title: CB₂ cannabinoid receptors inhibit synaptic transmission when expressed in cultured autaptic neurons.
abstract: The role of CB₂ in the central nervous system, particularly in neurons, has generated much controversy. Fueling the controversy are imperfect tools, which have made conclusive identification of CB₂ expressing neurons problematic. Imprecise localization of CB₂ has made it difficult to determine its function in neurons. Here we avoid the localization controversy and directly address the question if CB₂ can modulate neurotransmission. CB₂ was expressed in excitatory hippocampal autaptic neurons obtained from CB₁ null mice. Whole-cell patch clamp recordings were made from these neurons to determine the effects of CB₂ on short-term synaptic plasticity. CB₂ expression restored depolarization induced suppression of excitation to these neurons, which was lost following genetic ablation of CB₁. The endocannabinoid 2-arachidonylglycerol (2-AG) mimicked the effects of depolarization in CB₂ expressing neurons. Interestingly, ongoing basal production of 2-AG resulted in constitutive activation of CB₂, causing a tonic inhibition of neurotransmission that was relieved by the CB₂ antagonist AM630 or the diacylglycerol lipase inhibitor RHC80267. Through immunocytochemistry and analysis of spontaneous EPSCs, paired pulse ratios and coefficients of variation we determined that CB₂ exerts its function at a presynaptic site of action, likely through inhibition of voltage gated calcium channels. Therefore CB₂ expressed in neurons effectively mimics the actions of CB₁. Thus neuronal CB₂ is well suited to integrate into conventional neuronal endocannabinoid signaling processes, with its specific role determined by its unique and highly inducible expression profile.
authors.affiliation: Department of Psychological and Brain Sciences, Gill Center for Biomolecular Science, Indiana University, 1101 E. 10th Street, Bloomington, IN 47405, USA. atwoodbk@mail.nih.gov
authors.forename: Brady K
authors.initials: BK
authors.lastname: Atwood
authors.forename: Alex
authors.initials: A
authors.lastname: Straiker
authors.forename: Ken
authors.initials: K
authors.lastname: Mackie
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001095:Arachidonic Acids / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D001253:Astrocytes / Q000166:cytology; D002478:Cells, Cultured; D063388:Endocannabinoids / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005989:Glycerides / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D006579:Heterozygote; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D043884:Receptor, Cannabinoid, CB1 / Q000235:genetics / Q000378:metabolism; D043885:Receptor, Cannabinoid, CB2 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects
chemical_list: D001095:Arachidonic Acids; C571431:Cnr2 protein, mouse; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D005989:Glycerides; D009419:Nerve Tissue Proteins; D043884:Receptor, Cannabinoid, CB1; D043885:Receptor, Cannabinoid, CB2; D011993:Recombinant Fusion Proteins; C094503:glyceryl 2-arachidonate; D008071:Lipoprotein Lipase