Oxygen generates the energy that fuels cells and, in the process, releases free radicals (molecules that are missing an electron). Antioxidants help to defend against free radicals. Glutathione, one of the most powerful antioxidants in the body, is packed in highest concentration inside glia, specifically astrocytes. Thus, astrocytes can survive toxins that can produce high enough levels of reactive oxygen to kill neurons instantly. Astrocytes release antioxidants in an attempt to protect neurons that are in danger. (Fields, R. Douglas, PhD. The Other Brain. p 104-106. NY: Simon & Schuster, 2009.)