<i>RASGRF2</i> regulates alcohol-induced reinforcement by influencing mesolimbic dopamine neuron activity and dopamine release

The firing of mesolimbic dopamine neurons is important for drug-induced reinforcement, although underlying genetic factors remain poorly understood. In a recent genome-wide association metaanalysis of alcohol intake, we identified a suggestive association of SNP rs26907 in the ras-specific guanine-nucleotide releasing factor 2 ( RASGRF2 ) gene, encoding a protein that mediates Ca 2+ -dependent activation of the ERK pathway. We performed functional characterization of this gene in relation to alcohol-related phenotypes and mesolimbic dopamine function in both mice and adolescent humans. Ethanol intake and preference were decreased in Rasgrf2 −/− mice relative to WT controls. Accordingly, ethanol-induced dopamine release in the ventral striatum was blunted in Rasgrf2 −/− mice. Recording of dopamine neurons in the ventral tegmental area revealed reduced excitability in the absence of Ras-GRF2, likely because of lack of inhibition of the I A potassium current by ERK. This deficit provided an explanation for the altered dopamine release, presumably linked to impaired activation of dopamine neurons firing. Functional neuroimaging analysis of a monetary incentive–delay task in 663 adolescent boys revealed significant association of ventral striatal activity during reward anticipation with a RASGRF2 haplotype containing rs26907, the SNP associated with alcohol intake in our previous metaanalysis. This finding suggests a link between the RASGRF2 haplotype and reward sensitivity, a known risk factor for alcohol and drug addiction. Indeed, follow-up of these same boys at age 16 y revealed an association between this haplotype and number of drinking episodes. Together, these combined animal and human data indicate a role for RASGRF2 in the regulation of mesolimbic dopamine neuron activity, reward response, and alcohol use and abuse.