The interaction and adhesive mechanisms between axon and Schwann cell during central and peripheral nerve regeneration.

It is well known that the injured mammalian PNS can successfully regenerate, while the CNS such as the optic nerve of adult mammals is incapable of regeneration. It is now generally accepted that the inability of CNS neurons to regenerate appears to be caused by the glial environment made up of astrocytes and oligodendrocytes. However, recent studies show that such CNS neurons have the intrinsic capacity to regenerate which is triggered by an experimental replacement of inhibitorial glial environment to peripheral nerve segment. Thus, the PNS environment is suitable not only for the regeneration of PNS itself, but also for the elicitation of CNS regeneration. Schwann cell is the major component of PNS, which plays a central role both in PNS and CNS regeneration by producing various kinds of functional substances. The contact of axons to Schwann cells based upon the structural and molecular linkages seems to be indispensable for stable and successful regeneration. In addition to cell adhesion molecules, Schwann cells utilize short focal tight junctions to provide morphological stabilization of the contact with the elongating axon, as well as small scale gap junctions to facilitate traffic of substances between them. Thus, nerve regeneration is not a simple phenomenon of axonal elongation on the part of the Schwann cell membrane, but is based on direct and dynamic communication between the axon and the neighboring Schwann cell, which may be partly associated with the mechanisms of neural regeneration.