Schwann cells can induce collateral sprouting from intact axons: experimental study of end-to-side neurorrhaphy using...

Axonal regeneration across end-to-side neurorrhaphy has recently been reported; however, neither the mechanism by which collateral sprouting from intact axons is elicited, nor the origin of the regenerating axons are known. There has even been controversy over the presence of collateral axonal sprouting from intact axons altogether. This reported experimental study was designed to clarify these questions. A rat sciatic nerve model was used. To avoid any mechanical damage to the donor nerve during the procedure, a Y-shaped silicone chamber was employed instead of direct suture. Axonal regeneration from the intact tibial nerve across the gap into the peroneal nerve was assessed using a retrograde neurotracer and immunohistochemical staining. Axonal regeneration across the gap was observed in 66 percent of the animals. The neurotracer evaluation clearly showed that all regenerating axons were sensory axons from the dorsal root ganglia. The authors concluded that Schwann cells from the distal wallerian degeneration of nerve segments did elicit collateral axonal sprouting from intact sensory axons, but not from motor axons in end-to-side neurorrhaphy. Invasion of the Schwann cells into the epineurial layer was the crucial step for the initiation of collateral axonal sprouting from the intact axons.