Characteristics of ectopic discharges in a rat neuropathic pain model

injured afferent neurons produce spontaneous activity that is generated awa y from the normal impulse generation site. Since this activity, referred to as ectopic discharges, may play a significant role in neuropathic pain, it is important to systematically analyze the activity in various pain states . The present study used the segmental spinal nerve injury model of neuropa thic pain to quantify the ectopic discharges from injured afferents in the neuropathic rat under various conditions. All aspects of measured ectopic d ischarges declined as postoperative time lengthened. Neuropathic pain behav iors declined in a similar fashion over the same time period. Surgical symp athectomy on neuropathic animals lowered the level of ectopic discharges al ong with neuropathic pain behaviors. The data indicate that the level of ec topic discharges is well correlated with that of pain behaviors in a rat ne uropathic pain model, and this reinforces the supposition that ectopic disc harges an important to the maintenance of neuropathic pain behaviors. The d ata suggest that there are two components of ectopic discharge generator me chanisms: sympathetically dependent and sympathetically independent compone nts. (C) 2000 International Association for the Study of Pain. Published by Elsevier Science B.V.