Functional Considerations: Special Staining for Transmission Electron Microscopy

Many of the histochemical methods used in light microscopy have been adapted for electron microscopy. The use of low-molecular-weight dialdehydes, particularly glutaraldehyde, as primary fixatives has allowed application of many of the standard enzyme histochemical methods to tissue for TEM examination, often requiring only minor modifications of buffers and capture reagents. The phosphatase and esterase procedures have been well adapted for the TEM. The reactions are usually run on 50-/zm tissue slices that are subsequently fixed in osmium tetroxide and embedded for TEM sectioning (see Fig. 1.3).

Substitution of a heavy metal-containing compound for the fluorescent dye usually conjugated with an antibody has allowed adaptation of immunocytochemical methods to transmission electron microscopy, as has the adaptation of the diaminobenzidine-based peroxidase reaction. Similarly, refinement of techniques has also allowed development of routine EM autoradiography as an investigative method (see Fig. 1.5b). These methods have been particularly useful in elucidating the cellular sources and intracellular pathways of certain secretory products, the location on the cell surface of specific receptors, and the intracellular location of ingested drugs and substrates.

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