Fig. 1.

Integrated firing rate histogram of a dorsal hippocampus CA₃ pyramidal neuron, showing its responsiveness to microiontophoretic application of 5-HT in control (A) and rats treated with mirtazapine (B). These neurons were activated with a quisqualate ejection current of +1 and −1 nA. Horizontal bars indicate the duration of the applications (current given in nanoamperes). Note the altered effectiveness of 5-HT to suppress firing activity after administration of WAY 100635 (0.1 mg/kg, i.v.) in control (A) and treated rats (B). At the bottom ofA and B, the responsiveness to 5-HT in controls and rats treated with mirtazapine is expressed as the number of spikes suppressed per 10 nA; the number in the columns indicates the number of neurons and rats tested. *p < 0.01 (paired Student’s ttest).