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Nuclear neurons vs schizophrenia |
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Carbon-dating techniques are being used to determine the 'birth date' of neurons in the brain. |
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What does schizophrenia have to do with atom bomb testing from the 50s? A fluke of nuke history plus some top Aussie expertise might reveal startling new secrets about the brain.
Ever wondered how old you are? Most of you is a lot younger than you think. Most cells in the body are replaced regularly - skins cells every few weeks, muscle cells over the course of many years. But no-one knows for sure yet whether the brain creates new neurons during adult life. Answering that question could provide big insights into many brain disorders, including schizophrenia.
Until recently it's been difficult to measure how old a cell is, especially when you're talking about dating tiny samples from specific regions of the brain. ANSTO scientists have developed techniques that allow them to track down a cell's exact birthday using carbon-14, the same radioactive carbon isotope used to date archaeological artefacts.
"We're using a technique called Accelerator Mass Spectrometry (AMS), where you don't actually wait for the carbon-14 atoms to decay to detect them," Dr David Fink, a Project leader at ANSTO, explains. "All the carbon-14 atoms in the sample are 'dying' to decay, but why wait - instead, you can pick them out and count them. And if you know the initial concentration of carbon-14 in the atmosphere before the decay process started or just before the sample was disconnected from exchanging CO2 with the atmosphere, you can date it."
Above ground nuclear bomb testing in the 1950s and 1960s doubled the natural level of carbon-14 in the atmosphere. The 1963 nuclear test ban treaty allowed levels to gradually return to normal as oceans, plants and animals absorbed carbon-14 from the atmosphere. Atmospheric carbon-14 has have now returned almost to pre-test levels, but this temporary, artificial spike has provided a unique opportunity to date living tissues with great precision.
Because the level of bomb-produced carbon-14 has declined measurably year by year since the early sixties, it's possible to determine what year living tissue was formed by comparing the level of carbon-14 measured in its DNA to atmospheric levels recorded in tree rings over the last 40 years.
While there are many nuclear research labs around the world that can perform regular aspects of Accelerator Mass Spectrometry, ANSTO leads the world in the development of the sample processing and atom counting techniques needed to measure the microgram sample sizes involved in carbon dating human neurons.
This capability has caught the attention of brain researchers around the world, who are keen to utilise this expertise to answer some controversial questions about the brain.
Professor John McGrath, from the Queensland Centre for Mental Health Research, is interested in finding out if disturbances in the production of new neurons in parts of the brain are involved in schizophrenia. In partnership with other neurologists in Brisbane and Melbourne, he has formed a collaboration with the AMS team at ANSTO in order to determine whether cells in the hippocampus, an area of the brain known to shrink in size with the onset of schizophrenia, are a different age.
"If brain cells are dying in people with schizophrenia, then we would expect to see different cell birth dates compared to healthy brains," said John.
"There are two components we're particularly looking at, neuronal cells and glial cells. If glial cells are younger, that suggests they might be scavenging dead neurons. And if the birth dates of neurons in people with schizophrenia are different to healthy people, we can get an idea of whether adult neurogenesis plays a role" he explains.
Professor McGrath contacted the ANSTO team because David Fink's specialised AMS techniques allow carbon-14 dating of DNA from neurons and glial cells from post-mortem brain tissue.
Because the idea of adult neurogenesis is still a controversial one, it is an exciting and challenging area of brain research. If it pays off, this 1950s nuke fluke might give researchers fresh insights into the troubled brain. |
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Carbon-14 is a radioactive isotope of carbon that is formed naturally when cosmic-ray produced neutrons transform nitrogen atoms into carbon-14 in the upper atmosphere. About one in a trillion carbon atoms on earth are carbon-14, while the rest are stable carbon-12 and carbon-13 isotopes - that means modern wood has a ratio of 14C:12C of 1: 1 000 000 000 000 |
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Carbon-14 has a radioactive half-life of 5 730 years, and this long half-life makes it useful for dating once-living tissue. Plants take up carbon-14 containing carbon dioxide from the atmosphere through photosynthesis, and animals eat plants, giving them both a carbon-14 ratio equal to contemporary atmospheric levels. After they die, the carbon-14 slowly decays while the other carbon isotopes remain stable. The longer a living creature is dead, the less carbon-14 remains in its tissues, giving scientists a method of estimating when the organism died. |
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