Early transient ultrastructural and quantitative changes in nucleolar vacuoles of sympathetic neurons in isolated superior cervical ganglion of the rat

Nucleolar changes and their time-course following axotomy and decentralization were investigated using an ultrastructural and stereological analysis of sympathetic neurons in superior cervical ganglion. By comparison with ganglia fixed immediately after removal, incubation for 2 h, 3 h and 5 h in NCTC 109 medium at 37 degrees C was found to induce early changes in the nucleolar volume (first a 33% increase, followed by a 43% decrease and a subsequent recovery to control values after 5 h). Moreover, dense material (also called 'microspherules') appeared in nucleolar vacuoles as early as 2 h after the beginning of incubation and was present after 3 h, but disappeared after a 5 h incubation. The dense material may have been either fibrillar component involved in rDNA transcription, or granular component involved in the storage and/or transport of preribosomal particles. Such early, transient and quantitative changes were observed very earlier than in previous studies on the axon reaction.