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A.R. Gruber, K.E. Betts, G.P. Lewis, S.K. Fisher, D.K. Vaughan; Photoreceptor Antigens Are Altered During Seasonal Hibernation of a Cone–Dominant Rodent . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2845.
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© ARVO (1962-2015); The Authors (2016-present)
To test the hypothesis that photoreceptor antigens are seasonally altered in the retinas of deep winter hibernating ground squirrels, compared to the retinas of summer–active animals.
Thirteen–lined ground squirrels were caught from the wild and maintained in captivity until use. Central retina was collected in February, after 4 months of cyclic torpor, and in June, after 2 months of continuous arousal. Samples were fixed and prepared for immunoconfocal microscopy. Fluorescent probes applied were: antibodies to rod and red–green cone visual pigments, which differentiate between the outer segments (OSs) of the two photoreceptor types; an antibody to Cox–1, which labels the ellipsoid mitochondria of all photoreceptor types; an antibody to synaptophysin, which labels synaptic terminals of all photoreceptor types; and the PNA lectin, which binds to galactose residues of the cone interphotoreceptor matrix (IPM).
Antibody–labeled cone OSs appeared slightly shortened in hibernation, compared to aroused controls. In contrast, rod OSs showed no changes with hibernation. Mitochondrial labeling was noticeably reduced in red–green cone ellipsoids during hibernation, but was unchanged in rod ellipsoids. Synaptophysin labeling in the outer plexiform layer was unchanged. PNA labeling was intense in the IPM surrounding OSs during both seasons, and was both weaker and continuous from OSs to outer limiting membrane in aroused animals. However, in retinas of hibernating animals, PNA label was significantly reorganized and no longer continuous.
Winter hibernation, comprising months of darkness at body temperatures cycling between 37 and 5 degrees C, is associated with moderate changes in the expression of key photoreceptor antigens. Our data suggest moderate loss of cone light–capture ability and concomitant downregulation of mitochondrial function, whereas rods were unchanged. A key carbohydrate component of the cone IPM is largely maintained through the winter months, when much of the body has switched from an emphasis on carbohydrate to fatty acid catabolism. Overall, cone photoreceptors exhibited more changes, whereas rods were spared.
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