Silver Staining of Mitochondria in Rat Retina as Shown by Light and Electron Microscopy

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Abstract
Mitochondria of the rod terminal spherules localized in the outer plexiform layer of the rat's retina, have been selectively stained by the application of the Bodian Protargol method to paraffin and methacrylate sections of retinas fixed in Bensley's acetic-osmicbichromate mixture. In paraffin sections, the silver staining of mitochondria has a sharpness and clarity which surpasses similar sections stained by the anilin-acid fuchsin-methyl green procedure. By means of electron microscopy, particles of silver 0.4 μ in one dimension were seen within the mitochondria. It is thought that in paraffin sections, which are approximately 100 times thicker, these larger particles may be responsible for the observed mitochondrial staining. Smaller particles of silver, 200Å to 260Å, were deposited on other membranous structures of the rod spherule which include, the synaptic membranes of the rod-bipolar junction, the limiting plasma membranes of the spherule as well as some of the mitochondrial membranes, and the synaptic vesicles of the rod and bipolar cells in this region. The affinity of silver for a variety of membranous structures must be considered in evaluating the selectivity of the method for staining mitochondria in both neural and nonneural tissues.