serotonin

serotonin

(sĕr'ətō`nĭn), organic compound that was first recognized as a powerful vasoconstrictor occurring in blood serum. It was partially purified, crystallized, and named in 1948, and its structure was deduced a year later. Independent work indicated that serotonin was widely distributed in nature and occurred in tissues other than blood. It has been shown to be in many representatives of the animal kingdom, in wasp stings and scorpion venom, in various fruits, such as pineapples, bananas, and plums, and in various nuts. It has been estimated that an adult human contains about 5 to 10 mg of serotonin, 90% of which is in the intestine and the rest in blood platelets and the brain. One role of the compound is as a neurotransmitter whose participation is being sought in diverse functions including learning, sleep, and control of mood. The structural similarity of serotonin to several drugs known to cause mental aberrations, such as LSD, has prompted much speculation as to the role of serotonin in naturally occurring mental disorders such as schizophrenia or depression. Serotonin also acts as a hormone. Serotonin produced by the intestines inhibits the production of the bone tissue by osteoblasts, while in the brain it acts indirectly to promote the formation of bone. The placenta has been discovered to produce serotonin that stimulates the development of neural connections in the forebrain of the embryo. The function of serotonin in blood platelets is not entirely clear, but by acting as a vasoconstrictor and possibly in other ways it helps to regulate the clotting process. Its function in stings and venoms might be that of an irritant, since intravenous injections of serotonin in humans produce pain at the site of injection, gasping, coughing, a general tingling and prickling sensation, nausea, cramps, and other unpleasant symptoms.

Serotonin

A compound, also known as 5-hydroxytryptamine (5-HT), derived from tryptophan, an indole-containing amino acid. It is widely distributed in the animal and vegetable kingdoms. In mammals it is found in gastrointestinal enterochromaffin cells, in blood platelets, and in brain and nerve tissue. Serotonin is a local vasoconstrictor, plays a role in brain and nerve function and in regulation of gastric secretion and intestinal peristalsis, and has pharmacologic properties. It is inactivated by monoamine oxidases (MAO-A and -B), enzymes that also inactivate other neurotransmitters such as norepinephrine and dopamine.

Serotonin is concentrated in certain areas of the brain; the hypothalamus and midbrain contain large amounts, while the cortex and cerebellum contain low concentrations. Like most neurotransmitters, it is stored in granules inside nerve endings, and is thus not exposed to inactivation by monoamine oxidases until it is released into the synaptic space between nerves. When a serotonin-containing nerve fires, serotonin is released and can bind to any one of a series of at least 14 distinct downstream serotonin receptors (5-HT receptors). Release of serotonin or other stored neurotransmitters can also be induced by alkaloids such as reserpine, which have been used as tranquilizing agents in the treatment of nervous and mental disorders. Although pharmacologic doses of serotonin produce a type of sedation and other depressant conditions of the nervous system, several types of clinically useful antidepressants, such as monoamine oxidase (MAO) inhibitors, tricyclic antidepressants, and selective serotonin reuptake inhibitors (SSRIs), act by increasing the amount of active serotonin in nerve synapses in particular brain regions. Conversely, various conditions that lower serotonin levels are associated with depression, suggesting that normal to slightly elevated serotonin levels tend to elevate mood and prevent depression. See Affective disorders, Brain, Nervous system (vertebrate), Neurosecretion, Psychopharmacology

Serotonin

 

(also 5-hydroxytryptamine), a biologically active substance in human and animal blood and tissue that in several cases has proved to be a mediator of the nervous system, both on the periphery and in nerve centers (mainly, in the hypothalamus). Serotonin’s chemical structure is

Serotonin was first isolated and obtained in crystalline form from bovine serum in 1947. It has been found in all animal groups studied. It is present in large amounts in the poisons of coelenterates, mollusks, arthropods, and amphibians; it is also found in plants. In the body, serotonin is synthesized from the amino acid tryptophan; in humans and most vertebrates, serotonin synthesis is conducted mainly in the cells of the mucosal membrane of the small intestine, as well as in the pancreas and central nervous system. In tissues, serotonin is converted into 5-hydroxyindoleacetic acid, which is eliminated from the body by the kidneys. The enzyme monoamine oxidase is very important in the metabolism of serotonin.

Serotonin has a great influence on vascular tone and participates in the humoral regulation of the functions of the digestive, excretory, endocrine, and central nervous systems. Blood (primarily thrombocytes) contains 0.02 to 0.6 mg/liter of serotonin. The action of hallucinogens, including LSD and mescaline, is explained by disorders of serotonin metabolism and action in the central nervous system. It is believed that serotonin metabolism disorders may cause a variety of pathological conditions, including myocardial infarction, ulcers, and several men-taldiseases.

G. N. KASSIL’

serotonin

[‚sir·ə′tō·nən]

(biochemistry)

C₁₀H₁₂ON₂ A compound derived from tryptophan which functions as a local vasoconstrictor, plays a role in neurotransmission, and has pharmacologic properties. Also known as 5-hydroxytryptamine.