High density of nodes of Ranvier in the CNS-PNS transitional zone.

Node of Ranvier density was examined at three levels along rat lumbar motoneuron axon bundles: where they lie in the central nervous system, in the peripheral nervous system and in the transitional zone (TZ) between these. Density was considerably and significantly greater in the TZ than in either of the other locations. It is possible that such densely packed nodes in the TZ could interact electrically with one another. Because of its structure and position and because it contains a relatively pure fibre population, the rat L4 ventral rootlet TZ lends itself readily to electrophysiological investigation of this possibility.