Study On Animal Model,and Imaging Of The Central Nervous System And Peripheral Nerve Of Trigeminal Neuralgia In Rat Model

Objective:To establish a stable and reliable rat model of trigeminal neuralgia with accurate localization and simple operation under CT guidance.Transmission electron microscopy was used to investigate the pathophysiology of trigeminal neuralgia,and MRI was used to find pain-related brain areas.Method:Experiment 1:Twenty-four adult male Sprague-Dawley rats were randomly divided into two groups.Under CT guidance,0.2 ml of 20%talc powder suspension or saline was injected into the right infraorbital foramen region of rats in the talc group or saline group.Mechanical allodynia was tested in the right facial region of rats on the 3 days before surgery,the 3 and 7 days after surgery,and then once a week up to 12 weeks post operation.Experiment 2:Twelve adult male Sprague-Dawley rats were randomly divided into two groups.Rats in both groups were injected with 0.2 ml of 20%talc powder suspension or saline into the right infraorbital foramen region under CT guidance to establish a rat model of infraorbital neuroinflammation.Two rats were taken from each group at 4 weeks,8 weeks and 12 weeks after the operation.The infraorbital foramen segment and intracranial segment of the trigeminal nerve were taken to make ultrathin sections of the nerve and observe the damage of the nerve myelin sheath.Experiment 3:Ten adult male Sprague-Dawley rats’ heads were examined by MRI,and the structural images were segmented into gray and white matter images.To evaluate the quality of diffusion tensor imaging(DTI)and investigate whether 3.0T MRI can perform voxel-based morphometry(VBM)analysis in the rat brain.Experiment 4:Sixty adult male Sprague-Dawley rats were randomly divided into two groups.The rats were injected with 0.2 ml of 20%talc suspension or 0.2 ml of saline into the right infraorbital foramen area under CT guidance to establish the rat infraorbital neuroinflammation model.Ten rats from each group were taken at 4 weeks,8 weeks,and 12 weeks after surgery and underwent head MRI scanning.Gray and white matter segmentation was performed based on the axial 3D-MATRIX sequence of the SIGMA rat brain template to compare the differences in gray matter volume between the two groups of rats.Results:In experiment 1,compared to their preoerative value,rats in the talc group showed a significant decrease in the 50%mechanical pain threshold and were significantly lower than the saline group(P<0.001).The 50%pain threshold was maintained at a low level from day 3 to week 3 postoperatively,and the 50%pain threshold of rats in the talc group was still significantly lower than saline group until 10 weeks after surgery(P<0.05).In experiment 2,from 4 weeks to 12 weeks after operation,the nerve myelin sheath damage in the infraorbital foramen segment was gradually aggravated(P<0.001),and the nerve myelin sheath in the intracranial segment also showed significant damage(P<0.001).In experiment 3,the magnetic field in the 3.0T MRI limits the image quality,so the DTI of rat brain images is not conducive to data analysis.However,the gray and white matter images can be used for VBM analysis.In the experimental 4,rats in the talc group had significantly reduced volumes of the right hippocampus,right primary visual cortex,right secondary visual cortex,right temporal association cortex and left barrel cortex at 12 weeks after surgery(P<0.05).Analysis of variance in the saline group revealed that there was a difference in gray matter volume between the hippocampus and entorhinal cortex(P<0.05).Conclusion:The rat model of infraorbital neuroinflammation established by CT-guided injection of talc powder into the infraorbital foramen results in a simple operation and accurate location.This model has a rapid onset and long duration of pain and is an ideal model of trigeminal neuralgia.Transmission electron microscopy revealed that the peripheral branches of the trigeminal nerve were affected by inflammation that can spread along the nerve and then affect the trigeminal nerve in the intracranial segment.This indicates that demyelination of the trigeminal nerve in the intracranial segment may be involved by inflammation of peripheral branches.The volumes of the right hippocampus,right primary visual cortex,right secondary visual cortex,right temporal association cortex,and left barrel cortex were significantly reduced at 12 weeks after operation in rats with infraorbital neuroinflammation.This indicates that pain can cause significant changes in related brain regions at about 12 weeks.