Experimental aspects of spinal cord regeneration.

Sprouting, elongation, and functional reconnection are the necessary steps for successful regeneration of lesioned axons. Induction of growth-specific proteins in adult cells and of lesioned fibers sprouting can occur spontaneously in central nervous system neurons and may be enhanced by specific neurotrophic factors. The extremely limited elongation commonly observed in the adult central nervous system depends crucially on the presence of neurite growth-inhibitory molecules, such as those associated with central nervous system myelin or several candidate molecules expressed in glial scars. Optic nerve axons guided into their targets by peripheral nerve bridges were able to restore functional synapses in adult rats, showing that the relevant recognition mechanisms are present. Important steps in the cellular and molecular understanding of these basic processes of lesioned axon regeneration are being taken at present and significant progress can be expected in the near future.