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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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2
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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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3
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Roussel Y, Gaudreau SF, Kacer ER, Sengupta M, Bui TV. Modeling spinal locomotor circuits for movements in developing zebrafish. eLife 2021; 10:e67453. [PMID: 34473059 PMCID: PMC8492062 DOI: 10.7554/elife.67453] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 09/01/2021] [Indexed: 01/16/2023] Open
Abstract
Many spinal circuits dedicated to locomotor control have been identified in the developing zebrafish. How these circuits operate together to generate the various swimming movements during development remains to be clarified. In this study, we iteratively built models of developing zebrafish spinal circuits coupled to simplified musculoskeletal models that reproduce coiling and swimming movements. The neurons of the models were based upon morphologically or genetically identified populations in the developing zebrafish spinal cord. We simulated intact spinal circuits as well as circuits with silenced neurons or altered synaptic transmission to better understand the role of specific spinal neurons. Analysis of firing patterns and phase relationships helped to identify possible mechanisms underlying the locomotor movements of developing zebrafish. Notably, our simulations demonstrated how the site and the operation of rhythm generation could transition between coiling and swimming. The simulations also underlined the importance of contralateral excitation to multiple tail beats. They allowed us to estimate the sensitivity of spinal locomotor networks to motor command amplitude, synaptic weights, length of ascending and descending axons, and firing behavior. These models will serve as valuable tools to test and further understand the operation of spinal circuits for locomotion.
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Affiliation(s)
- Yann Roussel
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
- Blue Brain Project, École Polytechnique Fédérale de LausanneGenèveSwitzerland
| | - Stephanie F Gaudreau
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
| | - Emily R Kacer
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
| | - Mohini Sengupta
- Washington University School of Medicine, Department of NeuroscienceSt LouisUnited States
| | - Tuan V Bui
- Brain and Mind Research Institute, Centre for Neural Dynamics, Department of Biology, University of OttawaOttawaCanada
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4
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Baertsch NA, Bush NE, Burgraff NJ, Ramirez JM. Dual mechanisms of opioid-induced respiratory depression in the inspiratory rhythm-generating network. eLife 2021; 10:e67523. [PMID: 34402425 PMCID: PMC8390004 DOI: 10.7554/elife.67523] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Accepted: 08/14/2021] [Indexed: 12/20/2022] Open
Abstract
The analgesic utility of opioid-based drugs is limited by the life-threatening risk of respiratory depression. Opioid-induced respiratory depression (OIRD), mediated by the μ-opioid receptor (MOR), is characterized by a pronounced decrease in the frequency and regularity of the inspiratory rhythm, which originates from the medullary preBötzinger Complex (preBötC). To unravel the cellular- and network-level consequences of MOR activation in the preBötC, MOR-expressing neurons were optogenetically identified and manipulated in transgenic mice in vitro and in vivo. Based on these results, a model of OIRD was developed in silico. We conclude that hyperpolarization of MOR-expressing preBötC neurons alone does not phenocopy OIRD. Instead, the effects of MOR activation are twofold: (1) pre-inspiratory spiking is reduced and (2) excitatory synaptic transmission is suppressed, thereby disrupting network-driven rhythmogenesis. These dual mechanisms of opioid action act synergistically to make the normally robust inspiratory rhythm-generating network particularly prone to collapse when challenged with exogenous opioids.
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Affiliation(s)
- Nathan A Baertsch
- Center for Integrative Brain Research, Seattle Children’s Research InstituteSeattleUnited States
- Department of Pediatrics, University of WashingtonSeattleUnited States
| | - Nicholas E Bush
- Center for Integrative Brain Research, Seattle Children’s Research InstituteSeattleUnited States
| | - Nicholas J Burgraff
- Center for Integrative Brain Research, Seattle Children’s Research InstituteSeattleUnited States
| | - Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle Children’s Research InstituteSeattleUnited States
- Department of Pediatrics, University of WashingtonSeattleUnited States
- Department Neurological Surgery, University of WashingtonSeattleUnited States
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5
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Ashhad S, Feldman JL. Emergent Elements of Inspiratory Rhythmogenesis: Network Synchronization and Synchrony Propagation. Neuron 2020; 106:482-497.e4. [PMID: 32130872 PMCID: PMC11221628 DOI: 10.1016/j.neuron.2020.02.005] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Revised: 01/15/2020] [Accepted: 02/07/2020] [Indexed: 12/22/2022]
Abstract
We assessed the mechanism of mammalian breathing rhythmogenesis in the preBötzinger complex (preBötC) in vitro, where experimental tests remain inconsistent with hypotheses of canonical rhythmogenic cellular or synaptic mechanisms, i.e., pacemaker neurons or inhibition. Under rhythmic conditions, in each cycle, an inspiratory burst emerges as (presumptive) preBötC rhythmogenic neurons transition from aperiodic uncorrelated population spike activity to become increasingly synchronized during preinspiration (for ∼50-500 ms), which can trigger inspiratory bursts that propagate to motoneurons. In nonrhythmic conditions, antagonizing GABAA receptors can initiate this synchronization while inducing a higher conductance state in nonrhythmogenic preBötC output neurons. Our analyses uncover salient features of preBötC network dynamics where inspiratory bursts arise when and only when the preBötC rhythmogenic subpopulation strongly synchronizes to drive output neurons. Furthermore, downstream propagation of preBötC network activity, ultimately to motoneurons, is dependent on the strength of input synchrony onto preBötC output neurons exemplifying synchronous propagation of network activity.
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Affiliation(s)
- Sufyan Ashhad
- Department of Neurobiology, University of California, Los Angeles, Box 951763, Los Angeles, CA 90095-1763, USA
| | - Jack L Feldman
- Department of Neurobiology, University of California, Los Angeles, Box 951763, Los Angeles, CA 90095-1763, USA.
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6
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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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7
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Baertsch NA, Ramirez JM. Insights into the dynamic control of breathing revealed through cell-type-specific responses to substance P. eLife 2019; 8:51350. [PMID: 31804180 PMCID: PMC6957314 DOI: 10.7554/elife.51350] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2019] [Accepted: 12/04/2019] [Indexed: 12/23/2022] Open
Abstract
The rhythm generating network for breathing must continuously adjust to changing metabolic and behavioral demands. Here, we examined network-based mechanisms in the mouse preBötzinger complex using substance P, a potent excitatory modulator of breathing frequency and stability, as a tool to dissect network properties that underlie dynamic breathing. We find that substance P does not alter the balance of excitation and inhibition during breaths or the duration of the resulting refractory period. Instead, mechanisms of recurrent excitation between breaths are enhanced such that the rate that excitation percolates through the network is increased. We propose a conceptual framework in which three distinct phases of inspiration, the burst phase, refractory phase, and percolation phase, can be differentially modulated to control breathing dynamics and stability. Unraveling mechanisms that support this dynamic control may improve our understanding of nervous system disorders that destabilize breathing, many of which involve changes in brainstem neuromodulatory systems.
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Affiliation(s)
- Nathan A Baertsch
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, United States
| | - Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, United States.,Department of Neurological Surgery, University of Washington School of Medicine, Seattle, United States
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8
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Wei AD, Ramirez JM. Presynaptic Mechanisms and KCNQ Potassium Channels Modulate Opioid Depression of Respiratory Drive. Front Physiol 2019; 10:1407. [PMID: 31824331 PMCID: PMC6882777 DOI: 10.3389/fphys.2019.01407] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2019] [Accepted: 10/31/2019] [Indexed: 01/02/2023] Open
Abstract
Opioid-induced respiratory depression (OIRD) is the major cause of death associated with opioid analgesics and drugs of abuse, but the underlying cellular and molecular mechanisms remain poorly understood. We investigated opioid action in vivo in unanesthetized mice and in in vitro medullary slices containing the preBötzinger Complex (preBötC), a locus critical for breathing and inspiratory rhythm generation. Although hypothesized as a primary mechanism, we found that mu-opioid receptor (MOR1)-mediated GIRK activation contributed only modestly to OIRD. Instead, mEPSC recordings from genetically identified Dbx1-derived interneurons, essential for rhythmogenesis, revealed a prevalent presynaptic mode of action for OIRD. Consistent with MOR1-mediated suppression of presynaptic release as a major component of OIRD, Cacna1a KO slices lacking P/Q-type Ca2+ channels enhanced OIRD. Furthermore, OIRD was mimicked and reversed by KCNQ potassium channel activators and blockers, respectively. In vivo whole-body plethysmography combined with systemic delivery of GIRK- and KCNQ-specific potassium channel drugs largely recapitulated these in vitro results, and revealed state-dependent modulation of OIRD. We propose that respiratory failure from OIRD results from a general reduction of synaptic efficacy, leading to a state-dependent collapse of rhythmic network activity.
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Affiliation(s)
- Aguan D. Wei
- Seattle Children’s Research Institute, Center for Integrative Brain Research, Seattle, WA, United States
- Department of Neurological Surgery, University of Washington School of Medicine, Seattle, WA, United States
| | - Jan-Marino Ramirez
- Seattle Children’s Research Institute, Center for Integrative Brain Research, Seattle, WA, United States
- Department of Neurological Surgery, University of Washington School of Medicine, Seattle, WA, United States
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9
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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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10
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Kotani S, Yazawa I, Onimaru H, Izumizaki M. An aromatic substance, eugenol induces distinct depressant effects on respiratory activity in different postnatal developmental stages of the rat. Neurosci Res 2019; 155:20-26. [PMID: 31207260 DOI: 10.1016/j.neures.2019.06.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Revised: 05/18/2019] [Accepted: 06/13/2019] [Indexed: 11/15/2022]
Abstract
Eugenol modulates neuronal activity through actions on voltage-gated ionic channels and/or transient receptor potential channels. We previously suggested that eugenol inhibited cellular (and/or network) mechanisms essential for the maintenance of the respiratory burst activity in a brainstem-spinal cord preparation from newborn rat (postnatal day 0-3). Study of the distinct effects of eugenol in neonatal and later developmental stage rats may offer new information about postnatal developmental changes of respiratory neuron networks. In the present study, therefore, we compared effects of eugenol in an in vitro newborn rat preparation with those in an arterially perfused in situ preparation from juvenile rat (postnatal day 12-15). In the former preparation, application of 1 mM eugenol decreased respiratory rate and inspiratory burst duration. In contrast, in the latter preparation, 1 mM eugenol induced a gradual decrease in the amplitude of integrated phrenic nerve activity. Phrenic nerve activity gradually recovered at 25-30 min after washout with a burst duration similar to control values. We hypothesized that the depressant effects of eugenol were caused by inhibition of cell excitability in the neonatal rat in vitro preparation but by a reduction of synaptic interactions in the juvenile rat in situ preparation.
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Affiliation(s)
- Sayumi Kotani
- Department of Physiology, Showa University School of Medicine, Tokyo, 142-8555, Japan
| | - Itaru Yazawa
- Global Research Center for Innovative Life Science, Peptide Drug Innovation, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Tokyo, 142-8501, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Tokyo, 142-8555, Japan.
| | - Masahiko Izumizaki
- Department of Physiology, Showa University School of Medicine, Tokyo, 142-8555, Japan
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11
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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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12
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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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13
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Ramirez JM, Baertsch N. Defining the Rhythmogenic Elements of Mammalian Breathing. Physiology (Bethesda) 2019; 33:302-316. [PMID: 30109823 DOI: 10.1152/physiol.00025.2018] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Breathing's remarkable ability to adapt to changes in metabolic, environmental, and behavioral demands stems from a complex integration of its rhythm-generating network within the wider nervous system. Yet, this integration complicates identification of its specific rhythmogenic elements. Based on principles learned from smaller rhythmic networks of invertebrates, we define criteria that identify rhythmogenic elements of the mammalian breathing network and discuss how they interact to produce robust, dynamic breathing.
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Affiliation(s)
- Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, University of Washington School of Medicine , Seattle, Washington
| | - Nathan Baertsch
- Center for Integrative Brain Research, Seattle Children's Research Institute, University of Washington School of Medicine , Seattle, Washington
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14
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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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15
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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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Transient Receptor Potential Channels TRPM4 and TRPC3 Critically Contribute to Respiratory Motor Pattern Formation but not Rhythmogenesis in Rodent Brainstem Circuits. eNeuro 2018; 5:eN-NWR-0332-17. [PMID: 29435486 PMCID: PMC5806591 DOI: 10.1523/eneuro.0332-17.2018] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 01/12/2018] [Accepted: 01/16/2018] [Indexed: 12/17/2022] Open
Abstract
Transient receptor potential channel, TRPM4, the putative molecular substrate for Ca2+-activated nonselective cation current (ICAN), is hypothesized to generate bursting activity of pre-Bötzinger complex (pre-BötC) inspiratory neurons and critically contribute to respiratory rhythmogenesis. Another TRP channel, TRPC3, which mediates Na+/Ca2+ fluxes, may be involved in regulating Ca2+-related signaling, including affecting TRPM4/ICAN in respiratory pre-BötC neurons. However, TRPM4 and TRPC3 expression in pre-BötC inspiratory neurons and functional roles of these channels remain to be determined. By single-cell multiplex RT-PCR, we show mRNA expression for these channels in pre-BötC inspiratory neurons in rhythmically active medullary in vitro slices from neonatal rats and mice. Functional contributions were analyzed with pharmacological inhibitors of TRPM4 or TRPC3 in vitro as well as in mature rodent arterially perfused in situ brainstem-spinal cord preparations. Perturbations of respiratory circuit activity were also compared with those by a blocker of ICAN. Pharmacologically attenuating endogenous activation of TRPM4, TRPC3, or ICANin vitro similarly reduced the amplitude of inspiratory motoneuronal activity without significant perturbations of inspiratory frequency or variability of the rhythm. Amplitude perturbations were correlated with reduced inspiratory glutamatergic pre-BötC neuronal activity, monitored by multicellular dynamic calcium imaging in vitro. In more intact circuits in situ, the reduction of pre-BötC and motoneuronal inspiratory activity amplitude was accompanied by reduced post-inspiratory motoneuronal activity, without disruption of rhythm generation. We conclude that endogenously activated TRPM4, which likely mediates ICAN, and TRPC3 channels in pre-BötC inspiratory neurons play fundamental roles in respiratory pattern formation but are not critically involved in respiratory rhythm generation.
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Harris KD, Dashevskiy T, Mendoza J, Garcia AJ, Ramirez JM, Shea-Brown E. Different roles for inhibition in the rhythm-generating respiratory network. J Neurophysiol 2017; 118:2070-2088. [PMID: 28615332 PMCID: PMC5626906 DOI: 10.1152/jn.00174.2017] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 05/25/2017] [Accepted: 06/12/2017] [Indexed: 12/20/2022] Open
Abstract
Unraveling the interplay of excitation and inhibition within rhythm-generating networks remains a fundamental issue in neuroscience. We use a biophysical model to investigate the different roles of local and long-range inhibition in the respiratory network, a key component of which is the pre-Bötzinger complex inspiratory microcircuit. Increasing inhibition within the microcircuit results in a limited number of out-of-phase neurons before rhythmicity and synchrony degenerate. Thus unstructured local inhibition is destabilizing and cannot support the generation of more than one rhythm. A two-phase rhythm requires restructuring the network into two microcircuits coupled by long-range inhibition in the manner of a half-center. In this context, inhibition leads to greater stability of the two out-of-phase rhythms. We support our computational results with in vitro recordings from mouse pre-Bötzinger complex. Partial excitation block leads to increased rhythmic variability, but this recovers after blockade of inhibition. Our results support the idea that local inhibition in the pre-Bötzinger complex is present to allow for descending control of synchrony or robustness to adverse conditions like hypoxia. We conclude that the balance of inhibition and excitation determines the stability of rhythmogenesis, but with opposite roles within and between areas. These different inhibitory roles may apply to a variety of rhythmic behaviors that emerge in widespread pattern-generating circuits of the nervous system.NEW & NOTEWORTHY The roles of inhibition within the pre-Bötzinger complex (preBötC) are a matter of debate. Using a combination of modeling and experiment, we demonstrate that inhibition affects synchrony, period variability, and overall frequency of the preBötC and coupled rhythmogenic networks. This work expands our understanding of ubiquitous motor and cognitive oscillatory networks.
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Affiliation(s)
| | - Tatiana Dashevskiy
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington
| | - Joshua Mendoza
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington
| | - Alfredo J Garcia
- Institute for Integrative Physiology and Section of Emergency Medicine, University of Chicago, Chicago, Illinois; and
| | - Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington
- Department of Neurological Surgery, University of Washington School of Medicine, Seattle, Washington
| | - Eric Shea-Brown
- Department of Applied Mathematics, University of Washington, Seattle, Washington
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18
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Beltrán-Castillo S, Morgado-Valle C, Eugenín J. The Onset of the Fetal Respiratory Rhythm: An Emergent Property Triggered by Chemosensory Drive? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1015:163-192. [PMID: 29080027 DOI: 10.1007/978-3-319-62817-2_10] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The mechanisms responsible for the onset of respiratory activity during fetal life are unknown. The onset of respiratory rhythm may be a consequence of the genetic program of each of the constituents of the respiratory network, so they start to interact and generate respiratory cycles when reaching a certain degree of maturation. Alternatively, generation of cycles might require the contribution of recently formed sensory inputs that will trigger oscillatory activity in the nascent respiratory neural network. If this hypothesis is true, then sensory input to the respiratory generator must be already formed and become functional before the onset of fetal respiration. In this review, we evaluate the timing of the onset of the respiratory rhythm in comparison to the appearance of receptors, neurotransmitter machinery, and afferent projections provided by two central chemoreceptive nuclei, the raphe and locus coeruleus nuclei.
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Affiliation(s)
- Sebastián Beltrán-Castillo
- Laboratorio de Sistemas Neurales, Facultad de Química y Biología, Departamento de Biología, Universidad de Santiago de Chile, USACH, PO 9170022, Santiago, Chile
| | - Consuelo Morgado-Valle
- Centro de Investigaciones Cerebrales, Universidad Veracruzana, Campus Xalapa, Berlin 7, Fracc., Monte Magno Animas, C.P. 91190, Xalapa, Veracruz, Mexico.
| | - Jaime Eugenín
- Laboratorio de Sistemas Neurales, Facultad de Química y Biología, Departamento de Biología, Universidad de Santiago de Chile, USACH, PO 9170022, Santiago, Chile.
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Barkan CL, Zornik E, Kelley DB. Evolution of vocal patterns: tuning hindbrain circuits during species divergence. ACTA ACUST UNITED AC 2016; 220:856-867. [PMID: 28011819 DOI: 10.1242/jeb.146845] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 12/13/2016] [Indexed: 01/05/2023]
Abstract
The neural circuits underlying divergent courtship behaviors of closely related species provide a framework for insight into the evolution of motor patterns. In frogs, male advertisement calls serve as unique species identifiers and females prefer conspecific to heterospecific calls. Advertisement calls of three relatively recently (∼8.5 Mya) diverged species - Xenopus laevis, X. petersii and X. victorianus - include rapid trains of sound pulses (fast trills). We show that while fast trills are similar in pulse rate (∼60 pulses s-1) across the three species, they differ in call duration and period (time from the onset of one call to the onset of the following call). Previous studies of call production in X. laevis used an isolated brain preparation in which the laryngeal nerve produces compound action potentials that correspond to the advertisement call pattern (fictive calling). Here, we show that serotonin evokes fictive calling in X. petersii and X. victorianus as it does in X. laevis As in X. laevis, fictive fast trill in X. petersii and X. victorianus is accompanied by an N-methyl-d-aspartate receptor-dependent local field potential wave in a rostral hindbrain nucleus, DTAM. Across the three species, wave duration and period are strongly correlated with species-specific fast trill duration and period, respectively. When DTAM is isolated from the more rostral forebrain and midbrain and/or more caudal laryngeal motor nucleus, the wave persists at species-typical durations and periods. Thus, intrinsic differences within DTAM could be responsible for the evolutionary divergence of call patterns across these related species.
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Affiliation(s)
- Charlotte L Barkan
- Doctoral Program in Neurobiology and Behavior, Columbia University, New York, NY 10032, USA
| | - Erik Zornik
- Biology Department, Reed College, Portland, OR 97202, USA
| | - Darcy B Kelley
- Doctoral Program in Neurobiology and Behavior, Columbia University, New York, NY 10032, USA .,Department of Biological Sciences, Columbia University, New York, NY 10025, USA
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20
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Microcircuits in respiratory rhythm generation: commonalities with other rhythm generating networks and evolutionary perspectives. Curr Opin Neurobiol 2016; 41:53-61. [PMID: 27589601 DOI: 10.1016/j.conb.2016.08.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2016] [Revised: 08/16/2016] [Accepted: 08/17/2016] [Indexed: 02/07/2023]
Abstract
Rhythmicity is critical for the generation of rhythmic behaviors and higher brain functions. This review discusses common mechanisms of rhythm generation, including the role of synaptic inhibition and excitation, with a focus on the mammalian respiratory network. This network generates three phases of breathing and is highly integrated with brain regions associated with numerous non-ventilatory behaviors. We hypothesize that during evolution multiple rhythmogenic microcircuits were recruited to accommodate the generation of each breathing phase. While these microcircuits relied primarily on excitatory mechanisms, synaptic inhibition became increasingly important to coordinate the different microcircuits and to integrate breathing into a rich behavioral repertoire that links breathing to sensory processing, arousal, and emotions as well as learning and memory.
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21
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Robust network oscillations during mammalian respiratory rhythm generation driven by synaptic dynamics. Proc Natl Acad Sci U S A 2015. [PMID: 26195782 DOI: 10.1073/pnas.1421997112] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
How might synaptic dynamics generate synchronous oscillations in neuronal networks? We address this question in the preBötzinger complex (preBötC), a brainstem neural network that paces robust, yet labile, inspiration in mammals. The preBötC is composed of a few hundred neurons that alternate bursting activity with silent periods, but the mechanism underlying this vital rhythm remains elusive. Using a computational approach to model a randomly connected neuronal network that relies on short-term synaptic facilitation (SF) and depression (SD), we show that synaptic fluctuations can initiate population activities through recurrent excitation. We also show that a two-step SD process allows activity in the network to synchronize (bursts) and generate a population refractory period (silence). The model was validated against an array of experimental conditions, which recapitulate several processes the preBötC may experience. Consistent with the modeling assumptions, we reveal, by electrophysiological recordings, that SF/SD can occur at preBötC synapses on timescales that influence rhythmic population activity. We conclude that nondeterministic neuronal spiking and dynamic synaptic strengths in a randomly connected network are sufficient to give rise to regular respiratory-like rhythmic network activity and lability, which may play an important role in generating the rhythm for breathing and other coordinated motor activities in mammals.
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22
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Morquette P, Verdier D, Kadala A, Féthière J, Philippe AG, Robitaille R, Kolta A. An astrocyte-dependent mechanism for neuronal rhythmogenesis. Nat Neurosci 2015; 18:844-54. [PMID: 25938883 DOI: 10.1038/nn.4013] [Citation(s) in RCA: 105] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 04/02/2015] [Indexed: 12/22/2022]
Abstract
Communication between neurons rests on their capacity to change their firing pattern to encode different messages. For several vital functions, such as respiration and mastication, neurons need to generate a rhythmic firing pattern. Here we show in the rat trigeminal sensori-motor circuit for mastication that this ability depends on regulation of the extracellular Ca(2+) concentration ([Ca(2+)]e) by astrocytes. In this circuit, astrocytes respond to sensory stimuli that induce neuronal rhythmic activity, and their blockade with a Ca(2+) chelator prevents neurons from generating a rhythmic bursting pattern. This ability is restored by adding S100β, an astrocytic Ca(2+)-binding protein, to the extracellular space, while application of an anti-S100β antibody prevents generation of rhythmic activity. These results indicate that astrocytes regulate a fundamental neuronal property: the capacity to change firing pattern. These findings may have broad implications for many other neural networks whose functions depend on the generation of rhythmic activity.
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Affiliation(s)
- Philippe Morquette
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada
| | - Dorly Verdier
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada
| | - Aklesso Kadala
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada
| | - James Féthière
- Faculté de Pharmacie, Université de Montréal, Montréal, Québec, Canada
| | - Antony G Philippe
- 1] Faculté des Sciences du Sport, Université Montpellier 1, Montpellier, France. [2] Institut National de la Recherche Agronomique, UMR866 Dynamique Musculaire Et Métabolisme, Montpellier, France
| | - Richard Robitaille
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada
| | - Arlette Kolta
- 1] Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada. [2] Faculté de Médecine Dentaire and Réseau de Recherche en Santé Bucco-dentaire et Osseuse du Fonds de Recherche Québec-Santé, Université de Montréal, Montréal, Québec, Canada
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23
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Bui TV, Brownstone RM. Sensory-evoked perturbations of locomotor activity by sparse sensory input: a computational study. J Neurophysiol 2015; 113:2824-39. [PMID: 25673740 DOI: 10.1152/jn.00866.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 02/06/2015] [Indexed: 11/22/2022] Open
Abstract
Sensory inputs from muscle, cutaneous, and joint afferents project to the spinal cord, where they are able to affect ongoing locomotor activity. Activation of sensory input can initiate or prolong bouts of locomotor activity depending on the identity of the sensory afferent activated and the timing of the activation within the locomotor cycle. However, the mechanisms by which afferent activity modifies locomotor rhythm and the distribution of sensory afferents to the spinal locomotor networks have not been determined. Considering the many sources of sensory inputs to the spinal cord, determining this distribution would provide insights into how sensory inputs are integrated to adjust ongoing locomotor activity. We asked whether a sparsely distributed set of sensory inputs could modify ongoing locomotor activity. To address this question, several computational models of locomotor central pattern generators (CPGs) that were mechanistically diverse and generated locomotor-like rhythmic activity were developed. We show that sensory inputs restricted to a small subset of the network neurons can perturb locomotor activity in the same manner as seen experimentally. Furthermore, we show that an architecture with sparse sensory input improves the capacity to gate sensory information by selectively modulating sensory channels. These data demonstrate that sensory input to rhythm-generating networks need not be extensively distributed.
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Affiliation(s)
- Tuan V Bui
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada; Centre for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada;
| | - Robert M Brownstone
- Department of Surgery (Neurosurgery), Dalhousie University, Halifax, Nova Scotia, Canada; and Department of Medical Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada
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24
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Johnson SM, Hedrick MS, Krause BM, Nilles JP, Chapman MA. Respiratory neuron characterization reveals intrinsic bursting properties in isolated adult turtle brainstems (Trachemys scripta). Respir Physiol Neurobiol 2014; 224:52-61. [PMID: 25462012 DOI: 10.1016/j.resp.2014.11.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Revised: 11/03/2014] [Accepted: 11/06/2014] [Indexed: 11/25/2022]
Abstract
It is not known whether respiratory neurons with intrinsic bursting properties exist within ectothermic vertebrate respiratory control systems. Thus, isolated adult turtle brainstems spontaneously producing respiratory motor output were used to identify and classify respiratory neurons based on their firing pattern relative to hypoglossal (XII) nerve activity. Most respiratory neurons (183/212) had peak activity during the expiratory phase, while inspiratory, post-inspiratory, and novel pre-expiratory neurons were less common. During synaptic blockade conditions, ∼10% of respiratory neurons fired bursts of action potentials, with post-inspiratory cells (6/9) having the highest percentage of intrinsic burst properties. Most intrinsically bursting respiratory neurons were clustered at the level of the vagus (X) nerve root. Synaptic inhibition blockade caused seizure-like activity throughout the turtle brainstem, which shows that the turtle respiratory control system is not transformed into a network driven by intrinsically bursting respiratory neurons. We hypothesize that intrinsically bursting respiratory neurons are evolutionarily conserved and represent a potential rhythmogenic mechanism contributing to respiration in adult turtles.
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Affiliation(s)
- Stephen M Johnson
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, United States.
| | - Michael S Hedrick
- Department of Biological Sciences, California State University, East Bay, Hayward, CA 94542, United States
| | - Bryan M Krause
- Neuroscience Training Program, University of Wisconsin, Madison, WI 53706, United States
| | - Jacob P Nilles
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, United States
| | - Mark A Chapman
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, United States
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25
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Ramirez JM, Doi A, Garcia AJ, Elsen FP, Koch H, Wei AD. The cellular building blocks of breathing. Compr Physiol 2013; 2:2683-731. [PMID: 23720262 DOI: 10.1002/cphy.c110033] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Respiratory brainstem neurons fulfill critical roles in controlling breathing: they generate the activity patterns for breathing and contribute to various sensory responses including changes in O2 and CO2. These complex sensorimotor tasks depend on the dynamic interplay between numerous cellular building blocks that consist of voltage-, calcium-, and ATP-dependent ionic conductances, various ionotropic and metabotropic synaptic mechanisms, as well as neuromodulators acting on G-protein coupled receptors and second messenger systems. As described in this review, the sensorimotor responses of the respiratory network emerge through the state-dependent integration of all these building blocks. There is no known respiratory function that involves only a small number of intrinsic, synaptic, or modulatory properties. Because of the complex integration of numerous intrinsic, synaptic, and modulatory mechanisms, the respiratory network is capable of continuously adapting to changes in the external and internal environment, which makes breathing one of the most integrated behaviors. Not surprisingly, inspiration is critical not only in the control of ventilation, but also in the context of "inspiring behaviors" such as arousal of the mind and even creativity. Far-reaching implications apply also to the underlying network mechanisms, as lessons learned from the respiratory network apply to network functions in general.
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Affiliation(s)
- J M Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institut, Seattle, Washington, USA.
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26
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Montandon G, Horner RL. State-dependent contribution of the hyperpolarization-activated Na+/K+ and persistent Na+ currents to respiratory rhythmogenesis in vivo. J Neurosci 2013; 33:8716-28. [PMID: 23678115 PMCID: PMC6618818 DOI: 10.1523/jneurosci.5066-12.2013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Revised: 04/04/2013] [Accepted: 04/08/2013] [Indexed: 01/21/2023] Open
Abstract
How rhythms are generated by neuronal networks is fundamental to understand rhythmic behaviors such as respiration, locomotion, and mastication. Respiratory rhythm is generated by the preBötzinger complex (preBötC), an anatomically and functionally discrete population of brainstem neurons, central and necessary for respiratory rhythm. In specific in vitro conditions, preBötC neurons depend on voltage-dependent inward currents to generate respiratory rhythm. In the mature and intact organism, where preBötC neurons are deeply embedded in the respiratory network, the contribution of ionic currents to respiratory rhythm is unclear. We propose that a set of ionic currents plays a key role in generating respiratory rhythm in the mature organism in vivo. By microperfusing ionic current blockers into the preBötC of adult rats, we identify the hyperpolarization-activated cation current as a critical component of the mechanism promoting respiratory rhythm, and that this current, in combination with the persistent sodium current, is essential to respiratory rhythm in vivo. Importantly, both currents contribute to rhythmic activity in states of anesthesia, quiet wakefulness, and sleep, but not when the organism is engaged in active behaviors. These data show that a set of ionic currents at the preBötC imparts the network with rhythmicity in reduced states of arousal, although the network can override their contribution to adjust its activity for nonrhythmic behaviors in active wakefulness.
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Affiliation(s)
- Gaspard Montandon
- Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Richard L. Horner
- Departments of Medicine and Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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27
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Kang JJ, Wei XY, Liu JP, Wong-Riley MTT, Ju G, Liu YY. Expression of phospho-Ca(2+) /calmodulin-dependent protein kinase II in the pre-Bötzinger complex of rats. J Neurochem 2013; 126:349-59. [PMID: 23651084 DOI: 10.1111/jnc.12297] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2012] [Accepted: 05/06/2013] [Indexed: 11/28/2022]
Abstract
The pre-Bötzinger complex (pre-BötC) in the ventrolateral medulla oblongata is a presumed kernel of respiratory rhythmogenesis. Ca(2+) -activated non-selective cationic current is an essential cellular mechanism for shaping inspiratory drive potentials. Ca(2+) /calmodulin-dependent protein kinase II (CaMKII), an ideal 'interpreter' of diverse Ca(2+) signals, is highly expressed in neurons in mediating various physiological processes. Yet, less is known about CaMKII activity in the pre-BötC. Using neurokinin-1 receptor as a marker of the pre-BötC, we examined phospho (P)-CaMKII subcellular distribution, and found that P-CaMKII was extensively expressed in the region. P-CaMKII-ir neurons were usually oval, fusiform, or pyramidal in shape. P-CaMKII immunoreactivity was distributed within somas and dendrites, and specifically in association with the post-synaptic density. In dendrites, most synapses (93.1%) examined with P-CaMKII expression were of asymmetric type, occasionally with symmetric type (6.9%), whereas in somas, 38.1% were of symmetric type. P-CaMKII asymmetric synaptic identification implicates that CaMKII may sense and monitor Ca(2+) activity, and phosphorylate post-synaptic proteins to modulate excitatory synaptic transmission, which may contribute to respiratory modulation and plasticity. In somas, CaMKII acts on both symmetric and asymmetric synapses, mediating excitatory and inhibitory synaptic transmission. P-CaMKII was also localized to the perisynaptic and extrasynaptic regions in the pre-BötC.
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Affiliation(s)
- Jun-Jun Kang
- Institute of Neurosciences, The Fourth Military Medical University, Xi'an, China
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28
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Structural-functional properties of identified excitatory and inhibitory interneurons within pre-Botzinger complex respiratory microcircuits. J Neurosci 2013; 33:2994-3009. [PMID: 23407957 DOI: 10.1523/jneurosci.4427-12.2013] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
We comparatively analyzed cellular and circuit properties of identified rhythmic excitatory and inhibitory interneurons within respiratory microcircuits of the neonatal rodent pre-Bötzinger complex (pre-BötC), the structure generating inspiratory rhythm in the brainstem. We combined high-resolution structural-functional imaging, molecular assays for neurotransmitter phenotype identification in conjunction with electrophysiological property phenotyping, and morphological reconstruction of interneurons in neonatal rat and mouse slices in vitro. This approach revealed previously undifferentiated structural-functional features that distinguish excitatory and inhibitory interneuronal populations. We identified distinct subpopulations of pre-BötC glutamatergic, glycinergic, GABAergic, and glycine-GABA coexpressing interneurons. Most commissural pre-BötC inspiratory interneurons were glutamatergic, with a substantial subset exhibiting intrinsic oscillatory bursting properties. Commissural excitatory interneurons projected with nearly planar trajectories to the contralateral pre-BötC, many also with axon collaterals to areas containing inspiratory hypoglossal (XII) premotoneurons and motoneurons. Inhibitory neurons as characterized in the present study did not exhibit intrinsic oscillatory bursting properties, but were electrophysiologically distinguished by more pronounced spike frequency adaptation properties. Axons of many inhibitory neurons projected ipsilaterally also to regions containing inspiratory XII premotoneurons and motoneurons, whereas a minority of inhibitory neurons had commissural axonal projections. Dendrites of both excitatory and inhibitory interneurons were arborized asymmetrically, primarily in the coronal plane. The dendritic fields of inhibitory neurons were more spatially compact than those of excitatory interneurons. Our results are consistent with the concepts of a compartmental circuit organization, a bilaterally coupled excitatory rhythmogenic kernel, and a role of pre-BötC inhibitory neurons in shaping inspiratory pattern as well as coordinating inspiratory and expiratory activity.
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The rhythmic, transverse medullary slice preparation in respiratory neurobiology: contributions and caveats. Respir Physiol Neurobiol 2013; 186:236-53. [PMID: 23357617 DOI: 10.1016/j.resp.2013.01.011] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Revised: 01/18/2013] [Accepted: 01/21/2013] [Indexed: 11/23/2022]
Abstract
Our understanding of the sites and mechanisms underlying rhythmic breathing as well as the neuromodulatory control of respiratory rhythm, pattern, and respiratory motoneuron excitability during perinatal development has advanced significantly over the last 20 years. A major catalyst was the development in 1991 of the rhythmically-active medullary slice preparation, which provided precise mechanical and chemical control over the network as well as enhanced physical and optical access to key brainstem regions. Insights obtained in vitro have informed multiple mechanistic hypotheses. In vivo tests of these hypotheses, performed under conditions of reduced control and precision but more obvious physiological relevance, have clearly established the significance for respiratory neurobiology of the rhythmic slice preparation. We review the contributions of this preparation to current understanding/concepts in respiratory control, and outline the limitations of this approach in the context of studying rhythm and pattern generation, homeostatic control mechanisms and murine models of human genetic disorders that feature prominent breathing disturbances.
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Guinamard R, Simard C, Del Negro C. Flufenamic acid as an ion channel modulator. Pharmacol Ther 2013; 138:272-84. [PMID: 23356979 DOI: 10.1016/j.pharmthera.2013.01.012] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Accepted: 12/26/2012] [Indexed: 12/29/2022]
Abstract
Flufenamic acid has been known since the 1960s to have anti-inflammatory properties attributable to the reduction of prostaglandin synthesis. Thirty years later, flufenamic acid appeared to be an ion channel modulator. Thus, while its use in medicine diminished, its use in ionic channel research expanded. Flufenamic acid commonly not only affects non-selective cation channels and chloride channels, but also modulates potassium, calcium and sodium channels with effective concentrations ranging from 10(-6)M in TRPM4 channel inhibition to 10(-3)M in two-pore outwardly rectifying potassium channel activation. Because flufenamic acid effects develop and reverse rapidly, it is a convenient and widely used tool. However, given the broad spectrum of its targets, experimental results have to be interpreted cautiously. Here we provide an overview of ion channels targeted by flufenamic acid to aid in interpreting its effects at the molecular, cellular, and system levels. If it is used with good practices, flufenamic acid remains a useful tool for ion channel research. Understanding the targets of FFA may help reevaluate its physiological impacts and revive interest in its therapeutic potential.
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Smith JC, Abdala APL, Borgmann A, Rybak IA, Paton JFR. Brainstem respiratory networks: building blocks and microcircuits. Trends Neurosci 2012; 36:152-62. [PMID: 23254296 DOI: 10.1016/j.tins.2012.11.004] [Citation(s) in RCA: 269] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 11/10/2012] [Accepted: 11/12/2012] [Indexed: 01/18/2023]
Abstract
Breathing movements in mammals are driven by rhythmic neural activity generated within spatially and functionally organized brainstem neural circuits comprising the respiratory central pattern generator (CPG). This rhythmic activity provides homeostatic regulation of gases in blood and tissues and integrates breathing with other motor acts. We review new insights into the spatial-functional organization of key neural microcircuits of this CPG from recent multidisciplinary experimental and computational studies. The emerging view is that the microcircuit organization within the CPG allows the generation of multiple rhythmic breathing patterns and adaptive switching between them, depending on physiological or pathophysiological conditions. These insights open the possibility for site- and mechanism-specific interventions to treat various disorders of the neural control of breathing.
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Affiliation(s)
- Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, MD, USA.
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Abstract
Breathing is an essential behavior that presents a unique opportunity to understand how the nervous system functions normally, how it balances inherent robustness with a highly regulated lability, how it adapts to both rapidly and slowly changing conditions, and how particular dysfunctions result in disease. We focus on recent advancements related to two essential sites for respiratory rhythmogenesis: (a) the preBötzinger Complex (preBötC) as the site for the generation of inspiratory rhythm and (b) the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG) as the site for the generation of active expiration.
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Affiliation(s)
- Jack L Feldman
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1763, USA.
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Carroll MS, Ramirez JM. Cycle-by-cycle assembly of respiratory network activity is dynamic and stochastic. J Neurophysiol 2012; 109:296-305. [PMID: 22993257 DOI: 10.1152/jn.00830.2011] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Rhythmically active networks are typically composed of neurons that can be classified as silent, tonic spiking, or rhythmic bursting based on their intrinsic activity patterns. Within these networks, neurons are thought to discharge in distinct phase relationships with their overall network output, and it has been hypothesized that bursting pacemaker neurons may lead and potentially trigger cycle onsets. We used multielectrode recording from 72 experiments to test these ideas in rhythmically active slices containing the pre-Bötzinger complex, a region critical for breathing. Following synaptic blockade, respiratory neurons exhibited a gradient of intrinsic spiking to rhythmic bursting activities and thus defied an easy classification into bursting pacemaker and nonbursting categories. Features of their firing activity within the functional network were analyzed for correlation with subsequent rhythmic bursting in synaptic isolation. Higher firing rates through all phases of fictive respiration statistically predicted bursting pacemaker behavior. However, a cycle-by-cycle analysis indicated that respiratory neurons were stochastically activated with each burst. Intrinsically bursting pacemakers led some population bursts and followed others. This variability was not reproduced in traditional fully interconnected computational models, while sparsely connected network models reproduced these results both qualitatively and quantitatively. We hypothesize that pacemaker neurons do not act as clock-like drivers of the respiratory rhythm but rather play a flexible and dynamic role in the initiation and stabilization of each burst. Thus, at the behavioral level, each breath can be thought of as de novo assembly of a stochastic collaboration of network topology and intrinsic properties.
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Affiliation(s)
- Michael S Carroll
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, WA 98101, USA
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Lindsey BG, Rybak IA, Smith JC. Computational models and emergent properties of respiratory neural networks. Compr Physiol 2012; 2:1619-70. [PMID: 23687564 PMCID: PMC3656479 DOI: 10.1002/cphy.c110016] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Computational models of the neural control system for breathing in mammals provide a theoretical and computational framework bringing together experimental data obtained from different animal preparations under various experimental conditions. Many of these models were developed in parallel and iteratively with experimental studies and provided predictions guiding new experiments. This data-driven modeling approach has advanced our understanding of respiratory network architecture and neural mechanisms underlying generation of the respiratory rhythm and pattern, including their functional reorganization under different physiological conditions. Models reviewed here vary in neurobiological details and computational complexity and span multiple spatiotemporal scales of respiratory control mechanisms. Recent models describe interacting populations of respiratory neurons spatially distributed within the Bötzinger and pre-Bötzinger complexes and rostral ventrolateral medulla that contain core circuits of the respiratory central pattern generator (CPG). Network interactions within these circuits along with intrinsic rhythmogenic properties of neurons form a hierarchy of multiple rhythm generation mechanisms. The functional expression of these mechanisms is controlled by input drives from other brainstem components,including the retrotrapezoid nucleus and pons, which regulate the dynamic behavior of the core circuitry. The emerging view is that the brainstem respiratory network has rhythmogenic capabilities at multiple levels of circuit organization. This allows flexible, state-dependent expression of different neural pattern-generation mechanisms under various physiological conditions,enabling a wide repertoire of respiratory behaviors. Some models consider control of the respiratory CPG by pulmonary feedback and network reconfiguration during defensive behaviors such as cough. Future directions in modeling of the respiratory CPG are considered.
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Affiliation(s)
- Bruce G Lindsey
- Department of Molecular Pharmacology and Physiology and Neuroscience Program, University of South Florida College of Medicine, Tampa, Florida, USA.
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35
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Ben-Mabrouk F, Amos LB, Tryba AK. Metabotropic glutamate receptors (mGluR5) activate transient receptor potential canonical channels to improve the regularity of the respiratory rhythm generated by the pre-Bötzinger complex in mice. Eur J Neurosci 2012; 35:1725-37. [PMID: 22612431 DOI: 10.1111/j.1460-9568.2012.08091.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Metabotropic glutamate receptors (mGluRs) are hypothesized to play a key role in generating the central respiratory rhythm and other rhythmic activities driven by central pattern generators (e.g. locomotion). However, the functional role of mGluRs in rhythmic respiratory activity and many motor patterns is very poorly understood. Here, we used mouse respiratory brain-slice preparations containing the pre-Bötzinger complex (pre-BötC) to identify the role of group I mGluRs (mGluR1 and mGluR5) in respiratory rhythm generation. We found that activation of mGluR1/5 is not required for the pre-BötC to generate a respiratory rhythm. However, our data suggest that mGluR1 and mGluR5 differentially modulate the respiratory rhythm. Blocking endogenous mGluR5 activity with 2-Methyl-6-(phenylethynyl)pyridine (MPEP) decreases the inspiratory burst duration, burst area and frequency, whereas it increases the irregularity of the fictive eupneic inspiratory rhythm generated by the pre-BötC. In contrast, blocking mGluR1 reduces the frequency. Moreover, the mGluR1/5 agonist 3,5-dihydroxyphenylglycine increases the frequency and decreases the irregularity of the respiratory rhythm. Based on previous studies, we hypothesized that mGluR signaling decreases the irregularity of the respiratory rhythm by activating transient receptor potential canonical (TRPC) channels, which carry a non-specific cation current (ICAN). Indeed, 3,5-dihydroxyphenylglycine (DHPG) application reduces cycle-by-cycle variability and subsequent application of the TRPC channel blocker 1-[2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl]imidazole (SKF-96365) hydrochloride reverses this effect. Our data suggest that mGluR5 activation of ICAN-carrying TRPC channels plays an important role in governing the cycle-by-cycle variability of the respiratory rhythm. These data suggest that modulation of TRPC channels may correct irregular respiratory rhythms in some central neuronal diseases.
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Affiliation(s)
- Faiza Ben-Mabrouk
- Department of Physiology, Medical College of Wisconsin, 8701 Watertown Plank Rd, Milwaukee, WI 53226, USA
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Morquette P, Lavoie R, Fhima MD, Lamoureux X, Verdier D, Kolta A. Generation of the masticatory central pattern and its modulation by sensory feedback. Prog Neurobiol 2012; 96:340-55. [PMID: 22342735 DOI: 10.1016/j.pneurobio.2012.01.011] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Revised: 01/16/2012] [Accepted: 01/24/2012] [Indexed: 11/25/2022]
Abstract
The basic pattern of rhythmic jaw movements produced during mastication is generated by a neuronal network located in the brainstem and referred to as the masticatory central pattern generator (CPG). This network composed of neurons mostly associated to the trigeminal system is found between the rostral borders of the trigeminal motor nucleus and facial nucleus. This review summarizes current knowledge on the anatomical organization, the development, the connectivity and the cellular properties of these trigeminal circuits in relation to mastication. Emphasis is put on a population of rhythmogenic neurons in the dorsal part of the trigeminal sensory nucleus. These neurons have intrinsic bursting capabilities, supported by a persistent Na(+) current (I(NaP)), which are enhanced when the extracellular concentration of Ca(2+) diminishes. Presented evidence suggest that the Ca(2+) dependency of this current combined with its voltage-dependency could provide a mechanism for cortical and sensory afferent inputs to the nucleus to interact with the rhythmogenic properties of its neurons to adjust and adapt the rhythmic output. Astrocytes are postulated to contribute to this process by modulating the extracellular Ca(2+) concentration and a model is proposed to explain how functional microdomains defined by the boundaries of astrocytic syncitia may form under the influence of incoming inputs.
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Affiliation(s)
- Philippe Morquette
- Groupe de Recherche sur le Système Nerveux Central du FRSQ, Université de Montréal and Faculté de médecine dentaire, Université de Montréal, Canada
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Blitz DM, Nusbaum MP. Neural circuit flexibility in a small sensorimotor system. Curr Opin Neurobiol 2011; 21:544-52. [PMID: 21689926 DOI: 10.1016/j.conb.2011.05.019] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 05/02/2011] [Accepted: 05/24/2011] [Indexed: 01/06/2023]
Abstract
Neuronal circuits underlying rhythmic behaviors (central pattern generators: CPGs) can generate rhythmic motor output without sensory input. However, sensory input is pivotal for generating behaviorally relevant CPG output. Here we discuss recent work in the decapod crustacean stomatogastric nervous system (STNS) identifying cellular and synaptic mechanisms whereby sensory inputs select particular motor outputs from CPG circuits. This includes several examples in which sensory neurons regulate the impact of descending projection neurons on CPG circuits. This level of analysis is possible in the STNS due to the relatively unique access to identified circuit, projection, and sensory neurons. These studies are also revealing additional degrees of freedom in sensorimotor integration that underlie the extensive flexibility intrinsic to rhythmic motor systems.
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Affiliation(s)
- Dawn M Blitz
- 215 Stemmler Hall, Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, United States
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