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Magalhães-Gomes MPS, Camargos W, Valadão PAC, Garcias RS, Rodrigues HA, Andrade JN, Teixeira VP, Naves LA, Cavalcante WLG, Gallaci M, Guatimosim S, Prado VF, Prado MAM, Guatimosim C. Increased Cholinergic Tone Causes Pre-synaptic Neuromuscular Degeneration and is Associated with Impaired Diaphragm Function. Neuroscience 2021; 460:31-42. [PMID: 33548369 DOI: 10.1016/j.neuroscience.2020.12.025] [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: 04/02/2020] [Revised: 12/08/2020] [Accepted: 12/17/2020] [Indexed: 11/25/2022]
Abstract
In vertebrates, muscle activity is dependent on acetylcholine (ACh) released from neuromuscular junctions (NMJs), and changes in cholinergic neurotransmission are linked to a variety of neuromuscular diseases, including congenital myasthenic syndromes (CMS). The storage and release of ACh depends on the activity of the Vesicular Acetylcholine Transporter (VAChT), a rate-limiting step for cholinergic neurotransmission whose loss of function mutations was shown to cause human congenital myasthenia. However, we know much less about increased VAChT activity, due to copy number variations, for example. Therefore, here we investigated the impact of increased VAChT expression and consequently ACh levels at the synaptic cleft of the diaphragm NMJs. We analyzed structure and function of nerve and muscles from a mouse model of cholinergic hyperfunction (ChAT-ChR2-EYFP) with increased expression of VAChT. Our results showed a significant increase of ACh released under evoked stimuli. However, we observed deleterious changes in synaptic vesicles cycle (impaired endocytosis and decrease in vesicles number), together with structural alterations of NMJs. Interestingly, ultrastructure analyses showed that synaptic vesicles from ChAT-ChR2-EYFP mice NMJs were larger, which might be related to increased ACh load. We also observed that these larger synaptic vesicles were less rounded in comparison with control. Finally, we showed that ChAT-ChR2-EYFP mice NMJs have compromised safety factor, possible due to the structural alterations we described. These findings reveal that physiological cholinergic activity is important to maintain the structure and function of the neuromuscular system and help to understand some of the neuromuscular adverse effects experienced by chronically increased NMJ neurotransmission, such as individuals treated with cholinesterase inhibitors.
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Affiliation(s)
- Matheus P S Magalhães-Gomes
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil; Departamento de Medicina, Faculdade Ciências Médicas de Minas Gerais, FCMMG, Belo Horizonte, MG, Brazil.
| | - Wallace Camargos
- Departamento de Fisiologia e Biofísica, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Priscila A C Valadão
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Rubens S Garcias
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Hermann A Rodrigues
- Departamento de Ciências Básicas da Vida, Instituto de Ciências da Vida, Universidade Federal de Juiz de Fora, Campus Governador Valadares, UFJF, Governador Valadares, MG, Brazil
| | - Jéssica N Andrade
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Vanessa P Teixeira
- Departamento de Fisiologia e Biofísica, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Lígia A Naves
- Departamento de Fisiologia e Biofísica, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Walter L G Cavalcante
- Departamento de Farmacologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Marcia Gallaci
- Departamento de Farmacologia, Instituto de Biociências, UNESP, Distrito de Rubião Jr., Botucatu, São Paulo, Brazil
| | - Silvia Guatimosim
- Departamento de Fisiologia e Biofísica, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | - Vânia F Prado
- Robarts Research Institute and Department of Physiology and Pharmacology and Anatomy & Cell Biology, University of Western Ontario, London, ON, Canada
| | - Marco A M Prado
- Robarts Research Institute and Department of Physiology and Pharmacology and Anatomy & Cell Biology, University of Western Ontario, London, ON, Canada
| | - Cristina Guatimosim
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
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Pietrancosta N, Djibo M, Daumas S, El Mestikawy S, Erickson JD. Molecular, Structural, Functional, and Pharmacological Sites for Vesicular Glutamate Transporter Regulation. Mol Neurobiol 2020; 57:3118-3142. [PMID: 32474835 PMCID: PMC7261050 DOI: 10.1007/s12035-020-01912-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Accepted: 03/30/2020] [Indexed: 12/11/2022]
Abstract
Vesicular glutamate transporters (VGLUTs) control quantal size of glutamatergic transmission and have been the center of numerous studies over the past two decades. VGLUTs contain two independent transport modes that facilitate glutamate packaging into synaptic vesicles and phosphate (Pi) ion transport into the synaptic terminal. While a transmembrane proton electrical gradient established by a vacuolar-type ATPase powers vesicular glutamate transport, recent studies indicate that binding sites and flux properties for chloride, potassium, and protons within VGLUTs themselves regulate VGLUT activity as well. These intrinsic ionic binding and flux properties of VGLUTs can therefore be modulated by neurophysiological conditions to affect levels of glutamate available for release from synapses. Despite their extraordinary importance, specific and high-affinity pharmacological compounds that interact with these sites and regulate VGLUT function, distinguish between the various modes of transport, and the different isoforms themselves, are lacking. In this review, we provide an overview of the physiologic sites for VGLUT regulation that could modulate glutamate release in an over-active synapse or in a disease state.
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Affiliation(s)
- Nicolas Pietrancosta
- Neuroscience Paris Seine - Institut de Biologie Paris Seine (NPS - IBPS) INSERM, CNRS, Sorbonne Université, Paris, France. .,Laboratoire des Biomolécules, Sorbonne Université, CNRS, ENS, LBM, 75005, Paris, France.
| | - Mahamadou Djibo
- Sorbonne Paris Cité, Université Paris Descartes, LCBPT, UMR 8601, 75006, Paris, France
| | - Stephanie Daumas
- Neuroscience Paris Seine - Institut de Biologie Paris Seine (NPS - IBPS) INSERM, CNRS, Sorbonne Université, Paris, France
| | - Salah El Mestikawy
- Neuroscience Paris Seine - Institut de Biologie Paris Seine (NPS - IBPS) INSERM, CNRS, Sorbonne Université, Paris, France. .,Douglas Hospital Research Center, Department of Psychiatry, McGill University, 6875 boulevard Lasalle, Verdun, Montreal, QC, Canada.
| | - Jeffrey D Erickson
- Neuroscience Center, Louisiana State University, New Orleans, LA, 70112, USA. .,Department of Pharmacology, Louisiana State University, New Orleans, LA, 70112, USA.
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Neuromuscular synapse degeneration without muscle function loss in the diaphragm of a murine model for Huntington's Disease. Neurochem Int 2018. [PMID: 29530757 DOI: 10.1016/j.neuint.2018.03.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Huntington's disease (HD) is an autosomal dominant neurodegenerative disease characterized by chorea, incoordination and psychiatric and behavioral symptoms. The leading cause of death in HD patients is aspiration pneumonia, associated with respiratory dysfunction, decreased respiratory muscle strength and dysphagia. Although most of the motor symptoms are derived from alterations in the central nervous system, some might be associated with changes in the components of motor units (MU). To explore this hypothesis, we evaluated morphofunctional aspects of the diaphragm muscle in a mouse model for HD (BACHD). We showed that the axons of the phrenic nerves were not affected in 12-months-old BACHD mice, but the axon terminals that form the neuromuscular junctions (NMJs) were more fragmented in these animals in comparison with the wild-type mice. In BACHD mice, the synaptic vesicles of the diaphragm NMJs presented a decreased exocytosis rate. Quantal content and quantal size were smaller and there was less synaptic depression whereas the estimated size of the readily releasable vesicle pool was not changed. At the ultrastructure level, the diaphragm NMJs of these mice presented fewer synaptic vesicles with flattened and oval shapes, which might be associated with the reduced expression of the vesicular acetylcholine transporter protein. Furthermore, mitochondria of the diaphragm muscle presented signs of degeneration in BACHD mice. Interestingly, despite all these cellular alterations, BACHD diaphragmatic function was not compromised, suggesting a higher resistance threshold of this muscle. A putative resistance mechanism may be protecting this vital muscle. Our data contribute to expanding the current understanding of the effects of mutated huntingtin in the neuromuscular synapse and the diaphragm muscle function.
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Macias-Medri AE, Liendo JA, Silva RJ. An electrostatic and probabilistic simulation model to describe neurosecretion at the synaptic scale. NETWORK (BRISTOL, ENGLAND) 2017; 28:53-73. [PMID: 29120672 DOI: 10.1080/0954898x.2017.1386806] [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: 06/07/2023]
Abstract
A hybrid simulation model (macro-molecular dynamics and Monte Carlo method) is proposed to reproduce neurosecretion and exocytosis. A theory has been developed for vesicular dynamics based on quasi-static electric interactions and a simple transition-state model for the vesicular fusion. Under the non-equilibrium electric conditions in an electrolytic fluid, it is considered that the motion of each synaptic vesicle is influenced by electrostatic forces exerted by the membranes of the synaptic bouton, other vesicles, the intracellular and intravesicular fluids, and external elements to the neuron. In addition, friction between each vesicle and its surrounding intracellular fluid is included in the theory, resulting in a drift type movement. To validate the vesicle equations of motion, a molecular dynamics method has been implemented, where the synaptic pool was replaced by a straight angle parallelepiped, the vesicles were represented by spheres and the fusion between each vesicle and the presynaptic membrane was simulated by a Monte Carlo type probabilistic change of state. Density profiles showing clusters of preferential activity as well as fusion distributions similar to the Poisson distributions associated with miniature end-plate potentials were obtained in the simulations.
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Affiliation(s)
- A E Macias-Medri
- a Departamento de Física , Universidade Federal do Paraná , Curitiba , Brazil
| | - Jacinto A Liendo
- b Physics Department , Simón Bolívar University , Baruta , Venezuela
| | - Ricardo J Silva
- c Instituto Montenegro para la Investigación y Desarrollo de las Neurociencias Cognitivas , Unidad Médica I de la Clínica San Francisco , Guayaquil , Ecuador
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Dunant Y, Gisiger V. Ultrafast and Slow Cholinergic Transmission. Different Involvement of Acetylcholinesterase Molecular Forms. Molecules 2017; 22:E1300. [PMID: 28777299 PMCID: PMC6152031 DOI: 10.3390/molecules22081300] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 07/21/2017] [Accepted: 07/22/2017] [Indexed: 02/06/2023] Open
Abstract
Acetylcholine (ACh), an ubiquitous mediator substance broadly expressed in nature, acts as neurotransmitter in cholinergic synapses, generating specific communications with different time-courses. (1) Ultrafast transmission. Vertebrate neuromuscular junctions (NMJs) and nerve-electroplaque junctions (NEJs) are the fastest cholinergic synapses; able to transmit brief impulses (1-4 ms) at high frequencies. The collagen-tailed A12 acetylcholinesterase is concentrated in the synaptic cleft of NMJs and NEJs, were it curtails the postsynaptic response by ultrafast ACh hydrolysis. Here, additional processes contribute to make transmission so rapid. (2) Rapid transmission. At peripheral and central cholinergic neuro-neuronal synapses, transmission involves an initial, relatively rapid (10-50 ms) nicotinic response, followed by various muscarinic or nicotinic effects. Acetylcholinesterase (AChE) being not concentrated within these synapses, it does not curtail the initial rapid response. In contrast, the late responses are controlled by a globular form of AChE (mainly G4-AChE), which is membrane-bound and/or secreted. (3) SlowAChsignalling. In non-neuronal systems, in muscarinic domains, and in most regions of the central nervous system (CNS), many ACh-releasing structures (cells, axon terminals, varicosities, boutons) do not form true synaptic contacts, most muscarinic and also part of nicotinic receptors are extra-synaptic, often situated relatively far from ACh releasing spots. A12-AChE being virtually absent in CNS, G4-AChE is the most abundant form, whose function appears to modulate the "volume" transmission, keeping ACh concentration within limits in time and space.
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Affiliation(s)
- Yves Dunant
- Département des Neurosciences Fondamentales, Faculté de Médecine, Université de Genève, CH-1211-Genève 4, Switzerland.
| | - Victor Gisiger
- Département de Pathologie et Biologie Cellulaire, Faculté de Médecine, Université de Montréal, Montréal QC H3C 3J7, Canada.
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de Aragão BC, Rodrigues HA, Valadão PAC, Camargo W, Naves LA, Ribeiro FM, Guatimosim C. Changes in structure and function of diaphragm neuromuscular junctions from BACHD mouse model for Huntington's disease. Neurochem Int 2016; 93:64-72. [DOI: 10.1016/j.neuint.2015.12.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Revised: 12/17/2015] [Accepted: 12/28/2015] [Indexed: 10/22/2022]
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Cash F, Vernon SW, Phelan P, Goodchild J, Baines RA. Central cholinergic synaptic vesicle loading obeys the set-point model in Drosophila. J Neurophysiol 2016; 115:843-50. [PMID: 26655826 DOI: 10.1152/jn.01053.2015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 12/09/2015] [Indexed: 11/22/2022] Open
Abstract
Experimental evidence shows that neurotransmitter release, from presynaptic terminals, can be regulated by altering transmitter load per synaptic vesicle (SV) and/or through change in the probability of vesicle release. The vesicular acetylcholine transporter (VAChT) loads acetylcholine into SVs at cholinergic synapses. We investigated how the VAChT affects SV content and release frequency at central synapses in Drosophila melanogaster by using an insecticidal compound, 5Cl-CASPP, to block VAChT and by transgenic overexpression of VAChT in cholinergic interneurons. Decreasing VAChT activity produces a decrease in spontaneous SV release with no change to quantal size and no decrease in the number of vesicles at the active zone. This suggests that many vesicles are lacking in neurotransmitter. Overexpression of VAChT leads to increased frequency of SV release, but again with no change in quantal size or vesicle number. This indicates that loading of central cholinergic SVs obeys the "set-point" model, rather than the "steady-state" model that better describes loading at the vertebrate neuromuscular junction. However, we show that expression of a VAChT polymorphism lacking one glutamine residue in a COOH-terminal polyQ domain leads to increased spontaneous SV release and increased quantal size. This effect spotlights the poly-glutamine domain as potentially being important for sensing the level of neurotransmitter in cholinergic SVs.
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Affiliation(s)
- Francesca Cash
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Samuel W Vernon
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Pauline Phelan
- School of Biosciences, University of Kent, Kent, United Kingdom; and
| | - Jim Goodchild
- Syngenta Crop Protection Research, Bracknell, Berkshire, United Kingdom
| | - Richard A Baines
- Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom;
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Rodrigues HA, Fonseca MDC, Camargo WL, Lima PMA, Martinelli PM, Naves LA, Prado VF, Prado MAM, Guatimosim C. Reduced expression of the vesicular acetylcholine transporter and neurotransmitter content affects synaptic vesicle distribution and shape in mouse neuromuscular junction. PLoS One 2013; 8:e78342. [PMID: 24260111 PMCID: PMC3832638 DOI: 10.1371/journal.pone.0078342] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 09/18/2013] [Indexed: 12/03/2022] Open
Abstract
In vertebrates, nerve muscle communication is mediated by the release of the neurotransmitter acetylcholine packed inside synaptic vesicles by a specific vesicular acetylcholine transporter (VAChT). Here we used a mouse model (VAChT KDHOM) with 70% reduction in the expression of VAChT to investigate the morphological and functional consequences of a decreased acetylcholine uptake and release in neuromuscular synapses. Upon hypertonic stimulation, VAChT KDHOM mice presented a reduction in the amplitude and frequency of miniature endplate potentials, FM 1–43 staining intensity, total number of synaptic vesicles and altered distribution of vesicles within the synaptic terminal. In contrast, under electrical stimulation or no stimulation, VAChT KDHOM neuromuscular junctions did not differ from WT on total number of vesicles but showed altered distribution. Additionally, motor nerve terminals in VAChT KDHOM exhibited small and flattened synaptic vesicles similar to that observed in WT mice treated with vesamicol that blocks acetylcholine uptake. Based on these results, we propose that decreased VAChT levels affect synaptic vesicle biogenesis and distribution whereas a lower ACh content affects vesicles shape.
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Affiliation(s)
- Hermann A. Rodrigues
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Matheus de C. Fonseca
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Wallace L. Camargo
- Departamento de Fisiologia e Biofísica, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Patrícia M. A. Lima
- Departamento de Engenharia de Biossistemas, Universidade Federal de São João Del Rei, São João Del Rei, Brasil
| | - Patrícia M. Martinelli
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Lígia A. Naves
- Departamento de Fisiologia e Biofísica, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Vânia F. Prado
- Robarts Research Institute and Department of Physiology and Pharmacology and Anatomy & Cell Biology, University of Western Ontario, London, ON, Canada
| | - Marco A. M. Prado
- Robarts Research Institute and Department of Physiology and Pharmacology and Anatomy & Cell Biology, University of Western Ontario, London, ON, Canada
| | - Cristina Guatimosim
- Departamento de Morfologia, ICB, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
- * E-mail:
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9
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Rodrigues HA, Lima RF, Fonseca MDC, Amaral EA, Martinelli PM, Naves LA, Gomez MV, Kushmerick C, Prado MAM, Guatimosim C. Membrane cholesterol regulates different modes of synaptic vesicle release and retrieval at the frog neuromuscular junction. Eur J Neurosci 2013; 38:2978-87. [PMID: 23841903 DOI: 10.1111/ejn.12300] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2013] [Revised: 06/04/2013] [Accepted: 06/09/2013] [Indexed: 12/14/2022]
Abstract
We investigated the effects of cholesterol removal on spontaneous and KCl-evoked synaptic vesicle recycling at the frog neuromuscular junction. Cholesterol removal by methyl-β-cyclodextrin (MβCD) induced an increase in the frequency of miniature end-plate potentials (MEPPs) and spontaneous destaining of synaptic vesicles labeled with the styryl dye FM1-43. Treatment with MβCD also increased the size of MEPPs without causing significant changes in nicotinic receptor clustering. At the ultrastructural level, synaptic vesicles from nerve terminals treated with MβCD were larger than those from control. In addition, treatment with MβCD reduced the fusion of synaptic vesicles that are mobilized during KCl-evoked stimulation, but induced recycling of those vesicles that fuse spontaneously. We therefore suggest that MβCD might favor the release of vesicles that belong to a pool that is different from that involved in the KCl-evoked release. These results reveal fundamental differences in the synaptic vesicle cycle for spontaneous and evoked release, and suggest that deregulation of cholesterol affects synaptic vesicle biogenesis and increases transmitter packing.
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Affiliation(s)
- Hermann A Rodrigues
- Departamento de Morfologia, Universidade Federal de Minas Gerais, Av Antônio Carlos 6627, Belo Horizonte, MG 31270-901, Brasil
| | - Ricardo F Lima
- Departamento de Fisiologia e Biofísica, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Matheus de C Fonseca
- Departamento de Morfologia, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Belo Horizonte, MG, 31270-901, Brasil
| | - Ernani A Amaral
- Departamento de Morfologia, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Belo Horizonte, MG, 31270-901, Brasil
| | - Patrícia M Martinelli
- Departamento de Morfologia, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Belo Horizonte, MG, 31270-901, Brasil
| | - Lígia A Naves
- Departamento de Fisiologia e Biofísica, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Marcus V Gomez
- Núcleo Santa Casa de Pós-Graduação, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil.,INCT Molecular Medicine, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Christopher Kushmerick
- Departamento de Fisiologia e Biofísica, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil
| | - Marco A M Prado
- Robarts Research Institute and Department of Physiology and Pharmacology and Anatomy & Cell Biology, University of Western Ontario, London, ON, Canada
| | - Cristina Guatimosim
- Departamento de Morfologia, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Belo Horizonte, MG, 31270-901, Brasil
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Abreu BJ, Leite LF, Oliveira DL, Amaral E. Synaptic vesicle cycling is not impaired in a glutamatergic and a cholinergic synapse that exhibit deficits in acidification and filling. BRAZ J PHARM SCI 2012. [DOI: 10.1590/s1984-82502012000100017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The purpose of the present work was to investigate synaptic vesicle trafficking when vesicles exhibit alterations in filling and acidification in two different synapses: a cholinergic frog neuromuscular junction and a glutamatergic ribbon-type nerve terminal in the retina. These synapses display remarkable structural and functional differences, and the mechanisms regulating synaptic vesicle cycling might also differ between them. The lipophilic styryl dye FM1-43 was used to monitor vesicle trafficking. Both preparations were exposed to pharmacological agents that collapse ΔpH (NH4Cl and methylamine) or the whole ΔµH+ (bafilomycin), a necessary situation to provide the driving force for neurotransmitter accumulation into synaptic vesicles. The results showed that FM1-43 loading and unloading in neuromuscular junctions did not differ statistically between control and experimental conditions (P > 0.05). Also, FM1-43 labeling in bipolar cell terminals proved highly similar under all conditions tested. Despite remarkable differences in both experimental models, the present findings show that acidification and filling are not required for normal vesicle trafficking in either synapse.
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11
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Fast homeostatic plasticity of inhibition via activity-dependent vesicular filling. PLoS One 2008; 3:e2979. [PMID: 18714334 PMCID: PMC2495031 DOI: 10.1371/journal.pone.0002979] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2008] [Accepted: 07/14/2008] [Indexed: 11/30/2022] Open
Abstract
Synaptic activity in the central nervous system undergoes rapid state-dependent changes, requiring constant adaptation of the homeostasis between excitation and inhibition. The underlying mechanisms are, however, largely unclear. Chronic changes in network activity result in enhanced production of the inhibitory transmitter GABA, indicating that presynaptic GABA content is a variable parameter for homeostatic plasticity. Here we tested whether such changes in inhibitory transmitter content do also occur at the fast time scale required to ensure inhibition-excitation-homeostasis in dynamic cortical networks. We found that intense stimulation of afferent fibers in the CA1 region of mouse hippocampal slices yielded a rapid and lasting increase in quantal size of miniature inhibitory postsynaptic currents. This potentiation was mediated by the uptake of GABA and glutamate into presynaptic endings of inhibitory interneurons (the latter serving as precursor for the synthesis of GABA). Thus, enhanced release of inhibitory and excitatory transmitters from active networks leads to enhanced presynaptic GABA content. Thereby, inhibitory efficacy follows local neuronal activity, constituting a negative feedback loop and providing a mechanism for rapid homeostatic scaling in cortical circuits.
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12
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Glial-toxin-mediated disruption of spinal cord locomotor network function and its modulation by 5-HT. Neuroscience 2008; 153:1332-43. [PMID: 18440149 DOI: 10.1016/j.neuroscience.2008.03.034] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2007] [Revised: 03/18/2008] [Accepted: 03/19/2008] [Indexed: 11/22/2022]
Abstract
While it is established that glial cells actively influence neuronal and synaptic properties, the functional effects of glial-neuronal interactions are still not well understood. To address the role of glia at the network level we have examined the effects of the specific gliotoxin L-aminoadipic acid on the locomotor network output and cellular and synaptic properties in the lamprey spinal cord. The gliotoxic effect of aminoadipic acid was associated with a specific depolarization of glial cells. Aminoadipic acid depolarized the membrane potential of spinal cord neurons, suggesting a functional link between glia and neurons. The depolarization was significantly reduced by glutamate receptor antagonists in adults, but by gap junction blockers in larvae, suggesting a developmental difference in glial-neuronal interactions. Aminoadipic acid also reduced the amplitude of monosynaptic excitatory postsynaptic potentials (EPSPs), an effect that was not associated with changes in the presynaptic release probability or postsynaptic response to glutamate. These cellular and synaptic effects of aminoadipic acid were associated with disruption of the locomotor network output. This could not be accounted for by changes in glutamate uptake or potassium buffering by glia, suggesting a direct role for glia in the network. Interestingly, we found that the aminoadipic acid-evoked disruption of network activity and reduction of monosynaptic EPSP amplitudes did not occur in the presence of the endogenous spinal modulator 5-HT. These results thus provide evidence for an active functional role for glial cells in spinal cord locomotor networks, and suggest a potential glial modulatory effect of 5-HT.
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13
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Lu B, Zhou YC, Huber GA, Bond SD, Holst MJ, McCammon JA. Electrodiffusion: a continuum modeling framework for biomolecular systems with realistic spatiotemporal resolution. J Chem Phys 2007; 127:135102. [PMID: 17919055 DOI: 10.1063/1.2775933] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A computational framework is presented for the continuum modeling of cellular biomolecular diffusion influenced by electrostatic driving forces. This framework is developed from a combination of state-of-the-art numerical methods, geometric meshing, and computer visualization tools. In particular, a hybrid of (adaptive) finite element and boundary element methods is adopted to solve the Smoluchowski equation (SE), the Poisson equation (PE), and the Poisson-Nernst-Planck equation (PNPE) in order to describe electrodiffusion processes. The finite element method is used because of its flexibility in modeling irregular geometries and complex boundary conditions. The boundary element method is used due to the convenience of treating the singularities in the source charge distribution and its accurate solution to electrostatic problems on molecular boundaries. Nonsteady-state diffusion can be studied using this framework, with the electric field computed using the densities of charged small molecules and mobile ions in the solvent. A solution for mesh generation for biomolecular systems is supplied, which is an essential component for the finite element and boundary element computations. The uncoupled Smoluchowski equation and Poisson-Boltzmann equation are considered as special cases of the PNPE in the numerical algorithm, and therefore can be solved in this framework as well. Two types of computations are reported in the results: stationary PNPE and time-dependent SE or Nernst-Planck equations solutions. A biological application of the first type is the ionic density distribution around a fragment of DNA determined by the equilibrium PNPE. The stationary PNPE with nonzero flux is also studied for a simple model system, and leads to an observation that the interference on electrostatic field of the substrate charges strongly affects the reaction rate coefficient. The second is a time-dependent diffusion process: the consumption of the neurotransmitter acetylcholine by acetylcholinesterase, determined by the SE and a single uncoupled solution of the Poisson-Boltzmann equation. The electrostatic effects, counterion compensation, spatiotemporal distribution, and diffusion-controlled reaction kinetics are analyzed and different methods are compared.
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Affiliation(s)
- Benzhuo Lu
- Howard Hughes Medical Institute, University of California at San Diego, La Jolla, California 92093-0365, USA.
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14
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Brunk I, Höltje M, von Jagow B, Winter S, Sternberg J, Blex C, Pahner I, Ahnert-Hilger G. Regulation of vesicular monoamine and glutamate transporters by vesicle-associated trimeric G proteins: new jobs for long-known signal transduction molecules. Handb Exp Pharmacol 2007:305-25. [PMID: 16722242 DOI: 10.1007/3-540-29784-7_15] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Neurotransmitters of neurons and neuroendocrine cells are concentrated first in the cytosol and then in either small synaptic vesicles ofpresynaptic terminals or in secretory vesicles by the activity of specific transporters of the plasma and the vesicular membrane, respectively. In the central nervous system the postsynaptic response depends--amongst other parameters-on the amount of neurotransmitter stored in a given vesicle. Neurotransmitter packets (quanta) vary over a wide range which may be also due to a regulation of vesicular neurotransmitter filling. Vesicular filling is regulated by the availability of transmitter molecules in the cytoplasm, the amount of transporter molecules and an electrochemical proton-mediated gradient over the vesicular membrane. In addition, it is modulated by vesicle-associated heterotrimeric G proteins, Galphao2 and Galphaq. Galphao2 and Galphaq regulate vesicular monoamine transporter (VMAT) activities in brain and platelets, respectively. Galphao2 also regulates vesicular glutamate transporter (VGLUT) activity by changing its chloride dependence. It appears that the vesicular content activates the G protein, suggesting a signal transduction from the luminal site which might be mediated by a vesicular G protein-coupled receptor or as an alternative possibility by the transporter itself. Thus, G proteins control transmitter storage and thereby probablylink the regulation of the vesicular content to intracellular signal cascades.
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Affiliation(s)
- I Brunk
- AG Funktionelle Zellbiologie, Institut für Integrative Neuroanatomie, Centrum für Anatomie, Charité, Universitätsmedizin Berlin, Berlin, Germany
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15
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Liang SL, Carlson GC, Coulter DA. Dynamic regulation of synaptic GABA release by the glutamate-glutamine cycle in hippocampal area CA1. J Neurosci 2006; 26:8537-48. [PMID: 16914680 PMCID: PMC2471868 DOI: 10.1523/jneurosci.0329-06.2006] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Vesicular GABA and intraterminal glutamate concentrations are in equilibrium, suggesting inhibitory efficacy may depend on glutamate availability. Two main intraterminal glutamate sources are uptake by neuronal glutamate transporters and glutamine synthesized through the astrocytic glutamate-glutamine cycle. We examined the involvement of the glutamate-glutamine cycle in modulating GABAergic synaptic efficacy. In the absence of neuronal activity, disruption of the glutamate-glutamine cycle by blockade of neuronal glutamine transport with alpha-(methylamino) isobutyric acid (MeAIB; 5 mM) or inhibition of glutamine synthesis in astrocytes with methionine sulfoximine (MSO; 1.5 mM) had no effect on miniature IPSCs recorded in hippocampal area CA1 pyramidal neurons. However, after a period of moderate synaptic activity, application of MeAIB, MSO, or dihydrokainate (250 microM; an astrocytic glutamate transporter inhibitor) significantly reduced evoked IPSC (eIPSC) amplitudes. The MSO effect could be reversed by exogenous application of glutamine (5 mM), whereas glutamine could not rescue the eIPSC decreases induced by the neuronal glutamine transporter inhibitor MeAIB. The activity-dependent reduction in eIPSCs by glutamate-glutamine cycle blockers was accompanied by an enhanced blocking effect of the low-affinity GABA(A) receptor antagonist, TPMPA [1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid], consistent with diminished GABA release. We further corroborated this hypothesis by examining MeAIB effects on minimal stimulation-evoked quantal IPSCs (meIPSCs). We found that, in MeAIB-containing medium, moderate stimulation induced depression in potency of meIPSCs but no change in release probability, consistent with reduced vesicular GABA content. We conclude that the glutamate-glutamine cycle is a major contributor to synaptic GABA release under physiological conditions, which dynamically regulates inhibitory synaptic strength.
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16
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Colletier JP, Fournier D, Greenblatt HM, Stojan J, Sussman JL, Zaccai G, Silman I, Weik M. Structural insights into substrate traffic and inhibition in acetylcholinesterase. EMBO J 2006; 25:2746-56. [PMID: 16763558 PMCID: PMC1500847 DOI: 10.1038/sj.emboj.7601175] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2005] [Accepted: 05/08/2006] [Indexed: 11/08/2022] Open
Abstract
Acetylcholinesterase (AChE) terminates nerve-impulse transmission at cholinergic synapses by rapid hydrolysis of the neurotransmitter, acetylcholine. Substrate traffic in AChE involves at least two binding sites, the catalytic and peripheral anionic sites, which have been suggested to be allosterically related and involved in substrate inhibition. Here, we present the crystal structures of Torpedo californica AChE complexed with the substrate acetylthiocholine, the product thiocholine and a nonhydrolysable substrate analogue. These structures provide a series of static snapshots of the substrate en route to the active site and identify, for the first time, binding of substrate and product at both the peripheral and active sites. Furthermore, they provide structural insight into substrate inhibition in AChE at two different substrate concentrations. Our structural data indicate that substrate inhibition at moderate substrate concentration is due to choline exit being hindered by a substrate molecule bound at the peripheral site. At the higher concentration, substrate inhibition arises from prevention of exit of acetate due to binding of two substrate molecules within the active-site gorge.
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Affiliation(s)
- Jacques-Philippe Colletier
- Laboratoire de Biophysique Moléculaire, Institut de Biologie Structurale (CEA/CNRS/UJF), Grenoble Cedex, France
| | - Didier Fournier
- Groupe de Biotechnologie des Protéines, Institut de Pharmacologie et de Biologie Structurale (CNRS/UPS), Toulouse, France
| | - Harry M Greenblatt
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Jure Stojan
- Medical Faculty, Institute of Biochemistry, University of Ljubljana, Ljubljana, Slovenia
| | - Joel L Sussman
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Giuseppe Zaccai
- Laboratoire de Biophysique Moléculaire, Institut de Biologie Structurale (CEA/CNRS/UJF), Grenoble Cedex, France
- Institut Laue-Langevin, Grenoble Cedex, France
| | - Israel Silman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
| | - Martin Weik
- Laboratoire de Biophysique Moléculaire, Institut de Biologie Structurale (CEA/CNRS/UJF), Grenoble Cedex, France
- Laboratoire de Biophysique Moléculaire, Institut de Biologie Structurale (CEA/CNRS/UJF), 41 rue Jules Horowitz, 38027 Grenoble Cedex 1, France. Tel.: +33 4 38 78 95 69; Fax: +33 4 38 78 54 94; E-mail:
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17
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Winter S, Brunk I, Walther DJ, Höltje M, Jiang M, Peter JU, Takamori S, Jahn R, Birnbaumer L, Ahnert-Hilger G. Galphao2 regulates vesicular glutamate transporter activity by changing its chloride dependence. J Neurosci 2006; 25:4672-80. [PMID: 15872115 PMCID: PMC6725018 DOI: 10.1523/jneurosci.0549-05.2005] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Classical neurotransmitters, including monoamines, acetylcholine, glutamate, GABA, and glycine, are loaded into synaptic vesicles by means of specific transporters. Vesicular monoamine transporters are under negative regulation by alpha subunits of trimeric G-proteins, including Galpha(o2) and Galpha(q). Furthermore, glutamate uptake, mediated by vesicular glutamate transporters (VGLUTs), is decreased by the nonhydrolysable GTP-analog guanylylimidodiphosphate. Using mutant mice lacking various Galpha subunits, including Galpha(o1), Galpha(o2), Galpha(q), and Galpha11, and a Galpha(o2)-specific monoclonal antibody, we now show that VGLUTs are exclusively regulated by Galpha(o2). G-protein activation does not affect the electrochemical proton gradient serving as driving force for neurotransmitter uptake; rather, Galpha(o2) exerts its action by specifically affecting the chloride dependence of VGLUTs. All VGLUTs show maximal activity at approximately 5 mm chloride. Activated Galpha(o2) shifts this maximum to lower chloride concentrations. In contrast, glutamate uptake by vesicles isolated from Galpha(o2-/-) mice have completely lost chloride activation. Thus, Galpha(o2) acts on a putative regulatory chloride binding domain that appears to modulate transport activity of vesicular glutamate transporters.
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Affiliation(s)
- Sandra Winter
- AG Funktionelle Zellbiologie, Centrum für Anatomie, Charité Universitätsmedizin Berlin, D-10115 Berlin, Germany
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18
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Erickson JD, De Gois S, Varoqui H, Schafer MKH, Weihe E. Activity-dependent regulation of vesicular glutamate and GABA transporters: a means to scale quantal size. Neurochem Int 2006; 48:643-9. [PMID: 16546297 DOI: 10.1016/j.neuint.2005.12.029] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2005] [Accepted: 12/21/2005] [Indexed: 11/28/2022]
Abstract
The functional balance of glutamatergic and GABAergic signaling in neuronal cortical circuits is under homeostatic control. That is, prolonged alterations of global network activity leads to opposite changes in quantal amplitude at glutamatergic and GABAergic synapses. Such scaling of excitatory and inhibitory transmission within cortical circuits serves to restore and maintain a constant spontaneous firing rate of pyramidal neurons. Our recent work shows that this includes alterations in the levels of expression of vesicular glutamate (VGLUT1 and VGLUT2) and GABA (VIAAT) transporters. Other vesicle markers, such as synaptophysin or synapsin, are not regulated in this way. Endogenous regulation at the level of mRNA and synaptic protein controls the number of transporters per vesicle and hence, the level of vesicle filling with transmitter. Bidirectional and opposite activity-dependent regulation of VGLUT1 and VIAAT expression would serve to adjust the balance of glutamate and GABA release and therefore the level of postsynaptic receptor saturation. In some excitatory neurons and synapses, co-expression of VGLUT1 and VGLUT2 occurs. Bidirectional and opposite changes in the levels of two excitatory vesicular transporters would enable individual neocortical neurons to scale up or scale down the level of vesicular glutamate storage, and thus, the amount available for release at individual synapses. Regulated vesicular transmitter storage and release via selective changes in the level of expression of vesicular glutamate and GABA transporters indicates that homeostatic plasticity of synaptic strength at cortical synapses includes presynaptic elements.
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Affiliation(s)
- Jeffrey D Erickson
- Neuroscience Center, Louisiana State University Health Sciences Center, New Orleans, 70112, USA.
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19
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De Gois S, Schäfer MKH, Defamie N, Chen C, Ricci A, Weihe E, Varoqui H, Erickson JD. Homeostatic scaling of vesicular glutamate and GABA transporter expression in rat neocortical circuits. J Neurosci 2006; 25:7121-33. [PMID: 16079394 PMCID: PMC6725238 DOI: 10.1523/jneurosci.5221-04.2005] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Homeostatic control of pyramidal neuron firing rate involves a functional balance of feedforward excitation and feedback inhibition in neocortical circuits. Here, we reveal a dynamic scaling in vesicular excitatory (vesicular glutamate transporters VGLUT1 and VGLUT2) and inhibitory (vesicular inhibitory amino acid transporter VIAAT) transporter mRNA and synaptic protein expression in rat neocortical neuronal cultures, using a well established in vitro protocol to induce homeostatic plasticity. During the second and third week of synaptic differentiation, the predominant vesicular transporters expressed in neocortical neurons, VGLUT1 and VIAAT, are both dramatically upregulated. In mature cultures, VGLUT1 and VIAAT exhibit bidirectional and opposite regulation by prolonged activity changes. Endogenous coregulation during development and homeostatic scaling of the expression of the transporters in functionally differentiated cultures may serve to control vesicular glutamate and GABA filling and adjust functional presynaptic excitatory/inhibitory balance. Unexpectedly, hyperexcitation in differentiated cultures triggers a striking increase in VGLUT2 mRNA and synaptic protein, whereas decreased excitation reduces levels. VGLUT2 mRNA and protein are expressed in subsets of VGLUT1-encoded neocortical neurons that we identify in primary cultures and in neocortex in situ and in vivo. After prolonged hyperexcitation, downregulation of VGLUT1/synaptophysin intensity ratios at most synapses is observed, whereas a subset of VGLUT1-containing boutons selectively increase the expression of VGLUT2. Bidirectional and opposite regulation of VGLUT1 and VGLUT2 by activity may serve as positive or negative feedback regulators for cortical synaptic transmission. Intracortical VGLUT1/VGLUT2 coexpressing neurons have the capacity to independently modulate the level of expression of either transporter at discrete synapses and therefore may serve as a plastic interface between subcortical thalamic input (VGLUT2) and cortical output (VGLUT1) neurons.
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Affiliation(s)
- Stéphanie De Gois
- Neuroscience Center of Excellence, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA
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20
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Croft BG, Fortin GD, Corera AT, Edwards RH, Beaudet A, Trudeau LE, Fon EA. Normal biogenesis and cycling of empty synaptic vesicles in dopamine neurons of vesicular monoamine transporter 2 knockout mice. Mol Biol Cell 2004; 16:306-15. [PMID: 15496457 PMCID: PMC539174 DOI: 10.1091/mbc.e04-07-0559] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The neuronal isoform of vesicular monoamine transporter, VMAT2, is responsible for packaging dopamine and other monoamines into synaptic vesicles and thereby plays an essential role in dopamine neurotransmission. Dopamine neurons in mice lacking VMAT2 are unable to store or release dopamine from their synaptic vesicles. To determine how VMAT2-mediated filling influences synaptic vesicle morphology and function, we examined dopamine terminals from VMAT2 knockout mice. In contrast to the abnormalities reported in glutamatergic terminals of mice lacking VGLUT1, the corresponding vesicular transporter for glutamate, we found that the ultrastructure of dopamine terminals and synaptic vesicles in VMAT2 knockout mice were indistinguishable from wild type. Using the activity-dependent dyes FM1-43 and FM2-10, we also found that synaptic vesicles in dopamine neurons lacking VMAT2 undergo endocytosis and exocytosis with kinetics identical to those seen in wild-type neurons. Together, these results demonstrate that dopamine synaptic vesicle biogenesis and cycling are independent of vesicle filling with transmitter. By demonstrating that such empty synaptic vesicles can cycle at the nerve terminal, our study suggests that physiological changes in VMAT2 levels or trafficking at the synapse may regulate dopamine release by altering the ratio of fillable-to-empty synaptic vesicles, as both continue to cycle in response to neural activity.
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Affiliation(s)
- Benjamin G Croft
- Centre for Neuronal Survival and Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
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21
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French SJ, Totterdell S. Quantification of morphological differences in boutons from different afferent populations to the nucleus accumbens. Brain Res 2004; 1007:167-77. [PMID: 15064148 DOI: 10.1016/j.brainres.2004.02.018] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/11/2004] [Indexed: 11/16/2022]
Abstract
The nucleus accumbens (Acb) receives convergent glutamatergic inputs from the prefrontal cortex (PFC), central thalamus, basolateral amygdala and the ventral subiculum of the hippocampus. The principal neurons of the nucleus accumbens are modulated by specific sets of convergent afferent inputs, the local circuit neurons also receive a substantial number of glutamatergic inputs, but the full complement of these has yet to be established. The aim of these studies was to define characteristics of the different glutamatergic afferent inputs to the nucleus accumbens that would aid their identification. To enable the characterisation of the glutamatergic inputs to nucleus accumbens neurons we first labelled the four main glutamatergic sources of afferent input to the accumbens with the anterograde tracer biotinylated dextran amine (BDA). Using an unbiased systematic sampling method, the morphological characteristics of their synaptic boutons were measured and assessed at the electron microscopic level. From the criteria assessed, a comparison of the four afferent sources was made, characteristics such as bouton size and vesicle density had significantly different population means, however, the only characteristic that allowed discrimination between the four major glutamatergic afferent to the nucleus accumbens was that of vesicle size. The vesicles in boutons from amygdala were larger than the subiculum which, in turn, were larger than the prefrontal cortex, the thalamus were the smallest in size. The methods used also allow a comparison of the relative frequency of different sized postsynaptic structures targeted, the prefrontal cortex almost exclusively targeted spines whereas the thalamus and the subiculum, in addition to spines, targeted proximal and distal dendrites.
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Affiliation(s)
- Sarah Jane French
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.
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22
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Rheuben MB, Autio DM, Xu YF, Atchison WD. Morphometric characterization of the neuromuscular junction of rodents intoxicated with 2,4-dithiobiuret: evidence that nerve terminal recycling processes contribute to muscle weakness. Toxicol Appl Pharmacol 2004; 196:266-86. [PMID: 15081273 DOI: 10.1016/j.taap.2004.01.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2003] [Accepted: 01/13/2004] [Indexed: 11/29/2022]
Abstract
2,4-Dithiobiuret (DTB) causes ascending motor weakness when given chronically to rodents. In muscles of animals with DTB-induced weakness, quantal release of acetylcholine (ACh) is impaired. We examined in detail the structural changes that occurred at neuromuscular junctions and their associated Schwann cells of extensor digitorum longus (EDL) muscles of male rats treated with DTB to the onset of muscle weakness, 5-8 days. Our objective was to assess the involvement of the Schwann cells and to determine the most likely primary targets of DTB. At the onset of muscle weakness, nerve terminals exhibited some enlarged regions, but did not sprout. Terminal Schwann cells became flatter and expanded to cover most of the endplate. The extent of invasion of the synaptic cleft by Schwann cell processes was not significantly different from controls; extension of Schwann cell sprouts away from the junction was not seen. Thus, the morphology of the Schwann cells, although clearly affected by DTB, does not suggest that they contribute directly to the physiological defects of DTB-treated terminals. Abnormal tubulovesicular structures or tangles of neurofilaments were clustered in the centers of about 25% of treated terminals. Fewer synaptic vesicles occupied the region opposite the postsynaptic folds. Vesicle volumes were variable and included some very large vesicles, corresponding with the variable MEPP amplitudes reported previously for terminals of DTB-treated rodents. The postsynaptic area stained by rhodamine-labeled alpha-bungarotoxin expanded with terminal swelling, apparently by unpleating of the postsynaptic folds. No loss of ACh receptors or spread of ACh receptors beyond terminal boundaries was detected. Morphometric data are consistent with the conclusion that DTB affects, either directly or indirectly, vesicular release of ACh and the subsequent vesicular recycling process.
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Affiliation(s)
- Mary B Rheuben
- Department of Pathobiology and Diagnostic Investigation, Michigan State University, East Lansing, MI 48824, USA
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23
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Ahnert-Hilger G, Höltje M, Pahner I, Winter S, Brunk I. Regulation of vesicular neurotransmitter transporters. Rev Physiol Biochem Pharmacol 2004; 150:140-60. [PMID: 14517724 DOI: 10.1007/s10254-003-0020-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Neurotransmitters are key molecules of neurotransmission. They are concentrated first in the cytosol and then in small synaptic vesicles of presynaptic terminals by the activity of specific neurotransmitter transporters of the plasma and the vesicular membrane, respectively. It has been shown that postsynaptic responses to single neurotransmitter packets vary over a wide range, which may be due to a regulation of vesicular neurotransmitter filling. Vesicular filling depends on the availability of transmitter molecules in the cytoplasm and the active transport into secretory vesicles relying on a proton gradient. In addition, it is modulated by vesicle-associated heterotrimeric G proteins, Galphao2 and Galphaq, which regulate VMAT activities in brain and platelets, respectively, and may also be involved in the regulation of VGLUTs. It appears that the vesicular content activates the G protein, suggesting a signal transduction form the luminal site which might be mediated by a vesicular G-protein coupled receptor or, as an alternative, possibly by the transporter itself. These novel functions of G proteins in the control of transmitter storage may link regulation of the vesicular content to intracellular signal cascades.
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Affiliation(s)
- G Ahnert-Hilger
- Institut für Anatomie und Neurowissenschaftliches Zentrum der Charité, Humboldt-Universität zu Berlin, Philippstr. 12, 10115 Berlin, Germany.
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24
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Axmacher N, Stemmler M, Engel D, Draguhn A, Ritz R. Transmitter Metabolism as a Mechanism of Synaptic Plasticity: A Modeling Study. J Neurophysiol 2004; 91:25-39. [PMID: 13679396 DOI: 10.1152/jn.00797.2003] [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] [Indexed: 11/22/2022] Open
Abstract
The nervous system adapts to experience by changes in synaptic strength. The mechanisms of synaptic plasticity include changes in the probability of transmitter release and in postsynaptic responsiveness. Experimental and neuropharmacological evidence points toward a third variable in synaptic efficacy: changes in presynaptic transmitter concentration. Several groups, including our own, have reported changes in the amplitude and frequency of postsynaptic (miniature) events indicating that alterations in transmitter content cause alterations in vesicular transmitter content and vesicle dynamics. It is, however, not a priori clear how transmitter metabolism will affect vesicular transmitter content and how this in turn will affect pre- and postsynaptic functions. We therefore have constructed a model of the presynaptic terminal incorporating vesicular transmitter loading and the presynaptic vesicle cycle. We hypothesize that the experimentally observed synaptic plasticity after changes in transmitter metabolism puts predictable restrictions on vesicle loading, cytoplasmic–vesicular transmitter concentration gradient, and on vesicular cycling or release. The results of our model depend on the specific mechanism linking presynaptic transmitter concentration to vesicular dynamics, that is, alteration of vesicle maturation or alteration of release. It also makes a difference whether differentially filled vesicles are detected and differentially processed within the terminal or whether vesicle filling acts back onto the terminal by presynaptic autoreceptors. Therefore, the model allows one to decide, at a given synapse, how transmitter metabolism is linked to presynaptic function and efficacy.
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Affiliation(s)
- Nikolai Axmacher
- Johannes-Müller-Institut für Physiologie, Humboldt-Universität Berlin, 10117 Berlin, Germany
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25
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Van der Kloot W. Loading and recycling of synaptic vesicles in the Torpedo electric organ and the vertebrate neuromuscular junction. Prog Neurobiol 2003; 71:269-303. [PMID: 14698765 DOI: 10.1016/j.pneurobio.2003.10.003] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
In vertebrate motor nerve terminals and in the electromotor nerve terminals of Torpedo there are two major pools of synaptic vesicles: readily releasable and reserve. The electromotor terminals differ in that the reserve vesicles are twice the diameter of the readily releasable vesicles. The vesicles contain high concentrations of ACh and ATP. Part of the ACh is brought into the vesicle by the vesicular ACh transporter, VAChT, which exchanges two protons for each ACh, but a fraction of the ACh seems to be accumulated by different, unexplored mechanisms. Most of the vesicles in the terminals do not exchange ACh or ATP with the axoplasm, although ACh and ATP are free in the vesicle interior. The VAChT is controlled by a multifaceted regulatory complex, which includes the proteoglycans that characterize the cholinergic vesicles. The drug (-)-vesamicol binds to a site on the complex and blocks ACh exchange. Only 10-20% of the vesicles are in the readily releasable pool, which therefore is turned over fairly rapidly by spontaneous quantal release. The turnover can be followed by the incorporation of false transmitters into the recycling vesicles, and by the rate of uptake of FM dyes, which have some selectivity for the two recycling pathways. The amount of ACh loaded into recycling vesicles in the readily releasable pool decreases during stimulation. The ACh content of the vesicles can be varied over eight-fold range without changing vesicle size.
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Affiliation(s)
- William Van der Kloot
- Department of Physiology and Biophysics, SUNY at Stony Brook, 8661 SUNT, Stony Brook, NY 11794-8661, USA.
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26
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Van der Kloot W. A chloride channel blocker reduces acetylcholine uptake into synaptic vesicles at the frog neuromuscular junction. Brain Res 2003; 961:287-9. [PMID: 12531496 DOI: 10.1016/s0006-8993(02)03954-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A key mechanism for loading acetylcholine (ACh(+)) into synaptic vesicles uses energy to transport H(+) into the vesicle interior and then exchanges H(+) for ACh(+). This mechanism requires anions to follow the H(+) into the vesicles to prevent the building up of an overwhelming electrical gradient across the vesicle membrane. Frog nerve-muscle preparations were treated with hypertonic solution in which sodium gluconate was the major constituent, which substantially increases the sizes of the quanta by increasing their ACh(+) content. The Cl(-) channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) antagonized the increases in quantal size, so it seems likely that Cl(-) follows H(+) to prevent the buildup of a potential gradient across the vesicular membrane.
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