A new study from National Cheng Kung University throws light on the role of the bacteria inside our stomachs. The study examined the effect of a healthy gut microbiome on social behavior in mice. It found that mice without gut bacteria were unable to be sociable. Researchers say the findings could shed light on the links between the digestive system and the mind.

A mouse meets another unfamiliar mouse for the first time. But the reactions of the mice on left and right are totally different – and their gut bacteria is the key.

Chen Hung-chen
Ministry of Science and Technology
Everyone knows that our health and constitution are intimately linked. Our constitution is partially innate, but what’s more important is how we live, which is to say the microbes that live with us in symbiosis. These microbes affect our physiology. The bacteria in our gut also affect our stress levels and our social behavior.

The team from NCKU Hospital, led by Professor Wu Wei-li吳偉立, worked with a team from the California Institute of Technology. They found that gut bacteria affect the social behavior of the mice they live with. Researchers introduced a strange mouse to various groups: mice with no bacteria, mice on antibiotics, and mice with a normal gut microbiota. The mice with bacteria were curious and social, whereas the germ-free mice tried to hide. Researchers think the difference is down to differing levels of the stress hormone corticosterone.

Prof. Wu Wei-li
NCKU Department of Physiology
When they lack gut bacteria, corticosterone is abnormally elevated, causing certain neuronal circuits to activate and produce even more corticosterone, reducing the mouse’s social behavior.

Professor Wu’s team found that the mice with elevated stress hormones in their blood showed less interest in socializing with other mice. But certain bacteria in the gut inhibit corticosterone.

Prof. Wu Wei-li
NCKU Department of Physiology
We saw a situation where the social behavior was increased and the corticosterone decreased. We transplanted a gut bacterium into the germ-free mice, and got the result that their social behavior increased.

The study has been published in the prestigious scientific journal, “Nature,” and received widespread attention. Professor Wu says the team will continue their research to uncover more links between brain, gut and behavior.