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Boto T, Tomchik SM. Functional Imaging of Learning-Induced Plasticity in the Central Nervous System with Genetically Encoded Reporters in Drosophila. Cold Spring Harb Protoc 2024; 2024:pdb.top107799. [PMID: 37197830 DOI: 10.1101/pdb.top107799] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Learning and memory allow animals to adjust their behavior based on the predictive value of their past experiences. Memories often exist in complex representations, spread across numerous cells and synapses in the brain. Studying relatively simple forms of memory provides insights into the fundamental processes that underlie multiple forms of memory. Associative learning occurs when an animal learns the relationship between two previously unrelated sensory stimuli, such as when a hungry animal learns that a particular odor is followed by a tasty reward. Drosophila is a particularly powerful model to study how this type of memory works. The fundamental principles are widely shared among animals, and there is a wide range of genetic tools available to study circuit function in flies. In addition, the olfactory structures that mediate associative learning in flies, such as the mushroom body and its associated neurons, are anatomically organized, relatively well-characterized, and readily accessible to imaging. Here, we review the olfactory anatomy and physiology of the olfactory system, describe how plasticity in the olfactory pathway mediates learning and memory, and explain the general principles underlying calcium imaging approaches.
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Affiliation(s)
- Tamara Boto
- Department of Physiology, Trinity College Dublin, Dublin 2, Ireland
- Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland
| | - Seth M Tomchik
- Neuroscience and Pharmacology, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
- Stead Family Department of Pediatrics, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
- Iowa Neuroscience Institute, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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2
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Medeiros AT, Gratz S, Delgado A, Ritt J, O’Connor-Giles KM. Ca 2+ channel and active zone protein abundance intersects with input-specific synapse organization to shape functional synaptic diversity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.04.02.535290. [PMID: 37034654 PMCID: PMC10081318 DOI: 10.1101/2023.04.02.535290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
Abstract
Synaptic heterogeneity is a hallmark of nervous systems that enables complex and adaptable communication in neural circuits. To understand circuit function, it is thus critical to determine the factors that contribute to the functional diversity of synapses. We investigated the contributions of voltage-gated calcium channel (VGCC) abundance, spatial organization, and subunit composition to synapse diversity among and between synapses formed by two closely related Drosophila glutamatergic motor neurons with distinct neurotransmitter release probabilities (Pr). Surprisingly, VGCC levels are highly predictive of heterogeneous Pr among individual synapses of either low- or high-Pr inputs, but not between inputs. We find that the same number of VGCCs are more densely organized at high-Pr synapses, consistent with tighter VGCC-synaptic vesicle coupling. We generated endogenously tagged lines to investigate VGCC subunits in vivo and found that the α2δ-3 subunit Straightjacket along with the CAST/ELKS active zone (AZ) protein Bruchpilot, both key regulators of VGCCs, are less abundant at high-Pr inputs, yet positively correlate with Pr among synapses formed by either input. Consistently, both Straightjacket and Bruchpilot levels are dynamically increased across AZs of both inputs when neurotransmitter release is potentiated to maintain stable communication following glutamate receptor inhibition. Together, these findings suggest a model in which VGCC and AZ protein abundance intersects with input-specific spatial and molecular organization to shape the functional diversity of synapses.
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Affiliation(s)
- A. T. Medeiros
- Neuroscience Graduate Training Program, Brown University, Providence, RI
| | - S.J. Gratz
- Department of Neuroscience, Brown University, Providence, RI
| | - A. Delgado
- Department of Neuroscience, Brown University, Providence, RI
| | - J.T. Ritt
- Department of Neuroscience, Brown University, Providence, RI
- Carney Institute for Brain Science, Brown University, Providence, RI
| | - Kate M. O’Connor-Giles
- Neuroscience Graduate Training Program, Brown University, Providence, RI
- Department of Neuroscience, Brown University, Providence, RI
- Carney Institute for Brain Science, Brown University, Providence, RI
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Wang Z, Xu Z, Luo Y, Peng S, Song H, Li T, Zheng J, Liu N, Wu S, Zhang J, Zhang L, Hu Y, Liu Y, Lu D, Dai J, Zhang J. Reduced biophotonic activities and spectral blueshift in Alzheimer's disease and vascular dementia models with cognitive impairment. Front Aging Neurosci 2023; 15:1208274. [PMID: 37727319 PMCID: PMC10505668 DOI: 10.3389/fnagi.2023.1208274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 08/18/2023] [Indexed: 09/21/2023] Open
Abstract
Background Although clinically, Alzheimer's disease (AD) and vascular dementia (VaD) are the two major types of dementia, it is unclear whether the biophotonic activities associated with cognitive impairments in these diseases share common pathological features. Methods We used the ultraweak biophoton imaging system (UBIS) and synaptosomes prepared by modified percoll method to directly evaluate the functional changes in synapses and neural circuits in AD and VaD model animals. Results We found that biophotonic activities induced by glutamate were significantly reduced and spectral blueshifted in synaptosomes and brain slices. These changes could be partially reversed by pre-perfusion of the ifenprodil, a specific antagonist of the GluN2B subunit of N-methyl-D-aspartate receptors (NMDARs). Conclusion Our findings suggest that AD and VaD pathology present similar but complex changes in biophotonic activities and transmission at synapses and neural circuits, implying that communications and information processing of biophotonic signals in the brain are crucial for advanced cognitive functions.
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Affiliation(s)
- Zhuo Wang
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
- College of Life Science, Wuhan Institute for Neuroscience and Neuroengineering, South-Central Minzu University, Wuhan, China
- Medical Science Research Center, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Zhipeng Xu
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Yi Luo
- Department of Laboratory Medicine, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Sisi Peng
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Hao Song
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Tian Li
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Jiaxin Zheng
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Na Liu
- College of Life Science, Wuhan Institute for Neuroscience and Neuroengineering, South-Central Minzu University, Wuhan, China
| | - Shenjia Wu
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Junxia Zhang
- Academy of Chinese Medical Sciences, Henan University of Traditional Chinese Medicine, Zhengzhou, China
| | - Lei Zhang
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Yuan Hu
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Yanping Liu
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Dongwei Lu
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
| | - Jiapei Dai
- College of Life Science, Wuhan Institute for Neuroscience and Neuroengineering, South-Central Minzu University, Wuhan, China
| | - Junjian Zhang
- Department of Neurology, Zhongnan Hospital of Wuhan University, Wuhan, China
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Wang Y, Zhang R, Huang S, Valverde PTT, Lobb-Rabe M, Ashley J, Venkatasubramanian L, Carrillo RA. Glial Draper signaling triggers cross-neuron plasticity in bystander neurons after neuronal cell death. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.09.536190. [PMID: 37090512 PMCID: PMC10120647 DOI: 10.1101/2023.04.09.536190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
Abstract
Neuronal cell death and subsequent brain dysfunction are hallmarks of aging and neurodegeneration, but how the nearby healthy neurons (bystanders) respond to the cell death of their neighbors is not fully understood. In the Drosophila larval neuromuscular system, bystander motor neurons can structurally and functionally compensate for the loss of their neighbors by increasing their axon terminal size and activity. We termed this compensation as cross-neuron plasticity, and in this study, we demonstrated that the Drosophila engulfment receptor, Draper, and the associated kinase, Shark, are required in glial cells. Surprisingly, overexpression of the Draper-I isoform boosts cross-neuron plasticity, implying that the strength of plasticity correlates with Draper signaling. Synaptic plasticity normally declines as animals age, but in our system, functional cross-neuron plasticity can be induced at different time points, whereas structural cross-neuron plasticity can only be induced at early stages. Our work uncovers a novel role for glial Draper signaling in cross-neuron plasticity that may enhance nervous system function during neurodegeneration and provides insights into how healthy bystander neurons respond to the loss of their neighboring neurons.
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Knodel MM, Dutta Roy R, Wittum G. Influence of T-Bar on Calcium Concentration Impacting Release Probability. Front Comput Neurosci 2022; 16:855746. [PMID: 35586479 PMCID: PMC9108211 DOI: 10.3389/fncom.2022.855746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Accepted: 03/09/2022] [Indexed: 11/25/2022] Open
Abstract
The relation of form and function, namely the impact of the synaptic anatomy on calcium dynamics in the presynaptic bouton, is a major challenge of present (computational) neuroscience at a cellular level. The Drosophila larval neuromuscular junction (NMJ) is a simple model system, which allows studying basic effects in a rather simple way. This synapse harbors several special structures. In particular, in opposite to standard vertebrate synapses, the presynaptic boutons are rather large, and they have several presynaptic zones. In these zones, different types of anatomical structures are present. Some of the zones bear a so-called T-bar, a particular anatomical structure. The geometric form of the T-bar resembles the shape of the letter “T” or a table with one leg. When an action potential arises, calcium influx is triggered. The probability of vesicle docking and neurotransmitter release is superlinearly proportional to the concentration of calcium close to the vesicular release site. It is tempting to assume that the T-bar causes some sort of calcium accumulation and hence triggers a higher release probability and thus enhances neurotransmitter exocytosis. In order to study this influence in a quantitative manner, we constructed a typical T-bar geometry and compared the calcium concentration close to the active zones (AZs). We compared the case of synapses with and without T-bars. Indeed, we found a substantial influence of the T-bar structure on the presynaptic calcium concentrations close to the AZs, indicating that this anatomical structure increases vesicle release probability. Therefore, our study reveals how the T-bar zone implies a strong relation between form and function. Our study answers the question of experimental studies (namely “Wichmann and Sigrist, Journal of neurogenetics 2010”) concerning the sense of the anatomical structure of the T-bar.
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Affiliation(s)
- Markus M. Knodel
- Goethe Center for Scientific Computing (GCSC), Goethe Universität Frankfurt, Frankfurt, Germany
- *Correspondence: Markus M. Knodel ; orcid.org/0000-0001-8739-0803
| | | | - Gabriel Wittum
- Goethe Center for Scientific Computing (GCSC), Goethe Universität Frankfurt, Frankfurt, Germany
- Applied Mathematics and Computational Science, Computer, Electrical and Mathematical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
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Feghhi T, Hernandez RX, Stawarski M, Thomas CI, Kamasawa N, Lau AWC, Macleod GT. Computational modeling predicts ephemeral acidic microdomains in the glutamatergic synaptic cleft. Biophys J 2021; 120:5575-5591. [PMID: 34774503 DOI: 10.1016/j.bpj.2021.11.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 10/21/2021] [Accepted: 11/05/2021] [Indexed: 10/19/2022] Open
Abstract
At chemical synapses, synaptic vesicles release their acidic contents into the cleft, leading to the expectation that the cleft should acidify. However, fluorescent pH probes targeted to the cleft of conventional glutamatergic synapses in both fruit flies and mice reveal cleft alkalinization rather than acidification. Here, using a reaction-diffusion scheme, we modeled pH dynamics at the Drosophila neuromuscular junction as glutamate, ATP, and protons (H+) were released into the cleft. The model incorporates bicarbonate and phosphate buffering systems as well as plasma membrane calcium-ATPase activity and predicts substantial cleft acidification but only for fractions of a millisecond after neurotransmitter release. Thereafter, the cleft rapidly alkalinizes and remains alkaline for over 100 ms because the plasma membrane calcium-ATPase removes H+ from the cleft in exchange for calcium ions from adjacent pre- and postsynaptic compartments, thus recapitulating the empirical data. The extent of synaptic vesicle loading and time course of exocytosis have little influence on the magnitude of acidification. Phosphate but not bicarbonate buffering is effective at suppressing the magnitude and time course of the acid spike, whereas both buffering systems are effective at suppressing cleft alkalinization. The small volume of the cleft levies a powerful influence on the magnitude of alkalinization and its time course. Structural features that open the cleft to adjacent spaces appear to be essential for alleviating the extent of pH transients accompanying neurotransmission.
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Affiliation(s)
- Touhid Feghhi
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, Florida
| | - Roberto X Hernandez
- Integrative Biology & Neuroscience Graduate Program, Florida Atlantic University, Boca Raton, Florida; International Max Planck Research School for Brain and Behavior, Jupiter, Florida; Jupiter Life Sciences Initiative, Florida Atlantic University, Jupiter, Florida
| | - Michal Stawarski
- Wilkes Honors College, Florida Atlantic University, Jupiter, Florida
| | - Connon I Thomas
- Electron Microscopy Core Facility, Max Planck Florida Institute, Jupiter, Florida
| | - Naomi Kamasawa
- Electron Microscopy Core Facility, Max Planck Florida Institute, Jupiter, Florida
| | - A W C Lau
- Department of Physics, College of Science, Florida Atlantic University, Boca Raton, Florida
| | - Gregory T Macleod
- Jupiter Life Sciences Initiative, Florida Atlantic University, Jupiter, Florida; Wilkes Honors College, Florida Atlantic University, Jupiter, Florida; Brain Institute, Florida Atlantic University, Jupiter, Florida; Institute for Human Health & Disease Intervention, Florida Atlantic University, Jupiter, Florida.
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7
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Tyurikova O, Zheng K, Nicholson E, Timofeeva Y, Semyanov A, Volynski KE, Rusakov DA. Fluorescence lifetime imaging reveals regulation of presynaptic Ca 2+ by glutamate uptake and mGluRs, but not somatic voltage in cortical neurons. J Neurochem 2021; 156:48-58. [PMID: 32418206 PMCID: PMC8436763 DOI: 10.1111/jnc.15094] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 04/21/2020] [Accepted: 05/08/2020] [Indexed: 11/28/2022]
Abstract
Brain function relies on vesicular release of neurotransmitters at chemical synapses. The release probability depends on action potential-evoked presynaptic Ca2+ entry, but also on the resting Ca2+ level. Whether these basic aspects of presynaptic calcium homeostasis show any consistent trend along the axonal path, and how they are controlled by local network activity, remains poorly understood. Here, we take advantage of the recently advanced FLIM-based method to monitor presynaptic Ca2+ with nanomolar sensitivity. We find that, in cortical pyramidal neurons, action potential-evoked calcium entry (range 10-300 nM), but not the resting Ca2+ level (range 10-100 nM), tends to increase with higher order of axonal branches. Blocking astroglial glutamate uptake reduces evoked Ca2+ entry but has little effect on resting Ca2+ whereas both appear boosted by the constitutive activation of group 1/2 metabotropic glutamate receptors. We find no consistent effect of transient somatic depolarization or hyperpolarization on presynaptic Ca2+ entry or its basal level. The results unveil some key aspects of presynaptic machinery in cortical circuits, shedding light on basic principles of synaptic connectivity in the brain.
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Affiliation(s)
- Olga Tyurikova
- Queen Square Institute of NeurologyUniversity College LondonLondonUK
- Shemyakin‐Ovchinnikov Institute of Bioorganic ChemistryRussian Academy of SciencesMoscowRussia
| | - Kaiyu Zheng
- Queen Square Institute of NeurologyUniversity College LondonLondonUK
| | | | - Yulia Timofeeva
- Queen Square Institute of NeurologyUniversity College LondonLondonUK
- Department of Computer Science, Centre for Complexity Science, University of WarwickCoventryUK
| | - Alexey Semyanov
- Shemyakin‐Ovchinnikov Institute of Bioorganic ChemistryRussian Academy of SciencesMoscowRussia
- Sechenov First Moscow State Medical UniversityMoscowRussia
| | | | - Dmitri A. Rusakov
- Queen Square Institute of NeurologyUniversity College LondonLondonUK
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Qin JK, Zhou F, Wang J, Chen J, Wang C, Guo X, Zhao S, Pei Y, Zhen L, Ye PD, Lau SP, Zhu Y, Xu CY, Chai Y. Anisotropic Signal Processing with Trigonal Selenium Nanosheet Synaptic Transistors. ACS NANO 2020; 14:10018-10026. [PMID: 32806043 DOI: 10.1021/acsnano.0c03124] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Hardware implementation of an artificial neural network requires neuromorphic devices to process information with low energy consumption and high heterogeneity. Here we demonstrate an electrolyte-gated synaptic transistor (EGT) based on a trigonal selenium (t-Se) nanosheet. Due to the intrinsic low conductivity of the Se channel, the t-Se synaptic transistor exhibits ultralow energy consumption, less than 0.1 pJ per spike. More importantly, the intrinsic low symmetry of t-Se offers a strong anisotropy along its c- and a-axis in electrical conductance with a ratio of up to 8.6. The multiterminal EGT device exhibits an anisotropic response of filtering behavior to the same external stimulus, which enables it to mimic the heterogeneous signal transmission process of the axon-multisynapse biostructure in the human brain. The proof-of-concept device in this work represents an important step to develop neuromorphic electronics for processing complex signals.
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Affiliation(s)
- Jing-Kai Qin
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
- School of Materials Science and Engineering, Harbin Institute of Technology (Shen Zhen), Shen Zhen 518055, People's Republic of China
| | - Feichi Zhou
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
| | - Jingli Wang
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
- The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518055, People's Republic of China
| | - Jiewei Chen
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
| | - Cong Wang
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
| | - Xuyun Guo
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
| | - Shouxin Zhao
- School of Materials Science and Engineering, Harbin Institute of Technology (Shen Zhen), Shen Zhen 518055, People's Republic of China
| | - Yi Pei
- School of Materials Science and Engineering, Harbin Institute of Technology (Shen Zhen), Shen Zhen 518055, People's Republic of China
| | - Liang Zhen
- School of Materials Science and Engineering, Harbin Institute of Technology (Shen Zhen), Shen Zhen 518055, People's Republic of China
| | - Peide D Ye
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, United States
| | - Shu Ping Lau
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
- The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518055, People's Republic of China
| | - Ye Zhu
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
| | - Cheng-Yan Xu
- School of Materials Science and Engineering, Harbin Institute of Technology (Shen Zhen), Shen Zhen 518055, People's Republic of China
| | - Yang Chai
- Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, People's Republic of China
- The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518055, People's Republic of China
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Goel P, Nishimura S, Chetlapalli K, Li X, Chen C, Dickman D. Distinct Target-Specific Mechanisms Homeostatically Stabilize Transmission at Pre- and Post-synaptic Compartments. Front Cell Neurosci 2020; 14:196. [PMID: 32676010 PMCID: PMC7333441 DOI: 10.3389/fncel.2020.00196] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 06/05/2020] [Indexed: 12/28/2022] Open
Abstract
Neurons must establish and stabilize connections made with diverse targets, each with distinct demands and functional characteristics. At Drosophila neuromuscular junctions (NMJs), synaptic strength remains stable in a manipulation that simultaneously induces hypo-innervation on one target and hyper-innervation on the other. However, the expression mechanisms that achieve this exquisite target-specific homeostatic control remain enigmatic. Here, we identify the distinct target-specific homeostatic expression mechanisms. On the hypo-innervated target, an increase in postsynaptic glutamate receptor (GluR) abundance is sufficient to compensate for reduced innervation, without any apparent presynaptic adaptations. In contrast, a target-specific reduction in presynaptic neurotransmitter release probability is reflected by a decrease in active zone components restricted to terminals of hyper-innervated targets. Finally, loss of postsynaptic GluRs on one target induces a compartmentalized, homeostatic enhancement of presynaptic neurotransmitter release called presynaptic homeostatic potentiation (PHP) that can be precisely balanced with the adaptations required for both hypo- and hyper-innervation to maintain stable synaptic strength. Thus, distinct anterograde and retrograde signaling systems operate at pre- and post-synaptic compartments to enable target-specific, homeostatic control of neurotransmission.
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10
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Neuronal Glutamatergic Synaptic Clefts Alkalinize Rather Than Acidify during Neurotransmission. J Neurosci 2020; 40:1611-1624. [PMID: 31964719 DOI: 10.1523/jneurosci.1774-19.2020] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 01/14/2020] [Accepted: 01/15/2020] [Indexed: 12/11/2022] Open
Abstract
The dogma that the synaptic cleft acidifies during neurotransmission is based on the corelease of neurotransmitters and protons from synaptic vesicles, and is supported by direct data from sensory ribbon-type synapses. However, it is unclear whether acidification occurs at non-ribbon-type synapses. Here we used genetically encoded fluorescent pH indicators to examine cleft pH at conventional neuronal synapses. At the neuromuscular junction of female Drosophila larvae, we observed alkaline spikes of over 1 log unit during fictive locomotion in vivo. Ex vivo, single action potentials evoked alkalinizing pH transients of only ∼0.01 log unit, but these transients summated rapidly during burst firing. A chemical pH indicator targeted to the cleft corroborated these findings. Cleft pH transients were dependent on Ca2+ movement across the postsynaptic membrane, rather than neurotransmitter release per se, a result consistent with cleft alkalinization being driven by the Ca2+/H+ antiporting activity of the plasma membrane Ca2+-ATPase at the postsynaptic membrane. Targeting the pH indicators to the microenvironment of the presynaptic voltage gated Ca2+ channels revealed that alkalinization also occurred within the cleft proper at the active zone and not just within extrasynaptic regions. Application of the pH indicators at the mouse calyx of Held, a mammalian central synapse, similarly revealed cleft alkalinization during burst firing in both males and females. These findings, made at two quite different non-ribbon type synapses, suggest that cleft alkalinization during neurotransmission, rather than acidification, is a generalizable phenomenon across conventional neuronal synapses.SIGNIFICANCE STATEMENT Neurotransmission is highly sensitive to the pH of the extracellular milieu. This is readily evident in the neurological symptoms that accompany systemic acid/base imbalances. Imaging data from sensory ribbon-type synapses show that neurotransmission itself can acidify the synaptic cleft, likely due to the corelease of protons and glutamate. It is not clear whether the same phenomenon occurs at conventional neuronal synapses due to the difficulties in collecting such data. If it does occur, it would provide for an additional layer of activity-dependent modulation of neurotransmission. Our findings of alkalinization, rather than acidification, within the cleft of two different neuronal synapses encourages a reassessment of the scope of activity-dependent pH influences on neurotransmission and short-term synaptic plasticity.
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11
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Goel P, Dufour Bergeron D, Böhme MA, Nunnelly L, Lehmann M, Buser C, Walter AM, Sigrist SJ, Dickman D. Homeostatic scaling of active zone scaffolds maintains global synaptic strength. J Cell Biol 2019; 218:1706-1724. [PMID: 30914419 PMCID: PMC6504899 DOI: 10.1083/jcb.201807165] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 12/14/2018] [Accepted: 03/06/2019] [Indexed: 12/23/2022] Open
Abstract
Synaptic terminals grow and retract throughout life, yet synaptic strength is maintained within stable physiological ranges. To study this process, we investigated Drosophila endophilin (endo) mutants. Although active zone (AZ) number is doubled in endo mutants, a compensatory reduction in their size homeostatically adjusts global neurotransmitter output to maintain synaptic strength. We find an inverse adaptation in rab3 mutants. Additional analyses using confocal, STED, and electron microscopy reveal a stoichiometric tuning of AZ scaffolds and nanoarchitecture. Axonal transport of synaptic cargo via the lysosomal kinesin adapter Arl8 regulates AZ abundance to modulate global synaptic output and sustain the homeostatic potentiation of neurotransmission. Finally, we find that this AZ scaling can interface with two independent homeostats, depression and potentiation, to remodel AZ structure and function, demonstrating a robust balancing of separate homeostatic adaptations. Thus, AZs are pliable substrates with elastic and modular nanostructures that can be dynamically sculpted to stabilize and tune both local and global synaptic strength.
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Affiliation(s)
- Pragya Goel
- Department of Neurobiology, University of Southern California, Los Angeles, CA
| | | | - Mathias A Böhme
- Neurocure Cluster of Excellence, Charité Universitätsmedizin, Berlin, Germany
| | - Luke Nunnelly
- Department of Neurobiology, University of Southern California, Los Angeles, CA
| | - Martin Lehmann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Berlin, Germany
| | | | - Alexander M Walter
- Neurocure Cluster of Excellence, Charité Universitätsmedizin, Berlin, Germany
| | | | - Dion Dickman
- Department of Neurobiology, University of Southern California, Los Angeles, CA
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12
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A Screen for Synaptic Growth Mutants Reveals Mechanisms That Stabilize Synaptic Strength. J Neurosci 2019; 39:4051-4065. [PMID: 30902873 DOI: 10.1523/jneurosci.2601-18.2019] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 03/12/2019] [Accepted: 03/14/2019] [Indexed: 01/28/2023] Open
Abstract
Synapses grow, prune, and remodel throughout development, experience, and disease. This structural plasticity can destabilize information transfer in the nervous system. However, neural activity remains stable throughout life, implying that adaptive countermeasures exist that maintain neurotransmission within proper physiological ranges. Aberrant synaptic structure and function have been associated with a variety of neural diseases, including Fragile X syndrome, autism, and intellectual disability. We have screened 300 mutants in Drosophila larvae of both sexes for defects in synaptic growth at the neuromuscular junction, identifying 12 mutants with severe reductions or enhancements in synaptic growth. Remarkably, electrophysiological recordings revealed that synaptic strength was unchanged in all but one of these mutants compared with WT. We used a combination of genetic, anatomical, and electrophysiological analyses to illuminate three mechanisms that stabilize synaptic strength despite major disparities in synaptic growth. These include compensatory changes in (1) postsynaptic neurotransmitter receptor abundance, (2) presynaptic morphology, and (3) active zone structure. Together, this characterization identifies new mutants with defects in synaptic growth and the adaptive strategies used by synapses to homeostatically stabilize neurotransmission in response.SIGNIFICANCE STATEMENT This study reveals compensatory mechanisms used by synapses to ensure stable functionality during severe alterations in synaptic growth using the neuromuscular junction of Drosophila melanogaster as a model system. Through a forward genetic screen, we identify mutants that exhibit dramatic undergrown or overgrown synapses yet express stable levels of synaptic strength, with three specific compensatory mechanisms discovered. Thus, this study reveals novel insights into the adaptive strategies that constrain neurotransmission within narrow physiological ranges while allowing considerable flexibility in overall synapse number. More broadly, these findings provide insights into how stable synaptic function may be maintained in the nervous system during periods of intensive synaptic growth, pruning, and remodeling.
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Neuronal overexpression of Alzheimer's disease and Down's syndrome associated DYRK1A/minibrain gene alters motor decline, neurodegeneration and synaptic plasticity in Drosophila. Neurobiol Dis 2019; 125:107-114. [PMID: 30703437 PMCID: PMC6419573 DOI: 10.1016/j.nbd.2019.01.017] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 12/12/2018] [Accepted: 01/25/2019] [Indexed: 11/24/2022] Open
Abstract
Down syndrome (DS) is characterised by abnormal cognitive and motor development, and later in life by progressive Alzheimer's disease (AD)-like dementia, neuropathology, declining motor function and shorter life expectancy. It is caused by trisomy of chromosome 21 (Hsa21), but how individual Hsa21 genes contribute to various aspects of the disorder is incompletely understood. Previous work has demonstrated a role for triplication of the Hsa21 gene DYRK1A in cognitive and motor deficits, as well as in altered neurogenesis and neurofibrillary degeneration in the DS brain, but its contribution to other DS phenotypes is unclear. Here we demonstrate that overexpression of minibrain (mnb), the Drosophila ortholog of DYRK1A, in the Drosophila nervous system accelerated age-dependent decline in motor performance and shortened lifespan. Overexpression of mnb in the eye was neurotoxic and overexpression in ellipsoid body neurons in the brain caused age-dependent neurodegeneration. At the larval neuromuscular junction, an established model for mammalian central glutamatergic synapses, neuronal mnb overexpression enhanced spontaneous vesicular transmitter release. It also slowed recovery from short-term depression of evoked transmitter release induced by high-frequency nerve stimulation and increased the number of boutons in one of the two glutamatergic motor neurons innervating the muscle. These results provide further insight into the roles of DYRK1A triplication in abnormal aging and synaptic dysfunction in DS. Overexpression of minibrain (DYRK1A) causes Down's relevant phenotypes including: Age-dependent degeneration of brain neurons Accelerated age-dependent decline in motor performance and shorted lifespan Modified presynaptic structure and enhanced spontaneous transmitter release Slowed recovery from short-term depression of synaptic transmission
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14
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Endogenous Tagging Reveals Differential Regulation of Ca 2+ Channels at Single Active Zones during Presynaptic Homeostatic Potentiation and Depression. J Neurosci 2019; 39:2416-2429. [PMID: 30692227 PMCID: PMC6435823 DOI: 10.1523/jneurosci.3068-18.2019] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 01/14/2019] [Accepted: 01/21/2019] [Indexed: 12/19/2022] Open
Abstract
Neurons communicate through Ca2+-dependent neurotransmitter release at presynaptic active zones (AZs). Neurotransmitter release properties play a key role in defining information flow in circuits and are tuned during multiple forms of plasticity. Despite their central role in determining neurotransmitter release properties, little is known about how Ca2+ channel levels are modulated to calibrate synaptic function. We used CRISPR to tag the Drosophila CaV2 Ca2+ channel Cacophony (Cac) and, in males in which all Cac channels are tagged, investigated the regulation of endogenous Ca2+ channels during homeostatic plasticity. We found that heterogeneously distributed Cac is highly predictive of neurotransmitter release probability at individual AZs and differentially regulated during opposing forms of presynaptic homeostatic plasticity. Specifically, AZ Cac levels are increased during chronic and acute presynaptic homeostatic potentiation (PHP), and live imaging during acute expression of PHP reveals proportional Ca2+ channel accumulation across heterogeneous AZs. In contrast, endogenous Cac levels do not change during presynaptic homeostatic depression (PHD), implying that the reported reduction in Ca2+ influx during PHD is achieved through functional adaptions to pre-existing Ca2+ channels. Thus, distinct mechanisms bidirectionally modulate presynaptic Ca2+ levels to maintain stable synaptic strength in response to diverse challenges, with Ca2+ channel abundance providing a rapidly tunable substrate for potentiating neurotransmitter release over both acute and chronic timescales. SIGNIFICANCE STATEMENT Presynaptic Ca2+ dynamics play an important role in establishing neurotransmitter release properties. Presynaptic Ca2+ influx is modulated during multiple forms of homeostatic plasticity at Drosophila neuromuscular junctions to stabilize synaptic communication. However, it remains unclear how this dynamic regulation is achieved. We used CRISPR gene editing to endogenously tag the sole Drosophila Ca2+ channel responsible for synchronized neurotransmitter release, and found that channel abundance is regulated during homeostatic potentiation, but not homeostatic depression. Through live imaging experiments during the adaptation to acute homeostatic challenge, we visualize the accumulation of endogenous Ca2+ channels at individual active zones within 10 min. We propose that differential regulation of Ca2+ channels confers broad capacity for tuning neurotransmitter release properties to maintain neural communication.
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15
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Xing X, Wu CF. Inter-relationships among physical dimensions, distal-proximal rank orders, and basal GCaMP fluorescence levels in Ca 2+ imaging of functionally distinct synaptic boutons at Drosophila neuromuscular junctions. J Neurogenet 2018; 32:195-208. [PMID: 30322321 DOI: 10.1080/01677063.2018.1504043] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
GCaMP imaging is widely employed for investigating neuronal Ca2+ dynamics. The Drosophila larval neuromuscular junction (NMJ) consists of three distinct types of motor terminals (type Ib, Is and II). We investigated whether variability in synaptic bouton sizes and GCaMP expression levels confound interpretations of GCaMP readouts, in inferring the intrinsic Ca2+ handling properties among these functionally distinct synapses. Analysis of large data sets accumulated over years established the wide ranges of bouton sizes and GCaMP baseline fluorescence, with large overlaps among synaptic categories. We showed that bouton size and GCaMP baseline fluorescence were not confounding factors in determining the characteristic frequency responses among type Ib, Is and II synapses. More importantly, the drastic phenotypes that hyperexcitability mutations manifest preferentially in particular synaptic categories, were not obscured by bouton heterogeneity in physical size and GCaMP expression level. Our data enabled an extensive analysis of the distal-proximal gradient of GCaMP responses upon genetic and pharmacological manipulations. The results illustrate the conditions that disrupt or enhance the distal-proximal gradients. For example, stimulus frequencies just above the threshold level produced the steepest gradient in low Ca2+ (0.1 mM) saline, while supra-threshold stimulation flattened the gradient. Moreover, membrane hyperexcitability mutations (eag1 Sh120 and parabss1) and mitochondrial inhibition by dinitrophenol (DNP) disrupted the gradient. However, a novel distal-proximal gradient of decay kinetics appeared after long-term DNP incubation. We performed focal recording to assess the failure rates in transmission at low Ca2+ levels, which yielded indications of a mild distal-proximal gradient in release probability.
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Affiliation(s)
- Xiaomin Xing
- a Department of Biology , University of Iowa , Iowa City , IA , USA
| | - Chun-Fang Wu
- a Department of Biology , University of Iowa , Iowa City , IA , USA
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16
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Abstract
Understanding how activity patterns in specific neural circuits coordinate an animal’s behavior remains a key area of neuroscience research. Genetic tools and a brain of tractable complexity make Drosophila a premier model organism for these studies. Here, we review the wealth of reagents available to map and manipulate neuronal activity with light.
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17
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Stawarski M, Justs KA, Hernandez RX, Macleod GT. The application of 'kisser' probes for resolving the distribution and microenvironment of membrane proteins in situ. J Neurogenet 2018; 32:236-245. [PMID: 30175639 DOI: 10.1080/01677063.2018.1503260] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Membrane proteins play a lead role in the formation and function of synapses, but, despite revolutions in immunology and molecular genetics, limitations persist in our ability to investigate membrane proteins in the context of an intact synapse. Here, we introduce a simple but novel approach to resolving the distribution of endogenous membrane proteins in either live or fixed tissues. The technique involves transgenic expression of a protein with an extracellular tag, a generic transmembrane domain, and an intracellular terminus that mimics the intracellular anchoring motifs of the endogenous protein of interest. We provide three examples where these kisser probes can be used to answer questions regarding the synaptic distribution of endogenous proteins and their microenvironment that would be difficult to resolve by other contemporary means: (i) the live distribution of untagged proteins at the neuromuscular junction (Cacophony and Shaker), (ii) the relative distribution of an untagged protein (PMCA) in pre- versus post-synaptic membranes separated by only 20 nm across the cleft of a fixed synapse, and (iii) the live targeting of functional probes (chemical and protein fluorescent pH reporters) to membrane protein-defined subcellular domains.
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Affiliation(s)
- Michal Stawarski
- a Department of Biomedicine , University of Basel , Basel , Switzerland
| | - Karlis Anthony Justs
- b Wilkes Honors College , Florida Atlantic University, John D MacArthur Campus , Jupiter , FL, USA
| | - Roberto Xander Hernandez
- b Wilkes Honors College , Florida Atlantic University, John D MacArthur Campus , Jupiter , FL, USA
| | - Gregory Talisker Macleod
- b Wilkes Honors College , Florida Atlantic University, John D MacArthur Campus , Jupiter , FL, USA
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18
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Akbergenova Y, Cunningham KL, Zhang YV, Weiss S, Littleton JT. Characterization of developmental and molecular factors underlying release heterogeneity at Drosophila synapses. eLife 2018; 7:38268. [PMID: 29989549 PMCID: PMC6075867 DOI: 10.7554/elife.38268] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Accepted: 06/30/2018] [Indexed: 12/14/2022] Open
Abstract
Neurons communicate through neurotransmitter release at specialized synaptic regions known as active zones (AZs). Using biosensors to visualize single synaptic vesicle fusion events at Drosophila neuromuscular junctions, we analyzed the developmental and molecular determinants of release probability (Pr) for a defined connection with ~300 AZs. Pr was heterogeneous but represented a stable feature of each AZ. Pr remained stable during high frequency stimulation and retained heterogeneity in mutants lacking the Ca2+ sensor Synaptotagmin 1. Pr correlated with both presynaptic Ca2+ channel abundance and Ca2+ influx at individual release sites. Pr heterogeneity also correlated with glutamate receptor abundance, with high Pr connections developing receptor subtype segregation. Intravital imaging throughout development revealed that AZs acquire high Pr during a multi-day maturation period, with Pr heterogeneity largely reflecting AZ age. The rate of synapse maturation was activity-dependent, as both increases and decreases in neuronal activity modulated glutamate receptor field size and segregation. To send a message to its neighbor, a neuron releases chemicals called neurotransmitters into the gap – or synapse – between them. The neurotransmitter molecules bind to proteins on the receiver neuron called receptors. But what causes the sender neuron to release neurotransmitter in the first place? The process starts when an electrical impulse called an action potential arrives at the sender cell. Its arrival causes channels in the membrane of the sender neuron to open, so that calcium ions flood into the cell. The calcium ions interact with packages of neurotransmitter molecules, known as synaptic vesicles. This causes some of the vesicles to empty their contents into the synapse. But this process is not particularly reliable. Only a small fraction of action potentials cause vesicles to fuse with the synaptic membrane. How likely this is to occur varies greatly between neurons, and even between synapses formed by the same neuron. Synapses that are likely to release neurotransmitter are said to be strong. They are good at passing messages from the sender neuron to the receiver. Synapses with a low probability of release are said to be weak. But what exactly differs between strong and weak synapses? Akbergenova et al. studied synapses between motor neurons and muscle cells in the fruit fly Drosophila. Each motor neuron forms several hundred synapses. Some of these synapses are 50 times more likely to release neurotransmitter than others. Using calcium imaging and genetics, Akbergenova et al. showed that sender cells at strong synapses have more calcium channels than sender cells at weak synapses. The subtypes and arrangement of receptor proteins also differ between the receiver neurons of strong versus weak synapses. Finally, studies in larvae revealed that newly formed synapses all start out weak and then gradually become stronger. How fast this strengthening occurs depends on how active the neuron at the synapse is. This study has shown, in unprecedented detail, key molecular factors that make some fruit fly synapses more likely to release neurotransmitter than others. Many proteins at synapses of mammals resemble those at fruit fly synapses. This means that similar factors may also explain differences in synaptic strength in the mammalian brain. Changes in the strength of synapses underlie the ability to learn. Furthermore, many neurological and psychiatric disorders result from disruption of synapses. Understanding the molecular basis of synapses will thus provide clues to the origins of certain brain diseases.
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Affiliation(s)
- Yulia Akbergenova
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Karen L Cunningham
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States
| | - Yao V Zhang
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Shirley Weiss
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, United States.,Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
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19
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Latcheva NK, Viveiros JM, Waddell EA, Nguyen PTT, Liebl FLW, Marenda DR. Epigenetic crosstalk: Pharmacological inhibition of HDACs can rescue defective synaptic morphology and neurotransmission phenotypes associated with loss of the chromatin reader Kismet. Mol Cell Neurosci 2017; 87:77-85. [PMID: 29249293 DOI: 10.1016/j.mcn.2017.11.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 10/20/2017] [Accepted: 11/06/2017] [Indexed: 12/25/2022] Open
Abstract
We are beginning to appreciate the complex mechanisms by which epigenetic proteins control chromatin dynamics to tightly regulate normal development. However, the interaction between these proteins, particularly in the context of neuronal function, remains poorly understood. Here, we demonstrate that the activity of histone deacetylases (HDACs) opposes that of a chromatin remodeling enzyme at the Drosophila neuromuscular junction (NMJ). Pharmacological inhibition of HDAC function reverses loss of function phenotypes associated with Kismet, a chromodomain helicase DNA-binding (CHD) protein. Inhibition of HDACs suppresses motor deficits, overgrowth of the NMJ, and defective neurotransmission associated with loss of Kismet. We hypothesize that Kismet and HDACs may converge on a similar set of target genes in the nervous system. Our results provide further understanding into the complex interactions between epigenetic protein function in vivo.
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Affiliation(s)
- Nina K Latcheva
- Department of Biology, Drexel University, Philadelphia, PA, United States; Program in Molecular and Cellular Biology and Genetics, Drexel University College of Medicine, Philadelphia, PA, United States
| | | | - Edward A Waddell
- Department of Biology, Drexel University, Philadelphia, PA, United States
| | - Phuong T T Nguyen
- Department of Biology, Drexel University, Philadelphia, PA, United States
| | - Faith L W Liebl
- Department of Biological Sciences, Southern Illinois University Edwardsville, Edwardsville, IL, United States
| | - Daniel R Marenda
- Department of Biology, Drexel University, Philadelphia, PA, United States; Program in Molecular and Cellular Biology and Genetics, Drexel University College of Medicine, Philadelphia, PA, United States; Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, United States.
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20
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Newman ZL, Hoagland A, Aghi K, Worden K, Levy SL, Son JH, Lee LP, Isacoff EY. Input-Specific Plasticity and Homeostasis at the Drosophila Larval Neuromuscular Junction. Neuron 2017; 93:1388-1404.e10. [PMID: 28285823 DOI: 10.1016/j.neuron.2017.02.028] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 12/18/2016] [Accepted: 02/15/2017] [Indexed: 11/28/2022]
Abstract
Synaptic connections undergo activity-dependent plasticity during development and learning, as well as homeostatic re-adjustment to ensure stability. Little is known about the relationship between these processes, particularly in vivo. We addressed this with novel quantal resolution imaging of transmission during locomotive behavior at glutamatergic synapses of the Drosophila larval neuromuscular junction. We find that two motor input types, Ib and Is, provide distinct forms of excitatory drive during crawling and differ in key transmission properties. Although both inputs vary in transmission probability, active Is synapses are more reliable. High-frequency firing "wakes up" silent Ib synapses and depresses Is synapses. Strikingly, homeostatic compensation in presynaptic strength only occurs at Ib synapses. This specialization is associated with distinct regulation of postsynaptic CaMKII. Thus, basal synaptic strength, short-term plasticity, and homeostasis are determined input-specifically, generating a functional diversity that sculpts excitatory transmission and behavioral function.
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Affiliation(s)
- Zachary L Newman
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Adam Hoagland
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Krishan Aghi
- Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Kurtresha Worden
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Sabrina L Levy
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Jun Ho Son
- Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720, USA; Berkeley Sensor and Actuator Center, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Luke P Lee
- Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720, USA; Berkeley Sensor and Actuator Center, University of California, Berkeley, Berkeley, CA 94720, USA; Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, CA 94720, USA; Biomedical Institute for Global Health Research and Technology, National University of Singapore, 119077 Singapore, Singapore
| | - Ehud Y Isacoff
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
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21
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Schultz SR, Copeland CS, Foust AJ, Quicke P, Schuck R. Advances in two photon scanning and scanless microscopy technologies for functional neural circuit imaging. PROCEEDINGS OF THE IEEE. INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS 2017; 105:139-157. [PMID: 28757657 PMCID: PMC5526632 DOI: 10.1109/jproc.2016.2577380] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Recent years have seen substantial developments in technology for imaging neural circuits, raising the prospect of large scale imaging studies of neural populations involved in information processing, with the potential to lead to step changes in our understanding of brain function and dysfunction. In this article we will review some key recent advances: improved fluorophores for single cell resolution functional neuroimaging using a two photon microscope; improved approaches to the problem of scanning active circuits; and the prospect of scanless microscopes which overcome some of the bandwidth limitations of current imaging techniques. These advances in technology for experimental neuroscience have in themselves led to technical challenges, such as the need for the development of novel signal processing and data analysis tools in order to make the most of the new experimental tools. We review recent work in some active topics, such as region of interest segmentation algorithms capable of demixing overlapping signals, and new highly accurate algorithms for calcium transient detection. These advances motivate the development of new data analysis tools capable of dealing with spatial or spatiotemporal patterns of neural activity, that scale well with pattern size.
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Affiliation(s)
- Simon R Schultz
- Center for Neurotechnology and Department of Bioengineering Imperial College London, South Kensington, LondonSW7 2AZ, UK
| | - Caroline S Copeland
- Center for Neurotechnology and Department of Bioengineering Imperial College London, South Kensington, LondonSW7 2AZ, UK
| | - Amanda J Foust
- Center for Neurotechnology and Department of Bioengineering Imperial College London, South Kensington, LondonSW7 2AZ, UK
| | - Peter Quicke
- Center for Neurotechnology and Department of Bioengineering Imperial College London, South Kensington, LondonSW7 2AZ, UK
| | - Renaud Schuck
- Center for Neurotechnology and Department of Bioengineering Imperial College London, South Kensington, LondonSW7 2AZ, UK
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22
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Bruckner JJ, Zhan H, Gratz SJ, Rao M, Ukken F, Zilberg G, O'Connor-Giles KM. Fife organizes synaptic vesicles and calcium channels for high-probability neurotransmitter release. J Cell Biol 2016; 216:231-246. [PMID: 27998991 PMCID: PMC5223599 DOI: 10.1083/jcb.201601098] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Revised: 10/19/2016] [Accepted: 11/29/2016] [Indexed: 11/22/2022] Open
Abstract
Fife is a Piccolo-RIM–related protein that regulates neurotransmission and motor behavior through an unknown mechanism. Here, Bruckner et al. show that Fife organizes synaptic vesicle docking and coupling to calcium channels to establish and modulate synaptic strength. The strength of synaptic connections varies significantly and is a key determinant of communication within neural circuits. Mechanistic insight into presynaptic factors that establish and modulate neurotransmitter release properties is crucial to understanding synapse strength, circuit function, and neural plasticity. We previously identified Drosophila Piccolo-RIM-related Fife, which regulates neurotransmission and motor behavior through an unknown mechanism. Here, we demonstrate that Fife localizes and interacts with RIM at the active zone cytomatrix to promote neurotransmitter release. Loss of Fife results in the severe disruption of active zone cytomatrix architecture and molecular organization. Through electron tomographic and electrophysiological studies, we find a decrease in the accumulation of release-ready synaptic vesicles and their release probability caused by impaired coupling to Ca2+ channels. Finally, we find that Fife is essential for the homeostatic modulation of neurotransmission. We propose that Fife organizes active zones to create synaptic vesicle release sites within nanometer distance of Ca2+ channel clusters for reliable and modifiable neurotransmitter release.
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Affiliation(s)
- Joseph J Bruckner
- Cell and Molecular Biology Training Program, University of Wisconsin-Madison, Madison, WI 53706
| | - Hong Zhan
- Laboratory of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706
| | - Scott J Gratz
- Laboratory of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706
| | - Monica Rao
- Cell and Molecular Biology Training Program, University of Wisconsin-Madison, Madison, WI 53706
| | - Fiona Ukken
- Laboratory of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706
| | - Gregory Zilberg
- Laboratory of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706
| | - Kate M O'Connor-Giles
- Cell and Molecular Biology Training Program, University of Wisconsin-Madison, Madison, WI 53706 .,Laboratory of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706.,Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI 53706
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23
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Deshpande M, Feiger Z, Shilton AK, Luo CC, Silverman E, Rodal AA. Role of BMP receptor traffic in synaptic growth defects in an ALS model. Mol Biol Cell 2016; 27:2898-910. [PMID: 27535427 PMCID: PMC5042577 DOI: 10.1091/mbc.e16-07-0519] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 08/03/2016] [Indexed: 12/12/2022] Open
Abstract
In a Drosophila model of ALS, neuronal defects are associated with altered endosomal traffic of growth factor receptors and loss of growth-promoting signals. Manipulation of an endosomal recycling pathway suppresses these neuronal defects. The findings suggest that rerouting membrane traffic could be therapeutic in ALS. TAR DNA-binding protein 43 (TDP-43) is genetically and functionally linked to amyotrophic lateral sclerosis (ALS) and regulates transcription, splicing, and transport of thousands of RNA targets that function in diverse cellular pathways. In ALS, pathologically altered TDP-43 is believed to lead to disease by toxic gain-of-function effects on RNA metabolism, as well as by sequestering endogenous TDP-43 and causing its loss of function. However, it is unclear which of the numerous cellular processes disrupted downstream of TDP-43 dysfunction lead to neurodegeneration. Here we found that both loss and gain of function of TDP-43 in Drosophila cause a reduction of synaptic growth–promoting bone morphogenic protein (BMP) signaling at the neuromuscular junction (NMJ). Further, we observed a shift of BMP receptors from early to recycling endosomes and increased mobility of BMP receptor–containing compartments at the NMJ. Inhibition of the recycling endosome GTPase Rab11 partially rescued TDP-43–induced defects in BMP receptor dynamics and distribution and suppressed BMP signaling, synaptic growth, and larval crawling defects. Our results indicate that defects in receptor traffic lead to neuronal dysfunction downstream of TDP-43 misregulation and that rerouting receptor traffic may be a viable strategy for rescuing neurological impairment.
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Affiliation(s)
| | - Zachary Feiger
- Department of Biology, Brandeis University, Waltham, MA 02453
| | | | - Christina C Luo
- Department of Biology, Brandeis University, Waltham, MA 02453
| | - Ethan Silverman
- Department of Biology, Brandeis University, Waltham, MA 02453
| | - Avital A Rodal
- Department of Biology, Brandeis University, Waltham, MA 02453
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24
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Kittel RJ, Heckmann M. Synaptic Vesicle Proteins and Active Zone Plasticity. Front Synaptic Neurosci 2016; 8:8. [PMID: 27148040 PMCID: PMC4834300 DOI: 10.3389/fnsyn.2016.00008] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 03/31/2016] [Indexed: 11/13/2022] Open
Abstract
Neurotransmitter is released from synaptic vesicles at the highly specialized presynaptic active zone (AZ). The complex molecular architecture of AZs mediates the speed, precision and plasticity of synaptic transmission. Importantly, structural and functional properties of AZs vary significantly, even for a given connection. Thus, there appear to be distinct AZ states, which fundamentally influence neuronal communication by controlling the positioning and release of synaptic vesicles. Vice versa, recent evidence has revealed that synaptic vesicle components also modulate organizational states of the AZ. The protein-rich cytomatrix at the active zone (CAZ) provides a structural platform for molecular interactions guiding vesicle exocytosis. Studies in Drosophila have now demonstrated that the vesicle proteins Synaptotagmin-1 (Syt1) and Rab3 also regulate glutamate release by shaping differentiation of the CAZ ultrastructure. We review these unexpected findings and discuss mechanistic interpretations of the reciprocal relationship between synaptic vesicles and AZ states, which has heretofore received little attention.
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Affiliation(s)
- Robert J Kittel
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
| | - Manfred Heckmann
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
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25
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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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26
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Wong MY, Cavolo SL, Levitan ES. Synaptic neuropeptide release by dynamin-dependent partial release from circulating vesicles. Mol Biol Cell 2015; 26:2466-74. [PMID: 25904335 PMCID: PMC4571301 DOI: 10.1091/mbc.e15-01-0002] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 04/17/2015] [Indexed: 12/13/2022] Open
Abstract
Neurons release neuropeptides, enzymes, and neurotrophins by exocytosis of dense-core vesicles (DCVs). Peptide release from individual DCVs has been imaged in vitro with endocrine cells and at the neuron soma, growth cones, neurites, axons, and dendrites but not at nerve terminals, where peptidergic neurotransmission occurs. Single presynaptic DCVs have, however, been tracked in native terminals with simultaneous photobleaching and imaging (SPAIM) to show that DCVs undergo anterograde and retrograde capture as they circulate through en passant boutons. Here dynamin (encoded by the shibire gene) is shown to enhance activity-evoked peptide release at the Drosophila neuromuscular junction. SPAIM demonstrates that activity depletes only a portion of a single presynaptic DCV's content. Activity initiates exocytosis within seconds, but subsequent release occurs slowly. Synaptic neuropeptide release is further sustained by DCVs undergoing multiple rounds of exocytosis. Synaptic neuropeptide release is surprisingly similar regardless of anterograde or retrograde DCV transport into boutons, bouton location, and time of arrival in the terminal. Thus vesicle circulation and bidirectional capture supply synapses with functionally competent DCVs. These results show that activity-evoked synaptic neuropeptide release is independent of a DCV's past traffic and occurs by slow, dynamin-dependent partial emptying of DCVs, suggestive of kiss-and-run exocytosis.
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Affiliation(s)
- Man Yan Wong
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Samantha L Cavolo
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Edwin S Levitan
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
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Pech U, Revelo NH, Seitz KJ, Rizzoli SO, Fiala A. Optical dissection of experience-dependent pre- and postsynaptic plasticity in the Drosophila brain. Cell Rep 2015; 10:2083-95. [PMID: 25818295 DOI: 10.1016/j.celrep.2015.02.065] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 01/24/2015] [Accepted: 02/26/2015] [Indexed: 01/18/2023] Open
Abstract
Drosophila represents a key model organism for dissecting neuronal circuits that underlie innate and adaptive behavior. However, this task is limited by a lack of tools to monitor physiological parameters of spatially distributed, central synapses in identified neurons. We generated transgenic fly strains that express functional fluorescent reporters targeted to either pre- or postsynaptic compartments. Presynaptic Ca(2+) dynamics are monitored using synaptophysin-coupled GCaMP3, synaptic transmission is monitored using red fluorescent synaptophysin-pHTomato, and postsynaptic Ca(2+) dynamics are visualized using GCaMP3 fused with the postsynaptic matrix protein, dHomer. Using two-photon in vivo imaging of olfactory projection neurons, odor-evoked activity across populations of synapses is visualized in the antennal lobe and the mushroom body calyx. Prolonged odor exposure causes odor-specific and differential experience-dependent changes in pre- and postsynaptic activity at both levels of olfactory processing. The approach advances the physiological analysis of synaptic connections across defined groups of neurons in intact Drosophila.
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Affiliation(s)
- Ulrike Pech
- Department of Molecular Neurobiology of Behavior, Johann-Friedrich-Blumenbach-Institute for Zoology and Anthropology, Georg-August-University Göttingen, Julia-Lermontowa-Weg 3, 37077 Göttingen, Germany
| | - Natalia H Revelo
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, Humboldtallee 23, 37073 Göttingen, Germany
| | - Katharina J Seitz
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, Humboldtallee 23, 37073 Göttingen, Germany
| | - Silvio O Rizzoli
- Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, Humboldtallee 23, 37073 Göttingen, Germany
| | - André Fiala
- Department of Molecular Neurobiology of Behavior, Johann-Friedrich-Blumenbach-Institute for Zoology and Anthropology, Georg-August-University Göttingen, Julia-Lermontowa-Weg 3, 37077 Göttingen, Germany.
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Ball RW, Peled ES, Guerrero G, Isacoff EY. BMP signaling and microtubule organization regulate synaptic strength. Neuroscience 2015; 291:155-66. [PMID: 25681521 DOI: 10.1016/j.neuroscience.2015.01.069] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Revised: 12/24/2014] [Accepted: 01/29/2015] [Indexed: 12/14/2022]
Abstract
The strength of synaptic transmission between a neuron and multiple postsynaptic partners can vary considerably. We have studied synaptic heterogeneity using the glutamatergic Drosophila neuromuscular junction (NMJ), which contains multiple synaptic connections of varying strengths between a motor axon and muscle fiber. In larval NMJs, there is a gradient of synaptic transmission from weak proximal to strong distal boutons. We imaged synaptic transmission with the postsynaptically targeted fluorescent calcium sensor SynapCam, to investigate the molecular pathways that determine synaptic strength and set up this gradient. We discovered that mutations in the Bone Morphogenetic Protein (BMP) signaling pathway disrupt production of strong distal boutons. We find that strong connections contain unbundled microtubules in the boutons, suggesting a role for microtubule organization in transmission strength. The spastin mutation, which disorganizes microtubules, disrupted the transmission gradient, supporting this interpretation. We propose that the BMP pathway, shown previously to function in the homeostatic regulation of synaptic growth, also boosts synaptic transmission in a spatially selective manner that depends on the microtubule system.
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Affiliation(s)
- R W Ball
- Department of Molecular and Cell Biology and the Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, United States
| | - E S Peled
- Department of Molecular and Cell Biology and the Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, United States
| | - G Guerrero
- Department of Molecular and Cell Biology and the Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, United States
| | - E Y Isacoff
- Department of Molecular and Cell Biology and the Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, United States; Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
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Paul MM, Pauli M, Ehmann N, Hallermann S, Sauer M, Kittel RJ, Heckmann M. Bruchpilot and Synaptotagmin collaborate to drive rapid glutamate release and active zone differentiation. Front Cell Neurosci 2015; 9:29. [PMID: 25698934 PMCID: PMC4318344 DOI: 10.3389/fncel.2015.00029] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 01/16/2015] [Indexed: 11/13/2022] Open
Abstract
The active zone (AZ) protein Bruchpilot (Brp) is essential for rapid glutamate release at Drosophila melanogaster neuromuscular junctions (NMJs). Quantal time course and measurements of action potential-waveform suggest that presynaptic fusion mechanisms are altered in brp null mutants (brp(69) ). This could account for their increased evoked excitatory postsynaptic current (EPSC) delay and rise time (by about 1 ms). To test the mechanism of release protraction at brp(69) AZs, we performed knock-down of Synaptotagmin-1 (Syt) via RNAi (syt(KD) ) in wildtype (wt), brp(69) and rab3 null mutants (rab3(rup) ), where Brp is concentrated at a small number of AZs. At wt and rab3(rup) synapses, syt(KD) lowered EPSC amplitude while increasing rise time and delay, consistent with the role of Syt as a release sensor. In contrast, syt(KD) did not alter EPSC amplitude at brp(69) synapses, but shortened delay and rise time. In fact, following syt(KD) , these kinetic properties were strikingly similar in wt and brp(69) , which supports the notion that Syt protracts release at brp(69) synapses. To gain insight into this surprising role of Syt at brp(69) AZs, we analyzed the structural and functional differentiation of synaptic boutons at the NMJ. At 'tonic' type Ib motor neurons, distal boutons contain more AZs, more Brp proteins per AZ and show elevated and accelerated glutamate release compared to proximal boutons. The functional differentiation between proximal and distal boutons is Brp-dependent and reduced after syt(KD) . Notably, syt(KD) boutons are smaller, contain fewer Brp positive AZs and these are of similar number in proximal and distal boutons. In addition, super-resolution imaging via dSTORM revealed that syt(KD) increases the number and alters the spatial distribution of Brp molecules at AZs, while the gradient of Brp proteins per AZ is diminished. In summary, these data demonstrate that normal structural and functional differentiation of Drosophila AZs requires concerted action of Brp and Syt.
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Affiliation(s)
- Mila M Paul
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
| | - Martin Pauli
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
| | - Nadine Ehmann
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
| | - Stefan Hallermann
- Carl-Ludwig-Institute for Physiology, University of Leipzig Leipzig, Germany
| | - Markus Sauer
- Department of Biotechnology and Biophysics, Julius-Maximilians-University Würzburg Würzburg, Germany
| | - Robert J Kittel
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
| | - Manfred Heckmann
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
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Quantitative super-resolution imaging of Bruchpilot distinguishes active zone states. Nat Commun 2014; 5:4650. [PMID: 25130366 PMCID: PMC4143948 DOI: 10.1038/ncomms5650] [Citation(s) in RCA: 152] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2014] [Accepted: 07/09/2014] [Indexed: 12/18/2022] Open
Abstract
The precise molecular architecture of synaptic active zones (AZs) gives rise to different structural and functional AZ states that fundamentally shape chemical neurotransmission. However, elucidating the nanoscopic protein arrangement at AZs is impeded by the diffraction-limited resolution of conventional light microscopy. Here we introduce new approaches to quantify endogenous protein organization at single-molecule resolution in situ with super-resolution imaging by direct stochastic optical reconstruction microscopy (dSTORM). Focusing on the Drosophila neuromuscular junction (NMJ), we find that the AZ cytomatrix (CAZ) is composed of units containing ~137 Bruchpilot (Brp) proteins, three quarters of which are organized into about 15 heptameric clusters. We test for a quantitative relationship between CAZ ultrastructure and neurotransmitter release properties by engaging Drosophila mutants and electrophysiology. Our results indicate that the precise nanoscopic organization of Brp distinguishes different physiological AZ states and link functional diversification to a heretofore unrecognized neuronal gradient of the CAZ ultrastructure. Complex molecular interactions occur in the active zone cytomatrix (CAZ) within the presynaptic terminal to regulate synaptic plasticity. Here, the authors use imaging techniques to show that the CAZ is composed of units containing on average 137 Bruchpilot proteins, many of which are arranged into clusters.
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Gertner DM, Desai S, Lnenicka GA. Synaptic excitation is regulated by the postsynaptic dSK channel at the Drosophila larval NMJ. J Neurophysiol 2014; 111:2533-43. [PMID: 24671529 DOI: 10.1152/jn.00903.2013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the mammalian central nervous system, the postsynaptic small-conductance Ca(2+)-dependent K(+) (SK) channel has been shown to reduce postsynaptic depolarization and limit Ca(2+) influx through N-methyl-d-aspartate receptors. To examine further the role of the postsynaptic SK channel in synaptic transmission, we studied its action at the Drosophila larval neuromuscular junction (NMJ). Repetitive synaptic stimulation produced an increase in postsynaptic membrane conductance leading to depression of excitatory postsynaptic potential amplitude and hyperpolarization of the resting membrane potential (RMP). This reduction in synaptic excitation was due to the postsynaptic Drosophila SK (dSK) channel; synaptic depression, increased membrane conductance and RMP hyperpolarization were reduced in dSK mutants or after expressing a Ca(2+) buffer in the muscle. Ca(2+) entering at the postsynaptic membrane was sufficient to activate dSK channels based upon studies in which the muscle membrane was voltage clamped to prevent opening voltage-dependent Ca(2+) channels. Increasing external Ca(2+) produced an increase in resting membrane conductance and RMP that was not seen in dSK mutants or after adding the glutamate-receptor blocker philanthotoxin. Thus it appeared that dSK channels were also activated by spontaneous transmitter release and played a role in setting membrane conductance and RMP. In mammals, dephosphorylation by protein phosphatase 2A (PP2A) increased the Ca(2+) sensitivity of the SK channel; PP2A appeared to increase the sensitivity of the dSK channel since PP2A inhibitors reduced activation of the dSK channel by evoked synaptic activity or increased external Ca(2+). It is proposed that spontaneous and evoked transmitter release activate the postsynaptic dSK channel to limit synaptic excitation and stabilize synapses.
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Affiliation(s)
- Daniel M Gertner
- Department of Biological Sciences, University at Albany, Albany, New York
| | - Sunil Desai
- Department of Biological Sciences, University at Albany, Albany, New York
| | - Gregory A Lnenicka
- Department of Biological Sciences, University at Albany, Albany, New York
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de Castro C, Titlow J, Majeed ZR, Cooper RL. Analysis of various physiological salines for heart rate, CNS function, and synaptic transmission at neuromuscular junctions in Drosophila melanogaster larvae. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2013; 200:83-92. [PMID: 24190421 DOI: 10.1007/s00359-013-0864-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 10/12/2013] [Accepted: 10/15/2013] [Indexed: 10/26/2022]
Abstract
Drosophila serves as a playground for examining the effects of genetic mutations on development, physiological function and behavior. Many physiological measures that address the effects of mutations require semi-intact or cultured preparations. To obtain consistent physiological recordings, cellular function needs to remain viable. Numerous physiological salines have been developed for fly preparations, with emphasis on nervous system viability. The commonly used saline drifts in pH and will cause an alteration in the heart rate. We identify a saline that maintains a stable pH and physiological function in the larval heart, skeletal neuromuscular junction, and ventral nerve cord preparations. Using these common assays, we screened various pH buffers of differing concentrations to identify optimum conditions. Buffers at 25 mM produce a stable heart rate with minimal variation in pH. Excitatory junction potentials evoked directly on larval muscles or through sensory-CNS-motor circuits were unaffected by at buffers at 25 mM. The salines examined did not impede the modulatory effect of serotonin on heart rate or neural activity. Together, our results indicate that the higher buffer concentrations needed to stabilize pH in HL3 hemolymph-like saline do not interfere with the acute function of neurons or cardiac myocytes.
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Affiliation(s)
- Clara de Castro
- Sayre School, Upper School, 194 North Limestone, Lexington, KY, 40507, USA
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Chen TW, Wardill TJ, Sun Y, Pulver SR, Renninger SL, Baohan A, Schreiter ER, Kerr RA, Orger MB, Jayaraman V, Looger LL, Svoboda K, Kim DS. Ultrasensitive fluorescent proteins for imaging neuronal activity. Nature 2013; 499:295-300. [PMID: 23868258 PMCID: PMC3777791 DOI: 10.1038/nature12354] [Citation(s) in RCA: 4081] [Impact Index Per Article: 371.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Accepted: 06/04/2013] [Indexed: 12/15/2022]
Abstract
Fluorescent calcium sensors are widely used to image neural activity. Using structure-based mutagenesis and neuron-based screening, we developed a family of ultra-sensitive protein calcium sensors (GCaMP6) that outperformed other sensors in cultured neurons and in zebrafish, flies, and mice in vivo. In layer 2/3 pyramidal neurons of the mouse visual cortex, GCaMP6 reliably detected single action potentials in neuronal somata and orientation-tuned synaptic calcium transients in individual dendritic spines. The orientation tuning of structurally persistent spines was largely stable over timescales of weeks. Orientation tuning averaged across spine populations predicted the tuning of their parent cell. Although the somata of GABAergic neurons showed little orientation tuning, their dendrites included highly tuned dendritic segments (5 - 40 micrometers long). GCaMP6 sensors thus provide new windows into the organization and dynamics of neural circuits over multiple spatial and temporal scales.
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Affiliation(s)
- Tsai-Wen Chen
- Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, Virginia 20147, USA
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Caldwell L, Harries P, Sydlik S, Schwiening CJ. Presynaptic pH and vesicle fusion in Drosophila larvae neurones. Synapse 2013; 67:729-40. [PMID: 23649934 PMCID: PMC4282566 DOI: 10.1002/syn.21678] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Accepted: 04/22/2013] [Indexed: 11/11/2022]
Abstract
Both intracellular pH (pHi) and synaptic cleft pH change during neuronal activity yet little is known about how these pH shifts might affect synaptic transmission by influencing vesicle fusion. To address this we imaged pH- and Ca2+-sensitive fluorescent indicators (HPTS, Oregon green) in boutons at neuromuscular junctions. Electrical stimulation of motor nerves evoked presynaptic Ca2+i rises and pHi falls (∼0.1 pH units) followed by recovery of both Ca2+i and pHi. The plasma-membrane calcium ATPase (PMCA) inhibitor, 5(6)-carboxyeosin diacetate, slowed both the calcium recovery and the acidification. To investigate a possible calcium-independent role for the pHi shifts in modulating vesicle fusion we recorded post-synaptic miniature end-plate potential (mEPP) and current (mEPC) frequency in Ca2+-free solution. Acidification by propionate superfusion, NH4+ withdrawal, or the inhibition of acid extrusion on the Na+/H+ exchanger (NHE) induced a rise in miniature frequency. Furthermore, the inhibition of acid extrusion enhanced the rise induced by propionate addition and NH4+ removal. In the presence of NH4+, 10 out of 23 cells showed, after a delay, one or more rises in miniature frequency. These findings suggest that Ca2+-dependent pHi shifts, caused by the PMCA and regulated by NHE, may stimulate vesicle release. Furthermore, in the presence of membrane permeant buffers, exocytosed acid or its equivalents may enhance release through positive feedback. This hitherto neglected pH signalling, and the potential feedback role of vesicular acid, could explain some important neuronal excitability changes associated with altered pH and its buffering. Synapse 67:729–740, 2013.
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Affiliation(s)
- Lesley Caldwell
- Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3EG, United Kingdom
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36
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Rapid feedback regulation of synaptic efficacy during high-frequency activity at the Drosophila larval neuromuscular junction. Proc Natl Acad Sci U S A 2013; 110:9142-7. [PMID: 23674684 DOI: 10.1073/pnas.1221314110] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
High-frequency firing of neurons depresses transmitter release at many synapses. At the glutamatergic synapse of the Drosophila larval neuromuscular junction, we find that presynaptic depression is modulated by postsynaptic ionotropic glutamate receptor (iGluR) activity. Although basal release at low frequency was insensitive to postsynaptic iGluR activity, recovery from depression elicited by high-frequency presynaptic trains decreased with partial block of native iGluRs. Moreover, recovery from depression increased with optical activation of the light-gated mammalian iGluR6 (LiGluR) expressed postsynaptically. The enhancement of recovery from depression occurred within 2 min of optical activation of LiGluR and persisted for minutes after optical deactivation. This effect depended on cAMP-dependent presynaptic recruitment of vesicles from the reserve pool. Our findings reveal a unique dimension to postsynaptic iGluR activity: fast retrograde signaling that preserves transmission efficacy during high-frequency presynaptic firing.
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Abstract
Sustained neuronal communication relies on the coordinated activity of multiple proteins that regulate synaptic vesicle biogenesis and cycling within the presynaptic terminal. Synaptogyrin and synaptophysin are conserved MARVEL domain-containing transmembrane proteins that are among the most abundant synaptic vesicle constituents, although their role in the synaptic vesicle cycle has remained elusive. To further investigate the function of these proteins, we generated and characterized a synaptogyrin (gyr)-null mutant in Drosophila, whose genome encodes a single synaptogyrin isoform and lacks a synaptophysin homolog. We demonstrate that Drosophila synaptogyrin plays a modulatory role in synaptic vesicle biogenesis at larval neuromuscular junctions. Drosophila lacking synaptogyrin are viable and fertile and have no overt deficits in motor function. However, ultrastructural analysis of gyr larvae revealed increased synaptic vesicle diameter and enhanced variability in the size of synaptic vesicles. In addition, the resolution of endocytic cisternae into synaptic vesicles in response to strong stimulation is defective in gyr mutants. Electrophysiological analysis demonstrated an increase in quantal size and a concomitant decrease in quantal content, suggesting functional consequences for transmission caused by the loss of synaptogyrin. Furthermore, high-frequency stimulation resulted in increased facilitation and a delay in recovery from synaptic depression, indicating that synaptic vesicle exo-endocytosis is abnormally regulated during intense stimulation conditions. These results suggest that synaptogyrin modulates the synaptic vesicle exo-endocytic cycle and is required for the proper biogenesis of synaptic vesicles at nerve terminals.
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Abstract
The Drosophila larval neuromuscular junction (NMJ) is a powerful system for the genetic and molecular analysis of neuronal excitability, synaptic transmission, and synaptic development. However, its use for studying age-dependent processes, such as maintenance of neuronal viability and synaptic stability, are temporally limited by the onset of pupariation and metamorphosis. Here we characterize larval NMJ growth, growth regulation, structure, and function in a developmental variant with an extended third instar (ETI). RNAi-knockdown of the prothoracicotropic hormone receptor, torso, in the ring gland of developing larvae leaves the timing of first and second instar molts largely unchanged, but triples duration of the third instar from 3 to 9.5 d (McBrayer et al., 2007; Rewitz et al., 2009). During this ETI period, NMJs undergo additional growth (adding >50 boutons/NMJ), and this growth remains under the control of the canonical regulators Highwire and the TGFβ/BMP pathway. NMJ growth during the ETI period occurs via addition of new branches, satellite boutons, and interstitial boutons, and continues even after muscle growth levels off. Throughout the ETI, organization of synapses and active zones remains normal, and synaptic transmission is unchanged. These results establish the ETI larval system as a viable model for studying motor neuron diseases and for investigating time-dependent effects of perturbations that impair mechanisms of neuroprotection, synaptic maintenance, and response to neural injury.
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39
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Macleod GT. Calcium imaging at the Drosophila larval neuromuscular junction. Cold Spring Harb Protoc 2012; 2012:758-66. [PMID: 22753609 DOI: 10.1101/pdb.top070078] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Calcium imaging uses optical imaging techniques to measure the concentration of free calcium [Ca(2+)] in live cells. It is a highly informative technique in neurobiology because Ca(2+) is involved in many neuronal signaling pathways and serves as the trigger for neurotransmitter release. The technique relies on loading Ca(2+) indicators into cells, measuring the quantity and/or wavelength of the photons emitted by the Ca(2+) indicator, and interpreting these data in terms of [Ca(2+)]. There are several possible methods for loading synthetic Ca(2+) indicators into subcellular compartments, for example, topical application of membrane-permeant Ca(2+) indicators, forward-filling of dextran conjugates, and direct injection. These techniques are applicable to calcium imaging at the Drosophila larval neuromuscular junction (NMJ), and are also readily adaptable to Drosophila embryo and adult preparations.
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Lloyd TE, Machamer J, O'Hara K, Kim JH, Collins SE, Wong MY, Sahin B, Imlach W, Yang Y, Levitan ES, McCabe BD, Kolodkin AL. The p150(Glued) CAP-Gly domain regulates initiation of retrograde transport at synaptic termini. Neuron 2012; 74:344-60. [PMID: 22542187 DOI: 10.1016/j.neuron.2012.02.026] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/28/2012] [Indexed: 12/15/2022]
Abstract
p150(Glued) is the major subunit of dynactin, a complex that functions with dynein in minus-end-directed microtubule transport. Mutations within the p150(Glued) CAP-Gly microtubule-binding domain cause neurodegenerative diseases through an unclear mechanism. A p150(Glued) motor neuron degenerative disease-associated mutation introduced into the Drosophila Glued locus generates a partial loss-of-function allele (Gl(G38S)) with impaired neurotransmitter release and adult-onset locomotor dysfunction. Disruption of the p150(Glued) CAP-Gly domain in neurons causes a specific disruption of vesicle trafficking at terminal boutons (TBs), the distal-most ends of synapses. Gl(G38S) larvae accumulate endosomes along with dynein and kinesin motor proteins within swollen TBs, and genetic analyses show that kinesin and p150(Glued) function cooperatively at TBs to coordinate transport. Therefore, the p150(Glued) CAP-Gly domain regulates dynein-mediated retrograde transport at synaptic termini, and this function of dynactin is disrupted by a mutation that causes motor neuron disease.
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Affiliation(s)
- Thomas E Lloyd
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Transsynaptic control of presynaptic Ca²⁺ influx achieves homeostatic potentiation of neurotransmitter release. Curr Biol 2012; 22:1102-8. [PMID: 22633807 DOI: 10.1016/j.cub.2012.04.018] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Revised: 04/03/2012] [Accepted: 04/10/2012] [Indexed: 11/20/2022]
Abstract
Given the complexity of the nervous system and its capacity for change, it is remarkable that robust, reproducible neural function and animal behavior can be achieved. It is now apparent that homeostatic signaling systems have evolved to stabilize neural function. At the neuromuscular junction (NMJ) of organisms ranging from Drosophila to human, inhibition of postsynaptic neurotransmitter receptor function causes a homeostatic increase in presynaptic release that precisely restores postsynaptic excitation. Here we address what occurs within the presynaptic terminal to achieve homeostatic potentiation of release at the Drosophila NMJ. By imaging presynaptic Ca(2+) transients evoked by single action potentials, we reveal a retrograde, transsynaptic modulation of presynaptic Ca(2+) influx that is sufficient to account for the rapid induction and sustained expression of the homeostatic change in vesicle release. We show that the homeostatic increase in Ca(2+) influx and release is blocked by a point mutation in the presynaptic CaV2.1 channel, demonstrating that the modulation of presynaptic Ca(2+) influx through this channel is causally required for homeostatic potentiation of release. Together with additional analyses, we establish that retrograde, transsynaptic modulation of presynaptic Ca(2+) influx through CaV2.1 channels is a key factor underlying the homeostatic regulation of neurotransmitter release.
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Peng X, Parsons TD, Balice-Gordon RJ. Determinants of synaptic strength vary across an axon arbor. J Neurophysiol 2012; 107:2430-41. [PMID: 22279193 PMCID: PMC3362249 DOI: 10.1152/jn.00615.2011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Accepted: 01/23/2012] [Indexed: 12/20/2022] Open
Abstract
We used synaptophysin-pHluorin expressed in hippocampal neurons to address how functional properties of terminals, namely, evoked release, total vesicle pool size, and release fraction, vary spatially across individual axon arbors. Consistent with previous reports, over short arbor distances (≈ 100 μm), evoked release was spatially heterogeneous when terminals contacted different postsynaptic dendrites or neurons. Regardless of the postsynaptic configuration, the evoked release and total vesicle pool size spatially covaried, suggesting that the fraction of synaptic vesicles available for release (release fraction) was similar over short distances. Evoked release and total vesicle pool size were highly correlated with the amount of NMDA receptors and PSD-95 in postsynaptic specialization. However, when individual axons were followed over longer distances (several hundred micrometers), a significant increase in evoked release was observed distally that was associated with an increased release fraction in distal terminals. The increase in distal release fraction can be accounted for by changes in individual vesicle release probability as well as readily releasable pool size. Our results suggest that for a single axon arbor, presynaptic strength indicated by evoked release over short distances is correlated with heterogeneity in total vesicle pool size, whereas over longer distances presynaptic strength is correlated with the spatial modulation of release fraction. Thus the mechanisms that determine synaptic strength differ depending on spatial scale.
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Affiliation(s)
- Xiaoyu Peng
- Department of Biology Graduate Group, University of Pennsylvania School of Arts and Sciences, Philadelphia, PA, USA
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43
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Wong MY, Zhou C, Shakiryanova D, Lloyd TE, Deitcher DL, Levitan ES. Neuropeptide delivery to synapses by long-range vesicle circulation and sporadic capture. Cell 2012; 148:1029-38. [PMID: 22385966 DOI: 10.1016/j.cell.2011.12.036] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Revised: 10/13/2011] [Accepted: 12/16/2011] [Indexed: 12/11/2022]
Abstract
Neurotransmission requires anterograde axonal transport of dense core vesicles (DCVs) containing neuropeptides and active zone components from the soma to nerve terminals. However, it is puzzling how one-way traffic could uniformly supply sequential release sites called en passant boutons. Here, Drosophila neuropeptide-containing DCVs are tracked in vivo for minutes with a new method called simultaneous photobleaching and imaging (SPAIM). Surprisingly, anterograde DCVs typically bypass proximal boutons to accumulate initially in the most distal bouton. Then, excess distal DCVs undergo dynactin-dependent retrograde transport back through proximal boutons into the axon. Just before re-entering the soma, DCVs again reverse for another round of anterograde axonal transport. While circulating over long distances, both anterograde and retrograde DCVs are captured sporadically in en passant boutons. Therefore, vesicle circulation, which includes long-range retrograde transport and inefficient bidirectional capture, overcomes the limitations of one-way anterograde transport to uniformly supply release sites with DCVs.
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Affiliation(s)
- Man Yan Wong
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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Ahrens KF, Heider B, Lee H, Isacoff EY, Siegel RM. Two-photon scanning microscopy of in vivo sensory responses of cortical neurons genetically encoded with a fluorescent voltage sensor in rat. Front Neural Circuits 2012; 6:15. [PMID: 22461770 PMCID: PMC3310150 DOI: 10.3389/fncir.2012.00015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Accepted: 03/05/2012] [Indexed: 01/25/2023] Open
Abstract
A fluorescent voltage sensor protein “Flare” was created from a Kv1.4 potassium channel with YFP situated to report voltage-induced conformational changes in vivo. The RNA virus Sindbis introduced Flare into neurons in the binocular region of visual cortex in rat. Injection sites were selected based on intrinsic optical imaging. Expression of Flare occurred in the cell bodies and dendritic processes. Neurons imaged in vivo using two-photon scanning microscopy typically revealed the soma best, discernable against the background labeling of the neuropil. Somatic fluorescence changes were correlated with flashed visual stimuli; however, averaging was essential to observe these changes. This study demonstrates that the genetic modification of single neurons to express a fluorescent voltage sensor can be used to assess neuronal activity in vivo.
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Affiliation(s)
- Kurt F Ahrens
- Center for Molecular and Behavioral Neuroscience, Rutgers, The State University of New Jersey, Newark NJ, USA
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Russell JT. Imaging calcium signals in vivo: a powerful tool in physiology and pharmacology. Br J Pharmacol 2012; 163:1605-25. [PMID: 20718728 DOI: 10.1111/j.1476-5381.2010.00988.x] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The design and engineering of organic fluorescent Ca(2+) indicators approximately 30 years ago opened the door for imaging cellular Ca(2+) signals with a high degree of temporal and spatial resolution. Over this time, Ca(2+) imaging has revolutionized our approaches for tissue-level spatiotemporal analysis of functional organization and has matured into a powerful tool for in situ imaging of cellular activity in the living animal. In vivo Ca(2+) imaging with temporal resolution at the millisecond range and spatial resolution at micrometer range has been achieved through novel designs of Ca(2+) sensors, development of modern microscopes and powerful imaging techniques such as two-photon microscopy. Imaging Ca(2+) signals in ensembles of cells within tissue in 3D allows for analysis of integrated cellular function, which, in the case of the brain, enables recording activity patterns in local circuits. The recent development of miniaturized compact, fibre-optic-based, mechanically flexible microendoscopes capable of two-photon microscopy opens the door for imaging activity in awake, behaving animals. This development is poised to open a new chapter in physiological experiments and for pharmacological approaches in the development of novel therapies.
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Affiliation(s)
- James T Russell
- Section on Cell Biology and Signal Transduction, Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development/NIH, 49 Convent Drive, Bethesda, MD 20892-4480, USA.
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Abstract
The synaptic active zone, the site where Ca(2+)-triggered fusion of synaptic vesicles takes place, is commonly associated with protein-rich, electron-dense cytomatrices. The molecular composition and functional role of active zones, especially in the context of vesicular exo- and endocytosis, are under intense investigation. Per se, Drosophila synapses, which display so-called T-bars as electron-dense specializations, should be a highly suitable model system, as they allow for a combination of efficient genetics with ultrastructural and electrophysiological analyses. However, it needed a biochemical approach of the Buchner laboratory to "molecularly" access the T-bar by identification of the CAST/ERC-family member Bruchpilot as the first T-bar-residing protein. Genetic elimination of Bruchpilot revealed that the protein is essential for T-bar formation, calcium channel clustering, and hence proper vesicle fusion and patterned synaptic plasticity. Recently, Bruchpilot was shown to directly shape the T-bar, likely by adopting an elongated conformation. Moreover, first mechanisms that control the availability of Bruchpilot for T-bar assembly were described. This review seeks to summarize the information on T-bar structure, as well as on functional aspects, formulating the hypothesis that T-bars are genuine "plasticity modules."
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Affiliation(s)
- Carolin Wichmann
- NeuroCure Cluster of Excellence, Charité Berlin, Berlin, Germany
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Desai SA, Lnenicka GA. Characterization of postsynaptic Ca2+ signals at the Drosophila larval NMJ. J Neurophysiol 2011; 106:710-21. [PMID: 21593388 DOI: 10.1152/jn.00045.2011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Postsynaptic intracellular Ca(2+) concentration ([Ca(2+)](i)) has been proposed to play an important role in both synaptic plasticity and synaptic homeostasis. In particular, postsynaptic Ca(2+) signals can alter synaptic efficacy by influencing transmitter release, receptor sensitivity, and protein synthesis. We examined the postsynaptic Ca(2+) transients at the Drosophila larval neuromuscular junction (NMJ) by injecting the muscle fibers with Ca(2+) indicators rhod-2 and Oregon Green BAPTA-1 (OGB-1) and then monitoring their increased fluorescence during synaptic activity. We observed discrete postsynaptic Ca(2+) transients along the NMJ during single action potentials (APs) and quantal Ca(2+) transients produced by spontaneous transmitter release. Most of the evoked Ca(2+) transients resulted from the release of one or two quanta of transmitter and occurred largely at synaptic boutons. The magnitude of the Ca(2+) signals was correlated with synaptic efficacy; the Is terminals, which produce larger excitatory postsynaptic potentials (EPSPs) and have a greater quantal size than Ib terminals, produced a larger Ca(2+) signal per terminal length and larger quantal Ca(2+) signals than the Ib terminals. During a train of APs, the postsynaptic Ca(2+) signal increased but remained localized to the postsynaptic membrane. In addition, we showed that the plasma membrane Ca(2+)-ATPase (PMCA) played a role in extruding Ca(2+) from the postsynaptic region of the muscle. Drosophila melanogaster has a single PMCA gene, predicted to give rise to various isoforms by alternative splicing. Using RT-PCR, we detected the expression of multiple transcripts in muscle and nervous tissues; the physiological significance of the same is yet to be determined.
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Affiliation(s)
- Sunil A Desai
- Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA
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He T, Lnenicka GA. Ca²+ buffering at a drosophila larval synaptic terminal. Synapse 2011; 65:687-93. [PMID: 21218450 DOI: 10.1002/syn.20909] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2010] [Accepted: 12/23/2010] [Indexed: 11/12/2022]
Abstract
A quantitative analysis of Ca²+ dynamics requires knowledge of the Ca²+-binding ratio (κ(S) ); this has not been measured at Drosophila synaptic terminals or any invertebrate synaptic terminal. We measured κ(S) at a Ib motor terminal in Drosophila larvae comparing single-AP Ca²+ transients in synaptic terminals that contained varying concentrations of the Ca²+ indicator, Oregon Green 488 BAPTA-1 (OGB-1). Using a linear single-compartment model, κ(S) was calculated based upon the effect of [OGB-1] on the time constant (τ(decay) ) for the decay of intracellular free Ca²+ concentration ([Ca²+](i)). This gave a κ(S) of 77 indicating that nearly 99% of entering Ca²+ is immediately bound by endogenous fast Ca²+ buffers. Extrapolation to zero [OGB-1] gave a τ(decay) of 46 ms and a Ca²+-removal rate constant of 1641 s⁻¹ for single APs. We calculated that a single AP produced an increase in [Ca²+](i) of 196 nM and an increase in the total intracellular [Ca²+](free + bound) of 15.3 μM for measurements made in 1.0 mM external Ca²+. The increase in [Ca²+](i) for AP trains was 185 nM/ 10 Hz; this gave a Ca²+ extrusion rate constant of 827 s⁻¹, which likely reflects the activity of the plasma membrane Ca²+ ATPase. Experiments were performed to examine the effect of altering external Ca²+ or Mg²+ on Ca²+ influx at these terminals.
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Affiliation(s)
- Tao He
- Department of Biological Sciences, University at Albany, Suny, Albany, New York 12222, USA
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Peled ES, Isacoff EY. Optical quantal analysis of synaptic transmission in wild-type and rab3-mutant Drosophila motor axons. Nat Neurosci 2011; 14:519-26. [PMID: 21378971 DOI: 10.1038/nn.2767] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Accepted: 01/21/2011] [Indexed: 02/06/2023]
Abstract
Synaptic transmission from a neuron to its target cells occurs via neurotransmitter release from dozens to thousands of presynaptic release sites whose strength and plasticity can vary considerably. We report an in vivo imaging method that monitors real-time synaptic transmission simultaneously at many release sites with quantal resolution. We applied this method to the model glutamatergic system of the Drosophila melanogaster larval neuromuscular junction. We find that, under basal conditions, about half of release sites have a very low release probability, but these are interspersed with sites with as much as a 50-fold higher probability. Paired-pulse stimulation depresses high-probability sites, facilitates low-probability sites, and recruits previously silent sites. Mutation of the small GTPase Rab3 substantially increases release probability but still leaves about half of the sites silent. Our findings suggest that basal synaptic strength and short-term plasticity are regulated at the level of release probability at individual sites.
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Affiliation(s)
- Einat S Peled
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
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Abstract
Presynaptic inhibition is a widespread mechanism modulating the efficiency of synaptic transmission and in sensory pathways is coupled to primary afferent depolarizations. Axonal terminals of bush-cricket auditory afferents received 2-5 mV graded depolarizing inputs, which reduced the amplitude of invading spikes and indicated presynaptic inhibition. These inputs were linked to a picrotoxin-sensitive increase of Ca(2+) in the terminals. Electrophysiological recordings and optical imaging showed that in individual afferents the sound frequency tuning based on spike rates was different from the tuning of the graded primary afferent depolarizations. The auditory neuropil of the bush-cricket Mecopoda elongata is tonotopically organized, with low frequencies represented anteriorly and high frequencies represented posteriorly. In contrast graded depolarizing inputs were tuned to high-frequencies anteriorly and to low-frequencies posteriorly. Furthermore anterior and posterior axonal branches of individual afferents received different levels of primary afferent depolarization depending on sound frequency. The presence of primary afferent depolarization in the afferent terminals indicates that presynaptic inhibition may shape the synaptic transmission of frequency-specific activity to auditory interneurons.
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