Hyperplastic Changes Of Myodural Bridge Complex In Rats And Its Clinical Significance

Background and Purpose:Relevant studies on the dynamic mechanism of cerebrospinal fluid circulation showed that its influencing factors included cardiac and vascular pulsations,respiratory,posture,ciliary movement and skeletal muscles,etc.In recent years,some scholars have proposed a new theory that the myodural bridge complex(MDBC)may be one of the power sources of cerebrospinal fluid circulation.MDBC exists in the suboccipital region,including the rectus capitis posterior minor muscle,the rectus capitis posterior major muscle,the obliquus capitis inferior muscle,the nuchal ligament,and the vertebrodural ligament and the myodural bridging fibers from these structures.Myodural bridging fibers are primarily composed of Type I collagen fibers,which has the biological characteristics of high ductility and tension resistance.This theory points out that during head movement,the force generated by the contraction of the suboccipital muscles will be transmitted through the myodural bridge fibers and pulled the spinal dural mater.This will change the volume of subarachnoid space and generate negative pressure,thereby promoting the circulation of cerebrospinal fluid.Research shows that increased or decreased cerebrospinal fluid pressure can cause headache.In addition,a large number of previous studies have shown that the pathological changes of the MDBC may be associated with the pathogenesis of chronic headache.Therefore,we speculate that there may be a causal relationship between the pathological changes of MDBC,abnormal cerebrospinal fluid circulation and chronic headache,but this mechanism is still unclear.Bleomycin has a significant effect on proliferation of collagen fibers,especially type Ⅰ collagen fibers,which is a relatively mature reagent for producing animal models of collagen fiber proliferation.It is often used to build animal models of pulmonary fibrosis or scleroderma.In this study,adult SD rats were selected as the experimental objects,and bleomycin was injected to make a rat model of MDBC hyperplasia.The morphological changes of the MDBC hyperplasa induced by bleomycin were observed.And the behavioral changes and the expression levels of headache-related factors in some nuclei of the brain were analyzed.The purpose of this study is to provide the basis for the functional study of the MDBC,and further clarifies that the pathological changes of the MDBC can induce headache and reveal the relevant regulatory mechanism.Materials and Methods:Thirty-nine three-month-old male SD rats were randomly divided into three groups:bleomycin experimental group(BLM group),drug control group(PBS group)and blank control group(CTL group),with 13 rats in each group.Part Ⅰ:Four weeks after the drug injection,the neck of rats in each group were taken,embedded in paraffin and sectioned.Masson staining and semi-quantitative analysis method were performed on the neck of rats to observe the morphological changes of the MDBC and other tissues in the posterior atlanto-occipital interspace of rats in each group.Before sampling,the cerebrospinal fluid secretion rate of rats was measured to determine whether circulation of cerebrospinal fluid was affected.Part Ⅱ:Five weeks after the drug injection,the neck and brain tissues of rats in each group were taken,paraffin embedded and sectioned.Masson staining and semi-quantitative analysis were performed on the neck of rats to verify the success of the establishment of the hyperplastic model of the MDBC.The expression levels of CGRP and 5-HT in pain-related nuclei of the brain tissues were observed and analyzed by immunohistochemical staining method.Before and after drug injection,the behaviors of rats in each group such as head scratching,cage climbing and hair trimming were observed,and the differences between the groups were compared using behavioral scoring method.Results:Part Ⅰ:(1)Masson staining results of the upper neck:Compared with the other two groups,the rats in BLM group had denser myodural bridging fibers emitting from the ventral side of the rectus capitis dorsal minor muscle.And the number of myodural bridging fibers connected directly or indirectly with the spinal dura mater was significantly increased.Besides,the muscle fibers of the rectus capitis dorsal minor muscle in BLM group are closely arranged.(2)Results of the secretion rate of cerebrospinal fluid:The cerebrospinal fluid secretion rate of rats in BLM group was significantly higher than that of the other two groups,with statistical significance.Part Ⅱ:(1)Masson staining and semi-quantitative analysis results of the upper neck:The content of collagen fibers of the posterior atlanto-occipital membrane and myodural bridge fibers in the posterior atlanto-occipital space in the posterior atlanto-occipital interspace of rats in BLM group were significantly increased,suggesting that the establishment of the proliferative model of the MDBC was successful.(2)Behavioral observation results:The headache-related behavioral scores of BLM group were significantly higher than that of PBS and CTL groups;There were also significant differences in headache-related behavioral scores of rats in BLM group before and after BLM injection.(3)Immunohistochemical staining results of brain tissues:Compared with PBS and CTL groups,the expression levels of CGRP in the ventral posterior medial nucleus of thalamus,amygdala,parabrachial nucleus and spinal trigeminal nucleus in BLM group were significantly higher than that in PBS and CTL group in rats;The content of 5-HT in anterior cingulate cortex,amygdala and dorsal raphe nucleus was also increased in the BLM group compared to that of the other groups.Conclusion:The present study demonstrates that BLM injections have a significant hyperplastic effect on the MDBC in the posterior atlanto-occipital interspace of rats.These hyperplastic changes can cause abnormalities of cerebrospinal fluid and occurrence of chronic headaches in rats.This kind of headache might be transmitted through the craniofacial pain ascending pathway and accompanied with anxiety,depression and other emotional dysfunction.This study supports our theory that the MDB is a significant contributor to cerebrospinal fluid circulation,and also provides a new explanation for the pathogenesis of some chronic primary headaches.