Cellular and subcellular localizations of nonheme ferric and ferrous iron in the rat brain: a light and electron microscopic study by the perfusion-Perls and -Turnbull methods.

Iron in the brain is utilized for cellular respiration, neurotransmitter synthesis/degradation, and myelin formation. Iron, especially its ferrous form, also has the potential for catalyzing the Fenton reaction to generate highly cytotoxic hydroxyl radicals. The amount of iron in the brain must therefore be strictly controlled. In this study, we focused on the cellular and subcellular localizations of nonheme ferric (Fe(III)) and ferrous (Fe(II)) iron in the adult female rat brain using light and electron microscopic histochemistry. Although Fe(II) deposition was much less dominant than Fe(III), the brain contained iron in both forms. Among the cellular elements of the brain, oligodendrocytes were numerically the most prominent and heavily iron-storing cells. Pericapillary astrocytes and sporadic microglial cells also showed dense iron accumulation. Large neurons involved in the motor system were relatively strongly iron-positive. Subcellularly, Fe(III) and Fe(II) were mainly localized in lysosomes, and occasionally in the cytosol and mitochondria. Furthermore, capillary endothelial cells had Fe(III)-positive reactions in lysosomes and the cytosol, with Fe(II)-positive reactions on the luminal membrane. With advancing age, both Fe(III) and Fe(II) became more extensively distributed and accumulated more numerously in oligodendrocytes and astrocytes. These findings suggest that age-related increases in Fe(II) accumulation may raise the risk of tissue damage in the normal brain.