Objective To explore the relationship between NOS expression and neuron apoptosis in rat hippocampus after focal brain ischemic reperfusion,and to study the protective effect of salvia milteorrhiza(SM).Methods The method of reversible middle cerebral artery occlusion(MCAO) was used to establish the model of focal brain ischemia-reperfusion injury in rats.Immunohistchemistry was used to detect the expression of neuronal nitric oxide synthase(nNOS) and inducible NOS(iNOS) in the hippocampus,and image analysis was also used.The apoptosis of neurons observed with terminal deoxynucleotidyl tranferase mediated dUTP-flourescein nick end-labeling(TUNEL) assay.Results Compared with that of the control group,the expression of nNOS and iNOS in the CA1 and CA3 regions of hippocampusin the ischemic sideincreased at 2h after brain ischemic reperfusion and TUNEL-positive cells appeared in these regions.The expression of iNOS and the number of TUNEL_(-)positive cells progressively increased with time and peaked at 24h after reperfusion,whereasthe expression of nNOShad no significant change.The nNOS and iNOS expression and the neuron apoptosisof the SM group weresignificantly decreased compared with those of the IR group(P<0.01).Conclusion The increased expression of NOS and the increased amount of NO might be one of the mechanisms of neuron apoptosis after focal brain ischemic reperfusion.Salvia Milteorrhiza can significantly inhibit the apoptosis by means of inhibiting the expression of NOS and reducing the production of NO,thus alleviating the injury of ischemic reperfusion to the hippocampus.