Age-related changes of the argyrophilic nucleolar organizer regions in mouse neocortical neurons

To evaluate the developmental changes of the nucleolar activity of neurons, we enumerated the number of argyrophilic nucleolar organizer regions (AgNOR) in neocortical neurons of embryonic and postnatal mouse brains. The number of AgNOR changed with time, peaking at late embryonic life and falling gradually through 12 weeks postnatally. Our observation gives indirect evidence that the number of AgNORs is a marker of ribosomal RNA transcriptional activity as well as of ribosomal protein synthesis activity in neurons but not of their proliferative activity, because they are post-mitotic. These findings indicate that the AgNOR staining technique could be a useful adjunct in assessing neuronal activity of the brain.