Compounds known to selectively inhibit the neuronal reuptake of serotonin are clinically effective antidepressants. However, in a number of the behavioral models used for detecting and analysing antidepressant action these drugs are inactive. The forced swimming test is not consistently sensitive to these drugs but it has recently been reported that a variation of this procedure, the tail suspension test in mice, is sensitive. The present study showed that five compounds previously shown to be selective serotonin uptake inhibitors - fluoxetine, zimeldine, paroxetine, indalpine, and litoxetine- produced dose-related decreases in immobility in the tail suspension test typical of the effects shown by other antidepressants. In separate experiments, fluoxetine, zimeldine, and indalpine decreased locomotor activity at doses similar to those that decreased immobility. In contrast, paroxetine and litoxetine had no effect on locomotion at the dose ranges active in the tail suspension test. These results confirm the sensitivity of the tail suspension test and indicate that serotonin uptake inhibitors probably decrease immobility and reduce locomotor activity through different mechanisms.
