Microdialysis probes placement in ventral striatum / Nucleus Accumbens is shown in Figure 3A. Baseline DA levels did not differ between genotypes (F[1,22]= 6.9 × 10−6, n.s.) and were 2.42±0.4 nM for h/mOPRM1–118AA and 2.43±0.6 nM for h/mOPRM1–118GG mice, respectively (n=12/group). Alcohol injection (2g/kg, a dose that robustly induces conditioned place preference in C57BL/6 mice) increased dialysate DA in both lines (main effect: F[6,132]=12.4; p<0.0001), However, response differed markedly between genotypes (main genotype effect: F[1,22]=7.2; p<0.05; genotype x time interaction: F[6,132]= 12.4; p<0.005; Figure 3B). Peak DA increase was nearly 4-fold greater in GG mice than in AA animals. The genotype effect was specific for DA release induced by alcohol; although alcohol also significantly increased 5-HT (main effect: F[6,132]=15.6; p<0.0001), this was not affected by genotype (main genotype effect: F[1,22]=3.6; n.s; genotype x time interaction: F[6,132]=0.92; n.s.; Figure 3C).
