Figure 4.

Tianeptine (30 mg/kg) induced a conditioned place preference, and this effect was MOR-dependent. MOR+/+ and MOR–/– mice were allowed to freely explore two compartments for 20 min on days 1 and 5. The two compartments differed in their texture, color, and spatial configuration. On days 2, 3, and 4, mice were injected (i) with saline in the mornings and confined in one of the two compartments for 45 min and (ii) with 30 mg/kg of tianeptine or with saline for controls in the afternoons and confined in the other compartment again for 45 min. MOR+/+ mice that received tianeptine in the afternoons next preferred the tianeptine-associated compartment compared to the saline-associated compartment (in tianeptine-treated MOR+/+ mice, Main effect of Test, F_1,9 = 10.27, p = 0.01; Main effect of Compartment, F_1,9 = 5.88, p = 0.04; Test × Compartment interaction effect, F_1,9 = 6.55, p = 0.03; Bonferroni's multiple comparison tests vs. saline-associated vs. tianeptine-associated compartment, p = 0.01 on day 5). Tianeptine did not promote a conditioned place preference in MOR–/– mice. *p = 0.01, vs. a saline-associated compartment. N's = 6–10/group.