Axoplasmic flow of tritiated proline in the corticospinal tract of the rat

Summary The rates of axoplasmic transport were studied in the corticospinal tract of the rat by injecting tritiated proline into the sensory-motor cortex and subsequently analyzing the distribution of incorporated label in the spinal cord at intervals after injection. A mathematical model of the anatomy of the corticospinal tract was developed and used in analysis of the data. The rate of a fast component was calculated to be 240–420 mm per day, which is comparable with rates of fast components in the peripheral nervous system (PNS), but considerably greater than rates in other tracts in the central nervous system. A slow component was calculated to have a transport rate of 3–8 mm per day which is greater than rates found either in the CNS or PNS. This higher rate may be related to the greater length of the corticospinal tract as compared to other CNS tracts studied.This research was financed by the Veterans Administration research support awarded to Dr. Feringa by the Development Funds of the Department of Pathology, University of Michigan, and by the University of Michigan Medical Center Fund for Computing. The authors wish to express their appreciation to Ms. Linda Lee Austin for technical assistance, Ms. Diane Trakas and Ms. Barbara Reader for secretarial aid, and Mr. Richard Fritzler for assistance with graphics