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Lu CW, Lin TY, Chiu KM, Lee MY, Wang SJ. Gypenoside XVII Reduces Synaptic Glutamate Release and Protects against Excitotoxic Injury in Rats. Biomolecules 2024; 14:589. [PMID: 38785996 PMCID: PMC11118014 DOI: 10.3390/biom14050589] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2024] [Revised: 04/15/2024] [Accepted: 05/14/2024] [Indexed: 05/25/2024] Open
Abstract
Excitotoxicity is a common pathological process in neurological diseases caused by excess glutamate. The purpose of this study was to evaluate the effect of gypenoside XVII (GP-17), a gypenoside monomer, on the glutamatergic system. In vitro, in rat cortical nerve terminals (synaptosomes), GP-17 dose-dependently decreased glutamate release with an IC50 value of 16 μM. The removal of extracellular Ca2+ or blockade of N-and P/Q-type Ca2+ channels and protein kinase A (PKA) abolished the inhibitory effect of GP-17 on glutamate release from cortical synaptosomes. GP-17 also significantly reduced the phosphorylation of PKA, SNAP-25, and synapsin I in cortical synaptosomes. In an in vivo rat model of glutamate excitotoxicity induced by kainic acid (KA), GP-17 pretreatment significantly prevented seizures and rescued neuronal cell injury and glutamate elevation in the cortex. GP-17 pretreatment decreased the expression levels of sodium-coupled neutral amino acid transporter 1, glutamate synthesis enzyme glutaminase and vesicular glutamate transporter 1 but increased the expression level of glutamate metabolism enzyme glutamate dehydrogenase in the cortex of KA-treated rats. In addition, the KA-induced alterations in the N-methyl-D-aspartate receptor subunits GluN2A and GluN2B in the cortex were prevented by GP-17 pretreatment. GP-17 also prevented the KA-induced decrease in cerebral blood flow and arginase II expression. These results suggest that (i) GP-17, through the suppression of N- and P/Q-type Ca2+ channels and consequent PKA-mediated SNAP-25 and synapsin I phosphorylation, reduces glutamate exocytosis from cortical synaptosomes; and (ii) GP-17 has a neuroprotective effect on KA-induced glutamate excitotoxicity in rats through regulating synaptic glutamate release and cerebral blood flow.
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Affiliation(s)
- Cheng-Wei Lu
- Department of Anesthesiology, Far-Eastern Memorial Hospital, New Taipei 22060, Taiwan; (C.-W.L.); (T.-Y.L.)
- Department of Mechanical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan
| | - Tzu-Yu Lin
- Department of Anesthesiology, Far-Eastern Memorial Hospital, New Taipei 22060, Taiwan; (C.-W.L.); (T.-Y.L.)
- Department of Mechanical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan
| | - Kuan-Ming Chiu
- Division of Cardiovascular Surgery, Cardiovascular Center, Far-Eastern Memorial Hospital, New Taipei 22060, Taiwan;
- Department of Electrical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan
| | - Ming-Yi Lee
- Department of Medical Research, Far-Eastern Memorial Hospital, New Taipei 22060, Taiwan;
| | - Su-Jane Wang
- School of Medicine, Fu Jen Catholic University, New Taipei 24205, Taiwan
- Research Center for Chinese Herbal Medicine, College of Human Ecology, Chang Gung University of Science and Technology, Taoyuan 33303, Taiwan
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Cho W, Jung M, Yoon SH, Jeon J, Oh MA, Kim JY, Park M, Kang CM, Chung TD. On-Site Formation of Functional Dopaminergic Presynaptic Terminals on Neuroligin-2-Modified Gold-Coated Microspheres. ACS APPLIED MATERIALS & INTERFACES 2024; 16:3082-3092. [PMID: 38206769 DOI: 10.1021/acsami.3c13829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2024]
Abstract
Advancements in neural interface technologies have enabled the direct connection of neurons and electronics, facilitating chemical communication between neural systems and external devices. One promising approach is a synaptogenesis-involving method, which offers an opportunity for synaptic signaling between these systems. Janus synapses, one type of synaptic interface utilizing synaptic cell adhesion molecules for interface construction, possess unique features that enable the determination of location, direction of signal flow, and types of neurotransmitters involved, promoting directional and multifaceted communication. This study presents the first successful establishment of a Janus synapse between dopaminergic (DA) neurons and abiotic substrates by using a neuroligin-2 (NLG2)-mediated synapse-inducing method. NLG2 immobilized on gold-coated microspheres can induce synaptogenesis upon contact with spatially isolated DA axons. The induced DA Janus synapses exhibit stable synaptic activities comparable to that of native synapses over time, suggesting their suitability for application in neural interfaces. By calling for DA presynaptic organizations, the NLG2-immobilized abiotic substrate is a promising tool for the on-site detection of synaptic dopamine release.
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Affiliation(s)
- Wonkyung Cho
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
| | - Minji Jung
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
| | - Sun-Heui Yoon
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
| | - Joohee Jeon
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
| | - Min-Ah Oh
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
| | - Ji Yong Kim
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
| | - Minjung Park
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
| | - Chung Mu Kang
- Advanced Institutes of Convergence Technology, Suwon-si 16229, Gyeonggi-do, Republic of Korea
| | - Taek Dong Chung
- Department of Chemistry, Seoul National University, Seoul 08826, Republic of Korea
- Advanced Institutes of Convergence Technology, Suwon-si 16229, Gyeonggi-do, Republic of Korea
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Lu CW, Yeh KC, Chiu KM, Lee MY, Lin TY, Wang SJ. The Effect of Isosaponarin Derived from Wasabi Leaves on Glutamate Release in Rat Synaptosomes and Its Underlying Mechanism. Int J Mol Sci 2022; 23:ijms23158752. [PMID: 35955884 PMCID: PMC9368944 DOI: 10.3390/ijms23158752] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 08/05/2022] [Accepted: 08/05/2022] [Indexed: 11/23/2022] Open
Abstract
Excessive glutamate release is known to be involved in the pathogenesis of neurological diseases, and suppression of glutamate release from nerve terminals is considered to be a treatment strategy. In this study, we investigated whether isosaponarin, a flavone glycoside isolated from wasabi leaves, could affect glutamate release in rat cerebral cortex nerve terminals (synaptosomes). The release of glutamate was evoked by the K+ channel blocker 4-aminopyridine (4-AP) and measured by an online enzyme-coupled fluorimetric assay. Isosaponarin produced a concentration-dependent inhibition of 4-AP-evoked glutamate release with a half-maximum inhibition of release value of 22 μM. The inhibition caused by isosaponarin was prevented by eliminating extracellular Ca2+ or by using bafilomycin A1, an inhibitor of synaptic vesicle exocytosis. Isosaponarin decreased intrasynaptosomal rises in Ca2+ levels that were induced by 4-AP, without affecting the synaptosomal membrane potential. The isosaponarin-induced inhibition of glutamate release was significantly prevented in synaptosomes that were pretreated with a combination of the calcium channel blockers ω-conotoxin GVIA (N-type) and ω-agatoxin IVA (P/Q-types). The protein kinase C (PKC) pan-inhibitor GF109203X and the Ca2+-dependent PKC inhibitor Go6976 abolished the inhibition of glutamate release by isosaponarin, while the Ca2+-independent PKC inhibitor rottlerin did not show any effect. The results from immunoblotting assays also showed that isosaponarin lowered PKC, PKCα, synaptosomal-associated protein of 25 kDa (SNAP-25), and myristoylated alanine-rich C-kinase substrate (MARCKS) phosphorylation induced by 4-AP. In addition, FM1-43-labeled synaptic vesicles in synaptosomes showed that treatment with isosaponarin resulted in an attenuation of the 4-AP-induced decrease in fluorescence intensity that is consistent with glutamate release. Transmission electron microscopy of synaptosomes also provided evidence that isosaponarin altered the number of synaptic vesicles. These results indicate that isosaponarin suppresses the Ca2+-dependent PKC/SNAP-25 and MARCKS pathways in synaptosomes, causing a decrease in the number of available synaptic vesicles, which inhibits vesicular glutamate release from synaptosomes.
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Affiliation(s)
- Cheng-Wei Lu
- Department of Anesthesiology, Far-Eastern Memorial Hospital, New Taipei City 22060, Taiwan
- Department of Mechanical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan
| | - Kun-Chieh Yeh
- School of Medicine, Fu Jen Catholic University, New Taipei City 24205, Taiwan
- Department of Surgery, Taoyuan Armed Forces General Hospital, Taoyuan 325208, Taiwan
- Department of Surgery, Fu Jen Catholic University Hospital, Fu Jen Catholic University, New Taipei City 24205, Taiwan
| | - Kuan-Ming Chiu
- Division of Cardiovascular Surgery, Cardiovascular Center, Far-Eastern Memorial Hospital, New Taipei City 22060, Taiwan
- Department of Electrical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan
| | - Ming-Yi Lee
- Department of Medical Research, Far-Eastern Memorial Hospital, New Taipei 22060, Taiwan
| | - Tzu-Yu Lin
- Department of Anesthesiology, Far-Eastern Memorial Hospital, New Taipei City 22060, Taiwan
- Department of Mechanical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan
- Correspondence: (T.-Y.L.); (S.-J.W.); Tel.: +886-2-8966-7000 (T.-Y.L.); +886-2-2905-3465 (S.-J.W.)
| | - Su-Jane Wang
- School of Medicine, Fu Jen Catholic University, New Taipei City 24205, Taiwan
- Research Center for Chinese Herbal Medicine, College of Human Ecology, Chang Gung University of Science and Technology, Taoyuan 33303, Taiwan
- Correspondence: (T.-Y.L.); (S.-J.W.); Tel.: +886-2-8966-7000 (T.-Y.L.); +886-2-2905-3465 (S.-J.W.)
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Chang A, Hung CF, Hsieh PW, Ko HH, Wang SJ. Eupafolin Suppresses P/Q-Type Ca 2+ Channels to Inhibit Ca 2+/ Calmodulin-Dependent Protein Kinase II and Glutamate Release at Rat Cerebrocortical Nerve Terminals. Biomol Ther (Seoul) 2021; 29:630-636. [PMID: 34475273 PMCID: PMC8551735 DOI: 10.4062/biomolther.2021.046] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 05/04/2021] [Accepted: 05/28/2021] [Indexed: 12/26/2022] Open
Abstract
Eupafolin, a constituent of the aerial parts of Phyla nodiflora, has neuroprotective property. Because reducing the synaptic release of glutamate is crucial to achieving pharmacotherapeutic effects of neuroprotectants, we investigated the effect of eupafolin on glutamate release in rat cerebrocortical synaptosomes and explored the possible mechanism. We discovered that eupafolin depressed 4-aminopyridine (4-AP)-induced glutamate release, and this phenomenon was prevented in the absence of extracellular calcium. Eupafolin inhibition of glutamate release from synaptic vesicles was confirmed through measurement of the release of the fluorescent dye FM 1-43. Eupafolin decreased 4-AP-induced [Ca2+]i elevation and had no effect on synaptosomal membrane potential. The inhibition of P/Q-type Ca2+ channels reduced the decrease in glutamate release that was caused by eupafolin, and docking data revealed that eupafolin interacted with P/Q-type Ca2+ channels. Additionally, the inhibition of calcium/calmodulin-dependent protein kinase II (CaMKII) prevented the effect of eupafolin on evoked glutamate release. Eupafolin also reduced the 4-AP-induced activation of CaMK II and the subsequent phosphorylation of synapsin I, which is the main presynaptic target of CaMKII. Therefore, eupafolin suppresses P/Q-type Ca2+ channels and thereby inhibits CaMKII/synapsin I pathways and the release of glutamate from rat cerebrocortical synaptosomes.
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Affiliation(s)
- Anna Chang
- School of Medicine, Fu Jen Catholic University, New Taipei City 24205, Taiwan.,Department of Neurology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei 22060, Taiwan
| | - Chi-Feng Hung
- School of Medicine, Fu Jen Catholic University, New Taipei City 24205, Taiwan
| | - Pei-Wen Hsieh
- Research Center for Chinese Herbal Medicine, College of Human Ecology, Chang Gung University of Science and Technology, Taoyuan 33303, Taiwan.,Graduate Institute of Natural Products, School of Traditional Chinese Medicine, and Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan 33303, Taiwan.,Department of Anesthesiology, Chang Gung Memorial Hospital, Linkou 33305, Taiwan
| | - Horng-Huey Ko
- Department of Fragrance and Cosmetic Science, College of Pharmacy, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.,Drug Development and Value Creation Center, Kaohsiung Medical University, Kaohsiung 80708, Taiwan
| | - Su-Jane Wang
- School of Medicine, Fu Jen Catholic University, New Taipei City 24205, Taiwan.,Research Center for Chinese Herbal Medicine, College of Human Ecology, Chang Gung University of Science and Technology, Taoyuan 33303, Taiwan
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Wang CC, Kuo JR, Wang SJ. Fingolimod inhibits glutamate release through activation of S1P1 receptors and the G protein βγ subunit-dependent pathway in rat cerebrocortical nerve terminals. Neuropharmacology 2021; 185:108451. [PMID: 33428887 DOI: 10.1016/j.neuropharm.2021.108451] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Revised: 12/30/2020] [Accepted: 01/03/2021] [Indexed: 01/28/2023]
Abstract
Fingolimod, a sphingosine-1-phosphate (S1P) receptor modulator approved for treating multiple sclerosis, is reported to prevent excitotoxic insult. Because excessive glutamate release is a major cause of neuronal damage in various neurological disorders, the effect of fingolimod on glutamate release in rat cerebrocortical nerve terminals (synaptosomes) was investigated in the current study. Fingolimod decreased 4-aminopyridine (4-AP)-stimulated glutamate release and calcium concentration elevation. Fingolimod-mediated inhibition of 4-AP-induced glutamate release was dependent on extracellular calcium, persisted in the presence of the glutamate transporter inhibitor DL-TBOA or intracellular Ca2+-releasing inhibitors dantrolene and CGP37157, and was prevented by blocking vesicular transporters or N- and P/Q-type channels. Western blot and immunocytochemical analysis revealed the presence of S1P1 receptor proteins in presynaptic terminals. Fingolimod-mediated inhibition of 4-AP-induced glutamate release was also abolished by the sphingosine kinase inhibitor DMS, selective S1P1 receptor antagonist W146, Gi/o protein inhibitor pertussis toxin, and G protein βγ subunit inhibitor gallein; however, it was unaffected by the adenylyl cyclase inhibitor SQ22536, protein kinase A inhibitor H89, and phospholipase C inhibitor U73122. These data indicate that fingolimod decreases glutamate release from rat cerebrocortical synaptosomes by suppressing N- and P/Q-type Ca2+ channel activity; additionally, the activation of presynaptic S1P1 receptors and the G protein βγ subunit participates in achieving the effect.
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Affiliation(s)
- Che Chuan Wang
- Department of Neurology, Chi Mei Medical Center, Tainan, Taiwan; Biotechnology, Southern Taiwan University of Science and Technology, Tainan, Taiwan
| | - Jinn Rung Kuo
- Department of Neurology, Chi Mei Medical Center, Tainan, Taiwan; Biotechnology, Southern Taiwan University of Science and Technology, Tainan, Taiwan
| | - Su Jane Wang
- School of Medicine, Fu Jen Catholic University, No.510, Zhongzheng Rd, Xinzhuang Dist, New Taipei City, 24205, Taiwan; Graduate Institute of Biomedical and Pharmaceutical Science, Fu Jen Catholic University, No.510, Zhongzheng Rd, Xinzhuang Dist, New Taipei City, 24205, Taiwan; Research Center for Chinese Herbal Medicine, College of Human Ecology, Chang Gung University of Science and Technology, Taoyuan City, Taiwan.
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6
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Klockow JL, Hettie KS, Secor KE, Barman DN, Glass TE. Tunable Molecular Logic Gates Designed for Imaging Released Neurotransmitters. Chemistry 2015; 21:11446-51. [DOI: 10.1002/chem.201501379] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Jessica L. Klockow
- Department of Chemistry, University of Missouri, 601 S. College Ave. Columbia, MO 65211 (USA)
| | - Kenneth S. Hettie
- Department of Chemistry, University of Missouri, 601 S. College Ave. Columbia, MO 65211 (USA)
| | - Kristen E. Secor
- Department of Chemistry, University of Missouri, 601 S. College Ave. Columbia, MO 65211 (USA)
| | - Dipti N. Barman
- Department of Chemistry, University of Missouri, 601 S. College Ave. Columbia, MO 65211 (USA)
| | - Timothy E. Glass
- Department of Chemistry, University of Missouri, 601 S. College Ave. Columbia, MO 65211 (USA)
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Daniel JA, Malladi CS, Kettle E, McCluskey A, Robinson PJ. Analysis of synaptic vesicle endocytosis in synaptosomes by high-content screening. Nat Protoc 2012; 7:1439-55. [PMID: 22767087 DOI: 10.1038/nprot.2012.070] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Small molecules modulating synaptic vesicle endocytosis (SVE) may ultimately be useful for diseases where pathological neurotransmission is implicated. Only a small number of specific SVE modulators have been identified to date. Slow progress is due to the laborious nature of traditional approaches to study SVE, in which nerve terminals are identified and studied in cultured neurons, typically yielding data from 10-20 synapses per experiment. We provide a protocol for a quantitative, high-throughput method for studying SVE in thousands of nerve terminals. Rat forebrain synaptosomes are attached to 96-well microplates and depolarized; SVE is then quantified by uptake of the dye FM4-64, which is imaged by high-content screening. Synaptosomes that have been frozen and stored can be used in place of fresh synaptosomes, reducing the experimental time and animal numbers required. With a supply of frozen synaptosomes, the assay can be performed within a day, including data analysis.
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Affiliation(s)
- James A Daniel
- Cell Signalling Unit, Children's Medical Research Institute, University of Sydney, Westmead, New South Wales, Australia
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Abstract
Although drugs used to treat several neurological diseases are presumed to target synapses that secrete dopamine (DA), relatively little is known about synaptic vesicle (SV) release mechanisms at single DA synapses. We found that the relative probability of release (Pr) varied between individual DA synapses. Furthermore, DA terminals generally exhibited lower Pr than glutamatergic hippocampal (Hpc) terminals, suggesting that DA release is less reliable than the release of glutamate. Our mathematical model of fluorescence loss shows that Pr is regulated by two independent and heterogeneous elements. First, the size of the recycling SV pool regulates Pr. Second, Pr is also independently regulated by additional factors, which are reflected in the time constant of FM 1-43 destaining, tau. We found that the observed difference in Pr between Hpc and DA neurons results because the recycling SV pool is smaller in DA neurons than in Hpc neurons. However, tau does not vary between these two neuron populations. We also identified a population of functional nonsynaptic boutons in DA axons, which are not associated with a postsynaptic element and which are not functionally different from boutons that formed conventional synapses. Our work provides a new approach to the study of SV exocytosis in DA neurons and shows that synaptic terminals of DA neurons are functionally heterogeneous and differ from excitatory terminals in terms of Pr.
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Sánchez-Nogueiro J, Marín-García P, León D, León-Otegui M, Salas E, Gómez-Villafuertes R, Gualix J, Miras-Portugal MT. Axodendritic fibres of mouse cerebellar granule neurons exhibit a diversity of functional P2X receptors. Neurochem Int 2009; 55:671-82. [PMID: 19560503 DOI: 10.1016/j.neuint.2009.06.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2009] [Revised: 06/10/2009] [Accepted: 06/18/2009] [Indexed: 01/18/2023]
Abstract
Distribution and functional expression of P2X receptors were analyzed in mouse cerebellum axodendritic fibres, using different experimental approaches such as RT-PCR, western blot, immunochemistry, microfluorimetric experiments and exocytotic studies. RT-PCR and western blot demonstrated the presence of P2X1-4,7 subunits in both whole cerebellum and mouse cerebellar granule cultured neurons. Immunochemistry analysis of tissular and cellular location of P2X1-4,7 receptors confirmed their presence and unequal distribution between somas and axodendritic prolongations. Microfluorimetric experiments using a variety of modulators of the P2X subunits revealed the presence of different functional P2X receptors in the axodendritic fibres. The use of the synthetic agonist alpha,beta-meATP and the antagonist Ip(5)I revealed the activation of functional P2X1 and P2X3 receptors. Responses mediated by P2X1 subunits were also confirmed by using ZnSO(4). Activation of functional P2X4 receptors is observed when stimulated in the presence of ivermectin. Exocytotic studies confirmed the role of most P2X subunits in the activation of neurotransmitter release in axodendritic fibres from mouse cerebellar granule neurons.
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11
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León D, Sánchez-Nogueiro J, Marín-García P, Miras-Portugal MAT. Glutamate release and synapsin-I phosphorylation induced by P2X7 receptors activation in cerebellar granule neurons. Neurochem Int 2007; 52:1148-59. [PMID: 18242779 DOI: 10.1016/j.neuint.2007.12.004] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Revised: 11/30/2007] [Accepted: 12/07/2007] [Indexed: 10/22/2022]
Abstract
The present work reports that activation of P2X7 receptor induces synaptic vesicle release in granule neurons and phosphorylation of synapsin-I by calcium-calmodulin-dependent protein kinase II (CaMKII), which in turn modulates secretory event. ATP, in absence of magnesium, induced a concentration-dependent glutamate release with an EC50 value of 1.95 microM. The involvement of P2X7 receptor was suggested when maximal secretory response was significantly reduced by the selective P2X7 antagonist Brilliant Blue G (BBG; 100 nM) and abolished by removing extracellular Ca2+. The involvement of P2X7 receptor on synaptic vesicle release was confirmed by measuring the release of FM 1-43 dye. In this case, pharmacological activation of P2X7 was achieved with the more selective agonist 2'-3'-o-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP; 100 microM) showing a significant FM 1-43 release that was blocked by BBG (100 nM), by Zn2+ ions (100 microM), both P2X7 blockers, but not by suramin (100 microM), antagonist of P2X1, P2X2, P2X3 and P2X5. In addition, BzATP, through P2X7 receptor activation, significantly increased the phosphorylation of synapsin-I, the main presynaptic target of CaMKII. Both effects mediated by BzATP were inhibited by the CaMKII inhibitors KN-62 (10 microM) and KN-93 (10 microM). These results suggest, therefore, that Ca2+ entrance mediated by P2X7 receptor induces glutamate release and in parallel synapsin-I phosphorylation.
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Affiliation(s)
- David León
- Department of Biochemistry, Veterinary Faculty, Universidad Complutense de Madrid, Avda. Puerta de Hierro s/n, 28040 Madrid, Spain
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12
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Tyler WJ, Zhang XL, Hartman K, Winterer J, Muller W, Stanton PK, Pozzo-Miller L. BDNF increases release probability and the size of a rapidly recycling vesicle pool within rat hippocampal excitatory synapses. J Physiol 2006; 574:787-803. [PMID: 16709633 PMCID: PMC1817733 DOI: 10.1113/jphysiol.2006.111310] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Exerting its actions pre-, post- and peri-synaptically, brain-derived neurotrophic factor (BDNF) is one of the most potent modulators of hippocampal synaptic function. Here, we examined the effects of BDNF on a rapidly recycling pool (RRP) of vesicles within excitatory synapses. First, we estimated vesicular release in hippocampal cultures by performing FM4-64 imaging in terminals impinging on enhanced green fluorescent protein (eGFP)-labelled dendritic spines - a hallmark of excitatory synapses. Consistent with a modulation of the RRP, BDNF increased the evoked destaining rate of FM4-64 only during the initial phase of field stimulation. Multiphoton microscopy in acute hippocampal slices confirmed these observations by selectively imaging the RRP, which was loaded with FM1-43 by hyperosmotic shock. Slices exposed to BDNF showed an increase in the evoked and spontaneous rates of FM1-43 destaining from terminals in CA1 stratum radiatum, mostly representing excitatory terminals of Schaffer collaterals. Variance-mean analysis of evoked EPSCs in CA1 pyramidal neurons further confirmed that release probability is increased in BDNF-treated slices, without changes in the number of independent release sites or average postsynaptic quantal amplitude. Because BDNF was absent during dye loading, imaging, destaining and whole-cell recordings, these results demonstrate that BDNF induces a long-lasting enhancement in the probability of transmitter release at hippocampal excitatory synapses by modulating the RRP. Since the endogenous BDNF scavenger TrkB-IgG prevented the enhancement of FM1-43 destaining rate caused by induction of long-term potentiation in acute hippocampal slices, the modulation of a rapidly recycling vesicle pool may underlie the role of BDNF in hippocampal long-term synaptic plasticity.
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Affiliation(s)
- William J Tyler
- Department of Neurobiology, SHEL-1002, University of Alabama at Birmingham, 1825 University Blvd, Birmingham, AL 35294-2182, USA
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Nikonenko AG, Skibo GG. Estimation of the number of synaptic vesicles in asymmetric synapses between hippocampal neurons. NEUROPHYSIOLOGY+ 2006. [DOI: 10.1007/s11062-006-0043-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Abstract
Mammalian central synapses commonly specialize in one fast neurotransmitter, matching the content of their presynaptic vesicles with the appropriate receptors in their postsynaptic membrane. Here, I show that hippocampal cultures contain autaptic glutamatergic synapses that contravene this rule: in addition to postsynaptic glutamate receptors, they also express clusters of functional postsynaptic GABA(A) receptors yet lack presynaptic GABA. Hence, these synapses are presynaptically silent with respect to GABA. They can be unsilenced by loading GABA into presynaptic vesicles by endocytosis, after which a postload IPSC appears. This IPSC is similar to native IPSCs recorded from GABAergic interneurons in the same cultures. Thus, these "mistargeted" GABA(A) receptors, which apparently lack a signal that confers synaptic specificity, function almost normally. After GABA loading, glutamatergic miniature postsynaptic currents acquire a slow tail that is mediated by GABA(A) receptors, showing that synaptic vesicles can accommodate both the usual concentration of native glutamate and a saturating concentration of loaded GABA. After brief Ca(2+)-dependent exocytosis, endocytosis of GABA can proceed in low-Ca(2+) external solution. The amplitude of the postload IPSC declines exponentially with repetitive stimulation as the endocytosed GABA passes through the presynaptic vesicle cycle and is depleted. Hence, by using GABA as an exogenous but physiological tracer, the properties of these presynaptically silent synapses can provide novel insights into the content and cycling of vesicles in presynaptic terminals.
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15
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Guerrero G, Agarwal G, Reiff DF, Ball RW, Borst A, Goodman CS, Isacoff EY. Heterogeneity in synaptic transmission along a Drosophila larval motor axon. Nat Neurosci 2005; 8:1188-96. [PMID: 16116446 PMCID: PMC1402256 DOI: 10.1038/nn1526] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2005] [Accepted: 07/25/2005] [Indexed: 11/09/2022]
Abstract
At the Drosophila melanogaster larval neuromuscular junction (NMJ), a motor neuron releases glutamate from 30-100 boutons onto the muscle it innervates. How transmission strength is distributed among the boutons of the NMJ is unknown. To address this, we created synapcam, a version of the Ca2+ reporter Cameleon. Synapcam localizes to the postsynaptic terminal and selectively reports Ca2+ influx through glutamate receptors (GluRs) with single-impulse and single-bouton resolution. GluR-based Ca2+ signals were uniform within a given connection (that is, a given bouton/postsynaptic terminal pair) but differed considerably among connections of an NMJ. A steep gradient of transmission strength was observed along axonal branches, from weak proximal connections to strong distal ones. Presynaptic imaging showed a matching axonal gradient, with higher Ca2+ influx and exocytosis at distal boutons. The results suggest that transmission strength is mainly determined presynaptically at the level of individual boutons, possibly by one or more factors existing in a gradient.
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Affiliation(s)
- Giovanna Guerrero
- Department of Molecular and Cell Biology, 279 Life Sciences Addition, University of California, Berkeley, California 94720-3200, USA
| | - Gautam Agarwal
- Helen Wills Neuroscience Institute, 279 Life Sciences Addition, University of California, Berkeley, California 94720-3200, USA
| | - Dierk F. Reiff
- Department of Systems and Computational Neurobiology, Max-Planck-Institute of Neurobiology, Am Klopfersptiz 18 A, 82152 Martinsried, Germany
| | - Robin W. Ball
- Helen Wills Neuroscience Institute, 279 Life Sciences Addition, University of California, Berkeley, California 94720-3200, USA
| | - Alexander Borst
- Department of Systems and Computational Neurobiology, Max-Planck-Institute of Neurobiology, Am Klopfersptiz 18 A, 82152 Martinsried, Germany
| | - Corey S. Goodman
- Department of Molecular and Cell Biology, 279 Life Sciences Addition, University of California, Berkeley, California 94720-3200, USA
- Helen Wills Neuroscience Institute, 279 Life Sciences Addition, University of California, Berkeley, California 94720-3200, USA
- Current address: Renovis, Inc., Two Corporate Drive, South San Francisco, California 94080, USA
| | - Ehud Y. Isacoff
- Department of Molecular and Cell Biology, 279 Life Sciences Addition, University of California, Berkeley, California 94720-3200, USA
- Helen Wills Neuroscience Institute, 279 Life Sciences Addition, University of California, Berkeley, California 94720-3200, USA
- Physical Bioscience and Material Science Divisions, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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16
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Ma L, Bindokas VP, Kuznetsov A, Rhodes C, Hays L, Edwardson JM, Ueda K, Steiner DF, Philipson LH. Direct imaging shows that insulin granule exocytosis occurs by complete vesicle fusion. Proc Natl Acad Sci U S A 2004; 101:9266-71. [PMID: 15197259 PMCID: PMC438965 DOI: 10.1073/pnas.0403201101] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Confocal imaging of GFP-tagged secretory granules combined with the use of impermeant extracellular dyes permits direct observation of insulin packaged in secretory granules, trafficking of these granules to the plasma membrane, exocytotic fusion of granules with the plasma membrane, and eventually the retrieval of membranes by endocytosis. Most such studies have been done in tumor cell lines, using either confocal methods or total internal reflectance microscopy. Here we compared these methods by using GFP-syncollin or PC3-GFP plus rhodamine dextrans to study insulin granule dynamics in insulinoma cells, normal mouse islets, and primary pancreatic beta cells. We found that most apparently docked granules did not fuse with the plasma membrane after stimulation. Granules that did fuse typically fused completely, but a few dextran-filled granules lingered at the membrane. Direct recycling of granules occurred only rarely. Similar results were obtained with both confocal and total internal reflection microscopy, although each technique had advantages for particular aspects of the granule life cycle. We conclude that insulin exocytosis involves a prolonged interaction of secretory granules with the plasma membrane, and that the majority of exocytotic events occur by full, not partial, fusion.
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Affiliation(s)
- Li Ma
- Department of Medicine, University of Chicago, IL 60637, USA
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17
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Waters J, Smith SJ. Mitochondria and release at hippocampal synapses. Pflugers Arch 2003; 447:363-70. [PMID: 14556074 DOI: 10.1007/s00424-003-1182-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2003] [Revised: 07/24/2003] [Accepted: 09/12/2003] [Indexed: 10/26/2022]
Abstract
Mitochondria are present in some, but not all presynaptic terminals in the hippocampus. Mitochondria are capable of sequestering and storing large amounts of calcium, but it is unclear whether they influence release probability at these synapses. Using FM dye imaging techniques and confocal microscopy, we have examined the relationship between mitochondrial presence/absence and presynaptic vesicle release from rat hippocampal neurones in primary dissociated culture at room temperature. Following staining with the mitochondrial dye mitotracker green, we were able to resolve putative individual mitochondria associated with neuronal processes. The majority of mitochondria were positionally stable, although some exhibited periods of rapid motility (up to 0.4 microm/s) interspersed with periods of immobility. Co-staining with mitotracker green and the synaptic vesicle dye FM 4-64 indicated that 180 of 506 (36%) synapses were devoid of mitochondria. A comparison of vesicular release in response to stimulation at 1 Hz and at 10 Hz revealed no differences in release properties between synapses with and without mitochondria.
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Affiliation(s)
- Jack Waters
- Department of Molecular and Cellular Physiology, Beckman Center, Stanford Medical School, Stanford, CA 94305, USA.
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18
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Mohrmann R, Lessmann V, Gottmann K. Developmental maturation of synaptic vesicle cycling as a distinctive feature of central glutamatergic synapses. Neuroscience 2003; 117:7-18. [PMID: 12605887 DOI: 10.1016/s0306-4522(02)00835-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The formation of chemical synapses in the mammalian brain involves complex pre- and postsynaptic differentiation processes. Presynaptically, the progressive accumulation of synaptic vesicles is a hallmark of synapse maturation in the neocortex [J Neurocytol 12 (1983b) 697]. In this study, we analyzed the functional consequences of presynaptic vesicle-pool maturation at central glutamatergic and GABAergic synapses. Using (N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide (FM1-43) staining of recycling synaptic vesicles, we demonstrate a pronounced developmental increase in presynaptic vesicle accumulation during differentiation of neocortical neurons in culture. Using electrophysiological methods to study functional synaptic maturation, we found an improved recovery from hypertonic solution-induced depletion. As supported by the FM1-43 staining results, this change is most likely caused by a developmental increase in the number of reserve-pool vesicles. In addition, assuming a rapid reuse of freshly recycled vesicles, a developmental maturation of the endocytosis process may also contribute. The observed presynaptic maturation process occurred selectively at glutamatergic synapses, while GABAergic synapses did not show similar developmental alterations. Furthermore, we used high-frequency stimulation (HFS) of glutamatergic and GABAergic synapses to reveal the physiological consequences of reserve-pool maturation. As expected, recovery from HFS-induced depletion was incomplete at immature glutamatergic synapses and strongly improved during synapse maturation. Again, GABAergic synapses did not show similar developmental changes. Taken together, our study characterizes the functional consequences of a pronounced accumulation of reserve-pool vesicles occurring selectively at glutamatergic synapses.
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Affiliation(s)
- R Mohrmann
- Department of Cell Physiology ND4, Ruhr-University Bochum, Germany
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19
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Stuart JN, Sweedler JV. Ultrafast capillary electrophoresis and bioanalytical applications. Proc Natl Acad Sci U S A 2003; 100:3545-6. [PMID: 12657735 PMCID: PMC152953 DOI: 10.1073/pnas.0830869100] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Jeffrey N Stuart
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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20
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Gundelfinger ED, Kessels MM, Qualmann B. Temporal and spatial coordination of exocytosis and endocytosis. Nat Rev Mol Cell Biol 2003; 4:127-39. [PMID: 12563290 DOI: 10.1038/nrm1016] [Citation(s) in RCA: 181] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In secretory cells, exocytosis and compensatory endocytosis are tightly coupled membrane trafficking processes that control the surface area and composition of the plasma membrane. While exocytic and endocytic processes have been studied independently in great detail, at present there is much interest in understanding the mode of their coupling. This review discusses emerging insights into the coupling of these processes, both in the chemical synapses of neurons and in non-neuronal cells.
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Affiliation(s)
- Eckart D Gundelfinger
- Leibniz Institute for Neurobiology, Department of Neurochemistry and Molecular Biology, Brenneckestr. 6, 39118 Magdeburg, Germany.
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21
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Abstract
Optical approaches to investigate cerebral function and metabolism have long been applied in invasive studies. From the neuron cultured to the exposed cortex in the human during neurosurgical procedures, high spatial resolution can be reached and several processes such as membrane potential, cell swelling, metabolism of mitochondrial chromophores, and vascular response can be monitored, depending on the respective preparation. The authors focus on an extension of optical methods to the noninvasive application in the human. Starting with the pioneering work of Jöbsis 25 years ago, near-infrared spectroscopy (NIRS) has been used to investigate functional activation of the human cerebral cortex. Recently, several groups have started to use imaging systems that allow the generation of images of a larger area of the subject's head and, thereby, the production of maps of cortical oxygenation changes. Such images have a much lower spatial resolution compared with the invasively obtained optical images. The noninvasive NIRS images, however, can be obtained in undemanding set-ups that can be easily combined with other functional methods, in particular EEG. Moreover, NIRS is applicable to bedside use. The authors briefly review some of the abundant literature on intrinsic optical signals and the NIRS imaging studies of the past few years. The weaknesses and strengths of the approach are critically discussed. The authors conclude that NIRS imaging has two major advantages: it can address issues concerning neurovascular coupling in the human adult and can extend functional imaging approaches to the investigation of the diseased brain.
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Affiliation(s)
- Hellmuth Obrig
- Department of Neurology, Charité, Humboldt University, Berlin, Germany.
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22
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Waters J, Smith SJ. Vesicle pool partitioning influences presynaptic diversity and weighting in rat hippocampal synapses. J Physiol 2002; 541:811-23. [PMID: 12068042 PMCID: PMC2290351 DOI: 10.1113/jphysiol.2001.013485] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Hippocampal synapses display a range of release probabilities. This is partially the result of scaling of release probability with the total number of releasable vesicles at each synapse. We have compared synaptic release and vesicle pool sizes across a large number of hippocampal synapses using FM 1-43 and confocal fluorescence microscopy. We found that the relationship between the number of recycling vesicles at a synapse and its release probability is dependent on firing frequency. During firing at 10 Hz, the release probability of each synapse is closely related to the number of recycling vesicles that it contains. In contrast, during firing at 1 Hz, different synapses turn over their recycling vesicle pools at different rates leading to an indirect relationship between recycling vesicle pool size and release probability. Hence two synapses may release vesicles at markedly different rates during low frequency firing, even if they contain similar numbers of vesicles. Both further kinetic analyses and manipulation of the number of vesicles in the readily releasable pool using phorbol ester treatment suggested that this imprecise scaling observed during firing at 1 Hz resulted from synapse-to-synapse differences in the proportion of recycling vesicles partitioned into the readily releasable pool. Hence differential partitioning between vesicle pools affects presynaptic weighting in a frequency-dependent manner. Since hippocampal single unit firing rates shift between 1 Hz and 10 Hz regimes with behavioural state, differential partitioning may be a mechanism for encoding information in hippocampal circuits.
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Affiliation(s)
- Jack Waters
- Department of Molecular and Cellular Physiology, Beckman Center, Stanford Medical School, Stanford 94305, USA.
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23
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Neves G, Gomis A, Lagnado L. Calcium influx selects the fast mode of endocytosis in the synaptic terminal of retinal bipolar cells. Proc Natl Acad Sci U S A 2001; 98:15282-7. [PMID: 11734626 PMCID: PMC65021 DOI: 10.1073/pnas.261311698] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2001] [Indexed: 11/18/2022] Open
Abstract
To investigate the regulation of endocytosis by Ca(2+), we have made capacitance measurements in the synaptic terminal of depolarizing bipolar cells from the retina of goldfish. After a brief depolarization, all of the excess membrane was retrieved rapidly (tau approximately 1 s). But when the rise in free [Ca(2+)] was reduced by the introduction of Ca(2+) buffers [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA) or EGTA], a large fraction of the membrane was retrieved by a second, slower mechanism (tau > or = 10 s). The block of fast endocytosis by EGTA could be overcome by increasing the amplitude of the Ca(2+) current, demonstrating that Ca(2+) influx was the trigger for fast endocytosis. These manipulations of the Ca(2+) signal altered the relative proportions of fast and slow endocytosis but did not modulate the rate constants of these processes. A brief stimulus that triggered fast endocytosis did not generate a significant rise in the spatially averaged [Ca(2+)], indicating that Ca(2+) regulated endocytosis through an action close to the active zone. The slow mode of retrieval occurred at the resting [Ca(2+)]. These results demonstrate that Ca(2+) influx couples fast endocytosis and exocytosis at this synapse.
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Affiliation(s)
- G Neves
- Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom
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24
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Abstract
Endocytosis in cochlear hair cells was investigated by staining with the vital fluorescent dye FM 1-43, that partitions reversibly into membranes and is trapped in vesicles during endocytosis. The temporal development and spatial distribution of FM 1-43 induced fluorescence was investigated using confocal laser-scanning microscopy. FM 1-43 rapidly and intensely stained cochlear hair cells, leaving the supporting cells unstained. For short application (0.2-30 s), only the infracuticular region of outer hair cells (OHCs) was labeled, whereas for long application (30-60 s), the OHCs were also labeled in the infranuclear zone and along a central strand extending from the infracuticular zone down to the nucleus, as well as along the entire cell membrane. Except for the cell membrane, the infracuticular zone, directly below the cuticular plate, showed the most rapid and intense staining, and in most cases staining was spherically shaped with a diameter of 3-7 microm. Localization and size of this infracuticular staining coincided with Hensen's body, a specialized variant of the endoplasmic reticulum. In contrast to the OHCs, apical fluorescence of inner hair cells presented a homogeneous distribution. When OHCs were incubated in FM 1-43 for longer than 1 min, many points of contact between the central strand, the infracuticular zone and the lateral cell membrane were observed. Since Hensen's bodies are a specialty of OHCs and the fluorescent staining pattern of these cells was unique, it is proposed that Hensen's body is involved in the turnover of OHC-specific proteins, such as those involved in the molecular machinery of the motor action of the plasma membrane.
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Affiliation(s)
- J Meyer
- Department of Otolaryngology, Section of Physiological Acoustics and Communication, University of Tübingen, Germany
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25
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Abstract
We have investigated mechanisms in postendocytic processing of synaptic vesicles at hippocampal synapses, using synaptobrevin/vesicle-associated membrane protein (VAMP) tagged with variants of the green fluorescent protein. Following exocytosis, VAMP is retrieved at synaptic and adjoining axonal regions. Retrieved VAMP-containing vesicles return to synaptic vesicle clusters at a rate slower than endocytosis. Vesicles containing a different protein, synaptophysin, recluster at a similar rate, suggesting common vesicular intermediates for the two proteins. Activity prolongs the time taken by endocytosed vesicles to return to synapses. Exogenous calcium buffers slow endocytosis but have no additional effect on the time course of reclustering. In contrast, the protein kinase inhibitor staurosporine does not affect endocytosis but slows reclustering. Finally, since VAMP can move freely on surface membranes, sustained synaptic activity leads to mixing of this vesicular component between adjacent synapses.
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Affiliation(s)
- Z Li
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
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26
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Micheva KD, Holz RW, Smith SJ. Regulation of presynaptic phosphatidylinositol 4,5-biphosphate by neuronal activity. J Cell Biol 2001; 154:355-68. [PMID: 11470824 PMCID: PMC2150764 DOI: 10.1083/jcb.200102098] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phosphatidylinositol 4,5-biphosphate (PIP2) has been implicated in a variety of cellular processes, including synaptic vesicle recycling. However, little is known about the spatial distribution of this phospholipid in neurons and its dynamics. In this study, we have focused on these questions by transiently expressing the phospholipase C (PLC)-delta1 pleckstrin homology (PH) domain fused to green fluorescent protein (GFP) in cultured hippocampal neurons. This PH domain binds specifically and with high affinity to PIP2. Live confocal imaging revealed that in resting cells, PH-GFP is localized predominantly on the plasma membrane. Interestingly, no association of PH-GFP with synaptic vesicles in quiescent neurons was observed, indicating the absence of detectable PIP2 on mature synaptic vesicles. Electrical stimulation of hippocampal neurons resulted in a decrease of the PH-GFP signal at the plasma membrane, most probably due to a PLC-mediated hydrolysis of PIP2. This was accompanied in the majority of presynaptic terminals by a marked increase in the cytoplasmic PH-GFP signal, localized most probably on freshly endocytosed membranes. Further investigation revealed that the increase in PH-GFP signal was dependent on the activation of N-methyl-D-aspartate receptors and the consequent production of nitric oxide (NO). Thus, PIP2 in the presynaptic terminal appears to be regulated by postsynaptic activity via a retrograde action of NO.
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Affiliation(s)
- K D Micheva
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305, USA.
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27
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Abstract
Phorbol esters enhance release from a variety of cell types. The mechanism by which phorbol esters potentiate presynaptic release from central neurons is unclear, although effects of phorbol esters both on the readily releasable pool of vesicles and on presynaptic calcium channels have been shown. Using confocal microscopy and the fluorescent styryl dye FM 1-43, we have examined the effects of phorbol-12,13-dibutyrate (PDBu) on presynaptic vesicle turnover at individually identified synapses in dissociated cultures obtained from neonatal rat hippocampus. Using different dye staining and destaining protocols we were able to resolve two effects of PDBu. Potentiation of evoked release by PDBu was insensitive to calcium channel antagonists, suggesting that this effect results from an increased number of vesicles in the readily releasable pool. Since we observed no effect of PDBu on the size of the total recycling vesicle pool, we conclude that phorbol esters alter the equilibrium between reserve and readily releasable pools. An additional effect of PDBu on spontaneous release was observed. This effect was antagonized by nifedipine but not omega-conotoxin GVIA or omega-agatoxin IVA. We conclude that PDBu influences spontaneous and evoked release by two different mechanisms: through L-type calcium channels and through an increase in the proportion of recycling vesicles in the readily releasable pool. In addition to further clarifying the mechanism of action of phorbol esters, these results suggest that phorbol esters may be a useful tool with which to probe the function of the readily releasable pool of presynaptic vesicles at CNS synapses.
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28
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Abstract
Representations of optic flow are encoded in fly tangential neurons by pooling the signals of many retinotopically organized local motion-sensitive inputs as well as of other tangential cells originating in the ipsi- and contralateral half of the brain. In the so called HSE cell, a neuron involved in optomotor course control, two contralateral input elements, the H1 and H2 cells, mediate distinct EPSPs. These EPSPs frequently elicit spike-like depolarizations in the HSE cell. The synaptic transmission between the H2 and the HSE cell is analysed in detail and shown to be very reliable with respect to the amplitude and time-course of the postsynaptic potential. As a consequence of its synaptic input, the HSE cell responds best to wide-field motion, such as that generated on the eyes when the animal turns about its vertical body axis. It is shown that the specificity of the HSE cell for this type of optic flow is much enhanced if rapid membrane depolarizations, such as large-amplitude EPSPs or spike-like depolarizations, are taken into account rather than the average membrane potential.
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Affiliation(s)
- W Horstmann
- Lehrstuhl für Neurobiologie, Fakultät für Biologie, Universität Bielefeld, Postfach 10 01 31, D-33501 Bielefeld, Germany
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29
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Abstract
Electron cryomicroscopy of the clathrin coat and X-ray crystallography of parts of the clathrin heavy chain combine to give a detailed picture of the clathrin molecule, assembled as a cage. Recently determined domain structures of other components of the endocytic machinery, particularly the mu2 subunit and the alpha-appendage domain of the AP2 adaptor complex, provide important information on the sequence of recognition events involved in the dynamic process of clathrin coat assembly.
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Affiliation(s)
- B M Pearse
- Medical Research Council Laboratory of Molecular Biology, Cambridge, CB2 2QH, UK.
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