We have previously shown, using qualitative approaches, that oligodendroglial precursors are more readily damaged by free radicals than are astrocytes. In the present investigation we quantified the oxidative stress experienced by the cells using oxidation of dichlorofluorescin diacetate to dichlorofluorescein as a measure of oxidative stress; furthermore, we have delineated the physiological bases of the difference in susceptibility to oxidative stress found between oligodendroglial precursors and astrocytes. We demonstrate that (a) oligodendroglial precursors under normal culture conditions are under six times as much oxidative stress as astrocytes, (b) oxidative stress experienced by oligodendroglial precursors increases sixfold when exposed to 140 mW/m 2 of blue light, whereas astrocytic oxidative stress only doubles, (c) astrocytes have a three times higher concentration of GSH than oligodendroglial precursors, (d) oligodendroglial precursors have >20 times higher iron content than do astrocytes, and (e) oxidative stress in oligodendroglial precursors can be prevented either by chelating intracellular free iron or by raising intracellular GSH levels to astrocytic values. We conclude that GSH plays a central role in preventing free radical-mediated damage in glia. Key Words: Astrocyte-Desferrioxamine-Dichlorofluorescein-Free radical-Free radical scavenging-Glutathione peroxidase.

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