D2 receptor activation dose-dependently inhibits dopamine overflow.

<p>A) DA was electrically-evoked at intervals of 2 min. The peak amplitude of DA overflow is normalized to the average amplitude of the first 6 recordings (10 min) of the control period and graphically plotted against time (means ± SEM). The control trace (n = 8;6) shows that evoked DA overflow was stable over time. Quinpirole was applied for 4 min (represented by the gray bar) at 3 different doses. Drug effects were measured at their peak (rectangle at 16 min). Sulpiride (5 µM) blocked entirely the effect of quinpirole. (B) Histogram showing the peak effect of quinpirole on DA overflow. A one-way ANOVA was used to compare groups. The effect of quinpirole at 0.1 µM (n = 5;4), 0.5 µM (n = 7;4) and 1 µM (n = 27;18) was significant. The D3 receptor subtype blocker, GR103,691, only reduced quinpirole effect at the non-selective dose of 1 µM (n = 4;2), while its effect was non-significant at 100 nM (n = 6;2). Used at 1 µM, L741,626, a D2 subtype selective blocker, significantly reduced the effect of quinpirole (n = 6;2). Sulpiride (5 µM), a broad-spectrum D2-family receptor antagonist, complety blocked the effect of quinpirole (n = 3;2). *** p<0.001 <i>Abbreviations</i>: Q, Quinpirole; Quinp, Quinpirole; GR, GR103,691; L, L741,626, Sulp, Sulpiride.