Contributions Of Ectopic Discharges To Chronic Pain And Sympathetic Sprouting In Dorsal Root Ganglion In A Neuropathic Rat Model

Background: A growing evidence showed that the sympathetic activity plays an important role in the origin and maintenance of neuropathic pain. The sympathetic sprouting and so-called "basket-cell" occurred in the lesioned DRG following peripheral nerve injury may be a sympathetic-sensory coupling site at the DRG level. However, what factors eliciting sympathetic sprouting and basket formation are obscure at present. Our study aimed at whether the ectopic discharges following nerve injury contributed to the sympathetic sprouting and basket formation in the DRGs and the action of sympathetic sprouting on the origin and maintenance of chronic neuropathic pain. Objectives: (1) Increased or decreased background of ectopic discharges was made by repeat i.p. administrating K+channel blocker, 4-aminopyridine (4-AP, 10mM, 1.88mg/kg, qid) or M receptor blocker, anisodamine (1%, 10mg/kg, qid) within the first week postoperative on CCI rats. Using single unit recording technique, the sensitivities of ectopic discharge frequencies of injured A fibers to NE which were recorded from dorsal root were observed. (2) Measure the effects of 4-AP, anisodamine or MnCl₂ on heat-hyperalgesia, cold-allodynia and mechanical-allodynia, including action of single injection of 4-AP, MnCl₂ or anisodamine i.p. or perineurally on heat-hyperalgesia, cold-allodynia and mechanical-allodynia and the time course of development of heat-hyperalgesia, cold-allodynia of CCI rats which were injected 4-AP, MnCl₂ or anisodamine repeatedly within the first one or two week postoperative. (3) Observe the changes of basket cell numbers in injured DRGs of CCI rats...