N-METHYL-D-ASPARTATE INHIBITS APOPTOSIS THROUGH ACTIVATION OF PHOSPHATIDYLINOSITOL 3-KINASE IN CEREBELLAR GRANULE NEURONS - A ROLE FOR INSULIN-RECEPTOR SUBSTRATE-1 IN THE NEUROTROPHIC ACTION OF N-METHYL-D-ASPARTATE AND ITS INHIBITION BY ETHANOL

Primary cultured rat cerebellar granule neurons underwent apoptosis wh en switched from medium containing 25 mM K+ to one containing 5 mM K+, N-methyl-D-aspartate (NMDA) protected granule neurons from apoptosis in medium containing 5 mM K+. Inhibition of apoptosis by NMDA was bloc ked by the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor LY294 002, but it was unaffected by the mitogen-activated protein kinase kin ase inhibitor PD 98059. The antiapoptotic action of NMDA was associate d with an increase in the tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1), an increase in the binding of the regulatory sub unit of PI 3-kinase to IRS-1, and a stimulation of PI 3-kinase activit y. In the absence of extracellular Ca2+, NMDA was unable to prevent ap optosis or to phosphorylate IRS-1 and activate PI 3-kinase. Significan t inhibition of NMDA-mediated neuronal survival by ethanol (10-15%) wa s observed at 1 mM, and inhibition was half-maximal at 45-50 rmM. Inhi bition of neuronal survival by ethanol corresponded with a marked redu ction in the capacity of NMDA to increase the concentration of intrace llular Ca2+, phosphorylate IRS-1, and activate PI 3-kinase, These data demonstrate that the neurotrophic action of NMDA and its inhibition b y ethanol are mediated by alterations in the activity of a PI 3-kinase -dependent antiapoptotic signaling pathway.