Reduced dopamine D3 receptor expression in blood lymphocytes of smokers is negatively correlated with daily number of smoked cigarettes: A peripheral correlate of dopaminergic alterations in smokers

The mesolimbic dopaminergic system is known to mediate rewarding effects of nicotine administration, and dysfunctions of this system may underlie failure to stop cigarette smoking. Expression of dopamine receptors in peripheral blood lymphocytes (PBLs) has been indicated as a peripheral correlate of brain status. Dopamine receptor D 3 (DRD3) and D 4 (DRD4) mRNA expression in PBLs was measured by real-time polymerase chain reaction in smokers (n=26) and former smokers (n=14), compared with nonsmoking control subjects (n=35). A significant (p=.032, Bonferroni corrected) 30% reduction of DRD3 mRNA expression in PBLs was found in smokers but not former smokers in comparison with controls. DRD3 mRNA expression in PBLs in smokers but not former smokers was negatively correlated with daily number of cigarettes consumed (Pearson correlation coefficient r=-.54, p=.005). These data suggest a selective inhibiting effect of smoking on DRD3 mRNA expression and, with the known involvement of DRD3 in reward mediation, indicates a vicious-cycle explanation for the motivation for continued smoking.