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The G-protein coupled cannabinoid receptors CB1 and CB2 are activated by Δ9-tetrahydrocannabinol, the psychoactive ingredient of cannabis, and mediate physiological effects of endogenous cannabinoids (‘endocannabinoids’). CB1 genes have been identified in mammals, birds, amphibians and fish, whilst CB2 genes have been identified in mammals and in the puffer fish Fugu rubripes. Therefore, both CB1 and CB2 receptors probably occur throughout the vertebrates. However, cannabinoid receptor genes have yet to be identified in any invertebrate species and the evolutionary origin of cannabinoid receptors is unknown. Here we report the identification of CiCBR, a G-protein coupled receptor in a deuterostomian invertebrate – the urochordate Ciona intestinalis – that is orthologous to vertebrate cannabinoid receptors. The CiCBR cDNA encodes a protein with a predicted length (423 amino-acids) that is the intermediate of human CB1 (472 amino-acids) and human CB2 (360-amino-acid) receptors. Interestingly, the protein-coding region of the CiCBR gene is interrupted by seven introns, unlike in vertebrate cannabinoid receptor genes where the protein-coding region is typically intronless. Phylogenetic analysis revealed that CiCBR forms a clade with vertebrate cannabinoid receptors but is positioned outside the CB1 and CB2 clades of a phylogenetic tree, indicating that the common ancestor of CiCBR and vertebrate cannabinoid receptors predates a gene (genome) duplication event that gave rise to CB1- and CB2-type receptors in vertebrates. Importantly, the discovery of CiCBR and the absence of orthologues of CiCBR in protostomian invertebrates such as Drosophila melanogaster and Caenorhabditis elegans indicate that the ancestor of vertebrate CB1 and CB2 cannabinoid receptors originated in a deuterostomian invertebrate. [Copyright &y& Elsevier]

2-Arachidonoylglycerol (2-AG) is a naturally occurring monoglyceride that activates cannabinoid receptors and meets several key requisites of an endogenous cannabinoid substance. It is present in the brain (where its levels are 170-folds higher than those of anandamide), is produced by neurons in an activity- and calcium-dependent manner, and is rapidly eliminated. The mechanism of 2-AG inactivation is not completely understood, but is thought to involve carrier-mediated transport into cells followed by enzymatic hydrolysis. We examined the possible role of the serine hydrolase, monoglyceride lipase (MGL), in brain 2-AG inactivation. We identified by homology screening a cDNA sequence encoding for a 303-amino acid protein, which conferred MGL activity upon transfection to COS-7 cells. Northern blot and in situ hybridization analyses revealed that MGL mRNA is unevenly present in the rat brain, with highest levels in regions where CB1 cannabinoid receptors are also expressed (hippocampus, cortex, anterior thalamus and cerebellum). Immunohistochemical studies in the hippocampus showed that MGL distribution has striking laminar specificity, suggesting a presynaptic localization of the enzyme. Adenovirus-mediated transfer of MGL cDNA into rat cortical neurons increased the degradation of endogenously produced 2-AG in these cells, whereas no such effect was observed on anandamide degradation. These results indicate that hydrolysis via MGL may be a primary route of 2-AG inactivation in intact neuronal cells. [Copyright &y& Elsevier]

The major endocannabinoids, anandamide (N-arachidonoylethanolamide, 20:4n−6 N-acylethanolamine) and 2-arachidonoylglycerol (2-AG) are structurally and functionally similar, but they are produced by different metabolic pathways and their levels must therefore be regulated by different mechanisms. Both endocannabinoids are accompanied by cannabinoid receptor-inactive, saturated and mono- or di-unsaturated congeners which can influence their metabolism and function. Here we review published data on the presence and production of anandamide and 2-AG and their congeners in mammalian cells and discuss this information in terms of their proposed signaling functions. [Copyright &y& Elsevier]

This review examines pharmacological and biochemical evidence that suggests the existence of an as yet undefined endothelial receptor that mediates endocannabinoid-induced vasodilation. The signaling mechanisms triggered through this receptor and its potential physiological role are also discussed. Since vasodilation is often associated with hypotension, mechanisms involved in the hypotensive actions of cannabinoids, including the endocannabinoids anandamide and 2-arachidonoylglycerol, are also briefly reviewed. [Copyright &y& Elsevier]