Effect of tissue processing on colloidal gold cytochemistry.

The aim of cytochemical techniques is to localize specific biochemical components in particular tissue and cell compartments. However, since preparation of tissues for structural observation results in major alterations of the properties of their components, a major problem is to retain an adequate degree of their biochemical properties as well as adequate structural preservation. In the present study, we describe results obtained using various colloidal gold cytochemical techniques on tissues processed through different approaches. We found that any manipulation of the tissue during its processing can result in modifications of tissue components, leading to problems in cytochemistry. Indeed, washing of the tissue before fixation, the nature of the fixative solution, the chemical basis of the resins, and the physical conditions of embedding can all introduce changes in tissue components which can be cytochemically demonstrated. This has been illustrated with application of the protein A-gold, lectin-gold, and enzyme-gold cytochemical techniques on tissues submitted to different processings: fixation by perfusion or by immersion; glutaraldehyde vs paraformaldehyde fixative solutions; cryo-ultramicrotomy; embedding in epoxy, GMA, Lowicryl, or LR resins. The results obtained have demonstrated that conditions for optimal labeling must be worked out for each class of binding sites, and that no single procedure can be recommended as THE best approach in cytochemistry.