Objective To observe the correlation between the changes of neural cell apoptosis arid caspase-3 gene expression in brain tissues following acute severe traumatic injury to brain(TIB).Method A total of 120 adult Spraque-Dawley rats were divided into a control group(n=8)，TIB group(n=56)and TIB with administration of caspase-3 inhibitor group(n=56).TIB models of rats were made with Feeney's method.The z-DEVDfmk(5 μg)，caspase-3 inhibitor，was administered by intracerebral infusion，and the rats were sacrificed 1，6，24，48 hours and 3，7，14 days postinjury(n=8 for each interval).The specimens of the injured cerebral cortex，suhcerticai white matter，hippocampus，dentate gyrus and contrahteral corresponding brain tissues were taken for detecting apoptesis of neural cells by the terminal deoxynucleotidyl transferase mediated DUTP nick end labeling (TUNEL)methods and flow cytomeay.Caspase-3 mRNA and protein expression were detected by using RT-PCR，immunohistochemistry and western blot analysis.The caspase-3 activity was detected by using caspase-3 fluorescent assay kit.Student t-test and Spearman correlation analysis were used to analyze the data with SPSS version 10.1 software package.Results Apoptesis indexes(AI)and the apoptesis percentage(AP)of neural cells in the injured brain regions increased quickly after injury，and reached its peak 24 to 48 hours later，then decreased slowly,but it remained at higher level above that of normal till 14 days later(P＜0.01).The levels of caspase-3 mRNA,eastme-3 protein and caspase-3 activity were increased significantly post injury，and reached its peak at 24 to 48 hours，then it gradually decreased.Compared with control group，the levels ofoptical density of caspase-3 proteins in the injured hippocampus and subcortical white matter at 24 and 48 hours post injury increased 1484% and 1690%，caspase-3 mRNA expressiom increased 1043%and 1180%，and the degreas of caspase-3 activity increased 148% and 183%，respectively.The expression of caspase-3 proenzyme and its P17 subarrit increased.After trealment with caspase-3 inhibitor z-DEVD-fmk，the levels of caspase-3 mRNA，protein expression and caspase-3 activity were significantly decreased.and AI and AP were significantly decreased as well.The correlation between caspase-3 mRNA and level of neural apoptesis was positive(r=0.821，P＜0.01)，and it was likewise between caspase-3 protein and level of neural apoptosis(r=0.638.P＜0.01).Interestingly enough，a positive correlation was found between caspase-3 mRNA and easpase-3 proteins(r=0.945，P＜0.01).Conclusions The activation of caspase-3 leads to apoptosis of neural cells after acute TIB.The expression of caspase-3 are consistent with apoptosis of neural cells following TIB.The regulation of caspase-3 induced by TIB occurs at a ceriain critical link before transduction.Caspase-3 inhibitor can efficiently inhibit apoptosis of neural cells following TIB.