Abstract: Abstract: Objective To observe the dynamic changes of endothelial progenitor cells (EPCs) in peripheral blood and cognitive ability of rats with different degrees of traumatic brain injury (TBI). Methods A total of 28 male SD rats were randomly divided into 4 groups: sham group, mild traumatic brain injury group, moderate traumatic brain injury group and severe traumatic brain injury group, seven rats in each group. A hole was drilled on the right parietal skull (4.0 mm posterior from bregma and 3 mm lateral to the sagittal suture, hippocampal region) to expose the dura. Rats were subjected to different degrees of traumatic brain injury of 0.9, 2.1, 3.2 atm (1 atm=101.325 kPa). The dynamic changes of EPCs, white blood cell count (WBC) and platelets (PLT) in the circulating blood were measured before (0 h) and after TBI (3, 6, 24, 48, 72, 168, 240 and 336 h after trauma). Morris water maze (MWM) test was performed to record the escape latency and target quadrant change on day 21-25 after TBI in four groups. Results The number of circulating EPCs kept stable throughout the experiment in the sham group. The numbers of EPCs were significantly lower at 3 h after injury in mild, moderate and severe traumatic brain injury groups (17.4±3.1, 15.6±5.0 and 23.6±3.0) than those in the sham group (53.6±7.9, P＜0.05). The numbers of EPCs at 6 h after injury were increased rapidly, and which were significantly higher in the mild and moderate TBI group than those in sham group (P＜0.05). Then the number of EPCs dropped to the normal level on 48 h after injury. The changes of EPCs was inconsistent with the WBC and PLT during the whole experiment. The positioning cruise experiment showed that the escape latency shortened over time in each group. The escape latency was longer in TBI group than that in sham group during the same period. The spatial probe test showed that the percentages of the target quadrant were significantly lower in the moderate and severe TBI groups than those in the sham group and the mild TBI group. Conclusion With the severity of traumatic brain injury, the cognitive ability reduces in model rats. The level of endothelial progenitor cells in circulating blood is related to the severity of the traumatic brain injury, and can be used as a marker to judge the prognosis.

Key words: Key words: craniocerebral trauma, endothelial cells, cognition disorders, endothelial progenitor cells, flow cytometry, rats, Sprague-Dawley, water maze test