Vestibular afferent nerve fibers convey head position and motion signals from the inner ear to the brain, where they drive reflexes controlling gaze, posture and balance and contribute to perceptions of orientation and self-motion. We propose to study how electrical signals are generated in primary vestibular afferents, focusing on the contributions of intrinsic ion channels and calcium binding proteins. We will examine the origins of specific patterns of activity (firing patterns of action potentials, also called spikes) in vestibular afferents. In recordings made in vivo, vestibular afferents vary greatly in the regularity of inter-spike intervals;this variation is highly systematic, co-varying with many morphological and physiological properties. Thus, highly regular afferents tend to carry tonic signals, to have small diameters and extended dendritic arbors, and to innervate peripheral zones of the sensory epithelia. In contrast, highly irregular afferents tend to have phasic signals, to have large diameters and compact dendritic arbors with large, calyceal afferent terminals, to innervate central zones and to express particular Ca2+ binding proteins (CBPs). High regularity may enhance the information content and temporal encoding for head movement frequencies below ~20 Hz;high irregularity may reflect high sensitivity to synaptic currents. Over two decades ago, investigators exploring possible factors in setting firing patterns suggested that intrinsic ion channels in the afferent fibers were likely to be important. We now know that ion channel complements in vestibular ganglion neurons (VGNs), as in many brain neurons, are much more complex than previously imagined, and we have better tools to study this issue. We propose to use the whole-cell patch clamp method on VGNs from rodents to characterize firing patterns and the underlying voltage- and calcium-gated ion channels. VGNs will be studied in vitro as isolated somata and also within a semi-intact preparation that includes sensory epithelia and the ganglion. The two preparations have different advantages: isolated VGNs provide superior voltage clamp, while VGNs in the semi-intact preparation receive synaptic input from hair cells. Preliminary data suggest that VGNs express specific complements of ion channels, giving rise to distinct endogenous firing patterns in response to injected currents. We will test the hypothesis that the endogenous ion channels help establish different patterns of spike regularity in vivo, and the involvement of specific ion channels in setting firing patterns. We will use RT-PCR to screen for candidate ion channels and immunocytochemistry to localize channels according to afferent type, zone within the sensory epithelium, and cellular location (soma vs. afferent terminal). We will investigate whether specific CBPs help set firing patterns by modulating calcium-dependent potassium channels. We will develop computational models to test our comprehensive understanding of how ion channels contribute to firing patterns.

Public Health Relevance

A set of five vestibular organs in the inner ear conveys information about head position and head motion to the brain, where it drives reflexes that stabilize gaze, posture and balance, and provide a sense of self-motion and orientation. The proposed research will investigate how vestibular afferent neurons use ion channels to generate patterns of electrical activity with which they encode head motion and position. Detailed knowledge of electrical signaling by vestibular afferents is essential to understand how inner ear damage, which is widespread in the population, causes poor balance and disorientation. Such knowledge will also help us design prosthetics to electrically stimulate the vestibular system in order to restore function.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC002290-18
Application #
8078913
Study Section
Auditory System Study Section (AUD)
Program Officer
Cyr, Janet
Project Start
1994-04-01
Project End
2013-06-30
Budget Start
2011-07-01
Budget End
2012-06-30
Support Year
18
Fiscal Year
2011
Total Cost
$306,075
Indirect Cost
Name
Massachusetts Eye and Ear Infirmary
Department
Type
DUNS #
073825945
City
Boston
State
MA
Country
United States
Zip Code
02114
Eatock, Ruth Anne (2018) Specializations for Fast Signaling in the Amniote Vestibular Inner Ear. Integr Comp Biol 58:341-350
Liu, Xiao-Ping; Wooltorton, Julian R A; Gaboyard-Niay, Sophie et al. (2016) Sodium channel diversity in the vestibular ganglion: NaV1.5, NaV1.8, and tetrodotoxin-sensitive currents. J Neurophysiol 115:2536-55
McLean, Will J; McLean, Dalton T; Eatock, Ruth Anne et al. (2016) Distinct capacity for differentiation to inner ear cell types by progenitor cells of the cochlea and vestibular organs. Development 143:4381-4393
Schuth, Olga; McLean, Will J; Eatock, Ruth Anne et al. (2014) Distribution of Na,K-ATPase ? subunits in rat vestibular sensory epithelia. J Assoc Res Otolaryngol 15:739-54
Spoon, Corrie; Grant, Wally (2013) Biomechanical measurement of kinocilium. Methods Enzymol 525:21-43
Songer, Jocelyn E; Eatock, Ruth Anne (2013) Tuning and timing in mammalian type I hair cells and calyceal synapses. J Neurosci 33:3706-24
Spoon, Corrie; Grant, Wally (2011) Biomechanics of hair cell kinocilia: experimental measurement of kinocilium shaft stiffness and base rotational stiffness with Euler-Bernoulli and Timoshenko beam analysis. J Exp Biol 214:862-70
Lysakowski, Anna; Gaboyard-Niay, Sophie; Calin-Jageman, Irina et al. (2011) Molecular microdomains in a sensory terminal, the vestibular calyx ending. J Neurosci 31:10101-14
Eatock, Ruth Anne; Songer, Jocelyn E (2011) Vestibular hair cells and afferents: two channels for head motion signals. Annu Rev Neurosci 34:501-34
Kalluri, Radha; Xue, Jingbing; Eatock, Ruth Anne (2010) Ion channels set spike timing regularity of mammalian vestibular afferent neurons. J Neurophysiol 104:2034-51

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