Objective To investigate the effects of early hyperbaric oxygenation treatment(HBOT) on the expression of apoptosis genes Bcl-2 and Bax following the rat brain injury and study the neuronal protecting mechanism.Methods 100 Sprague-Dawley rats were divided into 3 groups: Normal group(20 rats),TBI group(40 rats),HBOT group(40 rats).Based upon the Feeney′s model of modified Allen′s method,experimental animals were treated with HBO within 6 hours.The animals were sacrificed at the 8th hour,and on days 1,3,5 and 8,respectively.Their hippocampus cells were observed for morphological changes by H-E staining;the apoptosis rate of injured hippocampus cortex was detected by flow cytometry;and the expression of protein Bcl-2 and Bax was detected with immunohistochemical staining.Results H-E staining indicated that,in contrast to TBI group,in HBOT group the hippocampus cortex and the hippocampus cells at appropriate times had regular morphology,orderly arrangement and more stratal distributions,with a significant reduction in nuclear dense-staining and pyknosis,and marked decrease in apoptosis rate of hippocampus cells(P0.05 or P0.01);increased expression of Bcl-2 in HBOT group(P0.05) and significantly decreased expression of Bax(P0.01).Conclusion The early HBOT can promote Bcl-2 expression and inhibit Bax expression,which is effective in inhibiting apoptosis rate following craniocerebral injury.