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Neyens DM, Brenner L, Calkins R, Winzenried ET, Ritter RC, Appleyard SM. CCK-sensitive C fibers activate NTS leptin receptor-expressing neurons via NMDA receptors. Am J Physiol Regul Integr Comp Physiol 2024; 326:R383-R400. [PMID: 38105761 DOI: 10.1152/ajpregu.00238.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 12/07/2023] [Accepted: 12/07/2023] [Indexed: 12/19/2023]
Abstract
The hormone leptin reduces food intake through actions in the peripheral and central nervous systems, including in the hindbrain nucleus of the solitary tract (NTS). The NTS receives viscerosensory information via vagal afferents, including information from the gastrointestinal tract, which is then relayed to other central nervous system (CNS) sites critical for control of food intake. Leptin receptors (lepRs) are expressed by a subpopulation of NTS neurons, and knockdown of these receptors increases both food intake and body weight. Recently, we demonstrated that leptin increases vagal activation of lepR-expressing neurons via increased NMDA receptor (NMDAR) currents, thereby potentiating vagally evoked firing. Furthermore, chemogenetic activation of these neurons was recently shown to inhibit food intake. However, the vagal inputs these neurons receive had not been characterized. Here we performed whole cell recordings in brain slices taken from lepRCre × floxedTdTomato mice and found that lepR neurons of the NTS are directly activated by monosynaptic inputs from C-type afferents sensitive to the transient receptor potential vanilloid type 1 (TRPV1) agonist capsaicin. CCK administered onto NTS slices stimulated spontaneous glutamate release onto lepR neurons and induced action potential firing, an effect mediated by CCKR1. Interestingly, NMDAR activation contributed to the current carried by spontaneous excitatory postsynaptic currents (EPSCs) and enhanced CCK-induced firing. Peripheral CCK also increased c-fos expression in these neurons, suggesting they are activated by CCK-sensitive vagal afferents in vivo. Our results indicate that the majority of NTS lepR neurons receive direct inputs from CCK-sensitive C vagal-type afferents, with both peripheral and central CCK capable of activating these neurons and NMDARs able to potentiate these effects.
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Affiliation(s)
- Drew M Neyens
- Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States
| | - Lynne Brenner
- Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States
| | - Rowan Calkins
- Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States
| | - Eric T Winzenried
- Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States
| | - Robert C Ritter
- Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States
| | - Suzanne M Appleyard
- Department of Integrated Physiology and Neuroscience, Washington State University, Pullman, Washington, United States
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2
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Pradeepan KS, McCready FP, Wei W, Khaki M, Zhang W, Salter MW, Ellis J, Martinez-Trujillo J. Calcium-Dependent Hyperexcitability in Human Stem Cell-Derived Rett Syndrome Neuronal Networks. BIOLOGICAL PSYCHIATRY GLOBAL OPEN SCIENCE 2024; 4:100290. [PMID: 38420187 PMCID: PMC10899066 DOI: 10.1016/j.bpsgos.2024.100290] [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: 10/18/2023] [Revised: 12/20/2023] [Accepted: 01/14/2024] [Indexed: 03/02/2024] Open
Abstract
Background Mutations in MECP2 predominantly cause Rett syndrome and can be modeled in vitro using human stem cell-derived neurons. Patients with Rett syndrome have signs of cortical hyperexcitability, such as seizures. Human stem cell-derived MECP2 null excitatory neurons have smaller soma size and reduced synaptic connectivity but are also hyperexcitable due to higher input resistance. Paradoxically, networks of MECP2 null neurons show a decrease in the frequency of network bursts consistent with a hypoconnectivity phenotype. Here, we examine this issue. Methods We reanalyzed multielectrode array data from 3 isogenic MECP2 cell line pairs recorded over 6 weeks (n = 144). We used a custom burst detection algorithm to analyze network events and isolated a phenomenon that we termed reverberating super bursts (RSBs). To probe potential mechanisms of RSBs, we conducted pharmacological manipulations using bicuculline, EGTA-AM, and DMSO on 1 cell line (n = 34). Results RSBs, often misidentified as single long-duration bursts, consisted of a large-amplitude initial burst followed by several high-frequency, low-amplitude minibursts. Our analysis revealed that MECP2 null networks exhibited increased frequency of RSBs, which produced increased bursts compared with isogenic controls. Bicuculline or DMSO treatment did not affect RSBs. EGTA-AM selectively eliminated RSBs and rescued network burst dynamics. Conclusions During early development, MECP2 null neurons are hyperexcitable and produce hyperexcitable networks. This may predispose them to the emergence of hypersynchronic states that potentially translate into seizures. Network hyperexcitability depends on asynchronous neurotransmitter release that is likely driven by presynaptic Ca2+ and can be rescued by EGTA-AM to restore typical network dynamics.
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Affiliation(s)
- Kartik S. Pradeepan
- Graduate Program in Neuroscience, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
- Robarts Research Institute, Western University, London, Ontario, Canada
| | - Fraser P. McCready
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
- Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Wei Wei
- Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Milad Khaki
- Robarts Research Institute, Western University, London, Ontario, Canada
| | - Wenbo Zhang
- Neuroscience & Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Michael W. Salter
- Neuroscience & Mental Health, The Hospital for Sick Children, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - James Ellis
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
- Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Julio Martinez-Trujillo
- Graduate Program in Neuroscience, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
- Robarts Research Institute, Western University, London, Ontario, Canada
- Western Institute for Neuroscience, Western University, London, Ontario, Canada
- Department of Physiology and Pharmacology, and Psychiatry, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
- Department of Psychiatry, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
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3
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Shields MC, Bowers MR, Kramer HL, Fulcer MM, Perinet LC, Metz MJ, Reist NE. The role of the C2A domain of synaptotagmin 1 in asynchronous neurotransmitter release. PLoS One 2020; 15:e0232991. [PMID: 32407359 PMCID: PMC7224543 DOI: 10.1371/journal.pone.0232991] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 04/24/2020] [Indexed: 11/22/2022] Open
Abstract
Following nerve stimulation, there are two distinct phases of Ca2+-dependent neurotransmitter release: a fast, synchronous release phase, and a prolonged, asynchronous release phase. Each of these phases is tightly regulated and mediated by distinct mechanisms. Synaptotagmin 1 is the major Ca2+ sensor that triggers fast, synchronous neurotransmitter release upon Ca2+ binding by its C2A and C2B domains. It has also been implicated in the inhibition of asynchronous neurotransmitter release, as blocking Ca2+ binding by the C2A domain of synaptotagmin 1 results in increased asynchronous release. However, the mutation used to block Ca2+ binding in the previous experiments (aspartate to asparagine mutations, sytD-N) had the unintended side effect of mimicking Ca2+ binding, raising the possibility that the increase in asynchronous release was directly caused by ostensibly constitutive Ca2+ binding. Thus, rather than modulating an asynchronous sensor, sytD-N may be mimicking one. To directly test the C2A inhibition hypothesis, we utilized an alternate C2A mutation that we designed to block Ca2+ binding without mimicking it (an aspartate to glutamate mutation, sytD-E). Analysis of both the original sytD-N mutation and our alternate sytD-E mutation at the Drosophila neuromuscular junction showed differential effects on asynchronous release, as well as on synchronous release and the frequency of spontaneous release. Importantly, we found that asynchronous release is not increased in the sytD-E mutant. Thus, our work provides new mechanistic insight into synaptotagmin 1 function during Ca2+-evoked synaptic transmission and demonstrates that Ca2+ binding by the C2A domain of synaptotagmin 1 does not inhibit asynchronous neurotransmitter release in vivo.
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Affiliation(s)
- Mallory C. Shields
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
| | - Matthew R. Bowers
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
| | - Hannah L. Kramer
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - McKenzie M. Fulcer
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Lara C. Perinet
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
| | - Marissa J. Metz
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
| | - Noreen E. Reist
- Department of Biomedical Sciences, Colorado State University, Fort Collins, Colorado, United States of America
- Molecular, Cellular, and Integrative Neuroscience Program, Colorado State University, Fort Collins, Colorado, United States of America
- * E-mail:
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Salmasi M, Loebel A, Glasauer S, Stemmler M. Short-term synaptic depression can increase the rate of information transfer at a release site. PLoS Comput Biol 2019; 15:e1006666. [PMID: 30601804 PMCID: PMC6355030 DOI: 10.1371/journal.pcbi.1006666] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2018] [Revised: 01/31/2019] [Accepted: 11/23/2018] [Indexed: 11/18/2022] Open
Abstract
The release of neurotransmitters from synapses obeys complex and stochastic dynamics. Depending on the recent history of synaptic activation, many synapses depress the probability of releasing more neurotransmitter, which is known as synaptic depression. Our understanding of how synaptic depression affects the information efficacy, however, is limited. Here we propose a mathematically tractable model of both synchronous spike-evoked release and asynchronous release that permits us to quantify the information conveyed by a synapse. The model transits between discrete states of a communication channel, with the present state depending on many past time steps, emulating the gradual depression and exponential recovery of the synapse. Asynchronous and spontaneous releases play a critical role in shaping the information efficacy of the synapse. We prove that depression can enhance both the information rate and the information rate per unit energy expended, provided that synchronous spike-evoked release depresses less (or recovers faster) than asynchronous release. Furthermore, we explore the theoretical implications of short-term synaptic depression adapting on longer time scales, as part of the phenomenon of metaplasticity. In particular, we show that a synapse can adjust its energy expenditure by changing the dynamics of short-term synaptic depression without affecting the net information conveyed by each successful release. Moreover, the optimal input spike rate is independent of the amplitude or time constant of synaptic depression. We analyze the information efficacy of three types of synapses for which the short-term dynamics of both synchronous and asynchronous release have been experimentally measured. In hippocampal autaptic synapses, the persistence of asynchronous release during depression cannot compensate for the reduction of synchronous release, so that the rate of information transmission declines with synaptic depression. In the calyx of Held, the information rate per release remains constant despite large variations in the measured asynchronous release rate. Lastly, we show that dopamine, by controlling asynchronous release in corticostriatal synapses, increases the synaptic information efficacy in nucleus accumbens. Fatigue is an intrinsic property of living systems and synapses are no exception. Synaptic depression reduces the ability of synapses to release vesicles in response to an incoming action potential. Whether synaptic depression simply reflects the exhaustion of neuronal resources or whether it serves some additional function is still an open question. We ask how synaptic depression modulates the information transfer between neurons by keeping the synapse in an appropriate operating range. Using a tractable mathematical model for synaptic depression of both synchronous spike-evoked and asynchronous release of neurotransmitter, we derive a closed-form expression for the mutual information rate. Depression, it turns out, can both enhance or impair information transfer, depending on the relative level of depression for synchronous spike-evoked and asynchronous releases. We also study the compromise a synapse makes between its energy consumption and the rate of information transmission. Interestingly, we show that synaptic depression can regulate energy use without affecting the information (measured in bits) per synaptic release. By applying our mathematical framework to experimentally measured synapses, we show that some synapses can compensate for intrinsic variability in asynchronous release rates; moreover, we show how neuromodulators such as dopamine act to improve the information transmission rate.
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Affiliation(s)
- Mehrdad Salmasi
- Graduate School of Systemic Neurosciences, Ludwig-Maximilians-Universität, Munich, Germany.,Bernstein Center for Computational Neuroscience, Munich, Germany.,German Center for Vertigo and Balance Disorders, Ludwig-Maximilians-Universität, Munich, Germany
| | - Alex Loebel
- Bernstein Center for Computational Neuroscience, Munich, Germany.,Department of Biology II, Ludwig-Maximilians-Universität, Munich, Germany
| | - Stefan Glasauer
- Bernstein Center for Computational Neuroscience, Munich, Germany.,German Center for Vertigo and Balance Disorders, Ludwig-Maximilians-Universität, Munich, Germany.,Chair of Computational Neuroscience, Brandenburg University of Technology Cottbus-Senftenberg, Senftenberg, Germany
| | - Martin Stemmler
- Bernstein Center for Computational Neuroscience, Munich, Germany.,Department of Biology II, Ludwig-Maximilians-Universität, Munich, Germany
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5
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Parker D. The Lesioned Spinal Cord Is a "New" Spinal Cord: Evidence from Functional Changes after Spinal Injury in Lamprey. Front Neural Circuits 2017; 11:84. [PMID: 29163065 PMCID: PMC5681538 DOI: 10.3389/fncir.2017.00084] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 10/16/2017] [Indexed: 01/13/2023] Open
Abstract
Finding a treatment for spinal cord injury (SCI) focuses on reconnecting the spinal cord by promoting regeneration across the lesion site. However, while regeneration is necessary for recovery, on its own it may not be sufficient. This presumably reflects the requirement for regenerated inputs to interact appropriately with the spinal cord, making sub-lesion network properties an additional influence on recovery. This review summarizes work we have done in the lamprey, a model system for SCI research. We have compared locomotor behavior (swimming) and the properties of descending inputs, locomotor networks, and sensory inputs in unlesioned animals and animals that have received complete spinal cord lesions. In the majority (∼90%) of animals swimming parameters after lesioning recovered to match those in unlesioned animals. Synaptic inputs from individual regenerated axons also matched the properties in unlesioned animals, although this was associated with changes in release parameters. This suggests against any compensation at these synapses for the reduced descending drive that will occur given that regeneration is always incomplete. Compensation instead seems to occur through diverse changes in cellular and synaptic properties in locomotor networks and proprioceptive systems below, but also above, the lesion site. Recovery of locomotor performance is thus not simply the reconnection of the two sides of the spinal cord, but reflects a distributed and varied range of spinal cord changes. While locomotor network changes are insufficient on their own for recovery, they may facilitate locomotor outputs by compensating for the reduction in descending drive. Potentiated sensory feedback may in turn be a necessary adaptation that monitors and adjusts the output from the “new” locomotor network. Rather than a single aspect, changes in different components of the motor system and their interactions may be needed after SCI. If these are general features, and where comparisons with mammalian systems can be made effects seem to be conserved, improving functional recovery in higher vertebrates will require interventions that generate the optimal spinal cord conditions conducive to recovery. The analyses needed to identify these conditions are difficult in the mammalian spinal cord, but lower vertebrate systems should help to identify the principles of the optimal spinal cord response to injury.
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Affiliation(s)
- David Parker
- Department of Physiology, Neuroscience and Development, University of Cambridge, Cambridge, United Kingdom
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6
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Chamberland S, Tóth K. Functionally heterogeneous synaptic vesicle pools support diverse synaptic signalling. J Physiol 2015; 594:825-35. [PMID: 26614712 DOI: 10.1113/jp270194] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2015] [Accepted: 11/23/2015] [Indexed: 12/15/2022] Open
Abstract
Synaptic communication between neurons is a highly dynamic process involving specialized structures. At the level of the presynaptic terminal, neurotransmission is ensured by fusion of vesicles to the membrane, which releases neurotransmitter in the synaptic cleft. Depending on the level of activity experienced by the terminal, the spatiotemporal properties of calcium invasion will dictate the timing and the number of vesicles that need to be released. Diverse presynaptic firing patterns are translated to neurotransmitter release with a distinct temporal feature. Complex patterns of neurotransmitter release can be achieved when different vesicles respond to distinct calcium dynamics in the presynaptic terminal. Specific vesicles from different pools are recruited during various modes of release as the particular molecular composition of their membrane proteins define their functional properties. Such diversity endows the presynaptic terminal with the ability to respond to distinct physiological signals via the mobilization of specific subpopulation of vesicles. There are several mechanisms by which a diverse vesicle population could be generated in single presynaptic terminals, including distinct recycling pathways that utilize various adaptor proteins. Several additional factors could potentially contribute to the development of a heterogeneous vesicle pool such as specialized release sites, spatial segregation within the terminal and specialized delivery pathways. Among these factors molecular heterogeneity plays a central role in defining the functional properties of different subpopulations of vesicles.
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Affiliation(s)
- Simon Chamberland
- Quebec Mental Health Institute, Department of Psychiatry and Neuroscience, Université Laval, Quebec City, Quebec, Canada, G1J 2G3
| | - Katalin Tóth
- Quebec Mental Health Institute, Department of Psychiatry and Neuroscience, Université Laval, Quebec City, Quebec, Canada, G1J 2G3
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7
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Evstratova A, Chamberland S, Faundez V, Tóth K. Vesicles derived via AP-3-dependent recycling contribute to asynchronous release and influence information transfer. Nat Commun 2014; 5:5530. [PMID: 25410111 PMCID: PMC4239664 DOI: 10.1038/ncomms6530] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Accepted: 10/10/2014] [Indexed: 12/21/2022] Open
Abstract
Action potentials trigger synchronous and asynchronous neurotransmitter release. Temporal properties of both types of release could be altered in an activity-dependent manner. While the effects of activity-dependent changes in synchronous release on postsynaptic signal integration have been studied, the contribution of asynchronous release to information transfer during natural stimulus patterns is unknown. Here we find that during trains of stimulations, asynchronous release contributes to the precision of action potential firing. Our data show that this form of release is selectively diminished in AP-3b2 KO animals, which lack functional neuronal AP-3, an adaptor protein regulating vesicle formation from endosomes generated during bulk endocytosis. We find that in the absence of neuronal AP-3, asynchronous release is attenuated and the activity-dependent increase in the precision of action potential timing is compromised. Lack of asynchronous release decreases the capacity of synaptic information transfer and renders synaptic communication less reliable in response to natural stimulus patterns.
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Affiliation(s)
- Alesya Evstratova
- Department of Psychiatry and Neuroscience, Quebec Mental Health Institute, Université Laval, Quebec City, Quebec, Canada G1J 2G3
| | - Simon Chamberland
- Department of Psychiatry and Neuroscience, Quebec Mental Health Institute, Université Laval, Quebec City, Quebec, Canada G1J 2G3
| | - Victor Faundez
- Department of Cell Biology, Emory University, Atlanta, Georgia 30322, USA
| | - Katalin Tóth
- Department of Psychiatry and Neuroscience, Quebec Mental Health Institute, Université Laval, Quebec City, Quebec, Canada G1J 2G3
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8
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Hauser JL, Liu X, Litvina EY, Chen C. Prolonged synaptic currents increase relay neuron firing at the developing retinogeniculate synapse. J Neurophysiol 2014; 112:1714-28. [PMID: 24966302 DOI: 10.1152/jn.00451.2014] [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: 01/01/2023] Open
Abstract
The retinogeniculate synapse, the connection between retinal ganglion cells (RGC) and thalamic relay neurons, undergoes robust changes in connectivity over development. This process of synapse elimination and strengthening of remaining inputs is thought to require synapse specificity. Here we show that glutamate spillover and asynchronous release are prominent features of retinogeniculate synaptic transmission during this period. The immature excitatory postsynaptic currents exhibit a slow decay time course that is sensitive to low-affinity glutamate receptor antagonists and extracellular calcium concentrations, consistent with glutamate spillover. Furthermore, we uncover and characterize a novel, purely spillover-mediated AMPA receptor current from immature relay neurons. The isolation of this current strongly supports the presence of spillover between boutons of different RGCs. In addition, fluorescence measurements of presynaptic calcium transients suggest that prolonged residual calcium contributes to both glutamate spillover and asynchronous release. These data indicate that, during development, far more RGCs contribute to relay neuron firing than would be expected based on predictions from anatomy alone.
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Affiliation(s)
- Jessica L Hauser
- Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts
| | - Xiaojin Liu
- Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts
| | - Elizabeth Y Litvina
- Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts
| | - Chinfei Chen
- Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts
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Jiang M, Yang M, Yin L, Zhang X, Shu Y. Developmental reduction of asynchronous GABA release from neocortical fast-spiking neurons. ACTA ACUST UNITED AC 2013; 25:258-70. [PMID: 23968835 DOI: 10.1093/cercor/bht236] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Delayed asynchronous release (AR) evoked by bursts of presynaptic action potentials (APs) occurs in certain types of hippocampal and neocortical inhibitory interneurons. Previous studies showed that AR provides long-lasting inhibition and desynchronizes the activity in postsynaptic cells. However, whether AR undergoes developmental change remains unknown. In this study, we performed whole-cell recording from fast-spiking (FS) interneurons and pyramidal cells (PCs) in prefrontal cortical slices obtained from juvenile and adult rats. In response to AP trains in FS neurons, AR occurred at their output synapses during both age periods, including FS autapses and FS-PC synapses; however, the AR strength was significantly weaker in adults than that in juveniles. Further experiments suggested that the reduction of AR in adult animals could be attributable to the rapid clearance of residual Ca(2+) from presynaptic terminals. Together, our results revealed that the AR strength was stronger at juvenile but weaker in adult, possibly resulting from changes in presynaptic Ca(2+) dynamics. AR changes may meet the needs of the neural network to generate different types of oscillations for cortical processing at distinct behavioral states.
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Affiliation(s)
- Man Jiang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, P. R. China
| | - Mingpo Yang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, P. R. China
| | - Luping Yin
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, P. R. China
| | - Xiaohui Zhang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, P. R. China
| | - Yousheng Shu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, P. R. China
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10
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Yao J, Gaffaney JD, Kwon SE, Chapman ER. Doc2 is a Ca2+ sensor required for asynchronous neurotransmitter release. Cell 2011; 147:666-77. [PMID: 22036572 DOI: 10.1016/j.cell.2011.09.046] [Citation(s) in RCA: 163] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Revised: 07/19/2011] [Accepted: 09/29/2011] [Indexed: 11/26/2022]
Abstract
Synaptic transmission involves a fast synchronous phase and a slower asynchronous phase of neurotransmitter release that are regulated by distinct Ca(2+) sensors. Though the Ca(2+) sensor for rapid exocytosis, synaptotagmin I, has been studied in depth, the sensor for asynchronous release remains unknown. In a screen for neuronal Ca(2+) sensors that respond to changes in [Ca(2+)] with markedly slower kinetics than synaptotagmin I, we observed that Doc2--another Ca(2+), SNARE, and lipid-binding protein--operates on timescales consistent with asynchronous release. Moreover, up- and downregulation of Doc2 expression levels in hippocampal neurons increased or decreased, respectively, the slow phase of synaptic transmission. Synchronous release, when triggered by single action potentials, was unaffected by manipulation of Doc2 but was enhanced during repetitive stimulation in Doc2 knockdown neurons, potentially due to greater vesicle availability. In summary, we propose that Doc2 is a Ca(2+) sensor that is kinetically tuned to regulate asynchronous neurotransmitter release.
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Affiliation(s)
- Jun Yao
- Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, WI 53706, USA
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11
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Volman V, Levine H, Sejnowski TJ. Shunting inhibition controls the gain modulation mediated by asynchronous neurotransmitter release in early development. PLoS Comput Biol 2010; 6:e1000973. [PMID: 21079676 PMCID: PMC2973817 DOI: 10.1371/journal.pcbi.1000973] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Accepted: 09/24/2010] [Indexed: 11/18/2022] Open
Abstract
The sensitivity of a neuron to its input can be modulated in several ways. Changes in the slope of the neuronal input-output curve depend on factors such as shunting inhibition, background noise, frequency-dependent synaptic excitation, and balanced excitation and inhibition. However, in early development GABAergic interneurons are excitatory and other mechanisms such as asynchronous transmitter release might contribute to regulating neuronal sensitivity. We modeled both phasic and asynchronous synaptic transmission in early development to study the impact of activity-dependent noise and short-term plasticity on the synaptic gain. Asynchronous release decreased or increased the gain depending on the membrane conductance. In the high shunt regime, excitatory input due to asynchronous release was divisive, whereas in the low shunt regime it had a nearly multiplicative effect on the firing rate. In addition, sensitivity to correlated inputs was influenced by shunting and asynchronous release in opposite ways. Thus, asynchronous release can regulate the information flow at synapses and its impact can be flexibly modulated by the membrane conductance.
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Affiliation(s)
- Vladislav Volman
- Center for Theoretical Biological Physics, University of California at San Diego, La Jolla, California, United States of America.
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12
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Developmental mechanisms for suppressing the effects of delayed release at the endbulb of Held. J Neurosci 2010; 30:11466-75. [PMID: 20739568 DOI: 10.1523/jneurosci.2300-10.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Delayed release of neurotransmitter, also called asynchronous release, is commonly observed at synapses, yet its influence on transmission of spike information is unknown. We examined this issue at endbulb of Held synapses, which are formed by auditory nerve fibers onto bushy cells in the cochlear nucleus. Endbulbs from CBA/CaJ mice aged P6-P49 showed prominent delayed release when driven at physiologically relevant rates. In bushy cells from mice before the onset of hearing (P6-P12), spikes were driven by delayed release up to 100 ms after presynaptic activity. However, no such spikes were observed in bushy cells from mice after the onset of hearing (>P14). Dynamic-clamp experiments indicated that delayed release can drive spikes in older bushy cells provided synchronous release is absent, suggesting that activity normally suppresses these spikes. Application of apamin or alpha-dendrotoxin revealed late spikes in older bushy cells, suggesting that postsynaptic activation of K(V)1.x and SK channels during spiking suppresses the subsequent effects of delayed release. The developmental upregulation of these potassium channels would be highly adaptive for temporally precise auditory processing. Furthermore, delayed release appeared to influence synchronous neurotransmitter release. Enhancement of delayed release using strontium was correlated with lower firing probability in current clamp and smaller synchronous EPSCs in voltage clamp. EGTA-AM had the opposite effects. These effects were consistent with delayed and synchronous release competing for a single vesicle pool. Thus delayed release apparently has negative presynaptic and postsynaptic consequences at the endbulb, which are partly mitigated by postsynaptic potassium channel expression.
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Chang CY, Mennerick S. Dynamic modulation of phasic and asynchronous glutamate release in hippocampal synapses. J Neurophysiol 2009; 103:392-401. [PMID: 19889850 DOI: 10.1152/jn.00683.2009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although frequency-dependent short-term presynaptic plasticity has been of long-standing interest, most studies have emphasized modulation of the synchronous, phasic component of transmitter release, most evident with a single or a few presynaptic stimuli. Asynchronous transmitter release, vesicle fusion not closely time locked to presynaptic action potentials, can also be prominent under certain conditions, including repetitive stimulation. Asynchrony has often been attributed to residual Ca(2+) buildup in the presynaptic terminal. We verified that a number of manipulations of Ca(2+) handling and influx selectively alter asynchronous release relative to phasic transmitter release during action potential trains in cultured excitatory autaptic hippocampal neurons. To determine whether other manipulations of vesicle release probability also selectively modulate asynchrony, we probed the actions of one thoroughly studied modulator class whose actions on phasic versus asynchronous release have not been investigated. We examined the effects of the phorbol ester PDBu, which has protein kinase C (PKC) dependent and independent actions on presynaptic transmitter release. PDBu increased phasic and asynchronous release in parallel. However, while PKC inhibition had relatively minor inhibitory effects on PDBu potentiation of phasic and total release during action potential trains, PKC inhibition strongly reduced phorbol-potentiated asynchrony, through actions most evident late during stimulus trains. These results lend new insight into PKC-dependent and -independent effects on transmitter release and suggest the possibility of differential control of synchronous versus asynchronous vesicle release.
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Affiliation(s)
- Chun Yun Chang
- Department of Psychiatry, Washington University School of Medicine, 660 South Euclid Ave., St. Louis, MO 63110, USA
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14
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Kasanetz F, Manzoni OJ. Maturation of Excitatory Synaptic Transmission of the Rat Nucleus Accumbens From Juvenile to Adult. J Neurophysiol 2009; 101:2516-27. [DOI: 10.1152/jn.91039.2008] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Precise control of synaptic strength is critical for maintaining accurate network activity and normal brain functions. Several major brain diseases are related to synaptic alterations in the adult brain. Detailed descriptions of the normal physiological properties of adult synapses are scarce, mainly because of the difficulties in performing whole cell patch-clamp recording in brain slices from adult animals. Here we present the portrait of excitatory synapses and intrinsic properties of medium spiny neurons (MSNs) of the nucleus accumbens (NAc), a central structure of the mesocorticolimbic system, from youth (P14) to adulthood (P120). We found that intrinsic neuronal excitability decreased over development, mainly due to an enhancement of potassium conductance and the consequent reduction in membrane resistance. The ratio between paired-pulse synaptic responses was similar in juvenile, adolescent, and adult MSNs, suggesting that the probability of neurotransmitter release was unaltered. α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)–mediated excitatory postsynaptic currents (EPSCs) decayed more slowly in adult MSN. In contrast, the kinetic properties and the subunit composition of N-methyl-d-aspartate receptor (NMDAR)–mediated EPSC in the NAc were conserved from youth to adulthood. Changes in synaptic strength were estimated from the ratio of AMPAR to NMDAR evoked and spontaneous EPSCs (AMPAR/NMDAR ratio). Although both AMPAR and NMDAR EPSCs decreased over development, there was an increase of the AMPAR/NMDAR ratio that was linked to changes in NMDAR EPSC. Furthermore, distribution of the AMPAR/NMDAR ratio was more heterogeneous in MSNs from adults, suggesting that synaptic strength is continuously refined during life.
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Cooke RM, Parker D. Locomotor Recovery after Spinal Cord Lesions in the Lamprey Is Associated with Functional and Ultrastructural Changes below Lesion Sites. J Neurotrauma 2009; 26:597-612. [PMID: 19271969 DOI: 10.1089/neu.2008.0660] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Ria Mishaal Cooke
- Department of Physiology, Development, and Neuroscience and Department of Zoology, University of Cambridge, Downing Site, Cambridge, United Kingdom
| | - David Parker
- Department of Physiology, Development, and Neuroscience and Department of Zoology, University of Cambridge, Downing Site, Cambridge, United Kingdom
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Iremonger KJ, Bains JS. Integration of asynchronously released quanta prolongs the postsynaptic spike window. J Neurosci 2007; 27:6684-91. [PMID: 17581955 PMCID: PMC6672686 DOI: 10.1523/jneurosci.0934-07.2007] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Classically, the release of glutamate in response to a presynaptic action potential causes a brief increase in postsynaptic excitability. Previous reports indicate that at some central synapses, a single action potential can elicit multiple, asynchronous release events. This raises the possibility that the temporal dynamics of neurotransmitter release may determine the duration of altered postsynaptic excitability. In response to physiological challenges, the magnocellular neurosecretory cells (MNCs) in the paraventricular nucleus of the hypothalamus (PVN) exhibit robust and prolonged increases in neuronal activity. Although the postsynaptic conductances that may facilitate this form of activity have been investigated thoroughly, the role of presynaptic release has been largely overlooked. Because the specific patterns of activity generated by MNCs require the activation of excitatory synaptic inputs, we sought to characterize the release dynamics at these synapses and determine whether they contribute to prolonged excitability in these cells. We obtained whole-cell recordings from MNCs in brain slices of postnatal day 21-44 rats. Stimulation of glutamatergic inputs elicited large and prolonged postsynaptic events that resulted from the summation of multiple, asynchronously released quanta. Asynchronous release was selectively inhibited by the slow calcium buffer EGTA-AM and potentiated by brief high-frequency stimulus trains. These trains caused a prolonged increase in postsynaptic spike activity that could also be eliminated by EGTA-AM. Our results demonstrate that glutamatergic terminals in PVN exhibit asynchronous release, which is important in generating large postsynaptic depolarizations and prolonged spiking in response to brief, high-frequency bursts of presynaptic activity.
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Affiliation(s)
- Karl J. Iremonger
- Hotchkiss Brain Institute and Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada T2N 4N1
| | - Jaideep S. Bains
- Hotchkiss Brain Institute and Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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Bonansco C, Fuenzalida M, Olivares V, Molina C, Roncagliolo M. Asynchronic transmission in the CA3–CA1 hippocampal synapses in the neurological mutanttaiep rat. J Neurosci Res 2006; 85:223-9. [PMID: 17086546 DOI: 10.1002/jnr.21109] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
For the taiep rat, a neurological mutant with severe astrogliosis secondary to demyelination, we have described alterations in spinal cord synaptic transmission. Asynchronous responses result from phasic action potential-derived glutamate release in this mutant. To evaluate whether this anomalous transmission is also produced in other regions of the taiep CNS and whether its nature involves a presynaptic or postsynaptic disruption, we studied the CA3-CA1 hippocampal synapses. Excitatory postsynaptic currents (EPSC) evoked by stimulation of Schaffer collaterals were recorded from CA1 pyramidal cells on picrotoxin-treated slices. Initial fast and time-locked EPSCs were evoked by conventional stimulation in both control and taiep neurons, showing similar latency and amplitude values unimodally distributed. In a high percentage of taiep neurons (47%), the initial EPSC was frequently followed by additional asynchronous synaptic currents (EPSC(ASYN)) with latencies ranging from 10 to 300 msec. As with initial EPSCs, EPSC(ASYN) were action potential dependent, sensitive to tetrodotoxin, and blocked by D-2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione. The occurrence probability of these events decayed monoexponentially as a function of poststimulus time. The elevation of extracellular Ca(2+) induced a reduction of amplitudes and a rate increase of EPSC(ASYN), in parallel with a reduction of paired pulse facilitation of initial EPSCs. The presynaptic fiber volley, extracellularly recorded, showed no significant differences between groups, with similar mean values of area and decay time. These findings in hippocampal circuitry suggest that, in taiep, the asynchronous evoked activity represents a rather generalized phenotype of the glutamatergic synapses and that EPSC(ASYN) seems to be determined by presynaptic alterations.
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Affiliation(s)
- Christian Bonansco
- Departamento de Fisiología, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
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