Schmidt-Lanterman Incisures. I. A quantitative teased fibre study of remyelinating peripheral nerve fibres.

The quantitative relationship between the number of Schmidt-Lanterman incisures per internode and fibre diameter has been investigated previously in normal, developing, and regenerating fibres and from such data inferences have been made concerning the function of incisures. We have, therefore, examined this quantitative relationship in remyelinating fibres and assessed the implications for incisural function. Using the rat sural nerve, demyelination was induced by local microinjection of lysophosphatidyl choline. At 100 days and 200 days post-injection remyelinating fibres together with normal control fibres were examined quantitatively for the distribution of Schmidt-Lanterman incisures and nodes of Ranvier. Regression lines relating the number of incisures per internode to fibre diameter showed a positive correlation and were not significantly different between the three groups of fibres. The results are compatible with those for normal, developing and regenerating fibres and support the hypothesis of a homeostatic mechanism controlling the number of incisures in relation to fibre diameter and myelin volume. However, in remyelinating fibres, as in regenerating fibres, there is a greater incisural frequency as a consequence of the short internodes.