How gut bacteria produce key brain chemical

Production of a key chemical, deficiency of which is linked to various diseases and disorders such as depression and anxiety, depends largely on a group of approximately 20 bacteria in the gut, says a new study.

Certain bacteria in the gut are important for the production of serotonin, which is well known as a brain neurotransmitter, the findings showed.

In fact, altered levels of this peripheral serotonin have also been linked to diseases such as irritable bowel syndrome, cardiovascular disease, and osteoporosis.

"Our work demonstrates that microbes normally present in the gut stimulate host intestinal cells to produce serotonin," said first author of the study Jessica Yano from the California Institute of Technology.

Peripheral serotonin is produced in the digestive tract by enterochromaffin (EC) cells and also by particular types of immune cells and neurons.

While previous work in the field indicated that some bacteria can make serotonin all by themselves, this new study suggests that much of the body's serotonin relies on particular bacteria that interact with the host to produce serotonin, Yano noted.

The researchers wanted to find out whether specific species of bacteria, out of the diverse pool of microbes that inhabit the gut, are interacting with EC cells to make serotonin.

They identified several particular metabolites -- products of the microbes' metabolism -- that were regulated by spore-forming bacteria and that elevated serotonin from EC cells in culture.

Furthermore, increasing these metabolites in germ-free mice increased their serotonin levels.

"Serotonin is an important neurotransmitter and hormone that is involved in a variety of biological processes. The finding that gut microbes modulate serotonin levels raises the interesting prospect of using them to drive changes in biology," senior author of the study Elaine Hsiao from the California Institute of Technology pointed out.

The study appeared in the journal Cell.