Eeffcts Of Preemptive Intrathecal Clonidine On Behavior And Expression Of Pcreb Protein In The Spinal Cord Of The Formalin Test Rats

Objective: The objective of this study was to investigate an antinocicepetive mechanism of preemptive intrathecal clonidine on behvaior and expression of pCREB protein in the spinal cord of the formalin test rats.And to investigate the best antinoeicpetive effect by different dosage of preemptive intrathecal clonidine.Methods: Forty healthy male adult SD rats(230-270g) were randomized into 5 groups.In the normal saline control group(groupNS),20μl of normal saline was injected intrathecally,followed by a subcutaneous administration of 100μl of nomral saline in to the hind plantar 10 minutes later.In the formalin control group(groupFOR),20μl of nomral saline was injected intrathecally,followed by an intra-plantar administration of 100μl of 5% formalin. In the intrathecal clonidine experiment groups(groups CF15-45,clonidine 15,30 and 45μg/20μl were administered intrathecally,respectively,followed by an intra-plantar administration of 100μl of 5% of formalin.The graded pain behavior was observed and the nociceptive behvaior index(NBI) was calculated every minutes for one hour immediately after the formalin injection. At the2-hour time Point,all the rats were deeply anesthetized and were perfused intrathecally: and then,the 4 and the 5 lamination of the spinal cord were removed for determination of expression of phosphorylated pCREB-immunoreaction(pCREB-IR) using immunohistochemistry.The pCREB-IR cells both in DRG and superficial dorsal horn neurons were quantified and analyzed.Results: 1.Almost no Pain response was observed in group NS. The typical biphase Pain response was observed in the formalin-injected groups. 2.The nociceptive behavior time in groupFOR was much more than group NS in both phase.(P<0.01). IT clonidine(30μg or 45μg )were both capable of inhibiting both Phases of formalin response.However , the expression of both the early and later phases was not significantly affected in other groups. 3.To make comparisons of the amount of pCREB-IR of the 4 and 5 lamination at the dorsal horn :the amount of pCREB-IR of in the formalin group was much more than that in the groupNS(p<0.01);the amount of pCREB-IR of in theCF15 was not significantly decreased than the formalin group(p>0.05); In the lamination at the dorsal horn,the amount of pCREB-IR of group (CF30and CF45) was much less than that in the formalin groups;The amount of pCREB-IR decreased with the increase in the clonidine dosage,but the difference was not significant when the dosage to 45μg;Conclusions: 1.The results provided evidence that the intrathecal injection of clonidine has been demonstrated to produce a antinociception ,significant analgesic effect at 30μg.In a rat model of formalin- induced inflammatory pain,but the dosage to 45μg not to increase the effect of antinociception ,and 15μg yet. 2.Rats in Formalin Test increases pCREB phosphorylation in superficial dorsal horn neurons of the spinal cord,which be reduced by clonidine. 3.The mechanisms of analgesia may be that clonidine to restrain the stimulation of Pcreb.