Resonance of Spike Discharge Modulation in Neurons of the Guinea Pig Medial Vestibular Nucleus

1 Laboratoire de Neurobiologie des Réseaux Sensorimoteurs, Centre National de la Recherche Scientifique, Université Paris 5, ESA 7060, 75270 Paris Cedex 06, France; and 2 Laboratory of Neurosciences, University of Mons-Hainaut, B-7000 Mons, Belgium Ris, L., M. Hachemaoui, N. Vibert, E. Godaux, P. P. Vidal, and L. E. Moore. Resonance of Spike Discharge Modulation in Neurons of the Guinea Pig Medial Vestibular Nucleus. J. Neurophysiol. 86: 703-716, 2001. The modulation of action potential discharge rates is an important aspect of neuronal information processing. In these experiments, we have attempted to determine how effectively spike discharge modulation reflects changes in the membrane potential in central vestibular neurons. We have measured how their spike discharge rate was modulated by various current inputs to obtain neuronal transfer functions. Differences in the modulation of spiking rates were observed between neurons with a single, prominent after hyperpolarization (AHP, type A neurons) and cells with more complex AHPs (type B neurons). The spike discharge modulation amplitudes increased with the frequency of the current stimulus, which was quantitatively described by a neuronal model that showed a resonance peak >10 Hz. Modeling of the resonance peak required two putative potassium conductances whose properties had to be markedly dependent on the level of the membrane potential. At low frequencies ( 0.4 Hz), the gain or magnitude functions of type A and B discharge rates were similar relative to the current input. However, resting input resistances obtained from the ratio of the membrane potential and current were lower in type B compared with type A cells, presumably due to a higher level of active potassium conductances at rest. The lower input resistance of type B neurons was compensated by a twofold greater sensitivity of their firing rate to changes in membrane potential, which suggests that synaptic inputs on their dendritic processes would be more efficacious. This increased sensitivity is also reflected in a greater ability of type B neurons to synchronize with low-amplitude sinusoidal current inputs, and in addition, their responses to steep slope ramp stimulation are enhanced over the more linear behavior of type A neurons. This behavior suggests that the type B MVNn are moderately tuned active filters that promote high-frequency responses and that type A neurons are like low-pass filters that are well suited for the resting tonic