You may not be able to relive your youth, but part of your
brain can. Johns Hopkins researchers have found that newly
made nerves in an adult brain's learning center experience
a one-month period when they are just as active as the
nerves in a developing child. The study, appearing in the
May 24 issue of Neuron, suggests that new adult
nerves have a deeper role than simply replacing dead
ones.
The researchers tracked the chemical signals received
by newly made nerve cells in the adult mouse hippocampus, a
brain structure dedicated to learning and memory, by
injecting virus particles to light up nerve progenitor
cells. Any freshly made nerves glowed green and became
permanently marked for later identification.
"In essence, we stamped a birth date on new adult
nerve cells," said Hongjun Song, assistant professor of
neurology at
Johns Hopkins' Institute
for Cell Engineering. "The brief heightened activity we
saw may help explain how adults continue to adapt to new
experiences even though adult brains are more hardwired
than children's brains." The slow and gradual addition of
new nerve cells may be like a fine-tuning system, allowing
adults to incorporate fresh information without altering
basic brain circuitry.
When they looked at brains from these mice, the
researchers noticed that hippocampal nerves that were
between 1 month and 2 months old could dramatically
increase or decrease the amount of signaling chemicals they
receive from neighboring nerves. This ability of nerves to
modulate their chemical inputs, known as synaptic
plasticity, is especially high in developing brains but
tends to become less intense in adults.
While the exact contribution that adult-born neurons
make to overall learning and memory remains mysterious,
Song noted that these results are promising for any future
nerve stem cell therapy. "If we can implant or stimulate
these adult stem cells in damaged areas, it's possible we
can do more than fill in lost nerve connections," he said.
"We might be able to rejuvenate an aging brain."
The research was funded by the National Institutes of
Health, the Whitehall Foundation, a Sloan Scholarship, a
Klingenstein Fellowship Award, a McKnight Scholar Award,
the Rett Syndrome Research Foundation and the American
Heart Association.
Authors on the paper are Chih-hao Yang and Kuei-sen
Hsu, both of National Cheng Kung University; and Shaoyo Ge,
Guo-li Ming and Song, all of Johns Hopkins.
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