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G.B. Jaissle, C.A. May, A. Wenzel, E. Claes, S. Haverkamp, U. Wolfrum, C.E. Remé, E. Lütjen–Drecoll, P. Humphries, M.W. Seeliger; In vivo and in vitro assessment of degenerative processes of retina, RPE, and vascular systems following the loss of photoreceptor cells in the rhodopsin knockout mouse . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5079.
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Purpose: The rhodopsin knockout (Rho–/–) mouse lacks rod opsin, leading to an early loss of rod cells. Subsequently, a secondary loss of cone cells occurs, which is complete at around 3 months of age. The purpose of this study was to investigate the degenerative processes of retina, RPE, and vascular systems following the complete loss of photoreceptors using in vivo and in vitro techniques. Methods: Rho–/– mice aged 3 to 16 months were used in this study. Native in vivo imaging and angiography with fluoresceine and indocyanine green dye to differentiate between retinal and choroidal vasculature was performed with a scanning–laser ophthalmoscope (Heidelberg Engineering HRA). Histological investigations included light– and electron microscopy, immunohistochemistry, and corrosion casts. Results: As long as there was at least one row of photoreceptor cells present, the degeneration was limited to the outer retina. Following the loss of this final row at about 3 months of age, alterations of the RPE became apparent. These included loss of gap–junction staining, changes in the size of the cells and the thickness of the layer, inclusion of inner retinal vessels, and finally loss of pigmentation and cell death. The RPE changes were also observable with the SLO in vivo. After the loss of photoreceptors, the hexagonal pattern of RPE cells became visible, which were also stained with fluoresceine dye due to their direct contact with retinal vessels. During the further course of degeneration, large confluent atrophic areas developed in the RPE, accompanied by a rarefication of the retinal vessels and eventually changes of the choriocapillaris. The structure of the inner retina remained relatively well preserved. Conclusions: This study provides a detailed assessment of the events following the loss of retinal photoreceptors in the Rho–/– mouse. The secondary degeneration described here, consecutively involving the RPE, retinal, and choroidal vasculature, may serve as a model for degenerative atrophic disease with loss of photoreceptor cells in humans.
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