WASHINGTON, Mar 09 (Reuters) -- Salmon with sticky deposits in their brains
may offer clues to treating or even preventing Alzheimer's disease in humans,
researchers said on Wednesday.
A team at the University of Colorado at Boulder found that salmon develop
deposits known as amyloid plaques in their brains that look much like the
plaques that characterize Alzheimer's.
Comparisons of brain tissue from salmon and from a human who died with
Alzheimer's disease showed they were "very similar if not identical," Tammy
Maldonado, who worked on the study, said in a statement.
The researchers said stress hormones set off an "alarm clock" that starts
the quick and relentless deterioration and death of salmon just after they
spawn, and that a similar process may be involved in human Alzheimer's.
But Maldonado and colleagues reported in Friday's issue of the journal Brain
Research that parts of the fishes' brains continued to work well despite
deposits of the amyloid plaques.
"Instead of being murderers, amyloid plaques may be allies of the brain
during times of stress and trauma," said Richard Jones, a professor emeritus in
the environmental, population and organismic biology department, who also worked
on the study.
"Our work on salmon could indicate amyloid plaques may form around dead
neurons somewhat like Band-Aids, preventing toxins produced by dead neurons from
reaching healthy neurons."
Alzheimer's, the most common cause of dementia, affects an estimated 4
million Americans. Many neurologists believe that beta amyloid protein causes
brain cells to degenerate and die.
Maldonado's team found that some areas of the salmon's brains did show the
classic signs of neuron damage when the amyloid protein was also present. But
other brain areas -- for instance, those used to help the fish find their way
home to spawn -- functioned well despite the plaques, Maldonado said.
The researchers studied salmon because the fish have remarkably similar
aging symptoms, including brain decay, cardiovascular disease, muscle atrophy
and skin lesions.
They castrated young kokanee salmon and found they lived to be 7 to 9 years
old, instead of dying at age 2 or 3 as normal kokanee do. The researchers said
that suggested salmon have an "aging alarm" timed to go off at reproduction.
They found that levels of a stress hormone known as cortisol surge just
before the onset of the rapid aging process and death.
"Cortisol surges may help these fish metabolize sugar and produce enough
energy to locate their home streams and reproduce, but the surges also
eventually may trigger brain aging and death," Maldonado said.
Other experiments have shown that cortisol spikes occur in Alzheimer
patients, and they are known to kill certain areas of neurons in the brain.
"If we find that stress hormones cause amyloid plaques to form in salmon
brains, that would be quite a breakthrough," said biology professor David
Norris, who also worked on the study.
