Glutamate Triggers Cell Death Specifically in Mature Central Neurons through a Necrotic Process

Abstract

Whereas immature neurons have been shown to be sensitive to hypoxia and to develop apoptosis, the role of glutamate in neuronal injury is more controversial. Effects of a 6-h exposure to glutamate or its analogues (100 μM) were studied over a period of 72 h in cultured central neurons at two maturational stages, i.e., after 6 and 13 daysin vitro.Glutamate was without toxic effects in 6-day-old neurons which became vulnerable to the excitatory amino acid when they were coexposed to 30 nM staurosporine, a protein kinase C inhibitor. In 13-day-old neurons, glutamate and derivatives led to cell death and altered functional activity of surviving neurons over the next 72 h, the greatest injury being observed with glutamate and NMDA. At this developmental stage, persistent inhibition of protein synthesis induced by glutamate, as well as lack of beneficial effect from cycloheximide, argues against programmed neuronal death. Accordingly, quantitative cell nuclear analysis using a fluorescent dye revealed that the effects of glutamate reflect necrosis but not apoptosis. Furthermore, the inability of immature neurons to inhibit protein kinase C may account for their higher resistance to excitotoxicity.