Objective To observe the expressions of AQP9 and AQP9 mRNA in cerebral cortex and hippocampus of rats after moderate traumatic brain injury (TBI).   Methods The moderate TBI model was established according to Feeney’s method. At different time points after TBI

the degree of cerebral ischemia by TTC staining

the expressions of AQP9 and its mRNA in brain by immunohistochemistry and RT-PCR respectively were performed.   Results No obvious ischemia in brain was found 6 h after TBI

but gradually the ischemic focus enlarged

and reached the maximum 72 h after TBI. The expressions of AQP9 and its mRNA were similar

increasing significantly 3 h after TBI

decreasing 6 h after TBI

then increasing again at 24 h in bilateral cerebral cortex and the hippocampus and reaching the maximum 48 h or 72 h after TBI.   Conclusion The increased expression of AQP9 after TBI is involved in the stress of early TBI and in later brain energy metabolism.