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M. Torvund, T. S. Ma, T. Ikenaga, V. P. Connaughton, F. Ono, R. F. Nelson; Processing of Cone Signals by the Stratified Amacrine Cells of Zebrafish Retina. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1856.
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© ARVO (1962-2015); The Authors (2016-present)
To identify cone signals within morphological types of zebrafish retinal amacrine cell that differ in dendritic stratification.
In perfused eyecups, electrodes filled with Alexa 594 dye were advanced through the inner plexiform layer (IPL) of wild type (EK, TL) or transgenic (Ge4a) zebrafish retinas to penetrate amacrine cells. Spectral functions were generated from light responses to 9 wavelengths from 650nm to 330nm. Dendritic morphology of dye-injected cells was documented in through-focus image stacks (0.6 µm z-axis increments). 3D branching patterns, reconstructed with Neurolucida, were rotated to identify branching planes within the s1-s6 zebrafish IPL strata. GE4a, a forward transgenic, provided amacrine- and ganglion-cell markers critical to establishing IPL stratification in whole-mount view.
In 7 reconstructed amacrine cells, 4 light response patterns were observed: sustained ON (3), sustained OFF (1), ON OFF (2), and chromatic (1). Peak response amplitudes ranged from 1-7 mV. The chromatic cell was blue ON opponent (r-g-B+u+). Remaining achromatic types were dominated by red cone signals. Sustained ON types were all monostratified in IPL s4. The sustained OFF type was monostratified in s2. One ON-OFF cell was monstratified in s3, the other, bistratified in s2/s5. The blue ON chromatic type was monostratified in s5. As a group dendritic areas (Hull convex polygons) ranged from 10,000-60,000 µm2 (110-275 µm equivalent diameter). The Sholl peak branching radius ranged from 40-70 µm, and dendritic surface areas ranged from 1500-6000 µm2.
Stratified amacrine cells of zebrafish retina appear to act as selective, wide-field integrators of cone signals found in different IPL strata. Results suggest an ON (sublamina b), and OFF (sublamina a) layering pattern for amacrine types with sustained responses, stratification patterns for ON-OFF cells that allow contacts within both the a and b IPL sublaminas, and a positioning of ON-type red cone signals in the more central IPL, and ON-type blue cone signals more towards the ganglion-cell side.
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