Repeated administration of fluoxetine, desipramine and tranylcypromine increases dopamine D2-like but not D1-like receptor function in the rat

We tested the effect of repeated treatment (twice daily for 14 days) of rats with the antidepressant drugs fluoxetine, desipramine and tranylcypromine, on the behavioural response to the non-selective dopamine (DA) receptor agonist, apomorphine, the D-1-like receptor agonists, SKF 38393 and SKF 81297 and the D-2-like receptor agonists, RU 24213 and quinpirole. Agonist-induced behaviour was monitored by automated activity meters and direct observation using a checklist scoring method. Fluoxetine, desipramine and tranylcypromine enhanced (albeit to a varying degree) the behavioural responses to apomorphine (0.75 mg/kg, s.c.), quinpirole (0.25 mg/kg, s.c.) and RU 24213 (0.75 mg/kg, s.c.). In contrast, fluoxetine, desipramine and tranylcypromine did not increase the behavioural responses to SKF 38393 (7.5 mg/kg, s.c.) and SKF 81297 (0.5 mg/kg, s.c.). Finally, fluoxetine, despiramine and tranylcypromine did not modify the behavioural responses to the concomitant administration of SKF 38393 (7.5 mg/kg, s.c.) and quinpirole (0.25 mg/kg, s.c.). Our data suggest that repeated administration of fluoxetine, desipramine and tranylcypromine increases central DA D-2-like but not D-1-like receptor function.