ULTRASTRUCTURAL-CHANGES IN SPINAL NERVE ROOTS INDUCED BY AUTOLOGOUS NUCLEUS PULPOSUS

Study Design. Ultrastructural changes were analyzed by transmission el ectron microscopy in nerve roots exposed to autologous nucleus pulposu s experimentally. Objectives. To assess if ultrastructural changes wer e present in areas with no light microscopic changes in nerve roots ex posed to autologous nucleus pulposus in a pig model. Summary of Backgr ound Data. Previous analyses have shown that there is focal nerve fibe r damage in nerve roots exposed to autologous nucleus pulposus in the pig. These changes could not fully explain the reduction in nerve cond uction velocity seen in the same nerve roots. In the present study, th e parts of the nerve roots that did not display breakdown of axons or myelin sheaths at the light microscopic level were analyzed regarding ultrastructural changes. Methods. In a previous study, nucleus pulposu s was harvested from a lumbar disc and placed epidurally onto the caud a equina at the sacrococcygeal level in pigs. Retroperitoneal fat was used as control. After 1, 3, and 7 days, the nerve roots were excised and processed for light microscopy. Parts of the nerve roots that appe ared normal at the light microscopic level were further processed for the present electron microscopic examination. Results. Significant ult rastructural changes, such as expansion of the Schwann cell cytoplasm and intracellular edema with vesicular swelling of the Schmidt-Lanterm an incisures, were observed in nerve fibers with normal axons. Althoug h present after nucleus pulposus and control application, the changes were more pronounced after the application of nucleus pulposus. Conclu sions. Epidural application of autologous nucleus without any pressure may induce not only nerve function impairment but also axonal injury and significant primary Schwann cell damage with vesicular swelling of the Schmidt-Lanterman incisures. However, because axonal and Schwann cell changes affected only part of the nerve fibers, further causes of the impaired nerve conduction need to be determined.