Abstract

Human tissues have carbon-isotope ratios (13C/12C) that reflect dietary ratios. This observation has been used to determine the extent of metabolic turnover of DNA in cells of the adult human cerebellum (90 percent of which are neuronal). If adult human neuronal DNA were metabolically stable, its 13C/12C would reflect that in the maternal diet during fetal development as nearly all neurons are formed during maturation of the fetal brain and do not undergo cell division thereafter. The 13C/12C ratios in the food chains and body tissues of Europeans differ from corresponding American ratios by about 50 parts per million on the average. Therefore, turnover was studied by comparing 13C/12C ratios in cerebellar DNA of American-born Americans, European-born Americans, and European-born Europeans. The 13C/12C ratios in cerebellar DNA from European-born Americans were closer to 13C/12C ratios in cerebellar DNA from European-born Europeans than from American-born Americans, indicating that there was little or no turnover of neuronal DNA.

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