Glossary
Serotonin
What is serotonin?
Serotonin, also called 5-HT, is a signaling molecule with many functions in the body and brain. It is involved in processes including mood, sleep, appetite, and cognition.
How it works
Most of the body's serotonin is outside the brain. Within the nervous system, its effects depend on the receptors and circuits involved. Berger, Gray, and Roth review this diversity in The Expanded Biology of Serotonin.
Where is serotonin produced?
Much of the body’s serotonin comes from enterochromaffin cells in the intestine. In the central nervous system, serotonin-producing neurons are concentrated in the raphe nuclei along the brainstem’s midline. Their projections are the long nerve-cell extensions through which they influence other regions: more rostral raphe groups project widely through the brain, while more caudal groups send pathways toward the spinal cord. The brain’s serotonin system is therefore a small population of source neurons with broad connections, not a substance produced equally by every brain cell.
Why receptors and circuits matter
The Berger, Gray, and Roth review gives a useful example: some cortical pyramidal neurons have both 5-HT1A and 5-HT2A receptors, which can exert opposing effects on firing. It also describes 5-HT2C involvement in several processes, including anxiety-related behavior, appetite, and reward processing. Thus, one receptor need not correspond to one behavior, and serotonin need not have the same effect in every cell or circuit.
Serotonin and medication
Selective serotonin reuptake inhibitors, or SSRIs, alter serotonin reuptake. That drug action does not establish that everyone treated has a serotonin deficiency.
Low serotonin is not a sufficient general explanation for depression, aggression, or impulsivity.