Electrophysiological characteristics of typical IB ACC neurons. A, Schematic representation of the location of the recorded neurons (a and b); B, Biocytin profiles of two representative IB 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 a big afterdepolarization (ADP), which could facilitate an action potential and therefore, formed a burst response; D, I-V plots constructed from the values of traces shown in (C) displayed a linear response in the voltage range between -60 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. When held at a hyperpolarized membrane potential, the burst response was evoked in response to the depolarizing current injections. By contrast, with gradual depolarization (Vm ≥ -65 mV) (left to right), a train of single spikes was evoked in response to the same current pulse and the burst was inactivated. The dotted line denotes the resting membrane potential. Note that 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 60, 80 and 100 pA from the holding potential of -70 mV. Note that a lower current intensity evoked an initial doublet of action potentials while higher current evoked an initial doublet of action potentials followed by a regular discharge. Note that the black traces were for cell (a) and gray traces for cell (b).