Oligodendrocytes and myelin sheaths in normal, quaking and shiverer brains are enriched in iron

Early studies employing iron histochemical techniques found a spatially restricted distribution of oligodendrocytes and myelin enriched in iron. In particular, oligodendrocytes and myelin positively stained for iron were found in sparsely myelinated brain regions but not in densely myelinated tracts. Subsequent studies modified the iron histochemical technique and demonstrated that oligodendrocytes and myelin were stained in densely myelinated brain regions but the staining occurred in patches rather than uniformly throughout densely myelinated tracts. This study further modified the iron histochemistry technique to establish that oligodendrocytes and myelin are enriched in iron throughout densely myelinated tracts. This finding supports biochemical studies that detected high levels of iron in white matter (Hallgren and Sourander, J Neurochem 3:41-51, 1958) and myelin fractions of brain homogenates (Rajan et al., Life Sci 18:423-432, 1976). Thus, this histochemical study and earlier biochemical studies indicate that white matter is a major site of iron concentration within the brain. The present study also examined the distribution of iron in oligodendrocytes and myelin from the dysmyelinating mutant mice quaking and shiverer. Results from these studies demonstrate that oligodendrocytes and myelin are enriched in iron in both quaking and shiverer brains. An unexpected finding was an intense staining of oval structures within the oligodendrocyte cytoplasm. This result indicates a concentration of iron in these structures and may be important for understanding how high concentrations of iron are processed by oligodendrocytes.