Irradiation injury to the developing nervous system: mechanisms of neuronal injury.

Undifferentiated neural cells in the developing brain are particularly vulnerable to irradiation and easily involved in cell death. We investigated in mice cytological features of radiation-induced death of neuron-precursor cells and their high sensitivity. The acute cell injury in the embryonic telencephalon by doses as low as 0.1 Gy was not reversed up to 6 hours and injured cells expressed apoptotic death which began at 2 hours after exposure and peaked at 6-9 hours. Radiation-induced cell death in the cerebellar -external granular layer of newborn mice exposed to 0.24 Gy was suppressed completely by cycloheximide, a protein synthesis inhibitor. The high incidence of radiation-induced apoptosis of the telencephalic ventricular cells observed at the beginning of cortical neuron production could be attributed to the emergence of radiosensitive G1phase cells at this stage. One of the significant factors determining the period of high sensitivity for radiation-induced apoptosis could be a certain initial phase of chemical cytodifferentiation prior to their actual morphological differentiation.