[Ultrastructure and the number of nucleoli in the neurons of the rat cerebellar cortex].

The ultrastructure and number of nucleoli in rat cerebellar nervous cells (the Purkinje and granule cells) were studied using the silver staining procedure and serial ultrathin sections. In the Purkinje cells one large nucleonemal nucleolus about 4 mcm in diameter was usually observed; fibrillar centers are weakly expressed. About 6% of the Purkinje cells had two nucleoli different in size. In granule cells 2-3 nucleoli about 1 mcm in diameter were detected. They contained a distinct fibrillar center and a dense fibrillar RNP-component, RNP-granules were barely visible. These data show that the Purkinje cells are more active transcriptionally than granule cells. The distinctions in the ultrastructure and number of nucleoli in the Purkinje and granule cells correspond to an earlier reported hypothesis about the intra- and interpopulation heterogeneity of cerebellar nervous cells for topography of ribosomal genes.