Figure 3. nAChR activation suppresses ON-evoked responses in MCs. Ai, Voltage-clamp recording from a representative MC. The ON was electrically stimulated at the two black arrows. A 1 s, 1 mm ACh/At puff was focally applied at the red arrow. Aii, Top traces, Left, Expanded trace of the ON-evoked EPSC from Ai under control conditions. Right, During the ACh/At-induced current, the eEPSC in Ai is suppressed. Bottom traces, During bath application of 10 μm GBz and 1 μm CGP 54626. Left, An eEPSC from the same cell as in Ai, in the presence of the GABA receptor blockers. Right, In the presence of the GABA receptor blockers, during the ACh-induced current, the nAChR-mediated suppression of eEPSCs is abolished. B, Left, Data from a single MC showing eEPSCs elicited by ON stimulation at various intensities (30–80 μA). Right, The same cell shows suppression of all ON responses when elicited during the ACh/At-induced currents. C, Left, Amplitude histogram showing a leftward shift of eEPSC amplitude distributions for relatively weak ON stimulation intensities in the presence of ACh/At (black) compared with control (gray; n = 8, p < 0.0001). Center, Similar leftward shift is observed for high ON stimulation intensities. eEPSC values in the left and center panels were normalized to the mean eEPSC values under control conditions for high stimulus intensities. Right, In the presence of 10 μm GBz + 1 μm CGP-54626, the leftward shift of the eEPSC distribution was abolished (black) and was significantly shifted to the right of the control distribution (gray; n = 5, p < 0.03, K-S test).