title: Immunocytochemical analysis of GABA-positive and calretinin-positive horizontal cells in the tiger salamander retina.
abstract: By using immunocytochemical techniques, we demonstrate that there are two distinct, nonoverlapping populations of horizontal cells (HCs) in the tiger salamander retina: GABA-positive cells account for about 72% and GABA-negative (calretinin-positive) cells account for 28% of the total HC somas. The calretinin-positive HCs have relatively sparse and thick dendrites: soma diameter of 19.72 +/- 0.29 microm, and soma density of 140 +/- 13 cells/mm(2), morphological features very much like the A-type HCs described in the accompanying article. The GABA-positive HCs have thinner dendritic and coarse axon-terminal-like processes of higher density: soma diameter of 18 +/- 0.18 microm, and soma density of 364 +/- 18 cells/mm(2), features that very much resemble the B-type HCs and B-type HC axon terminals in the accompanying article. By using double and triple immunostaining techniques we found that only 18% of the non-GABAergic HC dendritic clusters contact rods, whereas the remaining 82% of the dendritic clusters contact cones. This is consistent with the physiological finding in the accompanying article that the A-type HCs are cone-dominated. On the other hand, 32% of GABAergic HC dendrites contact rod pedicles and 68% contact cone pedicles, consistent with the physiological finding that B-type HCs and B-type HC axon terminals receive mixed rod/cone inputs. Detailed confocal microscope analysis shows that 4% rods, 6% principal double cones/single cones, and 100% accessory double cones contact calretinin-positive HCs, and 79% rods, 100% principal double cones, 14% accessory double cones, and 82% single cones contact GABAergic HCs. These results suggest that GABAergic and non-GABAergic HC input/output synapses differ and they may mediate different functional pathways in the outer retina.
authors.affiliation: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.forename: Ai-Jun
authors.initials: AJ
authors.lastname: Zhang
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Wu
mesh_terms: D000557:Ambystoma / Q000033:anatomy & histology / Q000502:physiology*; D000818:Animals; D001710:Biotin / Q000031:analogs & derivatives; D064032:Calbindin 2; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D007150:Immunohistochemistry; D007546:Isoquinolines; D018613:Microscopy, Confocal; D009433:Neural Inhibition / Q000502:physiology*; D009434:Neural Pathways / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D051248:Retinal Horizontal Cells / Q000166:cytology / Q000378:metabolism*; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology; D014794:Visual Fields / Q000502:physiology; D014795:Visual Pathways / Q000166:cytology / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D064032:Calbindin 2; D007546:Isoquinolines; D064030:S100 Calcium Binding Protein G; C070614:neurobiotin; D005680:gamma-Aminobutyric Acid; D001710:Biotin; C017475:lucifer yellow