title: Multiple Forms of Endocannabinoid and Endovanilloid Signaling Regulate the Tonic Control of GABA Release.
abstract: Persistent CB1 cannabinoid receptor activity limits neurotransmitter release at various synapses throughout the brain. However, it is not fully understood how constitutively active CB1 receptors, tonic endocannabinoid signaling, and its regulation by multiple serine hydrolases contribute to the synapse-specific calibration of neurotransmitter release probability. To address this question at perisomatic and dendritic GABAergic synapses in the mouse hippocampus, we used a combination of paired whole-cell patch-clamp recording, liquid chromatography/tandem mass spectrometry, stochastic optical reconstruction microscopy super-resolution imaging, and immunogold electron microscopy. Unexpectedly, application of the CB1 antagonist and inverse agonist AM251 [N-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide], but not the neutral antagonist NESS0327 [8-chloro-1-(2,4-dichlorophenyl)-N-piperidin-1-yl-5,6-dihydro-4H-benzo[2,3]cyclohepta[2,4-b]pyrazole-3-carboxamine], significantly increased synaptic transmission between CB1-positive perisomatic interneurons and CA1 pyramidal neurons. JZL184 (4-nitrophenyl 4-[bis(1,3-benzodioxol-5-yl)(hydroxy)methyl]piperidine-1-carboxylate), a selective inhibitor of monoacylglycerol lipase (MGL), the presynaptic degrading enzyme of the endocannabinoid 2-arachidonoylglycerol (2-AG), elicited a robust increase in 2-AG levels and concomitantly decreased GABAergic transmission. In contrast, inhibition of fatty acid amide hydrolase (FAAH) by PF3845 (N-pyridin-3-yl-4-[[3-[5-(trifluoromethyl)pyridin-2-yl]oxyphenyl]methyl]piperidine-1-carboxamide) elevated endocannabinoid/endovanilloid anandamide levels but did not change GABAergic synaptic activity. However, FAAH inhibitors attenuated tonic 2-AG increase and also decreased its synaptic effects. This antagonistic interaction required the activation of the transient receptor potential vanilloid receptor TRPV1, which was concentrated on postsynaptic intracellular membrane cisternae at perisomatic GABAergic symmetrical synapses. Interestingly, neither AM251, JZL184, nor PF3845 affected CB1-positive dendritic interneuron synapses. Together, these findings are consistent with the possibility that constitutively active CB1 receptors substantially influence perisomatic GABA release probability and indicate that the synaptic effects of tonic 2-AG release are tightly controlled by presynaptic MGL activity and also by postsynaptic endovanilloid signaling and FAAH activity.
  
  
  CONCLUSIONS
  Tonic cannabinoid signaling plays a critical role in the regulation of synaptic transmission. However, the mechanistic details of how persistent CB1 cannabinoid receptor activity inhibits neurotransmitter release have remained elusive. Therefore, electrophysiological recordings, lipid measurements, and super-resolution imaging were combined to elucidate those signaling molecules and mechanisms that underlie tonic cannabinoid signaling. The findings indicate that constitutive CB1 activity has pivotal function in the tonic control of hippocampal GABA release. Moreover, the endocannabinoid 2-arachidonoylglycerol (2-AG) is continuously generated postsynaptically, but its synaptic effect is regulated strictly by presynaptic monoacylglycerol lipase activity. Finally, anandamide signaling antagonizes tonic 2-AG signaling via activation of postsynaptic transient receptor potential vanilloid TRPV1 receptors. This unexpected mechanistic diversity may be necessary to fine-tune GABA release probability under various physiological and pathophysiological conditions.
authors.affiliation: Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California 92697.
authors.forename: Sang-Hun
authors.identifier: http://orcid.org/0000-0001-8880-2785
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Momentum Laboratory of Molecular Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary.
authors.forename: Marco
authors.initials: M
authors.lastname: Ledri
authors.affiliation: Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, H-1111 Budapest, Hungary.
authors.forename: Blanka
authors.initials: B
authors.lastname: Tóth
authors.affiliation: Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California 92697.
authors.forename: Ivan
authors.initials: I
authors.lastname: Marchionni
authors.affiliation: Momentum Laboratory of Molecular Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Henstridge
authors.affiliation: Momentum Laboratory of Molecular Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary, School of PhD Studies, Semmelweis University, H-1769 Budapest, Hungary.
authors.forename: Barna
authors.identifier: http://orcid.org/0000-0001-5078-0090
authors.initials: B
authors.lastname: Dudok
authors.affiliation: Momentum Laboratory of Molecular Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary.
authors.forename: Kata
authors.initials: K
authors.lastname: Kenesei
authors.affiliation: Momentum Laboratory of Molecular Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Barna
authors.affiliation: Momentum Laboratory of Molecular Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary.
authors.forename: Szilárd I
authors.initials: SI
authors.lastname: Szabó
authors.affiliation: Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, H-1111 Budapest, Hungary.
authors.forename: Tibor
authors.initials: T
authors.lastname: Renkecz
authors.affiliation: Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California 92697.
authors.forename: Michelle
authors.identifier: http://orcid.org/0000-0003-0993-489X
authors.initials: M
authors.lastname: Oberoi
authors.affiliation: Department of Anatomy, Hokkaido University School of Medicine, Sapporo 060-8638, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Watanabe
authors.affiliation: Department of Radiation Oncology, University of California, Irvine, California 92697.
authors.forename: Charles L
authors.initials: CL
authors.lastname: Limoli
authors.affiliation: Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, H-1111 Budapest, Hungary, MTA-BME Research Group of Technical Analytical Chemistry, H-1111 Budapest, Hungary, and.
authors.forename: George
authors.initials: G
authors.lastname: Horvai
authors.affiliation: Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California 92697.
authors.forename: Ivan
authors.initials: I
authors.lastname: Soltesz
authors.affiliation: Momentum Laboratory of Molecular Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary, katona@koki.hu.
authors.forename: István
authors.identifier: http://orcid.org/0000-0003-2808-3330
authors.initials: I
authors.lastname: Katona
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D063385:Cannabinoid Receptor Modulators / Q000494:pharmacology; D063388:Endocannabinoids / Q000378:metabolism* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005989:Glycerides / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D043884:Receptor, Cannabinoid, CB1 / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D005989:Glycerides; C557973:PF 3845; D010880:Piperidines; D011720:Pyrazoles; D011725:Pyridines; D043884:Receptor, Cannabinoid, CB1; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; C103505:AM 251; D005680:gamma-Aminobutyric Acid; C094503:glyceryl 2-arachidonate
keywords: 2-arachidonoylglycerol; GABA; TRPV1; endocannabinod; hippocampus; interneuron