Metal-catalyzed oxidation renders silver intensification selective. Applications for the histochemistry of diaminobenzidine and neurofibrillary changes.

Physical developers can increase the visibility of end products of certain histochemical reactions, such as oxidative polymerization of diaminobenzidine and selective binding of complex silver iodide ions to Alzheimer's neurofibrillary changes. Unfortunately, this intensification by silver coating is generally superimposed on a nonspecific staining originating from the argyrophil III reaction, which also takes place when tissue sections are treated with physical developers. The present study reveals that the argyrophil III reaction can be suppressed when tissue sections are treated with certain metal ions and hydrogen peroxide before they are transferred to the physical developer. The selective intensification of Alzheimer's neurofibrillary changes requires a pre-treatment with lanthanum nitrate (10 mM/liter) and 3% hydrogen peroxide for 1 hr. The diaminobenzidine reaction can be selectively intensified when physical development is preceded by consecutive treatments with copper sulfate (10 mM/liter, pH 5, 10 min) and hydrogen peroxide (3%, pH 7, 10 min). In peroxidase histochemistry, this high-grade intensification may help to increase specificity and reduce the threshold of detectability in tracing neurons with horseradish peroxidase or in immunohistochemistry when the peroxidase-antiperoxidase method is used.