Ovaries of Chinese hamsters were irradiated with 1 Gy of X-rays on day 0, 4, 8 and 14 after birth, and the late effects on pachytene and resting dictyate oocytes, which had been proven to be radioresistant and to survive acute oocyte-killing, were studied in the progeny of the irradiated females. Thirty hours after mating, fertilized ova were collected and female pronuclear chromosomes were karyotyped. On day 18.5 of gestation, the number of corpora lutea and implantation sites were counted and the live and dead fetuses were examined phenotypically.
There was no increase of chromosome aberrations in female pronuclei of one-cell embryos of the irradiated groups. There was no significant difference in the incidences of pre and postimplantation deaths and of congenital malformations between the irradiated groups and the non-irradiated controls. These findings indicated clearly that oocytes at the pachytene and resting dictyate stages which had survived the acute oocyte-killing effects of X-rays were also free from late deleterious effects on genetic and developmental abilities.
The radiosensitivity of oocytes of the Chinese hamster was compared with that of the mouse with respect to chromosome aberrations, lethal mutations and congenital anomalies, and the difference between both species was discussed.

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Ninety girl students have been identified, who were 14-15 years old when exposed to the atomic bomb while at the Central Telephone Office in Hiroshima located at a distance of 550 meters from the hypocenter. The mortality rate of the students exposed on the second floor of the building was estimated to be 50.9% and those exposed on the first floor (ground level) 33.3%. Doses to the students exposed on the second floor were estimated from cytogenetic evidence to be around 6 Gy in the T65 Dose system or appear to be 4 Gy in the DS86 system. These data indicate that LD50 is around 4 Gy in these young females. Among 28 students who were confirmed to be alive in 1965 and followed to the end of 1988, six students had breast cancer, mostly of invasive ductal type carcinoma. The incidence of breast cancer in the adolescent group was very high, the relative risk being 23.1 with 95% confidence limits of 12.9 to 42.2.

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Age-related change in immunological activity was examined at 10 to 91 weeks following whole-body irradiation by determining the specific anti-tumor cell-mediated immunity in host mice induced and/or enhanced by local irradiation to transplanted tumor. Median survival time of the non-irradiated C3H/He female mice was 98.6 weeks while the median life-span of the mice exposed to two and four Gy of 250kVp X-rays at the age of 10-12 weeks was shortened by 14.9 and 23.4 weeks, respectively. The rate of tumor reduction within two weeks after local irradiation to tumor and the growth inhibitory activity of spleen cells from tumor irradiated mice were reduced in a dose-dependent manner when assessed 10 weeks after whole-body irradiation, but recovered to the near-complete level of the non-irradiated controls within a few months, then gradually decreased with normal aging. These results suggest that the age-dependent decline of this immunological activity appears earlier in the irradiated mice as a result of whole-body X-irradiation at a young age, suggesting accelerated aging of the immune system.

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The effect of static magnetic field applied during in vitro exposure to 4.9 MeV protons and 23 MeV alpha particles on the induction of chromosome aberrations in human peripheral blood lymphocytes was studied. The mean frequency of dicentrics in cells irradiated in magnetic field of a magnitude about one Tesla tended to be higher than that irradiated in the absence of magnetic field for both protons and alpha particles, and the analysis of dose-effect relationships indicated that for protons the magnetic field significantly affected the dose-effect relationship. The intercellular distribution of chromosome aberrations, one of the measures of radiation quality, was not significantly influenced by the magnetic field.

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Radioprotective effect of a Shigoka extract was studied on split-dose irradiation. Mice were exposed to 4 Gy × 4 or 3 Gy × 4 for examining survival ratio or hemogram, respectively. The extract was i.p. injected immediately after each irradiation. The extract significantly (p<0.001) increased the survival ratio, and it increased leukocyte count within the period of the death (days 2-12 after the final exposure). Cerebral hemorrhage after 4 Gy × 4 was diminished by the extract. Recovery of leukocytogenesis seems much more important for survival at split-dose irradiation than at single acute irradiation.

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The behavioral and physiological effects of 10 Gray (Gy) LINAC electrons in male Swiss-Webster mice were followed for 12 days postirradiation (PR). In Experiment 1, aggressive behavior was assessed in irradiated or sham-irradiated resident mice using a resident-intruder paradigm. Aggressive offensive behavior in the irradiated residents was significantly decreased beginning 2 to 5 days PR, and remained suppressed. Defensive behavior in the nonirradiated intruders was decreased significantly by day 5 PR. In Experiment 2, spontaneous locomotor activity was monitored. Ambulation of irradiated mice was significantly depressed from day 5 PR on, while rearing was affected as early as day 2 PR and remained suppressed. Body weights of irradiated animals were significantly decreased by 5 days PR. In Experiment 3, blood parameters were examined. Compared to sham-irradiated controls, leukocytes, erythrocytes, and hematocrit of irradiated mice were reduced significantly beginning on day 1 PR and remained suppressed, while platelets and hemoglobin were decreased beginning day 2 PR. These results demonstrate that 10 Gy of high-energy electrons results in earlier behavioral deficits than has been observed previously with the same dose of gamma photons.

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