“…Stress not only can increase cytokine levels (Black, 2002;Deak et al, 2005;Minami et al, 1991;Nguyen et al, 1998;O'Connor et al, 2003;Shintani et al, 1995a, b;Shizuya et al, 1997;Suzuki et al, 1997) but also can augment the effects of a subsequent increase in cytokines by LPS or stress (Johnson et al, 2004;Munhoz et al, 2006;Takemura et al, 1997). These findings led to the hypothesis that cytokines are involved in depressive illness (Anisman and Merali, 2003;Dunn et al, 2005;Hayley et al, 2005;Raison et al, 2006;Simen et al, 2006) and addictive behavior (Crews et al, 2006;Friedman and Eisenstein, 2004).…”