Recent studies have revealed that miRNAs are highly abundant in brain and play important roles in a variety of biological processes such as neuronal differentiation (Cheng et al., 2009), brain development (Siegel et al., 2009), synapse formation and plasticity (Schratt et al., 2006), neuronal survival(Schaefer et al., 2007), and neurodegenerative diseases(Bushati and Cohen, 2008). MiRNAs may also mediate the cellular adaptations that occur in response to drug abuse and addiction. Specifically, changes in miRNA expression occur as a result of exposure to a number of drugs of abuse, including nicotine (Huang and Li, 2009; Shan et al., 2009), cocaine (Chandrasekar and Dreyer, 2009), morphine (Wu et al., 2008; Wu et al., 2009), and alcohol (Pietrzykowski et al., 2008; Sathyan et al., 2007; Tang et al., 2008).
