A method for flat embedding thick cryostat tissue sections in plastic resin.

In many histochemical procedures tissues are often sectioned at 30-50 nm (thick sections) to maximize penetration of the substrate into the tissues. After the histochemical reaction the sections can be embedded in plastic resins for thin sectioning and transmission electron microscopy study. Recently, we have used one such procedure to study endocytosis of horseradish peroxidase into Langerhans cells in the murine vaginal epithelium (Parr and Parr 1990). This enzyme has been used extensively as a protein tracer in biologic studies because it can be localized by a simple histochemical procedure for both light and electron microscopy (Graham and Karnovsky 1966). In carrying out the histochemical procedure we encountered problems embedding the thick cryostat sections because they became coiled and twisted during processing. In this report we describe a simple technique for flat embedding thick cryostat sections in plastic resin.