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K. A. Vessey, G. L. Yarborough, M. A. McCall; Characterization of ON-Center Retinal Ganglion Cell Function in the Coneless Mouse Reveals Two Rod-Pathways of Differing Sensitivity. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4600.
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© ARVO (1962-2015); The Authors (2016-present)
Under dim lighting conditions, rod photoreceptors mediate vision. When lighting conditions are bright, the rod response saturates and cones mediate vision. Here we investigate the sensitivity and receptive field (RF) organization of ON-center retinal ganglion cells (RGCs) in the absence of cone input under differing adaptation conditions.
C57B6/J (WT) and coneless mice (Soucy et al 1998) were anesthetized and action potentials were recorded in vivo from ON-center RGCs in the optic nervewith light- (20cd/m2, LA20; 50cd/m2, LA50) or dark-adapting (0 cd/m2, DA) backgrounds. RF organization was assessed using a series of bright spots (100cd/m2, LA; 3cd/m2, DA) of varying diameter (4.5-52°). RGC sensitivity was determined using optimally sized spots of increasing intensity (0-100cd/m2) on the DA background.
Under DA conditions, ON-center RGCs of coneless mice were 1.5 log units more sensitive than WT cells. Coneless RGC responses saturated when stimulus intensity reached 10cd/m2 (~1000 Rh/rod/s). Further intensity increases induced progressive reductions of the response, an effect rarely observed in WT cells. At DA levels, the RF organization of coneless and WT RGCs was similar. The RFs of coneless RGCs showed: center summation, with a clear preference for spots ~14° in diameter, and surround antagonism, whereby large spots reduced RGC responses. Under the LA20 condition, two groups of coneless ON-center RGCs were identified. One group of coneless RGCs failed to respond above spontaneous activity. The other group continued to respond and showed RF organization similar to WT RGCs. Under the LA50 condition, the distinction between the two groups of coneless RGCs was less apparent, as responses of the second group were reduced.
When driven by rod input, RGCs are more sensitive than when input is mixed from rods and cones. Use of the LA20 background reveals two groups of rod-mediated RGC responses, one that is saturated and unresponsive and another that can still encode changes in contrast. This indicates that in the coneless mouse, RGCs may be driven by two rod-mediated pathways of differing sensitivity.
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