Figure 9.

Cholinergic afferents to layer 4 mediate hyperpolarizing inhibition. A, Schematic of experimental setup. Glutamatergic EPSPs in layer 4 neuron were paired with single optical stimulus (5 ms), applied 1 s before electrical stimulation. Recordings were performed in the presence of APV (25 μm) to block recurrent activity. B, Glutamatergic-evoked spikes are significantly suppressed or delayed, as shown for several trials in control (black) or with paired optical stimulation (blue). C, Summary data showing cholinergic-mediated suppression of spiking suppression (n = 10 cells). **p < 0.01. D, mAChR-mIPSPs do not cause shunting of glutamatergic EPSPs. Top, Light-evoked mIPSP was paired with a train (40 Hz) of electrically evoked glutamatergic EPSPs (delay: 1 s). Bottom, Close-up of glutamatergic EPSPs in top trace showing that paired response (blue trace) is identical to linear sum of mIPSP and EPSPs evoked separately (red trace). E, Summary data quantifying both area under the paired EPSPs and amplitude of the first paired EPSP, normalized to their respective unpaired controls (n = 16 cells).