We have studied, by histological methods, cytological progression, frequency and distribution of apoptosis in the external granular layer of the cerebellum after whole-body irradiation of 14-day-old rats by gamma-rays from 60 Co. After acute exposure to 0.25, 0.5, 1.5 and 3 Gy (18 cGy/min), the duration of the apoptotic process gradually increased with dose from 6-9 h after 0.25 Gy, to > 24 h after 3 Gy. Up to 1 Gy, maximal frequency was found 6 h after exposures, and at this postirradiation time a linear increase in apoptosis with dose was observed. No effect of dose-rate on apoptosis induction could be demonstrated 6 h after delivering 1 Gy at dose-rates from 2.2 to 18 cGy/min. Continuous irradiation at 1.8 cGy/h induced a gradual increase of apoptosis that remained at a plateau value of about 3% from 15 to 29 h (controls 0.12%, SD = 0.07) and then gradually decreased to 1% at 53 h. At this time the mitotic index was similar to that measured in controls. Apoptosis occurring 3 h after acute irradiation, confined to proliferative cells, was only observed for doses of 1.5 and 3 Gy.

Rats were exposed to 2 ppm ozone for 5 hours to increase micronuclei formation in the different lung compartments one week after local irradiation. Animals were exposed to either radon and its progeny (300 and 1000 WLM) or local lung external irradiation using gamma rays from cobalt-60 (7.5 Gy).Animals were administered 5-bromo 2'deoxyuridine 18 and 12 hours before to label post replicative cells. They were killed 36, 48 and 60 hours after the beginning of the ozone exposures. Alveolar macrophages (AM) were recovered by lavage of the left lobe and the right lobes were fixed for histological studies using confocal microscopy.Micronuclei measurements in AM did provide only mean dose estimate to the deep lung. Histological observations showed a nearly homogeneous irradiation by gamma rays whereas, heterogeneous irradiation seemed to occur after radon exposure with a gradual dose increase from alveoli to bronchi.