Figure 3

Latencies between somatic spikes and axonal ones favor somatic origins of sequential spikes. A) Top panel shows an electrical circuit for cellular membrane, Cm, membrane capacitance; Rin input resistance and Rv, voltage-gated conductance. Middle panel illustrates sequential spikes (black line) subtracted from the responses (gray dot-line) by depolarization and hyperpolarization. Bottom shows the derivative of spike potentials with respect to time (dv/dt). B) shows the expanded waveforms of dv/dt vs. time for a somatic spike (red trace) and axonal one (blue). A vertical line shows a location of spike initiation, which is defined as a time point of minimal dv/dt but larger than zero. C) illustrates latencies between somatic spikes and axonal ones (ΔT = Tsoma-Taxon) versus spikes. D) shows the measurement in the amplitudes of spike dv/dt and the time of minimal dv/dt to peak in the intracellular use of QX-314 (0.5 mM). E) shows the proportional correlation between the amplitudes of spike dv/dt and the time of minimal dv/dt to peak (36 spikes from three cells) in the partial inactivation of VGSCs. F) The rising phase of spikes is better fitted into two exponentials under the control (r² = 0.99), and a single exponential (r² = 0.99) under QX-314 application.