The rewarding properties of cocaine were examined using CPP in mice lacking either kappa receptors or preprodynorphin. Preference for the drug-paired compartment was maintained in both animal models (McLaughlin et al., 2006a; McLaughlin et al., 2003; Redila and Chavkin, 2008). In presence of stress, cocaine CPP is typically increased in wild type mice but remained unchanged in kappa and pDyn KO mice (forced-swim stress in (McLaughlin et al., 2006a; McLaughlin et al., 2003); social defeat stress in (McLaughlin et al., 2006b)), indicating that the kappa/dynorphin system contributes to the stress-mediated response. Within this line, stress-induced reinstatement of extinguished cocaine CPP was decreased in pDyn KO, although this was not observed in kappa KO mice (Redila and Chavkin, 2008).
