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Rodriguez Gotor JJ, Mahfooz K, Perez-Otano I, Wesseling JF. Parallel processing of quickly and slowly mobilized reserve vesicles in hippocampal synapses. eLife 2024; 12:RP88212. [PMID: 38727712 PMCID: PMC11087054 DOI: 10.7554/elife.88212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2024] Open
Abstract
Vesicles within presynaptic terminals are thought to be segregated into a variety of readily releasable and reserve pools. The nature of the pools and trafficking between them is not well understood, but pools that are slow to mobilize when synapses are active are often assumed to feed pools that are mobilized more quickly, in a series. However, electrophysiological studies of synaptic transmission have suggested instead a parallel organization where vesicles within slowly and quickly mobilized reserve pools would separately feed independent reluctant- and fast-releasing subdivisions of the readily releasable pool. Here, we use FM-dyes to confirm the existence of multiple reserve pools at hippocampal synapses and a parallel organization that prevents intermixing between the pools, even when stimulation is intense enough to drive exocytosis at the maximum rate. The experiments additionally demonstrate extensive heterogeneity among synapses in the relative sizes of the slowly and quickly mobilized reserve pools, which suggests equivalent heterogeneity in the numbers of reluctant and fast-releasing readily releasable vesicles that may be relevant for understanding information processing and storage.
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Affiliation(s)
| | - Kashif Mahfooz
- Department of Pharmacology, University of OxfordOxfordUnited Kingdom
| | - Isabel Perez-Otano
- Instituto de Neurociencias de Alicante CSIC-UMHSan Juan de AlicanteSpain
| | - John F Wesseling
- Instituto de Neurociencias de Alicante CSIC-UMHSan Juan de AlicanteSpain
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Ralowicz AJ, Hokeness S, Hoppa MB. Frequency of Spontaneous Neurotransmission at Individual Boutons Corresponds to the Size of the Readily Releasable Pool of Vesicles. J Neurosci 2024; 44:e1253232024. [PMID: 38383495 PMCID: PMC11063817 DOI: 10.1523/jneurosci.1253-23.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 02/09/2024] [Accepted: 02/13/2024] [Indexed: 02/23/2024] Open
Abstract
Synapses maintain two forms of neurotransmitter release to support communication in the brain. First, evoked neurotransmitter release is triggered by the invasion of an action potential (AP) across en passant boutons that form along axons. The probability of evoked release (Pr) varies substantially across boutons, even within a single axon. Such heterogeneity is the result of differences in the probability of a single synaptic vesicle (SV) fusing (Pv) and in the number of vesicles available for immediate release, known as the readily releasable pool (RRP). Spontaneous release (also known as a mini) is an important form of neurotransmission that occurs in the absence of APs. Because it cannot be triggered with electrical stimulation, much less is known about potential heterogeneity in the frequency of spontaneous release between boutons. We utilized a photostable and bright fluorescent indicator of glutamate release (iGluSnFR3) to quantify both spontaneous and evoked release at individual glutamatergic boutons. We found that the rate of spontaneous release is quite heterogenous at the level of individual boutons. Interestingly, when measuring both evoked and spontaneous release at single synapses, we found that boutons with the highest rates of spontaneous release also displayed the largest evoked responses. Using a new optical method to measure RRP at individual boutons, we found that this heterogeneity in spontaneous release was strongly correlated with the size of the RRP, but not related to Pv. We conclude that the RRP is a critical and dynamic aspect of synaptic strength that contributes to both evoked and spontaneous vesicle release.
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Affiliation(s)
- Amelia J Ralowicz
- Department of Biology, Dartmouth College, Hanover, New Hampshire 03755
| | - Sasipha Hokeness
- Department of Biology, Dartmouth College, Hanover, New Hampshire 03755
| | - Michael B Hoppa
- Department of Biology, Dartmouth College, Hanover, New Hampshire 03755
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Feldthouse MG, Vyleta NP, Smith SM. PLC regulates spontaneous glutamate release triggered by extracellular calcium and readily releasable pool size in neocortical neurons. Front Cell Neurosci 2023; 17:1193485. [PMID: 37260580 PMCID: PMC10228687 DOI: 10.3389/fncel.2023.1193485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Accepted: 04/26/2023] [Indexed: 06/02/2023] Open
Abstract
Introduction Dynamic physiological changes in brain extracellular calcium ([Ca2+]o) occur when high levels of neuronal activity lead to substantial Ca2+ entry via ion channels reducing local [Ca2+]o. Perturbations of the extracellular microenvironment that increase [Ca2+]o are commonly used to study how [Ca2+] regulates neuronal activity. At excitatory synapses, the Ca2+-sensing receptor (CaSR) and other G-protein coupled receptors link [Ca2+]o and spontaneous glutamate release. Phospholipase C (PLC) is activated by G-proteins and is hypothesized to mediate this process. Methods Patch-clamping cultured neocortical neurons, we tested how spontaneous glutamate release was affected by [Ca2+]o and inhibition of PLC activity. We used hypertonic sucrose (HS) to evaluate the readily releasable pool (RRP) and test if it was affected by inhibition of PLC activity. Results Spontaneous glutamate release substantially increased with [Ca2+]o, and inhibition of PLC activity, with U73122, abolished this effect. PLC-β1 is an abundant isoform in the neocortex, however, [Ca2+]o-dependent spontaneous release was unchanged in PLC-β1 null mutants (PLC-β1-/-). U73122 completely suppressed this response in PLC-β1-/- neurons, indicating that this residual [Ca2+]o-sensitivity may be mediated by other PLC isoforms. The RRP size was substantially reduced after incubation in U73122, but not U73343. Phorbol esters increased RRP size after PLC inhibition. Discussion Together these data point to a strong role for PLC in mediating changes in spontaneous release elicited by [Ca2+]o and other extracellular cues, possibly by modifying the size of the RRP.
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Affiliation(s)
- Maya G. Feldthouse
- Section of Pulmonary and Critical Care Medicine and Research and Development, VA Portland Health Care System, Portland, OR, United States
| | - Nicholas P. Vyleta
- Division of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR, United States
| | - Stephen M. Smith
- Section of Pulmonary and Critical Care Medicine and Research and Development, VA Portland Health Care System, Portland, OR, United States
- Division of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR, United States
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Lee BJ, Lee U, Ryu SH, Han S, Lee SY, Lee JS, Ju A, Chang S, Lee SH, Kim SH, Ho WK. L-type Ca 2+ channels mediate regulation of glutamate release by subthreshold potential changes. Proc Natl Acad Sci U S A 2023; 120:e2220649120. [PMID: 36920925 PMCID: PMC10041175 DOI: 10.1073/pnas.2220649120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/16/2023] Open
Abstract
Subthreshold depolarization enhances neurotransmitter release evoked by action potentials and plays a key role in modulating synaptic transmission by combining analog and digital signals. This process is known to be Ca2+ dependent. However, the underlying mechanism of how small changes in basal Ca2+ caused by subthreshold depolarization can regulate transmitter release triggered by a large increase in local Ca2+ is not well understood. This study aimed to investigate the source and signaling mechanisms of Ca2+ that couple subthreshold depolarization with the enhancement of glutamate release in hippocampal cultures and CA3 pyramidal neurons. Subthreshold depolarization increased presynaptic Ca2+ levels, the frequency of spontaneous release, and the amplitude of evoked release, all of which were abolished by blocking L-type Ca2+ channels. A high concentration of intracellular Ca2+ buffer or blockade of calmodulin abolished depolarization-induced increases in transmitter release. Estimation of the readily releasable pool size using hypertonic sucrose showed depolarization-induced increases in readily releasable pool size, and this increase was abolished by the blockade of calmodulin. Our results provide mechanistic insights into the modulation of transmitter release by subthreshold potential change and highlight the role of L-type Ca2+ channels in coupling subthreshold depolarization to the activation of Ca2+-dependent signaling molecules that regulate transmitter release.
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Affiliation(s)
- Byoung Ju Lee
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
- Neuroscience Research Institute, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Unghwi Lee
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
- Neuroscience Research Institute, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Seung Hyun Ryu
- Interdisciplinary Program in Neuroscience, Seoul National University College of Natural Science, Seoul 08826, Korea
| | - Sukmin Han
- Department of Neuroscience, Graduate School, Kyung Hee University, Seoul 02447, Korea
| | - Seung Yeon Lee
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Jae Sung Lee
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Anes Ju
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
- Neuroscience Research Institute, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Sunghoe Chang
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
- Neuroscience Research Institute, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Suk-Ho Lee
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
- Neuroscience Research Institute, Seoul National University College of Medicine, Seoul 03080, Korea
- Department of Brain and Cognitive Science, Seoul National University College of Natural Science, Seoul 08826, Korea
| | - Sung Hyun Kim
- Department of Neuroscience, Graduate School, Kyung Hee University, Seoul 02447, Korea
- Department of Physiology, School of Medicine, Kyung Hee University, Seoul 02447, Korea
| | - Won-Kyung Ho
- Department of Physiology and Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
- Neuroscience Research Institute, Seoul National University College of Medicine, Seoul 03080, Korea
- Department of Brain and Cognitive Science, Seoul National University College of Natural Science, Seoul 08826, Korea
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Zhao J, Yin N, Li GL. Comparative study of ionic currents and exocytosis in hair cells of the basilar and amphibian papilla in bullfrogs. Front Cell Neurosci 2023; 16:1064886. [PMID: 36700157 PMCID: PMC9868640 DOI: 10.3389/fncel.2022.1064886] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2022] [Accepted: 12/13/2022] [Indexed: 01/11/2023] Open
Abstract
Hearing organs in the peripheral of different vertebrate species are extremely diverse in shape and function. In particular, while the basilar papilla (BP) is elongated and covers the sounds of both low and high frequencies in turtles and birds, it is round and responds to high frequencies only in frogs, leaving the low frequencies to the amphibian papilla (AP). In this study, we performed patch-clamp recordings in hair cells of both hearing organs in bullfrogs and conducted a comparative study of their ionic currents and exocytosis. Compared to hair cells in AP with a large tetraethylammonium (TEA)-sensitive slow-activating K+ current (I K), those in BP exhibited a small 4-aminopyridine (4-AP)-sensitive fast-inactivating K+ current (I A). Furthermore, hair cells in BP exhibited a significantly smaller Ca2+ current with a more positive half-activation voltage (Vhalf) and a slower slope of voltage dependency (k). In response to step depolarization, exocytosis (ΔCm) in BP hair cells was also significantly smaller, but the Ca2+ efficiency, assessed with the ratio between ΔCm and Ca2+ charge (QCa), was comparable to that of AP hair cells. Finally, we applied a paired-step depolarization and varied the interval in between, and we found that the replenishment of synaptic vesicles was significantly slower in BP hair cells. Together, our findings suggest that hair cells tuned to high frequencies in bullfrogs release less synaptic vesicles and recycle synaptic vesicles more slowly, allowing them to cope well with the large DC component found in their receptor potentials in vivo.
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Affiliation(s)
- Jingjing Zhao
- ENT Institute and Department of Otorhinolaryngology, Eye and ENT Hospital, Fudan University, Shanghai, China
| | - Ning Yin
- ENT Institute and Department of Otorhinolaryngology, Eye and ENT Hospital, Fudan University, Shanghai, China
| | - Geng-Lin Li
- ENT Institute and Department of Otorhinolaryngology, Eye and ENT Hospital, Fudan University, Shanghai, China,NHC Key Laboratory of Hearing Medicine, Fudan University, Shanghai, China,State Key Laboratory of Medical Neurobiology and MOE Frontiers Center for Brain Science, Fudan University, Shanghai, China,*Correspondence: Geng-Lin Li,
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Tan C, de Nola G, Qiao C, Imig C, Born RT, Brose N, Kaeser PS. Munc13 supports fusogenicity of non-docked vesicles at synapses with disrupted active zones. eLife 2022; 11:79077. [PMID: 36398873 PMCID: PMC9822248 DOI: 10.7554/elife.79077] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Accepted: 11/17/2022] [Indexed: 11/19/2022] Open
Abstract
Active zones consist of protein scaffolds that are tightly attached to the presynaptic plasma membrane. They dock and prime synaptic vesicles, couple them to voltage-gated Ca2+ channels, and direct neurotransmitter release toward postsynaptic receptor domains. Simultaneous RIM + ELKS ablation disrupts these scaffolds, abolishes vesicle docking, and removes active zone-targeted Munc13, but some vesicles remain releasable. To assess whether this enduring vesicular fusogenicity is mediated by non-active zone-anchored Munc13 or is Munc13-independent, we ablated Munc13-1 and Munc13-2 in addition to RIM + ELKS in mouse hippocampal neurons. The hextuple knockout synapses lacked docked vesicles, but other ultrastructural features were near-normal despite the strong genetic manipulation. Removing Munc13 in addition to RIM + ELKS impaired action potential-evoked vesicle fusion more strongly than RIM + ELKS knockout by further decreasing the releasable vesicle pool. Hence, Munc13 can support some fusogenicity without RIM and ELKS, and presynaptic recruitment of Munc13, even without active zone anchoring, suffices to generate some fusion-competent vesicles.
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Affiliation(s)
- Chao Tan
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Giovanni de Nola
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Claire Qiao
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Cordelia Imig
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.,Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Goettingen, Germany
| | - Richard T Born
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Goettingen, Germany
| | - Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, Boston, United States
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Abstract
Unrelated genetic mutations can lead to convergent manifestations of neurological disorders with similar behavioral phenotypes. Experimental data frequently show a lack of dramatic changes in neuroanatomy, indicating that the key cause of symptoms might arise from impairment in the communication between neurons. A transient imbalance between excitatory (glutamatergic) and inhibitory (GABAergic) synaptic transmission (the E/I balance) during early development is generally considered to underlie the development of several neurological disorders in adults. However, the E/I ratio is a multidimensional variable. Synaptic contacts are highly dynamic and the actual strength of synaptic projections is determined from the balance between synaptogenesis and synaptic elimination. During development, relatively slow postsynaptic receptors are replaced by fast ones that allow for fast stimulus-locked excitation/inhibition. Using the binomial model of synaptic transmission allows for the reassessing of experimental data from different mouse models, showing that a transient E/I shift is frequently counterbalanced by additional pre- and/or postsynaptic changes. Such changes—for instance, the slowing down of postsynaptic currents by means of immature postsynaptic receptors—stabilize the average synaptic strength, but impair the timing of information flow. Compensatory processes and/or astrocytic signaling may represent possible targets for medical treatments of different disorders directed to rescue the proper information processing.
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Abstract
Pancreatic β cells operate with a high rate of membrane recycling for insulin secretion, yet endocytosis in these cells is not fully understood. We investigate this process in mature mouse β cells by genetically deleting dynamin GTPase, the membrane fission machinery essential for clathrin-mediated endocytosis. Unexpectedly, the mice lacking all three dynamin genes (DNM1, DNM2, DNM3) in their β cells are viable, and their β cells still contain numerous insulin granules. Endocytosis in these β cells is severely impaired, resulting in abnormal endocytic intermediates on the plasma membrane. Although insulin granules are abundant, their release upon glucose stimulation is blunted in both the first and second phases, leading to hyperglycemia and glucose intolerance in mice. Dynamin triple deletion impairs insulin granule exocytosis and decreases intracellular Ca2+ responses and granule docking. The docking defect is correlated with reduced expression of Munc13-1 and RIM1 and reorganization of cortical F-actin in β cells. Collectively, these findings uncover the role of dynamin in dense-core vesicle endocytosis and secretory capacity. Insulin secretion deficiency in the absence of dynamin-mediated endocytosis highlights the risk of impaired membrane trafficking in endocrine failure and diabetes pathogenesis.
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Affiliation(s)
- Fan Fan
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226
| | - Yumei Wu
- HHMI, Yale University School of Medicine, New Haven, CT 06510
- Departments of Neuroscience and Cell Biology, Program in Cellular Neuroscience, Neurodegeneration and Repair, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT 06510
| | - Manami Hara
- Section of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Chicago, Chicago, IL 60637
| | - Adam Rizk
- Section of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Chicago, Chicago, IL 60637
| | - Chen Ji
- Synapses and Circuits section, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892
| | - Dan Nerad
- Emergency Medicine, Carl R. Darnall Army Medical Center, Fort Hood, TX 76544
| | - Natalia Tamarina
- Department of Medicine, The Kovler Diabetes Center, University of Chicago, Chicago, IL 60637
| | - Xuelin Lou
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226;
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Abstract
Several small guanosine triphosphatases (GTPases) from the Ras protein superfamily regulate glucose-stimulated insulin secretion in the pancreatic islet β-cell. The Rho family GTPases Cdc42 and Rac1 are primarily involved in relaying key signals in several cellular functions, including vesicle trafficking, plasma membrane homeostasis, and cytoskeletal dynamics. They orchestrate specific changes at each spatiotemporal region within the β-cell by coordinating with signal transducers, guanine nucleotide exchange factors (GEFs), GTPase-activating factors (GAPs), and their effectors. The Arf family of small GTPases is involved in vesicular trafficking (exocytosis and endocytosis) and actin cytoskeletal dynamics. Rab-GTPases regulate pre-exocytotic and late endocytic membrane trafficking events in β-cells. Several additional functions for small GTPases include regulating transcription factor activity and mitochondrial dynamics. Importantly, defects in several of these GTPases have been found associated with type 2 diabetes (T2D) etiology. The purpose of this review is to systematically denote the identities and molecular mechanistic steps in the glucose-stimulated insulin secretion pathway that leads to the normal release of insulin. We will also note newly identified defects in these GTPases and their corresponding regulatory factors (e.g., GDP dissociation inhibitors (GDIs), GEFs, and GAPs) in the pancreatic β-cells, which contribute to the dysregulation of metabolism and the development of T2D.
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Affiliation(s)
- Rajakrishnan Veluthakal
- Department of Molecular and Cellular Endocrinology, Arthur Riggs Diabetes & Metabolism Research Institute, City of Hope Beckman Research Institute, Duarte, CA 91010, USA
| | - Debbie C. Thurmond
- Department of Molecular and Cellular Endocrinology, Arthur Riggs Diabetes & Metabolism Research Institute, City of Hope Beckman Research Institute, Duarte, CA 91010, USA
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Abstract
BACKGROUND Huntington's disease (HD) is an inherited neurodegenerative disorder caused by expansion of CAG repeats in the Huntingtin gene (HTT). Studies suggest cortical to striatal (C-S) projections, which regulate movement and provide cell survival signals to SPNs, are altered in the pre-manifest and early symptomatic stages of HD. But whether and how presynaptic cortical terminals are affected in HD is not well explored. OBJECTIVE Test size and replenishment of readily releasable pool (RRP), and assess glutamate refill of C-S synapses in HD models. METHODS Immunocytochemistry was applied in C-S co-cultures generated from FVB/N (WT: wildtype) mice and YAC128, an HD mouse model expressing human HTT with 128 CAG repeats on the FVB/N background; Whole-cell patch clamp recordings from striatal neurons were performed both in cultures, with or without osmotic stimuli, and in acute brain slices from 6-month-old early symptomatic YAC128 mice and WT following prolonged trains of electrical stimuli in corpus callosum. RESULTS We found no change in the average size or vesicle replenishment rate of RRP in C-S synapses of YAC128, compared with WT, cultures at day in vitro 21, a time when immunocytochemistry showed comparable neuronal survival between the two genotypes. However, YAC128 C-S synapses showed a slowed rate of recovery of glutamate release in co-cultures as well as in acute brain slices. CONCLUSION Mutant HTT expression impairs glutamate refill but not RRP size or replenishment in C-S synapses. This work provides a foundation for examining the contribution of deficits in presynaptic cortical terminals on HD progression.
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Affiliation(s)
- Caodu Buren
- Graduate Program in Neuroscience, The University of British Columbia, Vancouver, Canada.,Department of Psychiatry and Djavad Mowafaghian Centre for Brain Health, The University of British Columbia, Vancouver, Canada
| | - Gaqi Tu
- School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China.,Department of Psychology, University of Toronto, Toronto, Ontario, Canada
| | - Lynn A Raymond
- Department of Psychiatry and Djavad Mowafaghian Centre for Brain Health, The University of British Columbia, Vancouver, Canada
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Vandael D, Borges-Merjane C, Zhang X, Jonas P. Short-Term Plasticity at Hippocampal Mossy Fiber Synapses Is Induced by Natural Activity Patterns and Associated with Vesicle Pool Engram Formation. Neuron 2020; 107:509-521.e7. [PMID: 32492366 PMCID: PMC7427323 DOI: 10.1016/j.neuron.2020.05.013] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 04/09/2020] [Accepted: 05/08/2020] [Indexed: 02/08/2023]
Abstract
Post-tetanic potentiation (PTP) is an attractive candidate mechanism for hippocampus-dependent short-term memory. Although PTP has a uniquely large magnitude at hippocampal mossy fiber-CA3 pyramidal neuron synapses, it is unclear whether it can be induced by natural activity and whether its lifetime is sufficient to support short-term memory. We combined in vivo recordings from granule cells (GCs), in vitro paired recordings from mossy fiber terminals and postsynaptic CA3 neurons, and “flash and freeze” electron microscopy. PTP was induced at single synapses and showed a low induction threshold adapted to sparse GC activity in vivo. PTP was mainly generated by enlargement of the readily releasable pool of synaptic vesicles, allowing multiplicative interaction with other plasticity forms. PTP was associated with an increase in the docked vesicle pool, suggesting formation of structural “pool engrams.” Absence of presynaptic activity extended the lifetime of the potentiation, enabling prolonged information storage in the hippocampal network. Natural activity patterns in hippocampal GCs in vivo induce PTP at mossy fiber synapses PTP is primarily caused by an increase in the readily releasable vesicle pool PTP is associated with an increase in the number of docked vesicles at active zones Sparse activity extends pool engram lifetime, increasing overlap with short-term memory
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Affiliation(s)
- David Vandael
- Cellular Neuroscience, Institute of Science and Technology (IST) Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Carolina Borges-Merjane
- Cellular Neuroscience, Institute of Science and Technology (IST) Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Xiaomin Zhang
- Cellular Neuroscience, Institute of Science and Technology (IST) Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Peter Jonas
- Cellular Neuroscience, Institute of Science and Technology (IST) Austria, Am Campus 1, 3400 Klosterneuburg, Austria.
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Borges-Merjane C, Kim O, Jonas P. Functional Electron Microscopy, "Flash and Freeze," of Identified Cortical Synapses in Acute Brain Slices. Neuron 2020; 105:992-1006.e6. [PMID: 31928842 DOI: 10.1016/j.neuron.2019.12.022] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 11/20/2019] [Accepted: 12/13/2019] [Indexed: 12/19/2022]
Abstract
How structural and functional properties of synapses relate to each other is a fundamental question in neuroscience. Electrophysiology has elucidated mechanisms of synaptic transmission, and electron microscopy (EM) has provided insight into morphological properties of synapses. Here we describe an enhanced method for functional EM (“flash and freeze”), combining optogenetic stimulation with high-pressure freezing. We demonstrate that the improved method can be applied to intact networks in acute brain slices and organotypic slice cultures from mice. As a proof of concept, we probed vesicle pool changes during synaptic transmission at the hippocampal mossy fiber-CA3 pyramidal neuron synapse. Our findings show overlap of the docked vesicle pool and the functionally defined readily releasable pool and provide evidence of fast endocytosis at this synapse. Functional EM with acute slices and slice cultures has the potential to reveal the structural and functional mechanisms of transmission in intact, genetically perturbed, and disease-affected synapses. Functional EM may be applied to acute brain slices and organotypic slice cultures Docked vesicle pool and RRP are overlapping Smaller-diameter vesicles have higher release probability than larger vesicles Endocytic pits after moderate stimulation suggest fast endocytosis
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Martínez San Segundo P, Terni B, Burgueño J, Monroy X, Dordal A, Merlos M, Llobet A. Outside-in regulation of the readily releasable pool of synaptic vesicles by α2δ-1. FASEB J 2019; 34:1362-1377. [PMID: 31914622 DOI: 10.1096/fj.201901551r] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Revised: 10/09/2019] [Accepted: 10/23/2019] [Indexed: 12/17/2022]
Abstract
The readily releasable pool (RRP) of synaptic vesicles is a key determinant of phasic neurotransmission. Although the size of the RRP is tightly regulated by intracellular factors, there is little evidence for its modification by extracellular signals. By studying the homogeneous population of synapses present in autaptic microcultures, we show that pregabalin, a prototypical gabapentinoid, decreases the effective RRP size. Simultaneous imaging of presynaptic calcium influx and recording of postsynaptic responses shows that the effect is not related to a reduction of calcium entry. The main cause is the impairment of the functional coupling among N-type calcium channels and the RRP, resembling an increase of intracellular mobile calcium buffers. The ectodomain of neurexin-1α shows a similar action to pregabalin, acting as an endogenous ligand of α2δ-1 that reduces the RRP size without affecting presynaptic calcium influx. The regulatory actions described for pregabalin and the ectodomain of neurexin-1α are mutually exclusive. The overexpression of α2δ-1 enhances the effect of pregabalin and the ectodomain of neurexin-1α on neurotransmission by decreasing their effective concentration. In contrast, knockdown of α2δ-1 causes a profound inhibition of synaptic transmission. These observations prompt to consider α2δ-1 as an outside-in signaling platform that binds exogenous and endogenous cues for regulating the coupling of voltage-gated calcium channels to synaptic vesicles.
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Affiliation(s)
- Pablo Martínez San Segundo
- Laboratory of Neurobiology, Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain.,Department of Pathology and Experimental Therapeutics, School of Medicine, Institute of Neurosciences, University of Barcelona, Barcelona, Spain
| | - Beatrice Terni
- Laboratory of Neurobiology, Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain.,Department of Pathology and Experimental Therapeutics, School of Medicine, Institute of Neurosciences, University of Barcelona, Barcelona, Spain
| | - Javier Burgueño
- Department of Pharmacology, Drug Discovery and Preclinical Development, ESTEVE, Barcelona, Spain
| | - Xavier Monroy
- Department of Pharmacology, Drug Discovery and Preclinical Development, ESTEVE, Barcelona, Spain
| | - Albert Dordal
- Department of Pharmacology, Drug Discovery and Preclinical Development, ESTEVE, Barcelona, Spain
| | - Manuel Merlos
- Department of Pharmacology, Drug Discovery and Preclinical Development, ESTEVE, Barcelona, Spain
| | - Artur Llobet
- Laboratory of Neurobiology, Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain.,Department of Pathology and Experimental Therapeutics, School of Medicine, Institute of Neurosciences, University of Barcelona, Barcelona, Spain
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Ratai O, Schirra C, Rajabov E, Brunk I, Ahnert-Hilger G, Chitirala P, Becherer U, Stevens DR, Rettig J. An Alternative Exon of CAPS2 Influences Catecholamine Loading into LDCVs of Chromaffin Cells. J Neurosci 2019; 39:18-27. [PMID: 30389842 DOI: 10.1523/JNEUROSCI.2040-18.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 10/01/2018] [Accepted: 10/27/2018] [Indexed: 11/21/2022] Open
Abstract
The calcium-dependent activator proteins for secretion (CAPS) are priming factors for synaptic and large dense-core vesicles (LDCVs), promoting their entry into and stabilizing the release-ready state. A modulatory role of CAPS in catecholamine loading of vesicles has been suggested. Although an influence of CAPS on monoamine transporter function and on vesicle acidification has been reported, a role of CAPS in vesicle loading is disputed. Using expression of naturally occurring splice variants of CAPS2 into chromaffin cells from CAPS1/CAPS2 double-deficient mice of both sexes, we show that an alternative exon of 40 aa is responsible for enhanced catecholamine loading of LDCVs in mouse chromaffin cells. The presence of this exon leads to increased activity of both vesicular monoamine transporters. Deletion of CAPS does not alter acidification of vesicles. Our results establish a splice-variant-dependent modulatory effect of CAPS on catecholamine content in LDCVs.SIGNIFICANCE STATEMENT The calcium activator protein for secretion (CAPS) promotes and stabilizes the entry of catecholamine-containing vesicles of the adrenal gland into a release-ready state. Expression of an alternatively spliced exon in CAPS leads to enhanced catecholamine content in chromaffin granules. This exon codes for 40 aa with a high proline content, consistent with an unstructured loop present in the portion of the molecule generally thought to be involved in vesicle priming. CAPS variants containing this exon promote serotonin uptake into Chinese hamster ovary cells expressing either vesicular monoamine transporter. Epigenetic tuning of CAPS variants may allow modulation of endocrine adrenaline and noradrenaline release. This mechanism may extend to monoamine release in central neurons or in the enteric nervous system.
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15
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Harris N, Fetter RD, Brasier DJ, Tong A, Davis GW. Molecular Interface of Neuronal Innate Immunity, Synaptic Vesicle Stabilization, and Presynaptic Homeostatic Plasticity. Neuron 2018; 100:1163-1179.e4. [PMID: 30344041 DOI: 10.1016/j.neuron.2018.09.048] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 07/06/2018] [Accepted: 09/21/2018] [Indexed: 10/28/2022]
Abstract
We define a homeostatic function for innate immune signaling within neurons. A genetic analysis of the innate immune signaling genes IMD, IKKβ, Tak1, and Relish demonstrates that each is essential for presynaptic homeostatic plasticity (PHP). Subsequent analyses define how the rapid induction of PHP (occurring in seconds) can be coordinated with the life-long maintenance of PHP, a time course that is conserved from invertebrates to mammals. We define a novel bifurcation of presynaptic innate immune signaling. Tak1 (Map3K) acts locally and is selective for rapid PHP induction. IMD, IKKβ, and Relish are essential for long-term PHP maintenance. We then define how Tak1 controls vesicle release. Tak1 stabilizes the docked vesicle state, which is essential for the homeostatic expansion of the readily releasable vesicle pool. This represents a mechanism for the control of vesicle release, and an interface of innate immune signaling with the vesicle fusion apparatus and homeostatic plasticity.
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Affiliation(s)
- Nathan Harris
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Richard D Fetter
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Daniel J Brasier
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Amy Tong
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Graeme W Davis
- Department of Biochemistry and Biophysics, Kavli Institute for Fundamental Neuroscience, University of California, San Francisco, San Francisco, CA 94158, USA.
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16
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Butola T, Wichmann C, Moser T. Piccolo Promotes Vesicle Replenishment at a Fast Central Auditory Synapse. Front Synaptic Neurosci 2017; 9:14. [PMID: 29118709 PMCID: PMC5660988 DOI: 10.3389/fnsyn.2017.00014] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 10/09/2017] [Indexed: 12/20/2022] Open
Abstract
Piccolo and Bassoon are the two largest cytomatrix of the active zone (CAZ) proteins involved in scaffolding and regulating neurotransmitter release at presynaptic active zones (AZs), but have long been discussed as being functionally redundant. We employed genetic manipulation to bring forth and segregate the role of Piccolo from that of Bassoon at central auditory synapses of the cochlear nucleus—the endbulbs of Held. These synapses specialize in high frequency synaptic transmission, ideally poised to reveal even subtle deficits in the regulation of neurotransmitter release upon molecular perturbation. Combining semi-quantitative immunohistochemistry, electron microscopy, and in vitro and in vivo electrophysiology we first studied signal transmission in Piccolo-deficient mice. Our analysis was not confounded by a cochlear deficit, as a short isoform of Piccolo (“Piccolino”) present at the upstream ribbon synapses of cochlear inner hair cells (IHC), is unaffected by the mutation. Disruption of Piccolo increased the abundance of Bassoon at the AZs of endbulbs, while that of RIM1 was reduced and other CAZ proteins remained unaltered. Presynaptic fiber stimulation revealed smaller amplitude of the evoked excitatory postsynaptic currents (eEPSC), while eEPSC kinetics as well as miniature EPSCs (mEPSCs) remained unchanged. Cumulative analysis of eEPSC trains indicated that the reduced eEPSC amplitude of Piccolo-deficient endbulb synapses is primarily due to a reduced readily releasable pool (RRP) of synaptic vesicles (SV), as was corroborated by a reduction of vesicles at the AZ found on an ultrastructural level. Release probability seemed largely unaltered. Recovery from short-term depression was slowed. We then performed a physiological analysis of endbulb synapses from mice which, in addition to Piccolo deficiency, lacked one functional allele of the Bassoon gene. Analysis of the double-mutant endbulbs revealed an increase in release probability, while the synapses still exhibited the reduced RRP, and the impairment in SV replenishment was exacerbated. We propose additive roles of Piccolo and Bassoon in SV replenishment which in turn influences the organization and size of the RRP, and an additional role of Bassoon in regulation of release probability.
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Affiliation(s)
- Tanvi Butola
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Göttingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences (GGNB), University of Göttingen, Göttingen, Germany.,International Max Planck Research School for Neurosciences (IMPRS), Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry (MPG), Göttingen, Germany
| | - Carolin Wichmann
- Göttingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences (GGNB), University of Göttingen, Göttingen, Germany.,Collaborative Research Centers 889 and 1286, University of Göttingen, Göttingen, Germany.,Molecular Architecture of Synapses Group, Center for Biostructural Imaging of Neurodegeneration (BIN), University of Göttingen, Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Göttingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences (GGNB), University of Göttingen, Göttingen, Germany.,International Max Planck Research School for Neurosciences (IMPRS), Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute for Biophysical Chemistry (MPG), Göttingen, Germany.,Collaborative Research Centers 889 and 1286, University of Göttingen, Göttingen, Germany.,Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University of Göttingen, Göttingen, Germany
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17
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Held RG, Liu C, Kaeser PS. ELKS controls the pool of readily releasable vesicles at excitatory synapses through its N-terminal coiled-coil domains. eLife 2016; 5. [PMID: 27253063 PMCID: PMC4935463 DOI: 10.7554/elife.14862] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Accepted: 06/01/2016] [Indexed: 12/27/2022] Open
Abstract
In a presynaptic nerve terminal, synaptic strength is determined by the pool of readily releasable vesicles (RRP) and the probability of release (P) of each RRP vesicle. These parameters are controlled at the active zone and vary across synapses, but how such synapse specific control is achieved is not understood. ELKS proteins are enriched at vertebrate active zones and enhance P at inhibitory hippocampal synapses, but ELKS functions at excitatory synapses are not known. Studying conditional knockout mice for ELKS, we find that ELKS enhances the RRP at excitatory synapses without affecting P. Surprisingly, ELKS C-terminal sequences, which interact with RIM, are dispensable for RRP enhancement. Instead, the N-terminal ELKS coiled-coil domains that bind to Liprin-α and Bassoon are necessary to control RRP. Thus, ELKS removal has differential, synapse-specific effects on RRP and P, and our findings establish important roles for ELKS N-terminal domains in synaptic vesicle priming.
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Affiliation(s)
- Richard G Held
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Changliang Liu
- Department of Neurobiology, Harvard Medical School, Boston, United States
| | - Pascal S Kaeser
- Department of Neurobiology, Harvard Medical School, Boston, United States
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18
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Hammond JW, Lu SM, Gelbard HA. Platelet Activating Factor Enhances Synaptic Vesicle Exocytosis Via PKC, Elevated Intracellular Calcium, and Modulation of Synapsin 1 Dynamics and Phosphorylation. Front Cell Neurosci 2016; 9:505. [PMID: 26778968 PMCID: PMC4705275 DOI: 10.3389/fncel.2015.00505] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 12/15/2015] [Indexed: 11/25/2022] Open
Abstract
Platelet activating factor (PAF) is an inflammatory phospholipid signaling molecule implicated in synaptic plasticity, learning and memory and neurotoxicity during neuroinflammation. However, little is known about the intracellular mechanisms mediating PAF’s physiological or pathological effects on synaptic facilitation. We show here that PAF receptors are localized at the synapse. Using fluorescent reporters of presynaptic activity we show that a non-hydrolysable analog of PAF (cPAF) enhances synaptic vesicle release from individual presynaptic boutons by increasing the size or release of the readily releasable pool and the exocytosis rate of the total recycling pool. cPAF also activates previously silent boutons resulting in vesicle release from a larger number of terminals. The underlying mechanism involves elevated calcium within presynaptic boutons and protein kinase C activation. Furthermore, cPAF increases synapsin I phosphorylation at sites 1 and 3, and increases dispersion of synapsin I from the presynaptic compartment during stimulation, freeing synaptic vesicles for subsequent release. These findings provide a conceptual framework for how PAF, regardless of its cellular origin, can modulate synapses during normal and pathologic synaptic activity.
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Affiliation(s)
- Jennetta W Hammond
- Center for Neural Development and Disease, University of Rochester Rochester, NY, USA
| | - Shao-Ming Lu
- Center for Neural Development and Disease, University of Rochester Rochester, NY, USA
| | - Harris A Gelbard
- Center for Neural Development and Disease, University of Rochester Rochester, NY, USA
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19
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Dicken MS, Hughes AR, Hentges ST. Gad1 mRNA as a reliable indicator of altered GABA release from orexigenic neurons in the hypothalamus. Eur J Neurosci 2015; 42:2644-53. [PMID: 26370162 DOI: 10.1111/ejn.13076] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 09/02/2015] [Accepted: 09/07/2015] [Indexed: 11/29/2022]
Abstract
The strength of γ-aminobutyric acid (GABA)-mediated inhibitory synaptic input is a principle determinant of neuronal activity. However, because of differences in the number of GABA afferent inputs and the sites of synapses, it is difficult to directly assay for altered GABA transmission between specific cells. The present study tested the hypothesis that the level of mRNA for the GABA synthetic enzyme glutamate decarboxylase (GAD) can provide a reliable proxy for GABA release. This was tested in a mouse hypothalamic circuit important in the regulation of energy balance. Fluorescent in situ hybridization results show that the expression of Gad1 mRNA (encoding the GAD67 enzyme) was increased in hypothalamic neuropeptide Y/agouti-related peptide (NPY/AgRP) neurons after an overnight fast, consistent with the ability of GABA from these neurons to stimulate food intake. Optogenetic studies confirmed that the observed increase in Gad1 mRNA correlated with an increase in the probability of GABA release from NPY/AgRP neurons onto downstream proopiomelanocortin neurons. Likewise, there was an increase in the readily releasable pool of GABA in NPY/AgRP neurons. Selective inhibition of GAD activity in NPY/AgRP neurons decreased GABA release, indicating that GAD67 activity, which is largely dictated by expression level, is a key determinant of GABA release. Altogether, it appears that Gad expression may be a reliable proxy of altered GABAergic transmission. Examining changes in Gad mRNA as a proxy for GABA release may be particularly helpful when the downstream targets are not known or when limited tools exist for detecting GABA release at a particular synapse.
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Affiliation(s)
- Matthew S Dicken
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, CO, 80523, USA
| | - Alexander R Hughes
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, CO, 80523, USA
| | - Shane T Hentges
- Department of Biomedical Sciences, Colorado State University, 1617 Campus Delivery, Fort Collins, CO, 80523, USA
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20
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Fernandes HB, Riordan S, Nomura T, Remmers CL, Kraniotis S, Marshall JJ, Kukreja L, Vassar R, Contractor A. Epac2 Mediates cAMP-Dependent Potentiation of Neurotransmission in the Hippocampus. J Neurosci 2015; 35:6544-53. [PMID: 25904804 DOI: 10.1523/JNEUROSCI.0314-14.2015] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Presynaptic terminal cAMP elevation plays a central role in plasticity at the mossy fiber-CA3 synapse of the hippocampus. Prior studies have identified protein kinase A as a downstream effector of cAMP that contributes to mossy fiber LTP (MF-LTP), but the potential contribution of Epac2, another cAMP effector expressed in the MF synapse, has not been considered. We investigated the role of Epac2 in MF-CA3 neurotransmission using Epac2(-/-) mice. The deletion of Epac2 did not cause gross alterations in hippocampal neuroanatomy or basal synaptic transmission. Synaptic facilitation during short trains was not affected by loss of Epac2 activity; however, both long-term plasticity and forskolin-mediated potentiation of MFs were impaired, demonstrating that Epac2 contributes to cAMP-dependent potentiation of transmitter release. Examination of synaptic transmission during long sustained trains of activity suggested that the readily releasable pool of vesicles is reduced in Epac2(-/-) mice. These data suggest that cAMP elevation uses an Epac2-dependent pathway to promote transmitter release, and that Epac2 is required to maintain the readily releasable pool at MF synapses in the hippocampus.
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21
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Chen Z, Das B, Nakamura Y, DiGregorio DA, Young SM Jr. Ca2+ channel to synaptic vesicle distance accounts for the readily releasable pool kinetics at a functionally mature auditory synapse. J Neurosci 2015; 35:2083-100. [PMID: 25653365 DOI: 10.1523/JNEUROSCI.2753-14.2015] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Precise regulation of synaptic vesicle (SV) release at the calyx of Held is critical for auditory processing. At the prehearing calyx of Held, synchronous and asynchronous release is mediated by fast and slow releasing SVs within the readily releasable pool (RRP). However, the posthearing calyx has dramatically different release properties. Whether developmental alterations in RRP properties contribute to the accelerated release time course found in posthearing calyces is not known. To study these questions, we performed paired patch-clamp recordings, deconvolution analysis, and numerical simulations of buffered Ca(2+) diffusion and SV release in postnatal day (P) 16-19 mouse calyces, as their release properties resemble mature calyces of Held. We found the P16-P19 calyx RRP consists of two pools: a fast pool (τ ≤ 0.9 ms) and slow pool (τ ∼4 ms), in which release kinetics and relative composition of the two pools were unaffected by 5 mm EGTA. Simulations of SV release from the RRP revealed that two populations of SVs were necessary to reproduce the experimental release rates: (1) SVs located close (∼5-25 nm) and (2) more distal (25-100 nm) to VGCC clusters. This positional coupling was confirmed by experiments showing 20 mm EGTA preferentially blocked distally coupled SVs. Lowering external [Ca(2+)] to in vivo levels reduced only the fraction SVs released from the fast pool. Therefore, we conclude that a dominant parameter regulating the mature calyx RRP release kinetics is the distance between SVs and VGCC clusters.
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22
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Dalby NO, Volbracht C, Helboe L, Larsen PH, Jensen HS, Egebjerg J, Elvang AB. Altered function of hippocampal CA1 pyramidal neurons in the rTg4510 mouse model of tauopathy. J Alzheimers Dis 2015; 40:429-42. [PMID: 24448785 DOI: 10.3233/jad-131358] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The formation of neurofibrillary tangles from the assembly of hyperphosphorylated tau leads to dendritic and axonal instability, synaptic degeneration, and neuronal loss. To understand the early physiological consequences of aberrant tau expression, we characterized the physiology of CA1 pyramidal neurons in rTg4510 female mice and non-transgenic (wt) littermate controls. We studied mice at the age of 10-12 weeks where only minimal hyperphosphorylated pretangle tau was present, and 22-24 weeks old mice with significant neurofibrillary tangle pathology. Our electrophysiological analysis included input-output relation, paired-pulse facilitation, and whole cell patch-clamp recordings of neurons to measure action potential threshold and action potential properties, chord-conductance, and characterization of AMPA receptor mediated synaptic transmission. We found that the input-output relation in field (excitatory postsynaptic potentials, EPSP) and whole cell recordings (excitatory postsynaptic currents, EPSC) were impaired in rTg4510 mice compared to wt controls at both ages. We measured a diminished tail current charge after depolarizing voltage input in rTg4510 mice compared to wt in both young and aged mice. Additionally, mini-EPSC properties (peak and decay time) were essentially similar between genotypes and age groups investigated. Surprisingly, in the 22-24 week old group, the mini-EPSC frequency was significantly increased (interevent interval 0.8 ± 0.1 in wt compared to 0.3 ± 0.1 in rTg4510 mice). These data indicate that the developmentally regulated expression of human P301L tau in CA1 pyramidal neurons coincide with changes in neuronal excitability but also that significant presynaptic changes occur late during the progression of tau pathology in this mouse model.
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Affiliation(s)
- Nils Ole Dalby
- Neuroscience Drug Discovery DK, H. Lundbeck A/S, Valby, Denmark
| | | | - Lone Helboe
- Neuroscience Drug Discovery DK, H. Lundbeck A/S, Valby, Denmark
| | | | | | - Jan Egebjerg
- Neuroscience Drug Discovery DK, H. Lundbeck A/S, Valby, Denmark
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Abstract
The dentate gyrus (DG) serves as a primary gate to control information transfer from the cortex to the hippocampus. Activation of incoming cortical inputs results in rapid synaptic excitation followed by slow GABA-mediated (GABAergic) synaptic inhibition onto DG granule cells (GCs). GABAergic inhibitory interneurons (INs) in the DG comprise fast-spiking (FS) and non-fast-spiking (non-FS) cells. Anatomical analyses of DG INs reveal that FS cells are soma-targeting INs, whereas non-FS cells are dendrite-targeting INs. These two IN classes are differentially recruited by excitatory inputs and in turn provide exquisite spatiotemporal control over GC activity. Yet, little is known how FS and non-FS cells transform their presynaptic dynamics into varying postsynaptic response amplitudes. Using paired recordings in rat hippocampal slices, we show that inhibition in the DG is dominated by somatic GABAergic inputs during periods of sparse presynaptic activity, whereas dendritic GABAergic inputs are rapidly shifted to powerful and sustained inhibition during periods of intense presynaptic activity. The variant dynamics of dendritic inhibition is dependent on presynaptic IN subtypes and their activity patterns and is attributed to Ca(2+)-dependent increases in the probability of release and the size of the readily releasable pool. Furthermore, the degree of dynamic GABA release can be reduced by blocking voltage-gated K(+) channels, which increases the efficacy of dendrite-targeting IN output synapses during sparse firing. Such rapid dynamic modulation of dendritic inhibition may act as a frequency-dependent filter to prevent overexcitation of GC dendrites and thus set the excitatory-inhibitory synaptic balance in the DG circuits.
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Oline SN, Burger RM. Short-term synaptic depression is topographically distributed in the cochlear nucleus of the chicken. J Neurosci 2014; 34:1314-24. [PMID: 24453322 PMCID: PMC3898291 DOI: 10.1523/jneurosci.3073-13.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 12/11/2013] [Accepted: 12/13/2013] [Indexed: 11/21/2022] Open
Abstract
In the auditory system, sounds are processed in parallel frequency-tuned circuits, beginning in the cochlea. Activity of auditory nerve fibers reflects this frequency-specific topographic pattern, known as tonotopy, and imparts frequency tuning onto their postsynaptic target neurons in the cochlear nucleus. In birds, cochlear nucleus magnocellularis (NM) neurons encode the temporal properties of acoustic stimuli by "locking" discharges to a particular phase of the input signal. Physiological specializations exist in gradients corresponding to the tonotopic axis in NM that reflect the characteristic frequency (CF) of their auditory nerve fiber inputs. One feature of NM neurons that has not been investigated across the tonotopic axis is short-term synaptic plasticity. NM offers a rather homogeneous population of neurons with a distinct topographical distribution of synaptic properties that is ideal for the investigation of specialized synaptic plasticity. Here we demonstrate for the first time that short-term synaptic depression (STD) is expressed topographically, where unitary high CF synapses are more robust with repeated stimulation. Correspondingly, high CF synapses drive spiking more reliably than their low CF counterparts. We show that postsynaptic AMPA receptor desensitization does not contribute to the observed difference in STD. Further, rate of recovery from depression, a presynaptic property, does not differ tonotopically. Rather, we show that another presynaptic feature, readily releasable pool (RRP) size, is tonotopically distributed and inversely correlated with vesicle release probability. Mathematical model results demonstrate that these properties of vesicle dynamics are sufficient to explain the observed tonotopic distribution of STD.
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Affiliation(s)
- Stefan N. Oline
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015
| | - R. Michael Burger
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015
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Ariel P, Hoppa MB, Ryan TA. Intrinsic variability in Pv, RRP size, Ca(2+) channel repertoire, and presynaptic potentiation in individual synaptic boutons. Front Synaptic Neurosci 2013; 4:9. [PMID: 23335896 PMCID: PMC3542534 DOI: 10.3389/fnsyn.2012.00009] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2012] [Accepted: 12/24/2012] [Indexed: 11/23/2022] Open
Abstract
The strength of individual synaptic contacts is considered a key modulator of information flow across circuits. Presynaptically the strength can be parsed into two key parameters: the size of the readily releasable pool (RRP) and the probability that a vesicle in that pool will undergo exocytosis when an action potential fires (Pv). How these variables are controlled and the degree to which they vary across individual nerve terminals is crucial to understand synaptic plasticity within neural circuits. Here we report robust measurements of these parameters in rat hippocampal neurons and their variability across populations of individual synapses. We explore the diversity of presynaptic Ca2+ channel repertoires and evaluate their effect on synaptic strength at single boutons. Finally, we study the degree to which synapses can be differentially modified by a known potentiator of presynaptic function, forskolin. Our experiments revealed that both Pv and RRP spanned a large range, even for synapses made by the same axon, demonstrating that presynaptic efficacy is governed locally at the single synapse level. Synapses varied greatly in their dependence on N or P/Q type Ca2+ channels for neurotransmission, but there was no association between specific channel repertoires and synaptic efficacy. Increasing cAMP concentration using forskolin enhanced synaptic transmission in a Ca2+-independent manner that was inversely related with a synapse's initial Pv, and independent of its RRP size. We propose a simple model based on the relationship between Pv and calcium entry that can account for the variable potentiation of synapses based on initial probability of vesicle fusion.
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Affiliation(s)
- Pablo Ariel
- Department of Biochemistry, Weill Cornell Medical College New York, NY, USA ; David Rockefeller Graduate Program, The Rockefeller University New York, NY, USA
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26
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Abstract
The serotonergic system in vertebrates and invertebrates has been a focus for over 50 years and will likely continue in the future. Recently, genomic analysis and discovery of alternative splicing and differential expression in tissues have increased the knowledge of serotonin (5-HT) receptor types. Comparative studies can provide useful insights to the wide variety of mechanistic actions of 5-HT responsible for behaviors regulated or modified by 5-HT. To determine cellular responses and influences on neural systems as well as the efferent control of behaviors by the motor units, preparations amenable to detailed studies of synapses are beneficial as working models. The invertebrate neuromuscular junctions (NMJs) offer some unique advantages for such investigations; action of 5-HT at crustacean NMJs has been widely studied, and leech and Aplysia continue to be key organisms. However, there are few studies in insects likely due to the focus in modulation within the CNS and lack of evidence of substantial action of 5-HT at the Drosophila NMJs. There are only a few reports in gastropods and annelids as well as other invertebrates. In this review we highlight some of the key findings of 5-HT actions and receptor types associated at NMJs in a variety of invertebrate preparations in hopes that future studies will build on this knowledge base.
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Affiliation(s)
- Wen-Hui Wu
- Department of Biology & Center for Muscle Biology, University of Kentucky, Lexington, KY 40506-0225, USA
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27
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Wölfel M, Lou X, Schneggenburger R. A mechanism intrinsic to the vesicle fusion machinery determines fast and slow transmitter release at a large CNS synapse. J Neurosci 2007; 27:3198-210. [PMID: 17376981 PMCID: PMC6672471 DOI: 10.1523/jneurosci.4471-06.2007] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2006] [Revised: 02/09/2007] [Accepted: 02/10/2007] [Indexed: 11/21/2022] Open
Abstract
Heterogeneity of release probability p between vesicles in the readily releasable pool (RRP) is expected to strongly influence the kinetics of depression at synapses, but the underlying mechanism(s) are not well understood. To test whether differences in the intrinsic Ca2+ sensitivity of vesicle fusion might cause heterogeneity of p, we made presynaptic Ca2+-uncaging measurements at the calyx of Held and analyzed the time course of transmitter release by EPSC deconvolution. Ca2+ uncaging, which produced spatially homogeneous elevations of [Ca2+]i, evoked a fast and a slow component of release over a wide range of [Ca2+]i, showing that mechanism(s) intrinsic to the vesicle fusion machinery cause fast and slow transmitter release. Surprisingly, the number of vesicles released in the fast component increased with Ca2+-uncaging stimuli of larger amplitudes, a finding that was most obvious below approximately 10 microM [Ca2+]i and that we call "submaximal release" of fast-releasable vesicles. During trains of action potential-like presynaptic depolarizations, submaximal release was also observed as an increase in the cumulative fast release at enhanced release probabilities. A model that assumes two separate subpools of RRP vesicles with different intrinsic Ca2+ sensitivities predicted the observed Ca2+ dependencies of fast and slow transmitter release but could not fully account for submaximal release. Thus, fast and slow transmitter release in response to prolonged [Ca2+]i elevations is caused by intrinsic differences between RRP vesicles, and an "a posteriori" reduction of the Ca2+ sensitivity of vesicle fusion after the onset of the stimulus might cause submaximal release of fast-releasable vesicles and contribute to short-term synaptic depression.
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Affiliation(s)
- Markus Wölfel
- AG Synaptic Dynamics and Modulation, Department of Membrane Biophysics, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, D-37077 Göttingen, Germany, and
| | - Xuelin Lou
- AG Synaptic Dynamics and Modulation, Department of Membrane Biophysics, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, D-37077 Göttingen, Germany, and
| | - Ralf Schneggenburger
- AG Synaptic Dynamics and Modulation, Department of Membrane Biophysics, Max-Planck-Institut für Biophysikalische Chemie, Am Fassberg 11, D-37077 Göttingen, Germany, and
- Laboratory of Synaptic Mechanisms, Brain-Mind Institute, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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28
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de Lange RPJ, de Roos ADG, Borst JGG. Two modes of vesicle recycling in the rat calyx of Held. J Neurosci 2003; 23:10164-73. [PMID: 14602833 PMCID: PMC6740849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/27/2023] Open
Abstract
Vesicle recycling was studied in the rat calyx of Held, a giant brainstem terminal involved in sound localization. Stimulation of brain slices containing the calyx-type synapse with a high extracellular potassium ion concentration in the presence of horseradish peroxidase resulted within several minutes in a reduction of the number of neurotransmitter vesicles and in the appearance of labeled endosome-like structures. After returning to normal solution, the endosome-like structures disappeared over a period of several minutes, whereas simultaneously the number of labeled vesicles increased. A comparison with afferent stimulation suggested that the endosome-like structures normally do not participate in the vesicle cycle. Afferent stimulation at 5 Hz resulted in sustained synaptic transmission, without vesicle depletion but with an estimated endocytotic activity of <0.2 synaptic vesicles per active zone per second. At 20 Hz, the presynaptic action potentials generally failed during prolonged stimulation. In identified synapses, the number of vesicles labeled by photoconversion after stimulation at 5 Hz in the presence of the styryl dye RH414 was much lower than the number of vesicles that were released, as determined by measuring EPSCs. No more than approximately 5% of the vesicles were labeled after 20 min stimulation at 5 Hz, whereas this stimulation protocol was sufficient to largely destain a terminal after previous loading. The results support a scheme for recycling in which two different modes coexist. At physiological demands, a pool of approximately 5% of all vesicles provides sufficient vesicles for release. During intense stimulation, such as occurs in the presence of high extracellular K+, the synapse resorts to bulk endocytosis, a very slow mode of recycling.
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Affiliation(s)
- R P J de Lange
- Department of Neuroscience, Erasmus MC, University Medical Center, 3000 DR Rotterdam, The Netherlands
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29
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Wölfel M, Schneggenburger R. Presynaptic capacitance measurements and Ca2+ uncaging reveal submillisecond exocytosis kinetics and characterize the Ca2+ sensitivity of vesicle pool depletion at a fast CNS synapse. J Neurosci 2003; 23:7059-68. [PMID: 12904466 PMCID: PMC6740656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/04/2023] Open
Abstract
The intracellular Ca2+ sensitivity of synaptic vesicle fusion is an important determinant of transmitter release probability, but it is unknown for most CNS synapses. We combined whole-cell membrane capacitance measurements and Ca2+ uncaging at the large calyx of Held nerve terminals to determine the Ca2+ sensitivity of synaptic vesicle fusion at a glutamatergic CNS synapse, independent of recording EPSCs. Capacitance increases measured 30-50 msec after elevating the intracellular Ca2+ concentration ([Ca2+]i) by Ca2+ uncaging were half-maximal at approximately 5 microm [Ca2+]i. At 10 microm [Ca2+]i, capacitance increases reached maximal values (256 +/- 125 fF; mean +/- SD), indicating the depletion of an average pool of approximately 4000 readily releasable vesicles. Vesicle pool depletion was confirmed in cross-depletion experiments, in which capacitance responses were measured after Ca2+ uncaging, or after combined stimuli of prolonged presynaptic depolarizations and Ca2+ uncaging. To analyze the Ca2+-dependent rates of vesicle pool depletion, the capacitance rise after Ca2+ uncaging was fitted with single- or double-exponential functions. The fast time constants of double-exponential fits, and the time constants of single-exponential fits were 2-3 msec at 10-15 microm [Ca2+]i and reached submillisecond values at 30 microm [Ca2+]i. These results suggest that three to five readily releasable vesicles can fuse within <1 msec at each active zone of a calyx of Held, given that [Ca2+]i rises sufficiently high. Submillisecond kinetics of exocytosis are reached at significantly lower [Ca2+]i than at ribbon-type sensory synapses previously investigated by capacitance measurements.
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Affiliation(s)
- Markus Wölfel
- Arbeitsgruppe Synaptische Dynamik und Modulation and Abteilung Membranbiophysik, Max-Planck-Institut für Biophysikalische Chemie, D-37077 Göttingen, Germany
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30
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de Kock CPJ, Wierda KDB, Bosman LWJ, Min R, Koksma JJ, Mansvelder HD, Verhage M, Brussaard AB. Somatodendritic secretion in oxytocin neurons is upregulated during the female reproductive cycle. J Neurosci 2003; 23:2726-34. [PMID: 12684458 PMCID: PMC6742088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023] Open
Abstract
During the female reproductive cycle, hypothalamic oxytocin (OT) neurons undergo sharp changes in excitability. In lactating mammals, bursts of electrical activity of OT neurons result in the release of large amounts of OT in the bloodstream, which causes milk ejection. One hypothesis is that OT neurons regulate their own firing activity and that of nearby OT neurons by somatodendritic release of OT. In this study, we show that OT neuron activity strongly reduces inhibitory synaptic transmission to these neurons. This effect is blocked by antagonists of both adenosine and OT receptors and is mimicked by OT application. Inhibition of soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex formation by tetanus toxin completely blocked the stimulation-induced reduction in inhibitory input, as did the calcium chelator BAPTA. During lactation, the readily releasable pool of secretory vesicles in OT cell bodies was doubled, and calcium currents were upregulated. This resulted in an increased inhibition of GABAergic synaptic transmission by somatodendritic release during lactation compared with the adult virgin stage. These results demonstrate that somatodendritic release is augmented during lactation, which is a novel form of plasticity to change the strength of synaptic transmission.
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Affiliation(s)
- Christiaan P J de Kock
- Department of Experimental Neurophysiology, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, The Netherlands
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31
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Wesseling JF, Lo DC. Limit on the role of activity in controlling the release-ready supply of synaptic vesicles. J Neurosci 2002; 22:9708-20. [PMID: 12427826 PMCID: PMC6757839] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2023] Open
Abstract
Typical fast chemical synapses in the brain weaken transiently during normal high-frequency use after expending their presynaptic supply of release-ready vesicles. Although it takes several seconds for the readily releasable pool (RRP) to refill during periods of rest, it has been suggested that the replenishment process may be orders of magnitude faster when synapses are active. Here, we measure this replenishment rate at active Schaffer collateral terminals by determining the maximum rate of release that can still be elicited when the RRP is almost completely exhausted. On average, we find that spent vesicles are replaced at a maximum unitary rate of 0.24/sec during periods of intense activity. Because the replenishment rate is similar during subsequent periods of rest, we conclude that no special mechanism accelerates the mobilization of neurotransmitter in active terminals beyond the previously reported, several-fold, residual calcium-driven modulation that persists for several seconds after bouts of intense synaptic activity. In the course of this analysis, we provide new evidence supporting the hypothesis that a simple enzymatic step limits the rate at which reserve synaptic vesicles become ready to undergo exocytosis.
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Affiliation(s)
- John F Wesseling
- Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
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Cabin DE, Shimazu K, Murphy D, Cole NB, Gottschalk W, McIlwain KL, Orrison B, Chen A, Ellis CE, Paylor R, Lu B, Nussbaum RL. Synaptic vesicle depletion correlates with attenuated synaptic responses to prolonged repetitive stimulation in mice lacking alpha-synuclein. J Neurosci 2002; 22:8797-807. [PMID: 12388586 PMCID: PMC6757677] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023] Open
Abstract
Although the mutation of alpha-synuclein, a protein associated with presynaptic vesicles, is implicated in the etiology and pathogenesis of Parkinson's disease, the biological function of the normal protein is unknown. Mice that lack alpha-synuclein have been generated by homologous recombination in embryonic stem cells. Electron microscopic examination of hippocampal synapses revealed a striking selective deficiency of undocked vesicles without affecting docked vesicles. Field recording of CA1 synapses in hippocampal slices from the mutant mice demonstrated normal basal synaptic transmission, paired-pulse facilitation, and response to a brief train of high-frequency stimulation (100 Hz, 40 pulses) that exhausts only docked vesicles. In contrast, the alpha-synuclein knock-out mice exhibited significant impairments in synaptic response to a prolonged train of repetitive stimulation (12.5 Hz, 300 pulses) capable of depleting docked as well as reserve pool vesicles. Moreover, the replenishment of the docked vesicles by reserve pool vesicles after depletion was slower in the mutant synapses. Thus, alpha-synuclein may be required for the genesis and/or maintenance of a subset of presynaptic vesicles, those in the "reserve" or "resting" pools. These results reveal, for the first time, the normal function of endogenous alpha-synuclein in regulating synaptic vesicle mobilization at nerve terminals.
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Affiliation(s)
- Deborah E Cabin
- Genetic Diseases Research Branch, National Human Genome Research Institute, Bethesda, Maryland 20892-4472, USA
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Mozhayeva MG, Sara Y, Liu X, Kavalali ET. Development of vesicle pools during maturation of hippocampal synapses. J Neurosci 2002; 22:654-65. [PMID: 11826095 PMCID: PMC6758530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023] Open
Abstract
We studied the emergence of vesicle pool organization at developing hippocampal synapses by monitoring vesicle recycling and neurotransmitter release as well as examining electron micrographs. Our analysis suggests that presynaptic boutons go through three distinct functional states to mature. At the onset the synapses lack readily releasable vesicles although they possess a pool of recycling vesicles that can release neurotransmitters under strong stimulation. In the next stage the majority of these recycling vesicles switches to a functionally docked state and forms the readily releasable pool (RRP). After assembly of the RRP, new vesicles build the reserve pool. At the mature state the size of the RRP increases linearly with increasing recycling pool size. Furthermore, this preferential filling of the RRP during early synapse maturation is reduced strikingly in synapses deficient in synapsin I and II. Taken together, these results expose a mechanism that ensures functionally effective allocation of a limited number of vesicles in a CNS synapse.
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Affiliation(s)
- Marina G Mozhayeva
- Center for Basic Neuroscience and Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9111, USA
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34
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Waters J, Smith SJ. Phorbol esters potentiate evoked and spontaneous release by different presynaptic mechanisms. J Neurosci 2000; 20:7863-70. [PMID: 11050105 PMCID: PMC6772716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023] Open
Abstract
Phorbol esters enhance release from a variety of cell types. The mechanism by which phorbol esters potentiate presynaptic release from central neurons is unclear, although effects of phorbol esters both on the readily releasable pool of vesicles and on presynaptic calcium channels have been shown. Using confocal microscopy and the fluorescent styryl dye FM 1-43, we have examined the effects of phorbol-12,13-dibutyrate (PDBu) on presynaptic vesicle turnover at individually identified synapses in dissociated cultures obtained from neonatal rat hippocampus. Using different dye staining and destaining protocols we were able to resolve two effects of PDBu. Potentiation of evoked release by PDBu was insensitive to calcium channel antagonists, suggesting that this effect results from an increased number of vesicles in the readily releasable pool. Since we observed no effect of PDBu on the size of the total recycling vesicle pool, we conclude that phorbol esters alter the equilibrium between reserve and readily releasable pools. An additional effect of PDBu on spontaneous release was observed. This effect was antagonized by nifedipine but not omega-conotoxin GVIA or omega-agatoxin IVA. We conclude that PDBu influences spontaneous and evoked release by two different mechanisms: through L-type calcium channels and through an increase in the proportion of recycling vesicles in the readily releasable pool. In addition to further clarifying the mechanism of action of phorbol esters, these results suggest that phorbol esters may be a useful tool with which to probe the function of the readily releasable pool of presynaptic vesicles at CNS synapses.
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Affiliation(s)
- J Waters
- Department of Molecular and Cellular Physiology, Beckman Center, Stanford Medical School, Stanford, California 94305, USA.
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35
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Giovannucci DR, Hlubek MD, Stuenkel EL. Mitochondria regulate the Ca(2+)-exocytosis relationship of bovine adrenal chromaffin cells. J Neurosci 1999; 19:9261-70. [PMID: 10531430 PMCID: PMC6782892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023] Open
Abstract
The present study expands the contemporary view of mitochondria as important participants in cellular Ca(2+) dynamics and provides evidence that mitochondria regulate the supply of release-competent secretory granules. Using pharmacological probes to inhibit mitochondrial Ca(2+) import, the ability of mitochondria to modulate secretory activity in single, patch-clamped bovine chromaffin cells was examined by simultaneously monitoring rapid changes in membrane surface area (DeltaC(m)) and cytosolic Ca(2+) levels ([Ca(2+)](c)). Repetitive step depolarizations or action potential waveforms were found to raise the [Ca(2+)](c) of chromaffin cells into the 1 microM to tens of micromolar range. Inhibiting mitochondria by treatment with carbonyl cyanide p-(trifuoro-methoxy)phenylhydrazone, antimycin-oligomycin, or ruthenium red revealed that mitochondria are a prominent component for the clearance of Ca(2+) that entered via voltage-activated Ca(2+) channels. Disruption of cellular Ca(2+) homeostasis by poisoning mitochondria enhanced the secretory responsiveness of chromaffin cells by increasing the amplitude of the transient rise and the time course of recovery to baseline of the evoked Delta[Ca(2+)](c). The enhancement of the secretory response was represented by significant deviation of the Ca(2+)-exocytosis relationship from a standard relationship that equates Ca(2+) influx and DeltaC(m). Thus, mitochondria would play a critical role in the control of secretory activity in chromaffin cells that undergo tonic or repetitive depolarizing activity, likely by limiting the Ca(2+)-dependent activation of specific proteins that recruit or prime secretory granules for exocytosis.
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Affiliation(s)
- D R Giovannucci
- Department of Physiology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0622, USA.
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