Dopaminergic, glutamatergic, and peptidergic signaling in the mesolimbic system are altered in response to cocaine. Repeated exposure to cocaine leads to sensitization, the progressive and persistent amplification of behavioral and motivational responses to a fixed dose of the same drug (Hyman et al., 2006). Sensitization may persist for weeks to years after cessation of drug taking, presumably contributing to a reformed addict’s risk for relapse (Saunders and Robinson, 2011), which occurs in up to ninety percent of addicted individuals (Wee and Koob, 2010; Kalivas and Volkow, 2011).
