Study on mice alters what we've always thought
By Nicolle Charbonneau
THURSDAY, July 6 (HealthSCOUT) -- Bruise your arm, break your leg or skin your knee, and your body eventually will repair the wound. But injure your brain, and there's little your body can do about it.
Or at least that's always been the prevailing wisdom.
Now, new research suggests that, at least in mice, an adult brain can grow new cells.
This raises hopes that someday new therapies will be developed to treat neurological diseases or brain traumas in people.
The research, by neuroscientists at Harvard Medical School, demonstrates for the first time that it's possible to trigger stem cells -- in this case, neural precursor cells -- to become mature neurons after other nerve cells have died. The findings appear in a recent issue of the journal Nature.
Building on previous research showing that transplanted precursor cells can be guided to form new neurons, the researchers theorized that bringing the molecular signals to where these precursors lie in the brain might be enough to activate them into becoming mature neurons.
Led by senior investigator Dr. Jeffrey Macklis, the researchers triggered apoptosis, or cell death, in a group of brain cells in the cerebral cortices of laboratory mice. Over the next 28 weeks, they discovered that the neural precursor cells migrated to the cortical area, matured into the same type of neurons that had been damaged and reached out to connect with distant brain cells.
"We're very excited about this result," says Macklis, an associate professor of neurology and neuroscience. "These experiments show very clearly that there exists a sequence and combination of control signals that can turn these endogenous precursors into mature neurons of the cerebral cortex. Now, the hard work is to uncover what that combination and sequence of molecules is."
"We may in the future be able to activate these cells toward brain repair from the inside out," Macklis says.
Still, there's no evidence yet that these cells actually took over the function of the dead brain cells, and this particular study can't tell researchers why, if it's capable of doing so, the brain doesn't automatically repair brain injuries or the damage of degenerative diseases.
Answering these questions, and learning how to activate the precursors without having to intentionally trigger cell death, are the challenges that now face researchers. But Macklis stresses that it may be 10 to 30 years before practical applications become available.
"These are the beginning and very basic science experiments that give a lot of hope and optimism, but are not ready for clinical application now," he says.
Dr. Anders Bjõrklund, a neuroscience professor at Lund University in Sweden, points out that the Harvard study involved a type of brain lesion that leaves the tissue architecture intact, which may trigger a response similar to what's seen during development. Plus, he adds, there are only a small number of these precursor cells. "This tiny number is unlikely to have any functional effect," he says.
"This is an intriguing observation that opens up interesting questions," says Bjõrklund. "But we don't really know the implications of it. There's a long way to go."
What To Do
The Brain Injury Association (http://www.biausa.org/) offers information and advocacy for people with brain injuries.
To find out more about structures in the brain, visit the Web site for the Whole Brain Atlas (http://www.med.harvard.edu/AANLIB/home.html). Or, check out this primer on stem cells from the National Institutes of Health (http://www.nih.gov/news/stemcell/primer.htm).
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