Symposium
Afferent and Efferent Circuits in the Cochlea: From Ribbon Synapses to Central Control
Chair
Juan Goutman
INGEBI - CONICET
Co-Chair
M. Eugenia Gomez-Casati
Instituto de Farmacologia, Facultad de Medicina - UBA
This symposium brings together leading experts in auditory neuroscience to present recent advances in our understanding of the afferent and efferent circuits that shape cochlear function. Talks will cover key aspects of ribbon synapses in sensory hair cells, including their morphological and functional diversity and their role in encoding sound information. In parallel, the symposium will explore the modulation of cochlear activity by the medial (MOC) and lateral (LOC) olivocochlear efferent systems, emphasizing their roles in development, synaptic plasticity, and auditory protection. Presentations will integrate a range of approaches from electrophysiology and neuroanatomy to single-cell RNA sequencing, offering a comprehensive view of the molecular identity, functional specialization, and connectivity of these auditory circuits. The goal of this symposium is to offer an integrated perspective on how afferent and efferent pathways shape auditory signaling from the cochlea to the brain, and how these circuits adapt, or become disrupted, under pathological conditions.
Elisabeth Glowatzki Ph. D.
Johns Hopkins School of Medicine, Baltimore MD, USA
Modulation of sound coding in auditory nerve fibers by feedback from the brain
In the inner ear, the sound signal is processed by the sensory cells, the hair cells, andtransmitted via specialized ribbon synapses to auditory nerve fibers, which forward the soundsignal to the brain. Neurons in specific brainstem nuclei perceive the ‘afferent sound signals’,and provide feedback modulation back to the periphery via transmitter release onto the auditorynerve fiber endings where these synapse with hair cells. Lateral olivocochlear (LOC) fibersrelease neurotransmitters like acetylcholine, dopamine and GABA onto auditory nerve fiberendings at the inner hair cell synapses, as well as neuropeptides like CGRP and NeuropeptideY. It is believed that such modulation can adjust the ‘gain’ at the first synapse in the auditorypathway, adjusting to the sound environment. However, the exact role of individual transmittersystems is mostly unknown. This presentation will focus on insights into mechanisms ofcholinergic and dopaminergic modulation of auditory nerve fiber activity via the LOC feedbacksystem from the brain.
Marcela Lipovsek
University College London, The Ear Institute, London, UK
How does maturation affect the potential to regenerate sensory hair cells? Searching for answers in chickens and mice, one cell at a time
Abstract TBA
Mark Rutherford
Associate Professor of Otolaryngology—Head & Neck Surgery,Washington University School of Medicine, St. Louis, MO, USA.
Calcium-permeable AMPA receptors in the cochlea: role in noise-induced synapse loss and sex-specific synaptopathy in the absence of synapse loss
Unlike typical glutamatergic synapses, the ribbon synapses in the cochlea have a highproportion of GluA2-lacking, calcium-permeable AMPA type glutamate receptors (CP-AMPARs) alongside the regular calcium-impermeable ones. These CP-AMPARs havea greater sodium conductance, in addition to calcium permeability, which is probablyimportant for rapid and efficient action potential generation in response to rapidlychanging acoustic inputs to the inner hair cell receptor potential. This powerful ribbonsynapse, estimated to contain thousands of receptors, comes with a vulnerability toexcitotoxicity. We discovered that blocking the CP-AMPARs is sufficient to preventnoise-induced synapse loss and concomitant reduction of cochlear output, while at thesame time allowing hearing function to persist with transmission via the calcium-impermeable receptors. Mice lacking the GluA3 pore-forming subunit or the auxiliarysubunit TARP-gamma-2 (Stargazin) have altered expression of the remaining subunits,which leads to progressive hearing loss specifically in female mice. Potential reasonsfor this, including a shift toward greater calcium permeability, will be discussed.
Amanda Lauer Ph. D.
Vice Director for Faculty AffairsOtolaryngology - HNSJohns Hopkins University School of Medicine
Role of the auditory brainstem-to-ear feedback system in hearing across the lifespan
The role of the medial olivocochlear system in hearing has been debated for manyyears due to conflicting and variable results in human and animal studies. Emergingevidence shows that this system is plastic and changes with acoustic experience andage. We have implemented a variety of behavioral assays, non-invasive physiologicaltests, and quantitative anatomical analyses to investigate how genetic manipulations ofthe olivocochlear system, acoustic experience, and natural aging interact to affecthearing across the lifespan in mouse models. Diminished olivocochlear functionappears to be most detrimental to hearing in very young and aged auditory systems.However, plasticity in this system reveals a remarkable capacity to adapt to differentacoustic environments. I will also highlight our recent findings in wild and wild-derivedbat species that may confer protection against a lifetime of exposure to loud sounds.