An ultrastructural characterization of the newly generated cells in the adult monkey dentate gyrus.

Recent studies of adult neurogenesis in the hippocampus have focused on the maturational sequence and on the identification of the neural stem cell in the adult brain. Ultrastructural verification of cell type and marker expression has become increasingly important in this research, yet no standards exist for the identification of adult generated cells in the hippocampus. In this study, six adult rhesus monkeys were used, four of which were given an injection of the DNA-synthesis phase marker bromodeoxyuridine (BrdU) and perfused 2 days, 3 weeks, or 6 weeks later. The ultrastructural features of BrdU labeled cells in the dentate gyrus were determined. The characteristics of the different types of BrdU labeled cells were then used to find similar, but unlabeled, immature cells in tissue routinely prepared for electron microscopy. This enabled optimal characterization of the ultrastructural features of the newly generated cells. The results demonstrate that immature neurons, immature astrocytes, and oligodendrocyte progenitor cells can be reliably distinguished by ultrastructural features, without immunohistochemical processing. (c) 2007 Wiley-Liss, Inc.