Strain‐Specific effects of chronic prenatal irradiation in mice

Female mice of the BALB/c and C57BL/6 strains were exposed to ionizing radiation 60Co at a rate of 89 R/hr for 15 days of the gestation period (total dose 320 R). Control animals were sham‐irradiated and the offspring produced were tested at 30 or 105 days of age for open‐field behavior and avoidance conditioning. The magnitude of the prenatal irradiation effect was found to be both strain and sex specific: the open‐field activity of irradiated BALB/c mice of both sexes and irradiated C57BL/6 males was significantly higher than that of control animals; the avoidance conditioning of irradiated BALB/c males was greater than that of any other group. Strain specificity was also seen in the viability and morphology of offspring as well as in maternal reproductivity, suggesting that irradiation may have both direct and maternally‐mediated effects on fetal development.