Effects of acute fluoxetine, paroxetine and desipramine on rats tested on the elevated plus-maze

Antidepressants are usually prescribed for the treatment of depression but more recently have also been recommended for the treatment of anxiety disorders. The purpose of this study was to investigate the anxiogenic- or anxiolytic-like effects of an acute administration of antidepressants (serotonergic and noradrenergic compounds) in male Wistar rats submitted to the elevated plus-maze. Fluoxetine (2.5, 5, 10, 15 mg/kg), paroxetine (0.1, 0.5, 3, 12 mg/kg) and desipramine (2.5, 5, 10 mg/kg) or their vehicles were administered intraperitoneally 30 min prior to testing. Diazepam (0.5, 1.5, 2.5 mg/kg) was used as a positive comparator for anxiolytic effect. In comparison with control animals, the percentage of time the rats treated with fluoxetine (5 and 10 mg/kg) and paroxetine (3 and 12 mg/kg) spent in the open arms decreased. The percent of inactive time spent in the open arms also decreased in rats given fluoxetine (5 and 10 mg/kg) and paroxetine (12 mg/kg). Desipramine was inactive on all these parameters. In conclusion, acute treatment with fluoxetine and paroxetine, but not with desipramine, produced a pattern of anxiety behavior. Thus, the pharmacological mechanism appears to be due more to serotonergic than adrenergic neurotransmission. The elevated plus-maze exhibits good sensitivity for detecting anxiogenic effects of antidepressant drugs and the conventional parameters are sufficient and reliable for detecting such effects.