An Investigation Into The Sensorimotor Function Recovery Of Rat Model Of Unilateral Internal Capsule Infarct Using Rs-fMRI Method

Part ?: An Investigation into The Impact of Three Anesthetic Regimes on Task-f MRI and Resting-State f MRI Results of RatsObjective To investigate the impacts of three anesthetic regimes on task-f MRI and resting-state f MRI(rs-f MRI)results of both SD and Wistar rats.Materials and Methods A total of 24 SD rats and 24 Wistar rats were included in the study.They were equally allocated to three groups and kept anesthetized in f MRI sessions with three kinds of anesthetic regimes,which included 2%-2.5% isoflurane(IFR group),initial dexmedetomidine bolus combined with continuous infusion of dexmedetomidine(MED group)and initial dexmedetomidine bolus combined with 0.3-0.5% isoflurane(MED&IFR group).A task-f MRI(electrical forepaw stimulation)session and an rs-f MRI session were performed with three runs at different time points in each of the rats.Mean percent BOLD signal response in contralateral S1 FL were compared among rat groups.For rs-f MRI analysis,symmetrical inter-hemispheric connectivity pattern was quantified by introducing a new variable called r ICS.Results SD showed a lower stimulation induced BOLD response than that of Wistar rats(F = 42.367,P < 0.001).Wistar rats in MED group have the most reliable and consistent activation in contralateral S1 FL in task-f MRI session(P < 0.001,compared to the other two groups).SD rats in MED&IFR group have the highest r ICS among all three groups(P < 0.001 and P = 0.001,compared to IFR group and MED group,respectively).Wistar rats demonstrated relatively lower r ICS.Conclusions Wistar rats did not seem to have a bilateral regional specific inter-hemispheric connectivity pattern seen in humans under the three anesthetic regimes.Initial dexmedetomidine bolus combined with low dose isoflurane appears to be a robust anesthetic regime for remain reliable inter-hemispheric functional connectivity in SD rats.There is an uncoupling of task-related BOLD activation and inter-hemispheric functional connectivity in both SD and Wistar rats.Part Ⅱ: Development of An Automatic Pipeline for Rat f MRI Data Analysis and Stimulation Device for Task-f MRI ExpermentObjective To build an automatic pipeline of rat f MRI data analysis based on MATLAB platform by modifying existing open-source image data analysis package for human f MRI data,and to develop an MRI compatible constant current electrical stimulator for rat forepaw electrical stimulation.Materials and Methods A total of 20 Wistar rats and 20 Sprague Dawley(SD)rats anesthetized with dexmedetomidine bolus and 0.3% isoflurane underwent resting-state f MRI.An average EPI template of the 40 rats was built by using SPM8.By combining a T2 rat template-atlas set from Tohoku University and MIVA atlas from University of Massachusetts Medical School,we build a new atlas which contains fine segmented cortical and subcortical brain regions and a new T2 template.By using the 3d Tagalign command in ANFI,we registered the T2 template set to the EPI template.We modified the DPARSF package and REST package to make these two packages compatible with the new template set.A brain surface file was built by using the AFQ-master and vistasoft-master package,and a node file of different brain regions was built using the new template set.Meanwhile,we developed an MRI compatible constant current electrical stimulator for rat forepaw electrical stimulation and a stimulation-scanning synchronized software for stimulation paradigm design.Results A digital atlas with 212 fine segmented cortical and subcortical brain regions,a template set with aligned structural T2 template and functional EPI template were built.The modified automatic f MRI data analysis for rats can automatically finish all the required steps of rat f MRI data preprocessing and relevant steps of postprocessing.The registration error for rat images is less than a voxel.The contralateral S1 FL of rat brain was significantly activated during unilateral electrical forepaw stimulation f MRI.The location of activated cluster coincides well with the S1 FL of the atlas.The peak percent BOLD signal change is 4.5% ± 0.6%。The modified template can be directly used in Rest Slice Viewer and the surface file and the node file made by the modified template can be used in Brainnet View.These files can be used as an underlay for f MRI result overlay and displayed in 3D mode.Conclusions Automatic software package based on the MATLAB platform for rat f MRI data analysis facilitates the rat f MRI data analysis greatly and improved the accuracy.These packages also facilitate the visualization and perception of the f MRI results.Part Ⅲ:Building A Rat Model of Unilateral Internal Capsular Infarct and Behavioral Evaluation of The ModelObjective To build a stable rat model of unilateral internal capsular(IC)infarct by combining stereotactic and photothrombosis and evaluate the sensory-motor deficit of the model by using multiple behavioral tests.Materials and Methods A total of 26 Sprague Dawley(SD)rats were included in the study.All the rats were anesthetized with 2%-2.5% isoflurane and immobilized in the stereotactic in the prone position.A small hole on the skull was made,and then an optical fiber was lowered to the 2mm posterior,3.1mm lateral and 7.2mm ventral of the bregma through a cannula.Rose Bengal dye was injected through a tail vein with a concentration of 20mg/kg.The internal capsule area was irradiated by 532 nm green light for 2 minutes.The rats were randomly equally separated into two groups,and rats of the two groups were irradiated by different laser powers(10 watts,20 watts).All the rats were performed with T2 weighted MRI to ensure they were successful internal capsular infarct models 24 hours after stroke experiment.The T2 weighted MR scanning and behavioral evaluations(Modified neurological severity score,m NSS)was performed on 1,3,5,7,11 and 27 days after operation of stroke model.Results T2 weighted MR images showed that a total of 19 rats were successful models.Small power groups(10w)has seven successful IC infarct rats,and large power group(20w)has 12 successful IC infarct rats.The average lesion size at 24 hours after the operation was 6.5 ± 1.8 mm3 in small power group and 29.8 ± 4.8 mm3 in large power group.The average lesion sizes in large power group significantly larger than those in small power group at all time points(all P < 0.001).The m NSS test showed that average m NSS scores of the small power group were lower than 4 at all time points,the average m NSS scores of the large power group significantly higher than those of small power group at all time points(all P < 0.01).Conclusions Internal capsular infarct rat models with stable and confined lesion size can be made by combining stereotactic and photothrombosis.A laser power larger than 10 watt is more suitable for building internal capsular infarct rat models with marked motor-sensory deficit and for research in this field.Part Ⅳ: Evaluating Sensorimotor Function Recovery of Unilateral Internal Capsule Infarct Rat Model Using rs-f MRI MethodObjective To explore the sensorimotor cortex inter-hemispheric functional connectivity and cortical-thalamic functional connectivity(FC)change in unilateral internal capsule(IC)infarct rat models using functional connectivity rs-f MRI method,and to investigate whether the aberrant FC pattern correlates to the sensorimotor function impairment after stroke.Materials and Methods A total of 56 Sprague Dawley(SD)rats were included in the study and 18 of the rats were set as a sham-operated group.All the rats underwent a baseline rs-f MRI scanning within 3 days before stroke experiment.They also underwent rs-f MRI sessions on 1 day and 20 days after the brain operation.Comprehensive behavior tests including modified neurological severity score test,modified balance beam test and Von-Frey filament test were performed on 1,4,10,20 days after brain operation to evaluate the sensorimotor function impairment at different time points.The ipsi-lesional S1F1 and M1 areas and contra-lesional thalamus were defined as seed for functional connectivity(FC)analysis to generate FC maps.Then repeated measure ANOVA was performed on these FC maps.Correlation analysis was performed between the FC signals of aberrant brain regions and the behavioral performance of rats.Finally,we try to introduce the rs-f MRI results on acute phase of stroke to build an early prognosis prediction model by using the logistic regression method.Results Rats which were successful models of internal capsule infarct were recognized as stroke group.Inter-hemispheric functional connectivity of 56 rats between bilateral S1 FL and bilateral M1 significantly decreased on 1 day and 20 days after brain operation(P < 0.001;P = 0.021).While there was no difference in these measurements between the stroke group and sham-operated group(P = 0.218;P = 0.164).The FC value between contralateral thalamus and contralateral S1 FL increased,while the FC value between contralateral thalamus and ipsilateral IC area decreased.Correlation analysis showed that FC value between contralateral thalamus and contralateral S1 FL on 1 day after stroke correlates with the performance of Von-Frey filament tests(r = 0.501,P = 0.002;r = 0.486,P = 0.003)1 day and 20 days after stroke and Modified balance beam tests(r = 0.533,P = 0.001)on 20 days after stroke.The logistic regression model showed that FC value between contralateral thalamus and contralateral S1 FL significantly improved the predictive performance of the model.Conclusions The decrease of FC between bilateral S1 FL and bilateral M1 were related to the operation but not IC infarct.The increase of FC between contralateral thalamus and contralateral S1 FL is not only correlated to the behavioral performance on acute stroke phase,but also correlated to the persistent sensorimotor impairment on chronic phase of stroke.These results indicate that FC between contralateral thalamus and contralateral S1 FL has the potential to serve as an early predictive factor of the prognosis of sensorimotor impairment after IC stroke.