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Abstract: Previously, it has been demonstrated that an "adaptive response" that includes the prevention, repair, and removal of oxidative damage can be evoked by radiation at dose rates substantially lower than those at which risks have been observed. The exact pathogenic mechanism of prion diseases is unknown, but circumstantial evidence suggests that oxidative stress plays a central role. Exposure of prion-infected mice to four 500mGy/fraction doses of 60Co γ-radiation administered every other day at a low dose rate (0.5mGy/min) starting at 2days before infection, 7days postinfection (dpi), or 50dpi significantly prolonged the survival of infected mice. The 500-mGy radiation treatments started at 50dpi also significantly prolonged the symptom-free period of the disease and caused a significant delay in the rise of the 8-hydroxydeoxyguanosine concentration observed in the urine of nonirradiated infected mice at 98dpi. The duration of the reduction in oxidative stress achieved by the radiation treatments was similar in length to the prolonged survival of the irradiated mice. This suggests that the adaptive response induced by low-dose whole-body radiation treatments prolongs the survival of prion-infected mice by reducing oxidative stress. [ABSTRACT FROM AUTHOR]