It is apparent that many neuronal gene expression changes in the drug-induced adaptive process are region specific and cell specific. The mesolimbic system is critically involved in drug-reward and drug-seeking behavior and has been a focus for studies of addiction. In the dorsal striatum and NAc, medium-sized spiny neurons mediate dopaminergic, glutamatergic, and GABAergic neurotransmission (Hyman & Malenka, 2001) and rodents exposed to cocaine or during withdrawal show significant changes in dopaminergic, glutamatergic, and GABAergic neurotransmission (Ghasemzadeh et al., 2009; Hyman & Malenka, 2001; Nestler, 2001). Expression changes of genes targeted by dopaminergic and glutamatergic transmissions or genes involved in mediating transmission were also initiated during adaptation to drug exposure. Some of these genes have been relatively well analyzed such as CART (Douglass, McKinzie, & Couceyro, 1995), the Fos family (Hope et al., 1992; Nestler, 2008), CREB (Carlezon et al., 2005), Arc (Fosnaugh, Bhat, Yamagata, Worley, & Baraban, 1995), EGR1 (O’Donovan, Tourtellotte, Millbrandt, & Baraban, 1999), Homer-1 (Swanson et al., 2001), MKP-1 (Ujike, Takaki, Kodama, & Kuroda, 2002), Narp (Hyman & Malenka, 2001), NFκB (Ang et al., 2001), and CdK5
