NUCLEOLAR ORGANIZER REGIONS AS MARKERS OF INCIPIENT CELLULAR ALTERATIONS IN SQUAMOUS EPITHELIUM

Transcriptionally active nucleolar organizer regions identified by sil ver staining (AgNOR) vary in number with cellular activity and/or mali gnant transformation and have been used as a diagnostic tool. A morpho metric study of AgNORs was performed in an experimental model of irrad iated squamous epithelium (Wistar rat sole skin) 4, 8, and 14 hours an d 1, 2, 5, and 7 days post-irradiation with 50 Gy of x-rays. A statist ically significant and progressive rise in AgNOR average volume of up to 238% and reduction in AgNOR number/nucleus of up to 40% were detect ed as a function of post-irradiation time. A statistically significant 46% increase in AgNOR volume was detected as early as 8 h post-irradi ation, when no histological changes were observable in routine prepara tions. These results suggest that AgNORs may be useful as a quantitati ve marker of incipient changes in cellular activity and caution agains t the indiscriminate use of AgNORs in the follow-up of lesions which m ay have been exposed to radiotherapy. Furthermore, this study suggests the possibility of using AgNORs as a sensitive biological dosimeter i n cases of uncontrolled exposure to radiation.