title: Distinct mechanisms regulate GABAA receptor and gephyrin clustering at perisomatic and axo-axonic synapses on CA1 pyramidal cells.
abstract: Pyramidal cells express various GABA(A) receptor (GABA(A)R) subtypes, possibly to match inputs from functionally distinct interneurons targeting specific subcellular domains. Postsynaptic anchoring of GABA(A)Rs is ensured by a complex interplay between the scaffolding protein gephyrin, neuroligin-2 and collybistin. Direct interactions between these proteins and GABA(A)R subunits might contribute to synapse-specific distribution of GABA(A)R subtypes. In addition, the dystrophin-glycoprotein complex, mainly localized at perisomatic synapses, regulates GABA(A)R postsynaptic clustering at these sites. Here, we investigated how the functional and molecular organization of GABAergic synapses in CA1 pyramidal neurons is altered in mice lacking the GABA(A)R α2 subunit (α2-KO). We report a marked, layer-specific loss of postsynaptic gephyrin and neuroligin-2 clusters, without changes in GABAergic presynaptic terminals. Whole-cell voltage-clamp recordings in slices from α2-KO mice show a 40% decrease in GABAergic mIPSC frequency, with unchanged amplitude and kinetics. Applying low/high concentrations of zolpidem to discriminate between α1- and α2/α3-GABA(A)Rs demonstrates that residual mIPSCs in α2-KO mice are mediated by α1-GABA(A)Rs. Immunofluorescence analysis reveals maintenance of α1-GABA(A)R and neuroligin-2 clusters, but not gephyrin clusters, in perisomatic synapses of mutant mice, along with a complete loss of these three markers on the axon initial segment. This striking subcellular difference correlates with the preservation of dystrophin clusters, colocalized with neuroligin-2 and α1-GABA(A)Rs on pyramidal cell bodies of mutant mice. Dystrophin was not detected on the axon initial segment in either genotype. Collectively, these findings reveal synapse-specific anchoring of GABA(A)Rs at postsynaptic sites and suggest that the dystrophin-glycoprotein complex contributes to stabilize α1-GABA(A)R and neuroligin-2, but not gephyrin, in perisomatic postsynaptic densities.
authors.affiliation: Department of Anatomy, Pharmacology and Forensic Medicine and National Institute of Neuroscience-Italy, University of Turin, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Panzanelli
authors.forename: Benjamin G
authors.initials: BG
authors.lastname: Gunn
authors.forename: Monika C
authors.initials: MC
authors.lastname: Schlatter
authors.forename: Dietmar
authors.initials: D
authors.lastname: Benke
authors.forename: Shiva K
authors.initials: SK
authors.lastname: Tyagarajan
authors.forename: Peter
authors.initials: P
authors.lastname: Scheiffele
authors.forename: Delia
authors.initials: D
authors.lastname: Belelli
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Lambert
authors.forename: Uwe
authors.initials: U
authors.lastname: Rudolph
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Fritschy
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000378:metabolism* / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism*; D015816:Cell Adhesion Molecules, Neuronal / Q000378:metabolism*; D016189:Dystrophin / Q000378:metabolism; D049028:Dystrophin-Associated Protein Complex / Q000378:metabolism*; D005260:Female; D053444:Inhibitory Postsynaptic Potentials; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D055369:Miniature Postsynaptic Potentials; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D017966:Pyramidal Cells / Q000378:metabolism* / Q000502:physiology; D011963:Receptors, GABA-A / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D013569:Synapses / Q000378:metabolism* / Q000502:physiology
chemical_list: D002352:Carrier Proteins; D015816:Cell Adhesion Molecules, Neuronal; D016189:Dystrophin; D049028:Dystrophin-Associated Protein Complex; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011963:Receptors, GABA-A; C073441:gephyrin; C098003:neuroligin 2