Figure 2.

Heterogeneous electrophysiological properties of spinal V3 interneurons. A, B, representative traces from two V3 INs responding to 1 s suprathreshold current steps. A, A dorsal V3 IN labeled by neurobiotin (Ai) displays initial bursts at low (Aiii, 40 pA) and high (Aii, 140 pA) injected currents. B, A ventral V3 IN (Bi) maintains tonic firing with 10 pA (Biii) and 50 pA (Bii) injected currents. White arrows in Ai and Bi point to the recorded cells; neuron's bodies are labeled with a white dot to show their position. Black arrows in Aii and iii point to the afterhyperpolarization potential after the depolarization pulses. The schematic diagrams show the injected currents. C, individual spike frequency is plotted versus time during 1 s injected current on dorsal cell (circles) and ventral cell (triangles). D, Average spike frequency of dorsal cells (circles) and ventral cells (triangles) was plotted versus injected currents. E, Representative traces from two V3 neurons hyperpolarized to −75 mV (black) and −105 mV (gray). The dashed lines indicate the membrane potentials. F, Plots of the size of sag voltage versus membrane potentials of the two cells. G, Histograms showing the distribution frequency of various electrophysiological properties of all recorded V3 neurons: C_m (i), sag voltage amplitude (ii), slope of f–I plot (iii), and frequency of first spike (first sp freq, iv).