A HISTOCHEMICAL-STUDY OF IRON-POSITIVE CELLS IN THE DEVELOPING RAT-BRAIN

The establishment of normal iron levels in the neonatal brain is criti cal for normal neurological development. Studies have shown that both iron uptake and iron concentration in the brain are relatively high du ring neonatal development. This histochemical study was undertaken to determine the pattern of iron development at the cellular level in the rat forebrain. Iron-stained cells were observed as early as postnatal day (PND) 3, which was the earliest time point examined. At PND 3, th ere were four major foci of iron-containing cells: the subventricular zone and three areas within the subcortical white matter. These latter foci are associated with myelinogenic regions. The blood vessels were prominently stained for iron throughout the brain. At PND 7, as in PN D 3, the majority of the iron-containing cells were in white matter. H owever, there were also patches of iron staining located specifically in the layer IV of the somatosensory cortex. These cortical patches we re no longer visible by PND 14. At PND 14, numerous iron-stained cells were dispersed throughout white matter regions and the tanycytes alig ning the third ventricle were prominently stained. The blood vessel st aining was less prominent than at earlier time periods. By PND 28, the adult pattern of iron staining was emerging. Iron-stained cells were aligned in rows in white matter and had an apparent preference for a l ocation near blood vessels. This clustering of iron-positive cells aro und blood vessels gave the white matter a ''patchy'' appearance. The p attern of development, cell distribution, and morphological appearance of the iron-stained cells are consistent with that reported for oligo dendrocytes. That iron-positive cells in the neonate may be oligodendr ocytes is consistent with the reports for iron staining in adult brain s. The recent reports that oligodendrocytes are highly susceptible to oxidative damage would be consistent with the high iron levels found i n these cells. These results indicate that oligodendrocytes play a maj or role in the development of iron homeostasis in the brain. The role of iron in oligodendrocytes may be associated with metabolic demands o f myelinogenesis, including cholesterol and fatty acid synthesis. Howe ver, these cells may be a morphologically similar but functionally dis tinct subset of oligodendrocytes whose function is to regulate the ava ilability of iron in the brain. (C) 1995 Wiley-Liss, Inc.