http://goo.gl/6RJ9np
"We have shown for the first time in an established mouse model of anxiety and depression that bacteria play a crucial role in inducing this abnormal behaviour," said Premysl Bercik, senior author of the paper and an associate professor of medicine with McMaster's Michael G. DeGroote School of Medicine. "But it's not only bacteria, it's the altered bi-directional communication between the stressed host -- mice subjected to early life stress -- and its microbiota, that leads to anxiety and depression."
It has been known for some time that intestinal bacteria can affect behaviour, but much of the previous research has used healthy, normal mice, said Bercik.