Directional regrowth of lesioned corticospinal tract axons in adult rat spinal cord.

During central nervous system development, gradients of diffusible molecules play an important role in the attraction of outgrowing axons. A diffusible tropic factor released by the cervical spinal gray matter attracts outgrowing corticospinal tract axons, as shown by in vitro collagen co-culture studies [Joosten E. A. J. et al. (1994) Neuroscience 59, 33-41]. Here we study the effects of local application of timed cervical spinal gray matter extracts on regrowth of injured corticospinal tract axons in the adult rat spinal cord. For local application of target-derived extracts at the site of lesion we used rat tail collagen type 1 as a matrix. Ingrowth of anterogradely labelled corticospinal tract axons into the collagen was studied four weeks after the spinal cord injury. No ingrowth of labelled corticospinal tract axons can be observed in the control experiment when collagen only was applied into the lesion gap. Furthermore, we found that local application of an extract derived from four-day, but not from one-day or 16-day-old, cervical spinal cord gray matter directs a substantial amount of the lesioned adult corticospinal tract axons into the collagen implant. We conclude that directional regrowth of injured corticospinal tract axons in the adult rat spinal cord is possible by local application of timed target-derived extracts. In this respect spatiotemporal aspects are of the utmost importance.