Laser sheds light on Parkinson’s disease

David Shenkenberg

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 analyte.

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 more error.

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.