Publications by authors named "Marcelo J Moglie"

7 Publications

  • Page 1 of 1

Synaptic Contributions to Cochlear Outer Hair Cell Ca Dynamics.

J Neurosci 2021 Aug 12;41(32):6812-6821. Epub 2021 Jul 12.

Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI) (Consejo Nacional de Investigaciones Científicas y Tecnológicas), Ciudad Autónoma de Buenos Aires 1428, Argentina

For normal cochlear function, outer hair cells (OHCs) require a precise control of intracellular Ca levels. In the absence of regulatory elements such as proteinaceous buffers or extrusion pumps, OHCs degenerate, leading to profound hearing impairment. Influx of Ca occurs both at the stereocilia tips and the basolateral membrane. In this latter compartment, two different origins for Ca influx have been poorly explored: voltage-gated L-type Ca channels (VGCCs) at synapses with Type II afferent neurons, and α9α10 cholinergic nicotinic receptors at synapses with medio-olivochlear complex (MOC) neurons. Using functional imaging in mouse OHCs, we dissected Ca influx individually through each of these sources, either by applying step depolarizations to activate VGCC, or stimulating MOC axons. Ca ions originated in MOC synapses, but not by VGCC activation, was confined by Ca-ATPases most likely present in nearby synaptic cisterns. Although Ca currents in OHCs are small, VGCC Ca signals were comparable in size to those elicited by α9α10 receptors, and were potentiated by ryanodine receptors (RyRs). In contrast, no evidence of potentiation by RyRs was found for MOC Ca signals over a wide range of presynaptic stimulation strengths. Our study shows that despite the fact that these two Ca entry sites are closely positioned, they differ in their regulation by intracellular cisterns and/or organelles, suggesting the existence of well-tuned mechanisms to separate the two different OHC synaptic functions. Outer hair cells (OHCs) are sensory cells in the inner ear operating under very special constraints. Acoustic stimulation leads to fast changes both in membrane potential and in the intracellular concentration of metabolites such as Ca Tight mechanisms for Ca control in OHCs have been reported. Interestingly, Ca is crucial for two important synaptic processes: inhibition by efferent cholinergic neurons, and glutamate release onto Type II afferent fibers. In the current study we functionally imaged Ca at these two different synapses, showing close positioning within the basolateral compartment of OHCs. In addition, we show differential regulation of these two Ca sources by synaptic cisterns and/or organelles, which could result crucial for functional segregation during normal hearing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.3008-20.2021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8360681PMC
August 2021

Loss of Choline Agonism in the Inner Ear Hair Cell Nicotinic Acetylcholine Receptor Linked to the α10 Subunit.

Front Mol Neurosci 2021 5;14:639720. Epub 2021 Feb 5.

Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.

The α9α10 nicotinic acetylcholine receptor (nAChR) plays a fundamental role in inner ear physiology. It mediates synaptic transmission between efferent olivocochlear fibers that descend from the brainstem and hair cells of the auditory sensory epithelium. The α9 and α10 subunits have undergone a distinct evolutionary history within the family of nAChRs. Predominantly in mammalian vertebrates, the α9α10 receptor has accumulated changes at the protein level that may ultimately relate to the evolutionary history of the mammalian hearing organ. In the present work, we investigated the responses of α9α10 nAChRs to choline, the metabolite of acetylcholine degradation at the synaptic cleft. Whereas choline is a full agonist of chicken α9α10 receptors it is a partial agonist of the rat receptor. Making use of the expression of α9α10 heterologous receptors, encompassing wild-type, heteromeric, homomeric, mutant, chimeric, and hybrid receptors, and molecular docking, we establish that the mammalian (rat) α10 nAChR subunit underscores the reduced efficacy of choline. Moreover, we show that whereas the complementary face of the α10 subunit does not play an important role in the activation of the receptor by ACh, it is strictly required for choline responses. Thus, we propose that the evolutionary changes acquired in the mammalian α9α10 nAChR resulted in the loss of choline acting as a full agonist at the efferent synapse, without affecting the triggering of ACh responses. This may have accompanied the fine-tuning of hair cell post-synaptic responses to the high-frequency activity of efferent medial olivocochlear fibers that modulate the cochlear amplifier.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fnmol.2021.639720DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7892445PMC
February 2021

Unraveling the Molecular Players at the Cholinergic Efferent Synapse of the Zebrafish Lateral Line.

J Neurosci 2021 01 17;41(1):47-60. Epub 2020 Nov 17.

Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, 1428 Buenos Aires, Argentina

The lateral line (LL) is a sensory system that allows fish and amphibians to detect water currents. LL responsiveness is modulated by efferent neurons that aid in distinguishing between external and self-generated stimuli, maintaining sensitivity to relevant cues. One component of the efferent system is cholinergic, the activation of which inhibits afferent activity. LL hair cells (HCs) share structural, functional, and molecular similarities with those of the cochlea, making them a popular model for studying human hearing and balance disorders. Because of these commonalities, one could propose that the receptor at the LL efferent synapse is a α9α10 nicotinic acetylcholine receptor (nAChR). However, the identities of the molecular players underlying ACh-mediated inhibition in the LL remain unknown. Surprisingly, through the analysis of single-cell expression studies and hybridization, we describe that α9, but not the α10, subunits are enriched in zebrafish HCs. Moreover, the heterologous expression of zebrafish α9 subunits indicates that homomeric receptors are functional and exhibit robust ACh-gated currents blocked by α-bungarotoxin and strychnine. In addition, Ca imaging on mechanically stimulated zebrafish LL HCs show that ACh elicits a decrease in evoked Ca signals, regardless of HC polarity. This effect is blocked by both α-bungarotoxin and apamin, indicating coupling of ACh-mediated effects to small-conductance Ca-activated potassium (SKs) channels. Our results indicate that an α9-containing (α9*) nAChR operates at the zebrafish LL efferent synapse. Moreover, the activation of α9* nAChRs most likely leads to LL HC hyperpolarization served by SK channels. The fish lateral line (LL) mechanosensory system shares structural, functional, and molecular similarities with those of the mammalian cochlea. Thus, it has become an accessible model for studying human hearing and balance disorders. However, the molecular players serving efferent control of LL hair cell (HC) activity have not been identified. Here we demonstrate that, different from the hearing organ of vertebrate species, a nicotinic acetylcholine receptor composed only of α9 subunits operates at the LL efferent synapse. Activation of α9-containing receptors leads to LL HC hyperpolarization because of the opening of small-conductance Ca-activated potassium channels. These results will further aid in the interpretation of data obtained from LL HCs as a model for cochlear HCs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.1772-20.2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7786207PMC
January 2021

Preventing presbycusis in mice with enhanced medial olivocochlear feedback.

Proc Natl Acad Sci U S A 2020 05 11;117(21):11811-11819. Epub 2020 May 11.

Instituto de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, 1121 Buenos Aires, Argentina;

"Growing old" is the most common cause of hearing loss. Age-related hearing loss (ARHL) (presbycusis) first affects the ability to understand speech in background noise, even when auditory thresholds in quiet are normal. It has been suggested that cochlear denervation ("synaptopathy") is an early contributor to age-related auditory decline. In the present work, we characterized age-related cochlear synaptic degeneration and hair cell loss in mice with enhanced α9α10 cholinergic nicotinic receptors gating kinetics ("gain of function" nAChRs). These mediate inhibitory olivocochlear feedback through the activation of associated calcium-gated potassium channels. Cochlear function was assessed via distortion product otoacoustic emissions and auditory brainstem responses. Cochlear structure was characterized in immunolabeled organ of Corti whole mounts using confocal microscopy to quantify hair cells, auditory neurons, presynaptic ribbons, and postsynaptic glutamate receptors. Aged wild-type mice had elevated acoustic thresholds and synaptic loss. Afferent synapses were lost from inner hair cells throughout the aged cochlea, together with some loss of outer hair cells. In contrast, cochlear structure and function were preserved in aged mice with gain-of-function nAChRs that provide enhanced olivocochlear inhibition, suggesting that efferent feedback is important for long-term maintenance of inner ear function. Our work provides evidence that olivocochlear-mediated resistance to presbycusis-ARHL occurs via the α9α10 nAChR complexes on outer hair cells. Thus, enhancement of the medial olivocochlear system could be a viable strategy to prevent age-related hearing loss.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.2000760117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7261056PMC
May 2020

Distinct Evolutionary Trajectories of Neuronal and Hair Cell Nicotinic Acetylcholine Receptors.

Mol Biol Evol 2020 04;37(4):1070-1089

Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.

The expansion and pruning of ion channel families has played a crucial role in the evolution of nervous systems. Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels with distinct roles in synaptic transmission at the neuromuscular junction, the central and peripheral nervous system, and the inner ear. Remarkably, the complement of nAChR subunits has been highly conserved along vertebrate phylogeny. To ask whether the different subtypes of receptors underwent different evolutionary trajectories, we performed a comprehensive analysis of vertebrate nAChRs coding sequences, mouse single-cell expression patterns, and comparative functional properties of receptors from three representative tetrapod species. We found significant differences between hair cell and neuronal receptors that were most likely shaped by the differences in coexpression patterns and coassembly rules of component subunits. Thus, neuronal nAChRs showed high degree of coding sequence conservation, coupled to greater coexpression variance and conservation of functional properties across tetrapod clades. In contrast, hair cell α9α10 nAChRs exhibited greater sequence divergence, narrow coexpression pattern, and great variability of functional properties across species. These results point to differential substrates for random change within the family of gene paralogs that relate to the segregated roles of nAChRs in synaptic transmission.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/molbev/msz290DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7086180PMC
April 2020

A Gain-of-Function Mutation in the α9 Nicotinic Acetylcholine Receptor Alters Medial Olivocochlear Efferent Short-Term Synaptic Plasticity.

J Neurosci 2018 04 23;38(16):3939-3954. Epub 2018 Mar 23.

Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, "Dr. Héctor N. Torres", Consejo Nacional de Investigaciones Científicas y Técnicas, 1428 Ciudad Autónoma de Buenos Aires, Argentina,

Gain control of the auditory system operates at multiple levels. Cholinergic medial olivocochlear (MOC) fibers originate in the brainstem and make synaptic contacts at the base of the outer hair cells (OHCs), the final targets of several feedback loops from the periphery and higher-processing centers. Efferent activation inhibits OHC active amplification within the mammalian cochlea, through the activation of a calcium-permeable α9α10 ionotropic cholinergic nicotinic receptor (nAChR), functionally coupled to calcium activated SK2 potassium channels. Correct operation of this feedback requires careful matching of acoustic input with the strength of cochlear inhibition (Galambos, 1956; Wiederhold and Kiang, 1970; Gifford and Guinan, 1987), which is driven by the rate of MOC activity and short-term facilitation at the MOC-OHC synapse (Ballestero et al., 2011; Katz and Elgoyhen, 2014). The present work shows (in mice of either sex) that a mutation in the α9α10 nAChR with increased duration of channel gating (Taranda et al., 2009) greatly elongates hair cell-evoked IPSCs and Ca signals. Interestingly, MOC-OHC synapses of ' mice presented reduced quantum content and increased presynaptic facilitation. These phenotypic changes lead to enhanced and sustained synaptic responses and OHC hyperpolarization upon high-frequency stimulation of MOC terminals. At the cochlear physiology level these changes were matched by a longer time course of efferent MOC suppression. This indicates that the properties of the MOC-OHC synapse directly determine the efficacy of the MOC feedback to the cochlea being a main player in the "gain control" of the auditory periphery. Plasticity can involve reciprocal signaling across chemical synapses. An opportunity to study this phenomenon occurs in the mammalian cochlea whose sensitivity is regulated by efferent olivocochlear neurons. These release acetylcholine to inhibit sensory hair cells. A point mutation in the hair cell's acetylcholine receptor that leads to increased gating of the receptor greatly elongates IPSCs. Interestingly, efferent terminals from mutant mice present a reduced resting release probability. However, upon high-frequency stimulation transmitter release facilitates strongly to produce stronger and far longer-lasting inhibition of cochlear function. Thus, central neuronal feedback on cochlear hair cells provides an opportunity to define plasticity mechanisms in cholinergic synapses other than the highly studied neuromuscular junction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.2528-17.2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5907056PMC
April 2018

Compartmentalization of antagonistic Ca signals in developing cochlear hair cells.

Proc Natl Acad Sci U S A 2018 02 8;115(9):E2095-E2104. Epub 2018 Feb 8.

Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres," Consejo Nacional de Investigaciones Científicas y Técnicas (INGEBI-CONICET), 1428 Buenos Aires, Argentina;

During a critical developmental period, cochlear inner hair cells (IHCs) exhibit sensory-independent activity, featuring action potentials in which Ca ions play a fundamental role in driving both spiking and glutamate release onto synapses with afferent auditory neurons. This spontaneous activity is controlled by a cholinergic input to the IHC, activating a specialized nicotinic receptor with high Ca permeability, and coupled to the activation of hyperpolarizing SK channels. The mechanisms underlying distinct excitatory and inhibitory Ca roles within a small, compact IHC are unknown. Making use of Ca imaging, afferent auditory bouton recordings, and electron microscopy, the present work shows that unusually high intracellular Ca buffering and "subsynaptic" cisterns provide efficient compartmentalization and tight control of cholinergic Ca signals. Thus, synaptic efferent Ca spillover and cross-talk are prevented, and the cholinergic input preserves its inhibitory signature to ensure normal development of the auditory system.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1719077115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5834711PMC
February 2018
-->