H1 receptor
Encyclopedia
The H1 receptor is a histamine receptor
belonging to the family of Rhodopsin like
G-protein-coupled receptors. This receptor, which is activated by the biogenic amine
histamine
, is expressed throughout the body, to be specific, in smooth muscles, on vascular endothelial cells, in the heart, and in the central nervous system
. The H1 receptor is linked to an intracellular G-protein (Gq) that activates phospholipase C and the phosphatidylinositol
(PIP2) signaling pathway. Antihistamine
s, which act on this receptor, are used as anti-allergic drugs. The crystal structure of the receptor have been determined(shown on the right).
induces the release of histamine from neurons, causing systemic vasodilation, along with increased cell permeability due to its action on H1 receptors.
Histamine H1 receptors are activated by endogenous histamine, which is released by neurons that have their cell bodies in the tuberomammillary nucleus
of the hypothalamus
. The histaminergic neurons of the tuberomammillary nucleus become active during the 'wake' cycle, firing at approximately 2 Hz; during slow wave sleep, this firing rate drops to approximately 0.5 Hz. Finally, during REM sleep, histaminergic neurons stop firing altogether. It has been reported that histaminergic neurons have the most wake-selective firing pattern of all known neuronal types.
In the cortex
, activation of H1 receptors leads to inhibition of cell membrane potassium channels. This depolarizes the neurons and increases the resistance of the neuronal cell membrane, bringing the cell closer to its firing threshold and increasing the excitatory voltage produced by a given excitatory current. H1 receptor antagonists, or antihistamines, produce drowsiness because they oppose this action, reducing neuronal excitation.
Histamine receptor
The histamine receptors are a class of G protein-coupled receptors with histamine as their endogenous ligand.There are four known histamine receptors:*H1 receptor*H2 receptor*H3 receptor*H4 receptor-Comparison:...
belonging to the family of Rhodopsin like
Rhodopsin-like receptors
Rhodopsin-like receptors are a family of proteins that comprise the largest group of G protein-coupled receptors.- Scope :G-protein-coupled receptors, GPCRs, constitute a vast protein family that encompasses a wide range of functions...
G-protein-coupled receptors. This receptor, which is activated by the biogenic amine
Biogenic amine
-Examples:Some prominent examples of biogenic amines include:* Histamine - a substance derived from the amino acid histidine that acts as a neurotransmitter mediating arousal and attention, as well as a pro-inflammatory signal released from mast cells in response to allergic reactions or tissue...
histamine
Histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
, is expressed throughout the body, to be specific, in smooth muscles, on vascular endothelial cells, in the heart, and in the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
. The H1 receptor is linked to an intracellular G-protein (Gq) that activates phospholipase C and the phosphatidylinositol
Phosphatidylinositol
Phosphatidylinositol is a negatively charged phospholipid and a minor component in the cytosolic side of eukaryotic cell membranes....
(PIP2) signaling pathway. Antihistamine
Antihistamine
An H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...
s, which act on this receptor, are used as anti-allergic drugs. The crystal structure of the receptor have been determined(shown on the right).
Role in inflammation
The production of prostaglandin E2 synthaseProstaglandin E synthase
Prostaglandin E synthase is an enzyme involved in eicosanoid and glutathione metabolism, a member of MAPEG family. It generates prostaglandin E from prostaglandin H2.The synthase generating PGE2 is a membrane-associated protein....
induces the release of histamine from neurons, causing systemic vasodilation, along with increased cell permeability due to its action on H1 receptors.
Neurophysiology
Histamine H1 receptors are activated by endogenous histamine, which is released by neurons that have their cell bodies in the tuberomammillary nucleus
Tuberomammillary nucleus
The tuberomammillary nucleus is a subnucleus of the posterior third of the hypothalamus. It consists of, largely, histaminergic neurons and is involved with the control of arousal, sleep and circadian rhythm....
of the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
. The histaminergic neurons of the tuberomammillary nucleus become active during the 'wake' cycle, firing at approximately 2 Hz; during slow wave sleep, this firing rate drops to approximately 0.5 Hz. Finally, during REM sleep, histaminergic neurons stop firing altogether. It has been reported that histaminergic neurons have the most wake-selective firing pattern of all known neuronal types.
In the cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, activation of H1 receptors leads to inhibition of cell membrane potassium channels. This depolarizes the neurons and increases the resistance of the neuronal cell membrane, bringing the cell closer to its firing threshold and increasing the excitatory voltage produced by a given excitatory current. H1 receptor antagonists, or antihistamines, produce drowsiness because they oppose this action, reducing neuronal excitation.