Auditory thalamic circuits and GABAA receptor function

Putative mechanisms in tinnitus pathology

Donald M. Caspary, Daniel A. Llano

Research output: Contribution to journalReview article

Abstract

Tinnitus is defined as a phantom sound (ringing in the ears), and can significantly reduce the quality of life for those who suffer its effects. Ten to fifteen percent of the general adult population report symptoms of tinnitus with 1–2% reporting that tinnitus negatively impacts their quality of life. Noise exposure is the most common cause of tinnitus and the military environment presents many challenging high-noise situations. Military noise levels can be so intense that standard hearing protection is not adequate. Recent studies suggest a role for inhibitory neurotransmitter dysfunction in response to noise-induced peripheral deafferentation as a key element in the pathology of tinnitus. The auditory thalamus, or medial geniculate body (MGB), is an obligate auditory brain center in a unique position to gate the percept of sound as it projects to auditory cortex and to limbic structures. Both areas are thought to be involved in those individuals most impacted by tinnitus. For MGB, opposing hypotheses have posited either a tinnitus-related pathologic decrease or pathologic increase in GABAergic inhibition. In sensory thalamus, GABA mediates fast synaptic inhibition via synaptic GABAA receptors (GABAARs) as well as a persistent tonic inhibition via high-affinity extrasynaptic GABAARs and slow synaptic inhibition via GABABRs. Down-regulation of inhibitory neurotransmission, related to partial peripheral deafferentation, is consistently presented as partially underpinning neuronal hyperactivity seen in animal models of tinnitus. This maladaptive plasticity/Gain Control Theory of tinnitus pathology (see Auerbach et al., 2014; Richardson et al., 2012) is characterized by reduced inhibition associated with increased spontaneous and abnormal neuronal activity, including bursting and increased synchrony throughout much of the central auditory pathway. A competing hypothesis suggests that maladaptive oscillations between the MGB and auditory cortex, thalamocortical dysrhythmia, predict tinnitus pathology (De Ridder et al., 2015). These unusual oscillations/rhythms reflect net increased tonic inhibition in a subset of thalamocortical projection neurons resulting in abnormal bursting. Hyperpolarizing de-inactivation of T-type Ca2+ channels switches thalamocortical projection neurons into burst mode. Thalamocortical dysrhythmia originating in sensory thalamus has been postulated to underpin neuropathies including tinnitus and chronic pain. Here we review the relationship between noise-induced tinnitus and altered inhibition in the MGB.

Original languageEnglish (US)
Pages (from-to)197-207
Number of pages11
JournalHearing Research
Volume349
DOIs
StatePublished - Jun 1 2017

Fingerprint

Tinnitus
GABA-A Receptors
Pathology
Geniculate Bodies
Auditory Cortex
Noise
Thalamus
Quality of Life
Auditory Pathways
Neurons
Neurotransmitter Receptor
Synaptic Transmission
Chronic Pain
gamma-Aminobutyric Acid
Hearing
Ear
Neurotransmitter Agents
Inhibition (Psychology)
Down-Regulation
Animal Models

Keywords

  • Auditory thalamus
  • GABA receptor
  • Medial geniculate body
  • Thalamocortical dysrhythmia
  • Tinnitus

ASJC Scopus subject areas

  • Sensory Systems

Cite this

Auditory thalamic circuits and GABAA receptor function : Putative mechanisms in tinnitus pathology. / Caspary, Donald M.; Llano, Daniel A.

In: Hearing Research, Vol. 349, 01.06.2017, p. 197-207.

Research output: Contribution to journalReview article

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