The Research Of Molecular Mechanism Of Hemifacial Spasm Caused By Vascular Compression

Background and objective:Hemifacial spasm(HFS)is a syndrome of unilateral facial nerve hyperactive dysfunction,characterized by frequent,involuntary facial muscle contractions.Microvascular decompression surgery(MVD)has been accepted as an effective treatment for HFS world widely.The pathogenesis of HFS is still controversial.Although the treatment result of hemifacial spasm is very good,so far its pathogenesis is still controversial.There is not yet a unified view to explain the specific occurrence and development process of HFS.So far,the exploration of HFS is mainly concentrated in the electrophysiology and pathology.In this study,voltage-gated sodium channel(VGSC)on the peripheral demyelinated portion of facial nerve is observed.The expression and the location of the sodium channel protein in HFS patients are analyzed to figure out whether there were upregulation and abnormal accumulation of VGSC.The impact of the sodium ion channel on the facial nerve function and clinical symptoms was analyzed.The correlation between different channel aggregation state and the conduction of facial nerve was investigated.The relationship between ectopic electrical activity and HFS is explored.In another part of this study,the characteristics facial motoneuron(FMN)is observed,to figure out whether the neuronal excitability is increased.Methods:Part I: The SD rat model of hemifacial spasm was established by demyelization and compression of the artery.The model was verified and evaluated by behaviordetection,histopathology and electrophysiology.Part II: To detect the expression of Nav1.6mRNA and its protein on the demyelinated portion,the facial nerve was examined by RT-PCT,Western blot and immunohistochemistry.Part III: Establish a stable method of the adult rat brain slice.The impact of different experimental conditions,solutions,as well as the incubation temperature on the activity and basic membrane potential of the brain slice were analyzed.Part IV: The FMN was observed and counted under Nissl staining.The potential characteristic of FMN(resting membrane potential,input impedance,the threshold and amplitude of action potential,etc.)was studied using patch-clamp technique.The current-voltage curve of sodium was analyzed.Results:Part I: The SD rise model of hemifacial spasm was established by demyelization and compression of the artery.The model was verified and evaluated by behavior detection,histopathology and electrophysiology successfully.Part II: By RT-PCR,the relative expression of Nav1.6 mRNA was 3.28 times that of the control group,which was significantly increased.By Western blot,the compression of Nav1.6 protein on the facial nerve of HFS was 4.23 times that of the control group.By immunohistochemistry,the Nav1.6 on facial axis of HFS showed cord-like expression,which was significantly prolonged compared with the control group.Part III: A method for the preparation of adult rat brain slices was established successfully.Cardiac perfusion by 4? ACSF preoperatively,incubated and sliced in high sucrose solution or low-calcium and high-magnesium ACSF,pre-incubation under the higher temperature can help to improve the quality of adult rat's brain slices.And these conditions had no impact on the neuronal resting membrane potential,threshold and amplitude of action potential of FMN.Part IV: By Nissl staining,there were no significant changes in quantity and appearance of FMN in HFS group.By patch-clamp technique,it was found that therewas no significant difference of resting membrane potential of FMN between HFS group and health control group.Compared to health control group,the input impedance of the resting membrane potential was increased,the rheobase was decreased,the threshold of action potential was decreased and the amplitude of the action potential was increased.The active threshold of sodium current of HFS group was decreased and the amplitude of peak sodium current was increased.Conclusions:In HFS model,the expression of Nav1.6mRNA and its protein were unregulated on the demyelinated portion of facial nerve.The excitement of facial motoneurons was increased and the sodium peak current was upregulated.Therefore,we hypothesized that: there might be a relationship between the pathogenesis of HFS and the upregulation and abnormal distribution of Nav1.6 on the demyelination site of facial nerve.On the other hand,the hyperexcitability of FMN also involved in the happening of hemifacial spasm.