Several animal models (CB1 −/− knockout) suggest that additional cannabinoid receptors may exist that mediate the effects of the 5 known endocannabinoids and other putative (e.g. palmitoylethanolamide) lipids. A recent study identified a G-protein coupled receptor, GPR55, which is expressed in some human brain regions and binds exogenous and endogenous cannabinoids [78-84]. The 17 kb gene encoding GPR55 resides on 2q37 and has 3 exons.
