Carbon dating nuclear testing
However, others have not corroborated these findings (20,22,23), or have found evidence for adult neurogenesis only under conditions of damage (21,25,31).
Methodological flaws have been proposed as explanations for putative false positive and false negative data on this subject (13,26).
As Paola Arlotta and Jeffrey Macklis from the Harvard Medical School write in an accompanying Cell perspective, historically, methods to label newborn cells, such as the use of tritium, bromodeoxyuridine (Brd U), or other halogenated urides, are toxic and cannot be used in humans, so the strategy developed by Spalding and colleagues “enables a more direct understanding of cell turnover, aging, and lifespan throughout the human body and those of other long-lived animals.” There is one small caveat, however.
Because atmospheric C14 levels are falling relatively quickly, the method will decrease in sensitivity with time, so the period during which it will be useful is limited and people born around the time of the nuclear tests will remain the most suited for study.
Cerebellar DNA was a few years older than the DNA in the cortex, which in turn was about 12 years older than the DNA in the small intestine.
This matches the pattern that would be expected when one considers the time taken for development of the human brain and the relatively rapid turnover of epithelial cells in the intestine.
Ever since it was shown that neurogenesis takes place in hippocampus of the adult brain (see ARF related news story), an outstanding question has been whether or not cortical neurons can be replenished in adults.
To tackle this question, the authors isolated neuronal and non-neuronal nuclei from cerebral cortex tissue samples.
Unlike many other macromolecules in a cell, DNA is chemically stable once laid down, so its C14 levels are not expected to change even if the DNA ages.Despite this rather large body of work, the findings were not well-received by the neuroscience community, and adult neurogenesis in the mammalian brain remained a matter of debate (17,27, 28).In the late 1990s, the use of a newer technique, bromodeoxyuridine (Brd U) labeling, in combination with confocal microscopy, led to new evidence in support of this phenomenon and the acceptance of adult neurogenesis in the olfactory bulb and the hippocampus (11,13,14,24).The authors suggest that previous reports of adult cortical neurogenesis might be technical artifacts.But they also state that their method is only sensitive enough to detect a minimum of 1 percent of newborn cells in a given cell population, so that leaves open the possibility that there is some, albeit a very small amount, of newborn cells in the cortex.