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Elshafey N, Mansour MA, Hamedo HA, Elnosary ME, Hagagy N, Ahmed Al-Ghamdi A, María Martínez-Espinosa R. Phylogeny and functional diversity of halophilic microbial communities from a thalasso environment. Saudi J Biol Sci 2023; 30:103841. [PMID: 38020223 PMCID: PMC10679952 DOI: 10.1016/j.sjbs.2023.103841] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 10/02/2023] [Accepted: 10/15/2023] [Indexed: 12/01/2023] Open
Abstract
The El-Rawda solar saltern, located in North Sinai, Egypt, is formed through the process of water evaporation from the Bradawil lagoon. This evaporation leads to the precipitation of gypsum, halite minerals, and salt flats, which subsequently cover the southern and eastern areas of the lagoon. This study employed the shotgun metagenomic approach, the illumine platform, and bioinformatic tools to investigate the taxonomic composition and functional diversity of halophilic microbial communities in solar saltern. The metagenomic reads obtained from the brine sample exhibited a greater count compared to those from the sediment sample. Notably, the brine sample was primarily characterized by an abundance of archaea, while the sediment sample displayed a dominant abundance of bacteria. Both samples exhibited a relatively low abundance of eukaryotes, while viruses were only found in the brine sample. Furthermore, the comparative analysis of functional pathways showed many important processes related to central metabolism and protein processing in brine and sediment samples. In brief, this research makes a valuable contribution to the understanding of very halophilic ecosystems in Egypt, providing insights into their microbial biodiversity and functional processes.
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Affiliation(s)
- Naglaa Elshafey
- Department of Botany and Microbiology, Faculty of Science, Arish University, Al-Arish 45511, Egypt
| | - Mohamed A.I. Mansour
- Department of Botany and Microbiology, Faculty of Science, Arish University, Al-Arish 45511, Egypt
| | - Hend A. Hamedo
- Department of Botany and Microbiology, Faculty of Science, Arish University, Al-Arish 45511, Egypt
| | - Mohamed E. Elnosary
- Department of Botany and Microbiology, Faculty of Science, Al-Azhar University,11884 Nasr City, Cairo, Egypt
| | - Nashwa Hagagy
- Botany and Microbiology Department, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt
| | - Abdullah Ahmed Al-Ghamdi
- Department of Botany and Microbiology, College of Science, King Saud University, P.O. 2455, Riyadh 11451, Saudi Arabia
| | - Rosa María Martínez-Espinosa
- Department of Biochemistry, Molecular Biology, Edaphology and Agricultural Chemistry. Faculty of Sciences, University of Alicante, Ap. 99, E-03080 Alicante, Spain
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2
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Ren J, Gosgnach S. Localization of Rhythm Generating Components of the Mammalian Locomotor Central Pattern Generator. Neuroscience 2023; 513:28-37. [PMID: 36702374 DOI: 10.1016/j.neuroscience.2023.01.013] [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: 10/14/2022] [Revised: 01/11/2023] [Accepted: 01/16/2023] [Indexed: 01/24/2023]
Abstract
Locomotor movements in mammals are generated by neural networks, situated in the spinal cord, known as central pattern generators (CPGs). Recently, significant strides have been made in the genetic identification of interneuronal components of the locomotor CPG and their specific function. Despite this progress, a population of interneurons that is required for locomotor rhythmogenesis has yet to be identified, and it has been suggested that subsets of interneurons belonging to several genetically-defined populations may be involved. In this study, rather than hunt for rhythmogenic neurons, we take a different approach and attempt to identify the specific region of the spinal cord in which they are located. Focal application of 5-hydroxytryptamine creatine sulfate complex (5-HT) and N-methyl-D-aspartate (NMDA) to the central canal of the rostral lumbar segments of newborn male and female mouse spinal cords quickly generates a robust pattern of fictive locomotion, while inhibition or ablation of neurons in this region disrupts the locomotor rhythm in both rostral and caudal lumbar segments. When applied to the central canal at caudal lumbar levels a higher volume of 5-HT and NMDA are required to elicit fictive locomotion, while inhibition of neurons surrounding the central canal at caudal levels again interrupts rhythmic activity at local segmental levels with minimal effects rostrally. The results of this study indicate that interneurons in the most medial laminae of the neonatal mouse spinal cord are both necessary and sufficient for the generation of locomotor activity, and suggests that this is the region where the rhythm generating core of the locomotor CPG resides.
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Affiliation(s)
- Jun Ren
- University of Alberta, Dept. of Physiology, 3-020M Katz Building, Edmonton, AL T6G 2E1, Canada
| | - Simon Gosgnach
- University of Alberta, Dept. of Physiology, 3-020M Katz Building, Edmonton, AL T6G 2E1, Canada.
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3
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Rutherford MA, Bhattacharyya A, Xiao M, Cai HM, Pal I, Rubio ME. GluA3 subunits are required for appropriate assembly of AMPAR GluA2 and GluA4 subunits on cochlear afferent synapses and for presynaptic ribbon modiolar-pillar morphology. eLife 2023; 12:e80950. [PMID: 36648432 PMCID: PMC9891727 DOI: 10.7554/elife.80950] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 01/16/2023] [Indexed: 01/18/2023] Open
Abstract
Cochlear sound encoding depends on α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs), but reliance on specific pore-forming subunits is unknown. With 5-week-old male C57BL/6J Gria3-knockout mice (i.e., subunit GluA3KO) we determined cochlear function, synapse ultrastructure, and AMPAR molecular anatomy at ribbon synapses between inner hair cells (IHCs) and spiral ganglion neurons. GluA3KO and wild-type (GluA3WT) mice reared in ambient sound pressure level (SPL) of 55-75 dB had similar auditory brainstem response (ABR) thresholds, wave-1 amplitudes, and latencies. Postsynaptic densities (PSDs), presynaptic ribbons, and synaptic vesicle sizes were all larger on the modiolar side of the IHCs from GluA3WT, but not GluA3KO, demonstrating GluA3 is required for modiolar-pillar synapse differentiation. Presynaptic ribbons juxtaposed with postsynaptic GluA2/4 subunits were similar in quantity, however, lone ribbons were more frequent in GluA3KO and GluA2-lacking synapses were observed only in GluA3KO. GluA2 and GluA4 immunofluorescence volumes were smaller on the pillar side than the modiolar side in GluA3KO, despite increased pillar-side PSD size. Overall, the fluorescent puncta volumes of GluA2 and GluA4 were smaller in GluA3KO than GluA3WT. However, GluA3KO contained less GluA2 and greater GluA4 immunofluorescence intensity relative to GluA3WT (threefold greater mean GluA4:GluA2 ratio). Thus, GluA3 is essential in development, as germline disruption of Gria3 caused anatomical synapse pathology before cochlear output became symptomatic by ABR. We propose the hearing loss in older male GluA3KO mice results from progressive synaptopathy evident in 5-week-old mice as decreased abundance of GluA2 subunits and an increase in GluA2-lacking, GluA4-monomeric Ca2+-permeable AMPARs.
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Affiliation(s)
- Mark A Rutherford
- Department of Otolaryngology, Washington University School of MedicineSt LouisUnited States
| | - Atri Bhattacharyya
- Department of Otolaryngology, Washington University School of MedicineSt LouisUnited States
| | - Maolei Xiao
- Department of Otolaryngology, Washington University School of MedicineSt LouisUnited States
| | - Hou-Ming Cai
- Department of Neurobiology, University of Pittsburgh School of MedicinePittsburghUnited States
| | - Indra Pal
- Department of Neurobiology, University of Pittsburgh School of MedicinePittsburghUnited States
| | - Maria Eulalia Rubio
- Department of Neurobiology, University of Pittsburgh School of MedicinePittsburghUnited States
- Department of Otolaryngology, University of Pittsburgh School of MedicinePittsburghUnited States
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4
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Hotz AL, Jamali A, Rieser NN, Niklaus S, Aydin E, Myren‐Svelstad S, Lalla L, Jurisch‐Yaksi N, Yaksi E, Neuhauss SCF. Loss of glutamate transporter eaat2a leads to aberrant neuronal excitability, recurrent epileptic seizures, and basal hypoactivity. Glia 2021; 70:196-214. [PMID: 34716961 PMCID: PMC9297858 DOI: 10.1002/glia.24106] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 10/05/2021] [Accepted: 10/06/2021] [Indexed: 11/13/2022]
Abstract
Astroglial excitatory amino acid transporter 2 (EAAT2, GLT‐1, and SLC1A2) regulates the duration and extent of neuronal excitation by removing glutamate from the synaptic cleft. Hence, an impairment in EAAT2 function could lead to an imbalanced brain network excitability. Here, we investigated the functional alterations of neuronal and astroglial networks associated with the loss of function in the astroglia predominant eaat2a gene in zebrafish. We observed that eaat2a−/− mutant zebrafish larvae display recurrent spontaneous and light‐induced seizures in neurons and astroglia, which coincide with an abrupt increase in extracellular glutamate levels. In stark contrast to this hyperexcitability, basal neuronal and astroglial activity was surprisingly reduced in eaat2a−/− mutant animals, which manifested in decreased overall locomotion. Our results reveal an essential and mechanistic contribution of EAAT2a in balancing brain excitability, and its direct link to epileptic seizures.
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Affiliation(s)
- Adriana L. Hotz
- Department of Molecular Life SciencesUniversity of ZurichZurichSwitzerland
- Life Science Zürich Graduate School ‐ NeuroscienceUniversity of Zurich and ETH ZurichZurichSwitzerland
| | - Ahmed Jamali
- Kavli Institute for Systems Neuroscience and Centre for Neural ComputationFaculty of Medicine and Health Sciences, Norwegian University of Science and TechnologyTrondheimNorway
| | - Nicolas N. Rieser
- Department of Molecular Life SciencesUniversity of ZurichZurichSwitzerland
- Life Science Zürich Graduate School ‐ NeuroscienceUniversity of Zurich and ETH ZurichZurichSwitzerland
| | - Stephanie Niklaus
- Department of Molecular Life SciencesUniversity of ZurichZurichSwitzerland
- Present address:
EraCal TherapeuticsSchlierenSwitzerland
| | - Ecem Aydin
- Kavli Institute for Systems Neuroscience and Centre for Neural ComputationFaculty of Medicine and Health Sciences, Norwegian University of Science and TechnologyTrondheimNorway
| | - Sverre Myren‐Svelstad
- Kavli Institute for Systems Neuroscience and Centre for Neural ComputationFaculty of Medicine and Health Sciences, Norwegian University of Science and TechnologyTrondheimNorway
- Department of Neurology and Clinical NeurophysiologySt. Olav's University HospitalTrondheimNorway
- Department of Neuromedicine and Movement Science, Faculty of Medicine and Health SciencesNorwegian University of Science and TechnologyTrondheimNorway
| | - Laetitia Lalla
- Kavli Institute for Systems Neuroscience and Centre for Neural ComputationFaculty of Medicine and Health Sciences, Norwegian University of Science and TechnologyTrondheimNorway
| | - Nathalie Jurisch‐Yaksi
- Kavli Institute for Systems Neuroscience and Centre for Neural ComputationFaculty of Medicine and Health Sciences, Norwegian University of Science and TechnologyTrondheimNorway
- Department of Neurology and Clinical NeurophysiologySt. Olav's University HospitalTrondheimNorway
- Department of Clinical and Molecular Medicine, Faculty of Medicine and Health SciencesNorwegian University of Science and TechnologyTrondheimNorway
| | - Emre Yaksi
- Kavli Institute for Systems Neuroscience and Centre for Neural ComputationFaculty of Medicine and Health Sciences, Norwegian University of Science and TechnologyTrondheimNorway
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5
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Montgomery JE, Wahlstrom‐Helgren S, Vanpelt KT, Masino MA. Repetitive optogenetic stimulation of glutamatergic neurons: An alternative to NMDA treatment for generating locomotor activity in spinalized zebrafish larvae. Physiol Rep 2021; 9:e14774. [PMID: 33769694 PMCID: PMC7995545 DOI: 10.14814/phy2.14774] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 01/29/2021] [Accepted: 02/01/2021] [Indexed: 11/29/2022] Open
Abstract
N-methyl-d-aspartate (NMDA) application has conventionally been used to activate spinal networks to induce locomotion in spinalized animals. We recently described an alternative approach in which application of continuous blue light activates channelrhodopsin-2 in vesicular glutamate transporter 2a (vglut2a)-expressing spinal neurons to produce organized, rhythmic locomotor activity in spinally-transected larval zebrafish. This technique arguably enhances research validity, because endogenous glutamate is released into existing synapses instead of activating only a subset of glutamatergic (NMDA) receptors with an exogenous compound. Here, we explored the viability of this approach in the context of using it for longer-term experiments. Fictive swimming was induced through repetitive application of 10-s blue light stimuli to spinalized preparations for up to 60 min at intervals of 1, 3, or 15 min. Locomotor activity was maintained throughout the experimental timecourse, demonstrating the robustness of the system. Although locomotor bursts remained organized into episodes of activity, the number of bursts elicited during each successive stimulus decreased. This was in contrast to NMDA bath application, in which bursts became less episodically organized while the overall number of bursts remained unchanged. The efficacy of the repetitive optogenetic stimulation paradigm was demonstrated through application of exogenous dopamine, which reversibly decreased the number of bursts produced per stimulus compared with untreated preparations. Finally, increasing the stimulus interval to 15 min lessened, but did not eliminate locomotor fatigue from repetitive activation. Altogether, we established repetitive optogenetic stimulation of vglut2a-expressing neurons as a viable alternative to NMDA application for activation of the zebrafish spinal locomotor network.
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Affiliation(s)
| | | | - Kayce T. Vanpelt
- Department of NeuroscienceUniversity of MinnesotaMinneapolisMNUSA
| | - Mark A. Masino
- Department of NeuroscienceUniversity of MinnesotaMinneapolisMNUSA
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6
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Li S, Raychaudhuri S, Lee SA, Brockmann MM, Wang J, Kusick G, Prater C, Syed S, Falahati H, Ramos R, Bartol TM, Hosy E, Watanabe S. Asynchronous release sites align with NMDA receptors in mouse hippocampal synapses. Nat Commun 2021; 12:677. [PMID: 33514725 PMCID: PMC7846561 DOI: 10.1038/s41467-021-21004-x] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 01/08/2021] [Indexed: 01/30/2023] Open
Abstract
Neurotransmitter is released synchronously and asynchronously following an action potential. Our recent study indicates that the release sites of these two phases are segregated within an active zone, with asynchronous release sites enriched near the center in mouse hippocampal synapses. Here we demonstrate that synchronous and asynchronous release sites are aligned with AMPA receptor and NMDA receptor clusters, respectively. Computational simulations indicate that this spatial and temporal arrangement of release can lead to maximal membrane depolarization through AMPA receptors, alleviating the pore-blocking magnesium leading to greater activation of NMDA receptors. Together, these results suggest that release sites are likely organized to activate NMDA receptors efficiently.
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Affiliation(s)
- Shuo Li
- Department of Cell Biology, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
- Department of Biological and Molecular Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
| | - Sumana Raychaudhuri
- Department of Cell Biology, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - Stephen Alexander Lee
- Neurobiology Course, The Marine Biological Laboratory, Woods Hole, MA, USA
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - Marisa M Brockmann
- Institute of Neurophysiology, Charité Universitätsmedizin, Berlin, Germany
| | - Jing Wang
- ThermoFisher Scientific, Hillsboro, OR, USA
| | - Grant Kusick
- Department of Cell Biology, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
- Biochemistry, Cellular and Molecular Biology Graduate Program, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - Christine Prater
- Neurobiology Course, The Marine Biological Laboratory, Woods Hole, MA, USA
- Department of Pharmacology and Neuroscience, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, USA
| | - Sarah Syed
- Department of Cell Biology, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - Hanieh Falahati
- Neurobiology Course, The Marine Biological Laboratory, Woods Hole, MA, USA
- Department of Neuroscience, Yale University School of Medicine, New Haven, CT, USA
| | - Raul Ramos
- Neurobiology Course, The Marine Biological Laboratory, Woods Hole, MA, USA
- Department of Biology, Brandeis University, Waltham, MA, USA
| | - Tomas M Bartol
- Salk Institute for Biological Studies, La Jolla, CA, USA
| | - Eric Hosy
- Centre National de la Recherche Scientifique, Bordeaux, France
- Interdisciplinary Institute for Neuroscience, University of Bordeaux, Bordeaux, France
| | - Shigeki Watanabe
- Department of Cell Biology, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
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7
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Phillips MB, Nigam A, Johnson JW. Interplay between Gating and Block of Ligand-Gated Ion Channels. Brain Sci 2020; 10:brainsci10120928. [PMID: 33271923 PMCID: PMC7760600 DOI: 10.3390/brainsci10120928] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 11/21/2020] [Accepted: 11/26/2020] [Indexed: 02/03/2023] Open
Abstract
Drugs that inhibit ion channel function by binding in the channel and preventing current flow, known as channel blockers, can be used as powerful tools for analysis of channel properties. Channel blockers are used to probe both the sophisticated structure and basic biophysical properties of ion channels. Gating, the mechanism that controls the opening and closing of ion channels, can be profoundly influenced by channel blocking drugs. Channel block and gating are reciprocally connected; gating controls access of channel blockers to their binding sites, and channel-blocking drugs can have profound and diverse effects on the rates of gating transitions and on the stability of channel open and closed states. This review synthesizes knowledge of the inherent intertwining of block and gating of excitatory ligand-gated ion channels, with a focus on the utility of channel blockers as analytic probes of ionotropic glutamate receptor channel function.
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Affiliation(s)
- Matthew B. Phillips
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Aparna Nigam
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
| | - Jon W. Johnson
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
- Correspondence: ; Tel.: +1-(412)-624-4295
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Devi SPS, Cheng Y, Tomita S, Howe JR, Zhang W. TARPs Modulate Receptor-Mediated Paired-Pulse Depression and Recovery from Desensitization. J Neurosci 2020; 40:8233-8247. [PMID: 32994336 PMCID: PMC7577600 DOI: 10.1523/jneurosci.3026-19.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2019] [Revised: 08/07/2020] [Accepted: 09/14/2020] [Indexed: 11/21/2022] Open
Abstract
Transmembrane AMPA receptor regulatory proteins (TARPs) are auxiliary AMPA receptor subunits that play a key role in receptor trafficking and in modulating receptor gating. The ability of TARPs to slow both deactivation and desensitization is isoform specific. However, TARP isoform-specific modulation of receptor properties remains uncharacterized. Here, we compare the isoform-specific effects of γ-2, γ-3, γ-4, and γ-8 TARPs on recovery from desensitization and responses to pairs of brief applications of glutamate. All four isoforms were able to reduce receptor-mediated paired-pulse depression and significantly speed recovery from desensitization in an isoform-specific manner. In the presence of TARPs, recovery time courses were observed to contain two components, fast and slow. The proportion of fast and slow components was determined by the TARP isoform. The time constant of recovery was also altered by the duration of glutamate application. When studies with TARP chimeras were performed, TARP extracellular loops were found to play a vital role in TARP modulation of recovery. Thus, isoform-specific differences in TARP modulation of recovery from desensitization influence receptor responses to repeated brief applications of glutamate, and these differences may impact frequency-dependent synaptic signaling in the mammalian central nervous system.SIGNIFICANCE STATEMENT AMPA receptors are major determinants of excitatory synaptic strength. The channel kinetics of AMPA receptors contribute to the kinetics of synaptic transmission. Transmembrane AMPA receptor regulatory proteins (TARPs) auxiliary subunits can modulate the decay kinetics of AMPA receptors. However, whether TARP isoforms specifically modulate receptor recovery is unclear. Here, we investigated the recovery kinetics of AMPA receptors by expressing various TARP isoforms and chimeras. We observed that the TARP isoforms and duration of glutamate application uniquely modulate time constants and the proportion of fast and slow components through a previously unidentified TARP domain. Given the impact of recovery kinetics on receptor responses to repetitive stimulation such as synaptic transmission, this work will be of great interest in the field of excitatory synaptic transmission research.
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Affiliation(s)
- Suma Priya Sudarsana Devi
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520
- Department of Surgery, University of Alabama at Birmingham, Birmingham, Alabama 35233
| | - Yiru Cheng
- Department of Pharmacology of Chinese Materia Medica, Institution of Chinese Integrative Medicine, Hebei Medical University, Shijiazhuang, Hebei Province 050017, China
| | - Susumu Tomita
- Department of Cellular and Molecular Physiology, Department of Neuroscience, and Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, Connecticut 06520
| | - James R Howe
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Wei Zhang
- Department of Pharmacology of Chinese Materia Medica, Institution of Chinese Integrative Medicine, Hebei Medical University, Shijiazhuang, Hebei Province 050017, China
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9
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Miraucourt LS, Accardi MV, Asin KE, Pugsley MK, Curtis MJ, Authier S. The application of electrophysiological methods to characterize AMPA receptors in dissociated adult rat and non-human primate cerebellar neurons for use in neuronal safety pharmacology assessments of the central nervous system. J Pharmacol Toxicol Methods 2020; 105:106883. [DOI: 10.1016/j.vascn.2020.106883] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Revised: 10/15/2019] [Accepted: 05/21/2020] [Indexed: 11/25/2022]
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10
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Ye Z, Liu F, Sun H, Barker M, Pitts RJ, Zwiebel LJ. Heterogeneous expression of the ammonium transporter AgAmt in chemosensory appendages of the malaria vector, Anopheles gambiae. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2020; 120:103360. [PMID: 32126276 PMCID: PMC7161093 DOI: 10.1016/j.ibmb.2020.103360] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Revised: 02/26/2020] [Accepted: 02/27/2020] [Indexed: 05/03/2023]
Abstract
Ammonia is one of the principal kairomones originating from human and other animal emanations and in that context, plays an essential role in the host-seeking behaviors of the malaria vector mosquito Anopheles gambiae. Nevertheless, despite its importance in directing host-seeking, the mechanisms underlying ammonia detection in the mosquito olfactory system remains largely unknown. In addition to ongoing efforts to identify and characterize the molecular receptors that underlie ammonia sensitivity, previous studies have revealed a prominent role for ammonium transporters (Amt) in modulating antennal and behavioral responses in Drosophila melanogaster and An. gambiae. In the former, localization of DmAmt in antennal sensilla to auxiliary cells surrounding the ammonia sensory neurons led to the hypothesis that its role was to clear excess ammonium ions in the sensillar lymph. In the latter, RT-PCR and heterologous expression have been used to examine the expression and functional characteristics of the An. gambiae ammonium transporter, AgAmt. We now employ advanced transgenic tools to comprehensively examine AgAmt spatial localization across the peripheral chemosensory appendages in larvae and adult female An. gambiae. In the larval antennae, AgAmt appears localized in both neuronal and auxiliary cells. In contrast to D. melanogaster, in the adult antennae, AgAmt-derived signals are observed in both non-neuronal auxiliary cells and in sensory neurons in ammonia-responsive basiconic and coeloconic sensilla. In the maxillary palps, labella, and tarsi, AgAmt appears restricted to sensory neurons. We have also characterized the responses to ammonia of adult antennal coeloconic sensilla and maxillary palp capitate pegs revealing a correlation between sensillar AgAmt expression and ammonia sensitivity. Taken together, these data suggest that AgAmt may play heterogeneous roles in the adult and larval chemosensory apparatus and potentially broad utility as a supra-receptor target in mosquito control.
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Affiliation(s)
- Zi Ye
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | - Feng Liu
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | - Huahua Sun
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | | | - R Jason Pitts
- Department of Biology, Baylor University, Waco, TX, 76706, USA
| | - Laurence J Zwiebel
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA.
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11
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Armada-Moreira A, Gomes JI, Pina CC, Savchak OK, Gonçalves-Ribeiro J, Rei N, Pinto S, Morais TP, Martins RS, Ribeiro FF, Sebastião AM, Crunelli V, Vaz SH. Going the Extra (Synaptic) Mile: Excitotoxicity as the Road Toward Neurodegenerative Diseases. Front Cell Neurosci 2020; 14:90. [PMID: 32390802 PMCID: PMC7194075 DOI: 10.3389/fncel.2020.00090] [Citation(s) in RCA: 145] [Impact Index Per Article: 36.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 03/26/2020] [Indexed: 12/13/2022] Open
Abstract
Excitotoxicity is a phenomenon that describes the toxic actions of excitatory neurotransmitters, primarily glutamate, where the exacerbated or prolonged activation of glutamate receptors starts a cascade of neurotoxicity that ultimately leads to the loss of neuronal function and cell death. In this process, the shift between normal physiological function and excitotoxicity is largely controlled by astrocytes since they can control the levels of glutamate on the synaptic cleft. This control is achieved through glutamate clearance from the synaptic cleft and its underlying recycling through the glutamate-glutamine cycle. The molecular mechanism that triggers excitotoxicity involves alterations in glutamate and calcium metabolism, dysfunction of glutamate transporters, and malfunction of glutamate receptors, particularly N-methyl-D-aspartic acid receptors (NMDAR). On the other hand, excitotoxicity can be regarded as a consequence of other cellular phenomena, such as mitochondrial dysfunction, physical neuronal damage, and oxidative stress. Regardless, it is known that the excessive activation of NMDAR results in the sustained influx of calcium into neurons and leads to several deleterious consequences, including mitochondrial dysfunction, reactive oxygen species (ROS) overproduction, impairment of calcium buffering, the release of pro-apoptotic factors, among others, that inevitably contribute to neuronal loss. A large body of evidence implicates NMDAR-mediated excitotoxicity as a central mechanism in the pathogenesis of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and epilepsy. In this review article, we explore different causes and consequences of excitotoxicity, discuss the involvement of NMDAR-mediated excitotoxicity and its downstream effects on several neurodegenerative disorders, and identify possible strategies to study new aspects of these diseases that may lead to the discovery of new therapeutic approaches. With the understanding that excitotoxicity is a common denominator in neurodegenerative diseases and other disorders, a new perspective on therapy can be considered, where the targets are not specific symptoms, but the underlying cellular phenomena of the disease.
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Affiliation(s)
- Adam Armada-Moreira
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus, Denmark
| | - Joana I. Gomes
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Carolina Campos Pina
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Oksana K. Savchak
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Joana Gonçalves-Ribeiro
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Nádia Rei
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Sara Pinto
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Tatiana P. Morais
- Neuroscience Division, School of Bioscience, Cardiff University, Cardiff, United Kingdom
| | - Robertta Silva Martins
- Laboratório de Neurofarmacologia, Instituto Biomédico, Universidade Federal Fluminense, Niterói, Brazil
| | - Filipa F. Ribeiro
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Ana M. Sebastião
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Vincenzo Crunelli
- Neuroscience Division, School of Bioscience, Cardiff University, Cardiff, United Kingdom
- Department of Physiology and Biochemistry, Faculty of Medicine and Surgery, University of Malta, Msida, Malta
| | - Sandra H. Vaz
- Instituto de Farmacologia e Neurociências, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
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Role of GluA3 AMPA Receptor Subunits in the Presynaptic and Postsynaptic Maturation of Synaptic Transmission and Plasticity of Endbulb-Bushy Cell Synapses in the Cochlear Nucleus. J Neurosci 2020; 40:2471-2484. [PMID: 32051325 DOI: 10.1523/jneurosci.2573-19.2020] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 01/22/2020] [Accepted: 02/02/2020] [Indexed: 11/21/2022] Open
Abstract
The AMPA receptor (AMPAR) subunit GluA3 has been suggested to shape synaptic transmission and activity-dependent plasticity in endbulb-bushy cell synapses (endbulb synapses) in the anteroventral cochlear nucleus, yet the specific roles of GluA3 in the synaptic transmission at endbulb synapses remains unexplored. Here, we compared WT and GluA3 KO mice of both sexes and identified several important roles of GluA3 in the maturation of synaptic transmission and short-term plasticity in endbulb synapses. We show that GluA3 largely determines the ultrafast kinetics of endbulb synapses glutamatergic currents by promoting the insertion of postsynaptic AMPARs that contain fast desensitizing flop subunits. In addition, GluA3 is also required for the normal function, structure, and development of the presynaptic terminal which leads to altered short term-depression in GluA3 KO mice. The presence of GluA3 reduces and slows synaptic depression, which is achieved by lowering the probability of vesicle release, promoting efficient vesicle replenishment, and increasing the readily releasable pool of synaptic vesicles. Surprisingly, GluA3 also makes the speed of synaptic depression rate-invariant. We propose that the slower and rate-invariant speed of depression allows an initial response window that still contains presynaptic firing rate information before the synapse is depressed. Because this response window is rate-invariant, GluA3 extends the range of presynaptic firing rates over which rate information in bushy cells can be preserved. This novel role of GluA3 may be important to allowing the postsynaptic targets of spherical bushy cells in mice use rate information for encoding sound intensity and sound localization.SIGNIFICANCE STATEMENT We report novel roles of the glutamate receptor subunit GluA3 in synaptic transmission in synapses between auditory nerve fibers and spherical bushy cells (BCs) in the cochlear nucleus. We show that GluA3 contributes to the generation of ultrafast glutamatergic currents at these synapses, which is important to preserve temporal information about the sound. Furthermore, we demonstrate that GluA3 contributes to the normal function and development of the presynaptic terminal, whose properties shape short-term plasticity. GluA3 slows and attenuates synaptic depression, and makes it less dependent on the presynaptic firing rates. This may help BCs to transfer information about the high rates of activity that occur at the synapse in vivo to postsynaptic targets that use rate information for sound localization.
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13
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Wahlstrom-Helgren S, Montgomery JE, Vanpelt KT, Biltz SL, Peck JH, Masino MA. Glutamate receptor subtypes differentially contribute to optogenetically activated swimming in spinally transected zebrafish larvae. J Neurophysiol 2019; 122:2414-2426. [PMID: 31642404 DOI: 10.1152/jn.00337.2019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The spinal cord (SC) contains neural networks that are capable of producing organized locomotor activity autonomously from the brain. Locomotor activity can be induced in spinally transected (spinalized) animals by adding a source of tonic excitation to activate spinal networks. This is commonly accomplished by activating N-methyl-d-aspartate (NMDA) glutamate receptors through bath application of NMDA. More recently, optogenetic approaches have enabled both activation and inactivation of neuronal cell populations to control the activity of locomotor networks. Larval zebrafish are exceptionally amenable to optogenetic techniques due to their transparency, which permits noninvasive light delivery. In this study, we induced locomotor activity in spinalized transgenic zebrafish larvae that expressed channelrhodopsin-2 in all subtypes of spinal vesicular glutamate transporter 2a (vglut2a)-expressing neurons by applying 10 s of constant blue light to the preparations. The resultant locomotor activity possessed all of the characteristics of swimming: bilateral alternation, rostrocaudal progression, and organization into discrete swimming episodes. Spatially restricted light application revealed that illumination of the rostral SC produced more robust activity than illumination of the caudal SC. Moreover, illumination of only three body segments was sufficient to produce fictive swimming. Intriguingly, organized swimming activity persisted during NMDA receptor antagonism but was disrupted by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonism. Hence, AMPA receptor signaling is required for episodically-organized swimming, whereas NMDA receptor signaling is not necessary.NEW & NOTEWORTHY Spinal locomotor networks have the intrinsic capacity to transform unpatterned excitatory input into patterned output. Conventionally, spinally mediated fictive locomotor activity is experimentally elicited by N-methyl-d-aspartate (NMDA) application to bias the network toward activation. We present a novel experimental paradigm that permits spatially and temporally controllable activation of spinal vesicular glutamate transporter 2a-expressing neurons in larval zebrafish, eliciting patterned locomotor activity that is not dependent on NMDA receptor signaling.
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Affiliation(s)
| | - Jacob E Montgomery
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota
| | - Kayce T Vanpelt
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota
| | - Samantha L Biltz
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota
| | - Jack H Peck
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota
| | - Mark A Masino
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota
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14
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Mechanisms of zinc modulation of olfactory bulb AMPA receptors. Neuroscience 2019; 410:160-175. [PMID: 31082537 DOI: 10.1016/j.neuroscience.2019.05.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Revised: 05/01/2019] [Accepted: 05/03/2019] [Indexed: 12/31/2022]
Abstract
The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of ionotropic glutamate receptors mediates most fast excitatory transmission. Glutamate binding to AMPA receptors (AMPARs) causes most AMPARs to rapidly and completely desensitize, and their desensitization kinetics influence synaptic timing. Thus, factors that alter AMPAR desensitization influence synaptic transmission. Synaptically released zinc is such a factor. Zinc is a neuromodulator with effects on amino acid receptors and synaptic transmission in many brain regions, including the olfactory bulb (OB). We have previously shown in the OB that zinc potentiates AMPAR-mediated currents at low concentrations (30 μM, 100 μM) and inhibits them at a higher concentration (1 mM). It has been hypothesized that zinc potentiates AMPARs by decreasing receptor desensitization. Here, we used cyclothiazide (CTZ), a drug that blocks AMPAR desensitization, to determine whether zinc-mediated potentiation and/or inhibition of AMPA-evoked currents reflect(s) changes in AMPAR desensitization. Zinc largely had biphasic concentration-dependent effects at OB AMPARs. CTZ completely blocked potentiation by zinc but had no significant effect on inhibition. There was a significant negative correlation between the degree of potentiation of AMPAR-mediated currents by 100 μM zinc and a quantitative measure of the degree of AMPAR desensitization (the steady-state to peak [S:P] ratio of AMPA-evoked currents), but no correlation between the degree of current inhibition by 1 mM zinc and the S:P ratio. Together, these findings suggest that low zinc concentrations potentiate rat OB AMPARs by decreasing receptor desensitization, but that the inhibitory effects of higher zinc concentrations are mediated by a separate mechanism.
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15
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Pálfi D, Chiovini B, Szalay G, Kaszás A, Turi GF, Katona G, Ábrányi-Balogh P, Szőri M, Potor A, Frigyesi O, Lukácsné Haveland C, Szadai Z, Madarász M, Vasanits-Zsigrai A, Molnár-Perl I, Viskolcz B, Csizmadia IG, Mucsi Z, Rózsa B. High efficiency two-photon uncaging coupled by the correction of spontaneous hydrolysis. Org Biomol Chem 2019; 16:1958-1970. [PMID: 29497727 DOI: 10.1039/c8ob00025e] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two-photon (TP) uncaging of neurotransmitter molecules is the method of choice to mimic and study the subtleties of neuronal communication either in the intact brain or in slice preparations. However, the currently available caged materials are just at the limit of their usability and have several drawbacks. The local and focal nature of their use may for example be jeopardized by a high spontaneous hydrolysis rate of the commercially available compounds with increased photochemical release rate. Here, using quantum chemical modelling we show the mechanisms of hydrolysis and two-photon activation, and synthesized more effective caged compounds. Furthermore, we have developed a new enzymatic elimination method removing neurotransmitters inadvertently escaping from their compound during experiment. This method, usable both in one and two-photon experiments, allows for the use of materials with an increased rate of photochemical release. The efficiency of the new compound and the enzymatic method and of the new compound are demonstrated in neurophysiological experiments.
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Affiliation(s)
- Dénes Pálfi
- Two-Photon Measurement Technology Research Group, The Faculty of Information Technology, Pázmány Péter Catholic University, Práter str 50, H-1083 Budapest, Hungary
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16
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Williams SB, Yorgason JT, Nelson AC, Lewis N, Nufer TM, Edwards JG, Steffensen SC. Glutamate Transmission to Ventral Tegmental Area GABA Neurons Is Altered by Acute and Chronic Ethanol. Alcohol Clin Exp Res 2018; 42:2186-2195. [PMID: 30204234 DOI: 10.1111/acer.13883] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Accepted: 08/27/2018] [Indexed: 12/19/2022]
Abstract
BACKGROUND Ventral tegmental area (VTA) GABA neurons have been heavily implicated in alcohol reinforcement and reward. In animals that self-administer alcohol, VTA GABA neurons exhibit increased excitability that may contribute to alcohol's rewarding effects. The present study investigated the effects of acute and chronic ethanol exposure on glutamate (GLU) synaptic transmission to VTA GABA neurons. METHODS Whole-cell recordings of evoked, spontaneous, and miniature excitatory postsynaptic currents (eEPSCs, sEPSCs, and mEPSCs, respectively) were performed on identified GABA neurons in the VTA of GAD67-GFP+ transgenic mice. Three ethanol exposure paradigms were used: acute ethanol superfusion; a single ethanol injection; and chronic vapor exposure. RESULTS Acute ethanol superfusion increased the frequency of EPSCs but inhibited mEPSC frequency and amplitude. During withdrawal from a single injection of ethanol, the frequency of sEPSCs was lower than saline controls. There was no difference in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/N-methyl-d-aspartate (NMDA) ratio between neurons following withdrawal from a single exposure to ethanol. However, following withdrawal from chronic ethanol, sEPSCs and mEPSCs had a greater frequency than air controls. There was no difference in AMPA/NMDA ratio following chronic ethanol. CONCLUSIONS These results suggest that presynaptic mechanisms involving local circuit GLU neurons, and not GLU receptors, contribute to adaptations in VTA GABA neuron excitability that accrue to ethanol exposure, which may contribute to the rewarding properties of alcohol via their regulation of mesolimbic dopamine transmission.
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Affiliation(s)
- Stephanie B Williams
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah
| | - Jordan T Yorgason
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah
| | - Ashley C Nelson
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah
| | - Natalie Lewis
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah
| | - Teresa M Nufer
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah
| | - Jeff G Edwards
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah
| | - Scott C Steffensen
- Department of Psychology and Center for Neuroscience, Brigham Young University, Provo, Utah
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17
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Gavrilov N, Golyagina I, Brazhe A, Scimemi A, Turlapov V, Semyanov A. Astrocytic Coverage of Dendritic Spines, Dendritic Shafts, and Axonal Boutons in Hippocampal Neuropil. Front Cell Neurosci 2018; 12:248. [PMID: 30174590 PMCID: PMC6108058 DOI: 10.3389/fncel.2018.00248] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Accepted: 07/19/2018] [Indexed: 01/22/2023] Open
Abstract
Distal astrocytic processes have a complex morphology, reminiscent of branchlets and leaflets. Astrocytic branchlets are rod-like processes containing mitochondria and endoplasmic reticulum, capable of generating inositol-3-phosphate (IP3)-dependent Ca2+ signals. Leaflets are small and flat processes that protrude from branchlets and fill the space between synapses. Here we use three-dimensional (3D) reconstructions from serial section electron microscopy (EM) of rat CA1 hippocampal neuropil to determine the astrocytic coverage of dendritic spines, shafts and axonal boutons. The distance to the maximum of the astrocyte volume fraction (VF) correlated with the size of the spine when calculated from the center of mass of the postsynaptic density (PSD) or from the edge of the PSD, but not from the spine surface. This suggests that the astrocytic coverage of small and larger spines is similar in hippocampal neuropil. Diffusion simulations showed that such synaptic microenvironment favors glutamate spillover and extrasynaptic receptor activation at smaller spines. We used complexity and entropy measures to characterize astrocytic branchlets and leaflets. The 2D projections of astrocytic branchlets had smaller spatial complexity and entropy than leaflets, consistent with the higher structural complexity and less organized distribution of leaflets. The VF of astrocytic leaflets was highest around dendritic spines, lower around axonal boutons and lowest around dendritic shafts. In contrast, the VF of astrocytic branchlets was similarly low around these three neuronal compartments. Taken together, these results suggest that astrocytic leaflets preferentially contact synapses as opposed to the dendritic shaft, an arrangement that might favor neurotransmitter spillover and extrasynaptic receptor activation along dendritic shafts.
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Affiliation(s)
- Nikolay Gavrilov
- UNN Institute of Neuroscience, N. I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia
| | - Inna Golyagina
- UNN Institute of Neuroscience, N. I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia
| | - Alexey Brazhe
- Department of Biophysics, Faculty of Biology, M. V. Lomonosov Moscow State University, Moscow, Russia
| | - Annalisa Scimemi
- Department of Biology, University at Albany, The State University of New York (SUNY), Albany, NY, United States
| | - Vadim Turlapov
- Institute of Information Technologies, Mathematics and Mechanics, N. I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia
| | - Alexey Semyanov
- UNN Institute of Neuroscience, N. I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia.,Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.,All-Russian Research Institute of Medicinal and Aromatic Plants, Moscow, Russia
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18
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The Transmembrane Domain of Synaptobrevin Influences Neurotransmitter Flux through Synaptic Fusion Pores. J Neurosci 2018; 38:7179-7191. [PMID: 30012692 DOI: 10.1523/jneurosci.0721-18.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 06/22/2018] [Accepted: 06/30/2018] [Indexed: 01/08/2023] Open
Abstract
The soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins synaptobrevin (Syb), syntaxin, and SNAP-25 function in Ca2+-triggered exocytosis in both endocrine cells and neurons. The transmembrane domains (TMDs) of Syb and syntaxin span the vesicle and plasma membrane, respectively, and influence flux through fusion pores in endocrine cells as well as fusion pores formed during SNARE-mediated fusion of reconstituted membranes. These results support a model for exocytosis in which SNARE TMDs form the initial fusion pore. The present study sought to test this model in synaptic terminals. Patch-clamp recordings of miniature EPSCs (mEPSCs) were used to probe fusion pore properties in cultured hippocampal neurons from mice of both sexes. Mutants harboring tryptophan at four different sites in the Syb TMD reduced the rate-of-rise of mEPSCs. A computer model that simulates glutamate diffusion and receptor activation kinetics could account for this reduction in mEPSC rise rate by slowing the flux of glutamate through synaptic fusion pores. TMD mutations introducing positive charge also reduced the mEPSC rise rate, but negatively charged residues and glycine, which should have done the opposite, had no effect. The sensitivity of mEPSCs to pharmacological blockade of receptor desensitization was enhanced by a mutation that slowed the mEPSC rate-of-rise, suggesting that the mutation prolonged the residence of glutamate in the synaptic cleft. The same four Syb TMD residues found here to influence synaptic release were found previously to influence endocrine release, leading us to propose that a similar TMD-lined fusion pore functions widely in Ca2+-triggered exocytosis in mammalian cells.SIGNIFICANCE STATEMENT SNARE proteins function broadly in biological membrane fusion. Evidence from non-neuronal systems suggests that SNARE proteins initiate fusion by forming a fusion pore lined by transmembrane domains, but this model has not yet been tested in synapses. The present study addressed this question by testing mutations in the synaptic vesicle SNARE synaptobrevin for an influence on the rise rate of miniature synaptic currents. These results indicate that synaptobrevin's transmembrane domain interacts with glutamate as it passes through the fusion pore. The sites in synaptobrevin that influence this flux are identical to those shown previously to influence flux through endocrine fusion pores. Thus, SNARE transmembrane domains may function in the fusion pores of Ca2+-triggered exocytosis of both neurotransmitters and hormones.
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19
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Extracellular Glutamate in the Nucleus Accumbens Is Nanomolar in Both Synaptic and Non-synaptic Compartments. Cell Rep 2017; 18:2576-2583. [PMID: 28297662 DOI: 10.1016/j.celrep.2017.02.047] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Revised: 01/26/2017] [Accepted: 02/15/2017] [Indexed: 12/25/2022] Open
Abstract
In the CNS, glutamate is both phasically and tonically released into the extracellular space and must be removed by excitatory amino acid transporters (EAATs) to prevent excitotoxic accumulation. There remains uncertainty, however, regarding the functional steady-state concentration, with estimates ranging from tens of nanomolar to tens of micromolar. Efforts to reconcile these disparate values have led to a hypothesis that the extracellular space comprises distinct compartments in which basal glutamate concentrations are maintained independently. We used electrophysiology and two-photon Ca2+ imaging to test this hypothesis in the nucleus accumbens (NAc), where it has been proposed that micromolar extracellular glutamate is necessary for normal function. We found that the average concentration of synaptic glutamate is nanomolar, in agreement with previous electrophysiological estimates. Furthermore, this held true when glutamate uptake was inhibited, indicating that extracellular glutamate is not compartmentalized by EAATs.
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20
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Wen W, Lin CY, Niu L. R/G editing in GluA2R flop modulates the functional difference between GluA1 flip and flop variants in GluA1/2R heteromeric channels. Sci Rep 2017; 7:13654. [PMID: 29057893 PMCID: PMC5651858 DOI: 10.1038/s41598-017-13233-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 09/20/2017] [Indexed: 12/12/2022] Open
Abstract
In α-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) receptors, RNA editing and alternative splicing generate sequence variants, and those variants, as in GluA2-4 AMPA receptor subunits, generally show different properties. Yet, earlier studies have shown that the alternatively spliced, flip and flop variants of GluA1 AMPA receptor subunit exhibit no functional difference in homomeric channel form. Using a laser-pulse photolysis technique, combined with whole-cell recording, we measured the rate of channel opening, among other kinetic properties, for a series of AMPA channels with different arginine/glycine (R/G) editing and flip/flop status. We find that R/G editing in the GluA2 subunit modulates the channel properties in both homomeric (GluA2Q) and complex (GluA2Q/2R and GluA1/2R) channel forms. However, R/G editing is only effective in flop channels. Specifically, editing at the R/G site on the GluA2R flop isoform accelerates the rate of channel opening and desensitization for GluA1/2R channels more pronouncedly with the GluA1 being in the flop form than in the flip form; yet R/G editing has no effect on either channel-closing rate or EC50. Our results suggest R/G editing via GluA2R serve as a regulatory mechanism to modulate the function of GluA2R-containing, native receptors involved in fast excitatory synaptic transmission.
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Affiliation(s)
- Wei Wen
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York, 12222, United States
| | - Chi-Yen Lin
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York, 12222, United States
| | - Li Niu
- Department of Chemistry, and Center for Neuroscience Research, University at Albany, SUNY, Albany, New York, 12222, United States.
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21
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Lu HW, Balmer TS, Romero GE, Trussell LO. Slow AMPAR Synaptic Transmission Is Determined by Stargazin and Glutamate Transporters. Neuron 2017; 96:73-80.e4. [PMID: 28919175 DOI: 10.1016/j.neuron.2017.08.043] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 07/25/2017] [Accepted: 08/28/2017] [Indexed: 01/23/2023]
Abstract
AMPARs mediate the briefest synaptic currents in the brain by virtue of their rapid gating kinetics. However, at the mossy fiber-to-unipolar brush cell synapse in the cerebellum, AMPAR-mediated EPSCs last for hundreds of milliseconds, and it has been proposed that this time course reflects slow diffusion from a complex synaptic space. We show that upon release of glutamate, synaptic AMPARs were desensitized by transmitter by >90%. As glutamate levels subsequently fell, recovery of transmission occurred due to the presence of the AMPAR accessory protein stargazin that enhances the AMPAR response to low levels of transmitter. This gradual increase in receptor activity following desensitization accounted for the majority of synaptic transmission at this synapse. Moreover, the amplitude, duration, and shape of the synaptic response was tightly controlled by plasma membrane glutamate transporters, indicating that clearance of synaptic glutamate during the slow EPSC is dictated by an uptake process.
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Affiliation(s)
- Hsin-Wei Lu
- Neuroscience Graduate Program, Oregon Health and Science University, Portland, OR, USA
| | - Timothy S Balmer
- Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Gabriel E Romero
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR, USA
| | - Laurence O Trussell
- Oregon Hearing Research Center and Vollum Institute, Oregon Health and Science University, Portland, OR, USA.
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Miyazaki T, Yamasaki M, Hashimoto K, Kohda K, Yuzaki M, Shimamoto K, Tanaka K, Kano M, Watanabe M. Glutamate transporter GLAST controls synaptic wrapping by Bergmann glia and ensures proper wiring of Purkinje cells. Proc Natl Acad Sci U S A 2017; 114:7438-7443. [PMID: 28655840 PMCID: PMC5514701 DOI: 10.1073/pnas.1617330114] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Astrocytes regulate synaptic transmission through controlling neurotransmitter concentrations around synapses. Little is known, however, about their roles in neural circuit development. Here we report that Bergmann glia (BG), specialized cerebellar astrocytes that thoroughly enwrap Purkinje cells (PCs), are essential for synaptic organization in PCs through the action of the l-glutamate/l-aspartate transporter (GLAST). In GLAST-knockout mice, dendritic innervation by the main ascending climbing fiber (CF) branch was significantly weakened, whereas the transverse branch, which is thin and nonsynaptogenic in control mice, was transformed into thick and synaptogenic branches. Both types of CF branches frequently produced aberrant wiring to proximal and distal dendrites, causing multiple CF-PC innervation. Our electrophysiological analysis revealed that slow and small CF-evoked excitatory postsynaptic currents (EPSCs) were recorded from almost all PCs in GLAST-knockout mice. These atypical CF-EPSCs were far more numerous and had significantly faster 10-90% rise time than those elicited by glutamate spillover under pharmacological blockade of glial glutamate transporters. Innervation by parallel fibers (PFs) was also affected. PF synapses were robustly increased in the entire dendritic trees, leading to impaired segregation of CF and PF territories. Furthermore, lamellate BG processes were retracted from PC dendrites and synapses, leading to the exposure of these neuronal elements to the extracellular milieus. These synaptic and glial phenotypes were reproduced in wild-type mice after functional blockade of glial glutamate transporters. These findings highlight that glutamate transporter function by GLAST on BG plays important roles in development and maintenance of proper synaptic wiring and wrapping in PCs.
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Affiliation(s)
- Taisuke Miyazaki
- Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan
| | - Miwako Yamasaki
- Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan
| | - Kouichi Hashimoto
- Department of Neurophysiology, Graduate School of Medicine, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
- Department of Neurophysiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8551, Japan
| | - Kazuhisa Kohda
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
- Department of Physiology, St. Marianna University School of Medicine, Kanagawa 216-8511, Japan
| | - Michisuke Yuzaki
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Keiko Shimamoto
- Bioorganic Research Institute, Suntory Foundation for Life Sciences, Kyoto, 619-0284, Japan
| | - Kohichi Tanaka
- Laboratory of Molecular Neuroscience, School of Biomedical Science and Medical Research Institute, Tokyo Medical and Dental University, Tokyo 113-8510, Japan
| | - Masanobu Kano
- Department of Neurophysiology, Graduate School of Medicine, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
| | - Masahiko Watanabe
- Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan;
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23
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Fu X, Mervin LH, Li X, Yu H, Li J, Mohamad Zobir SZ, Zoufir A, Zhou Y, Song Y, Wang Z, Bender A. Toward Understanding the Cold, Hot, and Neutral Nature of Chinese Medicines Using in Silico Mode-of-Action Analysis. J Chem Inf Model 2017; 57:468-483. [DOI: 10.1021/acs.jcim.6b00725] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Xianjun Fu
- School
of Information Management, Shandong University of Traditional Chinese Medicine, 250355 Jinan, China
- Centre
for Molecular Science Informatics, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Lewis H. Mervin
- Centre
for Molecular Science Informatics, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Xuebo Li
- School
of Information Management, Shandong University of Traditional Chinese Medicine, 250355 Jinan, China
| | - Huayun Yu
- College
of TCM, Shandong University of Traditional Chinese Medicine, 250355 Jinan, China
| | - Jiaoyang Li
- School
of Information Management, Shandong University of Traditional Chinese Medicine, 250355 Jinan, China
| | - Siti Zuraidah Mohamad Zobir
- Centre
for Molecular Science Informatics, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Azedine Zoufir
- Centre
for Molecular Science Informatics, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Yang Zhou
- School
of Information Management, Shandong University of Traditional Chinese Medicine, 250355 Jinan, China
| | - Yongmei Song
- School
of Information Management, Shandong University of Traditional Chinese Medicine, 250355 Jinan, China
| | - Zhenguo Wang
- School
of Information Management, Shandong University of Traditional Chinese Medicine, 250355 Jinan, China
| | - Andreas Bender
- Centre
for Molecular Science Informatics, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
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24
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Abstract
UNLABELLED AMPA and NMDA receptors are glutamate-gated ion channels that mediate fast excitatory synaptic transmission throughout the nervous system. In the continual presence of glutamate, AMPA and NMDA receptors containing the GluN2A or GluN2B subunit enter into a nonconducting, desensitized state that can impact synaptic responses and glutamate-mediated excitotoxicity. The process of desensitization is dramatically different between subtypes, but the basis for these differences is unknown. We generated an extensive sequence alignment of ionotropic glutamate receptors (iGluRs) from diverse animal phyla and identified a highly conserved motif, which we termed the "hydrophobic box," located at the extracellular interface of transmembrane helices. A single position in the hydrophobic box differed between mammalian AMPA and NMDA receptors. Surprisingly, we find that an NMDAR-to-AMPAR exchange mutation at this position in the rat GluN2A or GluN2B subunit had a dramatic and highly specific effect on NMDAR desensitization, making it AMPAR-like. In contrast, a reverse exchange mutation in AMPARs had minimal effects on desensitization. These experiments highlight differences in desensitization between iGluR subtypes and the highly specific contribution of the GluN2 subunit to this process. SIGNIFICANCE STATEMENT Rapid communication between cells in the nervous system depends on ion channels that are directly activated by neurotransmitter molecules. Here, we studied ionotropic glutamate receptors (iGluRs), which are ion channels activated by the neurotransmitter glutamate. By comparing the sequences of a vast number of iGluR proteins from diverse animal species, assisted by available structural information, we identified a highly conserved motif. We showed that a single amino acid difference in this motif between mammalian iGluR subtypes has dramatic effects on receptor function. These results have implications in both the evolution of synaptic function, as well as the role of iGluRs in health and disease.
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25
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Vainshtein A, Veenman L, Shterenberg A, Singh S, Masarwa A, Dutta B, Island B, Tsoglin E, Levin E, Leschiner S, Maniv I, Pe’er L, Otradnov I, Zubedat S, Aga-Mizrachi S, Weizman A, Avital A, Marek I, Gavish M. Quinazoline-based tricyclic compounds that regulate programmed cell death, induce neuronal differentiation, and are curative in animal models for excitotoxicity and hereditary brain disease. Cell Death Discov 2015; 1:15027. [PMID: 27551459 PMCID: PMC4979516 DOI: 10.1038/cddiscovery.2015.27] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 07/16/2015] [Indexed: 12/21/2022] Open
Abstract
Expanding on a quinazoline scaffold, we developed tricyclic compounds with biological activity. These compounds bind to the 18 kDa translocator protein (TSPO) and protect U118MG (glioblastoma cell line of glial origin) cells from glutamate-induced cell death. Fascinating, they can induce neuronal differentiation of PC12 cells (cell line of pheochromocytoma origin with neuronal characteristics) known to display neuronal characteristics, including outgrowth of neurites, tubulin expression, and NeuN (antigen known as 'neuronal nuclei', also known as Rbfox3) expression. As part of the neurodifferentiation process, they can amplify cell death induced by glutamate. Interestingly, the compound 2-phenylquinazolin-4-yl dimethylcarbamate (MGV-1) can induce expansive neurite sprouting on its own and also in synergy with nerve growth factor and with glutamate. Glycine is not required, indicating that N-methyl-D-aspartate receptors are not involved in this activity. These diverse effects on cells of glial origin and on cells with neuronal characteristics induced in culture by this one compound, MGV-1, as reported in this article, mimic the diverse events that take place during embryonic development of the brain (maintenance of glial integrity, differentiation of progenitor cells to mature neurons, and weeding out of non-differentiating progenitor cells). Such mechanisms are also important for protective, curative, and restorative processes that occur during and after brain injury and brain disease. Indeed, we found in a rat model of systemic kainic acid injection that MGV-1 can prevent seizures, counteract the process of ongoing brain damage, including edema, and restore behavior defects to normal patterns. Furthermore, in the R6-2 (transgenic mouse model for Huntington disease; Strain name: B6CBA-Tg(HDexon1)62Gpb/3J) transgenic mouse model for Huntington disease, derivatives of MGV-1 can increase lifespan by >20% and reduce incidence of abnormal movements. Also in vitro, these derivatives were more effective than MGV-1.
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Affiliation(s)
- A Vainshtein
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
| | - L Veenman
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
| | - A Shterenberg
- Technion – Israel Institute of Technology, Schulich Faculty of Chemistry, The Mallat Family Laboratory of Organic Chemistry, Haifa, Israel
| | - S Singh
- Technion – Israel Institute of Technology, Schulich Faculty of Chemistry, The Mallat Family Laboratory of Organic Chemistry, Haifa, Israel
| | - A Masarwa
- Technion – Israel Institute of Technology, Schulich Faculty of Chemistry, The Mallat Family Laboratory of Organic Chemistry, Haifa, Israel
| | - B Dutta
- Technion – Israel Institute of Technology, Schulich Faculty of Chemistry, The Mallat Family Laboratory of Organic Chemistry, Haifa, Israel
| | - B Island
- Technion – Israel Institute of Technology, Schulich Faculty of Chemistry, The Mallat Family Laboratory of Organic Chemistry, Haifa, Israel
| | - E Tsoglin
- Technion – Israel Institute of Technology, Schulich Faculty of Chemistry, The Mallat Family Laboratory of Organic Chemistry, Haifa, Israel
| | - E Levin
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
| | - S Leschiner
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
| | - I Maniv
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
| | - L Pe’er
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
| | - I Otradnov
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
| | - S Zubedat
- Department of Physiology, Technion – Israel Institute of Technology, The Behavioral Neuroscience Laboratory, Faculty of Medicine and Emek Medical Center, Haifa, Israel
| | - S Aga-Mizrachi
- Department of Physiology, Technion – Israel Institute of Technology, The Behavioral Neuroscience Laboratory, Faculty of Medicine and Emek Medical Center, Haifa, Israel
| | - A Weizman
- Tel Aviv University, Sackler Faculty of Medicine, The Felsenstein Medical Research Center, Geha Mental Health Center, Tel Aviv, Israel
| | - A Avital
- Department of Physiology, Technion – Israel Institute of Technology, The Behavioral Neuroscience Laboratory, Faculty of Medicine and Emek Medical Center, Haifa, Israel
| | - I Marek
- Technion – Israel Institute of Technology, Schulich Faculty of Chemistry, The Mallat Family Laboratory of Organic Chemistry, Haifa, Israel
| | - M Gavish
- Department of Neuroscience, Technion – Israel Institute of Technology, Faculty of Medicine, Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel
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26
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Sanchez JT, Quinones K, Otto-Meyer S. Factors Influencing Short-term Synaptic Plasticity in the Avian Cochlear Nucleus Magnocellularis. J Exp Neurosci 2015; 9:11-24. [PMID: 26527054 PMCID: PMC4620996 DOI: 10.4137/jen.s25472] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Revised: 09/20/2015] [Accepted: 09/21/2015] [Indexed: 11/15/2022] Open
Abstract
Defined as reduced neural responses during high rates of activity, synaptic depression is a form of short-term plasticity important for the temporal filtering of sound. In the avian cochlear nucleus magnocellularis (NM), an auditory brainstem structure, mechanisms regulating short-term synaptic depression include pre-, post-, and extrasynaptic factors. Using varied paired-pulse stimulus intervals, we found that the time course of synaptic depression lasts up to four seconds at late-developing NM synapses. Synaptic depression was largely reliant on exogenous Ca2+-dependent probability of presynaptic neurotransmitter release, and to a lesser extent, on the desensitization of postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptor (AMPA-R). Interestingly, although extrasynaptic glutamate clearance did not play a significant role in regulating synaptic depression, blocking glutamate clearance at early-developing synapses altered synaptic dynamics, changing responses from depression to facilitation. These results suggest a developmental shift in the relative reliance on pre-, post-, and extrasynaptic factors in regulating short-term synaptic plasticity in NM.
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Affiliation(s)
- Jason Tait Sanchez
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, The Hugh Knowles Hearing Research Center, School of Communication, Northwestern University, Evanston, IL, USA. ; Department of Neurobiology and Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL, USA
| | - Karla Quinones
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, The Hugh Knowles Hearing Research Center, School of Communication, Northwestern University, Evanston, IL, USA
| | - Sebastian Otto-Meyer
- Weinberg College of Arts and Sciences, Northwestern University, Evanston, IL, USA
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27
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Ramaswamy S, Markram H. Anatomy and physiology of the thick-tufted layer 5 pyramidal neuron. Front Cell Neurosci 2015; 9:233. [PMID: 26167146 PMCID: PMC4481152 DOI: 10.3389/fncel.2015.00233] [Citation(s) in RCA: 107] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Accepted: 06/08/2015] [Indexed: 11/13/2022] Open
Abstract
The thick-tufted layer 5 (TTL5) pyramidal neuron is one of the most extensively studied neuron types in the mammalian neocortex and has become a benchmark for understanding information processing in excitatory neurons. By virtue of having the widest local axonal and dendritic arborization, the TTL5 neuron encompasses various local neocortical neurons and thereby defines the dimensions of neocortical microcircuitry. The TTL5 neuron integrates input across all neocortical layers and is the principal output pathway funneling information flow to subcortical structures. Several studies over the past decades have investigated the anatomy, physiology, synaptology, and pathophysiology of the TTL5 neuron. This review summarizes key discoveries and identifies potential avenues of research to facilitate an integrated and unifying understanding on the role of a central neuron in the neocortex.
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Affiliation(s)
- Srikanth Ramaswamy
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Campus Biotech Geneva, Switzerland
| | - Henry Markram
- Blue Brain Project, Ecole Polytechnique Fédérale de Lausanne, Campus Biotech Geneva, Switzerland
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28
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The ubiquitous nature of multivesicular release. Trends Neurosci 2015; 38:428-38. [PMID: 26100141 DOI: 10.1016/j.tins.2015.05.008] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Revised: 05/20/2015] [Accepted: 05/24/2015] [Indexed: 11/21/2022]
Abstract
'Simplicity is prerequisite for reliability' (E.W. Dijkstra [1]) Presynaptic action potentials trigger the fusion of vesicles to release neurotransmitter onto postsynaptic neurons. Each release site was originally thought to liberate at most one vesicle per action potential in a probabilistic fashion, rendering synaptic transmission unreliable. However, the simultaneous release of several vesicles, or multivesicular release (MVR), represents a simple mechanism to overcome the intrinsic unreliability of synaptic transmission. MVR was initially identified at specialized synapses but is now known to be common throughout the brain. MVR determines the temporal and spatial dispersion of transmitter, controls the extent of receptor activation, and contributes to adapting synaptic strength during plasticity and neuromodulation. MVR consequently represents a widespread mechanism that extends the dynamic range of synaptic processing.
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29
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Hanson E, Armbruster M, Cantu D, Andresen L, Taylor A, Danbolt NC, Dulla CG. Astrocytic glutamate uptake is slow and does not limit neuronal NMDA receptor activation in the neonatal neocortex. Glia 2015; 63:1784-96. [PMID: 25914127 DOI: 10.1002/glia.22844] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 03/30/2015] [Accepted: 04/07/2015] [Indexed: 01/20/2023]
Abstract
Glutamate uptake by astrocytes controls the time course of glutamate in the extracellular space and affects neurotransmission, synaptogenesis, and circuit development. Astrocytic glutamate uptake has been shown to undergo post-natal maturation in the hippocampus, but has been largely unexplored in other brain regions. Notably, glutamate uptake has never been examined in the developing neocortex. In these studies, we investigated the development of astrocytic glutamate transport, intrinsic membrane properties, and control of neuronal NMDA receptor activation in the developing neocortex. Using astrocytic and neuronal electrophysiology, immunofluorescence, and Western blot analysis we show that: (1) glutamate uptake in the neonatal neocortex is slow relative to neonatal hippocampus; (2) astrocytes in the neonatal neocortex undergo a significant maturation of intrinsic membrane properties; (3) slow glutamate uptake is accompanied by lower expression of both GLT-1 and GLAST; (4) glutamate uptake is less dependent on GLT-1 in neonatal neocortex than in neonatal hippocampus; and (5) the slow glutamate uptake we report in the neonatal neocortex corresponds to minimal astrocytic control of neuronal NMDA receptor activation. Taken together, our results clearly show fundamental differences between astrocytic maturation in the developing neocortex and hippocampus, and corresponding changes in how astrocytes control glutamate signaling.
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Affiliation(s)
- Elizabeth Hanson
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts.,Neuroscience Program, Tufts Sackler School of Biomedical Sciences, Boston, Massachusetts
| | - Moritz Armbruster
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts
| | - David Cantu
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts
| | - Lauren Andresen
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts.,Neuroscience Program, Tufts Sackler School of Biomedical Sciences, Boston, Massachusetts
| | - Amaro Taylor
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts
| | - Niels Christian Danbolt
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Chris G Dulla
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts.,Neuroscience Program, Tufts Sackler School of Biomedical Sciences, Boston, Massachusetts
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30
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An RNA-seq screen of the Drosophila antenna identifies a transporter necessary for ammonia detection. PLoS Genet 2014; 10:e1004810. [PMID: 25412082 PMCID: PMC4238959 DOI: 10.1371/journal.pgen.1004810] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 10/06/2014] [Indexed: 01/18/2023] Open
Abstract
Many insect vectors of disease detect their hosts through olfactory cues, and thus it is of great interest to understand better how odors are encoded. However, little is known about the molecular underpinnings that support the unique function of coeloconic sensilla, an ancient and conserved class of sensilla that detect amines and acids, including components of human odor that are cues for many insect vectors. Here, we generate antennal transcriptome databases both for wild type Drosophila and for a mutant that lacks coeloconic sensilla. We use these resources to identify genes whose expression is highly enriched in coeloconic sensilla, including many genes not previously implicated in olfaction. Among them, we identify an ammonium transporter gene that is essential for ammonia responses in a class of coeloconic olfactory receptor neurons (ORNs), but is not required for responses to other odorants. Surprisingly, the transporter is not expressed in ORNs, but rather in neighboring auxiliary cells. Thus, our data reveal an unexpected non-cell autonomous role for a component that is essential to the olfactory response to ammonia. The defective response observed in a Drosophila mutant of this gene is rescued by its Anopheles ortholog, and orthologs are found in virtually all insect species examined, suggesting that its role is conserved. Taken together, our results provide a quantitative analysis of gene expression in the primary olfactory organ of Drosophila, identify molecular components of an ancient class of olfactory sensilla, and reveal that auxiliary cells, and not simply ORNs, play an essential role in the coding of an odor that is a critical host cue for many insect vectors of human disease. Olfaction underlies the attraction of insect pests and vectors of disease to their plant and human hosts. In the genetic model insect Drosophila, the neuronal basis of odor coding has been extensively analyzed in the antenna, its major olfactory organ, but the molecular basis of odor coding has not. Additionally, there has been little analysis of any olfactory cells other than neurons. We have undertaken a comprehensive and quantitative analysis of gene expression in the Drosophila antenna. This analysis revealed a surprisingly broad dynamic range of odor receptor and odor binding protein expression, and unexpected expression of taste receptor genes. Further analysis identified 250 genes that are expressed at reduced levels in a mutant lacking an evolutionarily ancient class of sensilla, antennal hairs housing neurons that respond to human odors. One of these genes, a transporter, is expressed in non-neuronal cells but is essential to the response of a neuron to ammonia, a key cue for insect vectors of disease. A mutation in this transporter can be rescued by its mosquito homolog. While many studies of sensory coding consider the neural circuit in isolation, our analysis reveals an essential role for an auxiliary cell.
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31
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Abstract
Few other neurotransmitters are of as intense interest to neuropsychiatry and neurology as dopamine, yet existing techniques to monitor dopamine release leave an important spatiotemporal gap in our understanding. Electrochemistry and fluorescence imaging tools have been developed to fill the gap, but these methods have important limitations. We circumvent these limitations by introducing a dopamine-gated chloride channel into rat dorsal striatal medium spiny neurons, targets of strong dopamine innervation, thereby transforming dopamine from a slow transmitter into a fast transmitter and revealing new opportunities for studying moment-to-moment regulation of dopamine release. We demonstrate pharmacological and biophysical properties of the channel that make it suitable for fast, local dopamine measurements, and we demonstrate for the first time spontaneous and evoked responses to vesicular dopamine release in the dorsal striatum. Evoked dopamine currents were separated into a fast, monosynaptic component and a slower-rising and decaying disynaptic component mediated by nicotinic receptor activation. In summary, LGC-53 represents a dopamine biosensor with properties suitable for temporal separation of distinct dopamine signals in targets of dopamine innervation.
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32
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Auditory neuroplasticity, hearing loss and cochlear implants. Cell Tissue Res 2014; 361:251-69. [DOI: 10.1007/s00441-014-2004-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 09/04/2014] [Indexed: 10/24/2022]
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33
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Hess GP, Lewis RW, Chen Y. Caged neurotransmitters and other caged compounds: design and application. Cold Spring Harb Protoc 2014; 2014:pdb.top084152. [PMID: 25275116 DOI: 10.1101/pdb.top084152] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The approaches using caged neurotransmitters described here enable transient kinetic investigations to be made with membrane-bound proteins (receptors) on a cell surface with the same time resolution as was previously possible only with proteins in solution.
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34
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Specialized postsynaptic morphology enhances neurotransmitter dilution and high-frequency signaling at an auditory synapse. J Neurosci 2014; 34:8358-72. [PMID: 24920639 DOI: 10.1523/jneurosci.4493-13.2014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Sensory processing in the auditory system requires that synapses, neurons, and circuits encode information with particularly high temporal and spectral precision. In the amphibian papillia, sound frequencies up to 1 kHz are encoded along a tonotopic array of hair cells and transmitted to afferent fibers via fast, repetitive synaptic transmission, thereby promoting phase locking between the presynaptic and postsynaptic cells. Here, we have combined serial section electron microscopy, paired electrophysiological recordings, and Monte Carlo diffusion simulations to examine novel mechanisms that facilitate fast synaptic transmission in the inner ear of frogs (Rana catesbeiana and Rana pipiens). Three-dimensional anatomical reconstructions reveal specialized spine-like contacts between individual afferent fibers and hair cells that are surrounded by large, open regions of extracellular space. Morphologically realistic diffusion simulations suggest that these local enlargements in extracellular space speed transmitter clearance and reduce spillover between neighboring synapses, thereby minimizing postsynaptic receptor desensitization and improving sensitivity during prolonged signal transmission. Additionally, evoked EPSCs in afferent fibers are unaffected by glutamate transporter blockade, suggesting that transmitter diffusion and dilution, and not uptake, play a primary role in speeding neurotransmission and ensuring fidelity at these synapses.
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35
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Ptak CP, Hsieh CL, Weiland GA, Oswald RE. Role of stoichiometry in the dimer-stabilizing effect of AMPA receptor allosteric modulators. ACS Chem Biol 2014; 9:128-33. [PMID: 24152170 PMCID: PMC3947009 DOI: 10.1021/cb4007166] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Protein dimerization provides a mechanism for the modulation of cellular signaling events. In α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors, the rapidly desensitizing, activated state has been correlated with a weakly dimeric, glutamate-binding domain conformation. Allosteric modulators can form bridging interactions that stabilize the dimer interface. While most modulators can only bind to one position with a one modulator per dimer ratio, some thiazide-based modulators can bind to the interface in two symmetrical positions with a two modulator per dimer ratio. Based on small-angle X-ray scattering (SAXS) experiments, dimerization curves for the isolated glutamate-binding domain show that a second modulator binding site produces both an increase in positive cooperativity and a decrease in the EC50 for dimerization. Four body binding equilibrium models that incorporate a second dimer-stabilizing ligand were developed to fit the experimental data. The work illustrates why stoichiometry should be an important consideration during the rational design of dimerizing modulators.
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Affiliation(s)
- Christopher P. Ptak
- Department of Molecular
Medicine and ‡Department of Population Medicine
and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, United States
| | - Ching-Lin Hsieh
- Department of Molecular
Medicine and ‡Department of Population Medicine
and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, United States
| | - Gregory A. Weiland
- Department of Molecular
Medicine and ‡Department of Population Medicine
and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, United States
| | - Robert E. Oswald
- Department of Molecular
Medicine and ‡Department of Population Medicine
and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, United States
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36
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Amperometric resolution of a prespike stammer and evoked phases of fast release from retinal bipolar cells. J Neurosci 2013; 33:8144-58. [PMID: 23658155 DOI: 10.1523/jneurosci.5062-12.2013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The neurotransmitter glutamate is used by most neurons in the brain to activate a multitude of different types of glutamate receptors and transporters involved in fast and relatively slower signaling. Synaptic ribbons are large presynaptic structures found in neurons involved in vision, balance, and hearing, which use a large number of glutamate-filled synaptic vesicles to meet their signaling demands. To directly measure synaptic vesicle release events, the ribbon-type presynaptic terminals of goldfish retinal bipolar cells were coaxed to release a false transmitter that could be monitored with amperometry by placing the carbon fiber directly on the larger synaptic terminal. Spontaneous secretion events formed a unimodal charge distribution, but single spike properties were heterogeneous. Larger events rose exponentially without interruption (τ ∼ 30 μs), and smaller events exhibited a stammer in their rising phase that is interpreted as a brief pause in pore dilation, a characteristic commonly associated with large dense core granule fusion pores. These events were entirely Ca(2+)-dependent. Holding the cells at -60 mV halted spontaneous release; and when the voltage was stepped to >-40 mV, secretion ensued. When stepping the voltage to 0 mV, novel kinetic phases of vesicle recruitment were revealed. Approximately 14 vesicles were released per ribbon in two kinetic phases with time constants of 1.5 and 16 ms, which are proposed to represent different primed states within the population of docked vesicles.
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37
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Major G, Larkum ME, Schiller J. Active Properties of Neocortical Pyramidal Neuron Dendrites. Annu Rev Neurosci 2013; 36:1-24. [DOI: 10.1146/annurev-neuro-062111-150343] [Citation(s) in RCA: 286] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Guy Major
- School of Biosciences, Cardiff University, Cardiff, CF10 3AX, United Kingdom;
| | - Matthew E. Larkum
- Charité University, Neuroscience Research Center (NWFZ), D-10117 Berlin, Germany;
| | - Jackie Schiller
- Department of Physiology, Technion Medical School, Haifa 31096, Israel;
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38
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Abstract
A recently discovered type of mammalian retinal ganglion cell encodes environmental light intensity and mediates non-image-forming visual behaviors, such as the pupillary reflex and circadian photoentrainment. These intrinsically photosensitive retinal ganglion cells (ipRGCs) generate endogenous, melanopsin-based photoresponses as well as extrinsic, rod/cone-driven responses. Because the ipRGCs' light responses and the behaviors they control are both remarkably tonic, these cells have been hypothesized to be capable of irradiance detection lasting throughout the day. I tested this hypothesis by obtaining multielectrode-array recordings from ipRGCs in a novel rat eyecup preparation that enhances the regeneration of rod/cone photopigments. I found that 10 h constant light could continuously evoke action potentials in these ganglion cells under conditions that stimulated (1) only melanopsin, (2) mainly the rod input, and (3) both intrinsic and extrinsic responses. In response to a 10 h stimulus with gradual intensity changes to simulate sunrise and sunset, ipRGC firing rates slowly increased during the "sunrise" phase and slowly decreased during the "sunset" phase. Furthermore, I recorded from putative ipRGCs of melanopsin-knock-out mice and found that these cells retained the ability to respond in a sustained fashion to 20 min light steps, indicating that melanopsin is not required for such tonic responses. In conclusion, ipRGCs can signal light continuously for at least 10 h and can probably track gradual irradiance changes over the course of the day. These results further suggest that the photoreceptors and ON bipolar cells presynaptic to ipRGCs may be able to respond to light continuously for 10 h.
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39
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Cho S, von Gersdorff H. Ca(2+) influx and neurotransmitter release at ribbon synapses. Cell Calcium 2012; 52:208-16. [PMID: 22776680 DOI: 10.1016/j.ceca.2012.06.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 06/10/2012] [Accepted: 06/13/2012] [Indexed: 12/11/2022]
Abstract
Ca(2+) influx through voltage-gated Ca(2+) channels triggers the release of neurotransmitters at presynaptic terminals. Some sensory receptor cells in the peripheral auditory and visual systems have specialized synapses that express an electron-dense organelle called a synaptic ribbon. Like conventional synapses, ribbon synapses exhibit SNARE-mediated exocytosis, clathrin-mediated endocytosis, and short-term plasticity. However, unlike non-ribbon synapses, voltage-gated L-type Ca(2+) channel opening at ribbon synapses triggers a form of multiquantal release that can be highly synchronous. Furthermore, ribbon synapses appear to be specialized for fast and high throughput exocytosis controlled by graded membrane potential changes. Here we will discuss some of the basic aspects of synaptic transmission at different types of ribbon synapses, and we will emphasize recent evidence that auditory and retinal ribbon synapses have marked differences. This will lead us to suggest that ribbon synapses are specialized for particular operating ranges and frequencies of stimulation. We propose that different types of ribbon synapses transfer diverse rates of sensory information by expressing a particular repertoire of critical components, and by placing them at precise and strategic locations, so that a continuous supply of primed vesicles and Ca(2+) influx leads to fast, accurate, and ongoing exocytosis.
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Affiliation(s)
- Soyoun Cho
- The Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA
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Wu YW, Grebenyuk S, McHugh TJ, Rusakov DA, Semyanov A. Backpropagating action potentials enable detection of extrasynaptic glutamate by NMDA receptors. Cell Rep 2012; 1:495-505. [PMID: 22832274 PMCID: PMC3740263 DOI: 10.1016/j.celrep.2012.03.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2011] [Revised: 01/11/2012] [Accepted: 03/22/2012] [Indexed: 12/19/2022] Open
Abstract
Synaptic NMDA receptors (NMDARs) are crucial for neural coding and plasticity. However, little is known about the adaptive function of extrasynaptic NMDARs occurring mainly on dendritic shafts. Here, we find that in CA1 pyramidal neurons, backpropagating action potentials (bAPs) recruit shaft NMDARs exposed to ambient glutamate. In contrast, spine NMDARs are “protected,” under baseline conditions, from such glutamate influences by perisynaptic transporters: we detect bAP-evoked Ca2+ entry through these receptors upon local synaptic or photolytic glutamate release. During theta-burst firing, NMDAR-dependent Ca2+ entry either downregulates or upregulates an h-channel conductance (Gh) of the cell depending on whether synaptic glutamate release is intact or blocked. Thus, the balance between activation of synaptic and extrasynaptic NMDARs can determine the sign of Gh plasticity. Gh plasticity in turn regulates dendritic input probed by local glutamate uncaging. These results uncover a metaplasticity mechanism potentially important for neural coding and memory formation.
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Affiliation(s)
- Yu-Wei Wu
- RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan
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Nonlinear interactions between excitatory and inhibitory retinal synapses control visual output. J Neurosci 2011; 31:15102-12. [PMID: 22016544 DOI: 10.1523/jneurosci.1801-11.2011] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The visual system is highly sensitive to dynamic features in the visual scene. However, it is not known how or where this enhanced sensitivity first occurs. We investigated this phenomenon by studying interactions between excitatory and inhibitory synapses in the second synaptic layer of the mouse retina. We found that these interactions showed activity-dependent changes that enhanced signaling of dynamic stimuli. Excitatory signaling from cone bipolar cells to ganglion cells exhibited strong synaptic depression, attributable to reduced glutamate release from bipolar cells. This depression was relieved by amacrine cell inhibitory feedback that activated presynaptic GABA(C) receptors. We found that the balance between excitation and feedback inhibition depended on stimulus frequency; at short interstimulus intervals, excitation was enhanced, attributable to reduced inhibitory feedback. This dynamic interplay may enrich visual processing by enhancing retinal responses to closely spaced temporal events, representing rapid changes in the visual environment.
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Yu J, Qian H, Chen N, Wang JH. Quantal glutamate release is essential for reliable neuronal encodings in cerebral networks. PLoS One 2011; 6:e25219. [PMID: 21949885 PMCID: PMC3176814 DOI: 10.1371/journal.pone.0025219] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Accepted: 08/29/2011] [Indexed: 12/05/2022] Open
Abstract
Background The neurons and synapses work coordinately to program the brain codes of controlling cognition and behaviors. Spike patterns at the presynaptic neurons regulate synaptic transmission. The quantitative regulations of synapse dynamics in spike encoding at the postsynaptic neurons remain unclear. Methodology/Principal Findings With dual whole-cell recordings at synapse-paired cells in mouse cortical slices, we have investigated the regulation of synapse dynamics to neuronal spike encoding at cerebral circuits assembled by pyramidal neurons and GABAergic ones. Our studies at unitary synapses show that postsynaptic responses are constant over time, such as glutamate receptor-channel currents at GABAergic neurons and glutamate transport currents at astrocytes, indicating quantal glutamate release. In terms of its physiological impact, our results demonstrate that the signals integrated from quantal glutamatergic synapses drive spike encoding at GABAergic neurons reliably, which in turn precisely set spike encoding at pyramidal neurons through feedback inhibition. Conclusion/Significance Our studies provide the evidences for the quantal glutamate release to drive the spike encodings precisely in cortical circuits, which may be essential for programming the reliable codes in the brain to manage well-organized behaviors.
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Affiliation(s)
- Jiandong Yu
- State Key Lab for Brain and Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- Graduate School of Chinese Academy of Sciences, Beijing, China
| | - Hao Qian
- State Key Lab for Brain and Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- Graduate School of Chinese Academy of Sciences, Beijing, China
| | - Na Chen
- State Key Lab for Brain and Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
| | - Jin-Hui Wang
- State Key Lab for Brain and Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- Graduate School of Chinese Academy of Sciences, Beijing, China
- * E-mail:
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Klug A. Short-term synaptic plasticity in the auditory brain stem by using in-vivo-like stimulation parameters. Hear Res 2011; 279:51-9. [DOI: 10.1016/j.heares.2011.05.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Revised: 04/29/2011] [Accepted: 05/05/2011] [Indexed: 10/18/2022]
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Cortical cultures coupled to micro-electrode arrays: a novel approach to perform in vitro excitotoxicity testing. Neurotoxicol Teratol 2011; 34:116-27. [PMID: 21856414 DOI: 10.1016/j.ntt.2011.08.001] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Revised: 07/03/2011] [Accepted: 08/04/2011] [Indexed: 01/08/2023]
Abstract
In vitro neuronal cultures exhibit spontaneous electrophysiological activity that can be modulated by chemical stimulation and can be monitored over time by using Micro-Electrode Arrays (MEAs), devices composed by a glass substrate and metal electrodes. Dissociated networks respond to transmitters, their blockers and many other pharmacological substances, including neurotoxic compounds. In this paper we present results related to the effects, both acute (i.e. 1 hour after the treatment) and chronic (3 days after the treatment), of increasing glutamatergic transmission induced by the application of rising concentrations of glutamate and its agonists (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid - AMPA, N-methyl-D-aspartate - NMDA and AMPA together with cyclothiazide - CTZ). Increase of available glutamate was obtained in two ways: 1) by direct application of exogenous glutamate and 2) by inhibiting the clearance of the endogenously released glutamate through DL-threo-β-benzyloxyaspartate (TBOA). Our findings show that fine modulations (i.e. low concentrations of drug) of the excitatory synaptic transmission are reflected in the electrophysiological activation of the network, while intervention leading to excessive direct stimulation of glutamatergic pathways (i.e. medium and high concentrations of drug) results in the abolishment of the electrophysiological activity and eventually cell death. The results obtained by means of the MEA recordings have been compared to the analysis of cell viability to confirm the excitotoxic effect of the applied drug. In conclusion, our study demonstrates that MEA-coupled cortical networks are very sensitive to pharmacological manipulation of the excitatory ionotropic glutamatergic transmission and might provide sensitive endpoints to detect acute and chronic neurotoxic effects of chemicals and drugs for predictive toxicity testing.
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Carlson SL, Fieber LA. Physiological evidence that D-aspartate activates a current distinct from ionotropic glutamate receptor currents in Aplysia californica neurons. J Neurophysiol 2011; 106:1629-36. [PMID: 21753031 DOI: 10.1152/jn.00403.2011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
D-Aspartate (D-Asp) activates an excitatory current in neurons of Aplysia californica. Although D-Asp is presumed to activate a subset of L-glutamate (L-Glu) channels, the identities of putative d-Asp receptors and channels are unclear. Whole cell voltage- and current-clamp studies using primary cultures of Aplysia buccal S cluster (BSC) neurons were executed to characterize D-Asp-activated ion channels. Both D-Asp and L-Glu evoked currents with similar current-voltage relationships, amplitudes, and relatively slow time courses of activation and inactivation when agonists were pressure applied. D-Asp-induced currents, however, were faster and desensitized longer, requiring 40 s to return to full amplitude. Of cells exposed to both agonists, 25% had D-Asp- but not L-Glu-induced currents, suggesting a receptor for D-Asp that was independent of l-Glu receptors. D-Asp channels were permeable to Na(+) and K(+), but not Ca²⁺, and were vulnerable to voltage-dependent Mg²⁺ block similarly to vertebrate NMDA receptor (NMDAR) channels. d-Asp may activate both NMDARs and non-l-Glu receptors in the nervous system of Aplysia.
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Affiliation(s)
- Stephen L Carlson
- Division of Marine Biology and Fisheries, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA
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Marty V, Kuzmiski JB, Baimoukhametova DV, Bains JS. Short-term plasticity impacts information transfer at glutamate synapses onto parvocellular neuroendocrine cells in the paraventricular nucleus of the hypothalamus. J Physiol 2011; 589:4259-70. [PMID: 21727221 DOI: 10.1113/jphysiol.2011.208082] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Glutamatergic synaptic inputs onto parvocellular neurosecretory cells (PNCs) in the paraventricular nucleus of the hypothalamus (PVN) regulate the hypothalamic-pituitary-adrenal (HPA) axis responses to stress and undergo stress-dependent changes in their capacity to transmit information. In spite of their pivotal role in regulating PNCs, relatively little is known about the fundamental rules that govern transmission at these synapses. Furthermore, since salient information in the nervous system is often transmitted in bursts, it is also important to understand the short-term dynamics of glutamate transmission under basal conditions. To characterize these properties, we obtained whole-cell patch clamp recordings from PNCs in brain slices from postnatal day 21-35 male Sprague-Dawley rats and examined EPSCs. EPSCs were elicited by electrically stimulating glutamatergic afferents along the periventricular aspect. In response to a paired-pulse stimulation protocol, EPSCs generally displayed a robust short-term depression that recovered within 5 s. Similarly, trains of synaptic stimuli (5-50 Hz) resulted in a frequency-dependent depression until a near steady state was achieved. Application of inhibitors of AMPA receptor (AMPAR) desensitization or the low-affinity, competitive AMPAR antagonist failed to affect the depression due to paired-pulse and trains of synaptic stimulation indicating that this use-dependent short-term synaptic depression has a presynaptic locus of expression. We used cumulative amplitude profiles during trains of stimulation and variance-mean analysis to estimate synaptic parameters. Finally, we report that these properties contribute to hamper the efficiency with which high frequency synaptic inputs generate spikes in PNCs, indicating that these synapses operate as effective low-pass filters in basal conditions.
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Affiliation(s)
- Vincent Marty
- Hotchkiss Brain Institute and Department of Physiology and Pharmacology, University of Calgary, Calgary, AB, Canada
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Wang Y, O'Donohue H, Manis P. Short-term plasticity and auditory processing in the ventral cochlear nucleus of normal and hearing-impaired animals. Hear Res 2011; 279:131-9. [PMID: 21586317 DOI: 10.1016/j.heares.2011.04.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 04/23/2011] [Accepted: 04/28/2011] [Indexed: 11/19/2022]
Abstract
The dynamics of synaptic transmission between neurons plays a major role in neural information processing. In the cochlear nucleus, auditory nerve synapses have a relatively high release probability and show pronounced synaptic depression that, in conjunction with the variability of interspike intervals, shapes the information transmitted to the postsynaptic cells. Cellular mechanisms have been best analyzed at the endbulb synapses, revealing that the recent history of presynaptic activity plays a complex, non-linear, role in regulating release. Emerging evidence suggests that the dynamics of synaptic function differs according to the target neuron within the cochlear nucleus. One consequence of hearing loss is changes in evoked release at surviving auditory nerve synapses, and in some situations spontaneous release is greatly enhanced. In contrast, even with cochlear ablation, postsynaptic excitability is less affected. The existing evidence suggests that different modes of hearing loss can result in different dynamic patterns of synaptic transmission between the auditory nerve and postsynaptic neurons. These changes in dynamics in turn will affect the efficacy with which different kinds of information about the acoustic environment can be processed by the parallel pathways in the cochlear nucleus.
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Affiliation(s)
- Yong Wang
- Division of Otolaryngology and Neuroscience Program, 3C120 School of Medicine, 30 North, 1900 East, Salt Lake City, University of Utah, UT 84132, USA.
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Lu U, Roach SM, Song D, Berger TW. A two-stage cascade nonlinear dynamical model of single neurons for the separation and quantification of pre- and post-synaptic mechanisms of synaptic transmission. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2011; 2011:1427-30. [PMID: 22254586 DOI: 10.1109/iembs.2011.6090353] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Neurons receive pre-synaptic spike trains and transform them into post-synaptic spike trains. This spike train to spike train temporal transformation underlies all cognitive functions performed by neurons, e.g., learning and memory. The transformation is a highly nonlinear dynamical process that involves both pre- and post-synaptic mechanisms. The ability to separate and quantify the nonlinear dynamics of pre- and post-synaptic mechanism is needed to gain insights into this transformation. In this study, we developed a Volterra kernel based two-stage cascade model of synaptic transmission using synaptically-driven intracellular activities, to which broadband stimulation conditions were imposed. The first stage of the model represents the pre-synaptic mechanisms and describes the nonlinear dynamical transformation from pre-synaptic spike trains to transmitter vesicle release strengths. The vesicle release strengths were obtained from the intracellularly recorded excitatory post-synaptic currents (EPSCs). The second stage of the model represents the post-synaptic mechanisms and describes the nonlinear dynamical transformation from release strengths to excitatory post-synaptic potentials (EPSPs). One application of this cascade model is to analyze the pre- and post-synaptic mechanism change induced by long-term potentiation (LTP). This future application is expected to shed new light on the expression locus of LTP.
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Affiliation(s)
- Ude Lu
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90089, USA.
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Featherstone DE. Glial solute carrier transporters in Drosophila and mice. Glia 2010; 59:1351-63. [PMID: 21732427 DOI: 10.1002/glia.21085] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Accepted: 09/07/2010] [Indexed: 01/17/2023]
Abstract
Glia regulate brain physiology primarily by regulating the movement and concentration of substances in the extracellular fluid. Therefore, one approach to understanding the role of glia in brain physiology is to study what happens when glial transporters are removed or modified. The largest and most highly conserved class of transporter is solute carrier (SLC) proteins. SLC proteins are highly expressed in brain, and many are found in glia. The function of many SLC proteins in the brain--particularly in glia--is very poorly understood. SLC proteins can be relatively easily knocked out or modified in genetic model organisms to better understand glial function. Drosophila are popular genetic model organisms that offer a nice balance between genetic malleability and brain complexity. They are ideal for such an endeavor. This article lists and discusses SLC transporter family members that are expressed in both mouse and Drosophila glia, in an effort to provide a foundation for studies of glial SLC transporters using Drosophila as a model.
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Affiliation(s)
- David E Featherstone
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA.
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