Effects of lumbar sympathectomy on pain behavioral changes caused by nucleus pulposus-induced spinal nerve damage in rats.

It has been suggested that lumbar sympathectomy can reduce pain behavior, including mechanical allodynia and thermal hyperalgesia, caused by ligation of the spinal nerve. One well-characterized model, which involves application of nucleus pulposus to the spinal nerve and displacement of the adjacent nerve, shows behavioral changes in rats. However, there have been no previous reports regarding sympathectomy performed in this model. Disk incision and adjacent spinal nerve displacement were performed with (n=6) or without (n=6) sympathectomy. Sham surgery was also performed with (n=6) or without (n=6) sympathectomy. The animals were tested for 3 days before surgery and on days 1, 3, 7, 14, and 21 after surgery. Non-noxious mechanical thresholds were tested by determining the hind paw withdrawal response to von Frey hair stimulation of the plantar surface of the footpad using a touch stimulator. Thermal nociceptive thresholds were tested using a sensitive thermal-testing device. While rats in the disk incision with displacement surgery group showed allodynia and hyperalgesia after surgery on the experimental side, sympathectomized animals did not. No allodynia was observed in the sham groups. Sympathectomy seemed to prevent the pain behavioral changes caused by the combination of disk incision and nerve displacement.