Background: Serotonin (5-HT) has a pleiotropic function in gastrointestinal, neurological/psychiatric and
liver diseases. The aim of this review was to elucidate whether the gut-microbiota played a critical role in regulating
peripheral serotonin levels.
Methods: We searched for relevant studies published in English using the PubMed database from 1993 to the present.
Results: Several studies suggested that alterations in the gut-microbiota may contribute to a modulation of serotonin
signalling. The first indication regarded the changes in the composition of the commensal bacteria and the intestinal
transit time caused by antibiotic treatment. The second indication regarded the changes in serotonin levels correlated
to specific bacteria. The third indication regarded the fact that decreased serotonin transporter expression was associated
with a shift in gut-microbiota from homeostasis to inflammatory type microbiota. Serotonin plays a key role in
the regulation of visceral pain, secretion, and initiation of the peristaltic reflex; however, its altered levels are also
detected in many different psychiatric disorders. Symptoms of some gastrointestinal functional disorders may be due
to deregulation in central nervous system activity, dysregulation at the peripheral level (intestine), or a combination
of both (brain-gut axis) by means of neuro-endocrine-immune stimuli. Moreover, several studies have demonstrated
the profibrogenic role of 5-HT in the liver, showing that it works synergistically with platelet-derived growth factor
in stimulating hepatic stellate cell proliferation.
Conclusion: Although the specific interaction mechanisms are still unclear, some studies have suggested that there is
a correlation between the gut-microbiota, some gastrointestinal and liver diseases and the serotonin metabolism.