The reduced cochlear output and the failure to adapt the central auditory response causes tinnitus in noise exposed rats

PLoS One. 2013;8(3):e57247. doi: 10.1371/journal.pone.0057247. Epub 2013 Mar 13.

Abstract

Tinnitus is proposed to be caused by decreased central input from the cochlea, followed by increased spontaneous and evoked subcortical activity that is interpreted as compensation for increased responsiveness of central auditory circuits. We compared equally noise exposed rats separated into groups with and without tinnitus for differences in brain responsiveness relative to the degree of deafferentation in the periphery. We analyzed (1) the number of CtBP2/RIBEYE-positive particles in ribbon synapses of the inner hair cell (IHC) as a measure for deafferentation; (2) the fine structure of the amplitudes of auditory brainstem responses (ABR) reflecting differences in sound responses following decreased auditory nerve activity and (3) the expression of the activity-regulated gene Arc in the auditory cortex (AC) to identify long-lasting central activity following sensory deprivation. Following moderate trauma, 30% of animals exhibited tinnitus, similar to the tinnitus prevalence among hearing impaired humans. Although both tinnitus and no-tinnitus animals exhibited a reduced ABR wave I amplitude (generated by primary auditory nerve fibers), IHCs ribbon loss and high-frequency hearing impairment was more severe in tinnitus animals, associated with significantly reduced amplitudes of the more centrally generated wave IV and V and less intense staining of Arc mRNA and protein in the AC. The observed severe IHCs ribbon loss, the minimal restoration of ABR wave size, and reduced cortical Arc expression suggest that tinnitus is linked to a failure to adapt central circuits to reduced cochlear input.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological*
  • Animals
  • Auditory Cortex / metabolism
  • Auditory Threshold
  • Behavior, Animal
  • Cochlea / metabolism
  • Cochlea / physiopathology*
  • Cytoskeletal Proteins / metabolism
  • Evoked Potentials, Auditory, Brain Stem*
  • Female
  • Hair Cells, Auditory, Inner / metabolism
  • Hearing Loss, Noise-Induced / physiopathology
  • Immunohistochemistry
  • Nerve Tissue Proteins / metabolism
  • Noise / adverse effects*
  • Rats
  • Tinnitus / etiology*
  • Tinnitus / metabolism

Substances

  • Cytoskeletal Proteins
  • Nerve Tissue Proteins
  • activity regulated cytoskeletal-associated protein

Grants and funding

This work was supported by the Marie Curie Research Training Network CavNET MRTN-CT-2006–035367, the Deutsche Forschungsgemeinschaft DFG-Kni-316-4-1 and Hahn Stiftung (Index AG). The authors acknowledge support by Deutsche Forschungsgemeinschaft and the Open Access Publishing Fund of Tuebingen University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.