A study of early ongoing activity in dorsal horn units following sciatic nerve constriction

An analysis was made of the background activity of spinal neurones involved in nociceptive processes during, and in the first hour after, sciatic nerve constriction in normal rats and in rats in which sciatic nerve conduction had been previously blocked with local anaesthetic. In both pure noxious and WDR neurones the results showed high frequency discharges at the time of ligation, followed by a slight but persistent increase in activity that reached, after 1 h, values 6-8 times those preligature. The increased post-injury discharge could be reduced by secondarily applying lidocaine on the peripheral site of constriction. There were no neuronal activity changes after the ligatures in rats with sciatic nerve pretreated with local anaesthetic. The likelihood that the early persistent increase in activity may have a role in the excitability change of spinal neurones observed in neuropathic pain is discussed.