The response of the (myelinating) Schwann cell population to multiple episodes of demyelination.

The effects of multiple intraneural injections of the known demyelinating agent lysophosphatidyl choline, LPC, have been studied in the sciatic nerves of adult mice. Up to six separate episodes of demyelination were induced at the same site within the tibial fascicle. Demyelination and subsequent remyelination occurred after each injection. The number of Schwann cells produced during each repair programme exceeded the number required for remyelination and some of the surplus cells temporarily remained associated with the remyelinating axon/Schwann cell units as supernumerary Schwann cells. There was a progressive decline in the proportion of promyelinated axons as the number of injections of LPC increased. The proposition that this could have reflected a more rapid repair following demyelination of thinly (re)myelinated axons was investigated in double LPC-injected nerves. No structures resembling onion bulbs characteristic of hypertrophic neuropathies in man were seen during the course of this study.