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Ivica J, Kejzar N, Ho H, Stockwell I, Kuchtiak V, Scrutton AM, Nakagawa T, Greger IH. Proton-triggered rearrangement of the AMPA receptor N-terminal domains impacts receptor kinetics and synaptic localization. Nat Struct Mol Biol 2024:10.1038/s41594-024-01369-5. [PMID: 39138332 DOI: 10.1038/s41594-024-01369-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2024] [Accepted: 07/08/2024] [Indexed: 08/15/2024]
Abstract
AMPA glutamate receptors (AMPARs) are ion channel tetramers that mediate the majority of fast excitatory synaptic transmission. They are composed of four subunits (GluA1-GluA4); the GluA2 subunit dominates AMPAR function throughout the forebrain. Its extracellular N-terminal domain (NTD) determines receptor localization at the synapse, ensuring reliable synaptic transmission and plasticity. This synaptic anchoring function requires a compact NTD tier, stabilized by a GluA2-specific NTD interface. Here we show that low pH conditions, which accompany synaptic activity, rupture this interface. All-atom molecular dynamics simulations reveal that protonation of an interfacial histidine residue (H208) centrally contributes to NTD rearrangement. Moreover, in stark contrast to their canonical compact arrangement at neutral pH, GluA2 cryo-electron microscopy structures exhibit a wide spectrum of NTD conformations under acidic conditions. We show that the consequences of this pH-dependent conformational control are twofold: rupture of the NTD tier slows recovery from desensitized states and increases receptor mobility at mouse hippocampal synapses. Therefore, a proton-triggered NTD switch will shape both AMPAR location and kinetics, thereby impacting synaptic signal transmission.
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Affiliation(s)
- Josip Ivica
- Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK
| | - Nejc Kejzar
- Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
| | - Hinze Ho
- Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
| | - Imogen Stockwell
- Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK
| | - Viktor Kuchtiak
- Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK
- Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic
| | - Alexander M Scrutton
- Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK
| | - Terunaga Nakagawa
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, USA.
- Center for Structural Biology, Vanderbilt University School of Medicine, Nashville, TN, USA.
- Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, TN, USA.
| | - Ingo H Greger
- Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK.
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2
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Durbin RJ, Heredia DJ, Gould TW, Renden RB. Postsynaptic Calcium Extrusion at the Mouse Neuromuscular Junction Alkalinizes the Synaptic Cleft. J Neurosci 2023; 43:5741-5752. [PMID: 37474311 PMCID: PMC10423045 DOI: 10.1523/jneurosci.0815-23.2023] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 07/07/2023] [Accepted: 07/14/2023] [Indexed: 07/22/2023] Open
Abstract
Neurotransmission is shaped by extracellular pH. Alkalization enhances pH-sensitive transmitter release and receptor activation, whereas acidification inhibits these processes and can activate acid-sensitive conductances in the synaptic cleft. Previous work has shown that the synaptic cleft can either acidify because of synaptic vesicular release and/or alkalize because of Ca2+ extrusion by the plasma membrane ATPase (PMCA). The direction of change differs across synapse types. At the mammalian neuromuscular junction (NMJ), the direction and magnitude of pH transients in the synaptic cleft during transmission remain ambiguous. We set out to elucidate the extracellular pH transients that occur at this cholinergic synapse under near-physiological conditions and identify their sources. We monitored pH-dependent changes in the synaptic cleft of the mouse levator auris longus using viral expression of the pseudoratiometric probe pHusion-Ex in the muscle. Using mice from both sexes, a significant and prolonged alkalization occurred when stimulating the connected nerve for 5 s at 50 Hz, which was dependent on postsynaptic intracellular Ca2+ release. Sustained stimulation for a longer duration (20 s at 50 Hz) caused additional prolonged net acidification at the cleft. To investigate the mechanism underlying cleft alkalization, we used muscle-expressed GCaMP3 to monitor the contribution of postsynaptic Ca2+ Activity-induced liberation of intracellular Ca2+ in muscle positively correlated with alkalization of the synaptic cleft, whereas inhibiting PMCA significantly decreased the extent of cleft alkalization. Thus, cholinergic synapses of the mouse NMJ typically alkalize because of cytosolic Ca2+ liberated in muscle during activity, unless under highly strenuous conditions where acidification predominates.SIGNIFICANCE STATEMENT Changes in synaptic cleft pH alter neurotransmission, acting on receptors and channels on both sides of the synapse. Synaptic acidification has been associated with a myriad of diseases in the central and peripheral nervous system. Here, we report that in near-physiological recording conditions the cholinergic neuromuscular junction shows use-dependent bidirectional changes in synaptic cleft pH-immediate alkalinization and a long-lasting acidification under prolonged stimulation. These results provide further insight into physiologically relevant changes at cholinergic synapses that have not been defined previously. Understanding and identifying synaptic pH transients during and after neuronal activity provides insight into short-term synaptic plasticity synapses and may identify therapeutic targets for diseases.
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Affiliation(s)
- Ryan J Durbin
- Integrative Neuroscience Graduate Program, University of Nevada, Reno, Reno, Nevada 89557
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557
| | - Dante J Heredia
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557
| | - Thomas W Gould
- Integrative Neuroscience Graduate Program, University of Nevada, Reno, Reno, Nevada 89557
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557
| | - Robert B Renden
- Integrative Neuroscience Graduate Program, University of Nevada, Reno, Reno, Nevada 89557
- Department of Physiology and Cell Biology, University of Nevada, Reno, School of Medicine, Reno, Nevada 89557
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3
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Davison A, Lux UT, Brandstätter JH, Babai N. T-Type Ca 2+ Channels Boost Neurotransmission in Mammalian Cone Photoreceptors. J Neurosci 2022; 42:6325-6343. [PMID: 35803735 PMCID: PMC9398539 DOI: 10.1523/jneurosci.1878-21.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2021] [Revised: 06/13/2022] [Accepted: 06/22/2022] [Indexed: 11/21/2022] Open
Abstract
It is a commonly accepted view that light stimulation of mammalian photoreceptors causes a graded change in membrane potential instead of developing a spike. The presynaptic Ca2+ channels serve as a crucial link for the coding of membrane potential variations into neurotransmitter release. Cav1.4 L-type Ca2+ channels are expressed in photoreceptor terminals, but the complete pool of Ca2+ channels in cone photoreceptors appears to be more diverse. Here, we discovered, employing whole-cell patch-clamp recording from cone photoreceptor terminals in both sexes of mice, that their Ca2+ currents are composed of low- (T-type Ca2+ channels) and high- (L-type Ca2+ channels) voltage-activated components. Furthermore, Ca2+ channels exerted self-generated spike behavior in dark membrane potentials, and spikes were generated in response to light/dark transition. The application of fast and slow Ca2+ chelators revealed that T-type Ca2+ channels are located close to the release machinery. Furthermore, capacitance measurements indicated that they are involved in evoked vesicle release. Additionally, RT-PCR experiments showed the presence of Cav3.2 T-type Ca2+ channels in cone photoreceptors but not in rod photoreceptors. Altogether, we found several crucial functions of T-type Ca2+ channels, which increase the functional repertoire of cone photoreceptors. Namely, they extend cone photoreceptor light-responsive membrane potential range, amplify dark responses, generate spikes, increase intracellular Ca2+ levels, and boost synaptic transmission.SIGNIFICANCE STATEMENT Photoreceptors provide the first synapse for coding light information. The key elements in synaptic transmission are the voltage-sensitive Ca2+ channels. Here, we provide evidence that mouse cone photoreceptors express low-voltage-activated Cav3.2 T-type Ca2+ channels in addition to high-voltage-activated L-type Ca2+ channels. The presence of T-type Ca2+ channels in cone photoreceptors appears to extend their light-responsive membrane potential range, amplify dark response, generate spikes, increase intracellular Ca2+ levels, and boost synaptic transmission. By these functions, Cav3.2 T-type Ca2+ channels increase the functional repertoire of cone photoreceptors.
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Affiliation(s)
- Adam Davison
- Department of Biology, Animal Physiology/Neurobiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Uwe Thorsten Lux
- Department of Biology, Animal Physiology/Neurobiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Johann Helmut Brandstätter
- Department of Biology, Animal Physiology/Neurobiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Norbert Babai
- Department of Biology, Animal Physiology/Neurobiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
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4
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Mukhopadhyay M, Pangrsic T. Synaptic transmission at the vestibular hair cells of amniotes. Mol Cell Neurosci 2022; 121:103749. [PMID: 35667549 DOI: 10.1016/j.mcn.2022.103749] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2021] [Revised: 05/09/2022] [Accepted: 06/01/2022] [Indexed: 11/19/2022] Open
Abstract
A harmonized interplay between the central nervous system and the five peripheral end organs is how the vestibular system helps organisms feel a sense of balance and motion in three-dimensional space. The receptor cells of this system, much like their cochlear equivalents, are the specialized hair cells. However, research over the years has shown that the vestibular endorgans and hair cells evolved very differently from their cochlear counterparts. The structurally unique calyceal synapse, which appeared much later in the evolutionary time scale, and continues to intrigue researchers, is now known to support several forms of synaptic neurotransmission. The conventional quantal transmission is believed to employ the ribbon structures, which carry several tethered vesicles filled with neurotransmitters. However, the field of vestibular hair cell synaptic molecular anatomy is still at a nascent stage and needs further work. In this review, we will touch upon the basic structure and function of the peripheral vestibular system, with the focus on the various modes of neurotransmission at the type I vestibular hair cells. We will also shed light on the current knowledge about the molecular anatomy of the vestibular hair cell synapses and vestibular synaptopathy.
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Affiliation(s)
- Mohona Mukhopadhyay
- Experimental Otology Group, InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, and Institute for Auditory Neuroscience, 37075 Göttingen, Germany
| | - Tina Pangrsic
- Experimental Otology Group, InnerEarLab, Department of Otolaryngology, University Medical Center Göttingen, and Institute for Auditory Neuroscience, 37075 Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Multidisciplinary Sciences, 37075 Göttingen, Germany; Collaborative Research Center 889, University of Göttingen, Göttingen, Germany; Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, 37075 Göttingen, Germany.
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5
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Feghhi T, Hernandez RX, Stawarski M, Thomas CI, Kamasawa N, Lau AWC, Macleod GT. Computational modeling predicts ephemeral acidic microdomains in the glutamatergic synaptic cleft. Biophys J 2021; 120:5575-5591. [PMID: 34774503 DOI: 10.1016/j.bpj.2021.11.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 10/21/2021] [Accepted: 11/05/2021] [Indexed: 10/19/2022] Open
Abstract
At chemical synapses, synaptic vesicles release their acidic contents into the cleft, leading to the expectation that the cleft should acidify. However, fluorescent pH probes targeted to the cleft of conventional glutamatergic synapses in both fruit flies and mice reveal cleft alkalinization rather than acidification. Here, using a reaction-diffusion scheme, we modeled pH dynamics at the Drosophila neuromuscular junction as glutamate, ATP, and protons (H+) were released into the cleft. The model incorporates bicarbonate and phosphate buffering systems as well as plasma membrane calcium-ATPase activity and predicts substantial cleft acidification but only for fractions of a millisecond after neurotransmitter release. Thereafter, the cleft rapidly alkalinizes and remains alkaline for over 100 ms because the plasma membrane calcium-ATPase removes H+ from the cleft in exchange for calcium ions from adjacent pre- and postsynaptic compartments, thus recapitulating the empirical data. The extent of synaptic vesicle loading and time course of exocytosis have little influence on the magnitude of acidification. Phosphate but not bicarbonate buffering is effective at suppressing the magnitude and time course of the acid spike, whereas both buffering systems are effective at suppressing cleft alkalinization. The small volume of the cleft levies a powerful influence on the magnitude of alkalinization and its time course. Structural features that open the cleft to adjacent spaces appear to be essential for alleviating the extent of pH transients accompanying neurotransmission.
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Affiliation(s)
- Touhid Feghhi
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, Florida
| | - Roberto X Hernandez
- Integrative Biology & Neuroscience Graduate Program, Florida Atlantic University, Boca Raton, Florida; International Max Planck Research School for Brain and Behavior, Jupiter, Florida; Jupiter Life Sciences Initiative, Florida Atlantic University, Jupiter, Florida
| | - Michal Stawarski
- Wilkes Honors College, Florida Atlantic University, Jupiter, Florida
| | - Connon I Thomas
- Electron Microscopy Core Facility, Max Planck Florida Institute, Jupiter, Florida
| | - Naomi Kamasawa
- Electron Microscopy Core Facility, Max Planck Florida Institute, Jupiter, Florida
| | - A W C Lau
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, Florida
| | - Gregory T Macleod
- Jupiter Life Sciences Initiative, Florida Atlantic University, Jupiter, Florida; Wilkes Honors College, Florida Atlantic University, Jupiter, Florida; Brain Institute, Florida Atlantic University, Jupiter, Florida; Institute for Human Health & Disease Intervention, Florida Atlantic University, Jupiter, Florida.
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6
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Sierksma MC, Borst JGG. Using ephaptic coupling to estimate the synaptic cleft resistivity of the calyx of Held synapse. PLoS Comput Biol 2021; 17:e1009527. [PMID: 34699519 PMCID: PMC8570497 DOI: 10.1371/journal.pcbi.1009527] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 11/05/2021] [Accepted: 10/05/2021] [Indexed: 11/19/2022] Open
Abstract
At synapses, the pre- and postsynaptic cells get so close that currents entering the cleft do not flow exclusively along its conductance, gcl. A prominent example is found in the calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB), where the presynaptic action potential can be recorded in the postsynaptic cell in the form of a prespike. Here, we developed a theoretical framework for ephaptic coupling via the synaptic cleft, and we tested its predictions using the MNTB prespike recorded in voltage-clamp. The shape of the prespike is predicted to resemble either the first or the second derivative of the inverted presynaptic action potential if cleft currents dissipate either mostly capacitively or resistively, respectively. We found that the resistive dissipation scenario provided a better description of the prespike shape. Its size is predicted to scale with the fourth power of the radius of the synapse, explaining why intracellularly recorded prespikes are uncommon in the central nervous system. We show that presynaptic calcium currents also contribute to the prespike shape. This calcium prespike resembled the first derivative of the inverted calcium current, again as predicted by the resistive dissipation scenario. Using this calcium prespike, we obtained an estimate for gcl of ~1 μS. We demonstrate that, for a circular synapse geometry, such as in conventional boutons or the immature calyx of Held, gcl is scale-invariant and only defined by extracellular resistivity, which was ~75 Ωcm, and by cleft height. During development the calyx of Held develops fenestrations. We show that these fenestrations effectively minimize the cleft potentials generated by the adult action potential, which might otherwise interfere with calcium channel opening. We thus provide a quantitative account of the dissipation of currents by the synaptic cleft, which can be readily extrapolated to conventional, bouton-like synapses.
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Affiliation(s)
- Martijn C. Sierksma
- Department of Neuroscience, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - J. Gerard G. Borst
- Department of Neuroscience, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
- * E-mail:
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7
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Kitcher SR, Pederson AM, Weisz CJC. Diverse identities and sites of action of cochlear neurotransmitters. Hear Res 2021; 419:108278. [PMID: 34108087 DOI: 10.1016/j.heares.2021.108278] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 04/30/2021] [Accepted: 05/18/2021] [Indexed: 11/18/2022]
Abstract
Accurate encoding of acoustic stimuli requires temporally precise responses to sound integrated with cellular mechanisms that encode the complexity of stimuli over varying timescales and orders of magnitude of intensity. Sound in mammals is initially encoded in the cochlea, the peripheral hearing organ, which contains functionally specialized cells (including hair cells, afferent and efferent neurons, and a multitude of supporting cells) to allow faithful acoustic perception. To accomplish the demanding physiological requirements of hearing, the cochlea has developed synaptic arrangements that operate over different timescales, with varied strengths, and with the ability to adjust function in dynamic hearing conditions. Multiple neurotransmitters interact to support the precision and complexity of hearing. Here, we review the location of release, action, and function of neurotransmitters in the mammalian cochlea with an emphasis on recent work describing the complexity of signaling.
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Affiliation(s)
- Siân R Kitcher
- Section on Neuronal Circuitry, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, United States
| | - Alia M Pederson
- Section on Neuronal Circuitry, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, United States
| | - Catherine J C Weisz
- Section on Neuronal Circuitry, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD 20892, United States.
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8
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Phase-Locking Requires Efficient Ca 2+ Extrusion at the Auditory Hair Cell Ribbon Synapse. J Neurosci 2021; 41:1625-1635. [PMID: 33446517 DOI: 10.1523/jneurosci.1324-18.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Revised: 08/25/2020] [Accepted: 12/27/2020] [Indexed: 11/21/2022] Open
Abstract
Proper perception of sounds in the environment requires auditory signals to be encoded with extraordinary temporal precision up to tens of microseconds, but how it originates from the hearing organs in the periphery is poorly understood. In particular, sound-evoked spikes in auditory afferent fibers in vivo are phase-locked to sound frequencies up to 5 kHz, but it is not clear how hair cells can handle intracellular Ca2+ changes with such high speed and efficiency. In this study, we combined patch-clamp recording and two-photon Ca2+ imaging to examine Ca2+ dynamics in hair cell ribbon synapses in the bullfrog amphibian papilla of both sexes. We found that Ca2+ clearance from single synaptic ribbons followed a double exponential function, and the weight of the fast component, but not the two time constants, was significantly reduced for prolonged stimulation, and during inhibition of the plasma membrane Ca2+ ATPase (PMCA), the mitochondrial Ca2+ uptake (MCU), or the sarcolemma/endoplasmic reticulum Ca2+ ATPase (SERCA), but not the Na+/Ca2+ exchanger (NCX). Furthermore, we found that both the basal Ca2+ level and the Ca2+ rise during sinusoidal stimulation were significantly increased by inhibition of PMCA, MCU, or SERCA. Consistently, phase-locking of synaptic vesicle releases from hair cells was also significantly reduced by blocking PMCA, MCU, or SERCA, but not NCX. We conclude that, in addition to fast diffusion mediated by mobile Ca2+ buffer, multiple Ca2+ extrusion pumps are required for phase-locking at the auditory hair cell ribbon synapse.SIGNIFICANCE STATEMENT Hair cell synapses can transmit sound-driven signals precisely in the kHz range. However, previous studies of Ca2+ handling in auditory hair cells have often been conducted in immature hair cells, with elevated extracellular Ca2+ concentration, or through steady-state stimulation that may not be physiologically relevant. Here we examine Ca2+ clearance from hair cell synaptic ribbons in a fully mature preparation at physiological concentration of external Ca2+ and at physiological temperature. By stimulating hair cells with sinusoidal voltage commands that mimic pure sound tones, we recapitulated the phase-locking of hair cell exocytosis with an in vitro approach. This allowed us to reveal the Ca2+ extrusion mechanisms that are required for phase-locking at auditory hair cell ribbon synapses.
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9
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Blaustein M, Wirth S, Saldaña G, Piantanida AP, Bogetti ME, Martin ME, Colman-Lerner A, Uchitel OD. A new tool to sense pH changes at the neuromuscular junction synaptic cleft. Sci Rep 2020; 10:20480. [PMID: 33235222 PMCID: PMC7687886 DOI: 10.1038/s41598-020-77154-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 11/06/2020] [Indexed: 12/12/2022] Open
Abstract
Synaptic transmission triggers transient acidification of the synaptic cleft. Recently, it has been shown that pH affects the opening of postsynaptic channels and therefore the production of tools that allow to study these behaviors should result of paramount value. We fused α-bungarotoxin, a neurotoxin derived from the snake Bungarus multicinctus that binds irreversibly to the acetylcholine receptor extracellular domain, to the pH sensitive GFP Super Ecliptic pHluorin, and efficiently expressed it in Pichia pastoris. This sensor allows synaptic changes in pH to be measured without the need of incorporating transgenes into animal cells. Here, we show that incubation of the mouse levator auris muscle with a solution containing this recombinant protein is enough to fluorescently label the endplate post synaptic membrane. Furthermore, we could physiologically alter and measure post synaptic pH by evaluating changes in the fluorescent signal of pHluorin molecules bound to acetylcholine receptors. In fact, using this tool we were able to detect a drop in 0.01 to 0.05 pH units in the vicinity of the acetylcholine receptors following vesicle exocytosis triggered by nerve electrical stimulation. Further experiments will allow to learn the precise changes in pH during and after synaptic activation.
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Affiliation(s)
- Matías Blaustein
- Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina. .,Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), FCEN, UBA, C1428EHA, Buenos Aires, Argentina.
| | - Sonia Wirth
- Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina.,Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), FCEN, CONICET-UBA, Buenos Aires, Argentina
| | - Gustavo Saldaña
- Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina.,Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-UBA, C1428EHA, Buenos Aires, Argentina
| | - Ana Paula Piantanida
- Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina.,Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-UBA, C1428EHA, Buenos Aires, Argentina
| | - María Eugenia Bogetti
- Instituto de Biología Celular y Neurociencias (IBCN) Dr. Eduardo de Robertis, Facultad de Medicina, CONICET-UBA, Buenos Aires, Argentina
| | - María Eugenia Martin
- Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina.,Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-UBA, C1428EHA, Buenos Aires, Argentina
| | - Alejandro Colman-Lerner
- Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina.,Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-UBA, C1428EHA, Buenos Aires, Argentina
| | - Osvaldo D Uchitel
- Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), Buenos Aires, Argentina. .,Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-UBA, C1428EHA, Buenos Aires, Argentina.
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10
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Neuronal Glutamatergic Synaptic Clefts Alkalinize Rather Than Acidify during Neurotransmission. J Neurosci 2020; 40:1611-1624. [PMID: 31964719 DOI: 10.1523/jneurosci.1774-19.2020] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 01/14/2020] [Accepted: 01/15/2020] [Indexed: 12/11/2022] Open
Abstract
The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of neurotransmitters and protons from synaptic vesicles, and is supported by direct data from sensory ribbon-type synapses. However, it is unclear whether acidification occurs at non-ribbon-type synapses. Here we used genetically encoded fluorescent pH indicators to examine cleft pH at conventional neuronal synapses. At the neuromuscular junction of female Drosophila larvae, we observed alkaline spikes of over 1 log unit during fictive locomotion in vivo. Ex vivo, single action potentials evoked alkalinizing pH transients of only ∼0.01 log unit, but these transients summated rapidly during burst firing. A chemical pH indicator targeted to the cleft corroborated these findings. Cleft pH transients were dependent on Ca2+ movement across the postsynaptic membrane, rather than neurotransmitter release per se, a result consistent with cleft alkalinization being driven by the Ca2+/H+ antiporting activity of the plasma membrane Ca2+-ATPase at the postsynaptic membrane. Targeting the pH indicators to the microenvironment of the presynaptic voltage gated Ca2+ channels revealed that alkalinization also occurred within the cleft proper at the active zone and not just within extrasynaptic regions. Application of the pH indicators at the mouse calyx of Held, a mammalian central synapse, similarly revealed cleft alkalinization during burst firing in both males and females. These findings, made at two quite different non-ribbon type synapses, suggest that cleft alkalinization during neurotransmission, rather than acidification, is a generalizable phenomenon across conventional neuronal synapses.SIGNIFICANCE STATEMENT Neurotransmission is highly sensitive to the pH of the extracellular milieu. This is readily evident in the neurological symptoms that accompany systemic acid/base imbalances. Imaging data from sensory ribbon-type synapses show that neurotransmission itself can acidify the synaptic cleft, likely due to the corelease of protons and glutamate. It is not clear whether the same phenomenon occurs at conventional neuronal synapses due to the difficulties in collecting such data. If it does occur, it would provide for an additional layer of activity-dependent modulation of neurotransmission. Our findings of alkalinization, rather than acidification, within the cleft of two different neuronal synapses encourages a reassessment of the scope of activity-dependent pH influences on neurotransmission and short-term synaptic plasticity.
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11
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Moser T, Grabner CP, Schmitz F. Sensory Processing at Ribbon Synapses in the Retina and the Cochlea. Physiol Rev 2020; 100:103-144. [DOI: 10.1152/physrev.00026.2018] [Citation(s) in RCA: 80] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In recent years, sensory neuroscientists have made major efforts to dissect the structure and function of ribbon synapses which process sensory information in the eye and ear. This review aims to summarize our current understanding of two key aspects of ribbon synapses: 1) their mechanisms of exocytosis and endocytosis and 2) their molecular anatomy and physiology. Our comparison of ribbon synapses in the cochlea and the retina reveals convergent signaling mechanisms, as well as divergent strategies in different sensory systems.
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Affiliation(s)
- Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
| | - Chad P. Grabner
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
| | - Frank Schmitz
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany; Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, Göttingen, Germany; Synaptic Nanophysiology Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany; and Institute for Anatomy and Cell Biology, Department of Neuroanatomy, Medical School, Saarland University, Homburg, Germany
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12
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Vincent PFY, Cho S, Tertrais M, Bouleau Y, von Gersdorff H, Dulon D. Clustered Ca 2+ Channels Are Blocked by Synaptic Vesicle Proton Release at Mammalian Auditory Ribbon Synapses. Cell Rep 2019; 25:3451-3464.e3. [PMID: 30566869 DOI: 10.1016/j.celrep.2018.11.072] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2018] [Revised: 08/31/2018] [Accepted: 11/16/2018] [Indexed: 12/25/2022] Open
Abstract
A Ca2+ current transient block (ICaTB) by protons occurs at some ribbon-type synapses after exocytosis, but this has not been observed at mammalian hair cells. Here we show that a robust ICaTB occurs at post-hearing mouse and gerbil inner hair cell (IHC) synapses, but not in immature IHC synapses, which contain non-compact active zones, where Ca2+ channels are loosely coupled to the release sites. Unlike ICaTB at other ribbon synapses, ICaTB in mammalian IHCs displays a surprising multi-peak structure that mirrors the EPSCs seen in paired recordings. Desynchronizing vesicular release with intracellular BAPTA or by deleting otoferlin, the Ca2+ sensor for exocytosis, greatly reduces ICaTB, whereas enhancing release synchronization by raising Ca2+ influx or temperature increases ICaTB. This suggests that ICaTB is produced by fast multivesicular proton-release events. We propose that ICaTB may function as a submillisecond feedback mechanism contributing to the auditory nerve's fast spike adaptation during sound stimulation.
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Affiliation(s)
- Philippe F Y Vincent
- Université de Bordeaux, Bordeaux Neurocampus, Equipe Neurophysiologie de la Synapse Auditive, Inserm U1120, 33076 Bordeaux, France
| | - Soyoun Cho
- Center for Sensory Neuroscience, Boys Town National Research Hospital, Omaha, NE 68131, USA; The Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA
| | - Margot Tertrais
- Université de Bordeaux, Bordeaux Neurocampus, Equipe Neurophysiologie de la Synapse Auditive, Inserm U1120, 33076 Bordeaux, France
| | - Yohan Bouleau
- Université de Bordeaux, Bordeaux Neurocampus, Equipe Neurophysiologie de la Synapse Auditive, Inserm U1120, 33076 Bordeaux, France
| | | | - Didier Dulon
- Université de Bordeaux, Bordeaux Neurocampus, Equipe Neurophysiologie de la Synapse Auditive, Inserm U1120, 33076 Bordeaux, France.
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13
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Contini D, Holstein GR, Art JJ. Synaptic cleft microenvironment influences potassium permeation and synaptic transmission in hair cells surrounded by calyx afferents in the turtle. J Physiol 2019; 598:853-889. [PMID: 31623011 DOI: 10.1113/jp278680] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 10/13/2019] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS In central regions of vestibular semicircular canal epithelia, the [K+ ] in the synaptic cleft ([K+ ]c ) contributes to setting the hair cell and afferent membrane potentials; the potassium efflux from type I hair cells results from the interdependent gating of three conductances. Elevation of [K+ ]c occurs through a calcium-activated potassium conductance, GBK , and a low-voltage-activating delayed rectifier, GK(LV) , that activates upon elevation of [K+ ]c . Calcium influx that enables quantal transmission also activates IBK , an effect that can be blocked internally by BAPTA, and externally by a CaV 1.3 antagonist or iberiotoxin. Elevation of [K+ ]c or chelation of [Ca2+ ]c linearizes the GK(LV) steady-state I-V curve, suggesting that the outward rectification observed for GK(LV) may result largely from a potassium-sensitive relief of Ca2+ inactivation of the channel pore selectivity filter. Potassium sensitivity of hair cell and afferent conductances allows three modes of transmission: quantal, ion accumulation and resistive coupling to be multiplexed across the synapse. ABSTRACT In the vertebrate nervous system, ions accumulate in diffusion-limited synaptic clefts during ongoing activity. Such accumulation can be demonstrated at large appositions such as the hair cell-calyx afferent synapses present in central regions of the turtle vestibular semicircular canal epithelia. Type I hair cells influence discharge rates in their calyx afferents by modulating the potassium concentration in the synaptic cleft, [K+ ]c , which regulates potassium-sensitive conductances in both hair cell and afferent. Dual recordings from synaptic pairs have demonstrated that, despite a decreased driving force due to potassium accumulation, hair cell depolarization elicits sustained outward currents in the hair cell, and a maintained inward current in the afferent. We used kinetic and pharmacological dissection of the hair cell conductances to understand the interdependence of channel gating and permeation in the context of such restricted extracellular spaces. Hair cell depolarization leads to calcium influx and activation of a large calcium-activated potassium conductance, GBK , that can be blocked by agents that disrupt calcium influx or buffer the elevation of [Ca2+ ]i , as well as by the specific KCa 1.1 blocker iberiotoxin. Efflux of K+ through GBK can rapidly elevate [K+ ]c , which speeds the activation and slows the inactivation and deactivation of a second potassium conductance, GK(LV) . Elevation of [K+ ]c or chelation of [Ca2+ ]c linearizes the GK(LV) steady-state I-V curve, consistent with a K+ -dependent relief of Ca2+ inactivation of GK(LV) . As a result, this potassium-sensitive hair cell conductance pairs with the potassium-sensitive hyperpolarization-activated cyclic nucleotide-gated channel (HCN) conductance in the afferent and creates resistive coupling at the synaptic cleft.
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Affiliation(s)
- Donatella Contini
- Department of Anatomy & Cell Biology, University of Illinois College of Medicine, 808 S. Wood St, Chicago, IL, 60612, USA
| | - Gay R Holstein
- Neurology, Icahn School of Medicine at Mount Sinai, 1468 Madison Ave, New York, NY, 10029, USA
| | - Jonathan J Art
- Department of Anatomy & Cell Biology, University of Illinois College of Medicine, 808 S. Wood St, Chicago, IL, 60612, USA
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14
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Uchitel OD, González Inchauspe C, Weissmann C. Synaptic signals mediated by protons and acid-sensing ion channels. Synapse 2019; 73:e22120. [PMID: 31180161 DOI: 10.1002/syn.22120] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Revised: 06/05/2019] [Accepted: 06/05/2019] [Indexed: 01/04/2023]
Abstract
Extracellular pH changes may constitute significant signals for neuronal communication. During synaptic transmission, changes in pH in the synaptic cleft take place. Its role in the regulation of presynaptic Ca2+ currents through multivesicular release in ribbon-type synapses is a proven phenomenon. In recent years, protons have been recognized as neurotransmitters that participate in neuronal communication in synapses of several regions of the CNS such as amygdala, nucleus accumbens, and brainstem. Protons are released by nerve stimulation and activate postsynaptic acid-sensing ion channels (ASICs). Several types of ASIC channels are expressed in the peripheral and central nervous system. The influx of Ca2+ through some subtypes of ASICs, as a result of synaptic transmission, agrees with the participation of ASICs in synaptic plasticity. Pharmacological and genetical inhibition of ASIC1a results in alterations in learning, memory, and phenomena like fear and cocaine-seeking behavior. The recognition of endogenous molecules, such as arachidonic acid, cytokines, histamine, spermine, lactate, and neuropeptides, capable of inhibiting or potentiating ASICs suggests the existence of mechanisms of synaptic modulation that have not yet been fully identified and that could be tuned by new emerging pharmacological compounds with potential therapeutic benefits.
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Affiliation(s)
- Osvaldo D Uchitel
- Departamento de Fisiología, Biología Molecular y Celular "Dr. Héctor Maldonado", Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología molecular y Neurociencias (IFIBYNE) CONICET, Universidad de Buenos Aires, Ciudad Universitaria, (C1428EGA), Ciudad Autónoma de Buenos Aires, Argentina
| | - Carlota González Inchauspe
- Departamento de Fisiología, Biología Molecular y Celular "Dr. Héctor Maldonado", Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología molecular y Neurociencias (IFIBYNE) CONICET, Universidad de Buenos Aires, Ciudad Universitaria, (C1428EGA), Ciudad Autónoma de Buenos Aires, Argentina
| | - Carina Weissmann
- Departamento de Fisiología, Biología Molecular y Celular "Dr. Héctor Maldonado", Facultad de Ciencias Exactas y Naturales, Instituto de Fisiología, Biología molecular y Neurociencias (IFIBYNE) CONICET, Universidad de Buenos Aires, Ciudad Universitaria, (C1428EGA), Ciudad Autónoma de Buenos Aires, Argentina
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15
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González-Inchauspe C, Gobetto MN, Uchitel OD. Modulation of acid sensing ion channel dependent protonergic neurotransmission at the mouse calyx of Held. Neuroscience 2019; 439:195-210. [PMID: 31022462 DOI: 10.1016/j.neuroscience.2019.04.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 04/04/2019] [Accepted: 04/05/2019] [Indexed: 11/18/2022]
Abstract
Acid-sensing ion channels (ASICs) regulate synaptic activities and play important roles in neurodegenerative diseases. It has been reported that homomeric ASIC-1a channels are expressed in neurons of the medial nucleus of the trapezoid body (MNTB) of the auditory system in the CNS. During synaptic transmission, acidification of the synaptic cleft presumably due to the co-release of neurotransmitter and H+ from synaptic vesicles activates postsynaptic ASIC-1a channels in mice up to 3 weeks old. This generates synaptic currents (ASIC1a-SCs) that add to the glutamatergic excitatory postsynaptic currents (EPSCs). Here we report that neuromodulators like histamine and natural products like lactate and spermine potentiate ASIC1a-SCs in an additive form such that excitatory ASIC synaptic currents as well as the associated calcium influx become significantly large and physiologically relevant. We show that ASIC1a-SCs enhanced by endogenous neuromodulators are capable of supporting synaptic transmission in the absence of glutamatergic EPSCs. Furthermore, at high frequency stimulation (HFS), ASIC1a-SCs contribute to diminish short term depression (STD) and their contribution is even more relevant at early stages of development. Since ASIC channels are present in almost all types of neurons and synaptic vesicles content is acid, the participation of protons in synaptic transmission and its potentiation by endogenous substances could be a general phenomenon across the central nervous system. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.
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Affiliation(s)
- Carlota González-Inchauspe
- Instituto de Fisiología, Biología molecular y Neurociencias (IFIBYNE) CONICET. Departamento de Fisiología, Biología Molecular y Celular "Dr. Héctor Maldonado", Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Ciudad Universitaria. (C1428EGA) Ciudad Autónoma de Buenos Aires, Argentina.
| | - María Natalia Gobetto
- Instituto de Fisiología, Biología molecular y Neurociencias (IFIBYNE) CONICET. Departamento de Fisiología, Biología Molecular y Celular "Dr. Héctor Maldonado", Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Ciudad Universitaria. (C1428EGA) Ciudad Autónoma de Buenos Aires, Argentina
| | - Osvaldo D Uchitel
- Instituto de Fisiología, Biología molecular y Neurociencias (IFIBYNE) CONICET. Departamento de Fisiología, Biología Molecular y Celular "Dr. Héctor Maldonado", Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Ciudad Universitaria. (C1428EGA) Ciudad Autónoma de Buenos Aires, Argentina
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16
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Vesicular Glutamatergic Transmission in Noise-Induced Loss and Repair of Cochlear Ribbon Synapses. J Neurosci 2019; 39:4434-4447. [PMID: 30926748 DOI: 10.1523/jneurosci.2228-18.2019] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Revised: 03/22/2019] [Accepted: 03/25/2019] [Indexed: 12/11/2022] Open
Abstract
Noise-induced excitotoxicity is thought to depend on glutamate. However, the excitotoxic mechanisms are unknown, and the necessity of glutamate for synapse loss or regeneration is unclear. Despite absence of glutamatergic transmission from cochlear inner hair cells in mice lacking the vesicular glutamate transporter-3 (Vglut3KO ), at 9-11 weeks, approximately half the number of synapses found in Vglut3WT were maintained as postsynaptic AMPA receptors juxtaposed with presynaptic ribbons and voltage-gated calcium channels (CaV1.3). Synapses were larger in Vglut3KO than Vglut3WT In Vglut3WT and Vglut3 +/- mice, 8-16 kHz octave-band noise exposure at 100 dB sound pressure level caused a threshold shift (∼40 dB) and a loss of synapses (>50%) at 24 h after exposure. Hearing threshold and synapse number partially recovered by 2 weeks after exposure as ribbons became larger, whereas recovery was significantly better in Vglut3WT Noise exposure at 94 dB sound pressure level caused auditory threshold shifts that fully recovered in 2 weeks, whereas suprathreshold hearing recovered faster in Vglut3WT than Vglut3 +/- These results, from mice of both sexes, suggest that spontaneous repair of synapses after noise depends on the level of Vglut3 protein or the level of glutamate release during the recovery period. Noise-induced loss of presynaptic ribbons or postsynaptic AMPA receptors was not observed in Vglut3KO , demonstrating its dependence on vesicular glutamate release. In Vglut3WT and Vglut3 +/-, noise exposure caused unpairing of presynaptic ribbons and presynaptic CaV1.3, but not in Vglut3KO where CaV1.3 remained clustered with ribbons at presynaptic active zones. These results suggest that, without glutamate release, noise-induced presynaptic Ca2+ influx was insufficient to disassemble the active zone. However, synapse volume increased by 2 weeks after exposure in Vglut3KO , suggesting glutamate-independent mechanisms.SIGNIFICANCE STATEMENT Hearing depends on glutamatergic transmission mediated by Vglut3, but the role of glutamate in synapse loss and repair is unclear. Here, using mice of both sexes, we show that one copy of the Vglut3 gene is sufficient for noise-induced threshold shift and loss of ribbon synapses, but both copies are required for normal recovery of hearing function and ribbon synapse number. Impairment of the recovery process in mice having only one functional copy suggests that glutamate release may promote synapse regeneration. At least one copy of the Vglut3 gene is necessary for noise-induced synapse loss. Although the excitotoxic mechanism remains unknown, these findings are consistent with the presumption that glutamate is the key mediator of noise-induced synaptopathy.
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17
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Pangrsic T, Singer JH, Koschak A. Voltage-Gated Calcium Channels: Key Players in Sensory Coding in the Retina and the Inner Ear. Physiol Rev 2019; 98:2063-2096. [PMID: 30067155 DOI: 10.1152/physrev.00030.2017] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Calcium influx through voltage-gated Ca (CaV) channels is the first step in synaptic transmission. This review concerns CaV channels at ribbon synapses in primary sense organs and their specialization for efficient coding of stimuli in the physical environment. Specifically, we describe molecular, biochemical, and biophysical properties of the CaV channels in sensory receptor cells of the retina, cochlea, and vestibular apparatus, and we consider how such properties might change over the course of development and contribute to synaptic plasticity. We pay particular attention to factors affecting the spatial arrangement of CaV channels at presynaptic, ribbon-type active zones, because the spatial relationship between CaV channels and release sites has been shown to affect synapse function critically in a number of systems. Finally, we review identified synaptopathies affecting sensory systems and arising from dysfunction of L-type, CaV1.3, and CaV1.4 channels or their protein modulatory elements.
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Affiliation(s)
- Tina Pangrsic
- Synaptic Physiology of Mammalian Vestibular Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen and Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine , Göttingen, Germany ; Department of Biology, University of Maryland , College Park, Maryland ; and Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck , Innsbruck , Austria
| | - Joshua H Singer
- Synaptic Physiology of Mammalian Vestibular Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen and Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine , Göttingen, Germany ; Department of Biology, University of Maryland , College Park, Maryland ; and Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck , Innsbruck , Austria
| | - Alexandra Koschak
- Synaptic Physiology of Mammalian Vestibular Hair Cells Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen and Auditory Neuroscience Group, Max Planck Institute of Experimental Medicine , Göttingen, Germany ; Department of Biology, University of Maryland , College Park, Maryland ; and Pharmacology and Toxicology, Institute of Pharmacy, University of Innsbruck , Innsbruck , Austria
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18
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Soto E, Ortega-Ramírez A, Vega R. Protons as Messengers of Intercellular Communication in the Nervous System. Front Cell Neurosci 2018; 12:342. [PMID: 30364044 PMCID: PMC6191491 DOI: 10.3389/fncel.2018.00342] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 09/14/2018] [Indexed: 12/18/2022] Open
Abstract
In this review, evidence demonstrating that protons (H+) constitute a complex, regulated intercellular signaling mechanisms are presented. Given that pH is a strictly regulated variable in multicellular organisms, localized extracellular pH changes may constitute significant signals of cellular processes that occur in a cell or a group of cells. Several studies have demonstrated that the low pH of synaptic vesicles implies that neurotransmitter release is always accompanied by the co-release of H+ into the synaptic cleft, leading to transient extracellular pH shifts. Also, evidence has accumulated indicating that extracellular H+ concentration regulation is complex and implies a source of protons in a network of transporters, ion exchangers, and buffer capacity of the media that may finally establish the extracellular proton concentration. The activation of membrane transporters, increased production of CO2 and of metabolites, such as lactate, produce significant extracellular pH shifts in nano- and micro-domains in the central nervous system (CNS), constituting a reliable signal for intercellular communication. The acid sensing ion channels (ASIC) function as specific signal sensors of proton signaling mechanism, detecting subtle variations of extracellular H+ in a range varying from pH 5 to 8. The main question in relation to this signaling system is whether it is only synaptically restricted, or a volume modulator of neuron excitability. This signaling system may have evolved from a metabolic activity detection mechanism to a highly localized extracellular proton dependent communication mechanism. In this study, evidence showing the mechanisms of regulation of extracellular pH shifts and of the ASICs and its function in modulating the excitability in various systems is reviewed, including data and its role in synaptic neurotransmission, volume transmission and even segregated neurotransmission, leading to a reliable extracellular signaling mechanism.
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Affiliation(s)
- Enrique Soto
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | | | - Rosario Vega
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
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19
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Park JS, Cederroth CR, Basinou V, Sweetapple L, Buijink R, Lundkvist GB, Michel S, Canlon B. Differential Phase Arrangement of Cellular Clocks along the Tonotopic Axis of the Mouse Cochlea Ex Vivo. Curr Biol 2017; 27:2623-2629.e2. [PMID: 28823676 PMCID: PMC6899219 DOI: 10.1016/j.cub.2017.07.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Revised: 06/15/2017] [Accepted: 07/07/2017] [Indexed: 12/18/2022]
Abstract
Topological distributions of individual cellular clocks have not been demonstrated in peripheral organs. The cochlea displays circadian patterns of core clock gene expression [1, 2]. PER2 protein is expressed in the hair cells and spiral ganglion neurons of the cochlea in the spiral ganglion neurons [1]. To investigate the topological organization of cellular oscillators in the cochlea, we recorded circadian rhythms from mouse cochlear explants using highly sensitive real-time tracking of PER2::LUC bioluminescence. Here, we show cell-autonomous and self-sustained oscillations originating from hair cells and spiral ganglion neurons. Multi-phased cellular clocks were arranged along the length of the cochlea with oscillations initiating at the apex (low-frequency region) and traveling toward the base (high-frequency region). Phase differences of 3 hr were found between cellular oscillators in the apical and middle regions and from isolated individual cochlear regions, indicating that cellular networks organize the rhythms along the tonotopic axis. This is the first demonstration of a spatiotemporal arrangement of circadian clocks at the cellular level in a peripheral organ. Cochlear rhythms were disrupted in the presence of either voltage-gated potassium channel blocker (TEA) or extracellular calcium chelator (BAPTA), demonstrating that multiple types of ion channels contribute to the maintenance of coherent rhythms. In contrast, preventing action potentials with tetrodotoxin (TTX) or interfering with cell-to-cell communication the broad-spectrum gap junction blocker (CBX [carbenoxolone]) had no influence on cochlear rhythms. These findings highlight a dynamic regulation and longitudinal distribution of cellular clocks in the cochlea.
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Affiliation(s)
- Jung-Sub Park
- Department of Physiology and Pharmacology, Karolinska Institutet, 17177 Stockholm, Sweden; Department of Otolaryngology, Ajou University School of Medicine, 164 Worldcup-ro, Yeongtong-gu, Suwon 16499, Korea
| | | | - Vasiliki Basinou
- Department of Physiology and Pharmacology, Karolinska Institutet, 17177 Stockholm, Sweden
| | - Lara Sweetapple
- Department of Physiology and Pharmacology, Karolinska Institutet, 17177 Stockholm, Sweden
| | - Renate Buijink
- Department of Molecular Cell Biology, Leiden University Medical Center, 2333 Leiden, the Netherlands
| | - Gabriella B Lundkvist
- Department of Physiology and Pharmacology, Karolinska Institutet, 17177 Stockholm, Sweden; Department of Neuroscience, Karolinska Institutet, 17177 Stockholm, Sweden; Max Planck Institute for Biology of Ageing, 50931 Cologne, Germany
| | - Stephan Michel
- Department of Molecular Cell Biology, Leiden University Medical Center, 2333 Leiden, the Netherlands
| | - Barbara Canlon
- Department of Physiology and Pharmacology, Karolinska Institutet, 17177 Stockholm, Sweden.
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20
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Distinct Actions of Voltage-Activated Ca 2+ Channel Block on Spontaneous Release at Excitatory and Inhibitory Central Synapses. J Neurosci 2017; 37:4301-4310. [PMID: 28320843 DOI: 10.1523/jneurosci.3488-16.2017] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 03/08/2017] [Accepted: 03/13/2017] [Indexed: 11/21/2022] Open
Abstract
At chemical synapses, voltage-activated calcium channels (VACCs) mediate Ca2+ influx to trigger action potential-evoked neurotransmitter release. However, the mechanisms by which Ca2+ regulates spontaneous transmission have not been fully determined. We have shown that VACCs are a major trigger of spontaneous release at neocortical inhibitory synapses but not at excitatory synapses, suggesting fundamental differences in spontaneous neurotransmission at GABAergic and glutamatergic synapses. Recently, VACC blockers were reported to reduce spontaneous release of glutamate and it was proposed that there was conservation of underlying mechanisms of neurotransmission at excitatory and inhibitory synapses. Furthermore, it was hypothesized that the different effects on excitatory and inhibitory synapses may have resulted from off-target actions of Cd2+, a nonselective VACC blocker, or other variations in experimental conditions. Here we report that in mouse neocortical neurons, selective and nonselective VACC blockers inhibit spontaneous release at inhibitory but not at excitatory terminals, and that this pattern is observed in culture and slice preparations as well as in synapses from acute slices of the auditory brainstem. The voltage dependence of Cd2+ block of VACCs accounts for the apparent lower potency of Cd2+ on spontaneous release of GABA than on VACC current amplitudes. Our findings indicate fundamental differences in the regulation of spontaneous release at inhibitory and excitatory synapses by stochastic VACC activity that extend beyond the cortex to the brainstem.SIGNIFICANCE STATEMENT Presynaptic Ca2+ entry via voltage-activated calcium channels (VACCs) is the major trigger of action potential-evoked synaptic release. However, the role of VACCs in the regulation of spontaneous neurotransmitter release (in the absence of a synchronizing action potential) remains controversial. We show that spontaneous release is affected differently by VACCs at excitatory and inhibitory synapses. At inhibitory synapses, stochastic openings of VACCs trigger the majority of spontaneous release, whereas they do not affect spontaneous release at excitatory synapses. We find this pattern to be wide ranging, holding for large and small synapses in the neocortex and brainstem. These findings indicate fundamental differences of the Ca2+ dependence of spontaneous release at excitatory and inhibitory synapses and heterogeneity of the mechanisms of release across the CNS.
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21
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Chiacchiaretta M, Latifi S, Bramini M, Fadda M, Fassio A, Benfenati F, Cesca F. Neuronal hyperactivity causes Na +/H + exchanger-induced extracellular acidification at active synapses. J Cell Sci 2017; 130:1435-1449. [PMID: 28254883 DOI: 10.1242/jcs.198564] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 02/28/2017] [Indexed: 12/12/2022] Open
Abstract
Extracellular pH impacts on neuronal activity, which is in turn an important determinant of extracellular H+ concentration. The aim of this study was to describe the spatio-temporal dynamics of extracellular pH at synaptic sites during neuronal hyperexcitability. To address this issue we created ex.E2GFP, a membrane-targeted extracellular ratiometric pH indicator that is exquisitely sensitive to acidic shifts. By monitoring ex.E2GFP fluorescence in real time in primary cortical neurons, we were able to quantify pH fluctuations during network hyperexcitability induced by convulsant drugs or high-frequency electrical stimulation. Sustained hyperactivity caused a pH decrease that was reversible upon silencing of neuronal activity and located at active synapses. This acidic shift was not attributable to the outflow of synaptic vesicle H+ into the cleft nor to the activity of membrane-exposed H+ V-ATPase, but rather to the activity of the Na+/H+-exchanger. Our data demonstrate that extracellular synaptic pH shifts take place during epileptic-like activity of neural cultures, emphasizing the strict links existing between synaptic activity and synaptic pH. This evidence may contribute to the understanding of the physio-pathological mechanisms associated with hyperexcitability in the epileptic brain.
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Affiliation(s)
- Martina Chiacchiaretta
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Shahrzad Latifi
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy
| | - Mattia Bramini
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy
| | - Manuela Fadda
- Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Anna Fassio
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Fabio Benfenati
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy.,Department of Experimental Medicine, University of Genova, Viale Benedetto XV 3, Genova 16132, Italy
| | - Fabrizia Cesca
- Center for Synaptic Neuroscience and Technology, Fondazione Istituto Italiano di Tecnologia, Largo Rosanna Benzi 10, Genova 16132, Italy
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Different Ca V1.3 Channel Isoforms Control Distinct Components of the Synaptic Vesicle Cycle in Auditory Inner Hair Cells. J Neurosci 2017; 37:2960-2975. [PMID: 28193694 DOI: 10.1523/jneurosci.2374-16.2017] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 01/27/2017] [Accepted: 02/01/2017] [Indexed: 12/16/2022] Open
Abstract
The mechanisms orchestrating transient and sustained exocytosis in auditory inner hair cells (IHCs) remain largely unknown. These exocytotic responses are believed to mobilize sequentially a readily releasable pool of vesicles (RRP) underneath the synaptic ribbons and a slowly releasable pool of vesicles (SRP) at farther distance from them. They are both governed by Cav1.3 channels and require otoferlin as Ca2+ sensor, but whether they use the same Cav1.3 isoforms is still unknown. Using whole-cell patch-clamp recordings in posthearing mice, we show that only a proportion (∼25%) of the total Ca2+ current in IHCs displaying fast inactivation and resistance to 20 μm nifedipine, a l-type Ca2+ channel blocker, is sufficient to trigger RRP but not SRP exocytosis. This Ca2+ current is likely conducted by short C-terminal isoforms of Cav1.3 channels, notably Cav1.342A and Cav1.343S, because their mRNA is highly expressed in wild-type IHCs but poorly expressed in Otof-/- IHCs, the latter having Ca2+ currents with considerably reduced inactivation. Nifedipine-resistant RRP exocytosis was poorly affected by 5 mm intracellular EGTA, suggesting that the Cav1.3 short isoforms are closely associated with the release site at the synaptic ribbons. Conversely, our results suggest that Cav1.3 long isoforms, which carry ∼75% of the total IHC Ca2+ current with slow inactivation and confer high sensitivity to nifedipine and to internal EGTA, are essentially involved in recruiting SRP vesicles. Intracellular Ca2+ imaging showed that Cav1.3 long isoforms support a deep intracellular diffusion of Ca2+SIGNIFICANCE STATEMENT Auditory inner hair cells (IHCs) encode sounds into nerve impulses through fast and indefatigable Ca2+-dependent exocytosis at their ribbon synapses. We show that this synaptic process involves long and short C-terminal isoforms of the Cav1.3 Ca2+ channel that differ in the kinetics of their Ca2+-dependent inactivation and their relative sensitivity to the l-type Ca2+ channel blocker nifedipine. The short C-terminal isoforms, having fast inactivation and low sensitivity to nifedipine, mainly control the fast fusion of the readily releasable pool (RRP); that is, they encode the phasic exocytotic component. The long isoforms, with slow inactivation and great sensitivity to nifedipine, mainly regulate the vesicular replenishment of the RRP; that is, the sustained or tonic exocytosis.
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Acid-Sensing Ion Channels Activated by Evoked Released Protons Modulate Synaptic Transmission at the Mouse Calyx of Held Synapse. J Neurosci 2017; 37:2589-2599. [PMID: 28159907 DOI: 10.1523/jneurosci.2566-16.2017] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 01/10/2017] [Accepted: 01/13/2017] [Indexed: 12/30/2022] Open
Abstract
Acid-sensing ion channels (ASICs) regulate synaptic activities and play important roles in neurodegenerative diseases. We found that these channels can be activated in neurons of the medial nucleus of the trapezoid body (MNTB) of the auditory system in the CNS. A drop in extracellular pH induces transient inward ASIC currents (IASICs) in postsynaptic MNTB neurons from wild-type mice. The inhibition of IASICs by psalmotoxin-1 (PcTx1) and the absence of these currents in knock-out mice for ASIC-1a subunit (ASIC1a-/-) suggest that homomeric ASIC-1as are mediating these currents in MNTB neurons. Furthermore, we detect ASIC1a-dependent currents during synaptic transmission, suggesting an acidification of the synaptic cleft due to the corelease of neurotransmitter and H+ from synaptic vesicles. These currents are capable of eliciting action potentials in the absence of glutamatergic currents. A significant characteristic of these homomeric ASIC-1as is their permeability to Ca2+ Activation of ASIC-1a in MNTB neurons by exogenous H+ induces an increase in intracellular Ca2+ Furthermore, the activation of postsynaptic ASIC-1as during high-frequency stimulation (HFS) of the presynaptic nerve terminal leads to a PcTx1-sensitive increase in intracellular Ca2+ in MNTB neurons, which is independent of glutamate receptors and is absent in neurons from ASIC1a-/- mice. During HFS, the lack of functional ASICs in synaptic transmission results in an enhanced short-term depression of glutamatergic EPSCs. These results strongly support the hypothesis of protons as neurotransmitters and demonstrate that presynaptic released protons modulate synaptic transmission by activating ASIC-1as at the calyx of Held-MNTB synapse.SIGNIFICANCE STATEMENT The manuscript demonstrates that postsynaptic neurons of the medial nucleus of the trapezoid body at the mouse calyx of Held synapse express functional homomeric Acid-sensing ion channel-1a (ASIC-1as) that can be activated by protons (coreleased with neurotransmitter from acidified synaptic vesicles). These ASIC-1as contribute to the generation of postsynaptic currents and, more relevant, to calcium influx, which could be involved in the modulation of presynaptic transmitter release. Inhibition or deletion of ASIC-1a leads to enhanced short-term depression, demonstrating that they are concerned with short-term plasticity of the synapse. ASICs represent a widespread communication system with unique properties. We expect that our experiments will have an impact in the neurobiology field and will spread in areas related to neuronal plasticity.
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The Coupling between Ca 2+ Channels and the Exocytotic Ca 2+ Sensor at Hair Cell Ribbon Synapses Varies Tonotopically along the Mature Cochlea. J Neurosci 2017; 37:2471-2484. [PMID: 28154149 PMCID: PMC5354352 DOI: 10.1523/jneurosci.2867-16.2017] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2016] [Revised: 01/06/2017] [Accepted: 01/10/2017] [Indexed: 11/24/2022] Open
Abstract
The cochlea processes auditory signals over a wide range of frequencies and intensities. However, the transfer characteristics at hair cell ribbon synapses are still poorly understood at different frequency locations along the cochlea. Using recordings from mature gerbils, we report here a surprisingly strong block of exocytosis by the slow Ca2+ buffer EGTA (10 mM) in basal hair cells tuned to high frequencies (∼30 kHz). In addition, using recordings from gerbil, mouse, and bullfrog auditory organs, we find that the spatial coupling between Ca2+ influx and exocytosis changes from nanodomain in low-frequency tuned hair cells (∼<2 kHz) to progressively more microdomain in high-frequency cells (∼>2 kHz). Hair cell synapses have thus developed remarkable frequency-dependent tuning of exocytosis: accurate low-latency encoding of onset and offset of sound intensity in the cochlea's base and submillisecond encoding of membrane receptor potential fluctuations in the apex for precise phase-locking to sound signals. We also found that synaptic vesicle pool recovery from depletion was sensitive to high concentrations of EGTA, suggesting that intracellular Ca2+ buffers play an important role in vesicle recruitment in both low- and high-frequency hair cells. In conclusion, our results indicate that microdomain coupling is important for exocytosis in high-frequency hair cells, suggesting a novel hypothesis for why these cells are more susceptible to sound-induced damage than low-frequency cells; high-frequency inner hair cells must have a low Ca2+ buffer capacity to sustain exocytosis, thus making them more prone to Ca2+-induced cytotoxicity. SIGNIFICANCE STATEMENT In the inner ear, sensory hair cells signal reception of sound. They do this by converting the sound-induced movement of their hair bundles present at the top of these cells, into an electrical current. This current depolarizes the hair cell and triggers the calcium-induced release of the neurotransmitter glutamate that activates the postsynaptic auditory fibers. The speed and precision of this process enables the brain to perceive the vital components of sound, such as frequency and intensity. We show that the coupling strength between calcium channels and the exocytosis calcium sensor at inner hair cell synapses changes along the mammalian cochlea such that the timing and/or intensity of sound is encoded with high precision.
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25
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Contini D, Price SD, Art JJ. Accumulation of K + in the synaptic cleft modulates activity by influencing both vestibular hair cell and calyx afferent in the turtle. J Physiol 2016; 595:777-803. [PMID: 27633787 DOI: 10.1113/jp273060] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Accepted: 09/11/2016] [Indexed: 12/16/2022] Open
Abstract
KEY POINTS In the synaptic cleft between type I hair cells and calyceal afferents, K+ ions accumulate as a function of activity, dynamically altering the driving force and permeation through ion channels facing the synaptic cleft. High-fidelity synaptic transmission is possible due to large conductances that minimize hair cell and afferent time constants in the presence of significant membrane capacitance. Elevated potassium maintains hair cells near a potential where transduction currents are sufficient to depolarize them to voltages necessary for calcium influx and synaptic vesicle fusion. Elevated potassium depolarizes the postsynaptic afferent by altering ion permeation through hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, and contributes to depolarizing the afferent to potentials where a single EPSP (quantum) can generate an action potential. With increased stimulation, hair cell depolarization increases the frequency of quanta released, elevates [K+ ]cleft and depolarizes the afferent to potentials at which smaller and smaller EPSPs would be sufficient to trigger APs. ABSTRACT Fast neurotransmitters act in conjunction with slower modulatory effectors that accumulate in restricted synaptic spaces found at giant synapses such as the calyceal endings in the auditory and vestibular systems. Here, we used dual patch-clamp recordings from turtle vestibular hair cells and their afferent neurons to show that potassium ions accumulating in the synaptic cleft modulated membrane potentials and extended the range of information transfer. High-fidelity synaptic transmission was possible due to large conductances that minimized hair cell and afferent time constants in the presence of significant membrane capacitance. Increased potassium concentration in the cleft maintained the hair cell near potentials that promoted the influx of calcium necessary for synaptic vesicle fusion. The elevated potassium concentration also depolarized the postsynaptic neuron by altering ion permeation through hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. This depolarization enabled the afferent to reliably generate action potentials evoked by single AMPA-dependent EPSPs. Depolarization of the postsynaptic afferent could also elevate potassium in the synaptic cleft, and would depolarize other hair cells enveloped by the same neuritic process increasing the fidelity of neurotransmission at those synapses as well. Collectively, these data demonstrate that neuronal activity gives rise to potassium accumulation, and suggest that potassium ion action on HCN channels can modulate neurotransmission, preserving the fidelity of high-speed synaptic transmission by dynamically shifting the resting potentials of both presynaptic and postsynaptic cells.
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Affiliation(s)
- Donatella Contini
- Department of Anatomy and Cell Biology, College of Medicine, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Steven D Price
- Department of Anatomy and Cell Biology, College of Medicine, University of Illinois at Chicago, Chicago, IL, 60612, USA
| | - Jonathan J Art
- Department of Anatomy and Cell Biology, College of Medicine, University of Illinois at Chicago, Chicago, IL, 60612, USA
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26
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Heil P, Peterson AJ. Spike timing in auditory-nerve fibers during spontaneous activity and phase locking. Synapse 2016; 71:5-36. [DOI: 10.1002/syn.21925] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 07/20/2016] [Accepted: 07/24/2016] [Indexed: 12/22/2022]
Affiliation(s)
- Peter Heil
- Department of Systems Physiology of Learning; Leibniz Institute for Neurobiology; Magdeburg 39118 Germany
- Center for Behavioral Brain Sciences; Magdeburg Germany
| | - Adam J. Peterson
- Department of Systems Physiology of Learning; Leibniz Institute for Neurobiology; Magdeburg 39118 Germany
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27
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Matsui K. Cytosolic pH as a messenger signal used in brain information processing. Nihon Yakurigaku Zasshi 2016; 148:64-8. [PMID: 27478043 DOI: 10.1254/fpj.148.64] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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28
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Warren TJ, Van Hook MJ, Supuran CT, Thoreson WB. Sources of protons and a role for bicarbonate in inhibitory feedback from horizontal cells to cones in Ambystoma tigrinum retina. J Physiol 2016; 594:6661-6677. [PMID: 27345444 DOI: 10.1113/jp272533] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 06/16/2016] [Indexed: 12/13/2022] Open
Abstract
KEY POINTS In the vertebrate retina, photoreceptors influence the signalling of neighbouring photoreceptors through lateral-inhibitory interactions mediated by horizontal cells (HCs). These interactions create antagonistic centre-surround receptive fields important for detecting edges and generating chromatically opponent responses in colour vision. The mechanisms responsible for inhibitory feedback from HCs involve changes in synaptic cleft pH that modulate photoreceptor calcium currents. However, the sources of synaptic protons involved in feedback and the mechanisms for their removal from the cleft when HCs hyperpolarize to light remain unknown. Our results indicate that Na+ -H+ exchangers are the principal source of synaptic cleft protons involved in HC feedback but that synaptic cleft alkalization during light-evoked hyperpolarization of HCs also involves changes in bicarbonate transport across the HC membrane. In addition to delineating processes that establish lateral inhibition in the retina, these results contribute to other evidence showing the key role for pH in regulating synaptic signalling throughout the nervous system. ABSTRACT Lateral-inhibitory feedback from horizontal cells (HCs) to photoreceptors involves changes in synaptic cleft pH accompanying light-evoked changes in HC membrane potential. We analysed HC to cone feedback by studying surround-evoked light responses of cones and by obtaining paired whole cell recordings from cones and HCs in salamander retina. We tested three potential sources for synaptic cleft protons: (1) generation by extracellular carbonic anhydrase (CA), (2) release from acidic synaptic vesicles and (3) Na+ /H+ exchangers (NHEs). Neither antagonizing extracellular CA nor blocking loading of protons into synaptic vesicles eliminated feedback. However, feedback was eliminated when extracellular Na+ was replaced with choline and significantly reduced by an NHE inhibitor, cariporide. Depriving NHEs of intracellular protons by buffering HC cytosol with a pH 9.2 pipette solution eliminated feedback, whereas alkalinizing the cone cytosol did not, suggesting that HCs are a major source for protons in feedback. We also examined mechanisms for changing synaptic cleft pH in response to changes in HC membrane potential. Increasing the trans-membrane proton gradient by lowering the extracellular pH from 7.8 to 7.4 to 7.1 strengthened feedback. While maintaining constant extracellular pH with 1 mm HEPES, removal of bicarbonate abolished feedback. Elevating intracellular bicarbonate levels within HCs prevented this loss of feedback. A bicarbonate transport inhibitor, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), also blocked feedback. Together, these results suggest that NHEs are the primary source of extracellular protons in HC feedback but that changes in cleft pH accompanying changes in HC membrane voltage also require bicarbonate flux across the HC membrane.
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Affiliation(s)
- Ted J Warren
- Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.,Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Matthew J Van Hook
- Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Claudiu T Supuran
- University of Florence, Neurofarba Department, Sesto Fiorentino, Italy
| | - Wallace B Thoreson
- Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.,Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
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29
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Okamoto Y, Lipstein N, Hua Y, Lin KH, Brose N, Sakaba T, Midorikawa M. Distinct modes of endocytotic presynaptic membrane and protein uptake at the calyx of Held terminal of rats and mice. eLife 2016; 5. [PMID: 27154627 PMCID: PMC4927297 DOI: 10.7554/elife.14643] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2016] [Accepted: 05/06/2016] [Indexed: 11/15/2022] Open
Abstract
Neurotransmitter is released at synapses by fusion of synaptic vesicles with the plasma membrane. To sustain synaptic transmission, compensatory retrieval of membranes and vesicular proteins is essential. We combined capacitance measurements and pH-imaging via pH-sensitive vesicular protein marker (anti-synaptotagmin2-cypHer5E), and compared the retrieval kinetics of membranes and vesicular proteins at the calyx of Held synapse. Membrane and Syt2 were retrieved with a similar time course when slow endocytosis was elicited. When fast endocytosis was elicited, Syt2 was still retrieved together with the membrane, but endocytosed organelle re-acidification was slowed down, which provides strong evidence for two distinct endocytotic pathways. Strikingly, CaM inhibitors or the inhibition of the Ca2+-calmodulin-Munc13-1 signaling pathway only impaired the uptake of Syt2 while leaving membrane retrieval intact, indicating different recycling mechanisms for membranes and vesicle proteins. Our data identify a novel mechanism of stimulus- and Ca2+-dependent regulation of coordinated endocytosis of synaptic membranes and vesicle proteins. DOI:http://dx.doi.org/10.7554/eLife.14643.001 Nerve cells release chemicals called neurotransmitters to communicate with each other. The neurotransmitters are packaged inside membrane-encased sacs called vesicles that fuse with the cell’s membrane and release their contents into the space between the nerve cells. The vesicle membrane (which also has proteins embedded in it) can then be retrieved into the cell, and recycled to make new vesicles ready to release more neurotransmitters. Recycling vesicle components requires highly coordinated mechanisms that regulate how much membrane and vesicle protein is retrieved from the cell membrane. Researchers interested in these processes have often studied them at a part of the brainstem of mammals known as the calyx of Held. However, many of the details about how vesicle proteins are recycled remained unclear. Okamoto et al. have now measured vesicle membrane and protein retrieval at the same time and in the same cell at the calyx of Held from rats and mice. The cell surface area was also measured, and the experiments focused on a fluorescently tagged version of a vesicle protein called Synaptotagmin2 that could be tracked under a microscope. Okamoto et al. found that, in weakly active nerve cells, the vesicle membrane and Synaptotagmin2 were retrieved together at a slow rate. The process was faster in more active nerve cells, and Synaptotagmin2 was still retrieved with the membrane but it appeared to be stored first in larger sacs. This suggests that membrane and vesicle proteins may be retrieved via two distinct modes depending on the activity strength. The results of further experiments went on to suggest that vesicle membranes might be recycled in a different way from vesicle proteins. Finally, Okamoto et al. also found a signaling pathway that couples the uptake of vesicle membrane with uptake of Synaptotagmin2. Future studies could now explore how these processes work in other types of nerve cell. DOI:http://dx.doi.org/10.7554/eLife.14643.002
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Affiliation(s)
- Yuji Okamoto
- Graduate School of Brain Science, Doshisha University, Kyoto, Japan
| | - Noa Lipstein
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Yunfeng Hua
- Department of Connectomics, Max Planck Institute of Brain Research, Frankfurt, Germany.,Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Kun-Han Lin
- Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Takeshi Sakaba
- Graduate School of Brain Science, Doshisha University, Kyoto, Japan
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30
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Zhang-Hooks Y, Agarwal A, Mishina M, Bergles DE. NMDA Receptors Enhance Spontaneous Activity and Promote Neuronal Survival in the Developing Cochlea. Neuron 2016; 89:337-50. [PMID: 26774161 PMCID: PMC4724245 DOI: 10.1016/j.neuron.2015.12.016] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2015] [Revised: 10/08/2015] [Accepted: 11/24/2015] [Indexed: 12/21/2022]
Abstract
Spontaneous bursts of activity in developing sensory pathways promote maturation of neurons, refinement of neuronal connections, and assembly of appropriate functional networks. In the developing auditory system, inner hair cells (IHCs) spontaneously fire Ca(2+) spikes, each of which is transformed into a mini-burst of action potentials in spiral ganglion neurons (SGNs). Here we show that NMDARs are expressed in SGN dendritic terminals and play a critical role during transmission of activity from IHCs to SGNs before hearing onset. NMDAR activation enhances glutamate-mediated Ca(2+) influx at dendritic terminals, promotes repetitive firing of individual SGNs in response to each synaptic event, and enhances coincident activity of neighboring SGNs that will eventually encode similar frequencies of sound. Loss of NMDAR signaling from SGNs reduced their survival both in vivo and in vitro, revealing that spontaneous activity in the prehearing cochlea promotes maturation of auditory circuitry through periodic activation of NMDARs in SGNs.
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Affiliation(s)
- YingXin Zhang-Hooks
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Amit Agarwal
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Masayoshi Mishina
- Brain Science Laboratory, the Research Organization of Science and Technology, Ritsumeikan University, Shiga 525-8577, Japan
| | - Dwight E Bergles
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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31
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Liu Z, Ciarleglio CM, Hamodi AS, Aizenman CD, Pratt KG. A population of gap junction-coupled neurons drives recurrent network activity in a developing visual circuit. J Neurophysiol 2016; 115:1477-86. [PMID: 26763780 DOI: 10.1152/jn.01046.2015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Accepted: 01/08/2016] [Indexed: 01/04/2023] Open
Abstract
In many regions of the vertebrate brain, microcircuits generate local recurrent activity that aids in the processing and encoding of incoming afferent inputs. Local recurrent activity can amplify, filter, and temporally and spatially parse out incoming input. Determining how these microcircuits function is of great interest because it provides glimpses into fundamental processes underlying brain computation. Within the Xenopus tadpole optic tectum, deep layer neurons display robust recurrent activity. Although the development and plasticity of this local recurrent activity has been well described, the underlying microcircuitry is not well understood. Here, using a whole brain preparation that allows for whole cell recording from neurons of the superficial tectal layers, we identified a physiologically distinct population of excitatory neurons that are gap junctionally coupled and through this coupling gate local recurrent network activity. Our findings provide a novel role for neuronal coupling among excitatory interneurons in the temporal processing of visual stimuli.
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Affiliation(s)
- Zhenyu Liu
- Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming; and
| | | | - Ali S Hamodi
- Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming; and
| | - Carlos D Aizenman
- Department of Neuroscience, Brown University, Providence, Rhode Island
| | - Kara G Pratt
- Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming; and
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