This is the competing renewal of a research program that examines the biophysical and molecular basis of cholinergic inhibition of cochlear hair cells. The neurotransmitter acetylcholine (ACh) opens ionotropic (cation-permeant) receptors (AChRs) composed of 19 and 110 subunits. Calcium influx through the AChR activates calcium-sensitive potassium channels (encoded by the SK2 gene) to hyperpolarize and inhibit the hair cell. While calcium influx through the AChR seems adequate to activate the SK channels, other observations suggest that calcium may be released from endoplasmic stores to extend and amplify that process. The structure of the efferent synapse includes a near-membrane cistern in the hair cell that may serve as a calcium store. Genetic alteration of the hair cell's AChR and associated SK channels has provided some insight into efferent function. In particular, alteration of a single amino acid in the permeation path of 19 produced a 'super receptor'with prolonged open times, greater sensitivity to ACh and slowed desensitization. In the knockin mouse possessing this receptor, efferent inhibition was greatly enhanced, and the animal was better protected from permanent loud sound damage. We will continue to probe the molecular mechanisms of cholinergic inhibition in this and other transgenic models. In addition, we will exploit functional and genetic differences between avian (chicken) and mammalian AChRs to explore the role of calcium flux in detail. Should progress warrant it, we will construct a transgenic mouse substituted with chicken 19. We will perform detailed ultrastructural analyses of synaptic cisterns in wildtype and transgenic mice lacking one or more components of the efferent synapse. The small cytoplasmic gap between cistern and postsynaptic membrane is replete with organized electron-densities, suggesting the presence of molecular 'connectors'that may include the cytoplasmic portions of AChRs and calcium release channels. This arrangement is strongly reminiscent of junctional complexes in muscle and suggests the possibility of 'conformational coupling'between AChRs and calcium release channels, in addition to calcium-based signaling. Efferent innervation of the inner ear modulates sensitivity and protects against acoustic trauma. Our growing knowledge of the molecular bases for this process has begun to reveal potential therapeutic targets, supported by the unique pharmacology of hair cell acetylcholine receptors. Thorough knowledge of the molecular bases of cholinergic inhibition will advance therapeutic strategies exploiting those mechanisms.

Public Health Relevance

Efferent innervation of the inner ear modulates sensitivity and protects against acoustic trauma. Our growing knowledge of the molecular bases for this process has begun to reveal potential therapeutic targets, supported by the unique pharmacology of hair cell acetylcholine receptors. Thorough knowledge of the molecular bases of cholinergic inhibition will advance therapeutic stragegies exploiting those mechanisms.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC001508-22
Application #
8519406
Study Section
Auditory System Study Section (AUD)
Program Officer
Cyr, Janet
Project Start
1992-09-30
Project End
2014-08-31
Budget Start
2013-09-01
Budget End
2014-08-31
Support Year
22
Fiscal Year
2013
Total Cost
$494,619
Indirect Cost
$165,460
Name
Johns Hopkins University
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Fuchs, Paul Albert (2014) A 'calcium capacitor' shapes cholinergic inhibition of cochlear hair cells. J Physiol 592:3393-401
Fuchs, Paul Albert; Lehar, Mohamed; Hiel, Hakim (2014) Ultrastructure of cisternal synapses on outer hair cells of the mouse cochlea. J Comp Neurol 522:717-29
Kong, Jee-Hyun; Zachary, Stephen; Rohmann, Kevin N et al. (2013) Retrograde facilitation of efferent synapses on cochlear hair cells. J Assoc Res Otolaryngol 14:17-27
Wedemeyer, Carolina; Zorrilla de San Martin, Javier; Ballestero, Jimena et al. (2013) Activation of presynaptic GABA(B(1a,2)) receptors inhibits synaptic transmission at mammalian inhibitory cholinergic olivocochlear-hair cell synapses. J Neurosci 33:15477-87
Elgoyhen, Ana Belen; Katz, Eleonora (2012) The efferent medial olivocochlear-hair cell synapse. J Physiol Paris 106:47-56
Lipovsek, Marcela; Im, Gi Jung; Franchini, Lucia F et al. (2012) Phylogenetic differences in calcium permeability of the auditory hair cell cholinergic nicotinic receptor. Proc Natl Acad Sci U S A 109:4308-13
Ballestero, Jimena; Zorrilla de San Martin, Javier; Goutman, Juan et al. (2011) Short-term synaptic plasticity regulates the level of olivocochlear inhibition to auditory hair cells. J Neurosci 31:14763-74
Elgoyhen, Ana Belen; Franchini, Lucia F (2011) Prestin and the cholinergic receptor of hair cells: positively-selected proteins in mammals. Hear Res 273:100-8
Wersinger, Eric; Fuchs, Paul Albert (2011) Modulation of hair cell efferents. Hear Res 279:1-12
Wersinger, Eric; McLean, Will J; Fuchs, Paul A et al. (2010) BK channels mediate cholinergic inhibition of high frequency cochlear hair cells. PLoS One 5:e13836

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