Research Of Brain Functional Plasticity In Rats With Neuropathic Pain Induced By Brachial Plexus Avulsion Injury And Treated By Electroacupuncture

Backgroud:Brachial plexus avulsion injury?BPAI?is the most severe type of brachial plexus injury.In addition to severe dysfunction,patients often have severe pain.In patients with brachial plexus injury,the incidence of pain is about 70%.Brachial plexus pain is a kind of chronic neuropathic pain.Common medical treatments are so incapable that neuromodulation techniques are often required.Regretfully,none of them leads to satisfactory outcome.More and more studies have shown that neuropathic pain is closely related to brain plasticity.Electroacupuncture?EA?for analgesia has a wide range of clinical applications and a positive effect.Few studies have evaluated the efficacy of EA in the treatment of neuropathic pain after BPAI and its effect on the central plasticity.In this study,EA in neck"Jiaji"was used to treat the rat model of brachial plexus pain.The animal behavioral assessments were used to investigate the analgesic effect of EA.Functional magnetic resonance imaging?f MRI?,immunohistochemistry and immunofluorescence technique were used to study the changes of brain plasticity during EA treatment for rats with neuropathic pain,to explore the analgesic effect of EA on brachial plexus pain and the changes of central pathway.In the study,we try to reveal the central effect of EA on brachial plexus pain and provide a therapeutic target and theoretical basis for the rehabilitation of neuropathic pain.Part ?.Behavioral Study of Electroacupuncture on Rats with Neuropathic Pain Induced by Brachial Plexus Avulsion InjuryObjective:To evaluate the analgesic effect of electroacupuncture on rats with neuropathic pain after brachial plexus avulsion injury.Methods:Experiments were conducted on 58 adult female Sprague-Dawley?SD?rats.8rats were randomly divided into normal group.After model establishment of global BPAI through posterior cervical laminectomy in the rest 50 rats,we screened the rats based on the presence of self-harm behavior in order to distinguish which of them presented neuropathic pain.24 rats with the presence of self-harm behavior remained in the study after the selection.The 24 rats were randomly divided into 3 groups:model group?n=8?,sham EA group?n=8?and EA group?n=8?.Rats of EA group was given the EA on the left side of C₅-C₇“jiaji”.In the sham EA group,three needles were inserted into 3mm beside C₅-C₇“jiaji”on the left side with no current stimulation.Rats of the model group and the normal group had no intervention.Mechanical withdrawal thresholds and thermal withdrawal latency were performed before modeling,30 days after modeling,after 1-month intervention,after 3-month intervention,and after 4 months(no intervention in the4^th month).Results:?1?Mechanical withdrawl threshold?MWT?:MWT of bilateral hindpaws after modeling was significantly lower than pre-modeling?P<0.05?;after the electroacupuncture intervention,MWT of the EA group was significantly higher than that of the sham EA group or model group?P<0.05?.After 4 months,the post-effects showed that the EA group was still significantly higher MWT than that of the sham EA group and the model group?P<0.05?.?2?Thermal withdrawl latency?TWL?:The TWL of the left hindpaw after modeling was significantly lower than that pre-modeling?P<0.05?.There was no difference at each time point after EA intervention.Conclusion:EA could significantly increase the MWT of rats with brachial plexus pain,which indicated that EA could relieve neuralgia in rats with brachial plexus pain with significant post-effect.Part ?.Electroacupuncture in Treating Rats with Neuropathic Pain Induced by Brachial Plexus Avulsion Injury:A Brain Function Neuroimaging StudyObjective:We utilized f MRI to provide a longitudinal description of cortical plasticity by EA of neuropathic pain after brachial plexus avulsion injury.We would explore the imaging presentation of neuro plasticity derived from acupuncture analgesia.Thus,it leads to a better understanding of the underlying central mechanism.Methods:Experiments were conducted on 58 adult female Sprague-Dawley?SD?rats.8rats were randomly divided into normal group.After model establishment in the rest 50rats,we screened the rats based on the presence of self-harm behavior in order to distinguish which of them presented neuropathic pain.24 rats with the presence of self-harm behavior remained in the study after the selection.The 24 rats were randomly divided into 3 groups:model group?n=8?,sham EA group?n=8?and EA group?n=8?.Rats of EA group was given the EA on the left side of C₅-C₇“jiaji”.In the sham EA group,three needles were inserted into 3mm beside C₅-C₇“jiaji”on the left side with no current stimulation.Rats of the model group and the normal group had no intervention.f MRI scans were performed before modeling,30 days after modeling,after 1-month intervention,after 3-month intervention,and after 4 months(no intervention in the 4^thmonth).The data analysis included brain activation in task-f MRI of the forelimb electrical stimulation before and after brachial plexus injury,ALFF analysis in Resting-State Scan,hub identification and reginal properties of functional brain network after EA intervention.Results:1.After brachial plexus injury,the results showed increased ALFF in multiple cerebral regions,including the left anterodorsal hippocampus,left mesencephalic region,left thalamus.Additionally,we found decreased ALFF values in the bilateral entorhinal cortex.2.The differences of activation in task-f MRI were mainly in the limbic-paralimbic system and somatosensory cortices.3.Hub identification and reginal properties of functional brain networks:?1?Hub identification:The result showed similar spatial distributions of hubs among the four groups.The hub regions were predominately located in the limbic system,parietal lobes,mesencephalic region,medial temporal lobe and subcortical regions?ventral pallidum and thalamus?.The node was identified to be higher hubness regions if any of its three nodal parameters was at least 2.5 standard deviation greater than the average value in the brain network.Statistical results showed that there were significant differences in the proportion of the higher hubness regions across all groups.After long-term intervention,the proportion of higher hubness regions in the model group was significantly higher than that in normal group,while that in EA group was significantly lower than that in the model group.The result of post-effect showed that the proportion of higher hubness regions in the model group was significantly higher than that in normal group,while that in EA group was lower than that in the model group.?2?Reginal properties of functional brain networks:The results showed similar with the results of the proportion of the higher hubness regions.The reginal properties in the model group were significantly higher than those in the normal group?e.g.the right mesencephalic region and hippocampus?,while those in the EA group were significantly lower degree than the model group.Conclusion:1.The entorhinal-hippocampus pathway was involved in the functional integrated areas of brachial plexus pain processing.The regions in the“pain matrix”showed expected activation when applying instant nociceptive stimulus but remained silent in the resting status.This research confirmed the involvement of cognitive function,which brought novel information to the potential new therapy for brachial plexus pain.2.Pain-related changes were associated with increased proportion of higher hubness regions and increased regional properties in hippocampal and mesencephalic regions.And these changes could be reversed after long-term EA intervention.We proposed that EA might restore an adaptive equilibrium in a disrupted network and suppress maladaptive plastic changes following neuropathic pain.Part ?.Study on the Changes of C-fos Expression in the Brain of Rats with Neuropathic Pain Induced by Brachial Plexus Avulsion Injury Treated by ElectroacupunctureObjective:Based on the alteration of regional plasticity revealed by previous f RMI analysis,we aim to explore the histological changes and provide structural evidence for the functional changes.In this part,immunohistochemistry and immunofluorescence staining would be utilized.Methods:Experiments were conducted on 30 adult female Sprague-Dawley?SD?rats.2rats were randomly divided into normal group.After model establishment in the rest 28rats,we screened the rats based on the presence of self-harm behavior in order to distinguish which of them presented neuropathic pain syndrome.10 rats with the presence of self-harm behavior remained in the study after the selection.The 10 rats were randomly divided into 2 groups:model group?n=5?and EA group?n=5?.Rats of EA group was given the EA on the left side of C₅-C₇“jiaji”from 30 days after modeling.Rats of the model group and the normal group had no intervention.Rats brain were taken out to carry out c-fos expression tests after modeling,after short-term intervention and after long-term intervention.Results:Under normal conditions,c-fos in the thalamus,hypothalamus,amygdala,periaqueductal gray and ventral tegmental area were all expressed,but sparse.After modeling,the expression of c-fos increased in the above brain regions.After EA intervention,the expression of c-fos in the above brain areas in the EA group was reduced compared with that after modeling.Conclusion:The expression of c-fos in hub regions in the brain function network of brachial plexus pain was increased,and EA could reverse the increase of c-fos.The results provided histological evidence for revealing the structural basis of the hub regions of the brain network.