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Abstract
Brain PCO2 is sensed primarily via changes in [H+]. Small pH changes are detected in the medulla oblongata and trigger breathing adjustments that help maintain arterial PCO2 constant. Larger perturbations of brain CO2/H+, possibly also sensed elsewhere in the CNS, elicit arousal, dyspnea, and stress, and cause additional breathing modifications. The retrotrapezoid nucleus (RTN), a rostral medullary cluster of glutamatergic neurons identified by coexpression of Phoxb and Nmb transcripts, is the lynchpin of the central respiratory chemoreflex. RTN regulates breathing frequency, inspiratory amplitude, and active expiration. It is exquisitely responsive to acidosis in vivo and maintains breathing autorhythmicity during quiet waking, slow-wave sleep, and anesthesia. The RTN response to [H+] is partly an intrinsic neuronal property mediated by proton sensors TASK-2 and GPR4 and partly a paracrine effect mediated by astrocytes and the vasculature. The RTN also receives myriad excitatory or inhibitory synaptic inputs including from [H+]-responsive neurons (e.g., serotonergic). RTN is silenced by moderate hypoxia. RTN inactivity (periodic or sustained) contributes to periodic breathing and, likely, to central sleep apnea. RTN development relies on transcription factors Egr2, Phox2b, Lbx1, and Atoh1. PHOX2B mutations cause congenital central hypoventilation syndrome; they impair RTN development and consequently the central respiratory chemoreflex.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, VA, United States.
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia, Charlottesville, VA, United States
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2
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Kajiwara R, Nakamura S, Ikeda K, Onimaru H, Yoshida A, Tsutsumi Y, Nakayama K, Mochizuki A, Dantsuji M, Nishimura A, Tachikawa S, Iijima T, Inoue T. Intrinsic properties and synaptic connectivity of Phox2b-expressing neurons in rat rostral parvocellular reticular formation. Neurosci Res 2021; 178:41-51. [PMID: 34973291 DOI: 10.1016/j.neures.2021.12.009] [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: 08/27/2021] [Revised: 12/24/2021] [Accepted: 12/27/2021] [Indexed: 10/19/2022]
Abstract
The paired-like homeobox 2b gene (Phox2b) is critical for the development of the autonomic nervous system. We have previously demonstrated the distinct characteristics of Phox2b-expressing (Phox2b+) neurons in the reticular formation dorsal to the trigeminal motor nucleus (RdV), which are likely related to jaw movement regulation. In this study, we focused on Phox2b+ neurons in the rostral parvocellular reticular formation (rPCRt), a critical region for controlling orofacial functions, using 2-11-day-old Phox2b-EYFP rats. Most Phox2b+ rPCRt neurons were glutamatergic, but not GABAergic or glycinergic. Approximately 65 % of Phox2b+ rPCRt neurons fired at a low frequency, and approximately 24 % of Phox2b+ rPCRt neurons fired spontaneously, as opposed to Phox2b+ RdV neurons. Stimulation of the RdV evoked inward postsynaptic currents in more than 50 % of Phox2b+ rPCRt neurons, while only one Phox2b+ rPCRt neuron responded to stimulation of the nucleus of the solitary tract. Five of the 10 Phox2b+ neurons sent their axons that ramified within the trigeminal motor nucleus (MoV). Of these, the axons of the two neurons terminated within both the MoV and rPCRt. Our findings suggest that Phox2b+ rPCRt neurons have distinct electrophysiological and synaptic properties that may be involved in the motor control of feeding behavior.
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Affiliation(s)
- Risa Kajiwara
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan; Department of Perioperative Medicine, Division of Anesthesiology, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo, 145-8515, Japan
| | - Shiro Nakamura
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan.
| | - Keiko Ikeda
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan
| | - Atsushi Yoshida
- Department of Oral Anatomy and Neurobiology, Osaka University Graduate School of Dentistry, 1-8 Yamada-Oka, Suita, Osaka, 565-0871, Japan
| | - Yumi Tsutsumi
- Department of Oral Anatomy and Neurobiology, Osaka University Graduate School of Dentistry, 1-8 Yamada-Oka, Suita, Osaka, 565-0871, Japan
| | - Kiyomi Nakayama
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan
| | - Ayako Mochizuki
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan
| | - Masanori Dantsuji
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan
| | - Akiko Nishimura
- Department of Perioperative Medicine, Division of Anesthesiology, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo, 145-8515, Japan
| | - Satoshi Tachikawa
- Department of Perioperative Medicine, Division of Anesthesiology, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo, 145-8515, Japan
| | - Takehiko Iijima
- Department of Perioperative Medicine, Division of Anesthesiology, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo, 145-8515, Japan
| | - Tomio Inoue
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan
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3
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Katsuki S, Ikeda K, Onimaru H, Dohi K, Izumizaki M. Effects of acetylcholine on hypoglossal and C4 nerve activity in brainstem-spinal cord preparations from newborn rat. Respir Physiol Neurobiol 2021; 293:103737. [PMID: 34229065 DOI: 10.1016/j.resp.2021.103737] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2021] [Revised: 06/17/2021] [Accepted: 07/01/2021] [Indexed: 11/17/2022]
Abstract
Effects of acetylcholine (ACh) on respiratory activity have been an intriguing theme especially in relation to central chemoreception and the control of hypoglossal nerve activity. We studied the effects of ACh on hypoglossal and phrenic (C4) nerve activities and inspiratory and pre-inspiratory neurons in the rostral ventrolateral medulla in brainstem-spinal cord preparations from newborn rats. ACh application increased respiratory rhythm, decreased inspiratory hypoglossal and C4 nerve burst amplitude, and enhanced pre-inspiratory hypoglossal activity. ACh induced membrane depolarization of pre-inspiratory neurons that might be involved in facilitation of respiratory rhythm by ACh. Effects of ACh on hypoglossal and C4 nerve activity were partially reversed by a nicotinic receptor blocker, mecamylamine. Further application of a muscarinic receptor antagonist, oxybutynin, resulted in slight increase of hypoglossal (but not C4) burst amplitude. Thus, ACh induced different effects on hypoglossal and C4 nerve activity in the brainstem-spinal cord preparation.
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Affiliation(s)
- Shino Katsuki
- Department of Physiology, Showa University School of Medicine, Tokyo 142-8555, Japan; Department of Emergency, Disaster and Critical Care Medicine, Showa University, Tokyo 142-8555, Japan
| | - Keiko Ikeda
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Tokyo 142-8555, Japan.
| | - Kenji Dohi
- Department of Emergency, Disaster and Critical Care Medicine, Showa University, Tokyo 142-8555, Japan
| | - Masahiko Izumizaki
- Department of Physiology, Showa University School of Medicine, Tokyo 142-8555, Japan
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4
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Biancardi V, Saini J, Pageni A, Prashaad M. H, Funk GD, Pagliardini S. Mapping of the excitatory, inhibitory, and modulatory afferent projections to the anatomically defined active expiratory oscillator in adult male rats. J Comp Neurol 2020; 529:853-884. [DOI: 10.1002/cne.24984] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Revised: 06/29/2020] [Accepted: 07/05/2020] [Indexed: 01/21/2023]
Affiliation(s)
- Vivian Biancardi
- Department of Physiology University of Alberta Edmonton Canada
- Women and Children's Health Research Institute, Faculty of Medicine and Dentistry University of Alberta Edmonton Canada
| | - Jashan Saini
- Department of Physiology University of Alberta Edmonton Canada
| | - Anileen Pageni
- Department of Physiology University of Alberta Edmonton Canada
| | | | - Gregory D. Funk
- Department of Physiology University of Alberta Edmonton Canada
- Women and Children's Health Research Institute, Faculty of Medicine and Dentistry University of Alberta Edmonton Canada
- Neuroscience and Mental Health Institute University of Alberta Edmonton Canada
| | - Silvia Pagliardini
- Department of Physiology University of Alberta Edmonton Canada
- Women and Children's Health Research Institute, Faculty of Medicine and Dentistry University of Alberta Edmonton Canada
- Neuroscience and Mental Health Institute University of Alberta Edmonton Canada
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5
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Ghali MGZ. Retracted: Control of hypoglossal pre‐inspiratory discharge. Exp Physiol 2020; 105:1232-1255. [DOI: 10.1113/ep087329] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2018] [Accepted: 06/11/2020] [Indexed: 12/22/2022]
Affiliation(s)
- Michael George Zaki Ghali
- Departments of Neurological Surgery, Internal Medicine, General Surgery, and Neuroscience Karolinska Institutet Huddinge Stockholm Sweden
- Departments of Neurological Surgery, Neurophysiology, Neuroscience University of Oslo Oslo Norway
- Departments of Neurological Surgery and Neurochemistry University of Helsinki Helsinki Finland
- Departments of Neurological Surgery, Internal Medicine, Cardiothoracic Surgery, and Neuroscience University of California Francisco San Francisco CA USA
- Departments of Neurological Surgery and Neuroscience Barrow Neurological Institute Phoenix AZ USA
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6
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Maia OAC, Malheiros-Lima MR, Oliveira MA, Castro CL, Moriya HT, Tavares-de-Lima W, Takakura AC, Moreira TS. Pilocarpine-induced status epilepticus reduces chemosensory control of breathing. Brain Res Bull 2020; 161:98-105. [PMID: 32433938 DOI: 10.1016/j.brainresbull.2020.05.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Revised: 04/27/2020] [Accepted: 05/02/2020] [Indexed: 12/14/2022]
Abstract
One of the possible causes of death in epilepsy is breathing disorders, especially apneas, which lead to an increase in CO2 levels (hypercapnia) and/or a decrease in O2 levels in arterial blood (hypoxemia). The respiratory neurons located in the ventral brainstem respiratory column are the main groups responsible for controlling breathing. Recent data from our group demonstrated respiratory changes in two experimental models of epilepsy, i.e. audiogenic epilepsy, and amygdala rapid kindling. Here, we aimed to evaluate respiratory changes in the classic model of temporal lobe epilepsy induced by intra-hippocampal injection of pilocarpine. Adult Wistar rats with stainless-steel cannulas implanted in the hippocampus region were used. The animals were submitted to pilocarpine injection (2.4 mg/μL, N = 12-15) or saline (N = 9) into the hippocampus. The respiratory parameters analyzed by whole-body plethysmography were respiratory rate (fR), tidal volume (VT) and ventilation (VE). Respiratory mechanics such as Newtonian airway resistance (Rn), viscance of the pulmonary parenchyma (G) and the elastance of the pulmonary parenchyma (H) were also investigated. No changes in baseline breathing were detected 15 or 30 days after pilocarpine-induced status epilepticus (SE). However, 30 days after pilocarpine-induced SE, a significant reduction in VE was observed during hypercapnic (7% CO2) stimulation, without affecting the hypoxia (8% O2) ventilatory response. We also did not observe changes in respiratory mechanics. The present results suggest that the impairment of the hypercapnia ventilatory response in pilocarpine-induced SE could be related to a presumable degeneration of brainstem respiratory neurons but not to peripheral mechanisms.
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Affiliation(s)
- Octávio A C Maia
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of Sao Paulo, 1524 Prof Lineu Prestes Av 05508-000, Sao Paulo, SP, Brazil
| | - Milene R Malheiros-Lima
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of Sao Paulo, 1524 Prof Lineu Prestes Av 05508-000, Sao Paulo, SP, Brazil
| | - Maria A Oliveira
- Department of Pharmacology, Institute of Biomedical Science, University of Sao Paulo, Sao Paulo, SP, Brazil
| | - Claudio L Castro
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of Sao Paulo, 1524 Prof Lineu Prestes Av 05508-000, Sao Paulo, SP, Brazil
| | - Henrique T Moriya
- Department of Engineering of Control and Telecommunication, University of Sao Paulo, Sao Paulo, SP, Brazil
| | - Wothan Tavares-de-Lima
- Department of Pharmacology, Institute of Biomedical Science, University of Sao Paulo, Sao Paulo, SP, Brazil
| | - Ana C Takakura
- Department of Pharmacology, Institute of Biomedical Science, University of Sao Paulo, Sao Paulo, SP, Brazil
| | - Thiago S Moreira
- Department of Physiology and Biophysics, Institute of Biomedical Science, University of Sao Paulo, 1524 Prof Lineu Prestes Av 05508-000, Sao Paulo, SP, Brazil.
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7
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Maternal cigarette smoke exposure disturbs glutamate/GABA balance in pFRG of neonatal rats. Respir Physiol Neurobiol 2020; 274:103383. [PMID: 31923590 DOI: 10.1016/j.resp.2020.103383] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 12/21/2019] [Accepted: 01/06/2020] [Indexed: 01/14/2023]
Abstract
We previously found that maternal cigarette smoke (CS) exposure resulted in impairment of central chemoreception and oxidative stress and mitochondrial dysfunction of parafacial respiratory group (pFRG, a critical site for mammalian central chemoreception) in neonatal rats. The present work was carried out to identify if maternal CS exposure could disturb the glutamate (GLU)-ergic and γ-aminobutyric acid (GABA)-ergic balance in pFRG of neonatal rats. We found that maternal CS exposure induced a decrease in GLU content and consequently in GLU/GABA ratio in pFRG of neonatal rats. Maternal CS exposure also decreased glutamine content and glutaminase and glutamine synthetase activity in offspring pFRG. In addition, expression of vesicular glutamate transporter 2 was depressed, and those of glutamate transporter 1 and GABA transporter 3 were elevated by maternal CS exposure. These results indicate that maternal CS exposure leads to a disturbance of GLU/GABA balance in pFRG of the neonatal rats, which might contribute to the suppression of central chemoreception in maternal CS-exposed offspring.
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Igarashi H, Ikeda K, Onimaru H, Kaneko R, Koizumi K, Beppu K, Nishizawa K, Takahashi Y, Kato F, Matsui K, Kobayashi K, Yanagawa Y, Muramatsu SI, Ishizuka T, Yawo H. Targeted expression of step-function opsins in transgenic rats for optogenetic studies. Sci Rep 2018; 8:5435. [PMID: 29615713 PMCID: PMC5882906 DOI: 10.1038/s41598-018-23810-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 03/20/2018] [Indexed: 12/12/2022] Open
Abstract
Rats are excellent animal models for experimental neuroscience. However, the application of optogenetics in rats has been hindered because of the limited number of established transgenic rat strains. To accomplish cell-type specific targeting of an optimized optogenetic molecular tool, we generated ROSA26/CAG-floxed STOP-ChRFR(C167A)-Venus BAC rats that conditionally express the step-function mutant channelrhodopsin ChRFR(C167A) under the control of extrinsic Cre recombinase. In primary cultured cortical neurons derived from this reporter rat, only Cre-positive cells expressing ChRFR(C167A) became bi-stable, that is, their excitability was enhanced by blue light and returned to the baseline by yellow~red light. In bigenic pups carrying the Phox2B-Cre driver, ChRFR(C167A) was specifically expressed in the rostral parafacial respiratory group (pFRG) in the medulla, where endogenous Phox2b immunoreactivity was detected. These neurons were sensitive to blue light with an increase in the firing frequency. Thus, this transgenic rat actuator/reporter system should facilitate optogenetic studies involving the effective in vivo manipulation of the activities of specific cell fractions using light of minimal intensity.
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Affiliation(s)
- Hiroyuki Igarashi
- Department of Physiology and Pharmacology, Tohoku University Graduate school of Medicine, Sendai, Japan. .,Research Fellow of the Japan Society for the Promotion of Science (JSPS Research Fellow), Tokyo, Japan.
| | - Keiko Ikeda
- Department of Physiology, International University of Health and Welfare, Narita, Chiba, Japan.,Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Shinagawa, Tokyo, Japan
| | - Ryosuke Kaneko
- Department of Genetic and Behavioural Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Kyo Koizumi
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Japan
| | - Kaoru Beppu
- Department of Super-network Brain Physiology, Tohoku University Graduate School of Life Sciences, Sendai, Japan
| | - Kayo Nishizawa
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima, Japan
| | - Yukari Takahashi
- Department of Neuroscience, The Jikei University School of Medicine, Tokyo, Japan
| | - Fusao Kato
- Department of Neuroscience, The Jikei University School of Medicine, Tokyo, Japan
| | - Ko Matsui
- Department of Super-network Brain Physiology, Tohoku University Graduate School of Life Sciences, Sendai, Japan
| | - Kazuto Kobayashi
- Department of Molecular Genetics, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima, Japan
| | - Yuchio Yanagawa
- Department of Genetic and Behavioural Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Shin-Ichi Muramatsu
- Division of Neurology, Jichi Medical School, Tochigi, Japan.,Center for Gene & Cell Therapy, The Institute of Medical Science, University of Tokyo, Tokyo, Japan
| | - Toru Ishizuka
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Japan
| | - Hiromu Yawo
- Department of Physiology and Pharmacology, Tohoku University Graduate school of Medicine, Sendai, Japan. .,Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Japan.
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9
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Onimaru H, Nakamura S, Ikeda K, Kawakami K, Inoue T. Confocal calcium imaging analysis of respiratory-related burst activity in the parafacial region. Brain Res Bull 2018; 139:16-20. [PMID: 29374604 DOI: 10.1016/j.brainresbull.2018.01.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Accepted: 01/18/2018] [Indexed: 11/25/2022]
Abstract
The parafacial respiratory group (pFRG) surrounding the ventrolateral part of the facial motor nucleus is one of respiratory rhythm generators that consists of pre-inspiratory (Pre-I) neurons. Previous studies showed that most of the Pre-I neurons locating in the Phox2b cluster of the rostral ventral medulla were also Phox2b positive and intrinsically CO2 sensitive. However, it is not clear what percentage of Phox2b-expressing cells in the pFRG of the ventral medulla are Pre-I neurons. To address this issue, we analyzed the activity of Phox2b-positive cells by calcium imaging using a confocal laser microscope in transgenic rats in which Phox2b-positive cells expressed EYFP. We found that more than 60% of the EYFP/Phox2b-positive cells showed Pre-I neuron-like rhythmic burst activity in the parafacial region of newborn rat.
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Affiliation(s)
- Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
| | - Shiro Nakamura
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Keiko Ikeda
- Department of Physiology, International University of Health and Welfare (IUHW), 4-3 Kozunomori, Narita City, Chiba 286-8686, Japan
| | - Kiyoshi Kawakami
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi 329-0498, Japan
| | - Tomio Inoue
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
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10
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Nagoya K, Nakamura S, Ikeda K, Onimaru H, Yoshida A, Nakayama K, Mochizuki A, Kiyomoto M, Sato F, Kawakami K, Takahashi K, Inoue T. Distinctive features of Phox2b-expressing neurons in the rat reticular formation dorsal to the trigeminal motor nucleus. Neuroscience 2017; 358:211-226. [PMID: 28673717 DOI: 10.1016/j.neuroscience.2017.06.035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 06/03/2017] [Accepted: 06/21/2017] [Indexed: 10/19/2022]
Abstract
Phox2b encodes a paired-like homeodomain-containing transcription factor essential for development of the autonomic nervous system. Phox2b-expressing (Phox2b+) neurons are present in the reticular formation dorsal to the trigeminal motor nucleus (RdV) as well as the nucleus of the solitary tract and parafacial respiratory group. However, the nature of Phox2b+ RdV neurons is still unclear. We investigated the physiological and morphological properties of Phox2b+ RdV neurons using postnatal day 2-7 transgenic rats expressing yellow fluorescent protein under the control of Phox2b. Almost all of Phox2b+ RdV neurons were glutamatergic, whereas Phox2b-negative (Phox2b-) RdV neurons consisted of a few glutamatergic, many GABAergic, and many glycinergic neurons. The majority (48/56) of Phox2b+ neurons showed low-frequency firing (LF), while most of Phox2b- neurons (35/42) exhibited high-frequency firing (HF) in response to intracellularly injected currents. All, but one, Phox2b+ neurons (55/56) did not fire spontaneously, whereas three-fourths of the Phox2b- neurons (31/42) were spontaneously active. K+ channel and persistent Na+ current blockers affected the firing of LF and HF neurons. The majority of Phox2b+ (35/46) and half of the Phox2b- neurons (19/40) did not respond to stimulations of the mesencephalic trigeminal nucleus, the trigeminal tract, and the principal sensory trigeminal nucleus. Biocytin labeling revealed that about half of the Phox2b+ (5/12) and Phox2b- RdV neurons (5/10) send their axons to the trigeminal motor nucleus. These results suggest that Phox2b+ RdV neurons have distinct neurotransmitter phenotypes and firing properties from Phox2b- RdV neurons and might play important roles in feeding-related functions including suckling and possibly mastication.
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Affiliation(s)
- Kouta Nagoya
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; Division of Oral Rehabilitation Medicine, Department of Special Needs Dentistry, Showa University School of Dentistry, 2-2-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, Japan
| | - Shiro Nakamura
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
| | - Keiko Ikeda
- Division of Biology, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, Hyogo 663-8501, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Atsushi Yoshida
- Department of Oral Anatomy and Neurobiology, Osaka University Graduate School of Dentistry, 1-8, Yamada-Oka, Suita, Osaka 565-0871, Japan
| | - Kiyomi Nakayama
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Ayako Mochizuki
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Masaaki Kiyomoto
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Fumihiko Sato
- Department of Oral Anatomy and Neurobiology, Osaka University Graduate School of Dentistry, 1-8, Yamada-Oka, Suita, Osaka 565-0871, Japan
| | - Kiyoshi Kawakami
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan
| | - Koji Takahashi
- Division of Oral Rehabilitation Medicine, Department of Special Needs Dentistry, Showa University School of Dentistry, 2-2-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, Japan
| | - Tomio Inoue
- Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
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11
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Hayes JA, Kottick A, Picardo MCD, Halleran AD, Smith RD, Smith GD, Saha MS, Del Negro CA. Transcriptome of neonatal preBötzinger complex neurones in Dbx1 reporter mice. Sci Rep 2017; 7:8669. [PMID: 28819234 PMCID: PMC5561182 DOI: 10.1038/s41598-017-09418-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 07/24/2017] [Indexed: 12/14/2022] Open
Abstract
We sequenced the transcriptome of brainstem interneurons in the specialized respiratory rhythmogenic site dubbed preBötzinger Complex (preBötC) from newborn mice. To distinguish molecular characteristics of the core oscillator we compared preBötC neurons derived from Dbx1-expressing progenitors that are respiratory rhythmogenic to neighbouring non-Dbx1-derived neurons, which support other respiratory and non-respiratory functions. Results in three categories are particularly salient. First, Dbx1 preBötC neurons express κ-opioid receptors in addition to μ-opioid receptors that heretofore have been associated with opiate respiratory depression, which may have clinical applications. Second, Dbx1 preBötC neurons express the hypoxia-inducible transcription factor Hif1a at levels three-times higher than non-Dbx1 neurons, which links core rhythmogenic microcircuits to O2-related chemosensation for the first time. Third, we detected a suite of transcription factors including Hoxa4 whose expression pattern may define the rostral preBötC border, Pbx3 that may influence ipsilateral connectivity, and Pax8 that may pertain to a ventrally-derived subset of Dbx1 preBötC neurons. These data establish the transcriptomic signature of the core respiratory oscillator at a perinatal stage of development.
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Affiliation(s)
- John A Hayes
- Department of Applied Science, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA
| | - Andrew Kottick
- Department of Applied Science, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA
| | - Maria Cristina D Picardo
- Department of Applied Science, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA
| | - Andrew D Halleran
- Department of Biology, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA
| | - Ronald D Smith
- Department of Applied Science, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA
| | - Gregory D Smith
- Department of Applied Science, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA
| | - Margaret S Saha
- Department of Biology, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA
| | - Christopher A Del Negro
- Department of Applied Science, Integrated Science Center, 540 Landrum Dr., The College of William and Mary, Williamsburg, VA, 23185, USA.
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12
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Ikeda K, Kawakami K, Onimaru H, Okada Y, Yokota S, Koshiya N, Oku Y, Iizuka M, Koizumi H. The respiratory control mechanisms in the brainstem and spinal cord: integrative views of the neuroanatomy and neurophysiology. J Physiol Sci 2016; 67:45-62. [PMID: 27535569 PMCID: PMC5368202 DOI: 10.1007/s12576-016-0475-y] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Accepted: 07/22/2016] [Indexed: 12/17/2022]
Abstract
Respiratory activities are produced by medullary respiratory rhythm generators and are modulated from various sites in the lower brainstem, and which are then output as motor activities through premotor efferent networks in the brainstem and spinal cord. Over the past few decades, new knowledge has been accumulated on the anatomical and physiological mechanisms underlying the generation and regulation of respiratory rhythm. In this review, we focus on the recent findings and attempt to elucidate the anatomical and functional mechanisms underlying respiratory control in the lower brainstem and spinal cord.
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Affiliation(s)
- Keiko Ikeda
- Division of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo, 663-8501, Japan.
| | - Kiyoshi Kawakami
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, 329-0498, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Shinagawa, Tokyo, 142-8555, Japan.
| | - Yasumasa Okada
- Clinical Research Center, Murayama Medical Center, Musashimurayama, Tokyo, 208-0011, Japan.
| | - Shigefumi Yokota
- Department of Anatomy and Morphological Neuroscience, Shimane University School of Medicine, Izumo, Shimane, 693-8501, Japan
| | - Naohiro Koshiya
- Cellular and Systems Neurobiology Section, NINDS, NIH, Bethesda, MD, 20892, USA.
| | - Yoshitaka Oku
- Department of Physiology, Hyogo College of Medicine, Nishinomiya, Hyogo, 663-8501, Japan.
| | - Makito Iizuka
- Department of Physiology, Showa University School of Medicine, Shinagawa, Tokyo, 142-8555, Japan.
| | - Hidehiko Koizumi
- Cellular and Systems Neurobiology Section, NINDS, NIH, Bethesda, MD, 20892, USA
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13
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Igarashi H, Koizumi K, Kaneko R, Ikeda K, Egawa R, Yanagawa Y, Muramatsu SI, Onimaru H, Ishizuka T, Yawo H. A Novel Reporter Rat Strain That Conditionally Expresses the Bright Red Fluorescent Protein tdTomato. PLoS One 2016; 11:e0155687. [PMID: 27195805 PMCID: PMC4873025 DOI: 10.1371/journal.pone.0155687] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 05/03/2016] [Indexed: 01/28/2023] Open
Abstract
Despite the strength of the Cre/loxP recombination system in animal models, its application in rats trails that in mice because of the lack of relevant reporter strains. Here, we generated a floxed STOP tdTomato rat that conditionally expresses a red fluorescent protein variant (tdTomato) in the presence of exogenous Cre recombinase. The tdTomato signal vividly visualizes neurons including their projection fibers and spines without any histological enhancement. In addition, a transgenic rat line (FLAME) that ubiquitously expresses tdTomato was successfully established by injecting intracytoplasmic Cre mRNA into fertilized ova. Our rat reporter system will facilitate connectome studies as well as the visualization of the fine structures of genetically identified cells for long periods both in vivo and ex vivo. Furthermore, FLAME is an ideal model for organ transplantation research owing to improved traceability of cells/tissues.
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Affiliation(s)
- Hiroyuki Igarashi
- Department of Physiology and Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
- Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo, Japan
- Tohoku University Division for Interdisciplinary Advanced Research and Education, Sendai, Miyagi, Japan
| | - Kyo Koizumi
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Miyagi, Japan
| | - Ryosuke Kaneko
- Department of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
- Bioresource center, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
| | - Keiko Ikeda
- Division of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan
| | - Ryo Egawa
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Miyagi, Japan
| | - Yuchio Yanagawa
- Department of Genetic and Behavioral Neuroscience, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
| | - Shin-ichi Muramatsu
- Division of Neurology, Department of Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan
- Center for Gene & Cell Therapy, The Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Shinagawa, Tokyo, Japan
| | - Toru Ishizuka
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Miyagi, Japan
| | - Hiromu Yawo
- Department of Physiology and Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences, Sendai, Miyagi, Japan
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14
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Ikeda K, Takahashi M, Sato S, Igarashi H, Ishizuka T, Yawo H, Arata S, Southard-Smith EM, Kawakami K, Onimaru H. A Phox2b BAC Transgenic Rat Line Useful for Understanding Respiratory Rhythm Generator Neural Circuitry. PLoS One 2015; 10:e0132475. [PMID: 26147470 PMCID: PMC4492506 DOI: 10.1371/journal.pone.0132475] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 06/15/2015] [Indexed: 11/21/2022] Open
Abstract
The key role of the respiratory neural center is respiratory rhythm generation to maintain homeostasis through the control of arterial blood pCO2/pH and pO2 levels. The neuronal network responsible for respiratory rhythm generation in neonatal rat resides in the ventral side of the medulla and is composed of two groups; the parafacial respiratory group (pFRG) and the pre-Bötzinger complex group (preBötC). The pFRG partially overlaps in the retrotrapezoid nucleus (RTN), which was originally identified in adult cats and rats. Part of the pre-inspiratory (Pre-I) neurons in the RTN/pFRG serves as central chemoreceptor neurons and the CO2 sensitive Pre-I neurons express homeobox gene Phox2b. Phox2b encodes a transcription factor and is essential for the development of the sensory-motor visceral circuits. Mutations in human PHOX2B cause congenital hypoventilation syndrome, which is characterized by blunted ventilatory response to hypercapnia. Here we describe the generation of a novel transgenic (Tg) rat harboring fluorescently labeled Pre-I neurons in the RTN/pFRG. In addition, the Tg rat showed fluorescent signals in autonomic enteric neurons and carotid bodies. Because the Tg rat expresses inducible Cre recombinase in PHOX2B-positive cells during development, it is a potentially powerful tool for dissecting the entire picture of the respiratory neural network during development and for identifying the CO2/O2 sensor molecules in the adult central and peripheral nervous systems.
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Affiliation(s)
- Keiko Ikeda
- Division of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan
- * E-mail:
| | - Masanori Takahashi
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan
| | - Shigeru Sato
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan
| | - Hiroyuki Igarashi
- Department of Physiology, and Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
| | - Toru Ishizuka
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences and JST/CREST, Sendai, Miyagi, Japan
| | - Hiromu Yawo
- Department of Physiology, and Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
- Department of Developmental Biology and Neuroscience, Tohoku University Graduate School of Life Sciences and JST/CREST, Sendai, Miyagi, Japan
| | - Satoru Arata
- Center for Biotechnology, Showa University, Shinagawa, Tokyo, Japan
| | - E. Michelle Southard-Smith
- Division of Genetic Medicine, Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
| | - Kiyoshi Kawakami
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Shinagawa, Tokyo, Japan
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15
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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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16
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Abstract
Lung ventilation fluctuates widely with behavior but arterial PCO2 remains stable. Under normal conditions, the chemoreflexes contribute to PaCO2 stability by producing small corrective cardiorespiratory adjustments mediated by lower brainstem circuits. Carotid body (CB) information reaches the respiratory pattern generator (RPG) via nucleus solitarius (NTS) glutamatergic neurons which also target rostral ventrolateral medulla (RVLM) presympathetic neurons thereby raising sympathetic nerve activity (SNA). Chemoreceptors also regulate presympathetic neurons and cardiovagal preganglionic neurons indirectly via inputs from the RPG. Secondary effects of chemoreceptors on the autonomic outflows result from changes in lung stretch afferent and baroreceptor activity. Central respiratory chemosensitivity is caused by direct effects of acid on neurons and indirect effects of CO2 via astrocytes. Central respiratory chemoreceptors are not definitively identified but the retrotrapezoid nucleus (RTN) is a particularly strong candidate. The absence of RTN likely causes severe central apneas in congenital central hypoventilation syndrome. Like other stressors, intense chemosensory stimuli produce arousal and activate circuits that are wake- or attention-promoting. Such pathways (e.g., locus coeruleus, raphe, and orexin system) modulate the chemoreflexes in a state-dependent manner and their activation by strong chemosensory stimuli intensifies these reflexes. In essential hypertension, obstructive sleep apnea and congestive heart failure, chronically elevated CB afferent activity contributes to raising SNA but breathing is unchanged or becomes periodic (severe CHF). Extreme CNS hypoxia produces a stereotyped cardiorespiratory response (gasping, increased SNA). The effects of these various pathologies on brainstem cardiorespiratory networks are discussed, special consideration being given to the interactions between central and peripheral chemoreflexes.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia
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17
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Onimaru H, Ikeda K, Mariho T, Kawakami K. Cytoarchitecture and CO(2) sensitivity of Phox2b-positive Parafacial neurons in the newborn rat medulla. PROGRESS IN BRAIN RESEARCH 2014; 209:57-71. [PMID: 24746043 DOI: 10.1016/b978-0-444-63274-6.00004-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Preinspiratory (Pre-I) neurons in the parafacial respiratory group (pFRG) compose one of the respiratory rhythm generators in the medulla of the newborn rat. It has been shown that a subgroup of pFRG/Pre-I neurons could also work as central chemoreceptor neurons, because the CO(2) sensitivity of these Pre-I neurons was preserved even after blockade of Na(+) channels and Ca(2+) channels, and the membrane depolarization induced by hypercapnic stimulation was mainly because of the closing of K(+) channels. These neurons, some of which were identified to be glutamatergic, express the transcription factor Phox2b. Phox2b expression was one of the most noticeable characteristics of pFRG/Pre-I neurons. We also found that Phox2b-expressing neurons in the parafacial region of the rostral ventral medulla tended to assemble around capillary blood vessels. In contrast, another subclass of the pFRG/Pre-I neurons was Phox2b-negative and CO(2)-insensitive. Some of these neurons were identified to be glycinergic or GABAergic. Thus, Phox2b expression is a key genetic marker that can be used to more clearly establish the cell architecture of the pFRG, which consists of heterogeneous neuronal subtypes. In this chapter, we elaborate on the CO(2) sensitivity of Phox2b-positive/negative parafacial neurons and the cytoarchitecture in the newborn rat medulla, and discuss ionic mechanisms of CO(2) responsiveness.
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Affiliation(s)
- Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, Shinagawa-ku, Tokyo, Japan.
| | - Keiko Ikeda
- Division of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan
| | - Tani Mariho
- Department of Physiology, Showa University School of Medicine, Shinagawa-ku, Tokyo, Japan
| | - Kiyoshi Kawakami
- Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, Japan
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18
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Guyenet PG, Abbott SBG, Stornetta RL. The respiratory chemoreception conundrum: light at the end of the tunnel? Brain Res 2013; 1511:126-37. [PMID: 23088963 PMCID: PMC3570739 DOI: 10.1016/j.brainres.2012.10.028] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 10/10/2012] [Accepted: 10/14/2012] [Indexed: 11/29/2022]
Abstract
Arterial PCO₂ is tightly regulated via changes in breathing. A rise in PCO₂ activates the carotid bodies and exerts additional effects on neurons located within the CNS, causing an increase in lung ventilation. Central respiratory chemoreception refers to the component of this homeostatic reflex that is triggered by activation of receptors located within the brain (central chemoreceptors). Throughout the body, CO₂ generally operates via the proxy of pH. Since countless proteins, ion channels and neurons display some degree of pH-sensitivity, the notion that central respiratory chemoreception could rely on a few specialized neurons seems a priori counter-intuitive. Yet, two types of neurons currently stand out as critically important for breathing regulation by CO₂: the retrotrapezoid nucleus (RTN) and the raphe. RTN neurons are glutamatergic, strongly activated by hypercapnia in vivo and by CO₂ or protons in slices. These neurons target selectively the pontomedullary regions implicated in generating the respiratory rhythm and pattern. Their response to CO₂ seems to involve both cell-autonomous and paracrine effects of CO₂, the latter presumably mediated by the surrounding glia. The specific connections that these excitatory neurons establish with the rest of the breathing network are likely to be the main explanation of their importance to respiratory chemoreception. Serotonergic neurons have a powerful stimulatory effect on breathing, they facilitate the chemoreflexes and a subset of them likely function as CO₂ sensors. Opto- and pharmacogenetic methods have played an important role in assessing the contribution of RTN and serotonergic neurons as well as glial cells to respiration. These particular experiments are emphasized here for thematic reasons although the current perception of the importance of the RTN and serotonergic cells to respiratory chemoreception also relies on many other types of evidence. A small portion of this evidence is presented as background. This article is part of a Special Issue entitled Optogenetics (7th BRES).
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, 1300 Jefferson Park Ave, Charlottesville, VA 22908, USA.
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