RESUMO
The mAgNOR and pAgNOR counts reflecting the number of rDNA genes being transcribed, showed a highly significant increase from control values following administration of 5X, 10X, 15X doses of enrofloxacin in chicken. The maximum increase for both, mAgNOR and pAgNOR was shown by birds receiving 15X dose, sacrificed 48 hr after the last drug injection. The increase of pAgNOR at 5X (24 hr) was not significant relative to control values. After 72 hr time interval, AgNOR counts were not feasible due to poor differentiation. Values at 15X (24 hr) showed a decrease in number of AgNOR counts (non-significant) relative to 10X, probably due to depression of transcriptional activity of rDNA genes, which, however, is removed at 48 hr. The general increase in mAgNOR and pAgNOR with dose reflects hypertranscription of rDNA genes so that the birds can cope up with the drug induced toxicity.