Two receptors have been identified as the main cannabinoid receptors, the CB1 and CB2 receptors. The receptors have been cloned [12,13], established as the primary targets for endogenous and exogenous cannabinoids [10,14,15], and shown to belong to the superfamily of G-protein coupled receptors (GPCRs), characterized by seven transmembrane domains and coupled to G-proteins, notably to Gi/Go proteins [14]. In humans, the genes encoding the CB1 (cnr1) and CB2 (cnr2) receptors are located on the 6q14-q15 and 1p36.11 chromosomes, respectively [10]. The two receptors share ~44% sequence identity and diverge significantly in their distribution. CB1 receptor (CB1R) is highly expressed in different brain regions [16,17,18] and is considered the most abundant GPCR in the brain (reviewed in [10,14,15]). The CB2 receptor (CB2R) is principally expressed in immune tissues, inflammatory cells and in much lower densities in brain [10].
