Adult-generated neurons in the dentate gyrus send axonal projections to field CA(3) and are surrounded by synaptic vesicles

The subgranule zone of the dentate gyrus in rats has been shown to be proli ferative into adulthood and senescence. However, the connectivity of newly generated, identified neurons in the adult has not been definitively descri bed. In the present study, 9 weeks after a series of intraperitoneal inject ions of 5-bromo-2'-deoxyuridine (BrdU), animals received stereotaxic iontop horetic injections of Fluoro-Gold (FG) into field CAB. Three weeks after FG injections, sections were analyzed for BrdU immunoreactivity (proliferativ e label), FG retrograde label, and either calbindin-D-28k or synaptophysin immunohistochemistry. A large proportion (up to 44%) of BrdU-labeled cells in the dentate gyrus within regions of FG retrograde label incorporated FG. All of the doubly labeled (BrdU-FG) neurons also immunolabeled with the an tibody to calbindin-D-28k. Many doubly labeled (BrdU-FG) cells were also su rrounded in three planes by synaptophysin immunoreactivity. We conclude tha t newly generated neurons in the dentate gyrus have the correct immunohisto chemical profile, send appropriate axonal projections to field CA(3), and a re surrounded by profiles containing synaptic vesicle proteins. J. Comp. Ne urol. 406:449-460, 1999. (C) 1999 Wiley-Liss, Inc.