Nitric oxide induced ectopic firing in a lumbar nerve root with cauda equina compression

Nitric oxide is thought to be involved in the pathophysiology of radiculopathy attributable to herniated intervertebral disc, but its effect on ectopic firing, which is the main source of sciatica, has not been investigated. The authors investigated whether ectopic firing is elicited when the lumbar nerve root is exposed to nitric oxide using rats with and without cauda equina compression. A group of animals had partial L3 laminectomy, and a silicone tube was inserted in the epidural space to compress the cauda equina. A sham operation group and nontreated control group also were prepared. Seven days later, ectopic firing of the nerve root was recorded from the sural nerve. The animals with cauda equina compression showed significantly higher spontaneous firing rates than other groups. After a lumbar epidural administration of sodium nitroprusside, only the animals with cauda equina compression showed a marked increase in the firing rate. These results showed that the nerve roots became hyperexcitable under compression as indicated by increased spontaneous firing and marked sensitivity to nitric oxide. This mechanism may play an important role in the development of sciatica.