Conduction of impulses by axons regenerated in a Schwann cell graft in thetransected adult rat thoracic spinal cord

Central nervous system axons regenerate into a Schwann cell implant placed in the transected thoracic spinal cord of an adult rat. The present study w as designed to test whether these regenerated axons are capable of conducti ng action potentials. Following the transection and removal of a 4- to 5-mm segment of the thoracic spinal cord (T8-T9), a polymer guidance channel fi lled with a mixture of adult rat Schwann cells and Matrigel was grafted int o a 4- to 5-mm-long gap in the transected thoracic spinal cord. The two cut ends of the spinal cord were eased into the guidance channel openings. Tra nsected control animals received a channel containing Matrigel only. Three months after implantation, electrophysiological studies were performed. Tun gsten microelectrodes were used for monopolar stimulation of regenerated ax ons within the Schwann cell graft. Glass microelectrodes were used to recor d responses in the spinal cord rostral to the stimulation site. Evoked resp onses to electrical stimulation of the axon cable were found in two out of nine Schwann cell-grafted animals. These responses had approximate latencie s in the range of those of myelinated axons. No responses were seen in any of the Matrigel-grafted animals. Histological analysis revealed that the tw o cases that showed evoked potentials had the largest number of myelinated axons present in the cable. This study demonstrates that axons regenerating through Schwann cell grafts in the complete transected spinal cord can pro duce measurable evoked responses following electrical stimulation. (C) 2001 Wiley-Liss, Inc.