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Dubicanac M, Strueve J, Mestre-Frances N, Verdier J, Zimmermann E, Joly M.2017. Photoperiodic regime influences onset of lens opacities in a non-human primate. PeerJ Preprints5:e2714v1https://doi.org/10.7287/peerj.preprints.2714v1
Background. Opacities of the lens are typical age related phenomena which have high influence on photoreception and consequently circadian rhythm. In mouse lemurs, a small bodied non-human primate, a high incidence (more than 50% when > 7 years) of cataract has been previously described during aging. Previous studies showed that photoperiodical induced accelerated annual rhythms alter some of mouse lemurs’ life history traits. Whether a modification of photoperiod also affects the onset of age dependent lens opacities has not been investigated so far. The aim of this study was therefore to characterize the type of opacity and the mouse lemurs’ age at its onset in two colonies with different photoperiodic regimen. Methods. Two of the largest mouse lemur colonies in Europe have been investigated; Colony 1 with a natural annual photoperiodic regime and Colony 2 with an induced accelerated annual cycle. A Slit-lamp was used to determine opacities in the lens and a subset of all animals which showed no opacities in the lens nucleus in the first examination but developed first changes in the following examination were further used to estimate the age at onset of opacities. In total 387 animals were examined and 57 represent the subset for age at onset estimation. Results. The first and most common observable opacity in the lens was nuclear sclerosis. Mouse lemurs from Colony 1 showed a delayed onset of nuclear sclerosis compared to mouse lemurs of Colony 2 (4.35 ± 1.50 years vs. 2.75 ± 0.99 years). For colony 1, the chronological age was equivalent to the number of seasonal cycles experienced by the mouse lemurs. For colony 2, in which seasonal cycles are accelerated by factor 1.5, mouse lemurs had experienced 4.13 ± 1.50 seasonal cycles in 2.75 ± 0.99 chronological years. Discussion. Our study showed clear differences in the age at the onset of nuclear sclerosis formation between lemurs kept under different photoperiodic regimes. Instead of measuring the chronological age, the number of seasonal cycles (N = 4) experienced by a mouse lemur can be used as an estimation for risk of beginning NS formation. Ophthalmological investigations should be taken into account when animals older than 5 - 6 seasonal cycles are used for experiments in which unrestricted visual ability has to be ensured. This study is the first to assess and demonstrate the influence of annual photoperiod regime on the incidence of lens opacities in a non-human primate.
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Animals with first signs of ocular opacities
The tables show all animals from colony 1 and 2 which showed opacities in following examinations but had no visible opacities in the previous investigations. These are all animals which have been used for statistical analysis.