Experimental Study on Morphological Changes of Proximal Segment of Severed Sciatic Nerve of Rats at Different Time Lapses

Morphological changes of proximal segment of severed rats' sciatic nerves at different time lapses after its severance at the sciatic notch together with difference in morphological changes between motor (anterior root) and sensory (posterior root) fibers were investigated with the following method and following results were obtained. [METHOD] Left sciatic nerve of twenty five rats was severed and ligated at the proximal portion of the sciatic notch. At two weeks, one month, two months, three months and six months after the severance, bilateral sciatic nerves were harvested from the severed level to the anterior and posterior root level. Morphological changes were investigated at three levels, i. e. 15-20 mm proximal to the severed level (level 1), just distal to the posterior root ganglion (level 2) and just proximal to the posterior root ganglion (level 3). Level 1 comprises motor and sensory fibers, level 2 and 3 comprise separate motor nerve fiber (anterior root) area and sensory nerve fiber (posterior root) area. With the particle size analizer, histogram of fiber diameters was made and mean diameter was calculated. [RESULTS] 1. At 15-20 mm proximal to the severed level (level 1) of the left sciatic nerve, axonal atrophy with myelin cleft, myelin crenation, infolded loops of myelin and redundant loops of myelin was observed. Besides, there were a few fibers which presented so-called indirect Wallerian degeneration and the histogram of fiber diameter shifted toward the side of smaller diameter. 2. At the anterior root level (level 2 and 3), motor fibers of anterior root showed slight degree of myelin crenation and their mean diameter was 80%-90% of that of the control with its histogram preserving two peaks as in the unaffected anterior root. 3. At level 2 and 3, i. e. distal and proximal to the posterior root ganglion, many sensory nerve fibers showed myelin infolding and redundant loops of myelin with marked increase of small-sized fibers with resultant decrease of mean diameter to 60-70% of that of the control and the histogram of sensory nerve diameters shifted markedly toward the side of smaller diameter