Microwave-Stimulated Fixation and Histochemical Application to Biological Specimens.

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Abstract
More than a decade ago, we introduced a technique using a computer controlled household microwave oven for biological tissue fixation. This microwave irradiation fixation (MWIF) method has produced excellent results, enabling quick and homogeneous infiltration of tissues with a fixative containing chemical reagents. We also described the application of MWIF to light and electron microscopy, including those for enzyme and immunocytochemistry, autoradiography and the distribution of calcium ions. In this review, we present an overview of our experience. To ascertain that microwave irradiation (MWI) would enable aldehyde to quickly and homogeneously penetrate a tissue block, microautoradiography was performed using [3H]-formaldehyde as a tracer. With MWI, prominently developed silver grains were distributed homogeneously in the section, while the control section only had silver grains around it and not inside. Biochemical analysis revealed that complete tissue fixation occurred only after chemical cross-linking of proteins with the infiltrating aldehyde, which was a gradual process. This means that the tissue blocks must be left in the fixative for at least 30-60 min after MWI. To fix soluble peptides and protein or detect Ca2+ with MWI, we used a fixative containing a small amount of tannic acid (0.1%) or chemical reagents, which are very effective for these peptides and proteins, or Ca2+ in cells. Staining using MWI is also very fast and reliable for both light and electron microscopy.