Histamine produces a Ca2+-sensitive depolarization of hippocampal pyramidal cells in vitro.

Electrophysiological activity was recorded intracellularly from pyramidal neurons in rat hippocampal slices. Topical application of histamine produced a slow depolarization that was not associated with conductance changes. The depolarization was accompanied by an increase in the rate of action potential discharges. These effects were markedly reduced in slices maintained in a low Ca2+, high Mg2+ medium, indicating that histamine may act presynaptically on hippocampal pyramidal neurons.