Naturally occurring cell death in the cerebral cortex and subcortical white matter is increased after X-irradiation, and this process is curbed with cycloheximide, an inhibitor of protein synthesis. However, cycloheximide alone increases cell death during development, and this effect is dose-dependent. This suggests that, in both normal and experimentally-induced cortical cell death during development, different proteins are activated or inhibited, depending on the agent, the time of its application, and the previous metabolic or functional state of the cell.