From: J. R. Molloy (jr@shasta.com)
Date: Fri Oct 15 1999 - 10:45:45 MDT
Study: Brain Regenerates Cells
WASHINGTON (AP) _ Contradicting a long-held belief, researchers
say the brain is constantly churning out new neurons for its
learning and memory center, according to a study that could lead to
novel ways to treat brains damaged by injury or diseases such as
Alzheimer's.
In studies using macaque monkeys, the researchers at Princeton
University have for the first time traced the path followed by
neurons that are created in one part of the brain and then migrate
to the neocortex, the center of the mind's ability to reason and
think.
Once the new neurons arrive in the neocortex, they ``plug in''
and become a new part of the brain's central circuitry, said
Elizabeth Gould, head of a Princeton brain research team.
``This shows that there is a naturally regenerative mechanism''
in the mature brain, said Gould, the first author of a study
appearing Friday in the journal Science. ``If we can understand
better how it works, maybe we could use that to direct the
regeneration and repopulation of neurons in damaged areas of the
brain.''
For decades, brain researchers have thought that once neurons
were lost in the neocortex, they were not replaced and that their
function forever was gone. It was believed the brain contains so
many cells that this natural attrition had little effect until late
in life.
Now the new Princeton study, if confirmed by other researchers,
shows that the mature primate brain does produce new neurons that
incorporate themselves into the thinking center.
``This study could be very significant in terms of understanding
the range of mechanisms that the cortex has available to it for the
storage of information and for repair,'' said William T. Greenough,
director of neuroscience at the University of Illinois' Beckman
Institute. ``These data scream for a reanalysis of human brain
development.''
Earlier studies had given strong hints that the brain had an
unsuspected regenerative power. Some researchers had shown in rats
and monkeys that new cells were regenerated in the hippocampus, a
very primitive part of the brain that controls basic functions and
is the same in many animals. But it generally was believed that the
neocortex, with its storehouse of memories and advanced reasoning
power, was unique, stable and unchanging.
The neocortex reaches its most sophisticated level of
development in primates, including humans. Most experts believe the
structure and function of the neocortex is very similar in all
primates and that basic processes in the brains of monkeys are like
those in humans. But Greenough and others cautioned that Gould's
study needs to be confirmed in humans.
In the Princeton study, Gould and her team injected monkeys with
a compound called bromodeoxyuridine, or BRDU, that is taken up by
cells in the process of making new cells.
An examination just hours after the injection showed that the
cells in one area of the brain took up the BRDU, proving that the
cells were dividing and making immature neurons.
An examination a week after injection showed that the new
neurons had migrated, matured, and, in effect, had plugged
themselves into the neocortex, the thinking center of the brain.
Just how these new neurons function is not known, Gould said.
They could take up existing memories from the old neurons in the
neocortex, or they could be like a new floppy disk in a computer _
clean and ready to start storing new data. Gould said more research
is needed to understand exactly how the brain uses these new cells.
Gould said it is not known if Alzheimer's or other dementia
disorders are linked to a failure or a decline of this natural
neuron regeneration process. But at least now, she said, ``it is
possible to consider that, to ask that question. It had not even
been considered previously.''
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