Fig. 5

Development of single-dose morphine-induced tolerance. The σ2R−/− (KO) mice developed a profound and lasting tolerance to acute administration of morphine (10 nmol, icv). The data are expressed as the mean ± SEM. * Indicates significantly different compared to the effects induced by the morphine priming dose (30 min) in wild-type (WT) and σ2R−/− mice; all data were analyzed by pairwise Holm-Sidak multiple comparison tests following ANOVA; p < 0.05