Role of spinal RhoA/ROCK signaling pathway in development of lipopolysaccharide-induced inflammatory pain in rats

Abstract

Objective To evaluate the role of spinal RhoA/ROCK signaling pathway in the development of lipopolysaccharide (IP)-induced inflammatory pain(IP) in rats. Methods Fifty-two male Sprague-Dawley rats, weighing 180-220 g, were equally randomized into 4 groups using a random number table: normal saline group (group NS), LPS group, RhoA inhibitor C3 exoenzyme group (group LC), and ROCK inhibitor Y27632 group (group LY). Inflammatory pain was induced by injecting LPS 25 μl (300 ng) into the plantar surface of hindpaws in IP, LC and LY groups, while the equal volume of normal saline was injected instead in NS group.C3 exoenzyme 10 pg and Y27632 10 nmol were injected intrathecally at 30 min prior to LPS administration in LC and LY groups, respectively.Before LPS injection (T0), and at 1, 3, 5, 12 and 24 h after LPS injection (T1-5), the mechanical and thermal pain thresholds were measured.Five rats in each group were sacrificed after pain thresholds were measured at T3, and L4, 5 segments of the spinal cord were removed for determination of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) mRNA expression in spinal dorsal horns by real-time reverse transcriptase-polymerase chain reaction. Results Compared with group NS, the mechanical and thermal pain thresholds were significantly decreased at T2-5 in IP, LC and LY groups, and TNF-α and IL-1β mRNA expression was up-regulated at T3 in IP group.Compared with group IP, the mechanical and thermal pain thresholds were significantly increased at T2-5, and TNF-α and IL-1β mRNA expression was down-regulated at T3 in LC and LY groups. Conclusion Spinal RhoA/ROCK signaling pathway is involved in the development of LPS-induced IP in rats. Key words: rho-associated kinases; Pain; Spinal cord; Inflammation