Polychromatic staining of epoxy semithin sections: a new and simple method.

A simple, rapid method is described for the polychromatic coloration of semithin sections, which is applicable to material routinely processed for transmission electron microscopy. Material fixed with a glutaraldehyde-paraformaldehyde mixture and postfixed in osmium tetroxide with or without potassium ferrocyanide and embedded in different types of resin (Durkupan-ACM, Spurr resin, Taab resin) can be used. Constant and homogenous results are obtained with this technique, the staining procedure being achieved at room temperature in no more than 10 min. Sections of 0.5-1 microns in thickness are oxidised and bleached. After washing, sections are stained in two steps with carbol methylene blue/carbol gentian violet solution and pararosaniline solution. Using the method described in this paper, a polychromatic coloration of the different cells and tissues was obtained (epithelial cells in various shades of blue-violet, connective tissue and elastic laminae of blood vessels in pink or red, etc.). This procedure provides greater contrast between cytoplasm and nuclei, and among the different types of cells and tissues than is seen with toluidine blue, which is very useful for observation and photography of semithin sections. Polychromatic methods found in the literature are normally complex and require a lengthy staining time or cannot be applied on material routinely processed for transmission electron microscopy. Our method is simple, rapid and can be used on any type of material routinely processed for transmission electron microscopy and embedded in epoxy resins.