Fig. 6. Dose-response relationship for the antidepressant effects of ketamine. A series of escalating doses of ketamine (1 mg/kg, 3 mg/kg, 10 mg/kg, and 20 mg/kg) were applied to rats 14 days after spared nerve injury (SNI) and are compared with saline control. The sucrose preference test was performed 1 day after drug administration. Statistical significance was found at 10 and 20 mg/kg ketamine. **P < 0.01 for 10 mg/kg, and *P < 0.05 for 20 mg/kg, two-way ANOVA with post hoc Bonferroni correction tests. 1 mg/kg group: n = 4; 3 mg/kg: n = 10; 10 mg/kg: n = 10; 20 mg/kg: n = 6.