Bugs in the belly could be to blame for anxiety and depression

In a word: mice.

Scientists at the McMaster University tested newborn mice to see how the amount of intestinal bugs they had compared to how they emotionally dealt with being temporarily separated from their mothers.

Those specimens with a normal range of bugs displayed signs of anxiety and depression. The germ-free mice, on the other hand, didn’t seem all that bothered by the separation, even though it altered their stress hormone levels, results reported in the Nature Communications journal showed.

But that soon changed when the carefree critters were colonised with bacteria from other mice and the anxiety, depression and even gut dysfunction sunk it after a few weeks.

So what does this mean for us?

Experts believe the results show that bacteria really does affect (mouse) behaviour, depending on how the host naturally reacts to it. So the next step is now to work out whether this also applies to humans.

Dr Premysl Bercik, of McMaster University, said: “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.

“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.”

He added that, because transferring bacteria from stressed to non-stressed mice seemed to have no impact on behaviour, this further suggests that, in this model, “both host and microbial factors are required for the development of anxiety and depression-like behaviour.”

“We are starting to explain the complex mechanisms of interaction and dynamics between the gut microbiota and its host. Our data show that relatively minor changes in microbiota profiles or its metabolic activity induced by neonatal stress can have profound effects on host behaviour in adulthood.

“It would be important to determine whether this also applies to humans. For instance, whether we can detect abnormal microbiota profiles or different microbial metabolic activity in patients with primary psychiatric disorders, like anxiety and depression.”