Diurnal rhythm of nucleolar volume in sympathetic neurons of the rat superior cervical ganglion.

Rhythmic variations of nucleolar volume in neurons from the superior cervical ganglion were studied in rats under artificial synchronization (light: 0700-1900 h; dark: 1900-0700 h) with free access to food and water. Groups of 3 animals were sacrificed by intracardiac perfusion every four hours during the 24-hour period and every two hours between 22 and 07 h. The mean nucleolar volume (Vnu) was estimated in the SCG neurons of each group by measuring the surface area of 450 semi-thin nucleolar sections using a camera lucida and a semi-quantitative analyzer. Stereological analysis demonstrated that variations in Vnu followed a normal curve distribution according to the time of sacrifice, the maximum Vnu being found during the dark between 00 and 01 h. During the 24-hour period, the Vnu (plus or minus SEM) which was low at 14 to 15 h (6.451 plus or minus 0.540 microns(3)), increased two fold to reach a maximum value (13.443 plus or minus 0.705 microns(3)) at 00 to 01 h and then decreased to its nadir at 14 to 15 h on the following day. The results of this study demonstrate that the more or less pronounced variation in the nucleolar volume of these interphase nuclei is related to a diurnal rhythm.