Electrophysiological characteristics of the IM cells. A, Schematic representation of the location of the recorded neurons (a and b); B, Biocytin profiles of those two representative IM ACC pyramidal neurons as visualized with confocal laser scanning microscopy. Scale bar = 50 μm. C, Superimposed current-clamp traces in response to a series of intracellular current pulses (1000 ms, 80 pA per step). The neurons exhibited an AHP with an early fast and a delayed slow component. Fast and slow components were intercalated by an afterdepolarization (ADP). D, I-V plots constructed from the values of traces shown in (C) showed a linear response in the voltage range between -65 and -85 mV. E, Traces evoked by the same current injections (400 ms, 100 pA) as the neurons were depolarized from -85 to -50 mV. Note that on no occasion did the IM neurons fire in bursts. The black traces were for cell (a) and gray traces for cell (b); F, Action potential trains were evoked by 400 ms current injection of 120, 140, 160 and 180 pA from the holding potential of -70 mV. Note that only the first spike was followed by an ADP. Traces reflect spike frequency adaptation in evoked action potential trains. The black traces were for cell (a) and gray traces for cell (b).