The Effect Of Inhibiting SDF-1/CXCR4in An Model Of Morphine Tolerance In Rats

ObjectiveIn today’s clinical diagnosis and treatment, the pain is very common andseriously influences the patient’s quality of life. Opioid medicines(eg: Morphine) arefrequently used in the present clinical and are the most exact analgesic effectanalgesics, which can alleviate the pain of traumatic,perioperative period and cancer.But the tolerance and low pain threshold induced by repeated used restricts its clinicalapplication greatly. Initially the researchers believed that Morphine tolerance andhyperpathia only caused by the change of opioid receptors of nerve cells. But recentstudies have shown that when the patient that long-term use of morphine treatmentwere injecting of morphine, organism will quickly produce many inflammatoryfactors. And these inflammatory factors maybe the primary cause of Morphinetolerance and hyperpathia.Chemokine plays an important role in the inflammatory response. There weresome investigations showed that Chemokines and chemokine receptors signalingpathways involved in the mechanism of hypepathia caused by morphine.Thenwhether Chemokines play an important role in the morphine tolerance mechanism? Itwas reported that the decrease of morphine analgesia effectted in chronic painpatients was due to the common development of the pharmacological tolerance of Morphine and related pain sensitivity,it also meaned that the partly reason ofTolerance producing is that hyperalgesia caused by long-term application of opioidagainst its′analgesic action. In some ways, they are not the pathological process ofisolation,but involved in a common base. Some studies indicated that inhibitingSDF-1/CXCR4could instantaneous reverse the low pain threshold by the long-termapplication of Morphine. But the SDF-1/CXCR4signal pathways were or notinvolved in morphine tolerance mechanism had not reported. The aim of this studywas to discuss the effect of the change of SDF-1/CXCR4in DRG and SP to morphinetolerance in an model of Morphine tolerance in rats.This study included two parts:the one was inhibiting SDF-1/CXCR4whethercould prevent or delay the produce of morphine tolerance. The other one was that therats has already produced morphine tolerance inhibit SDF-1/CXCR4whether couldinstantaneous reverse Morphine tolerance.Part1Materials and Methods60male SD rats of sheath built-in tube successfully, randomly divided into6groups (n=10):groups A-F recover in one week after sheath built-in tube successfully, then proceededanimal experiments(mechanical withdrawal threshold, hot guy threshold), familiarization training2-3times. Next proceeded basis tests3times,after determinating of basic values, starting withdrug and test it. After completing the above steps,in group A,intrathecal injected morphine10μg（10μl）2times a day,AMD3100(30minutes before the first time injection of morphine)5μg（10μl）,1time a day. Continuous injection of7days, proceeding tail withdrawal test in1hour at1d、3d、5d、7d after the first time injection, proceeding mechanical foot threshold test at2d、4d、6d before the first time injection. In group B,intrathecal injected morphine10μg（10μl）2timesa day,AMD3100(30minutes before the first time injection of morphine)10μg（10μl）,1timea day, with the same steps as group A. In group C,intrathecal injected morphine10μg（10μl）2times a day,AMD3100(30minutes before the first time injection of morphine)20μg（10μl）,1time a day, with the same steps as group A. In group D, after complete the basic value test,intrathecal injected morphine10μg（10μl）2times a day.In group E, after the success of the catheter, intrathecal injected NS,then test it.Group F without catheter,as normal group.Results1．The changes of Pain behavior in ratsComparison of the determine the basic value of the PMWT in each group, there was nostatistically significant difference.In4days after the jection, the value of PMWT significantlyreduced in group A,B,C and D. And in group A to C, with the increasing of the dose of AMD3100,the difference between the value of PMWT and the basis value was decreasing, especially ingroup D.There was no Morphine tolerance in group E and F.Comparison of the determine the basic value of Spin test in each group, there was nostatistically significant difference. After the jection, the value can achieved automatically cuttingoff in1st day and3rd day. Until the5th day, the time of drifting was significantly reducedunder the same heat intensity, especially in group D, Measured values even below basic values.2．The result analysis of Immunohistochemical methodsCompared with the staining results before jection, the expression of SDF-1and CXCR4In spinal cord and DRG significantly higher in1st day,3rd day,5th day and7th day, thehighest in7th day.Part2Materials and Methods60male SD rats of sheath built-in tube successfully, randomly divided into2groups (n=10):groups MA (morphine+AMD3100) and MN(morphine+NS),recovered in one week aftersheath built-in tube successfully, then proceeded animal experiments(mechanical withdrawalthreshold, hot guy threshold), familiarization training2-3times. Next proceeded basis tests3times, starting with drug and test it. Injected morphine10μg（10μl）in group MA,2times aday.Continuous injection of7days, determined the hot guy threshold at1d、3d、5d、7d, determinedthe PMWT at2d、4d、6d.And then begun to add AMD3100(30min before the first jection ofmorphine everyday),one time a day.Determined the hot guy threshold at1d、3d、5d、7d after theinjection of AMD3100,determined the PMWT in the fifth day after the injection of AMD3100.Then all the rats were killed.Injected morphine10μg（10μl）in group NA,2times a day.Continuous injection of7days, determined the hot guy threshold at1d、3d、5d、7d, determined the PMWT at2d、4d、6d.Andthen begun to add NS(30min before the first jection of morphine everyday),one time aday.Determined the hot guy threshold at1d、3d、5d、7d after the injection of NS. Then all the ratswere killed.ResultsComparison of the determine the basic value of the PMWT with both groups,there was no statistically significant difference..In7days after the morphine jection,the value of PMWT reduced in the two groups,and there was no statisticallysignificant difference. After the jection of AMD3100and NS respectively, the valueof PMWT were on the rise in group MA,but not in group MN.In spin experiment tests of two groups, comparison of the determination of thebasis value, there was no statistically significant difference. After the jection, thevalue can achieved automatically cutting off in1st day and3rd day. Until the5th day,the time of drifting was significantly reduced under the same heat intensity,measured values even below basic values. After the jection of AMD3100and NSrespectively,the determination of drifting threshold was on the rise in group MA,butnot in group MN.ConclusionBy means of blocking the SDF-1/CXCR4signaling pathways can reduce thephenomenon of hyperalgesia and delay the produce of morphine tolerance, butblocked this signaling pathways can not prevent the producing of morphine tolerance.For the one that present in morphine tolerance, by means of blocking the SDF-1/CXCR4signaling pathways can improve the degree of morphine tolerance.