Biology: A microbial link between stress and altered behavior

Anxious and depressive behaviour in mice following early life stress appears to be dependent on stress-induced changes to gut microbiota, reports a paper in Nature Communications. The authors found that both stressed mice and stressed mice with no gut microbiota showed similar hormonal changes, but only the mice with gut microbes demonstrated behavioural changes.

Maternal separation in mice, in which pups are periodically separated from their mothers, has been used to study the effects of early life stress, which leads to alterations in behaviour and gut function. The behavioural alterations in mice have previously been associated with changes in the gut microbiota and one of the main neuroendocrine systems in the body, the hypothalamic-pituitary-adrenal axis (HPA).

Premysl Bercik and colleagues explored the contribution of gut bacteria to the development of altered behaviour in a maternal separation mouse model. They used two groups of mice, the first with normal intestinal microbiota and the second lacking any microorganisms. Some of the animals in both groups were subjected to maternal separation, while others were not and acted as controls. The researchers also transferred the gut microbiota from the first group to some of the germ free mice.

They found that stress-induced changes in HPA activity occurred similarly in both groups. However, the germ-free mice did not display anxiety-like or depressive-like behaviour, unless they received the microbiota from maternally separated mice. The results indicate that changes in gut microbiota are required for the behavioural alterations associated with early life stress. Further research is needed to test whether the findings apply to humans, and whether potential therapies targeting intestinal microbes can benefit patients suffering from psychiatric or bowel disorders.