DIRECT MEASUREMENT OF FAST AXONAL-TRANSPORT RATES IN CORTICOSPINAL AXONS OF THE ADULT-RAT

The bi-directional movement of proteins from the soma to the axon term inal is called axonal transport. Fast anterograde transport moves orga nelles and membrane-bound proteins distally. Fast transport rates were measured in corticospinal tract axons of male Sprague-Dawley rats by microinjection of tritiated proline into the sensorimotor cortex. Anim als were killed after 3-5 h and the tract cut into 1 mm segments. A bi modal wave of radiolabeled proteins was evident, with the first peak a t the spine-medullary junction and the second peak in cervical spinal segments. The fast transport rate was calculated at the leading edge o f the distal wave, and found to be 303+/-44 mm/day.