Reduced dopamine D4 receptor mRNA expression in lymphocytes of long-term abstinent alcohol and heroin addicts

Aim It has been repeatedly suggested that dopamine receptor expression in peripheral blood lymphocytes reflects, to some extent, brain status. The aim of the present study was to investigate dopamine receptor expression in peripheral blood lymphocytes of long‐term abstinent alcohol and heroin addicts against the background of the hypothesis, that a persisting dysfunction of the dopaminergic system contributes a biological cause to the chronic character of addiction. Design Dopamine D3 and D4 receptor mRNA expression in peripheral blood lymphocytes was measured by real‐time polymerase chain reaction (PCR) in 19 alcohol addicts, abstinent for 6.2 ± 4.7 months (mean ± SD), and 20 heroin addicts, abstinent for 6.7 ± 3.7 months (mean ± SD), and compared to a control group of 29 age‐ and sex‐matched individuals with no life‐time history of substance abuse. Findings One‐way anova showed significant differences in D4 mRNA expression between the groups (P = 0.005): both groups of addicts showed an approximately 50% reduction in D4 receptor mRNA expression in peripheral blood lymphocytes (PBL) compared to controls. No differences were found for D3 mRNA expression between the groups. Conclusion The results of the present study indicate a withdrawal‐persisting dopaminergic imbalance in abstinent addicts as measured by a suggested peripheral marker.