MRI Measurement Of Cerebral Cortex Volume And Related Pathology Research In Autistic Rats

Objective: Brain volume may increase in the early stage of autism spectrum disorder(ASD).At present,however,the results of brain volume measured by MRI are not consistent for different brain regions,and the related pathologic changes is under experimental research.In this study,an ASD rat model was established and the volume of cerebral cortex in regions of interest(ROI)was measured and the relationship between ROI and autism-like behavior was studied.In addition,by measuring the content of GABA in ROI brain area,the changes of GABA content and the volume of ROI brain area were analyzed,and the possible mechanism of volume changes of each brain area in the early period of ASD was investigated.Methods: The rat ASD model was established by intraperitoneal injection of valproate(VPA)in pregnant rats.The three-chamber sociability test,open field test and self-grooming test were performed to verify the success of ASD model.After the ASD model was successfully established,the brain T2 WI images of rats in ASD group and control group were obtained by using a special 7.0 T MR scanner.The ASD-related brain regions including hippocampus(HC),cerebellar cortex(CC),prefrontal cortex(PFC),temporal cortex(TC)and somatosensory cortex(SC)were selected as ROI using Automatic Selection ROI method and the volume was calculated.The difference of brain area volume between the two groups was analyzed,and the correlation between brain area volume and behavior test results was analyzed.Western blot and immunofluorescence were used to detect the expression of GAD67(representing GABA content)in different brain areas,and the relationship between the content of Gad67 and the volume of the corresponding brain region was analyzed.Results:(1)Behavioral test: the three-box social experiment showed that the total time of VPA rats staying in the stranger box was significantly shorter(P <0.01)and the total time in the object box was significantly longer(P <0.05)than that in the control group,the number of entering into the center box and object box increased significantly(P<0.05),indicating that VPA rats had obvious social disorder and lack of interest in exploring unfamiliar things.The results of open field test showed that the number of crossing the central line and all the lines in VPA group decreased significantly(P<0.01)comparing with in control group,which indicated that the self-exploration behavior decreased in VPA rats.In the self-grooming experiment,the times and the total time of self-grooming in VPA group were more than that of the control group(P<0.05),which indicated that there were obvious anxiety and repetitive autism-like behaviors in VPA rats.(2)The volume of ROI brain region and its correlation with autism-like Behavior: compared with the control group,the volume of PFC and TC brain regions in ASD rats increased(P <0.05).There was no significant correlation between PFC volume and the communication time of ASD rats with stranger(r=0.57,P=0.14),but there was a significant negative correlation between PFC volume and the total number of crossing all lines in open field(r=0.87,P=0.005),and a significant positive correlation between TC volume and total time of self-grooming(r=0.83,P=0.01).There was a significant negative correlation between TC volume and communication time with stranger in ASD rats(r=0.82,P=0.01).There was no significant correlation between TC volume and the number of crossing(r=0.029,P=0.95)or the total time of self-combing(r=0.45,P=0.26).(3)Pathologic findings and correlation with brain region volume: Western blot and immunofluorescence results revealed the expression of GAD67 in HC,PFC and TC brain regions of ASD rats was decreased compared with control group(P<0.05).With the decrease of Gad67 expression(representing GABA content),the volume of corresponding brain region increased(r=-0.72,-0.79 and 0.71,respectively;P = 0.04,0.02 and 0.04,respectively).Conclusion: Behavioral tests showed that the model of autism rats was successfully established.Compared with the control group,part of the cerebral cortex of the autistic rats increased in volume,which was closely related to autism-like behaviors.GABA content decreased in some of the brain regions,which was related to the increase in volume of the corresponding brain regions.It is suggested that the volume increase of some brain regions could be explained by a compensatory mechanism,that is,the brain overgrows to compensate for the lack of GABA and correct the imbalance of excitation/inhibition system in corresponding brain regions in early stage of autism.