BRAIN CHEMISTRY BEHIND DRUG ABUSE INVESTIGATED

People with few dopamine D2 receptors may be at a greater risk of
abusing psychostimulants than those with more receptors, conclude
researchers this month. Nora Volkow (Brookhaven National Laboratory,
Upton, NY, USA) and colleagues believe that there is an "optimal range
for dopamine D2 stimulation". For people with few receptors, they
explain, psychostimulants boost stimulation into that optimal range,
but for those with many receptors, a similar drug dose causes
overstimulation and unpleasant drug responses.

The researchers assessed the number of dopamine D2 receptors in 23
healthy, non-drug-using men by use of positron emission tomography.
Then, on a separate day, each man was given methylphenidate 0B75
mg/kg intravenously after being told that he would receive drug or
placebo. Men with fewer receptors said that taking the drug was
pleasant; those with more receptors reported unpleasant effects
(p(0B7004; Am J Psychiatry 1999; 156: 1440-43).

"All addicted people that we've tested, whether they are taking
cocaine, alcohol, or heroin, have lower numbers of dopamine D2
receptors; the question is, what is this common denominator telling
us?", asks Volkow, who believes that assessing the numbers of
receptors may indicate whether an individual is likely to abuse drugs.

"Understanding these biological issues will help us learn why some
people are particularly vulnerable to abusing drugs", agrees Alan
Leshner of the US National Institute of Drug Abuse. It may also
provide new potential targets for prevention and treatment efforts, he
adds.