The regional distribution and cellular localization of iron in the rat brain.

The regional distribution and cellular localization of iron throughout the rat brain was determined with iron histochemistry. Densitometry was used to measure the intensity of stain of 51 iron-concentrating sites. Among the areas of highest iron content are the circumventricular organs, islands of Calleja, globus pallidus, ventral pallidum, substantia nigra pars reticulata, interpeduncular nucleus, dentate nucleus, and interpositus nucleus. Iron occurs most commonly in oligodendrocytes and in the fibrous network of the neuropil, but is also found in the interstitial spaces of circumventricular organs and in the tanycytes of the organum vasculosum of the lamina terminalis, median eminence, and walls of the third ventricle. In diverse areas throughout the brain--among them, the islands of Calleja, dentate gyrus of the hippocampal formation, lateral septal nucleus, and central amygdala--iron is found in association with the perikarya and neuronal processes of nerve cells. The overlapping distribution patterns of iron and gamma-aminobutyric acid, enkephalin, and luteinizing hormone-releasing hormone suggest that the distribution of iron is related to its association with the metabolism of one or more neurotransmitters or neuroactive compounds.