Axonal regeneration in spinal cord injury: a perspective and new technique.

A set of techniques is described for determining the response of mammalian spinal axons to transection. The logical selection and the advantages of these techniques are discussed. The dorsal column of guinea pig thoracic spinal cord was transected with a tungsten needle and the position of the lesion was marked by a staple-shaped wire device (Foerster: J. Comp. Neurol. 210:335-356, '82). The morphology of dorsal column axons projecting rostrally toward the lesion was examined between 1 and 50 days postlesion by anterograde staining with horseradish peroxidase, applied to a second lesion of the dorsal column two to three vertebral segments caudal to the first. Axons damaged by the original lesion were found to die back 1-2 mm from the plane of transection and at 18-20 hours were characterized by terminal club-shaped swellings attached to the proximal axon by a thin connection. At 50 days postlesion there was some evidence of limited regenerative responses in terms of growth-cone-like axon terminals, and the presence of aberrant axonal branching, but no evidence of regenerating axons approaching close to the plane of transection. These findings are in agreement with previous studies indicating little or no effective regrowth of myelinated axons in the mammalian spinal cord. These same techniques were used in a succeeding study to examine the effects of applied electric fields on the axonal response to transection.