TUNEL (TdT-mediated dUTP-biotin nick end-labeling)
provides determination of DNA breaks in situ [14]. Paraffin
blocks, frozen sections, or cultured cells can easily
be analyzed by this method. This assay gives clear
images of apoptotic cell death in a population of cells
(Figure 5). In general, the immunohistochemistry rules
are applied to the samples. But, instead of proteins, the
DNA is under study in this assay. The nuclei may be visualized
by either colorimetric or flourometric methods.