Fig. 1

CPP training prevents LFS-induced hippocampal depotentiation in vitro. a: The schema for a 5-day bias cocaine CPP task with a 3-day training period. Cocaine CPP was induced by giving the mouse cocaine (20 mg/kg, i.p.) and saline (Sal) injections, respectively, in its non-preferred and preferred arenas in the CPP apparatus daily for three days. In the saline-conditioned group, cocaine injections were replaced by saline injections. b: Bar graphs summarize the CPP scores for saline- and cocaine-conditioned groups of mice. Note that cocaine-, but not saline-, conditioned mice developed significant CPP (***p < 0.001, saline-conditioned group vs. cocaine-conditioned group in the test stage, two-way ANOVA with Bonferroni post hoc test). c: Time courses of the slope of fEPSPs recorded before, during theta burst stimulation (TBS, arrow) and low frequency stimulation (LFS, horizontal line), and after LFS in hippocampal slices prepared from naïve, saline- and cocaine-conditioned groups of mice after performing the CPP test on Day 5 . The slope of each fEPSP is expressed as % of the baseline fEPSP slope, which is the average of 20 fEPSPs recorded 10 min before TBS. Inset: Averaged traces of 20 fEPSPs recorded before (a) and 60 min after (b) LFS in each group. d: Bar graphs summarize the magnitudes of potentiation of fEPSP slope in naïve, saline-conditioned, and cocaine-conditioned groups. The magnitude of potentiation was calculated from the average of the slope of 20 fEPSPs recorded 50 ~ 60 min after LFS and expressed as % of baseline. The number in parentheses is the number of slices recorded. Data are mean ± S.E.M. *p < 0.05 vs. 100%, paired t-test. ^## p < 0.01 vs. the naïve group (one-way ANOVA with Newman-Keuls post-hoc analysis)