ABSTRACT
BACKGROUND: Phenol has effects like surgical neurectomy, but may evoke pain after local infiltration in nerves. Transection of peripheral nerves may induce neuropathic pain through increased spontaneous discharge and other mechanisms. Proto-oncogene, c-fos, is an indicator of neuronal activity, and its expression in the spinal cord may be related to pain development, because inhibition of c-fos expression has corresponding effects like analgesia. We evaluated the effects of local infiltration of phenol and transection injury at the sciatic nerve on c-fos expression in the spinal cords of rats. METHODS: Sixteen male Sprague-Dawley rats were divided into 2 groups; transection of the sciatic nerve was performed for group 1; phenol was infiltrated into the sciatic nerve in group 2. Three hours, 1 week, 2 weeks, and 3 weeks after the experiment, the corresponding spinal cord was stained immunohistochemically for c-fos. RESULTS: c-fos was expressed from 3 hours to 2 weeks over the laminae of the dorsal horn in each group. Phenol increased the expression of c-fos initially, but decreased 1 week later. Transection injury did not increase it initially, but showed the peak expression at 1 week, and maintained it for 2 weeks. Therefore, it seems that phenol, rather than the transection injury, stimulates c-fos expression early, but decreases later. CONCLUSIONS: Phenol treatment, caused by chemical block due to protein denaturation and nonspecific inflammation, may induce less neuropathic pain than the transection of a nerve.
