For the first time, researchers at McMaster University have conclusive evidence that bacteria residing in the gut influence brain chemistry and behavior. 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 research appears in the online edition of the journal Gastroenterology.
“The exciting results provide stimulus for further investigating a microbial component to the causation of behavioral illnesses,” said Stephen Collins, professor of medicine and associate dean 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.
For each person, the gut is home to about 1,000 trillium bacteria with which we live in 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 normal bacterial content of the gut with antibiotics produced changes in behavior; 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. “This was accompanied by restoration of normal behavior and brain chemistry,” Collins said.
To confirm that bacteria can influence behavior, the researchers colonized germ-free mice with bacteria taken from mice with a different behavioral pattern. They found that when germ-free mice with a genetic background associated with passive behavior were colonized with bacteria from mice with higher exploratory behavior, 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 behavior.
While previous research has focused on the role bacteria play in brain development early in life, Collins said this latest research indicates that while many factors determine behavior, the nature and stability of bacteria in the gut appear to influence behavior and any disruption from antibiotics or infection might produce changes in behavior.
Bercik said that these results lay the foundation for investigating the therapeutic potential of probiotic bacteria and their products in the treatment of behavioral disorders, particularly those associated with gastrointestinal conditions such as irritable bowel syndrome.
Material adapted from McMaster University.