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G protein-coupled receptor
5-HT receptor
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5-HT receptor

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The 5-HT1B receptor as an example of a metabotropic serotonin receptor. Its crystallographic structure in ribbon representation

5-HT receptors, 5-hydroxytryptamine receptors, or serotonin receptors, are a group of G protein-coupled receptor and ligand-gated ion channels found in the central and peripheral nervous systems. They mediate both excitatory and inhibitory neurotransmission. The serotonin receptors are activated by the neurotransmitter serotonin, which acts as their natural ligand.

The serotonin receptors modulate the release of many neurotransmitters, including glutamate, GABA, dopamine, epinephrine / norepinephrine, and acetylcholine, as well as many hormones, including oxytocin, prolactin, vasopressin, cortisol, corticotropin, and substance P, among others. Serotonin receptors influence various biological and neurological processes such as aggression, anxiety, appetite, cognition, learning, memory, mood, nausea, sleep, and thermoregulation. They are the target of a variety of pharmaceutical and recreational drugs, including many antidepressants, antipsychotics, anorectics, antiemetics, gastroprokinetic agents, antimigraine agents, hallucinogens, and entactogens.

Serotonin receptors are found in almost all animals and are even known to regulate longevity and behavioral aging in the primitive nematode, Caenorhabditis elegans.

Classification

5-hydroxytryptamine receptors or 5-HT receptors, or serotonin receptors are found in the central and peripheral nervous systems. They can be divided into 7 families of G protein-coupled receptors which activate an intracellular second messenger cascade to produce an excitatory or inhibitory response. The exception to this is the 5-HT3 receptor which is a ligand-gated ion channel. In 2014, a novel 5-HT receptor was isolated from the small white butterfly, Pieris rapae, and named pr5-HT8. It does not occur in mammals and shares relatively low similarity to the known 5-HT receptor classes.

Families

Family Type Mechanism Potential
5-HT1 Gi/Go-protein coupled. Decreasing cellular levels of cAMP. Inhibitory
5-HT2 Gq/G11-protein coupled. Increasing cellular levels of IP3 and DAG. Excitatory
5-HT3 Ligand-gated Na+ and K+ cation channel. Depolarizing plasma membrane. Excitatory
5-HT4 Gs-protein coupled. Increasing cellular levels of cAMP. Excitatory
5-HT5 Gi/Go-protein coupled. Decreasing cellular levels of cAMP. Inhibitory
5-HT6 Gs-protein coupled. Increasing cellular levels of cAMP. Excitatory
5-HT7 Gs-protein coupled. Increasing cellular levels of cAMP. Excitatory

Subtypes

The 7 general serotonin receptor classes include a total of 14 known serotonin receptors. The specific types have been characterized as follows:

Information on serotonin receptors (human isoforms if nothing else is stated)
Receptor First cloned – PDB entries Gene(s) Distribution Function Agonists Antagonists Uses of drugs that act on this receptor
Blood vessels CNS GI Tract Platelets PNS Smooth Muscle
5-HT1A 1987 –
  • 7e2x
  • 7e2y
  • 7e2z

7E2Y 5-HT1A receptor serotonin.png

Yes Yes No No No No
  • Addiction
  • Aggression
  • Anxiety
  • Appetite
  • Autoreceptor
  • Blood Pressure
  • Cardiovascular Function
  • Emesis
  • Heart Rate
  • Impulsivity
  • Memory
  • Mood
  • Nausea
  • Nociception
  • Penile Erection
  • Pupil Dilation
  • Respiration
  • Sexual Behavior
  • Sleep
  • Sociability
  • Thermoregulation
  • Vasoconstriction

Selective (for 5-HT1A over other 5-HT receptors)

Nonselective

5-HT1B 1992 –
  • 6g79
 Yes Yes No No No No
  • Addiction
  • Aggression
  • Anxiety
  • Autoreceptor
  • Learning
  • Locomotion
  • Memory
  • Mood
  • Penile Erection
  • Sexual Behavior
  • Vasoconstriction
5-HT1D 1991 –
  • 7e32

7E32 5-HT1D receptor.png

Yes Yes No No No No
5-HT1E 1992 –
  • 7e33

7E33 5-HT1E receptor.png

Yes Yes No No No No
  • None known
5-HT1F 1993 –
  • 7exd

7exd 5-HT1F receptor.png

No Yes No No No No
  • Migraine
  • None known
5-HT2A 1988 Yes Yes Yes Yes Yes Yes
  • Addiction (potentially modulating)
  • Anxiety
  • Appetite
  • Cognition
  • Imagination
  • Learning
  • Memory
  • Mood
  • Perception
  • Sexual Behavior
  • Sleep
  • Thermoregulation
  • Vasoconstriction
5-HT2B 1992 Yes Yes Yes Yes Yes Yes
  • Anxiety
  • Appetite
  • Cardiovascular Function
  • GI Motility
  • Sleep
  • Vasoconstriction
5-HT2C 1988 Yes Yes Yes Yes Yes Yes
  • Addiction. (potentially modulating)
  • Anxiety
  • Appetite
  • GI Motility
  • Heteroreceptor for norepinephrine and dopamine
  • Locomotion
  • Mood
  • Penile Erection
  • Sexual Behavior
  • Sleep
  • Thermoregulation
  • Vasoconstriction
5-HT3 1993 No Yes Yes No Yes No
  • Addiction
  • Anxiety
  • Emesis
  • GI Motility
  • Learning
  • Memory
  • Nausea
5-HT4 1995 No Yes Yes No Yes No
  • Anxiety
  • Appetite
  • GI Motility
  • Learning
  • Memory
  • Mood
  • Respiration
5-HT5A 1994 No Yes No No No No
  • None thus far
5-HT5B 1993 No No No No No No

Functions in rodents,
pseudogene in humans

  • None thus far
5-HT6 1993 No Yes No No No No
  • Anxiety
  • Cognition
  • Learning
  • Memory
  • Mood
5-HT7 1993 Yes Yes Yes No No No
  • Anxiety
  • Autoreceptor
  • Memory
  • Mood
  • Respiration
  • Sleep
  • Thermoregulation
  • Vasoconstriction

Note that there is no 5-HT1C receptor since, after the receptor was cloned and further characterized, it was found to have more in common with the 5-HT2 family of receptors and was redesignated as the 5-HT2C receptor.

Very nonselective agonists of 5-HT receptor subtypes include ergotamine (an antimigraine), which activates 5-HT1A, 5-HT1D, 5-HT1B, D2 and norepinephrine receptors. LSD (a psychedelic) is a 5-HT1A, 5-HT2A, 5-HT2C, 5-HT5A and 5-HT6 agonist.

Expression patterns

The genes coding for serotonin receptors are expressed across the mammalian brain. Genes coding for different receptors types follow different developmental curves. Specifically, there is a developmental increase of HTR5A expression in several subregions of the human cortex, paralleled by a decreased expression of HTR1A from the embryonic period to the post-natal one.

5-HT1-like

A number of receptors were classed as "5-HT1-like" - by 1998 it was being argued that, since these receptors were "a heterogeneous population of 5-HT1B, 5-HT1D and 5-HT7" receptors the classification was redundant.

External links


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