FIGURE 5.

Ni²⁺ application changed tonic firing mode into phasic. Spiking responses of a tonic (A) and a phasic (B) neuron to depolarizing current injection before (control), during (Ni²⁺), and after (washout) bath application of the Ca²⁺ channel blocker, Ni²⁺. All scale bars and legends, except for the vertical bar in the current waveforms, are shared between (A) and (B). (A1) Upper panel, Spiking responses obtained with threshold (gray trace) and three-time threshold (black trace) current injection. Corresponding current waveforms are shown in lower panel. Ni²⁺ application increased threshold current (see no spiking at control threshold current, black dotted lines) and changed the firing pattern of this tonic neuron into phasic. Threshold current and tonic firing behavior were recovered by washout. Initial response traces for 150 ms after current onset are shown in (A2). (A3) Superimposed traces of action potentials induced by threshold current injection. Traces are aligned at peak time and threshold voltage. Ni²⁺ application (cyan) reduced the amplitude and increased the width of action potentials from control (black). The effects recovered, at least partially, after washout (black dotted line). (B) Ni²⁺ application further facilitated spike frequency adaption and increased the threshold current intensity of the phasic neuron (B1 and initial 150 ms response B2), but effects on spike waveform were much smaller compared to tonic neurons (B3).