Antidepressant effects of pramipexole, a novel dopamine receptor agonist.

Pramipexole (2-amino-4,5,6,7-tetrahydro-6-propyl-amino-benzthiazole-dihydrochl oride), a new dopamine receptor agonist with preference for D3 compared to D2 and D4 receptors, was tested in rats in respect of its potential antidepressant activity. In the forced swimming test the drug under study, given three times in rats, reduced the immobility time. In the forced swimming test, joint treatment with antidepressants (imipramine, amitriptyline) and pramipexole evoked a more potent effect than any of the drugs given alone; however, the locomotor hyperactivity was weaker after joint administration. Citalopram and fluoxetine, inactive per se in the forced swimming tests, visibly enhanced the antidepressant-like effect of pramipexole but, on the other hand, they attenuated the locomotor hyperactivity evoked by the drug. Repeated treatment with pramipexole (0.3 or 1 mg/kg, twice daily for 14 days) increased the locomotor activity measured at 1 h after the last dose. Repeated administration of pramipexole (as above) potentiated the D-amphetamine- or quinpirole-induced locomotor hyperactivity. The obtained results indicate that, in the tests used, pramipexole evokes effects similar to those of typical antidepressants and, at the same time, enhances their activity (the forced swimming test in rats); therefore it may be regarded as a potential antidepressant drug.