What Is Serotonin? What Does Serotonin Do?

Serotonin, also known as 5-hydroxytryptamine is a hormone in the pineal gland, the digestive tract, the central nervous system, and blood platelets. A hormone is a substance our body produces that regulates and controls the activity of certain cells or organs.

The molecular formula of serotonin is C10H12N2O.

Serotonin is a neurotransmitter - this is a chemical substance that transmits nerve impulses across the space between nerve cells or neurons. We call these spaces synapses.

Serotonin plays an important part in the regulation of learning, mood, sleep and vasoconstriction (constriction of blood vessels). Experts say serotonin also might have a role in anxietymigraine, vomiting and appetite.

Alterations in serotonin levels in the brain may affect mood. Some antidepressant medications affect the action of serotonin, i.e. they are used to treat depression.

About 80% of our body's total serotonin is in the gut, in the enterochromaffin cells - where it regulates intestinal movements. The rest is synthesized in the serotonergic neurons in the central nervous system.

For some types of cells, serotonin is a growth factor - it may have a role in wound healing.

According to Medilexicon's medical dictionarySerotonin is:

"A vasoconstrictor, liberated by blood platelets, that inhibits gastric secretion and stimulates smooth muscle; present in relatively high concentrations in some areas of the central nervous system (hypothalamus, basal ganglia), and occurring in many peripheral tissues and cells and in carcinoid tumors."


A study carried out at Oxford University found that serotonin influences the way we rate intimacy and romance. They lowered serotonin activity in healthy volunteers and showed them photographs of couples. They were asked to rate them. The volunteers with lower serotonin activity rated the couples as less intimate than the volunteers with normal serotonin activity.

An animal experiment with mice found that those with a lack of serotonin lost their maternal instincts.

Serotonin levels change with the seasons - serotonin transporter protein, a brain chemical that lowers serotonin levels around brain cells, is more active during the winter months - meaning that serotonin levels are lower. Researchers from the University of Toronto and the Medical University of Vienna believe that this mechanism explains why some people feel miserable during the winter.

Brain's serotonin system differs between men and women

Scientists from the Karolinska Institutet, Sweden, showed that the brain's serotonin systems in males and females are different. They think they might have found one of the reasons why more women are affected with depression and chronic anxiety than men.

By using a PET scanner, the scientists found that in terms of the number of binding sites for certain parts of the brain, the two sexes are not the same.

They found that females have more of the most common serotonin receptors than men, and lower levels of the protein that carries serotonin back into the nerve cells that secrete serotonin. SSRI antidepressants block this protein.

Study leader, Anna-Lena Nordström, said:

"We don't know exactly what this means, but the results can help us understand why the occurrence of depression differs between the sexes and why men and women sometimes respond differently to treatment with antidepressant drugs."


Written by Christian Nordqvist

Original article date: 4th August 2011. Article updated: 31st October 2012. 

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