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5-HT receptor

Synonyms: serotonin receptor, 5-hydroxytryptamine receptor
German: 5-HT-Rezeptor, Serotoninrezeptor, 5-Hydroxytryptamin-Rezeptor

1 Definition

5-HT receptors, also known as serotonin receptors are receptors that are activated by serotonin. Almost all serotonin receptors are G protein–coupled receptors, with the exception of the 5-HT3 receptor subfamily which are ligand-gated ion channels.

2 Occurrence

Serotonin receptors are present in the central nervous system, as well as in the peripheral nervous system. They play important roles in various neuronal processes, including memory, mood, thermoregulation, appetite, cognition, and learning.

3 Classification

Serotonin receptors can be grouped into the following families and subfamilies:

Family G protein Mechanism of signal transduction Function Subtypes
5-HT1 receptor Gi/G0 Decreases intracellular cAMP concentration Inhibitory 1A, 1B, 1D, 1E, 1F
5-HT2 receptor Gq/11 Increases intracellular IP3 and DAG concentration Excitatory 2A, 2B, 2C
5-HT3 receptor Ligand-gated Na+-/K+ channel Depolarizes cell membrane Excitatory
5-HT4 receptor Gs Increases intracellular cAMP concentration Excitatory
5-HT5 receptor Gi/G0 Decreases intracellular cAMP concentration Inhibitory 5A, 5B
5-HT6 receptor Gs Increases intracellular cAMP concentration Excitatory
5-HT7 receptor Gs Increases intracellular cAMP concentration Excitatory

4 Effect

4.1 G protein–coupled 5-HT receptors

Except for 5-HT3 receptors, serotonin receptors are G protein-coupled receptors. 5-HT1A, 5-HT1B, 5-HT1D and 5-HT4 receptors inhibit the adenylyl cyclase protein. 5-HT1C and 5-HT2 receptors stimulate the transformation of inositol phosphates.

4.1.1 Inhibitory effect

The activation of, for example, a 5-HT1 receptor in pyramid cells of the hippocampus opens potassium channels via a G protein, which in turn causes the inhibition of neuronal activity due to the resulting hyperpolarization.

4.1.2 Excitatory effect

The activation of a 5-HT2 receptor stimulates phospholipase C which results in the synthesis of the messenger substance IP3 which effects the release of calcium from intracellular reservoirs, triggering the contraction of smooth muscle.

4.2 Ligand-gated ion channels

The 5-HT3 receptor belongs to the group of ligand-gated ion channels and is a non-selective cation channel. The physiologically most relevant ions passing through the channel are sodium and potassium. After the channel opens, Na+ flows into the cell and K+ leaves the cell, along their respective electrochemical gradients. The result is an ion current that is directed into the cell and results in depolarization. Thus, 5-HT3 receptors are excitatory. So far, they have been found in the autonomic nervous system, sensory pain fibers, and in the brain. The activation of 5-HT3 receptors in the solitary nucleus causes vomiting.

5 Clinical significance

Serotonin receptors are the target of multiple psychotropic drugs, including antidepressants. 5-HT3 receptor antagonists (e.g. Ondansetron or Granisetron) are used as antiemetic drugs, for example complementary to the use of cytostatic agents.

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