Effect of spinal cord stimulation on expression of spinal substance P and calcitonin gene-related peptide in rats with neuropathic pain

Objective To evaluate the effect of spinal cord stimulation (SCS) on the expression of spinal substance P (SP) and calcitonin gene-related peptide (CGRP) in rats with neuropathic pain. Methods Forty-eight male Sprague-Dawley rats, aged 8 weeks, weighing 250–300 g, were randomly divided into 4 groups (n=12 each) using a random number table: sham operation group (S group), neuropathic pain group (group NP), sham electrical stimulation group (N-SCS group), and SCS group.Neuropathic pain was induced by chronic constriction injury (CCI) in anesthetized rats.The sciatic nerve was exposed, and 4 loose ligatures were placed on the sciatic nerve at 1 mm intervals with 4-0 chromic catgut.Electrodes were placed into the epidural space at 5 days after CCI in N-SCS and SCS groups, and in addition, SCS was performed at 12–14 days after CCI in SCS group.The mechanical paw withdrawal threshold (MWT) was measured at 1 day before CCI, and 1, 4, 7 and 14 days after CCI.After measurement of pain threshold at day 14 after CCI, the animals were sacrificed, and the lumbar segments (L4-6) of the spinal cord were obtained for determination of the expression of SP and CGRP in the spinal cord by immunohistochemistry. Results Compared with group S, the MWT was significantly decreased, and the expression of SP and CGRP protein and mRNA was up-regulated in NP, N-SCS and SCS groups (P<0.05). Compared with group NP, the MWT was significantly increased, and the expression of SP and CGRP protein and mRNA was down-regulated in group SCS (P<0.05). Conclusion The mechanism by which SCS mitigates neuropathic pain may be related to down-regulated expression of SP and CGRP in the spinal cord of rats. Key words: Spinal cord; Electric stimulation therapy; Neuralgia; Substance P; Calcitonin gene-related peptide