Effects of Chemical Ischemia on Cerebral Cortex Slices Focus on Mitogen-Activated Protein Kinase Cascade

A variety of harmful stimuli, among them energy deple- tion occurring during transient brain ischemia, are thought to unbal- ance protein kinase cascades, ultimately leading to neuronal damage. In superfused, electrically stimulated rat cerebral cortex slices, chem- ical ischemia (CI) was induced by a 5-min treatment with the mito- chondrial toxin, sodium azide (10 mM), combined with the glycoly- sis blocker, 2-deoxyglucose (2 mM). Thereafter, 1 h reperfusion (REP) with normal medium followed. Western blot analysis of p21 Ras , extra- cellular signal-regulated protein kinases (ERK)1/2 (p44/42), phospho- ERK1/2, mitogen-activated protein kinase (MAPK)-p38, phospho-p38, stress-activated protein kinases/c-Jun NH2-terminal protein kinases (SAPK/JNK), phospho-SAPK/JNK was carried out. The level of p21 Ras was increased by 40% immediately after CI, and did not return to control values following REP. Both ERK1 and ERK2 levels were reduced by CI and recovered to control values following REP; no significant change in their phosphorylation degree (phosphorylated to total level ratio, about 50% in the controls) was observed. Neither p38 levels, nor phosphoryla- tion degree were changed following CI/REP. The activation of SAPK/JNK was significantly reduced under CI, and did not recover following REP. All CI/REP-induced effects were prevented by the NMDA receptor an- tagonist MK-801, 10 � M, suggesting the involvement of glutamate. The present findings show that although CI stimulates the p21 Ras protein, MAPK levels and/or phosphorylation are reduced, possibly because of acute energy depletion. Because the activation of SAPK/JNK has been related to both apoptosis and neuroprotection, the decrease observed