Hypoxia increases BrdU incorporation in cerebral cortical cultures. (a) Cortical cultures were stained with Ab’s against the indicated markers and counterstained with the nuclear stain DAPI (blue). (b) The percentage of cells expressing each marker is shown, indicating that most cells at this stage in culture are immature neurons. (c) Cultures were treated with BrdU and deprived of oxygen for up to 24 hours, and BrdU was visualized by immunocytochemistry and quantified by cell counting. (d) The hypoxia-induced increase in BrdU incorporation was reduced by the cell cycle inhibitors aphidicolin, cytosine arabinoside, and hydroxyurea. Data shown are representative fields (a) or mean ± SEM, n = 3 (b–d).