Association of iron-containing astrocytes with dopaminergic neurons of the arcuate nucleus

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Abstract
Specialized astrocytes, identified by cytoplasmic granules that are electron-dense and vividly stained by toluidine blue due to the presence in the granules of SH molecules and molecules of iron, have long been known to be present within the arcuate nucleus of the hypothalamus. Their function, however, is obscure. To determine whether or not these specialized astrocytes are in contact with dopaminergic neurons, rat brain sections were stained to detect tyrosine hydroxylase (TH) immunoreactive neurons by immunocytochemistry and were examined by both light and electron microscopy. Iron-rich astrocytes were located in the same general portion of the arcuate nucleus as were TH+ neurons, and most appeared closely associated with TH + structures (somas, dendrites, and fibers) at the light-microscopic level. At the ultrastructural level, close contact between TH + neurons and processes of iron-rich glia was confirmed. This unique anatomical association suggests a functional relationship between the two cell types that may be related to unusual histochemical features of both cell types and/or to the location of these cells in an area with a highly permeable blood-brain barrier.