New imaging approach promises insights into multiple sclerosis.

In light of our current assignment on a specific laboratory technique, I found an article that might be interesting to us all and can be found at http://news.uns.purdue.edu/x/2007a/070417ChengMyelin.html.

Three imaging techniques are combined in one experiment to study multiple sclerosis and its ability to cause an overproduction of astroglial filaments as well as the degradation of myelin sheath. Astroglial filaments form bundles between critical nerve fibers and interrupt spinal cord functions. Myelin sheaths insulate nerve fibers and assist them in conducting nerve impulses. The three imaging techniques used in this experiment are: sum frequency generation, two-photon excitation fluorescence, and coherent anti-stokes Raman scattering (CARS). The goal of this study is to slow down and reverse the development of multiple sclerosis.

These imaging techniques are very useful because they do not require the use of dyes to label cells, which in turn saves the cells and allows the study of living tissue. Along with this issue of cell life, CARS overcomes Raman scattering’s limitation of taking hours to create an image by creating images at one frame per second or faster. CARS uses two overlapped laser beams to produce a new beam whose frequency is the difference of the two original beams. The new beam makes molecules vibrate together “in phase,” which amplifies the Raman signal for those molecules. Sum frequency, the opposite of CARS, adds the frequencies of the two original beams and two-photon excitation fluorescence makes images brighter by using two photons to illuminate the target and provides higher contrast.

Myelin sheaths are made up of lipid molecules and the imaging techniques allow the experimenter to determine whether the chemical bond orientation in the lipid molecules are “scrambled” when the myelin sheaths are unhealthy or degraded due to disease. CARS allows the researcher to view the myelin sheath, sum frequency shows the astroglial filaments, and two-photon excitation fluorescence can show evidence of nerve fiber damage due to the influx of calcium into cells. This is also important because the astroglial filaments are part of the production of scar tissues from injuries to the central nervous system.