The Study Of Analgesic Effect Of Dexmedetomidine In Rats Of Formalin-induced Pain Model

Objective: To investigate the analgesic effect of intrathecal (IT) dexmedetomidine (DEX)on a formalin-induced rat pain model and the expression of c-fos and substance P (SP) inthe dorsal horn of spinal cord.Methods: The experiment was performed in two parts: In part one, we determine if ITDEX could modulate formalin-induced pain in the rat formalin test; In part two, withimmune-histochemistry we detected the spinal c-fos and SP expression in dorsal horn ofspinal cord in the rat of formalin-induced pain model after IT DEX. Sixty adult male SDrats, weighing250±10g, were randomly divided into6groups (n=10each): IT normalsaline20μl, ten minutes later, normal saline100μl was injected intracutaneously in the lefthindpaw in group C. IT normal saline20μl, ten minutes later,5%formalin100ul wasinjected intracutaneously in the left hindpaw in group F. IT DEX10μg·kg-120μl, tenminutes later,5%formalin100μl was injected intracutaneously in the left hindpaw ingroup D1. IT DEX20μg·kg-120μl, ten minutes later,5%formalin100ul was injectedintracutaneously in the left hindpaw in group D2.5%formalin100μl was injectedintracutaneously in the left hindpaw, ten minutes later, IT DEX10μg·kg-120μl in group D3.5%formalin100μl was injected intracutaneously in the left hindpaw, ten minutes later, ITDEX20μg·kg-120μl in group D4. The pain behaviours including licking biting and liftingof the injected paw were cumulatively recorded during phase1(0-5min) and phase2(15-60min), and then we scored it by Abbott scores after inject formalin. and opened thelamina of vertebra to expose the spinal cord of the intumescentia lumbalis, and then cut thespinal cord with an operating. spinal cord segments were removed for analysing theexpression of c-fos and SP.Results: there was no significant difference in the accumulative time of drawing legs andlicking claws of phase1in rats of each group respectively (P>0.05). The accumulativetime of drawing legs and licking claws of F group was obviously prolonged than that ofother groups, the expression of c-fos and substance P of the spinal cord in the F group weresignificantly higher than other groups (p<0.01). there was no significant difference in theaccumulative time of drawing legs and licking claws and the expression of c-fos and substance P of the spinal cord between groups D1and D2and between groups D3andD4.(p>0.05). the accumulative time of drawing legs and licking claws was prolonged andthe expression of c-fos and substance P of the spinal cord was up-regulated in the D3groupwas significant than D1group (p<0.01).Conclusion: Intrathecal injection of dexmedetomidine (10μg·kg-1or20μg·kg-1) informalin-induced rats leads the same analgesic effect and preemptive analgesic effectthrough down-regulation the expression of c-Fos protein and the SP release on the spinalcord, thereafter ameliorate the pain of formalin-induced rats.