Retrospective birth dating of cells in humans
One of the most disputed claims is that of adult neurogenesis in the neocortex.
We and others have reported positive evidence for adult-born neurons in the neocortex of rat and monkey (7,9,13,15).
We use this strategy to determine the age of cells in the cortex of the adult human brain and show that whereas nonneuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region.
Testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope C in genomic DNA closely parallels atmospheric levels and can be used to establish the time point when the DNA was synthesized and cells were born.
; DRUID Henrik ; FRISEN Jonas ; The generation of cells in the human body has been difficult to study, and our understanding of cell turnover is limited.
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).
Here we show that adipocyte number is a major determinant for the fat mass in adults.
However, the number of fat cells stays constant in adulthood in lean and obese individuals, even after marked weight loss, indicating that the number of adipocytes is set during childhood and adolescence.
"I just needed to read a little to realize that this was a rather stupid thought.
The half-life of C-14 is almost 6000 years, which provides miserable resolution for the time spans we were interested in." But Frisén didn't give up on the idea completely.