string: , 1991) and activation of cAMP–response element-binding protein (CREB) take place in the mesolimbic system after exposure to diverse drugs of abuse such as ethanol, opiates, cocaine, and amphetamine (Asher et al., 2002; Carlezon et al., 1998; Lu et al., 2003; McClung and Nestler, 2003; Shaw-Lutchman et al., 2002, 2003).