CELLULAR-DISTRIBUTION OF FERRITIN SUBUNITS IN POSTNATAL RAT-BRAIN

The normal development of the brain requires finely coordinated events , many of which require iron. Consequently, iron must be available to the brain in a timely manner and in a bioavailable form. However, the brain also requires stringent mechanisms to protect itself from iron-i nduced oxidative damage. The protein that is best suited to making iro n available but also adequately protecting the cell is the intracellul ar iron storage protein ferritin. Typically, ferritin is composed of 2 4 subunits of H and L chains, which are functionally distinct. This st udy was undertaken to determine the expression of ferritin subunits du ring normal development of the postnatal rat brain. There is a shift i n ferritin-containing cell types during development from predominantly microglia at postnatal day 5 (PND 5) to predominantly oligodendrocyte s by PND 30. At PND 5, microglia are found throughout gray and white m atter areas of the brain, but only amoeboid microglia in discrete foci in the subcortical white matter are ferritin positive. At PND 15, som e oligodendrocytes in the subcortical white matter express ferritin, b ut the majority of ferritin-containing cells within white matter are s till microglia. By PND 30, the predominant ferritin-containing cell ty pe within white matter are oligodendrocytes. Generally, the cellular d istribution of both ferritin subunits were identical with one major ex ception; H-ferritin, but not L-ferritin, was present in neuronal nucle i in the cortex. These data suggest that microglia play a role in brai n iron homeostasis during normal postnatal development and may influen ce myelination by competing with oligodendrocytes for iron. (C) 1998 W iley-Liss, Inc.