Quantitative examination of internodal length of remyelinated nerve fibres in the central nervous system.

The internodal length of remyelinated internodes was examined by observations on teased CNS nerve fibres following primary demyelination induced by intraspinal injections of lysolecithin into the white matter of cats. A remyelinated internode was identified as a thinly-myelinated internode, where a node of Ranvier was bounded by a thickly-myelinated internode on one side and a less-thickly-myelinated internode on the other; as an internode of less than 100 microns in length or below 2 standard deviations from the normal regression line of internodal length against fibre diameter; as an internode joined to one of similar myelin sheath thickness which fulfilled either or both of the previous two criteria. Using the above criteria, remyelinated internodes were found to be shorter than normal; some were very short with no relationship to axon diameter while others were longer, falling within the predicted range for a given fibre diameter. This study illustrates that examination of teased CNS fibres in pathological situations can yield valuable information. However, sampling and technical difficulties are far greater than in comparable studies on peripheral nerve fibres.