Correlation between nucleolar organizer region score and bromodeoxyuridine labeling index in C6 glioma cell line

Correlation between the mean number of nucleolar organizer region-associated argyrophilic proteins (AgNORs) per cell and BrdU labeling index (LI), the percentage of S-phase cells, was investigated in vitro using rat C6 glioma cells under several different conditions such as increased concentration of fetal calf serum (FCS) in a stepwise manner in medium. In addition, the effect of dibutyryladenosine cyclic monophosphate (d-cAMP) on the mean number of AgNORs and the BrdU LI was examined. C6 glioma cells cultured with no FCS showed 5.1% BrdU LI and 3.46 AgNOR score. BrdU LI and AgNOR score of the cells cultured with 1% FCS were 26.5% and 6.25, respectively. Those with 5% FCS were 44.7% and 8.41, with 10% FCS; 49.8% and 10.85, and with 20% FCS; 48.4% and 10.64. Treatment of d-cAMP with 10% FCS induced morphological differentiation and reduced BrdU LI (9.4%) and AgNORs score (4.90), compared with C6 cells cultured in medium containing 10% FCS without d-cAMP. Thus, the BrdU LI and AgNOR score of the C6 cells cultured under several different concentration of FCS were shown to be well linearly related (r = 0.97) and both values were decreased with morphological alteration of C6 glioma cells in the presence of 1 mM d-cAMP.