A recently completed study sheds new light on the likely reason for this difference. Individuals who have two linked genetic variations are far more likely to end up biting their nails following a jolt of caffeine than those who don't, reported Harriet de Wit of the University of Chicago on Sunday, Dec. 8 at the annual meeting of the American College of Neuropsychopharmacology held in San Juan, Puerto Rico.

"This is the first time that anyone has identified why people have different behavioral reactions to the same drug," said de Wit.

In addition to providing new information on why this commonplace drug affects some people differently than others, the results validate a methodology that should be capable of identifying individual differences in how people respond to a number of major drugs, she said.

Researchers from the University of Chicago and two German universities, M?nster and Wrzburg, recruited 94 healthy, infrequent users of caffeine. In a double-blind study, the researchers administered oral doses of caffeine or placebo and then recorded their physiological reactions and subjective mood states.

The researchers also took blood samples from the participants and investigated the genes that code for two proteins, called adenosine receptors, which are known to interact with caffeine. Receptors form special features on the surface of nerve cells that bind with specific neurotransmitters, in this case adenosine, and affect the nerve's internal processes. One of these receptors, A1, is widely distributed throughout the brain while the other, A2a, is concentrated in the basal ganglia, a region deep below the cerebral cortex in the middle of the brain.

The researchers observed four genetic variations of the adenosine receptor genes in their group. When they an
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Contact: Dr. Oakley Ray
oray@acnp.org
615-594-2631
American College of Neuropsychopharmacology
8-Dec-2002