Effect Of Preemptive Intrathecal Butorphanol And Ketamine On PKA And PCREB Expression In Spinal Dorsal Horn Of The Rats Of Formalin Pain

Background Butorphanol is an agitation-antagon opioid receptor, which has stronger analgesia,longer action time and lower side effect (e.g.respiratory depression,addiction)and applied in clinic generally,but intrathecal administration stays at the animal experiment stage nowdays. Recent study found that the antagon of the NMDAR and opioid drug might generate synergistic effect.PKA and CREB play an important role in transmitting and modulating pain and development and maintain of central sensitization of spinal cord.Therefore,it is important meaning to investigate the feasibility of association from intrathecal administration and molecular level mechanisms of analgesia for pain mechanisms and therapy.Objective To investigate the effect of preemptive intrathccal butorphanol tartrate and/or ketamine(non-competitive NMDA receptor antogonist)on PKA and pCREB expression in spinal dorsal horn and evaluate antinociception in the rats of formalin pain.Methods microspinal catheters were inserted intrathecally according to the method of Yaksh.After 5 days,40 male rat were divided into 7 groups randomly:control group(C group,n=5);saline group(NS group,n=5);low-dose butorphanol(LB group,n=6);high-dose of butorphanol(HB group,n=6);low-dose of ketamine(LK group,n=6); high-dose of ketamine(HK group,n=6);low-dose of butorphanol and low-dose of ketamine(LB+LK group,n=6).At 30 minutes before left palmaris paw subcutaneous formalin injection,the control group received no agent prior to formalin injection,the NS group rats were intrathecally pretreated with saline,the LB group were intrathecally pretreated with low-dose of butorphanol 12.5μg,the HB group were intrathecally pretreated with high-dose of butorphanol 25μg,the LK group were intrathecally pretreated with low-dose of ketamine 50μg,the HK group were intrathecally pretreated with high-dose of ketamine 100μg,the LB+LK group were intrathecally pretreated with butorphanol 12.5μg and ketamine 50μg.Pain intensity scoring(PIS)was utilized to assess pain behavior within 1 hour after formalin injection.2 hours later,PKA and pCREB expression in the spinal dorsal horn of the L₅ segment was assayed using immunohistochemistry and done the analysis of correlation.Result Intrathccal injection high-dose butorphanol 25μg or butorphanol 12.5μg with ketamine 50μg were both capable of inhibition both phases of formalin response,the PIS was decreased(p＜0.05 or 0.01). However,the expression of both the early and later phases was not significantly affected in other groups.Intrathecal pretreatment of high-dose butorphanol 25μg or ketamine 50μg with butorphanol 12.5μg both lowered the expression of spinal cord PKA and pCREB(p＜0.01). Conclusion1.In rat of formalin induced inflammatory pain,the effect of the antinociception of the intrathecal pre-treatment of butorphanol 25μg is similar with the effect of the intrathecal administration of the combination of butorphanol 12.5μg and ketamine 50μg.2.The expression of PKA and pCREB in the spinal dorsal horn is higher obviously,as well positive correlation,which indicates that the PKA-CREB pathway may be the formation and maintenance of the formalin induced inflammatory pain.3.In rat of formalin induced inflammatory pain,the expression of PKA and pCREB in the spinal dorsal horn is decreased obviously,as well positive correlation after the intrathecal pre-treatment of butorphanol 12.5μg and ketamine 50μg,the antinociception mechanisms may be connects with the inhibition of the PKA-CREB pathway.