Antinociceptive Tone Of Orexins And Its Possible Signaling Mechanism In The Hippocampus Of Mice After Neuropathic Pain

ObjectivesIn this study, morphological, behavioral science, molecular biology and immunology means are used to explore the orexins’possible role in the development of neuropathic pain with chronic constriction injury model in mice and its possible signaling mechanisms.In order to provide a theoretical basis for the prevention and-treatment of neuropathic pain. MethodsMale balb/c adult mice were randomly divided into sham group and CCI group. After the determination of base values of paw mechanical withdrawal threshold (PMWT) and paw thermal withdrawal latency (PTWL), a modified CCI to the sciatic nerve was performed on the left side according to Bennett and Xie, and the sham operation was just exposed the nerve but not ligated under anesthesia. PMWT and PTWL of each rat were measured 1,4,7,14,21 and 28 days after surgery. Model animals were sacrificed under deep anesthesia, removing the hypothalamus and hippocampus. Detecting the expression of hypothalamus p-orexin and hippocampus OXR-1 and OXR-2 by real-time quantitative PCR method. Detecting the expression of hippocampus pCREB and pERK by Western blot.Results1,Before CCI, there was no significant difference in PMWT and PTWL among all the mice (P> 0.05).After the 4-28 days of CCI mice at each time point PMWT significantly lower compared with Sham group(P<0.05). After the 1-28 days of CCI mice at each time point PTWL significantly reduced with Sham group (P<0.05).2, Using Real-time quantitative PCR, OXR-2 genes were lowered in the hippocampus after CCI 21,28 days compared with the Sham group (P<0.01).Hypothalamus P-orexin gene expression an upward trend after CCI 7 days compared with the Sham group (P <0.05), P-orexin gene expression downward trend after CCI 14 days compared with the Sham group (P<0.01). OXR-1 gene expression increased in the hippocampus of 14 and 21 days after CCI compared with Sham group (P<0.05).3, Applicating western blot, the expression of hippocampus pCREB, pERK is significantly lower in 21,28 days after CCI than the Sham group (P<0.05), the expression of hippocampal CREB, ERK in the days after CCI did not change.Conclusion1, Proved orexins system has analgesic effect in neuropathic pain by directly measuring orexins system.2, In the hippocampus of mice, may be mainly OXR-2 rather than OXR-1,involved in pain modulation in chronic neuropathic pain.3, It is may be through the MAPK (ERK)-CREB cell signal transduction pathways that OXR-2 receptors play an pain modulation effect.