Fig. 1. Immobility times (floating duration) of single-housed adult male B6J (A) and BALB/c mice (B) in the forced swim test as a function of water temperature. Mice were exposed to the forced swim test at water temperatures of either 20 °C, 25 °C or 30 °C (n = 10 per strain and temperature) for 6 min on 2 consecutive days (d1, d2). Data were analyzed and presented (mean ± S.E.M.) in 1 min intervals. ^*p < 0.05, ^**p < 0.01 vs. the two other groups (significant Temperature × Interval interaction in the 2-way ANOVA, followed by Newman–Keuls post hoc test; for main effects of Temperature see Text).

Fig. 2. Comparison of the influence of water temperature on immobility times of single-housed adult male B6J and BALB/c mice in the forced swim test on 2 consecutive days (d1, d2). Data represent the floating duration shown during the last 4 min of the exposure (cf. Fig. 1) normalized to the observation interval. Each data point (mean ± S.E.M.) derives from an independent group of mice. Data presentation as lines was chosen to better illustrate the opposite effects of water temperature on floating behaviour in the two strains. ^*p < 0.05, ^**p < 0.01, ^***p < 0.001 vs. BALB/c at the same water temperature (2-way ANOVA followed by Newman–Keuls post hoc test).

Fig. 3. Effect of desipramine on immobility times (floating duration; 1 min intervals) of single-housed adult male B6J (A) and BALB/c mice (B) in the forced swim test performed either with 25 °C or with 30 °C warm water. (C) Total floating duration shown during the last 4 min of the exposure (cf. grey shaded areas in A and B) normalized to the observation interval. Mice were treated either with desipramine (20 mg/kg; D) or with vehicle (V) 30 min before the exposure. ^**p < 0.01, ^***p < 0.001 vs. vehicle treatment (2-way ANOVA followed by Newman–Keuls post hoc test).

Fig. 4. Effects of desipramine treatment on forced swim stress-induced corticosterone secretion. Mice from Fig. 3, which had been treated either with desipramine (20 mg/kg, D) or with vehicle (V) and had been tested at either 25 °C or at 30 °C, were killed 10 min after onset of the stressor. ^**p < 0.01 (2-way ANOVA followed by Newman–Keuls post hoc test).