Although serotonin (image)is well known as a brain neurotransmitter, it is estimated that 90 percent of the body's serotonin is made in the digestive tract. In fact, altered levels of this peripheral serotonin have been linked to diseases such as irritable bowel syndrome, cardiovascular disease, and osteoporosis. New research at Caltech, published in the April 9 issue of the journal Cell, shows that certain bacteria in the gut are important for the production of peripheral serotonin. The title of the article is “Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis.” The Cell article is accompanied by a Cell Preview entitled “Gut Microbiota: The Link to Your Second Brain.” "More and more studies are showing that mice or other model organisms with changes in their gut microbes exhibit altered behaviors," explains Dr. Elaine Hsiao, Research Assistant Professor of Biology and Biological Engineering and senior author of the study. "We are interested in how microbes communicate with the nervous system. To start, we explored the idea that normal gut microbes could influence levels of neurotransmitters in their hosts." Peripheral serotonin is produced in the digestive tract by enterochromaffin (EC) cells and also by particular types of immune cells and neurons. Dr. Hsiao and her colleagues first wanted to know if gut microbes have any effect on serotonin production in the gut and, if so, in which types of cells. They began by measuring peripheral serotonin levels in mice with normal populations of gut bacteria and also in germ-free mice that lack these resident microbes. The researchers found that the EC cells from germ-free mice produced approximately 60 percent less serotonin than did their peers with conventional bacterial colonies.
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