Role of expression of phosphodiesterase 4B in spinal cord in inflammatory responses in a rat model of neuropathic pain: relationship with extracellular signal-regulated kinase

Abstract

Objective To evaluate the role of expression of phosphodiesterase 4B (PDE4B) in the spinal cord in inflammatory responses in a rat model of neuropathic pain and the relationship with extracellular signal-regulated kinase (ERK).Methods Sixty healthy male Sprague-Dawley rats,weighing 180-220 g,in which intrathecal catheters were implanted at L5,6 interspace,were used.The location of catheters was confirmed 6 days later.The rats were randomly divided into 5 groups (n =12 each):sham operation group (group Sham),normal saline (NS) group,vehicle group (group Ⅴ),mismatch siRNA group (group siR-M),and PDE4B-siRNA group (group siR-B).Neuropathic pain was induced by ligation of L5 spinal nerve (SNL).In Sham group,the L5 spinal nerve was only exposed,but not ligated.Immediately after ligation and on 1,3,5,and 7 days after ligation,10 μl NS,10 μl NS,LipofectaminTM RNAiMAX,PDE4B-siRNA (2 μg/10 μl) encapsulated in mismatch siRNA and PDE4B-siRNA (2 μg/10 μl) encapsulated in LipofectaminTM RNAiMAX were injected intrathecally in Sham,NS,V,siR-M,and siR-B groups,respectively.The mechanical pain threshold was measured at 1 day before and 2,4,6 and 8 days after operation.After behavioral testing on 8th day after operation,the rats were sacrificed and the lumbar segment of the spinal cord was removed for determination of PDE4B protein,ERK and phosphor-ERK (p-ERK)expression,and TNF-α,IL-1β and IL-6 levels.Results Compared with Sham group,the mechanical pain threshold was significantly decreased at 2,4,6 and 8 days after operation in NS,V,siR-M and siR-B groups (P ＜0.05),and no significant change was found in the mechanical pain threshold at 2,4,6 and 8 days after operation (P ＞ 0.05) and the expression of p-ERK and PDE4B protein,and levels of TNF-α,IL-1β and IL-6 were increased at 2,4,6 and 8 days after operation in V and siR-M groups (P ＜ 0.05).Compared with NS group,the mechanical pain threshold was significantly increased,and the expression of p-ERK and PDE4B protein and levels of TNF-α,IL-1β and IL-6 were decreased at 2,4,6 and 8 days after operation (P ＜ 0.05),and no significant change was found in the parameters mentioned above in V and siR-M groups (P ＞ 0.05).Conclusion Up-regulation of the expression of PDE4B protein in the spinal cord is involved in the development of neuropathic pain in rats,which may be related to promoted phosphorylation of ERK in the spinal cord and enhanced inflammatory responses. Key words: Cyclic nucleotide phosphodiesterases, type 4; Spinal cord; Neuralgia; Inflammation; Cyclic nucleotide-regulated protein kinases