A rat model of radicular pain induced by chronic compression of lumbar dorsal root ganglion with SURGIFLO™

Background: Radicular pain is a common and debilitating clinical pain condition. To date, the mechanisms of radicular pain remain unclear, partly because of the lack of suitable preclinical models. The authors report a modified rat model of radicular pain that could mimic a subset of clinical radicular pain conditions induced by the soft tissue compression on dorsal root ganglion. Methods: A rat model of radicular pain was produced by infiltrating the L5 intervertebral foramen with 60 mu 1 of a hemostatic matrix (SURGIFLO (TM); Johnson & Johnson, Somerville, NJ) resulting in chronic compression of lumbar dorsal root ganglion. Thermal hyperalgesia and mechanical allodynia were measured with or without epidural treatment with triamcinolone. Western blot was used to assess the expression of the NR1 subunit of the N-methyl-D-aspartate receptor and inhibitory factor kappa beta-alpha, an inflammatory marker, within the affected L5 dorsal root ganglion and spinal cord dorsal horn. Results: Chronic compression of lumbar dorsal root ganglion resulted in: (1) persistent mechanical allodynia and thermal hyperalgesia up to 4 or 5 postoperative weeks and (2) upregulation of the N-methyl-D-aspartate receptor and inhibitory factor kappa beta-alpha within the ipsilateral L5 dorsal root ganglion and spinal cord dorsal horn. Epidural administration of triamcinolone (6.25-100 mu g) on postoperative day 3 dose-dependently attenuated both thermal hyperalgesia and mechanical allodynia in rats with chronic compression of lumbar dorsal root ganglion. Conclusion: The data suggest that this modified rat model of chronic compression of lumbar dorsal root ganglion may be a useful tool to explore the mechanisms as well as new therapeutic options of radicular pain.