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E.M. Anger, P.K. Ahnelt; Electron Microscopic Reconstruction of DAB–Labeled Retinal S–Cone Photoreceptor Pedicles in Domestic Pig's Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4231.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The detection of specific morphological criteria at light microscopic level has lead to fine structural studies on differences in synaptic design between S– and L–cone pedicles of the mammalian retina (Ahnelt et al., 94; Goede and Kolb, 94). Immuno–cytochemical markers for cone subtypes have become available but their application for fine structural analysis of synaptic features is difficult, since different protocols are generally applied for either electron microscopic or immuno–histochemical studies. The present study has aimed to combine anti–opsin–labeling with optimized preservation to identify and reconstruct cone terminals in the cone rich retina of the dichromatic domestic pig. Methods: Retinas from eyes of domestic pigs obtained from veterinary pathology or from butchers were fixed in aldehydes. Different fixation routines and concentrations (0,5% – 2%) were used to find the best compromise for immuno–cytochemistry as well as for electron microscopy and reconstruction. Cryosections and small blocks of tissue were incubated with S–opsin antibody JH455 and other markers. Labeled samples were postfixed, resin embedded and serial sectioned to obtain electron micrograph montages of cone pedicles. Results: Even at higher aldehyde concentrations, resulting in adequate structural preservation, the antibody reaction was preserved allowing DAB visualization. Labeling led to characteristic damage of outer segment membranes but not in photoreceptor's cell body, axons and synaptic endings. Conclusions: Adequate variation of preparatory protocols allows to access cone connectivity at the fine structural level in mammalian species with no apparent distinguishing morphologies at the light microscopic level. Reconstruction and comparison of pedicles from the two photoreceptor subtypes will allow to clarify whether differences exist with respect to synaptic structure or gap junctional patterns, as described previously for the primate and ground squirrel retina.
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