AXOPLASMIC TRANSPORT OF LABELED PROTEINS IN RAT VENTRAL MOTONEURONS

Axoplasmic transport was studied in lumbar ventral motor neurons of adult rats by injecting l-leucine3-H directly into the spinal cord and subsequently analyzing the distribution of the incorporated label in the nerve roots and peripheral nerve. Very little of the label was found in the dorsal roots at distances in excess of 10 mm from the spinal cord during the period 1-40 days after injection, suggesting that the label was not carried into the nerve by diffusion in the endoneurial spaces. On the other hand, the rapid entry of the label into the ventral root and peripheral nerve conforms with the concept that axoplasmic proteins are synthetized in the neuron cell body and transported into the axon. It is suggested that the labeled axoplasmic protein was transported into the axon in possibly three sectors of the axoplasm: (a) a slowly moving sector which is transported at approximately 1 mm/day; (b) a sector which has a net somatofugal transport velocity of a few mm/day; and (c) a rapidly moving sector of the axoplasm in which components are transported at velocities in excess of 100 mm/day. © 1968.