Sympathectomy alleviates mechanical allodynia in an experimental animal model for neuropathy in the rat

We attempted to determine the effects of surgical sympathectomy on an animal model for neuropathic pain. The L₅ and L₆ spinal nerves on one side were tightly ligated in anesthetized rats. Mechanical sensitivity of the affected hind paw was significantly elevated from the first day after the surgery as evidenced by the increased occurrence of foot withdrawal to innocuous mechanical stimulation applied with von Frey filaments to the hind paw. The increased mechanical sensitivity continued for three weeks, at which time surgical sympathectomy was performed by removing the L₂-L₆ sympathetic chain. The sympathectomy produced an immediate and almost complete reversal of the increased mechanical sensitivity, whereas sham sympathectomy had no effect. The data suggest that sympathectomy alleviates mechanical allodynia in this experimental animal model.