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Abdelhady R, Cavalu S, Saber S, Elmowafy R, Morsy NE, Ibrahim S, Abdeldaiem MSI, Samy M, Abd-Eldayem MA, Shata A, Elgharabawy RM. Mirtazepine, an atypical antidepressant, mitigates lung fibrosis by suppressing NLPR3 inflammasome and fibrosis-related mediators in endotracheal bleomycin rat model. Biomed Pharmacother 2023; 161:114553. [PMID: 36934553 DOI: 10.1016/j.biopha.2023.114553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Revised: 03/05/2023] [Accepted: 03/15/2023] [Indexed: 03/19/2023] Open
Abstract
Idiopathic pulmonary fibrosis (IPF) is a progressive and irreversible lung disease with a poor prognosis. There is currently no definitive cure for IPF. The present study establishes a platform for the development of a novel therapeutic approach for the treatment of PF using the atypical antidepressant, mirtazapine. In the endotracheal bleomycin rat model, mirtazapine interfered with the activation of NLRP3 inflammasome via downregulating the NLRP3 on the gene and protein expression levels. Accordingly, the downstream mediators IL-1β and IL-18 were repressed. Such observation is potentially a direct result of the reported improvement in oxidative stress. Additionally, mirtazapine corrected the bleomycin-induced disparities in the levels of the fibrogenic mediators TGF-β, PDGF-BB, and TIMP-1, in consequence, the lung content of hydroxyproline and the expression of α-SMA were reduced. Besides, mirtazapine curbed the ICAM-1 and the chemotactic cytokines MCP-1 and CXCL4. This protective property of mirtazapine resulted in improving the BALF total and differential cell counts, diminishing LDH activity, and reducing the BALF total protein. Moreover, the inflammation and fibrosis scores were accordingly lower. To conclude, we reveal for the first time the efficacy of mirtazapine as a potential treatment for PF. The combination of social isolation, sleep problems, breathing difficulties, and fear of death can lead to psychological distress and depression in patients with IPF. Hence, mirtazapine is a promising treatment option that may improve the prognosis for IPF patients due to its antifibrotic effects, as well as its ability to alleviate depressive episodes.
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Affiliation(s)
- Rasha Abdelhady
- Pharmacology and Toxicology Department, Faculty of Pharmacy, Fayoum University, Fayoum 63514, Egypt.
| | - Simona Cavalu
- Faculty of Medicine and Pharmacy, University of Oradea, P-ta 1 Decembrie 10, 410087 Oradea, Romania.
| | - Sameh Saber
- Department of Pharmacology, Faculty of Pharmacy, Delta University for Science and Technology, Gamasa 11152, Egypt.
| | - Rasha Elmowafy
- Department of Medical Biochemistry and Molecular Biology, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt.
| | - Nesreen Elsayed Morsy
- Pulmonary Medicine Department, Mansoura University Sleep Center, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt.
| | - Samar Ibrahim
- Department of Pharmacy Practice, Faculty of Pharmacy, Ahram Canadian University, Giza 12451, Egypt.
| | | | - Mervat Samy
- Department of Clinical Pharmacology, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt.
| | - Marwa A Abd-Eldayem
- Department of Pharmacology and Biochemistry, Faculty of Pharmacy, Horus University, New Damietta, Egypt.
| | - Ahmed Shata
- Department of Clinical Pharmacology, Faculty of Medicine, Mansoura University, Mansoura 35516, Egypt; Department of Clinical Pharmacy, Faculty of Pharmacy, Delta University for Science and Technology, Gamasa 11152, Egypt.
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Gibbons TD, Dempsey JA, Thomas KN, Ainslie PN, Wilson LC, Stothers TAM, Campbell HA, Cotter JD. Carotid body hyperexcitability underlies heat-induced hyperventilation in exercising humans. J Appl Physiol (1985) 2022; 133:1394-1406. [PMID: 36302157 DOI: 10.1152/japplphysiol.00435.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Physical activity is the most common source of heat strain for humans. The thermal strain of physical activity causes overbreathing (hyperventilation) and this has adverse physiological repercussions. The mechanisms underlying heat-induced hyperventilation during exercise are unknown, but recent evidence supports a primary role of carotid body hyperexcitability (increased tonic activity and sensitivity) underpinning hyperventilation in passively heated humans. In a repeated-measures crossover design, 12 healthy participants (6 female) completed two low-intensity cycling exercise conditions (25% maximal aerobic power) in randomized order, one with core temperature (TC) kept relatively stable near thermoneutrality, and the other with progressive heat strain to +2°C TC. To provide a complete examination of carotid body function under graded heat strain, carotid body tonic activity was assessed indirectly by transient hyperoxia, and its sensitivity estimated by responses to both isocapnic and poikilocapnic hypoxia. Carotid body tonic activity was increased by 220 ± 110% during cycling alone, and by 400 ± 290% with supplemental thermal strain to +1°C TC, and 600 ± 290% at +2°C TC (interaction, P = 0.0031). During exercise with heat stress at both +1°C and +2°C TC, carotid body suppression by hyperoxia decreased ventilation below the rates observed during exercise without heat stress (P < 0.0147). Carotid body sensitivity was increased by up to 230 ± 190% with exercise alone, and by 290 ± 250% with supplemental heating to +1°C TC and 510 ± 470% at +2°C TC (interaction, P = 0.0012). These data indicate that the carotid body is further activated and sensitized by heat strain during exercise and this largely explains the added drive to breathe.NEW & NOTEWORTHY Physical activity is the most common way humans increase their core temperature, and excess breathing in the heat can limit heat tolerance and performance, and may increase the risk of heat-related injury. Dose-dependent increases in carotid body tonic activity and sensitivity with core heating provide compelling evidence that carotid body hyperexcitability is the primary cause of heat-induced hyperventilation during exercise.
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Affiliation(s)
- Travis D Gibbons
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan, School of Health and Exercise Science, Kelowna, British Columbia, Canada
| | - Jerome A Dempsey
- John Rankin Laboratory for Pulmonary Medicine, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin
| | - Kate N Thomas
- Department of Surgical Sciences, University of Otago, Dunedin, New Zealand
| | - Philip N Ainslie
- Centre for Heart, Lung and Vascular Health, University of British Columbia-Okanagan, School of Health and Exercise Science, Kelowna, British Columbia, Canada
| | - Luke C Wilson
- Department of Medicine, University of Otago, Dunedin, New Zealand
| | - Tiarna A M Stothers
- School of Physical Education, Sport & Exercise Sciences, University of Otago, Dunedin, New Zealand
| | - Holly A Campbell
- Department of Surgical Sciences, University of Otago, Dunedin, New Zealand
| | - James D Cotter
- School of Physical Education, Sport & Exercise Sciences, University of Otago, Dunedin, New Zealand
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Brain-Wide Synaptic Inputs to Aromatase-Expressing Neurons in the Medial Amygdala Suggest Complex Circuitry for Modulating Social Behavior. eNeuro 2022; 9:ENEURO.0329-21.2021. [PMID: 35074828 PMCID: PMC8925724 DOI: 10.1523/eneuro.0329-21.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2021] [Revised: 12/18/2021] [Accepted: 12/26/2021] [Indexed: 12/16/2022] Open
Abstract
Here, we reveal an unbiased view of the brain regions that provide specific inputs to aromatase-expressing cells in the medial amygdala, neurons that play an outsized role in the production of sex-specific social behaviors, using rabies tracing and light sheet microscopy. While the downstream projections from these cells are known, the specific inputs to the aromatase-expressing cells in the medial amygdala remained unknown. We observed established connections to the medial amygdala (e.g., bed nucleus of the stria terminalis and accessory olfactory bulb) indicating that aromatase neurons are a major target cell type for efferent input including from regions associated with parenting and aggression. We also identified novel and unexpected inputs from areas involved in metabolism, fear and anxiety, and memory and cognition. These results confirm the central role of the medial amygdala in sex-specific social recognition and social behavior, and point to an expanded role for its aromatase-expressing neurons in the integration of multiple sensory and homeostatic factors, which are likely used to modulate many other social behaviors.
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Edvinsson JCA, Maddahi A, Christiansen IM, Reducha PV, Warfvinge K, Sheykhzade M, Edvinsson L, Haanes KA. Lasmiditan and 5-Hydroxytryptamine in the rat trigeminal system; expression, release and interactions with 5-HT 1 receptors. J Headache Pain 2022; 23:26. [PMID: 35177004 PMCID: PMC8903724 DOI: 10.1186/s10194-022-01394-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 01/21/2022] [Indexed: 12/21/2022] Open
Abstract
Background 5-Hydroxytryptamine (5-HT) receptors 1B, 1D and 1F have key roles in migraine pharmacotherapy. Selective agonists targeting these receptors, such as triptans and ditans, are effective in aborting acute migraine attacks and inhibit the in vivo release of calcitonin gene-related peptide (CGRP) in human and animal models. The study aimed to examine the localization, genetic expression and functional aspects of 5- HT1B/1D/1F receptors in the trigeminal system in order to further understand the molecular sites of action of triptans (5-HT1B/1D) and ditans (5-HT1F). Methods Utilizing immunohistochemistry, the localization of 5-HT and of 5-HT1B/1D/1F receptors was examined in rat trigeminal ganglion (TG) and combined with quantitative polymerase chain reaction to quantify the level of expression for 5-HT1B/1D/1F receptors in the TG. The functional role of these receptors was examined ex vivo with a capsaicin/potassium induced 5-HT and CGRP release. Results 5-HT immunoreactivity (ir) was observed in a minority of CGRP negative C-fibres, most neuron somas and faintly in A-fibres and Schwann cell neurolemma. 5-HT1B/1D receptors were expressed in the TG, while the 5-HT1F receptor displayed a weak ir. The 5-HT1D receptor co-localized with receptor activity-modifying protein 1 (RAMP1) in Aδ-fibres in the TG, while 5-HT1B-ir was weakly expressed and 5-HT1F-ir was not detected in these fibres. None of the 5-HT1 receptors co-localized with CGRP-ir in C-fibres. 5-HT1D receptor mRNA was the most prominently expressed, followed by the 5-HT1B receptor and lastly the 5-HT1F receptor. The 5-HT1B and 5-HT1D receptor antagonist, GR127935, could reverse the inhibitory effect of Lasmiditan (a selective 5-HT1F receptor agonist) on CGRP release in the soma-rich TG but not in soma-poor TG or dura mater. 5-HT release in the soma-rich TG, and 5-HT content in the baseline samples, negatively correlated with CGRP levels, showing for the first time a physiological role for 5-HT induced inhibition. Conclusion This study reveals the presence of a subgroup of C-fibres that store 5-HT. The data shows high expression of 5-HT1B/1D receptors and suggests that the 5-HT1F receptor is a relatively unlikely target in the rat TG. Furthermore, Lasmiditan works as a partial agonist on 5-HT1B/1D receptors in clinically relevant dose regiments. Supplementary Information The online version contains supplementary material available at 10.1186/s10194-022-01394-z.
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Affiliation(s)
- Jacob C A Edvinsson
- Department of Clinical Experimental Research, Glostrup Research Institute, Rigshospitalet Glostrup, 2600, Glostrup, Denmark. .,Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Aida Maddahi
- Division of Experimental Vascular Research, Department of Clinical Sciences, Lund University Hospital, Lund, Sweden
| | - Isabella M Christiansen
- Department of Clinical Experimental Research, Glostrup Research Institute, Rigshospitalet Glostrup, 2600, Glostrup, Denmark.,Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Philip V Reducha
- Department of Clinical Experimental Research, Glostrup Research Institute, Rigshospitalet Glostrup, 2600, Glostrup, Denmark.,Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Karin Warfvinge
- Department of Clinical Experimental Research, Glostrup Research Institute, Rigshospitalet Glostrup, 2600, Glostrup, Denmark.,Division of Experimental Vascular Research, Department of Clinical Sciences, Lund University Hospital, Lund, Sweden
| | - Majid Sheykhzade
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lars Edvinsson
- Department of Clinical Experimental Research, Glostrup Research Institute, Rigshospitalet Glostrup, 2600, Glostrup, Denmark.,Division of Experimental Vascular Research, Department of Clinical Sciences, Lund University Hospital, Lund, Sweden
| | - Kristian A Haanes
- Department of Clinical Experimental Research, Glostrup Research Institute, Rigshospitalet Glostrup, 2600, Glostrup, Denmark.,Department of Biology, University of Copenhagen, Copenhagen, Denmark
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Teran FA, Bravo E, Richerson GB. Sudden unexpected death in epilepsy: Respiratory mechanisms. HANDBOOK OF CLINICAL NEUROLOGY 2022; 189:153-176. [PMID: 36031303 PMCID: PMC10191258 DOI: 10.1016/b978-0-323-91532-8.00012-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Epilepsy is one of the most common chronic neurologic diseases, with a prevalence of 1% in the US population. Many people with epilepsy live normal lives, but are at risk of sudden unexpected death in epilepsy (SUDEP). This mysterious comorbidity of epilepsy causes premature death in 17%-50% of those with epilepsy. Most SUDEP occurs after a generalized seizure, and patients are typically found in bed in the prone position. Until recently, it was thought that SUDEP was due to cardiovascular failure, but patients who died while being monitored in hospital epilepsy units revealed that most SUDEP is due to postictal central apnea. Some cases may occur when seizures invade the amygdala and activate projections to the brainstem. Evidence suggests that the pathophysiology is linked to defects in the serotonin system and central CO2 chemoreception, and that there is considerable overlap with mechanisms thought to be involved in sudden infant death syndrome (SIDS). Future work is needed to identify biomarkers for patients at highest risk, improve ascertainment, develop methods to alert caregivers when SUDEP is imminent, and find effective approaches to prevent these fatal events.
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Affiliation(s)
- Frida A Teran
- Department of Neurology, University of Iowa, Iowa City, IA, United States; Medical Scientist Training Program, University of Iowa, Iowa City, IA, United States.
| | - Eduardo Bravo
- Department of Neurology, University of Iowa, Iowa City, IA, United States
| | - George B Richerson
- Department of Neurology, University of Iowa, Iowa City, IA, United States; Department of Molecular Physiology & Biophysics, University of Iowa, Iowa City, IA, United States
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Yue Q, Cai M, Xiao B, Zhan Q, Zeng C. A High-Tryptophan Diet Reduces Seizure-Induced Respiratory Arrest and Alters the Gut Microbiota in DBA/1 Mice. Front Neurol 2021; 12:762323. [PMID: 34887831 PMCID: PMC8650499 DOI: 10.3389/fneur.2021.762323] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2021] [Accepted: 10/26/2021] [Indexed: 12/20/2022] Open
Abstract
Background and Aims: Central 5-hydroxytryptamine (5-HT) defects are responsible for the occurrence of sudden unexpected death in epilepsy (SUDEP). The DBA/1 mouse is an animal model of SUDEP since the mouse exhibits audiogenic seizure-induced respiratory arrest (S-IRA). The synthesis of central 5-HT is closely related to the gut microbiota. Moreover, emerging studies suggest a possible role for the microbiota in mitigating seizure likelihood. Based on this, we aimed to explore the effect of a high-tryptophan diet (HTD) on SUDEP as well as the synthesis and metabolism of central 5-HT. Furthermore, we investigated the involvement of the gut microbiota in this process. Methods: All DBA/1 mice were subjected to acoustic stimulation to induce seizures. Only those mice that exhibited S-IRA were randomly assigned to the normal diet (ND) group (n = 39) or HTD group (n = 53). After 1 month of dietary intervention, (1) S-IRA rates were evaluated, (2) the concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the plasma and brain were determined by ultra-high-pressure liquid chromatography, and (3) the fecal flora biodiversity and species composition were analyzed by 16S rDNA microbiota profiling. Results: The S-IRA rate in DBA/1 mice was significantly reduced in the HTD group compared with that in the control group. HTD increased the levels of 5-HT and 5-HIAA in both the telencephalon and midbrain. HTD significantly elevated the species richness and diversity of the gut microbiota. Moreover, there was a significant difference in the gut microbiota composition between the two groups, and the intestinal flora was dominated by Proteobacteria and Actinobacteria after HTD. Conclusions: HTD is efficient in lowering S-IRA rates and elevating the central 5-HT level in DBA/1 mice. The gut microbiota was altered after HTD intervention. The significant increase in Proteobacteria and Actinobacteria may be related to the SUDEP-protective effect of HTD. Our findings shed light on a candidate choice of dietary prevention for SUDEP.
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Affiliation(s)
- Qiang Yue
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
| | - Mingfei Cai
- Department of Neurology, The Second Xiangya Hospital, Central South University, Changsha, China
| | - Bo Xiao
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
| | - Qiong Zhan
- Department of Neurology, The Second Xiangya Hospital, Central South University, Changsha, China
| | - Chang Zeng
- Health Management Center, Xiangya Hospital, Central South University, Changsha, China
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Prowting J, Maresh S, Vaughan S, Kruppe E, Alsabri B, Badr MS, Sankari A. Mirtazapine reduces susceptibility to hypocapnic central sleep apnea in males with sleep-disordered breathing: a pilot study. J Appl Physiol (1985) 2021; 131:414-423. [PMID: 34080920 PMCID: PMC8325612 DOI: 10.1152/japplphysiol.00838.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Studies in humans and animal models with spinal cord injury (SCI) have demonstrated that medications targeting serotonin receptors may decrease the susceptibility to central sleep-disordered breathing (SDB). We hypothesized that mirtazapine would decrease the propensity to develop hypocapnic central sleep apnea (CSA) during sleep. We performed a single-blind pilot study on a total of 10 men with SDB (7 with chronic SCI and 3 noninjured) aged 52.0 ± 11.2 yr. Participants were randomly assigned to either mirtazapine (15 mg at bedtime) or a placebo for at least 1 wk, followed by a 7-day washout period before crossing over to the other intervention. Split-night studies included polysomnography and induction of hypocapnic CSA using a noninvasive ventilation (NIV) protocol. The primary outcome was CO2 reserve, defined as the difference between eupneic and end of NIV end-tidal CO2 ([Formula: see text]) preceding induced hypocapneic CSA. Secondary outcomes included controller gain (CG), other ventilatory parameters, and SDB severity. CG was defined as the ratio of change in minute ventilation (V̇e) between control and hypopnea to the change in CO2 during sleep. CO2 reserve was significantly widened on mirtazapine than placebo (-3.8 ± 1.2 vs. -2.0 ± 1.5 mmHg; P = 0.015). CG was significantly decreased on mirtazapine compared with placebo [2.2 ± 0.7 vs. 3.5 ± 1.9 L/(mmHg × min); P = 0.023]. There were no significant differences for other ventilatory parameters assessed or SDB severity between mirtazapine and placebo trials. These findings suggest that the administration of mirtazapine can decrease the susceptibility to central apnea by reducing chemosensitivity and increasing CO2 reserve; however, considering the lack of changes in apnea-hypopnea index (AHI), further research is required to understand the significance of this finding.NEW & NOTEWORTHY To our knowledge, this research study is novel as it is the first study in humans assessing the effect of mirtazapine on CO2 reserve and chemosensitivity in individuals with severe sleep-disordered breathing. This is also the first study to determine the potential therapeutic effects of mirtazapine on sleep parameters in individuals with a spinal cord injury.
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Affiliation(s)
- Joel Prowting
- 1Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan,2Wayne State University School of Medicine, Detroit, Michigan
| | - Scott Maresh
- 1Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan,2Wayne State University School of Medicine, Detroit, Michigan
| | - Sarah Vaughan
- 1Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan,2Wayne State University School of Medicine, Detroit, Michigan
| | - Elizabeth Kruppe
- 1Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan,2Wayne State University School of Medicine, Detroit, Michigan
| | - Bander Alsabri
- 1Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan,2Wayne State University School of Medicine, Detroit, Michigan
| | - M. Safwan Badr
- 1Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan,2Wayne State University School of Medicine, Detroit, Michigan
| | - Abdulghani Sankari
- 1Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan,2Wayne State University School of Medicine, Detroit, Michigan,3Ascension Providence Hospital, Southfield, Michigan
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Dale N. CO 2 sensing by connexin26 and its role in the control of breathing. Interface Focus 2021; 11:20200029. [PMID: 33633831 DOI: 10.1098/rsfs.2020.0029] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/09/2020] [Indexed: 12/14/2022] Open
Abstract
Breathing is essential to provide the O2 required for metabolism and to remove its inevitable CO2 by-product. The rate and depth of breathing is controlled to regulate the excretion of CO2 to maintain the pH of arterial blood at physiological values. A widespread consensus is that chemosensory cells in the carotid body and brainstem measure blood and tissue pH and adjust the rate of breathing to ensure its homeostatic regulation. In this review, I shall consider the evidence that underlies this consensus and highlight historical data indicating that direct sensing of CO2 also plays a significant role in the regulation of breathing. I shall then review work from my laboratory that provides a molecular mechanism for the direct detection of CO2 via the gap junction protein connexin26 (Cx26) and demonstrates the contribution of this mechanism to the chemosensory regulation of breathing. As there are many pathological mutations of Cx26 in humans, I shall discuss which of these alter the CO2 sensitivity of Cx26 and the extent to which these mutations could affect human breathing. I finish by discussing the evolution of the CO2 sensitivity of Cx26 and its link to the evolution of amniotes.
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Affiliation(s)
- Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK
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Leirão IP, Colombari DSA, da Silva GSF, Zoccal DB. Lesion of Serotonergic Afferents to the Retrotrapezoid Nucleus Impairs the Tachypneic Response to Hypercapnia in Unanesthetized Animals. Neuroscience 2020; 452:63-77. [PMID: 33212216 DOI: 10.1016/j.neuroscience.2020.11.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 10/30/2020] [Accepted: 11/03/2020] [Indexed: 12/17/2022]
Abstract
Hypercapnia promotes an increase in pulmonary ventilation due to the stimulation of brainstem chemosensory cells that are connected to the respiratory network. Among these cells are the raphe serotonergic neurons which widely send projections to distinct central respiratory compartments. Nevertheless, the physiological role of specific raphe serotonergic projections to other chemosensitive sites on the emergence of hypercapnia ventilatory response in vivo still remains to be elucidated. Here we investigated whether the ventilatory response to hypercapnia requires serotonergic inputs to the chemosensitive cells of the retrotrapezoid nucleus (RTN) in the ventrolateral medulla. To test this, pulmonary ventilation was evaluated under baseline conditions and during hypercapnia (7% CO2) in unanesthetized juvenile Holtzman rats (60-90 g) that received bilateral microinjections of either vehicle (control) or anti-SERT-SAP (0.1 mM, 10 pmol/100 nl) toxin in the RTN to retrogradely destroy serotonergic afferents to this region. Fifteen days after microinjections, baseline ventilation was not different between anti-SERT-SAP (n = 8) and control animals (n = 9). In contrast, the ablation of RTN-projecting serotonergic neurons markedly attenuated the hypercapnia-induced increase in respiratory frequency which was correlated with reduced numbers of serotonergic neurons in the raphe obscurus and magnus, but not in the raphe pallidus. The increase in tidal volume during hypercapnia was not significantly affected by anti-SERT-SAP microinjections in the RTN. Our data indicate that serotoninergic neurons that send projections to the RTN region are required for the processing of ventilatory reflex response during exposure to high CO2 in unanesthetized conditions.
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Affiliation(s)
- Isabela P Leirão
- Department of Physiology and Pathology, School of Dentistry, São Paulo State University (UNESP), Araraquara, SP, Brazil
| | - Débora S A Colombari
- Department of Physiology and Pathology, School of Dentistry, São Paulo State University (UNESP), Araraquara, SP, Brazil
| | - Glauber S F da Silva
- Department of Physiology and Biophysics. Institute of Biological Sciences, Federal University of Minas Gerais (ICB/UFMG), Belo Horizonte, MG, Brazil
| | - Daniel B Zoccal
- Department of Physiology and Pathology, School of Dentistry, São Paulo State University (UNESP), Araraquara, SP, Brazil.
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10
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van de Wiel J, Meigh L, Bhandare A, Cook J, Nijjar S, Huckstepp R, Dale N. Connexin26 mediates CO 2-dependent regulation of breathing via glial cells of the medulla oblongata. Commun Biol 2020; 3:521. [PMID: 32958814 PMCID: PMC7505967 DOI: 10.1038/s42003-020-01248-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Accepted: 08/21/2020] [Indexed: 01/12/2023] Open
Abstract
Breathing is highly sensitive to the PCO2 of arterial blood. Although CO2 is detected via the proxy of pH, CO2 acting directly via Cx26 may also contribute to the regulation of breathing. Here we exploit our knowledge of the structural motif of CO2-binding to Cx26 to devise a dominant negative subunit (Cx26DN) that removes the CO2-sensitivity from endogenously expressed wild type Cx26. Expression of Cx26DN in glial cells of a circumscribed region of the mouse medulla - the caudal parapyramidal area - reduced the adaptive change in tidal volume and minute ventilation by approximately 30% at 6% inspired CO2. As central chemosensors mediate about 70% of the total response to hypercapnia, CO2-sensing via Cx26 in the caudal parapyramidal area contributed about 45% of the centrally-mediated ventilatory response to CO2. Our data unequivocally link the direct sensing of CO2 to the chemosensory control of breathing and demonstrates that CO2-binding to Cx26 is a key transduction step in this fundamental process.
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Affiliation(s)
| | - Louise Meigh
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Amol Bhandare
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Jonathan Cook
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Sarbjit Nijjar
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Robert Huckstepp
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
| | - Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.
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11
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Maresh S, Prowting J, Vaughan S, Kruppe E, Alsabri B, Yarandi H, Badr MS, Sankari A. Buspirone decreases susceptibility to hypocapnic central sleep apnea in chronic SCI patients. J Appl Physiol (1985) 2020; 129:675-682. [PMID: 32816639 DOI: 10.1152/japplphysiol.00435.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spinal cord injury (SCI) is a risk factor for central sleep apnea (CSA). Previous studies in animal models with SCI have demonstrated a promising recovery in respiratory and phrenic nerve activity post-injury induced by the systemic and local administration of serotonin receptor agonists such as Buspirone and Trazodone. Human trials must be performed to determine whether individuals with SCI respond similarly. We hypothesized that Buspirone and Trazodone would decrease the propensity to hypocapnic CSA during sleep. We studied eight males with chronic SCI and sleep-disordered breathing (SDB) [age: 48.8 ± 14.2 yr; apnea-hypopnea index (AHI): 44.9 ± 23.1] in a single-blind crossover design. For 13 days, participants were randomly assigned either Buspirone (7.5-15 mg twice daily), Trazodone (100 mg), or a placebo followed by a 14-day washout period before crossing over to the other interventions. Study nights included polysomnography and induction of CSA using a noninvasive ventilation protocol. We assessed indexes of SDB, CO2 reserve, apneic threshold (AT), controller gain (CG), plant gain (PG), and ventilatory parameters. CO2 reserve was significantly widened on Buspirone (-3.6 ± 0.9 mmHg) compared with both Trazodone (-2.5 ± 1.0 mmHg, P = 0.009) and placebo (-1.8 ± 1.5 mmHg, P < 0.001) but not on Trazodone vs. placebo (P = 0.061). CG was significantly decreased on Buspirone compared with placebo (1.8 ± 0.4 vs. 4.0 ± 2.0 L/(mmHg·min), P = 0.025) but not on Trazodone compared with placebo (2.5 ± 1.1 vs. 4.0 ± 2.0 L/(mmHg·min); P = 0.065). There were no significant differences for PG, AT, or any SDB indexes (AHI, obstructive apnea index, central apnea index, oxygen desaturation index). The administration of Buspirone decreased the susceptibility to induced hypocapnic central apnea by reducing chemosensitivity and increasing CO2 reserve in chronic SCI patients.NEW & NOTEWORTHY This research study is novel as it is the first study in a humans that we are aware of that demonstrates the ability of Buspirone to increase CO2 reserve and hence decrease susceptibility to hypocapnic central apnea in patients with spinal cord injury.
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Affiliation(s)
- Scott Maresh
- Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Wayne State University, Detroit, Michigan
| | - Joel Prowting
- Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Wayne State University, Detroit, Michigan
| | - Sarah Vaughan
- Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Wayne State University, Detroit, Michigan
| | | | - Bander Alsabri
- Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Wayne State University, Detroit, Michigan
| | - Hossein Yarandi
- Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Wayne State University, Detroit, Michigan
| | - M Safwan Badr
- Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Wayne State University, Detroit, Michigan
| | - Abdulghani Sankari
- Sleep Research Laboratory, John D. Dingell Veterans Affairs Medical Center, Wayne State University, Detroit, Michigan.,Ascension Providence Hospital, Southfield, Michigan
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12
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Impaired endothelium-mediated cerebrovascular reactivity promotes anxiety and respiration disorders in mice. Proc Natl Acad Sci U S A 2020; 117:1753-1761. [PMID: 31896584 DOI: 10.1073/pnas.1907467117] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Carbon dioxide (CO2), the major product of metabolism, has a strong impact on cerebral blood vessels, a phenomenon known as cerebrovascular reactivity. Several vascular risk factors such as hypertension or diabetes dampen this response, making cerebrovascular reactivity a useful diagnostic marker for incipient vascular pathology, but its functional relevance, if any, is still unclear. Here, we found that GPR4, an endothelial H+ receptor, and endothelial Gαq/11 proteins mediate the CO2/H+ effect on cerebrovascular reactivity in mice. CO2/H+ leads to constriction of vessels in the brainstem area that controls respiration. The consequential washout of CO2, if cerebrovascular reactivity is impaired, reduces respiration. In contrast, CO2 dilates vessels in other brain areas such as the amygdala. Hence, an impaired cerebrovascular reactivity amplifies the CO2 effect on anxiety. Even at atmospheric CO2 concentrations, impaired cerebrovascular reactivity caused longer apneic episodes and more anxiety, indicating that cerebrovascular reactivity is essential for normal brain function. The site-specific reactivity of vessels to CO2 is reflected by regional differences in their gene expression and the release of vasoactive factors from endothelial cells. Our data suggest the central nervous system (CNS) endothelium as a target to treat respiratory and affective disorders associated with vascular diseases.
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13
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5-HT neurons and central CO2 chemoreception. ACTA ACUST UNITED AC 2020. [DOI: 10.1016/b978-0-444-64125-0.00021-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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14
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Wu Y, Proch KL, Teran FA, Lechtenberg RJ, Kothari H, Richerson GB. Chemosensitivity of Phox2b-expressing retrotrapezoid neurons is mediated in part by input from 5-HT neurons. J Physiol 2019; 597:2741-2766. [PMID: 30866045 PMCID: PMC6826216 DOI: 10.1113/jp277052] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2018] [Accepted: 03/07/2019] [Indexed: 01/18/2023] Open
Abstract
KEY POINTS Neurons of the retrotrapezoid nucleus (RTN) and medullary serotonin (5-HT) neurons are both candidates for central CO2 /pH chemoreceptors, but it is not known how interactions between them influence their responses to pH. We found that RTN neurons in brain slices were stimulated by exogenous 5-HT and by heteroexchange release of endogenous 5-HT, and these responses were blocked by antagonists of 5-HT7 receptors. The pH response of RTN neurons in brain slices was markedly reduced by the same antagonists of 5-HT7 receptors. Similar results were obtained in dissociated, primary cell cultures prepared from the ventral medulla, where it was also found that the pH response of RTN neurons was blocked by preventing 5-HT synthesis and enhanced by blocking 5-HT reuptake. Exogenous 5-HT did not enable latent intrinsic RTN chemosensitivity. RTN neurons may play more of a role as relays from other central and peripheral chemoreceptors than as CO2 sensors. ABSTRACT Phox2b-expressing neurons in the retrotrapezoid nucleus (RTN) and serotonin (5-HT) neurons in the medullary raphe have both been proposed to be central respiratory chemoreceptors. How interactions between these two sets of neurons influence their responses to acidosis is not known. Here we recorded from mouse Phox2b+ RTN neurons in brain slices, and found that their response to moderate hypercapnic acidosis (pH 7.4 to ∼7.2) was markedly reduced by antagonists of 5-HT7 receptors. RTN neurons were stimulated in response to heteroexchange release of 5-HT, indicating that RTN neurons are sensitive to endogenous 5-HT. This electrophysiological behaviour was replicated in primary, dissociated cell cultures containing 5-HT and RTN neurons grown together. In addition, pharmacological inhibition of 5-HT synthesis in culture reduced RTN neuron chemosensitivity, and blocking 5-HT reuptake enhanced chemosensitivity. The effect of 5-HT on RTN neuron chemosensitivity was not explained by a mechanism whereby activation of 5-HT7 receptors enables or potentiates intrinsic chemosensitivity of RTN neurons, as exogenous 5-HT did not enhance the pH response. The ventilatory response to inhaled CO2 of mice was markedly decreased in vivo after systemic treatment with ketanserin, an antagonist of 5-HT2 and 5-HT7 receptors. These data indicate that 5-HT and RTN neurons may interact synergistically in a way that enhances the respiratory chemoreceptor response. The primary role of RTN neurons may be as relays and amplifiers of the pH response from 5-HT neurons and other chemoreceptors rather than as pH sensors themselves.
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Affiliation(s)
- Yuanming Wu
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
| | - Katherine L. Proch
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
| | - Frida A. Teran
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
- Iowa Neuroscience InstituteUniversity of IowaIowa CityIA52242USA
| | | | - Harsh Kothari
- Department of PediatricsUniversity of IowaIowa CityIA52242USA
| | - George B. Richerson
- Department of NeurologyUniversity of IowaIowa CityIA52242USA
- Graduate Program in NeuroscienceUniversity of IowaIowa CityIA52242USA
- Department of Molecular Physiology & BiophysicsUniversity of IowaIowa CityIA52242USA
- Neurology ServiceVeterans Affairs Medical CenterIowa CityIA52242USA
- Iowa Neuroscience InstituteUniversity of IowaIowa CityIA52242USA
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15
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Puissant MM, Mouradian GC, Liu P, Hodges MR. Identifying Candidate Genes that Underlie Cellular pH Sensitivity in Serotonin Neurons Using Transcriptomics: A Potential Role for Kir5.1 Channels. Front Cell Neurosci 2017; 11:34. [PMID: 28270749 PMCID: PMC5318415 DOI: 10.3389/fncel.2017.00034] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 02/06/2017] [Indexed: 11/30/2022] Open
Abstract
Ventilation is continuously adjusted by a neural network to maintain blood gases and pH. Acute CO2 and/or pH regulation requires neural feedback from brainstem cells that encode CO2/pH to modulate ventilation, including but not limited to brainstem serotonin (5-HT) neurons. Brainstem 5-HT neurons modulate ventilation and are stimulated by hypercapnic acidosis, the sensitivity of which increases with increasing postnatal age. The proper function of brainstem 5-HT neurons, particularly during post-natal development is critical given that multiple abnormalities in the 5-HT system have been identified in victims of Sudden Infant Death Syndrome. Here, we tested the hypothesis that there are age-dependent increases in expression of pH-sensitive ion channels in brainstem 5-HT neurons, which may underlie their cellular CO2/pH sensitivity. Midline raphe neurons were acutely dissociated from neonatal and mature transgenic SSePet-eGFP rats [which have enhanced green fluorescent protein (eGFP) expression in all 5-HT neurons] and sorted with fluorescence-activated cell sorting (FACS) into 5-HT-enriched and non-5-HT cell pools for subsequent RNA extraction, cDNA library preparation and RNA sequencing. Overlapping differential expression analyses pointed to age-dependent shifts in multiple ion channels, including but not limited to the pH-sensitive potassium ion (K+) channel genes kcnj10 (Kir4.1), kcnj16 (Kir5.1), kcnk1 (TWIK-1), kcnk3 (TASK-1) and kcnk9 (TASK-3). Intracellular contents isolated from single adult eGFP+ 5-HT neurons confirmed gene expression of Kir4.1, Kir5.1 and other K+ channels, but also showed heterogeneity in the expression of multiple genes. 5-HT neuron-enriched cell pools from selected post-natal ages showed increases in Kir4.1, Kir5.1, and TWIK-1, fitting with age-dependent increases in Kir4.1 and Kir5.1 protein expression in raphe tissue samples. Immunofluorescence imaging confirmed Kir5.1 protein was co-localized to brainstem neurons and glia including 5-HT neurons as expected. However, Kir4.1 protein expression was restricted to glia, suggesting that it may not contribute to 5-HT neuron pH sensitivity. Although there are caveats to this approach, the data suggest that pH-sensitive Kir5.1 channels may underlie cellular CO2/pH chemosensitivity in brainstem 5-HT neurons.
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Affiliation(s)
- Madeleine M Puissant
- Department of Physiology, Medical College of Wisconsin, MilwaukeeWI, USA; Neuroscience Research Center, Medical College of Wisconsin, MilwaukeeWI, USA
| | - Gary C Mouradian
- Department of Physiology, Medical College of Wisconsin, MilwaukeeWI, USA; Center for Systems Molecular Medicine, Medical College of Wisconsin, MilwaukeeWI, USA
| | - Pengyuan Liu
- Department of Physiology, Medical College of Wisconsin, MilwaukeeWI, USA; Center for Systems Molecular Medicine, Medical College of Wisconsin, MilwaukeeWI, USA; Cancer Research Center, Medical College of Wisconsin, MilwaukeeWI, USA
| | - Matthew R Hodges
- Department of Physiology, Medical College of Wisconsin, MilwaukeeWI, USA; Neuroscience Research Center, Medical College of Wisconsin, MilwaukeeWI, USA; Center for Systems Molecular Medicine, Medical College of Wisconsin, MilwaukeeWI, USA
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16
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Wilson RJA, Teppema LJ. Integration of Central and Peripheral Respiratory Chemoreflexes. Compr Physiol 2016; 6:1005-41. [PMID: 27065173 DOI: 10.1002/cphy.c140040] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A debate has raged since the discovery of central and peripheral respiratory chemoreceptors as to whether the reflexes they mediate combine in an additive (i.e., no interaction), hypoadditive or hyperadditive manner. Here we critically review pertinent literature related to O2 and CO2 sensing from the perspective of system integration and summarize many of the studies on which these seemingly opposing views are based. Despite the intensity and quality of this debate, we have yet to reach consensus, either within or between species. In reviewing this literature, we are struck by the merits of the approaches and preparations that have been brought to bear on this question. This suggests that either the nature of combination is not important to system responses, contrary to what has long been supposed, or that the nature of the combination is more malleable than previously assumed, changing depending on physiological state and/or respiratory requirement.
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Affiliation(s)
- Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children Hospital Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Luc J Teppema
- Department of Anesthesiology, Leiden University Medical Center, Leiden, The Netherlands
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17
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Zhan Q, Buchanan GF, Motelow JE, Andrews J, Vitkovskiy P, Chen WC, Serout F, Gummadavelli A, Kundishora A, Furman M, Li W, Bo X, Richerson GB, Blumenfeld H. Impaired Serotonergic Brainstem Function during and after Seizures. J Neurosci 2016; 36:2711-22. [PMID: 26937010 PMCID: PMC4879214 DOI: 10.1523/jneurosci.4331-15.2016] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Revised: 01/11/2016] [Accepted: 01/23/2016] [Indexed: 12/30/2022] Open
Abstract
Impaired breathing, cardiac function, and arousal during and after seizures are important causes of morbidity and mortality. Previous work suggests that these changes are associated with depressed brainstem function in the ictal and post-ictal periods. Lower brainstem serotonergic systems are postulated to play an important role in cardiorespiratory changes during and after seizures, whereas upper brainstem serotonergic and other systems regulate arousal. However, direct demonstration of seizure-associated neuronal activity changes in brainstem serotonergic regions has been lacking. Here, we performed multiunit and single-unit recordings from medullary raphe and midbrain dorsal raphe nuclei in an established rat seizure model while measuring changes in breathing rate and depth as well as heart rate. Serotonergic neurons were identified by immunohistochemistry. Respiratory rate, tidal volume, and minute ventilation were all significantly decreased during and after seizures in this model. We found that population firing of neurons in the medullary and midbrain raphe on multiunit recordings was significantly decreased during the ictal and post-ictal periods. Single-unit recordings from identified serotonergic neurons in the medullary raphe revealed highly consistently decreased firing during and after seizures. In contrast, firing of midbrain raphe serotonergic neurons was more variable, with a mixture of increases and decreases. The markedly suppressed firing of medullary serotonergic neurons supports their possible role in simultaneously impaired cardiorespiratory function in seizures. Decreased arousal likely arises from depressed population activity of several neuronal pools in the upper brainstem and forebrain. These findings have important implications for preventing morbidity and mortality in people living with epilepsy. SIGNIFICANCE STATEMENT Seizures often cause impaired breathing, cardiac dysfunction, and loss of consciousness. The brainstem and, specifically, brainstem serotonin neurons are thought to play an important role in controlling breathing, cardiac function, and arousal. We used an established rat seizure model to study the overall neuronal activity in the brainstem as well as firing of specific serotonin neurons while measuring cardiorespiratory function. Our results demonstrated overall decreases in brainstem neuronal activity and marked downregulation of lower brainstem serotonin neuronal firing in association with decreased breathing and heart rate during and after seizures. These findings point the way toward new treatments to augment brainstem function and serotonin, aiming to prevent seizure complications and reduce morbidity and mortality in people living with epilepsy.
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Affiliation(s)
- Qiong Zhan
- Departments of Neurology, Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China, Department of Neurology, the Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China
| | | | | | | | | | | | | | | | | | | | - Wei Li
- Departments of Neurology, Department of Neurosurgery, Jinling Hospital, School of Medicine Nanjing University, Nanjing Jiangsu 210002, China, and
| | - Xiao Bo
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China
| | - George B Richerson
- Departments of Neurology and Molecular Physiology and Biophysics, and Veterans Affairs Medical Center, Iowa City, Iowa 52246
| | - Hal Blumenfeld
- Departments of Neurology, Neuroscience, and Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520,
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18
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Richerson GB, Boison D, Faingold CL, Ryvlin P. From unwitnessed fatality to witnessed rescue: Pharmacologic intervention in sudden unexpected death in epilepsy. Epilepsia 2016; 57 Suppl 1:35-45. [PMID: 26749015 PMCID: PMC4890608 DOI: 10.1111/epi.13236] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/05/2015] [Indexed: 12/11/2022]
Abstract
The mechanisms of sudden unexpected death in epilepsy (SUDEP) have been difficult to define, as most cases occur unwitnessed, and physiologic recordings have been obtained in only a handful of cases. However, recent data obtained from human cases and experimental studies in animal models have brought us closer to identifying potential mechanisms. Theories of SUDEP should be able to explain how a seizure starting in the forebrain can sometimes lead to changes in brainstem cardiorespiratory control mechanisms. Herein we focus on three major themes of work on the causes of SUDEP. First, evidence is reviewed identifying postictal hypoventilation as a major contributor to the cause of death. Second, data are discussed that brainstem serotonin and adenosine pathways may be involved, as well as how they may contribute. Finally, parallels are drawn between SIDS and SUDEP, and we highlight similarities pointing to the possibility of shared pathophysiology involving combined failure of respiratory and cardiovascular control mechanisms. Knowledge about the causes of SUDEP may lead to potential pharmacologic approaches for prevention. We end by describing how translation of this work may result in future applications to clinical care.
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Affiliation(s)
- George B Richerson
- Departments of Neurology and Molecular Physiology & Biophysics, University of Iowa & Veteran's Affairs Medical Center, Iowa City, Iowa, U.S.A
| | - Detlev Boison
- Robert Stone Dow Neurobiology Laboratories, Legacy Research Institute Portland, Portland, Oregon, U.S.A
| | - Carl L Faingold
- Departments of Pharmacology and Neurology and Division of Neurosurgery, Southern Illinois University School of Medicine, Springfield, Illinois, U.S.A
| | - Philippe Ryvlin
- Department of Clinical Neurosciences, Lausanne University Hospital, Lausanne, Switzerland
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19
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Harper RM, Kumar R, Macey PM, Harper RK, Ogren JA. Impaired neural structure and function contributing to autonomic symptoms in congenital central hypoventilation syndrome. Front Neurosci 2015; 9:415. [PMID: 26578872 PMCID: PMC4626648 DOI: 10.3389/fnins.2015.00415] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Accepted: 10/15/2015] [Indexed: 12/30/2022] Open
Abstract
Congenital central hypoventilation syndrome (CCHS) patients show major autonomic alterations in addition to their better-known breathing deficiencies. The processes underlying CCHS, mutations in the PHOX2B gene, target autonomic neuronal development, with frame shift extent contributing to symptom severity. Many autonomic characteristics, such as impaired pupillary constriction and poor temperature regulation, reflect parasympathetic alterations, and can include disturbed alimentary processes, with malabsorption and intestinal motility dyscontrol. The sympathetic nervous system changes can exert life-threatening outcomes, with dysregulation of sympathetic outflow leading to high blood pressure, time-altered and dampened heart rate and breathing responses to challenges, cardiac arrhythmia, profuse sweating, and poor fluid regulation. The central mechanisms contributing to failed autonomic processes are readily apparent from structural and functional magnetic resonance imaging studies, which reveal substantial cortical thinning, tissue injury, and disrupted functional responses in hypothalamic, hippocampal, posterior thalamic, and basal ganglia sites and their descending projections, as well as insular, cingulate, and medial frontal cortices, which influence subcortical autonomic structures. Midbrain structures are also compromised, including the raphe system and its projections to cerebellar and medullary sites, the locus coeruleus, and medullary reflex integrating sites, including the dorsal and ventrolateral medullary nuclei. The damage to rostral autonomic sites overlaps metabolic, affective and cognitive regulatory regions, leading to hormonal disruption, anxiety, depression, behavioral control, and sudden death concerns. The injuries suggest that interventions for mitigating hypoxic exposure and nutrient loss may provide cellular protection, in the same fashion as interventions in other conditions with similar malabsorption, fluid turnover, or hypoxic exposure.
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Affiliation(s)
- Ronald M Harper
- Brain Research Institute, University of California, Los Angeles Los Angeles, CA, USA ; Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA
| | - Rajesh Kumar
- Brain Research Institute, University of California, Los Angeles Los Angeles, CA, USA ; Department of Anesthesiology, David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA ; Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA ; Department of Bioengineering, University of California, Los Angeles Los Angeles, CA, USA
| | - Paul M Macey
- Brain Research Institute, University of California, Los Angeles Los Angeles, CA, USA ; UCLA School of Nursing, University of California, Los Angeles Los Angeles, CA, USA
| | - Rebecca K Harper
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA
| | - Jennifer A Ogren
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA
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20
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Self-transcendence trait and its relationship with in vivo serotonin transporter availability in brainstem raphe nuclei: An ultra-high resolution PET-MRI study. Brain Res 2015; 1629:63-71. [PMID: 26459992 DOI: 10.1016/j.brainres.2015.10.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2015] [Revised: 09/08/2015] [Accepted: 10/01/2015] [Indexed: 01/12/2023]
Abstract
Self-transcendence is an inherent human personality trait relating to the experience of spiritual aspects of the self. We examined the relationship between self-transcendence and serotonin transporter (SERT) availability in brainstem raphe nuclei, which are collections of five different serotonergic nuclei with rostro-caudal extension, using ultra-high resolution magnetic resonance imaging (MRI) and positron emission tomography (PET) with (11)C-3-amino-4-(2-dimethylaminomethylphenylthio)benzonitrile ([(11)C]DASB) to elucidate potential roles of serotonergic neuronal activities in this personality trait. Sixteen healthy subjects completed 7.0T MRI and High Resolution Research Tomograph (HRRT) PET. The regions of interest (ROIs) included the dorsal raphe nucleus (R1), median raphe nucleus (R2), raphe pontis (R3), and the caudal raphe nuclei (R4 and R5). For the estimation of SERT availability, the binding potential (BPND) was derived using the simplified reference tissue model (SRTM2). The Temperament and Character Inventory was used to measure self-transcendence. The analysis revealed that the self-transcendence total score had a significant negative correlation with the [(11)C]DASB BPND in the caudal raphe (R5). The subscale score for spiritual acceptance was significantly negatively correlated with the [(11)C]DASB BPND in the median raphe nucleus (R2). The results indicate that the self-transcendence trait is associated with SERT availability in specific raphe subnuclei, suggesting that the serotonin system may serve as an important biological basis for human self-transcendence. Based on the connections of these nuclei with cortico-limbic and visceral autonomic structures, the functional activity of these nuclei and their related neural circuitry may play a crucial role in the manifestation of self-transcendence.
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21
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Respiratory pathophysiology with seizures and implications for sudden unexpected death in epilepsy. J Clin Neurophysiol 2015; 32:10-3. [PMID: 25647768 DOI: 10.1097/wnp.0000000000000142] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
SUMMARY There is increasing evidence that periictal respiratory disturbances are an important contributor to the pathophysiological changes leading to sudden unexpected death in epilepsy (SUDEP). In patients with SUDEP occurring in epilepsy monitoring units, respiratory disturbances occurred early in the postictal period and frequently preceded terminal bradycardia and asystole. Periictal hypoxemia and hypercapnia are observed in about one-third of patients undergoing video-EEG telemetry. Pulmonary edema is frequently observed at autopsy in cases of SUDEP and may be relevant as a contributing cause in a subset of SUDEP. Animal studies support the notion that periictal respiratory disturbances are crucial to the pathophysiology of SUDEP. Serotonergic neurons modulate the excitability of the neuronal network generating the respiratory rhythm. Ictal and periictal impairment of serotonergic and glutaminergic neurons involved in the arousal system may also predispose to SUDEP by impeding the patient's ability to reposition the head and facilitate ventilation after a seizure. Periictal functional impairment of serotonergic neurons seems to be important in the pathophysiology of SUDEP and a potential target for pharmacotherapy aimed at SUDEP risk reduction.
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22
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The brain acid–base homeostasis and serotonin: A perspective on the use of carbon dioxide as human and rodent experimental model of panic. Prog Neurobiol 2015; 129:58-78. [DOI: 10.1016/j.pneurobio.2015.04.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Revised: 04/16/2015] [Accepted: 04/20/2015] [Indexed: 12/14/2022]
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Vollmer LL, Strawn JR, Sah R. Acid-base dysregulation and chemosensory mechanisms in panic disorder: a translational update. Transl Psychiatry 2015; 5:e572. [PMID: 26080089 PMCID: PMC4471296 DOI: 10.1038/tp.2015.67] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2014] [Revised: 02/19/2015] [Accepted: 04/06/2015] [Indexed: 12/13/2022] Open
Abstract
Panic disorder (PD), a complex anxiety disorder characterized by recurrent panic attacks, represents a poorly understood psychiatric condition which is associated with significant morbidity and an increased risk of suicide attempts and completed suicide. Recently however, neuroimaging and panic provocation challenge studies have provided insights into the pathoetiology of panic phenomena and have begun to elucidate potential neural mechanisms that may underlie panic attacks. In this regard, accumulating evidence suggests that acidosis may be a contributing factor in induction of panic. Challenge studies in patients with PD reveal that panic attacks may be reliably provoked by agents that lead to acid-base dysbalance such as CO2 inhalation and sodium lactate infusion. Chemosensory mechanisms that translate pH into panic-relevant fear, autonomic, and respiratory responses are therefore of high relevance to the understanding of panic pathophysiology. Herein, we provide a current update on clinical and preclinical studies supporting how acid-base imbalance and diverse chemosensory mechanisms may be associated with PD and discuss future implications of these findings.
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Affiliation(s)
- L L Vollmer
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, College of Medicine, Cincinnati, OH, USA
| | - J R Strawn
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, College of Medicine, Cincinnati, OH, USA,Cincinnati Children's Hospital Medical Center, Department of Psychiatry, Cincinnati, OH, USA
| | - R Sah
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, College of Medicine, Cincinnati, OH, USA,Veterens' Affairs Medical Center, Cincinnati, OH, USA,Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, 2170 East Galbraith Road, Cincinnati, OH 45237, USA. E-mail:
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24
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Buchanan GF, Smith HR, MacAskill A, Richerson GB. 5-HT2A receptor activation is necessary for CO2-induced arousal. J Neurophysiol 2015; 114:233-43. [PMID: 25925320 DOI: 10.1152/jn.00213.2015] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 04/29/2015] [Indexed: 11/22/2022] Open
Abstract
Hypercapnia-induced arousal from sleep is an important protective mechanism pertinent to a number of diseases. Most notably among these are the sudden infant death syndrome, obstructive sleep apnea and sudden unexpected death in epilepsy. Serotonin (5-HT) plays a significant role in hypercapnia-induced arousal. The mechanism of 5-HT's role in this protective response is unknown. Here we sought to identify the specific 5-HT receptor subtype(s) involved in this response. Wild-type mice were pretreated with antagonists against 5-HT receptor subtypes, as well as antagonists against adrenergic, cholinergic, histaminergic, dopaminergic, and orexinergic receptors before challenge with inspired CO2 or hypoxia. Antagonists of 5-HT(2A) receptors dose-dependently blocked CO2-induced arousal. The 5-HT(2C) receptor antagonist, RS-102221, and the 5-HT1A receptor agonist, 8-OH-DPAT, attenuated but did not completely block CO2-induced arousal. Blockade of non-5-HT receptors did not affect CO2-induced arousal. None of these drugs had any effect on hypoxia-induced arousal. 5-HT2 receptor agonists were given to mice in which 5-HT neurons had been genetically eliminated during embryonic life (Lmx1b(f/f/p)) and which are known to lack CO2-induced arousal. Application of agonists to 5-HT(2A), but not 5-HT(2C), receptors, dose-dependently restored CO2-induced arousal in these mice. These data identify the 5-HT(2A) receptor as an important mediator of CO2-induced arousal and suggest that, while 5-HT neurons can be independently activated to drive CO2-induced arousal, in the absence of 5-HT neurons and endogenous 5-HT, 5-HT receptor activation can act in a permissive fashion to facilitate CO2-induced arousal via another as yet unidentified chemosensor system.
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Affiliation(s)
- Gordon F Buchanan
- Department of Neurology, Yale University, New Haven, Connecticut; Veteran's Affairs Medical Center, West Haven, Connecticut; Department of Neurology, University of Iowa, Iowa City, Iowa;
| | - Haleigh R Smith
- Department of Neurology, Yale University, New Haven, Connecticut
| | - Amanda MacAskill
- University of Glasgow School of Medicine, Glasgow, Scotland, United Kingdom
| | - George B Richerson
- Department of Neurology, Yale University, New Haven, Connecticut; Department of Neurology, University of Iowa, Iowa City, Iowa; Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, Iowa; and Veteran's Affairs Medical Center, Iowa City, Iowa
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25
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Wu Y, Li SS, Jin X, Cui N, Zhang S, Jiang C. Optogenetic approach for functional assays of the cardiovascular system by light activation of the vascular smooth muscle. Vascul Pharmacol 2015; 71:192-200. [PMID: 25869510 DOI: 10.1016/j.vph.2015.03.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Revised: 02/16/2015] [Accepted: 03/29/2015] [Indexed: 01/12/2023]
Abstract
Cardiovascular diseases are the major challenge to modern medicine. Intervention to cardiovascular cells is crucial for treatment of the diseases. Here we report a novel intervention to vascular smooth muscle (VSM) cells by optogenetics. Channelrhodopsin in a tandem with YFP was selectively expressed in smooth muscle of transgenic mice in which YFP fluorescence was found in arterial walls of various tissues. In dissociated VSM cells from the mice blue light evoked inward currents, leading to depolarization and contraction. In isolated mesenteric arterial rings, optostimulation produced vasoconstriction that was reproducible, sustained, light intensity-dependent and comparable to popular vasoconstrictors. Blue light raised robustly coronary resistance without significant effects on heart rate and pulse pressure. Optostimulation produced renal vasoconstriction as well. The optical vasoconstriction had temporal resolutions less than 40s in these organs. These results indicate that optical vasoconstriction can be effectively produced in various organs with channelrhodopsin expression in VSM cells.
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Affiliation(s)
- Yang Wu
- Department of Biology, Georgia State University, 50 Decatur Street, Atlanta, GA 30302, USA
| | - Shan-Shan Li
- Department of Biology, Georgia State University, 50 Decatur Street, Atlanta, GA 30302, USA
| | - Xin Jin
- Department of Biology, Georgia State University, 50 Decatur Street, Atlanta, GA 30302, USA
| | - Ningren Cui
- Department of Biology, Georgia State University, 50 Decatur Street, Atlanta, GA 30302, USA
| | - Shuang Zhang
- Department of Biology, Georgia State University, 50 Decatur Street, Atlanta, GA 30302, USA
| | - Chun Jiang
- Department of Biology, Georgia State University, 50 Decatur Street, Atlanta, GA 30302, USA.
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26
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Massey CA, Iceman KE, Johansen SL, Wu Y, Harris MB, Richerson GB. Isoflurane abolishes spontaneous firing of serotonin neurons and masks their pH/CO₂ chemosensitivity. J Neurophysiol 2015; 113:2879-88. [PMID: 25695656 DOI: 10.1152/jn.01073.2014] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Accepted: 02/18/2015] [Indexed: 11/22/2022] Open
Abstract
Serotonin (5-hydroxytryptamine, 5-HT) neurons from the mouse and rat rostral medulla are stimulated by increased CO2 when studied in culture or brain slices. However, the response of 5-HT neurons has been variable when animals are exposed to hypercapnia in vivo. Here we examined whether halogenated inhalational anesthetics, which activate TWIK-related acid-sensitive K(+) (TASK) channels, could mask an effect of CO2 on 5-HT neurons. During in vivo plethysmography in mice, isoflurane (1%) markedly reduced the hypercapnic ventilatory response (HCVR) by 78-96% depending upon mouse strain and ambient temperature. In a perfused rat brain stem preparation, isoflurane (1%) reduced or silenced spontaneous firing of medullary 5-HT neurons in situ and abolished their responses to elevated perfusate Pco2. In dissociated cell cultures, isoflurane (1%) hyperpolarized 5-HT neurons by 6.52 ± 3.94 mV and inhibited spontaneous firing. A subsequent decrease in pH from 7.4 to 7.2 depolarized neurons by 4.07 ± 2.10 mV, but that was insufficient to reach threshold for firing. Depolarizing current restored baseline firing and the firing frequency response to acidosis, indicating that isoflurane did not block the underlying mechanisms mediating chemosensitivity. These results demonstrate that isoflurane masks 5-HT neuron chemosensitivity in vitro and in situ and markedly decreases the HCVR in vivo. The use of this class of anesthetic has a particularly potent inhibitory effect on chemosensitivity of 5-HT neurons.
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Affiliation(s)
- Cory A Massey
- Interdisciplinary Graduate Program in Neuroscience, University of Iowa Hospitals and Clinics, Iowa City, Iowa; Department of Neurology and NIH/NINDS Center for SUDEP Research, University of Iowa Hospitals and Clinics, Iowa City, Iowa;
| | - Kimberly E Iceman
- Department of Biology and Wildlife, University of Alaska, Fairbanks, Alaska
| | - Sara L Johansen
- Department of Biology and Wildlife, University of Alaska, Fairbanks, Alaska
| | - Yuanming Wu
- Department of Neurology and NIH/NINDS Center for SUDEP Research, University of Iowa Hospitals and Clinics, Iowa City, Iowa
| | - Michael B Harris
- Department of Biology and Wildlife, University of Alaska, Fairbanks, Alaska; Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska
| | - George B Richerson
- Department of Neurology and NIH/NINDS Center for SUDEP Research, University of Iowa Hospitals and Clinics, Iowa City, Iowa; Department of Molecular Physiology and Biophysics, University of Iowa Hospitals and Clinics, Iowa City, Iowa; and Department of Veterans Affairs Medical Center, Iowa City, Iowa
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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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Paul ED, Johnson PL, Shekhar A, Lowry CA. The Deakin/Graeff hypothesis: focus on serotonergic inhibition of panic. Neurosci Biobehav Rev 2014; 46 Pt 3:379-96. [PMID: 24661986 PMCID: PMC4170046 DOI: 10.1016/j.neubiorev.2014.03.010] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 02/15/2014] [Accepted: 03/01/2014] [Indexed: 12/20/2022]
Abstract
The Deakin/Graeff hypothesis proposes that different subpopulations of serotonergic neurons through topographically organized projections to forebrain and brainstem structures modulate the response to acute and chronic stressors, and that dysfunction of these neurons increases vulnerability to affective and anxiety disorders, including panic disorder. We outline evidence supporting the existence of a serotonergic system originally discussed by Deakin/Graeff that is implicated in the inhibition of panic-like behavioral and physiological responses. Evidence supporting this panic inhibition system comes from the following observations: (1) serotonergic neurons located in the 'ventrolateral dorsal raphe nucleus' (DRVL) as well as the ventrolateral periaqueductal gray (VLPAG) inhibit dorsal periaqueductal gray-elicited panic-like responses; (2) chronic, but not acute, antidepressant treatment potentiates serotonin's panicolytic effect; (3) contextual fear activates a central nucleus of the amygdala-DRVL/VLPAG circuit implicated in mediating freezing and inhibiting panic-like escape behaviors; (4) DRVL/VLPAG serotonergic neurons are central chemoreceptors and modulate the behavioral and cardiorespiratory response to panicogenic agents such as sodium lactate and CO2. Implications of the panic inhibition system are discussed.
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Affiliation(s)
- Evan D Paul
- Department of Integrative Physiology and Center for Neuroscience, University of Colorado Boulder, Boulder, CO 80309-0354, USA.
| | - Philip L Johnson
- Department of Integrative Physiology and Center for Neuroscience, University of Colorado Boulder, Boulder, CO 80309-0354, USA.
| | - Anantha Shekhar
- Department of Integrative Physiology and Center for Neuroscience, University of Colorado Boulder, Boulder, CO 80309-0354, USA.
| | - Christopher A Lowry
- Department of Integrative Physiology and Center for Neuroscience, University of Colorado Boulder, Boulder, CO 80309-0354, USA.
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29
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Imber AN, Santin JM, Graham CD, Putnam RW. A HCO(3)(-)-dependent mechanism involving soluble adenylyl cyclase for the activation of Ca²⁺ currents in locus coeruleus neurons. Biochim Biophys Acta Mol Basis Dis 2014; 1842:2569-78. [PMID: 25092170 DOI: 10.1016/j.bbadis.2014.07.027] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 07/23/2014] [Accepted: 07/24/2014] [Indexed: 01/19/2023]
Abstract
Hypercapnic acidosis activates Ca²⁺ channels and increases intracellular Ca²⁺ levels in neurons of the locus coeruleus, a known chemosensitive region involved in respiratory control. We have also shown that large conductance Ca²⁺-activated K⁺ channels, in conjunction with this pathway, limits the hypercapnic-induced increase in firing rate in locus coeruleus neurons. Here, we present evidence that the Ca²⁺ current is activated by a HCO(3)(-)-sensitive pathway. The increase in HCO(3)(-) associated with hypercapnia activates HCO(3)(-)-sensitive adenylyl cyclase (soluble adenylyl cyclase). This results in an increase in cyclic adenosine monophosphate levels and activation of Ca²⁺ channels via cyclic adenosine monophosphate-activated protein kinase A. We also show the presence of soluble adenylyl cyclase in the cytoplasm of locus coeruleus neurons, and that the cyclic adenosine monophosphate analogue db-cyclic adenosine monophosphate increases Ca²⁺i. Disrupting this pathway by decreasing HCO(3)(-) levels during acidification or inhibiting either soluble adenylyl cyclase or protein kinase A, but not transmembrane adenylyl cyclase, can increase the magnitude of the firing rate response to hypercapnia in locus coeruleus neurons from older neonates to the same extent as inhibition of K⁺ channels. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.
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Affiliation(s)
- Ann N Imber
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
| | - Joseph M Santin
- Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
| | - Cathy D Graham
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
| | - Robert W Putnam
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA.
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30
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Buchanan GF. Timing, sleep, and respiration in health and disease. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 119:191-219. [PMID: 23899599 DOI: 10.1016/b978-0-12-396971-2.00008-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Breathing is perhaps the physiological function that is most vital to human survival. Without breathing and adequate oxygenation of tissues, life ceases. As would be expected for such a vital function, breathing occurs automatically, without the requirement of conscious input. Breathing is subject to regulation by a variety of factors including circadian rhythms and vigilance state. Given the need for breathing to occur continuously with little tolerance for interruption, it is not surprising that breathing is subject to both circadian phase-dependent and vigilance-state-dependent regulation. Similarly, the information regarding respiratory state, including blood-gas concentrations, can affect circadian timing and sleep-wake state. The exact nature of the interactions between breathing, circadian phase, and vigilance state can vary depending upon the species studied and the methodologies employed. These interactions between breathing, circadian phase, and vigilance state may have important implications for a variety of human diseases, including sleep apnea, asthma, sudden unexpected death in epilepsy, and sudden infant death syndrome.
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Affiliation(s)
- Gordon F Buchanan
- Department of Neurology, Yale University School of Medicine, New Haven, and Veteran's Affairs Medical Center, West Haven, Connecticut, USA
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31
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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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32
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Teran FA, Massey CA, Richerson GB. Serotonin neurons and central respiratory chemoreception: where are we now? PROGRESS IN BRAIN RESEARCH 2014; 209:207-33. [PMID: 24746050 DOI: 10.1016/b978-0-444-63274-6.00011-4] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Serotonin (5-hydroxytryptamine, 5-HT) neurons are widely considered to play an important role in central respiratory chemoreception. Although many studies in the past decades have supported this hypothesis, there had been concerns about its validity until recently. One recurring claim had been that 5-HT neurons are not consistently sensitive to hypercapnia in vivo. Another belief was that 5-HT neurons do not stimulate breathing; instead, they inhibit or modulate respiratory output. It was also believed by some that 5-HT neuron chemosensitivity is dependent on TASK channels, but mice with genetic deletion of TASK-1 and TASK-3 have a normal hypercapnic ventilatory response. This review explains why these principal arguments against the hypothesis are not supported by existing data. Despite repeated challenges, a large body of evidence now supports the conclusion that at least a subset of 5-HT neurons are central chemoreceptors.
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Affiliation(s)
- Frida A Teran
- St. Mary's University, One Camino Santa Maria, San Antonio, TX, USA
| | - Cory A Massey
- Interdisciplinary Graduate Program in Neuroscience, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Department of Neurology, University of Iowa Carver College of Medicine, Iowa City, IA, USA
| | - George B Richerson
- Interdisciplinary Graduate Program in Neuroscience, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Department of Neurology, University of Iowa Carver College of Medicine, Iowa City, IA, USA; Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA, USA; VAMC, Iowa City, IA, USA.
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33
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34
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Abstract
Sudden unexpected death in epilepsy (SUDEP) is an exceptionally difficult condition to study in humans. Therefore, translational research in animal models has been very important in defining pathophysiological mechanisms of death and identifying potential treatments. These models are helping define whether the primary mechanism of death is cardiac or respiratory. They have also identified a link to the serotonergic system of the brainstem; this, in turn, led to recognition that SUDEP and sudden infant death syndrome (SIDS) may share a common final pathway in the sequence of events that lead to death.
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35
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Iceman KE, Harris MB. A group of non-serotonergic cells is CO2-stimulated in the medullary raphé. Neuroscience 2013; 259:203-13. [PMID: 24333211 DOI: 10.1016/j.neuroscience.2013.11.060] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Revised: 11/13/2013] [Accepted: 11/30/2013] [Indexed: 01/22/2023]
Abstract
Serotonin/substance P synthesizing cells in the raphé nuclei of the brain are candidates for designation as central chemoreceptors that are stimulated by CO2/pH. We have previously demonstrated that these neurons are CO2-stimulated in situ. Evidence also suggests that CO2-inhibited raphé neurons recorded in vitro and in situ synthesize GABA. Unknown is whether there are other types of chemosensitive cells in the raphé. Here, we showed that a previously unrecognized pool of raphé neurons also exhibit chemosensitivity, and that they are not serotonergic. We used extracellular recording of individual raphé neurons in the unanesthetized juvenile rat in situ perfused decerebrate brainstem preparation to assess chemosensitivity of raphé neurons. Subsequent juxtacellular labeling of individually recorded cells, and immunohistochemistry for the serotonin synthesizing enzyme tryptophan hydroxylase and for neurokinin-1 receptor (NK1R; the receptor for substance P) indicated a group of CO2-stimulated cells that are not serotonergic, but express NK1R and are closely apposed to surrounding serotonergic cells. CO2-stimulated 5-HT and non-5-HT cells constitute distinct groups that have different firing characteristics and hypercapnic sensitivities. Non-5-HT cells fire faster and are more robustly stimulated by CO2 than are 5-HT cells. Thus, we have characterized a previously unrecognized type of CO2-stimulated medullary raphé neuron that is not serotonergic, but may receive input from neighboring serotonin/substance P synthesizing chemosensitive neurons. The potential network properties of the three types of chemosensitive raphé neurons (the present non-5-HT cells, serotonergic cells, and CO2-inhibited cells) remain to be elucidated.
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Affiliation(s)
- K E Iceman
- Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA; Department of Biology and Wildlife, University of Alaska, Fairbanks, AK 99775, USA.
| | - M B Harris
- Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA; Department of Biology and Wildlife, University of Alaska, Fairbanks, AK 99775, USA
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36
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Dubois C, Kervern M, Naassila M, Pierrefiche O. Chronic ethanol exposure during development: Disturbances of breathing and adaptation. Respir Physiol Neurobiol 2013; 189:250-60. [DOI: 10.1016/j.resp.2013.06.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2013] [Revised: 06/20/2013] [Accepted: 06/20/2013] [Indexed: 12/11/2022]
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37
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Carbon dioxide inhalation as a human experimental model of panic: The relationship between emotions and cardiovascular physiology. Biol Psychol 2013; 94:331-40. [DOI: 10.1016/j.biopsycho.2013.06.004] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Revised: 05/28/2013] [Accepted: 06/19/2013] [Indexed: 11/23/2022]
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Sowers LP, Massey CA, Gehlbach BK, Granner MA, Richerson GB. Sudden unexpected death in epilepsy: fatal post-ictal respiratory and arousal mechanisms. Respir Physiol Neurobiol 2013; 189:315-23. [PMID: 23707877 DOI: 10.1016/j.resp.2013.05.010] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Revised: 05/13/2013] [Accepted: 05/14/2013] [Indexed: 01/04/2023]
Abstract
Sudden unexplained death in epilepsy (SUDEP) is the cause of premature death of up to 17% of all patients with epilepsy and as many as 50% with chronic refractory epilepsy. However, SUDEP is not widely recognized to exist. The etiology of SUDEP remains unclear, but growing evidence points to peri-ictal respiratory, cardiac, or autonomic nervous system dysfunction. How seizures affect these systems remains uncertain. Here we focus on respiratory mechanisms believed to underlie SUDEP. We highlight clinical evidence that indicates peri-ictal hypoxemia occurs in a large percentage of patients due to central apnea, and identify the proposed anatomical regions of the brain governing these responses. In addition, we discuss animal models used to study peri-ictal respiratory depression. We highlight the role 5-HT neurons play in respiratory control, chemoreception, and arousal. Finally, we discuss the evidence that 5-HT deficits contribute to SUDEP and sudden infant death syndrome and the striking similarities between the two.
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Affiliation(s)
- Levi P Sowers
- Department of Neurology, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242, United States; Roy J. and Lucille A. Carver College of Medicine, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242, United States
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39
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Coley AA, Ruffin VA, Moss FJ, Hopfer U, Boron WF. Immunocytochemical identification of electroneutral Na⁺-coupled HCO₃⁻ transporters in freshly dissociated mouse medullary raphé neurons. Neuroscience 2013; 246:451-67. [PMID: 23500099 DOI: 10.1016/j.neuroscience.2013.02.064] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2012] [Revised: 02/27/2013] [Accepted: 02/28/2013] [Indexed: 01/09/2023]
Abstract
The medullary raphé (MR) of the medulla oblongata contains chemosensitive neurons that respond to increases in arterial [CO₂], by altering firing rate, with increases being associated with serotonergic (5-hydroxytryptamine [5HT]) neurons and decreases, with GABAergic neurons. Both types of neurons contribute to increased alveolar ventilation. Decreases in intracellular pH are thought to link the rise in [CO₂] to increased ventilation. Because electroneutral Na(+)-coupled HCO₃(-) transporters (nNCBTs), which help protect cells from intracellular acidosis, are expressed robustly in the neurons of the central nervous system, a key question is whether these transporters are present in chemosensitive neurons. Therefore, we used an immunocytochemistry approach to identify neurons (using a microtubule associated protein-2 monoclonal antibody) and specifically 5HT neurons (TPH monoclonal antibody) or GABAergic neurons (GAD2 monoclonal antibody) in freshly dissociated cells from the mouse MR. We also co-labeled with polyclonal antibodies against the three nNCBTs: NBCn1, NDCBE, and NBCn2. We exploited ePet-EYFP (enhanced yellow fluorescent protein) mice (with EYFP-labeled 5HT neurons) as well as mice genetically deficient in each of the three nNCBTs. Quantitative image analysis distinguished positively stained cells from background signals. We found that >80% of GAD2(+) cells also were positive for NDCBE, and >90% of the TPH(+) and GAD2(+) cells were positive for the other nNCBTs. Assuming that the transporters are independently distributed among neurons, we can conclude that virtually all chemosensitive MR neurons contain at least one nNCBT.
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Affiliation(s)
- A A Coley
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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40
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Wong-Riley MTT, Liu Q, Gao XP. Peripheral-central chemoreceptor interaction and the significance of a critical period in the development of respiratory control. Respir Physiol Neurobiol 2013; 185:156-69. [PMID: 22684042 PMCID: PMC3467325 DOI: 10.1016/j.resp.2012.05.026] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Revised: 05/30/2012] [Accepted: 05/30/2012] [Indexed: 01/09/2023]
Abstract
Respiratory control entails coordinated activities of peripheral chemoreceptors (mainly the carotid bodies) and central chemosensors within the brain stem respiratory network. Candidates for central chemoreceptors include Phox2b-containing neurons of the retrotrapezoid nucleus, serotonergic neurons of the medullary raphé, and/or multiple sites within the brain stem. Extensive interconnections among respiratory-related nuclei enable central chemosensitive relay. Both peripheral and central respiratory centers are not mature at birth, but undergo considerable development during the first two postnatal weeks in rats. A critical period of respiratory development (∼P12-P13 in the rat) exists when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur. Environmental perturbations, including hypoxia, intermittent hypoxia, hypercapnia, and hyperoxia alter the development of the respiratory system. Carotid body denervation during the first two postnatal weeks in the rat profoundly affects the development and functions of central respiratory-related nuclei. Such denervation delays and prolongs the critical period, but does not eliminate it, suggesting that the critical period may be intrinsically and genetically determined.
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Affiliation(s)
- Margaret T T Wong-Riley
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
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41
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Basic mechanisms of migraine and its acute treatment. Pharmacol Ther 2012; 136:319-33. [DOI: 10.1016/j.pharmthera.2012.08.011] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Accepted: 08/13/2012] [Indexed: 12/27/2022]
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Onimaru H, Ikeda K, Kawakami K. Relationship between the distribution of the paired-like homeobox gene (Phox2b) expressing cells and blood vessels in the parafacial region of the ventral medulla of neonatal rats. Neuroscience 2012; 212:131-9. [DOI: 10.1016/j.neuroscience.2012.03.037] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Revised: 03/15/2012] [Accepted: 03/16/2012] [Indexed: 10/28/2022]
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Abstract
Central chemoreception traditionally refers to a change in ventilation attributable to changes in CO2/H(+) detected within the brain. Interest in central chemoreception has grown substantially since the previous Handbook of Physiology published in 1986. Initially, central chemoreception was localized to areas on the ventral medullary surface, a hypothesis complemented by the recent identification of neurons with specific phenotypes near one of these areas as putative chemoreceptor cells. However, there is substantial evidence that many sites participate in central chemoreception some located at a distance from the ventral medulla. Functionally, central chemoreception, via the sensing of brain interstitial fluid H(+), serves to detect and integrate information on (i) alveolar ventilation (arterial PCO2), (ii) brain blood flow and metabolism, and (iii) acid-base balance, and, in response, can affect breathing, airway resistance, blood pressure (sympathetic tone), and arousal. In addition, central chemoreception provides a tonic "drive" (source of excitation) at the normal, baseline PCO2 level that maintains a degree of functional connectivity among brainstem respiratory neurons necessary to produce eupneic breathing. Central chemoreception responds to small variations in PCO2 to regulate normal gas exchange and to large changes in PCO2 to minimize acid-base changes. Central chemoreceptor sites vary in function with sex and with development. From an evolutionary perspective, central chemoreception grew out of the demands posed by air versus water breathing, homeothermy, sleep, optimization of the work of breathing with the "ideal" arterial PCO2, and the maintenance of the appropriate pH at 37°C for optimal protein structure and function.
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Affiliation(s)
- Eugene Nattie
- Dartmouth Medical School, Department of Physiology, Lebanon, New Hampshire, USA.
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Abstract
Central chemoreception traditionally refers to a change in ventilation attributable to changes in CO2/H(+) detected within the brain. Interest in central chemoreception has grown substantially since the previous Handbook of Physiology published in 1986. Initially, central chemoreception was localized to areas on the ventral medullary surface, a hypothesis complemented by the recent identification of neurons with specific phenotypes near one of these areas as putative chemoreceptor cells. However, there is substantial evidence that many sites participate in central chemoreception some located at a distance from the ventral medulla. Functionally, central chemoreception, via the sensing of brain interstitial fluid H(+), serves to detect and integrate information on (i) alveolar ventilation (arterial PCO2), (ii) brain blood flow and metabolism, and (iii) acid-base balance, and, in response, can affect breathing, airway resistance, blood pressure (sympathetic tone), and arousal. In addition, central chemoreception provides a tonic "drive" (source of excitation) at the normal, baseline PCO2 level that maintains a degree of functional connectivity among brainstem respiratory neurons necessary to produce eupneic breathing. Central chemoreception responds to small variations in PCO2 to regulate normal gas exchange and to large changes in PCO2 to minimize acid-base changes. Central chemoreceptor sites vary in function with sex and with development. From an evolutionary perspective, central chemoreception grew out of the demands posed by air versus water breathing, homeothermy, sleep, optimization of the work of breathing with the "ideal" arterial PCO2, and the maintenance of the appropriate pH at 37°C for optimal protein structure and function.
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Affiliation(s)
- Eugene Nattie
- Dartmouth Medical School, Department of Physiology, Lebanon, New Hampshire, USA.
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Huckstepp RTR, Dale N. Redefining the components of central CO2 chemosensitivity--towards a better understanding of mechanism. J Physiol 2011; 589:5561-79. [PMID: 22005672 PMCID: PMC3249032 DOI: 10.1113/jphysiol.2011.214759] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Abstract The field of CO2 chemosensitivity has developed considerably in recent years. There has been a mounting number of competing nuclei proposed as chemosensitive along with an ever increasing list of potential chemosensory transducing molecules. Is it really possible that all of these areas and candidate molecules are involved in the detection of chemosensory stimuli? How do we discriminate rigorously between molecules that are chemosensory transducers at the head of a physiological reflexversusthose that just happen to display sensitivity to a chemosensory stimulus? Equally, how do we differentiate between nuclei that have a primary chemosensory function, versusthose that are relays in the pathway? We have approached these questions by proposing rigorous definitions for the different components of the chemosensory reflex, going from the salient molecules and ions, through the components of transduction to the identity of chemosensitive cells and chemosensitive nuclei. Our definitions include practical and rigorous experimental tests that can be used to establish the identity of these components. We begin by describing the need for central CO2 chemosensitivity and the problems that the field has faced. By comparing chemosensory mechanisms to those in the visual system we suggest stricter definitions for the components of the chemosensory pathway. We then, considering these definitions, re-evaluate current knowledge of chemosensory transduction, and propose the ‘multiple salient signal hypothesis’ as a framework for understanding the multiplicity of transduction mechanisms and brain areas seemingly involved in chemosensitivity.
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Kinney HC, Broadbelt KG, Haynes RL, Rognum IJ, Paterson DS. The serotonergic anatomy of the developing human medulla oblongata: implications for pediatric disorders of homeostasis. J Chem Neuroanat 2011; 41:182-99. [PMID: 21640183 DOI: 10.1016/j.jchemneu.2011.05.004] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2011] [Revised: 04/25/2011] [Accepted: 05/06/2011] [Indexed: 12/18/2022]
Abstract
The caudal serotonergic (5-HT) system is a critical component of a medullary "homeostatic network" that regulates protective responses to metabolic stressors such as hypoxia, hypercapnia, and hyperthermia. We define anatomically the caudal 5-HT system in the human medulla as 5-HT neuronal cell bodies located in the raphé (raphé obscurus, raphé magnus, and raphé pallidus), extra-raphé (gigantocellularis, paragigantocellularis lateralis, intermediate reticular zone, lateral reticular nucleus, and nucleus subtrigeminalis), and ventral surface (arcuate nucleus). These 5-HT neurons are adjacent to all of the respiratory- and autonomic-related nuclei in the medulla where they are positioned to modulate directly the responses of these effector nuclei. In the following review, we highlight the topography and development of the caudal 5-HT system in the human fetus and infant, and its inter-relationships with nicotinic, GABAergic, and cytokine receptors. We also summarize pediatric disorders in early life which we term "developmental serotonopathies" of the caudal (as well as rostral) 5-HT domain and which are associated with homeostatic imbalances. The delineation of the development and organization of the human caudal 5-HT system provides the critical foundation for the neuropathologic elucidation of its disorders directly in the human brain.
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Affiliation(s)
- Hannah C Kinney
- Department of Pathology, Children's Hospital Boston and Harvard Medical School, Boston, MA 02115, United States
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Richerson GB, Buchanan GF. The serotonin axis: Shared mechanisms in seizures, depression, and SUDEP. Epilepsia 2011; 52 Suppl 1:28-38. [PMID: 21214537 DOI: 10.1111/j.1528-1167.2010.02908.x] [Citation(s) in RCA: 150] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
There is a growing appreciation that patients with seizures are also affected by a number of comorbid conditions, including an increase in prevalence of depression (Kanner, 2009), sleep apnea (Chihorek et al., 2007), and sudden death (Ryvlin et al., 2006; Tomson et al., 2008). The mechanisms responsible for these associations are unclear. Herein we discuss the possibility that underlying pathology in the serotonin (5-HT) system of patients with epilepsy lowers the threshold for seizures, while also increasing the risk of depression and sudden death. We propose that postictal dysfunction of 5-HT neurons causes depression of breathing and arousal in some epilepsy patients, and this can lead to sudden unexpected death in epilepsy (SUDEP). We further draw parallels between SUDEP and sudden infant death syndrome (SIDS), which may share pathophysiologic mechanisms, and which have both been linked to defects in the 5-HT system.
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Hodges MR, Richerson GB. Medullary serotonin neurons and their roles in central respiratory chemoreception. Respir Physiol Neurobiol 2010; 173:256-63. [PMID: 20226279 PMCID: PMC4554718 DOI: 10.1016/j.resp.2010.03.006] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Revised: 03/03/2010] [Accepted: 03/04/2010] [Indexed: 11/13/2022]
Abstract
Much progress has been made in our understanding of central chemoreception since the seminal experiments of Fencl, Loeschcke, Mitchell and others, including identification of new brainstem regions and specific neuron types that may serve as central "sensors" of CO(2)/pH. In this review, we discuss key attributes, or minimal requirements a neuron/cell must possess to be defined as a central respiratory chemoreceptor, and summarize how well each of the various candidates fulfill these minimal criteria-especially the presence of intrinsic chemosensitivity. We then discuss some of the in vitro and in vivo evidence in support of the conclusion that medullary serotonin (5-HT) neurons are central chemoreceptors. We also provide an additional hypothesis that chemosensitive medullary 5-HT neurons are poised to integrate multiple synaptic inputs from various other sources thought to influence ventilation. Finally, we discuss open questions and future studies that may aid in continuing our advances in understanding central chemoreception.
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Affiliation(s)
- Matthew R Hodges
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
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Panneton WM, Gan Q, Dahms TE. Cardiorespiratory and neural consequences of rats brought past their aerobic dive limit. J Appl Physiol (1985) 2010; 109:1256-69. [PMID: 20705947 PMCID: PMC2971699 DOI: 10.1152/japplphysiol.00110.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Accepted: 08/05/2010] [Indexed: 11/22/2022] Open
Abstract
The mammalian diving response is a dramatic autonomic adjustment to underwater submersion affecting heart rate, arterial blood pressure, and ventilation. The bradycardia is known to be modulated by the parasympathetic nervous system, arterial blood pressure is modulated via the sympathetic system, and still other circuits modulate the respiratory changes. In the present study, we investigate the submergence of rats brought past their aerobic dive limit, defined as the diving duration beyond which blood lactate concentration increases above resting levels. Hemodynamic measurements were made during underwater submergence with biotelemetric transmitters, and blood was drawn from cannulas previously implanted in the rats' carotid arteries. Such prolonged submersion induces radical changes in blood chemistry; mean arterial PCO(2) rose to 62.4 Torr, while mean arterial PO(2) and pH reached nadirs of 21.8 Torr and 7.18, respectively. Despite these radical changes in blood chemistry, the rats neither attempted to gasp nor breathe while underwater. Immunohistochemistry for Fos protein done on their brains revealed numerous Fos-positive profiles. Especially noteworthy were the large number of immunopositive profiles in loci where presumptive chemoreceptors are found. Despite the activation of these presumptive chemoreceptors, the rats did not attempt to breathe. Injections of biotinylated dextran amine were made into ventral parts of the medullary dorsal horn, where central fibers of the anterior ethmoidal nerve terminate. Labeled fibers coursed caudal, ventral, and medial from the injection to neurons on the ventral surface of the medulla, where numerous Fos-labeled profiles were seen in the rats brought past their aerobic dive limit. We propose that this projection inhibits the homeostatic chemoreceptor reflex, despite the gross activation of chemoreceptors.
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Affiliation(s)
- W Michael Panneton
- Dept. of Pharmacological and Physiological Science, St. Louis Univ. School of Medicine, 1402 S. Grand Blvd., St. Louis, MO 63104-1004, USA.
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Abstract
There is a long-standing controversy about the role of serotonin in sleep/wake control, with competing theories that it either promotes sleep or causes arousal. Here, we show that there is a marked increase in wakefulness when all serotonin neurons are genetically deleted in mice hemizygous for ePet1-Cre and homozygous for floxed Lmx1b (Lmx1b(f/f/p)). However, this only occurs at cool ambient temperatures and can be explained by a thermoregulatory defect that leads to an increase in motor activity to generate heat. Because some serotonin neurons are stimulated by CO(2), and serotonin activates thalamocortical networks, we hypothesized that serotonin neurons cause arousal in response to hypercapnia. We found that Lmx1b(f/f/p) mice completely lacked any arousal response to inhalation of 10% CO(2) (with 21% O(2) in balance N(2)) but had normal arousal responses to hypoxia, sound, and air puff. We propose that serotonin neurons mediate the potentially life-saving arousal response to hypercapnia. Impairment of this response may contribute to sudden unexpected death in epilepsy, sudden infant death syndrome, and sleep apnea.
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