Figure 2.

Effect of the co-administration of ketamine and melatonin after two administrations of melatonin to mice submitted to the forced swimming test. First, 24 h before starting the behavioral test, mice (n = 8 per group) were i.p. injected at ZT 18 with either 4 or 16 mg/kg of MEL (first administration). A second dose of MEL was i.p. administrated at ZT 11 of the light cycle. Finally, in a third injection, mice received MEL at either of 4 or 16 mg/kg in combination with a non-effective dose of KET (1.5 mg/kg) at ZT 18 (A). Another independent group was given 15 mg/kg (i.p.) fluoxetine as a reference drug, following the same administration protocol (B). The forced swimming test was applied 30 min after the last injection. Results are the mean + error standard of the mean (SEM) of independent determinations of 8 to 12 mice per group. Data were analyzed using a one-way ANOVA followed by the Bonferroni post-test. (A) when compared with the vehicle (VEH) control group. For (B) a Student’s t-test was done (t₍₁₄₎ = 105.97, p ≤ 0.001). *** p < 0.001.