title: Transmembrane AMPAR regulatory protein γ-2 is required for the modulation of GABA release by presynaptic AMPARs.
abstract: Presynaptic ionotropic glutamate receptors (iGluRs) play important roles in the control of synaptogenesis and neurotransmitter release, yet their regulation is poorly understood. In particular, the contribution of transmembrane auxiliary proteins, which profoundly shape the trafficking and gating of somatodendritic iGluRs, is unknown. Here we examined the influence of transmembrane AMPAR regulatory proteins (TARPs) on presynaptic AMPARs in cerebellar molecular layer interneurons (MLIs). 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a partial agonist at TARP-associated AMPARs, enhanced spontaneous GABA release in wild-type mice but not in stargazer mice that lack the prototypical TARP stargazin (γ-2). These findings were replicated in mechanically dissociated Purkinje cells with functional adherent synaptic boutons, demonstrating the presynaptic locus of modulation. In dissociated Purkinje cells from stargazer mice, AMPA was able to enhance mIPSC frequency, but only in the presence of the positive allosteric modulator cyclothiazide. Thus, ordinarily, presynaptic AMPARs are unable to enhance spontaneous release without γ-2, which is required predominantly for its effects on channel gating. Presynaptic AMPARs are known to reduce action potential-driven GABA release from MLIs. Although a G-protein-dependent non-ionotropic mechanism has been suggested to underlie this inhibition, paradoxically we found that γ-2, and thus AMPAR gating, was required. Following glutamate spillover from climbing fibers or application of CNQX, evoked GABA release was reduced; in stargazer mice such effects were markedly attenuated in acute slices and abolished in the dissociated Purkinje cell-nerve bouton preparation. We suggest that γ-2 association, by increasing charge transfer, allows presynaptic AMPARs to depolarize the bouton membrane sufficiently to modulate both phasic and spontaneous release.
authors.affiliation: Department of Neuroscience Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom mark.rigby@kcl.ac.uk m.farrant@ucl.ac.uk.
authors.forename: Mark
authors.initials: M
authors.lastname: Rigby
authors.affiliation: Department of Neuroscience Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Stuart G
authors.initials: SG
authors.lastname: Cull-Candy
authors.affiliation: Department of Neuroscience Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom mark.rigby@kcl.ac.uk m.farrant@ucl.ac.uk.
authors.forename: Mark
authors.initials: M
authors.lastname: Farrant
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001581:Benzothiadiazines / Q000494:pharmacology; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002531:Cerebellum / Q000166:cytology / Q000254:growth & development; D004305:Dose-Response Relationship, Drug; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D011689:Purkinje Cells / Q000187:drug effects; D018091:Receptors, AMPA / Q000737:chemistry / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D055366:Synaptic Potentials / Q000187:drug effects / Q000235:genetics; D009435:Synaptic Transmission / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D001581:Benzothiadiazines; C113940:Cacng2 protein, mouse; D015220:Calcium Channels; D018683:Excitatory Amino Acid Agents; D018091:Receptors, AMPA; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C004639:cyclothiazide
keywords: AMPA receptor; IPSC; cerebellum; glutamate; molecular layer interneurons; neurotransmitter release