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Barna BF, Takakura AC, Mulkey DK, Moreira TS. Purinergic receptor blockade in the retrotrapezoid nucleus attenuates the respiratory chemoreflexes in awake rats. Acta Physiol (Oxf) 2016; 217:80-93. [PMID: 26647910 DOI: 10.1111/apha.12637] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Revised: 10/06/2015] [Accepted: 11/26/2015] [Indexed: 01/21/2023]
Abstract
AIM Recent evidence suggests that adenosine triphosfate (ATP)-mediated purinergic signalling at the level of the rostral ventrolateral medulla contributes to both central and peripheral chemoreceptor control of breathing and blood pressure: neurones in the retrotrapezoid nucleus (RTN) function as central chemoreceptors in part by responding to CO2 -evoked ATP release by activation of yet unknown P2 receptors, and nearby catecholaminergic C1 neurones regulate blood pressure responses to peripheral chemoreceptor activation by a P2Y1 receptor-dependent mechanism. However, potential contributions of purinergic signalling in the RTN to cardiorespiratory function in conscious animals have not been tested. METHODS Cardiorespiratory activity of unrestrained awake rats was measured in response to RTN injections of ATP, and during exposure to hypercapnia (7% CO2 ) or hypoxia (8% O2 ) under control conditions and after bilateral RTN injections of P2 receptor blockers (PPADS or MRS2179). RESULTS Unilateral injection of ATP into the RTN increased cardiorespiratory output by a P2-receptor-dependent mechanism. We also show that bilateral RTN injections of a non-specific P2 receptor blocker (pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS) reduced the ventilatory response to hypercapnia (7% CO2 ) and hypoxia (8% O2 ) in unanesthetized rats. Conversely, bilateral injections of a specific P2Y1 receptor blocker (MRS2179) into the RTN had no measurable effect on ventilatory responses elicited by hypercapnia or hypoxia. CONCLUSION These data exclude P2Y1 receptor involvement in the chemosensory control of breathing at the level of the RTN and show that ATP-mediated purinergic signalling contributes to central and peripheral chemoreflex control of breathing and blood pressure in awake rats.
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Affiliation(s)
- B. F. Barna
- Department of Physiology and Biophysics; Institute of Biomedical Science; University of São Paulo; São Paulo SP Brazil
| | - A. C. Takakura
- Department of Pharmacology; Institute of Biomedical Science; University of São Paulo; São Paulo SP Brazil
| | - D. K. Mulkey
- Department of Physiology and Neurobiology; University of Connecticut; Storrs CT USA
| | - T. S. Moreira
- Department of Physiology and Biophysics; Institute of Biomedical Science; University of São Paulo; São Paulo SP Brazil
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Silva JN, Lucena EV, Silva TM, Damasceno RS, Takakura AC, Moreira TS. Inhibition of the pontine Kölliker-Fuse nucleus reduces genioglossal activity elicited by stimulation of the retrotrapezoid chemoreceptor neurons. Neuroscience 2016; 328:9-21. [PMID: 27126558 DOI: 10.1016/j.neuroscience.2016.04.028] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2016] [Revised: 04/16/2016] [Accepted: 04/18/2016] [Indexed: 01/06/2023]
Abstract
The Kölliker-Fuse (KF) region, located in the dorsolateral pons, projects to several brainstem areas involved in respiratory regulation, including the chemoreceptor neurons within the retrotrapezoid nucleus (RTN). Several lines of evidence indicate that the pontine KF region plays an important role in the control of the upper airways for the maintenance of appropriate airflow to and from the lungs. Specifically, we hypothesized that the KF region is involved in mediating the response of the hypoglossal motor activity to central respiratory chemoreflex activation and to stimulation of the chemoreceptor neurons within the RTN region. To test this hypothesis, we combined immunohistochemistry and physiological experiments. We found that in the KF, the majority of biotinylated dextran amine (BDA)-labeled axonal varicosities contained detectable levels of vesicular glutamate transporter-2 (VGLUT2), but few contained glutamic acid decarboxylase-67 (GAD67). The majority of the RTN neurons that were FluorGold (FG)-immunoreactive (i.e., projected to the KF) contained hypercapnia-induced Fos, but did not express tyrosine hydroxylase. In urethane-anesthetized sino-aortic denervated and vagotomized male Wistar rats, hypercapnia (10% CO2) or N-methyl-d-aspartate (NMDA) injection (0.1mM) in the RTN increased diaphragm (DiaEMG) and genioglossus muscle (GGEMG) activities and elicited abdominal (AbdEMG) activity. Bilateral injection of muscimol (GABA-A agonist; 2mM) into the KF region reduced the increase in DiaEMG and GGEMG produced by hypercapnia or NMDA into the RTN. Our data suggest that activation of chemoreceptor neurons in the RTN produces a significant increase in the genioglossus muscle activity and the excitatory pathway is dependent on the neurons located in the dorsolateral pontine KF region.
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Affiliation(s)
- Josiane N Silva
- Department of Pharmacology, Institute of Biomedical Science, University of São Paulo (USP), 05508-000 São Paulo/SP, Brazil
| | - Elvis V Lucena
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo (USP), 05508-000 São Paulo/SP, Brazil
| | - Talita M Silva
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo (USP), 05508-000 São Paulo/SP, Brazil
| | - Rosélia S Damasceno
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo (USP), 05508-000 São Paulo/SP, Brazil
| | - Ana C Takakura
- Department of Pharmacology, Institute of Biomedical Science, University of São Paulo (USP), 05508-000 São Paulo/SP, Brazil
| | - Thiago S Moreira
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo (USP), 05508-000 São Paulo/SP, Brazil.
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Takakura AC, Moreira TS. The retrotrapezoid nucleus as a central brainstem area for central and peripheral chemoreceptor interactions. Exp Physiol 2016; 101:455-6. [DOI: 10.1113/ep085615] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Ana C. Takakura
- Department of Pharmacology; Institute of Biomedical Science, University of São Paulo (USP) 05508-000; São Paulo SP Brazil
| | - Thiago S. Moreira
- Department of Physiology and Biophysics; Institute of Biomedical Science, University of São Paulo (USP) 05508-000; São Paulo SP Brazil
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Silva JN, Tanabe FM, Moreira TS, Takakura AC. Neuroanatomical and physiological evidence that the retrotrapezoid nucleus/parafacial region regulates expiration in adult rats. Respir Physiol Neurobiol 2016; 227:9-22. [PMID: 26900003 DOI: 10.1016/j.resp.2016.02.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Revised: 02/11/2016] [Accepted: 02/11/2016] [Indexed: 01/09/2023]
Abstract
The rostroventrolateral medulla contains two functional neuronal populations: (1) the parafacial respiratory group (pFRG) neurons and (2) the chemosensitive retrotrapezoid nucleus (RTN) neurons. Using anatomical and physiological techniques, we investigated the role of the RTN/pFRG in CO2-induced active expiration (AE) in urethane-anesthetized rats. Anterograde tracing using biotinylated dextran amine (BDA) revealed dense neuronal projections emanating from the RTN/pFRG to the caudal ventral respiratory group (cVRG), 60% of which contained vesicular glutamate transporter-2. The minority (16%) of the RTN projections to the cVRG emanated from Phox2b positive neurons. Hypercapnia (10% CO2) increased DiaEMG and elicited AbdEMG activity. Bilateral injections of muscimol (2mM) into the RTN/pFRG reduced the activation of DiaEMG (23±4%) and abolished AE-induced by chemoreflex stimulation. Taken together, these results support the presence of direct excitatory projections from RTN/pFRG neurons to cVRG expiratory premotor neurons, playing a role in the generation/modulation of AE.
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Affiliation(s)
- Josiane N Silva
- Department of Pharmacology, Institute of Biomedical Sciences, University of São Paulo (USP), 05508-000 São Paulo, SP, Brazil
| | - Fabiola M Tanabe
- Department of Pharmacology, Institute of Biomedical Sciences, University of São Paulo (USP), 05508-000 São Paulo, SP, Brazil
| | - Thiago S Moreira
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of São Paulo (USP), 05508-000 São Paulo, SP, Brazil
| | - Ana C Takakura
- Department of Pharmacology, Institute of Biomedical Sciences, University of São Paulo (USP), 05508-000 São Paulo, SP, Brazil.
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Role of Astrocytes in Central Respiratory Chemoreception. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 949:109-145. [PMID: 27714687 DOI: 10.1007/978-3-319-40764-7_6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Astrocytes perform various homeostatic functions in the nervous system beyond that of a supportive or metabolic role for neurons. A growing body of evidence indicates that astrocytes are crucial for central respiratory chemoreception. This review presents a classical overview of respiratory central chemoreception and the new evidence for astrocytes as brainstem sensors in the respiratory response to hypercapnia. We review properties of astrocytes for chemosensory function and for modulation of the respiratory network. We propose that astrocytes not only mediate between CO2/H+ levels and motor responses, but they also allow for two emergent functions: (1) Amplifying the responses of intrinsic chemosensitive neurons through feedforward signaling via gliotransmitters and; (2) Recruiting non-intrinsically chemosensitive cells thanks to volume spreading of signals (calcium waves and gliotransmitters) to regions distant from the CO2/H+ sensitive domains. Thus, astrocytes may both increase the intensity of the neuron responses at the chemosensitive sites and recruit of a greater number of respiratory neurons to participate in the response to hypercapnia.
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Garg SK, Lioy DT, Knopp SJ, Bissonnette JM. Conditional depletion of methyl-CpG-binding protein 2 in astrocytes depresses the hypercapnic ventilatory response in mice. J Appl Physiol (1985) 2015. [DOI: 10.1152/japplphysiol.00411.2015] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mice that are deficient in the transcription factor methyl-CpG-binding protein 2 (MeCP2) have a depressed hypercapnic ventilatory response (HCVR). The expression of MeCP2 can be selectively removed from astrocytes or neurons, thus offering a tool to dissect the role of this transcription factor in astrocytes from that in neurons. Studies were carried out in the progeny of mice that were a cross between those harboring a tamoxifen (TAM)-inducible Cre recombinase transgene driven by the human astrocytic glial fibrillary acidic protein (hGFAP) promoter, or Cre recombinase under control of the synapsin promoter, with mice containing a Cre-excisable exon III in the Mecp2 gene. The TAM-conditional excision of the Mecp2 exon allowed the respiratory CO2 response to be studied in the same animals before and after selective depletion of MeCP2 in astrocytes. Immunohistochemistry showed that following TAM treatment only ∼20% of GFAP-labeled cells in the retrotrapazoid nucleus and in the raphé magnus were positive for MeCP2. The slope of the relative increase in minute ventilation as a function of 1, 3, and 5% inspired CO2 was depressed in mice with depleted astrocyte MeCP2 compared with wild-type littermates. In contrast, selective depletion of MeCP2 in neurons did not significantly affect slope. While neurons which constitute the respiratory network ultimately determine the ventilatory response to CO2, this study demonstrates that loss of MeCP2 in astrocytes alone is sufficient to result in a dramatic attenuation of the HCVR. We propose that the glial contribution to HCVR is under the control of the MeCP2 gene.
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Affiliation(s)
| | | | | | - John M. Bissonnette
- Department of Obstetrics and Gynecology, and
- Department of Cell, Developmental and Cancer Biology, Oregon Health and Science University, Portland, Oregon
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Smith CA, Blain GM, Henderson KS, Dempsey JA. Peripheral chemoreceptors determine the respiratory sensitivity of central chemoreceptors to CO2 : role of carotid body CO2. J Physiol 2015; 593:4225-43. [PMID: 26171601 DOI: 10.1113/jp270114] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Accepted: 06/26/2015] [Indexed: 11/08/2022] Open
Abstract
We asked if the type of carotid body (CB) chemoreceptor stimulus influenced the ventilatory gain of the central chemoreceptors to CO2 . The effect of CB normoxic hypocapnia, normocapnia and hypercapnia (carotid body PCO2 ≈ 22, 41 and 68 mmHg, respectively) on the ventilatory CO2 sensitivity of central chemoreceptors was studied in seven awake dogs with vascularly-isolated and extracorporeally-perfused CBs. Chemosensitivity with one CB was similar to that in intact dogs. In four CB-denervated dogs, absence of hyper-/hypoventilatory responses to CB perfusion with PCO2 of 19-75 mmHg confirmed separation of the perfused CB circulation from the brain. The group mean central CO2 response slopes were increased 303% for minute ventilation (V̇I)(P ≤ 0.01) and 251% for mean inspiratory flow rate (VT /TI ) (P ≤ 0.05) when the CB was hypercapnic vs. hypocapnic; central CO2 response slopes for tidal volume (VT ), breathing frequency (fb ) and rate of rise of the diaphragm EMG increased in 6 of 7 animals but the group mean changes did not reach statistical significance. Group mean central CO2 response slopes were also increased 237% for V̇I(P ≤ 0.01) and 249% for VT /TI (P ≤ 0.05) when the CB was normocapnic vs. hypocapnic, but no significant differences in any of the central ventilatory response indices were found between CB normocapnia and hypercapnia. These hyperadditive effects of CB hyper-/hypocapnia agree with previous findings using CB hyper-/hypoxia.We propose that hyperaddition is the dominant form of chemoreceptor interaction in quiet wakefulness when the chemosensory control system is intact, response gains physiological, and carotid body chemoreceptors are driven by a wide range of O2 and/or CO2 .
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Affiliation(s)
- Curtis A Smith
- The John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Grégory M Blain
- The John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA.,University of Nice Sophia Antipolis, Toulon, LAMHESS, EA 6309, F-06205, Nice, France
| | - Kathleen S Henderson
- The John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | - Jerome A Dempsey
- The John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
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Ruffault PL, D'Autréaux F, Hayes JA, Nomaksteinsky M, Autran S, Fujiyama T, Hoshino M, Hägglund M, Kiehn O, Brunet JF, Fortin G, Goridis C. The retrotrapezoid nucleus neurons expressing Atoh1 and Phox2b are essential for the respiratory response to CO₂. eLife 2015; 4. [PMID: 25866925 PMCID: PMC4429526 DOI: 10.7554/elife.07051] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 04/09/2015] [Indexed: 01/08/2023] Open
Abstract
Maintaining constant CO2 and H+ concentrations in the arterial blood is critical for life. The principal mechanism through which this is achieved in mammals is the respiratory chemoreflex whose circuitry is still elusive. A candidate element of this circuitry is the retrotrapezoid nucleus (RTN), a collection of neurons at the ventral medullary surface that are activated by increased CO2 or low pH and project to the respiratory rhythm generator. Here, we use intersectional genetic strategies to lesion the RTN neurons defined by Atoh1 and Phox2b expression and to block or activate their synaptic output. Photostimulation of these neurons entrains the respiratory rhythm. Conversely, abrogating expression of Atoh1 or Phox2b or glutamatergic transmission in these cells curtails the phrenic nerve response to low pH in embryonic preparations and abolishes the respiratory chemoreflex in behaving animals. Thus, the RTN neurons expressing Atoh1 and Phox2b are a necessary component of the chemoreflex circuitry. DOI:http://dx.doi.org/10.7554/eLife.07051.001 An adult at rest will typically breathe in and out up to 20 times per minute, inhaling oxygen and exhaling carbon dioxide in a process that, for the most part, occurs automatically. While we can choose to override this process and exert voluntary control over our breathing, we cannot suppress it indefinitely. Attempting to do so will ultimately trigger a reflex that forces us to start breathing again. This reflex is mostly a response to the rise of carbon dioxide (CO2) in the blood, which lowers the pH of the blood. This rise in CO2 is toxic and triggers an increase in breathing so that the excess CO2 is exhaled. The majority of the sensors that detect CO2 are in the brainstem, which is at the junction of the brain and the spinal cord. However, the precise location of these sensors is not clear. Ruffault et al. now argue that the sensors are in a region called the ‘retrotrapezoid nucleus’, and that they can be identified by the presence of two proteins, Atoh1 and Phox2b. In the brains of foetal mice, Ruffault et al. recorded cells in the retrotrapezoid nucleus and found that they fired in a rhythmic pattern, as would be expected for cells that control breathing. Moreover, the firing rate of these cells increased when the pH was lowered. Ruffault et al. then created genetically modified mice with mutations in genes for Atoh1 or Phox2b. The retrotrapezoid nucleus was either absent or abnormal in these mutant mice. Moreover, new-born pups with these mutations were not able to increase their breathing when the level of CO2 in their blood rose. These results shed light on the respiratory distress experienced by patients with a rare disorder called congenital central hypoventilation syndrome (CCHS) that is caused by mutations in Phox2b. More commonly, unstable or irregular breathing is seen in human infants that are born prematurely, and sometimes in infants born at full term. In the light of the new findings by Ruffault et al., it is possible that abnormal development or immaturity of the retrotrapezoid nucleus is the cause. DOI:http://dx.doi.org/10.7554/eLife.07051.002
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Affiliation(s)
- Pierre-Louis Ruffault
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, Gif-sur-Yvette, France
| | - Fabien D'Autréaux
- Institut de Biologie de l'École Normale Supérieure, Inserm U1024, and CNRS UMR 8197, Paris, France
| | - John A Hayes
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, Gif-sur-Yvette, France
| | - Marc Nomaksteinsky
- Institut de Biologie de l'École Normale Supérieure, Inserm U1024, and CNRS UMR 8197, Paris, France
| | - Sandra Autran
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, Gif-sur-Yvette, France
| | - Tomoyuki Fujiyama
- Department of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
| | - Mikio Hoshino
- Department of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
| | - Martin Hägglund
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Ole Kiehn
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Jean-François Brunet
- Institut de Biologie de l'École Normale Supérieure, Inserm U1024, and CNRS UMR 8197, Paris, France
| | - Gilles Fortin
- Université Paris-Saclay, Université Paris-Sud, CNRS, UMR 9197, Institut des Neurosciences Paris-Saclay, Gif-sur-Yvette, France
| | - Christo Goridis
- Institut de Biologie de l'École Normale Supérieure, Inserm U1024, and CNRS UMR 8197, Paris, France
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Abstract
Contiguous brain regions associated with a given behavior are increasingly being divided into subregions associated with distinct aspects of that behavior. Using recently developed neuronal hyperpolarizing technologies, we functionally dissect the parafacial region in the medulla, which contains key elements of the central pattern generator for breathing that are important in central CO2-chemoreception and for gating active expiration. By transfecting different populations of neighboring neurons with allatostatin or HM4D Gi/o-coupled receptors, we analyzed the effect of their hyperpolarization on respiration in spontaneously breathing vagotomized urethane-anesthetized rats. We identify two functionally separate parafacial nuclei: ventral (pFV) and lateral (pFL). Disinhibition of the pFL with bicuculline and strychnine led to active expiration. Hyperpolarizing pFL neurons had no effect on breathing at rest, or changes in inspiratory activity induced by hypoxia and hypercapnia; however, hyperpolarizing pFL neurons attenuated active expiration when it was induced by hypercapnia, hypoxia, or disinhibition of the pFL. In contrast, hyperpolarizing pFV neurons affected breathing at rest by decreasing inspiratory-related activity, attenuating the hypoxia- and hypercapnia-induced increase in inspiratory activity, and when present, reducing expiratory-related abdominal activity. Together with previous observations, we conclude that the pFV provides a generic excitatory drive to breathe, even at rest, whereas the pFL is a conditional oscillator quiet at rest that, when activated, e.g., during exercise, drives active expiration.
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60
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Mulkey DK, Hawkins VE, Hawryluk JM, Takakura AC, Moreira TS, Tzingounis AV. Molecular underpinnings of ventral surface chemoreceptor function: focus on KCNQ channels. J Physiol 2015; 593:1075-81. [PMID: 25603782 DOI: 10.1113/jphysiol.2014.286500] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Accepted: 01/12/2015] [Indexed: 12/12/2022] Open
Abstract
Central chemoreception is the mechanism by which CO₂/H(+) -sensitive neurons (i.e. chemoreceptors) regulate breathing in response to changes in tissue CO₂/H(+) . Neurons in the retrotrapezoid nucleus (RTN) directly regulate breathing in response to changes in tissue CO₂/H(+) and function as a key locus of respiratory control by integrating information from several respiratory centres, including the medullary raphe. Therefore, chemosensitive RTN neurons appear to be critically important for maintaining breathing, thus understanding molecular mechanisms that regulate RTN chemoreceptor function may identify therapeutic targets for the treatment of respiratory control disorders. We have recently shown that KCNQ (Kv7) channels in the RTN are essential determinants of spontaneous activity ex vivo, and downstream effectors for serotonergic modulation of breathing. Considering that loss of function mutations in KCNQ channels can cause certain types of epilepsy including those associated with sudden unexplained death in epilepsy (SUDEP), we propose that dysfunctions of KCNQ channels may be one cause for epilepsy and respiratory problems associated with SUDEP. In this review, we will summarize the role of KCNQ channels in the regulation of RTN chemoreceptor function, and suggest that these channels represent useful therapeutic targets for the treatment of respiratory control disorders.
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Affiliation(s)
- Daniel K Mulkey
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT, 06269, USA
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61
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Moreira TS, Wenker IC, Sobrinho CR, Barna BF, Takakura AC, Mulkey DK. Independent purinergic mechanisms of central and peripheral chemoreception in the rostral ventrolateral medulla. J Physiol 2015; 593:1067-74. [PMID: 25524282 DOI: 10.1113/jphysiol.2014.284430] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Accepted: 12/15/2014] [Indexed: 01/02/2023] Open
Abstract
The rostral ventrolateral medulla oblongata (RVLM) contains two functionally distinct types of neurons that control and orchestrate cardiovascular and respiratory responses to hypoxia and hypercapnia. One group is composed of the central chemoreceptor neurons of the retrotrapezoid nucleus, which provides a CO₂/H(+) -dependent drive to breathe and serves as an integration centre and a point of convergence of chemosensory information from other central and peripheral sites, including the carotid bodies. The second cluster of RVLM cells forms a population of neurons belonging to the C1 catecholaminergic group that controls sympathetic vasomotor tone in resting conditions and in conditions of hypoxia and hypercapnia. Recent evidence suggests that ATP-mediated purinergic signalling at the level of the RVLM co-ordinates cardiovascular and respiratory responses triggered by hypoxia and hypercapnia by activating retrotrapezoid nucleus and C1 neurons, respectively. The role of ATP-mediated signalling in the RVLM mechanisms of cardiovascular and respiratory activities is the main subject of this short review.
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Affiliation(s)
- Thiago S Moreira
- Department of Physiology and Biophysics, University of São Paulo, São Paulo, SP, 05508, Brazil
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62
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Molkov YI, Shevtsova NA, Park C, Ben-Tal A, Smith JC, Rubin JE, Rybak IA. A closed-loop model of the respiratory system: focus on hypercapnia and active expiration. PLoS One 2014; 9:e109894. [PMID: 25302708 PMCID: PMC4193835 DOI: 10.1371/journal.pone.0109894] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Accepted: 09/11/2014] [Indexed: 11/18/2022] Open
Abstract
Breathing is a vital process providing the exchange of gases between the lungs and atmosphere. During quiet breathing, pumping air from the lungs is mostly performed by contraction of the diaphragm during inspiration, and muscle contraction during expiration does not play a significant role in ventilation. In contrast, during intense exercise or severe hypercapnia forced or active expiration occurs in which the abdominal “expiratory” muscles become actively involved in breathing. The mechanisms of this transition remain unknown. To study these mechanisms, we developed a computational model of the closed-loop respiratory system that describes the brainstem respiratory network controlling the pulmonary subsystem representing lung biomechanics and gas (O2 and CO2) exchange and transport. The lung subsystem provides two types of feedback to the neural subsystem: a mechanical one from pulmonary stretch receptors and a chemical one from central chemoreceptors. The neural component of the model simulates the respiratory network that includes several interacting respiratory neuron types within the Bötzinger and pre-Bötzinger complexes, as well as the retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG) representing the central chemoreception module targeted by chemical feedback. The RTN/pFRG compartment contains an independent neural generator that is activated at an increased CO2 level and controls the abdominal motor output. The lung volume is controlled by two pumps, a major one driven by the diaphragm and an additional one activated by abdominal muscles and involved in active expiration. The model represents the first attempt to model the transition from quiet breathing to breathing with active expiration. The model suggests that the closed-loop respiratory control system switches to active expiration via a quantal acceleration of expiratory activity, when increases in breathing rate and phrenic amplitude no longer provide sufficient ventilation. The model can be used for simulation of closed-loop control of breathing under different conditions including respiratory disorders.
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Affiliation(s)
- Yaroslav I. Molkov
- Department of Mathematical Sciences, Indiana University - Purdue University, Indianapolis, Indiana, United States of America
| | - Natalia A. Shevtsova
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Choongseok Park
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Alona Ben-Tal
- Institute of Information and Mathematical Sciences, Massey University, Albany, Auckland, New Zealand
| | - Jeffrey C. Smith
- Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Jonathan E. Rubin
- Department of Mathematics, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Ilya A. Rybak
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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63
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Lemes EV, Zoccal DB. Vagal afferent control of abdominal expiratory activity in response to hypoxia and hypercapnia in rats. Respir Physiol Neurobiol 2014; 203:90-7. [PMID: 25218412 DOI: 10.1016/j.resp.2014.08.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 07/31/2014] [Accepted: 08/16/2014] [Indexed: 01/29/2023]
Abstract
In the present study, we tested the hypothesis that vagal afferent information modulates the pattern of expiratory response to hypercapnia and hypoxia. Simultaneous recordings of airflow, diaphragmatic (DIA) and oblique abdominal muscle (ABD) activities were performed in anesthetized (urethane, 1.2g/kg), tracheostomized, spontaneously breathing male Wistar rats (290-320g, n=12). The animals were exposed to hypercapnia (7 and 10% CO2 for 5min) and hypoxia (7% O2 for 1min) before and after bilateral vagotomy. We verified that the percentage increase in DIA burst amplitude elicited by hypercapnia and hypoxia episodes was similar between intact and vagotomized rats (P>0.05). In contrast, hypercapnia and hypoxia promoted a marked increase in ABD activity in vagotomized, but not in intact rats (P<0.01). These amplified expiratory motor changes after vagotomy were associated with enhanced expiratory airflow (P<0.01) and augmented tidal volume responses (P<0.01). Our data indicates that, in anesthetized conditions, the removal of peripheral afferent inputs facilitates the processing of active expiration in response to hypercapnia and hypoxia in rats.
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Affiliation(s)
- Eduardo V Lemes
- Department of Physiological Sciences, Center of Biological Sciences, Federal University of Santa Catarina (UFSC), Florianópolis, SC, Brazil
| | - Daniel B Zoccal
- Department of Physiological Sciences, Center of Biological Sciences, Federal University of Santa Catarina (UFSC), Florianópolis, SC, Brazil; Department of Physiology and Pathology, School of Dentistry of Araraquara, São Paulo State University (UNESP), Araraquara, SP, Brazil.
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