Figure 5. Blocking Ih reduces the spontaneous firing rate of GnRH neurons. A, B, Effect of ZD7288 on firing activity of GnRH neurons. Membrane potential under the trace indicates potential at onset of trace. B, Some cells exhibited frank hyperpolarization in addition to a reduction in firing activity. A 10 pA current injection shown at the end of the trace in B illustrates the cell is still capable of generating action potentials. C, Firing rate before (gray bars) and during (black bars) ZD7288 treatment in all GnRH neurons (left, n = 17) and in only responding GnRH neurons (right, n = 9). D, Examples of single spike and burst firing; brackets below trace indicate bursts. S, Single spike. E, Blocking Ih reduces both single spikes and the number of spikes/burst. *p < 0.01, #p < 0.05. F, Representative example of the effect of ZD7288 (red) on the slope of the recovery from the AHP following single spikes (n = 16). **p < 0.001. G, Mean ± SEM membrane potential at points A (AHP amplitude) and B (200 ms post AHP peak) in F (n = 10). H, Example of interspike membrane potential dynamics in a two-spike burst; red trace is after ZD7288. I, Representative current-clamp recordings with ZD7288 included in the pipette solution showing response to a 50 pA hyperpolarizing current injection; rebound and sag disappear over time. J, Mean ± SEM amplitude of sag and rebound over time with ZD7288 in the pipette. K, Representative recordings illustrating action potential waveform at times indicated with control internal (left) and ZD7288 internal (right).