Abstract: Abstract: Objective To investigate the effects of morphine preconditioning (MP) on middle cerebral artery occlusion (MCAO)-induced brain injuries and its possible mechanisms. Methods MCAO mouse models were established. The brain infarction sizes and edema ratio were determined by 2,3,5-Triphenyltetrazolium chloride (TTC), the neurological deficit score was also evaluated. Samples were collected from left cerebral cortex of Sham group, ischemic core (I), penumbra (P) and contralateral cortex (C) from both MCAO and 10mg/kg MP groups. Western blot analysis was used to determine Hsp70 protein expression levels. Western blot analysis was used to determine Hsp70 protein expression levels. Results The brain infarct size of MCAO group was 31.69%±4.19%, the edema rate was 8.98%±1.79%. MP reduced infarction size and edema ratio significantly compared to MCAO group (P<0.05), there were 23.34%±4.85% and 4.60%±0.86% respectively. MP could also improve MCAO-induced neurological deficits score of mice (P<0.05). Compared with that of Sham group, Hsp70 expression in mice under MCAO increased significantly (P<0.05), there was much higher expression of Hsp70 in the penumbra of MP group but not in the ischemic core and contraletaral compared with that of MCAO group. Conclusion Morphine preconditioning can attenuate MCAO-induced focal brain ischemic injuries in mice, and the high level of Hsp70 in penumbra may be involved in the neuroprotection.

Key words: Key words: Morphine Preconditioning (MP), MCAO, Penumbra, Hsp70