Abstract: Objective To investigate the effect of postconditioning after brain ischemia on the expresssion of MPO（myeloperoxidase）and TLR4（Toll-like receptor 4）and inflammation in cortex. Methods The thrombotic focal cerebral ischemia was induced by photochemical reaction in tree shrews, and ischemic postconditioning was established by 3 repeated cycles of 5 min of temporary right carotid artery clipped at 4h after the onset of photochemical reaction and 5 min reperfusion. The changes of histology of cortex (by Hematoxylin-and-eosin), MPO expression (by immunohistochemistry), TLR4 expression (by Western Blot Analysis) and TLR4 mRNA (by RT-PCR) were observed. Resulsts Our study found extensive neuronal injury and inflammation in cortex at 4, 24 and 72h, peak at 24h after the cerebral ischemia, while significantly attenuated after the postconditionng with less inflammation cells’ infiltration. Immunohistochemistry analysis showed that cerebral ischemia caused an increase in MPO expression in cortex, and ischemic postcondionting decreased the expression at 24h and 72h（P ＜0.05）. Cerebral ischemia caused an increase of the TLR4 expression in cortex （P ＜0.05），peak at 24h. Postcondionting caused a decrease in the TLR4 expression in cortex at 4 hours and 24 hours（P ＜0.05）, but an increase at 72 hours（P ＜0.05）. The levels of TLR4 mRNA in cortex showed the similar variation trend in accordance with the protein expression. Conclusion The protection mechanisms of the prostconditioning may be associated with inhibitting inflammation and regulating TLR4 expression.

Key words: photochemistry, Inflammation, brain ischemia, toll-like receptor 4, postconditioning