The immobility response in the forced swim test: paradoxical effect of imipramine

Rats immersed in a modified version of the forced swim test in which they are unable to touch the bottom of the cylinder with their feet while keeping their noses above water, initially paddle vigorously but eventually become relatively immobile. In the present study, we show that chronic treatment with imipramine and alprazolam increases rather than decreases the immobility response of rats in this test, whereas chronic treatment with propranolol is less effective. The results of this study indicate that the interpretation of the immobility response as 'behavioral despair', which is based on the response to the antidepressant drugs such as imipramine, needs to be reevaluated.