Molecule of the Day - Serotonin
Serotonin (C10H12N2O), also known as 5-hydroxytryptamine (5-HT), is a white solid that is slightly soluble in water under standard conditions. Like dopamine (Day 44), it is an important neurotransmitter that regulates vital processes in the body.
In the brain, serotonin is largely produced in the neurons of raphe nuclei, which are found in the brain stem. It regulates perceptions of resource availability, which can affect bodily functions and sensations such as mood, appetite, digestion, and sleep.
Serotonin is released from the presynaptic neuron into the synaptic cleft via the fusing of serotonin-containing vesicles with the presynaptic membrane. It then binds to 5-HT receptors on the postsynaptic membrane.
There are many different subtypes of 5-HT receptors, and each produces a different cellular response upon binding of serotonin.
For example, the binding of serotonin to 5-HT2A receptors results in psychedelia, whereas the binding of serotonin to 5-HT3 receptors results in vomiting.
Due to the diverse functions of serotonin in different cells, many classes of drugs, such as anxiolytics, antidepressants, antiemetics, and antimigraine drugs, are designed to target the serotonin system.
For example, selective serotonin reuptake inhibitors (SSRIs), such as sertraline (Zoloft) inhibit the reuptake of serotonin into the presynaptic membrane from the synaptic cleft. This increases the concentration of serotonin in the synaptic cleft, and the increased binding of serotonin to the 5-HT receptors. This results in an anxiolytic, antidepressive effect.
On the other hand, drugs such as ondansetron act on the receptors themselves; they act as antagonists to 5-HT3 receptors, preventing serotonin from binding to it. As a result, there is a reduction in nausea and vomiting, which are common side-effects in chemotherapy. Hence, such antiemetics are useful and are often co-administered together with chemotherapeutic agents.
In the human body, tryptophan is first hydroxylated via the action of tryptophan hydroxylase to produce 5-hydroxytryptophan, which is then decarboxylated by aromatic amino acid decarboxylase to produce serotonin.