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Jing Wang, Samuel Wu; Physiological and morphological characterization of ganglion cells in the salamander retina. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2388.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate physiological and morphological properties of ganglion cells (GCs) in dark-adapted salamander retina by measuring light responses via patch-clamp recording and visualizing three-dimensional morphology via confocal imaging.
1. A mixture of gap-junction-impermeable (Lucifer yellow, LY) and -permeable dye (Neurobiotin, NB) was applied to optic nerve stump of the salamander for retrograde labelling of GCs and cells coupled with GCs. 2. Light-evoked current responses were recorded from 41 GCs in dark-adapted salamander flat-mounted retinas by voltage-clamp recording and the cell morphology was revealed by intracellular LY loading under a confocal microscope.
1. In the GC layer, retrograde-identified GCs with both LY and NB labelling constituted 78±5% of total neurons; 8±1% of neurons with NB signal but no LY signal; and 14±1% with neither LY nor NB labelling. 2. LY loading experiments showed that majority of GCs (93%) have symmetrically-distributed dendritic fields. Narrow-field cells (< 200um) account for 19% of GCs; mediate-field (200 to 300um) 51%; and wide field (> 300um) 30%. 64% GCs receive mixed rod/cone inputs; 26% receive rod-dominated input; and 10% receive cone-dominated input. Based on physiological and morphological characteristics, seven types of GCs were identified. (1) Transient ON-OFF alpha GCs: large somas and dendritic fields and exhibit transient ON-OFF response to a light step. (2) ON alpha GCs: large somas and dendritic fields and exhibit ON responses. (3) OFF alpha GCs exhibit OFF light responses. (4) Transient ON-OFF beta GCs: smaller somas, dense dendritic field and exhibit ON-OFF responses. (5) Transient ON-OFF gamma GCs: sparsely branching dendrites and exhibit transient ON-OFF responses. (6) Transient ON-OFF theta GCs: small soma, densely branching dendrites and exhibit transient ON-OFF responses. (7) Asymmetrical unilateral GCs: >90% dendrites distributed in one side of the soma and exhibit ON response to 500 nm light and ON-OFF response to 700nm light.
By using both morphological and physiological criteria, we identified seven types of GCs in the GC layer of salamander retina. Analysis of response sensitivity, polarity and waveform suggests that some GCs receive segregated bipolar cell inputs where others receive mixed bipolar cell inputs. About 1/5 of neurons in salamander retinal GC layer are displaced amacrine cells.
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