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F. P. Gaillard, W. T. Allison, S. Kuny, Y. Sauve; Cone Photoreceptors in the Diurnal Laboratory Rodent, Arvicanthis niloticus. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1048.
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© ARVO (1962-2015); The Authors (2016-present)
The diurnal murine rodent Nile grass rat (Arvicanthis niloticus) has a high proportion of retinal cones (≈ 33-35% of the photoreceptors) and several ERG features found in humans but not in mice and rats. The present study highlights the topography of the cone photoreceptor population in the retina of the adult Nile grass rat.
Serial frozen sections (20µm thick) collected from 2 eyes and wholemounts prepared from 4 retinas were reacted with the cone specific antibodies anti-γ-transducin, anti-S-opsin and anti-M/L-opsin. Results were examined by confocal microscopy and quantified with Image J and StatView software.
The outer nuclear layer of the Nile grass rat retina (43 mm2 on average) is 5 rows thick centrally, with cone cell bodies (estimated total number = 1.460 x106) located exclusively in its outermost two rows. Cone density decreases from center to periphery by a factor of ≈ 1.5-1.8. There are two types of cones: M/L- and S-cones. As opposed to most rodents, there are no cones co-expressing both M/L- and S-opsins. M/L-cones (average density ≈ 31,580 ± 6,755/mm2; estimated total number ≈ 1.36 x106) distribute throughout the retina of A. niloticus. S-cones (average density ≈ 2317 ± 823/mm2; estimated total number = 100,000) are 12-14 fold less numerous than M/L-cones, representing therefore ≈ 6.8% of the total cone population. Contrary to mice, S-cones are found throughout the retina, peaking in density temporo-dorsally (3758 ± 344/ mm2). Nearest-neighbor distance and Voronoï domain analyses indicate that S-cones are randomly distributed. Ongoing genetic analysis will reveal whether these S-cones correspond to UV or blue sensitive cones.
The arrangement of S-cone photoreceptors in the Nile grass rat retina is closer to the "basic" mammalian pattern than the mouse pattern (Peichl L. Anat. Rec., 2005, 287A:1001-1012). This finding further supports that the Nile grass rat represents a potentially very useful model for studying pathologies involving cones.
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