Dopamine D1 receptor activation maintains motor coordination and balance in rats

Dopamine (DA) modulates motor coordination, and its depletion, as in Parkinson's disease, produces motor impairment. The basal ganglia, cerebellum and cerebral cortex are interconnected, have functional roles in motor coordination, and possess dopamine D-1 receptors (D(1)Rs), which are expressed at a particularly high density in the basal ganglia. In this study, we examined whether the activation of D(1)Rs modulates motor coordination and balance in the rat using a beam-walking test that has previously been used to detect motor coordination deficits. The systemic administration of the D1R agonist SKF-38393 at 2, 3, or 4 mg/kg did not alter the beam-walking scores, but the subsequent administration of the D1R antagonist SCH-23390 at 1 mg/kg did produce deficits in motor coordination, which were reversed by the full agonist SKF-82958. The co-administration of SKF-38393 and SCH-23390 did not alter the beam-walking scores compared with the control group, but significantly prevented the increase in beam-walking scores induced by SCH-23390. The effect of the D1R agonist to prevent and reverse the effect of the D1R antagonist in beam-walking scores is an indicator that the function of D(1)Rs is necessary to maintain motor coordination and balance in rats. Our results support that D(1)Rs mediate the SCH-23390-induced deficit in motor coordination.