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Canepari M, Ross WN. Spatial and temporal aspects of neuronal calcium and sodium signals measured with low-affinity fluorescent indicators. Pflugers Arch 2024; 476:39-48. [PMID: 37798555 DOI: 10.1007/s00424-023-02865-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 09/12/2023] [Accepted: 09/21/2023] [Indexed: 10/07/2023]
Abstract
Low-affinity fluorescent indicators for Ca2+ or Na+ allow measuring the dynamics of intracellular concentration of these ions with little perturbation from physiological conditions because they are weak buffers. When using synthetic indicators, which are small molecules with fast kinetics, it is also possible to extract spatial and temporal information on the sources of ion transients, their localization, and their disposition. This review examines these important aspects from the biophysical point of view, and how they have been recently exploited in neurophysiological studies. We first analyze the environment where Ca2+ and Na+ indicators are inserted, highlighting the interpretation of the two different signals. Then, we address the information that can be obtained by analyzing the rising phase and the falling phase of the Ca2+ and Na+ transients evoked by different stimuli, focusing on the kinetics of ionic currents and on the spatial interpretation of these measurements, especially on events in axons and dendritic spines. Finally, we suggest how Ca2+ or Na+ imaging using low-affinity synthetic fluorescent indicators can be exploited in future fundamental or applied research.
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Affiliation(s)
- Marco Canepari
- LIPhy, CNRS, Univ. Grenoble Alpes, F-38000, Grenoble, France.
- Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France.
- Institut National de la Santé et Recherche Médicale, Paris, France.
| | - William N Ross
- Department of Physiology, New York Medical College, Valhalla, NY, 10595, USA
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Liu K, Yin Y, Le Y, Ouyang W, Pan A, Huang J, Xie Z, Zhu Q, Tong J. Age-related Loss of miR-124 Causes Cognitive Deficits via Derepressing RyR3 Expression. Aging Dis 2022; 13:1455-1470. [PMID: 36186122 PMCID: PMC9466975 DOI: 10.14336/ad.2022.0204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 02/04/2022] [Indexed: 11/01/2022] Open
Affiliation(s)
- Kai Liu
- Department of Anesthesiology, Third Xiangya Hospital, Central South University, Changsha, Hunan, China.
- Hunan Province Key Laboratory of Brain Homeostasis, Third Xiangya Hospital, Central South University, Changsha, Hunan, China.
- Postdoctoral Research Station of Department of Anesthesiology, Third Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Yongjia Yin
- Xiangya School of Pharmaceutical Sciences, Central South University, Changsha, Hunan, China.
| | - Yuan Le
- Department of Anesthesiology, Third Xiangya Hospital, Central South University, Changsha, Hunan, China.
| | - Wen Ouyang
- Department of Anesthesiology, Third Xiangya Hospital, Central South University, Changsha, Hunan, China.
| | - Aihua Pan
- Department of Anatomy and Neurobiology, Central South University School of Basic Medical Sciences, Changsha, Hunan, China.
| | - Jufang Huang
- Department of Anatomy and Neurobiology, Central South University School of Basic Medical Sciences, Changsha, Hunan, China.
| | - Zhongcong Xie
- Geriatric Anesthesia Research Unit, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA.
| | - Qubo Zhu
- Xiangya School of Pharmaceutical Sciences, Central South University, Changsha, Hunan, China.
- Correspondence should be addressed to: Dr. Jianbin Tong, Third Xiangya Hospital, Changsha, Hunan, China, ; Dr. Qubo Zhu, Xiangya School of Pharmaceutical Sciences, Changsha 410013, Hunan, China, .
| | - Jianbin Tong
- Department of Anesthesiology, Third Xiangya Hospital, Central South University, Changsha, Hunan, China.
- Hunan Province Key Laboratory of Brain Homeostasis, Third Xiangya Hospital, Central South University, Changsha, Hunan, China.
- Correspondence should be addressed to: Dr. Jianbin Tong, Third Xiangya Hospital, Changsha, Hunan, China, ; Dr. Qubo Zhu, Xiangya School of Pharmaceutical Sciences, Changsha 410013, Hunan, China, .
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Blömer LA, Canepari M, Filipis L. Ultrafast Sodium Imaging of the Axon Initial Segment of Neurons in Mouse Brain Slices. Curr Protoc 2021; 1:e64. [PMID: 33657273 DOI: 10.1002/cpz1.64] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Monitoring Na+ influx in the axon initial segment (AIS) at high spatial and temporal resolution is fundamental to understanding the generation of an action potential (AP). Here, we present protocols to obtain this measurement, focusing on the AIS of layer 5 (L5) somatosensory cortex pyramidal neurons in mouse brain slices. We first outline how to prepare slices for this application, how to select and patch neurons, and how to optimize the image acquisition. Specifically, we describe the preparation of optimal slices, patching and loading of L5 pyramidal neurons with the Na+ indicator ING-2, and Na+ imaging at 100 µs temporal resolution with a pixel resolution of half a micron. Then, we present a data analysis strategy in order to extract information on the kinetics of activated voltage-gated Na+ channels by determining the change in Na+ by compensating for bleaching and calculating the time derivative of the resulting fit. In sum, this approach can be widely applied when investigating the function of Na+ channels during initiation of an AP and propagation under physiological or pathological conditions in neuronal subtypes. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Preparation of cortical slices Basic Protocol 2: Selection, patching, and Na+ fluorescence recording of a neuron Support Protocol: Calibrating Na+ fluorescence Basic Protocol 3: Data analysis.
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Affiliation(s)
- Laila Ananda Blömer
- Université Grenoble Alpes, CNRS, LIPhy, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbone, France
| | - Marco Canepari
- Université Grenoble Alpes, CNRS, LIPhy, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbone, France.,Institut National de la Santé et Recherche Médicale, Paris, France
| | - Luiza Filipis
- Université Grenoble Alpes, CNRS, LIPhy, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbone, France
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Blömer LA, Filipis L, Canepari M. Cal-520FF is the Present Optimal Ca 2+ Indicator for Ultrafast Ca 2+ Imaging and Optical Measurement of Ca 2+ Currents. J Fluoresc 2021; 31:619-623. [PMID: 33606130 DOI: 10.1007/s10895-021-02701-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2020] [Accepted: 02/11/2021] [Indexed: 11/29/2022]
Abstract
Ultrafast Ca2+ imaging using low-affinity fluorescent indicators allows the precise measurement of the kinetics of fast Ca2+ currents mediated by voltage-gated Ca2+ channels. Thus far, only a few indicators provided fluorescence transients with sufficient signal-to-noise ratio necessary to achieve this measurement, with Oregon Green BAPTA-5N exhibiting the best performance. Here we evaluated the performance of the low-affinity Ca2+ indicator Cal-520FF to record fast Ca2+ signals and to measure the kinetics of Ca2+ currents. Compared to Oregon Green BAPTA-5N and to Fluo4FF, Cal-520FF offers a superior signal-to-noise-ratio providing the optimal characteristics for this important type of biophysical measurement. This ability is the result of a relatively high fluorescence at zero Ca2+, necessary to detect enough photons at short exposure windows, and a high dynamic range leading to large fluorescence transients associated with short Ca2+ influx periods. We conclude that Cal-520FF is at present the optimal commercial low-affinity Ca2+ indicator for ultrafast Ca2+ imaging applications.
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Affiliation(s)
- Laila Ananda Blömer
- University Grenoble Alpes, CNRS, LIPhy, F-38000, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Luiza Filipis
- University Grenoble Alpes, CNRS, LIPhy, F-38000, Grenoble, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France
| | - Marco Canepari
- University Grenoble Alpes, CNRS, LIPhy, F-38000, Grenoble, France. .,Laboratories of Excellence, Ion Channel Science and Therapeutics, Valbonne, France. .,Institut National de la Santé et Recherche Médicale, Paris, France.
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Filipis L, Canepari M. Optical measurement of physiological sodium currents in the axon initial segment. J Physiol 2020; 599:49-66. [PMID: 33094478 DOI: 10.1113/jp280554] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Accepted: 10/16/2020] [Indexed: 01/06/2023] Open
Abstract
KEY POINTS Τhe axonal Na+ fluorescence underlying an action potential in the axon initial segment was optically measured at unprecedented temporal resolution. The measurement allowed resolution of the kinetics of the Na+ current at different axonal locations. The distinct components of the Na+ current were correlated with the kinetics of the action potential. NEURON simulations from a modified published model qualitatively predicted the experimentally measured Na+ current. The present method permits the direct investigation of the kinetic behaviour of native Na+ channels under physiological and pathological conditions. ABSTRACT In most neurons of the mammalian central nervous system, the action potential (AP) is generated in the axon initial segment (AIS) by a fast Na+ current mediated by voltage-gated Na+ channels. While the axonal Na+ signal associated with the AP has been measured using fluorescent Na+ indicators, the insufficient resolution of these recordings has not allowed tracking the Na+ current kinetics underlying this fundamental event. In this article, we report the first optical measurement of Na+ currents in the AIS of pyramidal neurons of layer 5 of the somatosensory cortex from brain slices of the mouse. This measurement was obtained by achieving a temporal resolution of 100 μs in the Na+ imaging technique, with a pixel resolution of 0.5 μm, and by calculating the time-derivative of the Na+ change corrected for longitudinal diffusion. We identified a subthreshold current before the AP, a fast-inactivating current peaking during the rise of the AP and a non-inactivating current during the AP repolarization. We established a correlation between the kinetics of the non-inactivating current at different distances from the soma and the kinetics of the somatic AP. We quantitatively compared the experimentally measured Na+ current with the current obtained by computer simulation of published NEURON models, demonstrating how the present approach can lead to the correct estimate of the native behaviour of Na+ channels. Finally, we discuss how the present approach can be used to investigate the physiological or pathological function of different channel types during AP initiation and propagation.
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Affiliation(s)
- Luiza Filipis
- University of Grenoble Alpes, CNRS, LIPhy, Grenoble, F38000, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, France
| | - Marco Canepari
- University of Grenoble Alpes, CNRS, LIPhy, Grenoble, F38000, France.,Laboratories of Excellence, Ion Channel Science and Therapeutics, France.,Institut National de la Santé et Recherche Médicale, France
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Quicke P, Howe CL, Song P, Jadan HV, Song C, Knöpfel T, Neil M, Dragotti PL, Schultz SR, Foust AJ. Subcellular resolution three-dimensional light-field imaging with genetically encoded voltage indicators. NEUROPHOTONICS 2020; 7:035006. [PMID: 32904628 PMCID: PMC7456658 DOI: 10.1117/1.nph.7.3.035006] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 08/07/2020] [Indexed: 05/13/2023]
Abstract
Significance: Light-field microscopy (LFM) enables high signal-to-noise ratio (SNR) and light efficient volume imaging at fast frame rates. Voltage imaging with genetically encoded voltage indicators (GEVIs) stands to particularly benefit from LFM's volumetric imaging capability due to high required sampling rates and limited probe brightness and functional sensitivity. Aim: We demonstrate subcellular resolution GEVI light-field imaging in acute mouse brain slices resolving dendritic voltage signals in three spatial dimensions. Approach: We imaged action potential-induced fluorescence transients in mouse brain slices sparsely expressing the GEVI VSFP-Butterfly 1.2 in wide-field microscopy (WFM) and LFM modes. We compared functional signal SNR and localization between different LFM reconstruction approaches and between LFM and WFM. Results: LFM enabled three-dimensional (3-D) localization of action potential-induced fluorescence transients in neuronal somata and dendrites. Nonregularized deconvolution decreased SNR with increased iteration number compared to synthetic refocusing but increased axial and lateral signal localization. SNR was unaffected for LFM compared to WFM. Conclusions: LFM enables 3-D localization of fluorescence transients, therefore eliminating the need for structures to lie in a single focal plane. These results demonstrate LFM's potential for studying dendritic integration and action potential propagation in three spatial dimensions.
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Affiliation(s)
- Peter Quicke
- Imperial College London, Department of Bioengineering, London, United Kingdom
- Imperial College London, Centre for Neurotechnology, London, United Kingdom
| | - Carmel L. Howe
- Imperial College London, Department of Bioengineering, London, United Kingdom
- Imperial College London, Centre for Neurotechnology, London, United Kingdom
| | - Pingfan Song
- Imperial College London, Department of Electrical and Electronic Engineering, London, United Kingdom
| | - Herman V. Jadan
- Imperial College London, Department of Electrical and Electronic Engineering, London, United Kingdom
| | - Chenchen Song
- Imperial College London, Department of Brain Sciences, London, United Kingdom
| | - Thomas Knöpfel
- Imperial College London, Centre for Neurotechnology, London, United Kingdom
- Imperial College London, Department of Brain Sciences, London, United Kingdom
| | - Mark Neil
- Imperial College London, Centre for Neurotechnology, London, United Kingdom
- Imperial College London, Department of Physics, London, United Kingdom
| | - Pier L. Dragotti
- Imperial College London, Department of Electrical and Electronic Engineering, London, United Kingdom
| | - Simon R. Schultz
- Imperial College London, Department of Bioengineering, London, United Kingdom
- Imperial College London, Centre for Neurotechnology, London, United Kingdom
- Address all correspondence to Simon R. Schultz, E-mail: ; Amanda J. Foust, E-mail:
| | - Amanda J. Foust
- Imperial College London, Department of Bioengineering, London, United Kingdom
- Imperial College London, Centre for Neurotechnology, London, United Kingdom
- Address all correspondence to Simon R. Schultz, E-mail: ; Amanda J. Foust, E-mail:
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The Origin of Physiological Local mGluR1 Supralinear Ca 2+ Signals in Cerebellar Purkinje Neurons. J Neurosci 2020; 40:1795-1809. [PMID: 31969470 DOI: 10.1523/jneurosci.2406-19.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 01/09/2020] [Accepted: 01/11/2020] [Indexed: 11/21/2022] Open
Abstract
In mouse cerebellar Purkinje neurons (PNs), the climbing fiber (CF) input provides a signal to parallel fiber (PF) synapses, triggering PF synaptic plasticity. This signal is given by supralinear Ca2+ transients, associated with the CF synaptic potential and colocalized with the PF Ca2+ influx, occurring only when PF activity precedes the CF input. Here, we unravel the biophysical determinants of supralinear Ca2+ signals associated with paired PF-CF synaptic activity. We used membrane potential (V m) and Ca2+ imaging to investigate the local CF-associated Ca2+ influx following a train of PF synaptic potentials in two cases: (1) when the dendritic V m is hyperpolarized below the resting V m, and (2) when the dendritic V m is at rest. We found that supralinear Ca2+ signals are mediated by type-1 metabotropic glutamate receptors (mGluR1s) when the CF input is delayed by 100-150 ms from the first PF input in both cases. When the dendrite is hyperpolarized only, however, mGluR1s boost neighboring T-type channels, providing a mechanism for local coincident detection of PF-CF activity. The resulting Ca2+ elevation is locally amplified by saturation of endogenous Ca2+ buffers produced by the PF-associated Ca2+ influx via the mGluR1-mediated nonselective cation conductance. In contrast, when the dendritic V m is at rest, mGluR1s increase dendritic excitability by inactivating A-type K+ channels, but this phenomenon is not restricted to the activated PF synapses. Thus, V m is likely a crucial parameter in determining PF synaptic plasticity, and the occurrence of hyperpolarization episodes is expected to play an important role in motor learning.SIGNIFICANCE STATEMENT In Purkinje neurons, parallel fiber synaptic plasticity, determined by coincident activation of the climbing fiber input, underlies cerebellar learning. We unravel the biophysical mechanisms allowing the CF input to produce a local Ca2+ signal exclusively at the sites of activated parallel fibers. We show that when the membrane potential is hyperpolarized with respect to the resting membrane potential, type-1 metabotropic glutamate receptors locally enhance Ca2+ influx mediated by T-type Ca2+ channels, and that this signal is amplified by saturation of endogenous buffer also mediated by the same receptors. The combination of these two mechanisms is therefore capable of producing a Ca2+ signal at the activated parallel fiber sites, suggesting a role of Purkinje neuron membrane potential in cerebellar learning.
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Moutaux E, Charlot B, Genoux A, Saudou F, Cazorla M. An integrated microfluidic/microelectrode array for the study of activity-dependent intracellular dynamics in neuronal networks. LAB ON A CHIP 2018; 18:3425-3435. [PMID: 30289147 DOI: 10.1039/c8lc00694f] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
In the central nervous system, neurons are organized in specific neural networks with distinct electrical patterns, input integration capacities, and intracellular dynamics. In order to better understand how neurons process information, it is crucial to keep the complex organization of brain circuits. However, performing subcellular investigations with high spatial and temporal resolution in vivo is technically challenging, especially in fine structures, such as axonal projections. Here, we present an on-a-chip system that combines a microfluidic platform with a dedicated matrix of electrodes to study activity-dependent dynamics in the physiological context of brain circuits. Because this system is compatible with high-resolution video-microscopy, it is possible to simultaneously record intracellular dynamics and electrical activity in presynaptic axonal projections and in their postsynaptic neuronal targets. Similarly, specific patterns of electrical activity can be applied to both compartments in order to investigate how intrinsic and network activities influence intracellular dynamics. The fluidic isolation of each compartment further allows the selective application of drugs at identified sites to study activity-dependent synaptic transmission. This integrated microfluidic/microelectrode array (microMEA) platform is a valuable tool for studying various intracellular and synaptic dynamics in response to neuronal activity in a physiologically relevant context that resembles in vivo brain circuits.
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Affiliation(s)
- Eve Moutaux
- Grenoble Institut des Neurosciences, Univ. Grenoble Alpes, INSERM U1216, Bat. Edmond J. Safra, Chemin F Ferrini, F-38000 Grenoble, France.
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