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de Carvalho D, Patrone LGA, Taxini CL, Biancardi V, Vicente MC, Gargaglioni LH. Neurochemical and electrical modulation of the locus coeruleus: contribution to CO2drive to breathe. Front Physiol 2014; 5:288. [PMID: 25183958 PMCID: PMC4135231 DOI: 10.3389/fphys.2014.00288] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 07/14/2014] [Indexed: 11/13/2022] Open
Abstract
The locus coeruleus (LC) is a dorsal pontine region, situated bilaterally on the floor of the fourth ventricle. It is considered to be the major source of noradrenergic innervation in the brain. These neurons are highly sensitive to CO2/pH, and chemical lesions of LC neurons largely attenuate the hypercapnic ventilatory response in unanesthetized adult rats. Developmental dysfunctions in these neurons are linked to pathological conditions such as Rett and sudden infant death syndromes, which can impair the control of the cardio-respiratory system. LC is densely innervated by fibers that contain glutamate, serotonin, and adenosine triphosphate, and these neurotransmitters strongly affect LC activity, including central chemoreflexes. Aside from neurochemical modulation, LC neurons are also strongly electrically coupled, specifically through gap junctions, which play a role in the CO2 ventilatory response. This article reviews the available data on the role of chemical and electrical neuromodulation of the LC in the control of ventilation.
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Affiliation(s)
- Débora de Carvalho
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, Universidade Estadual Paulista - São Paulo State University Jaboticabal, Brazil
| | - Luis G A Patrone
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, Universidade Estadual Paulista - São Paulo State University Jaboticabal, Brazil
| | - Camila L Taxini
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, Universidade Estadual Paulista - São Paulo State University Jaboticabal, Brazil
| | - Vivian Biancardi
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, Universidade Estadual Paulista - São Paulo State University Jaboticabal, Brazil
| | - Mariane C Vicente
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, Universidade Estadual Paulista - São Paulo State University Jaboticabal, Brazil
| | - Luciane H Gargaglioni
- Department of Animal Morphology and Physiology, Faculty of Agricultural and Veterinarian Sciences, Universidade Estadual Paulista - São Paulo State University Jaboticabal, Brazil
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Patrone LGA, Bícego KC, Hartzler LK, Putnam RW, Gargaglioni LH. Cardiorespiratory effects of gap junction blockade in the locus coeruleus in unanesthetized adult rats. Respir Physiol Neurobiol 2013; 190:86-95. [PMID: 24035835 DOI: 10.1016/j.resp.2013.09.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Revised: 09/02/2013] [Accepted: 09/04/2013] [Indexed: 12/18/2022]
Abstract
The locus coeruleus (LC) plays an important role in central chemoreception. In young rats (P9 or younger), 85% of LC neurons increase firing rate in response to hypercapnia vs. only about 45% of neurons from rats P10 or older. Carbenoxolone (CARB - gap junction blocker) does not affect the % of LC neurons responding in young rats but it decreases the % responding by half in older animals. We evaluated the participation of gap junctions in the CO2 ventilatory response in unanesthetized adult rats by bilaterally microinjecting CARB (300μM, 1mM or 3mM/100nL), glycyrrhizic acid (GZA, CARB analog, 3mM) or vehicle (aCSF - artificial cerebrospinal fluid) into the LC of Wistar rats. Bilateral gap junction blockade in LC neurons did not affect resting ventilation; however, the increase in ventilation produced by hypercapnia (7% CO2) was reduced by ∼25% after CARB 1mM or 3mM injection (1939.7±104.8mLkg(-1)min(-1) for the aCSF group and 1468.3±122.2mLkg(-1)min(-1) for 1mM CARB, P<0.05; 1939.7±104.8mLkg(-1)min(-1) for the aCSF group and 1540.9±68.4mLkg(-1)min(-1) for the 3mM CARB group, P<0.05) due largely to a decrease in respiratory frequency. GZA injection or CARB injection outside the LC (peri-LC) had no effect on ventilation under any conditions. The results suggest that gap junctions in the LC modulate the hypercapnic ventilatory response of adult rats.
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Affiliation(s)
- Luis G A Patrone
- Department of Animal Physiology and Morphology, Sao Paulo State University- UNESP/FCAV, Jaboticabal, SP, Brazil; National Institute of Science and Technology in Comparative Physiology (INCT, Fisiologia Comparada), Brazil
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Pokorski M, Izumizaki M, Shirasawa T. Chemosensory ventilatory responses in the mutant mice with Presbyterian hemoglobinopathy. Respir Physiol Neurobiol 2013; 187:18-25. [PMID: 23454025 DOI: 10.1016/j.resp.2013.02.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 02/19/2013] [Accepted: 02/20/2013] [Indexed: 10/27/2022]
Abstract
The working hypothesis of this study was that chronically increased tissue oxygenation would facilitate respiratory endurance to chemical stimuli. We investigated the ventilatory responses to hypoxia and hypercapnia before and after carotid chemodenervation in the anesthetized, spontaneously breathing Presbyterian, which carry a low affinity variant of hemoglobin, and in wild-type mice. We found a dampening of all chemosensory responses in Presbyterian hemoglobinopathy. Particularly, the Presbyterian mouse with intact carotid body innervation was more vulnerable to hypoxia than the wild-type mouse, showing an accelerated decline in breathing frequency which was not counterbalanced by tidal respiration. We further found that chemodenervation in the Presbyterian mouse, performed in normoxia, led to respiratory arrest. The study shows enhanced susceptibility of respiration to hypoxia and indispensability of neural input from the carotid body for upholding the central respiratory controller's function in Presbyterian hemoglobinopathy. The study also suggests a relationship between hemoglobin-oxygen dissociation and respiration, which points to a metabolic, tissue oxygenation-linked component of respiratory regulation.
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Affiliation(s)
- Mieczyslaw Pokorski
- Department of Respiratory Research, Medical Research Center, Polish Academy of Sciences, Warsaw, Poland.
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Huckstepp RTR, Dale N. Redefining the components of central CO2 chemosensitivity--towards a better understanding of mechanism. J Physiol 2011; 589:5561-79. [PMID: 22005672 PMCID: PMC3249032 DOI: 10.1113/jphysiol.2011.214759] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Abstract The field of CO2 chemosensitivity has developed considerably in recent years. There has been a mounting number of competing nuclei proposed as chemosensitive along with an ever increasing list of potential chemosensory transducing molecules. Is it really possible that all of these areas and candidate molecules are involved in the detection of chemosensory stimuli? How do we discriminate rigorously between molecules that are chemosensory transducers at the head of a physiological reflexversusthose that just happen to display sensitivity to a chemosensory stimulus? Equally, how do we differentiate between nuclei that have a primary chemosensory function, versusthose that are relays in the pathway? We have approached these questions by proposing rigorous definitions for the different components of the chemosensory reflex, going from the salient molecules and ions, through the components of transduction to the identity of chemosensitive cells and chemosensitive nuclei. Our definitions include practical and rigorous experimental tests that can be used to establish the identity of these components. We begin by describing the need for central CO2 chemosensitivity and the problems that the field has faced. By comparing chemosensory mechanisms to those in the visual system we suggest stricter definitions for the components of the chemosensory pathway. We then, considering these definitions, re-evaluate current knowledge of chemosensory transduction, and propose the ‘multiple salient signal hypothesis’ as a framework for understanding the multiplicity of transduction mechanisms and brain areas seemingly involved in chemosensitivity.
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Yates C, Garrison K, Reese NB, Charlesworth A, Garcia-Rill E. Chapter 11--novel mechanism for hyperreflexia and spasticity. PROGRESS IN BRAIN RESEARCH 2011; 188:167-80. [PMID: 21333809 DOI: 10.1016/b978-0-444-53825-3.00016-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We established that hyperreflexia is delayed after spinal transection in the adult rat and that passive exercise could normalize low frequency-dependent depression of the H-reflex. We were also able to show that such passive exercise will normalize hyperreflexia in patients with spinal cord injury (SCI). Recent results demonstrate that spinal transection results in changes in the neuronal gap junction protein connexin 36 below the level of the lesion. Moreover, a drug known to increase electrical coupling was found to normalize hyperreflexia in the absence of passive exercise, suggesting that changes in electrical coupling may be involved in hyperreflexia. We also present results showing that a measure of spasticity, the stretch reflex, is rendered abnormal by transection and normalized by the same drug. These data suggest that electrical coupling may be dysregulated in SCI, leading to some of the symptoms observed. A novel therapy for hyperreflexia and spasticity may require modulation of electrical coupling.
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Affiliation(s)
- C Yates
- Center for Translational Neuroscience, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA
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Voituron N, Shvarev Y, Menuet C, Bevengut M, Fasano C, Vigneault E, Mestikawy SE, Hilaire G. Fluoxetine treatment abolishes the in vitro respiratory response to acidosis in neonatal mice. PLoS One 2010; 5:e13644. [PMID: 21048979 PMCID: PMC2964329 DOI: 10.1371/journal.pone.0013644] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Accepted: 09/24/2010] [Indexed: 11/18/2022] Open
Abstract
Background To secure pH homeostasis, the central respiratory network must permanently adapt its rhythmic motor drive to environment and behaviour. In neonates, it is commonly admitted that the retrotrapezoid/parafacial respiratory group of neurons of the ventral medulla plays the primary role in the respiratory response to acidosis, although the serotonergic system may also contribute to this response. Methodology/Principal Findings Using en bloc medullary preparations from neonatal mice, we have shown for the first time that the respiratory response to acidosis is abolished after pre-treatment with the serotonin-transporter blocker fluoxetine (25–50 µM, 20 min), a commonly used antidepressant. Using mRNA in situ hybridization and immunohistology, we have also shown the expression of the serotonin transporter mRNA and serotonin-containing neurons in the vicinity of the RTN/pFRG of neonatal mice. Conclusions These results reveal that the serotonergic system plays a pivotal role in pH homeostasis. Although obtained in vitro in neonatal mice, they suggest that drugs targeting the serotonergic system should be used with caution in infants, pregnant women and breastfeeding mothers.
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Affiliation(s)
- Nicolas Voituron
- Maturation, Plasticité, Physiologie et Pathologie de la Respiration, Unité Mixte de Recherche 6231, Centre National de la Recherche Scientifique - Université de la Méditerranée - Université Paul Cézanne, Marseille, France
| | - Yuri Shvarev
- Maturation, Plasticité, Physiologie et Pathologie de la Respiration, Unité Mixte de Recherche 6231, Centre National de la Recherche Scientifique - Université de la Méditerranée - Université Paul Cézanne, Marseille, France
- Department of Woman and Child Health, Karolinska Institute, Stockholm, Sweden
- Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia
| | - Clément Menuet
- Maturation, Plasticité, Physiologie et Pathologie de la Respiration, Unité Mixte de Recherche 6231, Centre National de la Recherche Scientifique - Université de la Méditerranée - Université Paul Cézanne, Marseille, France
| | - Michelle Bevengut
- Maturation, Plasticité, Physiologie et Pathologie de la Respiration, Unité Mixte de Recherche 6231, Centre National de la Recherche Scientifique - Université de la Méditerranée - Université Paul Cézanne, Marseille, France
| | - Caroline Fasano
- Department of Psychiatry, Douglas Hospital Research Center, McGill University, Québec, Canada
| | - Erika Vigneault
- Department of Psychiatry, Douglas Hospital Research Center, McGill University, Québec, Canada
| | - Salah El Mestikawy
- Department of Psychiatry, Douglas Hospital Research Center, McGill University, Québec, Canada
- Unité 952, Institut National de la Santé et de la Recherche Médicale, Paris, France
- Unité Mixte de Recherche 7224, Centre National de la Recherche Scientifique, Paris, France
- Université Pierre et Marie Curie, Paris, France
| | - Gérard Hilaire
- Maturation, Plasticité, Physiologie et Pathologie de la Respiration, Unité Mixte de Recherche 6231, Centre National de la Recherche Scientifique - Université de la Méditerranée - Université Paul Cézanne, Marseille, France
- * E-mail:
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Erlichman JS, Leiter JC. Glia modulation of the extracellular milieu as a factor in central CO2 chemosensitivity and respiratory control. J Appl Physiol (1985) 2010; 108:1803-11. [PMID: 20110540 DOI: 10.1152/japplphysiol.01321.2009] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
We discuss the influence of astrocytes on respiratory function, particularly central CO2 chemosensitivity. Fluorocitrate (FC) poisons astrocytes, and studies in intact animals using FC provide strong evidence that disrupting astrocytic function can influence CO2 chemosensitivity and ventilation. Gap junctions interconnect astrocytes and contribute to K+ homeostasis in the extracellular fluid (ECF). Blocking gap junctions alters respiratory control, but proof that this is truly an astrocytic effect is lacking. Intracellular pH regulation of astrocytes has reciprocal effects on extracellular pH. Electrogenic sodium-bicarbonate transport (NBCe) is present in astrocytes. The activity of NBCe alkalinizes intracellular pH and acidifies extracellular pH when activated by depolarization (and a subset of astrocytes are depolarized by hypercapnia). Thus, to the extent that astrocytic intracellular pH regulation during hypercapnia lowers extracellular pH, astrocytes will amplify the hypercapnic stimulus and may influence central chemosensitivity. However, the data so far provide only inferential support for this hypothesis. A lactate shuttle from astrocytes to neurons seems to be active in the retrotrapezoid nucleus (RTN) and important in setting the chemosensory stimulus in the RTN (and possibly other chemosensory nuclei). Thus astrocytic processes, so vital in controlling the constituents of the ECF in the central nervous system, may profoundly influence central CO2 chemosensitivity and respiratory control.
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Affiliation(s)
- Joseph S Erlichman
- Department of Biology, St. Lawrence University, Canton, NY 13617-1475, USA.
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Erlichman JS, Boyer AC, Reagan P, Putnam RW, Ritucci NA, Leiter JC. Chemosensory responses to CO2 in multiple brain stem nuclei determined using a voltage-sensitive dye in brain slices from rats. J Neurophysiol 2009; 102:1577-90. [PMID: 19553484 DOI: 10.1152/jn.00381.2009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We used epifluorescence microscopy and a voltage-sensitive dye, di-8-ANEPPS, to study changes in membrane potential during hypercapnia with or without synaptic blockade in chemosensory brain stem nuclei: the locus coeruleus (LC), the nucleus of the solitary tract, lateral paragigantocellularis nucleus, raphé pallidus, and raphé obscurus and, in putative nonchemosensitive nuclei, the gigantocellularis reticular nucleus and the spinotrigeminal nucleus. We studied the response to hypercapnia in LC cells to evaluate the performance characteristics of the voltage-sensitive dye. Hypercapnia depolarized many LC cells and the voltage responses to hypercapnia were diminished, but not eradicated, by synaptic blockade (there were intrinsically CO2-sensitive cells in the LC). The voltage response to hypercapnia was substantially diminished after inhibiting fast Na+ channels with tetrodotoxin. Thus action potential-related activity was responsible for most of the optical signal that we detected. We systematically examined CO2 sensitivity among cells in brain stem nuclei to test the hypothesis that CO2 sensitivity is a ubiquitous phenomenon, not restricted to nominally CO2 chemosensory nuclei. We found intrinsically CO2 sensitive neurons in all the nuclei that we examined; even the nonchemosensory nuclei had small numbers of intrinsically CO2 sensitive neurons. However, synaptic blockade significantly altered the distribution of CO2-sensitive cells in all of the nuclei so that the cellular response to CO2 in more intact preparations may be difficult to predict based on studies of intrinsic neuronal activity. Thus CO2-sensitive neurons are widely distributed in chemosensory and nonchemosensory nuclei and CO2 sensitivity is dependent on inhibitory and excitatory synaptic activity even within brain slices. Neuronal CO2 sensitivity important for the behavioral response to CO2 in intact animals will thus be determined as much by synaptic mechanisms and patterns of connectivity throughout the brain as by intrinsic CO2 sensitivity.
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Juszczak GR, Swiergiel AH. Properties of gap junction blockers and their behavioural, cognitive and electrophysiological effects: animal and human studies. Prog Neuropsychopharmacol Biol Psychiatry 2009; 33:181-98. [PMID: 19162118 DOI: 10.1016/j.pnpbp.2008.12.014] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 12/22/2008] [Accepted: 12/22/2008] [Indexed: 10/21/2022]
Abstract
Gap junctions play an important role in brain physiology. They synchronize neuronal activity and connect glial cells participating in the regulation of brain metabolism and homeostasis. Gap junction blockers (GJBs) include various chemicals that impair gap junction communication, disrupt oscillatory neuronal activity over a wide range of frequencies, and decrease epileptic discharges. The behavioural and clinical effects of GJBs suggest that gap junctions can be involved in the regulation of locomotor activity, arousal, memory, and breathing. Severe neuropsychiatric side effects suggest the involvement of gap junctions in mechanisms of consciousness. Unfortunately, the available GJBs are not selective and can bind to targets other than gap junctions. Other problems in behavioural studies include the possible adverse effects of GJBs, for example, retinal toxicity and hearing disturbances, changes in blood-brain transport, and the metabolism of other drugs. Therefore, it is necessary to design experiments properly to avoid false, misleading or uninterpretable results. We review the pharmacological properties and electrophysiological, behavioural and cognitive effects of the available gap junction blockers, such as carbenoxolone, glycyrrhetinic acid, quinine, quinidine, mefloquine, heptanol, octanol, anandamide, fenamates, 2-APB, several anaesthetics, retinoic acid, oleamide, spermine, aminosulfonates, and sodium propionate. It is concluded that despite a number of different problems, the currently used gap junction blockers could be useful tools in pharmacology and neuroscience.
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Affiliation(s)
- Grzegorz R Juszczak
- Department of Animal Behaviour, Institute of Genetics and Animal Breeding, Jastrzebiec, ul. Postepu 1, 05-552 Wolka Kosowska, Poland.
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Johnson SM, Haxhiu MA, Richerson GB. GFP-expressing locus ceruleus neurons from Prp57 transgenic mice exhibit CO2/H+ responses in primary cell culture. J Appl Physiol (1985) 2008; 105:1301-11. [PMID: 18635881 PMCID: PMC2576037 DOI: 10.1152/japplphysiol.90414.2008] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Accepted: 07/12/2008] [Indexed: 11/22/2022] Open
Abstract
The locus ceruleus (LC) contains neurons that increase their firing rate (FR) in vitro when exposed to elevated CO(2)/H(+) and have been proposed to influence the respiratory network to make compensatory adjustments in ventilation. Prp57 transgenic mice express green fluorescent protein (GFP) in the LC and were used to isolate, culture, and target LC neurons for electrophysiological recording. We hypothesized that GFP-LC neurons would exhibit CO(2)/H(+) chemosensitivity under primary culture conditions, evidenced as a change in FR. This is the first study to quantify CO(2)/H(+) responses in LC neuron FR in cell culture. Neurons were continuously bathed with solutions containing antagonists of glutamate and GABA receptors, and the acid-base status was changed from control (5% CO(2); pH approximately 7.4) to hypercapnic acidosis (9% CO(2); pH approximately 7.2) and hypocapnic alkalosis (3% CO(2); pH approximately 7.6). FR was quantified during perforated patch current clamp recordings. Approximately 86% of GFP-LC neurons were stimulated, and approximately 14% were insensitive to changes in CO(2)/H(+). The magnitude of the response of these neurons depended on the baseline FR, ranging from 155.9 +/- 6% when FR started at 2.95 +/- 0.49 Hz to 381 +/- 55.6% when FR started at 1.32 +/- 0.31 Hz. These results demonstrate that cultured LC neurons from Prp57 transgenic mice retain functional sensing molecules necessary for CO(2)/H(+) responses. Prp57 transgenic mice will serve as a valuable model to delineate mechanisms involved in CO(2)/H(+) responsiveness in catecholaminergic neurons.
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Affiliation(s)
- Shereé M Johnson
- Department of Physiology and Biophysics, Howard University College of Medicine, 520 W Street Northwest, Washington, DC 20059, USA.
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Inhibition of monocarboxylate transporter 2 in the retrotrapezoid nucleus in rats: a test of the astrocyte-neuron lactate-shuttle hypothesis. J Neurosci 2008; 28:4888-96. [PMID: 18463242 DOI: 10.1523/jneurosci.5430-07.2008] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The astrocyte-neuronal lactate-shuttle hypothesis posits that lactate released from astrocytes into the extracellular space is metabolized by neurons. The lactate released should alter extracellular pH (pHe), and changes in pH in central chemosensory regions of the brainstem stimulate ventilation. Therefore, we assessed the impact of disrupting the lactate shuttle by administering 100 microM alpha-cyano-4-hydroxy-cinnamate (4-CIN), a dose that blocks the neuronal monocarboxylate transporter (MCT) 2 but not the astrocytic MCTs (MCT1 and MCT4). Administration of 4-CIN focally in the retrotrapezoid nucleus (RTN), a medullary central chemosensory nucleus, increased ventilation and decreased pHe in intact animals. In medullary brain slices, 4-CIN reduced astrocytic intracellular pH (pHi) slightly but alkalinized neuronal pHi. Nonetheless, pHi fell significantly in both cell types when they were treated with exogenous lactate, although 100 microM 4-CIN significantly reduced the magnitude of the acidosis in neurons but not astrocytes. Finally, 4-CIN treatment increased the uptake of a fluorescent 2-deoxy-D-glucose analog in neurons but did not alter the uptake rate of this 2-deoxy-D-glucose analog in astrocytes. These data confirm the existence of an astrocyte to neuron lactate shuttle in intact animals in the RTN, and lactate derived from astrocytes forms part of the central chemosensory stimulus for ventilation in this nucleus. When the lactate shuttle was disrupted by treatment with 4-CIN, neurons increased the uptake of glucose. Therefore, neurons seem to metabolize a combination of glucose and lactate (and other substances such as pyruvate) depending, in part, on the availability of each of these particular substrates.
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Yamauchi M, Dostal J, Strohl KP. Acetazolamide protects against posthypoxic unstable breathing in the C57BL/6J mouse. J Appl Physiol (1985) 2007; 103:1263-8. [PMID: 17673555 DOI: 10.1152/japplphysiol.01287.2006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acetazolamide (Acz), a carbonic anhydrase inhibitor, is used to manage periodic breathing associated with altitude and with heart failure. We examined whether Acz would alter posthypoxic ventilatory behavior in the C57BL/6J (B6) mouse model of recurrent central apnea. Experiments were performed with unanesthetized, awake adult male B6 mice (n = 9), ventilatory behavior was measured using flow-through whole body plethysmography. Mice were given an intraperitoneal injection of either vehicle or Acz (40 mg/kg), and 1 h later they were exposed to 1 min of 8% O(2)-balance N(2) (poikilocapnic hypoxia) or 12% O(2)-3% CO(2)-balance N(2) (isocapnic hypoxia) followed by rapid reoxygenation (100% O(2)). Hypercapnic response (8% CO(2)-balance O(2)) was examined in six mice. With Acz, ventilation, including respiratory frequency, tidal volume, and minute ventilation, in room air was significantly higher and hyperoxic hypercapnic ventilatory responsiveness was generally lower compared with vehicle. Poikilocapnic and isocapnic hypoxic ventilatory responsiveness were similar among treatments. One minute after reoxygenation, animals given Acz exhibited posthypoxic frequency decline, a lower coefficient of variability for frequency, and no tendency toward periodic breathing, compared with vehicle treatment. We conclude that Acz improves unstable breathing in the B6 model, without altering hypoxic response or producing short-term potentiation, but with some blunting of hypercapnic responsiveness.
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Affiliation(s)
- Motoo Yamauchi
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
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Schlenker E, Shi Y, Johnson C, Wipf J. Acetazolamide affects breathing differently in ICR and C57 mice. Respir Physiol Neurobiol 2006; 152:119-27. [PMID: 16140042 DOI: 10.1016/j.resp.2005.07.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2005] [Revised: 07/26/2005] [Accepted: 07/27/2005] [Indexed: 10/25/2022]
Abstract
Acetazolamide (ACZ) administration was compared on ventilation in outbred male ICR Swiss Webster (ICR) and inbred C57BL/6J (C57) mice, used in development of transgenic strains. We hypothesized that in both strains ACZ would affect breathing similarly. Mice received intraperitoneally vehicle and the next week ACZ (40 mg/kg), and were exposed to air for 90 min, followed by 5-min exposure to 10% O(2), air for 15 min, and to 5 min of 5% CO(2) in O(2). Ventilation was evaluated using plethysmography. ACZ stimulated ventilation in both stains exposed to air. C57 mice minimally increased frequency and tidal volume, whereas ICR mice markedly increased frequency. Strain differences in the ventilatory pattern in response to hypoxia and hypercapnia occurred. ACZ-treated ICR mice decreased hypoxic responsiveness to 50% of vehicle values, whereas ACZ had no effect in C57 mice. ACZ decreased hypercapnic ventilatory responsiveness in both strains. Differential effects of ACZ breathing in these two strains suggest that genetic factors modulate its effect on breathing.
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Affiliation(s)
- Evelyn Schlenker
- Division of Basic Biomedical Sciences, University of South Dakota School of Medicine, Vermillion, 57069, USA.
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Zhang ZH, Kang YM, Yu Y, Wei SG, Schmidt TJ, Johnson AK, Felder RB. 11beta-hydroxysteroid dehydrogenase type 2 activity in hypothalamic paraventricular nucleus modulates sympathetic excitation. Hypertension 2006; 48:127-33. [PMID: 16717146 DOI: 10.1161/01.hyp.0000224296.96235.dd] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Aldosterone stimulates the sympathetic nervous system by binding to a select population of brain mineralocorticoid receptors (MR). These MR have an equal affinity for corticosterone that is present in substantially higher concentrations, but are held in reserve for aldosterone by activity of the enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD-2), which converts corticosterone to an inactive metabolite. Thus, colocalization of MR and 11beta-HSD-2 activity may help identify brain regions that mediate the effects of aldosterone. The present studies tested the hypothesis that 11beta-HSD-2 activity regulates MR-mediated responses in the paraventricular nucleus (PVN) of the hypothalamus, a forebrain region implicated in sympathetic regulation. Real-time-polymerase chain reaction revealed the presence of 11beta-HSD-2 mRNA in PVN. In anesthetized adult male Sprague-Dawley rats, microinjection of the 11beta-HSD-2 inhibitor carbenoxolone (CBX) into PVN increased mean arterial pressure, heart rate, and renal sympathetic nerve activity. Intracerebroventricular injections of CBX excited PVN neurons and increased mean arterial pressure, heart rate, and renal sympathetic nerve activity. The ability of CBX to increase sympathetic activity by inhibiting 11beta-HSD-2, thereby permitting corticosterone to activate MR, was confirmed by the following: Intracerebroventricular glycyrrhizic acid, another 11beta-HSD-2 inhibitor, mimicked the sympathoexcitatory effects of CBX; the sympathoexcitatory effects of CBX were blocked by spironolactone, a MR antagonist. Neither CBX nor glycyrrhizic acid elicited a response in adrenalectomized rats. These findings suggest that MR in PVN contribute to sympathetic regulation and may be activated by aldosterone or corticosterone (or cortisol in humans) depending on the state of 11beta-HSD-2 activity.
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Affiliation(s)
- Zhi-Hua Zhang
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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Putnam RW, Conrad SC, Gdovin MJ, Erlichman JS, Leiter JC. Neonatal maturation of the hypercapnic ventilatory response and central neural CO2 chemosensitivity. Respir Physiol Neurobiol 2005; 149:165-79. [PMID: 15876557 PMCID: PMC1255969 DOI: 10.1016/j.resp.2005.03.004] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2005] [Revised: 03/22/2005] [Accepted: 03/24/2005] [Indexed: 11/16/2022]
Abstract
The ventilatory response to CO2 changes as a function of neonatal development. In rats, a ventilatory response to CO2 is present in the first 5 days of life, but this ventilatory response to CO2 wanes and reaches its lowest point around postnatal day 8. Subsequently, the ventilatory response to CO2 rises towards adult levels. Similar patterns in the ventilatory response to CO2 are seen in some other species, although some animals do not exhibit all of these phases. Different developmental patterns of the ventilatory response to CO2 may be related to the state of development of the animal at birth. The triphasic pattern of responsiveness (early decline, a nadir, and subsequent achievement of adult levels of responsiveness) may arise from the development of several processes, including central neural mechanisms, gas exchange, the neuromuscular junction, respiratory muscles and respiratory mechanics. We only discuss central neural mechanisms here, including altered CO2 sensitivity of neurons among the various sites of central CO2 chemosensitivity, changes in astrocytic function during development, the maturation of electrical and chemical synaptic mechanisms (both inhibitory and excitatory mechanisms) or changes in the integration of chemosensory information originating from peripheral and multiple central CO2 chemosensory sites. Among these central processes, the maturation of synaptic mechanisms seems most important and the relative maturation of synaptic processes may also determine how plastic the response to CO2 is at any particular age.
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Affiliation(s)
- Robert W Putnam
- Department of Anatomy and Physiology, Wright State University School of Medicine, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA.
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