Targeting inhibitory neurotransmission in tinnitus

Review

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Abstract

Tinnitus perception depends on the presence of its neural correlates within the auditory neuraxis and associated structures. 

Targeting specific circuits and receptors within the central nervous system in an effort to relieve the perception of tinnitus and its impact on one's emotional and mental state has become a focus of tinnitus research. 

One approach is to upregulate endogenous inhibitory neurotransmitter levels (e.g., glycine and GABA) and selectively target inhibitory receptors in key circuits to normalize tinnitus pathophysiology. 

Thus, the basic functional and molecular properties of two major ligand-gated inhibitory receptor systems, the GABA_A receptor (GABA_AR) and glycine receptor (GlyR) are described. 

Also reviewed is the rationale for targeting inhibition, which stems from reported tinnitus-related homeostatic plasticity of inhibitory neurotransmitter systems and associated enhanced neuronal excitability throughout most central auditory structures. 

However, the putative role of the medial geniculate body (MGB) in tinnitus has not been previously addressed, specifically in terms of its inhibitory afferents from inferior colliculus and thalamic reticular nucleus and its GABA_AR functional heterogeneity. 

This heterogeneous population of GABA_ARs, which may be altered in tinnitus pathology, and its key anatomical position in the auditory CNS make the MGB a compelling structure for tinnitus research.

Finally, some selective compounds, which enhance tonic inhibition, have successfully ameliorated tinnitus in animal studies, suggesting that the MGB and, to a lesser degree, the auditory cortex may be their primary locus of action. 

These pharmacological interventions are examined in terms of their mechanism of action and why these agents may be effective in tinnitus treatment.

This article is part of a Special Issue entitled Tinnitus Neuroscience.

Abbreviations

• CSF, cerebrospinal fluid;
• DCN, dorsal cochlear nucleus;
• FBN, Fischer Brown Norway;
• GABA, γ-aminobutyric acid;
• GABARAP, GABA_A receptor associated protein;
• GAD, glutamic acid decarboxylase;
• GlyR, glycine receptor;
• GABA_AR, GABA_A receptor;
• GABA-T, GABA transaminase;
• GAT, GABA transporter;
• HVA, high-voltage activated;
• IC, inferior colliculus;
• MGB, medial geniculate body;
• qRT-PCR, quantitative real-time polymerase chain reaction;
• SGC, spiral ganglion cell;
• TRN, thalamic reticular nucleus

Authors
 

• Ben D. Richardson^{a, 1,} ,
• Thomas J. Brozoski^{b, 1,} ,
• Lynne L. Ling^{a, 1,} ,
• Donald M. Caspary^{a, ,}

• ^a Department of Pharmacology, Southern Illinois University School of Medicine, 801 N Rutledge St, Rm. 3234, PO Box 19629, Springfield, IL 62794, USA
• ^b Division of Otolaryngology, Head and Neck Surgery, Southern Illinois University School of Medicine, 801 N Rutledge St, Rm. 3205, PO Box 19629, Springfield, IL 62794, USA

Fuente: http://dx.doi.org/10.1016/j.brainres.2012.02.014
Brain Research