Publications by authors named "Stefan Hallermann"

40 Publications

Large, Stable Spikes Exhibit Differential Broadening in Excitatory and Inhibitory Neocortical Boutons.

Cell Rep 2021 Jan;34(2):108612

Carl-Ludwig-Institute for Physiology, Faculty of Medicine, Leipzig University, 04103 Leipzig, Germany. Electronic address:

Presynaptic action potential spikes control neurotransmitter release and thus interneuronal communication. However, the properties and the dynamics of presynaptic spikes in the neocortex remain enigmatic because boutons in the neocortex are small and direct patch-clamp recordings have not been performed. Here, we report direct recordings from boutons of neocortical pyramidal neurons and interneurons. Our data reveal rapid and large presynaptic action potentials in layer 5 neurons and fast-spiking interneurons reliably propagating into axon collaterals. For in-depth analyses, we establish boutons of mature cultured neurons as models for excitatory neocortical boutons, demonstrating that the presynaptic spike amplitude is unaffected by potassium channels, homeostatic long-term plasticity, and high-frequency firing. In contrast to the stable amplitude, presynaptic spikes profoundly broaden during high-frequency firing in layer 5 pyramidal neurons, but not in fast-spiking interneurons. Thus, our data demonstrate large presynaptic spikes and fundamental differences between excitatory and inhibitory boutons in the neocortex.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2020.108612DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7809622PMC
January 2021

Autoimmune encephalitis: novel therapeutic targets at the preclinical level.

Expert Opin Ther Targets 2021 Jan 31;25(1):37-47. Epub 2020 Dec 31.

Section Translational Neuroimmunology, Department of Neurology, Jena University Hospital , Jena, Germany.

Introduction: Antibody-mediated encephalitides (AE) with pathogenic autoantibodies (aAB) against neuronal surface antigens are a growing group of diseases characterized by antineuronal autoimmunity in the brain. AE patients typically present with rapidly progressive encephalitis and characteristic disease symptoms dependent on the target antigen. Current treatment consists of an escalating immunotherapy strategy including plasma exchange, steroid application, and B cell depletion.

Areas Covered: For this review, we searched Medline database and google scholar with inclusive dates from 2000. We summarize current treatment strategies and present novel therapeutic approaches of target-specific interventions at the pre-clinical level as well as immunotherapy directed at antibody-induced pathology. Treatment options include modulation of target proteins, intervention with downstream pathways, antibody modification, and depletion of antibody-secreting cells.

Expert Opinion: Although current therapies in AE are effective in many patients, recovery is often prolonged and relapses as well as persistent deficits can occur. Specific immunotherapy together with supportive target-specific therapy may provide faster control of severe symptoms, shorten the disease course, and lead to long-lasting disease stability. Among the various novel therapeutic approaches, modulation of targeted receptors by small molecules crossing the blood-brain barrier as well as prevention of aAB binding is of particular interest.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/14728222.2021.1856370DOI Listing
January 2021

Loss of Piccolo Function in Rats Induces Cerebellar Network Dysfunction and Pontocerebellar Hypoplasia Type 3-like Phenotypes.

J Neurosci 2020 04 2;40(14):2943-2959. Epub 2020 Mar 2.

German Center for Neurodegenerative Diseases, Charité Medical University, 10117 Berlin, Germany,

Piccolo, a presynaptic active zone protein, is best known for its role in the regulated assembly and function of vertebrate synapses. Genetic studies suggest a further link to several psychiatric disorders as well as Pontocerebellar Hypoplasia type 3 (PCH3). We have characterized recently generated Piccolo KO ( ) rats. Analysis of rats of both sexes revealed a dramatic reduction in brain size compared with WT ( ) animals, attributed to a decrease in the size of the cerebral cortical, cerebellar, and pontine regions. Analysis of the cerebellum and brainstem revealed a reduced granule cell layer and a reduction in size of pontine nuclei. Moreover, the maturation of mossy fiber afferents from pontine neurons and the expression of the α6 GABA receptor subunit at the mossy fiber-granule cell synapse are perturbed, as well as the innervation of Purkinje cells by cerebellar climbing fibers. Ultrastructural and functional studies revealed a reduced size of mossy fiber boutons, with fewer synaptic vesicles and altered synaptic transmission. These data imply that Piccolo is required for the normal development, maturation, and function of neuronal networks formed between the brainstem and cerebellum. Consistently, behavioral studies demonstrated that adult rats display impaired motor coordination, despite adequate performance in tasks that reflect muscle strength and locomotion. Together, these data suggest that loss of Piccolo function in patients with PCH3 could be involved in many of the observed anatomical and behavioral symptoms, and that the further analysis of these animals could provide fundamental mechanistic insights into this devastating disorder. Pontocerebellar Hypoplasia Type 3 is a devastating developmental disorder associated with severe developmental delay, progressive microcephaly with brachycephaly, optic atrophy, seizures, and hypertonia with hyperreflexia. Recent genetic studies have identified non-sense mutations in the coding region of the PCLO gene, suggesting a functional link between this disorder and the presynaptic active zone. Our analysis of Piccolo KO rats supports this hypothesis, formally demonstrating that anatomical and behavioral phenotypes seen in patients with Pontocerebellar Hypoplasia Type 3 are also exhibited by these Piccolo deficient animals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.2316-19.2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7117892PMC
April 2020

Gradients in the mammalian cerebellar cortex enable Fourier-like transformation and improve storing capacity.

Elife 2020 02 5;9. Epub 2020 Feb 5.

Carl-Ludwig-Institute for Physiology, Medical Faculty, Leipzig University, Leipzig, Germany.

Cerebellar granule cells (GCs) make up the majority of all neurons in the vertebrate brain, but heterogeneities among GCs and potential functional consequences are poorly understood. Here, we identified unexpected gradients in the biophysical properties of GCs in mice. GCs closer to the white matter (inner-zone GCs) had higher firing thresholds and could sustain firing with larger current inputs than GCs closer to the Purkinje cell layer (outer-zone GCs). Dynamic Clamp experiments showed that inner- and outer-zone GCs preferentially respond to high- and low-frequency mossy fiber inputs, respectively, enabling dispersion of the mossy fiber input into its frequency components as performed by a Fourier transformation. Furthermore, inner-zone GCs have faster axonal conduction velocity and elicit faster synaptic potentials in Purkinje cells. Neuronal network modeling revealed that these gradients improve spike-timing precision of Purkinje cells and decrease the number of GCs required to learn spike-sequences. Thus, our study uncovers biophysical gradients in the cerebellar cortex enabling a Fourier-like transformation of mossy fiber inputs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7554/eLife.51771DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7002074PMC
February 2020

HCN channel-mediated neuromodulation can control action potential velocity and fidelity in central axons.

Elife 2019 09 9;8. Epub 2019 Sep 9.

Carl-Ludwig-Institute for Physiology, Medical Faculty, University Leipzig, Leipzig, Germany.

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels control electrical rhythmicity and excitability in the heart and brain, but the function of HCN channels at the subcellular level in axons remains poorly understood. Here, we show that the action potential conduction velocity in both myelinated and unmyelinated central axons can be bidirectionally modulated by a HCN channel blocker, cyclic adenosine monophosphate (cAMP), and neuromodulators. Recordings from mouse cerebellar mossy fiber boutons show that HCN channels ensure reliable high-frequency firing and are strongly modulated by cAMP (EC 40 µM; estimated endogenous cAMP concentration 13 µM). In addition, immunogold-electron microscopy revealed HCN2 as the dominating subunit in cerebellar mossy fibers. Computational modeling indicated that HCN2 channels control conduction velocity primarily by altering the resting membrane potential and are associated with significant metabolic costs. These results suggest that the cAMP-HCN pathway provides neuromodulators with an opportunity to finely tune energy consumption and temporal delays across axons in the brain.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7554/eLife.42766DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6733576PMC
September 2019

Enriched Environment Shortens the Duration of Action Potentials in Cerebellar Granule Cells.

Front Cell Neurosci 2019 16;13:289. Epub 2019 Jul 16.

Medical Faculty, Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig, Germany.

Environmental enrichment for rodents is known to enhance motor performance. Structural and molecular changes have been reported to be coupled with an enriched environment, but functional alterations of single neurons remain elusive. Here, we compared mice raised under control conditions and an enriched environment. We tested the motor performance on a rotarod and subsequently performed whole-cell patch-clamp recordings in cerebellar slices focusing on granule cells of lobule IX, which is known to receive vestibular input. Mice raised in an enriched environment were able to remain on an accelerating rotarod for a longer period of time. Electrophysiological analyses revealed normal passive properties of granule cells and a functional adaptation to the enriched environment, manifested in faster action potentials (APs) with a higher depolarized voltage threshold and larger AP overshoot. Furthermore, the maximal firing frequency of APs was higher in mice raised in an enriched environment. These data show that enriched environment causes specific alterations in the biophysical properties of neurons. Furthermore, we speculate that the ability of cerebellar granule cells to generate higher firing frequencies improves motor performance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fncel.2019.00289DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6646744PMC
July 2019

Complexin cooperates with Bruchpilot to tether synaptic vesicles to the active zone cytomatrix.

J Cell Biol 2019 03 19;218(3):1011-1026. Epub 2019 Feb 19.

Institute of Physiology, Department of Neurophysiology, University of Würzburg, Würzburg, Germany

Information processing by the nervous system depends on neurotransmitter release from synaptic vesicles (SVs) at the presynaptic active zone. Molecular components of the cytomatrix at the active zone (CAZ) regulate the final stages of the SV cycle preceding exocytosis and thereby shape the efficacy and plasticity of synaptic transmission. Part of this regulation is reflected by a physical association of SVs with filamentous CAZ structures via largely unknown protein interactions. The very C-terminal region of Bruchpilot (Brp), a key component of the CAZ, participates in SV tethering. Here, we identify the conserved SNARE regulator Complexin (Cpx) in an in vivo screen for molecules that link the Brp C terminus to SVs. Brp and Cpx interact genetically and functionally. Both proteins promote SV recruitment to the CAZ and counteract short-term synaptic depression. Analyzing SV tethering to active zone ribbons of knockout mice supports an evolutionarily conserved role of Cpx upstream of SNARE complex assembly.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1083/jcb.201806155DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6400551PMC
March 2019

Presynaptic Calcium En Passage through the Axon.

Biophys J 2018 10 27;115(7):1143-1145. Epub 2018 Aug 27.

Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Leipzig, Germany. Electronic address:

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.bpj.2018.08.022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6170594PMC
October 2018

Human Autoantibodies against the AMPA Receptor Subunit GluA2 Induce Receptor Reorganization and Memory Dysfunction.

Neuron 2018 10 23;100(1):91-105.e9. Epub 2018 Aug 23.

Hans-Berger Department of Neurology, Jena University Hospital, Am Klinikum 1, 07747 Jena, Germany; Center for Sepsis Control and Care (CSCC), Jena University Hospital, Am Klinikum 1, 07747 Jena, Germany. Electronic address:

AMPA receptors are essential for fast excitatory transmission in the CNS. Autoantibodies to AMPA receptors have been identified in humans with autoimmune encephalitis and severe defects of hippocampal function. Here, combining electrophysiology and high-resolution imaging with neuronal culture preparations and passive-transfer models in wild-type and GluA1-knockout mice, we analyze how specific human autoantibodies against the AMPA receptor subunit GluA2 affect receptor function and composition, synaptic transmission, and plasticity. Anti-GluA2 antibodies induce receptor internalization and a reduction of synaptic GluA2-containing AMPARs followed by compensatory ryanodine receptor-dependent incorporation of synaptic non-GluA2 AMPARs. Furthermore, application of human pathogenic anti-GluA2 antibodies to mice impairs long-term synaptic plasticity in vitro and affects learning and memory in vivo. Our results identify a specific immune-neuronal rearrangement of AMPA receptor subunits, providing a framework to explain disease symptoms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neuron.2018.07.048DOI Listing
October 2018

Apparent calcium dependence of vesicle recruitment.

J Physiol 2018 10 7;596(19):4693-4707. Epub 2018 Aug 7.

Carl-Ludwig-Institute for Physiology, Faculty of Medicine, Leipzig University, Leipzig, Germany.

Key Points: Synaptic transmission relies on the recruitment of neurotransmitter-filled vesicles to presynaptic release sites. Increased intracellular calcium buffering slows the recovery from synaptic depression, suggesting that vesicle recruitment is a calcium-dependent process. However, the molecular mechanisms of vesicle recruitment have only been investigated at some synapses. We investigate the role of calcium in vesicle recruitment at the cerebellar mossy fibre to granule cell synapse. We find that increased intracellular calcium buffering slows the recovery from depression following physiological stimulation. However, the recovery is largely resistant to perturbation of the molecular pathways previously shown to mediate calcium-dependent vesicle recruitment. Furthermore, we find two pools of vesicles with different recruitment speeds and show that models incorporating two pools of vesicles with different calcium-independent recruitment rates can explain our data. In this framework, increased calcium buffering prevents the release of intrinsically fast-recruited vesicles but does not change the vesicle recruitment rates themselves.

Abstract: During sustained synaptic transmission, recruitment of new transmitter-filled vesicles to the release site counteracts vesicle depletion and thus synaptic depression. An elevated intracellular Ca concentration has been proposed to accelerate the rate of vesicle recruitment at many synapses. This conclusion is often based on the finding that increased intracellular Ca buffering slows the recovery from synaptic depression. However, the molecular mechanisms of the activity-dependent acceleration of vesicle recruitment have only been analysed at some synapses. Using physiological stimulation patterns in postsynaptic recordings and step depolarizations in presynaptic bouton recordings, we investigate vesicle recruitment at cerebellar mossy fibre boutons. We show that increased intracellular Ca buffering slows recovery from depression dramatically. However, pharmacological and genetic interference with calmodulin or the calmodulin-Munc13 pathway, which has been proposed to mediate Ca -dependence of vesicle recruitment, barely affects vesicle recovery from depression. Furthermore, we show that cerebellar mossy fibre boutons have two pools of vesicles: rapidly fusing vesicles that recover slowly and slowly fusing vesicles that recover rapidly. Finally, models adopting such two pools of vesicles with Ca -independent recruitment rates can explain the slowed recovery from depression upon increased Ca buffering. Our data do not rule out the involvement of the calmodulin-Munc13 pathway during stronger stimuli or other molecular pathways mediating Ca -dependent vesicle recruitment at cerebellar mossy fibre boutons. However, we show that well-established two-pool models predict an apparent Ca -dependence of vesicle recruitment. Thus, previous conclusions of Ca -dependent vesicle recruitment based solely on increased intracellular Ca buffering should be considered with caution.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/JP275911DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6166083PMC
October 2018

How to maintain active zone integrity during high-frequency transmission.

Neurosci Res 2018 Feb 6;127:61-69. Epub 2017 Dec 6.

Carl-Ludwig-Institute for Physiology, Medical Faculty, Leipzig University, Liebigstr. 27, 04103 Leipzig, Germany. Electronic address:

In the central nervous system, the frequency at which reliable synaptic transmission can be maintained varies strongly between different types of synapses. Several pre- and postsynaptic processes must interact to enable high-frequency synaptic transmission. One of the mechanistically most challenging issues arises during repetitive neurotransmitter release, when synaptic vesicles fuse in rapid sequence with the presynaptic plasma membrane within the active zone (AZ), potentially interfering with the structural integrity of the AZ itself. Here we summarize potential mechanisms that help to maintain AZ integrity, including arrangement and mobility of release sites, calcium channel mobility, as well as release site clearance via lateral diffusion of vesicular proteins and via endocytotic membrane retrieval. We discuss how different types of synapses use these strategies to maintain high-frequency synaptic transmission.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neures.2017.10.013DOI Listing
February 2018

Neuroplastin and Basigin Are Essential Auxiliary Subunits of Plasma Membrane Ca-ATPases and Key Regulators of Ca Clearance.

Neuron 2017 Nov 19;96(4):827-838.e9. Epub 2017 Oct 19.

Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, 79104 Freiburg, Germany; Logopharm GmbH, Schlossstrasse 14, 79232 March-Buchheim, Germany; Center for Biological Signaling Studies (BIOSS), Schänzlestrasse 18, 79104 Freiburg, Germany. Electronic address:

Plasma membrane Ca-ATPases (PMCAs), a family of P-type ATPases, extrude Ca ions from the cytosol to the extracellular space and are considered to be key regulators of Ca signaling. Here we show by functional proteomics that native PMCAs are heteromeric complexes that are assembled from two pore-forming PMCA1-4 subunits and two of the single-span membrane proteins, either neuroplastin or basigin. Contribution of the two Ig domain-containing proteins varies among different types of cells and along postnatal development. Complex formation of neuroplastin or basigin with PMCAs1-4 occurs in the endoplasmic reticulum and is obligatory for stability of the PMCA proteins and for delivery of PMCA complexes to the surface membrane. Knockout and (over)-expression of both neuroplastin and basigin profoundly affect the time course of PMCA-mediated Ca transport, as well as submembraneous Ca concentrations under steady-state conditions. Together, these results establish neuroplastin and basigin as obligatory auxiliary subunits of native PMCAs and key regulators of intracellular Ca concentration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neuron.2017.09.038DOI Listing
November 2017

The Cerebellar Mossy Fiber Synapse as a Model for High-Frequency Transmission in the Mammalian CNS.

Trends Neurosci 2016 11 19;39(11):722-737. Epub 2016 Oct 19.

Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany. Electronic address:

The speed of neuronal information processing depends on neuronal firing frequency. Here, we describe the evolutionary advantages and ubiquitous occurrence of high-frequency firing within the mammalian nervous system in general. The highest firing frequencies so far have been observed at the cerebellar mossy fiber to granule cell synapse. The mechanisms enabling high-frequency transmission at this synapse are reviewed and compared with other synapses. Finally, information coding of high-frequency signals at the mossy fiber synapse is discussed. The exceptionally high firing frequencies and amenability to high-resolution technical approaches both in vitro and in vivo establish the cerebellar mossy fiber synapse as an attractive model to investigate high-frequency signaling from the molecular up to the network level.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.tins.2016.09.006DOI Listing
November 2016

Differential Regulation of Human Paired Associative Stimulation-Induced and Theta-Burst Stimulation-Induced Plasticity by L-type and T-type Ca2+ Channels.

Cereb Cortex 2017 08;27(8):4010-4021

Department of Neurology, University of Leipzig, Liebigstr. 20, 04103 Leipzig, Germany.

Activity-dependent changes of postsynaptic Ca2+-concentration are influenced by a variety of different Ca2+-channels and play an important role in synaptic plasticity. Paired associative stimulation (PAS) and theta-burst stimulation (TBS) are noninvasive magnetic stimulation protocols used in human subjects to induce lasting corticospinal excitability changes that have been likened to synaptic long-term potentiation and long-term depression. To better characterize the Ca2+-related physiological mechanisms underlying PAS- and TBS-induced plasticity, we examined the impact of different Ca2+-sources. PAS-induced facilitation of corticospinal excitability was blocked by NMDA-receptor blocker dextromethorphan (DXM) and L-type voltage gated Ca2+ channels (VGCC) blocker nimodipine (NDP), but turned into depression by T-type VGCC blocker ethosuximide (ESM). Although, surprisingly, static corticospinal excitability was increased by the combination of DXM and NDP, PAS-induced facilitation was blocked. TBS-induced facilitation of corticospinal excitability, which has previously been shown to be turned into depression by L-type VGCC blocker NDP (Wankerl K, Weise D, Gentner R, Rumpf J, Classen J. 2010. L-type voltage-gated Ca2+ channels: a single molecular switch for long-term potentiation/long-term depression-like plasticity and activity-dependent metaplasticity in humans. J Neurosci. 30(18):6197-6204.), was blocked, but not reverted, by T-type VGCC blocker ESM. The different patterns of Ca2+-channel modulation of PAS- and TBS-induced plasticity may point to an important role of backpropagating action potentials in PAS-induced plasticity, similar as in spike-timing dependent synaptic plasticity, and to a requirement of dendritic Ca2+-dependent spikes in TBS-induced plasticity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/cercor/bhw212DOI Listing
August 2017

Fast, Temperature-Sensitive and Clathrin-Independent Endocytosis at Central Synapses.

Neuron 2016 05 14;90(3):492-8. Epub 2016 Apr 14.

Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany. Electronic address:

The fusion of neurotransmitter-filled vesicles during synaptic transmission is balanced by endocytotic membrane retrieval. Despite extensive research, the speed and mechanisms of synaptic vesicle endocytosis have remained controversial. Here, we establish low-noise time-resolved membrane capacitance measurements that allow monitoring changes in surface membrane area elicited by single action potentials and stronger stimuli with high-temporal resolution at physiological temperature in individual bona-fide mature central synapses. We show that single action potentials trigger very rapid endocytosis, retrieving presynaptic membrane with a time constant of 470 ms. This fast endocytosis is independent of clathrin but mediated by dynamin and actin. In contrast, stronger stimuli evoke a slower mode of endocytosis that is clathrin, dynamin, and actin dependent. Furthermore, the speed of endocytosis is highly temperature dependent with a Q10 of ∼3.5. These results demonstrate that distinct molecular modes of endocytosis with markedly different kinetics operate at central synapses.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neuron.2016.03.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5125781PMC
May 2016

NMDA receptors amplify mossy fiber synaptic inputs at frequencies up to at least 750 Hz in cerebellar granule cells.

Synapse 2016 07 7;70(7):269-76. Epub 2016 Mar 7.

Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstr. 27, Leipzig, 04103, Germany.

Neuronal integration of high-frequency signals is important for rapid information processing. Cerebellar mossy fiber axons (MFs) can fire action potentials (APs) at frequencies of more than one kilohertz. However, it is unclear whether and how the postsynaptic cerebellar granule cells (GCs) are able to process these high-frequency MF inputs. Here, we measured AP firing in GCs during high-frequency MF stimulation and show that GC firing frequency increased non-linearly when MF stimulation frequency was increased from 100 to 750 Hz. To investigate the mechanisms enabling such high-frequency signaling, we analyzed the role of N-methyl-d-aspartate receptors (NMDARs), which have been implicated in synaptic signaling at lower frequencies. Application of D-2-amino-5-phosphonopentanoic acid (APV), a potent inhibitor of NMDARs, strongly impaired the GC firing frequency during high-frequency MF stimulation. APV had no significant effect on single excitatory postsynaptic potentials (EPSPs) or currents (EPSCs) evoked at 1 Hz at resting membrane potentials. However, the time course of EPSCs evoked at 1 Hz at depolarized potentials or following high-frequency MF stimulation was accelerated by APV. Thus, our results show that NMDAR-mediated currents amplify high-frequency MF inputs by prolonging the time courses of synaptic inputs, thereby causing greater synaptic summation of inputs. Hence, NMDARs support the integration of MF synaptic input at frequencies up to at least 750 Hz. Synapse 70:269-276, 2016. © 2016 Wiley Periodicals, Inc.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/syn.21898DOI Listing
July 2016

Looking into the Black Box of Synaptic Vesicle Recruitment.

Neuron 2015 Nov;88(3):435-7

Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany. Electronic address:

To sustain ongoing synaptic transmission, new transmitter-filled vesicles must be recruited to empty release sites rapidly. However, in this issue of Neuron, Midorikawa and Sakaba (2015) show that, before being released, vesicles are tethered at the membrane for seconds.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neuron.2015.10.028DOI Listing
November 2015

Reduced endogenous Ca2+ buffering speeds active zone Ca2+ signaling.

Proc Natl Acad Sci U S A 2015 Jun 26;112(23):E3075-84. Epub 2015 May 26.

Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, 04103 Leipzig, Germany;

Fast synchronous neurotransmitter release at the presynaptic active zone is triggered by local Ca(2+) signals, which are confined in their spatiotemporal extent by endogenous Ca(2+) buffers. However, it remains elusive how rapid and reliable Ca(2+) signaling can be sustained during repetitive release. Here, we established quantitative two-photon Ca(2+) imaging in cerebellar mossy fiber boutons, which fire at exceptionally high rates. We show that endogenous fixed buffers have a surprisingly low Ca(2+)-binding ratio (∼ 15) and low affinity, whereas mobile buffers have high affinity. Experimentally constrained modeling revealed that the low endogenous buffering promotes fast clearance of Ca(2+) from the active zone during repetitive firing. Measuring Ca(2+) signals at different distances from active zones with ultra-high-resolution confirmed our model predictions. Our results lead to the concept that reduced Ca(2+) buffering enables fast active zone Ca(2+) signaling, suggesting that the strength of endogenous Ca(2+) buffering limits the rate of synchronous synaptic transmission.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1508419112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4466756PMC
June 2015

Dendritic patch-clamp recordings from cerebellar granule cells demonstrate electrotonic compactness.

Front Cell Neurosci 2015 19;9:93. Epub 2015 Mar 19.

Medical Faculty, Carl-Ludwig Institute for Physiology, University of Leipzig Leipzig, Germany.

Cerebellar granule cells (GCs), the smallest neurons in the brain, have on average four short dendrites that receive high-frequency mossy fiber inputs conveying sensory information. The short length of the dendrites suggests that GCs are electrotonically compact allowing unfiltered integration of dendritic inputs. The small average diameter of the dendrites (~0.7 µm), however, argues for dendritic filtering. Previous studies based on somatic recordings and modeling indicated that GCs are electrotonically extremely compact. Here, we performed patch-clamp recordings from GC dendrites in acute brain slices of mice to directly analyze the electrotonic properties of GCs. Strikingly, the input resistance did not differ significantly between dendrites and somata of GCs. Furthermore, spontaneous excitatory postsynaptic potentials (EPSP) were similar in amplitude at dendritic and somatic recording sites. From the dendritic and somatic input resistances we determined parameters characterizing the electrotonic compactness of GCs. These data directly demonstrate that cerebellar GCs are electrotonically compact and thus ideally suited for efficient high-frequency information transfer.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fncel.2015.00093DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4365719PMC
April 2015

Bruchpilot and Synaptotagmin collaborate to drive rapid glutamate release and active zone differentiation.

Front Cell Neurosci 2015 5;9:29. Epub 2015 Feb 5.

Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany.

The active zone (AZ) protein Bruchpilot (Brp) is essential for rapid glutamate release at Drosophila melanogaster neuromuscular junctions (NMJs). Quantal time course and measurements of action potential-waveform suggest that presynaptic fusion mechanisms are altered in brp null mutants (brp(69) ). This could account for their increased evoked excitatory postsynaptic current (EPSC) delay and rise time (by about 1 ms). To test the mechanism of release protraction at brp(69) AZs, we performed knock-down of Synaptotagmin-1 (Syt) via RNAi (syt(KD) ) in wildtype (wt), brp(69) and rab3 null mutants (rab3(rup) ), where Brp is concentrated at a small number of AZs. At wt and rab3(rup) synapses, syt(KD) lowered EPSC amplitude while increasing rise time and delay, consistent with the role of Syt as a release sensor. In contrast, syt(KD) did not alter EPSC amplitude at brp(69) synapses, but shortened delay and rise time. In fact, following syt(KD) , these kinetic properties were strikingly similar in wt and brp(69) , which supports the notion that Syt protracts release at brp(69) synapses. To gain insight into this surprising role of Syt at brp(69) AZs, we analyzed the structural and functional differentiation of synaptic boutons at the NMJ. At 'tonic' type Ib motor neurons, distal boutons contain more AZs, more Brp proteins per AZ and show elevated and accelerated glutamate release compared to proximal boutons. The functional differentiation between proximal and distal boutons is Brp-dependent and reduced after syt(KD) . Notably, syt(KD) boutons are smaller, contain fewer Brp positive AZs and these are of similar number in proximal and distal boutons. In addition, super-resolution imaging via dSTORM revealed that syt(KD) increases the number and alters the spatial distribution of Brp molecules at AZs, while the gradient of Brp proteins per AZ is diminished. In summary, these data demonstrate that normal structural and functional differentiation of Drosophila AZs requires concerted action of Brp and Syt.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fncel.2015.00029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4318344PMC
February 2015

Ultrafast action potentials mediate kilohertz signaling at a central synapse.

Neuron 2014 Oct 11;84(1):152-163. Epub 2014 Sep 11.

Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstr. 27, 04103 Leipzig, Germany; European Neuroscience Institute Göttingen, Grisebachstr. 5, 37077 Göttingen, Germany. Electronic address:

Fast synaptic transmission is important for rapid information processing. To explore the maximal rate of neuronal signaling and to analyze the presynaptic mechanisms, we focused on the input layer of the cerebellar cortex, where exceptionally high action potential (AP) frequencies have been reported in vivo. With paired recordings between presynaptic cerebellar mossy fiber boutons and postsynaptic granule cells, we demonstrate reliable neurotransmission up to ∼1 kHz. Presynaptic APs are ultrafast, with ∼100 μs half-duration. Both Kv1 and Kv3 potassium channels mediate the fast repolarization, rapidly inactivating sodium channels ensure metabolic efficiency, and little AP broadening occurs during bursts of up to 1.5 kHz. Presynaptic Cav2.1 (P/Q-type) calcium channels open efficiently during ultrafast APs. Furthermore, a subset of synaptic vesicles is tightly coupled to Ca(2+) channels, and vesicles are rapidly recruited to the release site. These data reveal mechanisms of presynaptic AP generation and transmitter release underlying neuronal kHz signaling.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.neuron.2014.08.036DOI Listing
October 2014

Quantitative super-resolution imaging of Bruchpilot distinguishes active zone states.

Nat Commun 2014 Aug 18;5:4650. Epub 2014 Aug 18.

Department of Neurophysiology, Institute of Physiology, University of Würzburg, 97070 Würzburg, Germany.

The precise molecular architecture of synaptic active zones (AZs) gives rise to different structural and functional AZ states that fundamentally shape chemical neurotransmission. However, elucidating the nanoscopic protein arrangement at AZs is impeded by the diffraction-limited resolution of conventional light microscopy. Here we introduce new approaches to quantify endogenous protein organization at single-molecule resolution in situ with super-resolution imaging by direct stochastic optical reconstruction microscopy (dSTORM). Focusing on the Drosophila neuromuscular junction (NMJ), we find that the AZ cytomatrix (CAZ) is composed of units containing ~137 Bruchpilot (Brp) proteins, three quarters of which are organized into about 15 heptameric clusters. We test for a quantitative relationship between CAZ ultrastructure and neurotransmitter release properties by engaging Drosophila mutants and electrophysiology. Our results indicate that the precise nanoscopic organization of Brp distinguishes different physiological AZ states and link functional diversification to a heretofore unrecognized neuronal gradient of the CAZ ultrastructure.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncomms5650DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4143948PMC
August 2014

Calcium channels for endocytosis.

J Physiol 2014 Aug;592(16):3343-4

Carl-Ludwig-Institute of Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103, Leipzig, Germany

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/jphysiol.2014.278838DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4229332PMC
August 2014

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

J Physiol 2013 Jul 13;591(13):3355-70. Epub 2013 May 13.

Carl-Ludwig Institute for Physiology, University of Leipzig, Liebigstr. 27, 04103 Leipzig, Germany.

Paired-pulse facilitation (PPF) is a dynamic enhancement of transmitter release considered crucial in CNS information processing. The mechanisms of PPF remain controversial and may differ between synapses. Endogenous Ca(2+) buffers such as parvalbumin (PV) and calbindin-D28k (CB) are regarded as important modulators of PPF, with PV acting as an anti-facilitating buffer while saturation of CB can promote PPF. We analysed transmitter release and PPF at intracortical, recurrent Purkinje neuron (PN) to PN synapses, which show PPF during high-frequency activation (200 Hz) and strongly express both PV and CB. We quantified presynaptic Ca(2+) dynamics and quantal release parameters in wild-type (WT), and CB and PV deficient mice. Lack of CB resulted in increased volume averaged presynaptic Ca(2+) amplitudes and in increased release probability, while loss of PV had no significant effect on these parameters. Unexpectedly, none of the buffers significantly influenced PPF, indicating that neither CB saturation nor residual free Ca(2+) ([Ca(2+)]res) was the main determinant of PPF. Experimentally constrained, numerical simulations of Ca(2+)-dependent release were used to estimate the contributions of [Ca(2+)]res, CB, PV, calmodulin (CaM), immobile buffer fractions and Ca(2+) remaining bound to the release sensor after the first of two action potentials ('active Ca(2+)') to PPF. This analysis indicates that PPF at PN-PN synapses does not result from either buffer saturation or [Ca(2+)]res but rather from slow Ca(2+) unbinding from the release sensor.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/jphysiol.2013.254128DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3717232PMC
July 2013

Hippocampal and cerebellar mossy fibre boutons - same name, different function.

J Physiol 2013 Jul 7;591(13):3179-88. Epub 2013 Jan 7.

Carl-Ludwig Institute for Physiology, University of Leipzig, 04103 Leipzig, Germany.

Over a century ago, the Spanish anatomist Ramón y Cajal described 'mossy fibres' in the hippocampus and the cerebellum, which contain several presynaptic boutons. Technical improvements in recent decades have allowed direct patch-clamp recordings from both hippocampal and cerebellar mossy fibre boutons (hMFBs and cMFBs, respectively), making them ideal models to study fundamental properties of synaptic transmission. hMFBs and cMFBs have similar size and shape, but each hMFB contacts one postsynaptic hippocampal CA3 pyramidal neuron, while each cMFB contacts ∼50 cerebellar granule cells. Furthermore, hMFBs and cMFBs differ in terms of their functional specialization. At hMFBs, a large number of release-ready vesicles and low release probability (<0.1) contribute to marked synaptic facilitation. At cMFBs, a small number of release-ready vesicles, high release probability (∼0.5) and rapid vesicle reloading result in moderate frequency-dependent synaptic depression. These presynaptic mechanisms, in combination with faster postsynaptic currents of cerebellar granule cells compared with hippocampal CA3 pyramidal neurons, enable much higher transmission frequencies at cMFB compared with hMFB synapses. Analysing the underling mechanisms of synaptic transmission and information processing represents a fascinating challenge and may reveal insights into the structure-function relationship of the human brain.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/jphysiol.2012.248294DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3717221PMC
July 2013

Nanodomain coupling at an excitatory cortical synapse.

Curr Biol 2013 Feb 27;23(3):244-9. Epub 2012 Dec 27.

Carl-Ludwig Institute for Physiology, University of Leipzig, 04103 Leipzig, Germany.

The coupling distance between presynaptic Ca(2+) influx and the sensor for vesicular transmitter release determines speed and reliability of synaptic transmission. Nanodomain coupling (<100 nm) favors fidelity and is employed by synapses specialized for escape reflexes and by inhibitory synapses involved in synchronizing fast network oscillations. Cortical glutamatergic synapses seem to forgo the benefits of tight coupling, yet quantitative detail is lacking. The reduced transmission fidelity of loose coupling, however, raises the question whether it is indeed a general characteristic of cortical synapses. Here we analyzed excitatory parallel fiber to Purkinje cell synapses, major processing sites for sensory information and well suited for analysis because they typically harbor only a single active zone. We quantified the coupling distance by combining multiprobability fluctuation analyses, presynaptic Ca(2+) imaging, and reaction-diffusion simulations in wild-type and calretinin-deficient mice. We found a coupling distance of <30 nm at these synapses, much shorter than at any other glutamatergic cortical synapse investigated to date. Our results suggest that nanodomain coupling is a general characteristic of conventional cortical synapses involved in high-frequency transmission, allowing for dense gray matter packing and cost-effective neurotransmission.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cub.2012.12.007DOI Listing
February 2013

Sustaining rapid vesicular release at active zones: potential roles for vesicle tethering.

Trends Neurosci 2013 Mar 17;36(3):185-94. Epub 2012 Nov 17.

European Neuroscience Institute Göttingen, Grisebachstrasse 5, 37077 Göttingen, Germany.

Rapid information processing in our nervous system relies on high-frequency fusion of transmitter-filled vesicles at chemical synapses. Some sensory synapses possess prominent electron-dense ribbon structures that provide a scaffold for tethering synaptic vesicles at the active zone (AZ), enabling sustained vesicular release. Here, we review functional data indicating that some central and neuromuscular synapses can also sustain vesicle-fusion rates that are comparable to those of ribbon-type sensory synapses. Comparison of the ultrastructure across these different types of synapses, together with recent work showing that cytomatrix proteins can tether vesicles and speed vesicle reloading, suggests that filamentous structures may play a key role in vesicle supply. We discuss potential mechanisms by which vesicle tethering could contribute to sustained high rates of vesicle fusion across ribbon-type, central, and neuromuscular synapses.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.tins.2012.10.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4748400PMC
March 2013

State and location dependence of action potential metabolic cost in cortical pyramidal neurons.

Nat Neurosci 2012 Jun 3;15(7):1007-14. Epub 2012 Jun 3.

European Neuroscience Institute Göttingen, Göttingen, Germany.

Action potential generation and conduction requires large quantities of energy to restore Na(+) and K(+) ion gradients. We investigated the subcellular location and voltage dependence of this metabolic cost in rat neocortical pyramidal neurons. Using Na(+)/K(+) charge overlap as a measure of action potential energy efficiency, we found that action potential initiation in the axon initial segment (AIS) and forward propagation into the axon were energetically inefficient, depending on the resting membrane potential. In contrast, action potential backpropagation into dendrites was efficient. Computer simulations predicted that, although the AIS and nodes of Ranvier had the highest metabolic cost per membrane area, action potential backpropagation into the dendrites and forward propagation into axon collaterals dominated energy consumption in cortical pyramidal neurons. Finally, we found that the high metabolic cost of action potential initiation and propagation down the axon is a trade-off between energy minimization and maximization of the conduction reliability of high-frequency action potentials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nn.3132DOI Listing
June 2012

Rapid active zone remodeling during synaptic plasticity.

J Neurosci 2011 Apr;31(16):6041-52

Carl Ludwig Institute of Physiology, Medical Faculty, University of Leipzig, 04103 Leipzig, Germany.

How can synapses change the amount of neurotransmitter released during synaptic plasticity? Although release in general is intensely investigated, its determinants during plasticity are still poorly understood. As a model for plastic strengthening of synaptic release, we here use the well-established presynaptic homeostatic compensation during interference with postsynaptic glutamate receptors at the Drosophila neuromuscular junction. Combining short-term plasticity analysis, cumulative EPSC analysis, fluctuation analysis, and quantal short-term plasticity modeling, we found an increase in the number of release-ready vesicles during presynaptic strengthening. High-resolution light microscopy revealed an increase in the amount of the active zone protein Bruchpilot and an enlargement of the presynaptic cytomatrix structure. Furthermore, these functional and structural alterations of the active zone were not only observed after lifelong but already after minutes of presynaptic strengthening. Our results demonstrate that presynaptic plasticity can induce active zone remodeling, which regulates the number of release-ready vesicles within minutes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.6698-10.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6632979PMC
April 2011

Behavioral and synaptic plasticity are impaired upon lack of the synaptic protein SAP47.

J Neurosci 2011 Mar;31(9):3508-18

Neurobiologie und Genetik and Elektronenmikroskopie, Universität Würzburg, Biozentrum, 97074 Würzburg, Germany.

The synapse-associated protein of 47 kDa (SAP47) is a member of a phylogenetically conserved gene family of hitherto unknown function. In Drosophila, SAP47 is encoded by a single gene (Sap47) and is expressed throughout all synaptic regions of the wild-type larval brain; specifically, electron microscopy reveals anti-SAP47 immunogold labeling within 30 nm of presynaptic vesicles. To analyze SAP47 function, we used the viable and fertile deletion mutant Sap47(156), which suffers from a 1.7 kb deletion in the regulatory region and the first exon. SAP47 cannot be detected by either immunoblotting or immunohistochemistry in Sap47(156) mutants. These mutants exhibit normal sensory detection of odorants and tastants as well as normal motor performance and basic neurotransmission at the neuromuscular junction. However, short-term plasticity at this synapse is distorted. Interestingly, Sap47(156) mutant larvae also show a 50% reduction in odorant-tastant associative learning ability; a similar associative impairment is observed in a second deletion allele (Sap47(201)) and upon reduction of SAP47 levels using RNA interference. In turn, transgenically restoring SAP47 in Sap47(156) mutant larvae rescues the defect in associative function. This report thus is the first to suggest a function for SAP47. It specifically argues that SAP47 is required for proper behavioral and synaptic plasticity in flies-and prompts the question whether its homologs are required for proper behavioral and synaptic plasticity in other species as well.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1523/JNEUROSCI.2646-10.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6623913PMC
March 2011