Automated microdensitometry of nucleolar organizer regions using microspectrophoto-microscopy

Nucleolar organizer regions (NORs) are major sites of ribosomal RNA synthesis, providing an index of transcriptional activity and possibly determining the malignant status of cells. Difficulties lie in quantifying them. This study reports a methodology to assist in the standardization of the assessment of interphase NORs. Regenerating hepatocytes, which have increased rRNA synthesis, were chosen as a model to test automated microdensitometry for silver-stained NORs. Quantification employed a microspectrophoto-microscope as a microdensitometer. Significant differences in silver-stained NORs in hepatocytes were recorded among treatment/fixative groups. As the quantitative method avoids subjective observer error and thus improves the accuracy of measurement, it would potentially have routine application to diagnostic pathology.