Acetylcholine induced modulation of hippocampal pyramidal neurons.

Applications of acetylcholine to hippocampal slices maintained in vitro resulted in slow depolarizations and simultaneous increases in membrane resistance (RN)in hippocampal pyramidal neurons. Increases in RN had both voltage dependent and voltage independent components. These effects were associated with increases in cell discharge frequency, and development of spontaneous as well as synaptically and directly evoked burst discharges. The increase in RN and burst firing lasted for hours. Muscarinic antagonists blocked these actions and in addition, produced a decrease in membrane resistance, which appeared to be due to blockade of a tonic effect of acetylcholine on postsynaptic membrane properties. These findings suggest that ACh acts as a neuromodulator in the hippocampus.