Serotonin is a hormone, also known as 5-hydroxytryptamine or 5-HTP, found in the body. Primary centers containing this hormone are the brain, pineal gland, blood platelets and the intestines. Serotonin is formed in the body from L-tryptophan, an amino acid. The body then stores serotonin until it is activated by the enzyme monoamine oxidase. Serotonin is a neurotransmitter, meaning that it is responsible for transmitting messages or signals between nerve cells, causing a narrowing of the blood vessels.
Serotonin plays a major role in several important bodily functions, such as appetite and sleep. It is also known for the role it plays in regulating mood, learning, memory and behavior. Serotonin plays an important role in cardiovascular function, temperature regulation, endocrine regulation and muscle retraction. Serotonin is perhaps most famous for its role in depression.