Immunosuppressants promote adult dorsal root regeneration into the spinal cord

Immunosuppressants promote neurite extension in culture and facilitate regeneration of peripheral nerves in vivo. However, their neurotrophic effects in the CNS have not been well studied. We utilized a rat dorsal root transaction model to examine the effects of cyclosporine A (CsA) and FK 506 on regeneration of the dorsal root into the spinal cord. After surgery, the rats received daily subcutaneous injections of CsA or FK 506. One month after surgery, dorsal root axons were immunohistochemically labeled to evaluate the extent of regeneration into the spinal cord. Dorsal root axons of CsA/FK 506-treated rats frequently entered into the spinal cord and arborized extensively. Administration of immunosuppressants markedly promoted regeneration of dorsal root axons into the spinal cord.