Fewer Dopamine D2 Receptors Could Predict Response To Psychostimulants
WESTPORT, Sep 23, 1999 (Reuters Health) - Low levels of dopamine D2
receptor expression may contribute to drug addiction susceptibility, US
researchers report in the September issue of the American Journal of
Psychiatry.
Dr. Nora D. Volkow, from the Brookhaven National Laboratory in Upton,
New York, and multicenter colleagues used raclopride and positron
emission tomography to assess the effects of intravenous infusion of the
psychostimulant methylphenidate on the number of dopamine D2 receptors
in 23 healthy men. The normal volunteers also reported their subjective
responses to the drug infusion.
"When you inject methylphenidate intravenously there is tremendous
variation in the way people respond. This study shows that in subjects
with low levels of dopamine D2 receptors the responses of
methylphenidate were perceived as pleasurable. Whereas in subjects with
very high levels of receptors, methylphenidate made them feel very
unpleasant," Dr. Volkow said in an interview with Reuters Health.
"This documents clearly that the biochemical characteristics of the
brain of individuals modulates responses to this type of stimulant and
predicts that this might be the same for other types of stimulant drugs,
such as cocaine or amphetamines," the researcher continued.
Dr. Volkow and colleagues referred to previously published studies that
showed that patients who found the effects of methylphenidate to be
pleasant had a similar number of dopamine D2 receptors when compared
with cocaine users.
These results suggest to the authors that "...low D2 receptor levels in
cocaine abusers may have antedated their cocaine use and may have
contributed to their cocaine use," the team suggests.
"But evidently something else is required for addiction to
appear...[such as environmental] factors or variables such as stress,"
warned Dr. Volkow.
"As we learn the variables that, for example, create a predisposition to
drug addiction we may be better placed as therapists to actually develop
treatments. So if I have a [drug-addicted] subject with very low D2
receptors...I will be much more aggressive in treatment than with a drug
addict whose receptor levels are more or less normal," Dr. Volkow said.
Am J Psychiatry 1999;156:1440-1442.
Copyright 1999 Reuters Limited. All rights reserved.
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Judith Richards, London, Ontario, Canada
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