That anxiety may be in your gut, not in your head

bacteria in our guts play many important roles in our health and well being, but new research has found that bacteria residing in the gut influence brain chemistry and behaviour. For each person, the gut is home to about 1,000 trillion 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 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.
"This was accompanied by restoration of normal behaviour and brain chemistry," Collins said.
To confirm that bacteria can influence behaviour, the researchers colonized germ-free 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 behaviour.