Fig. 3.

(+)-Morphine microinjected into the posterior nucleus accumbens shell does not have any effect on the conditioned place preference. After completion of the preconditioning measurement on the 1^st day, groups of rats were place conditioned after microinjection with different doses of (+)-morphine (3, 10 or 100 pg) or vehicle into the posterior nucleus accumbens shell twice a day for three days. The post-conditioning was measured on the 5^th day. Each column represents the mean of the conditioned place preference score and the vertical bar represents the S.E.M.; n = 7–13 rats. Paired t test was used to compare production of conditioned place preference of individual dose: For the group of rats microinjected with vehicle or 3, 10 or 100 pg of (+)-morphine, t = 0.6, 1.7, 1.8 and 1.5 df = 12, 7, 7 and 9, respectively. One-way ANOVA followed by Dunnett’s post-test was used to test difference between groups; F_{(3, 34)} = 0.267.