Is dopamine a limiting factor of the antidepressant-like effect in the mouse forced swimming test?

To study the role of dopamine (DA) in antidepressant-like effect in the forced swimming test (FST), the relationship between the magnitude of the antidepressant-like effect of drugs [citalopram, fluoxetine, paroxetine (selective serotonin reuptake inhibitors), desipramine (tricyclic antidepressant), maprotiline (tetracyclic antidepressant), bupropion (DA reuptake inhibitor), and tranylcypromine (inhibitor of monoamine oxidase)] and the corresponding concentration of DA in the whole brain of mice was investigated. A trend for an inversely proportional linear relationship [(magnitude of the antidepressant-like effect) = -0.0145 x (concentration of DA in the whole brain) +34.773 (r = 0.276)] was observed between the magnitude of the antidepressant-like effect and the concentrations of DA in the whole brain, but this correlation was not significant. This result suggests that the high concentration of DA in the whole brain could be a limiting factor for the antidepressant-like effect of antidepressants such as tranylcypromine and seems to play a minor role in the antidepressant-like activity of another antidepressant such as bupropion in the FST.