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The effect of three different neurotrophins on axotomy-induced death of adult rat sensory neurons was examined. The ventral branch of the 13th spinal nerve was transected and the corresponding neurons in the 13th thoracic (T13) dorsal root ganglion (DRG) were pre-labelled with Fast Blue (FB). For a period of 4 weeks, animals received either no treatment, continuous intrathecal infusion of phosphate buffer, nerve growth factor (NGF), neurotrophin-3 (NT-3), or brain-derived neurotrophic factor (BDNF). Labelled neurons remaining after this period were counted. Inert, or no treatment, resulted in extensive loss of the DRG neurons. BDNF application was virtually non-effective, while NGF or NT-3 resulted in a greater number of FB-labelled neurons compared to normal controls. This suggests that NGF and NT-3 are survival factors for adult sensory neurons with a therapeutic potential in peripheral nerve injuries.

To address the need for the development of bioengineered replacement of a nerve graft, a novel two component fibrin glue conduit was combined with human mesenchymal stem cells (MSC) and immunosupressive treatment with cyclosporine A. The effects of MSC on axonal regeneration in the conduit and reaction of activated macrophages were investigated using sciatic nerve injury model. A 10mm gap in the sciatic nerve of a rat was created and repaired either with fibrin glue conduit containing diluted fibrin matrix or fibrin glue conduit containing fibrin matrix with MSC at concentration of 80×10(6) cells/ml. Cells were labeled with PKH26 prior to transplantation. The animals received daily injections of cyclosporine A. After 3 weeks the distance of regeneration and area occupied by regenerating axons and ED1 positives macrophages was measured. MSC survived in the conduit and enhanced axonal regeneration only when transplantation was combined with cyclosporine A treatment. Moreover, addition of cyclosporine A to the conduits with transplanted MSC significantly reduced the ED1 macrophage reaction.

Peripheral nerve injuries with loss of nervous tissue are a significant clinical problem and are currently treated using autologous nerve transplants. To avoid the need for donor nerve, which results in additional morbidity such as loss of sensation and scarring, alternative bridging methods have been sought. Recently we showed that an artificial nerve conduit moulded from fibrin glue is biocompatible to nerve regeneration. In this present study, we have used the fibrin conduit or a nerve graft to bridge either a 10 mm or 20 mm sciatic nerve gap and analyzed the muscle recovery in adult rats after 16 weeks. The gastrocnemius muscle weights of the operated side were similar for both gap sizes when treated with nerve graft. In contrast, muscle weight was 48.32 ± 4.96% of the contra-lateral side for the 10 mm gap repaired with fibrin conduit but only 25.20 ± 2.50% for the 20 mm gap repaired with fibrin conduit. The morphology of the muscles in the nerve graft groups showed an intact, ordered structure, with the muscle fibers grouped in fascicles whereas the 20 mm nerve gap fibrin group had a more chaotic appearance. The mean area and diameter of fast type fibers in the 20 mm gap repaired with fibrin conduits were significantly (P0.01) worse than those of the corresponding 10 mm gap group. In contrast, both gap sizes treated with nerve graft showed similar fiber size. Furthermore, the 10 mm gaps repaired with either nerve graft or fibrin conduit showed similar muscle fiber size. These results indicate that the fibrin conduit can effectively treat short nerve gaps but further modification such as the inclusion of regenerative cells may be required to attain the outcomes of nerve graft for long gaps.

Spinal cord injury (SCI) often results in necrotic changes leading to cavity formation and glial scar tissue in the lesion zone. We have examined the effects of continuous topical administration of brain-derived neurotrophic factor (BDNF) on cavity formation and neuronal death after SCI. Following retrograde prelabeling of the tibial motoneurons in the L4-L6 spinal cord segments with the fluorescent dye Fast blue, a spinal hemisection was performed in the L5 segment. At 4 weeks postoperatively, only 66% of the labeled motoneurons remained in the untreated animals, while BDNF treatment resulted in a significant reduction in size of the lesion cavity and 92% motoneuron survival. A therapeutic potential of BDNF in the early treatment of SCI is suggested.