REGROWTH OF AXONS WITHIN SCHWANN CELL-FILLED POLYCARBONATE TUBES IMPLANTED INTO THE DAMAGED OPTIC TRACT AND CEREBRAL-CORTEX OF RATS

The efficacy of Schwann cell-filled polycarbonate tubes as a bridging substrate for regrowing axons following lesions of the rat optic tract or cerebral cortex has been assessed after short (11-31 days) or long (82-119 days) survival times. Tubes were impregnated with laminin and poly-l-lysine, soaked in basic FGF and filled with Schwann cells. The y were implanted into optic tract lesions in 34 rats aged 15-21 days a nd into cortical lesion cavities in 3 adult rats. Gelfoam soaked in ba sic FGF and Schwann cell conditioned medium was placed over the tubes. In one group of rats, axon regrowth into implants was assessed using neurofilament antibody RT97; antibodies to proteolipid protein, P-o, l aminin, the low-affinity nerve growth factor receptor (NGFr), S-100 an d ED1 were also used to study myelination and the cellular content of the tubes. In a second group of rats, anterograde tracing techniques w ere used to specifically identify host retinal axons within the implan ted polymers. After long survival times, the relationships between reg rown axons and cells inside the tubes were also examined ultrastructur ally. In all implants examined immunohistochemically at short survival times, large numbers of RT97(+) axons were found throughout the tubes , usually in association with laminin(+), NGFr(+) Schwann cells. At lo nger survival times, viable Schwann cells were still present, but tube s contained fewer axons and less cellular material. This material ofte n formed a cord (200-250 mu m thick) which extended the length of the implant. In the second group of rats, labelled retinal axons were foun d in 11 of the 16 implants that were attached to the dLGN. Axons regre w up to 1 mm but did not reach the distal (tectal) end of the implants . Interestingly, there was no evidence of myelinogenesis by either imp lanted Schwann cells or by host-derived oligodendroglia which had migr ated into the tubes. Oligodendroglia were usually encircled by process es, many of which originated from Schwann cells, suggesting that the g rafted cells may have been involved in isolating the central glia. The data show that Schwann cell-filled polycarbonate tubes provided a fav ourable milieu for axonal regeneration in the short term; however over time there was a decrease in the cellular and fibre content of the tu bes. After intracranial implantation, an additional supporting matrix inside the polycarbonate tubes may aid in providing an environment con ducive to the long term maintenance of regenerated retinal and other a xons.