Ultrastructural changes in the frontal cortex of mice after irradiation: a study of dose-rate and field size effect

The dd-strain male mice were exposed to a dosage of 50 Gy high energy x-ray from a 6-MeV linear accelerator to elucidate the ultrastructural changes in the frontal cortex. After a single dose of whole body or head solely irradiation with a fixed rate of either 13.0 Gy/min. or 2.0 Gy/min., the frontal cortex was removed at different intervals and observed under electron microscope. The swelling of the astrocytic process and the damage of vasculoastrocytic units were observed with increasing degree following prolonged intervals of irradiation. Vacuolization, swelling of mitochondria, and the presence of electron dense particles in the cytoplasm of neuroglial cells were observed with these alterations being more prominent in the high dose-rate group. In addition, persistent degeneration was found in vasculoastrocytic units as well as neuroglial cells in this acute stage. Destruction of the presynaptic membrane or postsynaptic region, or an increase in number of the synaptic vesicles was not seen as time lapsed. Neurons were less vulnerable to radiation. Nerve fibers, moreover, seemed to be the most radioresistant at this dosage and high dose-rate irradiation.