Effects of voltage trajectory on action potential voltage threshold in simulations of cat spinal motoneurons

A single-cell neuronal model was used to investigate the effect of membrane trajectory on voltage threshold (V(th)) for action potential generation. Previous results suggested that hyperpolarization of V(th) could be produced by a rapid membrane depolarization, but this effect is limited to the first spike in a train. This study shows rapid current injections hyperpolarize V(th) because they are more effective in activating the sodium current underlying spiking. The hyperpolarization of V(th) induced by rapid membrane depolarization becomes less effective in altering V(th) when other mechanisms of enhancing the fast sodium current underlying action potentials are activated. (C) 2000 Published by Elsevier Science B.V. All rights reserved.