Neurotransmission is a complex, highly regulated process essential for the orderly function of the human brain. Among the diverse chemical messengers used by the nervous system, the indolamines represent a critical class of biogenic amines. Specifically, serotonin (5-hydroxytryptamine or 5-HT) serves as a primary regulator of physiological and psychological states, ranging from gastrointestinal motility to the complex nuances of human mood and appetite.
The Chemistry of Indolamines
Indolamines are a subset of biogenic amines derived from the amino acid tryptophan. Tryptophan is an essential amino acid that must be obtained through the diet—found in products such as grains, meat, dairy, and chocolate.
The synthesis of serotonin occurs in a two-step process. Because this process relies on the availability of tryptophan in the extracellular fluid, the rate of serotonin production is often limited by how much tryptophan is available to the neurons. Once synthesized, serotonin follows a standard neurotransmitter life cycle:
- Synthesis in the cell body or terminal.
- Packaging into vesicles.
- Release into the synaptic cleft.
- Binding to receptors.
- Inactivation via reuptake or enzymatic degradation.
In the case of serotonin, the action in the synaptic cleft is terminated by selective re-uptake back into the axon terminal. Once back inside the cell, the serotonin can either be re-loaded into vesicles for future use or enzymatically destroyed by the enzyme monoamine oxidase (MAO) located in the mitochondria.
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