• Seiji Ohtori, Gen Inoue, Takana Koshi, Toshinori Ito, Hideo Doya, Tomoko Saito, Hideshige Moriya, and Kazuhisa Takahashi.
• Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan. sohtori@faculty.chiba-u.jp
• Spine. 2006 Aug 15;31(18):2048-52.

Study DesignImmunocytochemistry for acid-sensing ion channel 3 (ASIC3) in neurons of rat dorsal root ganglions (DRGs) from animals exposed to a model of lumbar disc herniation.ObjectiveTo examine expression of ASIC3 in DRGs and the effect of a sodium channel blocker applied to the nerve root in a rat model of lumbar disc herniation.Summary Of Background DataRadicular pain is a common symptom of lumbar disc herniation in human beings. A depolarizing sodium channel gated by protons during tissue acidosis, ASIC3, is specifically expressed in sensory neurons. It has been associated with cardiac ischemic and inflammatory pain. We often perform spinal nerve root block for radicular pain using a sodium channel blocker, such as lidocaine; however, it has been unclear whether the effective period of this treatment is usually longer than the expected duration of efficacy.MethodsFor the lumbar disc herniation model, nucleus pulposus was harvested from the tail and applied to the L5 nerve root, and the nerve roots were pinched. We evaluated mechanical allodynia in sham-operated animals and a disc herniation model. Immunohistochemistry was used to examine ASIC3 expression in L5 DRGs. Finally, the effect of lidocaine on pain and ASIC3 expression in the disc herniation model was examined.ResultsAnimals exposed to the lumbar disc herniation model showed allodynia for 8 days, and ASIC3 immunoreactivity was up-regulated in DRG neurons. After administration of lidocaine to spinal nerve roots affected by disc herniation, ASIC3 immunoreactivity was down-regulated in DRG neurons, and the level of mechanical allodynia was significantly decreased for 8 days.ConclusionsOur results suggest that ASIC3 in DRG neurons may play an important role in nerve root pain caused by lumbar disc herniation. Lidocaine decreased ASIC3 expression in DRG neurons and pain associated with the disc herniation model.

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