IH and IM currents are not required for persistent firing. A, Bath application of the specific IH blocker ZD7288 (10 μm) hyperpolarized L5 pyramidal cells. Symbols represent the mean ± SEM. B, Blockade of IH by ZD7288 eliminated the membrane potential sag evident in responses to hyperpolarizing current steps (top) but did not abolish persistent firing evoked by a depolarizing step (bottom, both representative of 5 of 5 cells tested). C, ZD7288 significantly reduced sag ratio. *p = 0.0257, T = 3.464, df = 4, paired t test; for details of sag ratio analysis, see Materials and Methods). ZD7288 did not block persistent firing in 5 of 5 cells tested (n.s., p = 1.00, Fisher's exact test). D, Blockade of IH by ZD7288 did not occlude the ability of Terf to abolish persistent firing (representative of 4 of 4 experiments). E, Attenuation of IM current with XE991 (10 μm) did not occlude persistent firing in CCh. F, + Linopirdine (30 μm), another M current blocker, also failed to abolish persistent firing. G, Plot of the increase in number of spikes evoked during the depolarizing step before and after + Linopirdine. **p = 0.0087, T = 4.797, df = 4. H, Plot of the increase in number of spikes with linopridine following CCh treatment. *p = 0.020, T = 7.024, df = 2. Both paired t tests.