Identification and assessment of nucleolar organizer regions (NORs)--technical problems.

NORs are the loops of DNA containing ribosomal genes which are associated with non-histonic argyrophilic proteins. It permits their identification by using specific argyrophilic staining. NORs are visualized in light microscopy as AgNOR dots or argyrophilic NOR dots. Neoplastic and proliferative cells show differences with respect to the number, area and distribution of AgNOR dots. Major difficulties in the analysis of AgNOR dots are caused by technical problems associated with staining and fixation of the tissue. In our study we found that correct fixation of nucleolar proteins associated with AgNORs was a decisive factor in correct interpretation of the results.