Figure 6.
Electrophysiological properties of MHbVL and MHbVC neurons. A, Diagram of approximate location of MHbVL and MHbVC. B, Hyperpolarization-activated cation currents (Ih) in MHbVC and MHbVL. MHb neurons were voltage-clamped at −60 mV, and the command voltage was pulsed to −120 mV for 1 s. The amplitude of the voltage-dependent inward current response was measured beginning with the current value at the end of the capacitive transient (indicated by the broken line), ending with the current value at the end of the voltage step. Representative Ih current traces are shown for MHbVL and MHbVC cells. Calibration: 100 pA, 200 ms. C, Quantification of Ih currents. A bar graph is shown for all recorded MHbVC (n = 13) and MHbVL (n = 18) cells. **p < 0.01 (unpaired t test). D, Measurement of rebound (anode break) delay in MHbVC and MHbVL neurons. MHb neurons recorded in whole-cell configuration were current-clamped (I = 0), followed by injection of hyperpolarizing (−75 pA) current. The latency to firing an action potential after the end of the pulse (from the broken line to the arrowhead) was measured for MHbVC and MHbVL neurons. Representative current traces are shown for MHbVL and MHbVC cells. Calibration: 50 mV, 200 ms. E, Quantification of rebound delay responses. A bar graph is shown for all responses from MHbVL (n = 18) and MHbVC (n = 13) neurons. **p < 0.01 (unpaired t test). F, Action potential amplitude adaptation in MHb neurons. MHb neurons were current-clamped (I = 0), and depolarizing current (50 pA) was injected. The amplitude of the first and last spike in the train was measured (between the two broken lines), and the adaptation ratio (last spike amplitude/first spike amplitude) was calculated for each cell. Calibration: 50 mV, 200 ms. G, Quantification of adaptation ratio measurements from F. A bar graph is shown for all adaptation ratio responses from MHbVL (n = 18) and MHbVC (n = 13) cells. **p < 0.01 (unpaired t test). H, J, For each recorded MHbVL (H; black open circles) and MHbVC (J; red open circles) neuron, Ih current amplitude was plotted on the x-axis, and rebound delay was plotted on the y-axis. Linear regression analysis was performed on the plotted data points, and r2 and p values are shown. I, K, For each recorded MHbVL (I; black open circles) and MHbVC (K; red open circles) neuron, Ih current amplitude was plotted on the x-axis, and adaptation ratio was plotted on the y-axis. Linear regression analysis was performed on the plotted data points, and r and p values are shown.