Fig. 7.
The second derivative of voltage (d2V/dt2) at the onset of the depolarizing phase of the PD neurons decreased when Ih was blocked. DeP, depolarization phase; ReP, repolarization phase. The shaded sections show the repolarization phases. Arrowheads indicate the onset of the depolarizing phase. A1 and B1: black traces, the slow oscillations; gray traces, the original voltage traces. A2 and B2: voltage vs. the first derivative of voltage (dV/dt) diagrams, traces travel clockwise, dV/dt at the onset of the depolarizing phase decreased after application of 30 mM CsCl. A3 and B3: dV/dt vs. d2V/dt2 diagrams, black arrowhead shows d2V/dt2 at the onset of the depolarizing phase. Note that, after the onset, application of 30 mM CsCl (B3) causes the rate of depolarization to decelerate (d2V/dt2 < 0), leading to a much slower depolarization phase (B2 and B1).