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Serotonin

Synonyms: 5-hydroxytryptamine, 5-HT, enteramin

German: Serotonin

1 Definition

Serotonin is a biogenic amin that can be found as neurotransmitter in the peripheral nervous system and central nervous system. Outside the nervous system, serotonin can be found in the enterochromaffin cells of the intestinal mucosa an in platelets among others.

2 Biochemistry

Serotonin develops in a 2-step reaction through hydroxylation and subsequent decarboxylation from the amino acid tryptophan. The involved enzymes comprise tryptophan hydroxylase and aromatic L-amino acid decarboxylase. The non-proteinogenic amino acid 5-hydroxytryptophan results as intermediate product.

Serotonin is mainly produced int the enterochromaffin cells of the intestinal mucosa. However, since it cannot pass the blood-brain barrier, it is also synthesized in the brain. It s transported via the platelets in the blood, and itís stored in the end-feet of the neurons in vesicles.

Its empirical formula is: C10H12N2O

3 Physiology

95% of serotonin can be found in the gastrointestinal tract, 90% of it in the enterochromaffin cells of the intestinal mucosa, and the remaining 10% in the enteral nervous system. In the CNS, most of the serotonin can be found in the raphe nuclei of the brain stem. The total quantity of serotonin in the body is estimated around 10 mg.

The effects of serotonin are mediated via the so-called 5-HT receptors. Everywhere you can find 5-HT receptors, serotonin influences physiological processes. In the CNS, serotonin unfolds manifold effects. It contributes to the following processes, among others:

Furthermore, serotonin influences a variety of emotional processes such as aggression and anxiety. A disturbed serotonin balance can be found in diseases such as depression, compulsive disorders, and anxiety disorders.

Outside the CNS, serotonin has the following effects, among others:

Moreover, serotonin plays an important role in the vascular hemostasis component, since it is released from the granules of the activated platelets during their adhesion and contributes to vasoconstriction.

5-HT is eliminated from the synaptic cleft by the reuptake into the pre-synaptic entity. Various psychiatric drugs can inhibit the reuptake (eg. MDMA (ecstasy), cocaine, amphetamine, tricyclic antidepressants, selective serotonin-reuptake-inhibitors, shortly SSRI).

Serotonin is metabolized to 5-hydroxy-indolyl acetid acid (also called 5-HIAA) in the liver. 5-HIAA then is excreted by the kidneys.

4 Clinical presentation

In neuroendocrine tumors (NET) of the gastrointestinal tract, serotonin can be overproduced, which causes typical and diagnostically indicative symptoms such as hyperhidrosis, hypertension, tachycardia, insomnia, and hot flushes.

Moreover, serotonin plays an important role in the pathophysiology of migraine.

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