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D. Hicks, C. Bobu, J.A. Sahel, C. Craft, M. Masson–Pevet; Cyclic Rod and Cone Phagocytosis in a Novel Cone–Rich Rodent Animal Model . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3999.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Analysis of mammalian cone photoreceptor biology in vivo has been hampered by the lack of suitable small animal models. We sought a cone–rich rodent to investigate (i) rod and cone phagocytosis; (ii) cyclical variations in phagocytosis. Methods: Eyes were dissected from adult diurnally active Nile Rat (Arvicanthis ansorgeii), and prepared for immunohistochemistry. Retinal sections were immunolabeled with cone–specific antibodies (anti–murine cone arrestin, anti–murine red and blue cone opsin) and lectins (PNA), and rod–specific antibodies (anti–rhodopsin). Adult Arvicanthis were maintained on a standard 12 hrs light/12 hrs dark cycle (lights on at 8 a.m., off at 8 p.m.), and eyes collected at multiple time points. Frozen and semi–thin sections were obtained, and a morphometric system was designed for quantitating phagosome inclusions within the retinal pigmented epithelium (RPE) by immunofluorescence light microscopy. Transmission electron microscopy was also used to confirm cone structure and phagosome uptake. Results:Immunohistochemical labeling of retina from Arvicanthis revealed the presence of ∼33% cones, ten fold higher than rats or mice, arranged in two superficial layers. These were predominantly red/green opsin–immunopositive, with ∼10–20% blue opsin–immunopositive. Both rods and cones demonstrated fluctuating phagosome loading of the RPE, with distinct profiles for either photoreceptor type. Rods showed a large relatively brief burst in phagosome formation between 1–2 hours following light onset, with maximal levels some 20 fold higher than that observed at other times. Cones exhibited a much broader profile, phagosome number being low during the night then evidencing a shallow double peak during the day, with maxima at approximately 10 a.m. and 2 p.m. Conclusions: Arvicanthis constitutes a novel cone–rich small mammalian species suitable for studying cone pathophysiology in vivo and in vitro. The current data demonstrate that rod and cone phagocytosis can be monitored in parallel, and exhibit differential rhythmic control.
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