Epsilon protein kinase C mediated ischemic tolerance requires activation of the extracellular regulated kinase pathway in the organotypic hippocampal slice

Ischemic preconditioning (IPC) promotes brain tolerance against subsequent ischemic insults. Using the organotypic hippocampal slice culture, we conducted the present study to investigate (1) the role of adenosine A(1) receptor (A(1)AR) activation in IPC induction, (2) whether epsilon protein kinase C (epsilonPKC) activation after IPC is mediated by the phosphoinositol pathway, and (3) whether epsilonPKC protection is mediated by the extracellular signal-regulated kinase (ERK) pathway. Our results demonstrate that activation of A(1)AR emulated IPC, whereas blockade of the A(1)AR during IPC diminished neuroprotection. The neuroprotection promoted by the A(1)AR was also reduced by the ePKC antagonist. To determine whether epsilonPKC activation in IPC and A(1)AR preconditioning is mediated by activation of the phosphoinositol pathway, we incubated slices undergoing IPC or adenosine treatment with a phosphoinositol phospholipase C inhibitor. In both cases, preconditioning neuroprotection was significantly attenuated. To further characterize the subsequent signal transduction pathway that ensues after epsilonPKC activation, mitogen-activated protein kinase kinase was blocked during IPC and pharmacologic preconditioning (PPC) (with epsilonPKC, NMDA, or A(1)AR agonists). This treatment significantly attenuated IPC- and PPC-induced neuroprotoction. In conclusion, we demonstrate that ePKC activation after IPC/PPC is essential for neuroprotection against oxygen/glucose deprivation in organotypic slice cultures and that the ERK pathway is downstream to epsilonPKC.