[Remyelination by Schwann cell transplantation for CNS demyelinated axons: functional comparison with developmental...

Transplantation of Schwann cells(SCs) induced remyelination of demyelinated rat dorsal column(DC) axons and improved conduction. To investigate the difference between developmental oligodendrocytic myelination and SC myelination in conductive functions of axons, we compared normally developmental DCs(10 days old, 22-23 days old, and adult rat), demyelinated DCs, and remyelinated DCs by SC transplantation. DCs of adult rats were demyelinated at T 11 by X-ray irradiation and ethidium bromide, and transplanted with SCs(3 x 10(4)) of adult rats. Three weeks later, the spinal cord was removed and pinned in a recording chamber and compound action potentials (CAPs) were recorded, to investigate conduction properties(conduction velocity, amplitude of CAP and response after high frequency stimulation). Normal DCs were recorded in same manner. Following transplantation of SCs, histological examination revealed SC-like patterns of remyelination of demyelinated axons. The conduction velocities of 10 days old DCs(1.7 +/- 3.4 m/s, n = 4) increased early to 8.1 +/- 3.3 m/s(22-23 days old, n = 7) and 12.2 +/- 1.5 m/s (adult, n = 5). After SC transplantation the velocity significantly improved 7.7 +/- 1.5 m/s(n = 5) compared to demyelinated axons(1.2 +/- 0.4 m/s, n = 7), but less than adult. A 600 Hz 0.5 sec stimulus train led to an amplitude decrement of 7.1 +/- 7.5%(n = 7) in demyelinated axons. Following transplantation, amplitude decreased in 66.2 +/- 11.9%(SC, n = 5), same as 22-23 days(71.7 +/- 11.7%, n = 7) old or adult(76.6 +/- 15.6%, n = 6). The recovery properties after high frequency stimulation developed earlier than conduction velocity. Following SC transplantation, the recovery properties improved to that of normal adult, but not conduction velocity. Lower conduction velocity may be due to shorter internode distance of remyelination after transplantation, same as 22-23 days old pups, than normal adult rats. Though anatomical difference and/or time after transplantation influenced the conduction, these result suggested SC remyelination might result in insufficient for conduction velocity.