Effects of peripheral nerve implants on the regeneration of partially and fully innervated urodele forelimbs.

This study addresses the cellular mechanism of the nerve requirement for regeneration of the urodele forelimb. Others have suggested that only the Schwann cell lineage of the blastema requires nerves for regeneration and that upon limb denervation, Schwann cells arrest in the cell cycle and produce a factor that inhibits the cycling of the remaining blastema cells. Our objective was to test this Schwann cell inhibitor model. First, pieces of peripheral nerve were implanted into partially denervated (one third of the nerve supply cut) axolotl forelimbs in an attempt to provide sufficient additional Schwann cells to increase the threshold nerve requirement above that provided by the remaining nerves. These limbs showed delayed regeneration in 68% of the cases and mild deformities, as seen by Victoria Blue staining, in 10% of the cases, as compared with control, partially denervated contralateral limbs that received grafts of muscle or frozen/thawed nerve. Second, when pieces of peripheral nerve were implanted into fully innervated newt limbs, blastema formation was limited, and regeneration was delayed in 80% of experimental cases when compared with control, contralateral newt limbs with muscle or frozen/thawed nerve implants. The results support the inhibition model and further link the need for nerves in regeneration to a possible specific requirement by Schwann cells.