Glossary · Y học
Serotonin
A signalling chemical (5-hydroxytryptamine, 5-HT) that acts both as a neurotransmitter in the brain and as a signalling molecule in the periphery. In the brain, low serotonin is linked to sleep problems and depression; but most of the body's serotonin is not in the brain at all.
In the central nervous system, serotonin is a neurotransmitter. According to NINDS, it constricts blood vessels and brings on sleep, and is also involved in temperature regulation; low serotonin can cause sleep problems and depression, while too much can lead to seizures.
But most of the body's serotonin is not in the brain. The review by Terry and Margolis (2017) states that 95% of the body's serotonin is produced in the intestine, where it has hormonal, autocrine, paracrine and endocrine actions. Gut serotonin is made by enterochromaffin cells and helps regulate gut motility.
The two serotonin pools — in the brain and in the periphery — are made and regulated separately. Yano et al. (2015) showed that the gut microbiota regulates the biosynthesis of serotonin from enterochromaffin cells in mice, an illustration of how gut bacteria act on the host's signalling chemistry.