THE DISTRIBUTION OF IRON IN THE BRAIN - A PHYLOGENETIC ANALYSIS USINGIRON HISTOCHEMISTRY

Histochemical procedures can be used to detect the cellular distributi on of iron in the brain. The objective of the present study was to det ermine if the cellular distribution of iron enrichment is conserved be tween animals on different branches of the phylogenetic tree. This inf ormation can facilitate our understanding of the role of iron enrichme nt in cells of the brain. The animals studied were the mouse, rat, chi cken, frog, fish and fly. In order to optimize the detection of iron, two histochemical staining methods and three fixatives per staining me thod were examined for each species. The results indicated that there was no single cell type that displayed iron enrichment iii each of the species examined. In three out of five species in the phylum chordata , iron was enriched in oligodendrocytes; the exceptions to this were t he fish and frog, which had iron enrichment in neurons but not oligode ndrocytes. Iron was enriched in ependymal cells and endothelial cells in four out of the five species in the phylum chordata with the fish a nd the mouse being the respective exceptions. Myelin was stained in th e mouse and rat, and microglia were occasionally observed in the rat a nd chicken. Astrocyte staining was not observed in any of the species examined. In the fly third instar larvae, iron enrichment was found in border glia and in neuropil. The absence of a conserved staining patt ern between species suggests that iron enrichment probably does not pl ay a role in the main functions that have been attributed to those cel ls that were stained. These findings, taken together with previously p ublished data on the distribution of ferritin and transferrin, suggest s that iron-enriched cells serve as stores of iron for the brain.