Figure 7.
Influence of D1 and D2 receptor activation on the tonic current mediated by α4βδ GABAARs in D1-and D2-MSNs. A, Histogram illustrating the influence of D1 and D2 receptors on the tonic current mediated by α4βδ GABAARs expressed in D1-MSNs (white columns) and D2-MSNs (black columns). The acute application of the D1 antagonist SCH23390 (10 μm) had no effect on the tonic current of D1-MSNs. In contrast, the acute application of the D1 receptor agonist SKF81297 to D1-MSNs, but not to D2-MSNs, induced an inward current that was reduced by intracellular GDP-βS. Similarly, acute amphetamine (10 μm) induced an inward current for D1-MSNs. Note that the effect of amphetamine on D1-MSNs was prevented by the D1 antagonist SCH23390 (10 μm), demonstrating this psychostimulant to influence tonic inhibition by increasing ambient dopamine. The effect of D1 receptor activation on tonic inhibition is well maintained, because prolonged incubation (>1 hour) with SKF81297 caused a much greater tonic current (revealed by bicuculline 30 μm) in D1-MSNs compared with control. In contrast, D2 receptor activation by acute quinpirole (10 μm) and D2 receptor inhibition by acute sulpiride (2 μm) had no effect on the tonic current of D2-MSNs. However, prolonged incubation with quinpirole (10 μm) produced a modest decrease of the tonic current of D2-MSNs. The bars represent the mean ± SEM. *p < 0.05; **p < 0.01; ***p < 0.001, Student's unpaired t test. B, Representative trace demonstrating the increase in holding current produced by the bath application of SKF81297 (10 μm). Note that bicuculline (30 μm) reverses the increased current and reveals an additional outward current. The broken lines indicate the mean holding current. The corresponding all-points histograms are given to the right of the trace (white = control; black = + SKF81297; gray = SKF81297 + bicuculline). SKF, SKF81297; SULP, sulpiride; QUIN, quinpirole; SCH, SCH23390; AMPH, amphetamine; inc, incubated.