1
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Scheuer KS, Jansson AM, Zhao X, Jackson MB. Inter and intralaminar excitation of parvalbumin interneurons in mouse barrel cortex. PLoS One 2024; 19:e0289901. [PMID: 38870124 PMCID: PMC11175493 DOI: 10.1371/journal.pone.0289901] [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] [Received: 07/27/2023] [Accepted: 04/29/2024] [Indexed: 06/15/2024] Open
Abstract
Parvalbumin (PV) interneurons are inhibitory fast-spiking cells with essential roles in directing the flow of information through cortical circuits. These neurons set the balance between excitation and inhibition and control rhythmic activity. PV interneurons differ between cortical layers in their morphology, circuitry, and function, but how their electrophysiological properties vary has received little attention. Here we investigate responses of PV interneurons in different layers of primary somatosensory barrel cortex (BC) to different excitatory inputs. With the genetically-encoded hybrid voltage sensor, hVOS, we recorded voltage changes in many L2/3 and L4 PV interneurons simultaneously, with stimulation applied to either L2/3 or L4. A semi-automated procedure was developed to identify small regions of interest corresponding to single responsive PV interneurons. Amplitude, half-width, and rise-time were greater for PV interneurons residing in L2/3 compared to L4. Stimulation in L2/3 elicited responses in both L2/3 and L4 with longer latency compared to stimulation in L4. These differences in latency between layers could influence their windows for temporal integration. Thus, PV interneurons in different cortical layers of BC respond in a layer specific and input specific manner, and these differences have potential roles in cortical computations.
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Affiliation(s)
- Katherine S. Scheuer
- Cellular and Molecular Biology PhD Program, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Anna M. Jansson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Xinyu Zhao
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
- Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Meyer B. Jackson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
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2
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Shu WC, Jackson MB. Intrinsic and Synaptic Contributions to Repetitive Spiking in Dentate Granule Cells. J Neurosci 2024; 44:e0716232024. [PMID: 38503495 PMCID: PMC11063872 DOI: 10.1523/jneurosci.0716-23.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 03/03/2024] [Accepted: 03/05/2024] [Indexed: 03/21/2024] Open
Abstract
Repetitive firing of granule cells (GCs) in the dentate gyrus (DG) facilitates synaptic transmission to the CA3 region. This facilitation can gate and amplify the flow of information through the hippocampus. High-frequency bursts in the DG are linked to behavior and plasticity, but GCs do not readily burst. Under normal conditions, a single shock to the perforant path in a hippocampal slice typically drives a GC to fire a single spike, and only occasionally more than one spike is seen. Repetitive spiking in GCs is not robust, and the mechanisms are poorly understood. Here, we used a hybrid genetically encoded voltage sensor to image voltage changes evoked by cortical inputs in many mature GCs simultaneously in hippocampal slices from male and female mice. This enabled us to study relatively infrequent double and triple spikes. We found GCs are relatively homogeneous and their double spiking behavior is cell autonomous. Blockade of GABA type A receptors increased multiple spikes and prolonged the interspike interval, indicating inhibitory interneurons limit repetitive spiking and set the time window for successive spikes. Inhibiting synaptic glutamate release showed that recurrent excitation mediated by hilar mossy cells contributes to, but is not necessary for, multiple spiking. Blockade of T-type Ca2+ channels did not reduce multiple spiking but prolonged interspike intervals. Imaging voltage changes in different GC compartments revealed that second spikes can be initiated in either dendrites or somata. Thus, pharmacological and biophysical experiments reveal roles for both synaptic circuitry and intrinsic excitability in GC repetitive spiking.
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Affiliation(s)
- Wen-Chi Shu
- Department of Neuroscience and Biophysics Program, University of Wisconsin-Madison, Wisconsin 53705
| | - Meyer B Jackson
- Department of Neuroscience and Biophysics Program, University of Wisconsin-Madison, Wisconsin 53705
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3
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Scheuer KS, Judge JM, Zhao X, Jackson MB. Velocity of conduction between columns and layers in barrel cortex reported by parvalbumin interneurons. Cereb Cortex 2023; 33:9917-9926. [PMID: 37415260 PMCID: PMC10656945 DOI: 10.1093/cercor/bhad254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Revised: 06/21/2023] [Accepted: 06/22/2023] [Indexed: 07/08/2023] Open
Abstract
Inhibitory interneurons expressing parvalbumin (PV) play critical roles throughout the brain. Their rapid spiking enables them to control circuit dynamics on a millisecond time scale, and the timing of their activation by different excitatory pathways is critical to these functions. We used a genetically encoded hybrid voltage sensor to image PV interneuron voltage changes with sub-millisecond precision in primary somatosensory barrel cortex (BC) of adult mice. Electrical stimulation evoked depolarizations with a latency that increased with distance from the stimulating electrode, allowing us to determine conduction velocity. Spread of responses between cortical layers yielded an interlaminar conduction velocity and spread within layers yielded intralaminar conduction velocities in different layers. Velocities ranged from 74 to 473 μm/ms depending on trajectory; interlaminar conduction was 71% faster than intralaminar conduction. Thus, computations within columns are more rapid than between columns. The BC integrates thalamic and intracortical input for functions such as texture discrimination and sensory tuning. Timing differences between intra- and interlaminar PV interneuron activation could impact these functions. Imaging of voltage in PV interneurons reveals differences in signaling dynamics within cortical circuitry. This approach offers a unique opportunity to investigate conduction in populations of axons based on their targeting specificity.
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Affiliation(s)
- Katherine S Scheuer
- Cellular and Molecular Biology Program, University of Wisconsin-Madison, Madison, WI 53705, United States
| | - John M Judge
- Biophysics Program, University of Wisconsin-Madison, Madison, WI 53705, United States
| | - Xinyu Zhao
- Waisman Center, University of Wisconsin-Madison, Madison, WI 53705, United States
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705, United States
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705, United States
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4
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Scheuer KS, Jansson AM, Zhao X, Jackson MB. Inter and Intralaminar Excitation of Parvalbumin Interneurons in Mouse Barrel Cortex. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.02.543448. [PMID: 37398428 PMCID: PMC10312540 DOI: 10.1101/2023.06.02.543448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
Parvalbumin (PV) interneurons are inhibitory fast-spiking cells with essential roles in directing the flow of information through cortical circuits. These neurons set the balance between excitation and inhibition, control rhythmic activity, and have been linked to disorders including autism spectrum and schizophrenia. PV interneurons differ between cortical layers in their morphology, circuitry, and function, but how their electrophysiological properties vary has received little attention. Here we investigate responses of PV interneurons in different layers of primary somatosensory barrel cortex (BC) to different excitatory inputs. With the genetically-encoded hybrid voltage sensor, hVOS, we recorded voltage changes simultaneously in many L2/3 and L4 PV interneurons to stimulation in either L2/3 or L4. Decay-times were consistent across L2/3 and L4. Amplitude, half-width, and rise-time were greater for PV interneurons residing in L2/3 compared to L4. Stimulation in L2/3 elicited responses in both L2/3 and L4 with longer latency compared to stimulation in L4. These differences in latency between layers could influence their windows for temporal integration. Thus PV interneurons in different cortical layers of BC show differences in response properties with potential roles in cortical computations.
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Affiliation(s)
- Kate S Scheuer
- Cellular and Molecular Biology Program, University of Wisconsin-Madison, Madison, Wisconsin, 53705
| | - Anna M Jansson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, 53705
| | - Xinyu Zhao
- Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, 53705
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, 53705
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5
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Canales A, Scheuer KS, Zhao X, Jackson MB. Unitary synaptic responses of parvalbumin interneurons evoked by excitatory neurons in the mouse barrel cortex. Cereb Cortex 2023; 33:5108-5121. [PMID: 36227216 PMCID: PMC10151880 DOI: 10.1093/cercor/bhac403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 09/14/2022] [Accepted: 09/15/2022] [Indexed: 11/13/2022] Open
Abstract
The mammalian cortex integrates and processes information to transform sensory inputs into perceptions and motor outputs. These operations are performed by networks of excitatory and inhibitory neurons distributed through the cortical layers. Parvalbumin interneurons (PVIs) are the most abundant type of inhibitory cortical neuron. With axons projecting within and between layers, PVIs supply feedforward and feedback inhibition to control and modulate circuit function. Distinct populations of excitatory neurons recruit different PVI populations, but the specializations of these synapses are poorly understood. Here, we targeted a genetically encoded hybrid voltage sensor to PVIs and used fluorescence imaging in mouse somatosensory cortex slices to record their voltage changes. Stimulating a single visually identified excitatory neuron with small-tipped theta-glass electrodes depolarized multiple PVIs, and a common threshold suggested that stimulation elicited unitary synaptic potentials in response to a single excitatory neuron. Excitatory neurons depolarized PVIs in multiple layers, with the most residing in the layer of the stimulated neuron. Spiny stellate cells depolarized PVIs more strongly than pyramidal cells by up to 77%, suggesting a greater role for stellate cells in recruiting PVI inhibition and controlling cortical computations. Response half-width also varied between different excitatory inputs. These results demonstrate functional differences between excitatory synapses on PVIs.
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Affiliation(s)
- Alejandra Canales
- Department of Neuroscience, University of Wisconsin, Madison, WI 53705, United States
- Department of Neurological Surgery, University of California San Francisco, San Francisco, CA, United States
| | - Katherine S Scheuer
- Department of Neuroscience, University of Wisconsin, Madison, WI 53705, United States
| | - Xinyu Zhao
- Department of Neuroscience, University of Wisconsin, Madison, WI 53705, United States
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin, Madison, WI 53705, United States
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6
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Ma Y, Shu WC, Lin L, Cao XJ, Oertel D, Smith PH, Jackson MB. Imaging Voltage Globally and in Isofrequency Lamina in Slices of Mouse Ventral Cochlear Nucleus. eNeuro 2023; 10:ENEURO.0465-22.2023. [PMID: 36792362 PMCID: PMC9997695 DOI: 10.1523/eneuro.0465-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 02/02/2023] [Accepted: 02/06/2023] [Indexed: 02/17/2023] Open
Abstract
The cochlear nuclei (CNs) receive sensory information from the ear and perform fundamental computations before relaying this information to higher processing centers. These computations are performed by distinct types of neurons interconnected in circuits dedicated to the specialized roles of the auditory system. In the present study, we explored the use of voltage imaging to investigate CN circuitry. We tested two approaches based on fundamentally different voltage sensing technologies. Using a voltage-sensitive dye we recorded glutamate receptor-independent signals arising predominantly from axons. The mean conduction velocity of these fibers of 0.27 m/s was rapid but in range with other unmyelinated axons. We then used a genetically-encoded hybrid voltage sensor (hVOS) to image voltage from a specific population of neurons. Probe expression was controlled using Cre recombinase linked to c-fos activation. This activity-induced gene enabled targeting of neurons that are activated when a mouse hears a pure 15-kHz tone. In CN slices from these animals auditory nerve fiber stimulation elicited a glutamate receptor-dependent depolarization in hVOS probe-labeled neurons. These cells resided within a band corresponding to an isofrequency lamina, and responded with a high degree of synchrony. In contrast to the axonal origin of voltage-sensitive dye signals, hVOS signals represent predominantly postsynaptic responses. The introduction of voltage imaging to the CN creates the opportunity to investigate auditory processing circuitry in populations of neurons targeted on the basis of their genetic identity and their roles in sensory processing.
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Affiliation(s)
- Yihe Ma
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Wen-Chi Shu
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Lin Lin
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Xiao-Jie Cao
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Donata Oertel
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Philip H Smith
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
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Swanson JL, Chin PS, Romero JM, Srivastava S, Ortiz-Guzman J, Hunt PJ, Arenkiel BR. Advancements in the Quest to Map, Monitor, and Manipulate Neural Circuitry. Front Neural Circuits 2022; 16:886302. [PMID: 35719420 PMCID: PMC9204427 DOI: 10.3389/fncir.2022.886302] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 04/27/2022] [Indexed: 01/27/2023] Open
Abstract
Neural circuits and the cells that comprise them represent the functional units of the brain. Circuits relay and process sensory information, maintain homeostasis, drive behaviors, and facilitate cognitive functions such as learning and memory. Creating a functionally-precise map of the mammalian brain requires anatomically tracing neural circuits, monitoring their activity patterns, and manipulating their activity to infer function. Advancements in cell-type-specific genetic tools allow interrogation of neural circuits with increased precision. This review provides a broad overview of recombination-based and activity-driven genetic targeting approaches, contemporary viral tracing strategies, electrophysiological recording methods, newly developed calcium, and voltage indicators, and neurotransmitter/neuropeptide biosensors currently being used to investigate circuit architecture and function. Finally, it discusses methods for acute or chronic manipulation of neural activity, including genetically-targeted cellular ablation, optogenetics, chemogenetics, and over-expression of ion channels. With this ever-evolving genetic toolbox, scientists are continuing to probe neural circuits with increasing resolution, elucidating the structure and function of the incredibly complex mammalian brain.
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Affiliation(s)
- Jessica L. Swanson
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
| | - Pey-Shyuan Chin
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States
| | - Juan M. Romero
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States
- Medical Scientist Training Program, Baylor College of Medicine, Houston, TX, United States
| | - Snigdha Srivastava
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
- Medical Scientist Training Program, Baylor College of Medicine, Houston, TX, United States
| | - Joshua Ortiz-Guzman
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
| | - Patrick J. Hunt
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
- Medical Scientist Training Program, Baylor College of Medicine, Houston, TX, United States
| | - Benjamin R. Arenkiel
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States
- Medical Scientist Training Program, Baylor College of Medicine, Houston, TX, United States
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8
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Kumar P, Lavis LD. Melding Synthetic Molecules and Genetically Encoded Proteins to Forge New Tools for Neuroscience. Annu Rev Neurosci 2022; 45:131-150. [PMID: 35226826 DOI: 10.1146/annurev-neuro-110520-030031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Unraveling the complexity of the brain requires sophisticated methods to probe and perturb neurobiological processes with high spatiotemporal control. The field of chemical biology has produced general strategies to combine the molecular specificity of small-molecule tools with the cellular specificity of genetically encoded reagents. Here, we survey the application, refinement, and extension of these hybrid small-molecule:protein methods to problems in neuroscience, which yields powerful reagents to precisely measure and manipulate neural systems. Expected final online publication date for the Annual Review of Neuroscience, Volume 45 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Pratik Kumar
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, USA;
| | - Luke D Lavis
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, USA;
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9
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Bringing together the best of chemistry and biology: hybrid indicators for imaging neuronal membrane potential. J Neurosci Methods 2021; 363:109348. [PMID: 34480955 DOI: 10.1016/j.jneumeth.2021.109348] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Revised: 08/27/2021] [Accepted: 08/30/2021] [Indexed: 12/15/2022]
Abstract
Membrane potential is an indispensable biophysical signal in neurobiology. Imaging neuronal electrical signals with fluorescent indicators allows for non-invasive recording at high spatial resolution. Over the past decades, both genetically encoded voltage indicators (GEVIs) and organic voltage sensing dyes (OVSDs) have been developed to achieve imaging membrane potential dynamics in cultured neurons and in vivo. More recently, hybrid voltage indicators have gained increasing attention due to their superior fluorescent quantum yield and photostability as compared to conventional GEVIs. In this mini-review, we summarize the design, characterization and biological applications of hybrid voltage indicators, and discuss future improvements.
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10
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Ma Y, Bayguinov PO, McMahon SM, Scharfman HE, Jackson MB. Direct synaptic excitation between hilar mossy cells revealed with a targeted voltage sensor. Hippocampus 2021; 31:1215-1232. [PMID: 34478219 DOI: 10.1002/hipo.23386] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 08/09/2021] [Accepted: 08/21/2021] [Indexed: 12/18/2022]
Abstract
The dentate gyrus not only gates the flow of information into the hippocampus, it also integrates and processes this information. Mossy cells (MCs) are a major type of excitatory neuron strategically located in the hilus of the dentate gyrus where they can contribute to this processing through networks of synapses with inhibitory neurons and dentate granule cells. Some prior work has suggested that MCs can form excitatory synapses with other MCs, but the role of these synapses in the network activity of the dentate gyrus has received little attention. Here, we investigated synaptic inputs to MCs in mouse hippocampal slices using a genetically encoded hybrid voltage sensor (hVOS) targeted to MCs by Cre-lox technology. This enabled optical recording of voltage changes from multiple MCs simultaneously. Stimulating granule cells and CA3 pyramidal cells activated well-established inputs to MCs and elicited synaptic responses as expected. However, the weak blockade of MC responses to granule cell layer stimulation by DCG-IV raised the possibility of another source of excitation. To evaluate synapses between MCs as this source, single MCs were stimulated focally. Stimulation of one MC above its action potential threshold evoked depolarizing responses in neighboring MCs that depended on glutamate receptors. Short latency responses of MCs to other MCs did not depend on release from granule cell axons. However, granule cells did contribute to the longer latency responses of MCs to stimulation of other MCs. Thus, MCs transmit their activity to other MCs both through direct synaptic coupling and through polysynaptic coupling with dentate granule cells. MC-MC synapses can redistribute information entering the dentate gyrus and thus shape and modulate the electrical activity underlying hippocampal functions such as navigation and memory, as well as excessive excitation during seizures.
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Affiliation(s)
- Yihe Ma
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Peter O Bayguinov
- Washington University Center for Cellular Imaging, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Shane M McMahon
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Helen E Scharfman
- New York University Langone Health and the Nathan Kline Institute for Psychiatric Research, Orangeburg, New Jersey, USA
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, Wisconsin, USA
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11
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Couch T, Berger K, Kneisley DL, McCullock TW, Kammermeier P, Maclean DM. Topography and motion of acid-sensing ion channel intracellular domains. eLife 2021; 10:68955. [PMID: 34292153 PMCID: PMC8341984 DOI: 10.7554/elife.68955] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Accepted: 07/21/2021] [Indexed: 01/12/2023] Open
Abstract
Acid-sensing ion channels (ASICs) are trimeric cation-selective channels activated by decreases in extracellular pH. The intracellular N and C terminal tails of ASIC1 influence channel gating, trafficking, and signaling in ischemic cell death. Despite several X-ray and cryo-EM structures of the extracellular and transmembrane segments of ASIC1, these important intracellular tails remain unresolved. Here, we describe the coarse topography of the chicken ASIC1 intracellular domains determined by fluorescence resonance energy transfer (FRET), measured using either fluorescent lifetime imaging or patch clamp fluorometry. We find the C terminal tail projects into the cytosol by approximately 35 Å and that the N and C tails from the same subunits are closer than adjacent subunits. Using pH-insensitive fluorescent proteins, we fail to detect any relative movement between the N and C tails upon extracellular acidification but do observe axial motions of the membrane proximal segments toward the plasma membrane. Taken together, our study furnishes a coarse topographic map of the ASIC intracellular domains while providing directionality and context to intracellular conformational changes induced by extracellular acidification.
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Affiliation(s)
- Tyler Couch
- Graduate Program in Cellular and Molecular Pharmacology and Physiology, Reno, United States
| | - Kyle Berger
- Department of Pharmacology and Physiology, University of Rochester Medical Center, New York, United States
| | - Dana L Kneisley
- Department of Pharmacology and Physiology, University of Rochester Medical Center, New York, United States
| | - Tyler W McCullock
- Graduate Program in Cellular and Molecular Pharmacology and Physiology, Reno, United States
| | - Paul Kammermeier
- Department of Pharmacology and Physiology, University of Rochester Medical Center, New York, United States
| | - David M Maclean
- Department of Pharmacology and Physiology, University of Rochester Medical Center, New York, United States
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12
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Benlian BR, Klier PEZ, Martinez KN, Schwinn MK, Kirkland TA, Miller EW. Small Molecule-Protein Hybrid for Voltage Imaging via Quenching of Bioluminescence. ACS Sens 2021; 6:1857-1863. [PMID: 33723996 DOI: 10.1021/acssensors.1c00058] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We report a small-molecule enzyme pair for optical voltage sensing via quenching of bioluminescence. This quenching bioluminescent voltage indicator, or Q-BOLT, pairs the dark absorbing, voltage-sensitive dipicrylamine with membrane-localized bioluminescence from the luciferase NanoLuc (NLuc). As a result, bioluminescence is quenched through resonance energy transfer (QRET) as a function of membrane potential. Fusion of HaloTag to NLuc creates a two-acceptor bioluminescence resonance energy transfer (BRET) system when a tetramethylrhodamine (TMR) HaloTag ligand is ligated to HaloTag. In this mode, Q-BOLT is capable of providing direct visualization of changes in membrane potential in live cells via three distinct readouts: change in QRET, BRET, and the ratio between bioluminescence emission and BRET. Q-BOLT can provide up to a 29% change in bioluminescence (ΔBL/BL) and >100% ΔBRET/BRET per 100 mV change in HEK 293T cells, without the need for excitation light. In cardiac monolayers derived from human-induced pluripotent stem cells (hiPSCs), Q-BOLT readily reports on membrane potential oscillations. Q-BOLT is the first example of a hybrid small molecule-protein voltage indicator that does not require excitation light and may be useful in contexts where excitation light is limiting.
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Affiliation(s)
| | | | | | | | - Thomas A. Kirkland
- Promega Biosciences LLC, San Luis Obispo, California 93401, United States
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13
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Matamala E, Castillo C, Vivar JP, Rojas PA, Brauchi SE. Imaging the electrical activity of organelles in living cells. Commun Biol 2021; 4:389. [PMID: 33758369 PMCID: PMC7988155 DOI: 10.1038/s42003-021-01916-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Accepted: 02/24/2021] [Indexed: 12/25/2022] Open
Abstract
Eukaryotic cells are complex systems compartmentalized in membrane-bound organelles. Visualization of organellar electrical activity in living cells requires both a suitable reporter and non-invasive imaging at high spatiotemporal resolution. Here we present hVoSorg, an optical method to monitor changes in the membrane potential of subcellular membranes. This method takes advantage of a FRET pair consisting of a membrane-bound voltage-insensitive fluorescent donor and a non-fluorescent voltage-dependent acceptor that rapidly moves across the membrane in response to changes in polarity. Compared to the currently available techniques, hVoSorg has advantages including simple and precise subcellular targeting, the ability to record from individual organelles, and the potential for optical multiplexing of organellar activity.
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Affiliation(s)
- Ella Matamala
- Physiology Institute, Universidad Austral de Chile, Valdivia, Chile
- Millennium Nucleus of Ion Channel-Associated Diseases (MiNICAD), Valdivia, Chile
| | - Cristian Castillo
- Millennium Nucleus of Ion Channel-Associated Diseases (MiNICAD), Valdivia, Chile
| | - Juan P Vivar
- Physiology Institute, Universidad Austral de Chile, Valdivia, Chile
| | - Patricio A Rojas
- Laboratory of Neuroscience, Faculty of Chemistry and Biology, Universidad de Santiago de Chile, Santiago, Chile
| | - Sebastian E Brauchi
- Physiology Institute, Universidad Austral de Chile, Valdivia, Chile.
- Millennium Nucleus of Ion Channel-Associated Diseases (MiNICAD), Valdivia, Chile.
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, US.
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14
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A dark quencher genetically encodable voltage indicator (dqGEVI) exhibits high fidelity and speed. Proc Natl Acad Sci U S A 2021; 118:2020235118. [PMID: 33531364 PMCID: PMC8017929 DOI: 10.1073/pnas.2020235118] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Voltage sensing with genetically expressed optical probes is highly desirable for large-scale recordings of neuronal activity and detection of localized voltage signals in single neurons. Here we describe a method for a two-component (hybrid) genetically encodable fluorescent voltage sensing in neurons. The approach uses a glycosylphosphatidylinositol-tagged fluorescent protein (enhanced green fluorescent protein) that ensures the fluorescence to be specifically confined to the outside of the plasma membrane and D3, a voltage-dependent quencher. Previous hybrid genetically encoded voltage sensing approaches relied on a single quenching molecule, dipycrilamine (DPA), which is toxic, increases membrane capacitance, interferes with neurotransmitters, and is explosive. Our method uses a nontoxic and nonexplosive compound that performs better than DPA in all aspects of fluorescent voltage sensing. Voltage sensing with genetically expressed optical probes is highly desirable for large-scale recordings of neuronal activity and detection of localized voltage signals in single neurons. Most genetically encodable voltage indicators (GEVI) have drawbacks including slow response, low fluorescence, or excessive bleaching. Here we present a dark quencher GEVI approach (dqGEVI) using a Förster resonance energy transfer pair between a fluorophore glycosylphosphatidylinositol–enhanced green fluorescent protein (GPI-eGFP) on the outer surface of the neuronal membrane and an azo-benzene dye quencher (D3) that rapidly moves in the membrane driven by voltage. In contrast to previous probes, the sensor has a single photon bleaching time constant of ∼40 min, has a high temporal resolution and fidelity for detecting action potential firing at 100 Hz, resolves membrane de- and hyperpolarizations of a few millivolts, and has negligible effects on passive membrane properties or synaptic events. The dqGEVI approach should be a valuable tool for optical recordings of subcellular or population membrane potential changes in nerve cells.
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Forro C, Caron D, Angotzi GN, Gallo V, Berdondini L, Santoro F, Palazzolo G, Panuccio G. Electrophysiology Read-Out Tools for Brain-on-Chip Biotechnology. MICROMACHINES 2021; 12:124. [PMID: 33498905 PMCID: PMC7912435 DOI: 10.3390/mi12020124] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 01/18/2021] [Accepted: 01/19/2021] [Indexed: 02/07/2023]
Abstract
Brain-on-Chip (BoC) biotechnology is emerging as a promising tool for biomedical and pharmaceutical research applied to the neurosciences. At the convergence between lab-on-chip and cell biology, BoC couples in vitro three-dimensional brain-like systems to an engineered microfluidics platform designed to provide an in vivo-like extrinsic microenvironment with the aim of replicating tissue- or organ-level physiological functions. BoC therefore offers the advantage of an in vitro reproduction of brain structures that is more faithful to the native correlate than what is obtained with conventional cell culture techniques. As brain function ultimately results in the generation of electrical signals, electrophysiology techniques are paramount for studying brain activity in health and disease. However, as BoC is still in its infancy, the availability of combined BoC-electrophysiology platforms is still limited. Here, we summarize the available biological substrates for BoC, starting with a historical perspective. We then describe the available tools enabling BoC electrophysiology studies, detailing their fabrication process and technical features, along with their advantages and limitations. We discuss the current and future applications of BoC electrophysiology, also expanding to complementary approaches. We conclude with an evaluation of the potential translational applications and prospective technology developments.
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Affiliation(s)
- Csaba Forro
- Tissue Electronics, Fondazione Istituto Italiano di Tecnologia, Largo Barsanti e Matteucci, 53-80125 Naples, Italy; (C.F.); (F.S.)
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Davide Caron
- Enhanced Regenerative Medicine, Fondazione Istituto Italiano di Tecnologia, Via Morego, 30-16163 Genova, Italy; (D.C.); (V.G.)
| | - Gian Nicola Angotzi
- Microtechnology for Neuroelectronics, Fondazione Istituto Italiano di Tecnologia, Via Morego, 30-16163 Genova, Italy; (G.N.A.); (L.B.)
| | - Vincenzo Gallo
- Enhanced Regenerative Medicine, Fondazione Istituto Italiano di Tecnologia, Via Morego, 30-16163 Genova, Italy; (D.C.); (V.G.)
| | - Luca Berdondini
- Microtechnology for Neuroelectronics, Fondazione Istituto Italiano di Tecnologia, Via Morego, 30-16163 Genova, Italy; (G.N.A.); (L.B.)
| | - Francesca Santoro
- Tissue Electronics, Fondazione Istituto Italiano di Tecnologia, Largo Barsanti e Matteucci, 53-80125 Naples, Italy; (C.F.); (F.S.)
| | - Gemma Palazzolo
- Enhanced Regenerative Medicine, Fondazione Istituto Italiano di Tecnologia, Via Morego, 30-16163 Genova, Italy; (D.C.); (V.G.)
| | - Gabriella Panuccio
- Enhanced Regenerative Medicine, Fondazione Istituto Italiano di Tecnologia, Via Morego, 30-16163 Genova, Italy; (D.C.); (V.G.)
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Mollinedo-Gajate I, Song C, Knöpfel T. Genetically Encoded Voltage Indicators. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1293:209-224. [PMID: 33398815 DOI: 10.1007/978-981-15-8763-4_12] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Optogenetic approaches combine the power to allocate optogenetic tools (proteins) to specific cell populations (defined genetically or functionally) and the use of light-based interfaces between biological wetware (cells and tissues) and hardware (controllers and recorders). The optogenetic toolbox contains two main compartments: tools to interfere with cellular processes and tools to monitor cellular events. Among the latter are genetically encoded voltage indicators (GEVIs). This chapter outlines the development, current state of the art and prospects of emerging optical GEVI imaging technologies.
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Affiliation(s)
| | - Chenchen Song
- Laboratory for Neuronal Circuit Dynamics, Imperial College London, London, UK
| | - Thomas Knöpfel
- Laboratory for Neuronal Circuit Dynamics, Imperial College London, London, UK.
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Liu Y, Lu Y, Chen G, Wang Q. Recent Progress of Hybrid Optical Probes for Neural Membrane Potential Imaging. Biotechnol J 2020; 15:e2000086. [PMID: 32662937 DOI: 10.1002/biot.202000086] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Revised: 07/04/2020] [Indexed: 12/17/2022]
Abstract
The neural membrane potential of nerve cells is the basis of neural activity production, which controls advanced brain activities such as memory, emotion, and learning. In the past decades, optical voltage indicator has emerged as a promising tool to decode neural activities with high-fidelity and excellent spatiotemporal resolution. In particular, the hybrid optical probes can combine the advantageous photophysical properties of different components such as voltage-sensitive molecules, highly fluorescent fluorophores, membrane-targeting tags, and optogenetic materials, thus showing numerous advantages in improving the photoluminescence intensity, voltage sensitivity, photostability, and cell specificity of probes. In this review, the current state-of-the-art hybrid probes are highlighted, that are designed by using fluorescent proteins, organic dyes, and fluorescent nanoprobes as the fluorophores, respectively. Then, the design strategies, voltage-sensing mechanisms and the in vitro and in vivo neural activity imaging applications of the hybrid probes are summarized. Finally, based on the current achievements of voltage imaging studies, the challenges and prospects for design and application of hybrid optical probes in the future are presented.
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Affiliation(s)
- Yongyang Liu
- School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei, 230026, China.,CAS Key Laboratory of Nano-Bio Interface, Suzhou Key Laboratory of Functional Molecular Imaging Technology, Division of Nanobiomedicine and i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, 215123, China
| | - Yaxin Lu
- School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei, 230026, China.,CAS Key Laboratory of Nano-Bio Interface, Suzhou Key Laboratory of Functional Molecular Imaging Technology, Division of Nanobiomedicine and i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, 215123, China
| | - Guangcun Chen
- School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei, 230026, China.,CAS Key Laboratory of Nano-Bio Interface, Suzhou Key Laboratory of Functional Molecular Imaging Technology, Division of Nanobiomedicine and i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, 215123, China
| | - Qiangbin Wang
- School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei, 230026, China.,CAS Key Laboratory of Nano-Bio Interface, Suzhou Key Laboratory of Functional Molecular Imaging Technology, Division of Nanobiomedicine and i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, 215123, China.,College of Materials Sciences and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049, China
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18
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Beck C, Zhang D, Gong Y. Enhanced genetically encoded voltage indicators advance their applications in neuroscience. CURRENT OPINION IN BIOMEDICAL ENGINEERING 2019; 12:111-117. [PMID: 32864526 DOI: 10.1016/j.cobme.2019.10.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Genetically encoded voltage indicators report membrane voltage with high spatiotemporal resolution. Extensive recent efforts to improve the GEVIs' brightness, sensitivity, and kinetics have greatly increased the GEVIs' signal-to-noise performance over ten-fold and lowered their response time to the sub-millisecond regime. Such capabilities have broadened the GEVIs' ability to measure membrane voltage of neural populations at cellular resolution in vitro and in vivo, all at high speeds. The GEVIs' high voltage fidelity and fast response have revealed novel physiological phenomena in multiple neuroscientific applications. Such applications portend future targeted studies of voltage activity that take advantage of the GEVIs' ability to report rapid dynamics from genetically-targeted neural populations.
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Affiliation(s)
- Connor Beck
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA
| | - Diming Zhang
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA
| | - Yiyang Gong
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA
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19
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Ma Y, Bayguinov PO, Jackson MB. Optical Studies of Action Potential Dynamics with hVOS probes. CURRENT OPINION IN BIOMEDICAL ENGINEERING 2019; 12:51-58. [PMID: 32864524 DOI: 10.1016/j.cobme.2019.09.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The detection of action potentials and the characterization of their waveform represent basic benchmarks for evaluating optical sensors of voltage. The effectiveness of a voltage sensor in reporting action potentials will determine its usefulness in voltage imaging experiments designed for the study of neural circuitry. The hybrid voltage sensor (hVOS) technique is based on a sensing mechanism with a rapid response to voltage changes. hVOS imaging is thus well suited for optical studies of action potentials. This technique detects action potentials in intact brain slices with an excellent signal-to-noise ratio. These optical action potentials recapitulate voltage recordings with high temporal fidelity. In different genetically-defined types of neurons targeted by cre-lox technology, hVOS recordings of action potentials recapitulate the expected differences in duration. Furthermore, by targeting an hVOS probe to axons, imaging experiments can follow action potential propagation and document dynamic changes in waveform resulting from use-dependent plasticity.
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Affiliation(s)
- Yihe Ma
- Department of Neuroscience, University of Wisconsin - Madison
| | | | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin - Madison
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20
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Abstract
As a "holy grail" of neuroscience, optical imaging of membrane potential could enable high resolution measurements of spiking and synaptic activity in neuronal populations. This has been partly achieved using organic voltage-sensitive dyes in vitro, or in invertebrate preparations yet unspecific staining has prevented single-cell resolution measurements from mammalian preparations in vivo. The development of genetically encoded voltage indicators (GEVIs) and chemogenetic sensors has enabled targeting voltage indicators to plasma membranes and selective neuronal populations. Here, we review recent advances in the design and use of genetic voltage indicators and discuss advantages and disadvantages of three classes of them. Although genetic voltage indicators could revolutionize neuroscience, there are still significant challenges, particularly two-photon performance. To overcome them may require cross-disciplinary collaborations, team effort, and sustained support by large-scale research initiatives.
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Affiliation(s)
- Yuki Bando
- Neurotechnology Center, Department Biological Sciences, Columbia University, 550 W 120th Street, New York, NY, 10027, USA
- Present address: Department Organ and Tissue Anatomy, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, 431-3192, Japan
| | - Christiane Grimm
- Neurotechnology Center, Department Biological Sciences, Columbia University, 550 W 120th Street, New York, NY, 10027, USA
| | - Victor H Cornejo
- Neurotechnology Center, Department Biological Sciences, Columbia University, 550 W 120th Street, New York, NY, 10027, USA
| | - Rafael Yuste
- Neurotechnology Center, Department Biological Sciences, Columbia University, 550 W 120th Street, New York, NY, 10027, USA.
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21
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Grenier V, Daws BR, Liu P, Miller EW. Spying on Neuronal Membrane Potential with Genetically Targetable Voltage Indicators. J Am Chem Soc 2019; 141:1349-1358. [PMID: 30628785 DOI: 10.1021/jacs.8b11997] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Methods for optical measurement of voltage dynamics in living cells are attractive because they provide spatial resolution surpassing traditional electrode-based measurements and temporal resolution exceeding that of widely used Ca2+ imaging. Chemically synthesized voltage-sensitive dyes that use photoinduced electron transfer as a voltage-sensing trigger offer high voltage sensitivity and fast-response kinetics, but targeting chemical indicators to specific cells remains an outstanding challenge. Here, we present a new family of readily functionalizable, fluorescein-based voltage-sensitive fluorescent dyes (sarcosine-VoltageFluors) that can be covalently attached to a genetically encoded cell surface receptor to achieve voltage imaging from genetically defined neurons. We synthesized four new VoltageFluor derivatives that possess carboxylic acid functionality for simple conjugation to flexible tethers. The best of this new group of dyes was conjugated via a polyethylene glycol (PEG) linker to a small peptide (SpyTag, 13 amino acids) that directs binding and formation of a covalent bond with its binding partner, SpyCatcher (15 kDa). The new VoltageSpy dyes effectively label cells expressing cell-surface SpyCatcher, display good voltage sensitivity, and maintain fast-response kinetics. In cultured neurons, VoltageSpy dyes enable robust, single-trial optical detection of action potentials at neuronal soma with sensitivity exceeding genetically encoded voltage indicators. Importantly, genetic targeting of chemically synthesized dyes enables VoltageSpy to report on action potentials in axons and dendrites in single trials, tens to hundreds of micrometers away from the cell body. Genetic targeting of synthetic voltage indicators with VoltageSpy enables voltage imaging with low nanomolar dye concentration and offers a promising method for allying the speed and sensitivity of synthetic indicators with the enhanced cellular resolution of genetically encoded probes.
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Abstract
Fluorescent probes that indicate biologically important quantities are widely used for many different types of biological experiments across life sciences. During recent years, limitations of small molecule-based indicators have been overcome by the development of genetically encoded indicators. Here we focus on fluorescent calcium and voltage indicators and point to their applications mainly in neurosciences.
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Abstract
Voltage sensitive dyes (VSDs) are used for in vitro drug screening and for imaging of patterns of electrical activity in tissue. Wide application of this technology depends on the availability of sensors with high sensitivity (percent change of fluorescence per 100 mV), high fluorescence quantum yield, and fast response kinetics. A promising approach uses a two-component system consisting of anionic membrane permeable quenchers with fluorophores labeling one side of the membrane; this produces voltage-dependent fluorescence quenching. However, the quencher must be kept at low concentrations to minimize pharmacological effects, thus limiting sensitivity. By developing tethered bichromophoric fluorophore quencher (TBFQ) dyes, where the fluorophore and quencher are covalently connected by a long hydrophobic chain, the sensitivity is maximized and is independent of VSD concentration. A series of 13 TBFQ dyes based on the aminonaphthylethenylpyridinium (ANEP) fluorophore and the dipicrylamine anion (DPA) quencher have been synthesized and tested in an artificial lipid bilayer apparatus. The best of these, TBFQ1, shows a 2.5-fold change in fluorescence per 100 mV change in membrane potential, and the response kinetics is in the 10-20 ms range. This sensitivity is an order of magnitude better than that of commonly used VSDs. However, the fluorescence quantum yield is only 1.6%, which may make this first generation of TBFQ VSDs impractical for in vivo electrical imaging. Nevertheless, the design principles established here can serve as foundation for improved TBFQ VSDs. We believe this approach promises to greatly enhance our ability to monitor electrical activity in cells and tissues.
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Affiliation(s)
- Ping Yan
- Richard D. Berlin Center for Cell Analysis and Modeling, University of Connecticut Health Center, Farmington, Connecticut 06030, United States
| | - Corey D. Acker
- Richard D. Berlin Center for Cell Analysis and Modeling, University of Connecticut Health Center, Farmington, Connecticut 06030, United States
| | - Leslie M. Loew
- Richard D. Berlin Center for Cell Analysis and Modeling, University of Connecticut Health Center, Farmington, Connecticut 06030, United States
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Relative positioning of Kv11.1 (hERG) K + channel cytoplasmic domain-located fluorescent tags toward the plasma membrane. Sci Rep 2018; 8:15494. [PMID: 30341381 PMCID: PMC6195548 DOI: 10.1038/s41598-018-33492-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 10/01/2018] [Indexed: 12/17/2022] Open
Abstract
Recent cryo-EM data have provided a view of the KCNH potassium channels molecular structures. However, some details about the cytoplasmic domains organization and specially their rearrangements associated to channel functionality are still lacking. Here we used the voltage-dependent dipicrylamine (DPA)-induced quench of fluorescent proteins (FPS) linked to different positions at the cytoplasmic domains of KCNH2 (hERG) to gain some insights about the coarse structure of these channel parts. Fast voltage-clamp fluorometry with HEK293 cells expressing membrane-anchored FPs under conditions in which only the plasma membrane potential is modified, demonstrated DPA voltage-dependent translocation and subsequent FRET-triggered FP quenching. Our data demonstrate for the first time that the distance between an amino-terminal FP tag and the intracellular plasma membrane surface is shorter than that between the membrane and a C-terminally-located tag. The distances varied when the FPs were attached to other positions along the channel cytoplasmic domains. In some cases, we also detected slower fluorometric responses following the fast voltage-dependent dye translocation, indicating subsequent label movements orthogonal to the plasma membrane. This finding suggests the existence of additional conformational rearrangements in the hERG cytoplasmic domains, although their association with specific aspects of channel operation remains to be established.
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25
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Wang A, Feng J, Li Y, Zou P. Beyond Fluorescent Proteins: Hybrid and Bioluminescent Indicators for Imaging Neural Activities. ACS Chem Neurosci 2018; 9:639-650. [PMID: 29482322 DOI: 10.1021/acschemneuro.7b00455] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Optical biosensors have been invaluable tools in neuroscience research, as they provide the ability to directly visualize neural activity in real time, with high specificity, and with exceptional spatial and temporal resolution. Notably, a majority of these sensors are based on fluorescent protein scaffolds, which offer the ability to target specific cell types or even subcellular compartments. However, fluorescent proteins are intrinsically bulky tags, often insensitive to the environment, and always require excitation light illumination. To address these limitations, there has been a proliferation of alternative sensor scaffolds developed in recent years, including hybrid sensors that combine the advantages of synthetic fluorophores and genetically encoded protein tags, as well as bioluminescent probes. While still in their early stage of development as compared with fluorescent protein-based sensors, these novel probes have offered complementary solutions to interrogate various aspects of neuronal communication, including transmitter release, changes in membrane potential, and the production of second messengers. In this Review, we discuss these important new developments with a particular focus on design strategies.
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Affiliation(s)
- Anqi Wang
- College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Peking University, Beijing 100871, China
- Peking-Tsinghua Center for Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
| | - Jiesi Feng
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing 100871, China
- Peking-Tsinghua Center for Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
| | - Yulong Li
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing 100871, China
- Peking-Tsinghua Center for Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
| | - Peng Zou
- College of Chemistry and Molecular Engineering, Synthetic and Functional Biomolecules Center, Beijing National Laboratory for Molecular Sciences, Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Peking University, Beijing 100871, China
- Peking-Tsinghua Center for Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University, Beijing 100871, China
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Liu P, Grenier V, Hong W, Muller VR, Miller EW. Fluorogenic Targeting of Voltage-Sensitive Dyes to Neurons. J Am Chem Soc 2017; 139:17334-17340. [PMID: 29154543 DOI: 10.1021/jacs.7b07047] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
We present a method to target voltage-sensitive fluorescent dyes to specified cells using an enzyme-catalyzed fluorogenic reaction on cell surfaces. The dye/enzyme hybrids are composed of a photoinduced electron transfer (PeT)-based fluorescent voltage indicator and a complementary enzyme expressed on the cell surface. Action of the exogenous enzyme on the dye results in fluorogenic activation of the dye, enabling fast voltage imaging in defined neurons with sensitivity surpassing those of purely genetically encoded approaches. We employ a bulky methylcyclopropylacetoxymethyl ether to diminish the fluorescence of a PeT-based voltage-sensitive dye, or VoltageFluor. The hydrolytically stable ether can be removed by the action of porcine liver esterase (PLE) to reveal the bright unmodified VoltageFluor. We established that the chemically modified VoltageFluor is a substrate for PLE in vitro and in live cells. When PLE is targeted to the external face of cell membranes, it controls the apparent staining of cells. The use of neuron-specific promoters can direct staining to mammalian neurons to provide clear detection of neuronal action potentials in single trials. All of the new VoltageFluors targeted by esterase expression (VF-EXs) report single spikes in cultured mammalian neurons. The best, VF-EX2, does so with a signal-to-noise ratio nearly double that of comparable genetically encoded voltage reporters. By targeting PLE to neurons, VF-EX2 can interrogate the neuromodulatory effects of serotonin in cultured hippocampal neurons. Taken together, our results show that a combination of synthetic chemistry and biochemistry enables bright and fast voltage imaging from genetically defined neurons in culture.
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Affiliation(s)
- Pei Liu
- Department of Chemistry, ‡Department of Molecular and Cell Biology, and §Helen Wills Neuroscience Institute, University of California , Berkeley, California 94720, United States
| | - Vincent Grenier
- Department of Chemistry, ‡Department of Molecular and Cell Biology, and §Helen Wills Neuroscience Institute, University of California , Berkeley, California 94720, United States
| | - Wootack Hong
- Department of Chemistry, ‡Department of Molecular and Cell Biology, and §Helen Wills Neuroscience Institute, University of California , Berkeley, California 94720, United States
| | - Vikram R Muller
- Department of Chemistry, ‡Department of Molecular and Cell Biology, and §Helen Wills Neuroscience Institute, University of California , Berkeley, California 94720, United States
| | - Evan W Miller
- Department of Chemistry, ‡Department of Molecular and Cell Biology, and §Helen Wills Neuroscience Institute, University of California , Berkeley, California 94720, United States
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27
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Voltage and Calcium Imaging of Brain Activity. Biophys J 2017; 113:2160-2167. [PMID: 29102396 DOI: 10.1016/j.bpj.2017.09.040] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 09/14/2017] [Accepted: 09/21/2017] [Indexed: 01/02/2023] Open
Abstract
Sensors for imaging brain activity have been under development for almost 50 years. The development of some of these tools is relatively mature, whereas qualitative improvements of others are needed and are actively pursued. In particular, genetically encoded voltage indicators are just now starting to be used to answer neurobiological questions and, at the same time, more than 10 laboratories are working to improve them. In this Biophysical Perspective, we attempt to discuss the present state of the art and indicate areas of active development.
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Radivojevic M, Franke F, Altermatt M, Müller J, Hierlemann A, Bakkum DJ. Tracking individual action potentials throughout mammalian axonal arbors. eLife 2017; 6. [PMID: 28990925 PMCID: PMC5633342 DOI: 10.7554/elife.30198] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 09/28/2017] [Indexed: 12/18/2022] Open
Abstract
Axons are neuronal processes specialized for conduction of action potentials (APs). The timing and temporal precision of APs when they reach each of the synapses are fundamentally important for information processing in the brain. Due to small diameters of axons, direct recording of single AP transmission is challenging. Consequently, most knowledge about axonal conductance derives from modeling studies or indirect measurements. We demonstrate a method to noninvasively and directly record individual APs propagating along millimeter-length axonal arbors in cortical cultures with hundreds of microelectrodes at microsecond temporal resolution. We find that cortical axons conduct single APs with high temporal precision (~100 µs arrival time jitter per mm length) and reliability: in more than 8,000,000 recorded APs, we did not observe any conduction or branch-point failures. Upon high-frequency stimulation at 100 Hz, successive became slower, and their arrival time precision decreased by 20% and 12% for the 100th AP, respectively.
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Affiliation(s)
- Milos Radivojevic
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - Felix Franke
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - Michael Altermatt
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - Jan Müller
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - Andreas Hierlemann
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
| | - Douglas J Bakkum
- Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland
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29
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Imaging Voltage in Genetically Defined Neuronal Subpopulations with a Cre Recombinase-Targeted Hybrid Voltage Sensor. J Neurosci 2017; 37:9305-9319. [PMID: 28842412 DOI: 10.1523/jneurosci.1363-17.2017] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Revised: 08/09/2017] [Accepted: 08/16/2017] [Indexed: 12/16/2022] Open
Abstract
Genetically encoded voltage indicators create an opportunity to monitor electrical activity in defined sets of neurons as they participate in the complex patterns of coordinated electrical activity that underlie nervous system function. Taking full advantage of genetically encoded voltage indicators requires a generalized strategy for targeting the probe to genetically defined populations of cells. To this end, we have generated a mouse line with an optimized hybrid voltage sensor (hVOS) probe within a locus designed for efficient Cre recombinase-dependent expression. Crossing this mouse with Cre drivers generated double transgenics expressing hVOS probe in GABAergic, parvalbumin, and calretinin interneurons, as well as hilar mossy cells, new adult-born neurons, and recently active neurons. In each case, imaging in brain slices from male or female animals revealed electrically evoked optical signals from multiple individual neurons in single trials. These imaging experiments revealed action potentials, dynamic aspects of dendritic integration, and trial-to-trial fluctuations in response latency. The rapid time response of hVOS imaging revealed action potentials with high temporal fidelity, and enabled accurate measurements of spike half-widths characteristic of each cell type. Simultaneous recording of rapid voltage changes in multiple neurons with a common genetic signature offers a powerful approach to the study of neural circuit function and the investigation of how neural networks encode, process, and store information.SIGNIFICANCE STATEMENT Genetically encoded voltage indicators hold great promise in the study of neural circuitry, but realizing their full potential depends on targeting the sensor to distinct cell types. Here we present a new mouse line that expresses a hybrid optical voltage sensor under the control of Cre recombinase. Crossing this line with Cre drivers generated double-transgenic mice, which express this sensor in targeted cell types. In brain slices from these animals, single-trial hybrid optical voltage sensor recordings revealed voltage changes with submillisecond resolution in multiple neurons simultaneously. This imaging tool will allow for the study of the emergent properties of neural circuits and permit experimental tests of the roles of specific types of neurons in complex circuit activity.
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Toward Better Genetically Encoded Sensors of Membrane Potential. Trends Neurosci 2017; 39:277-289. [PMID: 27130905 DOI: 10.1016/j.tins.2016.02.005] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Revised: 01/25/2016] [Accepted: 02/22/2016] [Indexed: 11/24/2022]
Abstract
Genetically encoded optical sensors of cell activity are powerful tools that can be targeted to specific cell types. This is especially important in neuroscience because individual brain regions can include a multitude of different cell types. Optical imaging allows for simultaneous recording from numerous neurons or brain regions. Optical signals of membrane potential are useful because membrane potential changes are a direct sign of both synaptic and action potentials. Here we describe recent improvements in the in vitro and in vivo signal size and kinetics of genetically encoded voltage indicators (GEVIs) and discuss their relationship to alternative sensors of neural activity.
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Action Potential Dynamics in Fine Axons Probed with an Axonally Targeted Optical Voltage Sensor. eNeuro 2017; 4:eN-NWR-0146-17. [PMID: 28785728 PMCID: PMC5526655 DOI: 10.1523/eneuro.0146-17.2017] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 06/13/2017] [Accepted: 07/11/2017] [Indexed: 11/27/2022] Open
Abstract
The complex and malleable conduction properties of axons determine how action potentials propagate through extensive axonal arbors to reach synaptic terminals. The excitability of axonal membranes plays a major role in neural circuit function, but because most axons are too thin for conventional electrical recording, their properties remain largely unexplored. To overcome this obstacle, we used a genetically encoded hybrid voltage sensor (hVOS) harboring an axonal targeting motif. Expressing this probe in transgenic mice enabled us to monitor voltage changes optically in two populations of axons in hippocampal slices, the large axons of dentate granule cells (mossy fibers) in the stratum lucidum of the CA3 region and the much finer axons of hilar mossy cells in the inner molecular layer of the dentate gyrus. Action potentials propagated with distinct velocities in each type of axon. Repetitive firing broadened action potentials in both populations, but at an intermediate frequency the degree of broadening differed. Repetitive firing also attenuated action potential amplitudes in both mossy cell and granule cell axons. These results indicate that the features of use-dependent action potential broadening, and possible failure, observed previously in large nerve terminals also appear in much finer unmyelinated axons. Subtle differences in the frequency dependences could influence the propagation of activity through different pathways to excite different populations of neurons. The axonally targeted hVOS probe used here opens up the diverse repertoire of neuronal processes to detailed biophysical study.
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Pelosse M, Cottet-Rousselle C, Grichine A, Berger I, Schlattner U. Genetically Encoded Fluorescent Biosensors to Explore AMPK Signaling and Energy Metabolism. ACTA ACUST UNITED AC 2017; 107:491-523. [PMID: 27812993 DOI: 10.1007/978-3-319-43589-3_20] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Maintenance of energy homeostasis is a basic requirement for cell survival. Different mechanisms have evolved to cope with spatial and temporal mismatch between energy-providing and -consuming processes. Among these, signaling by AMP-activated protein kinase (AMPK) is one of the key players, regulated by and itself regulating cellular adenylate levels. Further understanding its complex cellular function requires deeper insight into its activation patterns in space and time at a single cell level. This may become possible with an increasing number of genetically encoded fluorescent biosensors, mostly based on fluorescence resonance energy transfer, which have been engineered to monitor metabolic parameters and kinase activities. Here, we review basic principles of biosensor design and function and the advantages and limitations of their use and provide an overview on existing FRET biosensors to monitor AMPK activation, ATP concentration, and ATP/ADP ratios, together with other key metabolites and parameters of energy metabolism.
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Affiliation(s)
- Martin Pelosse
- Laboratory of Fundamental and Applied Bioenergetics (LBFA) and SFR Environmental and Systems Biology (BEeSy), University Grenoble Alpes, Grenoble, France.,Inserm, U1055 and U1209, Grenoble, France
| | - Cécile Cottet-Rousselle
- Laboratory of Fundamental and Applied Bioenergetics (LBFA) and SFR Environmental and Systems Biology (BEeSy), University Grenoble Alpes, Grenoble, France.,Inserm, U1055 and U1209, Grenoble, France
| | - Alexei Grichine
- Inserm, U1055 and U1209, Grenoble, France.,Institute for Advanced Biosciences, University Grenoble Alpes, Grenoble, France
| | | | - Uwe Schlattner
- Laboratory of Fundamental and Applied Bioenergetics (LBFA) and SFR Environmental and Systems Biology (BEeSy), University Grenoble Alpes, Grenoble, France. .,Inserm, U1055 and U1209, Grenoble, France.
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Nakajima R, Jung A, Yoon BJ, Baker BJ. Optogenetic Monitoring of Synaptic Activity with Genetically Encoded Voltage Indicators. Front Synaptic Neurosci 2016; 8:22. [PMID: 27547183 PMCID: PMC4974255 DOI: 10.3389/fnsyn.2016.00022] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 07/25/2016] [Indexed: 11/13/2022] Open
Abstract
The age of genetically encoded voltage indicators (GEVIs) has matured to the point that changes in membrane potential can now be observed optically in vivo. Improving the signal size and speed of these voltage sensors has been the primary driving forces during this maturation process. As a result, there is a wide range of probes using different voltage detecting mechanisms and fluorescent reporters. As the use of these probes transitions from optically reporting membrane potential in single, cultured cells to imaging populations of cells in slice and/or in vivo, a new challenge emerges—optically resolving the different types of neuronal activity. While improvements in speed and signal size are still needed, optimizing the voltage range and the subcellular expression (i.e., soma only) of the probe are becoming more important. In this review, we will examine the ability of recently developed probes to report synaptic activity in slice and in vivo. The voltage-sensing fluorescent protein (VSFP) family of voltage sensors, ArcLight, ASAP-1, and the rhodopsin family of probes are all good at reporting changes in membrane potential, but all have difficulty distinguishing subthreshold depolarizations from action potentials and detecting neuronal inhibition when imaging populations of cells. Finally, we will offer a few possible ways to improve the optical resolution of the various types of neuronal activities.
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Affiliation(s)
- Ryuichi Nakajima
- Center for Functional Connectomics, Korea Institute of Science and Technology Seongbuk-gu, Seoul, South Korea
| | - Arong Jung
- Center for Functional Connectomics, Korea Institute of Science and TechnologySeongbuk-gu, Seoul, South Korea; College of Life Sciences and Biotechnology, Korea UniversitySeongbuk-gu, Seoul, South Korea
| | - Bong-June Yoon
- College of Life Sciences and Biotechnology, Korea University Seongbuk-gu, Seoul, South Korea
| | - Bradley J Baker
- Center for Functional Connectomics, Korea Institute of Science and TechnologySeongbuk-gu, Seoul, South Korea; Department of Neuroscience, Korea University of Science and TechnologyDaejeon, South Korea
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Pacheco J, Dominguez L, Bohórquez-Hernández A, Asanov A, Vaca L. A cholesterol-binding domain in STIM1 modulates STIM1-Orai1 physical and functional interactions. Sci Rep 2016; 6:29634. [PMID: 27459950 PMCID: PMC4962086 DOI: 10.1038/srep29634] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 06/20/2016] [Indexed: 11/09/2022] Open
Abstract
STIM1 and Orai1 are the main components of a widely conserved Calcium influx pathway known as store-operated calcium entry (SOCE). STIM1 is a calcium sensor, which oligomerizes and activates Orai channels when calcium levels drop inside the endoplasmic reticulum (ER). The series of molecular rearrangements that STIM1 undergoes until final activation of Orai1 require the direct exposure of the STIM1 domain known as SOAR (Stim Orai Activating Region). In addition to these complex molecular rearrangements, other constituents like lipids at the plasma membrane, play critical roles orchestrating SOCE. PI(4,5)P2 and enriched cholesterol microdomains have been shown as important signaling platforms that recruit the SOCE machinery in steps previous to Orai1 activation. However, little is known about the molecular role of cholesterol once SOCE is activated. In this study we provide clear evidence that STIM1 has a cholesterol-binding domain located inside the SOAR region and modulates Orai1 channels. We demonstrate a functional association of STIM1 and SOAR to cholesterol, indicating a close proximity of SOAR to the inner layer of the plasma membrane. In contrast, the depletion of cholesterol induces the SOAR detachment from the plasma membrane and enhances its association to Orai1. These results are recapitulated with full length STIM1.
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Affiliation(s)
- Jonathan Pacheco
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, México, DF 04510, México
| | - Laura Dominguez
- Departamento de Fisicoquímica, Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, México DF 04510, México
| | - A Bohórquez-Hernández
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, México, DF 04510, México
| | | | - Luis Vaca
- Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, México, DF 04510, México
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Structural rearrangement of the intracellular domains during AMPA receptor activation. Proc Natl Acad Sci U S A 2016; 113:E3950-9. [PMID: 27313205 DOI: 10.1073/pnas.1601747113] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are ligand-gated ion channels that mediate the majority of fast excitatory neurotransmission in the central nervous system. Despite recent advances in structural studies of AMPARs, information about the specific conformational changes that underlie receptor function is lacking. Here, we used single and dual insertion of GFP variants at various positions in AMPAR subunits to enable measurements of conformational changes using fluorescence resonance energy transfer (FRET) in live cells. We produced dual CFP/YFP-tagged GluA2 subunit constructs that had normal activity and displayed intrareceptor FRET. We used fluorescence lifetime imaging microscopy (FLIM) in live HEK293 cells to determine distinct steady-state FRET efficiencies in the presence of different ligands, suggesting a dynamic picture of the resting state. Patch-clamp fluorometry of the double- and single-insert constructs showed that both the intracellular C-terminal domain (CTD) and the loop region between the M1 and M2 helices move during activation and the CTD is detached from the membrane. Our time-resolved measurements revealed unexpectedly complex fluorescence changes within these intracellular domains, providing clues as to how posttranslational modifications and receptor function interact.
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Miller EW. Small molecule fluorescent voltage indicators for studying membrane potential. Curr Opin Chem Biol 2016; 33:74-80. [PMID: 27318561 DOI: 10.1016/j.cbpa.2016.06.003] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 05/31/2016] [Accepted: 06/01/2016] [Indexed: 11/18/2022]
Abstract
Voltage imaging has the potential to unravel the contributions that rapid changes in membrane voltage make to cellular physiology, especially in the context of neuroscience. In particular, small molecule fluorophores are especially attractive because they can, in theory, provide fast and sensitive measurements of membrane potential dynamics. A number of classes of small molecule voltage indicators will be discussed, including dyes with improved two-photon voltage sensing, near infrared optical profiles for use in in vivo applications, and newly developed electron-transfer based indicators, or VoltageFluors, that can be tuned across a range of wavelengths to enable all-optical voltage manipulation and measurement. Limitations and a 'wish-list' for voltage indicators will also be discussed.
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Affiliation(s)
- Evan W Miller
- Departments of Chemistry, Molecular & Cell Biology, and Helen Wills Neuroscience Institute, 227 Hildebrand Berkeley, CA 94720-1460, United States.
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Sasseville LJ, Morin M, Coady MJ, Blunck R, Lapointe JY. The Human Sodium-Glucose Cotransporter (hSGLT1) Is a Disulfide-Bridged Homodimer with a Re-Entrant C-Terminal Loop. PLoS One 2016; 11:e0154589. [PMID: 27137918 PMCID: PMC4854415 DOI: 10.1371/journal.pone.0154589] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 04/17/2016] [Indexed: 11/18/2022] Open
Abstract
Na-coupled cotransporters are proteins that use the trans-membrane electrochemical gradient of Na to activate the transport of a second solute. The sodium-glucose cotransporter 1 (SGLT1) constitutes a well-studied prototype of this transport mechanism but essential molecular characteristics, namely its quaternary structure and the exact arrangement of the C-terminal transmembrane segments, are still debated. After expression in Xenopus oocytes, human SGLT1 molecules (hSGLT1) were labelled on an externally accessible cysteine residue with a thiol-reactive fluorophore (tetramethylrhodamine-C5-maleimide, TMR). Addition of dipicrylamine (DPA, a negatively-charged amphiphatic fluorescence “quencher”) to the fluorescently-labelled oocytes is used to quench the fluorescence originating from hSGLT1 in a voltage-dependent manner. Using this arrangement with a cysteine residue introduced at position 624 in the loop between transmembrane segments 12 and 13, the voltage-dependent fluorescence signal clearly indicated that this portion of the 12–13 loop is located on the external side of the membrane. As the 12–13 loop begins on the intracellular side of the membrane, this suggests that the 12–13 loop is re-entrant. Using fluorescence resonance energy transfer (FRET), we observed that different hSGLT1 molecules are within molecular distances from each other suggesting a multimeric complex arrangement. In agreement with this conclusion, a western blot analysis showed that hSGLT1 migrates as either a monomer or a dimer in reducing and non-reducing conditions, respectively. A systematic mutational study of endogenous cysteine residues in hSGLT1 showed that a disulfide bridge is formed between the C355 residues of two neighbouring hSGLT1 molecules. It is concluded that, 1) hSGLT1 is expressed as a disulfide bridged homodimer via C355 and that 2) a portion of the intracellular 12–13 loop is re-entrant and readily accessible from the extracellular milieu.
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Affiliation(s)
- Louis J. Sasseville
- Groupe d'étude des protéines membranaires (GÉPROM) and Département de physique, Université de Montréal, Montréal, Québec
| | - Michael Morin
- Groupe d'étude des protéines membranaires (GÉPROM) and Département de physique, Université de Montréal, Montréal, Québec
| | - Michael J. Coady
- Groupe d'étude des protéines membranaires (GÉPROM) and Département de physique, Université de Montréal, Montréal, Québec
| | - Rikard Blunck
- Groupe d'étude des protéines membranaires (GÉPROM) and Département de physique, Université de Montréal, Montréal, Québec
| | - Jean-Yves Lapointe
- Groupe d'étude des protéines membranaires (GÉPROM) and Département de physique, Université de Montréal, Montréal, Québec
- * E-mail:
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Storace D, Rad MS, Han Z, Jin L, Cohen LB, Hughes T, Baker BJ, Sung U. Genetically Encoded Protein Sensors of Membrane Potential. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 859:493-509. [PMID: 26238066 DOI: 10.1007/978-3-319-17641-3_20] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Organic voltage-sensitive dyes offer very high spatial and temporal resolution for imaging neuronal function. However these dyes suffer from the drawbacks of non-specificity of cell staining and low accessibility of the dye to some cell types. Further progress in imaging activity is expected from the development of genetically encoded fluorescent sensors of membrane potential. Cell type specificity of expression of these fluorescent protein (FP) voltage sensors can be obtained via several different mechanisms. One is cell type specificity of infection by individual virus subtypes. A second mechanism is specificity of promoter expression in individual cell types. A third, depends on the offspring of transgenic animals with cell type specific expression of cre recombinase mated with an animal that has the DNA for the FP voltage sensor in all of its cells but its expression is dependent on the recombinase activity. Challenges remain. First, the response time constants of many of the new FP voltage sensors are slower (2-10 ms) than those of organic dyes. This results in a relatively small fractional fluorescence change, ΔF/F, for action potentials. Second, the largest signal presently available is only ~40% for a 100 mV depolarization and many of the new probes have signals that are substantially smaller. Large signals are especially important when attempting to detect fast events because the shorter measurement interval results in a relatively small number of detected photons and therefore a relatively large shot noise (see Chap. 1). Another kind of challenge has occurred when attempts were made to transition from one species to another or from one cell type to another or from cell culture to in vivo measurements.Several laboratories have recently described a number of novel FP voltage sensors. Here we attempt to critically review the current status of these developments in terms of signal size, time course, and in vivo function.
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Affiliation(s)
- Douglas Storace
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT, 06520, USA
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Lillis KP, Dulla C, Maheshwari A, Coulter D, Mody I, Heinemann U, Armbruster M, Žiburkus J. WONOEP appraisal: molecular and cellular imaging in epilepsy. Epilepsia 2015; 56:505-13. [PMID: 25779014 PMCID: PMC4397142 DOI: 10.1111/epi.12939] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/12/2015] [Indexed: 01/01/2023]
Abstract
Great advancements have been made in understanding the basic mechanisms of ictogenesis using single-cell electrophysiology (e.g., patch clamp, sharp electrode), large-scale electrophysiology (e.g., electroencephalography [EEG], field potential recording), and large-scale imaging (magnetic resonance imaging [MRI], positron emission tomography [PET], calcium imaging of acetoxymethyl ester [AM] dye-loaded tissue). Until recently, it has been challenging to study experimentally how population rhythms emerge from cellular activity. Newly developed optical imaging technologies hold promise for bridging this gap by making it possible to simultaneously record the many cellular elements that comprise a neural circuit. Furthermore, easily accessible genetic technologies for targeting expression of fluorescent protein-based indicators make it possible to study, in animal models of epilepsy, epileptogenic changes to neural circuits over long periods. In this review, we summarize some of the latest imaging tools (fluorescent probes, gene delivery methods, and microscopy techniques) that can lead to the advancement of cell- and circuit-level understanding of epilepsy, which in turn may inform and improve development of next generation antiepileptic and antiepileptogenic drugs.
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Affiliation(s)
- Kyle P Lillis
- Department of Neurology, Massachusetts General Hospital, Boston, Massachusetts, U.S.A; Harvard Medical School, Boston, Massachusetts, U.S.A
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Voltage Imaging in the Study of Hippocampal Circuit Function and Plasticity. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 859:197-211. [DOI: 10.1007/978-3-319-17641-3_8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
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Imaging Submillisecond Membrane Potential Changes from Individual Regions of Single Axons, Dendrites and Spines. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 859:57-101. [PMID: 26238049 PMCID: PMC5671121 DOI: 10.1007/978-3-319-17641-3_3] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
A central question in neuronal network analysis is how the interaction between individual neurons produces behavior and behavioral modifications. This task depends critically on how exactly signals are integrated by individual nerve cells functioning as complex operational units. Regional electrical properties of branching neuronal processes which determine the input-output function of any neuron are extraordinarily complex, dynamic, and, in the general case, impossible to predict in the absence of detailed measurements. To obtain such a measurement one would, ideally, like to be able to monitor, at multiple sites, subthreshold events as they travel from the sites of origin (synaptic contacts on distal dendrites) and summate at particular locations to influence action potential initiation. It became possible recently to carry out this type of measurement using high-resolution multisite recording of membrane potential changes with intracellular voltage-sensitive dyes. This chapter reviews the development and foundation of the method of voltage-sensitive dye recording from individual neurons. Presently, this approach allows monitoring membrane potential transients from all parts of the dendritic tree as well as from axon collaterals and individual dendritic spines.
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Ghitani N, Bayguinov PO, Ma Y, Jackson MB. Single-trial imaging of spikes and synaptic potentials in single neurons in brain slices with genetically encoded hybrid voltage sensor. J Neurophysiol 2014; 113:1249-59. [PMID: 25411462 DOI: 10.1152/jn.00691.2014] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Genetically encoded voltage sensors expand the optogenetics toolkit into the important realm of electrical recording, enabling researchers to study the dynamic activity of complex neural circuits in real time. However, these probes have thus far performed poorly when tested in intact neural circuits. Hybrid voltage sensors (hVOS) enable the imaging of voltage by harnessing the resonant energy transfer that occurs between a genetically encoded component, a membrane-tethered fluorescent protein that serves as a donor, and a small charged molecule, dipicrylamine, which serves as an acceptor. hVOS generates optical signals as a result of voltage-induced changes in donor-acceptor distance. We expressed the hVOS probe in mouse brain by in utero electroporation and in transgenic mice with a neuronal promoter. Under conditions favoring sparse labeling we could visualize single-labeled neurons. hVOS imaging reported electrically evoked fluorescence changes from individual neurons in slices from entorhinal cortex, somatosensory cortex, and hippocampus. These fluorescence signals tracked action potentials in individual neurons in a single trial with excellent temporal fidelity, producing changes that exceeded background noise by as much as 16-fold. Subthreshold synaptic potentials were detected in single trials in multiple distinct cells simultaneously. We followed signal propagation between different cells within one field of view and between dendrites and somata of the same cell. hVOS imaging thus provides a tool for high-resolution recording of electrical activity from genetically targeted cells in intact neuronal circuits.
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Affiliation(s)
- Nima Ghitani
- Neuroscience Training Program, University of Wisconsin, Madison, Wisconsin
| | - Peter O Bayguinov
- Department of Neuroscience, University of Wisconsin, Madison, Wisconsin
| | - Yihe Ma
- Physiology Graduate Training Program, University of Wisconsin, Madison, Wisconsin; and
| | - Meyer B Jackson
- Neuroscience Training Program, University of Wisconsin, Madison, Wisconsin; Physiology Graduate Training Program, University of Wisconsin, Madison, Wisconsin; and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin
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Hybrid voltage sensor imaging of eGFP-F expressing neurons in chicken midbrain slices. J Neurosci Methods 2014; 233:28-33. [PMID: 24906054 DOI: 10.1016/j.jneumeth.2014.05.034] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 05/21/2014] [Accepted: 05/28/2014] [Indexed: 12/15/2022]
Abstract
BACKGROUND Dendritic computation is essential for understanding information processing in single neurons and brain circuits. Optical methods are suited best to investigate function and biophysical properties of cellular compartments at high spatial and temporal resolution. Promising approaches include the use of voltage sensitive dyes, genetically encoded voltage sensors, or hybrid voltage sensors (hVoS) consisting of fluorescent proteins and voltage-dependent quenchers that, so far, are not available in avian neuroscience. NEW METHOD We have adapted a hVoS system for a chicken midbrain slice preparation by combining genetically expressed farnesylated eGFP with dipicrylamine (DPA). Depending on the cellular potential, DPA is shifted in the membrane, resulting in quenching of eGFP fluorescence linearly to the membrane potential by Förster resonance electron transfer. RESULTS In ovo electroporation resulted in labelled neurons throughout the midbrain with a high level of fine structural detail. After application of DPA, we were able to optically record electrically evoked action potentials with high signal-to-noise ratio and high spatio-temporal resolution. COMPARISON WITH EXISTING METHODS Standard methods available for avian neuroscience such as whole-cell patch clamp yield insufficient data for the analysis of dendritic computation in single neurons. The high spatial and temporal resolution of hVoS data overcomes this limitation. The results obtained by our method are comparable to hVoS data published for mammals. CONCLUSIONS With the protocol presented here, it is possible to optically record information processing in single avian neurons at such high spatial and temporal resolution, that cellular and subcellular events can be analysed.
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Manno C, Figueroa L, Fitts R, Ríos E. Confocal imaging of transmembrane voltage by SEER of di-8-ANEPPS. ACTA ACUST UNITED AC 2013; 141:371-87. [PMID: 23440278 PMCID: PMC3581694 DOI: 10.1085/jgp.201210936] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Imaging, optical mapping, and optical multisite recording of transmembrane potential (Vm) are essential for studying excitable cells and systems. The naphthylstyryl voltage-sensitive dyes, including di-8-ANEPPS, shift both their fluorescence excitation and emission spectra upon changes in Vm. Accordingly, they have been used for monitoring Vm in nonratioing and both emission and excitation ratioing modes. Their changes in fluorescence are usually much less than 10% per 100 mV. Conventional ratioing increases sensitivity to between 3 and 15% per 100 mV. Low sensitivity limits the value of these dyes, especially when imaged with low light systems like confocal scanners. Here we demonstrate the improvement afforded by shifted excitation and emission ratioing (SEER) as applied to imaging membrane potential in flexor digitorum brevis muscle fibers of adult mice. SEER—the ratioing of two images of fluorescence, obtained with different excitation wavelengths in different emission bands—was implemented in two commercial confocal systems. A conventional pinhole scanner, affording optimal setting of emission bands but less than ideal excitation wavelengths, achieved a sensitivity of up to 27% per 100 mV, nearly doubling the value found by conventional ratioing of the same data. A better pair of excitation lights should increase the sensitivity further, to 35% per 100 mV. The maximum acquisition rate with this system was 1 kHz. A fast “slit scanner” increased the effective rate to 8 kHz, but sensitivity was lower. In its high-sensitivity implementation, the technique demonstrated progressive deterioration of action potentials upon fatiguing tetani induced by stimulation patterns at >40 Hz, thereby identifying action potential decay as a contributor to fatigue onset. Using the fast implementation, we could image for the first time an action potential simultaneously at multiple locations along the t-tubule system. These images resolved the radially varying lag associated with propagation at a finite velocity.
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Affiliation(s)
- Carlo Manno
- Section of Cellular Signaling, Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612, USA
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De-la-Rosa V, Rangel-Yescas GE, Ladrón-de-Guevara E, Rosenbaum T, Islas LD. Coarse architecture of the transient receptor potential vanilloid 1 (TRPV1) ion channel determined by fluorescence resonance energy transfer. J Biol Chem 2013; 288:29506-17. [PMID: 23965996 DOI: 10.1074/jbc.m113.479618] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The transient receptor potential vanilloid 1 ion channel is responsible for the perception of high temperatures and low extracellular pH, and it is also involved in the response to some pungent compounds. Importantly, it is also associated with the perception of pain and noxious stimuli. Here, we attempt to discern the molecular organization and location of the N and C termini of the transient receptor potential vanilloid 1 ion channel by measuring FRET between genetically attached enhanced yellow and cyan fluorescent protein to the N or C terminus of the channel protein, expressed in transfected HEK 293 cells or Xenopus laevis oocytes. The static measurements of the domain organization were mapped into an available cryo-electron microscopy density of the channel with good agreement. These measurements also provide novel insights into the organization of terminal domains and their proximity to the plasma membrane.
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Wang D, McMahon S, Zhang Z, Jackson MB. Hybrid voltage sensor imaging of electrical activity from neurons in hippocampal slices from transgenic mice. J Neurophysiol 2012; 108:3147-60. [PMID: 22993267 DOI: 10.1152/jn.00722.2012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Gene targeting with genetically encoded optical voltage sensors brings the methods of voltage imaging to genetically defined neurons and offers a method of studying circuit activity in these selected populations. The present study reports the targeting of genetically encoded hybrid voltage sensors (hVOS) to neurons in transgenic mice. The hVOS family of probes employs a membrane-targeted fluorescent protein, which generates voltage-dependent fluorescence changes in the presence of dipicrylamine (DPA) as the result of a voltage-dependent optical interaction between the two molecules. We generated transgenic mice with two different high-performance hVOS probes under control of a neuron-specific thy-1 promoter. Hippocampal slices from these animals present distinct spatial patterns of expression, and electrical stimulation evoked fluorescence changes as high as 3%. Glutamate receptor and Na(+) channel antagonists blocked these responses. One hVOS probe tested here harbors an axonal targeting motif (from GAP-43) and shows preferential expression in axons; this probe can thus report axonal voltage changes. Voltage imaging in transgenic mice expressing hVOS probes opens the door to the study of functional activity in genetically defined populations of neurons in intact neural circuits.
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Affiliation(s)
- Dongsheng Wang
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
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Mutoh H, Akemann W, Knöpfel T. Genetically engineered fluorescent voltage reporters. ACS Chem Neurosci 2012; 3:585-92. [PMID: 22896802 DOI: 10.1021/cn300041b] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Accepted: 06/06/2012] [Indexed: 01/12/2023] Open
Abstract
Fluorescent membrane voltage indicators that enable optical imaging of neuronal circuit operations in the living mammalian brain are powerful tools for biology and particularly neuroscience. Classical voltage-sensitive dyes, typically low molecular-weight organic compounds, have been in widespread use for decades but are limited by issues related to optical noise, the lack of generally applicable procedures that enable staining of specific cell populations, and difficulties in performing imaging experiments over days and weeks. Genetically encoded voltage indicators (GEVIs) represent a newer alternative that overcomes several of the limitations inherent to classical voltage-sensitive dyes. We critically review the fundamental concepts of this approach, the variety of available probes and their state of development.
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Affiliation(s)
- Hiroki Mutoh
- Knöpfel
lab for Neuronal Circuit Dynamics, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako City,
Saitama, 351-0198 Japan
| | - Walther Akemann
- Knöpfel
lab for Neuronal Circuit Dynamics, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako City,
Saitama, 351-0198 Japan
| | - Thomas Knöpfel
- Knöpfel
lab for Neuronal Circuit Dynamics, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako City,
Saitama, 351-0198 Japan
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Fink AE, Bender KJ, Trussell LO, Otis TS, DiGregorio DA. Two-photon compatibility and single-voxel, single-trial detection of subthreshold neuronal activity by a two-component optical voltage sensor. PLoS One 2012; 7:e41434. [PMID: 22870221 PMCID: PMC3411718 DOI: 10.1371/journal.pone.0041434] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Accepted: 06/27/2012] [Indexed: 11/29/2022] Open
Abstract
Minimally invasive measurements of neuronal activity are essential for understanding how signal processing is performed by neuronal networks. While optical strategies for making such measurements hold great promise, optical sensors generally lack the speed and sensitivity necessary to record neuronal activity on a single-trial, single-neuron basis. Here we present additional biophysical characterization and practical improvements of a two-component optical voltage sensor (2cVoS), comprised of the neuronal tracer dye, DiO, and dipicrylamine (DiO/DPA). Using laser spot illumination we demonstrate that membrane potential-dependent fluorescence changes can be obtained in a wide variety of cell types within brain slices. We show a correlation between membrane labeling and the sensitivity of the magnitude of fluorescence signal, such that neurons with the brightest membrane labeling yield the largest ΔF/F values per action potential (AP; ∼40%). By substituting a blue-shifted donor for DiO we confirm that DiO/DPA works, at least in part, via a Förster resonance energy transfer (FRET) mechanism. We also describe a straightforward iontophoretic method for labeling multiple neurons with DiO and show that DiO/DPA is compatible with two-photon (2P) imaging. Finally, exploiting the high sensitivity of DiO/DPA, we demonstrate AP-induced fluorescence transients (fAPs) recorded from single spines of hippocampal pyramidal neurons and single-trial measurements of subthreshold synaptic inputs to granule cell dendrites. Our findings suggest that the 2cVoS, DiO/DPA, enables optical measurements of trial-to-trial voltage fluctuations with very high spatial and temporal resolution, properties well suited for monitoring electrical signals from multiple neurons within intact neuronal networks.
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Affiliation(s)
- Ann E Fink
- Unit of Dynamic Neuronal Imaging, Department of Neuroscience, Paris, France
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Perron A, Akemann W, Mutoh H, Knöpfel T. Genetically encoded probes for optical imaging of brain electrical activity. PROGRESS IN BRAIN RESEARCH 2012; 196:63-77. [PMID: 22341321 DOI: 10.1016/b978-0-444-59426-6.00004-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The combination of optical imaging methods with targeted expression of protein-based fluorescent probes constitutes a powerful approach for functional analysis of selected cell populations within intact neuronal circuitries. Herein, we lay out the conceptual motivation for optogenetic recording of brain electrical activity using genetically encoded voltage-sensitive fluorescent proteins (VSFPs), describe how the current generation of VSFPs has evolved, and demonstrate how VSFPs report membrane voltage signals in isolated cells, brain slices, and living animals. We conclude with a critical appraisal of VSFPs for voltage recording and highlight promising applications of this emerging methodology for bridging cellular and intact systems biology.
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Affiliation(s)
- Amélie Perron
- RIKEN Brain Science Institute, Hirosawa, Wako City, Saitama, Japan
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Devor A, Sakadžić S, Srinivasan VJ, Yaseen MA, Nizar K, Saisan PA, Tian P, Dale AM, Vinogradov SA, Franceschini MA, Boas DA. Frontiers in optical imaging of cerebral blood flow and metabolism. J Cereb Blood Flow Metab 2012; 32:1259-76. [PMID: 22252238 PMCID: PMC3390808 DOI: 10.1038/jcbfm.2011.195] [Citation(s) in RCA: 111] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In vivo optical imaging of cerebral blood flow (CBF) and metabolism did not exist 50 years ago. While point optical fluorescence and absorption measurements of cellular metabolism and hemoglobin concentrations had already been introduced by then, point blood flow measurements appeared only 40 years ago. The advent of digital cameras has significantly advanced two-dimensional optical imaging of neuronal, metabolic, vascular, and hemodynamic signals. More recently, advanced laser sources have enabled a variety of novel three-dimensional high-spatial-resolution imaging approaches. Combined, as we discuss here, these methods are permitting a multifaceted investigation of the local regulation of CBF and metabolism with unprecedented spatial and temporal resolution. Through multimodal combination of these optical techniques with genetic methods of encoding optical reporter and actuator proteins, the future is bright for solving the mysteries of neurometabolic and neurovascular coupling and translating them to clinical utility.
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Affiliation(s)
- Anna Devor
- Department of Neurosciences, UCSD, La Jolla, CA, USA.
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