The effects of punctured nucleus pulposus on lumbar radicular pain in rats: a behavioral and immunohistochemical study

Abstract

Application of the nucleus pulposus (NP) to the nerve root has been developed as a model of lumbar radicular pain. The relationship between disc degeneration and the induction of radicular pain, however, has not yet been fully explored. The authors of this study investigated pain-related behaviors and expression of tumor necrosis factor-alpha (TNF-alpha) in the dorsal root ganglion (DRG) to evaluate the effects of punctured NP on lumbar radiculopathy. An anular needle puncture model of intervertebral disc degeneration in a rat tail was established. Normal and previously punctured NP tissues were obtained and placed on the L-5 nerve root following a hemilaminectomy. Behavioral tests including assessment of motor function, mechanical threshold, and thermal withdrawal latency were performed before and after surgery. The TNF-alpha immunoreactivity in L-5 DRG specimens was examined through immunohistochemical study. The punctured discs showed significant degeneration 2 weeks after intervention. Application of both normal and punctured NP induced mechanical hyperalgesia in the ipsilateral paw for 10 days after surgery, but hyperalgesia was more severe in the punctured NP group. No statistically significant within-group changes in thermal withdrawal latency over time were found. A significant increase in the expression of TNF-alpha-positive neurons in DRG specimens was observed in both NP graft groups. Needle puncture led to degenerative changes in the rat tail disc, and the degenerated NP enhanced mechanical hyperalgesia induced by application of the NP to the lumbar nerve root. This model of disc degeneration and lumbar radicular pain is appropriate for evaluating the efficacy of biological treatments for degenerative disc diseases.