Serotoniin

Serotoniin, also called serotonin, is 5-hydroxytryptamine (5-HT), a monoamine neurotransmitter and hormone found throughout the body. About 90 percent is produced in the gastrointestinal tract by enterochromaffin cells, while the remainder is synthesized by serotonergic neurons in the brain. In the brain it modulates mood, sleep, appetite, cognition, and pain perception; in the gut it helps regulate motility and secretion. The blood-brain barrier largely separates peripheral and central serotonin pools.

Synthesis begins with the amino acid tryptophan, which is converted by tryptophan hydroxylase (TPH1 in peripheral tissues and TPH2 in the CNS) to 5-hydroxytryptophan, then to serotonin by aromatic L-amino acid decarboxylase. Serotonin is stored in vesicles in neurons and, peripherally, in platelets. Upon release, it acts on a family of 5-HT receptors (5-HT1 to 5-HT7) with diverse effects depending on receptor subtype and location.

Serotonin is primarily removed from the synaptic cleft by reuptake via the serotonin transporter (SERT). It is metabolized by monoamine oxidase A to 5-hydroxyindoleacetic acid (5-HIAA), which is excreted in urine and measured in CSF.

Clinically, altered serotonergic signaling is linked to mood disorders, migraines, and irritable bowel syndrome. Treatments include selective serotonin reuptake inhibitors (SSRIs) and drugs that target specific 5-HT receptors; triptans, for example, are 5-HT1B/1D agonists used in migraines. Excess serotonin can lead to serotonin syndrome, a potentially life-threatening condition.