Figure 3.

Calcium-dependent regenerative potential at the critical frequency. (A) Reconstruction of a biocytin-filled L5 pyramidal neuron from a 33-day-old rat with a dendritic whole-cell patch pipette located 670 μm from the soma and a second pipette located at the soma. (B) Control response recorded at the dendritic site (top trace) at the critical frequency (90 Hz, solid line) and subcritical frequency (80 Hz, dashed line). A small depolarization was observable at the soma (arrow, bottom trace; 90 Hz) corresponding to the fourth broad AP recorded at the dendritic site. (C) After the addition of the voltage-sensitive calcium channel blocker Cd²⁺ (50 μM), the response recorded at both sites was similar to the response at subcritical frequencies. The effect was largest on the last two APs in the train, with only a slight reduction in the duration of the second AP, suggesting that the increase in amplitude of the second AP is not dependent on Ca²⁺ influx. The horizontal dashed lines represent 0 mV at the dendritic recording.