Dopamine and opioid gene variants are associated with increased smoking reward and reinforcement owing to negative mood

Negative mood increases smoking reinforcement and risk of relapse. We explored associations of gene variants in the dopamine, opioid, and serotonin pathways with smoking reward ('liking') and reinforcement (latency to first puff and total puffs) as a function of negative mood and expected versus actual nicotine content of the cigarette. Smokers of European ancestry (n = 72) were randomized to one of four groups in a 2 x 2 balanced placebo design, corresponding with manipulation of actual (0.6 vs. 0.05 mg) and expected (told nicotine and told denicotinized) nicotine 'dose' in cigarettes during each of two sessions (negative vs. positive mood induction). Following mood induction and expectancy instructions, they sampled and rated the assigned cigarette, and then smoked additional cigarettes ad lib during continued mood induction. The increase in smoking amount owing to negative mood was associated with: dopamine D2 receptor (DRD2) C957T (CC > TT or CT), SLC6A3 (presence of 9 repeat > absence of 9), and among those given a nicotine cigarette, DRD4 (presence of 7 repeat>absence of 7) and DRD2/ANKK1 TaqIA (TT or CT > CC). SLC6A3, and DRD2/ANKK1 TaqIA were also associated with smoking reward and smoking latency. OPRM1 (AA > AG or GG) was associated with smoking reward, but SLC6A4 variable number tandem repeat was unrelated to any of these measures. These results warrant replication but provide the first evidence for genetic associations with the acute increase in smoking reward and reinforcement owing to negative mood.