Fig. 3

Application of a D2-like receptor (D2R) agonist did not affect all synapses in the deep cerebellar nuclei. A: Effects of the D2R agonist, quinpirole (QPR) on glutamatergic synapses in deep cerebellar nuclei neurons. Application of QPR induced a significant inhibitory effect on EPSC amplitude in a subset of synapses classified as “Responders” (filled circles; right inset traces; n = 8). In contrast, no substantial inhibition was observed in the remaining synapses, termed “Non-responders,” which showed no more than 90% inhibition by QPR (open circles; left inset traces; n = 6). B: Representative time course showing QPR-induced inhibition of eEPSC amplitude. Most synapses were inhibited by QPR application. The traces labeled a and b were obtained at the indicated time points in the graph and are superimposed for comparison (inset). C: Representative time course of a non-responder (QPR-insensitive) synapse. Approximately 30% of synapses did not show inhibitory effects following QPR application (traces a and b in the inset, before and after QPR application, respectively). By contrast, dopamine showed inhibitory effects (trace c, after DA application, in the inset). These results suggest that D2R-induced inhibitory effects exhibit heterogeneity due to variable receptor expression at glutamatergic synaptic terminals.