Effects of tempol administered via different routes on neuropathic pain in rats

Objective To evaluate the effects of tempol administered via different routes on neuropathic pain (NP) in rats. Methods Thirty-two male Sprague-Dawley rats, weighing 250-280 g, aged 8-10 weeks, were randomly divided into 4 groups (n=8 each) using a random number table: sham operation group (group S), group NP, intrathecal tempol group (group T1), and intraperitoneal tempol group (group T2). Neuropathic pain was induced by chronic constriction injury in chloral hydrate-anesthetized rats.The sciatic nerve was exposed and 4 loose ligatures were placed on the sciatic nerve at 1 mm intervals with 4-0 silk thread.The sciatic nerve was only exposed but not ligated in group S. After successful establishment of the model, a catheter was inserted at L4, 5 interspace into the epidural space.In S and NP groups, 0.9% normal saline 20 μl was injected intrathecally, and 0.9% normal saline 200 μl was injected intraperitoneally once a day for 7 consecutive days.In group T1, tempol 30 μg (in 20 μl of normal saline) was injected intrathecally, and 0.9% normal saline 200 μl was injected intraperitoneally once a day for 7 consecutive days.In group T2, tempol 30 μg (in 200 μl of normal saline) was injected intraperitoneally, and 0.9% normal saline 20 μl was injected intrathecally once a day for 7 consecutive days.The mechanical paw withdrawal threshold (MWT) and thermal paw withdrawal latency (TWL) were measured at 3 days before operation, and at 1, 3, 5, 7, 10 and 14 days after operation.The animals were sacrificed after measurement of pain threshold at day 14 after operation.The lumbar segment of the spinal cord was removed to detect malondialdehyde (MDA) content and superoxide dismutase (SOD) activity by enzyme-linked immunosorbent assay. Results Compared with group S, the MWT was significantly decreased, and the TWL was shortened at each time point after operation, the content of MDA in the spinal cord was increased (P 0.05). Compared with group NP, the MWT was significantly increased at 5, 7, 10 and 14 days after operation, the TWL was prolonged at 1, 3, 5, 7, 10 and 14 days after operation, the content of MDA in the spinal cord was decreased, and the SOD activity was increased in group T1 (P 0.05). Conclusion Intrathecal tempol can reduce NP in rats, and the mechanism is related to inhibition of lipid peroxidation in the spinal cord. Key words: Neuralgia; Injections, spinal; Injections, intraperitoneal; Tempol