[Occurrence of giant nucleolar fibrillar centers in neurons of rat superior cervical ganglia during dark period: sterological analysis].

In the rat, fibrillar centers (nucleolar organizers) of neurons in superior cervical ganglia are small during light period whereas quite giant ones are observed during dark period. Stereological analysis demonstrates that mean volume of fibrillar centers which is 11.9 x 10(-2) micron 3 in light period increases up to 159 x 10(-2) micron 3 in dark period. So, the more or less development of fibrillar centers in these interphasic nuclei is a circadian phenomenon.