Effects of monoamine oxidase-B (MAO-B) inhibitors, a dopamine (DA) agonist and a noradrenergic and specific serotonergic antidepressant (NaSSA) on a depression-like behavior in CD157/BST1 knockout (CD157 KO) mice subjected to the forced swimming test (FST). (A) A single administration of selegiline (1−10 mg/kg, subcutaneous, s.c.) reduced immobility time of CD157 KO mice in the FST. **P < 0.01, saline-treated CD157 KO mice vs. saline-treated wild-type (WT) mice (Student’s t-test), #P < 0.05, ####P < 0.001 vs. saline-treated CD157 KO mice (Dunnett’s test), F(3,64) = 12.539, P < 0.001. A two-way analysis of variance (ANOVA) showed a significant interaction between the effects of treatment and genotypes on the immobility time (F(3,128) = 3.904, P < 0.05). (B) A single s.c. administration of selegiline at 10 mg/kg, but not 3 mg/kg, significantly increased climbing time of CD157 KO mice. The data are expressed as the mean ± SEM (n = 21−22 for saline-treated WT and CD157 KO mice, n = 15−17 for selegiline-treated WT and CD157 KO mice). ***P < 0.005, saline-treated CD157 KO mice vs. saline-treated WT mice (Student’s t-test), #P < 0.05 vs. saline-treated CD157 KO mice (Dunnett’s test), F(3,67) = 4.382, P < 0.01. A two-way ANOVA showed no significant interaction between the effects of treatment and genotypes on the climbing time (F(3,131) = 1.684, P = 0.174). (C) A single administration of selegiline (Sel; 10 mg/kg, s.c.), rasagiline (Ras; 1, 10 mg/kg, s.c.), or pramipexole (Ppx; 1 mg/kg, s.c.) and repeated administration of mirtazapine (Mir; 1 mg/kg, intraperitoneally, i.p.) reduced immobility time of CD157 KO mice in the FST. ***P < 0.005, saline-treated CD157 KO mice vs. saline-treated WT mice (Student’s t-test), #P < 0.05, ####P < 0.001 vs. saline-treated CD157 KO mice (Dunnett’s test), F(5,86) = 10.276, P < 0.001. (D) Selegiline (10 mg/kg, s.c.) increased the climbing time of CD157 KO mice, but rasagiline, pramipexole and mirtazapine did not. Data are expressed as mean ± SEM (n = 22−24 for saline-treated WT and CD157 KO mice, n = 12−19 for drug-treated CD157 KO mice). ***P < 0.005, saline-treated CD157 KO mice vs. saline-treated WT mice (Student’s t-test), ####P < 0.001 vs. saline-treated CD157 KO mice (Dunnett’s test), F(5,87) = 8.471, P < 0.001.