Serotonin Production and Function in the Gut-Brain Axis

Intestinal Serotonin Production

Approximately 90-95% of the body's serotonin is produced in the gastrointestinal tract, primarily by specialized enterochromaffin cells, according to the American Gastroenterological Association 1, 2

The separation of central and peripheral serotonin systems has important implications for disorders of gut-brain interaction, as noted by the American Gastroenterological Association and the American College of Gastroenterology 1, 3
Altered serotonin metabolism has been observed in conditions like irritable bowel syndrome (IBS), as reported by the American Gastroenterological Association and the European Society of Gastroenterology 1, 2
Medications targeting serotonin systems must account for this separation, with tricyclic antidepressants (TCAs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) modulating both central and peripheral pain pathways, according to the American College of Gastroenterology 3, 4

Despite serotonin not crossing the blood-brain barrier, the gut and brain communicate through other mechanisms, including neural pathways via the vagus nerve, as noted by the European Society of Gastroenterology 2
Immune signaling molecules also play a role in this bidirectional communication, which forms the basis of the gut-brain axis, as reported by the American Gastroenterological Association 1

The gut commensals, particularly spore-forming Clostridiales within the Firmicutes phylum, may help regulate serotonin synthesis in the intestine, as noted by the American Gastroenterological Association 5
Changes in 5-HT metabolism have been detected in patients with post-infectious IBS, with colonic EC cell counts being higher in patients with Campylobacter-associated PI-IBS compared to healthy subjects, according to the American Gastroenterological Association 5
In Shigella-associated PI-IBS, both serotonin-containing EC cells and Peptide YY-containing EC cells are increased compared to healthy subjects, as reported by the American Gastroenterological Association 5