Effects of Aging on the Expression of Neuropathic Pain Produced by Injury of Sciatic Nerve Branches

Abstract

Peripheral nerve injury can lead to neuropathic pain which is a chronic pain state like hyperalgesia, spontaneous pain, mechanical allodynia, and thermal allodynia. Aging may affect the severity of neuropathic pain symptoms. In humans, there is difference between old and young persons in susceptibility of neuropathic pain. The present study was conducted to determine whether the behavioral signs of neuropathic pain following peripheral nerve injury depend on age at the time of the peripheral nerve injury. Under halothane anesthesia, the tibial and sural nerves were injured and the common peroneal nerve was left intact. Neuropathic pain behaviors were compared between young and old groups of rats. Rats with injury to the tibial and sural nerves showed the vigorous mechanical allodynia, cold allodynia, and spontaneous pain. Young rat group showed more profound mechanical allodynia, cold allodynia, and spontaneous pain compared to old rat group. The results suggested that all the behavioral signs of neuropathic pain may be manifested more robustly in young rat group rather than old rat group in our animal model of neuropathic pain which was produced by injury to the tibial and sural nerves, while leaving the common peroneal nerve intact. Aging appears to affect several factors related to the generation or maintenance of neuropathic pain.