| ObjectiveGenerally, chronic pain refers to that more than three months of pain, caused by tissue injuries, it may occures in work, life and sports activities, seriously affecting humans’health and social development. Clinical study found that most chronic pain derived from local abnormalities in skeletal muscle system, also known as chronic muscle pain. MTrP is defined as a hyperirritable spot in muscle taut band, it is considered to be a common cause of chronic muscle pain and associated with it, including some visceral system disorders. Pre-clinical studies found that wet acupuncture treatment abdominal MTrP for patients with primary dysmenorrheal have a long-term beneficial effect. It is believed that prostaglandin F2a is the main cause of primary dysmenorrhea, so we presumed that there may be something relationship between PGF2a and MTrP. Therefore, the present study was to establish a rat model of chronic MTrP, exploring the changing in peripheral blood concentrations of PGF2a, and to observe its effect on trigger point EMG activity via injection PGF2a, exploring the possible links between MTrP and PGF2a.In addition, the current electrophysiology studies about MTrP mainly focused on EMG research, MTrP fibers response to electrical stimulation is still very rare. The excitability and mechanical characteristics of MTrP fibers by an electrical stimulation has not been reported. Thus, MTrP fibers usually exhibited muscle pain, motor dysfunction and accelerated muscle fatiguability, so the second part of the present study is to explore the the excitability and endurance of MTrP fibres by an electrical stimulation.MethodsAll rats in this study were housed in SPF laboratory animal room in Shanghai University of Sport. Temperature 24±1℃, relative humidity 60±5%, approved by Scientific Research Ethics Committee of Shanghai University of Sport.Part one,48 female SD rats, average weight 200±15g, the rats were divided randomly into control groups (CG1, CG2) and model groups (TG1, TG2,TG3,TG4),8 rats in each group. The first day of a week with blunt blow and the next day with eccentric exercise of the model groups for 8 weeks, then 4 weeks to restore, the control group fed normally for 12 weeks. When the model was built, measured serum PGF2a concentration with Elisa of each group. Then, drug intervention for each group, CG1, TG2 were intramuscular saline. CG2, TG3 were intramuscular PGF2a. TG1 was blank control. TG4 group was intravenous injection PGF2a. EMG was recorded immediately in rest state after intervention.Part two,48 male SD rats, average weight 220±15g, the rats were randomly divided into control groups (CG1, CG2, CG3) and model groups (TG1, TG2, TG3), followed the above methods to establish the rat model of trigger point. When the model was built, connected with the organism function experiment system. Set up the parameters, subjected to trains of electrical stimulation of the muscle fibers. The electricial threshold intensity, maximal contraction force, electrical intensity dependent fatigue and electrical frequency dependent fatigue characteristics were assessed in different groups.ResultsPart one, after the model was built, the concentrations of PGF2a in serum were no significant difference between control group and model group measured by Elisa (P>0.05), but the model groups tended to increase. Administration immediately, the model groups could recorded an abnormal spontaneous potential and the control groups almostly had no electrical activity, EMG waveform likely a straight line. The frequency of SEA in CG1, CG2, TG1, TG2、TG3、TG4 occurring within 1s were 1.06±0.64、1.13±0.56、13.38±3.51、12.82±5.73、24.57±9.28、14.98±6.64, respectively. There was no significant difference between CG1 and CG2, TG1 and TG4 (P>0.05), the frequency of TG2 is significant higher than that in TG1 and TG2 (P<0.05). The amplitude in six groups were 22.20±6.03μV、24.07±5.75μV、36.83±13.38μV 40.37±9.59μV、71.80±11.85μV、43.57±15.34μV、respectively. There was no significant difference between CG1 and CG2, TGI and TG4 (P>0.05), the frequency of TG2 is significant higher than that in TGI and TG2 (P<0.01). The wavelength in six groups were 6.60±1.66 ms、6.60±1.73 ms、8.55±3.21 ms、9.22±1.63 ms、 14.19±4.26 ms、9.35±2.51 ms, respectively. There was no significant difference between CG1 and CG2, TGI and TG4 (P>0.05), The wavelength is significant higher than that in TGI and TG2 (P<0.05).Part two, the average threshold intensity for muscle contraction of TGI were significantly lower than that of CG1 (p<0.01). The optimal stimulus of TGI were significantly lower than that of CG1 (p<0.05). The maximum contraction force were not significantly difference between CG1 and TGI (P>0.05). Two-way ANOVA revealed that the MCF at 15th and 20th electrical stimulus were significantly lower than that at the 1st,5th,10th electrical stimulus in TG2 (p<0.01). MCF at the 10th, 15th,20th electrical stimulus were significantly lower than that in CG2 (p<0.01). There were no significant differences in MCF between the 1st,5th,10th electrical stimulus in TG2 (P>0.05). There also no significant differences in MCF at the 1st,5th electrical stimulus between CG2 and TG2 (P>0.05). The average frequency for muscle contraction of TG3 were significantly lower than that of CG3 (p<0.01). The average MCF of TG3 were significantly lower than that of CG3 (p<0.05).Conclusion1.PGF2a could enhance the EMG of MTrP fibres, indicating that the PGF2a can increased the MTrP fibres activity.2.The MTrP fibres were highly excitable to electrical stimulation and more vulnerable to fatigue than normal muscle fibers. |
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