(A) Representative dynamic clamp recordings, where INa generated by a non-LTI (black traces) or LTI (red traces) Nav model was injected in a neuron, under different levels of Nav conductance (GNa). The endogenous sodium current was blocked with bath-applied TTX. (B) Spiking frequency increases proportionally with GNa, over a range typical for neonatal RO neurons, with INa generated by either the non-LTI model (black symbols and fit line, mean ± SE; slope = 0.148 ± 0.011, intercept = 4.34 ± 0.14, n = 7, F-test, p=0.13) or the LTI model (red symbols and fit line; slope = 0.202 ± 0.026, intercept = 2.48 ± 0.346, n = 7, F-test, p=0.0093). The two datasets are statistically different (paired two-tailed t-test, p=0.0394). (C) Representative dynamic clamp traces obtained with INa generated by the non-LTI (top) or LTI (bottom) model, illustrating how the action potential and the interspike interval are shaped by GNa. The data were obtained without stimulation (IInj = 0) from RO neurons in neonatal rat brainstem slices.