Dark Rearing Does Not Prevent Rod Oxidative Stress In Vivo in Pde6b(rd10) Mice

PURPOSE: In cyclic light-reared Pde6b(rd10) mice, rod cell oxidative stress contributes to the degenerative phenotype. Dark rearing Pde6b(rd10) mice slows but does not prevent atrophy. This suggests that outer retinal oxidative stress occurs in Pde6b(rd10) mice independent of light exposure, a hypothesis tested in this study. METHODS: Mouse strains Pde6b(rd10) and C57Bl/6 (wild type) were dark reared until postnatal day (P) 23 (P23) or P30. In subgroups of dark-reared mice, (1) layer-specific excessive free radical production (i.e., an oxidative stress biomarker) in vivo via QUEnch-assiSTed magnetic resonance imaging (QUEST MRI) was indicated by a significant reduction in the greater-than-normal spin-lattice relaxation rate R1 (1/T1) with methylene blue, (2) superoxide production was measured ex vivo in whole retina (lucigenin), and (3) retinal layer spacing and thickness were assessed in vivo (optical coherence tomography, MRI). RESULTS: In P23 male Pde6b(rd10) mice, only the outer superior retina showed oxidative stress in vivo, as measured by QUEST MRI; a lucigenin assay confirmed supernormal superoxide production. In contrast, at P30, no evidence for retinal oxidative stress was observed. In P23 female Pde6b(rd10) mice, no retinal oxidative stress was apparent; however, at P30, oxidative stress was observed in superior inner and outer nuclear layers. Male and female Pde6b(rd10) mice at P23 had normal retinal thicknesses, whereas at P30, modest thinning was noted in inferior and superior retina. CONCLUSIONS: We confirmed that outer retinal oxidative stress occurs in male and female dark-reared Pde6b(rd10) mice. Male and female Pde6b(rd10) mice demonstrated similar degrees of retinal thinning, but with unexpectedly distinct spatial and temporal retinal oxidative stress patterns.