Effects of chronic ethanol exposure on oxidation and NMDA-stimulated neuronal death in primary cortical neuronal cultures.

Excessive oxidative radical formation has been implicated in a number of neurodegenerative processes, including glutamate-N-methyl-D-aspartate (NMDA)-mediated excitotoxicity. Previous studies have suggested that the formation of reactive oxygen species (ROS) during NMDA exposure is involved in triggering the excitotoxic cascade. Chronic exposure of primary neuronal cultures to ethanol has been shown to potentiate NMDA-mediated processes, such as nitric oxide formation and excitotoxicity. It was the objective of this study to investigate the role of NMDA and ROS formation in the development of NMDA supersensitivity after chronic ethanol exposure. The fluorescent dyes dichlorofluorescein diacetate (H2DCF) and propidium iodide, which have been shown to be reliable markers for the detection of cellular oxidation and cell death, respectively, in neuronal culture preparations, were used to examine the relationship between ROS production and NMDA-mediated neuronal death after chronic ethanol administration. Cultures treated chronically with ethanol (100 mM) for 96 hr displayed significantly less H2DCF oxidation when exposed to various concentrations of FeSO4 for 25 min. However, this decrease in intracellular oxidation did not have any apparent inhibitory effects on the amount of cell death observed 12 hr after the 25-min exposure to FeSO4. When NMDA-FeSO4-mediated oxidation was examined in cultures treated chronically with ethanol, dose-dependent increases in H2DCF oxidation were observed, but only in control-treated cultures. This blunting of intracellular H2DCF oxidation did not attenuate the potentiation of NMDA-mediated excitotoxicity observed after chronic ethanol exposure. These results suggest that the observed supersensitivity to NMDA is not due to increases in intracellular ROS formation and that chronic ethanol may induce neuronal factors that reduce ROS formation, but do not protect against normal death.