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Phillips RS, Baertsch NA. Interdependence of cellular and network properties in respiratory rhythm generation. Proc Natl Acad Sci U S A 2024; 121:e2318757121. [PMID: 38691591 PMCID: PMC11087776 DOI: 10.1073/pnas.2318757121] [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: 10/27/2023] [Accepted: 03/24/2024] [Indexed: 05/03/2024] Open
Abstract
How breathing is generated by the preBötzinger complex (preBötC) remains divided between two ideological frameworks, and a persistent sodium current (INaP) lies at the heart of this debate. Although INaP is widely expressed, the pacemaker hypothesis considers it essential because it endows a small subset of neurons with intrinsic bursting or "pacemaker" activity. In contrast, burstlet theory considers INaP dispensable because rhythm emerges from "preinspiratory" spiking activity driven by feed-forward network interactions. Using computational modeling, we find that small changes in spike shape can dissociate INaP from intrinsic bursting. Consistent with many experimental benchmarks, conditional effects on spike shape during simulated changes in oxygenation, development, extracellular potassium, and temperature alter the prevalence of intrinsic bursting and preinspiratory spiking without altering the role of INaP. Our results support a unifying hypothesis where INaP and excitatory network interactions, but not intrinsic bursting or preinspiratory spiking, are critical interdependent features of preBötC rhythmogenesis.
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Affiliation(s)
- Ryan S. Phillips
- Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, WA98101
| | - Nathan A. Baertsch
- Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, WA98101
- Pulmonary, Critical Care and Sleep Medicine, Department of Pediatrics, University of Washington, Seattle, WA98195
- Department of Physiology and Biophysics, University of Washington, Seattle, WA98195
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2
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Borrus DS, Stettler MK, Grover CJ, Kalajian EJ, Gu J, Conradi Smith GD, Del Negro CA. Inspiratory and sigh breathing rhythms depend on distinct cellular signalling mechanisms in the preBötzinger complex. J Physiol 2024; 602:809-834. [PMID: 38353596 PMCID: PMC10940220 DOI: 10.1113/jp285582] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Accepted: 12/21/2023] [Indexed: 02/21/2024] Open
Abstract
Breathing behaviour involves the generation of normal breaths (eupnoea) on a timescale of seconds and sigh breaths on the order of minutes. Both rhythms emerge in tandem from a single brainstem site, but whether and how a single cell population can generate two disparate rhythms remains unclear. We posit that recurrent synaptic excitation in concert with synaptic depression and cellular refractoriness gives rise to the eupnoea rhythm, whereas an intracellular calcium oscillation that is slower by orders of magnitude gives rise to the sigh rhythm. A mathematical model capturing these dynamics simultaneously generates eupnoea and sigh rhythms with disparate frequencies, which can be separately regulated by physiological parameters. We experimentally validated key model predictions regarding intracellular calcium signalling. All vertebrate brains feature a network oscillator that drives the breathing pump for regular respiration. However, in air-breathing mammals with compliant lungs susceptible to collapse, the breathing rhythmogenic network may have refashioned ubiquitous intracellular signalling systems to produce a second slower rhythm (for sighs) that prevents atelectasis without impeding eupnoea. KEY POINTS: A simplified activity-based model of the preBötC generates inspiratory and sigh rhythms from a single neuron population. Inspiration is attributable to a canonical excitatory network oscillator mechanism. Sigh emerges from intracellular calcium signalling. The model predicts that perturbations of calcium uptake and release across the endoplasmic reticulum counterintuitively accelerate and decelerate sigh rhythmicity, respectively, which was experimentally validated. Vertebrate evolution may have adapted existing intracellular signalling mechanisms to produce slow oscillations needed to optimize pulmonary function in mammals.
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Affiliation(s)
- Daniel S. Borrus
- Applied Science and Neuroscience, William & Mary, Williamsburg, VA 23185
| | - Marco K. Stettler
- Applied Science and Neuroscience, William & Mary, Williamsburg, VA 23185
| | - Cameron J. Grover
- Applied Science and Neuroscience, William & Mary, Williamsburg, VA 23185
| | - Eva J. Kalajian
- Applied Science and Neuroscience, William & Mary, Williamsburg, VA 23185
| | - Jeffrey Gu
- Applied Science and Neuroscience, William & Mary, Williamsburg, VA 23185
| | - Gregory D. Conradi Smith
- Applied Science and Neuroscience, William & Mary, Williamsburg, VA 23185
- Conradi Smith and Del Negro contributed equally
| | - Christopher A. Del Negro
- Applied Science and Neuroscience, William & Mary, Williamsburg, VA 23185
- Conradi Smith and Del Negro contributed equally
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3
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Phillips RS, Baertsch NA. Interdependence of cellular and network properties in respiratory rhythmogenesis. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.30.564834. [PMID: 37961254 PMCID: PMC10634953 DOI: 10.1101/2023.10.30.564834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
How breathing is generated by the preBötzinger Complex (preBötC) remains divided between two ideological frameworks, and the persistent sodium current (INaP) lies at the heart of this debate. Although INaP is widely expressed, the pacemaker hypothesis considers it essential because it endows a small subset of neurons with intrinsic bursting or "pacemaker" activity. In contrast, burstlet theory considers INaP dispensable because rhythm emerges from "pre-inspiratory" spiking activity driven by feed-forward network interactions. Using computational modeling, we discover that changes in spike shape can dissociate INaP from intrinsic bursting. Consistent with many experimental benchmarks, conditional effects on spike shape during simulated changes in oxygenation, development, extracellular potassium, and temperature alter the prevalence of intrinsic bursting and pre-inspiratory spiking without altering the role of INaP. Our results support a unifying hypothesis where INaP and excitatory network interactions, but not intrinsic bursting or pre-inspiratory spiking, are critical interdependent features of preBötC rhythmogenesis.
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Affiliation(s)
- Ryan S Phillips
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle WA, USA
| | - Nathan A Baertsch
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle WA, USA
- Pulmonary, Critical Care and Sleep Medicine, Department of Pediatrics, University of Washington, Seattle WA, USA
- Department of Physiology and Biophysics, University of Washington, Seattle WA, USA
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da Silva CA, Grover CJ, Picardo MCD, Del Negro CA. Role of Na V1.6-mediated persistent sodium current and bursting-pacemaker properties in breathing rhythm generation. Cell Rep 2023; 42:113000. [PMID: 37590134 PMCID: PMC10528911 DOI: 10.1016/j.celrep.2023.113000] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 06/16/2023] [Accepted: 08/01/2023] [Indexed: 08/19/2023] Open
Abstract
Inspiration is the inexorable active phase of breathing. The brainstem pre-Bötzinger complex (preBötC) gives rise to inspiratory neural rhythm, but its underlying cellular and ionic bases remain unclear. The long-standing "pacemaker hypothesis" posits that the persistent Na+ current (INaP) that gives rise to bursting-pacemaker properties in preBötC interneurons is essential for rhythmogenesis. We tested the pacemaker hypothesis by conditionally knocking out and knocking down the Scn8a (Nav1.6 [voltage-gated sodium channel 1.6]) gene in core rhythmogenic preBötC neurons. Deleting Scn8a substantially decreases the INaP and abolishes bursting-pacemaker activity, which slows inspiratory rhythm in vitro and negatively impacts the postnatal development of ventilation. Diminishing Scn8a via genetic interference has no impact on breathing in adult mice. We argue that the Scn8a-mediated INaP is not obligatory but that it influences the development and rhythmic function of the preBötC. The ubiquity of the INaP in respiratory brainstem interneurons could underlie breathing-related behaviors such as neonatal phonation or rhythmogenesis in different physiological conditions.
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Affiliation(s)
- Carlos A da Silva
- Department of Applied Science, William & Mary, Williamsburg, VA 23185, USA
| | - Cameron J Grover
- Department of Applied Science, William & Mary, Williamsburg, VA 23185, USA
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Morgado-Valle C, Smith JC, Fernandez-Ruiz J, Lopez-Meraz L, Beltran-Parrazal L. Modulation of inspiratory burst duration and frequency by bombesin in vitro. Pflugers Arch 2023; 475:101-117. [PMID: 35066612 DOI: 10.1007/s00424-022-02663-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Revised: 12/19/2021] [Accepted: 01/04/2022] [Indexed: 01/31/2023]
Abstract
Mammalian respiratory rhythm-generating circuits in the brainstem are subject to neuromodulation by multiple peptidergic afferent inputs controlling circuit behavior and outputs. Although functionally important, actions of neuropeptide modulators have not been fully characterized. We analyzed at cellular and circuit levels two inspiratory patterns intrinsically generated by the preBötzinger complex (preBötC) and their modulation by the neuropeptides bombesin and substance P (SP) in neonatal rat medullary slices in vitro. We found that, in recordings of hypoglossal nerve and preBötC neuron inspiratory activity, some inspiratory bursts occurring spontaneously under basal conditions have a biphasic shape with longer duration than normal inspiratory bursts and occur at a lower frequency. This biphasic burst pattern has been proposed to represent inspiratory activity underling periodic sighs. Bath-applied bombesin or SP decreased the period and increased the duration of both normal inspiratory and biphasic bursts and their underlying synaptic drives. The ratio of the biphasic long-duration burst period to the normal inspiratory burst period and the ratio of their burst durations remained the same before and after peptidergic modulation. Bombesin increased the frequency of the inspiratory rhythm in a Ca2+-independent manner and the frequency of long-duration bursts in a Ca2+-dependent manner. This finding suggests that period and burst duration coupling are due to intrinsic mechanisms controlling simultaneously timing and burst termination within the inspiratory rhythm-generating network. We propose a model in which signaling cascades activated by bombesin and SP modulate mechanisms controlling inspiratory burst frequency and duration to coordinate preBötC circuit behavioral outputs.
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Affiliation(s)
- Consuelo Morgado-Valle
- Instituto de Investigaciones Cerebrales, Dirección General de Investigaciones, Universidad Veracruzana, Xalapa Veracruz, México, 91190. .,Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke (NINDS). National Institutes of Health (NIH), Bethesda, MD, 20892, USA.
| | - Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke (NINDS). National Institutes of Health (NIH), Bethesda, MD, 20892, USA
| | - Juan Fernandez-Ruiz
- Facultad de Medicina, Universidad Nacional Autónoma de México. Ciudad de México, México City, 04510, México
| | - Leonor Lopez-Meraz
- Instituto de Investigaciones Cerebrales, Dirección General de Investigaciones, Universidad Veracruzana, Xalapa Veracruz, México, 91190
| | - Luis Beltran-Parrazal
- Instituto de Investigaciones Cerebrales, Dirección General de Investigaciones, Universidad Veracruzana, Xalapa Veracruz, México, 91190.
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Phillips RS, Koizumi H, Molkov YI, Rubin JE, Smith JC. Predictions and experimental tests of a new biophysical model of the mammalian respiratory oscillator. eLife 2022; 11:74762. [PMID: 35796425 PMCID: PMC9262387 DOI: 10.7554/elife.74762] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Accepted: 06/07/2022] [Indexed: 11/13/2022] Open
Abstract
Previously our computational modeling studies (Phillips et al., 2019) proposed that neuronal persistent sodium current (INaP) and calcium-activated non-selective cation current (ICAN) are key biophysical factors that, respectively, generate inspiratory rhythm and burst pattern in the mammalian preBötzinger complex (preBötC) respiratory oscillator isolated in vitro. Here, we experimentally tested and confirmed three predictions of the model from new simulations concerning the roles of INaP and ICAN: (1) INaP and ICAN blockade have opposite effects on the relationship between network excitability and preBötC rhythmic activity; (2) INaP is essential for preBötC rhythmogenesis; and (3) ICAN is essential for generating the amplitude of rhythmic output but not rhythm generation. These predictions were confirmed via optogenetic manipulations of preBötC network excitability during graded INaP or ICAN blockade by pharmacological manipulations in slices in vitro containing the rhythmically active preBötC from the medulla oblongata of neonatal mice. Our results support and advance the hypothesis that INaP and ICAN mechanistically underlie rhythm and inspiratory burst pattern generation, respectively, in the isolated preBötC.
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Affiliation(s)
- Ryan S Phillips
- Department of Mathematics, University of Pittsburgh
- Center for the Neural Basis of Cognition
| | | | - Yaroslav I Molkov
- Department of Mathematics and Statistics, Georgia State University
- Neuroscience Institute, Georgia State University
| | - Jonathan E Rubin
- Department of Mathematics, University of Pittsburgh
- Center for the Neural Basis of Cognition
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Burgraff NJ, Phillips RS, Severs LJ, Bush NE, Baertsch NA, Ramirez JM. Inspiratory rhythm generation is stabilized by Ih. J Neurophysiol 2022; 128:181-196. [PMID: 35675444 PMCID: PMC9291429 DOI: 10.1152/jn.00150.2022] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Cellular and network properties must be capable of generating rhythmic activity that is both flexible and stable. This is particularly important for breathing, a rhythmic behavior that dynamically adapts to environmental, behavioral, and metabolic changes from the first to the last breath. The pre-Bötzinger complex (preBötC), located within the ventral medulla, is responsible for producing rhythmic inspiration. Its cellular properties must be tunable, flexible as well as stabilizing. Here, we explore the role of the hyperpolarization-activated, nonselective cation current (Ih) for stabilizing PreBötC activity during opioid exposure and reduced excitatory synaptic transmission. Introducing Ih into an in silico preBötC network predicts that loss of this depolarizing current should significantly slow the inspiratory rhythm. By contrast, in vitro and in vivo experiments revealed that the loss of Ih minimally affected breathing frequency, but destabilized rhythmogenesis through the generation of incompletely synchronized bursts (burstlets). Associated with the loss of Ih was an increased susceptibility of breathing to opioid-induced respiratory depression or weakened excitatory synaptic interactions, a paradoxical depolarization at the cellular level, and the suppression of tonic spiking. Tonic spiking activity is generated by nonrhythmic excitatory and inhibitory preBötC neurons, of which a large percentage express Ih. Together, our results suggest that Ih is important for maintaining tonic spiking, stabilizing inspiratory rhythmogenesis, and protecting breathing against perturbations or changes in network state.NEW & NOTEWORTHY The Ih current plays multiple roles within the preBötC. This current is important for promoting intrinsic tonic spiking activity in excitatory and inhibitory neurons and for preserving rhythmic function during conditions that dampen network excitability, such as in the context of opioid-induced respiratory depression. We therefore propose that the Ih current expands the dynamic range of rhythmogenesis, buffers the preBötC against network perturbations, and stabilizes rhythmogenesis by preventing the generation of unsynchronized bursts.
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Affiliation(s)
- Nicholas J. Burgraff
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Ryan S. Phillips
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Liza J. Severs
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Nicholas E. Bush
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington
| | - Nathan A. Baertsch
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington,2Department of Pediatrics, University of Washington, Seattle, Washington
| | - Jan-Marino Ramirez
- 1Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, Washington,2Department of Pediatrics, University of Washington, Seattle, Washington,3Department of Neurological Surgery, University of Washington, Seattle, Washington
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A glibenclamide-sensitive TRPM4-mediated component of CA1 excitatory postsynaptic potentials appears in experimental autoimmune encephalomyelitis. Sci Rep 2022; 12:6000. [PMID: 35397639 PMCID: PMC8994783 DOI: 10.1038/s41598-022-09875-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 03/16/2022] [Indexed: 12/29/2022] Open
Abstract
The transient receptor potential melastatin 4 (TRPM4) channel contributes to disease severity in the murine experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis and to neuronal cell death in models of excitotoxicity and traumatic brain injury. As TRPM4 is activated by intracellular calcium and conducts monovalent cations, we hypothesized that TRPM4 may contribute to and boost excitatory synaptic transmission in CA1 pyramidal neurons of the hippocampus. Using single-spine calcium imaging and electrophysiology, we found no effect of the TRPM4 antagonists 9-phenanthrol and glibenclamide on synaptic transmission in hippocampal slices from healthy mice. In contrast, glibenclamide but not 9-phenanthrol reduced excitatory synaptic potentials in slices from EAE mice, an effect that was absent in slices from EAE mice lacking TRPM4. We conclude that TRPM4 plays little role in basal hippocampal synaptic transmission, but a glibenclamide-sensitive TRPM4-mediated contribution to excitatory postsynaptic responses is upregulated at the acute phase of EAE.
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Phillips RS, Rubin JE. Putting the theory into 'burstlet theory' with a biophysical model of burstlets and bursts in the respiratory preBötzinger complex. eLife 2022; 11:e75713. [PMID: 35380537 PMCID: PMC9023056 DOI: 10.7554/elife.75713] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Accepted: 04/04/2022] [Indexed: 11/17/2022] Open
Abstract
Inspiratory breathing rhythms arise from synchronized neuronal activity in a bilaterally distributed brainstem structure known as the preBötzinger complex (preBötC). In in vitro slice preparations containing the preBötC, extracellular potassium must be elevated above physiological levels (to 7-9 mM) to observe regular rhythmic respiratory motor output in the hypoglossal nerve to which the preBötC projects. Reexamination of how extracellular K+ affects preBötC neuronal activity has revealed that low-amplitude oscillations persist at physiological levels. These oscillatory events are subthreshold from the standpoint of transmission to motor output and are dubbed burstlets. Burstlets arise from synchronized neural activity in a rhythmogenic neuronal subpopulation within the preBötC that in some instances may fail to recruit the larger network events, or bursts, required to generate motor output. The fraction of subthreshold preBötC oscillatory events (burstlet fraction) decreases sigmoidally with increasing extracellular potassium. These observations underlie the burstlet theory of respiratory rhythm generation. Experimental and computational studies have suggested that recruitment of the non-rhythmogenic component of the preBötC population requires intracellular Ca2+ dynamics and activation of a calcium-activated nonselective cationic current. In this computational study, we show how intracellular calcium dynamics driven by synaptically triggered Ca2+ influx as well as Ca2+ release/uptake by the endoplasmic reticulum in conjunction with a calcium-activated nonselective cationic current can reproduce and offer an explanation for many of the key properties associated with the burstlet theory of respiratory rhythm generation. Altogether, our modeling work provides a mechanistic basis that can unify a wide range of experimental findings on rhythm generation and motor output recruitment in the preBötC.
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Affiliation(s)
- Ryan S Phillips
- Department of Mathematics and Center for the Neural Basis of Cognition, University of PittsburghPittsburghUnited States
| | - Jonathan E Rubin
- Department of Mathematics and Center for the Neural Basis of Cognition, University of PittsburghPittsburghUnited States
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Paton JFR, Machado BH, Moraes DJA, Zoccal DB, Abdala AP, Smith JC, Antunes VR, Murphy D, Dutschmann M, Dhingra RR, McAllen R, Pickering AE, Wilson RJA, Day TA, Barioni NO, Allen AM, Menuet C, Donnelly J, Felippe I, St-John WM. Advancing respiratory-cardiovascular physiology with the working heart-brainstem preparation over 25 years. J Physiol 2022; 600:2049-2075. [PMID: 35294064 PMCID: PMC9322470 DOI: 10.1113/jp281953] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 03/04/2022] [Indexed: 11/24/2022] Open
Abstract
Twenty‐five years ago, a new physiological preparation called the working heart–brainstem preparation (WHBP) was introduced with the claim it would provide a new platform allowing studies not possible before in cardiovascular, neuroendocrine, autonomic and respiratory research. Herein, we review some of the progress made with the WHBP, some advantages and disadvantages along with potential future applications, and provide photographs and technical drawings of all the customised equipment used for the preparation. Using mice or rats, the WHBP is an in situ experimental model that is perfused via an extracorporeal circuit benefitting from unprecedented surgical access, mechanical stability of the brain for whole cell recording and an uncompromised use of pharmacological agents akin to in vitro approaches. The preparation has revealed novel mechanistic insights into, for example, the generation of distinct respiratory rhythms, the neurogenesis of sympathetic activity, coupling between respiration and the heart and circulation, hypothalamic and spinal control mechanisms, and peripheral and central chemoreceptor mechanisms. Insights have been gleaned into diseases such as hypertension, heart failure and sleep apnoea. Findings from the in situ preparation have been ratified in conscious in vivo animals and when tested have translated to humans. We conclude by discussing potential future applications of the WHBP including two‐photon imaging of peripheral and central nervous systems and adoption of pharmacogenetic tools that will improve our understanding of physiological mechanisms and reveal novel mechanisms that may guide new treatment strategies for cardiorespiratory diseases.
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Affiliation(s)
- Julian F R Paton
- Manaaki Manawa - The Centre for Heart Research, Faculty of Medical & Health Science, University of Auckland, Park Road, Grafton, Auckland, 1142, New Zealand
| | - Benedito H Machado
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Davi J A Moraes
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Daniel B Zoccal
- Department of Physiology and Pathology, School of Dentistry of Araraquara, São Paulo State University, Araraquara, São Paulo, Brazil
| | - Ana P Abdala
- School of Physiology, Pharmacology and Neuroscience, Faculty of Biomedical Sciences, University of Bristol, Bristol, England, BS8 1TD, UK
| | - Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Vagner R Antunes
- Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - David Murphy
- Molecular Neuroendocrinology Research Group, Bristol Medical School: Translational Health Sciences, University of Bristol, Bristol, UK
| | - Mathias Dutschmann
- Florey institute of Neuroscience and Mental Health, University of Melbourne, 30, Royal Parade, Parkville, Victoria, 3052, Australia
| | - Rishi R Dhingra
- Florey institute of Neuroscience and Mental Health, University of Melbourne, 30, Royal Parade, Parkville, Victoria, 3052, Australia
| | - Robin McAllen
- Florey institute of Neuroscience and Mental Health, University of Melbourne, 30, Royal Parade, Parkville, Victoria, 3052, Australia
| | - Anthony E Pickering
- School of Physiology, Pharmacology and Neuroscience, Faculty of Biomedical Sciences, University of Bristol, Bristol, England, BS8 1TD, UK
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Trevor A Day
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Biology, Faculty of Science and Technology, Mount Royal University, Calgary, Alberta, Canada
| | - Nicole O Barioni
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Andrew M Allen
- Department of Anatomy & Physiology, The University of Melbourne, Victoria, 3010, Australia
| | - Clément Menuet
- Institut de Neurobiologie de la Méditerranée, INMED UMR1249, INSERM, Aix-Marseille Université, Marseille, France
| | - Joseph Donnelly
- Department of Medicine, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand
| | - Igor Felippe
- Manaaki Manawa - The Centre for Heart Research, Faculty of Medical & Health Science, University of Auckland, Park Road, Grafton, Auckland, 1142, New Zealand
| | - Walter M St-John
- Emeritus Professor, Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Dartmouth, New Hampshire, USA
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11
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Kallurkar PS, Picardo MCD, Sugimura YK, Saha MS, Conradi Smith GD, Del Negro CA. Transcriptomes of electrophysiologically recorded Dbx1-derived respiratory neurons of the preBötzinger complex in neonatal mice. Sci Rep 2022; 12:2923. [PMID: 35190626 PMCID: PMC8861066 DOI: 10.1038/s41598-022-06834-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 02/04/2022] [Indexed: 12/26/2022] Open
Abstract
Breathing depends on interneurons in the preBötzinger complex (preBötC) derived from Dbx1-expressing precursors. Here we investigate whether rhythm- and pattern-generating functions reside in discrete classes of Dbx1 preBötC neurons. In a slice model of breathing with ~ 5 s cycle period, putatively rhythmogenic Type-1 Dbx1 preBötC neurons activate 100-300 ms prior to Type-2 neurons, putatively specialized for output pattern, and 300-500 ms prior to the inspiratory motor output. We sequenced Type-1 and Type-2 transcriptomes and identified differential expression of 123 genes including ionotropic receptors (Gria3, Gabra1) that may explain their preinspiratory activation profiles and Ca2+ signaling (Cracr2a, Sgk1) involved in inspiratory and sigh bursts. Surprisingly, neuropeptide receptors that influence breathing (e.g., µ-opioid and bombesin-like peptide receptors) were only sparsely expressed, which suggests that cognate peptides and opioid drugs exert their profound effects on a small fraction of the preBötC core. These data in the public domain help explain the neural origins of breathing.
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Affiliation(s)
| | | | - Yae K Sugimura
- Department of Neuroscience, Jikei University School of Medicine, Tokyo, Japan
| | - Margaret S Saha
- Department of Biology, William & Mary, Williamsburg, VA, USA
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Smith JC. Respiratory rhythm and pattern generation: Brainstem cellular and circuit mechanisms. HANDBOOK OF CLINICAL NEUROLOGY 2022; 188:1-35. [PMID: 35965022 DOI: 10.1016/b978-0-323-91534-2.00004-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Breathing movements in mammals are driven by rhythmic neural activity automatically generated within spatially and functionally organized brainstem neural circuits comprising the respiratory central pattern generator (CPG). This chapter reviews up-to-date experimental information and theoretical studies of the cellular and circuit mechanisms of respiratory rhythm and pattern generation operating within critical components of this CPG in the lower brainstem. Over the past several decades, there have been substantial advances in delineating the spatial architecture of essential medullary regions and their regional cellular and circuit properties required to understand rhythm and pattern generation mechanisms. A fundamental concept is that the circuits in these regions have rhythm-generating capabilities at multiple cellular and circuit organization levels. The regional cellular properties, circuit organization, and control mechanisms allow flexible expression of neural activity patterns for a repertoire of respiratory behaviors under various physiologic conditions that are dictated by requirements for homeostatic regulation and behavioral integration. Many mechanistic insights have been provided by computational modeling studies driven by experimental results and have advanced understanding in the field. These conceptual and theoretical developments are discussed.
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Affiliation(s)
- Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States.
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13
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Pharmacological Modulation and (Patho)Physiological Roles of TRPM4 Channel-Part 2: TRPM4 in Health and Disease. Pharmaceuticals (Basel) 2021; 15:ph15010040. [PMID: 35056097 PMCID: PMC8779181 DOI: 10.3390/ph15010040] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 12/21/2021] [Accepted: 12/22/2021] [Indexed: 02/06/2023] Open
Abstract
Transient receptor potential melastatin 4 (TRPM4) is a unique member of the TRPM protein family and, similarly to TRPM5, is Ca2+ sensitive and permeable for monovalent but not divalent cations. It is widely expressed in many organs and is involved in several functions; it regulates membrane potential and Ca2+ homeostasis in both excitable and non-excitable cells. This part of the review discusses the currently available knowledge about the physiological and pathophysiological roles of TRPM4 in various tissues. These include the physiological functions of TRPM4 in the cells of the Langerhans islets of the pancreas, in various immune functions, in the regulation of vascular tone, in respiratory and other neuronal activities, in chemosensation, and in renal and cardiac physiology. TRPM4 contributes to pathological conditions such as overactive bladder, endothelial dysfunction, various types of malignant diseases and central nervous system conditions including stroke and injuries as well as in cardiac conditions such as arrhythmias, hypertrophy, and ischemia-reperfusion injuries. TRPM4 claims more and more attention and is likely to be the topic of research in the future.
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14
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Trpm5 channels encode bistability of spinal motoneurons and ensure motor control of hindlimbs in mice. Nat Commun 2021; 12:6815. [PMID: 34819493 PMCID: PMC8613399 DOI: 10.1038/s41467-021-27113-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Accepted: 11/02/2021] [Indexed: 11/09/2022] Open
Abstract
Bistable motoneurons of the spinal cord exhibit warmth-activated plateau potential driven by Na+ and triggered by a brief excitation. The thermoregulating molecular mechanisms of bistability and their role in motor functions remain unknown. Here, we identify thermosensitive Na+-permeable Trpm5 channels as the main molecular players for bistability in mouse motoneurons. Pharmacological, genetic or computational inhibition of Trpm5 occlude bistable-related properties (slow afterdepolarization, windup, plateau potentials) and reduce spinal locomotor outputs while central pattern generators for locomotion operate normally. At cellular level, Trpm5 is activated by a ryanodine-mediated Ca2+ release and turned off by Ca2+ reuptake through the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump. Mice in which Trpm5 is genetically silenced in most lumbar motoneurons develop hindlimb paresis and show difficulties in executing high-demanding locomotor tasks. Overall, by encoding bistability in motoneurons, Trpm5 appears indispensable for producing a postural tone in hindlimbs and amplifying the locomotor output.
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15
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Dynamics of ramping bursts in a respiratory neuron model. J Comput Neurosci 2021; 50:161-180. [PMID: 34704174 DOI: 10.1007/s10827-021-00800-w] [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] [Received: 04/24/2021] [Revised: 09/24/2021] [Accepted: 09/29/2021] [Indexed: 10/20/2022]
Abstract
Intensive computational and theoretical work has led to the development of multiple mathematical models for bursting in respiratory neurons in the pre-Bötzinger Complex (pre-BötC) of the mammalian brainstem. Nonetheless, these previous models have not captured the pre-inspiratory ramping aspects of these neurons' activity patterns, in which relatively slow tonic spiking gradually progresses to faster spiking and a full-blown burst, with a corresponding gradual development of an underlying plateau potential. In this work, we show that the incorporation of the dynamics of the extracellular potassium ion concentration into an existing model for pre-BötC neuron bursting, along with some parameter adjustments, suffices to induce this ramping behavior. Using fast-slow decomposition, we show that this activity can be considered as a form of parabolic bursting, but with burst termination at a homoclinic bifurcation rather than as a SNIC bifurcation. We also investigate the parameter-dependence of these solutions and show that the proposed model yields a greater dynamic range of burst frequencies, durations, and duty cycles than those produced by other models in the literature.
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16
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Li K, Abbott SBG, Shi Y, Eggan P, Gonye EC, Bayliss DA. TRPM4 mediates a subthreshold membrane potential oscillation in respiratory chemoreceptor neurons that drives pacemaker firing and breathing. Cell Rep 2021; 34:108714. [PMID: 33535052 PMCID: PMC7888550 DOI: 10.1016/j.celrep.2021.108714] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 12/04/2020] [Accepted: 01/12/2021] [Indexed: 12/01/2022] Open
Abstract
Brainstem networks that control regular tidal breathing depend on excitatory drive, including from tonically active, CO2/H+-sensitive neurons of the retrotrapezoid nucleus (RTN). Here, we examine intrinsic ionic mechanisms underlying the metronomic firing activity characteristic of RTN neurons. In mouse brainstem slices, large-amplitude membrane potential oscillations are evident in synaptically isolated RTN neurons after blocking action potentials. The voltage-dependent oscillations are abolished by sodium replacement; blocking calcium channels (primarily L-type); chelating intracellular Ca2+; and inhibiting TRPM4, a Ca2+-dependent cationic channel. Likewise, oscillation voltage waveform currents are sensitive to calcium and TRPM4 channel blockers. Extracellular acidification and serotonin (5-HT) evoke membrane depolarization that augments TRPM4-dependent oscillatory activity and action potential discharge. Finally, inhibition of TRPM4 channels in the RTN of anesthetized mice reduces central respiratory output. These data implicate TRPM4 in a subthreshold oscillation that supports the pacemaker-like firing of RTN neurons required for basal, CO2-stimulated, and state-dependent breathing.
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Affiliation(s)
- Keyong Li
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Stephen B G Abbott
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Yingtang Shi
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Pierce Eggan
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Elizabeth C Gonye
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA.
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17
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Chen X, Sooch G, Demaree IS, White FA, Obukhov AG. Transient Receptor Potential Canonical (TRPC) Channels: Then and Now. Cells 2020; 9:E1983. [PMID: 32872338 PMCID: PMC7565274 DOI: 10.3390/cells9091983] [Citation(s) in RCA: 76] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Revised: 08/26/2020] [Accepted: 08/27/2020] [Indexed: 12/13/2022] Open
Abstract
Twenty-five years ago, the first mammalian Transient Receptor Potential Canonical (TRPC) channel was cloned, opening the vast horizon of the TRPC field. Today, we know that there are seven TRPC channels (TRPC1-7). TRPCs exhibit the highest protein sequence similarity to the Drosophila melanogaster TRP channels. Similar to Drosophila TRPs, TRPCs are localized to the plasma membrane and are activated in a G-protein-coupled receptor-phospholipase C-dependent manner. TRPCs may also be stimulated in a store-operated manner, via receptor tyrosine kinases, or by lysophospholipids, hypoosmotic solutions, and mechanical stimuli. Activated TRPCs allow the influx of Ca2+ and monovalent alkali cations into the cytosol of cells, leading to cell depolarization and rising intracellular Ca2+ concentration. TRPCs are involved in the continually growing number of cell functions. Furthermore, mutations in the TRPC6 gene are associated with hereditary diseases, such as focal segmental glomerulosclerosis. The most important recent breakthrough in TRPC research was the solving of cryo-EM structures of TRPC3, TRPC4, TRPC5, and TRPC6. These structural data shed light on the molecular mechanisms underlying TRPCs' functional properties and propelled the development of new modulators of the channels. This review provides a historical overview of the major advances in the TRPC field focusing on the role of gene knockouts and pharmacological tools.
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Affiliation(s)
- Xingjuan Chen
- Institute of Medical Research, Northwestern Polytechnical University, Xi’an 710072, China;
| | - Gagandeep Sooch
- The Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (G.S.); (I.S.D.)
| | - Isaac S. Demaree
- The Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (G.S.); (I.S.D.)
| | - Fletcher A. White
- The Department of Anesthesia, Indiana University School of Medicine, Indianapolis, IN 46202, USA;
- Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Alexander G. Obukhov
- The Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, IN 46202, USA; (G.S.); (I.S.D.)
- Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA
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18
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Buntschu S, Tscherter A, Heidemann M, Streit J. Critical Components for Spontaneous Activity and Rhythm Generation in Spinal Cord Circuits in Culture. Front Cell Neurosci 2020; 14:81. [PMID: 32410961 PMCID: PMC7198714 DOI: 10.3389/fncel.2020.00081] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Accepted: 03/19/2020] [Indexed: 11/23/2022] Open
Abstract
Neuronal excitability contributes to rhythm generation in central pattern generating networks (CPGs). In spinal cord CPGs, such intrinsic excitability partly relies on persistent sodium currents (INaP), whereas respiratory CPGs additionally depend on calcium-activated cation currents (ICAN). Here, we investigated the contributions of INaP and ICAN to spontaneous rhythm generation in neuronal networks of the spinal cord and whether they mainly involve Hb9 neurons. We used cultures of ventral and transverse slices from the E13-14 embryonic rodent lumbar spinal cord on multielectrode arrays (MEAs). All cultures showed spontaneous bursts of network activity. Blocking synaptic excitation with the AMPA receptor antagonist CNQX suppressed spontaneous network bursts and left asynchronous intrinsic activity at about 30% of the electrodes. Such intrinsic activity was completely blocked at all electrodes by both the INaP blocker riluzole as well as by the ICAN blocker flufenamic acid (FFA) and the more specific TRPM4 channel antagonist 9-phenanthrol. All three antagonists also suppressed spontaneous bursting completely and strongly reduced stimulus-evoked bursts. Also, FFA reduced repetitive spiking that was induced in single neurons by injection of depolarizing current pulses to few spikes. Other antagonists of unspecific cation currents or calcium currents had no suppressing effects on either intrinsic activity (gadolinium chloride) or spontaneous bursting (the TRPC channel antagonists clemizole and ML204 and the T channel antagonist TTA-P2). Combined patch-clamp and MEA recordings showed that Hb9 interneurons were activated by network bursts but could not initiate them. Together these findings suggest that both INaP through Na+-channels and ICAN through putative TRPM4 channels contribute to spontaneous intrinsic and repetitive spiking in spinal cord neurons and thereby to the generation of network bursts.
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Affiliation(s)
| | | | | | - Jürg Streit
- Department of Physiology, University of Bern, Bern, Switzerland
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19
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Wang Y, Rubin JE. Complex bursting dynamics in an embryonic respiratory neuron model. CHAOS (WOODBURY, N.Y.) 2020; 30:043127. [PMID: 32357647 DOI: 10.1063/1.5138993] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Accepted: 03/23/2020] [Indexed: 06/11/2023]
Abstract
Pre-Bötzinger complex (pre-BötC) network activity within the mammalian brainstem controls the inspiratory phase of the respiratory rhythm. While bursting in pre-BötC neurons during the postnatal period has been extensively studied, less is known regarding inspiratory pacemaker neuron behavior at embryonic stages. Recent data in mouse embryo brainstem slices have revealed the existence of a variety of bursting activity patterns depending on distinct combinations of burst-generating INaP and ICAN conductances. In this work, we consider a model of an isolated embryonic pre-BötC neuron featuring two distinct bursting mechanisms. We use methods of dynamical systems theory, such as phase plane analysis, fast-slow decomposition, and bifurcation analysis, to uncover mechanisms underlying several different types of intrinsic bursting dynamics observed experimentally including several forms of plateau bursts, bursts involving depolarization block, and various combinations of these patterns. Our analysis also yields predictions about how changes in the balance of the two bursting mechanisms contribute to alterations in an inspiratory pacemaker neuron activity during prenatal development.
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Affiliation(s)
- Yangyang Wang
- Department of Mathematics, The University of Iowa, Iowa City, Iowa 52242, USA
| | - Jonathan E Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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20
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Evaluating the Burstlet Theory of Inspiratory Rhythm and Pattern Generation. eNeuro 2020; 7:ENEURO.0314-19.2019. [PMID: 31888961 PMCID: PMC6964920 DOI: 10.1523/eneuro.0314-19.2019] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 12/17/2019] [Accepted: 12/17/2019] [Indexed: 12/12/2022] Open
Abstract
The preBötzinger complex (preBötC) generates the rhythm and rudimentary motor pattern for inspiratory breathing movements. Here, we test “burstlet” theory (Kam et al., 2013a), which posits that low amplitude burstlets, subthreshold from the standpoint of inspiratory bursts, reflect the fundamental oscillator of the preBötC. In turn, a discrete suprathreshold process transforms burstlets into full amplitude inspiratory bursts that drive motor output, measurable via hypoglossal nerve (XII) discharge in vitro. We recap observations by Kam and Feldman in neonatal mouse slice preparations: field recordings from preBötC demonstrate bursts and concurrent XII motor output intermingled with lower amplitude burstlets that do not produce XII motor output. Manipulations of excitability affect the relative prevalence of bursts and burstlets and modulate their frequency. Whole-cell and photonic recordings of preBötC neurons suggest that burstlets involve inconstant subsets of rhythmogenic interneurons. We conclude that discrete rhythm- and pattern-generating mechanisms coexist in the preBötC and that burstlets reflect its fundamental rhythmogenic nature.
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21
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Phillips RS, Rubin JE. Effects of persistent sodium current blockade in respiratory circuits depend on the pharmacological mechanism of action and network dynamics. PLoS Comput Biol 2019; 15:e1006938. [PMID: 31469828 PMCID: PMC6742421 DOI: 10.1371/journal.pcbi.1006938] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2019] [Revised: 09/12/2019] [Accepted: 06/15/2019] [Indexed: 02/05/2023] Open
Abstract
The mechanism(s) of action of most commonly used pharmacological blockers of voltage-gated ion channels are well understood; however, this knowledge is rarely considered when interpreting experimental data. Effects of blockade are often assumed to be equivalent, regardless of the mechanism of the blocker involved. Using computer simulations, we demonstrate that this assumption may not always be correct. We simulate the blockade of a persistent sodium current (INaP), proposed to underlie rhythm generation in pre-Bötzinger complex (pre-BötC) respiratory neurons, via two distinct pharmacological mechanisms: (1) pore obstruction mediated by tetrodotoxin and (2) altered inactivation dynamics mediated by riluzole. The reported effects of experimental application of tetrodotoxin and riluzole in respiratory circuits are diverse and seemingly contradictory and have led to considerable debate within the field as to the specific role of INaP in respiratory circuits. The results of our simulations match a wide array of experimental data spanning from the level of isolated pre-BötC neurons to the level of the intact respiratory network and also generate a series of experimentally testable predictions. Specifically, in this study we: (1) provide a mechanistic explanation for seemingly contradictory experimental results from in vitro studies of INaP block, (2) show that the effects of INaP block in in vitro preparations are not necessarily equivalent to those in more intact preparations, (3) demonstrate and explain why riluzole application may fail to effectively block INaP in the intact respiratory network, and (4) derive the prediction that effective block of INaP by low concentration tetrodotoxin will stop respiratory rhythm generation in the intact respiratory network. These simulations support a critical role for INaP in respiratory rhythmogenesis in vivo and illustrate the importance of considering mechanism when interpreting and simulating data relating to pharmacological blockade. The application of pharmacological agents that affect transmembrane ionic currents in neurons is a commonly used experimental technique. A simplistic interpretation of experiments involving these agents suggests that antagonist application removes the impacted current and that subsequently observed changes in activity are attributable to the loss of that current’s effects. The more complex reality, however, is that different drugs may have distinct mechanisms of action, some corresponding not to a removal of a current but rather to a changing of its properties. We use computational modeling to explore the implications of the distinct mechanisms associated with two drugs, riluzole and tetrodotoxin, that are often characterized as sodium channel blockers. Through this approach, we offer potential explanations for disparate findings observed in experiments on neural respiratory circuits and show that the experimental results are consistent with a key role for the persistent sodium current in respiratory rhythm generation.
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Affiliation(s)
- Ryan S. Phillips
- Department of Mathematics and Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
- * E-mail:
| | - Jonathan E. Rubin
- Department of Mathematics and Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
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22
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Robustness of respiratory rhythm generation across dynamic regimes. PLoS Comput Biol 2019; 15:e1006860. [PMID: 31361738 PMCID: PMC6697358 DOI: 10.1371/journal.pcbi.1006860] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 08/16/2019] [Accepted: 06/06/2019] [Indexed: 11/19/2022] Open
Abstract
A central issue in the study of the neural generation of respiratory rhythms is the role of the intrinsic pacemaking capabilities that some respiratory neurons exhibit. The debate on this issue has occurred in parallel to investigations of interactions among respiratory network neurons and how these contribute to respiratory behavior. In this computational study, we demonstrate how these two issues are inextricably linked. We use simulations and dynamical systems analysis to show that once a conditional respiratory pacemaker, which can be tuned across oscillatory and non-oscillatory dynamic regimes in isolation, is embedded into a respiratory network, its dynamics become masked: the network exhibits similar dynamical properties regardless of the conditional pacemaker node's tuning, and that node's outputs are dominated by network influences. Furthermore, the outputs of the respiratory central pattern generator as a whole are invariant to these changes of dynamical properties, which ensures flexible and robust performance over a wide dynamic range.
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23
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Phillips RS, John TT, Koizumi H, Molkov YI, Smith JC. Biophysical mechanisms in the mammalian respiratory oscillator re-examined with a new data-driven computational model. eLife 2019; 8:41555. [PMID: 30907727 PMCID: PMC6433470 DOI: 10.7554/elife.41555] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 02/07/2019] [Indexed: 12/11/2022] Open
Abstract
An autorhythmic population of excitatory neurons in the brainstem pre-Bötzinger complex is a critical component of the mammalian respiratory oscillator. Two intrinsic neuronal biophysical mechanisms—a persistent sodium current (INaP) and a calcium-activated non-selective cationic current (ICAN)—were proposed to individually or in combination generate cellular- and circuit-level oscillations, but their roles are debated without resolution. We re-examined these roles in a model of a synaptically connected population of excitatory neurons with ICAN and INaP. This model robustly reproduces experimental data showing that rhythm generation can be independent of ICAN activation, which determines population activity amplitude. This occurs when ICAN is primarily activated by neuronal calcium fluxes driven by synaptic mechanisms. Rhythm depends critically on INaP in a subpopulation forming the rhythmogenic kernel. The model explains how the rhythm and amplitude of respiratory oscillations involve distinct biophysical mechanisms.
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Affiliation(s)
- Ryan S Phillips
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States.,Department of Physics, University of New Hampshire, Durham, United States
| | - Tibin T John
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Hidehiko Koizumi
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Yaroslav I Molkov
- Department of Mathematics and Statistics, Georgia State University, Atlanta, United States.,Neuroscience Institute, Georgia State University, Atlanta, United States
| | - Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
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24
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Ramirez JM, Baertsch NA. Modeling breathing rhythms. eLife 2019; 8:46033. [PMID: 30907725 PMCID: PMC6433460 DOI: 10.7554/elife.46033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2019] [Accepted: 03/20/2019] [Indexed: 11/13/2022] Open
Abstract
Computational models are helping researchers to understand how certain properties of neurons contribute to respiratory rhythms.
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Affiliation(s)
- Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, United States.,Department of Neurological Surgery, University of Washington, Seattle, United States.,Department of Pediatrics, University of Washington, Seattle, United States
| | - Nathan A Baertsch
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, United States
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25
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Picardo MCD, Sugimura YK, Dorst KE, Kallurkar PS, Akins VT, Ma X, Teruyama R, Guinamard R, Kam K, Saha MS, Del Negro CA. Trpm4 ion channels in pre-Bötzinger complex interneurons are essential for breathing motor pattern but not rhythm. PLoS Biol 2019; 17:e2006094. [PMID: 30789900 PMCID: PMC6400419 DOI: 10.1371/journal.pbio.2006094] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Revised: 03/05/2019] [Accepted: 02/05/2019] [Indexed: 12/21/2022] Open
Abstract
Inspiratory breathing movements depend on pre-Bötzinger complex (preBötC) interneurons that express calcium (Ca2+)-activated nonselective cationic current (ICAN) to generate robust neural bursts. Hypothesized to be rhythmogenic, reducing ICAN is predicted to slow down or stop breathing; its contributions to motor pattern would be reflected in the magnitude of movements (output). We tested the role(s) of ICAN using reverse genetic techniques to diminish its putative ion channels Trpm4 or Trpc3 in preBötC neurons in vivo. Adult mice transduced with Trpm4-targeted short hairpin RNA (shRNA) progressively decreased the tidal volume of breaths yet surprisingly increased breathing frequency, often followed by gasping and fatal respiratory failure. Mice transduced with Trpc3-targeted shRNA survived with no changes in breathing. Patch-clamp and field recordings from the preBötC in mouse slices also showed an increase in the frequency and a decrease in the magnitude of preBötC neural bursts in the presence of Trpm4 antagonist 9-phenanthrol, whereas the Trpc3 antagonist pyrazole-3 (pyr-3) showed inconsistent effects on magnitude and no effect on frequency. These data suggest that Trpm4 mediates ICAN, whose influence on frequency contradicts a direct role in rhythm generation. We conclude that Trpm4-mediated ICAN is indispensable for motor output but not the rhythmogenic core mechanism of the breathing central pattern generator.
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Affiliation(s)
- Maria Cristina D. Picardo
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
| | - Yae K. Sugimura
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
| | - Kaitlyn E. Dorst
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
| | - Prajkta S. Kallurkar
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
| | - Victoria T. Akins
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
| | - Xingru Ma
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
| | - Ryoichi Teruyama
- Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, United States of America
| | - Romain Guinamard
- Signalisation, Electrophysiologie et Imagerie des Lésions d’Ischémie-Reperfusion Myocardique, Normandie Université, UNICAEN, Caen, France
| | - Kaiwen Kam
- Department of Cell Biology and Anatomy, Chicago Medical School, Rosalind Franklin University, Chicago, Illinois, United States of America
| | - Margaret S. Saha
- Department of Biology, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
| | - Christopher A. Del Negro
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, Virginia, United States of America
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26
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Yamanishi T, Koizumi H, Navarro MA, Milescu LS, Smith JC. Kinetic properties of persistent Na + current orchestrate oscillatory bursting in respiratory neurons. J Gen Physiol 2018; 150:1523-1540. [PMID: 30301870 PMCID: PMC6219691 DOI: 10.1085/jgp.201812100] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 08/14/2018] [Accepted: 09/19/2018] [Indexed: 01/08/2023] Open
Abstract
The rhythmic pattern of breathing depends on the pre-Bötzinger complex (preBötC) in the brainstem, a vital circuit that contains a population of neurons with intrinsic oscillatory bursting behavior. Here, we investigate the specific kinetic properties that enable voltage-gated sodium channels to establish oscillatory bursting in preBötC inspiratory neurons, which exhibit an unusually large persistent Na+ current (INaP). We first characterize the kinetics of INaP in neonatal rat brainstem slices in vitro, using whole-cell patch-clamp and computational modeling, and then test the contribution of INaP to rhythmic bursting in live neurons, using the dynamic clamp technique. We provide evidence that subthreshold activation, persistence at suprathreshold potentials, slow inactivation, and slow recovery from inactivation are kinetic features of INaP that regulate all aspects of intrinsic rhythmic bursting in preBötC neurons. The slow and cumulative inactivation of INaP during the burst active phase controls burst duration and termination, while the slow recovery from inactivation controls the duration of the interburst interval. To demonstrate this mechanism, we develop a Markov state model of INaP that explains a comprehensive set of voltage clamp data. By adding or subtracting a computer-generated INaP from a live neuron via dynamic clamp, we are able to convert nonbursters into intrinsic bursters, and vice versa. As a control, we test a model with inactivation features removed. Adding noninactivating INaP into nonbursters results in a pattern of random transitions between sustained firing and quiescence. The relative amplitude of INaP is the key factor that separates intrinsic bursters from nonbursters and can change the fraction of intrinsic bursters in the preBötC. INaP could thus be an important target for regulating network rhythmogenic properties.
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Affiliation(s)
- Tadashi Yamanishi
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD.,The First Department of Oral and Maxillofacial Surgery, Osaka University Graduate School of Dentistry, Osaka, Japan
| | - Hidehiko Koizumi
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD
| | - Marco A Navarro
- Division of Biological Sciences, University of Missouri, Columbia, MO
| | - Lorin S Milescu
- Division of Biological Sciences, University of Missouri, Columbia, MO
| | - Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD
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