alcoholics, miR-15, belongs to one of the only two other groups of miRNAs that have predicted binding sites within the 3′ UTR of the β2AR mRNA (Wang et al., 2011). Recent evidence supports a role for β-adrenergic receptors in retrieval of cocaine-associated memories, mediated by norepinephrine acting at central β-adrenergic receptors in rats (Otis and Mueller, 2011). With this work, Otis and Mueller also demonstrated that propranolol, a commonly prescribed β-blocker, can be used as an adjunct to exposure therapy for the treatment of cocaine addiction. In addition, activation of β2AR also appears to be required for some of the key neurochemical changes that characterize chronic opioid administration in mice (Liang et al., 2007). Yet another let-7 family member, let-7d, was reported to be downregulated by cocaine in rat mesolimbic brain slices, and overexpression of this miRNA in hybrid NG108-15 cells downregulated the dopamine D3 receptor (Chandrasekar and Dreyer, 2009). It is well known that drugs of abuse induce persistent structural and functional changes in the mesolimbic dopaminergic system that lead to high-risk, drug-seeking behaviors, and relapse (Chandrasekar and Dreyer, 2011).
