Histamine induces a persistent increase of the firing rate of MnPO neurons.

A. Spontaneous firing activity recorded before and during local application of histamine (50 µM). Histamine induced a depolarization (∼3 mV) and increased the firing rate from 1.7 Hz to 3.6 Hz. Histamine (50 µM) was reapplied twice following a ∼22 min washout period after each application (middle and lower traces). Note that after the first histamine incubation the firing rate recovered only partially and remained elevated throughout the experiment. B. Average firing rate (for every 20 s) recorded before, during and after three incubations with histamine (50 µM), separated by ∼22 min washout periods. Data are from three MnPO neurons recorded in slices. The white circles (○) correspond to the experiment presented in A.