Hyperalgesia due to nerve injury: Role of neutrophils

The hypothesis that the early inflammatory cell, the neutrophil, contribute s to the hyperalgesia resulting from peripheral nerve injury was tested in rats in which the sciatic nerve was partially transected on one side. The e xtent and time-course of neutrophilic infiltration of the sciatic nerve and innervated paw skin after partial nerve damage was characterized using imm unocytochemistry, The number of endoneurial neutrophils was significantly e levated in sections of operated nerve compared to sections of sham-operated nerve for the entire period studied, i.e. up to seven days post-surgery. T his considerable elevation in endoneurial neutrophil numbers was only obser ved at the site of nerve injury. Depletion of circulating neutrophils at th e time of nerve injury significantly attenuated the induction of hyperalges ia. However, depletion of circulating neutrophils at day 8 post-injury did nor alleviate hyperalgesia after its normal induction. It is concluded that endoneurial accumulation of neutrophils at the site of peripheral nerve injury is important in the early genesis of the resultant hyperalgesia, The findings support the notion that a neuroimmune interacti on occurs as a result of peripheral nerve injury and is important in the su bsequent development of neuropathic pain. (C) 2000 IBRO. Published by Elsev ier Science Ltd. All rights reserved.