1
|
Amaral-Silva L, Santin JM. Molecular profiling of CO 2/pH-sensitive neurons in the locus coeruleus of bullfrogs reveals overlapping noradrenergic and glutamatergic cell identity. Comp Biochem Physiol A Mol Integr Physiol 2023; 283:111453. [PMID: 37230318 PMCID: PMC10492231 DOI: 10.1016/j.cbpa.2023.111453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 05/03/2023] [Accepted: 05/18/2023] [Indexed: 05/27/2023]
Abstract
Locus coeruleus (LC) neurons regulate breathing by sensing CO2/pH. Neurons within the vertebrate LC are the main source of norepinephrine within the brain. However, they also use glutamate and GABA for fast neurotransmission. Although the amphibian LC is recognized as a site involved in central chemoreception for the control of breathing, the neurotransmitter phenotype of these neurons is unknown. To address this question, we combined electrophysiology and single-cell quantitative PCR to detect mRNA transcripts that define norepinephrinergic, glutamatergic, and GABAergic phenotypes in LC neurons activated by hypercapnic acidosis (HA) in American bullfrogs. Most LC neurons activated by HA had overlapping expression of noradrenergic and glutamatergic markers but did not show strong support for GABAergic transmission. Genes that encode the pH-sensitive K+ channel, TASK2, and acid-sensing cation channel, ASIC2, were most abundant, while Kir5.1 was present in 1/3 of LC neurons. The abundance of transcripts related to norepinephrine biosynthesis linearly correlated with those involved in pH sensing. These results suggest that noradrenergic neurons in the amphibian LC also use glutamate as a neurotransmitter and that CO2/pH sensitivity may be linkedto the noradrenergic cell identity.
Collapse
Affiliation(s)
- Lara Amaral-Silva
- Division of Biological Sciences, University of Missouri, Columbia, MO, USA. https://twitter.com/amaralsilva_l
| | - Joseph M Santin
- Division of Biological Sciences, University of Missouri, Columbia, MO, USA.
| |
Collapse
|
2
|
Janes TA, Guay LM, Fournier S, Kinkead R. Persistent augmentation of fictive air breathing by hypoxia: An in vitro study of the role of GABA B signaling in pre-metamorphic tadpoles. Comp Biochem Physiol A Mol Integr Physiol 2023; 281:111437. [PMID: 37088410 DOI: 10.1016/j.cbpa.2023.111437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Revised: 04/14/2023] [Accepted: 04/18/2023] [Indexed: 04/25/2023]
Abstract
Tadpole development is influenced by environmental cues and hypoxia can favor the emergence of the neural networks driving air breathing. Exposing isolated brainstems from pre-metamorphic tadpoles to acute hypoxia (~0% O2; 15 min) leads to a progressive increase in fictive air breaths (~3 fold) in the hours that follow stimulation. Here, we first determined whether this effect persists over longer periods (<18 h); we then evaluated maturity of the motor output by comparing the breathing pattern of hypoxia-exposed brainstems to that of preparations from adult bullfrogs under basal conditions. Because progressive withdrawal of GABAB-mediated inhibition contributes to the developmental increase in fictive lung ventilation, we then hypothesised that hypoxia reduces respiratory sensitivity to baclofen (selective GABAB-agonist). Experiments were performed on isolated brainstem preparations from pre-metamorphic tadpoles (TK stages IV to XIV); respiratory-related neural activity was recorded from cranial nerves V/VII and X before and 18 h after exposure to hypoxia (0% O2 + 2% CO2; 25 min). Time-control experiments (no hypoxia) were performed. Exposing pre-metamorphic tadpoles to hypoxia did not affect gill burst frequency, but augmented the frequency of fictive lung bursts and the incidence of episodic breathing levels intermediate between pre-metamorphic and adult preparations. Addition of baclofen to the aCSF (0,2 μM - 20 min) reduced lung burst frequency, but the response of hypoxia-exposed brainstems was greater than controls. We conclude that acute hypoxia facilitates development and maturation of the motor command driving air breathing. We propose that a greater number of active rhythmogenic neurons expressing GABAb receptors contributes to this effect.
Collapse
Affiliation(s)
- Tara A Janes
- Department of Pediatrics, Université Laval & Research Center of the Québec Heart & Lung Institute, Québec, QC, Canada; Department of Physiology, Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Loralie Mei Guay
- Department of Pediatrics, Université Laval & Research Center of the Québec Heart & Lung Institute, Québec, QC, Canada
| | - Stéphanie Fournier
- Department of Pediatrics, Université Laval & Research Center of the Québec Heart & Lung Institute, Québec, QC, Canada
| | - Richard Kinkead
- Department of Pediatrics, Université Laval & Research Center of the Québec Heart & Lung Institute, Québec, QC, Canada.
| |
Collapse
|
3
|
Amaral-Silva L, Santin JM. Synaptic modifications transform neural networks to function without oxygen. BMC Biol 2023; 21:54. [PMID: 36927477 PMCID: PMC10022038 DOI: 10.1186/s12915-023-01518-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 01/18/2023] [Indexed: 03/18/2023] Open
Abstract
BACKGROUND Neural circuit function is highly sensitive to energetic limitations. Much like mammals, brain activity in American bullfrogs quickly fails in hypoxia. However, after emergence from overwintering, circuits transform to function for approximately 30-fold longer without oxygen using only anaerobic glycolysis for fuel, a unique trait among vertebrates considering the high cost of network activity. Here, we assessed neuronal functions that normally limit network output and identified components that undergo energetic plasticity to increase robustness in hypoxia. RESULTS In control animals, oxygen deprivation depressed excitatory synaptic drive within native circuits, which decreased postsynaptic firing to cause network failure within minutes. Assessments of evoked and spontaneous synaptic transmission showed that hypoxia impairs synaptic communication at pre- and postsynaptic loci. However, control neurons maintained membrane potentials and a capacity for firing during hypoxia, indicating that those processes do not limit network activity. After overwintering, synaptic transmission persisted in hypoxia to sustain motor function for at least 2 h. CONCLUSIONS Alterations that allow anaerobic metabolism to fuel synapses are critical for transforming a circuit to function without oxygen. Data from many vertebrate species indicate that anaerobic glycolysis cannot fuel active synapses due to the low ATP yield of this pathway. Thus, our results point to a unique strategy whereby synapses switch from oxidative to exclusively anaerobic glycolytic metabolism to preserve circuit function during prolonged energy limitations.
Collapse
Affiliation(s)
- Lara Amaral-Silva
- Division of Biological Sciences, The University of Missouri, Columbia, USA.
| | - Joseph M Santin
- Division of Biological Sciences, The University of Missouri, Columbia, USA.
| |
Collapse
|
4
|
Fonseca EM, Janes TA, Fournier S, Gargaglioni LH, Kinkead R. Orexin-A inhibits fictive air breathing responses to respiratory stimuli in the bullfrog tadpole (Lithobates catesbeianus). J Exp Biol 2021; 224:239725. [PMID: 33914034 DOI: 10.1242/jeb.240804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Accepted: 02/25/2021] [Indexed: 11/20/2022]
Abstract
In pre-metamorphic tadpoles, the neural network generating lung ventilation is present but actively inhibited; the mechanisms leading to the onset of air breathing are not well understood. Orexin (ORX) is a hypothalamic neuropeptide that regulates several homeostatic functions, including breathing. While ORX has limited effects on breathing at rest, it potentiates reflexive responses to respiratory stimuli mainly via ORX receptor 1 (OX1R). Here, we tested the hypothesis that OX1Rs facilitate the expression of the motor command associated with air breathing in pre-metamorphic bullfrog tadpoles (Lithobates catesbeianus). To do so, we used an isolated diencephalic brainstem preparation to determine the contributions of OX1Rs to respiratory motor output during baseline breathing, hypercapnia and hypoxia. A selective OX1R antagonist (SB-334867; 5-25 µmol l-1) or agonist (ORX-A; 200 nmol l-1 to 1 µmol l-1) was added to the superfusion media. Experiments were performed under basal conditions (media equilibrated with 98.2% O2 and 1.8% CO2), hypercapnia (5% CO2) or hypoxia (5-7% O2). Under resting conditions gill, but not lung, motor output was enhanced by the OX1R antagonist and ORX-A. Hypercapnia alone did not stimulate respiratory motor output, but its combination with SB-334867 increased lung burst frequency and amplitude, lung burst episodes, and the number of bursts per episode. Hypoxia alone increased lung burst frequency and its combination with SB-334867 enhanced this effect. Inactivation of OX1Rs during hypoxia also increased gill burst amplitude, but not frequency. In contrast with our initial hypothesis, we conclude that ORX neurons provide inhibitory modulation of the CO2 and O2 chemoreflexes in pre-metamorphic tadpoles.
Collapse
Affiliation(s)
- Elisa M Fonseca
- Department of Animal Morphology and Physiology, College of Agricultural and Veterinary Sciences, São Paulo State University, Unesp. Jaboticabal, SP 14884-900, Brazil.,Department of Pediatrics, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, QC, Canada, G1V 4G5
| | - Tara A Janes
- Department of Pediatrics, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, QC, Canada, G1V 4G5
| | - Stéphanie Fournier
- Department of Pediatrics, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, QC, Canada, G1V 4G5
| | - Luciane H Gargaglioni
- Department of Animal Morphology and Physiology, College of Agricultural and Veterinary Sciences, São Paulo State University, Unesp. Jaboticabal, SP 14884-900, Brazil
| | - Richard Kinkead
- Department of Pediatrics, Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, QC, Canada, G1V 4G5
| |
Collapse
|
5
|
Adams S, Zubov T, Bueschke N, Santin JM. Neuromodulation or energy failure? Metabolic limitations silence network output in the hypoxic amphibian brainstem. Am J Physiol Regul Integr Comp Physiol 2021; 320:R105-R116. [PMID: 33175586 PMCID: PMC7948128 DOI: 10.1152/ajpregu.00209.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 09/10/2020] [Accepted: 11/02/2020] [Indexed: 11/22/2022]
Abstract
Hypoxia tolerance in the vertebrate brain often involves chemical modulators that arrest neuronal activity to conserve energy. However, in intact networks, it can be difficult to determine whether hypoxia triggers modulators to stop activity in a protective manner or whether activity stops because rates of ATP synthesis are insufficient to support network function. Here, we assessed the extent to which neuromodulation or metabolic limitations arrest activity in the respiratory network of bullfrogs-a circuit that survives moderate periods of oxygen deprivation, presumably, by activating an inhibitory noradrenergic pathway. We confirmed that hypoxia and norepinephrine (NE) reduce network output, consistent with the view that hypoxia may cause the release of NE to inhibit activity. However, these responses differed qualitatively; hypoxia, but not NE, elicited a large motor burst and silenced the network. The stereotyped response to hypoxia persisted in the presence of both NE and an adrenergic receptor blocker that eliminates sensitivity to NE, indicating that noradrenergic signaling does not cause the arrest. Pharmacological inhibition of glycolysis and mitochondrial respiration recapitulated all features of hypoxia on network activity, implying that reduced ATP synthesis underlies the effects of hypoxia. Finally, activating modulatory mechanisms that dampen neuronal excitability when ATP levels fall, KATP channels and AMP-dependent protein kinase, did not resemble the hypoxic response. These results suggest that energy failure-rather than inhibitory modulation-silences the respiratory network during hypoxia and emphasize the need to account for metabolic limitations before concluding that modulators arrest activity as an adaptation for energy conservation in the nervous system.
Collapse
Affiliation(s)
- Sasha Adams
- Department of Biology, The University of North Carolina at Greensboro, Greensboro, North Carolina
| | - Tanya Zubov
- Department of Biology, The University of North Carolina at Greensboro, Greensboro, North Carolina
| | - Nikolaus Bueschke
- Department of Biology, The University of North Carolina at Greensboro, Greensboro, North Carolina
| | - Joseph M Santin
- Department of Biology, The University of North Carolina at Greensboro, Greensboro, North Carolina
| |
Collapse
|
6
|
Janes TA, Rousseau JP, Fournier S, Kiernan EA, Harris MB, Taylor BE, Kinkead R. Development of central respiratory control in anurans: The role of neurochemicals in the emergence of air-breathing and the hypoxic response. Respir Physiol Neurobiol 2019; 270:103266. [PMID: 31408738 PMCID: PMC7476778 DOI: 10.1016/j.resp.2019.103266] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Revised: 07/10/2019] [Accepted: 08/05/2019] [Indexed: 01/08/2023]
Abstract
Physiological and environmental factors impacting respiratory homeostasis vary throughout the course of an animal's lifespan from embryo to adult and can shape respiratory development. The developmental emergence of complex neural networks for aerial breathing dates back to ancestral vertebrates, and represents the most important process for respiratory development in extant taxa ranging from fish to mammals. While substantial progress has been made towards elucidating the anatomical and physiological underpinnings of functional respiratory control networks for air-breathing, much less is known about the mechanisms establishing these networks during early neurodevelopment. This is especially true of the complex neurochemical ensembles key to the development of air-breathing. One approach to this issue has been to utilize comparative models such as anuran amphibians, which offer a unique perspective into early neurodevelopment. Here, we review the developmental emergence of respiratory behaviours in anuran amphibians with emphasis on contributions of neurochemicals to this process and highlight opportunities for future research.
Collapse
Affiliation(s)
- Tara A Janes
- Department of Pediatrics, Université Laval & Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, QC, Canada
| | - Jean-Philippe Rousseau
- Department of Pediatrics, Université Laval & Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, QC, Canada
| | - Stéphanie Fournier
- Department of Pediatrics, Université Laval & Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, QC, Canada
| | - Elizabeth A Kiernan
- Department of Comparative Biosciences, University of Wisconsin-Madison, Madison Wisconsin, USA
| | - Michael B Harris
- Department of Biological Sciences, California State University Long Beach, California, USA
| | - Barbara E Taylor
- Department of Biological Sciences, California State University Long Beach, California, USA
| | - Richard Kinkead
- Department of Pediatrics, Université Laval & Institut Universitaire de Cardiologie et de Pneumologie de Québec, Québec, QC, Canada.
| |
Collapse
|
7
|
Santin JM. Motor inactivity in hibernating frogs: Linking plasticity that stabilizes neuronal function to behavior in the natural environment. Dev Neurobiol 2019; 79:880-891. [DOI: 10.1002/dneu.22721] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 09/07/2019] [Accepted: 09/30/2019] [Indexed: 12/12/2022]
Affiliation(s)
- Joseph M. Santin
- Department of BiologyUniversity of North Carolina at Greensboro Greensboro North Carolina
| |
Collapse
|
8
|
Reed MD, Iceman KE, Harris MB, Taylor BE. Buccal rhythmogenesis and CO 2 sensitivity in Lithobates catesbeianus tadpole brainstems across metamorphosis. Respir Physiol Neurobiol 2019; 268:103251. [PMID: 31279052 DOI: 10.1016/j.resp.2019.103251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Revised: 06/19/2019] [Accepted: 07/02/2019] [Indexed: 11/19/2022]
Abstract
Bullfrog tadpoles ventilate both the buccal cavity and lung. In isolated brainstems, the midbrain/pons influences CO2 responsiveness and timing of lung ventilatory bursting, depending on larval development. However, little is known about midbrain/pons influences on buccal burst patterns. As such, we investigated how removal of this region affects buccal burst shape and CO2 responsiveness across development. We measured facial nerve activity in brainstems isolated from tadpoles during early and late developmental stages, under normal and elevated levels of CO2. Brainstems were either left intact or transected by removing the midbrain/pons. In late stage preparations, buccal burst pattern differed between intact and reduced preparations, and bursts were responsive to elevated CO2 in these reduced preparations. These results suggest the midbrain/pons affects tadpole buccal burst pattern and CO2 responsiveness, perhaps similar to its influences on lung ventilation.
Collapse
Affiliation(s)
- Mitchell D Reed
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, 99775, United States.
| | - Kimberly E Iceman
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, 99775, United States; Department of Biology, Valparaiso University, Valparaiso, IN, 46383, United States
| | - Michael B Harris
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, 99775, United States; Department of Biology, California State University Long Beach, Long Beach, CA, 90840, United States
| | - Barbara E Taylor
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, 99775, United States; Department of Biology, California State University Long Beach, Long Beach, CA, 90840, United States
| |
Collapse
|
9
|
Janes TA, Fournier S, Chamberland S, Funk GD, Kinkead R. Respiratory motoneuron properties during the transition from gill to lung breathing in the American bullfrog. Am J Physiol Regul Integr Comp Physiol 2019; 316:R281-R297. [PMID: 30601705 PMCID: PMC6459380 DOI: 10.1152/ajpregu.00303.2018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 12/24/2018] [Accepted: 12/30/2018] [Indexed: 12/23/2022]
Abstract
Amphibian respiratory development involves a dramatic metamorphic transition from gill to lung breathing and coordination of distinct motor outputs. To determine whether the emergence of adult respiratory motor patterns was associated with similarly dramatic changes in motoneuron (MN) properties, we characterized the intrinsic electrical properties of American bullfrog trigeminal MNs innervating respiratory muscles comprising the buccal pump. In premetamorphic tadpoles (TK stages IX-XVIII) and adult frogs, morphometric analyses and whole cell recordings were performed in trigeminal MNs identified by fluorescent retrograde labeling. Based on the amplitude of the depolarizing sag induced by hyperpolarizing voltage steps, two MN subtypes (I and II) were identified in tadpoles and adults. Compared with type II MNs, type I MNs had larger sag amplitudes (suggesting a larger hyperpolarization-activated inward current), greater input resistance, lower rheobase, hyperpolarized action potential threshold, steeper frequency-current relationships, and fast firing rates and received fewer excitatory postsynaptic currents. Postmetamorphosis, type I MNs exhibited similar sag, enhanced postinhibitory rebound, and increased action potential amplitude with a smaller-magnitude fast afterhyperpolarization. Compared with tadpoles, type II MNs from frogs received higher-frequency, larger-amplitude excitatory postsynaptic currents. Input resistance decreased and rheobase increased postmetamorphosis in all MNs, concurrent with increased soma area and hyperpolarized action potential threshold. We suggest that type I MNs are likely recruited in response to smaller, buccal-related synaptic inputs as well as larger lung-related inputs, whereas type II MNs are likely recruited in response to stronger synaptic inputs associated with larger buccal breaths, lung breaths, or nonrespiratory behaviors involving powerful muscle contractions.
Collapse
Affiliation(s)
- Tara A Janes
- Department of Pediatrics, Université Laval and Institut Universitaire de Cardiologie et de Pneumologie de Québec , Québec City, Québec , Canada
| | - Stéphanie Fournier
- Department of Pediatrics, Université Laval and Institut Universitaire de Cardiologie et de Pneumologie de Québec , Québec City, Québec , Canada
| | - Simon Chamberland
- Department of Neuroscience and Physiology and New York University Neuroscience Institute, New York University Langone Medical Center , New York, New York
| | - Gregory D Funk
- Department of Physiology, Neuroscience and Mental Health Institute, Women and Children's Health Research Institute, University of Alberta , Edmonton, Alberta , Canada
| | - Richard Kinkead
- Department of Pediatrics, Université Laval and Institut Universitaire de Cardiologie et de Pneumologie de Québec , Québec City, Québec , Canada
| |
Collapse
|
10
|
Bartman ME, Johnson SM. Isolated adult turtle brainstems exhibit central hypoxic chemosensitivity. Comp Biochem Physiol A Mol Integr Physiol 2018; 225:65-73. [PMID: 30003967 DOI: 10.1016/j.cbpa.2018.07.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 06/27/2018] [Accepted: 07/03/2018] [Indexed: 10/28/2022]
Abstract
During hypoxia, red-eared slider turtles increase ventilation and decrease episodic breathing, but whether these responses are due to central mechanisms is not known. To test this question, isolated adult turtle brainstems were exposed to 240 min of hypoxic solution (bath PO2 = 32.6 ± 1.2 mmHg) and spontaneous respiratory-related motor bursts (respiratory event) were recorded on hypoglossal nerve roots. During hypoxia, burst frequency increased during the first 15 min, and then decreased during the remaining 35-240 min of hypoxia. Burst amplitude was maintained for 120 min, but then decreased during the last 120 min. The number of bursts/respiratory event decreased within 30 min and remained decreased. Pretreatment with either prazosin (α1-adrenergic antagonist) or MDL7222 (5-HT3 antagonist) blocked the hypoxia-induced short-term increase and the longer duration decrease in burst frequency. MDL7222, but not prazosin, blocked the hypoxia-induced decrease in bursts/respiratory event. Thus, during bath hypoxia, isolated turtle brainstems continued to produce respiratory motor output, but the frequency and pattern were altered in a manner that required endogenous α1-adrenergic and serotonin 5-HT3 receptor activation. This is the first example of isolated reptile brainstems exhibiting central hypoxic chemosensitivity similar to other vertebrate species.
Collapse
Affiliation(s)
- Michelle E Bartman
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
| | - Stephen M Johnson
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA.
| |
Collapse
|
11
|
Janes TA, Kinkead R. Central Hypoxia Elicits Long-Term Expression of the Lung Motor Pattern in Pre-metamorphic Lithobates Catesbeianus. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1071:75-82. [DOI: 10.1007/978-3-319-91137-3_9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
12
|
Santin JM, Hartzler LK. Environmentally induced return to juvenile-like chemosensitivity in the respiratory control system of adult bullfrog, Lithobates catesbeianus. J Physiol 2016; 594:6349-6367. [PMID: 27444338 DOI: 10.1113/jp272777] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 07/19/2016] [Indexed: 12/25/2022] Open
Abstract
KEY POINTS The degree to which developmental programmes or environmental signals determine physiological phenotypes remains a major question in physiology. Vertebrates change environments during development, confounding interpretation of the degree to which development (i.e. permanent processes) or phenotypic plasticity (i.e. reversible processes) produces phenotypes. Tadpoles mainly breathe water for gas exchange and frogs may breathe water or air depending on their environment and are, therefore, exemplary models to differentiate the degree to which life-stage vs. environmental context drives developmental phenotypes associated with neural control of lung breathing. Using isolated brainstem preparations and patch clamp electrophysiology, we demonstrate that adult bullfrogs acclimatized to water-breathing conditions do not exhibit CO2 and O2 chemosensitivity of lung breathing, similar to water-breathing tadpoles. Our results establish that phenotypes associated with developmental stage may arise from plasticity per se and suggest that a developmental trajectory coinciding with environmental change obscures origins of stage-dependent physiological phenotypes by masking plasticity. ABSTRACT An unanswered question in developmental physiology is to what extent does the environment vs. a genetic programme produce phenotypes? Developing animals inhabit different environments and switch from one to another. Thus a developmental time course overlapping with environmental change confounds interpretations as to whether development (i.e. permanent processes) or phenotypic plasticity (i.e. reversible processes) generates phenotypes. Tadpoles of the American bullfrog, Lithobates catesbeianus, breathe water at early life-stages and minimally use lungs for gas exchange. As adults, bullfrogs rely on lungs for gas exchange, but spend months per year in ice-covered ponds without lung breathing. Aquatic submergence, therefore, removes environmental pressures requiring lung breathing and enables separation of adulthood from environmental factors associated with adulthood that necessitate control of lung ventilation. To test the hypothesis that postmetamorphic respiratory control phenotypes arise through permanent developmental changes vs. reversible environmental signals, we measured respiratory-related nerve discharge in isolated brainstem preparations and action potential firing from CO2 -sensitive neurons in bullfrogs acclimatized to semi-terrestrial (air-breathing) and aquatic-overwintering (no air-breathing) habitats. We found that aquatic overwintering significantly reduced neuroventilatory responses to CO2 and O2 involved in lung breathing. Strikingly, this gas sensitivity profile reflects that of water-breathing tadpoles. We further demonstrated that aquatic overwintering reduced CO2 -induced firing responses of chemosensitive neurons. In contrast, respiratory rhythm generating processes remained adult-like after submergence. Our results establish that phenotypes associated with life-stage can arise from phenotypic plasticity per se. This provides evidence that developmental time courses coinciding with environmental changes obscure interpretations regarding origins of stage-dependent physiological phenotypes by masking plasticity.
Collapse
Affiliation(s)
- Joseph M Santin
- Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA. .,Biomedical Sciences PhD Program, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA.
| | - Lynn K Hartzler
- Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH, 45435, USA
| |
Collapse
|
13
|
Santin JM, Hartzler LK. Reassessment of chemical control of breathing in undisturbed bullfrogs, Lithobates catesbeianus, using measurements of pulmonary ventilation. Respir Physiol Neurobiol 2016; 224:80-9. [DOI: 10.1016/j.resp.2015.09.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 09/26/2015] [Accepted: 09/27/2015] [Indexed: 11/28/2022]
|
14
|
Rousseau JP, Fournier S, Kinkead R. Sex-specific response to hypoxia in a reduced brainstem preparation from Xenopus laevis. Respir Physiol Neurobiol 2015; 224:100-3. [PMID: 26528898 DOI: 10.1016/j.resp.2015.10.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Revised: 10/21/2015] [Accepted: 10/23/2015] [Indexed: 10/22/2022]
Abstract
Respiratory reflexes and tolerance to hypoxia show significant sexual dimorphism. However, the data supporting this notion originates exclusively from mammals. To determine whether this concept is limited to this group of vertebrates, we examined the sex-specific response to acute hypoxia in an adult reduced brainstem preparation from Xenopus laevis. Within the first 5min of exposure to hypoxic aCSF (98% N2/2% CO2), recordings of respiratory-related activity show a stronger increase in fictive breathing frequency in males than females. This initial response was followed by a decrease in respiratory-related activity; this depression occurred 6min sooner in males than females. These results represent new evidences of sexual dimorphism in respiratory control in amphibians and provide potential insight in understanding the homology with other groups of vertebrates, including mammals.
Collapse
Affiliation(s)
- Jean-Philippe Rousseau
- Département de Pédiatrie, Université Laval, Centre de Recherche du CHU de Québec, Hôpital St-François d'Assise, Québec, QC G1L 3L5, Canada.
| | - Stéphanie Fournier
- Département de Pédiatrie, Université Laval, Centre de Recherche du CHU de Québec, Hôpital St-François d'Assise, Québec, QC G1L 3L5, Canada
| | - Richard Kinkead
- Département de Pédiatrie, Université Laval, Centre de Recherche du CHU de Québec, Hôpital St-François d'Assise, Québec, QC G1L 3L5, Canada
| |
Collapse
|
15
|
Côté É, Rousseau JP, Fournier S, Kinkead R. Control of Breathing in In Vitro Brain Stem Preparation from Goldfish (Carassius auratus; Linnaeus). Physiol Biochem Zool 2014; 87:464-74. [DOI: 10.1086/675939] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
|
16
|
Santin JM, Watters KC, Putnam RW, Hartzler LK. Temperature influences neuronal activity and CO2/pH sensitivity of locus coeruleus neurons in the bullfrog, Lithobates catesbeianus. Am J Physiol Regul Integr Comp Physiol 2013; 305:R1451-64. [DOI: 10.1152/ajpregu.00348.2013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The locus coeruleus (LC) is a chemoreceptive brain stem region in anuran amphibians and contains neurons sensitive to physiological changes in CO2/pH. The ventilatory and central sensitivity to CO2/pH is proportional to the temperature in amphibians, i.e., sensitivity increases with increasing temperature. We hypothesized that LC neurons from bullfrogs, Lithobates catesbeianus, would increase CO2/pH sensitivity with increasing temperature and decrease CO2/pH sensitivity with decreasing temperature. Further, we hypothesized that cooling would decrease, while warming would increase, normocapnic firing rates of LC neurons. To test these hypotheses, we used whole cell patch-clamp electrophysiology to measure firing rate, membrane potential ( Vm), and input resistance ( Rin) in LC neurons in brain stem slices from adult bullfrogs over a physiological range of temperatures during normocapnia and hypercapnia. We found that cooling reduced chemosensitive responses of LC neurons as temperature decreased until elimination of CO2/pH sensitivity at 10°C. Chemosensitive responses increased at elevated temperatures. Surprisingly, chemosensitive LC neurons increased normocapnic firing rate and underwent membrane depolarization when cooled and decreased normocapnic firing rate and underwent membrane hyperpolarization when warmed. These responses to temperature were not observed in nonchemosensitive LC neurons or neurons in a brain stem slice 500 μm rostral to the LC. Our results indicate that modulation of cellular chemosensitivity within the LC during temperature changes may influence temperature-dependent respiratory drive during acid-base disturbances in amphibians. Additionally, cold-activated/warm-inhibited LC neurons introduce paradoxical temperature sensitivity in respiratory control neurons of amphibians.
Collapse
Affiliation(s)
- Joseph M. Santin
- Department of Biological Sciences, Wright State University, Dayton, Ohio; and
| | - Kayla C. Watters
- Department of Biological Sciences, Wright State University, Dayton, Ohio; and
| | - Robert W. Putnam
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio
| | - Lynn K. Hartzler
- Department of Biological Sciences, Wright State University, Dayton, Ohio; and
| |
Collapse
|
17
|
Santin J, Hartzler L. Respiratory signaling of locus coeruleus neurons during hypercapnic acidosis in the bullfrog, Lithobates catesbeianus. Respir Physiol Neurobiol 2013; 185:553-61. [DOI: 10.1016/j.resp.2012.11.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Revised: 11/02/2012] [Accepted: 11/03/2012] [Indexed: 10/27/2022]
|
18
|
Fournier S, Dubé PL, Kinkead R. Corticosterone promotes emergence of fictive air breathing in Xenopus laevis Daudin tadpole brainstems. J Exp Biol 2012; 215:1144-50. [DOI: 10.1242/jeb.061234] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
The emergence of air breathing during amphibian metamorphosis requires significant changes to the brainstem circuits that generate and regulate breathing. However, the mechanisms controlling this developmental process are unknown. Because corticosterone plays an important role in the neuroendocrine regulation of amphibian metamorphosis, we tested the hypothesis that corticosterone augments fictive air breathing frequency in Xenopus laevis. To do so, we compared the fictive air breathing frequency produced by in vitro brainstem preparations from pre-metamorphic tadpoles and adult frogs before and after 1 h application of corticosterone (100 nmol l–1). Fictive breathing measurements related to gill and lung ventilation were recorded extracellularly from cranial nerve rootlets V and X. Corticosterone application had no immediate effect on respiratory-related motor output produced by brainstems from either developmental stage. One hour after corticosterone wash out, fictive lung ventilation frequency was increased whereas gill burst frequency was decreased. This effect was stage specific as it was significant only in preparations from tadpoles. GABA application (0.001–0.5 mmol l–1) augmented fictive air breathing in tadpole preparations. However, this effect of GABA was no longer observed following corticosterone treatment. An increase in circulating corticosterone is one of the endocrine processes that orchestrate central nervous system remodelling during metamorphosis. The age-specific effects of corticosterone application indicate that this hormone can act as an important regulator of respiratory control development in Xenopus tadpoles. Concurrent changes in GABAergic neurotransmission probably contribute to this maturation process, leading to the emergence of air breathing in this species.
Collapse
Affiliation(s)
- Stéphanie Fournier
- Department of Paediatrics, Université Laval, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Hôpital St-François d’Assise, 10 rue de l’Espinay, Québec City, QC, Canada, G1L 3L5
| | - Pierre-Luc Dubé
- Department of Paediatrics, Université Laval, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Hôpital St-François d’Assise, 10 rue de l’Espinay, Québec City, QC, Canada, G1L 3L5
| | - Richard Kinkead
- Department of Paediatrics, Université Laval, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Hôpital St-François d’Assise, 10 rue de l’Espinay, Québec City, QC, Canada, G1L 3L5
| |
Collapse
|
19
|
Porteus C, Hedrick MS, Hicks JW, Wang T, Milsom WK. Time domains of the hypoxic ventilatory response in ectothermic vertebrates. J Comp Physiol B 2011; 181:311-33. [PMID: 21312038 PMCID: PMC3058336 DOI: 10.1007/s00360-011-0554-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2010] [Revised: 01/11/2011] [Accepted: 01/19/2011] [Indexed: 01/19/2023]
Abstract
Over a decade has passed since Powell et al. (Respir Physiol 112:123-134, 1998) described and defined the time domains of the hypoxic ventilatory response (HVR) in adult mammals. These time domains, however, have yet to receive much attention in other vertebrate groups. The initial, acute HVR of fish, amphibians and reptiles serves to minimize the imbalance between oxygen supply and demand. If the hypoxia is sustained, a suite of secondary adjustments occur giving rise to a more long-term balance (acclimatization) that allows the behaviors of normal life. These secondary responses can change over time as a function of the nature of the stimulus (the pattern and intensity of the hypoxic exposure). To add to the complexity of this process, hypoxia can also lead to metabolic suppression (the hypoxic metabolic response) and the magnitude of this is also time dependent. Unlike the original review of Powell et al. (Respir Physiol 112:123-134, 1998) that only considered the HVR in adult animals, we also consider relevant developmental time points where information is available. Finally, in amphibians and reptiles with incompletely divided hearts the magnitude of the ventilatory response will be modulated by hypoxia-induced changes in intra-cardiac shunting that also improve the match between O(2) supply and demand, and these too change in a time-dependent fashion. While the current literature on this topic is reviewed here, it is noted that this area has received little attention. We attempt to redefine time domains in a more 'holistic' fashion that better accommodates research on ectotherms. If we are to distinguish between the genetic, developmental and environmental influences underlying the various ventilatory responses to hypoxia, however, we must design future experiments with time domains in mind.
Collapse
Affiliation(s)
- Cosima Porteus
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
| | | | | | | | | |
Collapse
|
20
|
Biancardi V, da Silva LT, Bícego KC, Gargaglioni LH. Role of Locus coeruleus noradrenergic neurons in cardiorespiratory and thermal control during hypoxia. Respir Physiol Neurobiol 2010; 170:150-6. [DOI: 10.1016/j.resp.2009.12.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2009] [Revised: 12/11/2009] [Accepted: 12/14/2009] [Indexed: 12/29/2022]
|
21
|
Kinkead R. Phylogenetic trends in respiratory rhythmogenesis: Insights from ectothermic vertebrates. Respir Physiol Neurobiol 2009; 168:39-48. [DOI: 10.1016/j.resp.2009.05.011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Revised: 05/27/2009] [Accepted: 05/28/2009] [Indexed: 11/26/2022]
|