“…In preclinical studies, high anxiety as measured in the elevated plus maze (EPM) (Pellow et al 1985) predicts increased propensity to develop conditioned place preference for cocaine (Pelloux et al 2009), as well as higher oral intake levels (Walker et al 2009), and increased motivation to self-administer cocaine (Homberg et al 2002). Additionally, exposure to, or withdrawal from, cocaine and heroin increases anxiety (Rogerio and Takahashi 1992;Schulteis et al 1998;Zhou et al 2003;Le Merrer et al 2006;Ambrose-Lanci et al 2010;Salas-Ramirez et al 2010).…”