Study On The Relationship Between Myofascial Trigger Point Pain And Substance P Content And Synaptophysin In Spinal Cord

Objective: Myofascial trigger point is contracture nodules that can be easily touched by skeletal muscle.Its related clinical symptoms include pain,joint involvement,nerve numbness,fatigue,insomnia and some autonomic neurological symptoms.Pain is the main feature of myofascial trigger point.Local pain or distant pain may occur when deep compression is applied to the trigger point.There are many factors in the formation of trigger point,including acute and chronic injuries,fatigue,nutritional deficiency,mental stress,heredity and so on.All of them can induce the formation of trigger point.Therefore,the occurrence rate of trigger point is high in the population and a considerable part of chronic pain in the motor system is caused by the activation of trigger point.There are two hypotheses about the mechanism of trigger point pain: energy crisis hypothesis and central sensitization hypothesis.The mechanism of trigger point central sensitization is still in the hypothesis stage.The hypothesis holds that the root cause of pain sensitization lies in the central rather than the peripheral,including the excessive release of neurotransmitters such as substance P and the formation of false synapses.In some other animal models,central sensitization has been explored in terms of synaptic transmission efficiency and synaptic structure changes,but whether there is a similar mechanism for trigger point pain is unknown.It is worth noting that pain is an important diagnostic criterion for trigger point,but few studies have evaluated pain in myofascial trigger point animal model.In some other animal models,such as sciatic nerve pain model,plantar incision pain model,a large number of studies have assessed pain in animals.The evaluation methods include paw withdrawal thresholds,the cumulative pain score and sum of time of leg contraction and claw licking.In myofascial trigger point animal model,the construction of the model is generally located in the medial femoral muscle and gastrocnemius muscle.However,it is difficult to measure the pain of these two muscles.According to the trigger point theory,besides the pain of the muscle itself,the trigger points of gastrocnemius muscle can also form the pain in the sole and heel(the theory of fascial mechanics and referred pain).It is possible to observe the pain at the trigger points of the animal model by paw withdrawal thresholds.The main purpose of this study is to link the pain with substance P and synapses in spinal dorsal horn,to explore the biochemical and structural morphological changes in the spinal cord center of rats with myofascial trigger point and to verify Mense’s central sensitization hypothesis.Another purpose of this study was to compare the therapeutic effects of massage and acupuncture on trigger point.Comparatively,it can provide reference for patients to choose appropriate treatment methods.Methods: Sixty-four male SD rats(7 weeks old,weighing 220-260g)were randomly divided into control group(16 rats)and model group(48 rats)after one week of observation.Then the trigger point model was constructed in model group.The left hindlimb gastrocnemius muscle of rats was bluntly attacked on Wednesday,and centrifugal running was performed on the second day after attacking.The construction time of the model was 8 weeks.After the completion of the model construction,the model group was randomly divided into three groups(16 rats still in the model group,16 rats in the massage treatment group and 15 rats in the acupuncture treatment group).All rats rested for 4 weeks without any intervention.After 4 weeks,the pain threshold was measured and the trigger points were diagnosed.The two treatment groups were treated with massage or acupuncture once a week for 4 weeks.The control group and the model group were fed normally.The pain threshold and trigger point were diagnosed and evaluated again after that,and then the samples were taken for immunohistochemistry and immunoblotting.Results: The results of paw withdrawal thresholds showed that the average pain thresholds of rats in model group,massage treatment group and acupuncture treatment group before treatment were 30.08 g,29.55 g and 30.35 g respectively,which were significantly lower than 48.08 g of control group(P < 0.05),but there was no significant difference among these three groups.After the intervention period,the paw withdrawal thresholds of rats in the three groups increased,but the values in treatment groups were significantly higher than that of model group.There were significant differences between the treatment groups and the control group(P < 0.05).In the diagnosis of trigger point,it was found that there was no significant difference in the occurrence rate of trigger point nodules and abnormal spontaneous potential between control group and the treatment groups before treatment,but the occurrence rate of trigger points and spontaneous potential in the treatment groups were significantly improved after treatment,which were significantly lower than that in the model group(P < 0.05).The results of immunohistochemistry and immunoblotting showed that the content of substance P in the dorsal horn of spinal cord in model group was significantly higher than that in the other three groups(P < 0.05),but there was no significant difference among the other groups.There was no significant difference in synaptophysin content in spinal dorsal horn of rats in each group.Conclusions: 1.Myofascial trigger point model rats are more sensitive to pain than healthy rats,and their tolerance to pain is lower than that of normal rats.The trend of paw withdrawal thresholds coincides with electromyography,touch of trigger point and other indicators.Thus,pressure pain threshold of plantar can reflect dimensions of trigger point objectively and directly.2 The pain caused by myofascial trigger point is closely related to the release of substance P in the dorsal horn of spinal cord.The excessive release of substance P may be an important reason for the decrease of paw withdrawal thresholds in the myofascial trigger point model rats.3 Acupuncture and manipulation therapy have positive effects on alleviating the symptoms of myofascial trigger point,and acupuncture treatment may have better effects on relieving pain caused by myofascial trigger point.