High-Dose MK-801 Attenuated Early TTC-Defined Cortical Injury Even under the Conditions of Suppressed Rapamycin-Sensitive pS6 Signaling during Early Cerebral Ischemia-Reperfusion.

The interrelationship of mechanistic target of rapamycin (mTOR), brain-derived neurotrophic factor (BDNF), NMDA receptor and neuronal survival during early cerebral ischemia-reperfusion is not certain. We investigated this relationship by using MK-801, a non-competitive NMDA receptor antagonist and by determining infarct size and blood-brain barrier (BBB) disruption under the condition of markedly reduced mTORC1 activity. Rats received rapamycin (20 mg/kg, i.p.) for two days before transient middle cerebral artery occlusion (MCAO). At 15 min after MCAO, half of the rats received MK-801 (5 mg/kg i.v.). At two hours' reperfusion after 90 min MCAO, BBB permeability, plasma volume and infarct size were determined. In rats without MCAO, one hour after MK-801, protein levels of pS6 (Ser240/244), pAkt (Ser473), mBDNF, proBDNF and MMP-2 were analyzed by Western blot. MK-801 reduced the percentage of cortical infarct in the Control (8.4% ± 2.1 vs 4.7% ± 1.5) and in the Rapamycin Group (12.2% ± 2.3 vs 6.7% ± 2.0). The BBB permeability were not changed. The average plasma volume of the MK-801 Group was largest of all Groups. In the non-ischemic brain, MK-801 increased pS6 levels, which were markedly reduced by rapamycin pretreatment. MK-801 also increased proBDNF levels without affecting mBDNF levels, and neither response was altered by rapamycin pretreatment. In conclusion, our data indicate that high-dose MK-801 reduced TTC-defined cortical injury even under conditions of suppressed pS6 signaling and elevated proBDNF levels. The larger plasma volume observed in the MK-801-treated rats may have contributed to the reduced cortical injury. Therefore, mechanisms other than mTORC1 signaling should be considered in the neuroprotective effects of MK-801 during the early stage of cerebral ischemia-reperfusion.