Abstract

Neuropathic pain produced by nerve injury is very intolerable and uncontrollable. It is also resistant to analgesics including opioids. Until now the mechanism of neuropathic pain symptoms has been unknown at least in part because there is no reasonable and reliable animal model. Recently we developed new animal model of neuropathic pain in which the tibial and sural nerves of the sciatic nerve branches were injured and the common peroneal nerve was left intact. The present study was conducted to determine whether this animal model of neuropathic pain represent sympathetically maintained or independent pain. Under halothane anesthesia, rats were subjected to neuropathic surgery by cutting the tibial and sural nerves, leaving the common peroneal nerve intact. Two weeks after neuropathic surgery, the animals were anesthetized with urethane for electrophysiological experiments. Almost all the nerve fibers of L4 or L5 dorsal root, regardless whose peripheral axons were injured or not, did not respond to adrenergic drugs. These results suggest that this new animal model of neuropathic pain produced by the injury of the tibial and sural nerves, leaving the common peroneal nerve intact, may represent sympathetically independent pain.