Isolated axons of Wlds mice regrow centralward.

We have conjectured that axons embody a post transcriptional sprouting programme repressed by mature Schwann cells. Injured nerves of Wld(s) mice neither degenerate nor regenerate for several weeks but axons do regrow if the resident cells of the distal stump are destroyed. To test our hypothesis we made an extended crush in Wld(s) nerves to destroy resident cells, transected the nerve at the proximal end of the lesion, and searched for sprouts in the injured domain. These isolated axons regrew centralward as supported by ultrastructure, labelling with horseradish peroxidase, and staining with DiI. This result indicates that: (i) axons embody a post transcriptional sprouting programme; (ii) resident cells of the nerve, probably Schwann cells, repress this programme, and (iii) navigation of regrowing axons is determined by the environment.