Research About The Function Of P38Mapk During Masseter Adaptive Changes In Unilateral Chewing Rats

Objectives:To study the changes of P38mitogen-activated protein kinase mRNA expression, Ca2+concentration and ultrastructure of masseter muscle induced by unilateral chewing, and to discuss the role that p38played in these changes. This study intended to provide a theoretical basis for the treatment of masticatory muscle disorder syndrome.Methods:368-week-old female Wistar rats (provided by the Experimental Animal Center of Shandong University), weighing from250-300g, were randomly divided into control groups (n=3) and experimental groups (n=6). The animal models were established by extracting the left maxillary molars. The rats were killed in2weeks,4weeks,6weeks and8weeks after teeth extraction respectively and the masseter tissues were prepared to be tested. The Ca2+concentration was evaluated by atomic spectrophotometric method; the relative expression of P38MAPK mRNA was detected by real-time fluorescent quantitative PCR; the ultrastructural changes of myocytes were observed under the transmission electrion microscope (TEM) and the abnormal z-line rate was calculated.Results:1) Ca2+concentration:The Ca2+concentration of the masseter muscle in the extraction side was significantly higher than that of control groups (P<0.05), and Ca2+concentrations of the masseter muscle in the extraction side in4weeks and6weeks after teeth extraction were greatly higher than those in2weeks and8weeks after teeth extraction (P<0.05).4weeks after extraction, the Ca2+concentration of the masseter muscle in the extraction side was significantly higher than that in the non-extraction side(P<0.05).2) The relative expression of P38MAPK mRNA:2weeks and4weeks after extraction, the P38MAPK mRNA expression of the masseter muscle in the extraction sides were higher than that of the non-extraction sides significantly (P<0.05), and both of them were higher than that of the control groups significantly (P<0.05).6 weeks and8weeks after extraction, no significant differences were found among the extraction sides, the non-extraction sides and the control groups(P<0.05).4weeks after extraction, the expression of P38MAPK mRNA of the masseter muscle in the extraction sides reached the highest level.3) The ultrastructural changes of the rat masseter muscle under TEM:The muscle fibers in extraction side and non-extraction side showed intermyofibrillar loose arrangement, intermyofibrillar edema, broken curly z-lines and m-lines, swollen mitochondria. The impairment of the masseter musclein the4th week after teeth extraction was most severe and the masseter muscle of the extraction side showed a more severe pathological manifestation than that of the non-extraction side.4) The abnormal z-line rate:In the2th and4th week after teeth extraction, the abnormal z-line rate of the extraction side was higher than that of the non-extraction side (P<0.05), and both were higher than that of the control groups (P<0.05); While6and8weeks after teeth extraction, there were no significant difference among the extraction sides, the non-extraction sides and the control groups (P>0.05). The abnormal z-line rate of the extraction side reached the highest level in the4th week after teeth extraction, and the rate decreased from the6th week and continued to decrease to the lowest point in the8th week. In the2th and the4th week after teeth extraction, the abnormal z-line rate of the non-extraction sides showed no significant difference (P>0.05), and the rate began to decline in the6th week.Conclusions:long-term unilateral chewing may activate P38MAPK signal pathway via up regulating the expression of P38MAPK mRNA, which may participate in adaptive changes of masseter muscle.