GPR18
N-arachidonyl glycine receptor also known as G-protein coupled receptor 18 (GPR18) is a protein that in humans is encoded by the GPR18 gene. Along with the other previously "orphan" receptors GPR55 and GPR119, GPR18 has been found to be a receptor for endogenous lipid neurotransmitters, several of which also bind to cannabinoid receptors.
Research supports the hypothesis that GPR18 is the abnormal cannabidiol receptor and N-arachidonoyl glycine, the endogenous lipid metabolite of anandamide, initiates directed microglial migration in the CNS through activation of GPR18, though recent evidence demonstrates that NAGly was not shown to be a GPR18 agonist in rat sympathetic neurons.
Ligands
Ligands found to bind to GPR18 as agonists include:
N-Arachidonoylglycine (NAGly)
Abnormal cannabidiol (Abn-CBD)
AM-251 - partial agonist
Cannabidiol - partial agonist
O-1602
Δ9-Tetrahydrocannabinol (Δ9-THC) - THC is actually a more potent agonist at GPR18 than at CB1 or CB2, with Ki of 0.96nM at GPR18, 8.1nM at GPR55, 25.1nM at CB1 and 35.2nM at CB2.