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van Onselen R, Downing TG. Uptake of β-N-methylamino-L-alanine (BMAA) into glutamate-specific synaptic vesicles: Exploring the validity of the excitotoxicity mechanism of BMAA. Neurosci Lett 2024; 821:137593. [PMID: 38103629 DOI: 10.1016/j.neulet.2023.137593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 12/01/2023] [Accepted: 12/07/2023] [Indexed: 12/19/2023]
Abstract
The first mechanism of toxicity proposed for the cyanobacterial neurotoxin β-N-methylamino-L-alanine (BMAA) was excitotoxicity, and this was supported by numerous in vitro studies in which overactivation of both ionotropic and metabotropic glutamate receptors was reported. However, the excitotoxicity of BMAA is weak in comparison with other known excitotoxins and on par with that of glutamate, implying that to achieve sufficient synaptic concentrations of BMAA to cause classical in vivo excitotoxicity, BMAA must either accumulate in synapses to allow persistent glutamate receptor activation or it must be released in sufficiently high concentrations into synapses to cause the overexcitation. Since it has been shown that BMAA can be readily removed from synapses, release of high concentrations of BMAA into synapses must be shown to confirm its role as an excitotoxin in in vivo systems. This study therefore sought to evaluate the uptake of BMAA into synaptic vesicles and to determine if BMAA affects the uptake of glutamate into synaptic vesicles. There was no evidence to support uptake of BMAA into glutamate-specific synaptic vesicles but there was some indication that BMAA may affect the uptake of glutamate into synaptic vesicles. The uptake of BMAA into synaptic vesicles isolated from areas other than the cerebral cortex should be investigated before definite conclusions can be drawn about the role of BMAA as an excitotoxin.
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Affiliation(s)
- Rianita van Onselen
- Biomedical Research and Innovation Platform, South African Medical Research Council, Cape Town, South Africa; Department of Biochemistry and Microbiology, Nelson Mandela University, Gqeberha, South Africa
| | - Tim G Downing
- Department of Biochemistry and Microbiology, Nelson Mandela University, Gqeberha, South Africa.
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Ludwig M, Apps D, Menzies J, Patel JC, Rice ME. Dendritic Release of Neurotransmitters. Compr Physiol 2016; 7:235-252. [PMID: 28135005 DOI: 10.1002/cphy.c160007] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Release of neuroactive substances by exocytosis from dendrites is surprisingly widespread and is not confined to a particular class of transmitters: it occurs in multiple brain regions, and includes a range of neuropeptides, classical neurotransmitters, and signaling molecules, such as nitric oxide, carbon monoxide, ATP, and arachidonic acid. This review is focused on hypothalamic neuroendocrine cells that release vasopressin and oxytocin and midbrain neurons that release dopamine. For these two model systems, the stimuli, mechanisms, and physiological functions of dendritic release have been explored in greater detail than is yet available for other neurons and neuroactive substances. © 2017 American Physiological Society. Compr Physiol 7:235-252, 2017.
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Affiliation(s)
- Mike Ludwig
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh, United Kingdom
| | - David Apps
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh, United Kingdom
| | - John Menzies
- Centre for Integrative Physiology, University of Edinburgh, Edinburgh, United Kingdom
| | - Jyoti C Patel
- Department of Neurosurgery, New York University School of Medicine, New York, USA
| | - Margaret E Rice
- Department of Neurosurgery, New York University School of Medicine, New York, USA.,Department of Neuroscience and Physiology, New York University School of Medicine, New York, USA
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Ludwig M, Stern J. Multiple signalling modalities mediated by dendritic exocytosis of oxytocin and vasopressin. Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2014.0182. [PMID: 26009761 DOI: 10.1098/rstb.2014.0182] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The mammalian hypothalamic magnocellular neurons of the supraoptic and paraventricular nuclei are among the best understood of all peptidergic neurons. Through their anatomical features, vasopressin- and oxytocin-containing neurons have revealed many important aspects of dendritic functions. Here, we review our understanding of the mechanisms of somato-dendritic peptide release, and the effects of autocrine, paracrine and hormone-like signalling on neuronal networks and behaviour.
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Affiliation(s)
- Mike Ludwig
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, UK
| | - Javier Stern
- Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, GA, USA
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Zakharov AV, Petrov AM, Kotov NV, Zefirov AL. Experimental and modeling investigation of the mechanism of synaptic vesicles recycling. Biophysics (Nagoya-shi) 2012. [DOI: 10.1134/s0006350912040203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Zhang Z, Nguyen KT, Barrett EF, David G. Vesicular ATPase inserted into the plasma membrane of motor terminals by exocytosis alkalinizes cytosolic pH and facilitates endocytosis. Neuron 2011; 68:1097-108. [PMID: 21172612 DOI: 10.1016/j.neuron.2010.11.035] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/29/2010] [Indexed: 01/29/2023]
Abstract
Key components of vesicular neurotransmitter release, such as Ca(2+) influx and membrane recycling, are affected by cytosolic pH. We measured the pH-sensitive fluorescence of Yellow Fluorescent Protein transgenically expressed in mouse motor nerve terminals, and report that Ca(2+) influx elicited by action potential trains (12.5-100 Hz) evokes a biphasic pH change: a brief acidification (∼ 13 nM average peak increase in [H(+)]), followed by a prolonged alkalinization (∼ 30 nM peak decrease in [H(+)]) that outlasts the stimulation train. The alkalinization is selectively eliminated by blocking vesicular exocytosis with botulinum neurotoxins, and is prolonged by the endocytosis-inhibitor dynasore. Blocking H(+) pumping by vesicular H(+)-ATPase (with folimycin or bafilomycin) suppresses stimulation-induced alkalinization and reduces endocytotic uptake of FM1-43. These results suggest that H(+)-ATPase, known to transfer cytosolic H(+) into prefused vesicles, continues to extrude cytosolic H(+) after being exocytotically incorporated into the plasma membrane. The resulting cytosolic alkalinization may facilitate vesicular endocytosis.
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Affiliation(s)
- Zhongsheng Zhang
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL 33136, USA
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Borycz JA, Borycz J, Kubów A, Kostyleva R, Meinertzhagen IA. Histamine compartments of the Drosophila brain with an estimate of the quantum content at the photoreceptor synapse. J Neurophysiol 2005; 93:1611-9. [PMID: 15738275 DOI: 10.1152/jn.00894.2004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Reliable estimates of the quantum size in histaminergic neurons are not available. We have exploited two unusual opportunities in the fly's (Drosophila melanogaster) visual system to make such determinations for histaminergic photoreceptor synapses: 1) the possibility to microdissect successively from whole fly heads freeze-dried in acetone: the compound eyes; the first optic neuropils, or lamina; and the rest of the brain; and 2) the uniform sheaves of lamina synaptic terminals of photoreceptors R1-R6. We used this organization to count scrupulously the numbers of 30-nm synaptic vesicles from electron micrographs of R1-R6 profiles, and from microdissections we determined the regional contents of histamine in the compound eye, lamina, and central brain. Total head histamine averages 1.98 ng of which 9% was lost after freeze-drying in acetone and a further 28% after the brain was microdissected. Of the remainder, 71% was in the eye and lamina. Assuming that histamine loss from the tissue occurred mostly by diffusion evenly distributed among all regions, the overall lamina content of the head would be 0.1935 ng before dissection. From published values for the volumes of the brain's compartments, the computed regional concentrations of histamine are highest in the lamina (4.35 mM) because of the terminals of R1-R6. The concentration in the retina is approximately 13% that in the lamina, suggesting that most histamine is vesicular. There are approximately 43,500 +/- 7,400 (SD) synaptic vesicles per terminal and, if all histamine is allocated equally and exclusively among these, the vesicle contents would be 858 +/- 304 x 10(-21) moles or approximately 5,000 +/- 1,800 (SD) molecules at an approximate concentration of 670 mM. These values are compared with the vesicle contents at synapses using acetylcholine and catecholamines.
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Affiliation(s)
- J A Borycz
- Life Sciences Centre, Dalhousie University, 1355 Oxford St., Halifax, Nova Scotia, Canada B3H 4J1
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Van der Kloot W, Colasante C, Cameron R, Molgó J. Recycling and refilling of transmitter quanta at the frog neuromuscular junction. J Physiol 2000; 523 Pt 1:247-58. [PMID: 10673559 PMCID: PMC2269784 DOI: 10.1111/j.1469-7793.2000.00247.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. Fluorescent dyes have been used at the frog neuromuscular junction to label synaptic vesicular membrane. Retrieved membrane is reformed into vesicles, which are released along with pre-existing vesicles. Consequently, if vesicular refilling with acetylcholine (ACh) is depressed by inhibitors, two sizes of quanta should be released: normal and smaller. As recycling continues the fraction of smaller size quanta should increase exponentially. 2. We enhanced the rate of quantal release by elevating the K+ concentration. The principal inhibitors were (-)-vesamicol (VES), hemicholinium-3 (HC3), and NH4+. Quantal size measurements were fitted to one and to two cumulative lognormal probability distribution functions. When two fitted better, the statistical significance assessment took into account the three additional parameters used in calculating the fit. 3. After recycling in the presence of inhibitor, many sets were fitted better by two lognormal functions. As recycling continued, the fraction of the miniature endplate potential voltage-time integrals ( MEPPs) in the larger sub-population decreased exponentially. 4. The size of the releasable pool was estimated by counting the quanta released by carbonyl cyanide m-chlorophenylhydrazone (CCCP). This was compared to pool sizes calculated from the inhibitor experiments. The two estimates of pool size were indistinguishable, with mean values ranging from about 170,000 to 270,000. 5. With all of the treatments tested, the means of the sizes in the smaller sub-population of MEPPs were about 1/3 those of the larger sub-populations. 6. Recycling synaptic vesicles appear to be incorporated into the releasable pool from which they have roughly the same probability of release as the pre-existing vesicles.
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Affiliation(s)
- W Van der Kloot
- Department of Physiology and Biophysics, SUNY, Stony Brook, NY 11794-8661, USA.
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Abstract
The recycling of synaptic vesicles in nerve terminals involves multiple steps, underlies all aspects of synaptic transmission, and is a key to understanding the basis of synaptic plasticity. The development of styryl dyes as fluorescent molecules that label recycling synaptic vesicles has revolutionized the way in which synaptic vesicle recycling can be investigated, by allowing an examination of processes in neurons that have long been inaccessible. In this review, we evaluate the major aspects of synaptic vesicle recycling that have been revealed and advanced by studies with styryl dyes, focussing upon synaptic vesicle fusion, retrieval, and trafficking. The greatest impact of styryl dyes has been to allow the routine visualization of endocytosis in central nerve terminals for the first time. This has revealed the kinetics of endocytosis, its underlying sequential steps, and its regulation by Ca2+. In studies of exocytosis, styryl dyes have helped distinguish between different modes of vesicle fusion, provided direct support for the quantal nature of exocytosis and endocytosis, and revealed how the probability of exocytosis varies enormously from one nerve terminal to another. Synaptic vesicle labelling with styryl dyes has helped our understanding of vesicle trafficking by allowing better understanding of different synaptic vesicle pools within the nerve terminal, vesicle intermixing, and vesicle clustering at release sites. Finally, the dyes are now being used in innovative ways to reveal further insights into synaptic plasticity.
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Affiliation(s)
- M A Cousin
- Cell Signalling Unit, Children's Medical Research Institute, Wentworthville, New South Wales, Australia
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Prior IA, Clague MJ. Localization of a class II phosphatidylinositol 3-kinase, PI3KC2alpha, to clathrin-coated vesicles. MOLECULAR CELL BIOLOGY RESEARCH COMMUNICATIONS : MCBRC 1999; 1:162-6. [PMID: 10356367 DOI: 10.1006/mcbr.1999.0126] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have analysed phosphatidylinositol 3-kinase activity associated with subcellular fractions prepared from rat brains. Phosphatidylinositol 3-kinase activity is not markedly enriched with synaptic vesicle purification; whilst the activity associated with the most pure fractions is inhibited at low concentrations of wortmannin (IC50 approximately 4-5 nM). In contrast, clathrin-coated vesicle (CCV) fractions showed increased enzyme activity compared to light membrane fractions from which they are purified. In addition to a wortmannin-sensitive activity, we also detected an activity that could only be inhibited at higher concentrations of wortmannin (IC50 approximately 400 nM), characteristic of certain class II enzymes (including phosphatidylinositol 3-kinase C2alpha) to be highly enriched in CCV fractions. Immunoblotting with an antibody raised against phosphatidylinositol 3-kinase C2alpha, confirmed that this enzyme is highly enriched in CCVs and displays an enrichment profile during the purification that mirrors enrichment of the low nanomolar wortmannin-insensitive activity. If the CCV purification protocol is adapted to favour nerve terminally derived vesicles, we find reduced levels of the C2alpha enzyme in the CCV fractions, suggesting that the enzyme may principally reside on vesicles associated with the cell body.
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Affiliation(s)
- I A Prior
- Physiological Laboratory, University of Liverpool, United Kingdom
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Brodin L, Bakeeva L, Shupliakov O. Presynaptic mitochondria and the temporal pattern of neurotransmitter release. Philos Trans R Soc Lond B Biol Sci 1999; 354:365-72. [PMID: 10212485 PMCID: PMC1692500 DOI: 10.1098/rstb.1999.0388] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Mitochondria are critical for the function of nerve terminals as the cycling of synaptic vesicle membrane requires an efficient supply of ATP. In addition, the presynaptic mitochondria take part in functions such as Ca2+ buffering and neurotransmitter synthesis. To learn more about presynaptic mitochondria, we have examined their organization in two types of synapse in the lamprey, both of which are glutamatergic but are adapted to different temporal patterns of activity. The first is the giant lamprey reticulospinal synapse, which is specialized to transmit phasic signals (i.e. bursts of impulses). The second is the synapse established by sensory dorsal column axons, which is adapted to tonic activity. In both cases, the presynaptic axons were found to contain two distinct types of mitochondria; small 'synaptic' mitochondria, located near release sites, and larger mitochondria located in more central parts of the axon. The size of the synapse-associated mitochondria was similar in both types of synapse. However, their number differed considerably. Whereas the reticulospinal synapses contained only single mitochondria within 1 micron distance from the edge of the active zone (on average 1.2 per active zone, range of 1-3), the tonic dorsal column synapses were surrounded by clusters of mitochondria (4.5 per active zone, range of 3-6), with individual mitochondria sometimes apparently connected by intermitochondrial contacts. In conjunction with studies of crustacean neuromuscular junctions, these observations indicate that the temporal pattern of transmitter release is an important determinant of the organization of presynaptic mitochondria.
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Affiliation(s)
- L Brodin
- Department of Neuroscience, Nobel Institute for Neurophysiology, Karolinska Institute, Stockholm, Sweden.
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11
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Abstract
Observation of the flow of material along the endocytic pathway has lead to the description of the basic architecture of the pathway and provided insight into the relationship between compartments. Significant advances have been made in the study of endocytic transport steps at the molecular level, of which studies of cargo selection, vesicle budding and membrane fusion events comprise the major part. Progress in this area has been driven by two approaches, yeast genetics and in vitro or cell-free assays, which reconstitute particular transport steps and allow biochemical manipulation. The complex protein machineries that control vesicle budding and fusion are significantly conserved between the secretory and endocytic pathways such that proteins that regulate particular steps are often part of a larger family of proteins which exercise a conserved function at other locations within the cell. Well characterized examples include vesicle coat proteins, rabs (small GTPases) and soluble N-ethylmaleimide-sensitive fusion protein (NSF) attachment protein (SNAP) receptors (SNAREs). Intracompartmental pH, lipid composition and cytoskeletal organization have also been identified as important determinants of the orderly flow of material within the endocytic pathway.
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Affiliation(s)
- M J Clague
- Physiological Laboratory, University of Liverpool, Crown Street, Liverpool L69 3BX, U.K.
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Smith CJ, Grigorieff N, Pearse BM. Clathrin coats at 21 A resolution: a cellular assembly designed to recycle multiple membrane receptors. EMBO J 1998; 17:4943-53. [PMID: 9724631 PMCID: PMC1170823 DOI: 10.1093/emboj/17.17.4943] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We present a map at 21 A resolution of clathrin assembled into cages with the endocytic adaptor complex, AP-2. The map was obtained by cryo-electron microscopy and single-particle reconstruction. It reveals details of the packing of entire clathrin molecules as they interact to form a cage with two nested polyhedral layers. The proximal domains of each triskelion leg depart from a cage vertex in a skewed orientation, forming a slightly twisted bundle with three other leg domains. Thus, each triskelion contributes to two connecting edges of the polyhedral cage. The clathrin heavy chains continue inwards under the vertices with local 3-fold symmetry, the terminal domains contributing to 'hook-like' features which form an intermediate network making possible contacts with the surface presented by the inner adaptor shell. A node of density projecting inwards from the vertex may correspond to the C-termini of clathrin heavy chains which form a protrusion on free triskelions at the vertex. The inter-subunit interactions visible in this map provide a structural basis for considering the assembly of clathrin coats on a membrane and show the contacts which will need to be disrupted during disassembly.
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Affiliation(s)
- C J Smith
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
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Brodin L, Löw P, Gad H, Gustafsson J, Pieribone VA, Shupliakov O. Sustained neurotransmitter release: new molecular clues. Eur J Neurosci 1997; 9:2503-11. [PMID: 9517455 DOI: 10.1111/j.1460-9568.1997.tb01679.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Chemical synapses convey impulses at high frequency by exocytosis of synaptic vesicles. To avoid failure of synaptic transmission, rapid replenishment of synaptic vesicles must occur. Recent molecular perturbation studies have confirmed that the recycling of synaptic vesicles involves clathrin-mediated endocytosis. The rate of exocytosis would thus be limited by the capacity of the synaptic clathrin machinery unless vesicles could be drawn from existing pools. The mobilization of vesicles from the pool clustered at the release sites appears to provide a mechanism by which the rate of exocytosis can intermittently exceed the rate of recycling. Perturbation of synapsins causes disruption of vesicle clusters and impairment of synaptic transmission at high but not at low frequencies. Both clathrin-mediated recycling and mobilization of vesicles from the reserve pool are thus important in the replenishment of synaptic vesicles. The efficacy of each mechanism appears to differ between synapses which operate with different patterns of activity.
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Affiliation(s)
- L Brodin
- Department of Neuroscience, Nobel Institute for Neurophysiology, Karolinska Institutet, Stockholm, Sweden
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