Fig. 5
Dopamine (DA)-induced inhibitory action correlated with sensitivity to the D2-like receptor (D2R) agonist. A: In the presence of the α2-AdR antagonist RS79948, the DA-induced inhibitory effect was reduced on average. Pooled data from 14 experiments revealed that DA application decreased eEPSC amplitude below 90% of the baseline in nine cases, which were selected and plotted (filled circles, n = 9). Following DA application, the D2R agonist quinpirole (QPR) was applied. Five synapses tested showed reduced sensitivity to DA, with eEPSC amplitude remaining above 90% of the baseline (open circles, n = 5). Modulatory effects of QPR were similarly less effective at these synapses. A schematic drawing of the action sites of the two types of catecholaminergic receptors is shown on the right. B: A highly significant correlation was observed between the inhibitory effects of QPR and DA-induced inhibition under conditions where α2-AdRs were blocked (r2 = 0.71).
