Figure 4.

TTX reduces both amplification and prolongation, whereas Ni²⁺ selectively reduces prolongation. A, Average response in a typical tonic neuron to near-threshold stimulation under three conditions: control, with Ni²⁺, and with Ni²⁺ plus TTX. B, Average response in a different tonic neuron before and after application of TTX alone. As illustrated here, TTX did not noticeably affect the response to brief hyperpolarizing stimulation, which was similarly true for Ni²⁺ (data not shown). C, Cumulative data confirms that Ni²⁺ had no effect on ratio of peak voltage change (peak_depol/peak_hyperpol), whereas TTX significantly reduced it (n = 4; ^*p < 0.05; Mann-Whitney U test), implicating a Na⁺ current in amplification while ruling out Ca²⁺ currents. D, In contrast, the ratio of area under the curve (area_depol/area_hyperpol) was significantly reduced by Ni²⁺ (n = 4; ^*p < 0.05; Mann-Whitney U test), although subsequent application of TTX reduced it even further (n = 4; ^*p < 0.05; Mann-Whitney U test), indicating both Na⁺ and Ca²⁺ currents contribute to prolongation.