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Feldthouse MG, Vyleta NP, Smith SM. PLC regulates spontaneous glutamate release triggered by extracellular calcium and readily releasable pool size in neocortical neurons. Front Cell Neurosci 2023; 17:1193485. [PMID: 37260580 PMCID: PMC10228687 DOI: 10.3389/fncel.2023.1193485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Accepted: 04/26/2023] [Indexed: 06/02/2023] Open
Abstract
Introduction Dynamic physiological changes in brain extracellular calcium ([Ca2+]o) occur when high levels of neuronal activity lead to substantial Ca2+ entry via ion channels reducing local [Ca2+]o. Perturbations of the extracellular microenvironment that increase [Ca2+]o are commonly used to study how [Ca2+] regulates neuronal activity. At excitatory synapses, the Ca2+-sensing receptor (CaSR) and other G-protein coupled receptors link [Ca2+]o and spontaneous glutamate release. Phospholipase C (PLC) is activated by G-proteins and is hypothesized to mediate this process. Methods Patch-clamping cultured neocortical neurons, we tested how spontaneous glutamate release was affected by [Ca2+]o and inhibition of PLC activity. We used hypertonic sucrose (HS) to evaluate the readily releasable pool (RRP) and test if it was affected by inhibition of PLC activity. Results Spontaneous glutamate release substantially increased with [Ca2+]o, and inhibition of PLC activity, with U73122, abolished this effect. PLC-β1 is an abundant isoform in the neocortex, however, [Ca2+]o-dependent spontaneous release was unchanged in PLC-β1 null mutants (PLC-β1-/-). U73122 completely suppressed this response in PLC-β1-/- neurons, indicating that this residual [Ca2+]o-sensitivity may be mediated by other PLC isoforms. The RRP size was substantially reduced after incubation in U73122, but not U73343. Phorbol esters increased RRP size after PLC inhibition. Discussion Together these data point to a strong role for PLC in mediating changes in spontaneous release elicited by [Ca2+]o and other extracellular cues, possibly by modifying the size of the RRP.
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Affiliation(s)
- Maya G. Feldthouse
- Section of Pulmonary and Critical Care Medicine and Research and Development, VA Portland Health Care System, Portland, OR, United States
| | - Nicholas P. Vyleta
- Division of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR, United States
| | - Stephen M. Smith
- Section of Pulmonary and Critical Care Medicine and Research and Development, VA Portland Health Care System, Portland, OR, United States
- Division of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR, United States
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2
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Chiantia G, Hidisoglu E, Marcantoni A. The Role of Ryanodine Receptors in Regulating Neuronal Activity and Its Connection to the Development of Alzheimer's Disease. Cells 2023; 12:cells12091236. [PMID: 37174636 PMCID: PMC10177020 DOI: 10.3390/cells12091236] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 04/19/2023] [Accepted: 04/21/2023] [Indexed: 05/15/2023] Open
Abstract
Research into the early impacts of Alzheimer's disease (AD) on synapse function is one of the most promising approaches to finding a treatment. In this context, we have recently demonstrated that the Abeta42 peptide, which builds up in the brain during the processing of the amyloid precursor protein (APP), targets the ryanodine receptors (RyRs) of mouse hippocampal neurons and potentiates calcium (Ca2+) release from the endoplasmic reticulum (ER). The uncontrolled increase in intracellular calcium concentration ([Ca2+]i), leading to the development of Ca2+ dysregulation events and related excitable and synaptic dysfunctions, is a consolidated hallmark of AD onset and possibly other neurodegenerative diseases. Since RyRs contribute to increasing [Ca2+]i and are thought to be a promising target for AD treatment, the goal of this review is to summarize the current level of knowledge regarding the involvement of RyRs in governing neuronal function both in physiological conditions and during the onset of AD.
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Affiliation(s)
| | - Enis Hidisoglu
- Department of Drug and Science Technology, University of Torino, Corso Raffaello 30, 10125 Torino, Italy
| | - Andrea Marcantoni
- Department of Drug and Science Technology, University of Torino, Corso Raffaello 30, 10125 Torino, Italy
- N.I.S. Center, University of Torino, 10125 Turin, Italy
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3
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Grasskamp AT, Jusyte M, McCarthy AW, Götz TWB, Ditlevsen S, Walter AM. Spontaneous neurotransmission at evocable synapses predicts their responsiveness to action potentials. Front Cell Neurosci 2023; 17:1129417. [PMID: 36970416 PMCID: PMC10030884 DOI: 10.3389/fncel.2023.1129417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Accepted: 02/16/2023] [Indexed: 03/29/2023] Open
Abstract
Synaptic transmission relies on presynaptic neurotransmitter (NT) release from synaptic vesicles (SVs) and on NT detection by postsynaptic receptors. Transmission exists in two principal modes: action-potential (AP) evoked and AP-independent, "spontaneous" transmission. AP-evoked neurotransmission is considered the primary mode of inter-neuronal communication, whereas spontaneous transmission is required for neuronal development, homeostasis, and plasticity. While some synapses appear dedicated to spontaneous transmission only, all AP-responsive synapses also engage spontaneously, but whether this encodes functional information regarding their excitability is unknown. Here we report on functional interdependence of both transmission modes at individual synaptic contacts of Drosophila larval neuromuscular junctions (NMJs) which were identified by the presynaptic scaffolding protein Bruchpilot (BRP) and whose activities were quantified using the genetically encoded Ca2+ indicator GCaMP. Consistent with the role of BRP in organizing the AP-dependent release machinery (voltage-dependent Ca2+ channels and SV fusion machinery), most active BRP-positive synapses (>85%) responded to APs. At these synapses, the level of spontaneous activity was a predictor for their responsiveness to AP-stimulation. AP-stimulation resulted in cross-depletion of spontaneous activity and both transmission modes were affected by the non-specific Ca2+ channel blocker cadmium and engaged overlapping postsynaptic receptors. Thus, by using overlapping machinery, spontaneous transmission is a continuous, stimulus independent predictor for the AP-responsiveness of individual synapses.
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Affiliation(s)
| | - Meida Jusyte
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
- Einstein Center for Neurosciences, Charité–Universitätsmedizin Berlin, Berlin, Germany
| | | | - Torsten W. B. Götz
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | - Susanne Ditlevsen
- Department of Mathematical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Alexander M. Walter
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
- Einstein Center for Neurosciences, Charité–Universitätsmedizin Berlin, Berlin, Germany
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
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4
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Mechanisms Underlying the Recruitment of Inhibitory Interneurons in Fictive Swimming in Developing Xenopus laevis Tadpoles. J Neurosci 2023; 43:1387-1404. [PMID: 36693757 PMCID: PMC9987577 DOI: 10.1523/jneurosci.0520-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 10/27/2022] [Accepted: 12/02/2022] [Indexed: 01/26/2023] Open
Abstract
Developing spinal circuits generate patterned motor outputs while many neurons with high membrane resistances are still maturing. In the spinal cord of hatchling frog tadpoles of unknown sex, we found that the firing reliability in swimming of inhibitory interneurons with commissural and ipsilateral ascending axons was negatively correlated with their cellular membrane resistance. Further analyses showed that neurons with higher resistances had outward rectifying properties, low firing thresholds, and little delay in firing evoked by current injections. Input synaptic currents these neurons received during swimming, either compound, unitary current amplitudes, or unitary synaptic current numbers, were scaled with their membrane resistances, but their own synaptic outputs were correlated with membrane resistances of their postsynaptic partners. Analyses of neuronal dendritic and axonal lengths and their activities in swimming and cellular input resistances did not reveal a clear correlation pattern. Incorporating these electrical and synaptic properties into a computer swimming model produced robust swimming rhythms, whereas randomizing input synaptic strengths led to the breakdown of swimming rhythms, coupled with less synchronized spiking in the inhibitory interneurons. We conclude that the recruitment of these developing interneurons in swimming can be predicted by cellular input resistances, but the order is opposite to the motor-strength-based recruitment scheme depicted by Henneman's size principle. This form of recruitment/integration order in development before the emergence of refined motor control is progressive potentially with neuronal acquisition of mature electrical and synaptic properties, among which the scaling of input synaptic strengths with cellular input resistance plays a critical role.SIGNIFICANCE STATEMENT The mechanisms on how interneurons are recruited to participate in circuit function in developing neuronal systems are rarely investigated. In 2-d-old frog tadpole spinal cord, we found the recruitment of inhibitory interneurons in swimming is inversely correlated with cellular input resistances, opposite to the motor-strength-based recruitment order depicted by Henneman's size principle. Further analyses showed the amplitude of synaptic inputs that neurons received during swimming was inversely correlated with cellular input resistances. Randomizing/reversing the relation between input synaptic strengths and membrane resistances in modeling broke down swimming rhythms. Therefore, the recruitment or integration of these interneurons is conditional on the acquisition of several electrical and synaptic properties including the scaling of input synaptic strengths with cellular input resistances.
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5
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Horvath PM, Piazza MK, Kavalali ET, Monteggia LM. MeCP2 loss-of-function dysregulates microRNAs regionally and disrupts excitatory/inhibitory synaptic transmission balance. Hippocampus 2022; 32:610-623. [PMID: 35851733 PMCID: PMC9344394 DOI: 10.1002/hipo.23455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 06/11/2022] [Accepted: 06/25/2022] [Indexed: 11/06/2022]
Abstract
Rett syndrome is a leading cause of intellectual disability in females primarily caused by loss of function mutations in the transcriptional regulator MeCP2. Loss of MeCP2 leads to a host of synaptic phenotypes that are believed to underlie Rett syndrome pathophysiology. Synaptic deficits vary by brain region upon MeCP2 loss, suggesting distinct molecular alterations leading to disparate synaptic outcomes. In this study, we examined the contribution of MeCP2's newly described role in miRNA regulation to regional molecular and synaptic impairments. Two miRNAs, miR-101a and miR-203, were identified and confirmed as upregulated in MeCP2 KO mice in the hippocampus and cortex, respectively. miR-101a overexpression in hippocampal cultures led to opposing effects at excitatory and inhibitory synapses and in spontaneous and evoked neurotransmission, revealing the potential for a single miRNA to broadly regulate synapse function in the hippocampus. These results highlight the importance of regional alterations in miRNA expression and the specific impact on synaptic function with potential implications for Rett syndrome.
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Affiliation(s)
- Patricia M. Horvath
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee, USA,Department of Neuroscience, The University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Michelle K. Piazza
- Vanderbilt Brain Institute, Vanderbilt University, Nashville, Tennessee, USA,Neuroscience Program, Vanderbilt University, Nashville, Tennessee, USA
| | - Ege T. Kavalali
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee, USA,Vanderbilt Brain Institute, Vanderbilt University, Nashville, Tennessee, USA
| | - Lisa M. Monteggia
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee, USA,Vanderbilt Brain Institute, Vanderbilt University, Nashville, Tennessee, USA
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6
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Guzikowski NJ, Kavalali ET. Nano-Organization at the Synapse: Segregation of Distinct Forms of Neurotransmission. Front Synaptic Neurosci 2022; 13:796498. [PMID: 35002671 PMCID: PMC8727373 DOI: 10.3389/fnsyn.2021.796498] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2021] [Accepted: 11/19/2021] [Indexed: 01/01/2023] Open
Abstract
Synapses maintain synchronous, asynchronous, and spontaneous modes of neurotransmission through distinct molecular and biochemical pathways. Traditionally a single synapse was assumed to have a homogeneous organization of molecular components both at the active zone and post-synaptically. However, recent advancements in experimental tools and the further elucidation of the physiological significance of distinct forms of release have challenged this notion. In comparison to rapid evoked release, the physiological significance of both spontaneous and asynchronous neurotransmission has only recently been considered in parallel with synaptic structural organization. Active zone nanostructure aligns with postsynaptic nanostructure creating a precise trans-synaptic alignment of release sites and receptors shaping synaptic efficacy, determining neurotransmission reliability, and tuning plasticity. This review will discuss how studies delineating synaptic nanostructure create a picture of a molecularly heterogeneous active zone tuned to distinct forms of release that may dictate diverse synaptic functional outputs.
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Affiliation(s)
- Natalie J Guzikowski
- Department of Pharmacology, Vanderbilt University, Nashville, TN, United States.,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN, United States
| | - Ege T Kavalali
- Department of Pharmacology, Vanderbilt University, Nashville, TN, United States.,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN, United States
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7
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Hays CL, Sladek AL, Thoreson WB. Resting and stimulated mouse rod photoreceptors show distinct patterns of vesicle release at ribbon synapses. J Gen Physiol 2021; 152:211528. [PMID: 33175961 PMCID: PMC7664508 DOI: 10.1085/jgp.202012716] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 10/01/2020] [Accepted: 10/19/2020] [Indexed: 01/04/2023] Open
Abstract
The vertebrate visual system can detect and transmit signals from single photons. To understand how single-photon responses are transmitted, we characterized voltage-dependent properties of glutamate release in mouse rods. We measured presynaptic glutamate transporter anion current and found that rates of synaptic vesicle release increased with voltage-dependent Ca2+ current. Ca2+ influx and release rate also rose with temperature, attaining a rate of ∼11 vesicles/s/ribbon at -40 mV (35°C). By contrast, spontaneous release events at hyperpolarized potentials (-60 to -70 mV) were univesicular and occurred at random intervals. However, when rods were voltage clamped at -40 mV for many seconds to simulate maintained darkness, release occurred in coordinated bursts of 17 ± 7 quanta (mean ± SD; n = 22). Like fast release evoked by brief depolarizing stimuli, these bursts involved vesicles in the readily releasable pool of vesicles and were triggered by the opening of nearby ribbon-associated Ca2+ channels. Spontaneous release rates were elevated and bursts were absent after genetic elimination of the Ca2+ sensor synaptotagmin 1 (Syt1). This study shows that at the resting potential in darkness, rods release glutamate-filled vesicles from a pool at the base of synaptic ribbons at low rates but in Syt1-dependent bursts. The absence of bursting in cones suggests that this behavior may have a role in transmitting scotopic responses.
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Affiliation(s)
- Cassandra L Hays
- Cellular and Integrative Physiology, College of Medicine, University of Nebraska Medical Center, Omaha, NE.,Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, College of Medicine, University of Nebraska Medical Center, Omaha, NE
| | - Asia L Sladek
- Pharmacology and Experimental Neuroscience, College of Medicine, University of Nebraska Medical Center, Omaha, NE
| | - Wallace B Thoreson
- Pharmacology and Experimental Neuroscience, College of Medicine, University of Nebraska Medical Center, Omaha, NE.,Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, College of Medicine, University of Nebraska Medical Center, Omaha, NE
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8
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Jiang H, Liu JP, Xi K, Liu LY, Kong LY, Cai J, Cai SQ, Han XY, Song JG, Yang XM, Wan Y, Xing GG. Contribution of AMPA Receptor-Mediated LTD in LA/BLA-CeA Pathway to Comorbid Aversive and Depressive Symptoms in Neuropathic Pain. J Neurosci 2021; 41:7278-7299. [PMID: 34272314 PMCID: PMC8387122 DOI: 10.1523/jneurosci.2678-20.2021] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2020] [Revised: 06/30/2021] [Accepted: 07/08/2021] [Indexed: 11/21/2022] Open
Abstract
Comorbid anxiety and depressive symptoms in chronic pain are a common health problem, but the underlying mechanisms remain unclear. Previously, we have demonstrated that sensitization of the CeA neurons via decreased GABAergic inhibition contributes to anxiety-like behaviors in neuropathic pain rats. In this study, by using male Sprague Dawley rats, we reported that the CeA plays a key role in processing both sensory and negative emotional-affective components of neuropathic pain. Bilateral electrolytic lesions of CeA, but not lateral/basolateral nucleus of the amygdala (LA/BLA), abrogated both pain hypersensitivity and aversive and depressive symptoms of neuropathic rats induced by spinal nerve ligation (SNL). Moreover, SNL rats showed structural and functional neuroplasticity manifested as reduced dendritic spines on the CeA neurons and enhanced LTD at the LA/BLA-CeA synapse. Disruption of GluA2-containing AMPAR trafficking and endocytosis from synapses using synthetic peptides, either pep2-EVKI or Tat-GluA2(3Y), restored the enhanced LTD at the LA/BLA-CeA synapse, and alleviated the mechanical allodynia and comorbid aversive and depressive symptoms in neuropathic rats, indicating that the endocytosis of GluA2-containing AMPARs from synapses is probably involved in the LTD at the LA/BLA-CeA synapse and the comorbid aversive and depressive symptoms in neuropathic pain in SNL-operated rats. These data provide a novel mechanism for elucidating comorbid aversive and depressive symptoms in neuropathic pain and highlight that structural and functional neuroplasticity in the amygdala may be important as a promising therapeutic target for comorbid negative emotional-affective disorders in chronic pain.SIGNIFICANCE STATEMENT Several studies have demonstrated the high comorbidity of negative affective disorders in patients with chronic pain. Understanding the affective aspects related to chronic pain may facilitate the development of novel therapies for more effective management. Here, we unravel that the CeA plays a key role in processing both sensory and negative emotional-affective components of neuropathic pain, and LTD at the amygdaloid LA/BLA-CeA synapse mediated by GluA2-containing AMPAR endocytosis underlies the comorbid aversive and depressive symptoms in neuropathic pain. This study provides a novel mechanism for elucidating comorbid aversive and depressive symptoms in neuropathic pain and highlights that structural and functional neuroplasticity in the amygdala may be important as a promising therapeutic target for comorbid negative emotional-affective disorders in chronic pain.
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Affiliation(s)
- Hong Jiang
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Jiang-Ping Liu
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Ke Xi
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Ling-Yu Liu
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Ling-Yu Kong
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Jie Cai
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Si-Qing Cai
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Xi-Yuan Han
- Second Affiliated Hospital of Xinxiang Medical University, Henan, Xinxiang 453002, China
| | - Jing-Gui Song
- Second Affiliated Hospital of Xinxiang Medical University, Henan, Xinxiang 453002, China
| | - Xiao-Mei Yang
- Department of Human anatomy and Embryology, School of Basic Medical Sciences, Peking University, Beijing, 100191, China
| | - You Wan
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
| | - Guo-Gang Xing
- Neuroscience Research Institute, Peking University, Department of Neurobiology, School of Basic Medical Sciences, Peking University Health Science Center; Key Laboratory for Neuroscience, Ministry of Education of China & National Health Commission of China, Beijing, 100191, China
- Second Affiliated Hospital of Xinxiang Medical University, Henan, Xinxiang 453002, China
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9
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Abstract
In mammals, the selective transformation of transient experience into stored memory occurs in the hippocampus, which develops representations of specific events in the context in which they occur. In this review, we focus on the development of hippocampal circuits and the self-organized dynamics embedded within them since the latter critically support the role of the hippocampus in learning and memory. We first discuss evidence that adult hippocampal cells and circuits are sculpted by development as early as during embryonic neurogenesis. We argue that these primary developmental programs provide a scaffold onto which later experience of the external world can be grafted. Next, we review the different sequences in the development of hippocampal cells and circuits at anatomical and functional levels. We cover a period extending from neurogenesis and migration to the appearance of phenotypic diversity within hippocampal cells, and their wiring into functional networks. We describe the progressive emergence of network dynamics in the hippocampus, from sensorimotor-driven early sharp waves to sequences of place cells tracking relational information. We outline the critical turn points and discontinuities in that developmental journey, and close by formulating open questions. We propose that rewinding the process of hippocampal development helps understand the main organization principles of memory circuits.
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Affiliation(s)
- Rosa Cossart
- Inserm, INMED, Turing Center for Living Systems, Aix Marseille University, Marseille, France
| | - Rustem Khazipov
- Inserm, INMED, Turing Center for Living Systems, Aix Marseille University, Marseille, France.,Laboratory of Neurobiology, Kazan Federal University, Kazan Russia
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10
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Chiang CW, Shu WC, Wan J, Weaver BA, Jackson MB. Recordings from neuron-HEK cell cocultures reveal the determinants of miniature excitatory postsynaptic currents. J Gen Physiol 2021; 153:211910. [PMID: 33755721 PMCID: PMC7992392 DOI: 10.1085/jgp.202012849] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 01/26/2021] [Accepted: 02/23/2021] [Indexed: 11/20/2022] Open
Abstract
Spontaneous exocytosis of single synaptic vesicles generates miniature synaptic currents, which provide a window into the dynamic control of synaptic transmission. To resolve the impact of different factors on the dynamics and variability of synaptic transmission, we recorded miniature excitatory postsynaptic currents (mEPSCs) from cocultures of mouse hippocampal neurons with HEK cells expressing the postsynaptic proteins GluA2, neuroligin 1, PSD-95, and stargazin. Synapses between neurons and these heterologous cells have a molecularly defined postsynaptic apparatus, while the compact morphology of HEK cells eliminates the distorting effect of dendritic filtering. HEK cells in coculture produced mEPSCs with a higher frequency, larger amplitude, and more rapid rise and decay than neurons from the same culture. However, mEPSC area indicated that nerve terminals in synapses with both neurons and HEK cells release similar populations of vesicles. Modulation by the glutamate receptor ligand aniracetam revealed receptor contributions to mEPSC shape. Dendritic cable effects account for the slower mEPSC rise in neurons, whereas the slower decay also depends on other factors. Lastly, expression of synaptobrevin transmembrane domain mutants in neurons slowed the rise of HEK cell mEPSCs, thus revealing the impact of synaptic fusion pores. In summary, we show that cocultures of neurons with heterologous cells provide a geometrically simplified and molecularly defined system to investigate the time course of synaptic transmission and to resolve the contribution of vesicles, fusion pores, dendrites, and receptors to this process.
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Affiliation(s)
- Chung-Wei Chiang
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI
| | - Wen-Chi Shu
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI
| | - Jun Wan
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI
| | - Beth A Weaver
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI
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11
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Wu D, Jin Y, Shapiro TM, Hinduja A, Baas PW, Tom VJ. Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury. Nat Commun 2020; 11:6131. [PMID: 33257677 PMCID: PMC7705672 DOI: 10.1038/s41467-020-19914-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Accepted: 11/05/2020] [Indexed: 12/26/2022] Open
Abstract
After a dorsal root crush injury, centrally-projecting sensory axons fail to regenerate across the dorsal root entry zone (DREZ) to extend into the spinal cord. We find that chemogenetic activation of adult dorsal root ganglion (DRG) neurons improves axon growth on an in vitro model of the inhibitory environment after injury. Moreover, repeated bouts of daily chemogenetic activation of adult DRG neurons for 12 weeks post-crush in vivo enhances axon regeneration across a chondroitinase-digested DREZ into spinal gray matter, where the regenerating axons form functional synapses and mediate behavioral recovery in a sensorimotor task. Neuronal activation-mediated axon extension is dependent upon changes in the status of tubulin post-translational modifications indicative of highly dynamic microtubules (as opposed to stable microtubules) within the distal axon, illuminating a novel mechanism underlying stimulation-mediated axon growth. We have identified an effective combinatory strategy to promote functionally-relevant axon regeneration of adult neurons into the CNS after injury.
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Affiliation(s)
- Di Wu
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Ying Jin
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Tatiana M Shapiro
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Abhishek Hinduja
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Peter W Baas
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Veronica J Tom
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, USA.
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12
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Kuhlmann N, Milnerwood AJ. A Critical LRRK at the Synapse? The Neurobiological Function and Pathophysiological Dysfunction of LRRK2. Front Mol Neurosci 2020; 13:153. [PMID: 32973447 PMCID: PMC7482583 DOI: 10.3389/fnmol.2020.00153] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 07/22/2020] [Indexed: 12/25/2022] Open
Abstract
Since the discovery of LRRK2 mutations causal to Parkinson's disease (PD) in the early 2000s, the LRRK2 protein has been implicated in a plethora of cellular processes in which pathogenesis could occur, yet its physiological function remains elusive. The development of genetic models of LRRK2 PD has helped identify the etiological and pathophysiological underpinnings of the disease, and may identify early points of intervention. An important role for LRRK2 in synaptic function has emerged in recent years, which links LRRK2 to other genetic forms of PD, most notably those caused by mutations in the synaptic protein α-synuclein. This point of convergence may provide useful clues as to what drives dysfunction in the basal ganglia circuitry and eventual death of substantia nigra (SN) neurons. Here, we discuss the evolution and current state of the literature placing LRRK2 at the synapse, through the lens of knock-out, overexpression, and knock-in animal models. We hope that a deeper understanding of LRRK2 neurobiology, at the synapse and beyond, will aid the eventual development of neuroprotective interventions for PD, and the advancement of useful treatments in the interim.
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Affiliation(s)
- Naila Kuhlmann
- Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.,Department of Neurology & Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada
| | - Austen J Milnerwood
- Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.,Department of Neurology & Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada
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13
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Tang BL. Vesicle transport through interaction with t-SNAREs 1a (Vti1a)'s roles in neurons. Heliyon 2020; 6:e04600. [PMID: 32775753 PMCID: PMC7398939 DOI: 10.1016/j.heliyon.2020.e04600] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 06/03/2020] [Accepted: 07/28/2020] [Indexed: 01/01/2023] Open
Abstract
The Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family mediates membrane fusion during membrane trafficking and autophagy in all eukaryotic cells, with a number of SNAREs having cell type-specific functions. The endosome-trans-Golgi network (TGN) localized SNARE, Vesicle transport through interaction with t-SNAREs 1A (Vti1a), is unique among SNAREs in that it has numerous neuron-specific functions. These include neurite outgrowth, nervous system development, spontaneous neurotransmission, synaptic vesicle and dense core vesicle secretion, as well as a process of unconventional surface transport of the Kv4 potassium channel. Furthermore, the human VT11A gene is known to form fusion products with neighboring genes in cancer tissues, and VT11A variants are associated with risk in cancers, including glioma. In this review, I highlight VTI1A's known physio-pathological roles in brain neurons, as well as unanswered questions in these regards.
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Affiliation(s)
- Bor Luen Tang
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University Health System, Singapore.,NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore, Singapore
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14
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Bonnycastle K, Davenport EC, Cousin MA. Presynaptic dysfunction in neurodevelopmental disorders: Insights from the synaptic vesicle life cycle. J Neurochem 2020; 157:179-207. [PMID: 32378740 DOI: 10.1111/jnc.15035] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 04/14/2020] [Accepted: 04/22/2020] [Indexed: 12/11/2022]
Abstract
The activity-dependent fusion, retrieval and recycling of synaptic vesicles is essential for the maintenance of neurotransmission. Until relatively recently it was believed that most mutations in genes that were essential for this process would be incompatible with life, because of this fundamental role. However, an ever-expanding number of mutations in this very cohort of genes are being identified in individuals with neurodevelopmental disorders, including autism, intellectual disability and epilepsy. This article will summarize the current state of knowledge linking mutations in presynaptic genes to neurodevelopmental disorders by sequentially covering the various stages of the synaptic vesicle life cycle. It will also discuss how perturbations of specific stages within this recycling process could translate into human disease. Finally, it will also provide perspectives on the potential for future therapy that are targeted to presynaptic function.
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Affiliation(s)
- Katherine Bonnycastle
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK.,Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK.,Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
| | - Elizabeth C Davenport
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK.,Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK.,Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
| | - Michael A Cousin
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, UK.,Muir Maxwell Epilepsy Centre, University of Edinburgh, Edinburgh, UK.,Simons Initiative for the Developing Brain, University of Edinburgh, Edinburgh, UK
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15
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Static Magnetic Field Induced Neural Stem/Progenitor Cell Early Differentiation and Promotes Maturation. Stem Cells Int 2019; 2019:8790176. [PMID: 31737078 PMCID: PMC6816009 DOI: 10.1155/2019/8790176] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 08/21/2019] [Accepted: 09/13/2019] [Indexed: 12/11/2022] Open
Abstract
The potential impacts of magnetic field exposures on brain development have raised public concern. In the present study, we aimed to investigate the biophysical effects of moderate-intensity (0.5 T, Tesla) static magnetic field (SMF) on mice neural progenitor cells (mNPCs). Our results showed that the SMF exposure increased the number of neurosphere formation and enhanced proliferative activity in mNPCs. In addition, our flow cytometry data demonstrated that the proportions of S phase and G2/M phase mNPCs were remarkably increased following 5 days of SMF exposure. Moreover, the level of a mitotic regulatory protein, cyclin B, was upregulated after SMF exposure. Furthermore, the mNPCs exposed to SMF exhibited a significant increase in Sox2 expression. When mNPCs were induced to differentiation, our immunofluorescence assay revealed that the percentage of neurons (Tuj-1-positive cells) but not astrocyte (s100β-positive cells) was significantly higher and displayed morphological complexity in the SMF group. Finally, our electrophysiological results demonstrated the mNPC-derived neurons from the SMF group showing a significantly increased in input resistance, which indicated more functional maturation. Based on these findings, it appears reasonable to suggest that SMF exposure could affect normal neurogenesis and promote neural lineage differentiation as well as neuronal maturation.
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16
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Burk K, Ramachandran B, Ahmed S, Hurtado-Zavala JI, Awasthi A, Benito E, Faram R, Ahmad H, Swaminathan A, McIlhinney J, Fischer A, Perestenko P, Dean C. Regulation of Dendritic Spine Morphology in Hippocampal Neurons by Copine-6. Cereb Cortex 2019; 28:1087-1104. [PMID: 28158493 DOI: 10.1093/cercor/bhx009] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Indexed: 12/20/2022] Open
Abstract
Dendritic spines compartmentalize information in the brain, and their morphological characteristics are thought to underly synaptic plasticity. Here we identify copine-6 as a novel modulator of dendritic spine morphology. We found that brain-derived neurotrophic factor (BDNF) - a molecule essential for long-term potentiation of synaptic strength - upregulated and recruited copine-6 to dendritic spines in hippocampal neurons. Overexpression of copine-6 increased mushroom spine number and decreased filopodia number, while copine-6 knockdown had the opposite effect and dramatically increased the number of filopodia, which lacked PSD95. Functionally, manipulation of post-synaptic copine-6 levels affected miniature excitatory post-synaptic current (mEPSC) kinetics and evoked synaptic vesicle recycling in contacting boutons, and post-synaptic knockdown of copine-6 reduced hippocampal LTP and increased LTD. Mechanistically, copine-6 promotes BDNF-TrkB signaling and recycling of activated TrkB receptors back to the plasma membrane surface, and is necessary for BDNF-induced increases in mushroom spines in hippocampal neurons. Thus copine-6 regulates BDNF-dependent changes in dendritic spine morphology to promote synaptic plasticity.
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Affiliation(s)
- Katja Burk
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany
| | - Binu Ramachandran
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany
| | - Saheeb Ahmed
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany.,Department of Diagnostic and Interventional Radiology, University Medical Center Göttingen, Robert Koch Strasse 40, 37075 Göttingen, Germany
| | - Joaquin I Hurtado-Zavala
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany
| | - Ankit Awasthi
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany
| | - Eva Benito
- German Center for Neurodegenerative Diseases (DZNE) Göttingen, von Siebold Str. 3A, 37075 Göttingen , Germany
| | - Ruth Faram
- MRC Anatomical Neuropharmacology Unit, University of Oxford, Mansfield Road, Oxford OX1 3TH , UK
| | - Hamid Ahmad
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany.,Johannes Gutenberg University Mainz, Saarstrasse 21, 55122 Mainz, Germany
| | - Aarti Swaminathan
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany
| | - Jeffrey McIlhinney
- MRC Anatomical Neuropharmacology Unit, University of Oxford, Mansfield Road, Oxford OX1 3TH , UK
| | - Andre Fischer
- German Center for Neurodegenerative Diseases (DZNE) Göttingen, von Siebold Str. 3A, 37075 Göttingen , Germany
| | - Pavel Perestenko
- MRC Anatomical Neuropharmacology Unit, University of Oxford, Mansfield Road, Oxford OX1 3TH , UK
| | - Camin Dean
- Trans-synaptic Signaling Group, European Neuroscience Institute, Grisebachstrasse 5, 37077 Göttingen, Germany
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17
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Metzbower SR, Joo Y, Benavides DR, Blanpied TA. Properties of Individual Hippocampal Synapses Influencing NMDA-Receptor Activation by Spontaneous Neurotransmission. eNeuro 2019; 6:ENEURO.0419-18.2019. [PMID: 31110134 PMCID: PMC6541874 DOI: 10.1523/eneuro.0419-18.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 05/05/2019] [Accepted: 05/12/2019] [Indexed: 12/14/2022] Open
Abstract
NMDA receptor (NMDAR) activation is critical for maintenance and modification of synapse strength. Specifically, NMDAR activation by spontaneous glutamate release has been shown to mediate some forms of synaptic plasticity as well as synaptic development. Interestingly, there is evidence that within individual synapses each release mode may be segregated such that postsynaptically there are distinct pools of responsive receptors. To examine potential regulators of NMDAR activation because of spontaneous glutamate release in cultured hippocampal neurons, we used GCaMP6f imaging at single synapses in concert with confocal and super-resolution imaging. Using these single-spine approaches, we found that Ca2+ entry activated by spontaneous release tends to be carried by GluN2B-NMDARs. Additionally, the amount of NMDAR activation varies greatly both between synapses and within synapses, and is unrelated to spine and synapse size, but does correlate loosely with synapse distance from the soma. Despite the critical role of spontaneous activation of NMDARs in maintaining synaptic function, their activation seems to be controlled factors other than synapse size or synapse distance from the soma. It is most likely that NMDAR activation by spontaneous release influenced variability in subsynaptic receptor position, release site position, vesicle content, and channel properties. Therefore, spontaneous activation of NMDARs appears to be regulated distinctly from other receptor types, notably AMPARs, within individual synapses.
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Affiliation(s)
| | - Yuyoung Joo
- Department of Neurology, University of Maryland School of Medicine, Baltimore, Maryland, 21201
| | - David R Benavides
- Department of Neurology, University of Maryland School of Medicine, Baltimore, Maryland, 21201
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18
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Jin Y, Seo KH, Ko HM, Jung TW, Chung YH, Lee JH, Park HH, Kim HC, Jeong JH, Lee SH. Various approaches for measurement of synaptic vesicle endocytosis at the central nerve terminal. Arch Pharm Res 2019; 42:455-465. [PMID: 31115782 DOI: 10.1007/s12272-019-01161-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2019] [Accepted: 05/16/2019] [Indexed: 10/26/2022]
Abstract
At the presynaptic terminal, neurotransmitters are stored in synaptic vesicles (SVs), which are released and recycled via exo- and endocytosis. SV endocytosis is crucial for sustaining synaptic transmission by maintaining the SV pool. Many studies have shown that presynaptic dysfunction, particularly impairment of SV endocytosis, is related to neurological disorders. Notably, the presynaptic terminal is considered to be a sensitive structure because certain presynaptic dysfunctions, manifested as impaired SV endocytosis or ultrastructural changes in the presynaptic terminal, can be observed before there is a biochemical or pathological evidence of a neurological disorder. Therefore, monitoring and assessing the presynaptic function by SV endocytosis facilitates the development of early markers for neurological disorders. In this study, we reviewed the current methods for assessing and visualizing SV endocytosis at the central nerve terminal.
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Affiliation(s)
- Yeonsun Jin
- College of Pharmacy, Chung-Ang University, Seoul, 06974, Republic of Korea
| | - Kyoung Hee Seo
- College of Pharmacy, Chung-Ang University, Seoul, 06974, Republic of Korea
| | - Hyun Myung Ko
- Department of Life Science, College of Science and Technology, Woosuk University, Jincheon, 27841, Republic of Korea
| | - Tae Woo Jung
- Research Administration Team, Seoul National University Bundang Hospital, Seongnam, Korea
| | - Yoon Hee Chung
- Department of Anatomy, College of Medicine, Chung-Ang University, Seoul, Republic of Korea
| | - Jong Hyuk Lee
- Department of Pharmaceutical Engineering, College of Life and Health Science, Hoseo University, Asan, 31499, Republic of Korea
| | - Hyun Ho Park
- College of Pharmacy, Chung-Ang University, Seoul, 06974, Republic of Korea
| | - Hyoung-Chun Kim
- Neuropsychopharmacology and Toxicology Program, College of Pharmacy, Kangwon National University, Chunchon, 24341, Republic of Korea
| | - Ji Hoon Jeong
- Department of Pharmacology, College of Medicine, Chung-Ang University, Seoul, 06974, Republic of Korea
| | - Sung Hoon Lee
- College of Pharmacy, Chung-Ang University, Seoul, 06974, Republic of Korea.
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19
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Sculpting neurotransmission during synaptic development by 2D nanostructured interfaces. NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE 2018; 14:2521-2532. [DOI: 10.1016/j.nano.2017.01.020] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 12/08/2016] [Accepted: 01/04/2017] [Indexed: 11/23/2022]
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20
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Lazarevic V, Yang Y, Ivanova D, Fejtova A, Svenningsson P. Riluzole attenuates the efficacy of glutamatergic transmission by interfering with the size of the readily releasable neurotransmitter pool. Neuropharmacology 2018; 143:38-48. [PMID: 30222983 DOI: 10.1016/j.neuropharm.2018.09.021] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 08/11/2018] [Accepted: 09/12/2018] [Indexed: 01/02/2023]
Abstract
Riluzole is a potent neuroprotective agent which primarily inhibits excitatory neurotransmission interfering with presynaptic release, uptake and postsynaptic actions of glutamate by mechanisms that are not well understood. Riluzole and related prodrugs with improved blood brain barrier penetrance, are shown to be effective for the treatment of amyotrophic lateral sclerosis, ataxias, epilepsy and mood disorders. Our study was undertaken to decipher molecular and subcellular mechanisms of riluzole's antiglutamatergic effect, particularly focusing on presynaptic active zone structure and function. Applying multifarious live cell imaging techniques and amperometric glutamate recordings, we measured the impact of riluzole on presynaptic activity, synaptic vesicle recycling and glutamate release. Our in vitro and in vivo data revealed a unique mechanism whereby riluzole reduces the efficacy of glutamatergic transmission by selectively lowering the size of the readily releasable pool. This effect was correlated with the inhibition of protein kinase C-dependent Munc18-1 phosphorylation which is known to interfere with neurotransmitter release.
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Affiliation(s)
- Vesna Lazarevic
- Translational Neuropharmacology, Department of Clinical Neuroscience, Center for Molecular Medicine, Karolinska Institute, Stockholm, Sweden.
| | - Yunting Yang
- Translational Neuropharmacology, Department of Clinical Neuroscience, Center for Molecular Medicine, Karolinska Institute, Stockholm, Sweden
| | - Daniela Ivanova
- RG Presynaptic Plasticity, Leibniz Institute for Neurobiology, Magdeburg, Germany
| | - Anna Fejtova
- RG Presynaptic Plasticity, Leibniz Institute for Neurobiology, Magdeburg, Germany; Molecular Psychiatry, Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Per Svenningsson
- Translational Neuropharmacology, Department of Clinical Neuroscience, Center for Molecular Medicine, Karolinska Institute, Stockholm, Sweden
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21
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Chanaday NL, Kavalali ET. Presynaptic origins of distinct modes of neurotransmitter release. Curr Opin Neurobiol 2018; 51:119-126. [PMID: 29597140 PMCID: PMC6066415 DOI: 10.1016/j.conb.2018.03.005] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 02/22/2018] [Accepted: 03/12/2018] [Indexed: 11/17/2022]
Abstract
Presynaptic nerve terminals release neurotransmitter synchronously, asynchronously or spontaneously. During synchronous neurotransmission release is precisely coupled to action potentials, in contrast, asynchronous release events show only loose temporal coupling to presynaptic activity whereas spontaneous neurotransmission occurs independent of presynaptic activity. The mechanisms that give rise to this diversity in neurotransmitter release modes are poorly understood. Recent studies have described several presynaptic molecular pathways controlling synaptic vesicle pool segregation and recycling, which in turn may dictate distinct modes of neurotransmitter release. In this article, we review this recent work regarding neurotransmitter release modes and their relationship to synaptic vesicle pool dynamics as well as the molecular machinery that establishes synaptic vesicle pool identity.
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Affiliation(s)
- Natali L Chanaday
- Department of Neuroscience, the University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
| | - Ege T Kavalali
- Department of Neuroscience, the University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA.
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22
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Böhme MA, Grasskamp AT, Walter AM. Regulation of synaptic release-site Ca 2+ channel coupling as a mechanism to control release probability and short-term plasticity. FEBS Lett 2018; 592:3516-3531. [PMID: 29993122 DOI: 10.1002/1873-3468.13188] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Revised: 06/26/2018] [Accepted: 07/06/2018] [Indexed: 12/31/2022]
Abstract
Synaptic transmission relies on the rapid fusion of neurotransmitter-containing synaptic vesicles (SVs), which happens in response to action potential (AP)-induced Ca2+ influx at active zones (AZs). A highly conserved molecular machinery cooperates at SV-release sites to mediate SV plasma membrane attachment and maturation, Ca2+ sensing, and membrane fusion. Despite this high degree of conservation, synapses - even within the same organism, organ or neuron - are highly diverse regarding the probability of APs to trigger SV fusion. Additionally, repetitive activation can lead to either strengthening or weakening of transmission. In this review, we discuss mechanisms controlling release probability and this short-term plasticity. We argue that an important layer of control is exerted by evolutionarily conserved AZ scaffolding proteins, which determine the coupling distance between SV fusion sites and voltage-gated Ca2+ channels (VGCC) and, thereby, shape synapse-specific input/output behaviors. We propose that AZ-scaffold modifications may occur to adapt the coupling distance during synapse maturation and plastic regulation of synapse strength.
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Affiliation(s)
- Mathias A Böhme
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | | | - Alexander M Walter
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
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23
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Taylor SE, Taylor RD, Price J, Andreae LC. Single-molecule fluorescence in-situ hybridization reveals that human SHANK3 mRNA expression varies during development and in autism-associated SHANK3 heterozygosity. Stem Cell Res Ther 2018; 9:206. [PMID: 30064494 PMCID: PMC6069870 DOI: 10.1186/s13287-018-0957-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Revised: 06/13/2018] [Accepted: 07/16/2018] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Deletions and mutations in the SHANK3 gene are strongly associated with autism spectrum disorder and underlie the autism-associated disorder Phelan-McDermid syndrome. SHANK3 is a scaffolding protein found at the post-synaptic membrane of excitatory neurons. METHODS Single-molecule fluorescence in-situ hybridization (smFISH) allows the visualization of single mRNA transcripts in vitro. Here we perform and quantify smFISH in human inducible pluripotent stem cell (hiPSC)-derived cortical neurons, targeting the SHANK3 transcript. RESULTS Both smFISH and conventional immunofluorescence staining demonstrated a developmental increase in SHANK3 mRNA and protein, respectively, in control human cortical neurons. Analysis of single SHANK3 mRNA molecules in neurons derived from an autistic individual heterozygous for SHANK3 indicated that while the number of SHANK3 mRNA transcripts remained comparable with control levels in the cell soma, there was a 50% reduction within neuronal processes, suggesting that local, dendritic targeting of SHANK3 mRNA may be specifically affected in SHANK3 haploinsufficiency. CONCLUSION Human SHANK3 mRNA shows developmentally regulated dendritic localization in hiPSC-derived neurons, which is reduced in neurons generated from a haploinsufficient individual with autism. Although further replication is needed, given the importance of local mRNA translation in synaptic function, this could represent an important early abnormality.
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Affiliation(s)
- Samuel E Taylor
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, SE1 1UL, UK.,MRC Centre for Neurodevelopmental Disorders, King's College London, London, UK
| | - Ruth D Taylor
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, SE1 1UL, UK.,MRC Centre for Neurodevelopmental Disorders, King's College London, London, UK
| | - Jack Price
- MRC Centre for Neurodevelopmental Disorders, King's College London, London, UK.,Department of Basic and Clinical Neuroscience, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, SE5 8AF, UK
| | - Laura C Andreae
- Centre for Developmental Neurobiology, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, SE1 1UL, UK. .,MRC Centre for Neurodevelopmental Disorders, King's College London, London, UK.
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24
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Schrod N, Vanhecke D, Laugks U, Stein V, Fukuda Y, Schaffer M, Baumeister W, Lucic V. Pleomorphic linkers as ubiquitous structural organizers of vesicles in axons. PLoS One 2018; 13:e0197886. [PMID: 29864134 PMCID: PMC5986143 DOI: 10.1371/journal.pone.0197886] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 05/10/2018] [Indexed: 11/30/2022] Open
Abstract
Many cellular processes depend on a precise structural organization of molecular components. Here, we established that neurons grown in culture provide a suitable system for in situ structural investigations of cellular structures by cryo-electron tomography, a method that allows high resolution, three-dimensional imaging of fully hydrated, vitrified cellular samples. A higher level of detail of cellular components present in our images allowed us to quantitatively characterize presynaptic and cytoskeletal organization, as well as structures involved in axonal transport and endocytosis. In this way we provide a structural framework into which information from other methods need to fit. Importantly, we show that short pleomorphic linkers (tethers and connectors) extensively interconnect different types of spherical vesicles and other lipid membranes in neurons imaged in a close-to-native state. These linkers likely serve to organize and precisely position vesicles involved in endocytosis, axonal transport and synaptic release. Hence, structural interactions via short linkers may serve as ubiquitous vesicle organizers in neuronal cells.
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Affiliation(s)
- Nikolas Schrod
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany
| | - Dimitri Vanhecke
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany
| | - Ulrike Laugks
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany
| | - Valentin Stein
- Institute of Physiology II, University of Bonn, Bonn, Germany
| | - Yoshiyuki Fukuda
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany
| | - Miroslava Schaffer
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany
| | - Wolfgang Baumeister
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany
| | - Vladan Lucic
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany
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25
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Williams CL, Smith SM. Calcium dependence of spontaneous neurotransmitter release. J Neurosci Res 2018; 96:335-347. [PMID: 28699241 PMCID: PMC5766384 DOI: 10.1002/jnr.24116] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 06/16/2017] [Accepted: 06/19/2017] [Indexed: 01/14/2023]
Abstract
Spontaneous release of neurotransmitters is regulated by extracellular [Ca2+ ] and intracellular [Ca2+ ]. Curiously, some of the mechanisms of Ca2+ signaling at central synapses are different at excitatory and inhibitory synapses. While the stochastic activity of voltage-activated Ca2+ channels triggers a majority of spontaneous release at inhibitory synapses, this is not the case at excitatory nerve terminals. Ca2+ release from intracellular stores regulates spontaneous release at excitatory and inhibitory terminals, as do agonists of the Ca2+ -sensing receptor. Molecular machinery triggering spontaneous vesicle fusion may differ from that underlying evoked release and may be one of the sources of heterogeneity in release mechanisms.
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Affiliation(s)
- Courtney L Williams
- Department of Medicine, Division of Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon
- Section of Pulmonary & Critical Care Medicine, VA Portland Health Care System, Portland, Oregon
| | - Stephen M Smith
- Department of Medicine, Division of Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon
- Section of Pulmonary & Critical Care Medicine, VA Portland Health Care System, Portland, Oregon
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26
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Kavalali ET. Spontaneous neurotransmission: A form of neural communication comes of age. J Neurosci Res 2017; 96:331-334. [PMID: 29219198 DOI: 10.1002/jnr.24207] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Revised: 11/25/2017] [Accepted: 11/27/2017] [Indexed: 12/25/2022]
Affiliation(s)
- Ege T Kavalali
- Department of Neuroscience, the University of Texas Southwestern Medical Center, Dallas, TX 75390-9111, USA
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27
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Nandi S, Alviña K, Lituma PJ, Castillo PE, Hébert JM. Neurotrophin and FGF Signaling Adapter Proteins, FRS2 and FRS3, Regulate Dentate Granule Cell Maturation and Excitatory Synaptogenesis. Neuroscience 2017; 369:192-201. [PMID: 29155277 DOI: 10.1016/j.neuroscience.2017.11.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 11/07/2017] [Accepted: 11/11/2017] [Indexed: 12/15/2022]
Abstract
Dentate granule cells (DGCs) play important roles in cognitive processes. Knowledge about how growth factors such as FGFs and neurotrophins contribute to the maturation and synaptogenesis of DGCs is limited. Here, using brain-specific and germline mouse mutants we show that a module of neurotrophin and FGF signaling, the FGF Receptor Substrate (FRS) family of intracellular adapters, FRS2 and FRS3, are together required for postnatal brain development. In the hippocampus, FRS promotes dentate gyrus morphogenesis and DGC maturation during developmental neurogenesis, similar to previously published functions for both neurotrophins and FGFs. Consistent with a role in DGC maturation, two-photon imaging revealed that Frs2,3-double mutants have reduced numbers of dendritic branches and spines in DGCs. Functional analysis further showed that double-mutant mice exhibit fewer excitatory synaptic inputs onto DGCs. These observations reveal roles for FRS adapters in DGC maturation and synaptogenesis and suggest that FRS proteins may act as an important node for FGF and neurotrophin signaling in postnatal hippocampal development.
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Affiliation(s)
- Sayan Nandi
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Karina Alviña
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409, USA
| | - Pablo J Lituma
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Pablo E Castillo
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Jean M Hébert
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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Babiec WE, O'Dell TJ. Novel Ca 2+-dependent mechanisms regulate spontaneous release at excitatory synapses onto CA1 pyramidal cells. J Neurophysiol 2017; 119:597-607. [PMID: 29142096 DOI: 10.1152/jn.00628.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Although long thought to simply be a source of synaptic noise, spontaneous, action potential-independent release of neurotransmitter from presynaptic terminals has multiple roles in synaptic function. We explored whether and to what extent the two predominantly proposed mechanisms for explaining spontaneous release, stochastic activation of voltage-gated Ca2+ channels (VGCCs) or activation of Ca2+-sensing receptors (CaSRs) by extracellular Ca2+, played a role in the sensitivity of spontaneous release to the level of extracellular Ca2+ concentration at excitatory synapses at CA1 pyramidal cells of the adult male mouse hippocampus. Blocking VGCCs with Cd2+ had no effect on spontaneous release, ruling out stochastic activation of VGCCs. Although divalent cation agonists of CaSRs, Co2+ and Mg2+, dramatically enhanced miniature excitatory postsynaptic current (mEPSC) frequency, potent positive and negative allosteric modulators of CaSRs had no effect. Moreover, immunoblot analysis of hippocampal lysates failed to detect CaSR expression, ruling out the CaSR. Instead, the increase in mEPSC frequency induced by Co2+ and Mg2+ was mimicked by lowering postsynaptic Ca2+ levels with BAPTA. Together, our results suggest that a reduction in intracellular Ca2+ may trigger a homeostatic-like compensatory response that upregulates spontaneous transmission at excitatory synapses onto CA1 pyramidal cells in the adult hippocampus. NEW & NOTEWORTHY We show that the predominant theories for explaining the regulation of spontaneous, action potential-independent synaptic release do not explain the sensitivity of this type of synaptic transmission to external Ca2+ concentration at excitatory synapses onto hippocampal CA1 pyramidal cells. In addition, our data indicate that intracellular Ca2+ levels in CA1 pyramidal cells regulate spontaneous release, suggesting that excitatory synapses onto CA1 pyramidal cells may express a novel, rapid form of homeostatic plasticity.
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Affiliation(s)
- Walter E Babiec
- Department of Physiology, David Geffen School of Medicine at UCLA , Los Angeles, California
| | - Thomas J O'Dell
- Department of Physiology, David Geffen School of Medicine at UCLA , Los Angeles, California.,UCLA Integrative Center for Learning and Memory, Brain Research Institute, UCLA, Los Angeles, California
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29
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Andreae LC, Burrone J. The role of spontaneous neurotransmission in synapse and circuit development. J Neurosci Res 2017; 96:354-359. [PMID: 29034487 PMCID: PMC5813191 DOI: 10.1002/jnr.24154] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 08/18/2017] [Accepted: 08/21/2017] [Indexed: 12/12/2022]
Abstract
In the past, the spontaneous release of neurotransmitter from presynaptic terminals has been thought of as a side effect of evoked release, with little functional significance. As our understanding of the process of spontaneous release has increased over time, this notion has gradually changed. In this review, we focus on the importance of this form of release during neuronal development, a time of extreme levels of plasticity that includes the growth of dendrites and axons as well as the formation of new synaptic contacts. This period also encompasses high levels of neurotransmitter release from growing axons, and recent studies have found that spontaneous transmitter release plays an important role in shaping neuronal morphology as well as modulating the properties of newly forming synaptic contacts in the brain. Here, we bring together the latest findings across different species to argue that the spontaneous release of neurotransmitter is an important player in the wiring of the brain during development.
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Affiliation(s)
- Laura C Andreae
- Centre for Developmental Neurobiology, King's College London, New Hunt's House, 4th Floor, Guy's Hospital Campus, London, SE1 1UL, UK.,MRC Centre for Neurodevelopmental Disorders, King's College London, New Hunt's House, 4th Floor, Guy's Hospital Campus, London, SE1 1UL, UK.,FENS-Kavli Network of Excellence, Europe-wide
| | - Juan Burrone
- Centre for Developmental Neurobiology, King's College London, New Hunt's House, 4th Floor, Guy's Hospital Campus, London, SE1 1UL, UK.,MRC Centre for Neurodevelopmental Disorders, King's College London, New Hunt's House, 4th Floor, Guy's Hospital Campus, London, SE1 1UL, UK
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Altered Development of Synapse Structure and Function in Striatum Caused by Parkinson's Disease-Linked LRRK2-G2019S Mutation. J Neurosci 2017; 36:7128-41. [PMID: 27383589 DOI: 10.1523/jneurosci.3314-15.2016] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 05/26/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) can cause Parkinson's disease (PD), and the most common disease-associated mutation, G2019S, increases kinase activity. Because LRRK2 expression levels rise during synaptogenesis and are highest in dorsal striatal spiny projection neurons (SPNs), we tested the hypothesis that the LRRK2-G2019S mutation would alter development of excitatory synaptic networks in dorsal striatum. To circumvent experimental confounds associated with LRRK2 overexpression, we used mice expressing LRRK2-G2019S or D2017A (kinase-dead) knockin mutations. In whole-cell recordings, G2019S SPNs exhibited a fourfold increase in sEPSC frequency compared with wild-type SPNs in postnatal day 21 mice. Such heightened neural activity was increased similarly in direct- and indirect-pathway SPNs, and action potential-dependent activity was particularly elevated. Excitatory synaptic activity in D2017A SPNs was similar to wild type, indicating a selective effect of G2019S. Acute exposure to LRRK2 kinase inhibitors normalized activity, supporting that excessive neural activity in G2019S SPNs is mediated directly and is kinase dependent. Although dendritic arborization and densities of excitatory presynaptic terminals and postsynaptic dendritic spines in G2019S SPNs were similar to wild type, G2019S SPNs displayed larger spines that were matched functionally by a shift toward larger postsynaptic response amplitudes. Acutely isolating striatum from overlying neocortex normalized sEPSC frequency in G2019S mutants, supporting that abnormal corticostriatal activity is involved. These findings indicate that the G2019S mutation imparts a gain-of-abnormal function to SPN activity and morphology during a stage of development when activity can permanently modify circuit structure and function. SIGNIFICANCE STATEMENT Mutations in the kinase domain of leucine-rich repeat kinase 2 (LRRK2) follow Parkinson's disease (PD) heritability. How such mutations affect brain function is poorly understood. LRRK2 expression levels rise after birth at a time when synapses are forming and are highest in dorsal striatum, suggesting that LRRK2 regulates development of striatal circuits. During a period of postnatal development when activity plays a large role in permanently shaping neural circuits, our data show how the most common PD-causing LRRK2 mutation dramatically alters excitatory synaptic activity and the shape of postsynaptic structures in striatum. These findings provide new insight into early functional and structural aberrations in striatal connectivity that may predispose striatal circuitry to both motor and nonmotor dysfunction later in life.
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Loss of Doc2-Dependent Spontaneous Neurotransmission Augments Glutamatergic Synaptic Strength. J Neurosci 2017; 37:6224-6230. [PMID: 28539418 DOI: 10.1523/jneurosci.0418-17.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Revised: 05/02/2017] [Accepted: 05/13/2017] [Indexed: 11/21/2022] Open
Abstract
Action potential-evoked vesicle fusion comprises the majority of neurotransmission within chemical synapses, but action potential-independent spontaneous neurotransmission also contributes to the collection of signals sent to the postsynaptic cell. Previous work has implicated spontaneous neurotransmission in homeostatic synaptic scaling, but few studies have selectively manipulated spontaneous neurotransmission without substantial changes in evoked neurotransmission to study this function in detail. Here we used a quadruple knockdown strategy to reduce levels of proteins within the soluble calcium-binding double C2 domain (Doc2)-like protein family to selectively reduce spontaneous neurotransmission in cultured mouse and rat neurons. Activity-evoked responses appear normal while both excitatory and inhibitory spontaneous events exhibit reduced frequency. Excitatory miniature postsynaptic currents (mEPSCs), but not miniature inhibitory postsynaptic currents (mIPSCs), increase in amplitude after quadruple knockdown. This increase in synaptic efficacy correlates with reduced phosphorylation levels of eukaryotic elongation factor 2 and also requires the presence of elongation factor 2 kinase. Together, these data suggest that spontaneous neurotransmission independently contributes to the regulation of synaptic efficacy, and action potential-evoked and spontaneous neurotransmission can be segregated at least partially on a molecular level.SIGNIFICANCE STATEMENT Action potential-evoked and spontaneous neurotransmission have been observed in nervous system circuits as long as methods have existed to measure them. Despite being well studied, controversy still remains about whether these forms of neurotransmission are regulated independently on a molecular level or whether they are simply a continuum of neurotransmission modes. In this study, members of the Doc2 family of presynaptic proteins were eliminated, which caused a reduction in spontaneous neurotransmission, whereas action potential-evoked neurotransmission remained relatively normal. This protein loss also caused an increase in synaptic strength, suggesting that spontaneous neurotransmission is able to communicate independently with the postsynaptic neuron and trigger downstream signaling cascades that regulate the synaptic state.
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Bart Martens M, Frega M, Classen J, Epping L, Bijvank E, Benevento M, van Bokhoven H, Tiesinga P, Schubert D, Nadif Kasri N. Euchromatin histone methyltransferase 1 regulates cortical neuronal network development. Sci Rep 2016; 6:35756. [PMID: 27767173 PMCID: PMC5073331 DOI: 10.1038/srep35756] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 10/05/2016] [Indexed: 12/12/2022] Open
Abstract
Heterozygous mutations or deletions in the human Euchromatin histone methyltransferase 1 (EHMT1) gene cause Kleefstra syndrome, a neurodevelopmental disorder that is characterized by autistic-like features and severe intellectual disability (ID). Neurodevelopmental disorders including ID and autism may be related to deficits in activity-dependent wiring of brain circuits during development. Although Kleefstra syndrome has been associated with dendritic and synaptic defects in mice and Drosophila, little is known about the role of EHMT1 in the development of cortical neuronal networks. Here we used micro-electrode arrays and whole-cell patch-clamp recordings to investigate the impact of EHMT1 deficiency at the network and single cell level. We show that EHMT1 deficiency impaired neural network activity during the transition from uncorrelated background action potential firing to synchronized network bursting. Spontaneous bursting and excitatory synaptic currents were transiently reduced, whereas miniature excitatory postsynaptic currents were not affected. Finally, we show that loss of function of EHMT1 ultimately resulted in less regular network bursting patterns later in development. These data suggest that the developmental impairments observed in EHMT1-deficient networks may result in a temporal misalignment between activity-dependent developmental processes thereby contributing to the pathophysiology of Kleefstra syndrome.
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Affiliation(s)
- Marijn Bart Martens
- Department of Neuroinformatics, Radboud University Nijmegen, Faculty of Science, Heyendaalseweg 135, 6525 AJ Nijmegen, the Netherlands
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Monica Frega
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Cognitive Neuroscience, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Jessica Classen
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Cognitive Neuroscience, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Lisa Epping
- Department of Neuroinformatics, Radboud University Nijmegen, Faculty of Science, Heyendaalseweg 135, 6525 AJ Nijmegen, the Netherlands
| | - Elske Bijvank
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Cognitive Neuroscience, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Marco Benevento
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Cognitive Neuroscience, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Hans van Bokhoven
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Cognitive Neuroscience, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Human Genetics, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Paul Tiesinga
- Department of Neuroinformatics, Radboud University Nijmegen, Faculty of Science, Heyendaalseweg 135, 6525 AJ Nijmegen, the Netherlands
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Dirk Schubert
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Cognitive Neuroscience, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Nael Nadif Kasri
- Donders Institute for Brain, Cognition and Behaviour, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Cognitive Neuroscience, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
- Department of Human Genetics, Radboudumc, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
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Martens MB, Celikel T, Tiesinga PHE. A Developmental Switch for Hebbian Plasticity. PLoS Comput Biol 2015; 11:e1004386. [PMID: 26172394 PMCID: PMC4501799 DOI: 10.1371/journal.pcbi.1004386] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 06/08/2015] [Indexed: 12/12/2022] Open
Abstract
Hebbian forms of synaptic plasticity are required for the orderly development of sensory circuits in the brain and are powerful modulators of learning and memory in adulthood. During development, emergence of Hebbian plasticity leads to formation of functional circuits. By modeling the dynamics of neurotransmitter release during early postnatal cortical development we show that a developmentally regulated switch in vesicle exocytosis mode triggers associative (i.e. Hebbian) plasticity. Early in development spontaneous vesicle exocytosis (SVE), often considered as 'synaptic noise', is important for homogenization of synaptic weights and maintenance of synaptic weights in the appropriate dynamic range. Our results demonstrate that SVE has a permissive, whereas subsequent evoked vesicle exocytosis (EVE) has an instructive role in the expression of Hebbian plasticity. A timed onset for Hebbian plasticity can be achieved by switching from SVE to EVE and the balance between SVE and EVE can control the effective rate of Hebbian plasticity. We further show that this developmental switch in neurotransmitter release mode enables maturation of spike-timing dependent plasticity. A mis-timed or inadequate SVE to EVE switch may lead to malformation of brain networks thereby contributing to the etiology of neurodevelopmental disorders. Neurotransmitter release is the principal form of chemical communication in the brain. When an action potential reaches a synapse, calcium influx activates the machinery for neurotransmitter release. During early neuronal development this machinery matures such that neurotransmitter release becomes time-locked to action potentials. By modeling this change in neurotransmitter release, we mechanistically show that the maturation process can be solely responsible for switching on associative (i.e. Hebbian) plasticity in the brain. The relevant proteins of the release machinery can thereby regulate the rate at which neural circuits represent sensory input, providing a novel mechanism to control the learning rate and onset. Appropriately timing of the onset of Hebbian plasticity is important because during early development sensory experience fine-tunes, often irreversibly, the neural wiring in our brain.
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Affiliation(s)
- Marijn B. Martens
- Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Department of Neuroinformatics, Radboud University Nijmegen, Nijmegen, The Netherlands
- * E-mail:
| | - Tansu Celikel
- Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Department of Neurophysiology, Radboud University Nijmegen, Nijmegen, The Netherlands
| | - Paul H. E. Tiesinga
- Donders Institute for Brain, Cognition and Behaviour, Centre for Neuroscience, Department of Neuroinformatics, Radboud University Nijmegen, Nijmegen, The Netherlands
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Abstract
Fast synaptic communication in the brain requires synchronous vesicle fusion that is evoked by action potential-induced Ca(2+) influx. However, synaptic terminals also release neurotransmitters by spontaneous vesicle fusion, which is independent of presynaptic action potentials. A functional role for spontaneous neurotransmitter release events in the regulation of synaptic plasticity and homeostasis, as well as the regulation of certain behaviours, has been reported. In addition, there is evidence that the presynaptic mechanisms underlying spontaneous release of neurotransmitters and their postsynaptic targets are segregated from those of evoked neurotransmission. These findings challenge current assumptions about neuronal signalling and neurotransmission, as they indicate that spontaneous neurotransmission has an autonomous role in interneuronal communication that is distinct from that of evoked release.
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36
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Andreae LC, Burrone J. Spontaneous Neurotransmitter Release Shapes Dendritic Arbors via Long-Range Activation of NMDA Receptors. Cell Rep 2015; 10:873-882. [PMID: 25683710 PMCID: PMC4542315 DOI: 10.1016/j.celrep.2015.01.032] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Revised: 12/19/2014] [Accepted: 01/10/2015] [Indexed: 12/01/2022] Open
Abstract
Spontaneous neurotransmitter release is a core element of synaptic communication in mature neurons, but despite exceptionally high levels of spontaneous vesicle cycling occurring in developing axons, little is known of its function during this period. We now show that high-level, spontaneous axonal release of the neurotransmitter glutamate can signal at long range to NMDA receptors on developing dendrites, prior to synapse formation and, indeed, axodendritic contact. Blockade of NMDA signaling during this early period of spontaneous vesicle cycling leads to a reduction in dendritic arbor complexity, indicating an important role for early spontaneous release in dendritic arbor growth. New role for spontaneous neurotransmitter release in dendritic arbor formation Vesicular glutamate can activate distant “long-range” dendritic NMDA receptors Presynaptic and postsynaptic machinery operate before synaptic contact Spontaneous glutamate release may provide local dendritic guidance or branching cue
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Affiliation(s)
- Laura C Andreae
- MRC Centre for Developmental Neurobiology, King's College London, London SE1 1UL, UK.
| | - Juan Burrone
- MRC Centre for Developmental Neurobiology, King's College London, London SE1 1UL, UK.
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37
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Truckenbrodt S, Rizzoli SO. Spontaneous vesicle recycling in the synaptic bouton. Front Cell Neurosci 2014; 8:409. [PMID: 25538561 PMCID: PMC4259163 DOI: 10.3389/fncel.2014.00409] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Accepted: 11/11/2014] [Indexed: 11/13/2022] Open
Abstract
The trigger for synaptic vesicle exocytosis is Ca2+, which enters the synaptic bouton following action potential stimulation. However, spontaneous release of neurotransmitter also occurs in the absence of stimulation in virtually all synaptic boutons. It has long been thought that this represents exocytosis driven by fluctuations in local Ca2+ levels. The vesicles responding to these fluctuations are thought to be the same ones that release upon stimulation, albeit potentially triggered by different Ca2+ sensors. This view has been challenged by several recent works, which have suggested that spontaneous release is driven by a separate pool of synaptic vesicles. Numerous articles appeared during the last few years in support of each of these hypotheses, and it has been challenging to bring them into accord. We speculate here on the origins of this controversy, and propose a solution that is related to developmental effects. Constitutive membrane traffic, needed for the biogenesis of vesicles and synapses, is responsible for high levels of spontaneous membrane fusion in young neurons, probably independent of Ca2+. The vesicles releasing spontaneously in such neurons are not related to other synaptic vesicle pools and may represent constitutively releasing vesicles (CRVs) rather than bona fide synaptic vesicles. In mature neurons, constitutive traffic is much dampened, and the few remaining spontaneous release events probably represent bona fide spontaneously releasing synaptic vesicles (SRSVs) responding to Ca2+ fluctuations, along with a handful of CRVs that participate in synaptic vesicle turnover.
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Affiliation(s)
- Sven Truckenbrodt
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, European Neuroscience Institute, Cluster of Excellence Nanoscale Microscopy and Molecular Physiology of the Brain Göttingen, Germany ; International Max Planck Research School for Molecular Biology Göttingen, Germany
| | - Silvio O Rizzoli
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, European Neuroscience Institute, Cluster of Excellence Nanoscale Microscopy and Molecular Physiology of the Brain Göttingen, Germany
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38
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Leitz J, Kavalali ET. Fast retrieval and autonomous regulation of single spontaneously recycling synaptic vesicles. eLife 2014; 3:e03658. [PMID: 25415052 PMCID: PMC4270043 DOI: 10.7554/elife.03658] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 11/21/2014] [Indexed: 11/13/2022] Open
Abstract
Presynaptic terminals release neurotransmitters spontaneously in a manner that can be regulated by Ca(2+). However, the mechanisms underlying this regulation are poorly understood because the inherent stochasticity and low probability of spontaneous fusion events has curtailed their visualization at individual release sites. Here, using pH-sensitive optical probes targeted to synaptic vesicles, we visualized single spontaneous fusion events and found that they are retrieved extremely rapidly with faster re-acidification kinetics than their action potential-evoked counterparts. These fusion events were coupled to postsynaptic NMDA receptor-driven Ca(2+) signals, and at elevated Ca(2+) concentrations there was an increase in the number of vesicles that would undergo fusion. Furthermore, spontaneous vesicle fusion propensity in a synapse was Ca(2+)-dependent but regulated autonomously: independent of evoked fusion probability at the same synapse. Taken together, these results expand classical quantal analysis to incorporate endocytic and exocytic phases of single fusion events and uncover autonomous regulation of spontaneous fusion.
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Affiliation(s)
- Jeremy Leitz
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, United States
| | - Ege T Kavalali
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, United States
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, United States
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39
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Ramirez DMO, Kavalali ET. The role of non-canonical SNAREs in synaptic vesicle recycling. CELLULAR LOGISTICS 2014; 2:20-27. [PMID: 22645707 PMCID: PMC3355972 DOI: 10.4161/cl.20114] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
An increasing number of studies suggest that distinct pools of synaptic vesicles drive specific forms of neurotransmission. Interspersed with these functional studies are analyses of the synaptic vesicle proteome which have consistently detected the presence of so-called “non-canonical” SNAREs that typically function in fusion and trafficking of other subcellular structures within the neuron. The recent identification of certain non-canonical vesicular SNAREs driving spontaneous (e.g., VAMP7 and vti1a) or evoked asynchronous (e.g., VAMP4) release integrates and corroborates existing data from functional and proteomic studies and implies that at least some complement of non-canonical SNAREs resident on synaptic vesicles function in neurotransmission. Here, we discuss the specific roles in neurotransmission of proteins homologous to each member of the classical neuronal SNARE complex consisting of synaptobrevin2, syntaxin-1 and SNAP-25.
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40
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Andreae LC, Burrone J. The role of neuronal activity and transmitter release on synapse formation. Curr Opin Neurobiol 2014; 27:47-52. [PMID: 24632375 PMCID: PMC4127784 DOI: 10.1016/j.conb.2014.02.008] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Revised: 01/16/2014] [Accepted: 02/06/2014] [Indexed: 01/08/2023]
Abstract
The long history of probing the role of neuronal activity in the development of nervous system circuitry has recently taken an interesting turn. Although undoubtedly activity plays a critical part in the maintenance and refinement of synaptic connections, often via competitive mechanisms, evidence is building that it also drives the process of synapse formation itself. Perhaps predictably, this turns out not to be a uniform process. It seems that different circuits, indeed specific synaptic connections, are differentially sensitive to the effects of activity. We examine possible ways in which neurotransmitter may drive synapse formation, and speculate on how the environment of the developing brain may allow a different spatiotemporal range for neuronal activity to operate in the generation of connectivity.
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Affiliation(s)
- Laura C Andreae
- MRC Centre for Developmental Neurobiology, King's College London, New Hunt's House, 4th Floor, Guy's Hospital Campus, London SE1 1UL, UK.
| | - Juan Burrone
- MRC Centre for Developmental Neurobiology, King's College London, New Hunt's House, 4th Floor, Guy's Hospital Campus, London SE1 1UL, UK.
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41
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Abstract
Synaptic vesicle recycling is one of the best-studied cellular pathways. Many of the proteins involved are known, and their interactions are becoming increasingly clear. However, as for many other pathways, it is still difficult to understand synaptic vesicle recycling as a whole. While it is generally possible to point out how synaptic reactions take place, it is not always easy to understand what triggers or controls them. Also, it is often difficult to understand how the availability of the reaction partners is controlled: how the reaction partners manage to find each other in the right place, at the right time. I present here an overview of synaptic vesicle recycling, discussing the mechanisms that trigger different reactions, and those that ensure the availability of reaction partners. A central argument is that synaptic vesicles bind soluble cofactor proteins, with low affinity, and thus control their availability in the synapse, forming a buffer for cofactor proteins. The availability of cofactor proteins, in turn, regulates the different synaptic reactions. Similar mechanisms, in which one of the reaction partners buffers another, may apply to many other processes, from the biogenesis to the degradation of the synaptic vesicle.
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Affiliation(s)
- Silvio O Rizzoli
- Department of Neuro- and Sensory Physiology, University Medical Center Göttingen European Neuroscience Institute, Göttingen, Germany
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42
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Kavalali ET, Jorgensen EM. Visualizing presynaptic function. Nat Neurosci 2013; 17:10-6. [PMID: 24369372 DOI: 10.1038/nn.3578] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 10/14/2013] [Indexed: 12/15/2022]
Abstract
Synaptic communication in the nervous system is initiated by the fusion of synaptic vesicles with the presynaptic plasma membrane and subsequent neurotransmitter release. In the 1980s, this process was characterized by electron microscopy, albeit without the ability to follow processes in living cells. In the last two decades, fluorescence imaging methods have been developed that report synaptic vesicle fusion, endocytosis and recycling. These probes have provided unprecedented insight into synaptic vesicle trafficking in individual synaptic terminals and revealed heterogeneity in recycling pathways as well as synaptic vesicle populations. These methods either take advantage of uptake of fluorescent probes into recycling vesicles or exogenous expression of synaptic vesicle proteins tagged with a pH-sensitive fluorescent marker at regions facing the vesicle lumen. We provide an overview of these methods, with particular emphasis on the challenges associated with their use and the opportunities for future investigations.
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Affiliation(s)
- Ege T Kavalali
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Erik M Jorgensen
- 1] Howard Hughes Medical Institute, University of Utah, Salt Lake City, Utah, USA. [2] Department of Biology, University of Utah, Salt Lake City, Utah, USA
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Jung J, Loy K, Schilling EM, Röther M, Brauner JM, Huth T, Schlötzer-Schrehardt U, Alzheimer C, Kornhuber J, Welzel O, Groemer TW. The Antidepressant Fluoxetine Mobilizes Vesicles to the Recycling Pool of Rat Hippocampal Synapses During High Activity. Mol Neurobiol 2013; 49:916-30. [DOI: 10.1007/s12035-013-8569-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 10/03/2013] [Indexed: 11/29/2022]
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Crispino M, Chun JT, Cefaliello C, Perrone Capano C, Giuditta A. Local gene expression in nerve endings. Dev Neurobiol 2013; 74:279-91. [PMID: 23853157 DOI: 10.1002/dneu.22109] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Revised: 06/28/2013] [Accepted: 07/05/2013] [Indexed: 12/11/2022]
Abstract
At the Nobel lecture for physiology in 1906, Ramón y Cajal famously stated that "the nerve elements possess reciprocal relationships in contiguity but not in continuity," summing up the neuron doctrine. Sixty years later, by the time the central dogma of molecular biology formulated the axis of genetic information flow from DNA to mRNA, and then to protein, it became obvious that neurons with extensive ramifications and long axons inevitably incur an innate problem: how can the effect of gene expression be extended from the nucleus to the remote and specific sites of the cell periphery? The most straightforward solution would be to deliver soma-produced proteins to the target sites. The influential discovery of axoplasmic flow has supported this scheme of protein supply. Alternatively, mRNAs can be dispatched instead of protein, and translated locally at the strategic target sites. Over the past decades, such a local system of protein synthesis has been demonstrated in dendrites, axons, and presynaptic terminals. Moreover, the local protein synthesis in neurons might even involve intercellular trafficking of molecules. The innovative concept of glia-neuron unit suggests that the local protein synthesis in the axonal and presynaptic domain of mature neurons is sustained by a local supply of RNAs synthesized in the surrounding glial cells and transferred to these domains. Here, we have reviewed some of the evidence indicating the presence of a local system of protein synthesis in axon terminals, and have examined its regulation in various model systems.
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Affiliation(s)
- Marianna Crispino
- Department of Biology, University of Naples Federico II, Naples, Italy
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Abstract
Many presynaptic transcripts have been observed in axons, yet their role in synapse development remains unknown. Using visually and pharmacologically isolated presynaptic terminals from dissociated rat hippocampal neurons, we found that ribosomes and β-catenin mRNA preferentially localize to recently formed boutons. Locally translated β-catenin accumulates at presynaptic terminals, where it regulates synaptic vesicle release dynamics. Thus, local translation of β-catenin is a newly described mechanism for axons to independently functionalize nerve terminals at great distances from cellular somata.
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Chung C, Raingo J. Vesicle dynamics: how synaptic proteins regulate different modes of neurotransmission. J Neurochem 2013; 126:146-54. [PMID: 23517499 DOI: 10.1111/jnc.12245] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 03/05/2013] [Accepted: 03/18/2013] [Indexed: 01/09/2023]
Abstract
Central synapses operate neurotransmission in several modes: synchronous/fast neurotransmission (neurotransmitters release is tightly coupled to action potentials and fast), asynchronous neurotransmission (neurotransmitter release is slower and longer lasting), and spontaneous neurotransmission (where small amounts of neurotransmitter are released without being evoked by an action potential). A substantial body of evidence from the past two decades suggests that seemingly identical synaptic vesicles possess distinct propensities to fuse, thus selectively serving different modes of neurotransmission. In efforts to better understand the mechanism(s) underlying the different modes of synaptic transmission, many research groups found that synaptic vesicles used in different modes of neurotransmission differ by a number of synaptic proteins. Synchronous transmission with higher temporal fidelity to stimulation seems to require synaptotagmin 1 and complexin for its Ca²⁺ sensitivity, RIM proteins for closer location of synaptic vesicles (SV) to the voltage operated calcium channels (VGCC), and dynamin for SV retrieval. Asynchronous release does not seem to require functional synaptotagmin 1 as a calcium sensor or complexins, but the activity of dynamin is indispensible for its maintenance. On the other hand, the control of spontaneous neurotransmission remains less clear as deleting a number of essential synaptic proteins does not abolish this type of synaptic vesicle fusion. VGCC distance from the SV seems to have little control on spontaneous transmission, while there is an involvement of functional synaptic proteins including synaptotagmins and complexin. Recently, presynaptic deficits have been proposed to contribute to a number of pathological conditions including cognitive and mental disorders. In this review, we evaluate recent advances in understanding the regulatory mechanisms of synaptic vesicle dynamics and in understanding how different molecular substrates maintain selective modes of neurotransmission. We also highlight the implications of these studies in understanding pathological conditions.
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Affiliation(s)
- ChiHye Chung
- Department of Biological Sciences, Konkuk University, Seoul, South Korea
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Reduction of AP180 and CALM produces defects in synaptic vesicle size and density. Neuromolecular Med 2012; 15:49-60. [PMID: 22851330 DOI: 10.1007/s12017-012-8194-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Accepted: 07/14/2012] [Indexed: 10/28/2022]
Abstract
Clathrin assembly proteins AP180 and CALM regulate the assembly of clathrin-coated vesicles (CCVs), which mediate diverse intracellular trafficking processes, including synaptic vesicle (SV) recycling at the synapse. Although studies using several invertebrate model systems have indicated a role for AP180 in SV recycling, less is known about AP180's or CALM's function in the synapse of mammalian neurons. In this study, we examined synapses of rat hippocampal neurons in which the level of AP180 or CALM had been reduced by RNA interference (RNAi). Using light microscopy, we visualized synaptic puncta in these AP180- or CALM-reduced neurons by co-expressing Synaptophysin::EGFP (Syp::EGFP). We found that neurons with reduced AP180 or reduced CALM had smaller Syp::EGFP-illuminated puncta. Using electron microscopy, we further examined the ultrastructure of the AP180- or CALM-reduced presynaptic terminals. We found that SVs became variably enlarged in both the AP180-reduced and CALM-reduced presynaptic terminals. Lower AP180 and CALM also reduced the density of SVs and the size of SV clusters. Our findings demonstrate that in the presynaptic terminals of hippocampal neurons, AP180 and CALM have a similar role in regulating synaptic vesicles. This overlapping activity may be necessary for high-precision and high-efficacy SV formation during endocytosis.
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