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Stress Puts Brake on New Neurons
High levels of stress hormones inhibit neurons from regenerating in one part
of the brain. The discovery, reported in the October Nature Neuroscience,
could potentially lead to drugs that prevent or restore memory loss.
For years, researchers thought that neurons in the human brain form
only before birth. But about a year ago came the finding that neurons in a
part of the hippocampus responsible for memory, called the dentate gyrus,
continue to reproduce in adulthood (ScienceNOW, 29 October 1998). It was
unclear, however, whether these neurons actually work. Researchers also
discovered that this regeneration drops dramatically in the elderly.
Researchers wondered whether this lack of regeneration could put the
brakes on memory in old age. Because elderly people with memory loss due to
normal aging have higher levels of stress hormones called corticosteroids,
neuroscientists Heather Cameron and Ronald McKay, both at that National
Institute of Neurological Disorders and Stroke in Bethesda, Maryland, also
wondered whether these steroids might be influencing neurons.
To find out, the researchers removed the adrenal glands--the organ
that makes corticosteroids--from 4-year-old rats, which are at the very end
of their life-span. Like people, old rats show a decline in neuron
regeneration. One week and 2 weeks after the operation, the researchers
injected a chemical marker called bromodeoxyuridine, which labels the DNA of
dividing cells. Four weeks after the surgery, they killed the rats and
counted the marked cells in the dentate gyrus. Rats deprived of their
adrenal glands had three times as many new neurons in the dentate gyrus as
control rats. McKay next plans to check whether these new neurons are hooked
up to other neurons.
"This is very exciting," says Elizabeth Gould, a psychologist at
Princeton University. "If people confirm that there is a strong correlation
between elevated corticosteroid levels and memory problems," McKay adds,
"then there will be some real interest in producing drugs to manipulate
these steroids."
--Kate O'Rourke
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http://www.academicpress.com/inscight/10041999/grapha.htm
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John
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