AQP4 Expression And Diffusion Tensor Imaging In Rat Brainstem After Diffuse Axonal Injury

PURPOSE:To investigate the changes of magnetic resonance diffusion tensor image after traumatic brain injury (DAI) in rats brainstem. At various stages, diffusion tensor image was used to measure apparent diffusion coefficient (ADC) and fractional anisotropy (FA), with immunostaining being used to determine Aquaporin 4 (AQP4). The reaearch provided a theory basis for the classification, mechanism and development of brain edema after DAI by AQP4 expression combining with ADC value,.METHODS:Diffusion axonal injury (DAI) was induced in 38 rats by a weight drop trauma model. Five separate parallel groups of six to eight rats per group were injured and imaged at 3h,6h,12h,24h,72h post-injury. Rats in DAI group were sacrificed for histology immediately after the scan. A control group of ten rats was imaged and sacrificed for histology but not injured. Each group was studied by conventional MR imaging, diffusion tensor imaging (GE 1.5T scanner) and histologically examination including HE, silver staining, and immunohistochemistry of AQP4. The results of conventional MR I and DTI were compared with the changes of histopathology found.RESULTS:DTI have the potential for evaluation axonal damage and brain edema in vivo. ADC, FA measurements and AQP4 expression change of brainstem regions were detected within 72 hours after DAI at every time point. AQP4 expression was up regulated and formed a peak at 48h, IOD was 0.331±0.007, and then dawn regulated. ADC value increased and formed a peak of 1.584±0.200 at 12h, and then decreased. FA value decreased consecutively. There was significant correlation of ADC value and AQP4 expression in brainstem between DAI group and control subjects within 12h and from 24 to 72h, from 12 to 24h (P<0.01), there was no significant correlation(P>0.05). AQP4 expression was strongly correlated with FA value (P <0 .01)CONCLUSION:The expression of AQP4 protein after DAI is time-dependent and possibly implicated in the formation and resolution of DAI-induced cerebral edema. ADC measurements in brainstem were correlated with AQP4 after DAI. Combining with AQP4 expression and ADC value were helpful for reflecting the classification between vasogenic brain edema and cytotoxic brain edema.