Since the therapeutic effects of antidepressants usually occur after prolonged treatment, we then tested if chronic imipramine treatment (20 mg/kg, i.p.) may regulate brain FoxOs. Before testing brain FoxOs, mice were subjected to the FST after receiving chronic imipramine treatment (23 days) to confirm an antidepressant-like effect of this treatment. The result demonstrated that the chronic imipramine treatment used in our experiment reduced the immobility time when compared to saline treatment (Figure 3a). Interestingly, chronic imipramine treatment (28 days) caused significant increases in phospho-Ser256-FoxO1 and phospho-Ser253-FoxO3a in the cerebral cortex, hippocampus, and striatum, whereas the levels of total FoxO1 and FoxO3a were not affected by chronic imipramine treatment (Figure 3b and 3c). This effect of imipramine was accompanied by a moderate increase in phospho-Thr308-Akt but no change was observed in the level of total Akt. Thus, a therapeutically relevant imipramine treatment can inhibit FoxO1 and FoxO3a in mouse brain.
