Fig. 1.

Acetylcholine (ACh)-mediated slow currents and increased spontaneous inhibitory postsynaptic current (sIPSC) frequency in external tufted (ET) cells. Ai: an ET cell loaded with Alexa 488 dextran displays the extensive dendritic arborization within a glomerulus. Scale bar = 10 μm. Aii, top trace: a 1-s, 1 mM ACh/atropine (At) application (arrow) leads to a barrage of sIPSCs (upward deflections) in the ET cell from Ai, held at −30 mV. Bottom trace: the same cell, when held at −70 mV, displays a small, slow inward current upon ACh/At application, that is superimposed on spontaneous excitatory postsynaptic currents (sEPSCs) (downward deflections). Bi: a few individual sIPSCs from the barrage in the upper trace in Aii. Bii: frequency plot of sIPSCs in the ET cell upon three consecutive ACh/At (1 s) applications (beginning at arrows). C: ACh/At application increased the average sIPSC frequency by 20.3 ± 1.7-fold (n = 52, ***P < 0.001). Di: an ET cell, under current clamp, exhibits an increase in its average spike frequency upon 1 mM ACh/At application (1 s beginning at arrow). Action potential (AP) frequencies were calculated for 5 s from the onset of agonist application. Dii: ET cells exhibit a significant increase in average firing frequency (n = 11, *P < 0.05) upon nicotinic acetylcholine receptor (nAChR) activation, recorded under whole-cell current clamp.