Abstract: Objective To investigate the dynamic experiences of pathological changes in brain and the injured role of brainstem auditory evoked potential (BAEP) after closed Mild Traumatic Brain Injury (MTBI) in rat. Methods A closed diffuse brain injury model was successfully produced in rat by hit the parietal bone with a spring-droved steel stick. The auditory brainstem response evoked by click at 50 Hz stimulating frequency were recorded at pre-trauma, 15 min and 1,3,6 ,12 h and 1,2,4,7,10,14,21 d after brain injury. The pathological changes of brain were observed under light microscope and the brain edema was detected by wet weight/dry weight rations. Results The Ⅰ-Ⅴ, Ⅲ-Ⅴof BAEP wave inter peak latency (IPL) in MTBI group increased immediately in 15 minutes after injury. The Ⅲ,Ⅴ wave peak latency (PL) and Ⅰ-Ⅴ, Ⅲ-Ⅴwave IPL became longer than the pre-trauma level in 6, 12 h post-injury (P<0.05). The Ⅲ,Ⅴ wave PL and Ⅰ-Ⅲ,Ⅰ-Ⅴ, Ⅲ-Ⅴ wave IPL became longer than the pre-trauma level in 1, 2 d after injury(P<0.001), the BAEP retuned to normal level in 14 d after brain injury. At 15 minutes after injury, the water content in brain increased and met its peak in 1 d, decreased gradually in 4 d, then decreased slowly and returned to normal level in 10 d after injury. Conclusion The regular changes of BAEP could be an objective tool for evaluating hearing dysfunction after closed mild diffuse traumatic brain injury.

Key words: mild traumatic brain injury, closed, pathology, brainstem auditory evoked potential(BAEP), rat