Frequency of accumulation of filaments in adaxonal cytoplasm of Schwann cells of myelinated fibers of rat spinal roots. Comparison between ventral and dorsal roots and between growing and mature rats.

The frequency of accumulation of 6-nm filaments in the adaxonal cytoplasm of Schwann cells in the 6th lumbar dorsal and ventral roots was evaluated in 4-, 8-, 26- and 45-week-old Sprague-Dawley rats. The frequency was higher in 4- and 8-week-old (growing) rats than in 26- and 45-week-old (mature) rats, and also higher in ventral than in dorsal roots in 4-, 8- and 26-week old rats. There were no clusters on certain groups of myelinated fibers according to the size of transverse axonal area, in both the ventral and dorsal roots. Therefore, this accumulation may reflect certain functions of the adaxonal cytoplasm of Schwann cell during natural growth and maturation of the axon and myelin sheath.