51
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Clarke SE. Analog Signaling With the "Digital" Molecular Switch CaMKII. Front Comput Neurosci 2018; 12:92. [PMID: 30524260 PMCID: PMC6262075 DOI: 10.3389/fncom.2018.00092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Accepted: 10/31/2018] [Indexed: 11/13/2022] Open
Abstract
Molecular switches, such as the protein kinase CaMKII, play a fundamental role in cell signaling by decoding inputs into either high or low states of activity; because the high activation state can be turned on and persist after the input ceases, these switches have earned a reputation as "digital." Although this on/off, binary perspective has been valuable for understanding long timescale synaptic plasticity, accumulating experimental evidence suggests that the CaMKII switch can also control plasticity on short timescales. To investigate this idea further, a non-autonomous, nonlinear ordinary differential equation, representative of a general bistable molecular switch, is analyzed. The results suggest that switch activity in regions surrounding either the high- or low-stable states of activation could act as a reliable analog signal, whose short timescale fluctuations relative to equilibrium track instantaneous input frequency. The model makes intriguing predictions and is validated against previous work demonstrating its suitability as a minimal representation of switch dynamics; in combination with existing experimental evidence, the theory suggests a multiplexed encoding of instantaneous frequency information over short timescales, with integration of total activity over longer timescales.
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Affiliation(s)
- Stephen E Clarke
- Department of Bioengineering, Department of Neurosurgery, Stanford University, Stanford, CA, United States
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52
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Lübbert M, Goral RO, Keine C, Thomas C, Guerrero-Given D, Putzke T, Satterfield R, Kamasawa N, Young SM. Ca V2.1 α 1 Subunit Expression Regulates Presynaptic Ca V2.1 Abundance and Synaptic Strength at a Central Synapse. Neuron 2018; 101:260-273.e6. [PMID: 30545599 DOI: 10.1016/j.neuron.2018.11.028] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 10/22/2018] [Accepted: 11/15/2018] [Indexed: 11/28/2022]
Abstract
The abundance of presynaptic CaV2 voltage-gated Ca2+ channels (CaV2) at mammalian active zones (AZs) regulates the efficacy of synaptic transmission. It is proposed that presynaptic CaV2 levels are saturated in AZs due to a finite number of slots that set CaV2 subtype abundance and that CaV2.1 cannot compete for CaV2.2 slots. However, at most AZs, CaV2.1 levels are highest and CaV2.2 levels are developmentally reduced. To investigate CaV2.1 saturation states and preference in AZs, we overexpressed the CaV2.1 and CaV2.2 α1 subunits at the calyx of Held at immature and mature developmental stages. We found that AZs prefer CaV2.1 to CaV2.2. Remarkably, CaV2.1 α1 subunit overexpression drove increased CaV2.1 currents and channel numbers and increased synaptic strength at both developmental stages examined. Therefore, we propose that CaV2.1 levels in the AZ are not saturated and that synaptic strength can be modulated by increasing CaV2.1 levels to regulate neuronal circuit output. VIDEO ABSTRACT.
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Affiliation(s)
- Matthias Lübbert
- Research Group Molecular Mechanisms of Synaptic Function, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - R Oliver Goral
- Department of Anatomy and Cell Biology, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA 52242, USA
| | - Christian Keine
- Department of Anatomy and Cell Biology, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA 52242, USA
| | - Connon Thomas
- Max Planck Florida Electron Microscopy Core, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Debbie Guerrero-Given
- Max Planck Florida Electron Microscopy Core, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Travis Putzke
- Research Group Molecular Mechanisms of Synaptic Function, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Rachel Satterfield
- Research Group Molecular Mechanisms of Synaptic Function, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Naomi Kamasawa
- Max Planck Florida Electron Microscopy Core, Max Planck Florida Institute for Neuroscience, Jupiter, FL 33458, USA
| | - Samuel M Young
- Department of Anatomy and Cell Biology, Iowa Neuroscience Institute, University of Iowa, Iowa City, IA 52242, USA; Department of Otolaryngology, Iowa Neuroscience Institute, Aging Mind Brain Initiative, University of Iowa, Iowa City, IA 52242, USA.
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53
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Balakrishnan S, Mironov SL. Regenerative glutamate release in the hippocampus of Rett syndrome model mice. PLoS One 2018; 13:e0202802. [PMID: 30256804 PMCID: PMC6157837 DOI: 10.1371/journal.pone.0202802] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Accepted: 08/09/2018] [Indexed: 11/18/2022] Open
Abstract
Excess glutamate during intense neuronal activity is not instantly cleared and may accumulate in the extracellular space. This has various long-term consequences such as ectopic signaling, modulation of synaptic efficacy and excitotoxicity; the latter implicated in various neurodevelopmental and neurodegenerative diseases. In this study, the quantitative imaging of glutamate homeostasis of hippocampal slices from methyl-CpG binding protein 2 knock-out (Mecp2-/y) mice, a model of Rett syndrome (RTT), revealed unusual repetitive glutamate transients. They appeared in phase with bursts of action potentials in the CA1 neurons. Both glutamate transients and bursting activity were suppressed by the blockade of sodium, AMPA and voltage-gated calcium channels (T- and R-type), and enhanced after the inhibition of HCN channels. HCN and calcium channels in RTT and wild-type (WT) CA1 neurons displayed different voltage-dependencies and kinetics. Both channels modulated postsynaptic integration and modified the pattern of glutamate spikes in the RTT hippocampus. Spontaneous glutamate transients were much less abundant in the WT preparations, and, when observed, had smaller amplitude and frequency. The basal ambient glutamate levels in RTT were higher and transient glutamate increases (spontaneous and evoked by stimulation of Schaffer collaterals) decayed slower. Both features indicate less efficient glutamate uptake in RTT. To explain the generation of repetitive glutamate spikes, we designed a novel model of glutamate-induced glutamate release. The simulations correctly predicted the patterns of spontaneous glutamate spikes observed under different experimental conditions. We propose that pervasive spontaneous glutamate release is a hallmark of Mecp2-/y hippocampus, stemming from and modulating the hyperexcitability of neurons.
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Affiliation(s)
- Saju Balakrishnan
- CNMPB (Centre for Nanoscale Microscopy and Molecular Physiology of the Brain, DFG Research Center 103), Institute of Neuro and Sensory Physiology, Georg-August-University, Göttingen, Germany
| | - Sergej L. Mironov
- CNMPB (Centre for Nanoscale Microscopy and Molecular Physiology of the Brain, DFG Research Center 103), Institute of Neuro and Sensory Physiology, Georg-August-University, Göttingen, Germany
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54
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Singh M, Lujan B, Renden R. Presynaptic GCaMP expression decreases vesicle release probability at the calyx of Held. Synapse 2018; 72:e22040. [PMID: 29935099 PMCID: PMC6186185 DOI: 10.1002/syn.22040] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 06/04/2018] [Accepted: 06/05/2018] [Indexed: 12/15/2022]
Abstract
Synaptic vesicle (SV) exocytosis is intimately dependent on free local Ca2+ near active zones. Genetically encoded calcium indicators (GECIs) have become an indispensable tool to monitor calcium dynamics during physiological responses, and they are widely used as a proxy to monitor activity in neuronal ensembles and at synaptic terminals. However, GECIs’ ability to bind Ca2+ at physiologically relevant concentration makes them strong candidates to affect calcium homeostasis and alter synaptic transmission by exogenously increasing Ca2+ buffering. In the present study, we show that genetically expressed GCaMP6m modulates SV release probability at the mouse calyx of Held synapse. GCaMP6m expression for approximately three weeks decreased initial SV release for both low‐frequency stimulation and high‐frequency stimulation trains, and slowed presynaptic short‐term depression. However, GCaMP6m does not affect quantal events during spontaneous activity at this synapse. This study emphasizes the careful use of GECIs as monitors of neuronal activity and inspects the role of these transgenic indicators which may alter calcium‐dependent physiological responses.
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Affiliation(s)
- Mahendra Singh
- Department of Physiology and Cell Biology, University of Nevada, Reno, Nevada, 89557
| | - Brendan Lujan
- Department of Physiology and Cell Biology, University of Nevada, Reno, Nevada, 89557.,Currently at Vollum Institute, Oregon Health and Science University, Portland, Oregon
| | - Robert Renden
- Department of Physiology and Cell Biology, University of Nevada, Reno, Nevada, 89557
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55
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Jeans AF, van Heusden FC, Al-Mubarak B, Padamsey Z, Emptage NJ. Homeostatic Presynaptic Plasticity Is Specifically Regulated by P/Q-type Ca 2+ Channels at Mammalian Hippocampal Synapses. Cell Rep 2018; 21:341-350. [PMID: 29020622 PMCID: PMC5643522 DOI: 10.1016/j.celrep.2017.09.061] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 08/11/2017] [Accepted: 09/19/2017] [Indexed: 11/17/2022] Open
Abstract
Voltage-dependent Ca2+ channels (VGCC) represent the principal source of Ca2+ ions driving evoked neurotransmitter release at presynaptic boutons. In mammals, presynaptic Ca2+ influx is mediated mainly via P/Q-type and N-type VGCC, which differ in their properties. Changes in their relative contributions tune neurotransmission both during development and in Hebbian plasticity. However, whether this represents a functional motif also present in other forms of activity-dependent regulation is unknown. Here, we study the role of VGCC in homeostatic plasticity (HSP) in mammalian hippocampal neurons using optical techniques. We find that changes in evoked Ca2+ currents specifically through P/Q-type, but not N-type, VGCC mediate bidirectional homeostatic regulation of both neurotransmitter release efficacy and the size of the major synaptic vesicle pools. Selective dependence of HSP on P/Q-type VGCC in mammalian terminals has important implications for phenotypes associated with P/Q-type channelopathies, including migraine and epilepsy. P/Q-type VGCC regulate homeostatic synaptic plasticity (HSP) in mammals Changes in synaptic vesicle pool sizes during HSP are also mediated via P/Q-type VGCC Expression of HSP is independent of N-type VGCC regulation P/Q-type regulation of HSP may explain phenotypes of P/Q-type channelopathies
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Affiliation(s)
- Alexander F Jeans
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.
| | - Fran C van Heusden
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK
| | - Bashayer Al-Mubarak
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK; Department of Genetics, King Faisal Specialist Hospital and Research Center, PO Box 3354, Riyadh 11211, Saudi Arabia
| | - Zahid Padamsey
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK
| | - Nigel J Emptage
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.
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56
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Orr BO, Gorczyca D, Younger MA, Jan LY, Jan YN, Davis GW. Composition and Control of a Deg/ENaC Channel during Presynaptic Homeostatic Plasticity. Cell Rep 2018; 20:1855-1866. [PMID: 28834749 DOI: 10.1016/j.celrep.2017.07.074] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 04/10/2017] [Accepted: 07/25/2017] [Indexed: 01/08/2023] Open
Abstract
The homeostatic control of presynaptic neurotransmitter release stabilizes information transfer at synaptic connections in the nervous system of organisms ranging from insect to human. Presynaptic homeostatic signaling centers upon the regulated membrane insertion of an amiloride-sensitive degenerin/epithelial sodium (Deg/ENaC) channel. Elucidating the subunit composition of this channel is an essential step toward defining the underlying mechanisms of presynaptic homeostatic plasticity (PHP). Here, we demonstrate that the ppk1 gene encodes an essential subunit of this Deg/ENaC channel, functioning in motoneurons for the rapid induction and maintenance of PHP. We provide genetic and biochemical evidence that PPK1 functions together with PPK11 and PPK16 as a presynaptic, hetero-trimeric Deg/ENaC channel. Finally, we highlight tight control of Deg/ENaC channel expression and activity, showing increased PPK1 protein expression during PHP and evidence for signaling mechanisms that fine tune the level of Deg/ENaC activity during PHP.
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Affiliation(s)
- Brian O Orr
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA
| | - David Gorczyca
- Howard Hughes Medical Institute, Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Meg A Younger
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Lily Y Jan
- Howard Hughes Medical Institute, Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Yuh-Nung Jan
- Howard Hughes Medical Institute, Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA.
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57
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Wentzel C, Delvendahl I, Sydlik S, Georgiev O, Müller M. Dysbindin links presynaptic proteasome function to homeostatic recruitment of low release probability vesicles. Nat Commun 2018; 9:267. [PMID: 29348419 PMCID: PMC5773495 DOI: 10.1038/s41467-017-02494-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2017] [Accepted: 12/01/2017] [Indexed: 12/27/2022] Open
Abstract
Here we explore the relationship between presynaptic homeostatic plasticity and proteasome function at the Drosophila neuromuscular junction. First, we demonstrate that the induction of homeostatic plasticity is blocked after presynaptic proteasome perturbation. Proteasome inhibition potentiates release under baseline conditions but not during homeostatic plasticity, suggesting that proteasomal degradation and homeostatic plasticity modulate a common pool of vesicles. The vesicles that are regulated by proteasome function and recruited during homeostatic plasticity are highly EGTA sensitive, implying looser Ca2+ influx-release coupling. Similar to homeostatic plasticity, proteasome perturbation enhances presynaptic Ca2+ influx, readily-releasable vesicle pool size, and does not potentiate release after loss of specific homeostatic plasticity genes, including the schizophrenia-susceptibility gene dysbindin. Finally, we provide genetic evidence that Dysbindin levels regulate the access to EGTA-sensitive vesicles. Together, our data suggest that presynaptic protein degradation opposes the release of low-release probability vesicles that are potentiated during homeostatic plasticity and whose access is controlled by dysbindin.
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Affiliation(s)
- Corinna Wentzel
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Igor Delvendahl
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Sebastian Sydlik
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.,Zurich Ph.D. Program in Molecular Life Sciences, Winterthurerstrasse 190, Zurich, 8057, Switzerland
| | - Oleg Georgiev
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Martin Müller
- Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland. .,Zurich Ph.D. Program in Molecular Life Sciences, Winterthurerstrasse 190, Zurich, 8057, Switzerland. .,Neuroscience Center Zurich, Winterthurerstrasse 190, Zurich, 8057, Switzerland.
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58
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Wang T, Jones RT, Whippen JM, Davis GW. α2δ-3 Is Required for Rapid Transsynaptic Homeostatic Signaling. Cell Rep 2017; 16:2875-2888. [PMID: 27626659 DOI: 10.1016/j.celrep.2016.08.030] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 07/12/2016] [Accepted: 08/09/2016] [Indexed: 11/18/2022] Open
Abstract
The homeostatic modulation of neurotransmitter release, termed presynaptic homeostatic potentiation (PHP), is a fundamental type of neuromodulation, conserved from Drosophila to humans, that stabilizes information transfer at synaptic connections throughout the nervous system. Here, we demonstrate that α2δ-3, an auxiliary subunit of the presynaptic calcium channel, is required for PHP. The α2δ gene family has been linked to chronic pain, epilepsy, autism, and the action of two psychiatric drugs: gabapentin and pregabalin. We demonstrate that loss of α2δ-3 blocks both the rapid induction and sustained expression of PHP due to a failure to potentiate presynaptic calcium influx and the RIM-dependent readily releasable vesicle pool. These deficits are independent of α2δ-3-mediated regulation of baseline calcium influx and presynaptic action potential waveform. α2δ proteins reside at the extracellular face of presynaptic release sites throughout the nervous system, a site ideal for mediating rapid, transsynaptic homeostatic signaling in health and disease.
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Affiliation(s)
- Tingting Wang
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Ryan T Jones
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Jenna M Whippen
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
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59
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Valente P, Farisello P, Valtorta F, Baldelli P, Benfenati F. Impaired GABA B-mediated presynaptic inhibition increases excitatory strength and alters short-term plasticity in synapsin knockout mice. Oncotarget 2017; 8:90061-90076. [PMID: 29163811 PMCID: PMC5685732 DOI: 10.18632/oncotarget.21405] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 09/03/2017] [Indexed: 11/25/2022] Open
Abstract
Synapsins are a family of synaptic vesicle phosphoproteins regulating synaptic transmission and plasticity. SYN1/2 genes are major epilepsy susceptibility genes in humans. Consistently, synapsin I/II/III triple knockout (TKO) mice are epileptic and exhibit severe impairments in phasic and tonic GABAergic inhibition that precede the appearance of the epileptic phenotype. These changes are associated with an increased strength of excitatory transmission that has never been mechanistically investigated. Here, we observed that an identical effect in excitatory transmission could be induced in wild-type (WT) Schaffer collateral-CA1 pyramidal cell synapses by blockade of GABAB receptors (GABABRs). The same treatment was virtually ineffective in TKO slices, suggesting that the increased strength of the excitatory transmission results from an impairment of GABAB presynaptic inhibition. Exogenous stimulation of GABABRs in excitatory autaptic neurons, where GABA spillover is negligible, demonstrated that GABABRs were effective in inhibiting excitatory transmission in both WT and TKO neurons. These results demonstrate that the decreased GABA release and spillover, previously observed in TKO hippocampal slices, removes the tonic brake of presynaptic GABABRs on glutamate transmission, making the excitation/inhibition imbalance stronger.
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Affiliation(s)
- Pierluigi Valente
- Department of Experimental Medicine, Section of Physiology, University of Genoa, 16132 Genova, Italy
| | - Pasqualina Farisello
- Department of Experimental Medicine, Section of Physiology, University of Genoa, 16132 Genova, Italy.,Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, 16132 Genova, Italy
| | - Flavia Valtorta
- S. Raffaele Scientific Institute and Vita-Salute University, 20132 Milano, Italy
| | - Pietro Baldelli
- Department of Experimental Medicine, Section of Physiology, University of Genoa, 16132 Genova, Italy.,Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, 16132 Genova, Italy
| | - Fabio Benfenati
- Department of Experimental Medicine, Section of Physiology, University of Genoa, 16132 Genova, Italy.,Center for Synaptic Neuroscience and Technology, Istituto Italiano di Tecnologia, 16132 Genova, Italy
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60
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Wilson-Poe AR, Jeong HJ, Vaughan CW. Chronic morphine reduces the readily releasable pool of GABA, a presynaptic mechanism of opioid tolerance. J Physiol 2017; 595:6541-6555. [PMID: 28815604 DOI: 10.1113/jp274157] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 08/11/2017] [Indexed: 12/14/2022] Open
Abstract
KEY POINTS Chronic treatment with opioids, such as morphine, leads to analgesic tolerance. While postsynaptic opioid tolerance is well documented, the involvement of presynaptic mechanisms remains unclear. We show that chronic morphine reduces the ability of periaqueductal grey (PAG) neurons to maintain GABAergic transmission. This depression of GABAergic transmission was due to a reduction in the effective size of the readily releasable pool. This also led to a reduction in opioid presynaptic inhibition; these presynaptic adaptations need to be considered in the development of strategies to reduce opioid tolerance. ABSTRACT The midbrain periaqueductal grey (PAG) plays a critical role in tolerance to the analgesic actions of opioids such as morphine. While numerous studies have identified the postsynaptic adaptations induced by chronic morphine treatment in this and other brain regions, the presence of presynaptic adaptations remains uncertain. We examined GABAergic synaptic transmission within rat PAG brain slices from animals which underwent a low dose morphine treatment protocol which produces tolerance, but not withdrawal. Evoked GABAergic IPSCs (inhibitory postsynaptic currents) were less in morphine compared to control saline treated animals. Postsynaptic GABAA receptor mediated currents and desensitization, presynaptic release probability (Pr ), and inhibition by endogenous neurotransmitters were similar in morphine and saline treated animals. By contrast, the effective size of the readily releasable pool (RRP) was smaller in morphine treated animals. While the μ-opioid agonist DAMGO produced a reduction in Pr and RRP size in saline treated animals, it only reduced Pr in morphine treated animals. Consequently, DAMGO-induced inhibition of evoked IPSCs during short burst stimulation was less in morphine, compared to saline treated animals. These results indicate that low dose chronic morphine treatment reduces presynaptic μ-opioid inhibition by reducing the size of the pool of vesicles available for action potential dependent release. This novel presynaptic adaptation may provide important insights into the development of efficacious pain therapies that can circumvent the development of opioid tolerance.
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Affiliation(s)
- Adrianne R Wilson-Poe
- Pain Management Research Institute, Kolling Institute of Medical Research, Northern Clinical School, The University of Sydney and Royal North Shore Hospital, St Leonards, New South Wales, 2065, Australia
| | - Hyo-Jin Jeong
- Pain Management Research Institute, Kolling Institute of Medical Research, Northern Clinical School, The University of Sydney and Royal North Shore Hospital, St Leonards, New South Wales, 2065, Australia
| | - Christopher W Vaughan
- Pain Management Research Institute, Kolling Institute of Medical Research, Northern Clinical School, The University of Sydney and Royal North Shore Hospital, St Leonards, New South Wales, 2065, Australia
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61
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Changes in Properties of Auditory Nerve Synapses following Conductive Hearing Loss. J Neurosci 2017; 37:323-332. [PMID: 28077712 DOI: 10.1523/jneurosci.0523-16.2016] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 11/10/2016] [Accepted: 11/19/2016] [Indexed: 02/08/2023] Open
Abstract
Auditory activity plays an important role in the development of the auditory system. Decreased activity can result from conductive hearing loss (CHL) associated with otitis media, which may lead to long-term perceptual deficits. The effects of CHL have been mainly studied at later stages of the auditory pathway, but early stages remain less examined. However, changes in early stages could be important because they would affect how information about sounds is conveyed to higher-order areas for further processing and localization. We examined the effects of CHL at auditory nerve synapses onto bushy cells in the mouse anteroventral cochlear nucleus following occlusion of the ear canal. These synapses, called endbulbs of Held, normally show strong depression in voltage-clamp recordings in brain slices. After 1 week of CHL, endbulbs showed even greater depression, reflecting higher release probability. We observed no differences in quantal size between control and occluded mice. We confirmed these observations using mean-variance analysis and the integration method, which also revealed that the number of release sites decreased after occlusion. Consistent with this, synaptic puncta immunopositive for VGLUT1 decreased in area after occlusion. The level of depression and number of release sites both showed recovery after returning to normal conditions. Finally, bushy cells fired fewer action potentials in response to evoked synaptic activity after occlusion, likely because of increased depression and decreased input resistance. These effects appear to reflect a homeostatic, adaptive response of auditory nerve synapses to reduced activity. These effects may have important implications for perceptual changes following CHL. SIGNIFICANCE STATEMENT Normal hearing is important to everyday life, but abnormal auditory experience during development can lead to processing disorders. For example, otitis media reduces sound to the ear, which can cause long-lasting deficits in language skills and verbal production, but the location of the problem is unknown. Here, we show that occluding the ear causes synapses at the very first stage of the auditory pathway to modify their properties, by decreasing in size and increasing the likelihood of releasing neurotransmitter. This causes synapses to deplete faster, which reduces fidelity at central targets of the auditory nerve, which could affect perception. Temporary hearing loss could cause similar changes at later stages of the auditory pathway, which could contribute to disorders in behavior.
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62
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Fatigue in Rapsyn-Deficient Zebrafish Reflects Defective Transmitter Release. J Neurosci 2017; 36:10870-10882. [PMID: 27798141 DOI: 10.1523/jneurosci.0505-16.2016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 09/03/2016] [Indexed: 12/29/2022] Open
Abstract
Rapsyn-deficient myasthenic syndrome is characterized by a weakness in voluntary muscle contraction, a direct consequence of greatly reduced synaptic responses that result from poorly clustered acetylcholine receptors. As with other myasthenic syndromes, the general muscle weakness is also accompanied by use-dependent fatigue. Here, we used paired motor neuron target muscle patch-clamp recordings from a rapsyn-deficient mutant line of zebrafish to explore for the first time the mechanisms causal to fatigue. We find that synaptic responses in mutant fish can follow faithfully low-frequency stimuli despite the reduced amplitude. This is in part helped by a compensatory increase in the number of presynaptic release sites in the mutant fish. In response to high-frequency stimulation, both wild-type and mutant neuromuscular junctions depress to steady-state response levels, but the latter shows exaggerated depression. Analysis of the steady-state transmission revealed that vesicle reloading and release at individual release sites is significantly slower in mutant fish during high-frequency activities. Therefore, reductions in postsynaptic receptor density and compromised presynaptic release collectively serve to reduce synaptic strength to levels that fall below the threshold for muscle action potential generation, thus accounting for use-dependent fatigue. Our findings raise the possibility that defects in motor neuron function may also be at play in other myasthenic syndromes that have been mapped to mutations in muscle-specific proteins. SIGNIFICANCE STATEMENT Use-dependent fatigue accompanies many neuromuscular myasthenic syndromes, including muscle rapsyn deficiency. Here, using a rapsyn-deficient line of zebrafish, we performed paired motor neuron target muscle patch-clamp recordings to investigate the mechanisms causal to this phenomenon. Our findings indicate that the reduced postsynaptic receptor density resulting from defective rapsyn contributes to weakness, but is not solely responsible for use-dependent fatigue. Instead, we find unexpected involvement of altered transmitter release from the motor neuron. Specifically, slowed reloading of vesicle release sites leads to augmented synaptic depression during repeated action potentials. Even at moderate stimulus frequencies, the depression levels for evoked synaptic responses fall below the threshold for the generation of muscle action potentials. The associated contraction failures are manifest as use-dependent fatigue.
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63
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Kaeser PS, Regehr WG. The readily releasable pool of synaptic vesicles. Curr Opin Neurobiol 2017; 43:63-70. [PMID: 28103533 DOI: 10.1016/j.conb.2016.12.012] [Citation(s) in RCA: 143] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 11/26/2016] [Accepted: 12/31/2016] [Indexed: 10/20/2022]
Abstract
Each presynaptic bouton is densely packed with many vesicles, only a small fraction of which are available for immediate release. These vesicles constitute the readily releasable pool (RRP). The RRP size, and the probability of release of each vesicle within the RRP, together determine synaptic strength. Here, we discuss complications and recent advances in determining the size of the physiologically relevant RRP. We consider molecular mechanisms to generate and regulate the RRP, and discuss the relationship between vesicle docking and the RRP. We conclude that many RRP vesicles are docked, that some docked vesicles may not be part of the RRP, and that undocked vesicles can contribute to the RRP by rapid recruitment to unoccupied, molecularly activated ready-to-release sites.
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Affiliation(s)
- Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, United States.
| | - Wade G Regehr
- Department of Neurobiology, Harvard Medical School, United States.
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Turecek J, Jackman SL, Regehr WG. Synaptic Specializations Support Frequency-Independent Purkinje Cell Output from the Cerebellar Cortex. Cell Rep 2016; 17:3256-3268. [PMID: 28009294 PMCID: PMC5870134 DOI: 10.1016/j.celrep.2016.11.081] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 11/14/2016] [Accepted: 11/28/2016] [Indexed: 11/23/2022] Open
Abstract
The output of the cerebellar cortex is conveyed to the deep cerebellar nuclei (DCN) by Purkinje cells (PCs). Here, we characterize the properties of the PC-DCN synapse in juvenile and adult mice and find that prolonged high-frequency stimulation leads to steady-state responses that become increasingly frequency independent within the physiological firing range of PCs in older animals, resulting in a linear relationship between charge transfer and activation frequency. We used a low-affinity antagonist to show that GABAA-receptor saturation occurs at this synapse but does not underlie frequency-invariant transmission. We propose that PC-DCN synapses have two components of release: one prominent early in trains and another specialized to maintain transmission during prolonged activation. Short-term facilitation offsets partial vesicle depletion to produce frequency-independent transmission.
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Affiliation(s)
- Josef Turecek
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave., Boston, MA 02115, USA
| | - Skyler L Jackman
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave., Boston, MA 02115, USA
| | - Wade G Regehr
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave., Boston, MA 02115, USA.
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Delvendahl I, Hallermann S. The Cerebellar Mossy Fiber Synapse as a Model for High-Frequency Transmission in the Mammalian CNS. Trends Neurosci 2016; 39:722-737. [DOI: 10.1016/j.tins.2016.09.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 09/17/2016] [Accepted: 09/20/2016] [Indexed: 10/20/2022]
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Abstract
UNLABELLED Many neurons fire spontaneously, and the rate of this firing is subject to neuromodulation. How this firing affects functional connectivity within a neural network remains largely unexplored. Here we show that changes in spontaneous firing of cartwheel interneurons in the mouse dorsal cochlear nucleus (DCN) alter the effective convergence ratio of interneurons onto their postsynaptic targets through short-term synaptic plasticity. Spontaneous firing of cartwheel cells led to activity-dependent synaptic depression of individual cartwheel synapses. Depression was rapid and profound at stimulation frequencies between 10 and 200 Hz, suggesting the presence of high release probability (Pr) vesicles at these inhibitory synapses. Weak, transient synaptic facilitation could be induced after synapses were predepressed, indicating that low-Pr vesicles are also recruited, and may thus support steady-state transmission. A two-pool vesicle depletion model with 10-fold differences in Pr could account for the synaptic depression over a wide range of stimulus conditions. As a result of depression during high spontaneous activity, more cartwheel interneurons were required for effective inhibition. Convergence of four interneurons was sufficient to compensate for the effects of depression during physiologically expected rates of activity. By simulating synaptic release during spontaneous firing, we found that recruitment of low-Pr vesicles at the synapse plays a critical role in maintaining effective inhibition within a small population of interneurons. The interplay between spontaneous spiking, short-term synaptic plasticity, and vesicle recruitment thus determines the effective size of a convergent neural network. SIGNIFICANCE STATEMENT We examined the relationship between the structure of a small neural circuit and the properties of its individual synapses. Successful synaptic inhibition of a target cell firing requires a critical inhibitory synaptic strength. Synapses often become depressed during spontaneous presynaptic activity, and this increases the number of presynaptic neurons needed to mediate inhibition. We show that depression is limited by the presence of a pool of vesicles that resist depletion. Thus, the size of this vesicle pool determines the size of the circuit needed to mediate inhibition during different patterns of activity.
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Mahapatra S, Lou X. Dynamin-1 deletion enhances post-tetanic potentiation and quantal size after tetanic stimulation at the calyx of Held. J Physiol 2016; 595:193-206. [PMID: 27229184 DOI: 10.1113/jp271937] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Accepted: 05/18/2016] [Indexed: 01/09/2023] Open
Abstract
KEY POINTS Post-tetanic potentiation (PTP) is attributed mainly to an increase in release probability (Pr ) and/or readily-releasable pool (RRP) in many synapses, but the role of endocytosis in PTP is unknown. Using the calyx of Held synapse from tissue-specific dynamin-1 knockout (cKO) mice (P16-20), we report that cKO synapses show enhanced PTP compared to control. We found significant increases in both spontaneous excitatory postsynaptic current (spEPSC) amplitude and RRP size (estimated by a train of 30 APs at 100 Hz) in cKO over control during PTP. Actin depolymerization blocks the increase in spEPSC amplitude in both control and cKO, and it abolishes the enhancement of PTP in cKO. PTP is sensitive to the PKC inhibitor GF109203X in both control and cKO. We conclude that an activity-dependent quantal size increase contributes to the enhancement of PTP in cKO over control and an altered endocytosis affects short-term plasticity through quantal size changes. ABSTRACT High-frequency stimulation leads to post-tetanic potentiation (PTP) at many types of synapses. Previous studies suggest that PTP results primarily from a protein kinase C (PKC)-dependent increase in release probability (Pr ) and/or readily-releasable pool (RRP) of synaptic vesicles (SVs), but the role of SV endocytosis in PTP is unknown. Using the mature calyx of Held (P16-20), we report that tissue-specific ablation of dynamin-1 (cKO), an endocytic protein crucial for SV regeneration, enhances PTP in cKO over control. To explore the mechanism of this enhancement, we estimated the changes in paired-pulse ratios (PPRs) and RRP size during PTP. RRP was estimated by the back-extrapolation of cumulative EPSC amplitudes during a train of 30 action potentials at 100 Hz (termed RRPtrain ). We found an increase in RRPtrain during PTP in both control and cKO, but no significant changes in the PPR. Moreover, the amplitude and frequency of spontaneous excitatory postsynaptic currents (spEPSCs) increased during PTP in both control and cKO; however, the spEPSC amplitude in cKO during PTP was significantly larger than in control. Actin depolymerization reagent latrunculin-B (Lat-B) abolished the activity-dependent increase in spEPSC amplitude in both control and cKO, but selectively blocked the enhancement of PTP in cKO, without affecting PTP in control. PKC inhibitor GF109203X nearly abolished PTP in both control and cKO. These data suggest that the quantal size increase contributes to the enhancement of PTP in dynamin-1 cKO, and this change depends on strong synaptic activity and actin polymerization.
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Affiliation(s)
- Satyajit Mahapatra
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Xuelin Lou
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53706, USA
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68
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Hoffman AF, Spivak CE, Lupica CR. Enhanced Dopamine Release by Dopamine Transport Inhibitors Described by a Restricted Diffusion Model and Fast-Scan Cyclic Voltammetry. ACS Chem Neurosci 2016; 7:700-9. [PMID: 27018734 DOI: 10.1021/acschemneuro.5b00277] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Fast-scan cyclic voltammetry (FSCV) using carbon fiber electrodes is widely used to rapidly monitor changes in dopamine (DA) levels in vitro and in vivo. Current analytical approaches utilize parameters such as peak oxidation current amplitude and decay times to estimate release and uptake processes, respectively. However, peak amplitude changes are often observed with uptake inhibitors, thereby confounding the interpretation of these parameters. To overcome this limitation, we demonstrate that a simple five-parameter, two-compartment model mathematically describes DA signals as a balance of release (r/ke) and uptake (ku), summed with adsorption (kads and kdes) of DA to the carbon electrode surface. Using nonlinear regression, we demonstrate that our model precisely describes measured DA signals obtained in brain slice recordings. The parameters extracted from these curves were then validated using pharmacological manipulations that selectively alter vesicular release or DA transporter (DAT)-mediated uptake. Manipulation of DA release through altering the Ca(2+)/Mg(2+) ratio or adding tetrodotoxin reduced the release parameter with no effect on the uptake parameter. DAT inhibitors methylenedioxypyrovalerone, cocaine, and nomifensine significantly reduced uptake and increased vesicular DA release. In contrast, a low concentration of amphetamine reduced uptake but had no effect on DA release. Finally, the kappa opioid receptor agonist U50,488 significantly reduced vesicular DA release but had no effect on uptake. Together, these data demonstrate a novel analytical approach to distinguish the effects of manipulations on DA release or uptake that can be used to interpret FSCV data.
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Affiliation(s)
- Alexander F. Hoffman
- Electrophysiology Research
Section, Cellular Neurobiology Branch, National Institute on Drug Abuse Intramural Research Program, Baltimore, Maryland 21224, United States
| | - Charles E. Spivak
- Electrophysiology Research
Section, Cellular Neurobiology Branch, National Institute on Drug Abuse Intramural Research Program, Baltimore, Maryland 21224, United States
| | - Carl R. Lupica
- Electrophysiology Research
Section, Cellular Neurobiology Branch, National Institute on Drug Abuse Intramural Research Program, Baltimore, Maryland 21224, United States
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69
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Howell RD, Pugh JR. Biphasic modulation of parallel fibre synaptic transmission by co-activation of presynaptic GABAA and GABAB receptors in mice. J Physiol 2016; 594:3651-66. [PMID: 27061582 DOI: 10.1113/jp272124] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 03/30/2016] [Indexed: 01/23/2023] Open
Abstract
KEY POINTS Many excitatory synapses co-express presynaptic GABAA and GABAB receptors, despite their opposing actions on synaptic transmission. It is still unclear how co-activation of these receptors modulates synapse function. We measured presynaptic GABA receptor function at parallel fibre synapses onto stellate cells in the cerebellum using whole-cell patch-clamp recording and photolytic uncaging of RuBi-GABA. Activation of presynaptic GABA receptors results in a transient (∼100 ms) enhancement of synaptic transmission (mediated by GABAA receptors) followed by a long lasting (>500 ms) inhibition of transmission (mediated by GABAB receptors). When activated just prior to high-frequency trains of stimulation, presynaptic GABAA and GABAB receptors work together to reduce short-term facilitation/enhance depression, altering the filtering properties of synaptic transmission. Inhibition of synaptic transmission by GABAB receptors is more sensitive to GABA than enhancement by GABAA receptors, suggesting GABAB receptors may be activated by ambient GABA or release from greater distances. ABSTRACT GABAA and GABAB receptors are co-expressed at many presynaptic terminals in the central nervous system. Previous studies have shown that GABAA receptors typically enhance vesicle release while GABAB receptors inhibit release. However, it is not clear how the competing actions of these receptors modulate synaptic transmission when co-activated, as is likely in vivo. We investigated this question at parallel fibre synapses in the cerebellum, which co-express presynaptic GABAA and GABAB receptors. In acute slices from C57BL/6 mice, we find that co-activation of presynaptic GABA receptors by photolytic uncaging of RuBi-GABA has a biphasic effect on EPSC amplitudes recorded from stellate cells. Synchronous and asynchronous EPSCs evoked within ∼100 ms of GABA uncaging were increased, while EPSCs evoked ∼300-600 ms after GABA uncaging were reduced compared to interleaved control sweeps. We confirmed these effects are presynaptic by measuring the paired-pulse ratio, variance of EPSC amplitudes, and response probability. During trains of high-frequency stimulation GABAA and GABAB receptors work together (rather than oppose one another) to reduce short-term facilitation when GABA is uncaged just prior to the onset of stimulation. We also find that GABAB receptor-mediated inhibition can be elicited by lower GABA concentrations than GABAA receptor-mediated enhancement of EPSCs, suggesting GABAB receptors may be selectively activated by ambient GABA or release from more distance synapses. These data suggest that GABA, acting through both presynaptic GABAA and GABAB receptors, modulate the amplitude and short-term plasticity of excitatory synapses, a result not possible from activation of either receptor type alone.
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Affiliation(s)
- Rebecca D Howell
- University of Texas Health Science Center at San Antonio, Department of Physiology, San Antonio, TX 78229, USA
| | - Jason R Pugh
- University of Texas Health Science Center at San Antonio, Department of Physiology, San Antonio, TX 78229, USA
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70
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Harris N, Braiser DJ, Dickman DK, Fetter RD, Tong A, Davis GW. The Innate Immune Receptor PGRP-LC Controls Presynaptic Homeostatic Plasticity. Neuron 2016; 88:1157-1164. [PMID: 26687223 DOI: 10.1016/j.neuron.2015.10.049] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Revised: 08/28/2015] [Accepted: 10/22/2015] [Indexed: 10/22/2022]
Abstract
It is now appreciated that the brain is immunologically active. Highly conserved innate immune signaling responds to pathogen invasion and injury and promotes structural refinement of neural circuitry. However, it remains generally unknown whether innate immune signaling has a function during the day-to-day regulation of neural function in the absence of pathogens and irrespective of cellular damage or developmental change. Here we show that an innate immune receptor, a member of the peptidoglycan pattern recognition receptor family (PGRP-LC), is required for the induction and sustained expression of homeostatic synaptic plasticity. This receptor functions presynaptically, controlling the homeostatic modulation of the readily releasable pool of synaptic vesicles following inhibition of postsynaptic glutamate receptor function. Thus, PGRP-LC is a candidate receptor for retrograde, trans-synaptic signaling, a novel activity for innate immune signaling and the first known function of a PGRP-type receptor in the nervous system of any organism.
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Affiliation(s)
- Nathan Harris
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158-0822, USA
| | - Daniel J Braiser
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158-0822, USA
| | - Dion K Dickman
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158-0822, USA
| | - Richard D Fetter
- Janelia Research Campus of HHMI, 19700 Helix Dr. Ashburn, VA 20147, USA
| | - Amy Tong
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158-0822, USA
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158-0822, USA.
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71
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Mahfooz K, Singh M, Renden R, Wesseling JF. A Well-Defined Readily Releasable Pool with Fixed Capacity for Storing Vesicles at Calyx of Held. PLoS Comput Biol 2016; 12:e1004855. [PMID: 27035349 PMCID: PMC4818018 DOI: 10.1371/journal.pcbi.1004855] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2015] [Accepted: 03/07/2016] [Indexed: 11/19/2022] Open
Abstract
The readily releasable pool (RRP) of vesicles is a core concept in studies of presynaptic function. However, operating principles lack consensus definition and the utility for quantitative analysis has been questioned. Here we confirm that RRPs at calyces of Held from 14 to 21 day old mice have a fixed capacity for storing vesicles that is not modulated by Ca2+. Discrepancies with previous studies are explained by a dynamic flow-through pool, established during heavy use, containing vesicles that are released with low probability despite being immediately releasable. Quantitative analysis ruled out a posteriori explanations for the vesicles with low release probability, such as Ca2+-channel inactivation, and established unexpected boundary conditions for remaining alternatives. Vesicles in the flow-through pool could be incompletely primed, in which case the full sequence of priming steps downstream of recruitment to the RRP would have an average unitary rate of at least 9/s during heavy use. Alternatively, vesicles with low and high release probability could be recruited to distinct types of release sites; in this case the timing of recruitment would be similar at the two types, and the downstream transition from recruited to fully primed would be much faster. In either case, further analysis showed that activity accelerates the upstream step where vesicles are initially recruited to the RRP. Overall, our results show that the RRP can be well defined in the mathematical sense, and support the concept that the defining mechanism is a stable group of autonomous release sites. Short-term plasticity has a dramatic impact on the connection strength of almost every type of synapse during normal use. Some synapses enhance, some depress, and many enhance or depress depending on the recent history of use. A better understanding is needed for modeling information processing in biological circuits and for studying the molecular biology of neurotransmission. Here we show that first principles at the calyx of Held, such as whether or not a readily-releasable pool of vesicles in the presynaptic terminal has a fixed capacity for storing vesicles, are unexpectedly similar to synapse types that are used at much lower frequencies. Our study establishes new methods for studying the function of presynaptic molecules, and the results suggest that a tractable general model of short-term plasticity can capture the full computational power of dynamic synaptic modulation across a large range of synapse types and situations.
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Affiliation(s)
- Kashif Mahfooz
- Department Neurociencias (CIMA), Universidad de Navarra, Pamplona, Spain
| | - Mahendra Singh
- Department of Physiology & Cell Biology, University of Nevada School of Medicine, Reno, Nevada, United States of America
| | - Robert Renden
- Department of Physiology & Cell Biology, University of Nevada School of Medicine, Reno, Nevada, United States of America
| | - John F. Wesseling
- Department Neurociencias (CIMA), Universidad de Navarra, Pamplona, Spain
- * E-mail:
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72
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Baydyuk M, Xu J, Wu LG. The calyx of Held in the auditory system: Structure, function, and development. Hear Res 2016; 338:22-31. [PMID: 27018297 DOI: 10.1016/j.heares.2016.03.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Revised: 03/10/2016] [Accepted: 03/17/2016] [Indexed: 12/19/2022]
Abstract
The calyx of Held synapse plays an important role in the auditory system, relaying information about sound localization via fast and precise synaptic transmission, which is achieved by its specialized structure and giant size. During development, the calyx of Held undergoes anatomical, morphological, and physiological changes necessary for performing its functions. The large dimensions of the calyx of Held nerve terminal are well suited for direct electrophysiological recording of many presynaptic events that are difficult, if not impossible to record at small conventional synapses. This unique accessibility has been used to investigate presynaptic ion channels, transmitter release, and short-term plasticity, providing invaluable information about basic presynaptic mechanisms of transmission at a central synapse. Here, we review anatomical and physiological specializations of the calyx of Held, summarize recent studies that provide new mechanisms important for calyx development and reliable synaptic transmission, and examine fundamental presynaptic mechanisms learned from studies using calyx as a model nerve terminal. This article is part of a Special Issue entitled <Annual Reviews 2016>.
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Affiliation(s)
- Maryna Baydyuk
- National Institute of Neurological Disorders and Stroke, 35 Convent Dr., Bldg 35, Bethesda, MD 20892, USA.
| | - Jianhua Xu
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA; Department of Neurology, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA
| | - Ling-Gang Wu
- National Institute of Neurological Disorders and Stroke, 35 Convent Dr., Bldg 35, Bethesda, MD 20892, USA
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73
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Thanawala MS, Regehr WG. Determining synaptic parameters using high-frequency activation. J Neurosci Methods 2016; 264:136-152. [PMID: 26972952 DOI: 10.1016/j.jneumeth.2016.02.021] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 02/23/2016] [Accepted: 02/26/2016] [Indexed: 12/25/2022]
Abstract
BACKGROUND The specific properties of a synapse determine how neuronal activity evokes neurotransmitter release. Evaluating changes in synaptic properties during sustained activity is essential to understanding how genetic manipulations and neuromodulators regulate neurotransmitter release. Analyses of postsynaptic responses to high-frequency stimulation have provided estimates of the size of the readily-releasable pool (RRP) of vesicles (N0) and the probability of vesicular release (p) at multiple synapses. NEW METHOD Here, we introduce a model-based approach at the calyx of Held synapse in which depletion and the rate of replenishment (R) determine the number of available vesicles, and facilitation leads to a use-dependent increase in p when initial p is low. RESULTS When p is high and R is low, we find excellent agreement between estimates based on all three methods and the model. However, when p is low or when significant replenishment occurs between stimuli, estimates of different methods diverge, and model estimates are between the extreme estimates provided by the other approaches. COMPARISON WITH OTHER METHODS We compare our model-based approach to three other approaches that rely on different simplifying assumptions. Our findings suggest that our model provides a better estimate of N0 and p than previously-established methods, likely due to inaccurate assumptions about replenishment. More generally, our findings suggest that approaches commonly used to estimate N0 and p at other synapses are often applied under experimental conditions that yield inaccurate estimates. CONCLUSIONS Careful application of appropriate methods can greatly improve estimates of synaptic parameters.
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Affiliation(s)
- Monica S Thanawala
- Department of Neurobiology, Harvard Medical School, Boston, MA, United States
| | - Wade G Regehr
- Department of Neurobiology, Harvard Medical School, Boston, MA, United States.
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74
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Körber C, Kuner T. Molecular Machines Regulating the Release Probability of Synaptic Vesicles at the Active Zone. Front Synaptic Neurosci 2016; 8:5. [PMID: 26973506 PMCID: PMC4773589 DOI: 10.3389/fnsyn.2016.00005] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 02/17/2016] [Indexed: 11/13/2022] Open
Abstract
The fusion of synaptic vesicles (SVs) with the plasma membrane of the active zone (AZ) upon arrival of an action potential (AP) at the presynaptic compartment is a tightly regulated probabilistic process crucial for information transfer. The probability of a SV to release its transmitter content in response to an AP, termed release probability (Pr), is highly diverse both at the level of entire synapses and individual SVs at a given synapse. Differences in Pr exist between different types of synapses, between synapses of the same type, synapses originating from the same axon and even between different SV subpopulations within the same presynaptic terminal. The Pr of SVs at the AZ is set by a complex interplay of different presynaptic properties including the availability of release-ready SVs, the location of the SVs relative to the voltage-gated calcium channels (VGCCs) at the AZ, the magnitude of calcium influx upon arrival of the AP, the buffering of calcium ions as well as the identity and sensitivity of the calcium sensor. These properties are not only interconnected, but can also be regulated dynamically to match the requirements of activity patterns mediated by the synapse. Here, we review recent advances in identifying molecules and molecular machines taking part in the determination of vesicular Pr at the AZ.
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Affiliation(s)
- Christoph Körber
- Department of Functional Neuroanatomy, Institute of Anatomy and Cell Biology, Heidelberg University Heidelberg, Germany
| | - Thomas Kuner
- Department of Functional Neuroanatomy, Institute of Anatomy and Cell Biology, Heidelberg University Heidelberg, Germany
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75
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Extremely Low Frequency Electromagnetic Fields Facilitate Vesicle Endocytosis by Increasing Presynaptic Calcium Channel Expression at a Central Synapse. Sci Rep 2016; 6:21774. [PMID: 26887777 PMCID: PMC4757866 DOI: 10.1038/srep21774] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2015] [Accepted: 02/01/2016] [Indexed: 12/24/2022] Open
Abstract
Accumulating evidence suggests significant biological effects caused by extremely low frequency electromagnetic fields (ELF-EMF). Although exo-endocytosis plays crucial physical and biological roles in neuronal communication, studies on how ELF-EMF regulates this process are scarce. By directly measuring calcium currents and membrane capacitance at a large mammalian central nervous synapse, the calyx of Held, we report for the first time that ELF-EMF critically affects synaptic transmission and plasticity. Exposure to ELF-EMF for 8 to 10 days dramatically increases the calcium influx upon stimulation and facilitates all forms of vesicle endocytosis, including slow and rapid endocytosis, endocytosis overshoot and bulk endocytosis, but does not affect the RRP size and exocytosis. Exposure to ELF-EMF also potentiates PTP, a form of short-term plasticity, increasing its peak amplitude without impacting its time course. We further investigated the underlying mechanisms and found that calcium channel expression, including the P/Q, N, and R subtypes, at the presynaptic nerve terminal was enhanced, accounting for the increased calcium influx upon stimulation. Thus, we conclude that exposure to ELF-EMF facilitates vesicle endocytosis and synaptic plasticity in a calcium-dependent manner by increasing calcium channel expression at the nerve terminal.
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76
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Acuna C, Liu X, Gonzalez A, Südhof TC. RIM-BPs Mediate Tight Coupling of Action Potentials to Ca(2+)-Triggered Neurotransmitter Release. Neuron 2015; 87:1234-1247. [PMID: 26402606 DOI: 10.1016/j.neuron.2015.08.027] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Revised: 07/25/2015] [Accepted: 08/17/2015] [Indexed: 01/08/2023]
Abstract
Ultrafast neurotransmitter release requires tight colocalization of voltage-gated Ca(2+) channels with primed, release-ready synaptic vesicles at the presynaptic active zone. RIM-binding proteins (RIM-BPs) are multidomain active zone proteins that bind to RIMs and to Ca(2+) channels. In Drosophila, deletion of RIM-BPs dramatically reduces neurotransmitter release, but little is known about RIM-BP function in mammalian synapses. Here, we generated double conditional knockout mice for RIM-BP1 and RIM-BP2, and analyzed RIM-BP-deficient synapses in cultured hippocampal neurons and the calyx of Held. Surprisingly, we find that in murine synapses, RIM-BPs are not essential for neurotransmitter release as such, but are selectively required for high-fidelity coupling of action potential-induced Ca(2+) influx to Ca(2+)-stimulated synaptic vesicle exocytosis. Deletion of RIM-BPs decelerated action-potential-triggered neurotransmitter release and rendered it unreliable, thereby impairing the fidelity of synaptic transmission. Thus, RIM-BPs ensure optimal organization of the machinery for fast release in mammalian synapses without being a central component of the machinery itself.
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Affiliation(s)
- Claudio Acuna
- Department of Cellular and Molecular Physiology and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA.
| | - Xinran Liu
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Aneysis Gonzalez
- Department of Cellular and Molecular Physiology and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Thomas C Südhof
- Department of Cellular and Molecular Physiology and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA.
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77
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Abstract
Synaptic depression is prominent among synapses, but the underlying mechanisms remain uncertain. Here, we use paired patch clamp recording to study neuromuscular transmission between the caudal primary motor neuron and target skeletal muscle in zebrafish. This synapse has an unusually low number of release sites, all with high probabilities of release in response to low-frequency stimulation. During high-frequency stimulation, the synapse undergoes short-term depression and reaches steady-state levels of transmission that sustain the swimming behavior. To determine the release parameters underlying this steady state, we applied variance analysis. Our analysis revealed two functionally distinct subclasses of release sites differing by over 60-fold in rates of vesicle reloading. A slow reloading class requires seconds to recover and contributes to depression onset but not the steady-state transmission. By contrast, a fast reloading class recovers within tens of milliseconds and is solely responsible for steady-state transmission. Thus, in contrast to most current models that assign levels of steady-state depression to vesicle availability, our findings instead assign this function to nonuniform release site kinetics. The duality of active-site properties accounts for the highly nonlinear dependence of steady-state depression levels on frequency.
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78
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Thoreson WB, Van Hook MJ, Parmelee C, Curto C. Modeling and measurement of vesicle pools at the cone ribbon synapse: Changes in release probability are solely responsible for voltage-dependent changes in release. Synapse 2015; 70:1-14. [PMID: 26541100 DOI: 10.1002/syn.21871] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 09/21/2015] [Accepted: 10/06/2015] [Indexed: 12/16/2022]
Abstract
Postsynaptic responses are a product of quantal amplitude (Q), size of the releasable vesicle pool (N), and release probability (P). Voltage-dependent changes in presynaptic Ca(2+) entry alter postsynaptic responses primarily by changing P but have also been shown to influence N. With simultaneous whole cell recordings from cone photoreceptors and horizontal cells in tiger salamander retinal slices, we measured N and P at cone ribbon synapses by using a train of depolarizing pulses to stimulate release and deplete the pool. We developed an analytical model that calculates the total pool size contributing to release under different stimulus conditions by taking into account the prior history of release and empirically determined properties of replenishment. The model provided a formula that calculates vesicle pool size from measurements of the initial postsynaptic response and limiting rate of release evoked by a train of pulses, the fraction of release sites available for replenishment, and the time constant for replenishment. Results of the model showed that weak and strong depolarizing stimuli evoked release with differing probabilities but the same size vesicle pool. Enhancing intraterminal Ca(2+) spread by lowering Ca(2+) buffering or applying BayK8644 did not increase PSCs evoked with strong test steps, showing there is a fixed upper limit to pool size. Together, these results suggest that light-evoked changes in cone membrane potential alter synaptic release solely by changing release probability.
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Affiliation(s)
- Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska.,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska
| | - Matthew J Van Hook
- Truhlsen Eye Institute, Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska
| | - Caitlyn Parmelee
- Department of Mathematics, University of Nebraska, Lincoln, Nebraska
| | - Carina Curto
- Department of Mathematics, University of Nebraska, Lincoln, Nebraska.,Department of Mathematics, Pennsylvania State University, State College, Pennsylvania
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79
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Dicken MS, Hughes AR, Hentges ST. Gad1 mRNA as a reliable indicator of altered GABA release from orexigenic neurons in the hypothalamus. Eur J Neurosci 2015; 42:2644-53. [PMID: 26370162 DOI: 10.1111/ejn.13076] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 09/02/2015] [Accepted: 09/07/2015] [Indexed: 11/29/2022]
Abstract
The strength of γ-aminobutyric acid (GABA)-mediated inhibitory synaptic input is a principle determinant of neuronal activity. However, because of differences in the number of GABA afferent inputs and the sites of synapses, it is difficult to directly assay for altered GABA transmission between specific cells. The present study tested the hypothesis that the level of mRNA for the GABA synthetic enzyme glutamate decarboxylase (GAD) can provide a reliable proxy for GABA release. This was tested in a mouse hypothalamic circuit important in the regulation of energy balance. Fluorescent in situ hybridization results show that the expression of Gad1 mRNA (encoding the GAD67 enzyme) was increased in hypothalamic neuropeptide Y/agouti-related peptide (NPY/AgRP) neurons after an overnight fast, consistent with the ability of GABA from these neurons to stimulate food intake. Optogenetic studies confirmed that the observed increase in Gad1 mRNA correlated with an increase in the probability of GABA release from NPY/AgRP neurons onto downstream proopiomelanocortin neurons. Likewise, there was an increase in the readily releasable pool of GABA in NPY/AgRP neurons. Selective inhibition of GAD activity in NPY/AgRP neurons decreased GABA release, indicating that GAD67 activity, which is largely dictated by expression level, is a key determinant of GABA release. Altogether, it appears that Gad expression may be a reliable proxy of altered GABAergic transmission. Examining changes in Gad mRNA as a proxy for GABA release may be particularly helpful when the downstream targets are not known or when limited tools exist for detecting GABA release at a particular synapse.
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Affiliation(s)
- Matthew S Dicken
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, CO, 80523, USA
| | - Alexander R Hughes
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, CO, 80523, USA
| | - Shane T Hentges
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, CO, 80523, USA
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80
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Van Hook MJ, Thoreson WB. Weak endogenous Ca2+ buffering supports sustained synaptic transmission by distinct mechanisms in rod and cone photoreceptors in salamander retina. Physiol Rep 2015; 3:3/9/e12567. [PMID: 26416977 PMCID: PMC4600400 DOI: 10.14814/phy2.12567] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Differences in synaptic transmission between rod and cone photoreceptors contribute to different response kinetics in rod- versus cone-dominated visual pathways. We examined Ca2+ dynamics in synaptic terminals of tiger salamander photoreceptors under conditions that mimicked endogenous buffering to determine the influence on kinetically and mechanistically distinct components of synaptic transmission. Measurements of ICl(Ca) confirmed that endogenous Ca2+ buffering is equivalent to ˜0.05 mmol/L EGTA in rod and cone terminals. Confocal imaging showed that with such buffering, depolarization stimulated large, spatially unconstrained [Ca2+] increases that spread throughout photoreceptor terminals. We calculated immediately releasable pool (IRP) size and release efficiency in rods by deconvolving excitatory postsynaptic currents and presynaptic Ca2+ currents. Peak efficiency of ˜0.2 vesicles/channel was similar to that of cones (˜0.3 vesicles/channel). Efficiency in both cell types was not significantly affected by using weak endogenous Ca2+ buffering. However, weak Ca2+ buffering speeded Ca2+/calmodulin (CaM)-dependent replenishment of vesicles to ribbons in both rods and cones, thereby enhancing sustained release. In rods, weak Ca2+ buffering also amplified sustained release by enhancing CICR and CICR-stimulated release of vesicles at nonribbon sites. By contrast, elevating [Ca2+] at nonribbon sites in cones with weak Ca2+ buffering and by inhibiting Ca2+ extrusion did not trigger additional release, consistent with the notion that exocytosis from cones occurs exclusively at ribbons. The presence of weak endogenous Ca2+ buffering in rods and cones facilitates slow, sustained exocytosis by enhancing Ca2+/CaM-dependent replenishment of ribbons in both rods and cones and by stimulating nonribbon release triggered by CICR in rods.
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Affiliation(s)
- Matthew J Van Hook
- Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska
| | - Wallace B Thoreson
- Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska
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81
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Neher E. Merits and Limitations of Vesicle Pool Models in View of Heterogeneous Populations of Synaptic Vesicles. Neuron 2015; 87:1131-1142. [DOI: 10.1016/j.neuron.2015.08.038] [Citation(s) in RCA: 156] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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82
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Activity-dependent, homeostatic regulation of neurotransmitter release from auditory nerve fibers. Proc Natl Acad Sci U S A 2015; 112:6479-84. [PMID: 25944933 DOI: 10.1073/pnas.1420885112] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Information processing in the brain requires reliable synaptic transmission. High reliability at specialized auditory nerve synapses in the cochlear nucleus results from many release sites (N), high probability of neurotransmitter release (Pr), and large quantal size (Q). However, high Pr also causes auditory nerve synapses to depress strongly when activated at normal rates for a prolonged period, which reduces fidelity. We studied how synapses are influenced by prolonged activity by exposing mice to constant, nondamaging noise and found that auditory nerve synapses changed to facilitating, reflecting low Pr. For mice returned to quiet, synapses recovered to normal depression, suggesting that these changes are a homeostatic response to activity. Two additional properties, Q and average excitatory postsynaptic current (EPSC) amplitude, were unaffected by noise rearing, suggesting that the number of release sites (N) must increase to compensate for decreased Pr. These changes in N and Pr were confirmed physiologically using the integration method. Furthermore, consistent with increased N, endbulbs in noise-reared animals had larger VGlut1-positive puncta, larger profiles in electron micrographs, and more release sites per profile. In current-clamp recordings, noise-reared BCs had greater spike fidelity even during high rates of synaptic activity. Thus, auditory nerve synapses regulate excitability through an activity-dependent, homeostatic mechanism, which could have major effects on all downstream processing. Our results also suggest that noise-exposed bushy cells would remain hyperexcitable for a period after returning to normal quiet conditions, which could have perceptual consequences.
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83
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Synaptic plasticity in the auditory system: a review. Cell Tissue Res 2015; 361:177-213. [PMID: 25896885 DOI: 10.1007/s00441-015-2176-x] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Accepted: 03/18/2015] [Indexed: 01/19/2023]
Abstract
Synaptic transmission via chemical synapses is dynamic, i.e., the strength of postsynaptic responses may change considerably in response to repeated synaptic activation. Synaptic strength is increased during facilitation, augmentation and potentiation, whereas a decrease in synaptic strength is characteristic for depression and attenuation. This review attempts to discuss the literature on short-term and long-term synaptic plasticity in the auditory brainstem of mammals and birds. One hallmark of the auditory system, particularly the inner ear and lower brainstem stations, is information transfer through neurons that fire action potentials at very high frequency, thereby activating synapses >500 times per second. Some auditory synapses display morphological specializations of the presynaptic terminals, e.g., calyceal extensions, whereas other auditory synapses do not. The review focuses on short-term depression and short-term facilitation, i.e., plastic changes with durations in the millisecond range. Other types of short-term synaptic plasticity, e.g., posttetanic potentiation and depolarization-induced suppression of excitation, will be discussed much more briefly. The same holds true for subtypes of long-term plasticity, like prolonged depolarizations and spike-time-dependent plasticity. We also address forms of plasticity in the auditory brainstem that do not comprise synaptic plasticity in a strict sense, namely short-term suppression, paired tone facilitation, short-term adaptation, synaptic adaptation and neural adaptation. Finally, we perform a meta-analysis of 61 studies in which short-term depression (STD) in the auditory system is opposed to short-term depression at non-auditory synapses in order to compare high-frequency neurons with those that fire action potentials at a lower rate. This meta-analysis reveals considerably less STD in most auditory synapses than in non-auditory ones, enabling reliable, failure-free synaptic transmission even at frequencies >100 Hz. Surprisingly, the calyx of Held, arguably the best-investigated synapse in the central nervous system, depresses most robustly. It will be exciting to reveal the molecular mechanisms that set high-fidelity synapses apart from other synapses that function much less reliably.
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84
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Gaviño MA, Ford KJ, Archila S, Davis GW. Homeostatic synaptic depression is achieved through a regulated decrease in presynaptic calcium channel abundance. eLife 2015; 4. [PMID: 25884248 PMCID: PMC4443758 DOI: 10.7554/elife.05473] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 04/16/2015] [Indexed: 11/13/2022] Open
Abstract
Homeostatic signaling stabilizes synaptic transmission at the neuromuscular junction (NMJ) of Drosophila, mice, and human. It is believed that homeostatic signaling at the NMJ is bi-directional and considerable progress has been made identifying mechanisms underlying the homeostatic potentiation of neurotransmitter release. However, very little is understood mechanistically about the opposing process, homeostatic depression, and how bi-directional plasticity is achieved. Here, we show that homeostatic potentiation and depression can be simultaneously induced, demonstrating true bi-directional plasticity. Next, we show that mutations that block homeostatic potentiation do not alter homeostatic depression, demonstrating that these are genetically separable processes. Finally, we show that homeostatic depression is achieved by decreased presynaptic calcium channel abundance and calcium influx, changes that are independent of the presynaptic action potential waveform. Thus, we identify a novel mechanism of homeostatic synaptic plasticity and propose a model that can account for the observed bi-directional, homeostatic control of presynaptic neurotransmitter release.
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Affiliation(s)
- Michael A Gaviño
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | - Kevin J Ford
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | - Santiago Archila
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
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85
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Ca2+ channel to synaptic vesicle distance accounts for the readily releasable pool kinetics at a functionally mature auditory synapse. J Neurosci 2015; 35:2083-100. [PMID: 25653365 DOI: 10.1523/jneurosci.2753-14.2015] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Precise regulation of synaptic vesicle (SV) release at the calyx of Held is critical for auditory processing. At the prehearing calyx of Held, synchronous and asynchronous release is mediated by fast and slow releasing SVs within the readily releasable pool (RRP). However, the posthearing calyx has dramatically different release properties. Whether developmental alterations in RRP properties contribute to the accelerated release time course found in posthearing calyces is not known. To study these questions, we performed paired patch-clamp recordings, deconvolution analysis, and numerical simulations of buffered Ca(2+) diffusion and SV release in postnatal day (P) 16-19 mouse calyces, as their release properties resemble mature calyces of Held. We found the P16-P19 calyx RRP consists of two pools: a fast pool (τ ≤ 0.9 ms) and slow pool (τ ∼4 ms), in which release kinetics and relative composition of the two pools were unaffected by 5 mm EGTA. Simulations of SV release from the RRP revealed that two populations of SVs were necessary to reproduce the experimental release rates: (1) SVs located close (∼5-25 nm) and (2) more distal (25-100 nm) to VGCC clusters. This positional coupling was confirmed by experiments showing 20 mm EGTA preferentially blocked distally coupled SVs. Lowering external [Ca(2+)] to in vivo levels reduced only the fraction SVs released from the fast pool. Therefore, we conclude that a dominant parameter regulating the mature calyx RRP release kinetics is the distance between SVs and VGCC clusters.
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86
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Abstract
Vesicle recycling is pivotal for maintaining reliable synaptic signaling, but its basic properties remain poorly understood. Here, we developed an approach to quantitatively analyze the kinetics of vesicle recycling with exquisite signal and temporal resolution at the calyx of Held synapse. The combination of this electrophysiological approach with electron microscopy revealed that ∼80% of vesicles (∼270,000 out of ∼330,000) in the nerve terminal are involved in recycling. Under sustained stimulation, recycled vesicles start to be reused in tens of seconds when ∼47% of the preserved vesicles in the recycling pool (RP) are depleted. The heterogeneity of vesicle recycling as well as two kinetic components of RP depletion revealed the existence of a replenishable pool of vesicles before the priming stage and led to a realistic kinetic model that assesses the size of the subpools of the RP. Thus, our study quantified the kinetics of vesicle recycling and kinetically dissected the whole vesicle pool in the calyceal terminal into the readily releasable pool (∼0.6%), the readily priming pool (∼46%), the premature pool (∼33%), and the resting pool (∼20%).
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87
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Müller M, Genç Ö, Davis GW. RIM-binding protein links synaptic homeostasis to the stabilization and replenishment of high release probability vesicles. Neuron 2015; 85:1056-69. [PMID: 25704950 DOI: 10.1016/j.neuron.2015.01.024] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Revised: 11/11/2014] [Accepted: 01/18/2015] [Indexed: 01/27/2023]
Abstract
Here we define activities of RIM-binding protein (RBP) that are essential for baseline neurotransmission and presynaptic homeostatic plasticity. At baseline, rbp mutants have a ∼10-fold decrease in the apparent Ca(2+) sensitivity of release that we attribute to (1) impaired presynaptic Ca(2+) influx, (2) looser coupling of vesicles to Ca(2+) influx, and (3) limited access to the readily releasable vesicle pool (RRP). During homeostatic plasticity, RBP is necessary for the potentiation of Ca(2+) influx and the expansion of the RRP. Remarkably, rbp mutants also reveal a rate-limiting stage required for the replenishment of high release probability (p) vesicles following vesicle depletion. This rate slows ∼4-fold at baseline and nearly 7-fold during homeostatic signaling in rbp. These effects are independent of altered Ca(2+) influx and RRP size. We propose that RBP stabilizes synaptic efficacy and homeostatic plasticity through coordinated control of presynaptic Ca(2+) influx and the dynamics of a high-p vesicle pool.
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Affiliation(s)
- Martin Müller
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Özgür Genç
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
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88
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McElvain LE, Faulstich M, Jeanne JM, Moore JD, du Lac S. Implementation of linear sensory signaling via multiple coordinated mechanisms at central vestibular nerve synapses. Neuron 2015; 85:1132-44. [PMID: 25704949 DOI: 10.1016/j.neuron.2015.01.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2014] [Revised: 11/10/2014] [Accepted: 01/16/2015] [Indexed: 12/29/2022]
Abstract
Signal transfer in neural circuits is dynamically modified by the recent history of neuronal activity. Short-term plasticity endows synapses with nonlinear transmission properties, yet synapses in sensory and motor circuits are capable of signaling linearly over a wide range of presynaptic firing rates. How do such synapses achieve rate-invariant transmission despite history-dependent nonlinearities? Here, ultrastructural, biophysical, and computational analyses demonstrate that concerted molecular, anatomical, and physiological refinements are required for central vestibular nerve synapses to linearly transmit rate-coded sensory signals. Vestibular synapses operate in a physiological regime of steady-state depression imposed by tonic firing. Rate-invariant transmission relies on brief presynaptic action potentials that delimit calcium influx, large pools of rapidly mobilized vesicles, multiple low-probability release sites, robust postsynaptic receptor sensitivity, and efficient transmitter clearance. Broadband linear synaptic filtering of head motion signals is thus achieved by coordinately tuned synaptic machinery that maintains physiological operation within inherent cell biological limitations.
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Affiliation(s)
- Lauren E McElvain
- Neurosciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA; Salk Institute for Biological Studies, La Jolla, CA 92037, USA; Champalimaud Neuroscience Programme, Champalimaud Centre for the Unknown, Av. Brasília, Doca de Pedrouços, Lisbon 1400-038, Portugal.
| | | | - James M Jeanne
- Neurosciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA
| | - Jeffrey D Moore
- Neurosciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA
| | - Sascha du Lac
- Neurosciences Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA; Salk Institute for Biological Studies, La Jolla, CA 92037, USA; Howard Hughes Medical Institute, La Jolla, CA 92037, USA; Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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89
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Valente P, Orlando M, Raimondi A, Benfenati F, Baldelli P. Fine Tuning of Synaptic Plasticity and Filtering by GABA Released from Hippocampal Autaptic Granule Cells. Cereb Cortex 2015; 26:1149-67. [PMID: 25576534 DOI: 10.1093/cercor/bhu301] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The functional consequence of γ-aminobutyric acid (GABA) release at mossy fiber terminals is still a debated topic. Here, we provide multiple evidence of GABA release in cultured autaptic hippocampal granule cells. In ∼50% of the excitatory autaptic neurons, GABA, VGAT, or GAD67 colocalized with vesicular glutamate transporter 1-positive puncta, where both GABAB and GABAA receptors (Rs) were present. Patch-clamp recordings showed a clear enhancement of autaptic excitatory postsynaptic currents in response to the application of the GABABR antagonist CGP58845 only in neurons positive to the selective granule cell marker Prox1, and expressing low levels of GAD67. Indeed, GCP non-responsive excitatory autaptic neurons were both Prox1- and GAD67-negative. Although the amount of released GABA was not sufficient to activate functional postsynaptic GABAARs, it effectively activated presynaptic GABABRs that maintain a tonic "brake" on the probability of release and on the size of the readily releasable pool and contributed to resting potential hyperpolarization possibly through extrasynaptic GABAAR activation. The autocrine inhibition exerted by GABABRs on glutamate release enhanced both paired-pulse facilitation and post-tetanic potentiation. Such GABABR-mediated changes in short-term plasticity confer to immature granule cells the capability to modulate their filtering properties in an activity-dependent fashion, with remarkable consequences on the dynamic behavior of neural circuits.
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Affiliation(s)
- Pierluigi Valente
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Genova 16163, Italy Department of Experimental Medicine, Section of Physiology, University of Genova, Genova 16132, Italy
| | - Marta Orlando
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Genova 16163, Italy
| | - Andrea Raimondi
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Genova 16163, Italy
| | - Fabio Benfenati
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Genova 16163, Italy Department of Experimental Medicine, Section of Physiology, University of Genova, Genova 16132, Italy
| | - Pietro Baldelli
- Department of Neuroscience and Brain Technologies, Istituto Italiano di Tecnologia, Genova 16163, Italy Department of Experimental Medicine, Section of Physiology, University of Genova, Genova 16132, Italy
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90
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Abstract
It is well established that the active properties of nerve and muscle cells are stabilized by homeostatic signaling systems. In organisms ranging from Drosophila to humans, neurons restore baseline function in the continued presence of destabilizing perturbations by rebalancing ion channel expression, modifying neurotransmitter receptor surface expression and trafficking, and modulating neurotransmitter release. This review focuses on the homeostatic modulation of presynaptic neurotransmitter release, termed presynaptic homeostasis. First, we highlight criteria that can be used to define a process as being under homeostatic control. Next, we review the remarkable conservation of presynaptic homeostasis at the Drosophila, mouse, and human neuromuscular junctions and emerging parallels at synaptic connections in the mammalian central nervous system. We then highlight recent progress identifying cellular and molecular mechanisms. We conclude by reviewing emerging parallels between the mechanisms of homeostatic signaling and genetic links to neurological disease.
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Affiliation(s)
- Graeme W Davis
- Department of Biochemistry and Biophysics, University of California, San Francisco, California 94158;
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91
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Ultrafast Action Potentials Mediate Kilohertz Signaling at a Central Synapse. Neuron 2014; 84:152-163. [DOI: 10.1016/j.neuron.2014.08.036] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/17/2014] [Indexed: 01/27/2023]
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92
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Fioravante D, Chu Y, de Jong AP, Leitges M, Kaeser PS, Regehr WG. Protein kinase C is a calcium sensor for presynaptic short-term plasticity. eLife 2014; 3:e03011. [PMID: 25097249 PMCID: PMC5841930 DOI: 10.7554/elife.03011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Accepted: 06/24/2014] [Indexed: 01/02/2023] Open
Abstract
In presynaptic boutons, calcium (Ca(2+)) triggers both neurotransmitter release and short-term synaptic plasticity. Whereas synaptotagmins are known to mediate vesicle fusion through binding of high local Ca(2+) to their C2 domains, the proteins that sense smaller global Ca(2+) increases to produce short-term plasticity have remained elusive. Here, we identify a Ca(2+) sensor for post-tetanic potentiation (PTP), a form of plasticity thought to underlie short-term memory. We find that at the functionally mature calyx of Held synapse the Ca(2+)-dependent protein kinase C isoforms α and β are necessary for PTP, and the expression of PKCβ in PKCαβ double knockout mice rescues PTP. Disruption of Ca(2+) binding to the PKCβ C2 domain specifically prevents PTP without impairing other PKCβ-dependent forms of synaptic enhancement. We conclude that different C2-domain-containing presynaptic proteins are engaged by different Ca(2+) signals, and that Ca(2+) increases evoked by tetanic stimulation are sensed by PKCβ to produce PTP.DOI: http://dx.doi.org/10.7554/eLife.03011.001.
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Affiliation(s)
- Diasynou Fioravante
- Department of Neurobiology, Harvard Medical School, Boston, United States Center for Neuroscience, University of California, Davis, Davis, United States
| | - YunXiang Chu
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Arthur Ph de Jong
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Michael Leitges
- The Biotechnology Center of Oslo, University of Oslo, Oslo, Norway
| | - Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Wade G Regehr
- Department of Neurobiology, Harvard Medical School, Boston, United States
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93
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A presynaptic role of microtubule-associated protein 1/Futsch in Drosophila: regulation of active zone number and neurotransmitter release. J Neurosci 2014; 34:6759-71. [PMID: 24828631 DOI: 10.1523/jneurosci.4282-13.2014] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Structural microtubule-associated proteins (MAPs), like MAP1, not only control the stability of microtubules, but also interact with postsynaptic proteins in the nervous system. Their presynaptic role has barely been studied. To tackle this question, we used the Drosophila model in which there is only one MAP1 homolog: Futsch, which is expressed at the larval neuromuscular junction, presynaptically only. We show that Futsch regulates neurotransmitter release and active zone density. Importantly, we provide evidence that this role of Futsch is not just the consequence of its microtubule-stabilizing function. Using high-resolution microscopy, we show that Futsch and microtubules are almost systematically present in close proximity to active zones, with Futsch being localized in-between microtubules and active zones. Using proximity ligation assays, we further demonstrate the proximity of Futsch, but not microtubules, to active zone components. Altogether our data are in favor of a model by which Futsch locally stabilizes active zones, by reinforcing their link with the underlying microtubule cytoskeleton.
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94
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Mori M, Tanifuji S, Mochida S. Kinetic organization of Ca2+ signals that regulate synaptic release efficacy in sympathetic neurons. Mol Pharmacol 2014; 86:297-305. [PMID: 24981043 DOI: 10.1124/mol.114.094029] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium regulation of neurotransmitter release is essential for maintenance of synaptic transmission. However, the temporal and spatial organization of Ca(2+) dynamics that regulate synaptic vesicle (SV) release efficacy in sympathetic neurons is poorly understood. Here, we investigate the N-type Ca(2+) channel-mediated kinetic structure of Ca(2+) regulation of cholinergic transmission of sympathetic neurons. We measured the effect of Ca(2+) chelation with fast 1,2-bis(2-aminophenoxy) ethane-tetraacetic acid (BAPTA) and slow ethyleneglycol-tetraacetic acid (EGTA) buffers on exocytosis, synaptic depression, and recovery of the readily releasable vesicle pool (RRP), after both single action potential (AP) and repetitive APs. Surprisingly, postsynaptic potentials peaking at ~12 milliseconds after the AP was inhibited by both rapid and slow Ca(2+) buffers suggests that, in addition to the well known fast Ca(2+) signals at the active zone (AZ), slow Ca(2+) signals at the peak of Ca(2+) entry also contribute to paired-pulse or repetitive AP responses. Following a single AP, discrete Ca(2+) transient increase regulated synaptic depression in rapid (<30-millisecond) and slow (<120-millisecond) phases. In contrast, following prolonged AP trains, synaptic depression was reduced by a slow Ca(2+) signal regulation lasting >200 milliseconds. Finally, after an AP burst, recovery of the RRP was mediated by an AP-dependent rapid Ca(2+) signal, and the expansion of releasable SV number by an AP firing activity-dependent slow Ca(2+) signal. These data indicate that local Ca(2+) signals operating near Ca(2+) sources in the AZ are organized into discrete fast and slow temporal phases that remodel exocytosis and short-term plasticity to ensure long-term stability in acetylcholine release efficacy.
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Affiliation(s)
- Michinori Mori
- Department of Physiology, Tokyo Medical University, Tokyo, Japan
| | - Shota Tanifuji
- Department of Physiology, Tokyo Medical University, Tokyo, Japan
| | - Sumiko Mochida
- Department of Physiology, Tokyo Medical University, Tokyo, Japan
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Midorikawa M, Okamoto Y, Sakaba T. Developmental changes in Ca2+ channel subtypes regulating endocytosis at the calyx of Held. J Physiol 2014; 592:3495-510. [PMID: 24907302 DOI: 10.1113/jphysiol.2014.273243] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
At the mammalian central synapse, Ca(2+) influx through Ca(2+) channels triggers neurotransmitter release by exocytosis of synaptic vesicles, which fuse with the presynaptic membrane and are subsequently retrieved by endocytosis. At the calyx of Held terminal, P/Q-type Ca(2+) channels mainly mediate exocytosis, while N- and R-type channels have a minor role in young terminals (postnatal days 8-11). The role of each Ca(2+) channel subtype in endocytosis remains to be elucidated; therefore, we examined the role of each type of Ca(2+) channel in endocytosis, by using whole-cell patch-clamp recordings in conjunction with capacitance measurement techniques. We found that at the young calyx terminal, when R-type Ca(2+) channels were blocked, the slow mode of endocytosis was further slowed, while blocking of either P/Q- or N-type Ca(2+) channels had no major effect. In more mature terminals (postnatal days 14-17), the slow mode of endocytosis was mainly triggered by P/Q-type Ca(2+) channels, suggesting developmental changes in the regulation of the slow mode of endocytosis by different Ca(2+) channel subtypes. In contrast, a fast mode of endocytosis was observed after strong stimulation in young terminals that was mediated mainly by P/Q-type, but not R- or N-type Ca(2+) channels. These results suggest that different types of Ca(2+) channels regulate the two different modes of endocytosis. The results may also suggest that exo- and endocytosis are regulated independently at different sites in young animals but are more tightly coupled in older animals, allowing more efficient synaptic vesicle cycling adapted for fast signalling.
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Affiliation(s)
| | - Yuji Okamoto
- Graduate School of Brain Science, Doshisha University, Kyoto, 6190225, Japan
| | - Takeshi Sakaba
- Graduate School of Brain Science, Doshisha University, Kyoto, 6190225, Japan
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96
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Calcium-dependent PKC isoforms have specialized roles in short-term synaptic plasticity. Neuron 2014; 82:859-71. [PMID: 24794094 DOI: 10.1016/j.neuron.2014.04.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/26/2014] [Indexed: 01/04/2023]
Abstract
Posttetanic potentiation (PTP) is a widely observed form of short-term plasticity lasting for tens of seconds after high-frequency stimulation. Here we show that although protein kinase C (PKC) mediates PTP at the calyx of Held synapse in the auditory brainstem before and after hearing onset, PTP is produced primarily by an increased probability of release (p) before hearing onset, and by an increased readily releasable pool of vesicles (RRP) thereafter. We find that these mechanistic differences, which have distinct functional consequences, reflect unexpected differential actions of closely related calcium-dependent PKC isoforms. Prior to hearing onset, when PKCγ and PKCβ are both present, PKCγ mediates PTP by increasing p and partially suppressing PKCβ actions. After hearing onset, PKCγ is absent and PKCβ produces PTP by increasing RRP. In hearing animals, virally expressed PKCγ overrides PKCβ to produce PTP by increasing p. Thus, two similar PKC isoforms mediate PTP in distinctly different ways.
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97
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Cav2.1 channels control multivesicular release by relying on their distance from exocytotic Ca2+ sensors at rat cerebellar granule cells. J Neurosci 2014; 34:1462-74. [PMID: 24453334 DOI: 10.1523/jneurosci.2388-13.2014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The concomitant release of multiple numbers of synaptic vesicles [multivesicular release (MVR)] in response to a single presynaptic action potential enhances the flexibility of synaptic transmission. However, the molecular mechanisms underlying MVR at a single CNS synapse remain unclear. Here, we show that the Cav2.1 subtype (P/Q-type) of the voltage-gated calcium channel is specifically responsible for the induction of MVR. In the rat cerebellar cortex, paired-pulse activation of granule cell (GC) ascending fibers leads not only to a facilitation of the peak amplitude (PPFamp) but also to a prolongation of the decay time (PPPdecay) of the EPSCs recorded from molecular layer interneurons. PPFamp is elicited by a transient increase in the number of released vesicles. PPPdecay is highly dependent on MVR and is caused by dual mechanisms: (1) a delayed release and (2) an extrasynaptic spillover of the GC transmitter glutamate and subsequent pooling of the glutamate among active synapses. PPPdecay was specifically suppressed by the Cav2.1 channel blocker ω-agatoxin IVA, while PPFamp responded to Cav2.2/Cav2.3 (N-type/R-type) channel blockers. The membrane-permeable slow Ca(2+) chelator EGTA-AM profoundly reduced the decay time constant (τdecay) of the second EPSC; however, it only had a negligible impact on that of the first, thereby eliminating PPPdecay. These results suggest that the distance between presynaptic Cav2.1 channels and exocytotic Ca(2+) sensors is a key determinant of MVR. By transducing presynaptic action potential firings into unique Ca(2+) signals and vesicle release profiles, Cav2.1 channels contribute to the encoding and processing of neural information.
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98
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Rapid dynamic changes of dendritic inhibition in the dentate gyrus by presynaptic activity patterns. J Neurosci 2014; 34:1344-57. [PMID: 24453325 DOI: 10.1523/jneurosci.2566-13.2014] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The dentate gyrus (DG) serves as a primary gate to control information transfer from the cortex to the hippocampus. Activation of incoming cortical inputs results in rapid synaptic excitation followed by slow GABA-mediated (GABAergic) synaptic inhibition onto DG granule cells (GCs). GABAergic inhibitory interneurons (INs) in the DG comprise fast-spiking (FS) and non-fast-spiking (non-FS) cells. Anatomical analyses of DG INs reveal that FS cells are soma-targeting INs, whereas non-FS cells are dendrite-targeting INs. These two IN classes are differentially recruited by excitatory inputs and in turn provide exquisite spatiotemporal control over GC activity. Yet, little is known how FS and non-FS cells transform their presynaptic dynamics into varying postsynaptic response amplitudes. Using paired recordings in rat hippocampal slices, we show that inhibition in the DG is dominated by somatic GABAergic inputs during periods of sparse presynaptic activity, whereas dendritic GABAergic inputs are rapidly shifted to powerful and sustained inhibition during periods of intense presynaptic activity. The variant dynamics of dendritic inhibition is dependent on presynaptic IN subtypes and their activity patterns and is attributed to Ca(2+)-dependent increases in the probability of release and the size of the readily releasable pool. Furthermore, the degree of dynamic GABA release can be reduced by blocking voltage-gated K(+) channels, which increases the efficacy of dendrite-targeting IN output synapses during sparse firing. Such rapid dynamic modulation of dendritic inhibition may act as a frequency-dependent filter to prevent overexcitation of GC dendrites and thus set the excitatory-inhibitory synaptic balance in the DG circuits.
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99
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Vyleta NP, Jonas P. Loose Coupling Between Ca2+ Channels and Release Sensors at a Plastic Hippocampal Synapse. Science 2014; 343:665-70. [DOI: 10.1126/science.1244811] [Citation(s) in RCA: 149] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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100
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Singla N, Dhawan DK. Influence of Zinc on Calcium-Dependent Signal Transduction Pathways During Aluminium-Induced Neurodegeneration. Mol Neurobiol 2014; 50:613-25. [DOI: 10.1007/s12035-014-8643-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 01/13/2014] [Indexed: 11/29/2022]
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