1
|
John SR, Phillips RS, Rubin JE. A novel mechanism for ramping bursts based on slow negative feedback in model respiratory neurons. CHAOS (WOODBURY, N.Y.) 2024; 34:063131. [PMID: 38865093 PMCID: PMC11191356 DOI: 10.1063/5.0201472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Accepted: 05/24/2024] [Indexed: 06/13/2024]
Abstract
Recordings from pre-Bötzinger complex neurons responsible for the inspiratory phase of the respiratory rhythm reveal a ramping burst pattern, starting around the time that the transition from expiration to inspiration begins, in which the spike rate gradually rises until a transition into a high-frequency burst occurs. The spike rate increase along the burst is accompanied by a gradual depolarization of the plateau potential that underlies the spikes. These effects may be functionally important for inducing the onset of inspiration and hence maintaining effective respiration; however, most mathematical models for inspiratory bursting do not capture this activity pattern. Here, we study how the modulation of spike height and afterhyperpolarization via the slow inactivation of an inward current can support various activity patterns including ramping bursts. We use dynamical systems methods designed for multiple timescale systems, such as bifurcation analysis based on timescale decomposition and averaging over fast oscillations, to generate an understanding of and predictions about the specific dynamic effects that lead to ramping bursts. We also analyze how transitions between ramping and other activity patterns may occur with parameter changes, which could be associated with experimental manipulations, environmental conditions, and/or development.
Collapse
Affiliation(s)
- Sushmita R. John
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| | - Ryan S. Phillips
- Seattle Children’s Research Institute, Seattle, Washington 98109, USA
| | - Jonathan E. Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| |
Collapse
|
2
|
More-Potdar S, Golowasch J. Oscillatory network spontaneously recovers both activity and robustness after prolonged removal of neuromodulators. Front Cell Neurosci 2023; 17:1280575. [PMID: 38162002 PMCID: PMC10757639 DOI: 10.3389/fncel.2023.1280575] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2023] [Accepted: 11/08/2023] [Indexed: 01/03/2024] Open
Abstract
Robustness of neuronal activity is a property necessary for a neuronal network to withstand perturbations, which may otherwise disrupt or destroy the system. The robustness of complex systems has been shown to depend on a number of features of the system, including morphology and heterogeneity of the activity of the component neurons, size of the networks, synaptic connectivity, and neuromodulation. The activity of small networks, such as the pyloric network of the crustacean stomatogastric nervous system, appears to be robust despite some of the factors not being consistent with the expected properties of complex systems, e.g., small size and homogeneity of the synaptic connections. The activity of the pyloric network has been shown to be stable and robust in a neuromodulatory state-dependent manner. When neuromodulatory inputs are severed, activity is initially disrupted, losing both stability and robustness. Over the long term, however, stable activity homeostatically recovers without the restoration of neuromodulatory input. The question we address in this study is whether robustness can also be restored as the network reorganizes itself to compensate for the loss of neuromodulatory input and recovers the lost activity. Here, we use temperature changes as a perturbation to probe the robustness of the network's activity. We develop a simple metric of robustness, i.e., the variances of the network phase relationships, and show that robustness is indeed restored simultaneously along with its stable network activity, indicating that, whatever the reorganization of the network entails, it is deep enough also to restore this important property.
Collapse
Affiliation(s)
| | - Jorge Golowasch
- Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ, United States
| |
Collapse
|
3
|
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.
Collapse
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
| | | | | |
Collapse
|
4
|
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.
Collapse
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.
| |
Collapse
|
5
|
de Sousa Abreu RP, Bondarenko E, Feldman JL. Phase- and state-dependent modulation of breathing pattern by preBötzinger complex somatostatin expressing neurons. J Physiol 2022; 600:143-165. [PMID: 34783033 PMCID: PMC9261878 DOI: 10.1113/jp282002] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 11/12/2021] [Indexed: 01/03/2023] Open
Abstract
As neuronal subtypes are increasingly categorized, delineating their functional role is paramount. The preBötzinger complex (preBötC) subpopulation expressing the neuropeptide somatostatin (SST) is classified as mostly excitatory, inspiratory-modulated and not rhythmogenic. We further characterized their phenotypic identity: 87% were glutamatergic and the balance were glycinergic and/or GABAergic. We then used optogenetics to investigate their modulatory role in both anaesthetized and freely moving mice. In anaesthetized mice, short photostimulation (100 ms) of preBötC SST+ neurons modulated breathing-related variables in a combinatory phase- and state-dependent manner; changes in inspiratory duration, inspiratory peak amplitude (Amp), and phase were different at higher (≥2.5 Hz) vs. lower (<2.5 Hz) breathing frequency (f). Moreover, we observed a biphasic effect of photostimulation during expiration that is probabilistic, that is photostimulation given at the same phase in consecutive cycles can evoke opposite responses (lengthening vs. shortening of the phase). These unexpected probabilistic state- and phase-dependent responses to photostimulation exposed properties of the preBötC that were not predicted and cannot be readily accounted for in current models of preBötC pattern generation. In freely moving mice, prolonged photostimulation decreased f in normoxia, hypoxia or hypercapnia, and increased Amp and produced a phase advance, which was similar to the results in anaesthetized mice when f ≥ 2.5 Hz. We conclude that preBötC SST+ neurons are a key mediator of the extraordinary and essential lability of breathing pattern. KEY POINTS: PreBötzinger complex (preBötC) SST+ neurons, which modulate respiratory pattern but are not rhythmogenic, were transfected with channelrhodopsin to investigate phase- and state-dependent modulation of breathing pattern in anaesthetized and freely behaving mice in normoxia, hypoxia and hypercapnia. In anaesthetized mice, photostimulation during inspiration increased inspiratory duration and amplitude regardless of baseline f, yet the effects were more robust at higher f. In anaesthetized mice with low f (<2.5 Hz), photostimulation during expiration evoked either phase advance or phase delay, whereas in anaesthetized mice with high f (≥2.5 Hz) and in freely behaving mice in normoxia, hypoxia or hypercapnia, photostimulation always evoked phase advance. Phase- and state-dependency is a function of overall breathing network excitability. The f-dependent probabilistic modulation of breathing pattern by preBötC SST+ neurons was unexpected, requiring reconsideration of current models of preBötC function, which neither predict nor can readily account for such responses.
Collapse
Affiliation(s)
- Raquel P. de Sousa Abreu
- Department of Neurobiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, 90095
| | - Evgeny Bondarenko
- Department of Neurobiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, 90095
| | - Jack L. Feldman
- Department of Neurobiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, 90095
| |
Collapse
|
6
|
Burgraff NJ, Bush NE, Ramirez JM, Baertsch NA. Dynamic Rhythmogenic Network States Drive Differential Opioid Responses in the In Vitro Respiratory Network. J Neurosci 2021; 41:9919-9931. [PMID: 34697095 PMCID: PMC8638687 DOI: 10.1523/jneurosci.1329-21.2021] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 09/02/2021] [Accepted: 09/07/2021] [Indexed: 11/21/2022] Open
Abstract
Death from opioid overdose is typically caused by opioid-induced respiratory depression (OIRD). A particularly dangerous characteristic of OIRD is its apparent unpredictability. The respiratory consequences of opioids can be surprisingly inconsistent, even within the same individual. Despite significant clinical implications, most studies have focused on average dose-r esponses rather than individual variation, and there remains little insight into the etiology of this apparent unpredictability. The preBötzinger complex (preBötC) in the ventral medulla is an important site for generating the respiratory rhythm and OIRD. Here, using male and female C57-Bl6 mice in vitro, we demonstrate that the preBötC can assume different network states depending on the excitability of the preBötC and the intrinsic membrane properties of preBötC neurons. These network states predict the functional consequences of opioids in the preBötC, and depending on network state, respiratory rhythmogenesis can be either stabilized or suppressed by opioids. We hypothesize that the dynamic nature of preBötC rhythmogenic properties, required to endow breathing with remarkable flexibility, also plays a key role in the dangerous unpredictability of OIRD.SIGNIFICANCE STATEMENT Opioids can cause unpredictable, life-threatening suppression of breathing. This apparent unpredictability makes clinical management of opioids difficult while also making it challenging to define the underlying mechanisms of OIRD. Here, we find in brainstem slices that the preBötC, an opioid-sensitive subregion of the brainstem, has an optimal configuration of cellular and network properties that results in a maximally stable breathing rhythm. These properties are dynamic, and the state of each individual preBötC network relative to the optimal configuration of the network predicts how vulnerable rhythmogenesis is to the effects of opioids. These insights establish a framework for understanding how endogenous and exogenous modulation of the rhythmogenic state of the preBötC can increase or decrease the risk of OIRD.
Collapse
Affiliation(s)
- Nicholas J Burgraff
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington 98101
| | - Nicholas E Bush
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington 98101
| | - Jan M Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington 98101
- Departments of Pediatrics, University of Washington, Seattle, Washington 98195
- Neurological Surgery, University of Washington, Seattle, Washington 98195
| | - Nathan A Baertsch
- Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington 98101
- Departments of Pediatrics, University of Washington, Seattle, Washington 98195
| |
Collapse
|
7
|
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.
Collapse
|
8
|
The M-current works in tandem with the persistent sodium current to set the speed of locomotion. PLoS Biol 2020; 18:e3000738. [PMID: 33186352 PMCID: PMC7688130 DOI: 10.1371/journal.pbio.3000738] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Revised: 11/25/2020] [Accepted: 10/13/2020] [Indexed: 01/20/2023] Open
Abstract
The central pattern generator (CPG) for locomotion is a set of pacemaker neurons endowed with inherent bursting driven by the persistent sodium current (INaP). How they proceed to regulate the locomotor rhythm remained unknown. Here, in neonatal rodents, we identified a persistent potassium current critical in regulating pacemakers and locomotion speed. This current recapitulates features of the M-current (IM): a subthreshold noninactivating outward current blocked by 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone dihydrochloride (XE991) and enhanced by N-(2-chloro-5-pyrimidinyl)-3,4-difluorobenzamide (ICA73). Immunostaining and mutant mice highlight an important role of Kv7.2-containing channels in mediating IM. Pharmacological modulation of IM regulates the emergence and the frequency regime of both pacemaker and CPG activities and controls the speed of locomotion. Computational models captured these results and showed how an interplay between IM and INaP endows the locomotor CPG with rhythmogenic properties. Overall, this study provides fundamental insights into how IM and INaP work in tandem to set the speed of locomotion.
Collapse
|
9
|
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.
Collapse
|
10
|
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.
Collapse
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
| |
Collapse
|
11
|
Abstract
Breathing is a well-described, vital and surprisingly complex behaviour, with behavioural and physiological outputs that are easy to directly measure. Key neural elements for generating breathing pattern are distinct, compact and form a network amenable to detailed interrogation, promising the imminent discovery of molecular, cellular, synaptic and network mechanisms that give rise to the behaviour. Coupled oscillatory microcircuits make up the rhythmic core of the breathing network. Primary among these is the preBötzinger Complex (preBötC), which is composed of excitatory rhythmogenic interneurons and excitatory and inhibitory pattern-forming interneurons that together produce the essential periodic drive for inspiration. The preBötC coordinates all phases of the breathing cycle, coordinates breathing with orofacial behaviours and strongly influences, and is influenced by, emotion and cognition. Here, we review progress towards cracking the inner workings of this vital core.
Collapse
Affiliation(s)
- Christopher A Del Negro
- Department of Applied Science, Integrated Science Center, William & Mary, Williamsburg, VA, USA
| | - Gregory D Funk
- Department of Physiology, Neuroscience and Mental Health Institute, Women's and Children's Health Research Institute (WCHRI), Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Jack L Feldman
- Department of Neurobiology, David Geffen School of Medicine, Center for Health Sciences, University of California at Los Angeles, Los Angeles, CA, USA.
| |
Collapse
|
12
|
Berg RW. Neuronal Population Activity in Spinal Motor Circuits: Greater Than the Sum of Its Parts. Front Neural Circuits 2017; 11:103. [PMID: 29311842 PMCID: PMC5742103 DOI: 10.3389/fncir.2017.00103] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2017] [Accepted: 11/29/2017] [Indexed: 11/27/2022] Open
Abstract
The core elements of stereotypical movements such as locomotion, scratching and breathing are generated by networks in the lower brainstem and the spinal cord. Ensemble activities in spinal motor networks had until recently been merely a black box, but with the emergence of ultra-thin Silicon multi-electrode technology it was possible to reveal the spiking activity of larger parts of the network. A series of experiments revealed unexpected features of spinal networks, such as multiple spiking regimes and lognormal firing rate distributions. The lognormality renders the widespread idea of a typical firing rate ± standard deviation an ill-suited description, and therefore these findings define a new arithmetic of motor networks. Focusing on the population activity behind motor pattern generation this review summarizes this advance and discusses its implications.
Collapse
Affiliation(s)
- Rune W. Berg
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| |
Collapse
|
13
|
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.
Collapse
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
| |
Collapse
|
14
|
Functional Interactions between Mammalian Respiratory Rhythmogenic and Premotor Circuitry. J Neurosci 2017; 36:7223-33. [PMID: 27383596 DOI: 10.1523/jneurosci.0296-16.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 05/27/2016] [Indexed: 01/21/2023] Open
Abstract
UNLABELLED Breathing in mammals depends on rhythms that originate from the preBötzinger complex (preBötC) of the ventral medulla and a network of brainstem and spinal premotor neurons. The rhythm-generating core of the preBötC, as well as some premotor circuits, consist of interneurons derived from Dbx1-expressing precursors (Dbx1 neurons), but the structure and function of these networks remain incompletely understood. We previously developed a cell-specific detection and laser ablation system to interrogate respiratory network structure and function in a slice model of breathing that retains the preBötC, the respiratory-related hypoglossal (XII) motor nucleus and XII premotor circuits. In spontaneously rhythmic slices, cumulative ablation of Dbx1 preBötC neurons decreased XII motor output by ∼50% after ∼15 cell deletions, and then decelerated and terminated rhythmic function altogether as the tally increased to ∼85 neurons. In contrast, cumulatively deleting Dbx1 XII premotor neurons decreased motor output monotonically but did not affect frequency nor stop XII output regardless of the ablation tally. Here, we couple an existing preBötC model with a premotor population in several topological configurations to investigate which one may replicate the laser ablation experiments best. If the XII premotor population is a "small-world" network (rich in local connections with sparse long-range connections among constituent premotor neurons) and connected with the preBötC such that the total number of incoming synapses remains fixed, then the in silico system successfully replicates the in vitro laser ablation experiments. This study proposes a feasible configuration for circuits consisting of Dbx1-derived interneurons that generate inspiratory rhythm and motor pattern. SIGNIFICANCE STATEMENT To produce a breathing-related motor pattern, a brainstem core oscillator circuit projects to a population of premotor interneurons, but the assemblage of this network remains incompletely understood. Here we applied network modeling and numerical simulation to discover respiratory circuit configurations that successfully replicate photonic cell ablation experiments targeting either the core oscillator or premotor network, respectively. If premotor neurons are interconnected in a so-called "small-world" network with a fixed number of incoming synapses balanced between premotor and rhythmogenic neurons, then our simulations match their experimental benchmarks. These results provide a framework of experimentally testable predictions regarding the rudimentary structure and function of respiratory rhythm- and pattern-generating circuits in the brainstem of mammals.
Collapse
|
15
|
Abstract
Breathing is vital for survival but also interesting from the perspective of rhythm generation. This rhythmic behavior is generated within the brainstem and is thought to emerge through the interaction between independent oscillatory neuronal networks. In mammals, breathing is composed of three phases - inspiration, post-inspiration, and active expiration - and this article discusses the concept that each phase is generated by anatomically distinct rhythm-generating networks: the preBötzinger complex (preBötC), the post-inspiratory complex (PiCo), and the lateral parafacial nucleus (pF L), respectively. The preBötC was first discovered 25 years ago and was shown to be both necessary and sufficient for the generation of inspiration. More recently, networks have been described that are responsible for post-inspiration and active expiration. Here, we attempt to collate the current knowledge and hypotheses regarding how respiratory rhythms are generated, the role that inhibition plays, and the interactions between the medullary networks. Our considerations may have implications for rhythm generation in general.
Collapse
Affiliation(s)
- Tatiana M. Anderson
- Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, WA, USA
- Graduate Program for Neuroscience, University of Washington School of Medicine, Seattle, WA, USA
| | - Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle Children’s Research Institute, Seattle, WA, USA
- Department of Neurological Surgery and Pediatrics, University of Washington School of Medicine, Seattle, WA, USA
| |
Collapse
|
16
|
Oku Y, Hülsmann S. A computational model of the respiratory network challenged and optimized by data from optogenetic manipulation of glycinergic neurons. Neuroscience 2017; 347:111-122. [PMID: 28215988 DOI: 10.1016/j.neuroscience.2017.01.041] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2016] [Revised: 01/25/2017] [Accepted: 01/25/2017] [Indexed: 12/14/2022]
Abstract
The topology of the respiratory network in the brainstem has been addressed using different computational models, which help to understand the functional properties of the system. We tested a neural mass model by comparing the result of activation and inhibition of inhibitory neurons in silico with recently published results of optogenetic manipulation of glycinergic neurons [Sherman, et al. (2015) Nat Neurosci 18:408]. The comparison revealed that a five-cell type model consisting of three classes of inhibitory neurons [I-DEC, E-AUG, E-DEC (PI)] and two excitatory populations (pre-I/I) and (I-AUG) neurons can be applied to explain experimental observations made by stimulating or inhibiting inhibitory neurons by light sensitive ion channels.
Collapse
Affiliation(s)
- Yoshitaka Oku
- Department of Physiology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501, Japan.
| | - Swen Hülsmann
- Clinic for Anesthesiology, University Hospital Göttingen, Göttingen 37099, Germany; DFG Research Center for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), Göttingen, Germany.
| |
Collapse
|
17
|
Lal A, Oku Y, Someya H, Miwakeichi F, Tamura Y. Emergent Network Topology within the Respiratory Rhythm-Generating Kernel Evolved In Silico. PLoS One 2016; 11:e0154049. [PMID: 27152967 PMCID: PMC4859517 DOI: 10.1371/journal.pone.0154049] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Accepted: 04/07/2016] [Indexed: 12/30/2022] Open
Abstract
We hypothesize that the network topology within the pre-Bötzinger Complex (preBötC), the mammalian respiratory rhythm generating kernel, is not random, but is optimized in the course of ontogeny/phylogeny so that the network produces respiratory rhythm efficiently and robustly. In the present study, we attempted to identify topology of synaptic connections among constituent neurons of the preBötC based on this hypothesis. To do this, we first developed an effective evolutionary algorithm for optimizing network topology of a neuronal network to exhibit a ‘desired characteristic’. Using this evolutionary algorithm, we iteratively evolved an in silico preBötC ‘model’ network with initial random connectivity to a network exhibiting optimized synchronous population bursts. The evolved ‘idealized’ network was then analyzed to gain insight into: (1) optimal network connectivity among different kinds of neurons—excitatory as well as inhibitory pacemakers, non-pacemakers and tonic neurons—within the preBötC, and (2) possible functional roles of inhibitory neurons within the preBötC in rhythm generation. Obtained results indicate that (1) synaptic distribution within excitatory subnetwork of the evolved model network illustrates skewed/heavy-tailed degree distribution, and (2) inhibitory subnetwork influences excitatory subnetwork primarily through non-tonic pacemaker inhibitory neurons. Further, since small-world (SW) network is generally associated with network synchronization phenomena and is suggested as a possible network structure within the preBötC, we compared the performance of SW network with that of the evolved model network. Results show that evolved network is better than SW network at exhibiting synchronous bursts.
Collapse
Affiliation(s)
- Amit Lal
- Department of Biomedical Engineering, Peking University, Beijing, 100871 P. R. China
| | - Yoshitaka Oku
- Department of Physiology, Hyogo College of Medicine, Nishinomiya, 663-8501 Japan
- * E-mail:
| | - Hiroshi Someya
- School of Information Science and Technology, Tokai University, Hiratsuka, 259-1292 Japan
| | - Fumikazu Miwakeichi
- Department of Statistical Modeling, The Institute of Statistical Mathematics, Tachikawa, 190-8562 Japan
- Department of Statistical Science, School of Multidisciplinary Sciences, The Graduate University for Advanced Studies, Tachikawa, 190-8562, Japan
| | - Yoshiyasu Tamura
- Department of Statistical Modeling, The Institute of Statistical Mathematics, Tachikawa, 190-8562 Japan
- Department of Statistical Science, School of Multidisciplinary Sciences, The Graduate University for Advanced Studies, Tachikawa, 190-8562, Japan
| |
Collapse
|
18
|
Feldman JL, Kam K. Facing the challenge of mammalian neural microcircuits: taking a few breaths may help. J Physiol 2015; 593:3-23. [PMID: 25556783 DOI: 10.1113/jphysiol.2014.277632] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Accepted: 11/01/2014] [Indexed: 12/27/2022] Open
Abstract
Breathing in mammals is a seemingly straightforward behaviour controlled by the brain. A brainstem nucleus called the preBötzinger Complex sits at the core of the neural circuit generating respiratory rhythm. Despite the discovery of this microcircuit almost 25 years ago, the mechanisms controlling breathing remain elusive. Given the apparent simplicity and well-defined nature of regulatory breathing behaviour, the identification of much of the circuitry, and the ability to study breathing in vitro as well as in vivo, many neuroscientists and physiologists are surprised that respiratory rhythm generation is still not well understood. Our view is that conventional rhythmogenic mechanisms involving pacemakers, inhibition or bursting are problematic and that simplifying assumptions commonly made for many vertebrate neural circuits ignore consequential detail. We propose that novel emergent mechanisms govern the generation of respiratory rhythm. That a mammalian function as basic as rhythm generation arises from complex and dynamic molecular, synaptic and neuronal interactions within a diverse neural microcircuit highlights the challenges in understanding neural control of mammalian behaviours, many (considerably) more elaborate than breathing. We suggest that the neural circuit controlling breathing is inimitably tractable and may inspire general strategies for elucidating other neural microcircuits.
Collapse
Affiliation(s)
- Jack L Feldman
- Systems Neurobiology Laboratory, Department of Neurobiology, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, USA
| | | |
Collapse
|
19
|
Rybak IA, Molkov YI, Jasinski PE, Shevtsova NA, Smith JC. Rhythmic bursting in the pre-Bötzinger complex: mechanisms and models. PROGRESS IN BRAIN RESEARCH 2015; 209:1-23. [PMID: 24746040 DOI: 10.1016/b978-0-444-63274-6.00001-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
The pre-Bötzinger complex (pre-BötC), a neural structure involved in respiratory rhythm generation, can generate rhythmic bursting activity in vitro that persists after blockade of synaptic inhibition. Experimental studies have identified two mechanisms potentially involved in this activity: one based on the persistent sodium current (INaP) and the other involving calcium (ICa) and/or calcium-activated nonspecific cation (ICAN) currents. In this modeling study, we investigated bursting generated in single neurons and excitatory neural populations with randomly distributed conductances of INaP and ICa. We analyzed the possible roles of these currents, the Na(+)/K(+) pump, synaptic mechanisms, and network interactions in rhythmic bursting generated under different conditions. We show that a population of synaptically coupled excitatory neurons with randomly distributed INaP- and/or ICAN-mediated burst generating mechanisms can operate in different oscillatory regimes with bursting dependent on either current or independent of both. The existence of multiple oscillatory regimes and their state dependence may explain rhythmic activities observed in the pre-BötC under different conditions.
Collapse
Affiliation(s)
- Ilya A Rybak
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA.
| | - Yaroslav I Molkov
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA; Department of Mathematical Sciences, Indiana University-Purdue University, Indianapolis, IN, USA
| | - Patrick E Jasinski
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Natalia A Shevtsova
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
| |
Collapse
|
20
|
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.
Collapse
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
| |
Collapse
|
21
|
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.
Collapse
Affiliation(s)
- J M Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institut, Seattle, Washington, USA.
| | | | | | | | | | | |
Collapse
|
22
|
Distinct inspiratory rhythm and pattern generating mechanisms in the preBötzinger complex. J Neurosci 2013; 33:9235-45. [PMID: 23719793 DOI: 10.1523/jneurosci.4143-12.2013] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
In the mammalian respiratory central pattern generator, the preBötzinger complex (preBötC) produces rhythmic bursts that drive inspiratory motor output. Cellular mechanisms initiated by each burst are hypothesized to be necessary to determine the timing of the subsequent burst, playing a critical role in rhythmogenesis. To explore mechanisms relating inspiratory burst generation to rhythmogenesis, we compared preBötC and hypoglossal (XII) nerve motor activity in medullary slices from neonatal mice in conditions where periods between successive inspiratory XII bursts were highly variable and distributed multimodally. This pattern resulted from rhythmic preBötC neural population activity that consisted of bursts, concurrent with XII bursts, intermingled with significantly smaller "burstlets". Burstlets occurred at regular intervals during significantly longer XII interburst intervals, at times when a XII burst was expected. When a preBötC burst occurred, its high amplitude inspiratory component (I-burst) was preceded by a preinspiratory component that closely resembled the rising phase of burstlets. Cadmium (8 μM) eliminated preBötC and XII bursts, but rhythmic preBötC burstlets persisted. Burstlets and preinspiratory activity were observed in ~90% of preBötC neurons that were active during I-bursts. When preBötC excitability was raised significantly, burstlets could leak through to motor output in medullary slices and in vivo in adult anesthetized rats. Thus, rhythmic bursting, a fundamental mode of nervous system activity and an essential element of breathing, can be deconstructed into a rhythmogenic process producing low amplitude burstlets and preinspiratory activity that determine timing, and a pattern-generating process producing suprathreshold I-bursts essential for motor output.
Collapse
|
23
|
Tsuruyama K, Hsiao CF, Chandler SH. Participation of a persistent sodium current and calcium-activated nonspecific cationic current to burst generation in trigeminal principal sensory neurons. J Neurophysiol 2013; 110:1903-14. [PMID: 23883859 DOI: 10.1152/jn.00410.2013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The properties of neurons participating in masticatory rhythmogenesis are not clearly understood. Neurons within the dorsal trigeminal principal sensory nucleus (dPrV) are potential candidates as components of the masticatory central pattern generator (CPG). The present study examines in detail the ionic mechanisms controlling burst generation in dPrV neurons in rat (postnatal day 8-12) brain stem slices using whole cell and perforated patch-clamp methods. Nominal extracellular Ca(2+) concentration transformed tonic discharge in response to a maintained step pulse of current into rhythmical bursting in 38% of nonbursting neurons. This change in discharge mode was suppressed by riluzole, a persistent Na(+) current (INaP) antagonist. Veratridine, which suppresses the Na(+) channel inactivation mechanism, induced rhythmical bursting in nonbursting neurons in normal artificial cerebrospinal fluid, suggesting that INaP contributes to burst generation. Nominal extracellular Ca(2+) exposed a prominent afterdepolarizing potential (ADP) following a single spike induced by a 3-ms current pulse, which was suppressed, but not completely blocked, by riluzole. Application of BAPTA, a Ca(2+) chelator, intracellularly, or flufenamic acid, a Ca(2+)-activated nonspecific cationic channel (ICAN) antagonist, extracellularly to the bath, suppressed rhythmical bursting and the postspike ADP. Application of drugs to alter Ca(2+) release from endoplasmic reticulum also suppressed bursting. Finally, voltage-clamp methods demonstrated that nominal Ca(2+) facilitated INaP and induced ICAN. These data demonstrate for the first time that the previously observed induction in dPrV neurons of rhythmical bursting in nominal Ca(2+) is mediated by enhancement of INaP and onset of ICAN, which are dependent on intracellular Ca(2+).
Collapse
Affiliation(s)
- Kentaro Tsuruyama
- Department of Integrative Biology and Physiology and the Brain Research Institute, University of California at Los Angeles, California
| | | | | |
Collapse
|
24
|
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.
Collapse
|
25
|
Jasinski PE, Molkov YI, Shevtsova NA, Smith JC, Rybak IA. Sodium and calcium mechanisms of rhythmic bursting in excitatory neural networks of the pre-Bötzinger complex: a computational modelling study. Eur J Neurosci 2013; 37:212-30. [PMID: 23121313 PMCID: PMC3659238 DOI: 10.1111/ejn.12042] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2012] [Revised: 08/13/2012] [Accepted: 09/26/2012] [Indexed: 11/29/2022]
Abstract
The neural mechanisms generating rhythmic bursting activity in the mammalian brainstem, particularly in the pre-Bötzinger complex (pre-BötC), which is involved in respiratory rhythm generation, and in the spinal cord (e.g. locomotor rhythmic activity) that persist after blockade of synaptic inhibition remain poorly understood. Experimental studies in rodent medullary slices containing the pre-BötC identified two mechanisms that could potentially contribute to the generation of rhythmic bursting: one based on the persistent Na(+) current (I(NaP)), and the other involving the voltage-gated Ca(2+) current (I(Ca)) and the Ca(2+) -activated nonspecific cation current (I(CAN)), activated by intracellular Ca(2+) accumulated from extracellular and intracellular sources. However, the involvement and relative roles of these mechanisms in rhythmic bursting are still under debate. In this theoretical/modelling study, we investigated Na(+)-dependent and Ca(2+)-dependent bursting generated in single cells and heterogeneous populations of synaptically interconnected excitatory neurons with I(NaP) and I(Ca) randomly distributed within populations. We analysed the possible roles of network connections, ionotropic and metabotropic synaptic mechanisms, intracellular Ca(2+) release, and the Na(+)/K(+) pump in rhythmic bursting generated under different conditions. We show that a heterogeneous population of excitatory neurons can operate in different oscillatory regimes with bursting dependent on I(NaP) and/or I(CAN), or independent of both. We demonstrate that the operating bursting mechanism may depend on neuronal excitation, synaptic interactions within the network, and the relative expression of particular ionic currents. The existence of multiple oscillatory regimes and their state dependence demonstrated in our models may explain different rhythmic activities observed in the pre-BötC and other brainstem/spinal cord circuits under different experimental conditions.
Collapse
Affiliation(s)
- Patrick E. Jasinski
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Yaroslav I. Molkov
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
- Department of Mathematical Sciences, Indiana University – Purdue University, Indianapolis, IN, USA
| | - Natalia A. Shevtsova
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Jeffrey C. Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA
| | - Ilya A. Rybak
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| |
Collapse
|
26
|
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.
Collapse
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.
| | | | | | | | | |
Collapse
|
27
|
Toporikova N, Butera RJ. Dynamics of neuromodulatory feedback determines frequency modulation in a reduced respiratory network: a computational study. Respir Physiol Neurobiol 2012. [PMID: 23202052 DOI: 10.1016/j.resp.2012.11.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Neuromodulators, such as amines and neuropeptides, alter the activity of neurons and neuronal networks. In this work, we investigate how neuromodulators, which activate G(q)-protein second messenger systems, can modulate the bursting frequency of neurons in a critical portion of the respiratory neural network, the pre-Bötzinger complex (preBötC). These neurons are a vital part of the ponto-medullary neuronal network, which generates a stable respiratory rhythm whose frequency is regulated by neuromodulator release from the nearby Raphe nucleus. Using a simulated 50-cell network of excitatory preBötC neurons with a heterogeneous distribution of persistent sodium conductance and Ca(2+), we determined conditions for frequency modulation in such a network by simulating interaction between Raphe and preBötC nuclei. We found that the positive feedback between the Raphe excitability and preBötC activity induces frequency modulation in the preBötC neurons. In addition, the frequency of the respiratory rhythm can be regulated via phasic release of excitatory neuromodulators from the Raphe nucleus. We predict that the application of a G(q) antagonist will eliminate this frequency modulation by the Raphe and keep the network frequency constant and low. In contrast, application of a G(q) agonist will result in a high frequency for all levels of Raphe stimulation. Our modeling results also suggest that high [K(+)] requirement in respiratory brain slice experiments may serve as a compensatory mechanism for low neuromodulatory tone.
Collapse
Affiliation(s)
- Natalia Toporikova
- Department of Biology, Washington and Lee University, Lexington, VA, USA
| | | |
Collapse
|
28
|
Martell AL, Ramirez JM, Lasky RE, Dwyer JE, Kohrman M, van Drongelen W. The role of voltage dependence of the NMDA receptor in cellular and network oscillation. Eur J Neurosci 2012; 36:2121-36. [PMID: 22805058 DOI: 10.1111/j.1460-9568.2012.08083.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Unraveling the mechanisms underlying oscillatory behavior is critical for understanding normal and pathological brain processes. Here we used electrophysiology in mouse neocortical slices and principles of nonlinear dynamics to demonstrate how an increase in the N-methyl-d-aspartic acid receptor (NMDAR) conductance can create a nonlinear whole-cell current-voltage (I-V) relationship which leads to changes in cellular stability. We discovered two behaviorally and morphologically distinct pyramidal cell populations. Under control conditions, both cell types responded to depolarizing current injection with regular spiking patterns. However, upon NMDAR activation, an intrinsic oscillatory (IO) cell type (n = 44) showed a nonlinear whole-cell I-V relationship, intrinsic voltage-dependent oscillations plus amplification of alternating input current, and these properties persisted after disabling action potential generation with tetrodotoxin (TTX). The other non-oscillatory (NO) neuronal population (n = 24) demonstrated none of these behaviors. Simultaneous intra- and extracellular recordings demonstrated the NMDAR's capacity to promote low-frequency seizure-like network oscillations via its effects on intrinsic neuronal properties. The two pyramidal cell types demonstrated different relationships with network oscillation--the IO cells were leaders that were activated early in the population activity cycle while the activation of the NO cell type was distributed across network bursts. The properties of IO neurons disappeared in a low-magnesium environment where the voltage dependence of the receptor is abolished; concurrently, the cellular contribution to network oscillation switched to synchronous firing. Thus, depending upon the efficacy of NMDAR in altering the linearity of the whole-cell I-V relationship, the two cell populations played different roles in sustaining network oscillation.
Collapse
Affiliation(s)
- Amber L Martell
- Department of Pediatrics, The University of Chicago, KCBD 4124, 900 E 57th Street, Chicago, IL 60637, USA
| | | | | | | | | | | |
Collapse
|
29
|
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.
Collapse
Affiliation(s)
- Jack L Feldman
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1763, USA.
| | | | | |
Collapse
|
30
|
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.
Collapse
Affiliation(s)
- Bruce G Lindsey
- Department of Molecular Pharmacology and Physiology and Neuroscience Program, University of South Florida College of Medicine, Tampa, Florida, USA.
| | | | | |
Collapse
|
31
|
Crone SA, Viemari JC, Droho S, Mrejeru A, Ramirez JM, Sharma K. Irregular Breathing in Mice following Genetic Ablation of V2a Neurons. J Neurosci 2012; 32:7895-906. [PMID: 22674265 PMCID: PMC3652431 DOI: 10.1523/jneurosci.0445-12.2012] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Neural networks called central pattern generators (CPGs) generate repetitive motor behaviors such as locomotion and breathing. Glutamatergic neurons are required for the generation and inhibitory neurons for the patterning of the motor activity associated with repetitive motor behaviors. In the mouse, glutamatergic V2a neurons coordinate the activity of left and right leg CPGs in the spinal cord enabling mice to generate an alternating gait. Here, we investigate the role of V2a neurons in the neural control of breathing, an essential repetitive motor behavior. We find that, following the ablation of V2a neurons, newborn mice breathe at a lower frequency. Recordings of respiratory activity in brainstem-spinal cord and respiratory slice preparations demonstrate that mice lacking V2a neurons are deficient in central respiratory rhythm generation. The absence of V2a neurons in the respiratory slice preparation can be compensated for by bath application of neurochemicals known to accelerate the breathing rhythm. In this slice preparation, V2a neurons exhibit a tonic firing pattern. The existence of direct connections between V2a neurons in the medial reticular formation and neurons of the pre-Bötzinger complex indicates that V2a neurons play a direct role in the function of the respiratory CPG in newborn mice. Thus, neurons of the embryonic V2a lineage appear to have been recruited to neural networks that control breathing and locomotion, two prominent CPG-driven, repetitive motor behaviors.
Collapse
Affiliation(s)
| | - Jean-Charles Viemari
- 4Institut de Neurosciences de la Timone, Laboratoire P3M, UMR 7289–CNRS–Aix Marseille University, 13385 Marseille Cedex 05, France, and
| | - Steven Droho
- 1Department of Neurobiology,
- 2Committee on Developmental Biology, and
| | - Ana Mrejeru
- 3Committee on Neurobiology, University of Chicago, Chicago, Illinois 60637,
| | - Jan-Marino Ramirez
- 3Committee on Neurobiology, University of Chicago, Chicago, Illinois 60637,
- 5Center for Integrative Brain Research, Seattle Children's Research Institute, Department of Neurological Surgery, University of Washington, Seattle, Washington 98101
| | - Kamal Sharma
- 1Department of Neurobiology,
- 2Committee on Developmental Biology, and
- 3Committee on Neurobiology, University of Chicago, Chicago, Illinois 60637,
| |
Collapse
|
32
|
Mellen NM, Thoby-Brisson M. Respiratory circuits: development, function and models. Curr Opin Neurobiol 2012; 22:676-85. [PMID: 22281058 DOI: 10.1016/j.conb.2012.01.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 01/04/2012] [Accepted: 01/04/2012] [Indexed: 01/27/2023]
Abstract
Breathing is a rhythmic motor behavior generated and controlled by hindbrain neuronal networks. Respiratory motor output arises from two distinct, but functionally interacting, rhythmogenic networks: the pre-Bötzinger complex (preBötC) and the retrotrapezoïd nucleus/parafacial respiratory group (RTN/pFRG). This review outlines recent advances in delineating the genetic specification of the neuronal constituents of these two rhythmogenic networks, their respective roles in respiratory function and how they interact to constitute a functional respiratory circuit ensemble. The often lethal consequences of disruption to these networks found in naturally occurring developmental disorders, transgenic animals, and highly specific lesion studies are described. In addition, we discuss how recent computational models enhance our understanding of how respiratory networks generate and regulate respiratory behavior.
Collapse
Affiliation(s)
- Nicholas M Mellen
- Department of Pediatrics, University of Louisville, School of Medicine, Louisville, KY 40202-3830, USA
| | | |
Collapse
|
33
|
Fietkiewicz C, Loparo KA, Wilson CG. Drive latencies in hypoglossal motoneurons indicate developmental change in the brainstem respiratory network. J Neural Eng 2011; 8:065011. [PMID: 22056507 DOI: 10.1088/1741-2560/8/6/065011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The respiratory rhythm originates and diverges from the brainstem to drive thousands of motoneurons that are responsible for control of the diaphragm, intercostals and upper airway. These motoneurons are known to have a wide range of phase relationships, even within a single motoneuron pool. The proposed source of this rhythm, the preBötzinger complex (preBötC), responds to an array of developmental changes in the first days post-birth, specifically at postnatal day 3 (P3). We hypothesize that such developmental changes in the preBötC have a direct effect on motoneuron phase relationships and should be detectable around age P3. To test our hypothesis, we obtained single- and dual-voltage-clamp recordings of hypoglossal motoneurons in an in vitro slice preparation. We introduce a novel approach to analyzing the phase relationships between motoneurons by using cross-correlation analysis to determine the drive latencies. This analysis reveals that the distribution of drive latencies undergoes a significant change at or before age P3. We use a computational model of the in vitro slice to demonstrate the observed phase differences and hypothesize that network heterogeneity alone may not be sufficient to explain them. Through simulations, we show the effects on the preBötC of different network characteristics such as clustering and common inputs.
Collapse
Affiliation(s)
- Christopher Fietkiewicz
- Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH 44106, USA.
| | | | | |
Collapse
|
34
|
Dunmyre JR, Del Negro CA, Rubin JE. Interactions of persistent sodium and calcium-activated nonspecific cationic currents yield dynamically distinct bursting regimes in a model of respiratory neurons. J Comput Neurosci 2011; 31:305-28. [PMID: 21234794 PMCID: PMC3370680 DOI: 10.1007/s10827-010-0311-y] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2010] [Revised: 12/19/2010] [Accepted: 12/21/2010] [Indexed: 11/25/2022]
Abstract
The preBötzinger complex (preBötC) is a heterogeneous neuronal network within the mammalian brainstem that has been experimentally found to generate robust, synchronous bursts that drive the inspiratory phase of the respiratory rhythm. The persistent sodium (NaP) current is observed in every preBötC neuron, and significant modeling effort has characterized its contribution to square-wave bursting in the preBötC. Recent experimental work demonstrated that neurons within the preBötC are endowed with a calcium-activated nonspecific cationic (CAN) current that is activated by a signaling cascade initiated by glutamate. In a preBötC model, the CAN current was shown to promote robust bursts that experience depolarization block (DB bursts). We consider a self-coupled model neuron, which we represent as a single compartment based on our experimental finding of electrotonic compactness, under variation of g (NaP), the conductance of the NaP current, and g (CAN), the conductance of the CAN current. Varying these two conductances yields a spectrum of activity patterns, including quiescence, tonic activity, square-wave bursting, DB bursting, and a novel mixture of square-wave and DB bursts, which match well with activity that we observe in experimental preparations. We elucidate the mechanisms underlying these dynamics, as well as the transitions between these regimes and the occurrence of bistability, by applying the mathematical tools of bifurcation analysis and slow-fast decomposition. Based on the prevalence of NaP and CAN currents, we expect that the generalizable framework for modeling their interactions that we present may be relevant to the rhythmicity of other brain areas beyond the preBötC as well.
Collapse
Affiliation(s)
- Justin R. Dunmyre
- Department of Mathematics and Complex Biological Systems Group, University of Pittsburgh, 301 Thackeray Hall, Pittsburgh, PA 15260, USA
| | | | - Jonathan E. Rubin
- Department of Mathematics and Complex Biological Systems Group, University of Pittsburgh, 301 Thackeray Hall, Pittsburgh, PA 15260, USA
| |
Collapse
|
35
|
Conflicting effects of excitatory synaptic and electric coupling on the dynamics of square-wave bursters. J Comput Neurosci 2011; 31:701-11. [PMID: 21584773 DOI: 10.1007/s10827-011-0340-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 04/13/2011] [Accepted: 05/02/2011] [Indexed: 10/18/2022]
Abstract
Using two-cell and 50-cell networks of square-wave bursters, we studied how excitatory coupling of individual neurons affects the bursting output of the network. Our results show that the effects of synaptic excitation vs. electrical coupling are distinct. Increasing excitatory synaptic coupling generally increases burst duration. Electrical coupling also increases burst duration for low to moderate values, but at sufficiently strong values promotes a switch to highly synchronous bursts where further increases in electrical or synaptic coupling have a minimal effect on burst duration. These effects are largely mediated by spike synchrony, which is determined by the stability of the in-phase spiking solution during the burst. Even when both coupling mechanisms are strong, one form (in-phase or anti-phase) of spike synchrony will determine the burst dynamics, resulting in a sharp boundary in the space of the coupling parameters. This boundary exists in both two cell and network simulations. We use these results to interpret the effects of gap-junction blockers on the neuronal circuitry that underlies respiration.
Collapse
|
36
|
N-methyl-D-aspartate-induced oscillatory properties in neocortical pyramidal neurons from patients with epilepsy. J Clin Neurophysiol 2011; 27:398-405. [PMID: 21076319 DOI: 10.1097/wnp.0b013e3182007c7d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
N-Methyl-D-aspartate (NMDA) receptors have been implicated in epileptogenesis, but how these receptors contribute to epilepsy remains unknown. In particular, their role is likely to be complicated because of their voltage-dependent behavior. Here, the authors investigate how activation of NMDA receptors can affect the intrinsic production of oscillation and the resonance properties of neocortical pyramidal neurons from children with intractable epilepsy. Intracellular whole-cell patch clamp recordings in cortical slices from these patients revealed that pyramidal neurons do not produce spontaneous oscillation under control conditions. However, they did exhibit resonance around 1.5 Hz. On NMDA receptor activation, with bath-applied NMDA (10 μM), the majority of neurons produced voltage-dependent intrinsic oscillation associated with a change in the stability of the neuronal system as reflected by the whole-cell I-V curve. Furthermore, the degree of resonance was amplified while the frequency of resonance was shifted to lower frequencies (∼1 Hz) in NMDA. These results suggest that NMDA receptors may both promote the production of low-frequency oscillation and sharpen the response of the cell to lower frequencies. Both these behaviors may be amplified in tissue from patients with epilepsy, resulting in an increased propensity to generate seizures.
Collapse
|
37
|
Gaiteri C, Rubin JE. The interaction of intrinsic dynamics and network topology in determining network burst synchrony. Front Comput Neurosci 2011; 5:10. [PMID: 21373358 PMCID: PMC3044261 DOI: 10.3389/fncom.2011.00010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2010] [Accepted: 02/10/2011] [Indexed: 01/21/2023] Open
Abstract
The pre-Bötzinger complex (pre-BötC), within the mammalian respiratory brainstem, represents an ideal system for investigating the synchronization properties of complex neuronal circuits via the interaction of cell-type heterogeneity and network connectivity. In isolation, individual respiratory neurons from the pre-BötC may be tonically active, rhythmically bursting, or quiescent. Despite this intrinsic heterogeneity, coupled networks of pre-BötC neurons en bloc engage in synchronized bursting that can drive inspiratory motor neuron activation. The region's connection topology has been recently characterized and features dense clusters of cells with occasional connections between clusters. We investigate how the dynamics of individual neurons (quiescent/bursting/tonic) and the betweenness centrality of neurons' positions within the network connectivity graph interact to govern network burst synchrony, by simulating heterogeneous networks of computational model pre-BötC neurons. Furthermore, we compare the prevalence and synchrony of bursting across networks constructed with a variety of connection topologies, analyzing the same collection of heterogeneous neurons in small-world, scale-free, random, and regularly structured networks. We find that several measures of network burst synchronization are determined by interactions of network topology with the intrinsic dynamics of neurons at central network positions and by the strengths of synaptic connections between neurons. Surprisingly, despite the functional role of synchronized bursting within the pre-BötC, we find that synchronized network bursting is generally weakest when we use its specific connection topology, which leads to synchrony within clusters but poor coordination across clusters. Overall, our results highlight the relevance of interactions between topology and intrinsic dynamics in shaping the activity of networks and the concerted effects of connectivity patterns and dynamic heterogeneities.
Collapse
Affiliation(s)
- Chris Gaiteri
- Department of Psychiatry, University of Pittsburgh Pittsburgh, PA, USA
| | | |
Collapse
|
38
|
Brocard F, Tazerart S, Vinay L. Do pacemakers drive the central pattern generator for locomotion in mammals? Neuroscientist 2010; 16:139-55. [PMID: 20400712 DOI: 10.1177/1073858409346339] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Locomotor disorders profoundly impact quality of life of patients with spinal cord injury. Understanding the neuronal networks responsible for locomotion remains a major challenge for neuroscientists and a fundamental prerequisite to overcome motor deficits. Although neuronal circuitry governing swimming activities in lower vertebrates has been studied in great details, determinants of walking activities in mammals remain elusive. The manuscript reviews some of the principles relevant to the functional organization of the mammalian locomotor network and mainly focuses on mechanisms involved in rhythmogenesis. Based on recent publications supplemented with new experimental data, the authors will specifically discuss a new working hypothesis in which pacemakers, cells characterized by inherent oscillatory properties, might be functionally integrated in the locomotor network in mammals.
Collapse
Affiliation(s)
- Frédéric Brocard
- Lab Plasticité et Physio-Pathologie de la Motricité, Centre National De La Recherche Scientifique, Université Aix-Marseille, Marseille, France.
| | | | | |
Collapse
|
39
|
Toporikova N, Butera RJ. Two types of independent bursting mechanisms in inspiratory neurons: an integrative model. J Comput Neurosci 2010; 30:515-28. [PMID: 20838868 DOI: 10.1007/s10827-010-0274-z] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2010] [Revised: 08/19/2010] [Accepted: 08/25/2010] [Indexed: 02/02/2023]
Abstract
The network of coupled neurons in the pre-Bötzinger complex (pBC) of the medulla generates a bursting rhythm, which underlies the inspiratory phase of respiration. In some of these neurons, bursting persists even when synaptic coupling in the network is blocked and respiratory rhythmic discharge stops. Bursting in inspiratory neurons has been extensively studied, and two classes of bursting neurons have been identified, with bursting mechanism depends on either persistent sodium current or changes in intracellular Ca(2+), respectively. Motivated by experimental evidence from these intrinsically bursting neurons, we present a two-compartment mathematical model of an isolated pBC neuron with two independent bursting mechanisms. Bursting in the somatic compartment is modeled via inactivation of a persistent sodium current, whereas bursting in the dendritic compartment relies on Ca(2+) oscillations, which are determined by the neuromodulatory tone. The model explains a number of conflicting experimental results and is able to generate a robust bursting rhythm, over a large range of parameters, with a frequency adjusted by neuromodulators.
Collapse
Affiliation(s)
- Natalia Toporikova
- Laboratory for Neuroengineering, School of Electrical and Computer Engineering, Atlanta, GA 30332-0250, USA
| | | |
Collapse
|
40
|
Bradley PJ, Wiesenfeld K, Butera RJ. Effects of heterogeneity in synaptic conductance between weakly coupled identical neurons. J Comput Neurosci 2010; 30:455-69. [PMID: 20799058 DOI: 10.1007/s10827-010-0270-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2010] [Revised: 08/05/2010] [Accepted: 08/12/2010] [Indexed: 10/19/2022]
Abstract
A significant degree of heterogeneity in synaptic conductance is present in neuron to neuron connections. We study the dynamics of weakly coupled pairs of neurons with heterogeneities in synaptic conductance using Wang-Buzsaki and Hodgkin-Huxley model neurons which have Types I and II excitability, respectively. This type of heterogeneity breaks a symmetry in the bifurcation diagrams of equilibrium phase difference versus the synaptic rate constant when compared to the identical case. For weakly coupled neurons coupled with identical values of synaptic conductance a phase locked solution exists for all values of the synaptic rate constant, α. In particular, in-phase and anti-phase solutions are guaranteed to exist for all α. Heterogeneity in synaptic conductance results in regions where no phase locked solution exists and the general loss of the ubiquitous in-phase and anti-phase solutions of the identically coupled case. We explain these results through examination of interaction functions using the weak coupling approximation and an in-depth analysis of the underlying multiple cusp bifurcation structure of the systems of coupled neurons.
Collapse
Affiliation(s)
- Patrick J Bradley
- Laboratory for Neuroengineering, Georgia Institute, of Technology, Atlanta, GA 30332-0250, USA.
| | | | | |
Collapse
|
41
|
Fong AY. Postnatal changes in the cardiorespiratory response and ability to autoresuscitate from hypoxic and hypothermic exposure in mammals. Respir Physiol Neurobiol 2010; 174:146-55. [PMID: 20797451 DOI: 10.1016/j.resp.2010.08.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Revised: 08/17/2010] [Accepted: 08/17/2010] [Indexed: 11/28/2022]
Abstract
Most mammals are born immature and a great deal of maturational changes must occur early in the early postnatal life to prepare for life as an adult. In addition to the obvious changes such as physical and musculoskeletal growth, a myriad of physiological changes including the cardiorespiratory responses to hypoxia and hypothermia must also occur. The most intriguing developmental effect is perhaps the change in the ability to autoresuscitate, or spontaneous recovery from cardiorespiratory arrest induced by extreme hypoxia or hypothermia. For decades the ability of young animals to autoresuscitate from cardiorespiratory arrest induced by hypoxic or hypothermic exposure has been documented. In some mammalian species, including rats and humans, this ability is lost over development while others retain this ability. This review will examine the changes that occur in the cardiorespiratory response to hypoxia and hypothermia and the change to the ability to autoresuscitate from cardiorespiratory arrest over early postnatal development. Furthermore, the review will explore some of the potential neuroanatomical, neurochemical and neurophysiological changes during early postnatal development that might contribute to the altered reflex response to hypoxia and hypothermia and the ability to autoresuscitate.
Collapse
Affiliation(s)
- Angelina Y Fong
- Australian School of Advanced Medicine, Macquarie University, North Ryde, NSW, Australia.
| |
Collapse
|
42
|
Functional anatomical evidence for respiratory rhythmogenic function of endogenous bursters in rat medulla. J Neurosci 2010; 30:8383-92. [PMID: 20573885 DOI: 10.1523/jneurosci.5510-09.2010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endogenous burster neurons (EBs) have been found at the level of the facial nucleus (VIIn), and 500 mum caudally, within the pre-Bötzinger complex (preBötC). They have been proposed as either causal to or playing no role in respiratory rhythmogenesis. Little is known about their broader distribution in ventrolateral medulla. Here, a Ca(2+) indicator was used to record respiratory network activity in ventrolateral medulla, and, following synaptic blockade, to identify EBs active at perfusate K(+) concentrations ([K(+)](o)) of 3, 6, and 9 mm. Recordings were made along the respiratory column, extending 300 mum rostrally, and 1100 mum caudally from the caudal pole of VIIn (VIIc), in the in vitro tilted sagittal slab preparation, isolated from neonate male and female Sprague Dawley rats. Activity under matching [K(+)](o) in the intact respiratory network was subsequently investigated. Respiratory neurons (n = 401) formed statistically significant clusters at the VIIc, within the preBötC, and 100 mum caudal to the preBötC. EBs (n = 693) formed statistically significant clusters that overlapped with respiratory clusters at the VIIc and preBötC. EB activity increased significantly as [K(+)](o) was increased, as did neurons that remained coupled following synaptic blockade. The overlap between respiratory and EB clusters in regions of ventrolateral medulla identified as rhythmogenic supports the hypothesis that EBs are constituents of rhythmogenic networks. In addition, the observation of truncated inspiratory bursts and ectopic bursting in respiratory neurons when [K(+)](o) was elevated in the intact network is consistent with a causal role for EBs in respiratory rhythmogenesis.
Collapse
|
43
|
Newman JP, Butera RJ. Mechanism, dynamics, and biological existence of multistability in a large class of bursting neurons. CHAOS (WOODBURY, N.Y.) 2010; 20:023118. [PMID: 20590314 PMCID: PMC2902537 DOI: 10.1063/1.3413995] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2009] [Accepted: 04/06/2010] [Indexed: 05/29/2023]
Abstract
Multistability, the coexistence of multiple attractors in a dynamical system, is explored in bursting nerve cells. A modeling study is performed to show that a large class of bursting systems, as defined by a shared topology when represented as dynamical systems, is inherently suited to support multistability. We derive the bifurcation structure and parametric trends leading to multistability in these systems. Evidence for the existence of multirhythmic behavior in neurons of the aquatic mollusc Aplysia californica that is consistent with our proposed mechanism is presented. Although these experimental results are preliminary, they indicate that single neurons may be capable of dynamically storing information for longer time scales than typically attributed to nonsynaptic mechanisms.
Collapse
Affiliation(s)
- Jonathan P Newman
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0535, USA.
| | | |
Collapse
|
44
|
Mellen NM. Degeneracy as a substrate for respiratory regulation. Respir Physiol Neurobiol 2010; 172:1-7. [PMID: 20412870 DOI: 10.1016/j.resp.2010.04.013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Revised: 04/13/2010] [Accepted: 04/13/2010] [Indexed: 11/27/2022]
Abstract
Recent studies in vivo and in vitro suggest that both respiratory rhythmogenesis and its central chemosensory modulation arise from multiple, mechanistically and/or anatomically distinct networks whose outputs are similar. These observations are consistent with degeneracy, defined as the ability of structurally distinct elements to generate similar function. This review argues that degeneracy is an essential feature of respiratory networks, ensuring the survival of the individual organism over the course of development, and accounting for the transformation of respiratory biomechanics over evolutionary time. At faster timescales, respiration must adapt continuously and rapidly to changes in metabolic demand and ambient conditions to maintain blood-gas homeostasis. Control theory, which formalizes homeostasis, states axiomatically that rapid responsiveness can only be achieved with high gain, but high gain comes at the cost of instability. Homeostatic systems displaying highly optimized tolerance (HOT) mitigate the instability accompanying high gain by incorporating regulatory mechanisms that provide protection against expected perturbations, yet these systems remain fragile to catastrophic failure in response to rare events. Because the multiple mechanisms that are conjectured to mediate respiratory rhythmogenesis and chemosensation have distinct ranges of activity and responses to modulatory input, they provide a richer substrate for respiratory regulation than those of any single mechanism. Respiration, though robust, remains fragile to rare perturbations, matching a key feature of HOT. These observations support the conclusion that degeneracy provides the substrate for respiratory regulation, and that the resulting regulatory system conforms to HOT.
Collapse
Affiliation(s)
- Nicholas M Mellen
- Kosair Children's Hospital Research Institute, University of Louisville, 570 S. Preston Street, Baxter Building 1, Suite 304, Louisville, KY 40202, USA.
| |
Collapse
|
45
|
TASK channels contribute to the K+-dominated leak current regulating respiratory rhythm generation in vitro. J Neurosci 2010; 30:4273-84. [PMID: 20335463 DOI: 10.1523/jneurosci.4017-09.2010] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Leak channels regulate neuronal activity and excitability. Determining which leak channels exist in neurons and how they control electrophysiological behavior is fundamental. Here we investigated TASK channels, members of the two-pore domain K(+) channel family, as a component of the K(+)-dominated leak conductance that controls and modulates rhythm generation at cellular and network levels in the mammalian pre-Bötzinger complex (pre-BötC), an excitatory network of neurons in the medulla critically involved in respiratory rhythmogenesis. By voltage-clamp analyses of pre-BötC neuronal current-voltage (I-V) relations in neonatal rat medullary slices in vitro, we demonstrated that pre-BötC inspiratory neurons have a weakly outward-rectifying total leak conductance with reversal potential that was depolarized by approximately 4 mV from the K(+) equilibrium potential, indicating that background K(+) channels are dominant contributors to leak. This K(+) channel component had I-V relations described by constant field theory, and the conductance was reduced by acid and was augmented by the volatile anesthetic halothane, which are all hallmarks of TASK. We established by single-cell RT-PCR that pre-BötC inspiratory neurons express TASK-1 and in some cases also TASK-3 mRNA. Furthermore, acid depolarized and augmented bursting frequency of pre-BötC inspiratory neurons with intrinsic bursting properties. Microinfusion of acidified solutions into the rhythmically active pre-BötC network increased network bursting frequency, halothane decreased bursting frequency, and acid reversed the depressant effects of halothane, consistent with modulation of network activity by TASK channels. We conclude that TASK-like channels play a major functional role in chemosensory modulation of respiratory rhythm generation in the pre-Bötzinger complex in vitro.
Collapse
|
46
|
Abstract
The preBötzinger complex (preBötC) is essential for normal respiratory rhythm generation in rodents, for which the underlying mechanisms remain unknown. Excitatory preBötC pacemaker neurons are proposed to be necessary for rhythm generation. Here we report the presence of a population of preBötC glycinergic pacemaker neurons. We used rhythmic in vitro transverse slice preparations from transgenic mice where neurons expressing the glycine transporter 2 (GlyT2) gene coexpress enhanced green fluorescent protein (EGFP). We combined epifluorescence and whole-cell patch-clamp recording to study preBötC EGFP-labeled, i.e., glycinergic, inspiratory-modulated neurons with pacemaker properties. We defined glycinergic pacemaker neurons as those preBötC EGFP neurons that exhibited the following: (1) ectopic bursting in rhythmic slices when depolarized during their normally silent period and (2) bursting when depolarized in nonrhythmic slices (following AMPA receptor blockade). Forty-two percent of EGFP-labeled neurons were inspiratory (n = 48 of 115), of which 23% (n = 11 of 48 inspiratory; 10% of the total recorded) were pacemakers. We conclude that there is a population of preBötC inspiratory-modulated glycinergic, presumably inhibitory, pacemaker neurons that constitute a substantial fraction of all preBötC pacemaker neurons. These findings challenge contemporary models for respiratory rhythmogenesis that assume the excitatory nature of preBötC pacemaker neurons. Testable and nontrivial predictions of the functional role of excitatory and inhibitory pacemaker neurons need to be proposed and the necessary experiments performed.
Collapse
|
47
|
Gajda BM, Fong AY, Milsom WK. Species differences in respiratory rhythm generation in rodents. Am J Physiol Regul Integr Comp Physiol 2010; 298:R887-98. [DOI: 10.1152/ajpregu.00339.2009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined the role of riluzole (RIL)- and flufenamic acid (FFA)-sensitive mechanisms in respiratory rhythmogenesis in rats and hamsters using the in situ arterially perfused preparation. Based on the hypothesis that respiratory networks in animals capable of autoresuscitation would have a greater prevalence of membrane mechanisms that promote endogenous bursting, we predicted that older (weaned) hamsters (a hibernating species) would be more sensitive to the blockade of RIL- and FFA-sensitive mechanisms than age-matched rats and that younger (preweaned) rats would behave more like hamsters. Consistent with this, we found that respiratory motor output in weaned hamsters [>21 days postnatal (P21)] was highly sensitive to RIL (0.2–20 μM), while in young rats (P12–14) it was less so (only affected at higher concentrations of RIL), and weaned rats were not affected at all. On the other hand, respiratory motor output was equally reduced by FFA (0.25–25 μM) in both young and weaned rats but was unaffected in weaned hamsters. Coapplication of RIL and FFA (RIL + FFA) produced greater inhibition of respiration in both young and weaned rats compared with either drug alone. In contrast, in weaned hamsters, FFA coapplication offset the inhibitory effect of RIL alone. Increasing respiratory drive with hypercapnia/acidosis ameliorated the respiratory inhibition produced by RIL + FFA in weaned rats but had no effect in young rats. Data from the present study indicate that respiratory rhythmogenesis in young rats is more dependent on excitatory RIL-sensitive and FFA-sensitive mechanisms than older rats and that fundamental differences exist in the respiratory rhythmogenic mechanisms between rats and hamsters.
Collapse
Affiliation(s)
- B. M. Gajda
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - A. Y. Fong
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - W. K. Milsom
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| |
Collapse
|
48
|
Shirahata T. The effect of hyperpolarizing inputs on the dynamics of a bursting pacemaker neuron model in the pre-Bötzinger complex. Neurosci Lett 2010; 473:16-21. [PMID: 20152884 DOI: 10.1016/j.neulet.2010.02.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Revised: 02/02/2010] [Accepted: 02/04/2010] [Indexed: 11/25/2022]
Abstract
The pre-Bötzinger complex (pre-BötC), a subregion of the ventrolateral medulla involved in respiratory rhythm generation, contains intrinsically bursting pacemaker neurons. A previous study proposed Hodgkin-Huxley type minimal models for pacemaker neurons and predicted the effect of a hyperpolarizing input on the dynamics of a model under certain conditions. In this model, bursting is explained by the dynamics of a persistent sodium current. In the present study, the effect of a hyperpolarizing input on the dynamics of a model was investigated under variable conditions. It was observed that immediately after an input of sufficient intensity and duration, an increase in the maximal value of the gating variable h of a persistent sodium current was brought about by a decrease in the timing of the hyperpolarizing input. This corresponds to an observation that immediately after the input, a monotonic increase in the number of spikes in the neuron model was brought about by a decrease in the timing of the hyperpolarizing input. In addition, the dependency of burst duration immediately after the input on the timing of the hyperpolarizing input varied depending on the condition of input. The present study is the first to elucidate that the influence of hyperpolarizing inputs on the number of spikes within a burst in a pacemaker neuron model in the pre-BötC is dependent on the timing of the hyperpolarizing input and to clarify the possible mechanism of this influence, thereby facilitating a detailed understanding of the dynamics of a pacemaker neuron model in the pre-BötC.
Collapse
Affiliation(s)
- Takaaki Shirahata
- Laboratory of Pharmaceutics, Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan.
| |
Collapse
|
49
|
Harris-Warrick RM. General principles of rhythmogenesis in central pattern generator networks. PROGRESS IN BRAIN RESEARCH 2010; 187:213-22. [PMID: 21111210 DOI: 10.1016/b978-0-444-53613-6.00014-9] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
The cellular and ionic mechanisms that generate the rhythm in central pattern generator (CPG) networks for simple movements are not well understood. Using vertebrate locomotion, respiration and mastication as exemplars, I describe four main principles of rhythmogenesis: (1) rhythmogenic ionic currents underlie all CPG networks, regardless of whether they are driven by a network pacemaker or an endogenous pacemaker neuron kernel; (2) fast synaptic transmission often evokes slow currents that can affect cycle frequency; (3) there are likely to be multiple and redundant mechanisms for rhythmogenesis in any essential CPG network; and (4) glial cells may participate in CPG network function. The neural basis for rhythmogenesis in simple behaviors has been studied for almost 100 years, yet we cannot identify with certainty the detailed mechanisms by which rhythmic behaviors are generated in any vertebrate system. Early studies focused on whether locomotor rhythms were generated by a chain of coupled reflexes that require sensory feedback, or by a central neural network. By now there is general agreement that for the major rhythmic behaviors (including locomotion, respiration, and mastication, the subjects of this book), there exist CPG networks within the central nervous system that are able to drive the basic rhythmic behavior in the complete absence of sensory feedback. This of course does not eliminate an important role for sensory feedback, which certainly affects cycle frequency and for some behaviors determines the timing of one phase of the behavior (Borgmann et al., 2009; Pearson, 2008). Given the existence of CPGs, the question of rhythmogenesis can be rephrased to ask how these networks determine the timing of the rhythmic behavior. In this chapter, I focus on cellular and molecular mechanisms that could underlie rhythmogenesis in CPG networks, especially those that drive locomotion, respiration, and mastication.
Collapse
Affiliation(s)
- Ronald M Harris-Warrick
- Department of Neurobiology and Behavior, Seeley G. Mudd Hall, Cornell University, Ithaca, New York, USA
| |
Collapse
|
50
|
Smith JC, Abdala APL, Rybak IA, Paton JFR. Structural and functional architecture of respiratory networks in the mammalian brainstem. Philos Trans R Soc Lond B Biol Sci 2009; 364:2577-87. [PMID: 19651658 DOI: 10.1098/rstb.2009.0081] [Citation(s) in RCA: 189] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Neural circuits controlling breathing in mammals are organized within serially arrayed and functionally interacting brainstem compartments extending from the pons to the lower medulla. The core circuit components that constitute the neural machinery for generating respiratory rhythm and shaping inspiratory and expiratory motor patterns are distributed among three adjacent structural compartments in the ventrolateral medulla: the Bötzinger complex (BötC), pre-Bötzinger complex (pre-BötC) and rostral ventral respiratory group (rVRG). The respiratory rhythm and inspiratory-expiratory patterns emerge from dynamic interactions between: (i) excitatory neuron populations in the pre-BötC and rVRG active during inspiration that form inspiratory motor output; (ii) inhibitory neuron populations in the pre-BötC that provide inspiratory inhibition within the network; and (iii) inhibitory populations in the BötC active during expiration that generate expiratory inhibition. Network interactions within these compartments along with intrinsic rhythmogenic properties of pre-BötC neurons form a hierarchy of multiple oscillatory mechanisms. The functional expression of these mechanisms is controlled by multiple drives from more rostral brainstem components, including the retrotrapezoid nucleus and pons, which regulate the dynamic behaviour of the core circuitry. The emerging view is that the brainstem respiratory network has rhythmogenic capabilities at multiple hierarchical levels, which allows flexible, state-dependent expression of different rhythmogenic mechanisms under different physiological and metabolic conditions and enables a wide repertoire of respiratory behaviours.
Collapse
Affiliation(s)
- Jeffrey C Smith
- Porter Neuroscience Research Center, Building 35, Room 3C-917, 35 Convent Drive, NINDS, NIH, Bethesda, MD 20892, USA.
| | | | | | | |
Collapse
|