Difficulties involved in diaminobenzidine histochemistry of endogenous peroxidase

FM1-43 dye ultrastructural localization in and release from frog motor nerve terminals

Previous work has shown that the fluorescent styryl dye FM1-43 stains nerve terminals in an activity-dependent fashion. This dye appears to label the membranes of recycled synaptic vesicles by being trapped during endocytosis. Stained terminals can subsequently be destained by repeating nerve stimulation in the absence of dye; the destaining evidently reflects escape of dye into the bathing medium from membranes of exocytosing synaptic vesicles. In the present study we tested two key aspects of this interpretation of FM1-43 behavior, namely: (i) that the dye is localized in synaptic vesicles, and (ii) that it is actually released into the bathing medium during destaining. To accomplish this, we first photolyzed the internalized dye in the presence of diaminobenzidine. This created an electron-dense reaction product that could be visualized in the electron microscope. Reaction product was confined to synaptic vesicles, as predicted. Second, using spectrofluorometry, we quantified the release of dye liberated into the medium from tubocurarine-treated nerve-muscle preparations. Nerve stimulation increased the amount of FM1-43 released, and we estimate that normally a stained synaptic vesicle contains a few hundred molecules of the dye. The key to the successful detection of released FM1-43 was to add the micelle-forming detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), which increased FM1-43 quantum yield by more than two orders of magnitude.

Present status of estrogen-receptor immunohistochemistry

Anti-estradiol is used as the primary antibody in the peroxidase-anti-peroxidase (PAP) immunoperoxidase (IP) method to visualize putative estrogen-binding sites in potential hormone-dependent tissues and tumours. Basically, 2 different methods are used. The 1st is carried out on fresh-frozen cryostat sections; the 2nd has the advantage to be applicable on current laboratory material, i.e. formalin-fixed and paraffin-embedded material. The various steps of both techniques are analyzed and compared: the potential influence of tissue processing, the necessity of preincubation in estrogens, the physico-chemical conditions of incubation, and the specificity of controls. Van Bogaert (1983) analyzed the drawbacks of the presently available cytochemical techniques used to stain putative estrogen binding sites (EBS) in human breast cancer. In the present paper, a similar investigation is carried out with the aim to evaluate both the technical advantages and possible pitfalls of immunohistochemistry of estrogen receptors (ER) in human mammary carcinoma.

Diaminobenzidine histochemistry in light microscopy

Basically the DAB-technique localizes 3 enzymes, i.e. peroxidase, catalase, and cytochrome oxidase, but also pseudoperoxidatic activity of hemeenzymes (hemoglobin, myoglobin, etc.). Although at the ultrastructural level, i.e. in cytochemistry, the appropriate conditions for specific identification of each of these enzymatic activities have been extensively studied and reported in the literature, the subject remains open to investigation. In light microscopy DAB staining has been less thoroughly studied. Since DAB histochemistry might have practical interest in daily diagnostic pathology, it appeared worthwhile to work out a method convenient for paraffin embedded tissues. The method consisted of a prolonged incubation 48 h) of small tissue blocks, which had been prefixed for 1 h in 4% formaldehyde. Dehydration and rehydration occurred in graded ethanols; counterstain was obtained by toluidine blue. Although further experiments are needed to specify the physico-chemical conditions for the three enzymatic activities, the results are morphologically superior to that of frozen sections.