By providing zinc, metallothionein is able to regulate cell division, differentiation, metabolism, signal transduction, and transmission of genetic information. With the exception of calcium and magnesium, zinc is the most abundant cation in the brain. In addition, the distribution of zinc in the brain is nonuniform and its concentration is highest in the cerebellum, hippocampus, retina, and the pineal gland. Furthermore, the mammalian hippocampi not only contain high concentrations of zinc, but also exhibit subregional variation in this essential element, with its concentration highest in the hilar region and lowest in the fimbria. In addition to protein-bound zinc designated as the 'structural pool of zinc' and enzyme-bound © 1994 S. Karger AG, Basel