Abstract: Objective The purpose of this study was to determine whether xenon post-conditioning affects mTOR signaling as well as endoplasmic reticulum stress (ERS)-apoptosis pathway in rats with spinal cord ischemia/reperfusion injury. Methods Fifty male rats were randomized equally into sham-operated group (Sham group), I/R model group (I/R group), I/R model + xenon post-conditioning group (Xe group), I/R model+rapamycin (a mTOR signaling pathway inhibitor) treatment group (I/R+ Rapa group), and I/R model + xenon post- conditioning with rapamycin treatment group (Xe + Rapa group). In the latter 4 groups, SCIRI was induced by clamping the abdominal aorta for 85 min followed by reperfusion for 4 h. Rapamycin (or vehicle) was administered by daily intraperitoneal injection (4 mg/kg) for 3 days before SCIRI, and xenon post-conditioning by inhalation of 1∶1 mixture of xenon and oxygen for 1 h at 1 h after initiation of reperfusion; the rats without xenon post-conditioning were given inhalation of nitrogen and oxygen (1∶1). After the reperfusion, motor function and histopathologic changes in the rats were examined. Western blotting and real-time PCR were used to detect the protein and mRNA expressions of GRP78, ATF6, IRE1α, PERK, mTOR, p-mTOR, Bax, Bcl-2 and caspase-3 in the spinal cord. Results The rats showed significantly lowered hind limb motor function following SCIRI (P<0.01) with a decreased count of normal neurons, increased mRNA and protein expressions of GRP78, ATF6, IRE1α, PERK, and caspase-3, and elevated p-mTOR/mTOR ratio and Bax/Bcl-2 ratio (P<0.01). Xenon post-conditioning significantly decreased the mRNA and protein levels of GRP78, ATF6, IRE1α, PERK and caspase-3 (P<0.05 or 0.01) and reduced p-mTOR/mTOR and Bax/Bcl-2 ratios (P<0.01) in rats with SCIRI; the mRNA contents and protein levels of GRP78 and ATF6 were significantly decreased in I/R +Rapa group (P< 0.01). Compared with those in Xe group, the rats in I/R+Rapa group and Xe+Rapa had significantly lowered BBB and Tarlov scores of the hind legs (P<0.01), and caspase-3 protein level and Bax/Bcl-2 ratio were significantly lowered in Xe+Rapa group (P<0.05 or 0.01). Conclusion By inhibiting ERS and neuronal apoptosis, xenon post-conditioning may have protective effects against SCIRI in rats. The mTOR signaling pathway is partially involved in this process.

Key words: spinal cord ischemia/reperfusion injury; xenon post-conditioning; mTOR; endoplasmic reticulum stress; apoptosis