title: Targeted Deletion of Vesicular GABA Transporter from Retinal Horizontal Cells Eliminates Feedback Modulation of Photoreceptor Calcium Channels.
abstract: The cellular mechanisms underlying feedback signaling from horizontal cells to photoreceptors, which are important for the formation of receptive field surrounds of early visual neurons, remain unsettled. Mammalian horizontal cells express a complement of synaptic proteins that are necessary and sufficient for calcium-dependent exocytosis of inhibitory neurotransmitters at their contacts with photoreceptor terminals, suggesting that they are capable of releasing GABA via vesicular release. To test whether horizontal cell vesicular release is involved in feedback signaling, we perturbed inhibitory neurotransmission in these cells by targeted deletion of the vesicular GABA transporter (VGAT), the protein responsible for the uptake of inhibitory transmitter by synaptic vesicles. To manipulate horizontal cells selectively, an iCre mouse line with Cre recombinase expression controlled by connexin57 (Cx57) regulatory elements was generated. In Cx57-iCre mouse retina, only horizontal cells expressed Cre protein, and its expression occurred in all retinal regions. After crossing with a VGAT(flox/flox) mouse line, VGAT was selectively eliminated from horizontal cells, which was confirmed immunohistochemically. Voltage-gated ion channel currents in horizontal cells of Cx57-VGAT(-/-) mice were the same as Cx57-VGAT(+/+) controls, as were the cell responses to the ionotropic glutamate receptor agonist kainate, but the response to the GABAA receptor agonist muscimol in Cx57-VGAT(-/-) mice was larger. In contrast, the feedback inhibition of photoreceptor calcium channels, which in control animals is induced by horizontal cell depolarization, was completely absent in Cx57-VGAT(-/-) mice. The results suggest that vesicular release of GABA from horizontal cells is required for feedback inhibition of photoreceptors.
authors.affiliation: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095; Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California 90073.
authors.forename: Arlene A
authors.identifier: 0000-0001-8842-3582
authors.initials: AA
authors.lastname: Hirano
authors.affiliation: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles , Los Angeles, California 90095.
authors.forename: Xue
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, Hatos Research Center for Neuropharmacology, Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California, Los Angeles , Los Angeles, California 90095.
authors.forename: Jim
authors.initials: J
authors.lastname: Boulter
authors.affiliation: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles , Los Angeles, California 90095.
authors.forename: James
authors.initials: J
authors.lastname: Grove
authors.affiliation: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles , Los Angeles, California 90095.
authors.forename: Luis
authors.initials: L
authors.lastname: Pérez de Sevilla Müller
authors.affiliation: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095; Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California 90073; Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada; Department of Ophthalmology & Visual Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Steven
authors.initials: S
authors.lastname: Barnes
authors.affiliation: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095; Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California 90073; Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095; Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095.
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Brecha
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D025461:Feedback, Physiological / Q000187:drug effects / Q000502:physiology*; D005260:Female; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000235:genetics / Q000378:metabolism; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D009118:Muscimol / Q000494:pharmacology; D010786:Photoreceptor Cells / Q000378:metabolism*; D012160:Retina / Q000166:cytology; D051248:Retinal Horizontal Cells / Q000502:physiology*; D017384:Sequence Deletion / Q000235:genetics*; D050495:Vesicular Inhibitory Amino Acid Transport Proteins / Q000172:deficiency* / Q000235:genetics; D014795:Visual Pathways / Q000502:physiology; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D017630:Connexins; D018690:Excitatory Amino Acid Agonists; D058785:GABA-A Receptor Agonists; C119811:Gja10 protein, mouse; D050495:Vesicular Inhibitory Amino Acid Transport Proteins; C492244:Viaat protein, mouse; D009118:Muscimol; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D051960:GTP-Binding Protein alpha Subunit, Gi2; C498016:Gnai2 protein, mouse; D007608:Kainic Acid
keywords: Ca channels; Cx57-iCre; GABA receptors; inhibitory feedback; retinal horizontal cells; synaptic vesicles