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.











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.










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.





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.






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.







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.











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.








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.









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.


1        A good title for this article might be

A.     Stimulating Mice at the Salk Institute

B.     Research Gives Hope for Mending Ravaged Brains

C.     The Living Brain

2        The thesis of the article is

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.

3        Researchers in California concentrated on

A.     Discovering the progression of malignant tumors.

B.     Proving that neural cells mature.

C.     Studying the creation of neural cells.

4        The main idea of paragraph 2 is

A.     Marmoset monkeys can produce new brain cells.

B.     The hippocampus generates new brain cells.

C.     The brain continues to develop after infancy.


5        Research indicates that ________ does not help stimulate brain cell growth.

A.     Mental exercises

B.     Therapeutic manipulation of human stem cells

C.     Stimulating environments


6        Which paragraph suggests that genetic engineering of brain cells may have therapeutic uses?

A.     Paragraph 2

B.     Paragraph 7

C.     Paragraph 9


7        Research on the brain indicates that ________ new neurons can be generated by non-invasive methods.

A.     Twice as many

B.     1-2%

C.     15%

8        New neural cells mature in which part of the brain?

A.     Hippocampus

B.     Medulla

C.     Cerebellum

9        Researchers believe that some new cells mature because

A.     A chemical stain has been applied to them.

B.     They were able to differentiate into embryonic stem cells.

C.     Other parts of the brain need them

10    Research involving _________ indicates that cells growth can be promoted.

A.     Infant song birds

B.     Cancer patients

C.     Rats

11    Gage and Eriksson’s research examined the brains of people who were _____.

A.     Young

B.     Living

C.     Dead

12    The main idea of paragraph 6 is _____.

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.

13    This article was most likely written for

A.     Alzheimer patients

B.     Neurologists at the University of California

C.     The general public

14    Research on the brain indicates that new neurons can be generated by non-invasive methods.

A.     True

B.     False

Directions: Choose the best synonym for the underlined word in each sentence below.

15    In line 3, “discovered” means

A.     regenerated

B.     detected

C.     thought

16    In line 6, “hinted” means

A.     clearly indicated

B.     suggested

C.     concluded

17    In line 26, “collaborators” means

A.     People working jointly with Eriksson

B.     People working with the enemy

C.     People helping elderly patients

18    In line 32, “disparity” does not mean

A.     Difference

B.     Variation

C.     Hypothesis

Directions: Choose the best answer for the questions below and the next page.

19     “It” in line 22 refers to

A.     Nature Medicine

B.     BrdU

C.     DNA

20     “This question” in line 38 refers to

A.     Which techniques are considered the best by scientist

B.     Why some brain cells are dying while new ones are being generated

C.     Which scientists are considered to be the best