APOPTOTIC CELL-DEATH OCCURS IN HIPPOCAMPAL-NEURONS CULTURED IN A HIGH OXYGEN ATMOSPHERE

When embryonic rat hippocampal neurons were cultured in a 50% oxygen atmosphere, neurons gradually died after 20 h in culture. This death pattern was found to be mediated by an intracellular active death program, so called apoptosis, as follows: (1) Cycloheximide and actinomycin-D, protein and RNA synthesis inhibitors, respectively, prevented cell death, indicating that cell death required new protein biosynthesis. (2) DNA fragmentation (called a ''DNA ladder''), a specific biochemical marker of apoptosis, was detected during the course of cell death. (3) Depolarization with high K+ medium (26-50 mM) prevented cell death. This effect was suppressed by some dihydropyridine derivatives, L-type Ca channel blockers, such as nifedipine and nicardipine. These results indicate that increased levels of oxygen activate an apoptotic mechanism in the cultured hippocampal neurons, and suggest that neuronal activity may protect the neurons from oxygen-induced apoptosis.