scholarly journals Ultrafast glutamate sensors resolve high-frequency release at Schaffer collateral synapses

2017 ◽  
Author(s):  
Nordine Helassa ◽  
Céline D. Dürst ◽  
Catherine Coates ◽  
Silke Kerruth ◽  
Urwa Arif ◽  
...  
Keyword(s):  
Glutamate Receptors ◽  
High Frequency ◽  
Glutamate Release ◽  
Synaptic Cleft ◽  
Spike Trains ◽  
Slice Culture ◽  
Schaffer Collateral ◽  
Paired Pulse ◽  
Paired Pulse Facilitation ◽  
Hippocampal Slice Culture

ABSTRACTGlutamatergic 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 (iGluf) and ultrafast (iGluu) variants with comparable brightness, but increased Kd for glutamate (137 μM and 600 μM, respectively). Compared to iGluSnFR, iGluu has a 6-fold faster dissociation rate in vitro and 5-fold 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 iGluu is sufficiently fast to resolve individual glutamate release events, revealing that glutamate is rapidly cleared from the synaptic cleft. Depression of iGluu 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.Significance StatementExcitatory synapses convert presynaptic action potentials into chemical signals that are sensed by postsynaptic glutamate receptors. To eavesdrop on synaptic transmission, genetically encoded fluorescent sensors for glutamate have been developed. However, even the best available sensors lag behind the very fast glutamate dynamics in the synaptic cleft. Here we report the development of an ultrafast genetically encoded glutamate sensor, iGluu, which allowed us to image glutamate clearance and synaptic depression during 100 Hz spike trains. We found that only boutons showing paired-pulse facilitation were able to rapidly recover from depression. Thus, presynaptic boutons act as frequency-specific filters to transmit select features of the spike train to specific postsynaptic cells.

scholarly journals Ultrafast glutamate sensors resolve high-frequency release at Schaffer collateral synapses

2018 ◽  
Vol 115 (21) ◽  
pp. 5594-5599 ◽  
Author(s):  
Nordine Helassa ◽  
Céline D. Dürst ◽  
Catherine Coates ◽  
Silke Kerruth ◽  
Urwa Arif ◽  
...  
Keyword(s):  
High Frequency ◽  
Glutamate Release ◽  
Synaptic Cleft ◽  
Dissociation Rate ◽  
High Frequency Stimulation ◽  
Slice Culture ◽  
Schaffer Collateral ◽  
Hippocampal Slice Culture ◽  
Large Conformational Change

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 (iGluf) and ultrafast (iGluu) variants with comparable brightness but increased Kd for glutamate (137 μM and 600 μM, respectively). Compared with iGluSnFR, iGluu 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 iGluu is sufficiently fast to resolve individual glutamate release events, revealing that glutamate is rapidly cleared from the synaptic cleft. Depression of iGluu 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.

Volatile Anesthetics Depress Glutamate Transmission Via Presynaptic Actions

1996 ◽  
Vol 85 (4) ◽  
pp. 823-834 ◽  
Author(s):  
Bruce M. MacIver ◽  
Anthony A. Mikulec ◽  
Shanti M. Amagasu ◽  
Frances A. Monroe
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Minimum Alveolar Concentration ◽  
Glutamate Release ◽  
Volatile Anesthetics ◽  
Excitatory Postsynaptic Potential ◽  
Dependent Manner ◽  
Paired Pulse ◽  
Paired Pulse Facilitation ◽  
Sites Of Action

Background Recent evidence for a presynaptic depression of glutamate release produced by volatile anesthetics prompted the current study of isoflurane and halothane effects on glutamate-mediated transmission in the mammalian central nervous system. Methods Electrophysiologic recordings from CA1 neurons in rat hippocampal brain slices were used to measure anesthetic effects on glutamate-mediated excitatory postsynaptic potential (EPSP) amplitudes and paired pulse facilitation. Paired pulse facilitation is known to be altered when the calcium-dependent release of glutamate is depressed, but not when EPSP amplitudes are depressed by postsynaptic mechanisms. Results Isoflurane depressed EPSP amplitudes over a concentration range of 0.35-2.8 vol %, with a 50% depression (EC50) occurring at 1.0 vol % (0.71 rat minimum alveolar concentration). This depression was accompanied by an increase in paired-pulse facilitation of approximately 30% at 1.7 vol %, using interpulse intervals of 120 ms. Halothane depressed EPSP amplitudes in a concentration-dependent manner (0.3-2.4 vol %, EC50 = 1.1 minimum alveolar concentration; 1.3 vol %) and also increased facilitation by approximately 20% at 1.2 vol %. These effects persisted in the presence of 10 microM bicuculline, indicating that enhanced gamma-aminobutyric acid-mediated inhibition was not involved. The anesthetic-induced increase in facilitation and EPSP depression was mimicked by lowering extracellular calcium, which is known to depress glutamate release at these synapses. The postsynaptic glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione depressed EPSP amplitudes with no change in facilitation. Conclusions Our results confirm earlier findings that clinically relevant concentrations of volatile anesthetics depress glutamate-mediated synaptic transmission. The observed increases in synaptic facilitation support recent findings from biochemical and electrophysiologic studies indicating presynaptic sites of action contribute to anesthetic-induced depression of excitatory transmission. This anesthetic-induced reduction in glutamate release would contribute to the central nervous system depression associated with anesthesia by adding to postsynaptic depressant actions on glutamate receptors.

scholarly journals Paired-pulse facilitation at recurrent Purkinje neuron synapses is independent of calbindin and parvalbumin during high-frequency activation

2013 ◽  
Vol 591 (13) ◽  
pp. 3355-3370 ◽  
Author(s):  
Grit Bornschein ◽  
Oliver Arendt ◽  
Stefan Hallermann ◽  
Simone Brachtendorf ◽  
Jens Eilers ◽  
...  
Keyword(s):  
High Frequency ◽  
Purkinje Neuron ◽  
Paired Pulse ◽  
Paired Pulse Facilitation

Frequency-dependent depression of excitatory synaptic transmission is independent of activation of MCPG-sensitive presynaptic metabotropic glutamate receptors in cultured hippocampal neurons

1995 ◽  
Vol 74 (4) ◽  
pp. 1671-1674 ◽  
Author(s):  
R. Maki ◽  
D. D. Cummings ◽  
M. A. Dichter
Keyword(s):  
Glutamate Receptors ◽  
High Frequency ◽  
Hippocampal Neurons ◽  
Metabotropic Glutamate Receptors ◽  
Frequency Dependent ◽  
Paired Pulse ◽  
Metabotropic Glutamate ◽  
Whole Cell Patch Clamp ◽  
Mglur Antagonist ◽  
Cultured Hippocampal Neurons

1. A paired-pulse paradigm, and a high-frequency train followed by a test pulse, were used to investigate the possible role of presynaptic metabotropic glutamate receptors (mGluRs) in frequency-dependent modulation of the amplitude of excitatory post-synaptic currents (EPSCs). Paired whole cell patch-clamp recordings from monosynaptically connected hippocampal neurons maintained in very low-density cultures were performed, using the mGluR antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG, 500 microM) and the mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD, 100 microM]. 2. Paired-pulse depression (PPD) was observed in all the excitatory pairs recorded. The average PPD ratio (amplitude of the 2nd EPSC divided by the amplitude of the 1st EPSC) was 0.80 +/- 0.1 (SD) (n = 8). Application of the mGluR antagonist MCPG had no effect on the amplitude of the EPSCs and did not affect the ratio of the two EPSCs (PPD ratio 0.79 +/- 0.2). 3. The amplitudes of 10 successive EPSCs stimulated at a high frequency (20 Hz) decremented on average in both 4 mM extracellular Ca2+ (n = 5) and in 1 mM extracellular Ca2+ (n = 6). In all pairs tested, posttetanic depression (PTD) was observed (PTD ratio 0.7 +/- 0.2). Bath application of MCPG (500 microM) did not affect the amplitudes of the EPSCs during the train; MCPG also did not affect PTD. 4. The mGluR agonist (1S,3R)-ACPD depressed the amplitudes of the EPSCs in both the paired-pulse (1st EPSC, 35 +/- 9%; 2nd EPSC, 36 +/- 10%) and posttetanic pulse (1 and 4 mM extracellular Ca2+) paradigms. The amount of depression observed, both PPD and PTD, remained unaffected by application of (1S,3R)-ACPD. Coapplication of the antagonist MCPG (500 microM) blocked the effects of (1S,3R)-ACPD (100 microM). 5. We conclude that frequency-dependent depression of EPSC amplitudes occurs independent of endogenous activation of MCPG-sensitive mGluRs in cultured hippocampal neurons. Moreover, we demonstrate that exogenous activation of mGluRs by the agonist (1S,3R)-ACPD can produce additional EPSC depression above that already present due to frequency-dependent mechanisms.

scholarly journals The G Protein-Coupled Glutamate Receptors as Novel Molecular Targets in Schizophrenia Treatment—A Narrative Review

2021 ◽  
Vol 10 (7) ◽  
pp. 1475
Author(s):  
Waldemar Kryszkowski ◽  
Tomasz Boczek
Keyword(s):  
Glutamate Receptors ◽  
Metabotropic Glutamate Receptors ◽  
Glutamate Release ◽  
Molecular Targets ◽  
Brain Regions ◽  
Psychotic Symptoms ◽  
Unknown Etiology ◽  
Metabotropic Glutamate ◽  
G Protein Coupled

Schizophrenia is a severe neuropsychiatric disease with an unknown etiology. The research into the neurobiology of this disease led to several models aimed at explaining the link between perturbations in brain function and the manifestation of psychotic symptoms. The glutamatergic hypothesis postulates that disrupted glutamate neurotransmission may mediate cognitive and psychosocial impairments by affecting the connections between the cortex and the thalamus. In this regard, the greatest attention has been given to ionotropic NMDA receptor hypofunction. However, converging data indicates metabotropic glutamate receptors as crucial for cognitive and psychomotor function. The distribution of these receptors in the brain regions related to schizophrenia and their regulatory role in glutamate release make them promising molecular targets for novel antipsychotics. This article reviews the progress in the research on the role of metabotropic glutamate receptors in schizophrenia etiopathology.

Paired-pulse facilitation in the dentate gyrus: a patch-clamp study in rat hippocampus in vitro

1994 ◽  
Vol 72 (1) ◽  
pp. 326-336 ◽  
Author(s):  
M. Andreasen ◽  
J. J. Hablitz
Keyword(s):  
Patch Clamp ◽  
Dentate Gyrus ◽  
Time Constant ◽  
Rise Time ◽  
Time Course ◽  
Nmda Antagonist ◽  
Paired Pulse ◽  
Stimulation Intensity ◽  
Paired Pulse Facilitation ◽  
Epsc Amplitude

1. Whole-cell patch-clamp recordings were used to study paired-pulse facilitation (PPF) of the lateral perforant path input to the dentate gyrus in thin hippocampal slices. 2. Orthodromic stimulation of the lateral perforant pathway evoked a excitatory postsynaptic current (EPSC) with a latency of 3.3 +/- 0.1 ms (mean +/- SE) that fluctuated in amplitude. The EPSC had a rise time (10-90%) of 2.79 +/- 0.06 ms (n = 35) and decayed with a single exponential time course with a time-constant of 9.14 +/- 0.24 ms (n = 35). No correlation was found between the amplitude of the EPSC and the rise time or decay time-constant. The non-N-methyl-D-aspartate (NMDA) antagonist 6-cyano-7-nitroquinoxaline-2,3-dione completely blocked the EPSC whereas the NMDA antagonist D-aminophosphonovaleric acid (APV) had modest effects. 3. When a test (T-)EPSC was preceded at an interval of 100 ms by a conditioning (C-)EPSC, a significant increase in the amplitude of the T-EPSC was seen in 38 out of 44 trials analyzed from a total of 27 granule cells. The average amount of PPF was 35.7 +/- 2.1%. There was no apparent correlation between the amount of PPF and the stimulation intensity or mean amplitude of the C-EPSC. The time course of the facilitated T-EPSC was not significantly different from that of the C-EPSC. 4. No correlation was found between the amplitude of the C-EPSC and that of the T-EPSC. Estimates of quantal content (mcv) were determined by calculating the ratio of the squared averaged EPSC amplitude (from 48 responses) to the variance of these responses (M2/sigma 2) whereas quantal amplitudes (qcv) were estimated by calculating the ratio of the response variance to average EPSC amplitude (sigma 2/M). PPF was found to be associated with an average increase in mcv of 64.8 +/- 7.2% (n = 38) whereas qcv was decreased by 12.1 +/- 3.8%. 5. The time course of PPF was studied by varying the interval between the C- and T-pulse from 10 to 400 ms while keeping the stimulation intensity constant. Maximal facilitation of the T-EPSC was obtained with interpulse intervals < or = 25 ms where the average facilitation amounted to approximately 70% (n = 6). The decline of facilitation was nearly exponential and was no longer evident with intervals > 350 ms.(ABSTRACT TRUNCATED AT 400 WORDS

scholarly journals Direct assessment of presynaptic modulation of cortico-striatal glutamate release in a Huntington’s disease mouse model

2018 ◽  
Vol 120 (6) ◽  
pp. 3077-3084 ◽  
Author(s):  
Ellen T. Koch ◽  
Cameron L. Woodard ◽  
Lynn A. Raymond
Keyword(s):  
Mouse Model ◽  
Huntington's Disease ◽  
Huntington’S Disease ◽  
High Frequency ◽  
Glutamate Release ◽  
Presynaptic Receptors ◽  
High Frequency Stimulation ◽  
Presynaptic Modulation ◽  
Frequency Stimulation

Glutamate is the main excitatory neurotransmitter in the brain, and impairments in its signaling are associated with many neurological disorders, including Huntington’s disease (HD). Previous studies in HD mouse models demonstrate altered glutamate receptor distribution and signaling at cortico-striatal synapses, and some studies suggest that glutamate release is altered; however, traditional methods to study synaptic glutamate release are indirect or have poor temporal resolution. Here we utilize iGluSnFR, a modified green fluorescent protein reporter for real-time imaging of glutamate transmission, to study presynaptic modulation of cortical glutamate release in the striatum of the YAC128 HD mouse model. We determined that iGluSnFR can be used to accurately measure short- and long-term changes in glutamate release caused by modulation of extracellular Ca2+ levels, activation of presynaptic receptors, and high-frequency stimulation (HFS) protocols. We also confirmed a difference in the expression of HFS-induced long-term depression in YAC128. Together, this research demonstrates the utility of iGluSnFR in studying presynaptic modulation of glutamate release in healthy mice and disease models that display impairments in glutamate signaling. NEW & NOTEWORTHY We use iGluSnFR to directly assess presynaptic modulation of cortico-striatal glutamate release in brain slice and compare changes in glutamate release between wild type and a Huntington’s disease mouse model, YAC128. We observed reductions in glutamate release after low extracellular Ca2+ and activation of various presynaptic receptors. We also demonstrate a presynaptic mechanism of reduced glutamate release in high-frequency stimulation-induced long-term depression and show this to be altered in YAC128.

Postsynaptic Receptive Field Size and Spike Threshold Determine Encoding of High-Frequency Information Via Sensitivity to Synchronous Presynaptic Activity

2009 ◽  
Vol 101 (3) ◽  
pp. 1160-1170 ◽  
Author(s):  
Jason W. Middleton ◽  
André Longtin ◽  
Jan Benda ◽  
Leonard Maler
Keyword(s):  
High Frequency ◽  
Time Window ◽  
Pyramidal Cells ◽  
Spike Trains ◽  
Small Time ◽  
Field Size ◽  
Recent Experimental Data ◽  
Neuron Models ◽  
High Frequency Signal ◽  
Unit Spike

Parallel sensory streams carrying distinct information about various stimulus properties have been observed in several sensory systems, including the visual system. What remains unclear is why some of these streams differ in the size of their receptive fields (RFs). In the electrosensory system, neurons with large RFs have short-latency responses and are tuned to high-frequency inputs. Conversely, neurons with small RFs are low-frequency tuned and exhibit longer-latency responses. What principle underlies this organization? We show experimentally that synchronous electroreceptor afferent (P-unit) spike trains selectively encode high-frequency stimulus information from broadband signals. This finding relies on a comparison of stimulus-spike output coherence using output trains obtained by either summing pairs of recorded afferent spike trains or selecting synchronous spike trains based on coincidence within a small time window. We propose a physiologically realistic decoding mechanism, based on postsynaptic RF size and postsynaptic output rate normalization that tunes target pyramidal cells in different electrosensory maps to low- or high-frequency signal components. By driving realistic neuron models with experimentally obtained P-unit spike trains, we show that a small RF is matched with a postsynaptic integration regime leading to responses over a broad range of frequencies, and a large RF with a fluctuation-driven regime that requires synchronous presynaptic input and therefore selectively encodes higher frequencies, confirming recent experimental data. Thus our work reveals that the frequency content of a broadband stimulus extracted by pyramidal cells, from P-unit afferents, depends on the amount of feedforward convergence they receive.

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