The identification of a common haplotype in 2 independent populations is an important step toward identifying functionally significant regions of DAT1. Interaction between DAT1 genotypes and maternal use of alcohol during pregnancy suggests that DAT1 moderates the environmental risk and has implications for the prevention of ADHD. Further studies are required to delineate the precise causal risk factor involved in this interaction.

The dopamine (DA) transporter DAT1 is a major target bound by cocaine in brain. We examined the influence of functional genetic variants in DAT1 on cocaine addiction. Repeat polymorphisms, including a 30-bp variable-number tandem repeat (VNTR) in intron 8 (Int8 VNTR) with two common alleles, were genotyped in cocaine-dependent abusers (n ‫؍‬ 699) and in controls with no past history of drug abuse (n ‫؍‬ 866) from Sã o Paulo, Brazil. Positive association was observed with allele 3 of the Int8 VNTR and cocaine abuse (allele odds ratio ‫؍‬ 1.2, 95% confidence interval ‫؍‬ 1.01-1.37, P ‫؍‬ 0.036; 3͞3 homozygote odds ratio ‫؍‬ 1.45, 95% confidence interval ‫؍‬ 1.18 -1.78, P ‫؍‬ 0.0008). Population stratification was assessed and did not affect the results. Haplotypic analyses using additional polymorphisms indicated that the Int8 VNTR is responsible for the observed association. Functional analyses in reportergene constructs, demonstrated that allele 3 mediates significant (P < 0.05) but small reduced expression compared with the ''protective'' allele 2. This difference increased when 1 and 10 M cocaine was added to the cell culture (Ϸ40% reduction of the 3 allele expression versus the 2 allele). The 3 allele also demonstrated Ϸ3-fold-increased expression over the 2 allele in response to KCl plus forskolin challenge. We demonstrate a robust association between cocaine dependence and a VNTR allele in SLC6A3, conferring a small but detectible effect, and we show that this VNTR may be functional. This study suggests that DAT1 gene variation may play a role in cocaine dependence etiology.addiction ͉ genetics ͉ SLC6A3

Because GABA A receptors containing α2 subunits are highly represented in areas of the brain, such as nucleus accumbens (NAcc), frontal cortex, and amygdala, regions intimately involved in signaling motivation and reward, we hypothesized that manipulations of this receptor subtype would influence processing of rewards. Voltageclamp recordings from NAcc medium spiny neurons of mice with α2 gene deletion showed reduced synaptic GABA A receptor-mediated responses. Behaviorally, the deletion abolished cocaine's ability to potentiate behaviors conditioned to rewards (conditioned reinforcement), and to support behavioral sensitization. In mice with a point mutation in the benzodiazepine binding pocket of α2-GABA A receptors (α2H101R), GABAergic neurotransmission in medium spiny neurons was identical to that of WT (i.e., the mutation was silent), but importantly, receptor function was now facilitated by the atypical benzodiazepine Ro 15-4513 (ethyl 8-amido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5-a] [1,4] benzodiazepine-3-carboxylate). In α2H101R, but not WT mice, Ro 15-4513 administered directly into the NAcc-stimulated locomotor activity, and when given systemically and repeatedly, induced behavioral sensitization. These data indicate that activation of α2−GABA A receptors (most likely in NAcc) is both necessary and sufficient for behavioral sensitization. Consistent with a role of these receptors in addiction, we found specific markers and haplotypes of the GABRA2 gene to be associated with human cocaine addiction.GABRA2 | behavioral sensitization | nucleus accumbens | mutant mouse | human genetics