Cannabinoid receptor 1

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(Redirected from
CB1 receptor
)

CNR1
Gene ontology
Molecular function
Cellular component
Biological process
Sources:Amigo / QuickGO
Ensembl
UniProt
RefSeq (mRNA)

NM_007726
NM_001355020
NM_001355021
NM_001365881

RefSeq (protein)

NP_031752
NP_001341949
NP_001341950
NP_001352810

Location (UCSC)Chr 6: 88.14 – 88.17 MbChr 4: 33.92 – 33.95 Mb
PubMed search[3][4]
Wikidata
View/Edit HumanView/Edit Mouse

Cannabinoid receptor 1 (CB1), is a

phytocannabinoids, such as docosatetraenoylethanolamide found in wild daga, the compound THC which is an active constituent of the psychoactive drug cannabis; and synthetic analogs of THC. CB1 is antagonized by the phytocannabinoid tetrahydrocannabivarin (THCV).[7][8]

The primary endogenous agonist of the human CB1 receptor is anandamide.[5]

Structure

The CB1 receptor shares the structure characteristic of all G-protein-coupled receptors, possessing seven transmembrane domains connected by three extracellular and three intracellular loops, an extracellular N-terminal tail, and an intracellular C-terminal tail.

classes of G-protein-coupled receptors. Observed heterodimers include A2A–CB1, CB1D2, OX1–CB1, μOR–CB1, while many more may only be stable enough to exist in vivo.[11][12] The CB1 receptor possesses an allosteric modulatory binding site.[13]

The CB1 receptor is encoded by the gene CNR1,

mammals
.

The CNR1 gene has a structure consisting of a single coding-exon and multiple alternative 5' untranslated exons. The CB1 receptor is created by transcription of the last exon on the CNR1 gene. [17]

Mechanism

The CB1 receptor is a pre-synaptic

endocannabinoids) or exogenously, normally through cannabis or a related synthetic
compound.

Research suggests that the majority of CB1 receptors are coupled through Gi/o proteins. Upon activation, CB1 receptor exhibits its effects mainly through activation of

c-jun, and others.[19]

In terms of function, the inhibition of intracellular cAMP expression shortens the duration of pre-synaptic action potentials by prolonging the rectifying potassium A-type currents, which is normally inactivated upon phosphorylation by PKA. This inhibition grows more pronounced when considered with the effect of activated CB1 receptors to limit calcium entry into the cell, which does not occur through cAMP but by a direct G-protein-mediated inhibition. As presynaptic calcium entry is a requirement for vesicle release, this function will decrease the transmitter that enters the synapse upon release.[15] The relative contribution of each of these two inhibitory mechanisms depends on the variance of ion channel expression by cell type.

The CB1 receptor can also be

THC impairs long-term potentiation and leads to a reduction of phosphorylated CREB.[23]

The signaling properties of activated CB1 are furthermore modified by the presence of SGIP1, that hinders receptor internalization and decreases ERK1/2 signalling while augmenting the interaction with GRK3, β-arrestin-2.[24][25]

In summary, CB1 receptor activity has been found to be coupled to certain ion channels, in the following manner:[12]

  • Positively to inwardly rectifying and A-type outward potassium channels.
  • Negatively to D-type outward potassium channels
  • Negatively to N-type and P/Q-type calcium channels.

Expression

CB1 receptors are localized throughout the central and peripheral nervous systems, particularly on axon terminals in the cerebellum, hippocampus, basal ganglia, frontal cortex, amygdala, hypothalamus, and midbrain.[17] The CB1 receptor is primarily expressed in the presynaptic terminals of GABAergic (amygdala and cerebellum), glutamatergic (cortex, hippocampus and amygdala), dopaminergic, GABAergic interneurons, cholinergic neurons, noradrenergic, and serotonergic neurons.[26] Acting as a neuromodulator, the CB1 receptor inhibits the release of both excitatory and inhibitory neurotransmitters including acetylcholine, glutamate, GABA, noradrenaline, 5-HT, dopamine, D-aspartate, and cholecystokinin.[17] Repeated administration of receptor agonists may result in receptor internalization and/or a reduction in receptor protein signaling.[12]

The inverse agonist MK-9470 makes it possible to produce in vivo images of the distribution of CB1 receptors in the human brain with positron emission tomography.[27]

Brain

The CB1 receptor is recognized as the most abundant

cerebellar cortex.[19]

Cnr1
is widely expressed in all major regions of the postnatal day 14 mouse brain, but is conspicuously absent in much of the thalamus.

CB1 receptors are expressed most densely in the central nervous system and are largely responsible for mediating the effects of cannabinoid binding in the brain. Endocannabinoids released by a depolarized neuron bind to CB1 receptors on pre-synaptic glutamatergic and GABAergic neurons, resulting in a respective decrease in either glutamate or GABA release. Limiting glutamate release causes reduced excitation, while limiting GABA release suppresses inhibition, a common form of short-term

GABA-mediated inhibition, in effect exciting the postsynaptic cell.[15]

Brainstem

High expression of CB1 is found in brainstem medullary nuclei, including the nucleus of the solitary tract and area postrema. CB1 receptor is relatively low in medullary respiratory brainstem control centers.[26]

Hippocampal formation

CB1

glutamate. Cannabinoids suppress the induction of LTP and LTD in the hippocampus by inhibiting these glutamatergic neurons. By reducing the concentration of glutamate released below the threshold necessary to depolarize the postsynaptic receptor NMDA,[15]
a receptor known to be directly related to the induction of LTP and LTD, cannabinoids are a crucial factor in the selectivity of memory. These receptors are highly expressed by GABAergic interneurons as well as glutamatergic principal neurons. However, a higher density is found within GABAergic cells.[28] This means that, although synaptic strength/frequency, and thus potential to induce LTP, is lowered, net hippocampal activity is raised. In addition, CB1 receptors in the hippocampus indirectly inhibit the release of acetylcholine. This serves as the modulatory axis opposing GABA, decreasing neurotransmitter release. Cannabinoids also likely play an important role in the development of memory through their neonatal promotion of myelin formation, and thus the individual segregation of axons.

Basal ganglia

CB1 receptors are expressed throughout the

cannabinoids, whereas an enhancement of movement may occur upon moderate dosages.[15]
However, these dose-dependent effects have been studied predominately in rodents, and the physiological basis for this triphasic pattern warrants future research in humans. Effects may vary based on the site of cannabinoid application, input from higher cortical centers, and whether drug application is unilateral or bilateral.

Cerebellum and neocortex

The role of the CB1 receptor in the regulation of motor movements is complicated by the additional expression of this receptor in the

GABA release from the terminals of basket cells. In the neocortex, these receptors are concentrated on local interneurons in cerebral layers II-III and V-VI.[15] Compared to rat brains, humans express more CB1 receptors in the cerebral cortex and amygdala and less in the cerebellum, which may help explain why motor function seems to be more compromised in rats than humans upon cannabinoid application.[28]

Spine

Many of the documented analgesic effects of cannabinoids are based on the interaction of these compounds with CB1 receptors on

dorsal horn, known for its role in nociceptive processing. In particular, the CB1 is heavily expressed in layers 1 and 2 of the spinal cord dorsal horn and in lamina 10 by the central canal. Dorsal root ganglion also express these receptors, which target a variety of peripheral terminals involved in nociception. Signals on this track are also transmitted to the periaqueductal gray (PAG) of the midbrain. Endogenous cannabinoids are believed to exhibit an analgesic effect on these receptors by limiting both GABA and glutamate of PAG cells that relate to nociceptive input processing, a hypothesis consistent with the finding that anandamide release in the PAG is increased in response to pain-triggering stimuli.[15]

Other

CB1 is expressed on several types of cells in

lungs and the kidney
.

CB1 is present on

ovaries, oviducts myometrium, decidua, and placenta. It has also been implicated in the proper development of the embryo.[19]

CB1 is also expressed in the retina. In the retina, they are expressed in the photoreceptors, inner plexiform, outer plexiform, bipolar cells, ganglion cells, and retinal pigment epithelium cells.[29] In the visual system, cannabinoids agonist induce a dose dependent modulation of calcium, chloride and potassium channels. This alters vertical transmission between photoreceptor, bipolar and ganglion cells. Altering vertical transmission in turn results in the way vision is perceived.[30]

Physiological and pathological conditions

The activation of CB1 in the human body generally promotes neurotransmitter release, controls pain, regulates metabolism, and monitors the cardiovascular system.[31] CB1 receptors are implicated in a number of physiological processes related to the central nervous system (CNS) including brain development, learning and memory, motor behavior, regulation of appetite, body temperature, pain perception, and inflammation.[6]

The localization of CB1 receptors is expressed in several neuronal types, including GABAergic, glutamatergic, and serotonergic neurons. CB1 receptors localized in GABAergic neurons can modulate food intake, learning and memory processes, drug addiction, and running related behaviors. CB1 receptors localized in glutamatergic neurons are capable of mediating olfactory processes, neuroprotection, social behaviors, anxiety, and fear memories. The localization of CB1 receptors in serotonergic neurons can regulate emotional responses.[6]

Clinically, CB1 is a direct drug target for addiction, pain, epilepsy, and obesity.[31] CB1 receptor function is involved with several psychiatric, neurological, neurodevelopmental, and neurodegenerative disorders including Huntington's disease (HD), multiple sclerosis (MS), and Alzheimer's disease (AD). Major loss of CB1 receptors is reported in patients with HD. However, stimulation of the CB1 receptor has potential to reduce the progression of HD. Improvements from use of CB agonist in MS are associated with the activation of CB1 and CB2 receptors, leading to dual anti-inflammatory and neuroprotective effects throughout the CNS. Similarly, activation of CB1 and CB2 receptors could provide neuroprotective effects against amyloid-β (Aβ) toxicity in AD.[32] In several brain regions, including the dorsolateral prefrontal cortex (DLPFC) and hippocampus, dysregulation of the CB1 receptor is implicated in the development of schizophrenia. Abnormal functioning of the CB1 receptor compromises intricate neural systems that are responsible for controlling cognition and memory, which contributes to the pathology.[17] PET imaging modalities implicate that alterations of CB1 levels in certain brain systems are strongly associated with schizophrenia symptoms. Neurobehavioral disorders, such as attention deficit hyperactivity disorder (ADHD), are associated with genetic variants of CNR1 in rat models of ADHD.[26]

Use of antagonists

Selective CB1 agonists may be used to isolate the effects of the receptor from the CB1 receptor, as most cannabinoids and endocannabinoids bind to both receptor types.[15]

TM38837
has been developed as a CB1 receptor antagonist that is restricted to targeting only peripheral CB1 receptors.

Ligands

Agonists

Selective

Unspecified efficacy

Partial

Endogenous
Phyto

Full

Endogenous
Synthetic

Allosteric agonist

Antagonists

Inverse agonists

Allosteric modulators

Binding affinities

CB1 affinity (Ki) Efficacy towards CB1 CB2 affinity (Ki) Efficacy towards CB2 Type References
Anandamide 78 nM Partial agonist 370 nM Partial agonist Endogenous
N-Arachidonoyl dopamine 250 nM Agonist 12000 nM ? Endogenous [36]
2-Arachidonoylglycerol 58.3 nM Full agonist 145 nM Full agonist Endogenous [36]
2-Arachidonyl glyceryl ether 21 nM Full agonist 480 nM Full agonist Endogenous
Tetrahydrocannabinol 10 nM Partial agonist 24 nM Partial agonist Phytogenic [37]
EGCG
33600 nM Agonist 50000+ nM ? Phytogenic
AM-1221 52.3 nM Agonist 0.28 nM Agonist Synthetic [38]
AM-1235 1.5 nM Agonist 20.4 nM Agonist Synthetic [39]
AM-2232 0.28 nM Agonist 1.48 nM Agonist Synthetic [39]
UR-144 150 nM Full agonist 1.8 nM Full agonist Synthetic [40]
JWH-007 9.0 nM Agonist 2.94 nM Agonist Synthetic [41]
JWH-015 383 nM Agonist 13.8 nM Agonist Synthetic [41]
JWH-018 9.00 ± 5.00 nM Full agonist 2.94 ± 2.65 nM Full agonist Synthetic [42]

Evolution

The CNR1 gene is used in animals as a

dermopterans as the closest primate relatives.[46]

Paralogues

Source:[47]

See also

  • Discovery and development of Cannabinoid Receptor 1 Antagonists
  • Cannabinoid receptor
  • Cannabinoid receptor type 2
    (CB2)

References

  1. ^ a b c GRCh38: Ensembl release 89: ENSG00000118432 - Ensembl, May 2017
  2. ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000044288 - Ensembl, May 2017
  3. ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. ^ a b c Abood M, Barth F, Bonner TI, Cabral G, Casellas P, Cravatt BF, et al. (22 August 2018). "CB1 Receptor". IUPHAR/BPS Guide to Pharmacology. International Union of Basic and Clinical Pharmacology. Retrieved 9 November 2018.
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  14. ^ a b c "Entrez Gene: CNR1 cannabinoid receptor 1 (brain)".
  15. ^
    PMID 11316486
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  16. ^ a b "OrthoMaM phylogenetic marker: CNR1 coding sequence". Archived from the original on 22 December 2015. Retrieved 23 November 2009.
  17. ^
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  37. ^ "PDSP Database – UNC". Archived from the original on 8 November 2013. Retrieved 11 June 2013.
  38. ^ WO patent 200128557, Makriyannis A, Deng H, "Cannabimimetic indole derivatives", granted 2001-06-07 
  39. ^ a b US patent 7241799, Makriyannis A, Deng H, "Cannabimimetic indole derivatives", granted 2007-07-10 
  40. PMID 19921781
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  47. ^ "CNR1 paralogs". GeneCards®: The Human Gene Database.

External links

This article incorporates text from the United States National Library of Medicine, which is in the public domain.