Abstract
Stabilized methadone-maintained former heroin addicts (MTPs) treated with effective doses of methadone have markedly reduced drug craving; reduction or elimination of heroin use; normalized stress-responsive hypothalamic-pituitary-adrenal, reproductive, and gastrointestinal function; and marked improvement in immune function and normal responses to pain, all of which are physiological indices modulated in part by endogenous and exogenous opioids directed at the mu and, in some cases, the kappa-opioid systems. This study was performed to explore opioid receptor binding in MTPs. Fourteen normal, healthy volunteers and 14 long-term MTPs in treatment for 2 to 27 years and receiving 30 to 90 mg/day of methadone were studied with positron emission tomography using tracer amounts of [18F]cyclofoxy, an opioid antagonist that labels mu and kappa opioid receptors. Imaging was performed in the morning, 22 h after the last dose of methadone in patients, and concurrent plasma levels of methadone were determined. Five brain regions of specific interest for addiction and pain research (thalamus, amygdala, caudate, anterior cingulate cortex, and putamen) were among the six regions of highest [18F]cyclofoxy binding. Specific binding of [18F]cyclofoxy was lower by 19 to 32% in these regions in MTPs compared with those in normal volunteers. The degree to which specific binding was lower in caudate and putamen correlated with methadone plasma levels (P < .01 andP < .05, respectively), suggesting that these lower levels of binding may be related to receptor occupancy with methadone and that significant numbers of opioid receptors may be available to function in their normal physiological roles.
Footnotes
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Send reprint requests to: Mary Jeanne Kreek, M.D., Laboratory of the Biology of Addictive Diseases, The Rockefeller University, 1230 York Ave., Box 171, New York, NY 10021. E-mail:Russos{at}rockvax.rockefeller.edu
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↵1 This work was supported in part by NIH National Institute on Drug Abuse Grants DA-P50-05130 and DA-KO5-00049 and NIH Center for Research Resources Grant M01-RR00102.
- Abbreviations:
- MTP
- methadone-maintained former heroin addicts
- PET
- positron emission tomography
- ROI
- region of interest
- RUH
- Rockefeller University Hospital
- NIH
- National Institutes of Health
- Received May 15, 2000.
- Accepted August 25, 2000.
- U.S. Government
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