Glial immunoreactivity for metallothionein in the rat brain

A series of frozen and vibratome coronal sections of the rat brain were examined by immunocytochemistry for the presence of a cysteine‐rich metal binding protein, metallothionein (MT). Astrocytes throughout the brain and brainstem stained positively for MT; neurons and oligodendroglia were unstained. Ependymal cells and tanycyte processes in the hypothalamus were also immunoreactive, along with a narrow zone of immunopositivity along the margins of the area postrema. Gomori‐positive astrocytes in the hypothalamus, identifiable by toluidine blue staining, metal‐containing cytoplasmic granules, represented a subset of MT‐positive astrocytes that may be involved in reactions to blood‐borne metal compounds that penetrate into circumventricular organs of the brain.