Chronic effects of the nucleus pulposus applied to nerve roots on ectopic firing and conduction velocity

Study Design, This study analyzed the effects of the autologous nucleus pulposus (NP) on nerve root function using electrophysiologic methods. Objectives. To investigate the chronic effects of the NP applied to nerve roots and dorsal root ganglions (DRGs) on ectopic firing and nerve conduction velocity. Summary of Background Data. It was reported that ectopic firing in DRGs is involved in abnormal sensation such as sciatica and that ectopic firing was increased shortly after application of the NP to nerve roots. It was also reported that various inflammatory reactions occur around herniated NP clinically, which may affect nerve roots. However, the chronic action of NP on ectopic firing in the stage of inflammatory reaction is unknown. Methods. Forty-six rats were divided into three groups: nucleus pulposus (NP) group, sham group, an control group. In the NP group the autologous NP was applied to L4 and L5 nerve roots. At 1, 2, 4, and 8 weeks after treatment, antidromically propagated ectopic firing from nerve roots was recorded from the sural nerve, and the nerve conduction velocity between the cauda equina and sciatic nerve was analyzed. The frequencies of ectopic firing in the three groups were compared. The ratios of the nerve conduction velocities on the treatment side and opposite side were compared between the NP and sham groups. Results. The frequency was significantly higher in the NP group than in the sham group at 4 weeks, There were no significant differences among the three groups at 8 weeks. There was no significant difference in the treatment side/opposite side ratio of nerve conduction velocity between the NP and sham groups at any time point. Conclusions. Increased ectopic firing in the stage of inflammatory reaction to NP may be related to abnormal sensation.