Evaluation of efficacies of different classes of antidepressants in the forced swimming test in mice at different ages

1. The efficacies of different classes of antidepressants were investigated using the forced swimming test with mice at different ages. 2. Imipramine (4-32 mg/kg), desipramine (2-16 mg/kg) and bupropion (32, 64 mg/kg) showed activity in all age groups. 3. The selective serotonin reuptake inhibitors (SSRIs) citalopram (16 and 32 mg) and paroxetine (4 and 8 mg) were inactive in the oldest (40 weeks) group of mice, despite showing activity at the same doses in mice ranging in age from 4-24 weeks old. 4. Both SSRIs showed anti-immobility effects at low doses, (paroxetine: 1 and 2 mg/kg; citalopram: 4 and 8 mg/kg) in the 40-week old mice. These effects were not evident in the three younger groups of mice. 5.Moclobemide, a reversible selective inhibitor of monoamine oxidase-A, showed activity only at a high dose (128 mg/kg) and only in 12-week old animals. 6. Since SSRIs have been reported to have relatively selective effects on 5-HT1B receptors, the present results suggest that further studies comparing the effectiveness of SSRIs and other antidepressants in elderly patients should be done, Studies of the effects of aging on the density and/or affinity of 5-HT1A and 5-HT1B/1D receptors are also warranted.