Neutron irradiation of late mouse embryos (15-19 days) in utero.
Pregnant female C57B1/6 mice were irradiated with a single whole-body dose of 0.5 Gy neutrons. The F1 hybrid embryos were exposed to the neutrons in utero on Day 17 +/- 2 of gestation. 178/439 (40.6%) of the irradiated fetuses and 26/217 (12%) of the control mice died within 2 weeks after birth. In both irradiated and control mice, most deaths (95 and 77%, respectively) occurred within 3 days of birth: most animals in both groups died on Day 2. There was no significant difference in the number of living young born per litter (7.2) between the neutron-irradiated mothers and their unirradiated controls. The irradiated mice weighed significantly less than their controls. On the first day after birth, body weights of mice irradiated in utero averaged only 85% of control weights. Body weights did not reach control levels until 6 months after birth. Several organs were weighed at regular intervals in both irradiated and control mice. Spleens and thymus glands showed no significant differences between the two groups. The livers and kidneys of the irradiated mice weighed slightly less than their controls. The brain weight of 21-day-old neutron-irradiated mice was 30-35% less than control brains. The weight loss of the brain was not only a relative loss, but also an absolute one, based on brain weight/body weight ratios. Histological analysis of the central nervous system showed pycnotic nuclei, inhibition of mitosis in neuroblasts, and cell death in the irradiated brains. The weight reduction of the brain was not due to water loss. Our hypothesis is that the early mortality after birth is related to the killing of the radiation-sensitive neuroblasts. When newborn mice (1-7 days old) were irradiated in vivo with the same neutron dose of 0.5 Gy, neither the reduction in brain weight nor the early mortality was observed. The early deaths of the neutron-irradiated mouse embryos does not appear to be caused by either the hematological or the gastrointestinal radiation syndrome.
D000818:Animals; D001724:Birth Weight / Q000528:radiation effects; D001835:Body Weight / Q000528:radiation effects; D005260:Female; D005313:Fetal Death / Q000209:etiology; D005333:Fetus / Q000528:radiation effects*; D051379:Mice; D009502:Neutrons; D009929:Organ Size / Q000528:radiation effects; D011247:Pregnancy