Expression of p-ERK and cytochrome C signals in rat brain neurons after transient MCAO

In order to determine the possible coordinate expression of major survival and pro-apoptotic signals, immunofluorescent analyses for phosphorylated extracellular signal-regulated kinase (p-ERK) and cytochrome C were performed after 90 min of transient middle cerebral artery occlusion (MCAO) in rats. Strong induction of p-ERK was primarily expressed in the ischemic penumbra, while that of cytosolic cytochrome C signal appeared more in the ischemic core from 3 min to 3 h of reperfusion. The double-stained cells with p-ERK strong/cytochrome C weak became most apparent at 3 min primarily expressed in the ischemic penumbra, whereas the cells with p-ERK weak/cytochrome C strong were dominantly found in the ischemic core at 3 h. The proportion of double-positive cells among the total number of single positive cells decreased in the ischemic core and increased in the ischemic penumbra. These findings suggest that the coordinate expression of p-ERK and cytochrome C is fundamentally involved in cell survival or death at the early stage of reperfusion, and that they could play roles in different temporal and spatial profiles.