Expression Of Aquaporin-4 (AQP-4) And Its Effect On Permeability Of Blood-brain Barrier During Traumatic Brain Injury In Rats

Objective:To investigate the expression level of cerebral aquaporin-4(AQP-4)and its effect on permeability of blood-brain barrier during traumatic brain injury (TBI) in rats.Methods: We choosed inbred, clean and ripe male SD rats. Their weight was controlled between 250 and 300g. 49 SD rats were divided randomly into control group(SO group, n=7)and experimental group(TBI group, n=42).The experimental group (TBI group) was divided into six groups during traumatic brain injury. The each group was divided into 4h, 8h,12h,24h,48h and 72h group. The experimental TBI model was established by bumpiness of free falling body according to Feeney's. The rats'cerebral edema were imaged with magnetic resonance image (MRI) , The changes of brain water content and permeability of blood-brain barrier (BBB) were measured by the methods of wet and dry weight and Evans blue fluorometry. The expression of AQP-4mRNA was examined by reverse transcriptase polymerase chain reaction (RT-PCR). The protein expression of AQP-4 was examined by western blot.Results:After TBI, the MRI performance of the experimental group is the T1W1 low signal or the equisignal and the T2W1 high signal. There is no obvious abnormal signal in the control group. Compared with the control group, water content of brain tissue and EB content in the contusion side significantly increased 4h after TBI, the expression of AQP-4mRNA and the protein expression of AQP-4 in contusion marginal region began to in- crease.They reached the summit at 24h after operation, afterward dropped gradually,and still maintained at the high level after 72h(p<0.05). There was significantly positive correlation between expression of AQP-4mRNA, protein expression of AQP4 and change of EB content.Conclusion:Damage of blood-brain barrier of cerebral tissue in the contusion side after TBI is the morphology basis for the occurrence of cerebral edema. The change of AQP-4mRNA and AQP-4 Protein expression are closely related to the destruction of BBB and the formation and development of brain edema during the early stage after traumatic brain injury.The early up-regulated expression of AQP-4 may increase permeabi- lity of blood-brain barrier, which is concerned with the development of brain edema after the brain injury.