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Indigenous Gut Bacteria Modulate Serotonin Synthesis In the Intestinal Tract


It has been known for a while that most of the serotonin produced in the human body is not in the brain but in enterochromaffin cells of the gut; this is true of mammals in general.  Now a research group at Cal Tech has demonstrated that a particular group of bacteria in the gut help the cells of the gut wall produce serotonin.

First of all, mice raised to be germ free with no bacteria in their guts only produce less than half of the serotonin that normal mice produce.  The research group tested the various genera of bacteria that normally inhabit the mouse gut and found that a certain group of spore forming bacteria specifically induce the gut wall to produce 60% more serotonin.  Finally, they were able to demonstrate that a specific metabolite produced by the bacteria modulates this effect: apparently, the enterochromaffin cells take up this metabolite, and from it, produce more serotonin.

The increase in serotonin that is found from this bacteria causes an increase in gut motility and changes in the activity of blood platelets, who depend on serotonin for clotting.

An abstract of the research article can be found at: and a Cal Tech news release and explainer at:

The significance of this finding is that there is a commensal relationship between the mammalian organism and the bacteria in its gut; what role the serotonin plays in behavior or illness remains to be explored.

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