Observations on the morphology and the axon conduction velocity of axotomized and regenerating sciatic motoneurons in the kitten.

In 1 week old kittens a 10 mm long segment of the sciatic nerve was removed distal to the hamstring branch point. After 70-85 days sciatic motoneurons were injected intracellularly with horseradish peroxidase (HRP). The cell body diameter, the summed diameter of the 1st order dendrites, the intramedullary axon diameter and the axon conduction velocity proximal to the lesion were determined in individual neurons and related to the conduction velocity of the regenerating segment of the axons. The lesioned neurons were compared with normal sciatic motoneurons in 7-8 and 77-92 days old kittens. In motoneurons which seemed to lack regenerating axons or had regenerating axon segments with a low conduction velocity there was a clear growth retardation of all studied parameters. In those neurons, however, which had regenerating axon segments conducting faster than 10 m/s, all parameters above the lesion, except for the conduction velocity of the axon, had attained normal values. The intramedullary part of the axon seemed to be less affected by the injury than all other studied parts of the neuron proximal to the lesion.