Is dopamine implicated in the antidepressant-like effects of selective serotonin reuptake inhibitors in the mouse forced swimming test?

Rationale: Microdialysis, binding and behavioural studies have shown that the dopaminergic system plays a role in antidepressant treatment. Objectives: The present study determined whether the antidepressant-like effects of selective serotonin reuptake inhibitors measured in the mouse forced swimming test are mediated via dopamine receptors. Methods: Male Swiss mice were randomly assigned to groups of 24 animals and injected IP with citalopram, fluoxetine, fluvoxamine, sertraline, or paroxetine alone or in combination with the dopamine D1 agonist SKF 38393, the D1 antagonist SCH 23390, the D2 agonist bromocriptine, the D2 antagonist sulpiride, the D3 agonist PD 128 907, or the D3 antagonist nafadotride. Results: The anti-immobility effects of paroxetine, fluvoxamine and citalopram were increased by co-administration of SKF 38393 (0.5 and 2 mg/kg), SCH 23390 (0.06 mg/kg), bromocriptine (0.5 and 2 mg/kg) or PD 128 907 (1 and 2 mg/kg), and were attenuated by SCH 23390 (0.5 mg/kg). The anti-immobility effects of paroxetine and fluvoxamine were also increased with sulpiride (0.5 and 2 mg/kg). The anti-immobility effect of fluoxetine was increased by SKF 38393 (2 mg/kg) and PD 128 907(1 and 2 mg/kg) co-administration. The anti-immobility effect of sertraline (16 mg/kg) was increased by SKF 38393 (0.5 mg/kg), bromocriptine (2 mg/kg) and PD 128 907 (2 mg/kg) and the effect of sertraline (2 mg/kg) was increased by bromocriptine (2 mg/kg). The anti-immobility effect of paroxetine (4 mg/kg) was increased by nafadotride (2 mg/kg). Conclusions: These data indicate that the antidepressant activity of various SSRIs involves different dopamine receptor subtypes and that the serotoninergic and dopaminergic systems interact with each other.