The dopaminergic system has an important role in the rewarding properties of nicotine. Gene polymorphisms of DRD2 and DβH that regulate dopamine neurotransmission or metabolism could influence smoking behavior. Additionally, the ability of a 5-HT2CR agonist to block mesolimbic dopamine activation produced by nicotine at the level of ventral tegmental area, suggests a possible interaction between dopaminergic and serotonergic systems in smoking initiation. In the present study, DRD2 TaqIA and DβH -1021C>T polymorphisms and their interactions with 5-HT2CR - 759C>T and -697G>C and 5HTTLPR S/L polymorphisms of serotonergic system were analyzed in 166 smoking initiators (SI) and 244 non-initiators (NI) of Greek origin, using PCR-RFLP method. No differences were found in genotype distributions of DRDR2 TaqIA and DβH -1021C>T polymorphisms between SI and NI. Also, we found no interaction of DRD2 TaqIA and DβH -1021C>T with smoking initiation. When DRD2 TaqIA polymorphism was combined with 5- HT2CR -759C>T and -697G>C polymorphisms, the interaction of DRD2 TaqIA1 and 5-HT2CR -759T alleles was associated with smoking initiation in a model adjusted for age, sex, BMI and type 2 diabetes mellitus (OR=0.70, p=0.022) but did not improve the model that includes 5-HT2CR -759C>T polymorphism alone (OR=0.52, p=0.028). DRDR2 TaqIA and DβH -1021C>T polymorphisms were not associated with smoking initiation. The lower risk for smoking initiation conferred by the combination of DRD2 TaqIA1 and 5-HT2CR -759T variant alleles, indicates the presence of dopaminergic/serotonergic system interaction in smoking behavior; however, this interaction does not substantially improve the predictive value of 5-HT2CR -759T allele alone on smoking initiation risk. To the best of our knowledge, this is the first study of gene polymorphisms in multiple dopaminergic components in relation to smoking initiation, and of the interaction of gene polymorphisms of dopaminergic and serotonergic components in relation to this smoking phenotype in a large sample free of alcohol or drug dependencies.
Keywords: Dopamine, DβH, DRD2, genes, serotonin, smoking, 5-HT2CR, 5HTTLPR.