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Anxiolytic-like effect of quinpirole in combination with a low dose of 17β-estradiol in ovariectomized rats.

The aim of this study was to explore effects on anxiety-like behavior of the D2 dopamine receptor agonist, quinpirole and of the D2 dopamine receptor antagonist, sulpiride given alone or in combination with a low dose of 17β-estradiol (17β-E2) to ovariectomized (OVX) rats. Two weeks after surgery, OVX rats began 14 days of treatment with the vehicle, a low dose of 17β-E2 (5.0 μg/rat, s.c.), quinpirole (0.1 mg/kg, i.p.), sulpiride (10.0 mg/kg, i.p.), quinpirole plus 17β-E2 or sulpiride plus 17β-E2. The animals were then tested in the black and white model (BWM) and the open field test (OFT). Quinpirole (0.1 mg/kg, i.p.) administered alone or in a combination with a low dose of 17β-E2 (5.0 μg/rat, s.c.) resulted in anxiolytic-like effect in OVX rats in the BWM. Repeated treatment of quinpirole and 17β-E2 profoundly increased anxiolytic-like effect of the single substances they exert per se. Co-administration of quinpirole with 17β-E2 increased frequency of rearing and grooming in OVX rats in the OFT. Sulpiride (10.0 mg/kg, i.p.) treatment failed to alter anxiety-like behavior in OVX rats in the BWM. In addition, sulpiride blocked the anxiolytic-like effect of 17β-E2 in OVX rats. Application of neither sulpiride nor sulpiride plus 17β-E2 led to any changes of rearing and grooming behavior in OVX rats in the OFT. The results of the present study suggest that 17β-E2 and quinpirole interact to exert anxiolytic-like action and that each of these drugs can potentiate effects of each other. Further research is needed to elucidate detailed mechanisms by which quinpirole and 17β-E2 exert synergistic effect on anxiety-related behavior.