POLYAXONAL MYELINATION IN DEVELOPING DYSTROPHIC AND NORMAL MOUSE NERVES

Myelin-forming Schwann cells in the peripheral nervous system characteristically surround and myelinate only single axons. Polyaxonal myelination is an anomaly of this 1-to-1 relationship whereby 1 normal-appearing Schwann cell myelinates multiple axons. The ventral roots and the proximal sciatic and posterior tibial nerves of developing normal mice and of dy2J/dy2J dystrophic mice with proximal failure of myelination were examined. Polyaxonal myelination was a rare feature in normal nerves. Examples of polyaxonal myelination were observed 6 times more often in dystrophic than in normal mice and were most abundant in proximal sciatic nerves. Polyaxonal myelination could result from either an axonal or a Schwann-cell abnormality, or it may be the nonspecific response of uncommitted Schwann cells to an early failure of myelination.