Schwann cell recruitment from intact nerve fibers.

Two proximal branches of the rat facial nerve were transected and anastomosed end-to-end within a silicone tube, each of them being exposed to a massive invasion of ascending regenerating axons. The proximal nerves contained extremely large bundles of regenerated fibers, often associated with preexistent "parent fibers." The bundles showed many signs of rash and disordered cell proliferation and myelination. These included multiple Schwann cells surrounded by a common basement membrane, occurrence of different phases of myelination and even myelination of two axons by one Schwann cell. There was no evidence of mitogenic signals for fibrocytes. This model may be used for studying the mitogenic effect of axons on Schwann cells. It also suggests that so-called "groups of regenerating fibers" in neuropathy are caused by Schwann cell recruitment.