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Yiming Lu, Jacopo Benedetti, Xincheng Yao; Light-induced length shrinkage of photoreceptor outer segment. Invest. Ophthalmol. Vis. Sci. 2018;59(9):606.
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Light-induced outer segment (OS) shrinkage of rod photoreceptor has been recently observed in both amphibian (frog) and mammalian (mouse) retinas. This study is to investigate the anatomic source of the light-induced OS length change at disc-level resolution.
Time-lapse microscopy was employed to confirm a direct observation of the stimulus-evoked conformational change of isolated single rod OS (Fig. 1A1). To verify the light-induced change of rod OS in intact retina, comparative histological study was performed on overall 120 retinal locations of three pairs of dark- and light-adapted retinas (Fig. 1B1 and 1B2). Corresponding rod OS length ratios (rod OS length normalized by local retinal thickness) were compared. Transmission electron microscopy (TEM) of dark- and light-adapted retinas were conducted to evaluate the light-driven structural change of rod OS at disc level (Fig. 1C1 and 1C2). 2,200 measurements of inter-disc and intra-disc distance were collected from 36 individual rod OSs and then quantitatively compared.
Light-induced rod OS shrinkage was observed in freshly isolated rod photoreceptors (Fig. 1A2). Statistically significant (p < 0.01) difference was found between the rod OS length ratios of dark-adapted (0.24 ± 0.017) and light-adapted (0.22 ± 0.012) retinas (Fig. 1B). The TEM study showed a significantly (p < 0.001) shortened inter-disc distance in the light-adapted retinas (5.803 ± 1.88 nm) than that in the dark-adapted retinas (7.750 ± 1.79 nm) (Fig. 1C). In contrary, comparable intra-distances were observed in light-adapted (13.362 ± 1.52 nm) and dark-adapted (13.668 ± 1.84 nm) retinas.
Light-induced rod OS length shrinkage was confirmed using light microscopy of isolated rod photoreceptors and retinal slices. Comparative TEM revealed that the rod OS length shrinkage is correlated with the light-driven decrease of the inter-disc spaces, not the disc thickness itself, of rod OS.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure 1. (A1) Representative time-lapse microscopic images of one freshly isolated rod OS. (A2) Averaged time course of the normalized rod OS shrinkage ratio. Representative histological images of dark-adapted (B1) and light-adapted (B2) retinas. Representative TEM images of the lamellar structure of discs in dark-adapted (C1) and light-adapted (C2) rod OSs. Each of the vertical bars covers 15 discs.
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