title: Efferent Vestibular Neurons Show Homogenous Discharge Output But Heterogeneous Synaptic Input Profile In Vitro.
abstract: Despite the importance of our sense of balance we still know remarkably little about the central control of the peripheral balance system. While previous work has shown that activation of the efferent vestibular system results in modulation of afferent vestibular neuron discharge, the intrinsic and synaptic properties of efferent neurons themselves are largely unknown. Here we substantiate the location of the efferent vestibular nucleus (EVN) in the mouse, before characterizing the input and output properties of EVN neurons in vitro. We made transverse serial sections through the brainstem of 4-week-old mice, and performed immunohistochemistry for calcitonin gene-related peptide (CGRP) and choline acetyltransferase (ChAT), both expressed in the EVN of other species. We also injected fluorogold into the posterior canal and retrogradely labelled neurons in the EVN of ChAT:: tdTomato mice expressing tdTomato in all cholinergic neurons. As expected the EVN lies dorsolateral to the genu of the facial nerve (CNVII). We then made whole-cell current-, and voltage-clamp recordings from visually identified EVN neurons. In current-clamp, EVN neurons display a homogeneous discharge pattern. This is characterized by a high frequency burst of action potentials at the onset of a depolarizing stimulus and the offset of a hyperpolarizing stimulus that is mediated by T-type calcium channels. In voltage-clamp, EVN neurons receive either exclusively excitatory or inhibitory inputs, or a combination of both. Despite this heterogeneous mixture of inputs, we show that synaptic inputs onto EVN neurons are predominantly excitatory. Together these findings suggest that the inputs onto EVN neurons, and more specifically the origin of these inputs may underlie EVN neuron function.
authors.affiliation: Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Miranda A
authors.initials: MA
authors.lastname: Mathews
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University, New York, United States of America.
authors.forename: Andrew
authors.initials: A
authors.lastname: Murray
authors.affiliation: Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Rajiv
authors.initials: R
authors.lastname: Wijesinghe
authors.affiliation: Discipline of Anatomy and Histology, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Karen
authors.initials: K
authors.lastname: Cullen
authors.affiliation: Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Victoria W K
authors.initials: VW
authors.lastname: Tung
authors.affiliation: Discipline of Biomedical Science, Bosch Institute, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Camp
mesh_terms: D000200:Action Potentials; D000818:Animals; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009473:Neuronal Plasticity; D009476:Neurons, Efferent / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D014726:Vestibular Nuclei / Q000378:metabolism; D014722:Vestibule, Labyrinth / Q000378:metabolism*