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Knut Stieger, Daniela Klein, Alexandra Mendes-Madeira, Birgit Lorenz, Fabienne Rolling, Silke Haverkamp; Immunohistochemical Characterization of the Retina and the Outer Plexiform Layer (OPL) in Briard Dogs with RPE65 Deficiency. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2364.
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Early onset severe retinal dystrophy (EOSRD) associated with mutations in the RPE65 gene is a rare form of retinal blindness in man that is characterized by severe visual impairment within the first years of life and legal blindness at the end of the second decade. A similar form of disease caused by a null mutation in the RPE65 gene has been described in the Swedish Briard dog, characterized by an early loss of vision with absence of ERG recordings, but only a slow degeneration of retinal neurons. The aim of this study was to characterize the retinal neurons and the synaptic architecture in the outer plexiform layer (OPL) of dogs with RPE65 deficiency at several time points, in order to further increase the knowledge about the degenerative processes during the disease.
Retinae from 7 dogs (n=14) were used in this study, 4 affected and 3 unaffected animals. Age varied between 3 months and 6.5 years. Different cell markers were used as primary antibodies, including CtBP2 (synaptic ribbons), PKCalpha (rod Bipolar cells), Calbindin (Horizontal cells), Calretinin (Amarcrine cells), GOalpha (ON cone bipolar cells) and GFAP (Muller cells).
At early time points of the disease (less than 3 years of age), rod and cone photoreceptor numbers were stable. Within the posterior (tapetal) part of the retina, no macroscopic changes in number and structure of the synaptic ribbons in the OPL were observed. At later stages of the disease (above 3 years of age), the total number of photoreceptors was decreased and Horizontal and Bipolar cell dendrite sprouting was observed in all parts of the retina.
Early loss of photoreceptor function is not associated with macroscopic alterations of the retina or the OPL in particular in dogs with RPE65 deficiency. Sprouting of Horizontal and Bipolar cell dendrites as sign of degenerative processes is only observed at later stages, when photoreceptor degeneration has already started. The information gathered from this study will increase the knowledge about the phenomenon of early loss of function but unaltered morphology of the OPL during the natural history of the RPE65 deficiency in dogs.
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