EXTRA-TERRITORIAL PAIN IN RATS WITH A PERIPHERAL MONONEUROPATHY - MECHANO-HYPERALGESIA AND MECHANO-ALLODYNIA IN THE TERRITORY OF AN UNINJURED NERVE

The abnormal pain sensations that accompany peripheral neuropathies ar e sometimes found in a distribution that does not coincide with the te rritories of nerves or posterior roots. This 'extra-territorial' pain is one of the lines of evidence that has been advanced to support the proposal that these patients suffer from a psychogenic disorder. In th e present experiments, rats were prepared with a unilateral chronic co nstriction injury (CCI) to the sciatic nerve. Beginning on the first p ostoperative day and continuing for at least 18 days, exaggerated with drawal reflexes to pinprick stimulation, indicative of mechano-hyperal gesia, were seen on the side of nerve injury in the hindpaw territorie s of both the injured sciatic nerve and the uninjured saphenous nerve. Beginning on postoperative day 4 and continuing for at least the next 3 weeks, the withdrawal responses to von Prey hair stimulation on the nerve-injured side occurred at a significantly Lower threshold, indic ating the presence of mechano-allodynia. The severity and time course of the mechano-allodynia were similar in both nerve territories. When tested 18 days after the CCI, mechano-allodynia in the saphenous terri tory was abolished by an acute saphenous transection, but unaffected b y sciatic transection. Conversely, mechano-allodynia evoked from the m id-plantar sciatic territory was abolished by acute sciatic transectio n, but unaffected by saphenous transection. These results show that ra ts with an experimental painful peripheral mononeuropathy have extra-t erritorial pain like that seen in man. Extra-territorial pain may be p artly or entirely due to a peripheral nerve injury-evoked dysfunction of pain processing neurons in the central nervous system.