By: Anne M. Stark
Enhanced photograph of human brain cells under microscopic magnification.
It seems peculiar that looking at the atmospheric content of carbon before and after above ground nuclear testing could tell us something about the age of our brain cells.
But that’s exactly what Bruce Buchholz of the Laboratory’s Center for Accelerator Mass Spectrometry (CAMS) and colleagues from the Karolinska Institute in Sweden did.
The researchers applied carbon dating to DNA to confirm that cells in the brain live longer than most others. Carbon dating is typically used in archeology and paleontology to date the age of artifacts. However, in this application which appeared in the July 15 issue of the magazine Cell, the scientists used the pulse of radiocarbon to pinpoint individual cell’s birth dates to within two years.
Radiocarbon or carbon-14 is naturally produced by cosmic ray interactions with air and is present at low levels in the atmosphere and food. Its concentration remained relatively constant during the past 4,000 years, but atmospheric testing of nuclear weapons from 1950-1963 produced a global pulse in the amount of radiocarbon in the atmosphere, Buchholz said.
Traditional carbon dating uses the ratio of radiocarbon to normal carbon in an organism to date its age. Previous research showed that while an animal or plant lives, eats and breathes, the ratio of normal carbon to radioactive will be equal to that found in the atmosphere. When it dies, the radiocarbon concentration decreases as it decays since new carbon is not replacing it.
Cells in the body, such as red blood cells, are often regenerating. But DNA is a material that doesn’t exchange carbon after cell division, so it serves as a time capsule for carbon and in turn can serve as a way to pinpoint the birth dates of individual cells.
“But it wasn’t clear whether we create neurons after birth,” Buchholz said.
Using CAMS, Buchholz dated DNA from different kinds of cells in the body. The conclusion when it comes to certain brain cells was “When it comes to neurons, what you’re born with is what you’ve got for life,” he said.
Using research cadavers, the scientists dated neurons in people born prior to 1950 and those born after 1963 (the year that above ground nuclear testing ended). What they found was that the neurons in those born prior to 1950 showed no spike in radioactive carbon from the atmospheric testing.
“There was no bomb carbon in their neurons,” Buchholz said. “But those born after 1963 had levels that were consistent with what was in the atmosphere at the time of their birth. The conclusion was that there is no neurogenesis occurring in the cortex after birth.”
Research is supported by the NIH National Resource for Biomedical Accelerator Mass Spectrometry at CAMS and by the Human Frontier Science Program (HFSP). HFSP supports multi-national, multi-discipline collaborations and is funded by Japan, the European Union, Germany, France, Italy, the United Kingdom, Switzerland, Canada, the National Institutes of Health, and the National Science Foundation.
Buchholz said further research will delve into other brain regions to determine the origin of neurodegenerative diseases.
“This is another opportunity to help solve a problem they (Karolinska researchers) couldn’t get at other than using AMS,” Buchholz said.