title: Vesicular gamma-aminobutyric acid transporter expression in amacrine and horizontal cells.
abstract: The vesicular gamma-aminobutyric acid (GABA) transporter (VGAT), which transports the inhibitory amino acid transmitters GABA and glycine, is localized to synaptic vesicles in axon terminals. The localization of VGAT immunoreactivity to mouse and rat retina was evaluated with light and electron microscopy by using well-characterized VGAT antibodies. Specific VGAT immunoreactivity was localized to numerous varicose processes in all laminae of the inner plexiform layer (IPL) and to the outer plexiform layer (OPL). Amacrine cell somata characterized by weak VGAT immunoreactivity in the cytoplasm were located in the ganglion cell layer and proximal inner nuclear layer (INL) adjacent to the IPL. In rat retina, VGAT-immunoreactive cell bodies also contained GABA, glycine, or parvalbumin (PV) immunoreactivity, suggesting vesicular uptake of GABA or glycine by these cells. A few varicose VGAT-immunoreactive processes entered the OPL from the IPL. VGAT immunoreactivity in the OPL was predominantly localized to horizontal cell processes. VGAT and calcium binding protein-28K immunoreactivities (CaBP; a marker for horizontal cells) were colocalized in processes and terminals distributed to the OPL. Furthermore, VGAT immunoreactivity overlapped or was immediately adjacent to postsynaptic density-95 (PSD-95) immunoreactivity, which is prominent in photoreceptor terminals. Preembedding immunoelectron microscopy of mouse and rat retinae showed that VGAT immunoreactivity was localized to horizontal cell processes and their terminals. Immunoreactivity was distributed throughout the cytoplasm of the horizontal cell processes. Taken together, these findings demonstrate VGAT immunoreactivity in both amacrine and horizontal cell processes, suggesting these cells contain vesicles that accumulate GABA and glycine, possibly for vesicular release.
authors.affiliation: Department of Neurobiology, University of California at Los Angeles, Los Angeles, California 90095-1763, USA. jcueva@mednet.ucla.edu
authors.forename: Juan G
authors.initials: JG
authors.lastname: Cueva
authors.forename: Silke
authors.initials: S
authors.lastname: Haverkamp
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Reimer
authors.forename: Robert
authors.initials: R
authors.lastname: Edwards
authors.forename: Heinz
authors.initials: H
authors.lastname: Wässle
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Brecha
mesh_terms: D025042:Amacrine Cells / Q000737:chemistry / Q000648:ultrastructure*; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis*; D050485:GABA Plasma Membrane Transport Proteins; D005998:Glycine; D007150:Immunohistochemistry; D008297:Male; D008565:Membrane Proteins / Q000032:analysis*; D026901:Membrane Transport Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D027361:Organic Anion Transporters; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000737:chemistry / Q000648:ultrastructure*; D005680:gamma-Aminobutyric Acid
chemical_list: D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D005680:gamma-Aminobutyric Acid; D005998:Glycine