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P. de la Villa, R. Barhoum, E. Zurita, L. Montoliu; Functional Cone Deficit in Albino Outbred NMRI/Ha Mice. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1284.
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To characterize the deficit in cone vision in albino outbred NMRI/Ha mice. Previous studies have shown that a significant percentage of NMRI mice appear to contain fewer number of cone cells in the retina. Since these mice are often used for transgenic technology studies, we have studied the degree of cone function in a series of NMRI mice as an attempt to standardize the visual test necessary for a complete characterization of cone function in this commonly used mouse strain.
Full field flash electroretinographic (ERG) responses were recorded in adult NMRI mice. Rod and cone contribution to the ERG responses were studied by analyzing the rod, mixed and cone responses; oscillatory potentials and flicker responses were also tested under dark or light adaptation. Histological studies were performed on whole-mount retinae or in retinal frozen sections. Selective labeling of cone cells was accomplished by the use of specific markers bound to fluorescent substrates. A quantitative analysis of the number of cone cells was performed on histological preparations. Cone function was also tested by the use of optomotor tests.
Scotopic electroretinographic responses from NMRI albino mice (rod and mixed responses and oscillatory potentials) did not show significant differences among animals. However, photopic responses were altered in a significant number of animals (ca. 30%), thus indicating a serious deficit in cone function. The b-wave amplitude in the photopic ERG responses were decreased in one third of animals and flicker responses (20 Hz) were absolutely flat in these animals. Histological studies were performed on selected NMRI individuals that were previously tested by ERG. Those animals showing a decrease in cone function mostly correlate with a decrease in the total number of cones. Optomotor tests were applied to the NMRI animals in order to test how cone cell deficit affect the moving detection ability of NMRI mice.
Our results suggest that up to one third of NMRI animals usually lack cone function when tested by standard ERG, as confirmed by histological analyses. Since NMRI animals are commonly used for transgenic research, we suggest that standard ERG test should be performed in all NMRI animals as a previous step before any subsequent phenotype characterization.
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