title: Retroinhibition of presynaptic Ca2+ currents by endocannabinoids released via postsynaptic mGluR activation at a calyx synapse.
abstract: We investigated the mechanisms by which activation of group I metabotropic glutamate receptors (mGluRs) and CB1 cannabinoid receptors (CB1Rs) leads to inhibition of synaptic currents at the calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB) of the rat auditory brainstem. In approximately 50% of the MNTB neurons tested, activation of group I mGluRs by the specific agonist (s)-3,5-dihydroxyphenylglycine (DHPG) reversibly inhibited AMPA receptor- and NMDA receptor-mediated EPSCs to a similar extent and reduced paired-pulse depression, suggestive of an inhibition of glutamate release. Presynaptic voltage-clamp experiments revealed a reversible reduction of Ca2+ currents by DHPG, with no significant modification of the presynaptic action potential waveform. Likewise, in approximately 50% of the tested cells, the CB1 receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN) reversibly inhibited EPSCs, presynaptic Ca2+ currents, and exocytosis. For a given cell, the amount of inhibition by DHPG correlated with that by WIN. Moreover, the inhibitory action of DHPG was blocked by the CB1R antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) and occluded by WIN, indicating that DHPG and WIN operate via a common pathway. The inhibition of EPSCs by DHPG, but not by WIN, was abolished after dialyzing 40 mm BAPTA into the postsynaptic cell, suggesting that DHPG activated postsynaptic mGluRs. Light and electron microscopy immunolabeling indicated a presynaptic expression of CB1Rs and postsynaptic localization of mGluR1a. Our data suggest that activation of postsynaptic mGluRs triggers the Ca2+-dependent release of endocannabinoids that activate CB1 receptors on the calyx terminal, which leads to a reduction of presynaptic Ca2+ current and glutamate release.
authors.affiliation: The Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Kushmerick
authors.forename: Gareth D
authors.initials: GD
authors.lastname: Price
authors.forename: Holger
authors.initials: H
authors.lastname: Taschenberger
authors.forename: Nagore
authors.initials: N
authors.lastname: Puente
authors.forename: Robert
authors.initials: R
authors.lastname: Renden
authors.forename: Jacques I
authors.initials: JI
authors.lastname: Wadiche
authors.forename: Robert M
authors.initials: RM
authors.lastname: Duvoisin
authors.forename: Pedro
authors.initials: P
authors.lastname: Grandes
authors.forename: Henrique
authors.initials: H
authors.lastname: von Gersdorff
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D048588:Benzoxazines; D001933:Brain Stem / Q000187:drug effects / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects*; D063385:Cannabinoid Receptor Modulators / Q000502:physiology*; D063388:Endocannabinoids; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000187:drug effects / Q000502:physiology*; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects / Q000502:physiology*; D017661:Receptors, Presynaptic / Q000187:drug effects / Q000502:physiology*; D012118:Resorcinols / Q000494:pharmacology; D012601:Scopolamine / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects*; D014966:Xanthenes / Q000494:pharmacology
chemical_list: D015763:2-Amino-5-phosphonovalerate; D000596:Amino Acids; D048588:Benzoxazines; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D005998:Glycine; D009025:Morpholines; D009281:Naphthalenes; D010852:Picrotoxin; D010880:Piperidines; D011720:Pyrazoles; D011810:Quinoxalines; D043884:Receptor, Cannabinoid, CB1; D018094:Receptors, Metabotropic Glutamate; D017661:Receptors, Presynaptic; D012118:Resorcinols; D012601:Scopolamine; D014966:Xanthenes; C114624:LY 341495; C104331:cyclopropyl-4-phosphonophenylglycine; C104077:metabotropic glutamate receptor type 1; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C103505:AM 251; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; C079215:3,5-dihydroxyphenylglycine