Functional Characterization of Intrinsic Cholinergic Interneurons in the Cortex

Activation of EGFP/ChAT-positive neurons leads to an increase in the frequency of spontaneous EPSCs in pyramidal neurons. A, Spontaneous EPSCs were recorded in a pyramidal neuron (2) before, during, and after activation of an adjacent EGFP/ChAT-positive neurons (1). B, The average increase of spontaneous sEPSC frequency in pyramidal neurons is 0.6 Hz after the activation of the EGFP/ChAT-positive neurons (Δf_{stim − pre}). The increase is significantly different from the change from the pre period to control periods, during which the EGFP/ChAT cell was not stimulated (Δf_{ctr(stim) − pre}, Δf_{ctr(post) − pre}). There is no significant increase in the sEPSC frequency in the post period (Δf_{post − pre}). The effect can be blocked with hexamethonium, a blocker of nAChRs. Activation of “control” pyramidal (pyr, 3 in C) cells does not show this effect. The activation of EGFP/ChAT-positive neurons does not alter the frequency of sIPSCs. Error bars indicate ±SEM (p < 0.05). C, Experimental configuration and proposed mechanism. The modulatory effect induced by EGFP/ChAT-positive neuron activation (1) is mediated by presynaptic nAChRs. SEPSCs were recorded in pyramidal cells (2). Stimulation of control pyramidal cells (3).