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Subkhangulova A, Gonzalez-Lozano MA, Groffen AJA, van Weering JRT, Smit AB, Toonen RF, Verhage M. Tomosyn affects dense core vesicle composition but not exocytosis in mammalian neurons. eLife 2023; 12:e85561. [PMID: 37695731 PMCID: PMC10495110 DOI: 10.7554/elife.85561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Accepted: 08/28/2023] [Indexed: 09/13/2023] Open
Abstract
Tomosyn is a large, non-canonical SNARE protein proposed to act as an inhibitor of SNARE complex formation in the exocytosis of secretory vesicles. In the brain, tomosyn inhibits the fusion of synaptic vesicles (SVs), whereas its role in the fusion of neuropeptide-containing dense core vesicles (DCVs) is unknown. Here, we addressed this question using a new mouse model with a conditional deletion of tomosyn (Stxbp5) and its paralogue tomosyn-2 (Stxbp5l). We monitored DCV exocytosis at single vesicle resolution in tomosyn-deficient primary neurons using a validated pHluorin-based assay. Surprisingly, loss of tomosyns did not affect the number of DCV fusion events but resulted in a strong reduction of intracellular levels of DCV cargos, such as neuropeptide Y (NPY) and brain-derived neurotrophic factor (BDNF). BDNF levels were largely restored by re-expression of tomosyn but not by inhibition of lysosomal proteolysis. Tomosyn's SNARE domain was dispensable for the rescue. The size of the trans-Golgi network and DCVs was decreased, and the speed of DCV cargo flux through Golgi was increased in tomosyn-deficient neurons, suggesting a role for tomosyns in DCV biogenesis. Additionally, tomosyn-deficient neurons showed impaired mRNA expression of some DCV cargos, which was not restored by re-expression of tomosyn and was also observed in Cre-expressing wild-type neurons not carrying loxP sites, suggesting a direct effect of Cre recombinase on neuronal transcription. Taken together, our findings argue against an inhibitory role of tomosyns in neuronal DCV exocytosis and suggests an evolutionary conserved function of tomosyns in the packaging of secretory cargo at the Golgi.
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Affiliation(s)
- Aygul Subkhangulova
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Vrije Universiteit (VU) AmsterdamAmsterdamNetherlands
| | - Miguel A Gonzalez-Lozano
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research (CNCR), Vrije Universiteit (VU) AmsterdamAmsterdamNetherlands
| | - Alexander JA Groffen
- Department of Human Genetics, Center for Neurogenomics and Cognitive Research (CNCR), Amsterdam University Medical Center (UMC)AmsterdamNetherlands
| | - Jan RT van Weering
- Department of Human Genetics, Center for Neurogenomics and Cognitive Research (CNCR), Amsterdam University Medical Center (UMC)AmsterdamNetherlands
| | - August B Smit
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research (CNCR), Vrije Universiteit (VU) AmsterdamAmsterdamNetherlands
| | - Ruud F Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Vrije Universiteit (VU) AmsterdamAmsterdamNetherlands
| | - Matthijs Verhage
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research (CNCR), Vrije Universiteit (VU) AmsterdamAmsterdamNetherlands
- Department of Human Genetics, Center for Neurogenomics and Cognitive Research (CNCR), Amsterdam University Medical Center (UMC)AmsterdamNetherlands
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2
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De Alwis AC, Denison JD, Shah R, McCarty GS, Sombers LA. Exploiting Microelectrode Geometry for Comprehensive Detection of Individual Exocytosis Events at Single Cells. ACS Sens 2023; 8:3187-3194. [PMID: 37552870 PMCID: PMC10464603 DOI: 10.1021/acssensors.3c00884] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Accepted: 07/25/2023] [Indexed: 08/10/2023]
Abstract
Carbon fiber microelectrodes are commonly used for real-time monitoring of individual exocytosis events at single cells. Since the nature of an electrochemical signal is fundamentally governed by mass transport to the electrode surface, microelectrode geometry can be exploited to achieve precise and accurate measurements. Researchers traditionally pair amperometric measurements of exocytosis with a ∼10-μm diameter, disk microelectrode in an "artificial synapse" configuration to directly monitor individual release events from single cells. Exocytosis is triggered, and released molecules diffuse to the "post-synaptic" electrode for oxidation. This results in a series of distinct current spikes corresponding to individual exocytosis events. However, it remains unclear how much of the material escapes detection. In this work, the performance of 10- and 34-μm diameter carbon fiber disk microelectrodes was directly compared in monitoring exocytosis at single chromaffin cells. The 34-μm diameter electrode was more sensitive to catecholamines and enkephalins than its traditional, 10-μm diameter counterpart, and it more effectively covered the entire cell. As such, the larger sensor detected more exocytosis events overall, as well as a larger quantal size, suggesting that the traditional tools underestimate the above measurements. Both sensors reliably measured l-DOPA-evoked changes in quantal size, and both exhibited diffusional loss upon adjustment of cell-electrode spacing. Finite element simulations using COMSOL support the improved collection efficiency observed using the larger sensor. Overall, this work demonstrates how electrode geometry can be exploited for improved detection of exocytosis events by addressing diffusional loss─an often-overlooked source of inaccuracy in single-cell measurements.
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Affiliation(s)
- A. Chathuri De Alwis
- Department
of Chemistry and Comparative Medicine Institute, North Carolina
State University, Raleigh, North Carolina 27695, United States
| | - J. Dylan Denison
- Department
of Chemistry and Comparative Medicine Institute, North Carolina
State University, Raleigh, North Carolina 27695, United States
| | - Ruby Shah
- Department
of Chemistry and Comparative Medicine Institute, North Carolina
State University, Raleigh, North Carolina 27695, United States
| | - Gregory S. McCarty
- Department
of Chemistry and Comparative Medicine Institute, North Carolina
State University, Raleigh, North Carolina 27695, United States
| | - Leslie A. Sombers
- Department
of Chemistry and Comparative Medicine Institute, North Carolina
State University, Raleigh, North Carolina 27695, United States
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3
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Zhang P, Rumschitzki D, Edwards RH. High-speed imaging reveals the bimodal nature of dense core vesicle exocytosis. Proc Natl Acad Sci U S A 2023; 120:e2214897120. [PMID: 36574702 DOI: 10.1073/pnas.2214897120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
During exocytosis, the fusion of secretory vesicle with plasma membrane forms a pore that regulates release of neurotransmitter and peptide. Heterogeneity of fusion pore behavior has been attributed to stochastic variation in a common exocytic mechanism, implying a lack of biological control. Using a fluorescent false neurotransmitter (FFN), we imaged dense core vesicle (DCV) exocytosis in primary mouse adrenal chromaffin cells by total internal reflection fluorescence microscopy at millisecond resolution and observed strikingly divergent modes of release, with fast events lasting <30 ms and slow events persisting for seconds. Dual imaging of slow events shows a delay in the entry of external dye relative to FFN release, suggesting exclusion by an extremely narrow pore <1 nm in diameter. Unbiased comprehensive analysis shows that the observed variation cannot be explained by stochasticity alone, but rather involves distinct mechanisms, revealing the bimodal nature of DCV exocytosis. Further, loss of calcium sensor synaptotagmin 7 increases the proportion of slow events without changing the intrinsic properties of either class, indicating the potential for independent regulation. The identification of two distinct mechanisms for release capable of independent regulation suggests a biological basis for the diversity of fusion pore behavior.
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4
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Sung H, Lloyd TE. Defective axonal transport of endo-lysosomes and dense core vesicles in a Drosophila model of C9-ALS/FTD. Traffic 2022; 23:430-441. [PMID: 35908282 DOI: 10.1111/tra.12861] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 06/28/2022] [Accepted: 07/26/2022] [Indexed: 10/16/2022]
Abstract
A GGGGCC (G4 C2 ) repeat expansion in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although disruptions in axonal transport are implicated in the pathogenesis of multiple neurodegenerative diseases, the underlying mechanisms causing these defects remain unclear. Here, we performed live imaging of Drosophila motor neurons expressing expanded G4 C2 repeats in third-instar larvae and investigated the axonal transport of multiple organelles in vivo. Expression of expanded G4 C2 repeats causes an increase in static axonal lysosomes, while it impairs trafficking of late endosomes (LEs) and dense core vesicles (DCVs). Surprisingly, however, axonal transport of mitochondria is unaffected in motor axons expressing expanded G4 C2 repeats. Thus, our data indicate that expanded G4 C2 repeat expression differentially impacts axonal transport of vesicular organelles and mitochondria in Drosophila models of C9orf72-associated ALS/FTD. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Hyun Sung
- Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, MD.,Solomon H. Snyder Department of Neuroscience, School of Medicine, Johns Hopkins University, Baltimore, MD
| | - Thomas E Lloyd
- Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, MD.,Solomon H. Snyder Department of Neuroscience, School of Medicine, Johns Hopkins University, Baltimore, MD
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5
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Zhang Q, Liu B, Li Y, Yin L, Younus M, Jiang X, Lin Z, Sun X, Huang R, Liu B, Wu Q, Zhu F, Zhou Z. Regulating quantal size of neurotransmitter release through a GPCR voltage sensor. Proc Natl Acad Sci U S A 2020; 117:26985-95. [PMID: 33046653 DOI: 10.1073/pnas.2005274117] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Current models emphasize that membrane voltage (Vm) depolarization-induced Ca2+ influx triggers the fusion of vesicles to the plasma membrane. In sympathetic adrenal chromaffin cells, activation of a variety of G protein coupled receptors (GPCRs) can inhibit quantal size (QS) through the direct interaction of G protein Giβγ subunits with exocytosis fusion proteins. Here we report that, independently from Ca2+, Vm (action potential) per se regulates the amount of catecholamine released from each vesicle, the QS. The Vm regulation of QS was through ATP-activated GPCR-P2Y12 receptors. D76 and D127 in P2Y12 were the voltage-sensing sites. Finally, we revealed the relevance of the Vm dependence of QS for tuning autoinhibition and target cell functions. Together, membrane voltage per se increases the quantal size of dense-core vesicle release of catecholamine via Vm → P2Y12(D76/D127) → Giβγ → QS → myocyte contractility, offering a universal Vm-GPCR signaling pathway for its functions in the nervous system and other systems containing GPCRs.
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6
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Bednarska J, Novak P, Korchev Y, Rorsman P, Tarasov AI, Shevchuk A. Release of insulin granules by simultaneous, high-speed correlative SICM-FCM. J Microsc 2020; 282:21-29. [PMID: 33089519 DOI: 10.1111/jmi.12972] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Accepted: 10/19/2020] [Indexed: 11/27/2022]
Abstract
Exocytosis of peptides and steroids stored in a dense core vesicular (DCV) form is the final step of every secretory pathway, indispensable for the function of nervous, endocrine and immune systems. The lack of live imaging techniques capable of direct, label-free visualisation of DCV release makes many aspects of the exocytotic process inaccessible to investigation. We describe the application of correlative scanning ion conductance and fluorescence confocal microscopy (SICM-FCM) to study the exocytosis of individual granules of insulin from the top, nonadherent, surface of pancreatic β-cells. Using SICM-FCM, we were first to directly follow the topographical changes associated with physiologically induced release of insulin DCVs. This allowed us to report the kinetics of the full fusion of the insulin vesicle as well as the subsequent solubilisation of the released insulin crystal.
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Affiliation(s)
- J Bednarska
- Department of Medicine, Imperial College London, London, U.K
| | - P Novak
- Department of Medicine, Imperial College London, London, U.K.,National University of Science and Technology 'MISIS', Moscow, Russian Federation
| | - Y Korchev
- Department of Medicine, Imperial College London, London, U.K.,Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa, Japan
| | - P Rorsman
- OCDEM, Radcliffe Department of Medicine, University of Oxford, Oxford, U.K
| | - A I Tarasov
- OCDEM, Radcliffe Department of Medicine, University of Oxford, Oxford, U.K.,School of Biomedical Sciences, Ulster University, Coleraine, U.K
| | - Andrew Shevchuk
- Department of Medicine, Imperial College London, London, U.K
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7
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Ding K, Han Y, Seid TW, Buser C, Karigo T, Zhang S, Dickman DK, Anderson DJ. Imaging neuropeptide release at synapses with a genetically engineered reporter. eLife 2019; 8:e46421. [PMID: 31241464 PMCID: PMC6609332 DOI: 10.7554/elife.46421] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 06/25/2019] [Indexed: 12/26/2022] Open
Abstract
Research on neuropeptide function has advanced rapidly, yet there is still no spatio-temporally resolved method to measure the release of neuropeptides in vivo. Here we introduce Neuropeptide Release Reporters (NPRRs): novel genetically-encoded sensors with high temporal resolution and genetic specificity. Using the Drosophila larval neuromuscular junction (NMJ) as a model, we provide evidence that NPRRs recapitulate the trafficking and packaging of native neuropeptides, and report stimulation-evoked neuropeptide release events as real-time changes in fluorescence intensity, with sub-second temporal resolution.
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Affiliation(s)
- Keke Ding
- Division of Biology and Biological EngineeringCalifornia Institute of TechnologyPasadenaUnited States
| | - Yifu Han
- Department of NeurobiologyUniversity of Southern CaliforniaLos AngelesUnited States
- Neuroscience Graduate ProgramUniversity of Southern CaliforniaLos AngelesUnited States
| | - Taylor W Seid
- Division of Biology and Biological EngineeringCalifornia Institute of TechnologyPasadenaUnited States
| | | | - Tomomi Karigo
- Division of Biology and Biological EngineeringCalifornia Institute of TechnologyPasadenaUnited States
| | - Shishuo Zhang
- Division of Biology and Biological EngineeringCalifornia Institute of TechnologyPasadenaUnited States
| | - Dion K Dickman
- Department of NeurobiologyUniversity of Southern CaliforniaLos AngelesUnited States
| | - David J Anderson
- Division of Biology and Biological EngineeringCalifornia Institute of TechnologyPasadenaUnited States
- Howard Hughes Medical Institute, California Institute of TechnologyPasadenaUnited States
- Tianqiao and Chrissy Chen Institute for Neuroscience, California Institute of TechnologyPasadenaUnited States
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8
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Morrison LM, Edwards SL, Manning L, Stec N, Richmond JE, Miller KG. Sentryn and SAD Kinase Link the Guided Transport and Capture of Dense Core Vesicles in Caenorhabditis elegans. Genetics 2018; 210:925-946. [PMID: 30401764 PMCID: PMC6218223 DOI: 10.1534/genetics.118.300847] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Accepted: 08/27/2018] [Indexed: 11/18/2022] Open
Abstract
Dense core vesicles (DCVs) can transmit signals by releasing neuropeptides from specialized synaptic regions called active zones. DCVs reach the active zone by motorized transport through a long axon. A reverse motor frequently interrupts progress by taking DCVs in the opposite direction. "Guided transport" refers to the mechanism by which outward movements ultimately dominate to bring DCVs to the synaptic region. After guided transport, DCVs alter their interactions with motors and enter a "captured" state. The mechanisms of guided transport and capture of DCVs are unknown. Here, we discovered two proteins that contribute to both processes in Caenorhabditis elegans SAD kinase and a novel conserved protein we named Sentryn are the first proteins found to promote DCV capture. By imaging DCVs moving in various regions of single identified neurons in living animals, we found that DCV guided transport and capture are linked through SAD kinase, Sentryn, and Liprin-α. These proteins act together to regulate DCV motorized transport in a region-specific manner. Between the cell body and the synaptic region, they promote forward transport. In the synaptic region, where all three proteins are highly enriched at active zones, they promote DCV pausing by inhibiting transport in both directions. These three proteins appear to be part of a special subset of active zone-enriched proteins because other active zone proteins do not share their unique functions.
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Affiliation(s)
- Logan M Morrison
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma 73104
| | - Stacey L Edwards
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma 73104
| | - Laura Manning
- Department of Biological Sciences, University of Illinois at Chicago, Illinois 60607
| | - Natalia Stec
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma 73104
| | - Janet E Richmond
- Department of Biological Sciences, University of Illinois at Chicago, Illinois 60607
| | - Kenneth G Miller
- Genetic Models of Disease Laboratory, Oklahoma Medical Research Foundation, Oklahoma 73104
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9
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Jung JH, Szule JA, Stouder K, Marshall RM, McMahan UJ. Active Zone Material-Directed Orientation, Docking, and Fusion of Dense Core Vesicles Alongside Synaptic Vesicles at Neuromuscular Junctions. Front Neuroanat 2018; 12:72. [PMID: 30271328 PMCID: PMC6146030 DOI: 10.3389/fnana.2018.00072] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Accepted: 08/17/2018] [Indexed: 12/13/2022] Open
Abstract
Active zone material is an organelle that is common to active zones along the presynaptic membrane of chemical synapses. Electron tomography on active zones at frog neuromuscular junctions has provided evidence that active zone material directs the docking of synaptic vesicles (SVs) on the presynaptic membrane at this synapse. Certain active zone material macromolecules connect to stereotypically arranged macromolecules in the membrane of undocked SVs, stably orienting a predetermined fusion domain of the vesicle membrane toward the presynaptic membrane while bringing and holding the two membranes together. Docking of the vesicles is required for the impulse-triggered vesicle membrane-presynaptic membrane fusion that releases the vesicles’ neurotransmitter into the synaptic cleft. As at other synapses, axon terminals at frog neuromuscular junctions contain, in addition to SVs, vesicles that are larger, are much less frequent and, when viewed by electron microscopy, have a distinctive electron dense core. Dense core vesicles at neuromuscular junctions are likely to contain peptides that are released into the synaptic cleft to regulate formation, maintenance and behavior of cellular apparatus essential for synaptic impulse transmission. We show by electron tomography on axon terminals of frog neuromuscular junctions fixed at rest and during repetitive impulse transmission that dense core vesicles selectively dock on and fuse with the presynaptic membrane alongside SVs at active zones, and that active zone material connects to the dense core vesicles undergoing these processes in the same way it connects to SVs. We conclude that undocked dense core vesicles have a predetermined fusion domain, as do undocked SVs, and that active zone material directs oriented docking and fusion of these different vesicle types at active zones of the presynaptic membrane by similar macromolecular interactions.
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Affiliation(s)
- Jae H Jung
- Department of Biology, Texas A&M University, College Station, TX, United States.,Department of Neurobiology, Stanford University School of Medicine, Stanford University, Stanford, CA, United States
| | - Joseph A Szule
- Department of Biology, Texas A&M University, College Station, TX, United States.,Department of Neurobiology, Stanford University School of Medicine, Stanford University, Stanford, CA, United States
| | - Kylee Stouder
- Department of Biology, Texas A&M University, College Station, TX, United States
| | - Robert M Marshall
- Department of Biology, Texas A&M University, College Station, TX, United States.,Department of Neurobiology, Stanford University School of Medicine, Stanford University, Stanford, CA, United States
| | - Uel J McMahan
- Department of Biology, Texas A&M University, College Station, TX, United States.,Department of Neurobiology, Stanford University School of Medicine, Stanford University, Stanford, CA, United States
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10
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Tao CL, Liu YT, Zhou ZH, Lau PM, Bi GQ. Accumulation of Dense Core Vesicles in Hippocampal Synapses Following Chronic Inactivity. Front Neuroanat 2018; 12:48. [PMID: 29942253 PMCID: PMC6004418 DOI: 10.3389/fnana.2018.00048] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Accepted: 05/23/2018] [Indexed: 01/03/2023] Open
Abstract
The morphology and function of neuronal synapses are regulated by neural activity, as manifested in activity-dependent synapse maturation and various forms of synaptic plasticity. Here we employed cryo-electron tomography (cryo-ET) to visualize synaptic ultrastructure in cultured hippocampal neurons and investigated changes in subcellular features in response to chronic inactivity, a paradigm often used for the induction of homeostatic synaptic plasticity. We observed a more than 2-fold increase in the mean number of dense core vesicles (DCVs) in the presynaptic compartment of excitatory synapses and an almost 20-fold increase in the number of DCVs in the presynaptic compartment of inhibitory synapses after 2 days treatment with the voltage-gated sodium channel blocker tetrodotoxin (TTX). Short-term treatment with TTX and the N-methyl-D-aspartate receptor (NMDAR) antagonist amino-5-phosphonovaleric acid (AP5) caused a 3-fold increase in the number of DCVs within 100 nm of the active zone area in excitatory synapses but had no significant effects on the overall number of DCVs. In contrast, there were very few DCVs in the postsynaptic compartments of both synapse types under all conditions. These results are consistent with a role for presynaptic DCVs in activity-dependent synapse maturation. We speculate that these accumulated DCVs can be released upon reactivation and may contribute to homeostatic metaplasticity.
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Affiliation(s)
- Chang-Lu Tao
- Center for Integrative Imaging, National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.,School of Life Sciences, University of Science and Technology of China, Hefei, China.,CAS Key Laboratory of Brain Function and Disease, University of Science and Technology of China, Hefei, China
| | - Yun-Tao Liu
- Center for Integrative Imaging, National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.,School of Life Sciences, University of Science and Technology of China, Hefei, China.,CAS Key Laboratory of Brain Function and Disease, University of Science and Technology of China, Hefei, China
| | - Z Hong Zhou
- Center for Integrative Imaging, National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.,School of Life Sciences, University of Science and Technology of China, Hefei, China.,The California NanoSystems Institute, University of California, Los Angeles, Los Angeles, CA, United States.,Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, Los Angeles, CA, United States
| | - Pak-Ming Lau
- Center for Integrative Imaging, National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.,School of Life Sciences, University of Science and Technology of China, Hefei, China.,CAS Key Laboratory of Brain Function and Disease, University of Science and Technology of China, Hefei, China
| | - Guo-Qiang Bi
- Center for Integrative Imaging, National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China.,School of Life Sciences, University of Science and Technology of China, Hefei, China.,CAS Key Laboratory of Brain Function and Disease, University of Science and Technology of China, Hefei, China.,CAS Center for Excellence in Brain Science and Intelligence Technology, University of Science and Technology of China, Hefei, China
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11
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Gandasi NR, Yin P, Omar-Hmeadi M, Ottosson Laakso E, Vikman P, Barg S. Glucose-Dependent Granule Docking Limits Insulin Secretion and Is Decreased in Human Type 2 Diabetes. Cell Metab 2018; 27:470-478.e4. [PMID: 29414688 DOI: 10.1016/j.cmet.2017.12.017] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 04/26/2017] [Accepted: 12/23/2017] [Indexed: 01/19/2023]
Abstract
Glucose-stimulated insulin secretion is biphasic, with a rapid first phase and a slowly developing sustained second phase; both are disturbed in type 2 diabetes (T2D). Biphasic secretion results from vastly different release probabilities of individual insulin granules, but the morphological and molecular basis for this is unclear. Here, we show that human insulin secretion and exocytosis critically depend on the availability of membrane-docked granules and that T2D is associated with a strong reduction in granule docking. Glucose accelerated granule docking, and this effect was absent in T2D. Newly docked granules only slowly acquired release competence; this was regulated by major signaling pathways, but not glucose. Gene expression analysis indicated that key proteins involved in granule docking are downregulated in T2D, and overexpression of these proteins increased granule docking. The findings establish granule docking as an important glucose-dependent step in human insulin secretion that is dysregulated in T2D.
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Affiliation(s)
- Nikhil R Gandasi
- Department of Medical Cell Biology, Uppsala University, BMC 571, 75123 Uppsala, Sweden
| | - Peng Yin
- Department of Medical Cell Biology, Uppsala University, BMC 571, 75123 Uppsala, Sweden
| | - Muhmmad Omar-Hmeadi
- Department of Medical Cell Biology, Uppsala University, BMC 571, 75123 Uppsala, Sweden
| | - Emilia Ottosson Laakso
- Diabetes and Endocrinology Unit, Department of Clinical Sciences, Lund University Diabetes Centre, 20502 Malmö, Sweden
| | - Petter Vikman
- Diabetes and Endocrinology Unit, Department of Clinical Sciences, Lund University Diabetes Centre, 20502 Malmö, Sweden
| | - Sebastian Barg
- Department of Medical Cell Biology, Uppsala University, BMC 571, 75123 Uppsala, Sweden.
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12
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Miyake K, Ohta T, Nakayama H, Doe N, Terao Y, Oiki E, Nagatomo I, Yamashita Y, Abe T, Nishikura K, Kumanogoh A, Hashimoto K, Kawahara Y. CAPS1 RNA Editing Promotes Dense Core Vesicle Exocytosis. Cell Rep 2017; 17:2004-2014. [PMID: 27851964 DOI: 10.1016/j.celrep.2016.10.073] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Revised: 10/03/2016] [Accepted: 10/20/2016] [Indexed: 12/20/2022] Open
Abstract
Calcium-dependent activator protein for secretion 1 (CAPS1) plays a distinct role in the priming step of dense core vesicle (DCV) exocytosis. CAPS1 pre-mRNA is known to undergo adenosine-to-inosine RNA editing in its coding region, which results in a glutamate-to-glycine conversion at a site in its C-terminal region. However, the physiological significance of CAPS1 RNA editing remains elusive. Here, we created mutant mice in which edited CAPS1 was solely expressed. These mice were lean due to increased energy expenditure caused by physical hyperactivity. Electrophysiological and biochemical analyses demonstrated that the exocytosis of DCVs was upregulated in the chromaffin cells and neurons of these mice. Furthermore, we showed that edited CAPS1 bound preferentially to the activated form of syntaxin-1A, a component of the exocytotic fusion complex. These findings suggest that RNA editing regulates DCV exocytosis in vivo, affecting physical activity.
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Affiliation(s)
- Kotaro Miyake
- Department of RNA Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan; Department of Respiratory Medicine, Allergy and Rheumatic Diseases, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan
| | - Toshio Ohta
- Department of Veterinary Pharmacology, Faculty of Agriculture, Tottori University, Tottori, Tottori 680-8553, Japan
| | - Hisako Nakayama
- Department of Neurophysiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Hiroshima 734-8551, Japan
| | - Nobutaka Doe
- General Education Center, Hyogo University of Health Sciences, Kobe, Hyogo 650-8530, Japan
| | - Yuri Terao
- Center for Medical Research and Education, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan
| | - Eiji Oiki
- Center for Medical Research and Education, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan
| | - Izumi Nagatomo
- Department of Respiratory Medicine, Allergy and Rheumatic Diseases, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan
| | - Yui Yamashita
- Animal Resource Development Unit, RIKEN Center for Life Science Technologies, Kobe, Hyogo 650-0047, Japan; Genetic Engineering Team, RIKEN Center for Life Science Technologies, Kobe, Hyogo 650-0047, Japan
| | - Takaya Abe
- Genetic Engineering Team, RIKEN Center for Life Science Technologies, Kobe, Hyogo 650-0047, Japan
| | | | - Atsushi Kumanogoh
- Department of Respiratory Medicine, Allergy and Rheumatic Diseases, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan
| | - Kouichi Hashimoto
- Department of Neurophysiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Hiroshima 734-8551, Japan
| | - Yukio Kawahara
- Department of RNA Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan.
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13
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Fathali H, Dunevall J, Majdi S, Cans AS. Extracellular Osmotic Stress Reduces the Vesicle Size while Keeping a Constant Neurotransmitter Concentration. ACS Chem Neurosci 2017; 8:368-375. [PMID: 27966899 DOI: 10.1021/acschemneuro.6b00350] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Secretory cells respond to hypertonic stress by cell shrinking, which causes a reduction in exocytosis activity and the amount of signaling molecules released from single exocytosis events. These changes in exocytosis have been suggested to result from alterations in biophysical properties of cell cytoplasm and plasma membrane, based on the assumption that osmotic stress does not affect the secretory vesicle content and size prior to exocytosis. To further investigate whether vesicles in secretory cells are affected by the osmolality of the extracellular environment, we used intracellular electrochemical cytometry together with transmission electron microscopy imaging to quantify and determine the catecholamine concentration of dense core vesicles in situ before and after cell exposure to osmotic stress. In addition, single cell amperometry recordings of exocytosis at chromaffin cells were used to monitor the effect on exocytosis activity and quantal release when cells were exposed to osmotic stress. Here we show that hypertonic stress hampers exocytosis secretion after the first pool of readily releasable vesicles have been fused and that extracellular osmotic stress causes catecholamine filled vesicles to shrink, mainly by reducing the volume of the halo solution surrounding the protein matrix in dense core vesicles. In addition, the vesicles demonstrate the ability to perform adjustments in neurotransmitter content during shrinking, and intracellular amperometry measurements in situ suggest that vesicles reduce the catecholamine content to maintain a constant concentration within the vesicle compartment. Hence, the secretory vesicles in the cell cytoplasm are highly affected and respond to extracellular osmotic stress, which gives a new perspective to the cause of reduction in quantal size by these vesicles when undergoing exocytosis.
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Affiliation(s)
- Hoda Fathali
- Department
of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden
| | - Johan Dunevall
- Department
of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden
| | - Soodabeh Majdi
- Department
of Chemistry and Molecular Biology, University of Gothenburg, 41296 Gothenburg, Sweden
| | - Ann-Sofie Cans
- Department
of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden
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14
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Zhang L, Hernández VS, Vázquez-Juárez E, Chay FK, Barrio RA. Thirst Is Associated with Suppression of Habenula Output and Active Stress Coping: Is there a Role for a Non-canonical Vasopressin-Glutamate Pathway? Front Neural Circuits 2016; 10:13. [PMID: 27065810 PMCID: PMC4814529 DOI: 10.3389/fncir.2016.00013] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 02/29/2016] [Indexed: 12/12/2022] Open
Abstract
Water-homeostasis is a fundamental physiological process for terrestrial life. In vertebrates, thirst drives water intake, but the neuronal circuits that connect the physiology of water regulation with emotional context are poorly understood. Vasopressin (VP) is a prominent messenger in this circuit, as well as L-glutamate. We have investigated the role of a VP circuit and interaction between thirst and motivational behaviors evoked by life-threatening stimuli in rats. We demonstrate a direct pathway from hypothalamic paraventricular VP-expressing, glutamatergic magnocellular neurons to the medial division of lateral habenula (LHbM), a region containing GABAergic neurons. In vivo recording and juxtacellular labeling revealed that GABAergic neurons in the LHbM had locally branching axons, and received VP-positive axon terminal contacts on their dendrites. Water deprivation significantly reduced freezing and immobility behaviors evoked by innate fear and behavioral despair, respectively, accompanied by decreased Fos expression in the lateral habenula. Our results reveal a novel VP-expressing hypothalamus to the LHbM circuit that is likely to evoke GABA-mediated inhibition in the LHbM, which promotes escape behavior during stress coping.
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Affiliation(s)
- Limei Zhang
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Vito S Hernández
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Erika Vázquez-Juárez
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Freya K Chay
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México Ciudad de México, Mexico
| | - Rafael A Barrio
- Departamento de Física Química, Instituto de Física, Universidad Nacional Autónoma de México Ciudad de México, Mexico
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15
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Xu X, Kozikowski AP, Pozzo-Miller L. A selective histone deacetylase-6 inhibitor improves BDNF trafficking in hippocampal neurons from Mecp2 knockout mice: implications for Rett syndrome. Front Cell Neurosci 2014; 8:68. [PMID: 24639629 PMCID: PMC3945638 DOI: 10.3389/fncel.2014.00068] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Accepted: 02/17/2014] [Indexed: 12/20/2022] Open
Abstract
Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function mutations in the transcriptional modulator methyl-CpG-binding protein 2 (MECP2). One of the most prominent gene targets of MeCP2 is brain-derived neurotrophic factor (Bdnf), a potent modulator of activity-dependent synaptic development, function and plasticity. Dysfunctional BDNF signaling has been demonstrated in several pathophysiological mechanisms of RTT disease progression. To evaluate whether the dynamics of BDNF trafficking is affected by Mecp2 deletion, we analyzed movements of BDNF tagged with yellow fluorescent protein (YFP) in cultured hippocampal neurons by time-lapse fluorescence imaging. We found that both anterograde and retrograde vesicular trafficking of BDNF-YFP are significantly impaired in Mecp2 knockout hippocampal neurons. Selective inhibitors of histone deacetylase 6 (HDAC6) show neuroprotective effects in neurodegenerative diseases and stimulate microtubule-dependent vesicular trafficking of BDNF-containing dense core vesicles. Here, we show that the selective HDAC6 inhibitor Tubastatin-A increased the velocity of BDNF-YFP vesicles in Mecp2 knockout neurons in both directions by increasing α–tubulin acetylation. Tubastatin-A also restored activity-dependent BDNF release from Mecp2 knockout neurons to levels comparable to those shown by wildtype neurons. These findings demonstrate that a selective HDAC6 inhibitor is a potential pharmacological strategy to reverse cellular and synaptic impairments in RTT resulting from impaired BDNF signaling.
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Affiliation(s)
- Xin Xu
- Department of Neurobiology, Civitan International Research Center, The University of Alabama at Birmingham Birmingham, AL, USA
| | - Alan P Kozikowski
- Drug Discovery Program, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago Chicago, IL, USA
| | - Lucas Pozzo-Miller
- Department of Neurobiology, Civitan International Research Center, The University of Alabama at Birmingham Birmingham, AL, USA
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16
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Trueta C, Kuffler DP, De-Miguel FF. Cycling of dense core vesicles involved in somatic exocytosis of serotonin by leech neurons. Front Physiol 2012; 3:175. [PMID: 22685436 PMCID: PMC3368391 DOI: 10.3389/fphys.2012.00175] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Accepted: 05/14/2012] [Indexed: 12/15/2022] Open
Abstract
We studied the cycling of dense core vesicles producing somatic exocytosis of serotonin. Our experiments were made using electron microscopy and vesicle staining with fluorescent dye FM1-43 in Retzius neurons of the leech, which secrete serotonin from clusters of dense core vesicles in a frequency-dependent manner. Electron micrographs of neurons at rest or after 1 Hz stimulation showed two pools of dense core vesicles. A perinuclear pool near Golgi apparatuses, from which vesicles apparently form, and a peripheral pool with vesicle clusters at a distance from the plasma membrane. By contrast, after 20 Hz electrical stimulation 47% of the vesicle clusters were apposed to the plasma membrane, with some omega exocytosis structures. Dense core and small clear vesicles apparently originating from endocytosis were incorporated in multivesicular bodies. In another series of experiments, neurons were stimulated at 20 Hz while bathed in a solution containing peroxidase. Electron micrographs of these neurons contained gold particles coupled to anti-peroxidase antibodies in dense core vesicles and multivesicular bodies located near the plasma membrane. Cultured neurons depolarized with high potassium in the presence of FM1-43 displayed superficial fluorescent spots, each reflecting a vesicle cluster. A partial bleaching of the spots followed by another depolarization in the presence of FM1-43 produced restaining of some spots, other spots disappeared, some remained without restaining and new spots were formed. Several hours after electrical stimulation the FM1-43 spots accumulated at the center of the somata. This correlated with electron micrographs of multivesicular bodies releasing their contents near Golgi apparatuses. Our results suggest that dense core vesicle cycling related to somatic serotonin release involves two steps: the production of clear vesicles and multivesicular bodies after exocytosis, and the formation of new dense core vesicles in the perinuclear region.
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Affiliation(s)
- Citlali Trueta
- Instituto Nacional de Psiquiatría "Ramón de la Fuente Muñiz," México D. F., México
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17
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Pickel VM, Chan J. Ultrastructural localization of the serotonin transporter in limbic and motor compartments of the nucleus accumbens. J Neurosci 1999; 19:7356-66. [PMID: 10460242 PMCID: PMC6782507] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/1999] [Revised: 06/21/1999] [Accepted: 06/23/1999] [Indexed: 02/13/2023] Open
Abstract
Extracellular levels of serotonin [5-hydroxytryptamine (5-HT)] in the nucleus accumbens (NAc) can influence both cognitive and motor functions involving extensive connections with the frontal cortex. The 5-HT levels reflect vesicular release and plasmalemmal reuptake through the serotonin transporter (SERT). We used electron microscopic immunocytochemistry to determine the sites for SERT activation in the limbic shell and motor-associated core of the rat NAc. Of the SERT-immunoreactive profiles in each region, >90% were serotonergic axons and axon terminals; the remainder were nonserotonergic dendrites and glia. Axonal SERT immunogold labeling was seen mainly at nonsynaptic sites on plasma membranes and often near 5-HT-containing large dense core vesicles (DCVs). SERT-labeled axonal profiles were larger and had a higher numerical density in the shell versus the core but showed no regional differences in their content of SERT immunogold particles. In contrast, immunoreactive dendrites had a lower numerical density in the shell than in the core. SERT labeling in dendrites was localized to segments of plasma membrane near synaptic contacts from unlabeled terminals and/or dendritic appositions. Our results suggest that in the NAc (1) reuptake into serotonergic axons is most efficient after exocytotic release from DCVs, and (2) increased 5-HT release without concomitant increase in SERT expression in individual axons may contribute to higher extracellular levels of serotonin in the shell versus the core. These findings also indicate that SERT may play a minor substrate-dependent role in serotonin uptake or channel activity in selective nonserotonergic neurons and glia in the NAc.
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Affiliation(s)
- V M Pickel
- Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA
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