Figure 3.

Synaptic activation of M2 mAChRs evokes IPSCs mediated by GIRK channels. TRN neurons were recorded with a K-based internal solution, except in E and F. A, Biphasic (E–I) postsynaptic response in a TRN neuron, with inward current blocked by the nAChR antagonist DHβE (3 μm). The remaining outward current was blocked by the mAChR antagonist atropine (10 μm). B, Plot of the cumulative distribution of E/I ratios (n = 17 experiments). For biphasic responses, E was defined as the current integral between nEPSC onset and zero crossing (inward current). I was defined as the current integral following the zero crossing (outward current). C, D, IPSCs display inward rectification. IPSCs were evoked for a range of different holding potentials (C). IPSC amplitudes are plotted against membrane potential for the same neuron (D). E, Representative experiments showing cholinergic postsynaptic currents recorded with a K-based internal solution (left) or Cs-based internal solution (right), under control condition (black traces) and following application of AF-DX 116 (10 μm, gray traces). F, Summary data plot half width of the nEPSC recorded with a K-based internal solution (left) or a Cs-based internal solution (right) before and following AF-DX 116 (10 μm) application. **p < 0.01, paired Student's t test. n = 6. G, In TRN neurons recorded with an internal solution supplemented with GDPβS (1 mm), isolated muIPSC amplitude strongly attenuated following establishment of whole-cell configuration at t = 0 (filled circles). Control (open circles) shows recordings without GDPβS. Experiments were performed in the presence of hexamethonium (100 μm) to block nEPSC. n = 6–7. H, Summary showing the effect of atropine (10 μm), AF-DX 116 (10 μm), GDPβS (1 mm), Ba²⁺ (200 μm), tertiapin-Q (200 nm) on the isolated muIPSC amplitude, normalized to control. For tertiapin-Q experiments, cells were held at ∼−105 mV to measure inward currents. n = 5–7.