SHEATH LENGTHS OF LARGE MOTOR AXONS IN THE VENTRAL ROOT L5 OF NEONATAL AND ADULT-RATS

This study examines the developmental sheath elongation in the rat ven tral root L5. Electron microscopic analysis of serial transverse secti ons through roots from newborn rats shows an average internuclear dist ance (IND) of 66 mu m (calculated fresh length 73 mu m). Light microsc opic analysis of teased adult roots shows that the largest fibers have an average internodal length of some 1250 mu m at 5 months. Hence, la rge fibers exhibit a developmental sheath elongation of 17 times. The ventral root L5 elongates 11 times only. This mismatch necessitates a myelin sheath remodelling.