RADIOTRACER CHEMISTRY TIP SHEET
Positron emission tomography (PET) opens a window on human health and behavior
with its ability to visualize biochemical activity in the living body. The
technique relies on short-lived, radioactive chemicals that emit bursts of
energy as they decay. Scientists use these chemicals to harmlessly tag
substances and trace their effect in the body through PET scan images. The
following is a summary of one paper concerning radiotracer chemistry that will
be presented in Dallas at the national meeting of the American Chemical
Society, world's largest scientific society.
SEEING HOW THE BRAIN CHANGES DURING AGING
As we age, our brains lose valuable dopamine receptors, which help govern our
motor and cognitive skills. Joanna S. Fowler, Ph.D. and colleague Nora D.
Volkow, M.D., of Brookhaven National Laboratory report that multiple radiotracer
chemicals are helping researchers to study more precisely how the dopamine
system changes as we age. These radiotracers can also shed light on brain
changes associated with such conditions as Parkinson's disease and smoking.
Raclopride and d-threo methylphenidate are two substances taken up by different
parts of the dopamine cell. By tagging each substance with the radiotracer
carbon-11, researchers can observe the dopamine system in action with a PET
scan. The Brookhaven team used these radiotracers to study persons ranging in
age from 23 to 86. The researchers asked each person to perform motor and
cognitive tests and then used the PET scan to "watch" how their dopamine systems
worked. The older the person, the more poorly they performed the tests and the
lower their level of dopamine activity. Fowler's group has also
developed a radiotracer that monitors the level of an enzyme called MAO B that
breaks down dopamine. Levels of MAO B increase as we age, contributing to
dopamine deficiency. A drug called L-Deprenyl inhibits MAO B and is used to
treat patients with Parkinson's and Alzheimer's disease. Fowler says that the
PET studies suggest that if we can do things to enhance the activity of dopamine
in the human brain, we may be able to slow down some of the cognitive and motor
declines in aging and might be able to help determine what doses of the drug
would be most beneficial to an individual.
Paper ORGN 4 will be presented by J. S. Fowler from 11:00 a.m. to 12:00 noon, Sun., March 29, in the Convention Center Ballroom A I, Level 3.
A nonprofit organization with a membership of more than 155,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.