Ultrastructure and stereological analysis of nucleoli of rat nodose ganglion neuron during a 24-h period: a comparison with sympathetic neurons of rat superior cervical ganglion.

The nucleoli of rat nodose ganglion were investigated during a 24-h span (light span 07.00-19.00 h). The mean volume of nucleoli and that of their components, especially fibrillar centers considered to be the interphasic counterpart of nucleolus-organizing regions, were determined by stereological analysis. The quantitative data showed that (1) nucleoli volumes of rat nodose ganglion neurons did not oscillate diurnally but that (2) there were diurnal dimensional changes in the volume of their fibrillar centers which strongly suggest an ultradian rhythmicity. These results are different from those obtained in studies of superior cervical ganglion neurons, in which nucleoli and nucleolar components followed a circadian rhythm with peak values during daily periods of darkness. Although the nucleoli of these 2 kinds of neurons involved in autonomic nervous system reactions do not show the same behavioural patterns, the present data bring to light a new example of circadian fluctuation in nucleoli and describes their organization in this respect.