Low Level of u.v.-Induced Unscheduled DNA Synthesis in Postmitotic Brain Cells of Hamsters: Possible Relevance to Aging

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DNA repair was measured in brain and liver cells in terms of their ability to undergo unscheduled DNA synthesis (UDS) in response to u.v. radiation. The proportion of brain cells exhibiting u.v.-induced UDS decreased from 13.4 to 4.2% as hamsters aged from 4-8 days to 38-57 days and then remained at this low level at least to day 551, which is approx. 2 3 of the maximum life span of this strain of hamster. Repair synthesis in brain cells during this long period was approx. 9.6% of that found in adult lung cells, 22.4% of that found in adult kidney cells and, at most, 50% of that in adult liver cells. This suggests that the postmitotic brain has a low repair capacity compared to other tissues. If this rate of repair is less than the rate at which endogenous DNA damage occurs, then such damage would accumulate and perhaps contribute significantly to normal aging.