Effects of ethanol on fight- or swim-stressed mice in Porsolt's swim test.

The effects of ethanol in Porsolt's swim test on mice preexposed to fight- or swim-stressors were investigated. The control mice did not change their behavior in the swim test after an acute injection of 0.4 or 0.8 g/kg ethanol; 1.2 g/kg ethanol increased their immobility in one but not in another experiment. The mice exposed to continuous fight-attacks in their home cage by one dominant mouse shortened immobility after 0.8 g/kg ethanol as well as tended to shorten it after 0.4 g/kg ethanol. The mice that were forced to swim in the water twice before the actual swim test responded to 0.4 g/kg ethanol by shortening immobility; 0.8 g/kg tended to have the same effect; 1.2 g/kg ethanol just failed to lengthen immobility of the fight-stressed mice and had no effect on the swim-stressed mice. Because antidepressant drugs decrease and stressors increase immobility in the swim test, the test may serve as a putative animal model of depression. The present findings showed that low doses of ethanol reverse lengthened immobility of mice preexposed to a stressor. This suggests that ethanol either has antidepressant-like properties, or it improves animal's ability to cope with a stressful situation, or both.