EXPRESSION OF ARGYROPHILIC NUCLEOLAR ORGANIZER REGIONS (AGNORS) CAN BE USED TO ASSESS CELLULAR PROLIFERATION AS SHOWN IN RAT THYMIC SECTIONS

Silver-stained nucleolar organizer regions (AgNORs) were studied in th ymic sections from 4- and 30-day-old rats. By direct examination under the light microscope cells with a low or high content of AgNORs (type I and type II cells, respectively) were identified and their relative numbers calculated. The mean area of AgNORs per cell was calculated f or each type of cell and age group. Additionally, the proportion of ce lls labelled with bromodeoxyuridine was calculated in sections from th e same animals. Visual identification of type I and type II cells was confirmed by a significant (p < 0.01) difference in the mean AgNOR are a in both types of cell. Both the proportion of cells with a high expr ession of AgNORs (type 11 cells) and that of bromodeoxyuridine-labelle d cells were significantly greater (p < 0.01) in 4-day-old rats than i n 30-day-old rats. A significant correlation was found between both va riables (R2 = 0.45; p = 0.002), the relation being best between both v ariables and age (R2 = 0.91; p = < 0.001). These data offer support fo r an easy interpretation of the AgNOR reaction in which the proportion of cells with a high expression of AgNORs can be used as an index of proliferative activity in a tissue sample.