Laser sheds light on Parkinson’s disease
Worldwide, millions of people suffer from Parkinson’s disease, and they gradually lose
control of their movements. For example, their hands may shake uncontrollably, or
their muscles may suddenly become rigid. Although the cause of the disease is not
fully understood, researchers led by John D. Simon at Duke University in Durham,
N.C., have provided evidence that may offer some clues, thanks to the use of the
university’s free-electron laser.
In the lower left of this picture, the snakelike body of the free-electron
laser comes to a halt beside the stairs. At that end, the researchers placed their
These scientists believed that answers lie within
a pigment, called neuromelanin, that is composed of two other pigments, eumelanin
and pheomelanin. They hypothesized that eumelanin forms a protective coat around
pheomelanin, a chemical that activates a deadly form of oxygen. Because eumelanin
progressively disappears in Parkinson’s patients, they thought that pheomelanin
might become unleashed and begin killing surrounding cells. Therefore, Simon and
colleagues at his university, at North Carolina State University in Raleigh and
at the Institute of Biomedical Technologies in Segrate, Italy, investigated the
structure of neuromelanin.
Initial experiments performed with
a scanning electron microscope from FEI Co. and a Digital Instruments atomic force
microscope revealed that the surface of neuromelanin comprises 350-nm granules that
consist of spherical particles with a diameter of 30 ±10 nm. Next, the researchers
used the free-electron laser to determine at what point the surface of neuromelanin
activates oxygen because that chemical characteristic would tell them whether the
surface comprises eumelanin or pheomelanin.
Using a free-electron laser, researchers performed
photoemission electron microscopy on neuromelanin, a pigment that gradually degrades
in the brain of patients with Parkinson’s disease.
More specifically, the free-electron
laser ionized the surface of neuromelanin by bombarding it with electrons. The researchers
plugged the resulting numbers into an equation and calculated the point at which
it activates oxygen. Simon said that they could have used conventional light sources
to derive the same information, but that it would have taken much longer and introduced
They operated the free-electron laser
in spontaneous emission mode between 5.0 and 3.0 eV with an energy full width at
half maximum of ±0.1 eV, and they captured the images with a DVC digital camera
with a resolution of 1300 x 1030 pixels x 12 bits.
The results from the free-electron
laser experiment confirmed the researchers’ hypothesis that eumelanin forms
a protective outer layer that surrounds the pheomelanin core. However, Simon emphasized
that the structure has not been fully elucidated. He would like to perform a different
method of imaging with the laser to determine how eumelanin and pheomelanin are
organized within the granules.
PNAS, Oct. 3, 2006, pp. 14785-14789.
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