacteria residing in the gut influence brain chemistry and behaviour.
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 provide stimulus for further investigating a microbial component
to the causation of behavioural illnesses," said Stephen Collins, professor of medicine
and associate dean of research, Michael G. DeGroote School of Medicine. Collins and
Premysl Bercik, assistant professor of medicine, undertook the research in the
Farncombe Family Digestive Health Research Institute.
The research appears in the online edition of the journal Gastroenterology.
For each person, the gut is home to about 1,000 trillion bacteria with which we live
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 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
bacterial content of the gut with antibiotics produced changes in behaviour; 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.
was accompanied by restoration of normal behaviour and brain chemistry," Collins said.
To confirm that bacteria can influence behaviour, the researchers colonized germ-
mice with bacteria taken from mice with a different behavioural pattern. They found
that when germ-free mice with a genetic background associated with passive behaviour
were colonized with bacteria from mice with higher exploratory behaviour, 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
While previous research has focused on the role bacteria play in brain development
in life, Collins said this latest research indicates that while many factors determine
behaviour, the nature and stability of bacteria in the gut appear to influence behaviour
and any disruption from antibiotics or infection might produce changes in behaviour.
Bercik said that these results lay the foundation for investigating the therapeutic
potential of probiotic bacteria and their products in the treatment of behavioural
disorders, particularly those associated with gastrointestinal conditions such as irritable
The research was funded by grants from the Canadian Institutes of Health Research
(CIHR) and the Crohn's and Colitis Foundation of Canada (CCFC).
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