신경병 흰쥐에서 A-β신경섬유의 활동의존 전도속도의 변화

ACTIVITY-DEPENDENT VARIATIONS IN CONDUCTION VELOCITY OF A-β FIBERS : COMPARISON BETWEEN NEUROPATHIC AND NORMAL RATS

Partial injury to peripheral nerves can often result in abnormal pain sensation, neuropathic pain or causalgia, which is characterized by spontaneous homing pain combined with hyperalgesia and allodynia. Neuropathic pain persists for years or decades after all possible tissue healing has occurred. Nerve injury appears to induce changes of excitability in the damaged peripheral nerve. Many of the injured A-beta axons exhibited spontaneous discharges as early as 1 day post-injury. The demyelinated region of the damaged nerve was also very sensitive to both TEA and noradrenaline, suggesting the presence of new ion channels or receptors, absent in normal, in the damaged region. However, there has been few study to test the activity-dependent excitability changes in intact axons of the neuropathic rats. The hypothesis is that impulse transmissions through the uninjured axons of either dorsal root or sciatic nerve may have been altered in neuropathic rat. To test this hypothesis we used an experimental rat model where L4 and L6 spinal nerves were tightly ligated unilaterally, leaving the L5 intact. Changes of the conduction latency were characterized following impulse activity (1 min duration, sustained stimulation, 0.5, 1, 5, 10, 25, 50, 100 and 200 Hz) in single A-beta fibers of L5 dorsal root and in peripheral sciatic A-beta fibers of neuropathic rats (L4 and L6 dorsal roots ligated) anesthetized with urethane. As a results, the profiles of activity-dependent increases of latency in A-beta fibers of L5 dorsal root of neuropathic rat were significantly stronger (P<0.01, from 50-200 Hz) than those in normal rat following different rates of impulse activity. However, activity-dependent latency changes recorded from sciatic nerves distal to the dorsal root ganglion were not significantly different between neuropathic and normal rats. These results suggest that excitability changes may have been occurred in the intact dorsal root fibers of neuropathic rat and that these changes may be related to the allodynia observed in neuropathic pain.