A ruthenium red-toluidine blue procedure for staining epoxy sections in the light microscopy.

Ruthenium red (RR) has been widely used as a fixation additive for electron microscopy on the basis of its capacity to retain acid mucopolysaccharide residues of the cell surface coat. Little is known about the properties of this compound as a direct staining agent for epoxy-resin embedded material. In this study, semithin sections of Epon-infiltrated muscle tissue samples have been treated with 1% RR followed by counterstaining with 1% toluidine blue. This 2 step staining procedure has proven to be simple, rapid, and reliable and to give a dramatic improvement in image resolution and contrast. Thus, we believe that histochemical procedures employing RR may find in the future interesting applications for the direct staining of epoxy-resin embedded tissues.