title: Differential intrinsic response dynamics determine synaptic signal processing in frog vestibular neurons.
abstract: Central vestibular neurons process head movement-related sensory signals over a wide dynamic range. In the isolated frog whole brain, second-order vestibular neurons were identified by monosynaptic responses after electrical stimulation of individual semicircular canal nerve branches. Neurons were classified as tonic or phasic vestibular neurons based on their different discharge patterns in response to positive current steps. With increasing frequency of sinusoidally modulated current injections, up to 100 Hz, there was a concomitant decrease in the impedance of tonic vestibular neurons. Subthreshold responses as well as spike discharge showed classical low-pass filter-like characteristics with corner frequencies ranging from 5 to 20 Hz. In contrast, the impedance of phasic vestibular neurons was relatively constant over a wider range of frequencies or showed a resonance at approximately 40 Hz. Above spike threshold, single spikes of phasic neurons were synchronized with the sinusoidal stimulation between approximately 20 and 50 Hz, thus showing characteristic bandpass filter-like properties. Both the subthreshold resonance and bandpass filter-like discharge pattern depend on the activation of an I(D) potassium conductance. External current or synaptic stimulation that produced impedance increases (i.e., depolarization in tonic or hyperpolarization in phasic neurons) had opposite and complementary effects on the responses of the two types of neurons. Thus, membrane depolarization by current steps or repetitive synaptic excitation amplified synaptic inputs in tonic vestibular neurons and reduced them in phasic neurons. These differential, opposite membrane response properties render the two neuronal types particularly suitable for either integration (tonic neurons) or signal detection (phasic neurons), respectively, and dampens variations of the resting membrane potential in the latter.
authors: Laboratoire de Neurobiologie des Réseaux Sensorimoteurs, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7060, Université Paris Descartes, 75270 Paris cedex 06, France.
authors: Mathieu
authors: M
authors: Beraneck
authors: Sandra
authors: S
authors: Pfanzelt
authors: Isabelle
authors: I
authors: Vassias
authors: Martin
authors: M
authors: Rohregger
authors: Nicolas
authors: N
authors: Vibert
authors: Pierre-Paul
authors: PP
authors: Vidal
authors: Lee E
authors: LE
authors: Moore
authors: Hans
authors: H
authors: Straka
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D001933:Brain Stem; D017097:Electric Impedance; D066298:In Vitro Techniques; D051662:Kv1.1 Potassium Channel / Q000032:analysis; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism*; D011896:Rana temporaria; D012249:Rhombencephalon / Q000502:physiology*; D012665:Semicircular Canals / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D013696:Temperature; D014725:Vestibular Nerve / Q000502:physiology; D014722:Vestibule, Labyrinth / Q000166:cytology / Q000502:physiology*
chemical_list: D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated; D051662:Kv1.1 Potassium Channel; D015761:4-Aminopyridine