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Genetic ablation of VIAAT in glycinergic neurons causes a severe respiratory phenotype and perinatal death. Brain Struct Funct 2014; 220:2835-49. [PMID: 25027639 DOI: 10.1007/s00429-014-0829-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 06/21/2014] [Indexed: 12/14/2022]
Abstract
Both glycinergic and GABAergic neurons require the vesicular inhibitory amino acid transporter (VIAAT) for synaptic vesicle filling. Presynaptic GABA concentrations are determined by the GABA-synthesizing enzymes glutamate decarboxylase (GAD)65 and GAD67, whereas the presynaptic glycine content depends on the plasma membrane glycine transporter 2 (GlyT2). Although severely impaired, glycinergic transmission is not completely absent in GlyT2-knockout mice, suggesting that other routes of glycine uptake or de novo synthesis of glycine exist in presynaptic terminals. To investigate the consequences of a complete loss of glycinergic transmission, we generated a mouse line with a conditional ablation of VIAAT in glycinergic neurons by crossing mice with loxP-flanked VIAAT alleles with a GlyT2-Cre transgenic mouse line. Interestingly, conditional VIAAT knockout (VIAAT cKO) mice were not viable at birth. In addition to the dominant respiratory failure, VIAAT cKO showed an umbilical hernia and a cleft palate. Immunohistochemistry revealed an almost complete depletion of VIAAT in the brainstem. Electrophysiology revealed the absence of both spontaneous glycinergic and GABAergic inhibitory postsynaptic currents from hypoglossal motoneurons. Our results demonstrate that the deletion of VIAAT in GlyT2-Cre expressing neurons also strongly affects GABAergic transmission and suggest a large overlap of the glycinergic and the GABAergic neuron population during early development in the caudal parts of the brain.
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Tupal S, Huang WH, Picardo MCD, Ling GY, Del Negro CA, Zoghbi HY, Gray PA. Atoh1-dependent rhombic lip neurons are required for temporal delay between independent respiratory oscillators in embryonic mice. eLife 2014; 3:e02265. [PMID: 24842997 PMCID: PMC4060005 DOI: 10.7554/elife.02265] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
All motor behaviors require precise temporal coordination of different muscle groups. Breathing, for example, involves the sequential activation of numerous muscles hypothesized to be driven by a primary respiratory oscillator, the preBötzinger Complex, and at least one other as-yet unidentified rhythmogenic population. We tested the roles of Atoh1-, Phox2b-, and Dbx1-derived neurons (three groups that have known roles in respiration) in the generation and coordination of respiratory output. We found that Dbx1-derived neurons are necessary for all respiratory behaviors, whereas independent but coupled respiratory rhythms persist from at least three different motor pools after eliminating or silencing Phox2b- or Atoh1-expressing hindbrain neurons. Without Atoh1 neurons, however, the motor pools become temporally disorganized and coupling between independent respiratory oscillators decreases. We propose Atoh1 neurons tune the sequential activation of independent oscillators essential for the fine control of different muscles during breathing.DOI: http://dx.doi.org/10.7554/eLife.02265.001.
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Affiliation(s)
- Srinivasan Tupal
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St Louis, United States
| | - Wei-Hsiang Huang
- Program in Developmental Biology, Baylor College of Medicine, Houston, United States Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital, Baylor College of Medicine, Houston, United States
| | | | - Guang-Yi Ling
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St Louis, United States
| | | | - Huda Y Zoghbi
- Program in Developmental Biology, Baylor College of Medicine, Houston, United States Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital, Baylor College of Medicine, Houston, United States Department of Molecular and Human Genetics, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, United States
| | - Paul A Gray
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St Louis, United States
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Koshiya N, Oku Y, Yokota S, Oyamada Y, Yasui Y, Okada Y. Anatomical and functional pathways of rhythmogenic inspiratory premotor information flow originating in the pre-Bötzinger complex in the rat medulla. Neuroscience 2014; 268:194-211. [DOI: 10.1016/j.neuroscience.2014.03.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Revised: 03/02/2014] [Accepted: 03/04/2014] [Indexed: 01/30/2023]
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Chapuis C, Autran S, Fortin G, Simmers J, Thoby-Brisson M. Emergence of sigh rhythmogenesis in the embryonic mouse. J Physiol 2014; 592:2169-81. [PMID: 24591570 DOI: 10.1113/jphysiol.2013.268730] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
In mammals, eupnoeic breathing is periodically interrupted by spontaneous augmented breaths (sighs) that include a larger-amplitude inspiratory effort, typically followed by a post-sigh apnoea. Previous in vitro studies in newborn rodents have demonstrated that the respiratory oscillator of the pre-Bötzinger complex (preBötC) can generate the distinct inspiratory motor patterns for both eupnoea- and sigh-related behaviour. During mouse embryonic development, the preBötC begins to generate eupnoeic rhythmicity at embryonic day (E) 15.5, but the network's ability to also generate sigh-like activity remains unexplored at prenatal stages. Using transverse brainstem slice preparations we monitored the neuronal population activity of the preBötC at different embryonic ages. Spontaneous sigh-like rhythmicity was found to emerge progressively, being expressed in 0/32 slices at E15.5, 7/30 at E16.5, 9/22 at E17.5 and 23/26 at E18.5. Calcium imaging showed that the preBötC cell population that participates in eupnoeic-like discharge was also active during fictive sighs. However, patch-clamp recordings revealed the existence of an additional small subset of neurons that fired exclusively during sigh activity. Changes in glycinergic inhibitory synaptic signalling, either by pharmacological blockade, functional perturbation or natural maturation of the chloride co-transporters KCC2 or NKCC1 selectively, and in an age-dependent manner, altered the bi-phasic nature of sigh bursts and their coordination with eupnoeic bursting, leading to the generation of an atypical monophasic sigh-related event. Together our results demonstrate that the developmental emergence of a sigh-generating capability occurs after the onset of eupnoeic rhythmogenesis and requires the proper maturation of chloride-mediated glycinergic synaptic transmission.
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Affiliation(s)
- Coralie Chapuis
- University of Bordeaux, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, CNRS UMR 5287, 33076 Bordeaux, France
| | - Sandra Autran
- Institut de Neurobiologie Alfred Fessard, Neurobiology and Development, CNRS UPR 3294, 91190 Gif sur Yvette, France
| | - Gilles Fortin
- Institut de Neurobiologie Alfred Fessard, Neurobiology and Development, CNRS UPR 3294, 91190 Gif sur Yvette, France
| | - John Simmers
- University of Bordeaux, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, CNRS UMR 5287, 33076 Bordeaux, France
| | - Muriel Thoby-Brisson
- University of Bordeaux, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, CNRS UMR 5287, 33076 Bordeaux, France
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When norepinephrine becomes a driver of breathing irregularities: how intermittent hypoxia fundamentally alters the modulatory response of the respiratory network. J Neurosci 2014; 34:36-50. [PMID: 24381266 DOI: 10.1523/jneurosci.3644-12.2014] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Neuronal networks are endogenously modulated by aminergic and peptidergic substances. These modulatory processes are critical for maintaining normal activity and adapting networks to changes in metabolic, behavioral, and environmental conditions. However, disturbances in neuromodulation have also been associated with pathologies. Using whole animals (in vivo) and functional brainstem slices (in vitro) from mice, we demonstrate that exposure to acute intermittent hypoxia (AIH) leads to fundamental changes in the neuromodulatory response of the respiratory network located within the preBötzinger complex (preBötC), an area critical for breathing. Norepinephrine, which normally regularizes respiratory activity, renders respiratory activity irregular after AIH. Respiratory irregularities are caused both in vitro and in vivo by AIH, which increases synaptic inhibition within the preBötC when norepinephrine is endogenously or exogenously increased. These irregularities are prevented by blocking synaptic inhibition before AIH. However, regular breathing cannot be reestablished if synaptic inhibition is blocked after AIH. We conclude that subtle changes in synaptic transmission can have dramatic consequences at the network level as endogenously released neuromodulators that are normally adaptive become the drivers of irregularity. Moreover, irregularities in the preBötC result in irregularities in the motor output in vivo and in incomplete transmission of inspiratory activity to the hypoglossus motor nucleus. Our finding has basic science implications for understanding network functions in general, and it may be clinically relevant for understanding pathological disturbances associated with hypoxic episodes such as those associated with myocardial infarcts, obstructive sleep apneas, apneas of prematurity, Rett syndrome, and sudden infant death syndrome.
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Zavala-Tecuapetla C, Tapia D, Rivera-Angulo AJ, Galarraga E, Peña-Ortega F. Morphological characterization of respiratory neurons in the pre-Bötzinger complex. PROGRESS IN BRAIN RESEARCH 2014; 209:39-56. [PMID: 24746042 DOI: 10.1016/b978-0-444-63274-6.00003-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Although the pre-Bötzinger complex (preBötC) was defined as the inspiratory rhythm generator long ago, the functional-anatomical characterization of its neuronal components is still being achieved. Recent advances have identified the expression of molecular markers in the preBötC neurons that, however, are not exclusive to specific respiratory neuron subtypes and have not always been related to specific cell morphologies. Here, we evaluated the morphology and the axonal projections of electrophysiologically defined respiratory neurons in the preBötC using whole-cell recordings and intracellular biocytin labeling. We found that respiratory pacemaker neurons are larger than expiratory neurons and that inspiratory neurons are smaller than pacemaker and expiratory neurons. Other morphological features such as somata shapes or dendritic branching patterns were not found to be significantly different among the preBötC neurons sampled. We also found that both pacemaker and inspiratory nonpacemaker neurons, but not expiratory neurons, show extensive axonal projections to the contralateral preBötC and show signs of electrical coupling. Overall, our data suggest that there are morphological differences between subtypes of preBötC respiratory neurons. It will be important to take such differences in consideration since morphological differences would influence synaptic responses and action potential propagation.
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Affiliation(s)
- Cecilia Zavala-Tecuapetla
- Departamento de Neurobiología del Desarrollo y Neurofisiología, Instituto de Neurobiología, UNAM Campus Juriquilla, Querétaro, Mexico; Laboratorio de Nanotecnología, Instituto Nacional de Neurología y Neurocirugía-MVS, Mexico D.F., Mexico; Departamento de Farmacobiología, Centro de Investigación y de Estudios Avanzados Sede Sur, Mexico D.F., Mexico
| | - Dagoberto Tapia
- Departamento de Biofísica, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico D.F., Mexico
| | - Ana Julia Rivera-Angulo
- Departamento de Neurobiología del Desarrollo y Neurofisiología, Instituto de Neurobiología, UNAM Campus Juriquilla, Querétaro, Mexico
| | - Elvira Galarraga
- Departamento de Biofísica, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico D.F., Mexico
| | - Fernando Peña-Ortega
- Departamento de Neurobiología del Desarrollo y Neurofisiología, Instituto de Neurobiología, UNAM Campus Juriquilla, Querétaro, Mexico.
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57
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Ramirez JM, Doi A, Garcia AJ, Elsen FP, Koch H, Wei AD. The cellular building blocks of breathing. Compr Physiol 2013; 2:2683-731. [PMID: 23720262 DOI: 10.1002/cphy.c110033] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Respiratory brainstem neurons fulfill critical roles in controlling breathing: they generate the activity patterns for breathing and contribute to various sensory responses including changes in O2 and CO2. These complex sensorimotor tasks depend on the dynamic interplay between numerous cellular building blocks that consist of voltage-, calcium-, and ATP-dependent ionic conductances, various ionotropic and metabotropic synaptic mechanisms, as well as neuromodulators acting on G-protein coupled receptors and second messenger systems. As described in this review, the sensorimotor responses of the respiratory network emerge through the state-dependent integration of all these building blocks. There is no known respiratory function that involves only a small number of intrinsic, synaptic, or modulatory properties. Because of the complex integration of numerous intrinsic, synaptic, and modulatory mechanisms, the respiratory network is capable of continuously adapting to changes in the external and internal environment, which makes breathing one of the most integrated behaviors. Not surprisingly, inspiration is critical not only in the control of ventilation, but also in the context of "inspiring behaviors" such as arousal of the mind and even creativity. Far-reaching implications apply also to the underlying network mechanisms, as lessons learned from the respiratory network apply to network functions in general.
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Affiliation(s)
- J M Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institut, Seattle, Washington, USA.
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58
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Viemari JC, Garcia AJ, Doi A, Elsen G, Ramirez JM. β-Noradrenergic receptor activation specifically modulates the generation of sighs in vivo and in vitro. Front Neural Circuits 2013; 7:179. [PMID: 24273495 PMCID: PMC3824105 DOI: 10.3389/fncir.2013.00179] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 10/23/2013] [Indexed: 11/13/2022] Open
Abstract
The pre-Bötzinger complex (preBötC), an area that is critical for generating breathing (eupnea), gasps and sighs is continuously modulated by catecholamines. These amines and the generation of sighs have also been implicated in the regulation of arousal. Here we studied the catecholaminergic modulation of sighs not only in anesthetized freely breathing mice (in vivo), but also in medullary slice preparations that contain the preBötC and that generate fictive eupneic and sigh rhythms in vitro. We demonstrate that activating β-noradrenergic receptors (β-NR) specifically increases the frequency of sighs, while eupnea remains unaffected both in vitro and in vivo. β-NR activation specifically increased the frequency of intrinsically bursting pacemaker neurons that rely on persistent sodium current (I(Nap)). By contrast, all parameters of bursting pacemakers that rely on the non-specific cation current (I(CAN)) remained unaffected. Moreover, riluzole, which blocks bursting in I(Nap) pacemakers abolished sighs altogether, while flufenamic acid (FFA) which blocks the I(CAN) current did not alter the sigh-increasing effect caused by β-NR. Our results suggest that the selective β-NR action of sighs may result from the modulation of I(Nap) pacemaker activity and that disturbances in noradrenergic system may contribute to abnormal arousal response. The β-NR action on the preBötC may be an important mechanism in modulating behaviors that are specifically associated with sighs, such as the regulation of the early events leading to the arousal response.
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Affiliation(s)
- Jean-Charles Viemari
- Team P3M, Institut de Neurosciences de la Timone, UMR 7289, CNRS, Aix Marseille Univesité , Marseille, France
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59
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Viemari JC, Menuet C, Hilaire G. [Electrophysiological, molecular and genetic identifications of the pre-Bötzinger complex]. Med Sci (Paris) 2013; 29:875-82. [PMID: 24148126 DOI: 10.1051/medsci/20132910015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
From birth onwards, rhythmic breathing is required for blood oxygenation and survival in mammals. During their lifespan, human or mouse or elephant will spontaneously produce several hundreds of millions of respiratory movements. The central nervous command responsible for these spontaneous rhythmic movements is elaborated by a complex neural network extending within the brainstem. In the medulla, a special part of this network contains respiratory pacemaker neurons that play a crucial role in respiratory rhythmogenesis: the pre-Bötzinger complex. This review summarizes and discusses the main electrophysiological, molecular and genetic mechanisms contributing to the function and the perinatal maturation of the pre-Bötzinger complex.
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Affiliation(s)
- Jean-Charles Viemari
- Équipe P3M (plasticité et physiopathologie de la motricité), institut de neurosciences de la Timone, UMR 7289, CNRS-Aix-Marseille université, 27, boulevard Jean Moulin, 13385 Marseille Cedex 05, France
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60
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Liu Q, Wong-Riley MTT. Postnatal development of glycine receptor subunits α1, α2, α3, and β immunoreactivity in multiple brain stem respiratory-related nuclear groups of the rat. Brain Res 2013; 1538:1-16. [PMID: 24080401 DOI: 10.1016/j.brainres.2013.09.028] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 09/16/2013] [Accepted: 09/20/2013] [Indexed: 01/01/2023]
Abstract
The respiratory system is immature at birth and significant development occurs postnatally. A critical period of respiratory development occurs in rats around postnatal days 12-13, when enhanced inhibition dominates over suppressed excitation. The mechanisms underlying the heightened inhibition are not fully understood. The present study tested our hypothesis that the inhibition is marked by a switch in glycine receptor subunits from neonatal to adult form around the critical period. An in-depth immunohistochemical and single neuron optical densitometric study was undertaken on four respiratory-related nuclear groups (the pre-Bötzinger complex, nucleus ambiguus, hypoglossal nucleus, and ventrolateral subnucleus of solitary tract nucleus), and a non-respiratory cuneate nucleus in P2-21 rats. Our data revealed that in the respiratory-related nuclear groups: (1) the expressions of GlyRα2 and GlyRα3 were relatively high at P2, but declined after 1-1½ weeks to their lowest levels at P21; (2) the expression of GlyRα1 increased with age and reached significance at P12; and (3) the expression of GlyRβ rose from P2 to P12 followed by a slight decline until P21. No distinct increase in GlyRα1 at P12 was noted in the cuneate nucleus. Thus, there is a switch in dominance of expression from neonatal GlyRα2/α3 to the adult GlyRα1 and a heightened expression of GlyRα1 around the critical period in all respiratory-related nuclear groups, thereby supporting enhanced inhibition at that time. The rise in the expression of GlyRβ around P12 indicates that it plays an important role in forming the mature heteropentameric glycine receptors in these brain stem nuclear groups.
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Affiliation(s)
- Qiuli Liu
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
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61
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Picardo MCD, Weragalaarachchi KTH, Akins VT, Del Negro CA. Physiological and morphological properties of Dbx1-derived respiratory neurons in the pre-Botzinger complex of neonatal mice. J Physiol 2013; 591:2687-703. [PMID: 23459755 PMCID: PMC3678050 DOI: 10.1113/jphysiol.2012.250118] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Accepted: 02/27/2013] [Indexed: 12/30/2022] Open
Abstract
Breathing in mammals depends on an inspiratory-related rhythm that is generated by glutamatergic neurons in the pre-Bötzinger complex (preBötC) of the lower brainstem. A substantial subset of putative rhythm-generating preBötC neurons derive from a single genetic line that expresses the transcription factor Dbx1, but the cellular mechanisms of rhythmogenesis remain incompletely understood. To elucidate these mechanisms, we carried out a comparative analysis of Dbx1-expressing neurons (Dbx1(+)) and non-Dbx1-derived (Dbx1(-)) neurons in the preBötC. Whole-cell recordings in rhythmically active newborn mouse slice preparations showed that Dbx1(+) neurons activate earlier in the respiratory cycle and discharge greater magnitude inspiratory bursts compared with Dbx1(-) neurons. Furthermore, Dbx1(+) neurons required less input current to discharge spikes (rheobase) in the context of network activity. The expression of intrinsic membrane properties indicative of A-current (IA) and hyperpolarization-activated current (Ih) tended to be mutually exclusive in Dbx1(+) neurons. In contrast, there was no such relationship in the expression of currents IA and Ih in Dbx1(-) neurons. Confocal imaging and digital morphological reconstruction of recorded neurons revealed dendritic spines on Dbx1(-) neurons, but Dbx1(+) neurons were spineless. The morphology of Dbx1(+) neurons was largely confined to the transverse plane, whereas Dbx1(-) neurons projected dendrites to a greater extent in the parasagittal plane. The putative rhythmogenic nature of Dbx1(+) neurons may be attributable, in part, to a higher level of intrinsic excitability in the context of network synaptic activity. Furthermore, Dbx1(+) neuronal morphology may facilitate temporal summation and integration of local synaptic inputs from other Dbx1(+) neurons, taking place largely in the dendrites, which could be important for initiating and maintaining bursts and synchronizing activity during the inspiratory phase.
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Affiliation(s)
- Maria Cristina D Picardo
- Department of Applied Science, McGlothlin-Street Hall, Room 318, The College of William & Mary, Williamsburg, VA 23187-8795, USA.
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62
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Burke PGR, Sousa LO, Tallapragada VJ, Goodchild AK. Inhibition of protein kinase A activity depresses phrenic drive and glycinergic signalling, but not rhythmogenesis in anaesthetized rat. Eur J Neurosci 2013; 38:2260-70. [PMID: 23627348 DOI: 10.1111/ejn.12230] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Revised: 03/20/2013] [Accepted: 03/25/2013] [Indexed: 11/28/2022]
Abstract
The cAMP-protein kinase A (PKA) pathway plays a critical role in regulating neuronal activity. Yet, how PKA signalling shapes the population activity of neurons that regulate respiratory rhythm and motor patterns in vivo is poorly defined. We determined the respiratory effects of focally inhibiting endogenous PKA activity in defined classes of respiratory neurons in the ventrolateral medulla and spinal cord by microinjection of the membrane-permeable PKA inhibitor Rp-adenosine 3',5'-cyclic monophosphothioate (Rp-cAMPS) in urethane-anaesthetized adult Sprague Dawley rats. Phrenic nerve activity, end-tidal CO2 and arterial pressure were recorded. Rp-cAMPS in the preBötzinger complex (preBötC) caused powerful, dose-dependent depression of phrenic burst amplitude and inspiratory period. Rp-cAMPS powerfully depressed burst amplitude in the phrenic premotor nucleus, but had no effect at the phrenic motor nucleus, suggesting a lack of persistent PKA activity here. Surprisingly, inhibition of PKA activity in the preBötC increased phrenic burst frequency, whereas in the Bötzinger complex phrenic frequency decreased. Pretreating the preBötC with strychnine, but not bicuculline, blocked the Rp-cAMPS-evoked increase in frequency, but not the depression of phrenic burst amplitude. We conclude that endogenous PKA activity in excitatory inspiratory preBötzinger neurons and phrenic premotor neurons, but not motor neurons, regulates network inspiratory drive currents that underpin the intensity of phrenic nerve discharge. We show that inhibition of PKA activity reduces tonic glycinergic transmission that normally restrains the frequency of rhythmic respiratory activity. Finally, we suggest that the maintenance of the respiratory rhythm in vivo is not dependent on endogenous cAMP-PKA signalling.
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Affiliation(s)
- P G R Burke
- Australian School of Advanced Medicine, Level 1, 2 Technology Drive, Macquarie University, Sydney, NSW, Australia
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63
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Structural-functional properties of identified excitatory and inhibitory interneurons within pre-Botzinger complex respiratory microcircuits. J Neurosci 2013; 33:2994-3009. [PMID: 23407957 DOI: 10.1523/jneurosci.4427-12.2013] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
We comparatively analyzed cellular and circuit properties of identified rhythmic excitatory and inhibitory interneurons within respiratory microcircuits of the neonatal rodent pre-Bötzinger complex (pre-BötC), the structure generating inspiratory rhythm in the brainstem. We combined high-resolution structural-functional imaging, molecular assays for neurotransmitter phenotype identification in conjunction with electrophysiological property phenotyping, and morphological reconstruction of interneurons in neonatal rat and mouse slices in vitro. This approach revealed previously undifferentiated structural-functional features that distinguish excitatory and inhibitory interneuronal populations. We identified distinct subpopulations of pre-BötC glutamatergic, glycinergic, GABAergic, and glycine-GABA coexpressing interneurons. Most commissural pre-BötC inspiratory interneurons were glutamatergic, with a substantial subset exhibiting intrinsic oscillatory bursting properties. Commissural excitatory interneurons projected with nearly planar trajectories to the contralateral pre-BötC, many also with axon collaterals to areas containing inspiratory hypoglossal (XII) premotoneurons and motoneurons. Inhibitory neurons as characterized in the present study did not exhibit intrinsic oscillatory bursting properties, but were electrophysiologically distinguished by more pronounced spike frequency adaptation properties. Axons of many inhibitory neurons projected ipsilaterally also to regions containing inspiratory XII premotoneurons and motoneurons, whereas a minority of inhibitory neurons had commissural axonal projections. Dendrites of both excitatory and inhibitory interneurons were arborized asymmetrically, primarily in the coronal plane. The dendritic fields of inhibitory neurons were more spatially compact than those of excitatory interneurons. Our results are consistent with the concepts of a compartmental circuit organization, a bilaterally coupled excitatory rhythmogenic kernel, and a role of pre-BötC inhibitory neurons in shaping inspiratory pattern as well as coordinating inspiratory and expiratory activity.
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64
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The rhythmic, transverse medullary slice preparation in respiratory neurobiology: contributions and caveats. Respir Physiol Neurobiol 2013; 186:236-53. [PMID: 23357617 DOI: 10.1016/j.resp.2013.01.011] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Revised: 01/18/2013] [Accepted: 01/21/2013] [Indexed: 11/23/2022]
Abstract
Our understanding of the sites and mechanisms underlying rhythmic breathing as well as the neuromodulatory control of respiratory rhythm, pattern, and respiratory motoneuron excitability during perinatal development has advanced significantly over the last 20 years. A major catalyst was the development in 1991 of the rhythmically-active medullary slice preparation, which provided precise mechanical and chemical control over the network as well as enhanced physical and optical access to key brainstem regions. Insights obtained in vitro have informed multiple mechanistic hypotheses. In vivo tests of these hypotheses, performed under conditions of reduced control and precision but more obvious physiological relevance, have clearly established the significance for respiratory neurobiology of the rhythmic slice preparation. We review the contributions of this preparation to current understanding/concepts in respiratory control, and outline the limitations of this approach in the context of studying rhythm and pattern generation, homeostatic control mechanisms and murine models of human genetic disorders that feature prominent breathing disturbances.
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65
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Rahman J, Latal AT, Besser S, Hirrlinger J, Hülsmann S. Mixed miniature postsynaptic currents resulting from co-release of glycine and GABA recorded from glycinergic neurons in the neonatal respiratory network. Eur J Neurosci 2013; 37:1229-41. [DOI: 10.1111/ejn.12136] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Revised: 12/17/2012] [Accepted: 12/18/2012] [Indexed: 12/28/2022]
Affiliation(s)
| | - A. Tobias Latal
- DFG Research Center for Molecular Physiology of the Brain (CMPB); University of Göttingen; Göttingen; Germany
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66
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Smith JC, Abdala APL, Borgmann A, Rybak IA, Paton JFR. Brainstem respiratory networks: building blocks and microcircuits. Trends Neurosci 2012; 36:152-62. [PMID: 23254296 DOI: 10.1016/j.tins.2012.11.004] [Citation(s) in RCA: 269] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 11/10/2012] [Accepted: 11/12/2012] [Indexed: 01/18/2023]
Abstract
Breathing movements in mammals are driven by rhythmic neural activity generated within spatially and functionally organized brainstem neural circuits comprising the respiratory central pattern generator (CPG). This rhythmic activity provides homeostatic regulation of gases in blood and tissues and integrates breathing with other motor acts. We review new insights into the spatial-functional organization of key neural microcircuits of this CPG from recent multidisciplinary experimental and computational studies. The emerging view is that the microcircuit organization within the CPG allows the generation of multiple rhythmic breathing patterns and adaptive switching between them, depending on physiological or pathophysiological conditions. These insights open the possibility for site- and mechanism-specific interventions to treat various disorders of the neural control of breathing.
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Affiliation(s)
- Jeffrey C Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, MD, USA.
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67
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Abstract
Breathing is an essential behavior that presents a unique opportunity to understand how the nervous system functions normally, how it balances inherent robustness with a highly regulated lability, how it adapts to both rapidly and slowly changing conditions, and how particular dysfunctions result in disease. We focus on recent advancements related to two essential sites for respiratory rhythmogenesis: (a) the preBötzinger Complex (preBötC) as the site for the generation of inspiratory rhythm and (b) the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG) as the site for the generation of active expiration.
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Affiliation(s)
- Jack L Feldman
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1763, USA.
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68
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Okada Y, Sasaki T, Oku Y, Takahashi N, Seki M, Ujita S, Tanaka KF, Matsuki N, Ikegaya Y. Preinspiratory calcium rise in putative pre-Botzinger complex astrocytes. J Physiol 2012; 590:4933-44. [PMID: 22777672 DOI: 10.1113/jphysiol.2012.231464] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The neural inspiratory activity originates from a ventrolateral medullary region called the pre-Bötzinger complex (preBötC), yet the mechanism underlying respiratory rhythmogenesis is not completely understood. Recently, the role of not only neurons but astrocytes in the central respiratory control has attracted considerable attention. Here we report our discovery that an intracellular calcium rise in a subset of putative astrocytes precedes inspiratory neuronal firing in rhythmically active slices. Functional calcium imaging from hundreds of preBötC cells revealed that a subset of putative astrocytes exhibited rhythmic calcium elevations preceding inspiratory neuronal activity with a time lag of approximately 2 s. These preinspiratory putative astrocytes maintained their rhythmic activities even during the blockade of neuronal activity with tetrodotoxin, whereas the rhythm frequency was lowered and the intercellular phases of these rhythms were decoupled. In addition, optogenetic stimulation of preBötC putative astrocytes induced firing of inspiratory neurons. These findings raise the possibility that astrocytes in the preBötC are actively involved in respiratory rhythm generation in rhythmically active slices.
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Affiliation(s)
- Yasumasa Okada
- Division of Internal Medicine and Laboratory of Electrophysiology, Murayama Medical Center, 2-37-1 Gakuen, Musashimurayama, Tokyo 208-0011, Japan.
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69
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Lindsey BG, Rybak IA, Smith JC. Computational models and emergent properties of respiratory neural networks. Compr Physiol 2012; 2:1619-70. [PMID: 23687564 PMCID: PMC3656479 DOI: 10.1002/cphy.c110016] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Computational models of the neural control system for breathing in mammals provide a theoretical and computational framework bringing together experimental data obtained from different animal preparations under various experimental conditions. Many of these models were developed in parallel and iteratively with experimental studies and provided predictions guiding new experiments. This data-driven modeling approach has advanced our understanding of respiratory network architecture and neural mechanisms underlying generation of the respiratory rhythm and pattern, including their functional reorganization under different physiological conditions. Models reviewed here vary in neurobiological details and computational complexity and span multiple spatiotemporal scales of respiratory control mechanisms. Recent models describe interacting populations of respiratory neurons spatially distributed within the Bötzinger and pre-Bötzinger complexes and rostral ventrolateral medulla that contain core circuits of the respiratory central pattern generator (CPG). Network interactions within these circuits along with intrinsic rhythmogenic properties of neurons form a hierarchy of multiple rhythm generation mechanisms. The functional expression of these mechanisms is controlled by input drives from other brainstem components,including the retrotrapezoid nucleus and pons, which regulate the dynamic behavior of the core circuitry. The emerging view is that the brainstem respiratory network has rhythmogenic capabilities at multiple levels of circuit organization. This allows flexible, state-dependent expression of different neural pattern-generation mechanisms under various physiological conditions,enabling a wide repertoire of respiratory behaviors. Some models consider control of the respiratory CPG by pulmonary feedback and network reconfiguration during defensive behaviors such as cough. Future directions in modeling of the respiratory CPG are considered.
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Affiliation(s)
- Bruce G Lindsey
- Department of Molecular Pharmacology and Physiology and Neuroscience Program, University of South Florida College of Medicine, Tampa, Florida, USA.
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70
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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.
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Affiliation(s)
- Nicholas M Mellen
- Department of Pediatrics, University of Louisville, School of Medicine, Louisville, KY 40202-3830, USA
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71
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Shevtsova NA, Manzke T, Molkov YI, Bischoff A, Smith JC, Rybak IA, Richter DW. Computational modelling of 5-HT receptor-mediated reorganization of the brainstem respiratory network. Eur J Neurosci 2011; 34:1276-91. [PMID: 21899601 DOI: 10.1111/j.1460-9568.2011.07825.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Brainstem respiratory neurons express the glycine α(3) receptor (Glyα(3) R), which is a target of modulation by several serotonin (5-HT) receptor agonists. Application of the 5-HT(1A) receptor (5-HT(1A) R) agonist 8-OH-DPAT was shown (i) to depress cellular cAMP, leading to dephosphorylation of Glyα(3) R and augmentation of postsynaptic inhibition of neurons expressing Glyα(3) R (Manzke et al., 2010) and (ii) to hyperpolarize respiratory neurons through 5-HT-activated potassium channels. These processes counteract opioid-induced depression and restore breathing from apnoeas often accompanying pharmacotherapy of pain. The effect is postulated to rely on the enhanced Glyα(3) R-mediated inhibition of inhibitory neurons causing disinhibition of their target neurons. To evaluate this proposal and investigate the neural mechanisms involved, an established computational model of the brainstem respiratory network (Smith et al., 2007), was extended by (i) incorporating distinct subpopulations of inhibitory neurons (glycinergic and GABAergic) and their synaptic interconnections within the Bötzinger and pre-Bötzinger complexes and (ii) assigning the 5-HT(1A) R-Glyα(3) R complex to some of these inhibitory neuron types in the network. The modified model was used to simulate the effects of 8-OH-DPAT on the respiratory pattern and was able to realistically reproduce a number of experimentally observed responses, including the shift in the onset of post-inspiratory activity to inspiration and conversion of the eupnoeic three-phase rhythmic pattern into a two-phase pattern lacking the post-inspiratory phase. The model shows how 5-HT(1A) R activation can produce a disinhibition of inspiratory neurons, leading to the recovery of respiratory rhythm from opioid-induced apnoeas.
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Affiliation(s)
- Natalia A Shevtsova
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
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72
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Champagnat J, Morin-Surun MP, Bouvier J, Thoby-Brisson M, Fortin G. Prenatal development of central rhythm generation. Respir Physiol Neurobiol 2011; 178:146-55. [PMID: 21527363 DOI: 10.1016/j.resp.2011.04.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 04/08/2011] [Accepted: 04/12/2011] [Indexed: 12/01/2022]
Abstract
Foetal breathing in mice results from prenatal activity of the two coupled hindbrain oscillators considered to be responsible for respiratory rhythm generation after birth: the pre-Bötzinger complex (preBötC) is active shortly before the onset of foetal breathing; the parafacial respiratory group (e-pF in embryo) starts activity one day earlier. Transcription factors have been identified that are essential to specify neural progenitors and lineages forming each of these oscillators during early development of the neural tube: Hoxa1, Egr2 (Krox20), Phox2b, Lbx1 and Atoh1 for the e-pF; Dbx1 and Evx1 for the preBötC which eventually grow contralateral axons requiring expression of Robo3. Inactivation of the genes encoding these factors leads to mis-specification of these neurons and distinct breathing abnormalities: apneic patterns and loss of central chemosensitivity for the e-pF (central congenital hypoventilation syndrome, CCHS, in humans), complete loss of breathing for the preBötC, right-left desynchronized breathing in Robo3 mutants. Mutations affecting development in more rostral (pontine) respiratory territories change the shape of the inspiratory drive without affecting the rhythm. Other (primordial) embryonic oscillators start in the mouse three days before the e-pF, to generate low frequency (LF) rhythms that are probably required for activity-dependent development of neurones at embryonic stages; in the foetus, however, they are actively silenced to avoid detrimental interaction with the on-going respiratory rhythm. Altogether, these observations provide a strong support to the previously proposed hypothesis that the functional organization of the respiratory generator is specified at early stages of development and is dual in nature, comprising two serially non-homologous oscillators.
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Affiliation(s)
- Jean Champagnat
- Neurobiologie et Développement (UPR 3294, CNRS), Neuro-Sud Paris (IFR 144), Centre de Recherche de Gif-sur Yvette (CNRS, FRC 3115), Gif-sur-Yvette, France.
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73
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The role of spiking and bursting pacemakers in the neuronal control of breathing. J Biol Phys 2011; 37:241-61. [PMID: 22654176 DOI: 10.1007/s10867-011-9214-z] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Accepted: 01/06/2011] [Indexed: 12/19/2022] Open
Abstract
Breathing is controlled by a distributed network involving areas in the neocortex, cerebellum, pons, medulla, spinal cord, and various other subcortical regions. However, only one area seems to be essential and sufficient for generating the respiratory rhythm: the preBötzinger complex (preBötC). Lesioning this area abolishes breathing and following isolation in a brain slice the preBötC continues to generate different forms of respiratory activities. The use of slice preparations led to a thorough understanding of the cellular mechanisms that underlie the generation of inspiratory activity within this network. Two types of inward currents, the persistent sodium current (I(NaP)) and the calcium-activated non-specific cation current (I(CAN)), play important roles in respiratory rhythm generation. These currents give rise to autonomous pacemaker activity within respiratory neurons, leading to the generation of intrinsic spiking and bursting activity. These membrane properties amplify as well as activate synaptic mechanisms that are critical for the initiation and maintenance of inspiratory activity. In this review, we describe the dynamic interplay between synaptic and intrinsic membrane properties in the generation of the respiratory rhythm and we relate these mechanisms to rhythm generating networks involved in other behaviors.
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74
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Pagliardini S, Janczewski WA, Tan W, Dickson CT, Deisseroth K, Feldman JL. Active expiration induced by excitation of ventral medulla in adult anesthetized rats. J Neurosci 2011; 31:2895-905. [PMID: 21414911 PMCID: PMC3142740 DOI: 10.1523/jneurosci.5338-10.2011] [Citation(s) in RCA: 177] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 12/02/2010] [Accepted: 12/21/2010] [Indexed: 11/21/2022] Open
Abstract
Data from perinatal and juvenile rodents support our hypothesis that the preBötzinger complex generates inspiratory rhythm and the retrotrapezoid nucleus-parafacial respiratory group (RTN/pFRG) generates active expiration (AE). Although the role of the RTN/pFRG in adulthood is disputed, we hypothesized that its rhythmogenicity persists but is typically silenced by synaptic inhibition. We show in adult anesthetized rats that local pharmacological disinhibition or optogenetic excitation of the RTN/pFRG can generate AE and transforms previously silent RTN/pFRG neurons into rhythmically active cells whose firing is correlated with late-phase active expiration. Brief excitatory stimuli also reset the respiratory rhythm, indicating strong coupling of AE to inspiration. The AE network location in adult rats overlaps with the perinatal pFRG and appears lateral to the chemosensitive region of adult RTN. We suggest that (1) the RTN/pFRG contains a conditional oscillator that generates AE, and (2) at rest and in anesthesia, synaptic inhibition of RTN/pFRG suppresses AE.
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Affiliation(s)
- Silvia Pagliardini
- Systems Neurobiology Laboratory, Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095-1763
| | - Wiktor A. Janczewski
- Systems Neurobiology Laboratory, Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095-1763
| | - Wenbin Tan
- Systems Neurobiology Laboratory, Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095-1763
| | - Clayton T. Dickson
- Departments of Psychology
- Physiology, and
- Centre for Neuroscience, University of Alberta, Edmonton, Alberta T6G 2E9, Canada, and
| | - Karl Deisseroth
- Departments of Bioengineering and
- Psychiatry, Stanford University, Stanford, California 94305
| | - Jack L. Feldman
- Systems Neurobiology Laboratory, Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095-1763
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75
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Jordan LM, Sławińska U. Chapter 12--modulation of rhythmic movement: control of coordination. PROGRESS IN BRAIN RESEARCH 2011; 188:181-95. [PMID: 21333810 DOI: 10.1016/b978-0-444-53825-3.00017-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Three rhythmic movements, breathing, walking, and chewing, are considered from the perspective of the emerging factors that control their coordination. This takes us beyond the concept of a core excitatory kernel and into the common principles that govern the interaction between components of the neural networks that must be orchestrated properly to produce meaningful movement beyond the production of the basic rhythm. We focus on the role of neuromodulators, especially 5-hydroxytryptamine (5-HT), in the production of coordinated breathing, walking, and chewing, and we review the evidence that at least in the case of breathing and walking, 5-HT input to the CPGs acts through the selection of inhibitory interneurons that are essential for coordination. We review data from recently developed mouse models that offer insight into the contributions of inhibitory coordinating neurons, including the development of a new model that has allowed the revelation that there are glycinergic pacemaker neurons that likely contribute to the production of the respiratory rhythm. Perhaps walking and chewing will not be far behind.
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Affiliation(s)
- Larry M Jordan
- Department of Physiology, Spinal Cord Research Centre, University of Manitoba, Winnipeg MB, Canada
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76
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Abstract
I provide a personal view of the developments since ~1986 that underlie the contemporary view(s) about how the rhythm of breathing is generated and how the pattern of breathing is modulated. Two sites in the mammalian brainstem are likely to participate in respiratory rhythm generation: the preBötzinger Complex (preBötC), first described and intensely investigated since 1990, plays a well-documented essential role in normal breathing in mammals of all ages and may be principally involved in controlling inspiratory motor activity, and the retrotrapezoid/parafacial respiratory group (RTN/pFRG) that appears to play at least a modulatory role in neonatal and juvenile rodents and may be a conditional oscillator that controls active expiration.
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Affiliation(s)
- Jack L Feldman
- Department of Neurobiology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA
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77
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Abstract
A subset of preBötzinger Complex (preBötC) neurokinin 1 receptor (NK1R) and somatostatin peptide (SST)-expressing neurons are necessary for breathing in adult rats, in vivo. Their developmental origins and relationship to other preBötC glutamatergic neurons are unknown. Here we show, in mice, that the "core" of preBötC SST(+)/NK1R(+)/SST 2a receptor(+) (SST2aR) neurons, are derived from Dbx1-expressing progenitors. We also show that Dbx1-derived neurons heterogeneously coexpress NK1R and SST2aR within and beyond the borders of preBötC. More striking, we find that nearly all non-catecholaminergic glutamatergic neurons of the ventrolateral medulla (VLM) are also Dbx1 derived. PreBötC SST(+) neurons are born between E9.5 and E11.5 in the same proportion as non-SST-expressing neurons. Additionally, preBötC Dbx1 neurons are respiratory modulated and show an early inspiratory phase of firing in rhythmically active slice preparations. Loss of Dbx1 eliminates all glutamatergic neurons from the respiratory VLM including preBötC NK1R(+)/SST(+) neurons. Dbx1 mutant mice do not express any spontaneous respiratory behaviors in vivo. Moreover, they do not generate rhythmic inspiratory activity in isolated en bloc preparations even after acidic or serotonergic stimulation. These data indicate that preBötC core neurons represent a subset of a larger, more heterogeneous population of VLM Dbx1-derived neurons. These data indicate that Dbx1-derived neurons are essential for the expression and, we hypothesize, are responsible for the generation of respiratory behavior both in vitro and in vivo.
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78
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Galán RF, Dick TE, Baekey DM. Analysis and modeling of ensemble recordings from respiratory pre-motor neurons indicate changes in functional network architecture after acute hypoxia. Front Comput Neurosci 2010; 4. [PMID: 20890445 PMCID: PMC2947924 DOI: 10.3389/fncom.2010.00131] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2009] [Accepted: 08/17/2010] [Indexed: 11/26/2022] Open
Abstract
We have combined neurophysiologic recording, statistical analysis, and computational modeling to investigate the dynamics of the respiratory network in the brainstem. Using a multielectrode array, we recorded ensembles of respiratory neurons in perfused in situ rat preparations that produce spontaneous breathing patterns, focusing on inspiratory pre-motor neurons. We compared firing rates and neuronal synchronization among these neurons before and after a brief hypoxic stimulus. We observed a significant decrease in the number of spikes after stimulation, in part due to a transient slowing of the respiratory pattern. However, the median interspike interval did not change, suggesting that the firing threshold of the neurons was not affected but rather the synaptic input was. A bootstrap analysis of synchrony between spike trains revealed that both before and after brief hypoxia, up to 45% (but typically less than 5%) of coincident spikes across neuronal pairs was not explained by chance. Most likely, this synchrony resulted from common synaptic input to the pre-motor population, an example of stochastic synchronization. After brief hypoxia most pairs were less synchronized, although some were more, suggesting that the respiratory network was transiently “rewired” after the stimulus. To investigate this hypothesis, we created a simple computational model with feed-forward divergent connections along the inspiratory pathway. Assuming that (1) the number of divergent projections was not the same for all presynaptic cells, but rather spanned a wide range and (2) that the stimulus increased inhibition at the top of the network; this model reproduced the reduction in firing rate and bootstrap-corrected synchrony subsequent to hypoxic stimulation observed in our experimental data.
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Affiliation(s)
- Roberto Fernández Galán
- Department of Neurosciences, School of Medicine, Case Western Reserve University Cleveland, OH, USA
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79
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K(+) and Ca²(+) dependence of inspiratory-related rhythm in novel "calibrated" mouse brainstem slices. Respir Physiol Neurobiol 2010; 175:37-48. [PMID: 20833274 DOI: 10.1016/j.resp.2010.09.004] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2010] [Revised: 08/31/2010] [Accepted: 09/02/2010] [Indexed: 11/21/2022]
Abstract
Recently developed transversal newborn rat brainstem slices with "calibrated" rostrocaudal margins unraveled novel features of rhythmogenic inspiratory active pre-Bötzinger complex (preBötC) neural networks (Ballanyi and Ruangkittisakul, 2009). For example, slice rhythm in physiological (3 mM) superfusate K(+) is depressed by modestly raised Ca²(+) and restored by raised K(+). Correspondingly, we generated here calibrated preBötC slices from commonly used newborn C57BL/6 mice in which rostrocaudal extents of respiratory marker structures, e.g., the inferior olive, turned out to be smaller than in newborn rats. Slices of 400-600 μm thickness with likely centered preBötC kernel ("m-preBötC slices") generated rhythm in 3 mM K(+) and 1mM Ca(2+) for several hours although its rate decreased to < 5 bursts/min after >1 h. Rhythm was stable at 8-12 bursts/min in 6-7 mM K(+), depressed by 2 mM Ca²(+), and restored by 9 mM K(+). Our findings provide the basis for future structure-function analyses of the mouse preBötC, whose activity depends critically on a "Ca(+)/K(+) antagonism" as in rats.
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80
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Molkov YI, Abdala APL, Bacak BJ, Smith JC, Paton JFR, Rybak IA. Late-expiratory activity: emergence and interactions with the respiratory CpG. J Neurophysiol 2010; 104:2713-29. [PMID: 20884764 DOI: 10.1152/jn.00334.2010] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The respiratory rhythm and motor pattern are hypothesized to be generated by a brain stem respiratory network with a rhythmogenic core consisting of neural populations interacting within and between the pre-Bötzinger (pre-BötC) and Bötzinger (BötC) complexes and controlled by drives from other brain stem compartments. Our previous large-scale computational model reproduced the behavior of this network under many different conditions but did not consider neural oscillations that were proposed to emerge within the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG) and drive preinspiratory (or late-expiratory, late-E) discharges in the abdominal motor output. Here we extend the analysis of our previously published data and consider new data on the generation of abdominal late-E activity as the basis for extending our computational model. The extended model incorporates an additional late-E population in RTN/pFRG, representing a source of late-E oscillatory activity. In the proposed model, under normal metabolic conditions, this RTN/pFRG oscillator is inhibited by BötC/pre-BötC circuits, and the late-E oscillations can be released by either hypercapnia-evoked activation of RTN/pFRG or by hypoxia-dependent suppression of RTN/pFRG inhibition by BötC/pre-BötC. The proposed interactions between BötC/pre-BötC and RTN/pFRG allow the model to reproduce several experimentally observed behaviors, including quantal acceleration of abdominal late-E oscillations with progressive hypercapnia and quantal slowing of phrenic activity with progressive suppression of pre-BötC excitability, as well as to predict a release of late-E oscillations by disinhibition of RTN/pFRG under normal conditions. The extended model proposes mechanistic explanations for the emergence of RTN/pFRG oscillations and their interaction with the brain stem respiratory network.
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Affiliation(s)
- Yaroslav I Molkov
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA
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81
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Hindbrain interneurons and axon guidance signaling critical for breathing. Nat Neurosci 2010; 13:1066-74. [PMID: 20680010 DOI: 10.1038/nn.2622] [Citation(s) in RCA: 165] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Accepted: 07/22/2010] [Indexed: 01/04/2023]
Abstract
Breathing is a bilaterally synchronous behavior that relies on a respiratory rhythm generator located in the brainstem. An essential component of this generator is the preBötzinger complex (preBötC), which paces inspirations. Little is known about the developmental origin of the interneuronal populations forming the preBötC oscillator network. We found that the homeobox gene Dbx1 controls the fate of glutamatergic interneurons required for preBötC rhythm generation in the mouse embryo. We also found that a conditional inactivation in Dbx1-derived cells of the roundabout homolog 3 (Robo3) gene, which is necessary for axonal midline crossing, resulted in left-right de-synchronization of the preBötC oscillator. Together, these findings identify Dbx1-derived interneurons as the core rhythmogenic elements of the preBötC oscillator and indicate that Robo3-dependent guidance signaling in these cells is required for bilaterally synchronous activity.
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82
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Takita K, Morimoto Y. Effects of sevoflurane on respiratory rhythm oscillators in the medulla oblongata. Respir Physiol Neurobiol 2010; 173:86-94. [DOI: 10.1016/j.resp.2010.06.016] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2010] [Revised: 06/28/2010] [Accepted: 06/28/2010] [Indexed: 11/29/2022]
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83
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Bongianni F, Mutolo D, Cinelli E, Pantaleo T. Respiratory responses induced by blockades of GABA and glycine receptors within the Bötzinger complex and the pre-Bötzinger complex of the rabbit. Brain Res 2010; 1344:134-47. [PMID: 20483350 DOI: 10.1016/j.brainres.2010.05.032] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2010] [Revised: 05/05/2010] [Accepted: 05/11/2010] [Indexed: 01/01/2023]
Abstract
The respiratory role of GABA(A), GABA(B) and glycine receptors within the Bötzinger complex (BötC) and the pre-Bötzinger complex (preBötC) was investigated in alpha-chloralose-urethane anesthetized, vagotomized, paralysed and artificially ventilated rabbits by using bilateral microinjections (30-50 nl) of GABA and glycine receptor agonists and antagonists. GABA(A) receptor blockade by bicuculline (5mM) or gabazine (2mM) within the BötC induced strong depression of respiratory activity up to apnea. The latter was reversed by hypercapnia. Glycine receptor blockade by strychnine (5mM) within the BötC decreased the frequency and amplitude of phrenic bursts. Bicuculline microinjections into the preBötC caused decreases in respiratory frequency and the appearance of two alternating different levels of peak phrenic activity. Strychnine microinjections into the preBötC increased respiratory frequency and decreased peak phrenic amplitude. GABA(A), but not glycine receptor antagonism within the preBötC restored respiratory rhythmicity during apnea due to bicuculline or gabazine applied to the BötC. GABA(B) receptor blockade by CGP-35348 (50mM) within the BötC and the preBötC did not affect baseline respiratory activity, though microinjections of the GABA(B) receptor agonist baclofen (1mM) into the same regions altered respiratory activity. The results show that only GABA(A) and glycine receptors within the BötC and the preBötC mediate a potent control on both the intensity and frequency of inspiratory activity during eupneic breathing. This study is the first to provide evidence that these inhibitory receptors have a respiratory function within the BötC.
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Affiliation(s)
- Fulvia Bongianni
- Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze, Viale GB Morgagni 63, I-50134 Firenze, Italy.
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84
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Del Negro CA, Hayes JA, Pace RW, Brush BR, Teruyama R, Feldman JL. Synaptically activated burst-generating conductances may underlie a group-pacemaker mechanism for respiratory rhythm generation in mammals. PROGRESS IN BRAIN RESEARCH 2010; 187:111-36. [PMID: 21111204 PMCID: PMC3370336 DOI: 10.1016/b978-0-444-53613-6.00008-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Breathing, chewing, and walking are critical life-sustaining behaviors in mammals that consist essentially of simple rhythmic movements. Breathing movements in particular involve the diaphragm, thorax, and airways but emanate from a network in the lower brain stem. This network can be studied in reduced preparations in vitro and using simplified mathematical models that make testable predictions. An iterative approach that employs both in vitro and in silico models argues against canonical mechanisms for respiratory rhythm in neonatal rodents that involve reciprocal inhibition and pacemaker properties. We present an alternative model in which emergent network properties play a rhythmogenic role. Specifically, we show evidence that synaptically activated burst-generating conductances-which are only available in the context of network activity-engender robust periodic bursts in respiratory neurons. Because the cellular burst-generating mechanism is linked to network synaptic drive we dub this type of system a group pacemaker.
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Affiliation(s)
- Christopher A. Del Negro
- Department of Applied Science, McGlothlin-Street Hall, The College of William & Mary, Williamsburg, Virginia, USA. Ryland W. Pace Tel: 757-645-8904, . Benjamin R. Brush Tel: 774-278-0645,
| | - John A. Hayes
- Department of Applied Science, McGlothlin-Street Hall, The College of William & Mary, Williamsburg, Virginia, USA. Ryland W. Pace Tel: 757-645-8904, . Benjamin R. Brush Tel: 774-278-0645,
| | - Ryland W. Pace
- Department of Applied Science, McGlothlin-Street Hall, The College of William & Mary, Williamsburg, Virginia, USA. Ryland W. Pace Tel: 757-645-8904, . Benjamin R. Brush Tel: 774-278-0645,
| | - Benjamin R. Brush
- Department of Applied Science, McGlothlin-Street Hall, The College of William & Mary, Williamsburg, Virginia, USA. Ryland W. Pace Tel: 757-645-8904, . Benjamin R. Brush Tel: 774-278-0645,
| | - Ryoichi Teruyama
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, USA. Tel: 225-578-4623, Fax: 225-578-2597,
| | - Jack L. Feldman
- Department of Neurobiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California, USA. Tel: 310-825-0954, Fax: 310-825-2224,
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Zimmer MB, Nantwi K, Goshgarian HG. Effect of spinal cord injury on the respiratory system: basic research and current clinical treatment options. J Spinal Cord Med 2007; 203:98-108. [PMID: 17853653 DOI: 10.1016/j.resp.2014.08.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 08/11/2014] [Accepted: 08/12/2014] [Indexed: 02/09/2023] Open
Abstract
Spinal cord injury (SCI) often leads to an impairment of the respiratory system. The more rostral the level of injury, the more likely the injury will affect ventilation. In fact, respiratory insufficiency is the number one cause of mortality and morbidity after SCI. This review highlights the progress that has been made in basic and clinical research, while noting the gaps in our knowledge. Basic research has focused on a hemisection injury model to examine methods aimed at improving respiratory function after SCI, but contusion injury models have also been used. Increasing synaptic plasticity, strengthening spared axonal pathways, and the disinhibition of phrenic motor neurons all result in the activation of a latent respiratory motor pathway that restores function to a previously paralyzed hemidiaphragm in animal models. Human clinical studies have revealed that respiratory function is negatively impacted by SCI. Respiratory muscle training regimens may improve inspiratory function after SCI, but more thorough and carefully designed studies are needed to adequately address this issue. Phrenic nerve and diaphragm pacing are options available to wean patients from standard mechanical ventilation. The techniques aimed at improving respiratory function in humans with SCI have both pros and cons, but having more options available to the clinician allows for more individualized treatment, resulting in better patient care. Despite significant progress in both basic and clinical research, there is still a significant gap in our understanding of the effect of SCI on the respiratory system.
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Affiliation(s)
- M Beth Zimmer
- Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan 48201, USA.
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