A Mechanism of the Pain Related Behavior Inducedby a Degenerative Nucleus Pulposus Associated with a Ph Change in Rats

Introduction Low back and radicular pain induced by lumbar disc herniation are a major clinical problem with huge monetary. The study of low back pain has been hindered, until recently, by the absence of an adequate animal model. Recently we have reported applying nucleus pulposus tissue, obtained from tail intervertebral discs that had been subjected to chronic mechanical compression, to the lumbar nerve roots produces greater and of longer duration hyperalgesia, which is thought to be a pain related behavior, compared with normal nucleus pulposus. In this model, the underlying mechanisms producing pain related behavior are still unclear although the nucleus pulposus in the compressedtail vertebrae with an Ilizarov-type apparatus showed a certain histological degeneration. Previous reports have described that a reduction of pH of the lumbar disc may be associated with low back pain or radiculopathy in humans, and a change in pH may result in the hyperalgesia produced by loose ligation of the sciatic nerve with chromic gut sutures. Moreover, it has been shown that inflammatory bioactive substances, related to arachidonic acid such as phospholipase A2 (PLA2) and proinflammatory cytokines such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNFα) expressed by the NP around the nerve root are related to hyperalgesia. The purpose of this study were: 1) to evaluate if the expressions of PLA2, IL-1β, TNF-α and the pH change in the nucleus pulposus have a relation to pain-related behavior which was induced by application of the degenerative nucleus pulposus on the nerve root.