|
1 5 |
Brain cells die from old
age, injury and disease, but they are never replaced – or so people had long
believed. A group of American and Swedish researchers have discovered
that adult humans continue to grow new brain cells even in their sixties and
seventies. The finding may reveal ways to mend a brain ravaged by Alzheimer's
or Parkinson's diseases. |
|
10 15 |
Earlier studies had
already hinted that the brain's development does not halt in infancy.
About 30 years ago, scientists learned that neural cells divide and mature in
the hippocampus (one of the brain's key memory centers) of adult rats. In the
1980s, Fernando Nottebohm of Rockefeller University detected cell growth in
the brains of mature songbirds. Just this spring, Bruce McEwen, also of
Rockefeller, and Elizabeth Gould of Princeton University discovered that
adult marmoset monkeys also can produce new brain cells. At about the same
time, William Shankle, a neurologist at the University of California at
Irvine, reported cell growth in the brains of children under age six – a
strong indicator that humans shared the regenerative capabilities of the
other animals. |
|
20 |
Now there is no doubt
about it. Fred Gage and his colleagues at the Salk Institute for Biological
Studies in La Jolla, California, along with Peter Eriksson and others at
Sahlgrenska University Hospital in Goteborg, Sweden, studied five throat or
larynx cancer patients between the ages of 55 and 70. As described in the
November issue of Nature Medicine,
the researchers injected a chemical marker called bromodeoxyuridine, or BrdU,
into each patient three weeks to two years prior to death. BrdU is a protein
that attaches to the DNA of dividing cells; it is given to cancer
patients to track the progression of a malignant tumor, in which the cells
replicate rapidly. BrdU can also track the normal reproduction of cells in
other parts of the body, however. |
|
25 |
After the patients died,
Eriksson had sections of their brains removed and then examined them for
signs of the BrdU marker. He and his collaborators found that
primitive cells in the elderly patients' brains had divided and created new
neural cells, right up to the time of death. Each patient had produced
between 500 to 1,000 new brain cells a day. |
|
30 |
When researchers applied a
chemical stain that sticks only to mature cells, they saw that most of the
new cells failed to develop into neurons capable of forming connections with
other brain cells. But the newly divided cells did mature in one part of the brain
– the hippocampus. This disparity may exist because other areas of the
brain do not need to put these new cells to work as much as the hippocampus,
the part of the brain involved in learning and memory. |
|
35 40 |
The hippocampus, which
occupies one to two percent of the cortex, is one of the key areas where cell
loss occurs in Alzheimer's and Parkinson's patients. Researchers are
struggling to understand why these degenerative neuronal diseases happen even
as new cells are replacing old ones. The answer to this question
could lead to techniques for repairing and regenerating the injured brain.
But first scientists need to find ways of making new brain cells appear at
the right time in the right places. |
|
45 50 |
One promising way of
getting that to happen focuses on manipulating human stem cells – generalized
cells that can differentiate into many other kinds of cells. Recently,
scientists have made headlines by isolating embryonic stem cells, which are
so flexible that they can develop into any type of cell in the body;
therapeutic use of such cells lies far in the future, however. Two related
studies, both of which appeared in the November issue of Nature Biotechnology, report the isolation of a more specific
variety, neuronal stem cells. These cells are already predisposed to become
neurons and so could theoretically be used to mend damaged nerves or patch a
diseased part of the brain. The current work indicates that neuronal stem
cells can be grown in a petri dish and then successfully be incorporated into
living rat brains. |
|
55 |
Gage, the Salk Institute
neurobiologist who studied the cancer patients, has shown a much less
invasive way to promote brain cell growth. He took a group of slow-learning
mice, a strain known to learn more slowly than other mice, and exposed them
to a highly stimulating environment: toys, exercise apparatus, and intensive
social interaction with other mice. After as little as five weeks in the
enriched setting, the slow-learning mice moved through a maze 15 percent faster
than mice from the same litter raised in less stimulating environments. |
|
60 65 |
Autopsies indicated that
the stimulated mice had created twice as many new neurons in the hippocampus
as the mice in the control group. That finding suggests that even specially
tailored mental exercises might help Alzheimer's or Parkinson's patients
stimulate brain cell growth at faster rates than was observed in the cancer
patients. Whether the patient's brain would be able to utilize the new cells
is still unclear. "It's premature to say that the new cells are being
used for learning and memory," says Daniel Peterson of the Salk
Institute, Gates's co-author. "But given their location in the brain, it
seems reasonable to suggest that they do." |
Directions: Choose the best answer for the questions below.
A. Stimulating Mice
at the Salk Institute
B. Research Gives
Hope for Mending Ravaged Brains
C. The Living Brain
A. Studies in brain
cell growth may lead to mending damaged brains.
B. New brain cells
fail to develop into neurons.
C. Degenerative
neuronal diseases happen even as new cells replace old ones.
A. Discovering the
progression of malignant tumors.
B. Proving that
neural cells mature.
C. Studying the
creation of neural cells.
A. Marmoset monkeys
can produce new brain cells.
B. The hippocampus
generates new brain cells.
C. The brain
continues to develop after infancy.
A. Mental exercises
B. Therapeutic
manipulation of human stem cells
A. Paragraph 2
B. Paragraph 7
A. Twice as many
B. 1-2%
A. Hippocampus
B. Medulla
A. A chemical stain
has been applied to them.
B. They were able to
differentiate into embryonic stem cells.
A. Infant song birds
B. Cancer patients
A. Young
B. Living
A. Researchers have found
a cure for Alzheimer’s and Parkinson’s disease.
B. New techniques
for repairing and regenerating the injured brain have been found.
C.
The timing of when new brain cells appear is important in treating
neuronal diseases.
A. Alzheimer
patients
B. Neurologists at
the University of California
Directions: Choose the best synonym for the underlined word in
each sentence below.
A. regenerated
B. detected
A. clearly indicated
B. suggested
A. People working
jointly with Eriksson
B. People working
with the enemy
A. Difference
Directions: Choose the best answer for the questions below and
the next page.
A. Nature Medicine
B. BrdU
A. Which techniques
are considered the best by scientist
B. Why some brain
cells are dying while new ones are being generated