title: GABAA alpha6-containing receptors are selectively compromised in cerebellar granule cells of the ataxic mouse, stargazer.
abstract: Stargazer mice fail to express the gamma2 isoform of transmembrane alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate (AMPA) receptor regulatory proteins that has been shown to be absolutely required for the trafficking and synaptic targeting of excitatory AMPA receptors in adult murine cerebellar granule cells. Here we show that 30 +/- 6% fewer inhibitory gamma-aminobutyric acid, type A (GABA(A)), receptors were expressed in adult stargazer cerebellum compared with controls because of a specific loss of GABA(A) receptor expression in the cerebellar granule cell layer. Radioligand binding assays allied to in situ immunogold-EM analysis and furosemide-sensitive tonic current estimates revealed that expression of the extrasynaptic (alpha6betaxdelta) alpha6-containing GABA(A) receptor were markedly and selectively reduced in stargazer. These observations were compatible with a marked reduction in expression of GABA(A) receptor alpha6, delta (mature cerebellar granule cell-specific proteins), and beta3 subunit expression in stargazer. The subunit composition of the residual alpha6-containing GABA(A) receptors was unaffected by the stargazer mutation. However, we did find evidence of an approximately 4-fold up-regulation of alpha1betadelta receptors that may compensate for the loss of alpha6-containing GABA(A) receptors. PCR analysis identified a dramatic reduction in the steady-state level of alpha6 mRNA, compatible with alpha6 being the primary target of the stargazer mutation-mediated GABA(A) receptor abnormalities. We propose that some aspects of assembly, trafficking, targeting, and/or expression of extrasynaptic alpha6-containing GABA(A) receptors in cerebellar granule cells are selectively regulated by AMPA receptor-mediated signaling.
authors.affiliation: Centre for Integrative Neurosciences, School of Biological and Biomedical Sciences, Science Research Laboratories, Durham University, South Road, Durham DH1 3LE, United Kingdom. H.L.Payne@durham.ac.uk
authors.forename: Helen L
authors.initials: HL
authors.lastname: Payne
authors.forename: William M
authors.initials: WM
authors.lastname: Connelly
authors.forename: Jane H
authors.initials: JH
authors.lastname: Ives
authors.forename: Reinhard
authors.initials: R
authors.lastname: Lehner
authors.forename: Birgit
authors.initials: B
authors.lastname: Furtmuller
authors.forename: Werner
authors.initials: W
authors.lastname: Sieghart
authors.forename: Priyanka
authors.initials: P
authors.lastname: Tiwari
authors.forename: John M
authors.initials: JM
authors.lastname: Lucocq
authors.forename: George
authors.initials: G
authors.lastname: Lees
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Thompson
mesh_terms: D000818:Animals; D001259:Ataxia / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics*; D002531:Cerebellum / Q000378:metabolism; D004594:Electrophysiology; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D012333:RNA, Messenger / Q000378:metabolism; D018091:Receptors, AMPA / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: C113940:Cacng2 protein, mouse; D015220:Calcium Channels; C546172:Gabra6 protein, mouse; D012333:RNA, Messenger; D018091:Receptors, AMPA; D011963:Receptors, GABA-A