| Objective: To observe the effect of p38/MCP-1 signaling pathway in ozone’s analgesic effect on formalin inflammatory pain in rats. Methods: The baselines of mechanical withdrawal threshold(MWT) and thermal withdrawal latency(TWL) of adult male sprague-dawley(SD) rats, weighing 250-300 g, were measured before they were randomly divided into 7 groups(n=12): control group(group C), inflammatory pain group(group F):with a subcutaneous injection of 100 μl 5% formalin reagent in the left plantar,inflammatory pain with a subcutaneous injection of oxygen(group FO2); inflammatory pain with a subcutaneous injection of ozone(group FO3); inflammatory pain with intraperitoneal injection of p38 inhibitor(group FSB); inflammatory pain with intraperitoneal injection of p38 inhibitor solvent(group FD) and inflammatory pain with intraperitoneal injection of MCP-1 neutralizing antibody(group FM). One hour after injection of formalin, 50 μl O2 or 50 μl ozone(30μg/ml) were given in group FO2 and group FO3 respectively; p38 inhibitor SB203580(10 μl/rat), DMSO(10 μl /rat) or MCP-1 neutralizing antibody(10 μl /rat, 1 mg/mL) were given in group FSB, group FD, group FM respectively. MWT and TWL were measured at 1 h, 2 h,4 h or 24 h after formalin injection, then the lumbar segment 4-6 of the spinal cord and L4-6 dorsal root ganglion(DRG)were removed at 1 h, 2 h,4h or 24 h after formalin injection. The expression of P-p38 and MCP-1 in the spinal cord and DRG were measured by immunohistochemical(IHC) and Western Blot. Results: 1. The histopathological observation: Compared with group C, there existed infiltration of inflammatory cells in the injection sites, in addition, fibrous tissue was loose and fiber fractured in the other 6 groups after 1 h of formalin injection. Compared with group F, the inflammatory reactions were significantly decreased and new generation of fiber cells appeared in 4 h and 24 h in group FO3 after formalin treatment. There was no significant difference between group FO2, group FSB, group FD and group FM. 2. The change of pain threshold in rats: There was no significant difference for the basic value of MWT, TWL among 7 groups. Compared with group C, the MWT and TWL were significantly decreased in the other 6 groups 1 h after formalin injection(P<0.01); Compared with group F, the MWT and TWL were significantly increased in 4 h and 24 h in group FO3 and group FSB after formalin treatment(P<0.01); While they were largely increased in group FM(P < 0.01); There were no difference between group FO2 and group FD on each time point after ozone treatment. 3. The expression of p38 and MCP-1 in spinal and DRG 3.1 P-p38: Western Blot results indicated the p38 was significantly decreased compared with group C in the other 6 groups 1 h after formalin given(P<0.01); Compared with group F, expression of p38 was significantly increased at 4 h and 24 h time points in group FO3, group FSB and group FM after formalin treatment(P<0.01). Expression of p38 was not changed between group FO2, group FD and group F at each time point. The data of immunohistochemisty was comparative with that of Western Blot. 3.2 MCP-1: Western Blot result showed the MCP-1 was significantly increased compared with group C in the other 6 groups 1 h after formalin injection(P < 0.01); Compared with group F, MCP-1 were significantly decreased in 4 h and 24 h in group FO3 and group FSB after formalin treatment(P <0.01); Expression of MCP-1 was comparable between group FO2, group FD and group F at each time point. The same trend was observed from immunohistochemisty result. Conclusion:.(1) The formalin which induces in thermal hyperalgesia and mechanical allodynia can effectively alleviated by injection of ozone in the sole of foot.(2) The expression of P-p38, MCP-1 in the spinal dorsal horn and dorsal root ganglia of formalin induced inflammatory pain of rats increasing,suggesting the expression up-regulation of P-p38,MCP-1 may be involved in the occurrence and development of inflammatory pain.(3) Ozone can inhibit p38/MCP-1 signaling pathway to reduce the effect of inflammatory pain. |
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