Biology subjects

Gomez-Casati, M. E.

Publications and source records attributed to Gomez-Casati, M. E..

5 recordsLinked to original sources

bioRxiv2026

Medial Olivocochlear Activity Modulates Central Auditory Synapse Structure and Function

In many mammals, the auditory system is immature at birth and undergoes activity-dependent refinement. The medial olivocochlear system (MOC) contributes to the maturation of central auditory connectivity by shaping spontaneous activity in the developing inner ear. Although altered MOC activity has been linked to electrical and synaptic dysfunctions in different central auditory nuclei, an in-depth analysis of the same synapse under conditions of absent versus enhanced MOC activity is lacking. In this work, we set out a physiological and structural analysis of the calyx of Held and the principal neurons of the medial nucleus of the trapezoid body (CH-MNTB) synapse at postnatal days 12-14 in three mouse models of either sex: wild-type (WT), 9 knock-in (9KI; with enhanced MOC activity), and 9 knock-out (9KO; which lacks MOC activity). Electrophysiological recordings in brain slices revealed a reduced synaptic strength efficacy in 9KI compared to WT, including smaller excitatory postsynaptic current (EPSC) amplitudes, stronger short-term depression during repetitive stimulation and a decrease readily releasable pool size. In contrast, 9KO mice showed minimal synaptic differences relative to WT. Serial block-face electron microscopy (SBEM) reconstructions demonstrated morphological alterations of the CH in both MOC-manipulated mouse models. However, 9KI mice exhibited the largest deviations, including fewer morphologically complex CHs and increased poly-innervation of MNTB cells. These results indicate that transient, well-regulated efferent control of cochlear activity is crucial for establishing accurate central auditory connectivity. Moreover, the enhancement of MOC activity drives more pronounced developmental changes in brainstem auditory circuitry than its absence. Significance StatementBefore hearing onset, inner hair cells in altricial mammals show spontaneous electrical activity crucial for proper auditory pathway development. This activity is finely regulated by descending efferent nerves from the central nervous system during a critical developmental period, ensuring precise auditory circuit formation. Our study shows that genetically manipulating efferent function --either by eliminating it or enhancing it-- leads to structural alterations and severe synaptic dysfunction within the auditory brainstem. These results indicate that transient, well-regulated efferent control of cochlear activity is crucial for establishing accurate central auditory connectivity. Importantly, enhancing efferent peripheral activity causes more pronounced central synaptic changes than its absence, highlighting the importance of balanced efferent modulation during early auditory system development for normal brainstem auditory function.

neuroscience↗

bioRxiv2025

Insights into early cochlear damage induced by potassium channel deficiency

Hearing loss (HL) is the most common sensory disorder, caused by genetic mutations and acquired factors like presbycusis and noise exposure. A critical factor in HL development is the dysfunction of potassium (K+) channels, essential for sensory cell function in the organ of Corti (OC). Inner and outer hair cells (IHCs and OHCs) convert sound into electrical signals, while supporting cells (SCs) maintain ionic and structural balance. KCNQ4 channels, located in the basal membrane of OHCs, regulate K+ efflux. Mutations in KCNQ4 are linked to progressive HL (DFNA2), noise-induced hearing loss, and presbycusis, leading to K+ accumulation, cellular stress, and OHC death. Gene editing or pharmacological activation of KCNQ4 has shown potential in partially preventing HL in mouse models. In this study, we demonstrate KCNQ4 deletion disrupts the localization of key proteins like prestin and BK channels, alters OHC organization, and induces apoptosis in sensory and SC. Spiral ganglion neurons (SGNs) also degenerate over time. Despite these structural changes, noise exposure does not exacerbate OHC damage in our KCNQ4-deficient model. This highlights KCNQ4s role in maintaining ion homeostasis and cochlear function, as its absence triggers widespread dysfunction in the OC. The present study demonstrates that disruptions in a single cell type can have a cascade effect on overall cochlear health. Understanding the molecular and cellular consequences of KCNQ4 mutations is crucial for developing targeted therapies to mitigate progressive HL caused by genetic and environmental factors. HighlightsO_LIHearing function is altered in KCNQ4 KO animals from young ages. C_LIO_LIInner hair cells show structural alterations before their death. C_LIO_LIKCNQ4 absence impairs membrane localization of key functional proteins. C_LIO_LIHair cell and neuron loss is mediated by apoptosis. C_LIO_LISupporting cells and satellite cells also contribute to tissue degeneration in KCNQ4 KO animals C_LIO_LINoise exposure does not exacerbate hair cell damage in KCNQ4-KO mice. C_LI

neuroscience↗

bioRxiv2025

Early Noise Exposure and Changes in Medial Olivocochlear Strength Alters Auditory Pathway Development

The early onset of peripheral deafness significantly alters the proper development of the auditory system. Likewise, exposure to loud noise during early development produces a similar disruptive effect. Before hearing onset in altricial mammals, cochlear inner hair cells exhibit spontaneous electrical activity that drives auditory circuit development. This activity is modulated by medial olivocochlear (MOC) efferent feedback through 910 nicotinic cholinergic receptors in inner hair cells. In adults, these receptors are restricted to outer hair cells, where they mediate MOC feedback to regulate cochlear amplification. Although the MOC systems protective role to prevent noise-induced hearing loss in adulthood is well-established, its influence during early developmental stages-especially in response to exposure to loud noise-remains largely unexplored. In this study, we investigated the role of MOC feedback during early postnatal development using 9 knockout (KO) and 9 knock-in (KI) mice of either sex, which respectively lack or exhibit enhanced cholinergic activity. Our findings reveal that both increased and absent olivocochlear activity result in altered auditory sensitivity at the onset of hearing, along with long- range alterations in the number and morphology of ribbon synapses. Early noise exposure caused lasting auditory damage in both wild-type and 9KO mice, with deficits persisting into adulthood. In contrast, 9KI mice were protected from noise-induced damage, with no long-term effects on auditory function. These results highlight the increased susceptibility of the auditory system during early postnatal development. Moreover, they indicate that an enhanced MOC feedback shields the auditory system from noise damage during this period. SIGNIFICANCE STATEMENTEarly development represents a sensitive window for shaping auditory function. We show that the medial olivocochlear system is critical for establishing normal ribbon synapse density and size; key features for proper hearing onset. We also show that the developing auditory system is especially vulnerable to loud noise, with early exposure causing more severe and lasting effects than similar noise later in life. Notably, enhancing 910 nAChR receptor activity during this early stage offers protection against noise-induced damage, revealing a time-sensitive opportunity to safeguard auditory development.

neuroscience↗

bioRxiv2018

Strengthening of the efferent olivocochlear system leads to synaptic dysfunction and tonotopy disruption of a central auditory nucleus

The auditory system in many mammals is immature at birth but precisely organized in adults. Spontaneous activity in the inner ear plays a critical role in guiding this process. This is shaped by an efferent pathway that descends from the brainstem and makes transient direct synaptic contacts with inner hair cells (IHCs). In this work, we used an 9 cholinergic receptor knock-in mouse model (of either sex) with enhanced medial efferent activity (Chrna9L9T, L9T) to understand the role of the olivocochlear system in the correct establishment of auditory circuits. Wave III of auditory brainstem responses (which represents synchronized activity of synapses within the superior olivary complex) were smaller in L9T mice, suggesting a central dysfunction. The mechanism underlying this functional alteration was analysed in brain slices containing the medial nucleus of the trapezoid body (MNTB), where neurons are topographically organized along a medio-lateral axis. The topographic organization of MNTB physiological properties observed in WT mice was abolished in the L9T mice. Additionally, electrophysiological recordings in slices evidenced MNTB synaptic alterations, which were further supported by morphological alterations. The present results suggest that the transient cochlear efferent innervation to IHCs during the critical period before the onset of hearing is involved in the refinement of topographic maps as well as in setting the correct synaptic transmission at central auditory nuclei.\n\nSignificance StatementCochlear inner hair cells of altricial mammals display spontaneous electrical activity before hearing onset. The pattern and firing rate of these cells is crucial for the correct maturation of the central auditory pathway. A descending efferent innervation from the central nervous system contacts hair cells during this developmental window. The function of this transient efferent innervation remains an open question. The present work shows that the genetic enhancement of efferent function disrupts the orderly topographic distribution at the medial nucleus of the trapezoid body level and causes severe synaptic dysfunction. Thus, the transient efferent innervation to the cochlea is necessary for the correct establishment of the central auditory circuitry.

neuroscience↗

bioRxiv2018

Positive Selection and Adaptation of Novel Inner Ear Genes in the Mammalian Lineage

The mammalian inner ear possesses functional and morphological innovations that contribute to its unique hearing capacities. The genetic bases underlying the evolution of this mammalian landmark are poorly understood. We propose that the emergence of morphological and functional innovations in the mammalian inner ear could have been driven by adaptive molecular evolution.\n\nIn this work, we analyzed the complete inner ear transcriptome in order to identify genes that show signatures of adaptive evolution in this lineage. We analyzed approximately 1,300 inner ear expressed genes and found that 13 % show signatures of positive selection in the mammalian lineage. Several of these genes are known to play an important function in the inner ear. In addition, we identified that a significant proportion of genes showing signatures of adaptive evolution in mammals have not been previously reported to participate in inner ear development and/or physiology. We focused our analysis in two of these novel genes: STRIP2 and ABLIM2 by generating null mutant mice and analyzed their auditory function. We found that mice lacking Strip2 displayed a decrease in neural response amplitudes. In addition, we observed a reduction in the number of afferent synapses, suggesting a potential cochlear neuropathy.\n\nThus, this study shows the usefulness of pursuing a high-throughput evolutionary approach followed by functional studies to track down novel genes that are important for inner ear function. Moreover, this approach sheds light on the genetic basis underlying the evolution of the mammalian inner ear.

evolutionary biology↗