Electron microscopic observations of peripheral myelin in a central nervous system lesion

After cyanide intoxication and after triethyltin implantation in the brain, cystic spaces were found in the forebrains, of two rats. Within these spaces, many examples of remyelinating axons were observed. Most of them displayed typical mature or developing "central type" myelin sheaths. Some, however, showed all the morphological features characteristic of mature or developing peripheral myelin. In both rats, the cavities of the cysts were open to the overlying subarachnoid spaces due to partial disruption of the subpial astrocytic layer. It was concluded that the myelin-forming cells responsible for the formation of the "peripheral type" myelin within the cyst were probably Schwann cells derived from peripheral nervous elements accompanying some subarachnoid blood vessels. It could not be determined whether the axons within the "peripheral type" sheaths were part of the central or peripheral nervous systems. These data might be relevant to the origin of central neurinomas.