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L. Peichl, P. Nemec, H. Burda; S-Cone Dominance in the Retinae of Subterranean African Mole-Rats (Rodentia, Bathyergidae) . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4170.
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Purpose: To determine the presence of spectral cone types in subterranean mole-rats of the bathyergid family, for which light and vision is of little importance. The subterranean blind mole-rat Spalax ehrenbergi of the murid family has a middle-to-long-wave sensitive (L-)cone opsin, but no short-wave sensitive (S-)cone opsin (David-Gray et al.: Nature Neurosci. 1: 655-656, 1998; EJN 16: 1186-1194, 2002). We were interested to see whether other subterranean rodents show the same pattern. Methods: We have studied three species of Bathyergidae (African mole-rats), Ansell's mole-rat Cryptomys anselli, giant mole-rat Cryptomys mechowi, and naked mole-rat Heterocephalus glaber. All animals came from our breeding colonies. Eyes were obtained from individuals sacrificed for an unrelated project. Retinae were fixed in paraformaldehyde or Bodian’s fixative. Spectral cone types were assessed using the antibodies JH492 and COS-1 against L-cone opsin, and JH455 and OS-2 against S-cone opsin (kindly provided by J. Nathans and A. Szél, respectively). Results: All three species have rod-dominated retinae but possess significant cone populations. A quantitative assessment in C. anselli revealed ca. 120,000-140,000 photoreceptors/mm², of which ca. 12,000-14,000/mm² (about 10%) were cones. In all three species, nearly all cones are strongly reactive to the S-opsin markers. The L-opsin markers produce very faint labeling barely above background. Only a few cones per retina show exclusive L-opsin label, but most of the strongly labeled S-cones also faintly label for L-opsin (potential dual pigment cones). Conclusions: In the bathyergid mole-rats studied here, S-cones dominate and L-opsin appears to be present at very low levels. In contrast, the murid mole-rat Spalax possesses the L-opsin and lacks the S-opsin. Evidently, within the order Rodentia an adaptation to fossorial life is compatible with very different spectral cone properties. The functional role of the cones in subterranean species remains to be determined.
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