Ischemic tolerance induced by normobaric hyperoxia and evaluation of group I and II metabotropic glutamate receptors.

Preconditioning-induced ischemic tolerance is one of the most important mechanisms, responsible for the increased brain resistance after stroke. Recent studies over the past years have provided interesting insights into the molecular mechanisms of this neuroprotective phenomenon. In this research, we attempted to see changes in the expression of group I and II metabotropic glutamate receptors (mGluR I and II) following intermittent hyperoxia preconditioning. Rats were divided into five groups (hyperoxia-intact, hyperoxia-MCAO, room air-intact, room air- MCAO, room air-sham). Hyperoxia groups were exposed to 95% inspired O2 for 4 h/day and 6 consecutive days. Oxygen level in room air groups was %21. 48 hours after pretreatment, MCAO-operated groups were subjected to focal cerebral ischemia for 60 min. 24 hours after reperfusion, neurologic deficit score (NDS) and brain infarct volume (IV) were evaluated in MCAO-operated subgroups. Sham-operated and intact groups were used to assess expression of group I and II mGluR and glutathione (GSH) levels of core, penumbra and subcortex regions. The results of this study showed that preconditioning with intermittent HO decreased NDS and IV, increased GSH levels in subcortex, and upregulated mGluRs I and II significantly. Although additional studies will be required to further elucidate precise mechanism(s) of ischemic tolerance, it seems that intermittent HO may exert its protective effects in part through upregulation of mGluR I and II.