AQP4 expression and diffusion tensor imaging in rat brainstem after diffuse axonal injury

Objective: To investigate the changes of magnetic resonance diffusion tensor image(DTI) after diffuse axonal 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).Methods: Forty-eight rats were randomly divided into 6 groups.Five separate groups with eight rats in each group were injured and imaged at 3h,6h,12h,24h,72h post-injury by a weight drop trauma model.One group as contral.Rats in DAI group were sacrificed for histology immediately after the scan.The control group of 8 rats was imaged and sacrificed for histology but not injured.Each group was studied by conventional MR imaging,diffusion tensor imaging and histologically examination including HE,silver staining,and immunohistochemistry of AQP4.The results of conventional MRI and DTI were compared with the changes of histopathology.Results: Histological examination showed axonal damage and brain edema in rats of DAI groups.AQP4 expression increased,reached the peak values at 24h and decreased gradually afterwards.ADC value increased and reached the peak values at 12h,and also decreased afterwards.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 between 24 to 72h(P0.01) respectively.There was no significant correlation between 12h to 24h(P0.05).AQP4 expression was strongly correlated with FA value(P0.01) within 72h.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 AQP4 expression and ADC value is helpful for reflecting the classification between vasogenic brain edema and cytotoxic brain edema.