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Web address:
http://www.sciencedaily.com/releases/2007/09/
070917173153.htm
Cell Death In Sparrow Brains May Provide Clues In Age-related Human Diseases
ScienceDaily (Sep. 20, 2007) — A remarkable change takes place in the brains of
tiny songbirds every year, and some day the mechanism controlling that change
may help researchers develop treatments for age-related degenerative diseases
of the brain such as Parkinson's and dementia.
Writing in the Proceedings of the National Academy of Sciences, researchers
from the University of Washington and the University of California, Berkeley,
report a striking shrinkage in the size of the brain regions that control
singing behavior of Gambel's white-crowned sparrows.
This transformation is triggered by the withdrawal of testosterone, a naturally
occurring steroid hormone, and is apparent within 12 hours. The study is the
first to report such rapid regression of brain nuclei caused by the withdrawal
of a hormone and a change in daylight conditions in adult animals.
"The changes are substantial," said Christopher Thompson, lead author of the
study and a UW doctoral student in neurobiology and behavior. "First, the
volume of a song-control region called the HVC collapses 12 hours after
testosterone is removed from circulation. Then, by four days, thousands of HVC
neurons are lost. We have good reason to believe that they are killed by a cell
suicide program call apoptosis."
Co-authors of the study are Eliot Brenowitz, a UW professor of psychology and
biology, and George Bentley, a former UW postdoctoral researcher who is now a
UC Berkeley assistant professor of integrative biology.
The research mimicked the natural seasonal changes that occur in the brains of
the sparrows. Their song-control regions expand in the spring and summer
leading up to the breeding season, as they use songs to establish territories
and attract mates in Alaska. Later in the summer, as the birds get ready to
migrate back to California, the same brain regions shrink.
"We've seen seasonal changes in the brains of fish, reptiles, amphibians, birds
and mammals such as gerbils, mice, and even in humans," said Brenowitz.
"However, the magnitude of changes in birds far exceeds that seen in other
animals."
To better understand what happens in the sparrows' brain, the researchers
received federal and state permits to capture 25 of the migrating male birds in
Eastern Washington. Next, they housed the birds for 12 weeks before exposing
them to 20 days of long-day conditions comparable to the natural lighting the
sparrows would experience in Alaska during the breeding season. The birds were
also implanted with testosterone.
At the end of 20 days, six of the birds were euthanized and the remaining 19
were castrated and testosterone implants were removed so there would not be any
circulating testosterone in their systems. After 12 hours five more birds were
euthanized and the remainder were euthanized at 2, 4, 7 and 20 days. These
procedures were done with the approval of the UW's Institutional Animal Care
and Use Committee and the National Institute of Mental Health. The latter
funded the research.
The researchers found that the size of the HVC region decreased 22 percent
within 12 hours after the withdrawal of testosterone and that the number of
neurons in this song-control region fell by 26 percent after four days. In
addition, the size of two other song-control regions called Area X and the RA
significantly regressed after 7 and 20 days, respectively.
Thompson said there are a number of potential medical implications relating to
age-related degenerative diseases and conditions marked by declining mental
abilities from this study.
"Having an animal model system with such robust neurodegeneration could be very
useful in uncovering the mechanisms that underlie these kinds of diseases," he
said. "We will be looking at the molecular mechanisms of what happens when
testosterone is removed. As men age, circulating levels of testosterone
decrease, and other researchers have shown that this decline may contribute to
cognitive impairment, brain disorders and neuron death."
Brenowitz added: "There is no reason to think that these processes are
restricted to birds. They are very similar to what happens in some mammals.
This study shows that regions of the brain that are hormonally sensitive are
going to regress without testosterone. The flip side is that hormones such as
testosterone protect neurons, so perhaps some form of hormone therapy may
provide protection. Steroids such as testosterone are very potent and have wide
implications for effects on the brain."
Adapted from materials provided by University of Washington.
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
APA
MLA
University of Washington (2007, September 20). Cell Death In Sparrow Brains May
Provide Clues In Age-related Human Diseases. ScienceDaily. Retrieved July 15,
2008, from http://www..sciencedaily.com /releases/2007/09/070917173153.htm
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