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Wei Li, Yichao Li, Fengyu Qiao, Joe G Hollyfield, Haohua Qian, Brent A Bell; Retinal Changes Associated with Hibernation Revealed by OCT Imaging. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2174.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate in vivo changes in retina and choroid in active and hibernating 13-line ground squirrel using ultra high resolution Spectral Domain Optical Coherence Tomography (OCT).
Thirteen-line ground squirrels (n=7, 8-12 months) were imaged by OCT (Envisu R2200 UHR, Bioptigen) before, during, and after hibernation and post-mortem. B-scans (20 frames @ 1000 A-scans/B-scan) were collected ventral to the visual streak at <2µm (axial) & 11µm (lateral) resolution. Image frames were coregistered and averaged. Profiles were corrected for imaging system background and responsivity to yield OCT signal amplitude. OCT signal morphology from retinal lamina were compared to histomorphology results. Quantitative changes to OCT signal amplitude were obtained from different metabolic states.
Non-hibernating animals showed bright, well-delineated outer retina morphology that correlated to the histology of this animal. Measurements of IS (20.8±1.5µm) and OS (6.5±1.1µm), as well as dimensions from the myoid (~12µm) and ellipsoid (~8µm) regions were similar to that reported previously (Reme & Young, 1977). During hibernation a dramatic reduction in signal amplitude and contrast was observed, which did not result in significant changes to thicknesses of any outer retinal layer relative to non-hibernating conditions. Choroidal thickness was significantly reduced (44%, p=.0008) during torpor, but returned to normal by 1 hr post-hibernation. Bright band signal amplitude decreased significantly in the IS-ellipsoid (p<.0001), OS (p=.001), RPE (p=.004) and Sattler’s layer of the choroid (p=.0007). The bright band that showed the greatest change in signal amplitude (~50%) corresponded to the ellipsoid region where mitochondria reside. Signal amplitude in all lamina was partially and fully restored to pre-hibernation levels after 1-3 & 24 hours of recovery, respectively. Results from post-mortem animals were similar to those observed in animals under deep hibernation.
OCT retinal signal amplitude and morphology contrast is substantially reduced during hibernation. The most dramatic changes occurred in the ellipsoid region, which suggests that OCT is capable of discerning changes to mitochondrial architecture, number or volume as a result of changing metabolic activity required for animals that undergo circannual hibernation.
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