I₁-imidazoline receptors mediate the moxonidine-induced inhibition of IPSCs. A, B, Moxonidine (mox; 30 μm) was applied in the presence of efaroxan (efa; 10 μm) or idazoxan (ida; 10 μm), which block both imidazoline receptors (I₁ for efaroxan and I_1,2 for idazoxan) and α2-adrenergic receptors. The inhibitory effect of moxonidine on IPSCs was primarily attenuated. C, D, No impairment of the moxonidine (30 μm)-induced inhibition of IPSCs in the presence of yohimbine (yoh; 10 μm) and SKF86466 (SKF; 10 μm), both of which are α2-adrenergic receptor antagonists with no affinity for imidazoline receptors. Each point represents the mean amplitude of six consecutive IPSCs evoked at 0.1 Hz. Example traces on each graph are the averaged IPSCs in control and in moxonidine (smaller trace). Calibration: 500 pA, 20 ms. E, Summary of the effects of imidazoline and/or α2-adrenergic receptor antagonists on the moxonidine-induced inhibition of IPSCs. Each column represents the mean ± SEM. The significance of differences between the values for the moxonidine alone (n = 5) and antagonist-treated groups (n = 4–5) was determined with the two-tailed multiple t test with Bonferroni’s correction following ANOVA (4 comparisons in 5 groups). **p < 0.01.