Glutamatergic somatosensory projections to the cochlear nucleus (CN) originate in trigeminal and dorsal column systems and terminate primarily in the CN granule cell domain (GCD). Stimulating these inputs alters spontaneous and sound-driven responses in principal neurons of the dorsal and ventral CN for extended periods of time. This long-term bimodal alteration is enhanced after unilateral deafness and could explain why patients are able to modulate their tinnitus by somatic maneuvers such as jaw clenching.
The aims of this proposal are to determine the physiological and molecular mechanisms underlying long-term suppression and enhancement of CN responses by somatosensory projection neurons and their implications for tinnitus generation and modulation.
Aim 1 a will examine long-term synaptic plasticity as a mechanism underlying bimodal enhancement and suppression in fusiform and bushy cells in normal and noise-damaged guinea pigs. We hypothesize that bimodal enhancement will predominate in noise-damaged animals with physiological correlates (increased spontaneous rates and synchrony) and behavioral evidence of tinnitus using the gap-detection tinnitus screening method (Aim 1b).
Aim 2 will examine the hypothesis that the predominance of bimodal enhancement in animals with tinnitus (preliminary data) is a result of up-regulation of specific Vglut2- positive somatosensory endings in the CN after deafness.
In Aim 2 a, tract-tracing and immunocytochemical studies will determine the precise origins and endings of the upregulated inputs in mouse.
Aim 2 b will utilize Vglut2-deficient mice to test the hypothesis that Vglut2+/- mice will be resistant to tinnitus induction. Mice will be tested for tinnitus using gap-detection before and after narrow-band noise overexposure. Preliminary data indicate that compared to matched wild-types, the Vglut2+/- mice show significantly less evidence of tinnitus, supporting this hypothesis.
Aim 2 c will then explore the involvement of the fibroblast growth factor, FGF22, as a postsynaptic signal for presynaptic upregulation of somatosensory mossy fibers to the CN after deafness. Our studies strongly implicate the somatosensory system, not only in the modulation, but also in the generation of tinnitus. Not surprisingly, more than half of tinnitus patients (~20 million) can modulate their tinnitus with somatic maneuvers, or attribute its onset to a somatosensory injury. Investigating underlying mechanisms in somatosensory-auditory integration after cochlear damage will allow us to elucidate the changes that contribute to tinnitus, and thus provide insights leading to successful interventions.

Public Health Relevance

The somatosensory (touch) system sends connections to the first auditory station in the brain, the cochlear nucleus. Since many patients can modulate the loudness and pitch of their tinnitus by touching their face or clenching their jaw, this implies tht these inputs may also produce the tinnitus in the first place. Here we examine the physiological and molecular mechanisms underlying somatosensory modulations of cochlear nucleus activity in animals with and without tinnitus, and examine how these mechanisms might lead to tinnitus. We hope that findings from these studies will lead to novel treatments and ultimately provide relief to millions of people across the world suffering from this often-debilitating disorder.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Auditory System Study Section (AUD)
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Miller, Roger
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University of Michigan Ann Arbor
Schools of Medicine
Ann Arbor
United States
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Heeringa, A N; Stefanescu, R A; Raphael, Y et al. (2016) Altered vesicular glutamate transporter distributions in the mouse cochlear nucleus following cochlear insult. Neuroscience 315:114-24
Wu, Calvin; Martel, David T; Shore, Susan E (2016) Increased Synchrony and Bursting of Dorsal Cochlear Nucleus Fusiform Cells Correlate with Tinnitus. J Neurosci 36:2068-73
Shore, Susan E; Roberts, Larry E; Langguth, Berthold (2016) Maladaptive plasticity in tinnitus--triggers, mechanisms and treatment. Nat Rev Neurol 12:150-60
Wu, Calvin; Stefanescu, Roxana A; Martel, David T et al. (2016) Tinnitus: Maladaptive auditory-somatosensory plasticity. Hear Res 334:20-9
Kurioka, Takaomi; Lee, Min Young; Heeringa, Amarins N et al. (2016) Selective hair cell ablation and noise exposure lead to different patterns of changes in the cochlea and the cochlear nucleus. Neuroscience 332:242-57
Wu, Calvin; Stefanescu, Roxana A; Martel, David T et al. (2015) Listening to another sense: somatosensory integration in the auditory system. Cell Tissue Res 361:233-50
Stefanescu, Roxana A; Koehler, Seth D; Shore, Susan E (2015) Stimulus-timing-dependent modifications of rate-level functions in animals with and without tinnitus. J Neurophysiol 113:956-70
Wu, Calvin; Martel, David T; Shore, Susan E (2015) Transcutaneous induction of stimulus-timing-dependent plasticity in dorsal cochlear nucleus. Front Syst Neurosci 9:116
Basura, Gregory J; Koehler, Seth D; Shore, Susan E (2015) Bimodal stimulus timing-dependent plasticity in primary auditory cortex is altered after noise exposure with and without tinnitus. J Neurophysiol 114:3064-75
Stefanescu, Roxana A; Shore, Susan E (2015) NMDA Receptors Mediate Stimulus-Timing-Dependent Plasticity and Neural Synchrony in the Dorsal Cochlear Nucleus. Front Neural Circuits 9:75

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