Spreading depression induces expression of calcium-independent protein kinase C subspecies in ischaemia-sensitive cortical, layers: Regulation by N-methyl-D-aspartate receptors and glucocorticoids

Spreading depression is a wave of sustained depolarization challenging the energy metabolism of the cells without causing irreversible damage. In the ischaemic brain, sreading depression-like depolarization contributes to the evolution of ischaemia to infarction. The depolarization is propagated by activation of N-methyl-D-aspartate receptors, but changes in signal transdu ction downstream of the receptors are not known. Because protein phosphoryl ation is a general mechanism whereby most cellular processes are regulated, and inhibition of N-methyl-n-aspartate receptors or protein kinase C is ne uroprotective, the expression of protein kinase C subspecies in spreading d epression was examined. Cortical treatment with KCI induced an upregulation of protein kinase C delta and zeta messenger RNA at 4 and 8 h, whereas pro tein kinase Ca, beta, gamma and is an element of did not show significant c hanges. The gene induction was the strangest in layers 2 and 3, and was fol lowed by an increased number of protein kinase C delta-immunoreactive neuro ns. Protein kinase C delta and zeta inductions were inhibited by pretreatme nt with an N-methyl-D-aspartate receptor antagonist, dizocilpine maleate, w hich also blocked spreading depression propagation, and with dexamethasone, which acted without blocking the propagation. Quinacrine, a phospholipase A(2) inhibitor, reduced only protein kinase C zeta induction. In addition, NG-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, did no t influence protein kinase C delta or zeta induction, whereas 6-nitro-7-sul phamoylbenzo[f]quinoxaline- an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepr opionate/kainase receptor antagonist, and the cyclo-oxygenase inhibitors in domethacin and diclophenac tended to increase gene expression. The data show that cortical spreading depression induces Ca2+-independent p rotein kinase C subspecies delta and zeta, but not Ca2+ dependent subspecie s, through activation of N-methyl-D-aspartate receptors and phospholipase A 2 Even though the signal pathway is similar to the induction described prev iously in ischaemia for genes implicated in delayed neuronal death, the gen e inductions observed here are not necessarily pathogenetic, but may repres ent a general reaction to metabolic stress. (C) 1999 IBRO. Published by Els evier Science Ltd.