The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Tomoyuki Takahashi - One of the best experts on this subject based on the ideXlab platform.
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impact of vesicular glutamate leakage on synaptic transmission at the Calyx of Held
The Journal of Physiology, 2017Co-Authors: Chihiro Takami, Tetsuya Hori, Kohgaku Eguchi, Tomoyuki TakahashiAbstract:Glutamate leaks out of synaptic vesicles when trans-vesicular proton gradient is dissipated in isolated vesicle preparations. In the nerve terminal, however, it is controversial whether glutamate can leak out of vesicles. To address this issue, we abolished vesicular glutamate uptake by washing out presynaptic cytosolic glutamate in whole-cell dialysis, or by blocking vacuolar ATPase using bafilomycin A1 (Baf), at the Calyx of Held in mice brainstem slices. Presynaptic glutamate washout or Baf application reduced the mean amplitude and frequency of spontaneous miniature (m) EPSCs and mean amplitude of EPSCs evoked every 10 min. The percentage reduction of mEPSC amplitude was much less than that of EPSC amplitude or mEPSC frequency, and tended to reach a plateau. The mean amplitude of mEPSCs after glutamate washout or Baf application remained high above the detection limit, deduced from the reduction of mEPSC amplitude by the AMPA receptor blocker CNQX. Membrane capacitance measurements from presynaptic terminals indicated no effect of glutamate washout on exocytosis or endocytosis of synaptic vesicles. We conclude that glutamate can leak out of vesicles unless it is continuously taken up from presynaptic cytosol. However, the magnitude of glutamate leakage was small and had only a minor effect on synaptic responses. By contrast, prominent rundowns of EPSC amplitude and mEPSC frequency observed after glutamate washout or Baf application are likely caused by accumulation of unfilled vesicles in presynaptic terminals retrieved after spontaneous and evoked glutamate release. This article is protected by copyright. All rights reserved
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vesicular glutamate filling and ampa receptor occupancy at the Calyx of Held synapse of immature rats
The Journal of Physiology, 2009Co-Authors: Takayuki Yamashita, Tomoyuki Takahashi, Kohgaku Eguchi, Takeshi KandaAbstract:At central glutamatergic synapses, neurotransmitter often saturates postsynaptic AMPA receptors (AMPARs), thereby restricting the dynamic range of synaptic efficacy. Here, using simultaneous pre- and postsynaptic whole-cell recordings, at the Calyx of Held synapse of immature rats, we have investigated the mechanism by which transmitter glutamate saturates postsynaptic AMPARs. When we loaded l-glutamate (1–100 mm) into presynaptic terminals, the quantal EPSC (qEPSC) amplitude changed in a concentration-dependent manner. At physiological temperature (36–37°C), the qEPSC amplitude increased when intraterminal l-glutamate concentration was elevated from 1 mm to 10 mm, but it reached a plateau at 10 mm. This plateau persisted after bath-application of the low affinity AMPAR antagonist kynurenate, suggesting that it was caused by saturation of vesicular filling with glutamate rather than by saturation of postsynaptic AMPARs. In contrast to qEPSCs, action potential-evoked EPSCs remained unchanged by increasing intraterminal l-glutamate from 1 mm to 100 mm, even at room temperature, indicating that multi-quantal glutamate saturated postsynaptic AMPARs. This saturation could be relieved by blocking AMPAR desensitization using cyclothiazide (100 μm). The concentration of ambient glutamate in the slice, estimated from NMDA receptor current fluctuations, was 55 nm; this was far below the concentration required for AMPAR desensitization. We conclude that rapid AMPAR desensitization, caused by glutamate released from multiple vesicles during synaptic transmission, underlies postsynaptic AMPAR saturation at this immature calyceal synapse before the onset of hearing.
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developmental changes in calcium calmodulin dependent inactivation of calcium currents at the rat Calyx of Held
The Journal of Physiology, 2008Co-Authors: Takeshi Nakamura, Tomoyuki Takahashi, Naoto Saitoh, Takayuki YamashitaAbstract:Ca2+-binding to calmodulin (CaM) causes facilitation and/or inactivation of recombinant Ca2+ channels. At the rat Calyx of Held, before hearing onset, presynaptic Ca2+ currents (IpCa) undergo Ca2+/CaM-dependent inactivation during repetitive activation at around 1 Hz, implying that this may be a major cause of short-term synaptic depression. However, it remains open whether the Ca2+/CaM-dependent inactivation of IpCa persists in more mature animals. To address this question, we tested the effect of CaM inhibitors on the activity-dependent modulation of IpCa in calyces, before (postnatal day (P) 7–9) and after (P13–15) hearing onset. Our results indicate that the CaM-dependent IpCa inactivation during low-frequency stimulation, and the ensuing synaptic depression, occur only at calyces in the prehearing period. However, CaM immunoreactivity in P8 and P14 calyces was equally strong. Even at P13–15, high frequency stimulation (200–500 Hz) could induce IpCa inactivation, which was attenuated by EGTA (10 mm) or a CaM inhibitor peptide loaded into the terminal. Furthermore, the CaM inhibitor peptide attenuated a transient facilitation of IpCa preceding inactivation observed at 500 Hz stimulation, whereas it had no effect on sustained IpCa facilitations during trains of 50–200 Hz stimulation. These results suggest that the Ca2+/CaM-dependent IpCa modulation requires a high intraterminal Ca2+ concentration, which can be attained at immature calyces during low frequency stimulation, but only during unusually high frequency stimulation at calyceal terminals in the posthearing period.
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involvement of ampa receptor desensitization in short term synaptic depression at the Calyx of Held in developing rats
The Journal of Physiology, 2008Co-Authors: Maki Koiketani, Tomoyuki Takahashi, Naoto Saitoh, Takayuki Yamashita, Takeshi KandaAbstract:Paired-pulse facilitation (PPF) and depression (PPD) are forms of short-term plasticity that are generally thought to reflect changes in transmitter release probability. However, desensitization of postsynaptic AMPA receptors (AMPARs) significantly contributes to PPD at many glutamatergic synapses. To clarify the involvement of AMPAR desensitization in synaptic PPD, we compared PPD with AMPAR desensitization, induced by paired-pulse glutamate application in patches excised from postsynaptic cells at the Calyx of Held synapse of developing rats. We found that AMPAR desensitization contributed significantly to PPD before the onset of hearing (P10–12), but that its contribution became negligible after hearing onset. During postnatal development (P7–21) the recovery of AMPARs from desensitization became faster. Concomitantly, glutamate sensitivity of AMPAR desensitization declined. Single-cell reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated a developmental decline of GluR1 expression that correlated with speeding of the recovery of AMPARs from desensitization. Transmitter release probability declined during the second postnatal week (P7–14). Manipulation of the extracellular Ca2+/Mg2+ ratio, to match release probability at P7–8 and P13–15 synapses, revealed that the release probability is also an important factor determining the involvement of AMPAR desensitization in PPD. We conclude that the extent of involvement of AMPAR desensitization in short-term synaptic depression is determined by both pre- and postsynaptic mechanisms.
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4 chloro m cresol an activator of ryanodine receptors inhibits voltage gated k channels at the rat Calyx of Held
European Journal of Neuroscience, 2007Co-Authors: Daisuke Suzuki, Tomoyuki Takahashi, Naoto Saitoh, Tetsuya HoriAbstract:4-Chloro-m-cresol (4-CmC) is thought to be a specific activator of ryanodine receptors (RyRs). Using this compound, we examined whether the RyR-mediated Ca(2+) release is involved in transmitter release at the rat Calyx of Held synapse in brainstem slices. Bath application of 4-CmC caused a dramatic increase in the amplitude of excitatory postsynaptic currents (TIFCs) with the half-maximal effective concentration of 0.12 mm. By making direct patch-clamp whole-cell recordings from presynaptic terminals, we investigated the mechanism by which 4-CmC facilitates transmitter release. 4-CmC markedly prolonged the duration of action potentials, with little effect on their rise time kinetics. In voltage-clamp recordings, 4-CmC inhibited voltage-gated presynaptic K(+) currents (I(pK)) by 53% (at +20 mV) but had no effect on voltage-gated presynaptic Ca(2+) currents (I(pCa)). In simultaneous pre- and postsynaptic recordings, 4-CmC had no effect on the TIFC evoked by I(pCa). Although immunocytochemical study of the calyceal terminals showed immunoreactivity to type 3 RyRs, ryanodine (0.02 mm) had no effect on the 4-CmC-induced TIFC potentiation. We conclude that the facilitatory effect of 4-CmC on nerve-evoked transmitter release is mediated by its inhibitory effect on I(pK).
Gerard J G Borst - One of the best experts on this subject based on the ideXlab platform.
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structure function relation of the developing Calyx of Held synapse in vivo
The Journal of Physiology, 2020Co-Authors: Johan A Slotman, Martijn C Sierksma, Adriaan B Houtsmuller, Gerard J G BorstAbstract:Key points: During development the giant, auditory Calyx of Held forms a one-to-one connection with a principal neuron of the medial nucleus of the trapezoid body. While anatomical studies described that most of the target cells are temporarily contacted by multiple calyces, multi-calyceal innervation was only sporadically observed in in vivo recordings, suggesting a structure–function discrepancy. We correlated synaptic strength of inputs, identified in in vivo recordings, with post hoc labelling of the recorded neuron and synaptic terminals containing vesicular glutamate transporters (VGluT). During development only one input increased to the level of the Calyx of Held synapse, and its strength correlated with the large VGluT cluster contacting the postsynaptic soma. As neither competing strong inputs nor multiple large VGluT clusters on a single cell were observed, our findings did not indicate a structure–function discrepancy. Abstract: In adult rodents, a principal neuron in the medial nucleus of the trapezoid (MNTB) is generally contacted by a single, giant axosomatic terminal called the Calyx of Held. How this one-on-one relation is established is still unknown, but anatomical evidence suggests that during development principal neurons are innervated by multiple calyces, which may indicate calyceal competition. However, in vivo electrophysiological recordings from principal neurons indicated that only a single strong synaptic connection forms per cell. To test whether a mismatch exists between synaptic strength and terminal size, we compared the strength of synaptic inputs with the morphology of the synaptic terminals. In vivo whole-cell recordings of the MNTB neurons from newborn Wistar rats of either sex were made while stimulating their afferent axons, allowing us to identify multiple inputs. The strength of the strongest input increased to calyceal levels in a few days across cells, while the strength of the second strongest input was stable. The recorded cells were subsequently immunolabelled for vesicular glutamate transporters (VGluT) to reveal axosomatic terminals with structured-illumination microscopy. Synaptic strength of the strongest input was correlated with the contact area of the largest VGluT cluster at the soma (r = 0.8), and no indication of a mismatch between structure and strength was observed. Together, our data agree with a developmental scheme in which one input strengthens and becomes the Calyx of Held, but not with multi-calyceal competition.
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structure function relation of the developing Calyx of Held synapse in vivo
bioRxiv, 2020Co-Authors: Martijn C Sierksma, Johan A Slotman, Adriaan B Houtsmuller, Gerard J G BorstAbstract:In adult rodents, a principal neuron in the medial nucleus of the trapezoid (MNTB) is generally contacted by a single, giant axosomatic terminal called the Calyx of Held, but how this one-on-one relation is established is still unknown. Anatomical evidence suggests that during development principal neurons are innervated by multiple calyces, which may indicate calyceal competition, but in vivo electrophysiological recordings from principal neurons have indicated that only a single strong synaptic connection forms per cell. To test whether a mismatch between synaptic strength and terminal size exists, we compared strength of synaptic inputs during early postnatal development with the morphology of the synaptic terminals. In vivo whole-cell recordings of the MNTB neurons from newborn rats of either sex were made while stimulating their afferent axons, allowing us to identify multiple inputs. The strength of the strongest input increased to calyceal levels in a few days across cells, while the strength of the second strongest input was stable. Cells were subsequently immunolabeled for vesicular glutamate transporters (VGluT) to reveal axosomatic terminals. Synaptic strength of the strongest input was correlated with the contact area of the largest VGluT cluster at the soma. No clear mismatch was observed between structure and strength. Together, our data agree with a developmental scheme in which one input strengthens and becomes the Calyx of Held, but not with multi-calyceal competition.
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Enhanced Transmission at the Calyx of Held Synapse in a Mouse Model for Angelman Syndrome
Frontiers Media S.A., 2018Co-Authors: Tiantian Wang, Geeske M. Van Woerden, Ype Elgersma, Gerard J G BorstAbstract:The neurodevelopmental disorder Angelman syndrome (AS) is characterized by intellectual disability, motor dysfunction, distinct behavioral aspects, and epilepsy. AS is caused by a loss of the maternally expressed UBE3A gene, and many of the symptoms are recapitulated in a Ube3a mouse model of this syndrome. At the cellular level, changes in the axon initial segment (AIS) have been reported, and changes in vesicle cycling have indicated the presence of presynaptic deficits. Here we studied the role of UBE3A in the auditory system by recording synaptic transmission at the Calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB) through in vivo whole cell and juxtacellular recordings. We show that MNTB principal neurons in Ube3a mice exhibit a hyperpolarized resting membrane potential, an increased action potential (AP) amplitude and a decreased AP half width. Moreover, both the pre- and postsynaptic AP in the Calyx of Held synapse of Ube3a mice showed significantly faster recovery from spike depression. An increase in AIS length was observed in the principal MNTB neurons of Ube3a mice, providing a possible substrate for these gain-of-function changes. Apart from the effect on APs, we also observed that EPSPs showed decreased short-term synaptic depression (STD) during long sound stimulations in AS mice, and faster recovery from STD following these tones, which is suggestive of a presynaptic gain-of-function. Our findings thus provide in vivo evidence that UBE3A plays a critical role in controlling synaptic transmission and excitability at excitatory synapses
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in vivo matching of postsynaptic excitability with spontaneous synaptic inputs during formation of the rat Calyx of Held synapse
The Journal of Physiology, 2017Co-Authors: Martijn C Sierksma, Milly S Tedja, Gerard J G BorstAbstract:Key points Neurons in the medial nucleus of the trapezoid body of anaesthetized rats of postnatal day (P)2–6 showed burst firing with a preferred interval of about 100 ms, which was stable, and a second preferred interval of 5–30 ms, which shortened during development. In 3 out of 132 cases, evidence for the presence of two large inputs was found. In vivo whole-cell recordings revealed that the excitability of the principal neuron and the size of its largest synaptic inputs were developmentally matched. At P2–4, action potentials were triggered by barrages of small synaptic events that summated to plateau potentials, while at later stages firing depended on a single, large and often prespike-associated input, which is probably the nascent Calyx of Held. Simulations with a Hodgkin–Huxley-like model, which was based on fits of the intrinsic postsynaptic properties, suggested an essential role for the low-threshold potassium conductance in this transition. Abstract In the adult, principal neurons of the medial nucleus of the trapezoid body (MNTB) are typically contacted by a single, giant terminal called the Calyx of Held, whereas during early development a principal neuron receives inputs from many axons. How these changes in innervation impact the postsynaptic activity has not yet been studied in vivo. We therefore recorded spontaneous inputs and intrinsic properties of principal neurons in anaesthetized rat pups during the developmental period in which the Calyx forms. A characteristic bursting pattern could already be observed at postnatal day (P)2, before formation of the Calyx. At this age, action potentials (APs) were triggered by barrages of summating EPSPs causing plateau depolarizations. In contrast, at P5, a single EPSP reliably triggered APs, resulting in a close match between pre- and postsynaptic firing. Postsynaptic excitability and the size of the largest synaptic events were developmentally matched. The developmental changes in intrinsic properties were estimated by fitting in vivo current injections to a Hodgkin–Huxley-type model of the principal neuron. Our simulations indicated that the developmental increases in Ih, low-threshold K+ channels and leak currents contributed to the reduction in postsynaptic excitability, but that low-threshold K+ channels specifically functioned as a dampening influence in the near-threshold range, thus precluding small inputs from triggering APs. Together, these coincident changes help to propagate bursting activity along the auditory brainstem, and are essential steps towards establishing the relay function of the Calyx of Held synapse.
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modulation of synaptic depression of the Calyx of Held synapse by gabab receptors and spontaneous activity
The Journal of Physiology, 2013Co-Authors: Tiantian Wang, S I Rusu, Bohdana Hruskova, Rostislav Turecek, Gerard J G BorstAbstract:The Calyx of Held synapse of the medial nucleus of the trapezoid body is a giant axosomatic synapse in the auditory brainstem, which acts as a relay synapse showing little dependence of its synaptic strength on firing frequency. The main mechanism that is responsible for its resistance to synaptic depression is its large number of release sites with low release probability. Here, we investigated the contribution of presynaptic GABA(B) receptors and spontaneous activity to release probability both in vivo and in vitro in young-adult mice. Maximal activation of presynaptic GABA(B) receptors by baclofen reduced synaptic output by about 45% in whole-cell voltage clamp slice recordings, which was accompanied by a reduction in short-term depression. A similar reduction in transmission was observed when baclofen was applied in vivo by microiontophoresis during juxtacellular recordings using piggyback electrodes. No significant change in synaptic transmission was observed during application of the GABA(B) receptor antagonist CGP54626 both during in vivo and slice recordings, suggesting a low ambient GABA concentration. Interestingly, we observed that synapses with a high spontaneous frequency showed almost no synaptic depression during auditory stimulation, whereas synapses with a low spontaneous frequency did depress during noise bursts. Our data thus suggest that spontaneous firing can tonically reduce release probability in vivo. In addition, our data show that the ambient GABA concentration in the auditory brainstem is too low to activate the GABA(B) receptor at the Calyx of Held significantly, but that activation of GABA(B) receptors can reduce sound-evoked synaptic depression.
Erwin Neher - One of the best experts on this subject based on the ideXlab platform.
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some subtle lessons from the Calyx of Held synapse
Biophysical Journal, 2017Co-Authors: Erwin NeherAbstract:The Calyx of Held is a giant nerve terminal that forms a glutamatergic synapse in the auditory pathway. Due to its large size, it offers a number of advantages for biophysical studies, including voltage-clamp of both pre- and postsynaptic compartments and the loading with indicator dyes and caged compounds. Three aspects of recent findings on the Calyx are reviewed here, each of which seems to have only subtle consequences for nerve-evoked excitatory postsynaptic currents: vesicle heterogeneity, refractoriness of release sites, and superpriming. Together, they determine short-term plasticity features that are superficially similar to those expected for a simple vesicle pool model. However, detailed consideration of these aspects may be required for the correct mechanistic interpretation of data from synapses with normal and perturbed function, as well as for modeling the dynamics of short-term plasticity.
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complexin stabilizes newly primed synaptic vesicles and prevents their premature fusion at the mouse Calyx of Held synapse
The Journal of Neuroscience, 2015Co-Authors: Shuwen Chang, Kerstin Reim, Meike Pedersen, Nils Brose, Erwin Neher, Holger TaschenbergerAbstract:Complexins (Cplxs) are small synaptic proteins that cooperate with SNARE-complexes in the control of synaptic vesicle (SV) fusion. Studies involving genetic mutation, knock-down, or knock-out indicated two key functions of Cplx that are not mutually exclusive but cannot easily be reconciled, one in facilitating SV fusion, and one in “clamping” SVs to prevent premature fusion. Most studies on the role of Cplxs in mammalian synapse function have relied on cultured neurons, heterologous expression systems, or membrane fusion assays in vitro, whereas little is known about the function of Cplxs in native synapses. We therefore studied consequences of genetic ablation of Cplx1 in the mouse Calyx of Held synapse, and discovered a developmentally exacerbating phenotype of reduced spontaneous and evoked transmission but excessive asynchronous release after stimulation, compatible with combined facilitating and clamping functions of Cplx1. Because action potential waveforms, Ca2+ influx, readily releasable SV pool size, and quantal size were unaltered, the reduced synaptic strength in the absence of Cplx1 is most likely a consequence of a decreased release probability, which is caused, in part, by less tight coupling between Ca2+ channels and docked SV. We found further that the excessive asynchronous release in Cplx1-deficient calyces triggered aberrant action potentials in their target neurons, and slowed-down the recovery of EPSCs after depleting stimuli. The augmented asynchronous release had a delayed onset and lasted hundreds of milliseconds, indicating that it predominantly represents fusion of newly recruited SVs, which remain unstable and prone to premature fusion in the absence of Cplx1.
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model of synaptic transmission in the Calyx of Held
BMC Neuroscience, 2009Co-Authors: Holger Taschenberger, Erwin Neher, Dmitry BibitchkovAbstract:The Calyx of Held is a giant synaptic terminal in the MNTBof the auditory brainstem. Observations of postsynapticresponses to repeated stimulation reveal that this synapseexhibits complex behavior, which results from the inter-play between processes such as vesicle pool depletion,activity-dependent recovery from depletion, synapticfacilitation and postsynaptic receptor desensitization.Intracellular calcium concentration ([Ca
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localization of calcium channels at the Calyx of Held
Biophysical Journal, 2009Co-Authors: Meike Pedersen, Samuel M Young, Erwin NeherAbstract:The Calyx of Held is a giant synapse in the auditory pathway. Due to its large size and its geometry it makes an excellent model system for studying the biophysical properties of synaptic transmission. Previous studies have demonstrated that the release rate of synaptic vesicles is governed by the distance between single synaptic vesicles and calcium channels. Therefore knowing the localization of presynaptic calcium channels is essential to understand the coupling of synaptic vesicle release with calcium influx into the Calyx. Prior studies have attempted to characterize calcium channel distribution in the Calyx, however results have been inconclusive in providing an accurate picture. In order to conclusively localize calcium channels we are exploring several possibilities to stain calcium channels for fluorescence and electron microscopy studies. The first approach is to express genetically tagged P/Q-type calcium channels in the Calyx utilizing an adenovirus expression system. We have tried an eGFP-tagged P/Q-type calcium channel and found that the eGFP accumulates in the nuclei of the cells indicating cleavage of the tags. The tag also reduced calcium currents twofold compared to untagged channel. Our second approach was to screen several constructs with HA epitope tags inserted into different positions on the P/Q-type calcium channel. We found that extracellular tags frequently impair channel function. However we did obtain constructs which showed current upon expression in HEK cells. Unfortunately accessibility of the tag for the antibody is impaired in neurons. Intracellular tags are accesible in primary neurons and behave similar to untagged channel electrophysiologically, but the staining is difficult to interpret because tagged overexpressed channels accumulate in intracellular compartments. In parallel experiments we have screened several antibodies against P/Q-type calcium channels aiming to find one that gives clean staining for high-resolution microscopy. Funding: LSHM-CT-1005-019055.
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synaptic vesicles in mature Calyx of Held synapses sense higher nanodomain calcium concentrations during action potential evoked glutamate release
The Journal of Neuroscience, 2008Co-Authors: Luyang Wang, Erwin Neher, Holger TaschenbergerAbstract:During development of the Calyx of Held synapse, presynaptic action potentials (APs) become substantially faster and briefer. Nevertheless, this synapse is able to upregulate quantal output triggered by arriving APs. Briefer APs lead to less effective gating of voltage-gated Ca2+ channels (VGCCs). Therefore, mechanisms downstream of Ca2+ entry must effectively compensate for the attenuated Ca2+ influx associated with shorter APs in more mature calyces. This compensation could be achieved by tighter spatial coupling between VGCCs and synaptic vesicles, so that the latter are exposed to higher intracellular Ca2+ concentration ([Ca2+]i). Alternatively or additionally, the Ca2+ sensitivity of the release apparatus may increase during synapse development. To differentiate between these possibilities, we combined paired patch-clamp recordings with Ca2+ imaging and flash photolysis of caged Ca2+ and estimated the [Ca2+]i requirements for vesicle release in the developing mouse Calyx of Held synapse. Surprisingly, the dose–response relationship between [Ca2+]i and release rate was shifted slightly to the right in more mature calyces, rendering their vesicles slightly less sensitive to incoming Ca2+. Taking into account the time course and peak rates of AP-evoked release transients for the corresponding developmental stages, we estimate the local [Ca2+]i“seen” by the Ca2+ sensors on synaptic vesicles to increase from 35 to 56 μm [from postnatal day 9 (P9)–P11 to P16–P19]. Our results reinforce the idea that developmental tightening of the spatial coupling between VGCCs and synaptic vesicles plays a predominant role in enhancing quantal output at this synapse and possibly other central synapses.
Ko Matsui - One of the best experts on this subject based on the ideXlab platform.
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evaluation of glutamate concentration transient in the synaptic cleft of the rat Calyx of Held
The Journal of Physiology, 2013Co-Authors: Timotheus Budisantoso, Harumi Harada, Ko Matsui, Yugo Fukazawa, Naomi Kamasawa, Ryuichi ShigemotoAbstract: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,whereasahugegradientlikelyexists.Modellingstudieshaveattemptedtodescribe this gradient, but two key parameters, the number of glutamate in a vesicle (NGlu) and its diffusion coefficient (DGlu) 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 NGlu and DGlu 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
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evaluation of glutamate concentration transient in the synaptic cleft of the rat Calyx of Held
The Journal of Physiology, 2013Co-Authors: Timotheus Budisantoso, Harumi Harada, Ko Matsui, Yugo Fukazawa, Naomi Kamasawa, Ryuichi ShigemotoAbstract: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.
Ian D. Forsythe - One of the best experts on this subject based on the ideXlab platform.
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wide band information transmission at the Calyx of Held
Neural Computation, 2009Co-Authors: Zhijun Yang, Ian D. Forsythe, Matthias H Hennig, Michael Postlethwaite, Bruce P GrahamAbstract:We use a mathematical model of the Calyx of Held to explore information transmission at this giant glutamatergic synapse. The significant depression of the postsynaptic response to repeated stimulation in vitro is a result of various activity-dependent processes in multiple timescales, which can be reproduced by multi exponential functions in this model. When the postsynaptic current is stimulated by Poisson-distributed spike trains, its amplitude varies considerably with the preceding interspike intervals. Here we quantify the information contained in the postsynaptic current amplitude about preceding inters pike intervals and determine the impact of different pre- and postsynaptic factors on information transmission. The mutual information between presynaptic spike times and the amplitude of the postsynaptic response in general decreases as the mean stimulation rate increases, but remains high even at frequencies greater than 100 Hz, unlike at many neocortical synapses. The maintenance of information transmission is attributable largely to vesicle recycling rates at low frequencies of stimulation, shifting to vesicle release probability at high frequencies. Also, at higher frequencies, the synapse operates largely in a release-ready mode in which most release sites contain a release-ready vesicle and release probabilities are low.
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analysis of the factors influencing information transmission at the Calyx of Held
BMC Neuroscience, 2007Co-Authors: Zhijun Yang, Ian D. Forsythe, Matthias H Hennig, Michael Postlethwaite, Bruce P GrahamAbstract:The Calyx of Held is a giant glutamatergic synapse located in the medial nucleus of the trapezoid body (MNTB) of the mammalian auditory brainstem. It is an important model system for studying short-term plasticity because each postsynaptic MNTB neuron receives only one giant synapse, and it is possible to record both pre- and postsynaptic events simultaneously. Physiological experiments show that the evoked excitatory postsynaptic current (EPSC) from the Calyx displays a significant depression in response amplitude during a sustained stimulus train [1]. This observation is the result of interactions between various pre- and postsynaptic components occurring across multiple time-scales. Hundreds of readily releasable vesicles (RRVP) aggregate at the different active zones on the presynaptic terminal. The stochastic release of neurotransmitter from the RRVPs (triggered by influx of calcium ions during action potentials, APs), can exhaust the supply of vesicles. Simultaneously, the depleted RRVPs are constantly replenished by a large vesicle reserve pool, and this replenishment is also enhanced by a calcium-dependent process (mediated by the presynaptic APs). The amplitude of the presynaptic AP-evoked calcium ion concentration is affected by inactivation and facilitation of voltage-gated calcium channels as well as activation of presynaptic metabotropic glutamate receptors (mGluRs). In this study we extend our deterministic, multiple time-scale model of the Calyx of Held [2,3] to a stochastic version. We use information theory to measure the amount of information transmitted between pre- and postsynaptic compartments [4]. A series of long, homogeneous Poisson spike trains with mean frequencies up to several hundred Hertz are used to stimulate the Calyx model. This spike train is repeated many times, allowing the calculation of the conditional and unconditional entropy of the postsynaptic EPSC amplitude in response to presynaptic interspike intervals (ISI). The mutual information, a measure of the information content of the postsynaptic response (EPSC) about the afferent spike train (ISI), is then computed in terms of conditional and unconditional entropies. The results show that the information content in the postsynaptic response is influenced by the degree of variation of presynaptic calcium ion concentration. Rapid onset and recovery from facilitation maintains high information transfer rates across the frequency range. Suppression of calcium transients by slowly recovering inactivation and mGluR activation results in less information transmission, but prevents depletion of the RRVPs. Fast-acting postsynaptic receptor desensitisation also contributes to information transmission, but in a competitive way to facilitation.
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a biophysical model of short term plasticity at the Calyx of Held
Neurocomputing, 2007Co-Authors: Matthias H Hennig, Ian D. Forsythe, Michael Postlethwaite, Bruce P GrahamAbstract:The Calyx of Held is a giant glutamatergic synapse in the auditory system and displays multiple forms of short-term facilitation and depression. This study presents a detailed model of short-term plasticity at this synapse. The main components of the model are the presynaptic vesicle dynamics, which include passive and activity-dependent recycling, calcium-dependent exocytosis and the postsynaptic AMPA receptor kinetics. The behaviour of the model is compared to experimental data and reproduces the time course and amplitude of synaptic depression during repetitive stimulation at different frequencies. A comparison of different manipulations of the model shows that accurate fits require the inclusion of fast activity-dependent vesicle recycling and a limited number of vesicle docking sites at each active zone.
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The Calyx of Held
Cell and Tissue Research, 2006Co-Authors: Ralf Schneggenburger, Ian D. ForsytheAbstract:The Calyx of Held is a large glutamatergic synapse in the mammalian auditory brainstem. By using brain slice preparations, direct patch-clamp recordings can be made from the nerve terminal and its postsynaptic target (principal neurons of the medial nucleus of the trapezoid body). Over the last decade, this preparation has been increasingly employed to investigate basic presynaptic mechanisms of transmission in the central nervous system. We review here the background to this preparation and summarise key findings concerning voltage-gated ion channels of the nerve terminal and the ionic mechanisms involved in exocytosis and modulation of transmitter release. The accessibility of this giant terminal has also permitted Ca^2+-imaging and -uncaging studies combined with electrophysiological recording and capacitance measurements of exocytosis. Together, these studies convey the panopoly of presynaptic regulatory processes underlying the regulation of transmitter release, its modulatory control and short-term plasticity within one identified synaptic terminal.
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functional compensation of p q by n type channels blocks short term plasticity at the Calyx of Held presynaptic terminal
The Journal of Neuroscience, 2004Co-Authors: Carlota Gonzalez Inchauspe, Ian D. Forsythe, Francisco J Martini, Osvaldo D UchitelAbstract:Calcium channels of the P/Q subtype mediate transmitter release at the neuromuscular junction and at many central synapses, such as the Calyx of Held. Transgenic mice in which alpha1A channels are ablated provide a powerful tool with which to test compensatory mechanisms at the synapse and to explore mechanisms of presynaptic regulation associated with expression of P/Q channels. Using the Calyx of Held preparation from the knock-out (KO) mice, we show here that N-type channels functionally compensate for the absence of P/Q subunits at the Calyx and evoke giant synaptic currents [approximately two-thirds of the magnitude of wild-type (WT) responses]. However, although evoked paired-pulse facilitation is prominent in WT, this facilitation is greatly diminished in the KO. In addition, direct recording of presynaptic calcium currents revealed that the major functional difference was the absence of calcium-dependent facilitation at the Calyx in the P/Q KO animals. We conclude that one physiological function of P/Q channels is to provide additional facilitatory drive, so contributing to maintenance of transmission as vesicles are depleted during high throughput synaptic transmission.
