"The brain is very resilient," said Bruce McEwen, head of the neuroendocrinology laboratory at Rockefeller University in New York City. "Give it a chance and it will make every effort to repair itself.

" McEwen was scheduled to present his research Friday to the annual convention of the American Psychological Association, in New Orleans.

 McEwen said his research has found even more signs that repeated stress actually causes neurons in the brain to shrink, at least in rats.

 Earlier research showed that the neurons shrink in the hippocampus, and that seems to impair memory in response to stress, he said. More recent research suggests that the same thing happens in the brain region called the prefrontal cortex, which is crucial for decision-making and attention, he said.

When stressed, rats lose what McEwen calls "mental flexibility" -- "the ability of the animal to use a familiar set of cues in a different way when the location of a food reward is shifted.

" What does this mean for humans? "Stress hormones act on the brain to remodel it and change it," McEwen said. "The brain of a stressed animal or human being is a different brain. It has different capacities, and it may be more anxious and have less ability to pay attention or learn or remember.

" But there are potential fixes for those with mental stress, McEwen said. "A combination of psychotherapy, cognitive behavior therapy and pharmaceuticals could actually change the brain and restore it more or less to normal," he said.

 Exercise is another potential booster, he said, adding, "there's growing evidence that exercise has very powerful effects.

" Outside the brain, stress can wreak havoc on the immune system, according to another study to be presented at the meeting.

 Research suggests that stress can shorten the chunks of DNA at the tips of chromosomes in cells, making it harder for them to work properly, according to the researcher, Elissa Epel, a psychologist at the University of California, San Francisco. The bits of DNA "are like the plastic caps on the ends of our shoelaces. They prevent the ends from fraying," she said.

 What does this mean? "We examined healthy women and found that psychological stress was related to shortened" tips, she said. As a result, the immune system of the stressed-out women is apparently aging at a faster rate.

The treatments for this problem are what you might expect. "Everything we already know about fighting off chronic disease, like getting sufficient sleep, staying active throughout life, and having a healthy diet" may stave off premature aging of the immune system, too, Epel said.

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