Neurotransmitters: Serotonin

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Serotonin is a neurotransmitter. It can be found throughout the body mainly within our brain and intestines. It is a biogenic amine that is derived from tryptophan through a process called serotonin biosynthesis. Serotonin is known for regulating mood, controlling appetite, promoting sleep, and aiding in digestion. It is a very important transmitter to maintain our well-being.

Serotonin Biosynthesis

The first step to serotonin biosynthesis involves an amino acid called tryptophan. We obtain tryptophan through our diet in food such as eggs, turkey, cheese and nuts. Once these food are broken down the amino acid is taken up by neurons and other cells to be synthesized. In our brain it is taken up by serotonergic neurons while in our gastrointestinal tract, which holds 90-95% of our serotonin, it is synthesized by enteric neurons.

The second step happens within the serogenic terminals within those neurons. This step involves the hydroxylation of tryptophan catalyzed by the enzyme tryptophan hydroxylase (THP). This emzyme requires tetrahydrobiopetrin (BH4) in order to function properly. There are two isoforms of tryptophan hydroxylase:

1. TPH1 : Found in peripheral tissue, such as the gut.
2. TPH2 : Found in mainly in the brain.

This process transforms tryptophan in to 5-hydroxytryptophan (5-HTP). 

The last step is decarboxylation of 5-HTP. This is process is catalyzed by the enzyme aromatic L-amino acid decarboxylase (AAAD), which is commonly know as dopamine decarboxylase. This transforms 5-HTP in serotonin (5-HT). This step does not require the presence of a cofactor beside pyridoxal phosphate (vitamin B6) to function properly.

Storage and Metabolism

Serotonin is stored within vesicles in serotonergic neurons.

Release and Re-uptake

Serotonin Receptors

Psychological/Behavioral Effects

Peripheral System

Disorders