Adult neurogenesis has been firmly established in animals, but has been more difficult to fully assess in humans due to technical constraints. The following strategy should help overcome these problems. Due to the large extent of above ground atomic bomb testing from 1954 to 1963, there was a sudden and dramatic increase in the atmospheric level of radiocarbon (14C) globally. An exponential decline in the levels of 14C has been occurring over the past 40 years, with a t1/2 of 11 years. This provides a fortuitous window of opportunity to measure 14C levels with a high degree of resolution. 14C levels from tree ring data closely follow the atmospheric data curve, indicating that the atmospheric 14C effectively enters the biosphere via plant respiration. Since humans eat plants or eat animals which ate plants, the atmospheric14C level is mirrored in human tissue. Genomic DNA is stable after a cell's last division, so that the carbon within the DNA can be used as a date marker. After extracting nuclei from cells of a given brain region, the neuronal population was isolated using fluorescence activated cell sorting with an antibody to NeuN. 14C analysis was performed on samples by accelerator mass spectrometry. The 14C data was related to the atmospheric 14C levels, and the birth date of the particular cell population was directly determined. Postnatal cortical neurogenesis has been a highly controversial topic in primates, so we have chosen to examine the human cerebral cortex. We did not detect any postnatal neurogenesis within the occipital cortex. However, the non-neuronal population was found to be younger than the person's age, implying that some cellular turnover was occurring after birth. Other brain regions are being investigated now, as well as tissue from various pathological states.
Supported by: Human Frontiers Science Program. Work performed in part under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract W-7405-Eng-48.
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