INaP slow inactivation and slow recovery from inactivation are required for oscillatory bursting. (A and B) INaP was added to preBötC nonbursters via DC by injecting the conductance (GNaP) predicted by Model 1 (A) or Model 2 (B). The recordings were obtained under bath-applied Cd2+ (200 µM) and CNQX (20 µM). (A) CC recording from a representative neuron, with INaP generated by Model 1. The neuron exhibits robust bursting activity, similar to intrinsic bursters. (B) Same cell as in A but with INaP generated by Model 2. The difference in GNaP accounts for the difference in maximum availability between the two models. The neuron now exhibits bimodal activity, with random transitions between sustained firing and quiescence. There are no isolated action potentials during the silent phase, as observed with Model 1 (A), and the bAHP and the gradual interburst depolarization are virtually absent. (C) Statistical comparison between Model 1– and Model 2–induced firing patterns within the same cell. The “on” interval refers to the burst (514.2 ± 89.6 ms) or sustained firing (4,257.6 ± 2,109.3 ms) duration, whereas the “off” interval refers to the interburst (4,774.7 ± 618.0 ms) or quiescent (1,927.6 ± 523.2 ms) interval, for Model 1 or Model 2, respectively. The bAHP is 2.4 ± 0.5 mV for Model 1 and 0.81 ± 0.4 mV for Model 2. All three parameters are significantly different between the two models (n = 12, paired t; on interval, P = 0.00075; off interval, P = 0.00012; bAHP, P = 0.000021). The data in C are mean ± SD.
