Effect of dexmedetomidine on content of nitric oxide and activity of nitric oxide synthase in cerebral cortex in rat neuropathic pain model

Abstract

Objective To study the effect of dexmedetomidine (DEX) on the content of nitric oxide (NO) and activity of nitric oxide synthase (NOS) in cerebral cortex in rats with neuropathic pain induced by spinal nerve ligation (SNL).Methods Adult Sprague-Dawley male rats were randomly divided into normal control group,sham operation group,SNL group and SNL + DEX group.Every group was subdivided into three sub-groups:3,7 and 14 days postoperation.Mechanical allodynia was represented by 50％ paw withdrawal threshold (PWT).NO content and NOS activity in cerebral cortex were measured by using spectrophotometry.Results As compared with sham operation group and normal control group,50％ PWT of the rats in SNL group was decreased (P ＜ 0.05).As compared with the rats in SNL group,there was an apparent increase of the mean score of 50％ PWT in SNL + DEX group three days later (3.38 ±0.91 vs.5.21 ± 1.54) (P ＜0.05).NOS activity and NO content of the spinal cord were increased significantly in SNL group as compared with those in sham operation group (P ＜ 0.01).NO content,and activity of ttotal nitric oxide synthase(TNOS) and inducible nitric oxide synthase (iNOS) of the spinal cord in SNL + DEX group (2.95 ± 0.25,11.84 ± 1.69 and 0.90 ± 0.15 respectively) were significantly lower than those in SNL group (3.41 ±0.27,13.90 ±2.09 and 1.30 ±0.35 respectively) (P ＜0.05 or P ＜0.01).Conclusion The content of NO and activity of NOS in the spinal cord and cerebral cortex were involved in the mechanism of neuropathic pain.Intrathecal administration of DEX could relieve both mechanical allodynia and cold-induced ongoing pain,which may be associated with the inhibition of the content of NO and activity of NOS in the cerebral cortex. Key words: Dexmedetomidine ; Neuropathic pain; Nitric oxide; Nitric oxide synthase