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Gafurova CR, Tsentsevitsky AN, Petrov AM. Frequency-Dependent Engagement of Synaptic Vesicle Pools in the Mice Motor Nerve Terminals. Cell Mol Neurobiol 2023; 43:729-739. [PMID: 35113291 DOI: 10.1007/s10571-022-01202-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 01/28/2022] [Indexed: 01/01/2023]
Abstract
Nerve terminals contain numerous synaptic vesicles (SVs) whose exo-endocytic cycling maintains neurotransmitter release. SVs may have different properties, thereby constituting separate pools. However, behavior of SV pools remains elusive in many synapses. To fill this gap, we studied the functioning of SV pools at both low- and higher-frequency stimulations utilizing microelectrode recording and dual-labeling of SVs with FM-dyes at the mice motor nerve terminals. It was found that higher-frequency stimulation caused exocytosis of different kinds of SVs. One type of SVs contributed to exocytosis exclusively at intense activities and their exocytotic rate was depended on the order in which these SVs were recovered by endocytosis. Another type of SVs can sustain the release in response to both low- and higher-frequency stimulations, but increasing activity did not lead to enhanced exocytotic rate of these SVs. In addition, depression of neurotransmitter release induced by 20 Hz stimulation occurred independent on previous episode of 10 Hz activity. We suggest that during prolonged stimulation at least two SV pools can operate. One termed "house-keeping" that would be active at different frequencies and the other termed "plug-in" that would respond to increasing activity.
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Affiliation(s)
- Chulpan R Gafurova
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Federal Research Center "Kazan Scientific Center of RAS", 2/31 Lobachevsky Street, Box 30, Kazan, Russia, 420111
| | - Andrei N Tsentsevitsky
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Federal Research Center "Kazan Scientific Center of RAS", 2/31 Lobachevsky Street, Box 30, Kazan, Russia, 420111
| | - Alexey M Petrov
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Federal Research Center "Kazan Scientific Center of RAS", 2/31 Lobachevsky Street, Box 30, Kazan, Russia, 420111. .,Kazan State Medial University, 49 Butlerova Street, Kazan, Russia, 420012.
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2
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Fogarty MJ, Khurram OU, Mantilla CB, Sieck GC. Brain derived neurotrophic factor/tropomyosin related kinase B signaling impacts diaphragm neuromuscular transmission in a novel rat chemogenetic model. Front Cell Neurosci 2022; 16:1025463. [PMID: 36385943 PMCID: PMC9650098 DOI: 10.3389/fncel.2022.1025463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2022] [Accepted: 10/12/2022] [Indexed: 11/29/2022] Open
Abstract
The neuromuscular junction (NMJ) mediates neural control of skeletal muscle fibers. Neurotrophic signaling, specifically brain derived neurotrophic factor (BDNF) acting through its high-affinity tropomyosin related kinase B (TrkB) receptor is known to improve neuromuscular transmission. BDNF/TrkB signaling also maintains the integrity of antero- and retrograde communication between the motor neuron soma, its distal axons and pre-synaptic terminals and influences neuromuscular transmission. In this study, we employed a novel rat chemogenetic mutation (TrkB F616), in which a 1-naphthylmethyl phosphoprotein phosphatase 1 (1NMPP1) sensitive knock-in allele allowed specific, rapid and sustained inhibition of TrkB kinase activity. In adult female and male TrkB F616 rats, treatment with either 1NMPP1 (TrkB kinase inhibition) or DMSO (vehicle) was administered in drinking water for 14 days. To assess the extent of neuromuscular transmission failure (NMTF), diaphragm muscle isometric force evoked by nerve stimulation at 40 Hz (330 ms duration trains repeated each s) was compared to isometric forces evoked by superimposed direct muscle stimulation (every 15 s). Chronic TrkB kinase inhibition (1NMPP1 group) markedly worsened NMTF compared to vehicle controls. Acute BDNF treatment did not rescue NMTF in the 1NMPP1 group. Chronic TrkB kinase inhibition did not affect the apposition of pre-synaptic terminals (labeled with synaptophysin) and post-synaptic endplates (labeled with α-Bungarotoxin) at diaphragm NMJs. We conclude that inhibition of BDNF/TrkB signaling in TrkB F616 rats disrupts diaphragm neuromuscular transmission in a similar manner to TrkB F616A mice, likely via a pre-synaptic mechanism independent of axonal branch point failure.
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Affiliation(s)
- Matthew J. Fogarty
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | - Obaid U. Khurram
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | - Carlos B. Mantilla
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | - Gary C. Sieck
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
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Egashira Y, Kumade A, Ojida A, Ono F. Spontaneously Recycling Synaptic Vesicles Constitute Readily Releasable Vesicles in Intact Neuromuscular Synapses. J Neurosci 2022; 42:3523-3536. [PMID: 35332083 PMCID: PMC9053852 DOI: 10.1523/jneurosci.2005-21.2022] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 03/08/2022] [Accepted: 03/10/2022] [Indexed: 12/14/2022] Open
Abstract
Emerging evidence shows that spontaneous synaptic transmission plays crucial roles on neuronal functions through presynaptic molecular mechanisms distinct from that of action potential (AP)-evoked transmission. However, whether the synaptic vesicle (SV) population undergoing the two forms of transmission is segregated remains controversial due in part to the conflicting results observed in cultured neurons. Here we address this issue in intact neuromuscular synapses using transgenic zebrafish larvae expressing two different indicators targeted in the SVs: a pH-sensitive fluorescent protein, pHluorin, and a tag protein, HaloTag. By establishing a quantitative measure of recycled SV fractions, we found that ∼85% of SVs were mobilized by high-frequency AP firings. In contrast, spontaneously recycling SVs were mobilized only from <8% of SVs with a time constant of 45 min at 25°C, although prolonged AP inhibition mobilized an additional population with a delayed onset. The mobilization of the early-onset population was less temperature-sensitive and resistant to tetanus toxin, whereas that of the late-onset population was more sensitive to temperature and was inhibited by tetanus toxin, indicating that prolonged AP inhibition activated a distinct molecular machinery for spontaneous SV fusion. Therefore, the early-onset population limited to <8% was likely the only source of spontaneous release that occurred physiologically. We further showed that this limited population was independent from those reluctant to fuse during AP firing and was used in both the hypertonic stimulation and the immediate phase of AP-evoked releases, thereby matching the characteristics of the readily releasable pool.SIGNIFICANCE STATEMENT Synaptic vesicles (SVs) are divided into functionally distinct pools depending on how they respond to action potential (AP) firing. The origin of SVs used for spontaneous fusion remains enigmatic despite intensive studies in cultured preparations. We addressed this question in intact neuromuscular synapses and provided two findings. First, prolonged AP inhibition activated a distinct population of fusion, which needs to be distinguished from genuine spontaneous fusion arising from a highly limited fraction. Second, the limited fraction observed early in the AP inhibition period exhibited the characteristics of readily releasable pool in the subsequent round of stimulation. Our study revealed that the origin of spontaneous SV fusion is restricted to the readily releasable pool among the SV pools involved in AP-evoked fusion.
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Affiliation(s)
- Yoshihiro Egashira
- Department of Physiology, Osaka Medical and Pharmaceutical University, Takatsuki, 569-8686, Japan
| | - Ayane Kumade
- Graduate School of Pharmaceutical Science, Kyushu University, Fukuoka, 812-8582, Japan
| | - Akio Ojida
- Graduate School of Pharmaceutical Science, Kyushu University, Fukuoka, 812-8582, Japan
| | - Fumihito Ono
- Department of Physiology, Osaka Medical and Pharmaceutical University, Takatsuki, 569-8686, Japan
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Takikawa K, Nishimune H. Similarity and Diversity of Presynaptic Molecules at Neuromuscular Junctions and Central Synapses. Biomolecules 2022; 12:biom12020179. [PMID: 35204679 PMCID: PMC8961632 DOI: 10.3390/biom12020179] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 01/17/2022] [Accepted: 01/19/2022] [Indexed: 12/04/2022] Open
Abstract
Synaptic transmission is essential for controlling motor functions and maintaining brain functions such as walking, breathing, cognition, learning, and memory. Neurotransmitter release is regulated by presynaptic molecules assembled in active zones of presynaptic terminals. The size of presynaptic terminals varies, but the size of a single active zone and the types of presynaptic molecules are highly conserved among neuromuscular junctions (NMJs) and central synapses. Three parameters play an important role in the determination of neurotransmitter release properties at NMJs and central excitatory/inhibitory synapses: the number of presynaptic molecular clusters, the protein families of the presynaptic molecules, and the distance between presynaptic molecules and voltage-gated calcium channels. In addition, dysfunction of presynaptic molecules causes clinical symptoms such as motor and cognitive decline in patients with various neurological disorders and during aging. This review focuses on the molecular mechanisms responsible for the functional similarities and differences between excitatory and inhibitory synapses in the peripheral and central nervous systems, and summarizes recent findings regarding presynaptic molecules assembled in the active zone. Furthermore, we discuss the relationship between functional alterations of presynaptic molecules and dysfunction of NMJs or central synapses in diseases and during aging.
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Affiliation(s)
- Kenji Takikawa
- Laboratory of Neurobiology of Aging, Tokyo Metropolitan Institute of Gerontology, 35-2 Sakaecho, Itabashi-ku, Tokyo 173-0015, Japan;
| | - Hiroshi Nishimune
- Laboratory of Neurobiology of Aging, Tokyo Metropolitan Institute of Gerontology, 35-2 Sakaecho, Itabashi-ku, Tokyo 173-0015, Japan;
- Department of Applied Biological Science, Tokyo University of Agriculture and Technology, 3-8-1 Harumi-cho, Fuchu-shi, Tokyo 183-8538, Japan
- Correspondence: ; Tel.: +81-3-3964-3241
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Methods of measuring presynaptic function with fluorescence probes. Appl Microsc 2021; 51:2. [PMID: 33730244 PMCID: PMC7969681 DOI: 10.1186/s42649-021-00051-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 03/09/2021] [Indexed: 01/02/2023] Open
Abstract
Synaptic vesicles, which are endogenous to neurotransmitters, are involved in exocytosis by active potentials and release neurotransmitters. Synaptic vesicles used in neurotransmitter release are reused via endocytosis to maintain a pool of synaptic vesicles. Synaptic vesicles show different types of exo- and endocytosis depending on animal species, type of nerve cell, and electrical activity. To accurately understand the dynamics of synaptic vesicles, direct observation of synaptic vesicles is required; however, it was difficult to observe synaptic vesicles of size 40-50 nm in living neurons. The exo-and endocytosis of synaptic vesicles was confirmed by labeling the vesicles with a fluorescent agent and measuring the changes in fluorescence intensity. To date, various methods of labeling synaptic vesicles have been proposed, and each method has its own characteristics, strength, and drawbacks. In this study, we introduce methods that can measure presynaptic activity and describe the characteristics of each technique.
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Properties of Glial Cell at the Neuromuscular Junction Are Incompatible with Synaptic Repair in the SOD1G37R ALS Mouse Model. J Neurosci 2020; 40:7759-7777. [PMID: 32859714 DOI: 10.1523/jneurosci.1748-18.2020] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 08/12/2020] [Accepted: 08/17/2020] [Indexed: 12/17/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting motoneurons (MNs) in a motor-unit (MU)-dependent manner. Glial dysfunction contributes to numerous aspects of the disease. At the neuromuscular junction (NMJ), early alterations in perisynaptic Schwann cell (PSC), glial cells at this synapse, may impact their ability to regulate NMJ stability and repair. Indeed, muscarinic receptors (mAChRs) regulate the repair phenotype of PSCs and are overactivated at disease-resistant NMJs [soleus muscle (SOL)] in SOD1G37R mice. However, it remains unknown whether this is the case at disease-vulnerable NMJs and whether it translates into an impairment of PSC-dependent repair mechanisms. We used SOL and sternomastoid (STM) muscles from SOD1G37R mice and performed Ca2+-imaging to monitor PSC activity and used immunohistochemistry to analyze their repair and phagocytic properties. We show that PSC mAChR-dependent activity was transiently increased at disease-vulnerable NMJs (STM muscle). Furthermore, PSCs from both muscles extended disorganized processes from denervated NMJs and failed to initiate or guide nerve terminal sprouts at disease-vulnerable NMJs, a phenomenon essential for compensatory reinnervation. This was accompanied by a failure of numerous PSCs to upregulate galectin-3 (MAC-2), a marker of glial axonal debris phagocytosis, on NMJ denervation in SOD1 mice. Finally, differences in these PSC-dependent NMJ repair mechanisms were MU type dependent, thus reflecting MU vulnerability in ALS. Together, these results reveal that neuron-glia communication is ubiquitously altered at the NMJ in ALS. This appears to prevent PSCs from adopting a repair phenotype, resulting in a maladapted response to denervation at the NMJ in ALS.SIGNIFICANCE STATEMENT Understanding how the complex interplay between neurons and glial cells ultimately lead to the degeneration of motor neurons and loss of motor function is a fundamental question to comprehend amyotrophic lateral sclerosis (ALS). An early and persistent alteration of glial cell activity takes place at the neuromuscular junction (NMJ), the output of motor neurons, but its impact on NMJ repair remains unknown. Here, we reveal that glial cells at disease-vulnerable NMJs often fail to guide compensatory nerve terminal sprouts and to adopt a phagocytic phenotype on denervated NMJs in SOD1G37R mice. These results show that glial cells at the NMJ elaborate an inappropriate response to NMJ degeneration in a manner that reflects motor-unit (MU) vulnerability and potentially impairs compensatory reinnervation.
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Homan AE, Meriney SD. Active zone structure-function relationships at the neuromuscular junction. Synapse 2018; 72:e22057. [PMID: 29956366 DOI: 10.1002/syn.22057] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 06/15/2018] [Accepted: 06/26/2018] [Indexed: 11/08/2022]
Abstract
The impact of presynaptic transmitter release site organization on synaptic function has been a vibrant area of research for synaptic physiologists. Because there is a highly nonlinear relationship between presynaptic calcium influx and subsequent neurotransmitter release at synapses, the organization and density of calcium sources (voltage-gated calcium channels [VGCCs]) relative to calcium sensors located on synaptic vesicles is predicted to play a major role in shaping the dynamics of neurotransmitter release at a synapse. Here we review the history of structure-function studies within transmitter release sites at the neuromuscular junction across three model preparations in an effort to discern the relationship between VGCC organization and synaptic function, and whether that organizational structure imparts evolutionary advantages for each species.
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Affiliation(s)
- Anne E Homan
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania
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8
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Badawi Y, Nishimune H. Presynaptic active zones of mammalian neuromuscular junctions: Nanoarchitecture and selective impairments in aging. Neurosci Res 2017; 127:78-88. [PMID: 29221906 DOI: 10.1016/j.neures.2017.11.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 11/17/2017] [Accepted: 11/27/2017] [Indexed: 12/16/2022]
Abstract
Neurotransmitter release occurs at active zones, which are specialized regions of the presynaptic membrane. A dense collection of proteins at the active zone provides a platform for molecular interactions that promote recruitment, docking, and priming of synaptic vesicles. At mammalian neuromuscular junctions (NMJs), muscle-derived laminin β2 interacts with presynaptic voltage-gated calcium channels to organize active zones. The molecular architecture of presynaptic active zones has been revealed using super-resolution microscopy techniques that combine nanoscale resolution and multiple molecular identification. Interestingly, the active zones of adult NMJs are not stable structures and thus become impaired during aging due to the selective degeneration of specific active zone proteins. This review will discuss recent progress in the understanding of active zone nanoarchitecture and the mechanisms underlying active zone organization in mammalian NMJs. Furthermore, we will summarize the age-related degeneration of active zones at NMJs, and the role of exercise in maintaining active zones.
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Affiliation(s)
- Yomna Badawi
- Department of Anatomy and Cell Biology, University of Kansas School of Medicine, Kansas City, KS, 66160, USA
| | - Hiroshi Nishimune
- Department of Anatomy and Cell Biology, University of Kansas School of Medicine, Kansas City, KS, 66160, USA.
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9
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Homan AE, Laghaei R, Dittrich M, Meriney SD. Impact of spatiotemporal calcium dynamics within presynaptic active zones on synaptic delay at the frog neuromuscular junction. J Neurophysiol 2017; 119:688-699. [PMID: 29167324 DOI: 10.1152/jn.00510.2017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The spatiotemporal calcium dynamics within presynaptic neurotransmitter release sites (active zones, AZs) at the time of synaptic vesicle fusion is critical for shaping the dynamics of neurotransmitter release. Specifically, the relative arrangement and density of voltage-gated calcium channels (VGCCs) as well as the concentration of calcium buffering proteins can play a large role in the timing, magnitude, and plasticity of release by shaping the AZ calcium profile. However, a high-resolution understanding of the role of AZ structure in spatiotemporal calcium dynamics and how it may contribute to functional heterogeneity at an adult synapse is currently lacking. We demonstrate that synaptic delay varies considerably across, but not within, individual synapses at the frog neuromuscular junction (NMJ). To determine how elements of the AZ could contribute to this variability, we performed a parameter search using a spatially realistic diffusion reaction-based computational model of a frog NMJ AZ (Dittrich M, Pattillo JM, King JD, Cho S, Stiles JR, Meriney SD. Biophys J 104: 2751-2763, 2013; Ma J, Kelly L, Ingram J, Price TJ, Meriney SD, Dittrich M. J Neurophysiol 113: 71-87, 2015). We demonstrate with our model that synaptic delay is sensitive to significant alterations in the spatiotemporal calcium dynamics within an AZ at the time of release caused by manipulations of the density and organization of VGCCs or by the concentration of calcium buffering proteins. Furthermore, our data provide a framework for understanding how AZ organization and structure are important for understanding presynaptic function and plasticity. NEW & NOTEWORTHY The structure of presynaptic active zones (AZs) can play a large role in determining the dynamics of neurotransmitter release across many model preparations by influencing the spatiotemporal calcium dynamics within the AZ at the time of vesicle fusion. However, less is known about how different AZ structural schemes may influence the timing of neurotransmitter release. We demonstrate that variations in AZ structure create different spatiotemporal calcium profiles that, in turn, lead to differences in synaptic delay.
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Affiliation(s)
- Anne E Homan
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
| | - Rozita Laghaei
- Biomedical Applications Group, Pittsburgh Supercomputing Center, Carnegie Mellon University , Pittsburgh, Pennsylvania
| | | | - Stephen D Meriney
- Department of Neuroscience, Center for Neuroscience, University of Pittsburgh , Pittsburgh, Pennsylvania
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10
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Wang X, Rich MM. Homeostatic synaptic plasticity at the neuromuscular junction in myasthenia gravis. Ann N Y Acad Sci 2017; 1412:170-177. [PMID: 28981978 DOI: 10.1111/nyas.13472] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 08/21/2017] [Accepted: 08/24/2017] [Indexed: 11/30/2022]
Abstract
A number of studies in the past 20 years have shown that perturbation of activity of the nervous system leads to compensatory changes in synaptic strength that serve to return network activity to its original level. This response has been termed homeostatic synaptic plasticity. Despite the intense interest in homeostatic synaptic plasticity, little attention has been paid to its role in the prototypic synaptic disease, myasthenia gravis. In this review, we discuss mechanisms that have been shown to mediate homeostatic synaptic plasticity at the mammalian neuromuscular junction. A subset of these mechanisms have been shown to occur in myasthenia gravis. The homeostatic changes occurring in myasthenia gravis appear to involve the presynaptic nerve terminal and may even involve changes in the excitability of motor neurons within the spinal cord. The finding of presynaptic homeostatic synaptic plasticity in myasthenia gravis leads us to propose that changes in the motor unit in myasthenia gravis may be more widespread than previously appreciated.
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Affiliation(s)
- Xueyong Wang
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, Ohio
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11
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Chamberland S, Tóth K. Functionally heterogeneous synaptic vesicle pools support diverse synaptic signalling. J Physiol 2015; 594:825-35. [PMID: 26614712 DOI: 10.1113/jp270194] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2015] [Accepted: 11/23/2015] [Indexed: 12/15/2022] Open
Abstract
Synaptic communication between neurons is a highly dynamic process involving specialized structures. At the level of the presynaptic terminal, neurotransmission is ensured by fusion of vesicles to the membrane, which releases neurotransmitter in the synaptic cleft. Depending on the level of activity experienced by the terminal, the spatiotemporal properties of calcium invasion will dictate the timing and the number of vesicles that need to be released. Diverse presynaptic firing patterns are translated to neurotransmitter release with a distinct temporal feature. Complex patterns of neurotransmitter release can be achieved when different vesicles respond to distinct calcium dynamics in the presynaptic terminal. Specific vesicles from different pools are recruited during various modes of release as the particular molecular composition of their membrane proteins define their functional properties. Such diversity endows the presynaptic terminal with the ability to respond to distinct physiological signals via the mobilization of specific subpopulation of vesicles. There are several mechanisms by which a diverse vesicle population could be generated in single presynaptic terminals, including distinct recycling pathways that utilize various adaptor proteins. Several additional factors could potentially contribute to the development of a heterogeneous vesicle pool such as specialized release sites, spatial segregation within the terminal and specialized delivery pathways. Among these factors molecular heterogeneity plays a central role in defining the functional properties of different subpopulations of vesicles.
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Affiliation(s)
- Simon Chamberland
- Quebec Mental Health Institute, Department of Psychiatry and Neuroscience, Université Laval, Quebec City, Quebec, Canada, G1J 2G3
| | - Katalin Tóth
- Quebec Mental Health Institute, Department of Psychiatry and Neuroscience, Université Laval, Quebec City, Quebec, Canada, G1J 2G3
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12
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Slater CR. The functional organization of motor nerve terminals. Prog Neurobiol 2015; 134:55-103. [DOI: 10.1016/j.pneurobio.2015.09.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 08/28/2015] [Accepted: 09/05/2015] [Indexed: 12/19/2022]
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13
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Marinković P, Godinho L, Misgeld T. Generation and Screening of Transgenic Mice with Neuronal Labeling Controlled by Thy1 Regulatory Elements. Cold Spring Harb Protoc 2015; 2015:875-882. [PMID: 26430261 DOI: 10.1101/pdb.top087668] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Major progress has been made using in vivo imaging in mice to study mammalian nervous system development, plasticity, and disease. This progress has depended in part on the wide availability of two-photon microscopy, which is capable of penetrating deep into scattering tissue. Equally important, however, is the generation of suitable transgenic mouse models, which provide a "Golgi staining"-like labeling of neurons that is sparse and bright enough for in vivo imaging. Particularly prominent among such transgenic mice are the so-called Thy1-XFP mice (in which XFP stands for any fluorescent protein) that are used in numerous studies, especially to visualize spine plasticity in the cortex and remodeling in peripheral synapses. New generations of Thy1-XFP mice are now being generated at a high rate, and these have allowed previously difficult experiments to become feasible. Moreover, with easy access to core facilities or commercial providers of pronuclear injections, generating simple Thy1 transgenic mice is now a possibility even for small laboratories. In this introduction, we discuss the Thy1 regulatory elements used to generate transgenic lines with neuronal labeling. We provide a brief overview of currently available Thy1 transgenic mice, including lines labeling neuronal organelles or reporting neuronal function.
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Linares-Clemente P, Rozas JL, Mircheski J, García-Junco-Clemente P, Martínez-López JA, Nieto-González JL, Vázquez ME, Pintado CO, Fernández-Chacón R. Different dynamin blockers interfere with distinct phases of synaptic endocytosis during stimulation in motoneurones. J Physiol 2015; 593:2867-88. [PMID: 25981717 DOI: 10.1113/jp270112] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2014] [Accepted: 04/29/2015] [Indexed: 01/05/2023] Open
Abstract
KEY POINTS Neurotransmitter release requires a tight coupling between synaptic vesicle exocytosis and endocytosis with dynamin being a key protein in that process. We used imaging techniques to examine the time course of endocytosis at mouse motor nerve terminals expressing synaptopHluorin, a genetically encoded reporter of the synaptic vesicle cycle. We separated two sequential phases of endocytosis taking place during the stimulation train: early and late endocytosis. Freshly released synaptic vesicle proteins are preferentially retrieved during the early phase, which is very sensitive to dynasore, an inhibitor of dynamin GTPase activity. Synaptic vesicle proteins pre-existing at the plasma membrane before the stimulation are preferentially retrieved during the late phase, which is very sensitive to myristyl trimethyl ammonium bromide (MitMAB), an inhibitor of the dynamin-phospholipid interaction. ABSTRACT Synaptic endocytosis is essential at nerve terminals to maintain neurotransmitter release by exocytosis. Here, at the neuromuscular junction of synaptopHluorin (spH) transgenic mice, we have used imaging to study exo- and endocytosis occurring simultaneously during nerve stimulation. We observed two endocytosis components, which occur sequentially during stimulation. The early component of endocytosis apparently internalizes spH molecules freshly exocytosed. This component was sensitive to dynasore, a blocker of dynamin 1 GTPase activity. In contrast, this early component was resistant to myristyl trimethyl ammonium bromide (MiTMAB), a competitive agent that blocks dynamin binding to phospholipid membranes. The late component of endocytosis is likely to internalize spH molecules that pre-exist at the plasma membrane before stimulation starts. This component was blocked by MiTMAB, perhaps by impairing the binding of dynamin or other key endocytic proteins to phospholipid membranes. Our study suggests the co-existence of two sequential synaptic endocytosis steps taking place during stimulation that are susceptible to pharmacological dissection: an initial step, preferentially sensitive to dynasore, that internalizes vesicular components immediately after they are released, and a MiTMAB-sensitive step that internalizes vesicular components pre-existing at the plasma membrane surface. In addition, we report that post-stimulus endocytosis also has several components with different sensitivities to dynasore and MiTMAB.
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Affiliation(s)
- Pedro Linares-Clemente
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - José L Rozas
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - Josif Mircheski
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - Pablo García-Junco-Clemente
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | - José A Martínez-López
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
| | | | - M Eugenio Vázquez
- Departamento Química Orgánica y Centro Singular de Investigación en Química Biolóxica y Materiais Moleculares (CIQUS), Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - C Oscar Pintado
- Centro Producción y Experimentación Animal, Universidad de Sevilla, Seville, Spain
| | - Rafael Fernández-Chacón
- Instituto de Biomedicina de Sevilla, IBiS, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla and Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, and CIBERNED, Seville, Spain
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15
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Daniele F, Di Cairano ES, Moretti S, Piccoli G, Perego C. TIRFM and pH-sensitive GFP-probes to evaluate neurotransmitter vesicle dynamics in SH-SY5Y neuroblastoma cells: cell imaging and data analysis. J Vis Exp 2015. [PMID: 25741799 DOI: 10.3791/52267] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Synaptic vesicles release neurotransmitters at chemical synapses through a dynamic cycle of fusion and retrieval. Monitoring synaptic activity in real time and dissecting the different steps of exo-endocytosis at the single-vesicle level are crucial for understanding synaptic functions in health and disease. Genetically-encoded pH-sensitive probes directly targeted to synaptic vesicles and Total Internal Reflection Fluorescence Microscopy (TIRFM) provide the spatio-temporal resolution necessary to follow vesicle dynamics. The evanescent field generated by total internal reflection can only excite fluorophores placed in a thin layer (<150 nm) above the glass cover on which cells adhere, exactly where the processes of exo-endocytosis take place. The resulting high-contrast images are ideally suited for vesicles tracking and quantitative analysis of fusion events. In this protocol, SH-SY5Y human neuroblastoma cells are proposed as a valuable model for studying neurotransmitter release at the single-vesicle level by TIRFM, because of their flat surface and the presence of dispersed vesicles. The methods for growing SH-SY5Y as adherent cells and for transfecting them with synapto-pHluorin are provided, as well as the technique to perform TIRFM and imaging. Finally, a strategy aiming to select, count, and analyze fusion events at whole-cell and single-vesicle levels is presented. To validate the imaging procedure and data analysis approach, the dynamics of pHluorin-tagged vesicles are analyzed under resting and stimulated (depolarizing potassium concentrations) conditions. Membrane depolarization increases the frequency of fusion events and causes a parallel raise of the net fluorescence signal recorded in whole cell. Single-vesicle analysis reveals modifications of fusion-event behavior (increased peak height and width). These data suggest that potassium depolarization not only induces a massive neurotransmitter release but also modifies the mechanism of vesicle fusion and recycling. With the appropriate fluorescent probe, this technique can be employed in different cellular systems to dissect the mechanisms of constitutive and stimulated secretion.
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Affiliation(s)
- Federica Daniele
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano
| | - Eliana S Di Cairano
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano
| | - Stefania Moretti
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano
| | | | - Carla Perego
- Department of Pharmacological and Biomolecular Sciences, Università degli Studi di Milano; CEND Center of Excellence in Neurodegenerative Diseases, Università degli Studi di Milano;
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16
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An assay to image neuronal microtubule dynamics in mice. Nat Commun 2014; 5:4827. [PMID: 25219969 PMCID: PMC4175586 DOI: 10.1038/ncomms5827] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 07/25/2014] [Indexed: 01/03/2023] Open
Abstract
Microtubule dynamics in neurons play critical roles in physiology, injury and disease and determine microtubule orientation, the cell biological correlate of neurite polarization. Several microtubule binding proteins, including end-binding protein 3 (EB3), specifically bind to the growing plus tip of microtubules. In the past, fluorescently tagged end-binding proteins have revealed microtubule dynamics in vitro and in non-mammalian model organisms. Here, we devise an imaging assay based on transgenic mice expressing yellow fluorescent protein-tagged EB3 to study microtubules in intact mammalian neurites. Our approach allows measurement of microtubule dynamics in vivo and ex vivo in peripheral nervous system and central nervous system neurites under physiological conditions and after exposure to microtubule-modifying drugs. We find an increase in dynamic microtubules after injury and in neurodegenerative disease states, before axons show morphological indications of degeneration or regrowth. Thus increased microtubule dynamics might serve as a general indicator of neurite remodelling in health and disease.
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17
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Evaluation of a novel calcium channel agonist for therapeutic potential in Lambert-Eaton myasthenic syndrome. J Neurosci 2013; 33:10559-67. [PMID: 23785168 DOI: 10.1523/jneurosci.4629-12.2013] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
We developed a novel calcium (Ca(2+)) channel agonist that is selective for N- and P/Q-type Ca(2+) channels, which are the Ca(2+) channels that regulate transmitter release at most synapses. We have shown that this new molecule (GV-58) slows the deactivation of channels, resulting in a large increase in presynaptic Ca(2+) entry during activity. GV-58 was developed as a modification of (R)-roscovitine, which was previously shown to be a Ca(2+) channel agonist, in addition to its known cyclin-dependent kinase activity. In comparison with the parent molecule, (R)-roscovitine, GV-58 has a ∼20-fold less potent cyclin-dependent kinase antagonist effect, a ∼3- to 4-fold more potent Ca(2+) channel agonist effect, and ∼4-fold higher efficacy as a Ca(2+) channel agonist. We have further evaluated GV-58 in a passive transfer mouse model of Lambert-Eaton myasthenic syndrome and have shown that weakened Lambert-Eaton myasthenic syndrome-model neuromuscular synapses are significantly strengthened following exposure to GV-58. This new Ca(2+) channel agonist has potential as a lead compound in the development of new therapeutic approaches to a variety of disorders that result in neuromuscular weakness.
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18
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Meriney SD, Dittrich M. Organization and function of transmitter release sites at the neuromuscular junction. J Physiol 2013; 591:3159-65. [PMID: 23613535 PMCID: PMC3717219 DOI: 10.1113/jphysiol.2012.248625] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 04/09/2013] [Indexed: 12/18/2022] Open
Abstract
The neuromuscular junction is known as a strong and reliable synapse. It is strong because it releases an excess of chemical transmitter, beyond what is required to bring the postsynaptic muscle cell to threshold. Because the synapse can sustain suprathreshold muscle activation during short trains of action potentials, it is also reliable. The presynaptic mechanisms that lead to reliability during short trains of activity have only recently been elucidated. It appears that there are relatively few calcium channels in individual active zones, that channels open with a low probability during action potential stimulation and that even if channels open the resulting calcium flux only rarely triggers vesicle fusion. Thus, each synaptic vesicle may only associate with a small number of calcium channels, forming an unreliable single vesicle release site. Strength and reliability of the neuromuscular junction emerge as a result of its assembly from thousands of these unreliable single vesicle release sites. Hence, these synapses are strong while at the same time only releasing a small subset of available docked vesicles during each action potential, thus conserving transmitter release resources. This prevents significant depression during short trains of action potential activity and confers reliability.
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Affiliation(s)
- Stephen D Meriney
- Department of Neuroscience, University of Pittsburgh, A210 Langley Hall, Pittsburgh, PA 15260, USA.
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19
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Cano R, Torres-Benito L, Tejero R, Biea AI, Ruiz R, Betz WJ, Tabares L. Structural and functional maturation of active zones in large synapses. Mol Neurobiol 2012; 47:209-19. [PMID: 22992975 DOI: 10.1007/s12035-012-8347-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 08/27/2012] [Indexed: 11/29/2022]
Abstract
Virtually all functions of the nervous system rely upon synapses, the sites of communication between neurons and between neurons and other cells. Synapses are complex structures, each one comprising hundreds of different types of molecules working in concert. They are organized by adhesive and scaffolding molecules that align presynaptic vesicular release sites, namely, active zones, with postsynaptic neurotransmitter receptors, thereby allowing rapid and reliable intercellular communication. Most synapses are relatively small, and acting alone exerts little effect on their postsynaptic partners. Some, however, are much larger and stronger, reliably driving the postsynaptic cell to its action potential threshold, acting essentially as electrical relays of excitation. These large synapses are among the best understood, and two of these are the subject of this review, namely, the vertebrate neuromuscular junction and the calyx of Held synapse in the mammalian auditory pathway of the brain stem. Both synapses undergo through a complex and well-coordinated maturation process, during which time the molecular elements and the biophysical properties of the secretory machinery are continuously adjusted to the synapse size and to the functional requirements. We here review the morphological and functional changes occurring during postnatal maturation, noting particular similarities and differences between these two large synapses.
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Affiliation(s)
- Raquel Cano
- Department of Medical Physiology and Biophysics, School of Medicine, University of Seville, Avda. Sanchez Pizjuan 4, 41009, Seville, Spain
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20
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Cano R, Ruiz R, Shen C, Tabares L, Betz WJ. The functional landscape of a presynaptic nerve terminal. Cell Calcium 2012; 52:321-6. [DOI: 10.1016/j.ceca.2012.04.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Revised: 04/09/2012] [Accepted: 04/18/2012] [Indexed: 11/16/2022]
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21
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Abstract
Synaptic vesicles release neurotransmitter at chemical synapses, thus initiating the flow of information in neural networks. To achieve this, vesicles undergo a dynamic cycle of fusion and retrieval to maintain the structural and functional integrity of the presynaptic terminals in which they reside. Moreover, compelling evidence indicates these vesicles differ in their availability for release and mobilization in response to stimuli, prompting classification into at least three different functional pools. Ongoing studies of the molecular and cellular bases for this heterogeneity attempt to link structure to physiology and clarify how regulation of vesicle pools influences synaptic strength and presynaptic plasticity. We discuss prevailing perspectives on vesicle pools, the role they play in shaping synaptic transmission, and the open questions that challenge current understanding.
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Affiliation(s)
- AbdulRasheed A Alabi
- Department of Molecular and Cellular Physiology, Stanford Institute for Neuro-Innovation and Translational Neurosciences, Stanford Medical School, Stanford, California 94305, USA
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22
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Clarke GL, Chen J, Nishimune H. Presynaptic Active Zone Density during Development and Synaptic Plasticity. Front Mol Neurosci 2012; 5:12. [PMID: 22438837 PMCID: PMC3305919 DOI: 10.3389/fnmol.2012.00012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2011] [Accepted: 01/30/2012] [Indexed: 12/13/2022] Open
Abstract
Neural circuits transmit information through synapses, and the efficiency of synaptic transmission is closely related to the density of presynaptic active zones, where synaptic vesicles are released. The goal of this review is to highlight recent insights into the molecular mechanisms that control the number of active zones per presynaptic terminal (active zone density) during developmental and stimulus-dependent changes in synaptic efficacy. At the neuromuscular junctions (NMJs), the active zone density is preserved across species, remains constant during development, and is the same between synapses with different activities. However, the NMJ active zones are not always stable, as exemplified by the change in active zone density during acute experimental manipulation or as a result of aging. Therefore, a mechanism must exist to maintain its density. In the central nervous system (CNS), active zones have restricted maximal size, exist in multiple numbers in larger presynaptic terminals, and maintain a constant density during development. These findings suggest that active zone density in the CNS is also controlled. However, in contrast to the NMJ, active zone density in the CNS can also be increased, as observed in hippocampal synapses in response to synaptic plasticity. Although the numbers of known active zone proteins and protein interactions have increased, less is known about the mechanism that controls the number or spacing of active zones. The following molecules are known to control active zone density and will be discussed herein: extracellular matrix laminins and voltage-dependent calcium channels, amyloid precursor proteins, the small GTPase Rab3, an endocytosis mechanism including synaptojanin, cytoskeleton protein spectrins and β-adducin, and a presynaptic web including spectrins. The molecular mechanisms that organize the active zone density are just beginning to be elucidated.
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Affiliation(s)
- Gwenaëlle L Clarke
- Department of Anatomy and Cell Biology, University of Kansas Medical School Kansas City, KS, USA
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23
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Nishimune H. Molecular mechanism of active zone organization at vertebrate neuromuscular junctions. Mol Neurobiol 2011; 45:1-16. [PMID: 22135013 DOI: 10.1007/s12035-011-8216-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Accepted: 10/24/2011] [Indexed: 02/08/2023]
Abstract
Organization of presynaptic active zones is essential for development, plasticity, and pathology of the nervous system. Recent studies indicate a trans-synaptic molecular mechanism that organizes the active zones by connecting the pre- and the postsynaptic specialization. The presynaptic component of this trans-synaptic mechanism is comprised of cytosolic active zone proteins bound to the cytosolic domains of voltage-dependent calcium channels (P/Q-, N-, and L-type) on the presynaptic membrane. The postsynaptic component of this mechanism is the synapse organizer (laminin β2) that is expressed by the postsynaptic cell and accumulates specifically on top of the postsynaptic specialization. The pre- and the postsynaptic components interact directly between the extracellular domains of calcium channels and laminin β2 to anchor the presynaptic protein complex in front of the postsynaptic specialization. Hence, the presynaptic calcium channel functions as a scaffolding protein for active zone organization and as an ion-conducting channel for synaptic transmission. In contrast to the requirement of calcium influx for synaptic transmission, the formation of the active zone does not require the calcium influx through the calcium channels. Importantly, the active zones of adult synapses are not stable structures and require maintenance for their integrity. Furthermore, aging or diseases of the central and peripheral nervous system impair the active zones. This review will focus on the molecular mechanisms that organize the presynaptic active zones and summarize recent findings at the neuromuscular junctions and other synapses.
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Affiliation(s)
- Hiroshi Nishimune
- Department of Anatomy and Cell Biology, and Kansas Intellectual and Developmental Disabilities Research Center, University of Kansas Medical School, 3901 Rainbow Blvd., MS 3051, HLSIC Rm. 2073, Kansas City, KS 66160, USA.
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24
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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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25
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Palmer AE, Qin Y, Park JG, McCombs JE. Design and application of genetically encoded biosensors. Trends Biotechnol 2011; 29:144-52. [PMID: 21251723 DOI: 10.1016/j.tibtech.2010.12.004] [Citation(s) in RCA: 170] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 12/03/2010] [Accepted: 12/11/2010] [Indexed: 10/24/2022]
Abstract
In the past 5-10 years, the power of the green fluorescent protein (GFP) and its numerous derivatives has been harnessed toward the development of genetically encoded fluorescent biosensors. These sensors are incorporated into cells or organisms as plasmid DNA, which leads the transcriptional and translational machinery of the cell to express a functional sensor. To date, over 100 different genetically encoded biosensors have been developed for targets as diverse as ions, molecules and enzymes. Such sensors are instrumental in providing a window into the real-time biochemistry of living cells and whole organisms, and are providing unprecedented insight into the inner workings of a cell.
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Affiliation(s)
- Amy E Palmer
- Department of Chemistry and Biochemistry, UCB 215, University of Colorado, Boulder, CO 80309, USA.
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26
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Denker A, Rizzoli SO. Synaptic vesicle pools: an update. Front Synaptic Neurosci 2010; 2:135. [PMID: 21423521 PMCID: PMC3059705 DOI: 10.3389/fnsyn.2010.00135] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2010] [Accepted: 08/02/2010] [Indexed: 12/04/2022] Open
Abstract
During the last few decades synaptic vesicles have been assigned to a variety of functional and morphological classes or “pools”. We have argued in the past (Rizzoli and Betz, 2005) that synaptic activity in several preparations is accounted for by the function of three vesicle pools: the readily releasable pool (docked at active zones and ready to go upon stimulation), the recycling pool (scattered throughout the nerve terminals and recycling upon moderate stimulation), and finally the reserve pool (occupying most of the vesicle clusters and only recycling upon strong stimulation). We discuss here the advancements in the vesicle pool field which took place in the ensuing years, focusing on the behavior of different pools under both strong stimulation and physiological activity. Several new findings have enhanced the three-pool model, with, for example, the disparity between recycling and reserve vesicles being underlined by the observation that the former are mobile, while the latter are “fixed”. Finally, a number of altogether new concepts have also evolved such as the current controversy on the identity of the spontaneously recycling vesicle pool.
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Affiliation(s)
- Annette Denker
- European Neuroscience Institute, DFG Center for Molecular Physiology of the Brain Göttingen, Germany
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27
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Motor neuron-specific overexpression of the presynaptic choline transporter: impact on motor endurance and evoked muscle activity. Neuroscience 2010; 171:1041-53. [PMID: 20888396 DOI: 10.1016/j.neuroscience.2010.09.057] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Revised: 09/23/2010] [Accepted: 09/24/2010] [Indexed: 11/23/2022]
Abstract
The presynaptic, hemicholinium-3 sensitive, high-affinity choline transporter (CHT) supplies choline for acetylcholine (ACh) synthesis. In mice, a homozygous deletion of CHT (CHT-/-) leads to premature cessation of spontaneous or evoked neuromuscular signaling and is associated with perinatal cyanosis and lethality within 1 h. Heterozygous (CHT+/-) mice exhibit diminished brain ACh levels and demonstrate an inability to sustain vigorous motor activity. We sought to explore the contribution of CHT gene dosage to motor function in greater detail using transgenic mice where CHT is expressed under control of the motor neuron promoter Hb9 (Hb9:CHT). On a CHT-/- background, the Hb9:CHT transgene conferred mice with the ability to move and breath for a postnatal period of ∼24 h, thus increasing survival. Conversely, Hb9:CHT expression on a wild-type background (CHT+/+;Hb9:CHT) leads to an increased capacity for treadmill running compared to wild-type littermates. Analysis of the stimulated compound muscle action potential (CMAP) in these animals under basal conditions established that CHT+/+;Hb9:CHT mice display an unexpected, bidirectional change, producing either elevated or reduced CMAP amplitude, relative to CHT+/+ animals. To examine whether these two groups arise from underlying changes in synaptic properties, we used high-frequency stimulation of motor axons to assess CMAP recovery kinetics. Although CHT+/+; Hb9:CHT mice in the two groups display an equivalent, time-dependent reduction in CMAP amplitude, animals with a higher basal CMAP amplitude demonstrate a significantly enhanced rate of recovery. To explain our findings, we propose a model whereby CHT support for neuromuscular signaling involves contributions to ACh synthesis as well as cholinergic synaptic vesicle availability.
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28
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Bélair EL, Vallée J, Robitaille R. In vivo long-term synaptic plasticity of glial cells. J Physiol 2010; 588:1039-56. [PMID: 20142269 DOI: 10.1113/jphysiol.2009.178988] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Evidence showing the ability of glial cells to detect, respond to and modulate synaptic transmission and plasticity has contributed to the notion of glial cells as active synaptic partners. However, synaptically induced plasticity of glia themselves remains ill defined. Here we used the amphibian neuromuscular junction (NMJ) to study plasticity of perisynaptic Schwann cells (PSCs), glial cells at this synapse, following long-term in vivo modifications of synaptic activity. We used two models that altered synaptic activity in different manners. First, chronic blockade of postsynaptic nicotinic receptors using alpha-bungarotoxin (alpha-BTx) decreased facilitation, increased synaptic depression and decreased post-tetanic potentiation (PTP). Second, chronic nerve stimulation increased facilitation and resistance to synaptic depression, while leaving PTP unaltered. Our results indicate that there is no direct relationship between transmitter release and PSC calcium responses. Indeed, despite changes in transmitter release and plasticity in stimulated NMJs, nerve-evoked PSC calcium responses were similar to control. Similarly, PSC calcium responses in alpha-BTx treated NMJs were delayed and smaller in amplitude, even though basal level of transmitter release was increased. Also, when isolating purinergic and muscarinic components of PSC calcium responses, we found an increased sensitivity to ATP and a decreased sensitivity to muscarine in chronically stimulated NMJs. Conversely, in alpha-BTx treated NMJs, PSC sensitivity remained unaffected, but ATP- and muscarine-induced calcium responses were prolonged. Thus, our results reveal complex modifications of PSC properties, with differential modulation of signalling pathways that might underlie receptor regulation or changes in Ca(2+) handling. Importantly, similar to neurons, perisynaptic glial cells undergo plastic changes induced by altered synaptic activity.
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Affiliation(s)
- Eve-Lyne Bélair
- Département de physiologie, Faculté de médecine, Université de Montréal, PO box 6128 Succursale Centre-ville, Montréal, Québec, Canada
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29
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Preferred sites of exocytosis and endocytosis colocalize during high- but not lower-frequency stimulation in mouse motor nerve terminals. J Neurosci 2009; 29:15308-16. [PMID: 19955383 DOI: 10.1523/jneurosci.4646-09.2009] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The spatial relationship of exocytosis and endocytosis in motor nerve terminals has been explored, with varied results, mostly in fixed preparations and without direct information on the utilization of each exocytic site. We sought to determine these spatial properties in real time using synaptopHluorin (spH) and FM4-64. Earlier we showed that nerve stimulation elicits the appearance of spH fluorescence hot spots, which mark preferred sites of exocytosis. Here we show that nerve stimulation in the presence of the styryl dye FM4-64 evokes hot spots of FM4-64 fluorescence. Their size, density, and rate of appearance are similar to the spH hot spots, but their rate of disappearance after stimulation was much slower (t(1/2) approximately 9 min vs approximately 10 s for spH hot spots), consistent with FM4-64 spots identifying bulk endocytosis and subsequent slow intracellular dispersion of nascent vesicles. Simultaneous imaging of both fluorophores revealed a strong colocalization of spH and FM4-64 spots, but only during high (100 Hz) stimulation. At 40 Hz stimulation, exocytic and endocytic spots did not colocalize. Our results are consistent with the hypothesis that hot spots of endocytosis, possibly in the form of bulk uptake, occur at or very near highly active exocytic sites during high-frequency stimulation.
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30
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Gaffield MA, Tabares L, Betz WJ. The spatial pattern of exocytosis and post-exocytic mobility of synaptopHluorin in mouse motor nerve terminals. J Physiol 2009; 587:1187-200. [PMID: 19153160 DOI: 10.1113/jphysiol.2008.166728] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We monitored the spatial distribution of exo- and endocytosis at 37 degrees C in mouse motor nerve terminals expressing synaptopHluorin (spH), confirming and extending earlier work at room temperature, which had revealed fluorescent 'hot spots' appearing in repeatable locations during tetanic stimulation. We also tested whether hot spots appeared during mild stimulation. Averaged responses from single shocks showed a clear fluorescence jump, but revealed no sign of hot spots; instead, fluorescence rose uniformly across the terminal. Only after 5-25 stimuli given at high frequency did hot spots appear, suggesting a novel initiation mechanism. Experiments showed that about half of the surface spH molecules were mobile, and that spH movement occurred out of hot spots, demonstrating their origin as exocytic sources, not endocytic sinks. Taken together, our results suggest that synaptic vesicles exocytose equally throughout the terminal with mild stimulation, but preferentially exocytose at specific, repeatable locations during tetanic stimulation.
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Affiliation(s)
- Michael A Gaffield
- Department of Physiology and Biophysics, University of Colorado Denver, Anschutz Medical Campus, Aurora, CO 80045, USA
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31
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Kerschensteiner M, Reuter MS, Lichtman JW, Misgeld T. Ex vivo imaging of motor axon dynamics in murine triangularis sterni explants. Nat Protoc 2008; 3:1645-53. [PMID: 18833201 DOI: 10.1038/nprot.2008.160] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We provide a protocol that describes an explant system that allows the dynamics of motor axons to be imaged. This method is based on nerve-muscle explants prepared from the triangularis sterni muscle of mice, a thin muscle that covers the inside of the thorax. These explants, which can be maintained alive for several hours, contain long stretches of peripheral motor axons including their terminal arborizations and neuromuscular junctions. Explants can be prepared from transgenic mouse lines that express fluorescent proteins in neurons or glial cells, which enables direct visualization of their cellular and subcellular morphology by fluorescence microscopy. Time-lapse imaging then provides a convenient and reliable approach to follow the dynamic behavior of motor axons, their surrounding glial cells and their intracellular organelles with high temporal and spatial resolution. Triangularis sterni explants can be prepared in 15 min, imaged ex vivo for several hours and processed for immunohistochemistry in about 2 h.
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Affiliation(s)
- Martin Kerschensteiner
- Research Unit Therapy Development, Institute of Clinical Neuroimmunology, Ludwig-Maximilians University Munich, München, Germany.
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