accumbens (NAc), the expression of genes involved in dopaminergic, glutamatergic, and GABAergic transmission (Ghasemzadeh, Mueller, & Vasudevan, 2009; Hyman & Malenka, 2001; McClung et al., 2005; Schumann & Yaka, 2009) and that play key roles in drug-reward and drug-seeking behavior is strongly altered. In the hippocampus, a brain region critical for associative learning and memory, addiction alters the expression of genes involved in long-term potentiation (LTP) (Zhou et al., 2011). Genetic studies, especially ones using genomic sequencing of animal models selectively bred for addiction phenotypes, have uncovered functional variants of genes involved in neural adaptation that are directly responsible for genetic differences in the propensity to use addictive agents and in response (Zhou et al., 2013). Using “omic” approaches, it has also become possible to analyze the whole transcriptome and epigenetic patterning of the genome, and new molecular adaptive processes that contribute to addiction have recently been revealed by applying these methods both in humans and in model organisms.
