2002-08-05 16:19:10 -0400
By Merritt McKinney
NEW YORK (Reuters Health)
New research on the brain's response to injury may point to ways to treat stroke as well as the mental impairment caused by radiation treatment for brain, head and neck cancer.
In one of two articles in the advance online edition of the journal Nature Medicine, scientists in Sweden report that the brain has a self-repair mechanism that aims to replace neurons destroyed by a stroke.
"We have discovered that after stroke, when many nerve cells die, the adult brain has a hitherto unknown capacity to repair itself," the study's lead author, Dr. Andreas Arvidsson of Lund University Hospital in Lund, told Reuters Health. He explained that the brain's own stem cells form new nerve cells, which then migrate to the damaged area to replace neurons that have died.
Arvidsson's team based the findings on rat experiments in which the researchers mimicked the damage of a stroke by blocking an artery that delivers blood to the brain.
"This research has revealed a mechanism for self-repair in the adult brain. We do not know, though, if the new nerve cells can work in the same way as those which have died," Arvidsson said.
In the rat experiments, the brain only replaced a handful of the lost neurons. Six weeks after the stroke-like injury, only 0.2% of dead neurons in the brain had been replaced. And what sort of effect these new neurons have on recovery after a stroke is still uncertain.
If these newly formed neurons do indeed take over the function of the killed cells and if this self-repair mechanism can be made more effective, "this could lead to new treatments to restore brain function after stroke," according to the Swedish researcher.
In a second study published in the same issue, a team led by Dr. Theo D. Palmer of Stanford University in California investigated whether certain side effects of radiation therapy may be caused by interference in the formation of new neurons in the brain.
Radiation therapy is used to treat several types of cancer, including cancer of the brain, head and neck, as well as other cancers that have spread into the central nervous system. Unfortunately, months to years after radiation treatment, many patients develop learning and memory problems.
Working with rats, Palmer's team found that radiation therapy has a dramatic effect on the ability of the hippocampus--a brain region involved in learning and memory--to regenerate neurons. The growth of new neurons is almost completely wiped out in this part of the brain after radiation. And the formation of cells that are precursors to neurons is reduced by 62%, according to the report.
Radiation "subtly changes the stem cell population" in the brain, Palmer told Reuters Health in an interview. He explained that the treatment seems to change the way the hippocampus, a brain region involved in memory, uses stem cells in the brain. The stem cells are still capable of forming neurons, but the brain "doesn't send the right signals to activate them," according to Palmer.
The Stanford researcher and his colleagues are continuing to study animals to see whether they can understand how changes in brain signaling prevent the growth of new neurons. There is some evidence that inflammation may interfere with these signals, raising the possibility of counteracting this effect with anti-inflammatory drugs, Palmer said. He cautioned, however, that it is too soon to know whether such a simple solution would work.
SOURCE: Nature Medicine advance online publication 2002
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