Mitotically active cells that generate neurons and astrocytes are present in multiple regions of the adult mouse hippocampus.

Previous studies of the adult hippocampus of rodents and primates have reported neuro- and gliogenesis restricted to the region of the dentate gyrus. In the present study, by employing a prolonged bromodeoxyuridine (BrdU) labeling protocol that attempts to account for cytokinetic changes as an animal ages, we have identified mitotically active cells in multiple regions of the hippocampus, especially in Ammon's horn, of the adult mouse. Immediately following the labeling period, the BrdU-labeled cells did not express known markers for neurons and astrocytes. Subsequent analysis at 3-24 weeks after labeling demonstrated BrdU-labeled neurons and glia in these regions of the hippocampus. Although neuro- and gliogenesis in the adult mammalian hippocampus have been reported previously, these results demonstrate that the phenomenon is not limited to the region of the dentate gyrus, but rather extends into Ammon's horn. Furthermore, it suggests that ongoing cell production, albeit discrete and limited in nature, may be widespread in the adult mammalian central nervous system.