chromosome 9 near the gene that encodes the dopamine D2 receptor, Drd2 (Bice et al., 2006). More recently, Bice et al. (2008) found that alcohol-naive HAP-1 mice showed significantly reduced levels of Drd2 mRNA expression in the nucleus accumbens and hippocampus, compared to LAP-1 mice. These findings are consistent with previous observations by Belknap and Atkins (2001) and Cunningham (1995) of a QTL near the Drd2 locus on chromosome 9 influencing alcohol consumption and conditioned-place preference. While those findings support the hypothesis that lower expression levels of D2 receptors may increase the risk to alcohol and drug use (e.g., Volkow et al., 1999), it is still unclear whether differences in the neurophysiological profile in HAP-1 and LAP-1 mice might be associated with any of these QTLs.
