On the retinae of Glis and Graphiurus: photoreceptor and ganglion cell populations, an absence of shortwave-sensitive cones, and some other features (Rodentia: Gliridae)

Pages	185–205
DOI	10.37520/lynx.2022.013
Keywords	Rodent retina, fat dormouse, Glis glis, African dormouse, Graphiurus, rod photoreceptors, cone photoreceptors, SWS1 opsin loss, visual acuity
Citation	PEICHL, Leo, RADIC, Tijana, SOLOVEI, Irina, WOLFRAM, Michael a GLÖSMANN, Martin. On the retinae of Glis and Graphiurus: photoreceptor and ganglion cell populations, an absence of shortwave-sensitive cones, and some other features (Rodentia: Gliridae). Lynx, new series. Prague: National Museum, 2022, 53(1), 185–205. DOI: https://doi.org/10.37520/lynx.2022.013. ISSN 0024-7774 (print), 1804-6460 (online). Also available from: https://www.nm.cz/en/periodicals/lynx-new-series/53-1/on-the-retinae-of-glis-and-graphiurus-photoreceptor-and-ganglion-cell-populations-an-absence-of-shortwave-sensitive-cones-and-some-other-features-rodentia-gliridae

Lynx, new series | 2022/53/1

The retina of the fat dormouse Glis glis was studied histologically. Opsin immunolabeling identified an unusually dense population of rod photoreceptors (ca. 600,000–780,000/mm²) and a low-density population of L cone photoreceptors containing the longwave-sensitive (LWS) cone opsin, with a shallow maximum of ca. 3,300/mm² in temporal retina and ca. 2,000–3,000/mm² in the remaining retina. Hence the cones comprise only 0.25–0.50% of the photoreceptors. There are no S cones expressing the shortwave-sensitive (SWS1) opsin that is the second cone opsin in most mammals, conveying dichromatic colour vision. We conclude that the fat dormouse is a cone monochromat. Sequencing of the tuning-relevant exon 1 of the SWS1 opsin gene revealed that the gene would have coded for a UV-sensitive visual pigment, but that it contains mutational changes making it nonfunctional. Retinal interneurons (rod bipolar cells, horizontal cells, several amacrine cell types) have rodent-typical features. NeuN-labeled presumed retinal ganglion cells have densities between ca. 4000/mm² in temporal central retina and 850–1300/mm² in peripheral retina. The peak ganglion cell density would result in an estimated visual acuity maximum of ca. 1.8 cycles/degree or ca. 33 minutes of arc. Assessment of a further Gliridae species, the African dormouse Graphiurus sp., also revealed a high rod density, low L cone density, and an absence of SWS1 opsin.

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