Interaction Effects of Environmental Stress and Deuteron Irradiation of The Brain on Mortality and Longevity of C57BL/10 Mice. ∗

Summary

Observations were made on differences in mortality and longevity among 4 experimental subgroups of 6 successive cross-sectional age samples of non-irradiated and brain-irradiated C57BL/10 mice during their entire life span. The 4 subgroups of each main cross-sectional age sample included 1) steady-state controls, 2) temperature stress, 3) electric shock stress, and 4) combined temperature and electric shock stress. Irradiation of the brain was performed with a 20 Mev deuteron beam delivered at a dose rate of 383 rad/sec through an anti-Bragg wheel by the 60 inch Brookhaven cyclotron. The mice received a dose of 500 rads over the dorsal surface of the brain covering an area of 9 × 5 mm to a depth of 2.5 mm. All irradiated mice were then assigned to 4 cross-sectional groups and exposed to the same 4 experimental stress treatments in the 2 environmental chambers in accordance with the experimental design.

There was a highly significant decrease in the longevity of the brain irradiated mice. Contrary to expectation, stress resulted in a significant decrease in mortality and a longer life span of both the non-irradiated and brain-irradiated mice. The significant difference in mortality and longevity between males and females observed in the non-irradiated mice was not found in the brain irradiated mice. The significantly lower mortality and longer life span of stressed mice whose life expectancy had been reduced significantly by brain irradiation provided compelling evidence against some current “stress” theories of biological aging. In summary, environmental stress did not accelerate the aging of non-irradiated or brain-irradiated mice. From the non-additive interaction effects of environmental stress and deuteron irradiation of the brain on mortality and longevity of C57BL/10 mice, it was concluded that stress induced decreases in mortality and a longer life span were consistent with evolutionary theories of natural selection and survival of multicellular populations under fluctuating environmental conditions.