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Ji-Jie Pang, Fan Gao, Samuel M Wu; Morphological and physiological diversity of retinal ganglion cells in the vertebrate retina. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3575. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Many types of retinal ganglion cells (RGCs) have been defined anatomically and functionally. But how RGC morphology is correlated with light responses has been unclear. In order to better define functional subtypes of RGCs in the vertebrate retina, we studied light-evoked current responses of various types of RGCs and correlated them with cell morphology and dendritic ramification patterns in the inner plexiform layer (IPL).
Whole-cell patch-clamp techniques were used to record light responses and to fill cells with fluorophores. Three dimensional morphology of the recorded cells was examined by confocal microscopy.
100 RGCs from tiger salamander retinas were analyzed for light responses, dendritic ramification levels, soma size and dendritic field size. 22 subtypes of RGCs (G1-G22) were described. A) Most RGCs show medium sized somas (15-20 mm) and medium sized dendritic fields (150-350 mm), ramify in both sublaminas (SLs) and generate transient ON-OFF responses upon light stimuli of 500 nm wavelength, intensity -1 (-1 log unit attenuation of the light) and duration of 2.5 s. B) 71% of RGCs send dendrites to both SL-a and SL-b, 18% to the SL-b (G1-4 and 16) and 11% to the SL-a (G5-8). C) Excitatory inputs in most RGCs follow the general rules of the SLs, including the center-ramified ON-OFF cell G13, some SL-a-ramified OFF cells G5-8 and some SL-b-ramified ON cells G2 and 9. For diffuse- (G9, 10, 18) and broadly-ramified cells, more dendrites in the SL-b predict larger onset cation currents and more dendrites in SL-a contribute larger offset currents. D) But RGCs with any dendritic ramification patterns may show ON-OFF cation currents. E) Some G11,12 and 14 cells stratified in both SL-a and SL-b show the quickest kinetics of cation currents, while some diffuse- or broadly-ramified cells show kinetics 3 times slower.
1) Most RGC morphological subtypes process visual signals from both ON and OFF light pathways, slightly favoring the ON pathway. 2) RGC light response patterns are not clearly correlated with soma and dendritic field size. 3) Stratified cells covering both sublaminas could better detect edges and fast moving objects. 4) Broadly ramified cells are more suited for reporting light intensities.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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