A-437203 is a selective D₃ receptor antagonist with K_i of 71, 1.6, and 6220 nM for D₂, D₃, and D₄ receptors, respectively. IC50 & Target: Ki :71 nM (D₂ receptor), 1.6 nM (D₃ receptor), 6220 nM (D₄ receptor)^[1] In Vitro: A-437203 is an antagonist with high affinity for D₃ receptors and relatively high selectivity compared to other dopamine receptor subtypes (44-fold selective for D₃ vs D₂)^[1]. In Vivo: A-437203, a selective D₃ receptor antagonist, is initially tested alone in rat forced swim test (FST). Doses of A-437203 evaluated are 0.52, 1.75, 5.24, and 17.46 μmol/kg i.p. Doses are chosen based on the selectivity of A-437203 for D₃ vs D₂ dopamine receptors and reports indicating that the effects of A-437203 at doses of 17.46 μmol/kg (10 mg/kg) or lower are clearly mediated by D₃ but not D₂ receptors, since higher doses of the compound such as 174.6 μmol/kg (100 mg/kg) are necessary to bind and block D₂ receptor from the irreversible inactivation induced by the alkylating agent EEDG. ANOVA revealed no significant difference between the treatments for any of the behaviors analyzed (F_{4, 45}=1.12, p=0.359 for immobility, F_{4, 45}=0.188, p=0.943 for climbing, and F_{4, 45}=1.634, p=0.182 for swimming). Based on these results, the dose of 17.46 μmol/kg i.p. of A-437203 is selected for further experiments^[1].