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C. K. Leung, R. N. Weinreb, S. Liu, C. Ye, J. D. Lindsey, C. Pang, J. G. Crowston, D. S. Lam; Long Term in vivo Imaging and Measurement of Dendritic Shrinkage of Retinal Ganglion Cells (RGCs). Invest. Ophthalmol. Vis. Sci. 2010;51(13):1630.
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To characterize the axonal and dendritic morphology of RGCs, describe the patterns of axonal and dendritic degeneration, identify morphological predictors for cell survival, and estimate the rate of dendritic shrinkage after optic nerve crush with long term in vivo longitudinal imaging.
A CSLO was used to image the retina of the Thy-1 YFP transgenic mice every other day in the first 4 weeks and at least every week thereafter for 3 months. A total of 125 RGCs from 16 retinas were analyzed with reference to cell body size, axonal diameter, dendritic field, ending branch number, total branch length, symmetry, branching complexity, and distance from the optic disc. Baseline morphological parameters were analyzed with the Cox proportional hazards regression model to determine the predictors of RGC survival and a linear mixed model was used to estimate the rate of dendritic shrinkage.
The fluorescent cells can be unambiguously identified as the RGCs since the axons are clearly visible emerging from the cell bodies and converging toward the optic disc (Fig. 1a). The number and the branching of dendritic arborization imaged by the CSLO had direct correspondence with those observed in retinal wholemount (Fig. 1b). Most RGCs demonstrated progressive dendritic shrinkage followed by loss of axons and cell bodies (n=84, 68.9%) (Fig. 1c). In 3 RGCs, Wallerian degeneration with fragmentation and beading of the axon was observed following progressive dendritic shrinkage (Fig. 1d). Improved survival function was found in RGCs with a larger dendritic field, longer total branch length, or at a longer distance from the optic disc (all with p≤0.009). The rate of dendritic shrinkage of a RGC with a dendritic field 10000 µm2 located 300 µm from the optic disc was estimated at -3.71% per day.
Monitoring the rate of dendritic shrinkage may provide a new paradigm to investigate neuronal degeneration and evaluate the response of neuroprotective treatment.
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