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Palma-Cerda F, Papageorgiou G, Barbour B, Auger C, Ogden D. Photolysis of a Caged, Fast-Equilibrating Glutamate Receptor Antagonist, MNI-Caged γ-D-Glutamyl-Glycine, to Investigate Transmitter Dynamics and Receptor Properties at Glutamatergic Synapses. Front Cell Neurosci 2019; 12:465. [PMID: 30618624 PMCID: PMC6300705 DOI: 10.3389/fncel.2018.00465] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Accepted: 11/15/2018] [Indexed: 11/29/2022] Open
Abstract
Fast uncaging of low affinity competitive receptor antagonists can in principle measure the timing and concentration dependence of transmitter action at receptors during synaptic transmission. Here, we describe the development, synthesis and characterization of MNI-caged γ-D-glutamyl-glycine (γ-DGG), which combines the fast photolysis and hydrolytic stability of nitroindoline cages with the well-characterized fast-equilibrating competitive glutamate receptor antagonist γ-DGG. At climbing fiber-Purkinje cell (CF-PC) synapses MNI-caged-γ-DGG was applied at concentrations up to 5 mM without affecting CF-PC transmission, permitting release of up to 1.5 mM γ-DGG in 1 ms in wide-field flashlamp photolysis. In steady-state conditions, photoreleased γ-DGG at 0.55–1.7 mM inhibited the CF first and second paired EPSCs by on average 30% and 60%, respectively, similar to reported values for bath applied γ-DGG. Photolysis of the L-isomer MNI-caged γ-L-glutamyl-glycine was ineffective. The time-course of receptor activation by synaptically released glutamate was investigated by timed photolysis of MNI-caged-γ-DGG at defined intervals following CF stimulation in the second EPSCs. Photorelease of γ-DGG prior to the stimulus and up to 3 ms after showed strong inhibition similar to steady-state inhibition; in contrast γ-DGG applied by a flash at 3–4 ms post-stimulus produced weaker and variable block, suggesting transmitter-receptor interaction occurs mainly in this time window. The data also show a small and lasting component of inhibition when γ-DGG was released at 4–7 ms post stimulus, near the peak of the CF-PC EPSC, or at 10–11 ms. This indicates that competition for binding and activation of AMPA receptors occurs also during the late phase of the EPSC, due to either delayed transmitter release or persistence of glutamate in the synaptic region. The results presented here first show that MNI-caged-γ-DGG has properties suitable for use as a synaptic probe at high concentration and that its photolysis can resolve timing and extent of transmitter activation of receptors in glutamatergic transmission.
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Affiliation(s)
| | | | - Boris Barbour
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Ecole Normale Supérieure, CNRS, INSERM, PSL University, Paris, France
| | - Céline Auger
- Brain Physiology Lab, UMR8118 Université Paris Descartes, Paris, France
| | - David Ogden
- Brain Physiology Lab, UMR8118 Université Paris Descartes, Paris, France.,The Francis Crick Institute, London, United Kingdom
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52
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Rothman DL, Dienel GA. Development of a Model to Test Whether Glycogenolysis Can Support Astrocytic Energy Demands of Na +, K +-ATPase and Glutamate-Glutamine Cycling, Sparing an Equivalent Amount of Glucose for Neurons. ADVANCES IN NEUROBIOLOGY 2019; 23:385-433. [PMID: 31667817 DOI: 10.1007/978-3-030-27480-1_14] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Recent studies of glycogen in brain have suggested a much more important role in brain energy metabolism and function than previously recognized, including findings of much higher than previously recognized concentrations, consumption at substantial rates compared with utilization of blood-borne glucose, and involvement in ion pumping and in neurotransmission and memory. However, it remains unclear how glycogenolysis is coupled to neuronal activity and provides support for neuronal as well as astroglial function. At present, quantitative aspects of glycogenolysis in brain functions are very difficult to assess due to its metabolic lability, heterogeneous distributions within and among cells, and extreme sensitivity to physiological stimuli. To begin to address this problem, the present study develops a model based on pathway fluxes, mass balance, and literature relevant to functions and turnover of pathways that intersect with glycogen mobilization. A series of equations is developed to describe the stoichiometric relationships between net glycogen consumption that is predominantly in astrocytes with the rate of the glutamate-glutamine cycle, rates of astrocytic and neuronal glycolytic and oxidative metabolism, and the energetics of sodium/potassium pumping in astrocytes and neurons during brain activation. Literature supporting the assumptions of the model is discussed in detail. The overall conclusion is that astrocyte glycogen metabolism is primarily coupled to neuronal function via fueling glycolytically pumping of Na+ and K+ and sparing glucose for neuronal oxidation, as opposed to previous proposals of coupling neurotransmission via glutamate transport, lactate shuttling, and neuronal oxidation of lactate.
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Affiliation(s)
- Douglas L Rothman
- Magnetic Resonance Research Center and Department of Radiology, Yale University, New Haven, CT, USA.
| | - Gerald A Dienel
- Department of Neurology, University of Arkansas for Medical Sciences, Little Rock, AR, USA.,Department of Cell Biology and Physiology, University of New Mexico, Albuquerque, NM, USA
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53
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Mousavi MPS, Abd El-Rahman MK, Mahmoud AM, Abdelsalam RM, Bühlmann P. In Situ Sensing of the Neurotransmitter Acetylcholine in a Dynamic Range of 1 nM to 1 mM. ACS Sens 2018; 3:2581-2589. [PMID: 30398333 DOI: 10.1021/acssensors.8b00950] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The neurotransmitter acetylcholine (ACh) plays a key role in the pathophysiology of brain disorders such as Alzheimer's disease. Understanding the dynamics of ACh concentration changes and kinetics of ACh degradation in the living brain is crucial to unravel the pathophysiology of such diseases and the rational design of therapeutics. In this work, an electrochemical sensor capable of dynamic, label-free, selective, and in situ detection of ACh in a range of 1 nM to 1 mM (with temporal resolution of less than one second) was developed. The sensor was employed for the direct detection of ACh in artificial cerebrospinal fluid and rat brain homogenate, without any prior separation steps. A potentiometric receptor-doped ion-selective electrode (ISE) with selectivity for ACh was designed by taking advantage of the positive charge of ACh. The dynamic range, limit of detection (LOD), and the selectivity of the sensor were optimized stepwise by (i) screening of hydrophobic biomimetic calixarenes to identify receptors that strongly bind to ACh based on shape-selective multitopic recognition, (ii) doping of the ISE sensing membrane with an ACh-binding hydrophobic calixarene to enable selective detection of ACh in complex matrices, (iii) utilizing a hydrophilic calixarene in the inner filling solution of the ISE to buffer the concentration of ACh and, thereby, lower the LOD of the sensor, and (iv) introducing a surface treatment step prior to the measurement by placing the sensor for ∼1 min in a solution of a hydrophilic calixarene to lower the LOD of the sensor even further.
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Affiliation(s)
- Maral P. S. Mousavi
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | | | | | | | - Philippe Bühlmann
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
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54
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Sanz-Lázaro S, Jiménez-Pompa A, Carmona-Hidalgo B, Ubeda M, Muñoz L, Caba-González JC, Hernández-Vivanco A, López-García S, Albillos A, Albillos A. The firing frequency of spontaneous action potentials and their corresponding evoked exocytosis are increased in chromaffin cells of CCl 4 -induced cirrhotic rats with respect to control rats. J Neurochem 2018; 148:359-372. [PMID: 30347483 DOI: 10.1111/jnc.14618] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 10/09/2018] [Accepted: 10/18/2018] [Indexed: 11/29/2022]
Abstract
High catecolamine plasma levels because of sympathetic nervous system over-activity contribute to cirrhosis progression. The aim of this study was to investigate whether chromaffin cells of the adrenal gland might potentiate the deleterious effect exerted by this over-activity. Electrophysiological patch-clamp and amperometric experiments with carbon-fibre electrodes were conducted in single chromaffin cells of control and CCl4 -induced cirrhotic rats. The spontaneous action potential firing frequency was increased in chromaffin cells of cirrhotic rats with respect to control rats. The exocytosis evoked by that firing was also increased. However, exocytosis elicited by ACh did not vary between control and cirrhotic rats. Exocytosis triggered by depolarizing pulses was also unchanged. Amperometric recordings confirmed the lack of increased catecholamine charge released in cirrhosis after ACh or depolarization stimuli. However, the amperometric spikes exhibited faster kinetics of release. The overall Ca2+ entry through voltage-dependent Ca2+ channels (VDCC), or in particular through Cav1 channels, did not vary between chromaffin cells of control and cirrhotic rats. The inhibition of VDCC by methionine-enkephaline or ATP was not either altered, but it was increased by adrenaline in cells of cirrhotic rats. When a cocktail composed by the three neurotransmitters was tested in order to approach a situation closer to the physiological condition, the inhibition of VDCC was similar between both types of cells. In summary, chromaffin cells of the adrenal gland might contribute to exacerbate the sympathetic nervous system over-activity in cirrhosis because of an increased exocytosis elicited by an enhanced spontaneous electrical activity.
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Affiliation(s)
- Sara Sanz-Lázaro
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Amanda Jiménez-Pompa
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Beatriz Carmona-Hidalgo
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - María Ubeda
- Laboratorio de Enfermedades del Sistema Inmune, Departamento de Medicina, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain.,Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), Instituto de Salud Carlos III, Madrid, Spain
| | - Leticia Muñoz
- Laboratorio de Enfermedades del Sistema Inmune, Departamento de Medicina, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain.,Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), Instituto de Salud Carlos III, Madrid, Spain
| | - Jose Carlos Caba-González
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Alicia Hernández-Vivanco
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Sarai López-García
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
| | - Agustín Albillos
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain.,Laboratorio de Enfermedades del Sistema Inmune, Departamento de Medicina, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain.,Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), Instituto de Salud Carlos III, Madrid, Spain.,Servicio de Gastroenterología y Hepatología, Hospital Universitario Ramón y Cajal, IRYCIS, Madrid, Spain
| | - Almudena Albillos
- Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain
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N-Ethylmaleimide differentiates between the M 2- and M 4-autoreceptor-mediated inhibition of acetylcholine release in the mouse brain. Naunyn Schmiedebergs Arch Pharmacol 2018; 391:1295-1299. [PMID: 30032313 DOI: 10.1007/s00210-018-1539-8] [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: 06/19/2018] [Accepted: 07/13/2018] [Indexed: 10/28/2022]
Abstract
Muscarinic M2 and M4 receptors resemble each other in brain distribution, function, and Gi/o protein signaling. However, there is evidence from human recombinant receptors that the M4 receptor also couples to Gs protein whereas such an alternative signaling is of minor importance for its M2 counterpart. The question arises whether this property is shared by native receptors, e.g., the murine hippocampal M2- and the striatal M4-autoreceptor. To this end, the electrically evoked tritium overflow was studied in mouse hippocampal and striatal slices pre-incubated with 3H-choline. 3H-Acetylcholine release in either region was inhibited by the potent muscarinic receptor agonist iperoxo (pIC50 8.6-8.8) in an atropine-sensitive manner (apparent pA2 8.6-8.8); iperoxo was much more potent than oxotremorine (pIC50 6.5-6.6). In hippocampal slices, N-ethylmaleimide (NEM) 32 μM, which inactivates Gi/o proteins, tended to shift the concentration-response curve of iperoxo (pIC50 8.8) to the right (pIC50 8.5) and depressed its maximum from 85 to 69%. In striatal slices, the inhibitory effect of iperoxo declined at concentrations higher than 0.1 μM, yielding a biphasic curve with a pIC50 of 8.6 for the falling part and a pEC50 of 6.4 for the rising part of the curve. The inhibitory effect of iperoxo 10 μM (47%) after NEM pre-treatment was lower by about 35% compared to the maximum (74%) obtained without NEM. In conclusion, our data, which need to be confirmed by pertussis toxin, might suggest that in the striatum, unlike the hippocampus, stimulatory Gs protein comes into play at high concentrations of a muscarinic receptor agonist.
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56
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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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57
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Shen M, Qu Z, DesLaurier J, Welle TM, Sweedler JV, Chen R. Single Synaptic Observation of Cholinergic Neurotransmission on Living Neurons: Concentration and Dynamics. J Am Chem Soc 2018; 140:7764-7768. [PMID: 29883110 DOI: 10.1021/jacs.8b01989] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Acetylcholine, the first neurotransmitter identified more than a century ago, plays critical roles in human activities and health; however, its synaptic concentration dynamics have remained unknown. Here, we demonstrate the in situ simultaneous measurements of synaptic cholinergic transmitter concentration and release dynamics. We used nanoscale electroanalytical methods: nanoITIES electrode of 15 nm in radius and nanoresolved scanning electrochemical microscopy (SECM). Time-resolved in situ measurements unveiled information on synaptic acetylcholine concentration and release dynamics of living Aplysia neurons. The measuring technique enabled the quantitative sensing of acetylcholine with negligible interference of other ionic and redox-active species. We measured cholinergic transmitter concentrations very close to the synapse, with values as high as 2.4 mM. We observed diverse synaptic transmitter concentration dynamics consisting of singlet, doublet and multiplet events with a signal-to-noise ratio of 6 to 130. The unprecedented details about synaptic neurotransmission unveiled are instrumental for understanding brain communication and diseases in a way distinctive from extra-synaptic studies.
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Affiliation(s)
- Mei Shen
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Matthews Avenue , Urbana , Illinois 61801 , United States
| | - Zizheng Qu
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Matthews Avenue , Urbana , Illinois 61801 , United States
| | - Justin DesLaurier
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Matthews Avenue , Urbana , Illinois 61801 , United States
| | - Theresa M Welle
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Matthews Avenue , Urbana , Illinois 61801 , United States
| | - Jonathan V Sweedler
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Matthews Avenue , Urbana , Illinois 61801 , United States
| | - Ran Chen
- Department of Chemistry , University of Illinois at Urbana-Champaign , 600 South Matthews Avenue , Urbana , Illinois 61801 , United States
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58
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Helassa N, Dürst CD, Coates C, Kerruth S, Arif U, Schulze C, Wiegert JS, Geeves M, Oertner TG, Török K. Ultrafast glutamate sensors resolve high-frequency release at Schaffer collateral synapses. Proc Natl Acad Sci U S A 2018; 115:5594-5599. [PMID: 29735711 PMCID: PMC6003469 DOI: 10.1073/pnas.1720648115] [Citation(s) in RCA: 100] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Glutamatergic synapses display a rich repertoire of plasticity mechanisms on many different time scales, involving dynamic changes in the efficacy of transmitter release as well as changes in the number and function of postsynaptic glutamate receptors. The genetically encoded glutamate sensor iGluSnFR enables visualization of glutamate release from presynaptic terminals at frequencies up to ∼10 Hz. However, to resolve glutamate dynamics during high-frequency bursts, faster indicators are required. Here, we report the development of fast (iGlu f ) and ultrafast (iGlu u ) variants with comparable brightness but increased Kd for glutamate (137 μM and 600 μM, respectively). Compared with iGluSnFR, iGlu u has a sixfold faster dissociation rate in vitro and fivefold faster kinetics in synapses. Fitting a three-state model to kinetic data, we identify the large conformational change after glutamate binding as the rate-limiting step. In rat hippocampal slice culture stimulated at 100 Hz, we find that iGlu u is sufficiently fast to resolve individual glutamate release events, revealing that glutamate is rapidly cleared from the synaptic cleft. Depression of iGlu u responses during 100-Hz trains correlates with depression of postsynaptic EPSPs, indicating that depression during high-frequency stimulation is purely presynaptic in origin. At individual boutons, the recovery from depression could be predicted from the amount of glutamate released on the second pulse (paired pulse facilitation/depression), demonstrating differential frequency-dependent filtering of spike trains at Schaffer collateral boutons.
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Affiliation(s)
- Nordine Helassa
- Molecular and Clinical Sciences Research Institute, St George's, University of London, SW17 0RE London, United Kingdom
| | - Céline D Dürst
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, 20251 Hamburg, Germany
| | - Catherine Coates
- Molecular and Clinical Sciences Research Institute, St George's, University of London, SW17 0RE London, United Kingdom
| | - Silke Kerruth
- Molecular and Clinical Sciences Research Institute, St George's, University of London, SW17 0RE London, United Kingdom
| | - Urwa Arif
- Molecular and Clinical Sciences Research Institute, St George's, University of London, SW17 0RE London, United Kingdom
| | - Christian Schulze
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, 20251 Hamburg, Germany
| | - J Simon Wiegert
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, 20251 Hamburg, Germany
| | - Michael Geeves
- School of Biosciences, University of Kent, CT2 7NZ Canterbury, United Kingdom
| | - Thomas G Oertner
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, 20251 Hamburg, Germany
| | - Katalin Török
- Molecular and Clinical Sciences Research Institute, St George's, University of London, SW17 0RE London, United Kingdom;
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59
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Analytical modelling of temperature effects on an AMPA-type synapse. J Comput Neurosci 2018; 44:379-391. [PMID: 29752691 PMCID: PMC5973960 DOI: 10.1007/s10827-018-0684-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 03/28/2018] [Accepted: 04/09/2018] [Indexed: 01/28/2023]
Abstract
It was previously reported, that temperature may significantly influence neural dynamics on the different levels of brain function. Thus, in computational neuroscience, it would be useful to make models scalable for a wide range of various brain temperatures. However, lack of experimental data and an absence of temperature-dependent analytical models of synaptic conductance does not allow to include temperature effects at the multi-neuron modeling level. In this paper, we propose a first step to deal with this problem: A new analytical model of AMPA-type synaptic conductance, which is able to incorporate temperature effects in low-frequency stimulations. It was constructed based on Markov model description of AMPA receptor kinetics using the set of coupled ODEs. The closed-form solution for the set of differential equations was found using uncoupling assumption (introduced in the paper) with few simplifications motivated both from experimental data and from Monte Carlo simulation of synaptic transmission. The model may be used for computationally efficient and biologically accurate implementation of temperature effects on AMPA receptor conductance in large-scale neural network simulations. As a result, it may open a wide range of new possibilities for researching the influence of temperature on certain aspects of brain functioning.
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60
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Bernareggi A, Ren E, Giniatullin A, Luin E, Sciancalepore M, Giniatullin R, Lorenzon P. Adenosine Promotes Endplate nAChR Channel Activity in Adult Mouse Skeletal Muscle Fibers via Low Affinity P1 Receptors. Neuroscience 2018; 383:1-11. [PMID: 29733889 DOI: 10.1016/j.neuroscience.2018.04.044] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Revised: 04/12/2018] [Accepted: 04/28/2018] [Indexed: 11/26/2022]
Abstract
Adenosine is a powerful modulator of skeletal neuromuscular transmission, operating via inhibitory or facilitatory purinergic-type P1 receptors. To date, studies have been focused mainly on the effect of adenosine on presynaptic P1 receptors controlling transmitter release. In this study, using two-microelectrode voltage-clamp and single-channel patch-clamp recording techniques, we have explored potential postsynaptic targets of adenosine and their modulatory effect on nicotinic acetylcholine receptor (nAChR)-mediated synaptic responses in adult mouse skeletal muscle fibers in vitro. In the whole-mount neuromuscular junction (NMJ) preparation, adenosine (100 μM) significantly reduced the frequency of the miniature endplate currents (MEPCs) and slowed their rising and decay time. Consistent with a postsynaptic site of action, adenosine and the potent P1 receptor agonist NECA significantly increased the open probability, the frequency and the open time of single nAChR channels, recorded at the endplate region. Using specific ligands for the P1 receptor subtypes, we found that the low-affinity P1 receptor subtype A2B was responsible for mediating the effects of adenosine on the nAChR channel openings. Our data suggest that at the adult mammalian NMJ, adenosine acts not only presynaptically to modulate acetylcholine transmitter release, but also at the postsynaptic level, to enhance the activity of nAChRs. Our findings open a new scenario in understanding of purinergic regulation of nAChR activity at the mammalian endplate region.
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Affiliation(s)
- Annalisa Bernareggi
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy.
| | - Elisa Ren
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy
| | | | - Elisa Luin
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy
| | - Marina Sciancalepore
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy
| | - Rashid Giniatullin
- Institute of Fundamental Medicine and Biology, Kazan (Volga Region) Federal University, Kazan, Russia; A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland
| | - Paola Lorenzon
- Department of Life Sciences, University of Trieste, Trieste, Italy; B.R.A.I.N., Centre for Neuroscience, Trieste, Italy
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61
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Stoichiometry of the Heteromeric Nicotinic Receptors of the Renshaw Cell. J Neurosci 2018; 38:4943-4956. [PMID: 29724797 DOI: 10.1523/jneurosci.0070-18.2018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2018] [Revised: 03/21/2018] [Accepted: 03/27/2018] [Indexed: 01/05/2023] Open
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) are pentamers built from a variety of subunits. Some are homomeric assemblies of α subunits, others heteromeric assemblies of α and β subunits which can adopt two stoichiometries (2α:3β or 3α:2β). There is evidence for the presence of heteromeric nAChRs with the two stoichiometries in the CNS, but it has not yet been possible to identify them at a given synapse. The 2α:3β receptors are highly sensitive to agonists, whereas the 3α:2β stoichiometric variants, initially described as low sensitivity receptors, are indeed activated by low and high concentrations of ACh. We have taken advantage of the discovery that two compounds (NS9283 and Zn) potentiate selectively the 3α:2β nAChRs to establish (in mice of either sex) the presence of these variants at the motoneuron-Renshaw cell (MN-RC) synapse. NS9283 prolonged the decay of the two-component EPSC mediated by heteromeric nAChRs. NS9283 and Zn also prolonged spontaneous EPSCs involving heteromeric nAChRs, and one could rule out prolongations resulting from AChE inhibition by NS9283. These results establish the presence of 3α:2β nAChRs at the MN-RC synapse. At the functional level, we had previously explained the duality of the EPSC by assuming that high ACh concentrations in the synaptic cleft account for the fast component and that spillover of ACh accounts for the slow component. The dual ACh sensitivity of 3α:2β nAChRs now allows to attribute to these receptors both components of the EPSC.SIGNIFICANCE STATEMENT Heteromeric nicotinic receptors assemble α and β subunits in pentameric structures, which can adopt two stoichiometries: 3α:2β or 2α:3β. Both stoichiometric variants are present in the CNS, but they have never been located and characterized functionally at the level of an identified synapse. Our data indicate that 3α:2β receptors are present at the spinal cord synapses between motoneurons and Renshaw cells, where their dual mode of activation (by high concentrations of ACh for synaptic receptors, by low concentrations of ACh for extrasynaptic receptors) likely accounts for the biphasic character of the synaptic current. More generally, 3α:2β nicotinic receptors appear unique by their capacity to operate both in the cleft of classical synapses and at extrasynaptic locations.
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Mukhametshina AR, Fedorenko SV, Petrov AM, Zakyrjanova GF, Petrov KA, Nurullin LF, Nizameev IR, Mustafina AR, Sinyashin OG. Targeted Nanoparticles for Selective Marking of Neuromuscular Junctions and ex Vivo Monitoring of Endogenous Acetylcholine Hydrolysis. ACS APPLIED MATERIALS & INTERFACES 2018; 10:14948-14955. [PMID: 29652477 DOI: 10.1021/acsami.8b04471] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The present work for the first time introduces nanosensors for luminescent monitoring of acetylcholinesterase (AChE)-catalyzed hydrolysis of endogenous acetylcholine (ACh) released in neuromuscular junctions of isolated muscles. The sensing function results from the quenching of Tb(III)-centered luminescence due to proton-induced degradation of luminescent Tb(III) complexes doped into silica nanoparticles (SNs, 23 nm), when acetic acid is produced from the enzymatic hydrolysis of ACh. The targeting of the silica nanoparticles by α-bungarotoxin was used for selective staining of the synaptic space in the isolated muscles by the nanosensors. The targeting procedure was optimized for the high sensing sensitivity. The measuring of the Tb(III)-centered luminescence intensity of the targeted SNs by fluorescent microscopy enables us to sense a release of endogenous ACh in neuromuscular junctions of the isolated muscles under their stimulation by a high-frequency train (20 Hz, for 3 min). The ability of the targeted SNs to sense an inhibiting effect of paraoxon on enzymatic activity of AChE in ex vivo conditions provides a way of mimicking external stimuli effects on enzymatic processes in the isolated muscles.
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Affiliation(s)
- Alsu R Mukhametshina
- Arbuzov Institute of Organic and Physical Chemistry , FRC Kazan Scientific Center of RAS , Arbuzov Str. 8 , 420088 Kazan , Russian Federation
| | - Svetlana V Fedorenko
- Arbuzov Institute of Organic and Physical Chemistry , FRC Kazan Scientific Center of RAS , Arbuzov Str. 8 , 420088 Kazan , Russian Federation
| | - Alexey M Petrov
- Kazan State Medial University , Butlerov Str. 49 , 420012 Kazan , Russian Federation
- Kazan Institute of Biochemistry and Biophysics , Federal Research Center "Kazan Scientific Center of RAS" , P.O. Box 30 , 420111 Kazan , Russian Federation
| | - Guzel F Zakyrjanova
- Kazan Institute of Biochemistry and Biophysics , Federal Research Center "Kazan Scientific Center of RAS" , P.O. Box 30 , 420111 Kazan , Russian Federation
| | - Konstantin A Petrov
- Arbuzov Institute of Organic and Physical Chemistry , FRC Kazan Scientific Center of RAS , Arbuzov Str. 8 , 420088 Kazan , Russian Federation
| | - Leniz F Nurullin
- Kazan Institute of Biochemistry and Biophysics , Federal Research Center "Kazan Scientific Center of RAS" , P.O. Box 30 , 420111 Kazan , Russian Federation
| | - Irek R Nizameev
- Arbuzov Institute of Organic and Physical Chemistry , FRC Kazan Scientific Center of RAS , Arbuzov Str. 8 , 420088 Kazan , Russian Federation
| | - Asiya R Mustafina
- Arbuzov Institute of Organic and Physical Chemistry , FRC Kazan Scientific Center of RAS , Arbuzov Str. 8 , 420088 Kazan , Russian Federation
| | - Oleg G Sinyashin
- Arbuzov Institute of Organic and Physical Chemistry , FRC Kazan Scientific Center of RAS , Arbuzov Str. 8 , 420088 Kazan , Russian Federation
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63
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Mohamet L, Jones VC, Dayanithi G, Verkhratsky A. Pathological human astroglia in Alzheimer's disease: opening new horizons with stem cell technology. FUTURE NEUROLOGY 2018. [DOI: 10.2217/fnl-2017-0029] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Pathological remodeling, degeneration and reactivity of astrocytes are fundamental astrogliopathies contributing to all neurological diseases. In neurodegenerative disorders (including Alzheimer's disease [AD]) astroglia undergo complex changes that range from atrophy with loss of function to accumulation of reactive cells around disease-specific lesions (senile plaques in the case of AD). The cellular pathology of astroglia in the context of human AD remains enigmatic; mainly because of the severe limitations of animal models, which, although reproducing some pathological features of the disease, do not mimic its progression in full. Human-induced pluripotent stem cells technology creates a novel and potentially revolutionizing platform for studying fundamental mechanisms of the disease and for screening to identify new therapeutic compounds.
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Affiliation(s)
- Lisa Mohamet
- StrataStem Ltd, Suite 112, 4a Rylands Street, Warrington, WA1 1EN, UK
| | - Vicky C Jones
- School of Pharmacy & Biomedical Sciences, The University of Central Lancashire, Preston PR1 2HE, UK
| | - Govindan Dayanithi
- Centre Nationale de la Recherche Scientifique Institut des Sciences Biologiques (INSB)3, rue Michel-Ange 75794 Paris cedex 16, France
- INSERM U1198, École Pratique des Hautes Études-Sorbonne, Université Montpellier34095 Montpellier, France
- Deptartment of Pharmacology & Toxicology, Faculty of Pharmacy, Charles University in Plzen, alej Svobody 76, 323 00 Plzeň-Czech Republic
| | - Alexei Verkhratsky
- Faculty of Biology, Medicine & Health, The University of Manchester, Manchester, UK
- IKERBASQUE, Basque Foundation for Science, 48011, Bilbao, Spain & Department of Neurosciences, University of the Basque Country UPV/EHU, 48940, Leioa, Spain
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64
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Hoshino K, Hasegawa K, Kamiya H, Morimoto Y. Synapse-specific effects of IL-1β on long-term potentiation in the mouse hippocampus. Biomed Res 2018. [PMID: 28637953 DOI: 10.2220/biomedres.38.183] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Interleukin-1β (IL-1β) is a key molecule in the inflammatory responses elicited during infection and injury. It exerts local effects on synaptic plasticity by binding to IL-1 receptors that are expressed at high levels in the hippocampus. We examined the effects of IL-1β on synaptic plasticity in different hippocampal regions in acute mouse brain slices by measuring long-term potentiation (LTP). IL-1β (1 ng/mL) was applied for 30 min before LTP was induced with high-frequency stimulation (HFS). LTP was significantly impaired by either IL-1β application to the Schaffer collateral-CA1 synapses or the associational/commissural (A/C) fiber-CA3 synapses, which are both dependent on N-methyl-D-aspartate (NMDA) receptor activation. However, mossy fiber-CA3 LTP, which is expressed presynaptically in an NMDA-independent manner, was not impaired by IL-1β. Our results demonstrate that IL-1β exerts variable effects on LTP at different kinds of synapses, indicating that IL-1β has synapse-specific effects on hippocampal synaptic plasticity.
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Affiliation(s)
- Koji Hoshino
- Department of Anesthesiology and Cristical Care Medicine, Hokkaido University Graduate School of medicine.,Department of Neurobiology, Hokkaido University Graduate School of Medicine
| | - Kan Hasegawa
- Department of Anesthesiology and Cristical Care Medicine, Hokkaido University Graduate School of medicine.,Department of Neurobiology, Hokkaido University Graduate School of Medicine
| | - Haruyuki Kamiya
- Department of Neurobiology, Hokkaido University Graduate School of Medicine
| | - Yuji Morimoto
- Department of Anesthesiology and Cristical Care Medicine, Hokkaido University Graduate School of medicine
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65
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Rose CR, Felix L, Zeug A, Dietrich D, Reiner A, Henneberger C. Astroglial Glutamate Signaling and Uptake in the Hippocampus. Front Mol Neurosci 2018; 10:451. [PMID: 29386994 PMCID: PMC5776105 DOI: 10.3389/fnmol.2017.00451] [Citation(s) in RCA: 128] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 12/22/2017] [Indexed: 12/22/2022] Open
Abstract
Astrocytes have long been regarded as essentially unexcitable cells that do not contribute to active signaling and information processing in the brain. Contrary to this classical view, it is now firmly established that astrocytes can specifically respond to glutamate released from neurons. Astrocyte glutamate signaling is initiated upon binding of glutamate to ionotropic and/or metabotropic receptors, which can result in calcium signaling, a major form of glial excitability. Release of so-called gliotransmitters like glutamate, ATP and D-serine from astrocytes in response to activation of glutamate receptors has been demonstrated to modulate various aspects of neuronal function in the hippocampus. In addition to receptors, glutamate binds to high-affinity, sodium-dependent transporters, which results in rapid buffering of synaptically-released glutamate, followed by its removal from the synaptic cleft through uptake into astrocytes. The degree to which astrocytes modulate and control extracellular glutamate levels through glutamate transporters depends on their expression levels and on the ionic driving forces that decrease with ongoing activity. Another major determinant of astrocytic control of glutamate levels could be the precise morphological arrangement of fine perisynaptic processes close to synapses, defining the diffusional distance for glutamate, and the spatial proximity of transporters in relation to the synaptic cleft. In this review, we will present an overview of the mechanisms and physiological role of glutamate-induced ion signaling in astrocytes in the hippocampus as mediated by receptors and transporters. Moreover, we will discuss the relevance of astroglial glutamate uptake for extracellular glutamate homeostasis, focusing on how activity-induced dynamic changes of perisynaptic processes could shape synaptic transmission at glutamatergic synapses.
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Affiliation(s)
- Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Duesseldorf, Duesseldorf, Germany
| | - Lisa Felix
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Duesseldorf, Duesseldorf, Germany
| | - Andre Zeug
- Cellular Neurophysiology, Hannover Medical School, Hannover, Germany
| | - Dirk Dietrich
- Department of Neurosurgery, University of Bonn Medical School, Bonn, Germany
| | - Andreas Reiner
- Cellular Neurobiology, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany
| | - Christian Henneberger
- Institute of Cellular Neurosciences, University of Bonn Medical School, Bonn, Germany.,German Center for Degenerative Diseases (DZNE), Bonn, Germany.,Institute of Neurology, University College London, London, United Kingdom
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66
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Tybrandt K. Exploring the potential of ionic bipolar diodes for chemical neural interfaces. SOFT MATTER 2017; 13:8171-8177. [PMID: 29104986 DOI: 10.1039/c7sm01732d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Technology interfaces which can imitate the chemically specific signaling of nervous tissues are attractive for studying and developing therapies for neurological disorders. As the signaling in nervous tissue is highly spatiotemporal in nature, an interfacing technology should provide local neurotransmitter release in the millisecond range. To obtain such a speed, the neurotransmitters must be stored close to the release point, while avoiding substantial passive leakage. Here we theoretically investigate whether ionic bipolar diodes can be used for this purpose. We find that if a sufficiently large reverse potential is applied, the passive leakage can be suppressed to negligible levels due to the high local electric field within the bipolar diode. The influences of various design parameters are studied to determine the optimal design and operation. Finally, the delivery speed of the component is evaluated using time-dependent simulations, which show that the release of neurotransmitters to physiologically relevant concentrations can be achieved in less than 10 ms. Altogether, the results suggest that ionic bipolar diodes constitute a highly attractive technology for achieving high speed low leakage addressable delivery circuits for neural interfaces.
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Affiliation(s)
- K Tybrandt
- Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, 601 74 Norrköping, Sweden.
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67
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Hartveit E, Zandt BJ, Madsen E, Castilho Á, Mørkve SH, Veruki ML. AMPA receptors at ribbon synapses in the mammalian retina: kinetic models and molecular identity. Brain Struct Funct 2017; 223:769-804. [PMID: 28936725 DOI: 10.1007/s00429-017-1520-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Accepted: 09/10/2017] [Indexed: 10/24/2022]
Abstract
In chemical synapses, neurotransmitter molecules released from presynaptic vesicles activate populations of postsynaptic receptors that vary in functional properties depending on their subunit composition. Differential expression and localization of specific receptor subunits are thought to play fundamental roles in signal processing, but our understanding of how that expression is adapted to the signal processing in individual synapses and microcircuits is limited. At ribbon synapses, glutamate release is independent of action potentials and characterized by a high and rapidly changing rate of release. Adequately translating such presynaptic signals into postsynaptic electrical signals poses a considerable challenge for the receptor channels in these synapses. Here, we investigated the functional properties of AMPA receptors of AII amacrine cells in rat retina that receive input at spatially segregated ribbon synapses from OFF-cone and rod bipolar cells. Using patch-clamp recording from outside-out patches, we measured the concentration dependence of response amplitude and steady-state desensitization, the single-channel conductance and the maximum open probability. The GluA4 subunit seems critical for the functional properties of AMPA receptors in AII amacrines and immunocytochemical labeling suggested that GluA4 is located at synapses made by both OFF-cone bipolar cells and rod bipolar cells. Finally, we used a series of experimental observables to develop kinetic models for AII amacrine AMPA receptors and subsequently used the models to explore the behavior of the receptors and responses generated by glutamate concentration profiles mimicking those occurring in synapses. These models will facilitate future in silico modeling of synaptic signaling and processing in AII amacrine cells.
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Affiliation(s)
- Espen Hartveit
- Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway.
| | - Bas-Jan Zandt
- Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway.,Blue Brain Project, École polytechnique fédérale de Lausanne (EPFL), Geneva, Switzerland
| | - Eirik Madsen
- Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway.,Department of Radiology, Førde Central Hospital, Førde, Norway
| | - Áurea Castilho
- Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway
| | - Svein Harald Mørkve
- Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway.,Department of Neurosurgery, Haukeland University Hospital, Bergen, Norway.,Department of Radiology, Haukeland University Hospital, Bergen, Norway
| | - Margaret Lin Veruki
- Department of Biomedicine, University of Bergen, Jonas Lies vei 91, 5009, Bergen, Norway.
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68
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Mangalath S, Abraham S, Joseph J. pH-Responsive Fluorescence Enhancement in Graphene Oxide-Naphthalimide Nanoconjugates: A Fluorescence Turn-On Sensor for Acetylcholine. Chemistry 2017. [PMID: 28621503 DOI: 10.1002/chem.201702198] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
A pH-sensitive, fluorescence "turn-on" sensor based on a graphene oxide-naphthalimide (GO-NI) nanoconjugate for the detection of acetylcholine (ACh) by monitoring the enzymatic activity of acetylcholinesterase (AChE) in aqueous solution is reported. These nanoconjugates were synthesized by covalently anchoring picolyl-substituted NI derivatives on the GO/reduced GO surface through a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide coupling strategy, and the morphological and photophysical properties were studied in detail. Synergistic effects of π-π interactions between GO and the NI chromophore, and efficient photoinduced electron- and energy-transfer processes, were responsible for the strong quenching of fluorescence of these nanoconjugates, which were perturbed under acidic pH conditions, leading to significant enhancement of fluorescence emission. This nanoconjugate was successfully employed for the efficient sensing of pH changes caused by the enzymatic activity of AChE, thereby demonstrating its utility as a fluorescence turn-on sensor for ACh in the neurophysiological range.
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Affiliation(s)
- Sreejith Mangalath
- Photosciences and Photonics Section, Chemical Sciences, and Technology Division, CSIR-National Institute for, Interdisciplinary Science and Technology, Thiruvananthapuram, 695019, Kerala, India.,Academy of Scientific and Innovative Research (AcSIR), CSIR-NIIST Campus, Thiruvananthapuram, 695019, Kerala, India
| | - Silja Abraham
- Photosciences and Photonics Section, Chemical Sciences, and Technology Division, CSIR-National Institute for, Interdisciplinary Science and Technology, Thiruvananthapuram, 695019, Kerala, India
| | - Joshy Joseph
- Photosciences and Photonics Section, Chemical Sciences, and Technology Division, CSIR-National Institute for, Interdisciplinary Science and Technology, Thiruvananthapuram, 695019, Kerala, India.,Academy of Scientific and Innovative Research (AcSIR), CSIR-NIIST Campus, Thiruvananthapuram, 695019, Kerala, India
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69
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In silico design of novel probes for the atypical opioid receptor MRGPRX2. Nat Chem Biol 2017; 13:529-536. [PMID: 28288109 PMCID: PMC5391270 DOI: 10.1038/nchembio.2334] [Citation(s) in RCA: 207] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 12/22/2016] [Indexed: 12/19/2022]
Abstract
The primate-exclusive MRGPRX2 G protein-coupled receptor (GPCR) has been suggested to modulate pain and itch. Despite putative peptide and small molecule MRGPRX2 agonists, selective nanomolar potency probes have not yet been reported. To identify a MRGPRX2 probe, we first screened 5,695 small molecules and found many opioid compounds activated MRGPRX2, including (−)- and (+)-morphine, hydrocodone, sinomenine, dextromethorphan and the prodynorphin-derived peptides, dynorphin A, dynorphin B, and α- and β-neoendorphin. We used these to select for mutagenesis-validated homology models and docked almost 4 million small molecules. From this docking, we predicted ZINC-3573, which represents a potent MRGPRX2-selective agonist, showing little activity against 315 other GPCRs and 97 representative kinases, and an essentially inactive enantiomer. ZINC-3573 activates endogenous MRGPRX2 in a human mast cell line inducing degranulation and calcium release. MRGPRX2 is a unique atypical opioid-like receptor important for modulating mast cell degranulation, which can now be specifically modulated with ZINC-3573.
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70
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Gupta R, Reneaux M. Role of Heterogeneous Macromolecular Crowding and Geometrical Irregularity at Central Excitatory Synapses in Shaping Synaptic Transmission. PLoS One 2016; 11:e0167505. [PMID: 27907112 PMCID: PMC5131996 DOI: 10.1371/journal.pone.0167505] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 11/15/2016] [Indexed: 01/24/2023] Open
Abstract
Besides the geometrical tortousity due to the extrasynaptic structures, macromolecular crowding and geometrical irregularities constituting the cleft composition at central excitatory synapses has a major and direct role in retarding the glutamate diffusion within the cleft space. However, the cleft composition may not only coarsely reduce the overall diffusivity of the glutamate but may also lead to substantial spatial variation in the diffusivity across the cleft space. Decrease in the overall diffusivity of the glutamate may have straightforward consequences to the glutamate transients in the cleft. However, how spatial variation in the diffusivity may further affect glutamate transients is an intriguing aspect. Therefore, to understand the role of cleft heterogeneity, the present study adopts a novel approach of glutamate diffusion which considers a gamma statistical distribution of the diffusion coefficient of glutamate (Dglut) across the cleft space, such that its moments discernibly capture the dual impacts of the cleft composition, and further applies the framework of superstatistics. The findings reveal a power law behavior in the glutamate transients, akin to the long-range anomalous subdiffusion, which leads to slower decay profile of cleft glutamate at higher intensity of cleft heterogeneity. Moreover, increase in the cleft heterogeneity is seen to eventually cause slower-rising excitatory postsynaptic currents with higher amplitudes, lesser noise, and prolonged duration of charge transfer across the postsynaptic membrane. Further, with regard to the conventional standard diffusion approach, the study suggests that the effective Dglut essentially derives from the median of the Dglut distribution and does not necessarily need to be the mean Dglut. Together, the findings indicate a strong implication of cleft heterogeneity to the metabolically cost-effective tuning of synaptic response during the phenomenon of plasticity at individual synapses and also provide an additional factor of variability in transmission across identical synapses.
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Affiliation(s)
- Rahul Gupta
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi, India 110067
| | - Melissa Reneaux
- School of Computational and Integrative Sciences, Jawaharlal Nehru University, New Delhi, India 110067
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71
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Quinta-Ferreira ME, Sampaio Dos Aidos FDS, Matias CM, Mendes PJ, Dionísio JC, Santos RM, Rosário LM, Quinta-Ferreira RM. Modelling zinc changes at the hippocampal mossy fiber synaptic cleft. J Comput Neurosci 2016; 41:323-337. [PMID: 27696002 DOI: 10.1007/s10827-016-0620-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/11/2016] [Accepted: 08/15/2016] [Indexed: 01/18/2023]
Abstract
Zinc, a transition metal existing in very high concentrations in the hippocampal mossy fibers from CA3 area, is assumed to be co-released with glutamate and to have a neuromodulatory role at the corresponding synapses. The synaptic action of zinc is determined both by the spatiotemporal characteristics of the zinc release process and by the kinetics of zinc binding to sites located in the cleft area, as well as by their concentrations. This work addresses total, free and complexed zinc concentration changes, in an individual synaptic cleft, following single, short and long periods of evoked zinc release. The results estimate the magnitude and time course of the concentrations of zinc complexes, assuming that the dynamics of the release processes are similar to those of glutamate. It is also considered that, for the cleft zinc concentrations used in the model (≤ 1 μM), there is no postsynaptic zinc entry. For this reason, all released zinc ends up being reuptaken in a process that is several orders of magnitude slower than that of release and has thus a much smaller amplitude. The time derivative of the total zinc concentration in the cleft is represented by the difference between two alpha functions, corresponding to the released and uptaken components. These include specific parameters that were chosen assuming zinc and glutamate co-release, with similar time courses. The peak amplitudes of free zinc in the cleft were selected based on previously reported experimental cleft zinc concentration changes evoked by single and multiple stimulation protocols. The results suggest that following a low amount of zinc release, similar to that associated with one or a few stimuli, zinc clearance is mainly mediated by zinc binding to the high-affinity sites on the NMDA receptors and to the low-affinity sites on the highly abundant GLAST glutamate transporters. In the case of higher zinc release brought about by a larger group of stimuli, most zinc binding occurs essentially to the GLAST transporters, having the corresponding zinc complex a maximum concentration that is more than one order of magnitude larger than that for the high and low affinity NMDA sites. The other zinc complexes considered in the model, namely those formed with sites on the AMPA receptors, calcium and KATP channels and with ATP molecules, have much smaller contributions to the synaptic zinc clearance.
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Affiliation(s)
- M E Quinta-Ferreira
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal.
- Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal.
| | - F D S Sampaio Dos Aidos
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal
- CFisUC, Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal
| | - C M Matias
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- UTAD- University of Trás-os-montes and Alto Douro, P-5000-801, Vila Real, Portugal
| | - P J Mendes
- Department of Physics, University of Coimbra, P-3004-516, Coimbra, Portugal
- LIP- Laboratory of Instrumentation and Experimental Particles Physics, P-3004-516, Coimbra, Portugal
| | - J C Dionísio
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Animal Biology, University of Lisbon, P-1749-016, Lisbon, Portugal
| | - R M Santos
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Life Sciences, University of Coimbra, P-3004-516, Coimbra, Portugal
| | - L M Rosário
- CNC- Center for Neuroscience and Cell Biology, University of Coimbra, P-3004-504, Coimbra, Portugal
- Department of Life Sciences, University of Coimbra, P-3004-516, Coimbra, Portugal
| | - R M Quinta-Ferreira
- CIEPQPF - Research Centre of Chemical Process Engineering and Forest Products, Department of Chemical Engineering, University of Coimbra, P-3030-790, Coimbra, Portugal
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72
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Calcium and protons affect the interaction of neurotransmitters and anesthetics with anionic lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2215-2222. [DOI: 10.1016/j.bbamem.2016.06.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Revised: 06/16/2016] [Accepted: 06/22/2016] [Indexed: 01/09/2023]
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73
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Armstrong E, Abarbanel HDI. Model of the songbird nucleus HVC as a network of central pattern generators. J Neurophysiol 2016; 116:2405-2419. [PMID: 27535375 DOI: 10.1152/jn.00438.2016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 08/10/2016] [Indexed: 01/06/2023] Open
Abstract
We propose a functional architecture of the adult songbird nucleus HVC in which the core element is a "functional syllable unit" (FSU). In this model, HVC is organized into FSUs, each of which provides the basis for the production of one syllable in vocalization. Within each FSU, the inhibitory neuron population takes one of two operational states: 1) simultaneous firing wherein all inhibitory neurons fire simultaneously, and 2) competitive firing of the inhibitory neurons. Switching between these basic modes of activity is accomplished via changes in the synaptic strengths among the inhibitory neurons. The inhibitory neurons connect to excitatory projection neurons such that during state 1 the activity of projection neurons is suppressed, while during state 2 patterns of sequential firing of projection neurons can occur. The latter state is stabilized by feedback from the projection to the inhibitory neurons. Song composition for specific species is distinguished by the manner in which different FSUs are functionally connected to each other. Ours is a computational model built with biophysically based neurons. We illustrate that many observations of HVC activity are explained by the dynamics of the proposed population of FSUs, and we identify aspects of the model that are currently testable experimentally. In addition, and standing apart from the core features of an FSU, we propose that the transition between modes may be governed by the biophysical mechanism of neuromodulation.
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Affiliation(s)
- Eve Armstrong
- BioCircuits Institute, University of California, San Diego, La Jolla, California;
| | - Henry D I Abarbanel
- Department of Physics, University of California, San Diego, La Jolla, California; and.,Marine Physical Laboratory (Scripps Institution of Oceanography), University of California, San Diego, La Jolla, California
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74
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Jones PD, Stelzle M. Can Nanofluidic Chemical Release Enable Fast, High Resolution Neurotransmitter-Based Neurostimulation? Front Neurosci 2016; 10:138. [PMID: 27065794 PMCID: PMC4815362 DOI: 10.3389/fnins.2016.00138] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2016] [Accepted: 03/18/2016] [Indexed: 11/13/2022] Open
Abstract
Artificial chemical stimulation could provide improvements over electrical neurostimulation. Physiological neurotransmission between neurons relies on the nanoscale release and propagation of specific chemical signals to spatially-localized receptors. Current knowledge of nanoscale fluid dynamics and nanofluidic technology allows us to envision artificial mechanisms to achieve fast, high resolution neurotransmitter release. Substantial technological development is required to reach this goal. Nanofluidic technology—rather than microfluidic—will be necessary; this should come as no surprise given the nanofluidic nature of neurotransmission. This perspective reviews the state of the art of high resolution electrical neuroprostheses and their anticipated limitations. Chemical release rates from nanopores are compared to rates achieved at synapses and with iontophoresis. A review of microfluidic technology justifies the analysis that microfluidic control of chemical release would be insufficient. Novel nanofluidic mechanisms are discussed, and we propose that hydrophobic gating may allow control of chemical release suitable for mimicking neurotransmission. The limited understanding of hydrophobic gating in artificial nanopores and the challenges of fabrication and large-scale integration of nanofluidic components are emphasized. Development of suitable nanofluidic technology will require dedicated, long-term efforts over many years.
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Nelson MD, Janssen T, York N, Lee KH, Schoofs L, Raizen DM. FRPR-4 Is a G-Protein Coupled Neuropeptide Receptor That Regulates Behavioral Quiescence and Posture in Caenorhabditis elegans. PLoS One 2015; 10:e0142938. [PMID: 26571132 PMCID: PMC4646455 DOI: 10.1371/journal.pone.0142938] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 10/28/2015] [Indexed: 01/09/2023] Open
Abstract
Neuropeptides signal through G-protein coupled receptors (GPCRs) to regulate a broad array of animal behaviors and physiological processes. The Caenorhabditis elegans genome encodes approximately 100 predicted neuropeptide receptor GPCRs, but in vivo roles for only a few have been identified. We describe here a role for the GPCR FRPR-4 in the regulation of behavioral quiescence and locomotive posture. FRPR-4 is activated in cell culture by several neuropeptides with an amidated isoleucine-arginine-phenylalanine (IRF) motif or an amidated valine-arginine-phenylalanine (VRF) motif at their carboxy termini, including those encoded by the gene flp-13. Loss of frpr-4 function results in a minor feeding quiescence defect after heat-induced cellular stress. Overexpression of frpr-4 induces quiescence of locomotion and feeding as well as an exaggerated body bend posture. The exaggerated body bend posture requires the gene flp-13. While frpr-4 is expressed broadly, selective overexpression of frpr-4 in the proprioceptive DVA neurons results in exaggerated body bends that require flp-13 in the ALA neuron. Our results suggest that FLP-13 and other neuropeptides signal through FRPR-4 and other receptors to regulate locomotion posture and behavioral quiescence.
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Affiliation(s)
- Matthew D Nelson
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.,Department of Biology, Saint Joseph's University, Philadelphia, Pennsylvania, United States of America
| | - Tom Janssen
- Functional Genomics and Proteomics lab, University of Leuven, Leuven, Belgium
| | - Neil York
- Department of Biology, Saint Joseph's University, Philadelphia, Pennsylvania, United States of America
| | - Kun He Lee
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Liliane Schoofs
- Functional Genomics and Proteomics lab, University of Leuven, Leuven, Belgium
| | - David M Raizen
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
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76
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Enzyme-linked DNA dendrimer nanosensors for acetylcholine. Sci Rep 2015; 5:14832. [PMID: 26442999 PMCID: PMC4595838 DOI: 10.1038/srep14832] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Accepted: 09/07/2015] [Indexed: 12/17/2022] Open
Abstract
It is currently difficult to measure small dynamics of molecules in the brain with high spatial and temporal resolution while connecting them to the bigger picture of brain function. A step towards understanding the underlying neural networks of the brain is the ability to sense discrete changes of acetylcholine within a synapse. Here we show an efficient method for generating acetylcholine-detecting nanosensors based on DNA dendrimer scaffolds that incorporate butyrylcholinesterase and fluorescein in a nanoscale arrangement. These nanosensors are selective for acetylcholine and reversibly respond to levels of acetylcholine in the neurophysiological range. This DNA dendrimer architecture has the potential to overcome current obstacles to sensing in the synaptic environment, including the nanoscale size constraints of the synapse and the ability to quantify the spatio-temporal fluctuations of neurotransmitter release. By combining the control of nanosensor architecture with the strategic placement of fluorescent reporters and enzymes, this novel nanosensor platform can facilitate the development of new selective imaging tools for neuroscience.
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77
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A Novel Application of Multiscale Entropy in Electroencephalography to Predict the Efficacy of Acetylcholinesterase Inhibitor in Alzheimer's Disease. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2015; 2015:953868. [PMID: 26120358 PMCID: PMC4450304 DOI: 10.1155/2015/953868] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 01/02/2015] [Indexed: 11/30/2022]
Abstract
Alzheimer's disease (AD) is the most common form of dementia. According to one hypothesis, AD is caused by the reduced synthesis of the neurotransmitter acetylcholine. Therefore, acetylcholinesterase (AChE) inhibitors are considered to be an effective therapy. For clinicians, however, AChE inhibitors are not a predictable treatment for individual patients. We aimed to disclose the difference by biosignal processing. In this study, we used multiscale entropy (MSE) analysis, which can disclose the embedded information in different time scales, in electroencephalography (EEG), in an attempt to predict the efficacy of AChE inhibitors. Seventeen newly diagnosed AD patients were enrolled, with an initial minimental state examination (MMSE) score of 18.8 ± 4.5. After 12 months of AChE inhibitor therapy, 7 patients were responsive and 10 patients were nonresponsive. The major difference between these two groups is Slope 2 (MSE6 to 20). The area below the receiver operating characteristic (ROC) curve of Slope 2 is 0.871 (95% CI = 0.69–1). The sensitivity is 85.7% and the specificity is 60%, whereas the cut-off value of Slope 2 is −0.024. Therefore, MSE analysis of EEG signals, especially Slope 2, provides a potential tool for predicting the efficacy of AChE inhibitors prior to therapy.
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78
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Li J, Xue B, Han T, Huang K, Gong L, Ma X, Liu K, Cui S, Zhang M, Kunze W, Liu C. Oxytocin down-regulates mesenteric afferent sensitivity via the enteric OTR/nNOS/NO/KATP pathway in rat. Neurogastroenterol Motil 2015; 27:51-62. [PMID: 25346204 DOI: 10.1111/nmo.12469] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 10/08/2014] [Indexed: 12/21/2022]
Abstract
BACKGROUND Oxytocin plays an analgesic role in modulation of nociception and pain. Most work to date has focused on the central mechanisms of oxytocin analgesia, but little is known about whether peripheral mechanisms are also involved. METHODS The mesenteric afferent discharge was recorded in vitro. The expressions of oxytocin receptor (OTR) and neuronal nitric oxide synthase (nNOS) in longitudinal muscle myenteric plexus (LMMP) was identified by immunofluorescence. KEY RESULTS Oxytocin per se had no effect on the jejunal mesenteric afferent discharge, however, it markedly attenuated the bradykinin- or distention-evoked increase of mesenteric afferent discharge, which was mimiced by the nitric oxide (NO) donor sodium nitroprusside (SNP). Pretreatment of either NOS inhibitor L-NAME or NPLA largely reduced the inhibitory effect of oxytocin on bradykinin-evoked mesenteric afferent discharge. Such effect, to a large extent, was also alleviated by N-and P-type voltage-dependent calcium channel antagonists or KATP blocker glibenclamide. In addition, immunofluorescence studies show strong colocalization of OTR with nNOS in LMMP of the rat jejunum. CONCLUSIONS & INFERENCES Oxytocin down-regulates the mesenteric afferent sensitivity through nNOS-NO-KATP pathway. Our findings may reveal a new peripheral mechanism for oxytocin analgesia.
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Affiliation(s)
- J Li
- Department of Physiology, Shandong Provincial Key Laboratory of Mental Disorders, Shandong University School of Medicine, Jinan, China
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Characterization of a prawn OA/TA receptor in Xenopus oocytes suggests functional selectivity between octopamine and tyramine. PLoS One 2014; 9:e111314. [PMID: 25350749 PMCID: PMC4211885 DOI: 10.1371/journal.pone.0111314] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 09/30/2014] [Indexed: 11/19/2022] Open
Abstract
Here we report the characterization of an octopamine/tyramine (OA/TA or TyrR1) receptor (OA/TAMac) cloned from the freshwater prawn, Macrobrachium rosenbergii, an animal used in the study of agonistic social behavior. The invertebrate OA/TA receptors are seven trans-membrane domain G-protein coupled receptors that are related to vertebrate adrenergic receptors. Behavioral studies in arthropods indicate that octopaminergic signaling systems modulate fight or flight behaviors with octopamine and/or tyramine functioning in a similar way to the adrenalins in vertebrate systems. Despite the importance of octopamine signaling in behavioral studies of decapod crustaceans there are no functional data available for any of their octopamine or tyramine receptors. We expressed OA/TAMac in Xenopus oocytes where agonist-evoked trans-membrane currents were used as readouts of receptor activity. The currents were most effectively evoked by tyramine but were also evoked by octopamine and dopamine. They were effectively blocked by yohimbine. The electrophysiological approach we used enabled the continuous observation of complex dynamics over time. Using voltage steps, we were able to simultaneously resolve two types of endogenous currents that are affected over different time scales. At higher concentrations we observe that octopamine and tyramine can produce different and opposing effects on both of these currents, presumably through the activity of the single expressed receptor type. The pharmacological profile and apparent functional-selectivity are consistent with properties first observed in the OA/TA receptor from the insect Drosophila melanogaster. As the first functional data reported for any crustacean OA/TA receptor, these results suggest that functional-selectivity between tyramine and octopamine is a feature of this receptor type that may be conserved among arthropods.
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80
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Stepanyuk A, Borisyuk A, Belan P. Maximum likelihood estimation of biophysical parameters of synaptic receptors from macroscopic currents. Front Cell Neurosci 2014; 8:303. [PMID: 25324721 PMCID: PMC4183100 DOI: 10.3389/fncel.2014.00303] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 09/09/2014] [Indexed: 11/13/2022] Open
Abstract
Dendritic integration and neuronal firing patterns strongly depend on biophysical properties of synaptic ligand-gated channels. However, precise estimation of biophysical parameters of these channels in their intrinsic environment is complicated and still unresolved problem. Here we describe a novel method based on a maximum likelihood approach that allows to estimate not only the unitary current of synaptic receptor channels but also their multiple conductance levels, kinetic constants, the number of receptors bound with a neurotransmitter, and the peak open probability from experimentally feasible number of postsynaptic currents. The new method also improves the accuracy of evaluation of unitary current as compared to the peak-scaled non-stationary fluctuation analysis, leading to a possibility to precisely estimate this important parameter from a few postsynaptic currents recorded in steady-state conditions. Estimation of unitary current with this method is robust even if postsynaptic currents are generated by receptors having different kinetic parameters, the case when peak-scaled non-stationary fluctuation analysis is not applicable. Thus, with the new method, routinely recorded postsynaptic currents could be used to study the properties of synaptic receptors in their native biochemical environment.
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Affiliation(s)
- Andrey Stepanyuk
- Laboratory of Molecular Biophysics, Bogomoletz Institute of Physiology Kiev, Ukraine ; State Key Laboratory of Molecular and Cellular Biology, Bogomoletz Institute of Physiology Kiev, Ukraine
| | - Anya Borisyuk
- Laboratory of Molecular Biophysics, Bogomoletz Institute of Physiology Kiev, Ukraine ; State Key Laboratory of Molecular and Cellular Biology, Bogomoletz Institute of Physiology Kiev, Ukraine
| | - Pavel Belan
- Laboratory of Molecular Biophysics, Bogomoletz Institute of Physiology Kiev, Ukraine ; State Key Laboratory of Molecular and Cellular Biology, Bogomoletz Institute of Physiology Kiev, Ukraine
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81
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Scimemi A. Plasticity of GABA transporters: an unconventional route to shape inhibitory synaptic transmission. Front Cell Neurosci 2014; 8:128. [PMID: 24860430 PMCID: PMC4026733 DOI: 10.3389/fncel.2014.00128] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Accepted: 04/22/2014] [Indexed: 11/13/2022] Open
Abstract
The brain relies on GABAergic neurons to control the ongoing activity of neuronal networks. GABAergic neurons control the firing pattern of excitatory cells, the temporal structure of membrane potential oscillations and the time window for integration of synaptic inputs. These actions require a fine control of the timing of GABA receptor activation which, in turn, depends on the precise timing of GABA release from pre-synaptic terminals and GABA clearance from the extracellular space. Extracellular GABA is not subject to enzymatic breakdown, and its clearance relies entirely on diffusion and uptake by specific transporters. In contrast to glutamate transporters, GABA transporters are abundantly expressed in neuronal pre-synaptic terminals. GABA transporters move laterally within the plasma membrane and are continuously trafficked to/from intracellular compartments. It is hypothesized that due to their proximity to GABA release sites, changes in the concentration and lateral mobility of GABA transporters may have a significant effect on the time course of the GABA concentration profile in and out of the synaptic cleft. To date, this hypothesis remains to be tested. Here we use 3D Monte Carlo reaction-diffusion simulations to analyze how changes in the density of expression and lateral mobility of GABA transporters in the cell membrane affect the extracellular GABA concentration profile and the activation of GABA receptors. Our results indicate that these manipulations mainly alter the GABA concentration profile away from the synaptic cleft. These findings provide novel insights into how the ability of GABA transporters to undergo plastic changes may alter the strength of GABAergic signals and the activity of neuronal networks in the brain.
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82
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Karpinsky-Semper D, Volmar CH, Brothers SP, Slepak VZ. Differential effects of the Gβ5-RGS7 complex on muscarinic M3 receptor-induced Ca2+ influx and release. Mol Pharmacol 2014; 85:758-68. [PMID: 24586057 DOI: 10.1124/mol.114.091843] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The G protein β subunit Gβ5 uniquely forms heterodimers with R7 family regulators of G protein signaling (RGS) proteins (RGS6, RGS7, RGS9, and RGS11) instead of Gγ. Although the Gβ5-RGS7 complex attenuates Ca(2+) signaling mediated by the muscarinic M3 receptor (M3R), the route of Ca(2+) entry (i.e., release from intracellular stores and/or influx across the plasma membrane) is unknown. Here, we show that, in addition to suppressing carbachol-stimulated Ca(2+) release, Gβ5-RGS7 enhanced Ca(2+) influx. This novel effect of Gβ5-RGS7 was blocked by nifedipine and 2-aminoethoxydiphenyl borate. Experiments with pertussis toxin, an RGS domain-deficient mutant of RGS7, and UBO-QIC {L-threonine,(3R)-N-acetyl-3-hydroxy-L-leucyl-(aR)-a-hydroxybenzenepropanoyl-2,3-idehydro-N-methylalanyl-L-alanyl-N-methyl-L-alanyl-(3R)-3-[[(2S,3R)-3-hydroxy-4- methyl-1-oxo-2-[(1-oxopropyl)amino]pentyl]oxy]-L-leucyl-N,O-dimethyl-,(7→1)-lactone (9CI)}, a novel inhibitor of Gq, showed that Gβ5-RGS7 modulated a Gq-mediated pathway. These studies indicate that Gβ5-RGS7, independent of RGS7 GTPase-accelerating protein activity, couples M3R to a nifedipine-sensitive Ca(2+) channel. We also compared the action of Gβ5-RGS7 on M3R-induced Ca(2+) influx and release elicited by different muscarinic agonists. Responses to Oxo-M [oxotremorine methiodide N,N,N,-trimethyl-4-(2-oxo-1-pyrrolidinyl)-2-butyn-1-ammonium iodide] were insensitive to Gβ5-RGS7. Pilocarpine responses consisted of a large release and modest influx components, of which the former was strongly inhibited whereas the latter was insensitive to Gβ5-RGS7. McN-A-343 [(4-hydroxy-2-butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride] was the only compound whose total Ca(2+) response was enhanced by Gβ5-RGS7, attributed to, in part, by the relatively small Ca(2+) release this partial agonist stimulated. Together, these results show that distinct agonists not only have differential M3R functional selectivity, but also confer specific sensitivity to the Gβ5-RGS7 complex.
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Affiliation(s)
- Darla Karpinsky-Semper
- Department of Molecular and Cellular Pharmacology (D.K.-S., V.Z.S.) and Center for Therapeutic Innovation, Department of Psychiatry and Behavioral Sciences (C.-H.V., S.P.B.), University of Miami Miller School of Medicine, Miami, Florida
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83
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Subunit composition and kinetics of the Renshaw cell heteromeric nicotinic receptors. Biochem Pharmacol 2013; 86:1114-21. [DOI: 10.1016/j.bcp.2013.06.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Revised: 06/12/2013] [Accepted: 06/16/2013] [Indexed: 11/24/2022]
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84
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Physiological concentrations of zinc reduce taurine-activated GlyR responses to drugs of abuse. Neuropharmacology 2013; 75:286-94. [PMID: 23973295 DOI: 10.1016/j.neuropharm.2013.07.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Revised: 07/26/2013] [Accepted: 07/29/2013] [Indexed: 02/07/2023]
Abstract
Taurine is an endogenous ligand acting on glycine receptors in many brain regions, including the hippocampus, prefrontal cortex, and nucleus accumbens (nAcc). These areas also contain low concentrations of zinc, which is known to potentiate glycine receptor responses. Despite an increasing awareness of the role of the glycine receptor in the rewarding properties of drugs of abuse, the possible interactions of these compounds with zinc has not been thoroughly addressed. Two-electrode voltage-clamp electrophysiological experiments were performed on α1, α2 α1β and α2β glycine receptors expressed in Xenopus laevis oocytes. The effects of zinc alone, and zinc in combination with other positive modulators on the glycine receptor, were investigated when activated by the full agonist glycine versus the partial agonist taurine. Low concentrations of zinc enhanced responses of maximally-effective concentrations of taurine but not glycine. Likewise, chelation of zinc from buffers decreased responses of taurine- but not glycine-mediated currents. Potentiating concentrations of zinc decreased ethanol, isoflurane, and toluene enhancement of maximal taurine currents with no effects on maximal glycine currents. Our findings suggest that the concurrence of high concentrations of taurine and low concentrations of zinc attenuate the effects of additional modulators on the glycine receptor, and that these conditions are more representative of in vivo functioning than effects seen when these modulators are applied in isolation.
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85
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Kessler JP. Control of cleft glutamate concentration and glutamate spill-out by perisynaptic glia: uptake and diffusion barriers. PLoS One 2013; 8:e70791. [PMID: 23951010 PMCID: PMC3741295 DOI: 10.1371/journal.pone.0070791] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Accepted: 06/25/2013] [Indexed: 01/17/2023] Open
Abstract
Most glutamatergic synapses in the mammalian central nervous system are covered by thin astroglial processes that exert a dual action on synaptically released glutamate: they form physical barriers that oppose diffusion and they carry specific transporters that remove glutamate from the extracellular space. The present study was undertaken to investigate the dual action of glia by means of computer simulation. A realistic synapse model based on electron microscope data and Monte Carlo algorithms were used for this purpose. Results show (1) that physical obstacles formed by glial processes delay glutamate exit from the cleft and (2) that this effect is efficiently counteracted by glutamate uptake. Thus, depending on transporter densities, the presence of perisynaptic glia may result in increased or decreased glutamate transient in the synaptic cleft. Changes in temporal profiles of cleft glutamate concentration induced by glia differentially impact the response of the various synaptic and perisynaptic receptor subtypes. In particular, GluN2B- and GluN2C-NMDA receptor responses are strongly modified while GluN2A-NMDA receptor responses are almost unaffected. Thus, variations in glial transporter expression may allow differential tuning of NMDA receptors according to their subunit composition. In addition, simulation data suggest that the sink effect generated by transporters accumulation in the vicinity of the release site is the main mechanism limiting glutamate spill-out. Physical obstacles formed by glial processes play a comparatively minor role.
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86
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Goyal RK, Chaudhury A. Structure activity relationship of synaptic and junctional neurotransmission. Auton Neurosci 2013; 176:11-31. [PMID: 23535140 PMCID: PMC3677731 DOI: 10.1016/j.autneu.2013.02.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2009] [Revised: 12/28/2012] [Accepted: 02/18/2013] [Indexed: 12/18/2022]
Abstract
Chemical neurotransmission may include transmission to local or remote sites. Locally, contact between 'bare' portions of the bulbous nerve terminal termed a varicosity and the effector cell may be in the form of either synapse or non-synaptic contact. Traditionally, all local transmissions between nerves and effector cells are considered synaptic in nature. This is particularly true for communication between neurons. However, communication between nerves and other effectors such as smooth muscles has been described as nonsynaptic or junctional in nature. Nonsynaptic neurotransmission is now also increasingly recognized in the CNS. This review focuses on the relationship between structure and function that orchestrate synaptic and junctional neurotransmissions. A synapse is a specialized focal contact between the presynaptic active zone capable of ultrafast release of soluble transmitters and the postsynaptic density that cluster ionotropic receptors. The presynaptic and the postsynaptic areas are separated by the 'closed' synaptic cavity. The physiological hallmark of the synapse is ultrafast postsynaptic potentials lasting milliseconds. In contrast, junctions are juxtapositions of nerve terminals and the effector cells without clear synaptic specializations and the junctional space is 'open' to the extracellular space. Based on the nature of the transmitters, postjunctional receptors and their separation from the release sites, the junctions can be divided into 'close' and 'wide' junctions. Functionally, the 'close' and the 'wide' junctions can be distinguished by postjunctional potentials lasting ~1s and tens of seconds, respectively. Both synaptic and junctional communications are common between neurons; however, junctional transmission is the rule at many neuro-non-neural effectors.
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Affiliation(s)
- Raj K Goyal
- Center for Swallowing and Motility Disorders, GI Division, VA Boston Healthcare System and Harvard Medical School, Boston, USA.
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87
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Alabi AA, Tsien RW. Perspectives on Kiss-and-Run: Role in Exocytosis, Endocytosis, and Neurotransmission. Annu Rev Physiol 2013; 75:393-422. [DOI: 10.1146/annurev-physiol-020911-153305] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- AbdulRasheed A. Alabi
- Department of Molecular and Cellular Physiology, Stanford Institute for Neuro-Innovation and Translational Neurosciences, Stanford Medical School, Stanford, California 94305;
| | - Richard W. Tsien
- Department of Physiology and Neuroscience, Center for Neural Science, NYU Neuroscience Institute, New York University, New York, NY 10016;
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Budisantoso T, Harada H, Kamasawa N, Fukazawa Y, Shigemoto R, Matsui K. Evaluation of glutamate concentration transient in the synaptic cleft of the rat calyx of Held. J Physiol 2012; 591:219-39. [PMID: 23070699 DOI: 10.1113/jphysiol.2012.241398] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Establishing the spatiotemporal concentration profile of neurotransmitter following synaptic vesicular release is essential for our understanding of inter-neuronal communication. Such profile is a determinant of synaptic strength, short-term plasticity and inter-synaptic crosstalk. Synaptically released glutamate has been suggested to reach a few millimolar in concentration and last for <1 ms. The synaptic cleft is often conceived as a single concentration compartment, whereas a huge gradient likely exists. Modelling studies have attempted to describe this gradient, but two key parameters, the number of glutamate in a vesicle (N(Glu)) and its diffusion coefficient (D(Glu)) in the extracellular space, remained unresolved. To determine this profile, the rat calyx of Held synapse at postnatal day 12-16 was studied where diffusion of glutamate occurs two-dimensionally and where quantification of AMPA receptor distribution on individual postsynaptic specialization on medial nucleus of the trapezoid body principal cells is possible using SDS-digested freeze-fracture replica labelling. To assess the performance of these receptors as glutamate sensors, a kinetic model of the receptors was constructed from outside-out patch recordings. From here, we simulated synaptic responses and compared them with the EPSC recordings. Combinations of N(Glu) and D(Glu) with an optimum of 7000 and 0.3 μm(2) ms(-1) reproduced the data, suggesting slow diffusion. Further simulations showed that a single vesicle does not saturate the synaptic receptors, and that glutamate spillover does not affect the conductance amplitude at this synapse. Using the estimated profile, we also evaluated how the number of multiple vesicle releases at individual active zones affects the amplitude of postsynaptic signals.
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Affiliation(s)
- Timotheus Budisantoso
- Division of Cerebral Structure, National Institute for Physiological Sciences, Okazaki 444-8787, Japan
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89
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The density of EAAC1 (EAAT3) glutamate transporters expressed by neurons in the mammalian CNS. J Neurosci 2012; 32:6000-13. [PMID: 22539860 DOI: 10.1523/jneurosci.5347-11.2012] [Citation(s) in RCA: 158] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The extracellular levels of excitatory amino acids are kept low by the action of the glutamate transporters. Glutamate/aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1) are the most abundant subtypes and are essential for the functioning of the mammalian CNS, but the contribution of the EAAC1 subtype in the clearance of synaptic glutamate has remained controversial, because the density of this transporter in different tissues has not been determined. We used purified EAAC1 protein as a standard during immunoblotting to measure the concentration of EAAC1 in different CNS regions. The highest EAAC1 levels were found in the young adult rat hippocampus. Here, the concentration of EAAC1 was ∼0.013 mg/g tissue (∼130 molecules μm⁻³), 100 times lower than that of GLT-1. Unlike GLT-1 expression, which increases in parallel with circuit formation, only minor changes in the concentration of EAAC1 were observed from E18 to adulthood. In hippocampal slices, photolysis of MNI-D-aspartate (4-methoxy-7-nitroindolinyl-D-aspartate) failed to elicit EAAC1-mediated transporter currents in CA1 pyramidal neurons, and D-aspartate uptake was not detected electron microscopically in spines. Using EAAC1 knock-out mice as negative controls to establish antibody specificity, we show that these relatively small amounts of EAAC1 protein are widely distributed in somata and dendrites of all hippocampal neurons. These findings raise new questions about how so few transporters can influence the activation of NMDA receptors at excitatory synapses.
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90
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Stepanyuk AR, Borisyuk AL, Belan PV. Efficient maximum likelihood estimation of kinetic rate constants from macroscopic currents. PLoS One 2012; 6:e29731. [PMID: 22242142 PMCID: PMC3248447 DOI: 10.1371/journal.pone.0029731] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2011] [Accepted: 12/03/2011] [Indexed: 01/24/2023] Open
Abstract
A new method is described that accurately estimates kinetic constants, conductance and number of ion channels from macroscopic currents. The method uses both the time course and the strength of correlations between different time points of macroscopic currents and utilizes the property of semiseparability of covariance matrix for computationally efficient estimation of current likelihood and its gradient. The number of calculation steps scales linearly with the number of channel states as opposed to the cubic dependence in a previously described method. Together with the likelihood gradient evaluation, which is almost independent of the number of model parameters, the new approach allows evaluation of kinetic models with very complex topologies. We demonstrate applicability of the method to analysis of synaptic currents by estimating accurately rate constants of a 7-state model used to simulate GABAergic macroscopic currents.
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Affiliation(s)
- Andrey R. Stepanyuk
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
| | - Anya L. Borisyuk
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
| | - Pavel V. Belan
- Bogomoletz Institute of Physiology, Kiev, Ukraine
- State Key Laboratory of Molecular and Cellular Biology, Kiev, Ukraine
- * E-mail:
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Barberis A, Petrini EM, Mozrzymas JW. Impact of synaptic neurotransmitter concentration time course on the kinetics and pharmacological modulation of inhibitory synaptic currents. Front Cell Neurosci 2011; 5:6. [PMID: 21734864 PMCID: PMC3123770 DOI: 10.3389/fncel.2011.00006] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Accepted: 06/05/2011] [Indexed: 12/26/2022] Open
Abstract
The time course of synaptic currents is a crucial determinant of rapid signaling between neurons. Traditionally, the mechanisms underlying the shape of synaptic signals are classified as pre- and post-synaptic. Over the last two decades, an extensive body of evidence indicated that synaptic signals are critically shaped by the neurotransmitter time course which encompasses several phenomena including pre- and post-synaptic ones. The agonist transient depends on neurotransmitter release mechanisms, diffusion within the synaptic cleft, spill-over to the extra-synaptic space, uptake, and binding to post-synaptic receptors. Most estimates indicate that the neurotransmitter transient is very brief, lasting between one hundred up to several hundreds of microseconds, implying that post-synaptic activation is characterized by a high degree of non-equilibrium. Moreover, pharmacological studies provide evidence that the kinetics of agonist transient plays a crucial role in setting the susceptibility of synaptic currents to modulation by a variety of compounds of physiological or clinical relevance. More recently, the role of the neurotransmitter time course has been emphasized by studies carried out on brain slice models that revealed a striking, cell-dependent variability of synaptic agonist waveforms ranging from rapid pulses to slow volume transmission. In the present paper we review the advances on studies addressing the impact of synaptic neurotransmitter transient on kinetics and pharmacological modulation of synaptic currents at inhibitory synapses.
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Affiliation(s)
- Andrea Barberis
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology Genova, Italy
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Ribrault C, Sekimoto K, Triller A. From the stochasticity of molecular processes to the variability of synaptic transmission. Nat Rev Neurosci 2011; 12:375-87. [PMID: 21685931 DOI: 10.1038/nrn3025] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The variability of the postsynaptic response following a single action potential arises from two sources: the neurotransmitter release is probabilistic, and the postsynaptic response to neurotransmitter release has variable timing and amplitude. At individual synapses, the number of molecules of a given type that are involved in these processes is small enough that the stochastic (random) properties of molecular events cannot be neglected. How the stochasticity of molecular processes contributes to the variability of synaptic transmission, its sensitivity and its robustness to molecular fluctuations has important implications for our understanding of the mechanistic basis of synaptic transmission and of synaptic plasticity.
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Affiliation(s)
- Claire Ribrault
- Laboratoire Matières et Systèmes Complexes, CNRS-UMR7057, Université Paris 7, F-75205 Paris cedex 13, France
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Gundelfinger ED, Frischknecht R, Choquet D, Heine M. Converting juvenile into adult plasticity: a role for the brain’s extracellular matrix. Eur J Neurosci 2010; 31:2156-65. [DOI: 10.1111/j.1460-9568.2010.07253.x] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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