Fig. 1.

Reduced immobility after a 2.5 min preswim defines the antidepressant effect of imipramine in the forced swim test, and α_2A-AR-KO mice are insensitive to this effect. WT and α_2A-AR-KO mice in the C57 Bl/6 genetic background were subjected to a 2.5 min preswim as described in Materials and Methods and by Sallinen et al. (1999). After the preswim, the mice were injected intraperitoneally with the indicated agents (saline, open bars; imipramine, filled bars). Twenty-four hours after the preswim, the mice were evaluated in a 5 min test swim that was videotaped and scored as described in Materials and Methods. The sum of the durations of floating, twitching, and kicking (immobile) behaviors (mean ± SEM) is presented as the dependent variable; n = 8–9 mice per group. [ANOVA results: genotype effect, F_(1,30) = 38.9,p < 0.0001; drug effect,F_(1,30) = 3.08, p = 0.0896; drug × genotype interaction,F_(1,30) = 6.57, p = 0.016. WT animals only, ANOVA results: drug effect,F_(1,16) = 6.54, p = 0.021 (indicated by *).] The detailed observations from the videotaped sessions are provided in Table 1.