1
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Verge VM, Tokarska N, Naniong JM. Unraveling the potential of acute intermittent hypoxia as a strategy for inducing robust repair in multiple sclerosis. Neural Regen Res 2024; 19:2339-2340. [PMID: 38526264 PMCID: PMC11090437 DOI: 10.4103/nrr.nrr-d-23-01663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 12/26/2023] [Accepted: 01/08/2024] [Indexed: 03/26/2024] Open
Affiliation(s)
- Valerie M.K. Verge
- Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, SK, Canada
- Cameco MS Neuroscience Research Center, University of Saskatchewan, Saskatoon, SK, Canada
| | - Nataliya Tokarska
- Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, SK, Canada
- Cameco MS Neuroscience Research Center, University of Saskatchewan, Saskatoon, SK, Canada
| | - Justin M. Naniong
- Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, SK, Canada
- Cameco MS Neuroscience Research Center, University of Saskatchewan, Saskatoon, SK, Canada
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2
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Welch JF, Mitchell GS. Inaugural Review Prize 2023: The exercise hyperpnoea dilemma: A 21st-century perspective. Exp Physiol 2024; 109:1217-1237. [PMID: 38551996 PMCID: PMC11291877 DOI: 10.1113/ep091506] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2024] [Accepted: 03/12/2024] [Indexed: 08/02/2024]
Abstract
During mild or moderate exercise, alveolar ventilation increases in direct proportion to metabolic rate, regulating arterial CO2 pressure near resting levels. Mechanisms giving rise to the hyperpnoea of exercise are unsettled despite over a century of investigation. In the past three decades, neuroscience has advanced tremendously, raising optimism that the 'exercise hyperpnoea dilemma' can finally be solved. In this review, new perspectives are offered in the hope of stimulating original ideas based on modern neuroscience methods and current understanding. We first describe the ventilatory control system and the challenge exercise places upon blood-gas regulation. We highlight relevant system properties, including feedforward, feedback and adaptive (i.e., plasticity) control of breathing. We then elaborate a seldom explored hypothesis that the exercise ventilatory response continuously adapts (learns and relearns) throughout life and ponder if the memory 'engram' encoding the feedforward exercise ventilatory stimulus could reside within the cerebellum. Our hypotheses are based on accumulating evidence supporting the cerebellum's role in motor learning and the numerous direct and indirect projections from deep cerebellar nuclei to brainstem respiratory neurons. We propose that cerebellar learning may be obligatory for the accurate and adjustable exercise hyperpnoea capable of tracking changes in life conditions/experiences, and that learning arises from specific cerebellar microcircuits that can be interrogated using powerful techniques such as optogenetics and chemogenetics. Although this review is speculative, we consider it essential to reframe our perspective if we are to solve the till-now intractable exercise hyperpnoea dilemma.
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Affiliation(s)
- Joseph F. Welch
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental SciencesUniversity of BirminghamEdgbastonBirminghamUK
| | - Gordon S. Mitchell
- Breathing Research and Therapeutics Centre, Department of Physical Therapy, McKnight Brain InstituteUniversity of FloridaGainesvilleFloridaUSA
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3
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Gonzalez-Rothi EJ, Allen LL, Seven YB, Ciesla MC, Holland AE, Santiago JV, Mitchell GS. Prolonged intermittent hypoxia differentially regulates phrenic motor neuron serotonin receptor expression in rats following chronic cervical spinal cord injury. Exp Neurol 2024; 378:114808. [PMID: 38750949 DOI: 10.1016/j.expneurol.2024.114808] [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: 12/22/2023] [Revised: 04/05/2024] [Accepted: 05/03/2024] [Indexed: 05/30/2024]
Abstract
Low-dose (< 2 h/day), acute intermittent hypoxia (AIH) elicits multiple forms of serotonin-dependent phrenic motor plasticity and is emerging as a promising therapeutic strategy to restore respiratory and non-respiratory motor function after spinal cord injury (SCI). In contrast, high-dose (> 8 h/day), chronic intermittent hypoxia (CIH) undermines some forms of serotonin-dependent phrenic motor plasticity and elicits pathology. CIH is a hallmark of sleep disordered breathing, which is highly prevalent in individuals with cervical SCI. Interestingly, AIH and CIH preconditioning differentially impact phrenic motor plasticity. Although mechanisms of AIH-induced plasticity in the phrenic motor system are well-described in naïve rats, we know little concerning how these mechanisms are affected by chronic SCI or intermittent hypoxia preconditioning. Thus, in a rat model of chronic, incomplete cervical SCI (lateral spinal hemisection at C2 (C2Hx), we assessed serotonin type 2A, 2B and 7 receptor expression in and near phrenic motor neurons and compared: 1) intact vs. chronically injured rats; and 2) the impact of preconditioning with varied "doses" of intermittent hypoxia (IH). While there were no effects of chronic injury or intermittent hypoxia alone, CIH affected multiple receptors in rats with chronic C2Hx. Specifically, CIH preconditioning (8 h/day; 28 days) increased serotonin 2A and 7 receptor expression exclusively in rats with chronic C2Hx. Understanding the complex, context-specific interactions between chronic SCI and CIH and how this ultimately impacts phrenic motor plasticity is important as we leverage AIH-induced motor plasticity to restore breathing and other non-respiratory motor functions in people with chronic SCI.
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Affiliation(s)
- Elisa J Gonzalez-Rothi
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA.
| | - Latoya L Allen
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Yasin B Seven
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Marissa C Ciesla
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Ashley E Holland
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Juliet V Santiago
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
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4
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Pearcey GEP, Afsharipour B, Holobar A, Sandhu MS, Rymer WZ. Acute intermittent hypoxia increases maximal motor unit discharge rates in people with chronic incomplete spinal cord injury. J Physiol 2024. [PMID: 39058666 DOI: 10.1113/jp285049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Accepted: 06/17/2024] [Indexed: 07/28/2024] Open
Abstract
Acute intermittent hypoxia (AIH) is an emerging technique for enhancing neuroplasticity and motor function in respiratory and limb musculature. Thus far, AIH-induced improvements in strength have been reported for upper and lower limb muscles after chronic incomplete cervical spinal cord injury (iSCI), but the underlying mechanisms have been elusive. We used high-density surface EMG (HDsEMG) to determine if motor unit discharge behaviour is altered after 15 × 60 s exposures to 9% inspired oxygen, interspersed with 21% inspired oxygen (AIH), compared to breathing only 21% air (SHAM). We recorded HDsEMG from the biceps and triceps brachii of seven individuals with iSCI during maximal elbow flexion and extension contractions, and motor unit spike trains were identified using convolutive blind source separation. After AIH, elbow flexion and extension torque increased by 54% and 59% from baseline (P = 0.003), respectively, whereas there was no change after SHAM. Across muscles, motor unit discharge rates increased by ∼4 pulses per second (P = 0.002) during maximal efforts, from before to after AIH. These results suggest that excitability and/or activation of spinal motoneurons is augmented after AIH, providing a mechanism to explain AIH-induced increases in voluntary strength. Pending validation, AIH may be helpful in conjunction with other therapies to enhance rehabilitation outcomes after incomplete spinal cord injury, due to these enhancements in motor unit function and strength. KEY POINTS: Acute intermittent hypoxia (AIH) causes increases in muscular strength and neuroplasticity in people living with chronic incomplete spinal cord injury (SCI), but how it affects motor unit discharge rates is unknown. Motor unit spike times were identified from high-density surface electromyograms during maximal voluntary contractions and tracked from before to after AIH. Motor unit discharge rates were increased following AIH. These findings suggest that AIH can facilitate motoneuron function in people with incomplete SCI.
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Affiliation(s)
- Gregory E P Pearcey
- School of Human Kinetics and Recreation, and Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Babak Afsharipour
- Department of Biomedical Engineering, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Aleš Holobar
- Institute of Computer Science, Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Milap S Sandhu
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
- Shirley Ryan AbilityLab, Chicago, IL, USA
| | - W Zev Rymer
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
- Shirley Ryan AbilityLab, Chicago, IL, USA
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5
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Kavanagh JJ. Oxygen deprivation is a muscle revelation: hypoxia enhances motor unit firing after spinal cord injury. J Physiol 2024. [PMID: 39032034 DOI: 10.1113/jp287134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/22/2024] Open
Affiliation(s)
- Justin J Kavanagh
- Neural Control of Movement laboratory, Menzies Health Institute Queensland, Griffith University, Gold Coast, Australia
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6
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O'Halloran KD. Intermittent hypoxia therapy for motor insufficiency: hype, hope or hard work? J Physiol 2024. [PMID: 39031530 DOI: 10.1113/jp287144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2024] [Accepted: 07/09/2024] [Indexed: 07/22/2024] Open
Affiliation(s)
- Ken D O'Halloran
- Department of Physiology, University College Cork, Cork, Ireland
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7
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McKenzie K, Veit N, Aalla S, Yang C, Giffhorn M, Lynott A, Buchler K, Kishta A, Barry A, Sandhu M, Moon Y, Rymer WZ, Jayaraman A. Combining Neuromodulation Strategies in Spinal Cord Injury Gait Rehabilitation: A Proof Of Concept, Randomized, Crossover Trial. Arch Phys Med Rehabil 2024:S0003-9993(24)01073-6. [PMID: 38969255 DOI: 10.1016/j.apmr.2024.06.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2024] [Revised: 06/17/2024] [Accepted: 06/18/2024] [Indexed: 07/07/2024]
Abstract
OBJECTIVES To evaluate if acute intermittent hypoxia (AIH) coupled with transcutaneous spinal cord stimulation (tSCS) enhances task-specific training and leads to superior and more sustained gait improvements as compared with each of these strategies used in isolation in persons with chronic, incomplete spinal cord injury. DESIGN Proof of concept, randomized crossover trial. SETTING Outpatient, rehabilitation hospital. INTERVENTIONS Ten participants completed 3 intervention arms: (1) AIH, tSCS, and gait training (AIH + tSCS); (2) tSCS plus gait training (SHAM AIH + tSCS); and (3) gait training alone (SHAM + SHAM). Each arm consisted of 5 consecutive days of intervention with a minimum of a 4-week washout between arms. The order of arms was randomized. The study took place from December 3, 2020, to January 4, 2023. MAIN OUTCOME MEASURES 10-meter walk test at self-selected velocity (SSV) and fast velocity, 6-minute walk test, timed Up and Go (TUG) and secondary outcome measures included isometric ankle plantarflexion and dorsiflexion torque RESULTS: TUG improvements were 3.44 seconds (95% CI: 1.24-5.65) significantly greater in the AIH + tSCS arm than the SHAM AIH + tSCS arm at post-intervention (POST), and 3.31 seconds (95% CI: 1.03-5.58) greater than the SHAM + SHAM arm at 1-week follow up (1WK). SSV was 0.08 m/s (95% CI: 0.02-0.14) significantly greater following the AIH + tSCS arm than the SHAM AIH + tSCS at POST. Although not significant, the AIH + tSCS arm also demonstrated the greatest average improvements compared with the other 2 arms at POST and 1WK for the 6-minute walk test, fast velocity, and ankle plantarflexion torque. CONCLUSIONS This pilot study is the first to demonstrate that combining these 3 neuromodulation strategies leads to superior improvements in the TUG and SSV for individuals with chronic incomplete spinal cord injury and warrants further investigation.
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Affiliation(s)
| | - Nicole Veit
- Shirley Ryan AbilityLab, Chicago; Department of Biomedical Engineering, Northwestern University, Evanston
| | | | - Chen Yang
- Shirley Ryan AbilityLab, Chicago; Feinberg School of Medicine, Northwestern University, Chicago
| | | | | | | | | | | | - Milap Sandhu
- Shirley Ryan AbilityLab, Chicago; Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago
| | - Yaejin Moon
- Shirley Ryan AbilityLab, Chicago; Feinberg School of Medicine, Northwestern University, Chicago
| | - William Zev Rymer
- Shirley Ryan AbilityLab, Chicago; Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago; Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago
| | - Arun Jayaraman
- Shirley Ryan AbilityLab, Chicago; Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago.
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8
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Ó Murchú SC, O'Halloran KD. BREATHE DMD: boosting respiratory efficacy after therapeutic hypoxic episodes in Duchenne muscular dystrophy. J Physiol 2024; 602:3255-3272. [PMID: 38837229 DOI: 10.1113/jp280280] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2024] [Accepted: 05/12/2024] [Indexed: 06/07/2024] Open
Abstract
Duchenne muscular dystrophy (DMD) is a fatal genetic neuromuscular disorder, characterised by progressive decline in skeletal muscle function due to the secondary consequences of dystrophin deficiency. Weakness extends to the respiratory musculature, and cardiorespiratory failure is the leading cause of death in men with DMD. Intermittent hypoxia has emerged as a potential therapy to counteract ventilatory insufficiency by eliciting long-term facilitation of breathing. Mechanisms of sensory and motor facilitation of breathing have been well delineated in animal models. Various paradigms of intermittent hypoxia have been designed and implemented in human trials culminating in clinical trials in people with spinal cord injury and amyotrophic lateral sclerosis. Application of therapeutic intermittent hypoxia to DMD is considered together with discussion of the potential barriers to progression owing to the complexity of this devastating disease. Notwithstanding the considerable challenges and potential pitfalls of intermittent hypoxia-based therapies for DMD, we suggest it is incumbent on the research community to explore the potential benefits in pre-clinical models. Intermittent hypoxia paradigms should be implemented to explore the proclivity to express respiratory plasticity with the longer-term aim of preserving and potentiating ventilation in pre-clinical models and people with DMD.
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Affiliation(s)
- Seán C Ó Murchú
- Department of Physiology, University College Cork, Cork, Ireland
| | - Ken D O'Halloran
- Department of Physiology, University College Cork, Cork, Ireland
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9
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Dallal-York J, Troche MS. Hypotussic cough in persons with dysphagia: biobehavioral interventions and pathways to clinical implementation. FRONTIERS IN REHABILITATION SCIENCES 2024; 5:1394110. [PMID: 38933659 PMCID: PMC11199739 DOI: 10.3389/fresc.2024.1394110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Accepted: 05/13/2024] [Indexed: 06/28/2024]
Abstract
Cough is a powerful, protective expulsive behavior that assists in maintaining respiratory health by clearing foreign material, pathogens, and mucus from the airways. Therefore, cough is critical to survival in both health and disease. Importantly, cough protects the airways and lungs from both antegrade (e.g., food, liquid, saliva) and retrograde (e.g., bile, gastric acid) aspirate contents. Aspiration is often the result of impaired swallowing (dysphagia), which allows oral and/or gastric contents to enter the lung, especially in individuals who also have cough dysfunction (dystussia). Cough hyposensitivity, downregulation, or desensitization- collectively referred to as hypotussia- is common in individuals with dysphagia, and increases the likelihood that aspirated material will reach the lung. The consequence of hypotussia with reduced airway clearance can include respiratory tract infection, chronic inflammation, and long-term damage to the lung parenchyma. Despite the clear implications for health, the problem of managing hypotussia in individuals with dysphagia is frequently overlooked. Here, we provide an overview of the current interventions and treatment approaches for hypotussic cough. We synthesize the available literature to summarize research findings that advance our understanding of these interventions, as well as current gaps in knowledge. Further, we highlight pragmatic resources to increase awareness of hypotussic cough interventions and provide support for the clinical implementation of evidence-based treatments. In culmination, we discuss potential innovations and future directions for hypotussic cough research.
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Affiliation(s)
- Justine Dallal-York
- Laboratory for the Study of Upper Airway Dysfunction, Department of Biobehavioral Sciences, Teachers College, Columbia University, New York, NY, United States
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10
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Marciante AB, Tadjalli A, Burrowes KA, Oberto JR, Luca EK, Seven YB, Nikodemova M, Watters JJ, Baker TL, Mitchell GS. Microglia regulate motor neuron plasticity via reciprocal fractalkine/adenosine signaling. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.07.592939. [PMID: 38765982 PMCID: PMC11100694 DOI: 10.1101/2024.05.07.592939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2024]
Abstract
Microglia are innate CNS immune cells that play key roles in supporting key CNS functions including brain plasticity. We now report a previously unknown role for microglia in regulating neuroplasticity within spinal phrenic motor neurons, the neurons driving diaphragm contractions and breathing. We demonstrate that microglia regulate phrenic long-term facilitation (pLTF), a form of respiratory memory lasting hours after repetitive exposures to brief periods of low oxygen (acute intermittent hypoxia; AIH) via neuronal/microglial fractalkine signaling. AIH-induced pLTF is regulated by the balance between competing intracellular signaling cascades initiated by serotonin vs adenosine, respectively. Although brainstem raphe neurons release the relevant serotonin, the cellular source of adenosine is unknown. We tested a model in which hypoxia initiates fractalkine signaling between phrenic motor neurons and nearby microglia that triggers extracellular adenosine accumulation. With moderate AIH, phrenic motor neuron adenosine 2A receptor activation undermines serotonin-dominant pLTF; in contrast, severe AIH drives pLTF by a unique, adenosine-dominant mechanism. Phrenic motor neuron fractalkine knockdown, cervical spinal fractalkine receptor inhibition on nearby microglia, and microglial depletion enhance serotonin-dominant pLTF with moderate AIH but suppress adenosine-dominant pLTF with severe AIH. Thus, microglia play novel functions in the healthy spinal cord, regulating hypoxia-induced neuroplasticity within the motor neurons responsible for breathing.
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Affiliation(s)
- Alexandria B. Marciante
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida; Gainesville, FL, USA 32610
| | - Arash Tadjalli
- Current Address: Nova Southeastern University, College of Allopathic Medicine (NSU MD), Department of Medical Education, 3200 South University Drive, Fort Lauderdale, FL 33328-2018
| | - Kayla A. Burrowes
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida; Gainesville, FL, USA 32610
| | - Jose R. Oberto
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida; Gainesville, FL, USA 32610
| | - Edward K. Luca
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida; Gainesville, FL, USA 32610
| | - Yasin B. Seven
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida; Gainesville, FL, USA 32610
| | - Maria Nikodemova
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida; Gainesville, FL, USA 32610
| | - Jyoti J. Watters
- Current Address: Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive, Madison, WI 53706
| | - Tracy L. Baker
- Current Address: Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive, Madison, WI 53706
| | - Gordon S. Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida; Gainesville, FL, USA 32610
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11
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Welch JF, Vose AK, Cavka K, Brunetti G, DeMark LA, Snyder H, Wauneka CN, Tonuzi G, Nair J, Mitchell GS, Fox EJ. Cardiorespiratory Responses to Acute Intermittent Hypoxia in Humans With Chronic Spinal Cord Injury. J Neurotrauma 2024. [PMID: 38468543 DOI: 10.1089/neu.2023.0353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/13/2024] Open
Abstract
Brief exposure to repeated episodes of low inspired oxygen, or acute intermittent hypoxia (AIH), is a promising therapeutic modality to improve motor function after chronic, incomplete spinal cord injury (SCI). Although therapeutic AIH is under extensive investigation in persons with SCI, limited data are available concerning cardiorespiratory responses during and after AIH exposure despite implications for AIH safety and tolerability. Thus, we recorded immediate (during treatment) and enduring (up to 30 min post-treatment) cardiorespiratory responses to AIH in 19 participants with chronic SCI (>1 year post-injury; injury levels C1 to T6; American Spinal Injury Association Impairment Scale A to D; mean age = 33.8 ± 14.1 years; 18 males). Participants completed a single AIH (15, 60-sec episodes, inspired O2 ≈ 10%; 90-sec intervals breathing room air) and Sham (inspired O2 ≈ 21%) treatment, in random order. During hypoxic episodes: (1) arterial oxyhemoglobin saturation decreased to 82.1 ± 2.9% (p < 0.001); (2) minute ventilation increased 3.83 ± 2.29 L/min (p = 0.008); and (3) heart rate increased 4.77 ± 6.82 bpm (p = 0.010). Considerable variability in cardiorespiratory responses was found among subjects; some individuals exhibited large hypoxic ventilatory responses (≥0.20 L/min/%, n = 11), whereas others responded minimally (<0.20 L/min/%, n = 8). Apneas occurred frequently during AIH and/or Sham protocols in multiple participants. All participants completed AIH treatment without difficulty. No significant changes in ventilation, heart rate, or arterial blood pressure were found 30 min post-AIH p > 0.05). In conclusion, therapeutic AIH is well tolerated, elicits variable chemoreflex activation, and does not cause persistent changes in cardiorespiratory control/function 30 min post-treatment in persons with chronic SCI.
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Affiliation(s)
- Joseph F Welch
- Breathing Research and Therapeutics Center and Department of Physical Therapy, University of Florida, Gainesville, Florida, USA
- McKnight Brain Institute, University of Florida, Gainesville, Florida, USA
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
| | - Alicia K Vose
- Breathing Research and Therapeutics Center and Department of Physical Therapy, University of Florida, Gainesville, Florida, USA
- McKnight Brain Institute, University of Florida, Gainesville, Florida, USA
- Brooks Rehabilitation, Jacksonville, Florida, USA
- Department of Neurology, College of Medicine-Jacksonville, University of Florida, Jacksonville, Florida, USA
| | - Kate Cavka
- Brooks Rehabilitation, Jacksonville, Florida, USA
| | | | | | | | | | | | - Jayakrishnan Nair
- Breathing Research and Therapeutics Center and Department of Physical Therapy, University of Florida, Gainesville, Florida, USA
- McKnight Brain Institute, University of Florida, Gainesville, Florida, USA
- Department of Physical Therapy, Thomas Jefferson University, Philadelphia, Pennsylvania, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center and Department of Physical Therapy, University of Florida, Gainesville, Florida, USA
- McKnight Brain Institute, University of Florida, Gainesville, Florida, USA
| | - Emily J Fox
- Breathing Research and Therapeutics Center and Department of Physical Therapy, University of Florida, Gainesville, Florida, USA
- Brooks Rehabilitation, Jacksonville, Florida, USA
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12
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Tan AQ, Tuthill C, Corsten AN, Barth S, Trumbower RD. A single sequence of intermittent hypoxia does not alter stretch reflex excitability in able-bodied individuals. Exp Physiol 2024; 109:576-587. [PMID: 38356241 PMCID: PMC10988685 DOI: 10.1113/ep091531] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Accepted: 12/21/2023] [Indexed: 02/16/2024]
Abstract
Spasticity attributable to exaggerated stretch reflex pathways, particularly affecting the ankle plantar flexors, often impairs overground walking in persons with incomplete spinal cord injury. Compelling evidence from rodent models underscores how exposure to acute intermittent hypoxia (AIH) can provide a unique medium to induce spinal plasticity in key inhibitory pathways mediating stretch reflex excitability and potentially affect spasticity. In this study, we quantify the effects of a single exposure to AIH on the stretch reflex in able-bodied individuals. We hypothesized that a single sequence of AIH will increase the stretch reflex excitability of the soleus muscle during ramp-and-hold angular perturbations applied to the ankle joint while participants perform passive and volitionally matched contractions. Our results revealed that a single AIH exposure did not significantly change the stretch reflex excitability during both passive and active matching conditions. Furthermore, we found that able-bodied individuals increased their stretch reflex response from passive to active matching conditions after both sham and AIH exposures. Together, these findings suggest that a single AIH exposure might not engage inhibitory pathways sufficiently to alter stretch reflex responses in able-bodied persons. However, the generalizability of our present findings requires further examination during repetitive exposures to AIH along with potential reflex modulation during functional movements, such as overground walking.
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Affiliation(s)
- Andrew Q. Tan
- Department of Integrative PhysiologyUniversity of ColoradoBoulderColoradoUSA
| | - Christopher Tuthill
- Department of Physical Medicine and RehabilitationHarvard Medical SchoolBostonMassachusettsUSA
- Department of Physical Medicine and RehabilitationINSPIRE LaboratorySpaulding Rehabilitation HospitalBostonMassachusettsUSA
| | - Anthony N. Corsten
- Department of Physical Medicine and RehabilitationINSPIRE LaboratorySpaulding Rehabilitation HospitalBostonMassachusettsUSA
| | - Stella Barth
- Department of Physical Medicine and RehabilitationINSPIRE LaboratorySpaulding Rehabilitation HospitalBostonMassachusettsUSA
| | - Randy D. Trumbower
- Department of Physical Medicine and RehabilitationHarvard Medical SchoolBostonMassachusettsUSA
- Department of Physical Medicine and RehabilitationINSPIRE LaboratorySpaulding Rehabilitation HospitalBostonMassachusettsUSA
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13
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Harmon JN, Chandran P, Chandrasekaran A, Hyde JE, Hernandez GJ, Reed MJ, Bruce MF, Khaing ZZ. Contrast-enhanced ultrasound imaging detects anatomical and functional changes in rat cervical spine microvasculature with normal aging. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.12.584672. [PMID: 38559128 PMCID: PMC10980054 DOI: 10.1101/2024.03.12.584672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Normal aging is associated with significant deleterious cerebrovascular changes; these have been implicated in disease pathogenesis and increased susceptibility to ischemic injury. While these changes are well documented in the brain, few studies have been conducted in the spinal cord. Here, we utilize specialized contrast-enhanced ultrasound (CEUS) imaging to investigate age-related changes in cervical spinal vascular anatomy and hemodynamics in male Fisher 344 rats, a common strain in aging research. Aged rats (24-26 mo., N=6) exhibited significant tortuosity in the anterior spinal artery and elevated vascular resistance compared to adults (4-6 mo., N=6; tortuosity index 2.20±0.15 vs 4.74±0.45, p<0.05). Baseline blood volume was lower in both larger vessels and the microcirculation in the aged cohort, specifically in white matter (4.44e14±1.37e13 vs 3.66e14±2.64e13 CEUS bolus AUC, p<0.05). To elucidate functional differences, animals were exposed to a hypoxia challenge; whereas adult rats exhibited significant functional hyperemia in both gray and white matter (GM: 1.13±0.10-fold change from normoxia, p<0.05; WM: 1.16±0.13, p<0.05), aged rats showed no response. Immunohistochemistry revealed reduced pericyte coverage and activated microglia behavior in aged rats, which may partially explain the lack of vascular response. This study provides the first in vivo description of age-related hemodynamic differences in the cervical spinal cord.
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Affiliation(s)
- Jennifer N. Harmon
- Department of Neurological Surgery, University of Washington, 1959 NE Pacific St., Seattle, WA, USA
| | - Preeja Chandran
- Department of Neurological Surgery, University of Washington, 1959 NE Pacific St., Seattle, WA, USA
| | | | - Jeffrey E. Hyde
- Department of Neurological Surgery, University of Washington, 1959 NE Pacific St., Seattle, WA, USA
| | - Gustavo J. Hernandez
- Department of Neurological Surgery, University of Washington, 1959 NE Pacific St., Seattle, WA, USA
| | - May J. Reed
- Department of Gerontology and Geriatric Medicine, University of Washington, Seattle, WA, USA
| | - Matthew F. Bruce
- Applied Physics Laboratory, University of Washington, Seattle, WA, USA
| | - Zin Z. Khaing
- Department of Neurological Surgery, University of Washington, 1959 NE Pacific St., Seattle, WA, USA
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14
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Miller S, Lopez EJ, Grittner JML, Dougherty BJ. Low level CO 2 supplementation maintains isocapnia and reveals ventilatory long-term facilitation in rats. Respir Physiol Neurobiol 2024; 320:104185. [PMID: 37935342 PMCID: PMC10842720 DOI: 10.1016/j.resp.2023.104185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Revised: 10/23/2023] [Accepted: 10/30/2023] [Indexed: 11/09/2023]
Abstract
Acute, intermittent hypoxia (AIH) induces ventilatory long-term facilitation (vLTF) in awake, freely behaving rats under poikilocapnic and isocapnic experimental conditions. Establishing pre-clinical methods for vLTF induction that more closely align with successful protocols in humans and anesthetized rats would minimize dissonance in experimental findings and improve translational aspects of vLTF. Here, we tested several levels of low-dose CO2 supplementation during and after AIH to determine 1) the lowest amount of inspired CO2 that would maintain isocapnia in rats during a vLTF protocol, and 2) the net impact of supplemental CO2 on vLTF expression. Rats received one of four levels of inspired CO2 (0%, 0.5%, 1% or 2%) administered during AIH and for the 60 min following AIH to quantify vLTF. Our findings indicated that 2% inspired CO2 was sufficient to maintain isocapnia across the AIH protocol and reveal significant vLTF. These findings provide evidence-based support for using 2% supplemental CO2 during and after AIH when assessing vLTF in rats.
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Affiliation(s)
- Shawn Miller
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Edgar Juarez Lopez
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Jessica M L Grittner
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA; Graduate Program in Rehabilitation Science, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Brendan J Dougherty
- Division of Physical Therapy, Department of Rehabilitation Medicine, University of Minnesota Medical School, Minneapolis, MN, USA.
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15
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Thakre PP, Fuller DD. Pattern sensitivity of ampakine-hypoxia interactions for evoking phrenic motor facilitation in anesthetized rat. J Neurophysiol 2024; 131:216-224. [PMID: 38116608 DOI: 10.1152/jn.00315.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 12/13/2023] [Accepted: 12/18/2023] [Indexed: 12/21/2023] Open
Abstract
Repeated hypoxic episodes can produce a sustained (>60 min) increase in neural drive to the diaphragm. The requirement of repeated hypoxic episodes (vs. a single episode) to produce phrenic motor facilitation (pMF) can be removed by allosteric modulation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors using ampakines. We hypothesized that the ampakine-hypoxia interaction resulting in pMF requires that ampakine dosing precedes the onset of hypoxia. Phrenic nerve recordings were made from urethane-anesthetized, mechanically ventilated, and vagotomized adult male Sprague-Dawley rats during isocapnic conditions. Ampakine CX717 (15 mg/kg iv) was given immediately before (n = 8), during (n = 8), or immediately after (n = 8) a 5-min hypoxic episode (arterial oxygen partial pressure 40-45 mmHg). Ampakine before hypoxia (Aprior) resulted in a sustained increase in inspiratory phrenic burst amplitude (i.e., pMF) reaching +70 ± 21% above baseline (BL) after 60 min. This was considerably greater than corresponding values in the groups receiving ampakine during hypoxia (+28 ± 47% above BL, P = 0.005 vs. Aprior) or after hypoxia (+23 ± 40% above BL, P = 0.005 vs. Aprior). Phrenic inspiratory burst rate, heart rate, and systolic, diastolic, and mean arterial pressure (mmHg) were similar across the three treatment groups (all P > 0.3, treatment effect). We conclude that the presentation order of ampakine and hypoxia impacts the magnitude of pMF, with ampakine pretreatment evoking the strongest response. Ampakine pretreatment may have value in the context of hypoxia-based neurorehabilitation strategies.NEW & NOTEWORTHY Phrenic motor facilitation (pMF) is evoked after repeated episodes of brief hypoxia. pMF can also be induced when an allosteric modulator of AMPA receptors (ampakine) is intravenously delivered immediately before a single brief hypoxic episode. Here we show that ampakine delivery before hypoxia (vs. during or after hypoxia) evokes the largest pMF with minimal impact on arterial blood pressure and heart rate. Ampakine pretreatment may have value in the context of hypoxia-based neurorehabilitation strategies.
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Affiliation(s)
- Prajwal P Thakre
- Department of Physical Therapy, University of Florida, Gainesville, Florida, United States
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
- McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
| | - David D Fuller
- Department of Physical Therapy, University of Florida, Gainesville, Florida, United States
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
- McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
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16
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Muter WM, Mansson L, Tuthill C, Aalla S, Barth S, Evans E, McKenzie K, Prokup S, Yang C, Sandhu M, Rymer WZ, Edgerton VR, Gad P, Mitchell GS, Wu SS, Shan G, Jayaraman A, Trumbower RD. A Research Protocol to Study the Priming Effects of Breathing Low Oxygen on Enhancing Training-Related Gains in Walking Function for Persons With Spinal Cord Injury: The BO 2ST Trial. Neurotrauma Rep 2023; 4:736-750. [PMID: 38028272 PMCID: PMC10659019 DOI: 10.1089/neur.2023.0036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2023] Open
Abstract
Brief episodes of low oxygen breathing (therapeutic acute intermittent hypoxia; tAIH) may serve as an effective plasticity-promoting primer to enhance the effects of transcutaneous spinal stimulation-enhanced walking therapy (WALKtSTIM) in persons with chronic (>1 year) spinal cord injury (SCI). Pre-clinical studies in rodents with SCI show that tAIH and WALKtSTIM therapies harness complementary mechanisms of plasticity to maximize walking recovery. Here, we present a multi-site clinical trial protocol designed to examine the influence of tAIH + WALKtSTIM on walking recovery in persons with chronic SCI. We hypothesize that daily (eight sessions, 2 weeks) tAIH + WALKtSTIM will elicit faster, more persistent improvements in walking recovery than either treatment alone. To test our hypothesis, we are conducting a placebo-controlled clinical trial on 60 SCI participants who randomly receive one of three interventions: tAIH + WALKtSTIM; Placebo + WALKtSTIM; and tAIH + WALKtSHAM. Participants receive daily tAIH (fifteen 90-sec episodes at 10% O2 with 60-sec intervals at 21% O2) or daily placebo (fifteen 90-sec episodes at 21% O2 with 60-sec intervals at 21% O2) before a 45-min session of WALKtSTIM or WALKtSHAM. Our primary outcome measures assess walking speed (10-Meter Walk Test), endurance (6-Minute Walk Test), and balance (Timed Up and Go Test). For safety, we also measure pain levels, spasticity, sleep behavior, cognition, and rates of systemic hypertension and autonomic dysreflexia. Assessments occur before, during, and after sessions, as well as at 1, 4, and 8 weeks post-intervention. Results from this study extend our understanding of the functional benefits of tAIH priming by investigating its capacity to boost the neuromodulatory effects of transcutaneous spinal stimulation on restoring walking after SCI. Given that there is no known cure for SCI and no single treatment is sufficient to overcome walking deficits, there is a critical need for combinatorial treatments that accelerate and anchor walking gains in persons with lifelong SCI. Trial Registration ClinicalTrials.gov, NCT05563103.
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Affiliation(s)
- William M. Muter
- Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
| | - Linda Mansson
- Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, Massachusetts, USA
| | - Christopher Tuthill
- Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, Massachusetts, USA
| | - Shreya Aalla
- Shirley Ryan AbilityLab, Max Nader Center for Rehabilitation Technologies and Outcomes Research, Chicago, Illinois, USA
| | - Stella Barth
- Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
- UMass Chan Medical School, University of Massachusetts, Worcester, Massachusetts, USA
| | - Emily Evans
- Department of Physical Therapy, Boston University, Boston, Massachusetts, USA
| | - Kelly McKenzie
- Shirley Ryan AbilityLab, Max Nader Center for Rehabilitation Technologies and Outcomes Research, Chicago, Illinois, USA
| | - Sara Prokup
- Shirley Ryan AbilityLab, Max Nader Center for Rehabilitation Technologies and Outcomes Research, Chicago, Illinois, USA
| | - Chen Yang
- Shirley Ryan AbilityLab, Max Nader Center for Rehabilitation Technologies and Outcomes Research, Chicago, Illinois, USA
| | - Milap Sandhu
- Shirley Ryan AbilityLab, Max Nader Center for Rehabilitation Technologies and Outcomes Research, Chicago, Illinois, USA
| | - W. Zev Rymer
- Shirley Ryan AbilityLab, Max Nader Center for Rehabilitation Technologies and Outcomes Research, Chicago, Illinois, USA
| | - Victor R. Edgerton
- Department of Integrative Biology and Physiology, University of California–Los Angeles, Los Angeles, California, USA
- SpineX Inc., Northridge, California, USA
| | - Parag Gad
- Department of Integrative Biology and Physiology, University of California–Los Angeles, Los Angeles, California, USA
- SpineX Inc., Northridge, California, USA
| | - Gordon S. Mitchell
- Department of Physical Therapy, University of Florida, Gainesville, Florida, USA
| | - Samuel S. Wu
- Department of Biostatistics, University of Florida, Gainesville, Florida, USA
| | - Guogen Shan
- Department of Biostatistics, University of Florida, Gainesville, Florida, USA
| | - Arun Jayaraman
- Shirley Ryan AbilityLab, Max Nader Center for Rehabilitation Technologies and Outcomes Research, Chicago, Illinois, USA
| | - Randy D. Trumbower
- Spaulding Rehabilitation Hospital, Charlestown, Massachusetts, USA
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, Massachusetts, USA
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17
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Panza GS, Burtscher J, Zhao F. Intermittent hypoxia: a call for harmonization in terminology. J Appl Physiol (1985) 2023; 135:886-890. [PMID: 37560767 PMCID: PMC10642510 DOI: 10.1152/japplphysiol.00458.2023] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 07/24/2023] [Accepted: 08/03/2023] [Indexed: 08/11/2023] Open
Abstract
Mild intermittent hypoxia may be a potent novel strategy to improve cardiovascular function, motor and cognitive function, and altitude acclimatization. However, there is still a stigma surrounding the field of intermittent hypoxia (IH). Major contributors to this stigma may be due to the overlapping terminology, heterogeneous methodological approaches, and an almost dogmatic focus on different mechanistic underpinnings in different fields of research. Many clinicians and investigators explore the pathophysiological outcomes following long-term exposure to IH in an attempt to improve our understanding of sleep apnea (SA) and develop new treatment plans. However, others use IH as a tool to improve physiological outcomes such as blood pressure, motor function, and altitude acclimatization. Unfortunately, studies investigating the pathophysiology of SA or the potential benefit of IH use similar, unstandardized terminologies facilitating a confusion surrounding IH protocols and the intentions of various studies. In this perspective paper, we aim to highlight IH terminology-related issues with the aim of spurring harmonization of the terminology used in the field of IH research to account for distinct outcomes of hypoxia exposure depending on protocol and individuum.
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Affiliation(s)
- Gino S Panza
- Department of Research and Development, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan, United States
- Department of Health Care Sciences, Program of Occupational Therapy, Wayne State University, Detroit, Michigan, United States
| | - Johannes Burtscher
- Institute of Sport Sciences, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland
| | - Fei Zhao
- Department of Research and Development, John D. Dingell Veterans Affairs Medical Center, Detroit, Michigan, United States
- Department of Health Care Sciences, Program of Occupational Therapy, Wayne State University, Detroit, Michigan, United States
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18
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Perim RR, Vinit S, Mitchell GS. Cervical spinal hemisection effects on spinal tissue oxygenation and long-term facilitation of phrenic, renal and splanchnic sympathetic nerve activity. Exp Neurol 2023; 368:114478. [PMID: 37451584 DOI: 10.1016/j.expneurol.2023.114478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 06/28/2023] [Accepted: 07/12/2023] [Indexed: 07/18/2023]
Abstract
HYPOTHESES Moderate acute intermittent hypoxia (mAIH) elicits plasticity in both respiratory (phrenic long-term facilitation; pLTF) and sympathetic nerve activity (sympLTF) in rats. Although mAIH produces pLTF in normal rats, inconsistent results are reported after cervical spinal cord injury (cSCI), possibly due to greater spinal tissue hypoxia below the injury site. There are no reports concerning cSCI effects on sympLTF. Since mAIH is being explored as a therapeutic modality to restore respiratory and non-respiratory movements in humans with chronic SCI, both effects are important. To understand cSCI effects on mAIH-induced pLTF and sympLTF, partial or complete C2 spinal hemisections (C2Hx) were performed and, 2 weeks later, we assessed: 1) ipsilateral cervical spinal tissue oxygen tension; 2) ipsilateral & contralateral pLTF; and 3) ipsilateral sympLTF in splanchnic and renal sympathetic nerves. METHODS Male Sprague-Dawley rats were studied intact, or after partial (single slice) or complete C2Hx (slice with ∼1 mm aspiration). Two weeks post-C2Hx, rats were anesthetized and prepared for recordings of bilateral phrenic nerve activity and spinal tissue oxygen pressure (PtO2). Splanchnic and renal sympathetic nerve activity was recorded in intact and complete C2Hx rats. RESULTS Spinal PtO2 near phrenic motor neurons was decreased after C2Hx, an effect most prominent with complete vs. partial injuries; baseline PtO2 was positively correlated with mean arterial pressure. Complete C2Hx impaired ipsilateral but not contralateral pLTF; with partial C2Hx, ipsilateral pLTF was unaffected. In intact rats, mAIH elicited splanchnic and renal sympLTF. Complete C2Hx had minimal impact on baseline ipsilateral splanchnic or renal sympathetic nerve activity and renal, but not splanchnic, sympLTF remained intact. CONCLUSION Greater tissue hypoxia likely impairs pLTF and splanchnic sympLTF post-C2Hx, although renal sympLTF remains intact. Increased sympathetic nerve activity post-mAIH may have therapeutic benefits in individuals living with chronic SCI since anticipated elevations in systemic blood pressure may mitigate hypotension characteristic of people living with SCI.
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Affiliation(s)
- Raphael R Perim
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL, USA
| | - Stéphane Vinit
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL, USA.
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19
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Dempsey JA, Welch JF. Control of Breathing. Semin Respir Crit Care Med 2023; 44:627-649. [PMID: 37494141 DOI: 10.1055/s-0043-1770342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/28/2023]
Abstract
Substantial advances have been made recently into the discovery of fundamental mechanisms underlying the neural control of breathing and even some inroads into translating these findings to treating breathing disorders. Here, we review several of these advances, starting with an appreciation of the importance of V̇A:V̇CO2:PaCO2 relationships, then summarizing our current understanding of the mechanisms and neural pathways for central rhythm generation, chemoreception, exercise hyperpnea, plasticity, and sleep-state effects on ventilatory control. We apply these fundamental principles to consider the pathophysiology of ventilatory control attending hypersensitized chemoreception in select cardiorespiratory diseases, the pathogenesis of sleep-disordered breathing, and the exertional hyperventilation and dyspnea associated with aging and chronic diseases. These examples underscore the critical importance that many ventilatory control issues play in disease pathogenesis, diagnosis, and treatment.
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Affiliation(s)
- Jerome A Dempsey
- John Rankin Laboratory of Pulmonary Medicine, Department of Population Health Sciences, University of Wisconsin, Madison, Wisconsin
| | - Joseph F Welch
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom
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20
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Afsharipour B, Pearcey GEP, Rymer WZ, Sandhu MS. Acute intermittent hypoxia enhances strength, and modulates spatial distribution of muscle activation in persons with chronic incomplete spinal cord injury. Exp Neurol 2023; 367:114452. [PMID: 37271217 DOI: 10.1016/j.expneurol.2023.114452] [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: 03/13/2023] [Revised: 05/10/2023] [Accepted: 05/30/2023] [Indexed: 06/06/2023]
Abstract
Acute intermittent hypoxia (AIH) is an emerging technique for facilitating neural plasticity in individuals with chronic incomplete spinal cord injury (iSCI). A single sequence of AIH enhances hand grip strength and ankle plantarflexion torque, but underlying mechanisms are not yet clear. We sought to examine how AIH-induced changes in magnitude and spatial distribution of the electromyogram (EMG) of the biceps and triceps brachii contributes to improved strength. Seven individuals with iSCI visited the laboratory on two occasions, and received either AIH or Sham AIH intervention in a randomized order. AIH consisted of 15 brief (∼60s) periods of low oxygen (fraction of inspired O2 = 0.09) alternating with 60s of normoxia, whereas Sham AIH consisted of repeated exposures to normoxic air. High-density surface EMG of biceps and triceps brachii was recorded during maximal elbow flexion and extension. We then generated spatial maps which distinguished active muscle regions prior to and 60 min after AIH or Sham AIH. After an AIH sequence, elbow flexion and extension forces increased by 91.7 ± 88.4% and 51.7 ± 57.8% from baseline, respectively, whereas there was no difference after Sham AIH. Changes in strength were associated with an altered spatial distribution of EMG and increased root mean squared EMG amplitude in both biceps and triceps brachii muscles. These data suggest that altered motor unit activation profiles may underlie improved volitional strength after a single dose of AIH and warrant further investigation using single motor unit analysis techniques to further elucidate mechanisms of AIH-induced plasticity.
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Affiliation(s)
- Babak Afsharipour
- Department of Biomedical Engineering, Faculty of Medicine and Dentistry, University of Alberta, Canada; Shirley Ryan AbilityLab, Chicago, IL, USA.
| | - Gregory E P Pearcey
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, NL, Canada; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; Shirley Ryan AbilityLab, Chicago, IL, USA.
| | - W Zev Rymer
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
| | - Milap S Sandhu
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
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21
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Marciante AB, Seven YB, Kelly MN, Perim RR, Mitchell GS. Magnitude and Mechanism of Phrenic Long-term Facilitation Shift Between Daily Rest Versus Active Phase. FUNCTION 2023; 4:zqad041. [PMID: 37753182 PMCID: PMC10519274 DOI: 10.1093/function/zqad041] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 07/26/2023] [Accepted: 07/27/2023] [Indexed: 09/28/2023] Open
Abstract
Plasticity is a fundamental property of the neural system controlling breathing. One key example of respiratory motor plasticity is phrenic long-term facilitation (pLTF), a persistent increase in phrenic nerve activity elicited by acute intermittent hypoxia (AIH). pLTF can arise from distinct cell signaling cascades initiated by serotonin versus adenosine receptor activation, respectively, and interact via powerful cross-talk inhibition. Here, we demonstrate that the daily rest/active phase and the duration of hypoxic episodes within an AIH protocol have profound impact on the magnitude and mechanism of pLTF due to shifts in serotonin/adenosine balance. Using the historical "standard" AIH protocol (3, 5-min moderate hypoxic episodes), we demonstrate that pLTF magnitude is unaffected by exposure in the midactive versus midrest phase, yet the mechanism driving pLTF shifts from serotonin-dominant (midrest) to adenosine-dominant (midactive). This mechanistic "flip" results from combined influences of hypoxia-evoked adenosine release and daily fluctuations in basal spinal adenosine. Since AIH evokes less adenosine with shorter (15, 1-min) hypoxic episodes, midrest pLTF is amplified due to diminished adenosine constraint on serotonin-driven plasticity; in contrast, elevated background adenosine during the midactive phase suppresses serotonin-dominant pLTF. These findings demonstrate the importance of the serotonin/adenosine balance in regulating the amplitude and mechanism of AIH-induced pLTF. Since AIH is emerging as a promising therapeutic modality to restore respiratory and nonrespiratory movements in people with spinal cord injury or ALS, knowledge of how time-of-day and hypoxic episode duration impact the serotonin/adenosine balance and the magnitude and mechanism of pLTF has profound biological, experimental, and translational implications.
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Affiliation(s)
- Alexandria B Marciante
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA
| | - Yasin B Seven
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA
| | - Mia N Kelly
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA
| | - Raphael R Perim
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA
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22
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Jacob DW, Morgenthaler LD, Harper JL, Limberg JK. The forearm vascular response to sympathetic activation is attenuated in female, but not male, participants following acute intermittent hypoxia. J Appl Physiol (1985) 2023; 135:352-361. [PMID: 37410902 PMCID: PMC10396222 DOI: 10.1152/japplphysiol.00760.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 06/05/2023] [Accepted: 06/30/2023] [Indexed: 07/08/2023] Open
Abstract
Acute exposure to hypoxia promotes both an increase in sympathetic nervous system activity (SNA) and local vasodilation. In rodents, intermittent hypoxia (IH)-mediated increases in SNA are associated with an increase in blood pressure in males but not females; notably, the protective effect of female sex is lost following ovariectomy. These data suggest the vascular response to hypoxia and/or SNA following IH may be sex- and/or hormone specific-although mechanisms are unclear. We hypothesized that hypoxia-mediated vasodilation and SNA-mediated vasoconstriction would be unchanged following acute IH in male adults. We further hypothesized that hypoxic vasodilation would be augmented and SNA-mediated vasoconstriction would be attenuated in female adults following acute IH, with the greatest effect when endogenous estradiol was high. Twelve male (25 ± 1 yr) and 10 female (25 ± 1 yr) participants underwent 30 min of IH. Females were studied in a low (early follicular) and high (late follicular) estradiol state. Preceding and following IH, participants completed two trials [steady-state hypoxia and cold pressor test (CPT)], where forearm blood flow and blood pressure were measured and used to determine forearm vascular conductance (FVC). The FVC response to hypoxia (P = 0.67) and sympathetic activation (P = 0.73) were unchanged following IH in males. There was no effect of IH on hypoxic vasodilation in females, regardless of estradiol state (P = 0.75). In contrast, the vascular response to sympathetic activation was attenuated in females following IH (P = 0.02), independent of estradiol state (P = 0.65). Present data highlight sex-related differences in neurovascular responsiveness following acute IH.NEW & NOTEWORTHY We examined the effects of acute intermittent hypoxia (AIH) on the vascular response to sympathetic activation and acute hypoxia. Present findings show, despite no effect of AIH on the vascular response to hypoxia, the forearm vasoconstrictor response to acute sympathetic activation is attenuated in females following AIH, independent of estradiol state. These data provide mechanistic understanding of potential benefits of AIH, as well as the impact of biological sex.
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Affiliation(s)
- Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, United States
| | - Leandra D Morgenthaler
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, United States
| | - Jennifer L Harper
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, United States
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri, United States
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States
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23
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Kang J, Lu N, Yang S, Guo B, Zhu Y, Wu S, Huang X, Wong-Riley MTT, Liu YY. Alterations in synapses and mitochondria induced by acute or chronic intermittent hypoxia in the pre-Bötzinger complex of rats: an ultrastructural triple-labeling study with immunocytochemistry and histochemistry. Front Cell Neurosci 2023; 17:1132241. [PMID: 37396926 PMCID: PMC10312010 DOI: 10.3389/fncel.2023.1132241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Accepted: 06/05/2023] [Indexed: 07/04/2023] Open
Abstract
Introduction The pre-Bötzinger complex (pre-BötC), a kernel of inspiratory rhythmogenesis, is a heterogeneous network with excitatory glutamatergic and inhibitory GABAergic and glycinergic neurons. Inspiratory rhythm generation relies on synchronous activation of glutamatergic neuron, whilst inhibitory neurons play a critical role in shaping the breathing pattern, endowing the rhythm with flexibility in adapting to environmental, metabolic, and behavioral needs. Here we report ultrastructural alterations in excitatory, asymmetric synapses (AS) and inhibitory, symmetric synapses (SS), especially perforated synapses with discontinuous postsynaptic densities (PSDs) in the pre-BötC in rats exposed to daily acute intermittent hypoxia (dAIH) or chronic (C) IH. Methods We utilized for the first time a combination of somatostatin (SST) and neurokinin 1 receptor (NK1R) double immunocytochemistry with cytochrome oxidase histochemistry, to reveal synaptic characteristics and mitochondrial dynamic in the pre-BötC. Results We found perforated synapses with synaptic vesicles accumulated in distinct pools in apposition to each discrete PSD segments. dAIH induced significant increases in the PSD size of macular AS, and the proportion of perforated synapses. AS were predominant in the dAIH group, whereas SS were in a high proportion in the CIH group. dAIH significantly increased SST and NK1R expressions, whereas CIH led to a decrease. Desmosome-like contacts (DLC) were characterized for the first time in the pre-BötC. They were distributed alongside of synapses, especially SS. Mitochondria appeared in more proximity to DLC than synapses, suggestive of a higher energy demand of the DLC. Findings of single spines with dual AS and SS innervation provide morphological evidence of excitation-inhibition interplay within a single spine in the pre-BötC. In particular, we characterized spine-shaft microdomains of concentrated synapses coupled with mitochondrial positioning that could serve as a structural basis for synchrony of spine-shaft communication. Mitochondria were found within spines and ultrastructural features of mitochondrial fusion and fission were depicted for the first time in the pre-BötC. Conclusion We provide ultrastructural evidence of excitation-inhibition synapses in shafts and spines, and DLC in association with synapses that coincide with mitochondrial dynamic in their contribution to respiratory plasticity in the pre-BötC.
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Affiliation(s)
- Junjun Kang
- Department of Neurobiology, The Fourth Military Medical University, Xi’an, China
| | - Naining Lu
- Department of Neurobiology, The Fourth Military Medical University, Xi’an, China
| | - Shoujing Yang
- Department of Pathology, The Fourth Military Medical University, Xi’an, China
| | - Baolin Guo
- Department of Neurobiology, The Fourth Military Medical University, Xi’an, China
| | - Yuanyuan Zhu
- Department of Neurobiology, The Fourth Military Medical University, Xi’an, China
| | - Shengxi Wu
- Department of Neurobiology, The Fourth Military Medical University, Xi’an, China
| | - Xiaofeng Huang
- Department of Pathology, Xi’an Gaoxin Hospital, Xi’an, China
| | - Margaret T. T. Wong-Riley
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI, United States
| | - Ying-Ying Liu
- Department of Neurobiology, The Fourth Military Medical University, Xi’an, China
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Nair J, Welch JF, Marciante AB, Hou T, Lu Q, Fox EJ, Mitchell GS. APOE4, Age, and Sex Regulate Respiratory Plasticity Elicited by Acute Intermittent Hypercapnic-Hypoxia. FUNCTION 2023; 4:zqad026. [PMID: 37575478 PMCID: PMC10413930 DOI: 10.1093/function/zqad026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 05/22/2023] [Accepted: 05/25/2023] [Indexed: 08/15/2023] Open
Abstract
Rationale Acute intermittent hypoxia (AIH) shows promise for enhancing motor recovery in chronic spinal cord injuries and neurodegenerative diseases. However, human trials of AIH have reported significant variability in individual responses. Objectives Identify individual factors (eg, genetics, age, and sex) that determine response magnitude of healthy adults to an optimized AIH protocol, acute intermittent hypercapnic-hypoxia (AIHH). Methods In 17 healthy individuals (age = 27 ± 5 yr), associations between individual factors and changes in the magnitude of AIHH (15, 1-min O2 = 9.5%, CO2 = 5% episodes) induced changes in diaphragm motor-evoked potential (MEP) amplitude and inspiratory mouth occlusion pressures (P0.1) were evaluated. Single nucleotide polymorphisms (SNPs) in genes linked with mechanisms of AIH induced phrenic motor plasticity (BDNF, HTR2A, TPH2, MAOA, NTRK2) and neuronal plasticity (apolipoprotein E, APOE) were tested. Variations in AIHH induced plasticity with age and sex were also analyzed. Additional experiments in humanized (h)ApoE knock-in rats were performed to test causality. Results AIHH-induced changes in diaphragm MEP amplitudes were lower in individuals heterozygous for APOE4 (i.e., APOE3/4) compared to individuals with other APOE genotypes (P = 0.048) and the other tested SNPs. Males exhibited a greater diaphragm MEP enhancement versus females, regardless of age (P = 0.004). Additionally, age was inversely related with change in P0.1 (P = 0.007). In hApoE4 knock-in rats, AIHH-induced phrenic motor plasticity was significantly lower than hApoE3 controls (P < 0.05). Conclusions APOE4 genotype, sex, and age are important biological determinants of AIHH-induced respiratory motor plasticity in healthy adults. Addition to Knowledge Base AIH is a novel rehabilitation strategy to induce functional recovery of respiratory and non-respiratory motor systems in people with chronic spinal cord injury and/or neurodegenerative disease. Figure 5 Since most AIH trials report considerable inter-individual variability in AIH outcomes, we investigated factors that potentially undermine the response to an optimized AIH protocol, AIHH, in healthy humans. We demonstrate that genetics (particularly the lipid transporter, APOE), age and sex are important biological determinants of AIHH-induced respiratory motor plasticity.
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Affiliation(s)
- Jayakrishnan Nair
- Breathing Research and Therapeutics Center, Department of Physical Therapy, University of Florida, Gainesville, 32603, USA
- Department of Physical Therapy, Thomas Jefferson University, Philadelphia, PA, 19107, USA
| | - Joseph F Welch
- Breathing Research and Therapeutics Center, Department of Physical Therapy, University of Florida, Gainesville, 32603, USA
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, 3- B15 2TT, UK
| | - Alexandria B Marciante
- Breathing Research and Therapeutics Center, Department of Physical Therapy, University of Florida, Gainesville, 32603, USA
| | - Tingting Hou
- Department of Biostatistics, University of Florida, Gainesville, 32603, USA
| | - Qing Lu
- Department of Biostatistics, University of Florida, Gainesville, 32603, USA
| | - Emily J Fox
- Breathing Research and Therapeutics Center, Department of Physical Therapy, University of Florida, Gainesville, 32603, USA
- Brooks Rehabilitation, Jacksonville, FL, 32216, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy, University of Florida, Gainesville, 32603, USA
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Michel-Flutot P, Lane MA, Lepore AC, Vinit S. Therapeutic Strategies Targeting Respiratory Recovery after Spinal Cord Injury: From Preclinical Development to Clinical Translation. Cells 2023; 12:1519. [PMID: 37296640 PMCID: PMC10252981 DOI: 10.3390/cells12111519] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Revised: 05/15/2023] [Accepted: 05/29/2023] [Indexed: 06/12/2023] Open
Abstract
High spinal cord injuries (SCIs) lead to permanent functional deficits, including respiratory dysfunction. Patients living with such conditions often rely on ventilatory assistance to survive, and even those that can be weaned continue to suffer life-threatening impairments. There is currently no treatment for SCI that is capable of providing complete recovery of diaphragm activity and respiratory function. The diaphragm is the main inspiratory muscle, and its activity is controlled by phrenic motoneurons (phMNs) located in the cervical (C3-C5) spinal cord. Preserving and/or restoring phMN activity following a high SCI is essential for achieving voluntary control of breathing. In this review, we will highlight (1) the current knowledge of inflammatory and spontaneous pro-regenerative processes occurring after SCI, (2) key therapeutics developed to date, and (3) how these can be harnessed to drive respiratory recovery following SCIs. These therapeutic approaches are typically first developed and tested in relevant preclinical models, with some of them having been translated into clinical studies. A better understanding of inflammatory and pro-regenerative processes, as well as how they can be therapeutically manipulated, will be the key to achieving optimal functional recovery following SCIs.
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Affiliation(s)
- Pauline Michel-Flutot
- END-ICAP, UVSQ, Inserm, Université Paris-Saclay, 78000 Versailles, France;
- Department of Neuroscience, Jefferson Synaptic Biology Center, Vickie and Jack Farber Institute for Neuroscience, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA;
| | - Michael A. Lane
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA;
| | - Angelo C. Lepore
- Department of Neuroscience, Jefferson Synaptic Biology Center, Vickie and Jack Farber Institute for Neuroscience, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA;
| | - Stéphane Vinit
- END-ICAP, UVSQ, Inserm, Université Paris-Saclay, 78000 Versailles, France;
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Casanova A, Wevers A, Navarro-Ledesma S, Pruimboom L. Mitochondria: It is all about energy. Front Physiol 2023; 14:1114231. [PMID: 37179826 PMCID: PMC10167337 DOI: 10.3389/fphys.2023.1114231] [Citation(s) in RCA: 31] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Accepted: 03/29/2023] [Indexed: 05/15/2023] Open
Abstract
Mitochondria play a key role in both health and disease. Their function is not limited to energy production but serves multiple mechanisms varying from iron and calcium homeostasis to the production of hormones and neurotransmitters, such as melatonin. They enable and influence communication at all physical levels through interaction with other organelles, the nucleus, and the outside environment. The literature suggests crosstalk mechanisms between mitochondria and circadian clocks, the gut microbiota, and the immune system. They might even be the hub supporting and integrating activity across all these domains. Hence, they might be the (missing) link in both health and disease. Mitochondrial dysfunction is related to metabolic syndrome, neuronal diseases, cancer, cardiovascular and infectious diseases, and inflammatory disorders. In this regard, diseases such as cancer, Alzheimer's, Parkinson's, amyotrophic lateral sclerosis (ALS), chronic fatigue syndrome (CFS), and chronic pain are discussed. This review focuses on understanding the mitochondrial mechanisms of action that allow for the maintenance of mitochondrial health and the pathways toward dysregulated mechanisms. Although mitochondria have allowed us to adapt to changes over the course of evolution, in turn, evolution has shaped mitochondria. Each evolution-based intervention influences mitochondria in its own way. The use of physiological stress triggers tolerance to the stressor, achieving adaptability and resistance. This review describes strategies that could recover mitochondrial functioning in multiple diseases, providing a comprehensive, root-cause-focused, integrative approach to recovering health and treating people suffering from chronic diseases.
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Affiliation(s)
- Amaloha Casanova
- Department of Physiotherapy, University of Granada, Granada, Spain
- Faculty of Health Sciences, Melilla, Spain
- PNI Europe, The Hague, Netherlands
- Chair of Clinical Psychoneuroimmunology, University of Granada and PNI Europe, Granada, Spain
| | - Anne Wevers
- Department of Physiotherapy, University of Granada, Granada, Spain
- Faculty of Health Sciences, Melilla, Spain
- PNI Europe, The Hague, Netherlands
- Chair of Clinical Psychoneuroimmunology, University of Granada and PNI Europe, Granada, Spain
| | - Santiago Navarro-Ledesma
- Department of Physiotherapy, University of Granada, Granada, Spain
- Faculty of Health Sciences, Melilla, Spain
- PNI Europe, The Hague, Netherlands
- Chair of Clinical Psychoneuroimmunology, University of Granada and PNI Europe, Granada, Spain
| | - Leo Pruimboom
- PNI Europe, The Hague, Netherlands
- Chair of Clinical Psychoneuroimmunology, University of Granada and PNI Europe, Granada, Spain
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Marciante AB, Mitchell GS. Mild inflammation impairs acute intermittent hypoxia-induced phrenic long-term facilitation by a spinal adenosine-dependent mechanism. J Neurophysiol 2023; 129:799-806. [PMID: 36883762 PMCID: PMC10069977 DOI: 10.1152/jn.00035.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 02/23/2023] [Accepted: 02/23/2023] [Indexed: 03/09/2023] Open
Abstract
Inflammation undermines neuroplasticity, including serotonin-dependent phrenic long-term facilitation (pLTF) following moderate acute intermittent hypoxia (mAIH: 3, 5-min episodes, arterial Po2: 40-50 mmHg; 5-min intervals). Mild inflammation elicited by a low dose of the TLR-4 receptor agonist, lipopolysaccharide (LPS; 100 µg/kg, ip), abolishes mAIH-induced pLTF by unknown mechanisms. In the central nervous system, neuroinflammation primes glia, triggering ATP release and extracellular adenosine accumulation. As spinal adenosine 2 A (A2A) receptor activation impairs mAIH-induced pLTF, we hypothesized that spinal adenosine accumulation and A2A receptor activation are necessary in the mechanism whereby LPS impairs pLTF. We report that 24 h after LPS injection in adult male Sprague Dawley rats: 1) adenosine levels increase in ventral spinal segments containing the phrenic motor nucleus (C3-C5; P = 0.010; n = 7/group) and 2) cervical spinal A2A receptor inhibition (MSX-3, 10 µM, 12 µL intrathecal) rescues mAIH-induced pLTF. In LPS vehicle-treated rats (saline, ip), MSX-3 enhanced pLTF versus controls (LPS: 110 ± 16% baseline; controls: 53 ± 6%; P = 0.002; n = 6/group). In LPS-treated rats, pLTF was abolished as expected (4 ± 6% baseline; n = 6), but intrathecal MSX-3 restored pLTF to levels equivalent to MSX-3-treated control rats (120 ± 14% baseline; P < 0.001; n = 6; vs. LPS controls with MSX-3: P = 0.539). Thus, inflammation abolishes mAIH-induced pLTF by a mechanism that requires increased spinal adenosine levels and A2A receptor activation. As repetitive mAIH is emerging as a treatment to improve breathing and nonrespiratory movements in people with spinal cord injury or ALS, A2A inhibition may offset undermining effects of neuroinflammation associated with these neuromuscular disorders.NEW & NOTEWORTHY Mild inflammation undermines motor plasticity elicited by mAIH. In a model of mAIH-induced respiratory motor plasticity (phrenic long-term facilitation; pLTF), we report that inflammation induced by low-dose lipopolysaccharide undermines mAIH-induced pLTF by a mechanism requiring increased cervical spinal adenosine and adenosine 2 A receptor activation. This finding advances the understanding of mechanisms impairing neuroplasticity, potentially undermining the ability to compensate for the onset of lung/neural injury or to harness mAIH as a therapeutic modality.
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Affiliation(s)
- Alexandria B Marciante
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy & McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
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Ostrowski D, Heesch CM, Kline DD, Hasser EM. Nucleus tractus solitarii is required for the development and maintenance of phrenic and sympathetic long-term facilitation after acute intermittent hypoxia. Front Physiol 2023; 14:1120341. [PMID: 36846346 PMCID: PMC9949380 DOI: 10.3389/fphys.2023.1120341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 01/26/2023] [Indexed: 02/11/2023] Open
Abstract
Exposure to acute intermittent hypoxia (AIH) induces prolonged increases (long term facilitation, LTF) in phrenic and sympathetic nerve activity (PhrNA, SNA) under basal conditions, and enhanced respiratory and sympathetic responses to hypoxia. The mechanisms and neurocircuitry involved are not fully defined. We tested the hypothesis that the nucleus tractus solitarii (nTS) is vital to augmentation of hypoxic responses and the initiation and maintenance of elevated phrenic (p) and splanchnic sympathetic (s) LTF following AIH. nTS neuronal activity was inhibited by nanoinjection of the GABAA receptor agonist muscimol before AIH exposure or after development of AIH-induced LTF. AIH but not sustained hypoxia induced pLTF and sLTF with maintained respiratory modulation of SSNA. nTS muscimol before AIH increased baseline SSNA with minor effects on PhrNA. nTS inhibition also markedly blunted hypoxic PhrNA and SSNA responses, and prevented altered sympathorespiratory coupling during hypoxia. Inhibiting nTS neuronal activity before AIH exposure also prevented the development of pLTF during AIH and the elevated SSNA after muscimol did not increase further during or following AIH exposure. Furthermore, nTS neuronal inhibition after the development of AIH-induced LTF substantially reversed but did not eliminate the facilitation of PhrNA. Together these findings demonstrate that mechanisms within the nTS are critical for initiation of pLTF during AIH. Moreover, ongoing nTS neuronal activity is required for full expression of sustained elevations in PhrNA following exposure to AIH although other regions likely also are important. Together, the data indicate that AIH-induced alterations within the nTS contribute to both the development and maintenance of pLTF.
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Affiliation(s)
- Daniela Ostrowski
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States,Department of Biology, Truman State University, Kirksville, MO, United States
| | - Cheryl M. Heesch
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States
| | - David D. Kline
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, United States
| | - Eileen M. Hasser
- Department of Biomedical Sciences, University of Missouri, Columbia, MO, United States,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, United States,*Correspondence: Eileen M. Hasser,
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Agosto-Marlin IM, Nikodemova M, Dale EA, Mitchell GS. BDNF-induced phrenic motor facilitation shifts from PKCθ to ERK dependence with mild systemic inflammation. J Neurophysiol 2023; 129:455-464. [PMID: 36695529 PMCID: PMC9942899 DOI: 10.1152/jn.00345.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Revised: 01/17/2023] [Accepted: 01/19/2023] [Indexed: 01/26/2023] Open
Abstract
Moderate acute intermittent hypoxia (mAIH) elicits a form of phrenic motor plasticity known as phrenic long-term facilitation (pLTF), which requires spinal 5-HT2 receptor activation, ERK/MAP kinase signaling, and new brain-derived neurotrophic factor (BDNF) synthesis. New BDNF protein activates TrkB receptors that normally signal through PKCθ to elicit pLTF. Phrenic motor plasticity elicited by spinal drug administration (e.g., BDNF) is referred to by a more general term: phrenic motor facilitation (pMF). Although mild systemic inflammation elicited by a low lipopolysaccharide (LPS) dose (100 µg/kg; 24 h prior) undermines mAIH-induced pLTF upstream from BDNF protein synthesis, it augments pMF induced by spinal BDNF administration through unknown mechanisms. Here, we tested the hypothesis that mild inflammation shifts BDNF/TrkB signaling from PKCθ to alternative pathways that enhance pMF. We examined the role of three known signaling pathways associated with TrkB (MEK/ERK MAP kinase, PI3 kinase/Akt, and PKCθ) in BDNF-induced pMF in anesthetized, paralyzed, and ventilated Sprague Dawley rats 24 h post-LPS. Spinal PKCθ inhibitor (TIP) attenuated early BDNF-induced pMF (≤30 min), with minimal effect 60-90 min post-BDNF injection. In contrast, MEK inhibition (U0126) abolished BDNF-induced pMF at 60 and 90 min. PI3K/Akt inhibition (PI-828) had no effect on BDNF-induced pMF at any time. Thus, whereas BDNF-induced pMF is exclusively PKCθ-dependent in normal rats, MEK/ERK is recruited by neuroinflammation to sustain, and even augment downstream plasticity. Because AIH is being developed as a therapeutic modality to restore breathing in people living with multiple neurological disorders, it is important to understand how inflammation, a common comorbidity in many traumatic or degenerative central nervous system disorders, impacts phrenic motor plasticity.NEW & NOTEWORTHY We demonstrate that even mild systemic inflammation shifts signaling mechanisms giving rise to BDNF-induced phrenic motor plasticity. This finding has important experimental, biological, and translational implications, particularly since BDNF-dependent spinal plasticity is being translated to restore breathing and nonrespiratory movements in diverse clinical disorders, such as spinal cord injury (SCI) and amyotrophic lateral sclerosis (ALS).
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Affiliation(s)
- Ibis M Agosto-Marlin
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin, United States
| | - Maria Nikodemova
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
- Department of Physical, Therapy University of Florida, Gainesville, Florida, United States
- McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
| | - Erica A Dale
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
- Department of Physiology and Aging, University of Florida, Gainesville, Florida, United States
- McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
| | - Gordon S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin, United States
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida, United States
- Department of Physical, Therapy University of Florida, Gainesville, Florida, United States
- McKnight Brain Institute, University of Florida, Gainesville, Florida, United States
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Zhang X, Xie W, Du W, Liu Y, Lin J, Yin W, Yang L, Yuan F, Zhang R, Liu H, Ma H, Zhang J. Consistent differences in brain structure and functional connectivity in high-altitude native Tibetans and immigrants. Brain Imaging Behav 2023; 17:271-281. [PMID: 36694086 DOI: 10.1007/s11682-023-00759-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 12/13/2022] [Accepted: 01/17/2023] [Indexed: 01/26/2023]
Abstract
It has been well-established that high-altitude (HA) environments affect the human brain; however, the differences in brain structural and functional networks between HA natives and acclimatized immigrants have not been well clarified. In this study, native HA Tibetans were recruited for comparison with Han immigrants (average of 2.3 ± 0.3 years at HA), with lowland residents recruited as controls. Cortical gray matter volume, thickness, and functional connectivity were investigated using magnetic resonance imaging data. In addition, reaction time and correct score in the visual movement task, hematology, and SpO2 were measured. In both Tibetans and HA immigrants vs. lowlanders, decreased SpO2, increased hematocrit and hemoglobin, and increased reaction time and correct score in the visual movement task were detected. In both Tibetans and HA immigrants vs. lowlanders, gray matter volumes and cortical thickness were increased in the left somatosensory and motor cortex, and functional connectivity was decreased in the visual, default mode, subcortical, somatosensory-motor, ventral attention, and subcortical networks. Furthermore, SpO2 increased, hematocrit and hemoglobin decreased, and gray matter volumes and cortical thickness increased in the visual cortex, left motor cortex, and right auditory cortex in native Tibetans compared to immigrants. Movement time and correct score in task were positively correlated with the thickness of the visual cortex. In conclusion, brain structural and functional network difference in both Tibetan natives and HA immigrants were largely consistent, with native Tibetans only showing more intense brain modulation. Different populations acclimatized to HA develop similar brain mechanisms to cope with hostile HA environmental factors.
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Affiliation(s)
- Xinjuan Zhang
- Institute of Brain Diseases and Cognition, School of Medicine, Xiamen University, Xiamen, 361102, China
| | - Weiwei Xie
- Plateau Brain Science Research Centre, Tibet University, Lhasa, 850012, China
| | - Wenrui Du
- Department of Clinical Medicine, School of Medicine, Xiamen University, Xiamen, 361102, China
| | - Yanqiu Liu
- Institute of Brain Diseases and Cognition, School of Medicine, Xiamen University, Xiamen, 361102, China
| | - Jianzhong Lin
- Department of Radiology, Zhongshan Hospital of Xiamen University, School of Medicine, Xiamen University, Xiamen, 361102, China
| | - Wu Yin
- Department of Radiology, Tibet Autonomous Region People's Hospital, Lhasa, Tibet Autonomous Region, 850000, China
| | - Lihui Yang
- Department of Endocrinology, Tibet Autonomous Region People's Hospital, Tibet Autonomous Region, Lhasa, 850000, China
| | - Fengjuan Yuan
- Institute of Brain Diseases and Cognition, School of Medicine, Xiamen University, Xiamen, 361102, China
| | - Ran Zhang
- Institute of Brain Diseases and Cognition, School of Medicine, Xiamen University, Xiamen, 361102, China
| | - Haipeng Liu
- Department of Radiology, Tibet Autonomous Region Women's and Children's Hospital, Tibet Autonomous Region, Lhasa, 850000, China
| | - Hailin Ma
- Plateau Brain Science Research Centre, Tibet University, Lhasa, 850012, China.
| | - Jiaxing Zhang
- Institute of Brain Diseases and Cognition, School of Medicine, Xiamen University, Xiamen, 361102, China.
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Pratscher SD, Sibille KT, Fillingim RB. Conscious connected breathing with breath retention intervention in adults with chronic low back pain: protocol for a randomized controlled pilot study. Pilot Feasibility Stud 2023; 9:15. [PMID: 36694217 PMCID: PMC9872326 DOI: 10.1186/s40814-023-01247-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 01/16/2023] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND Chronic pain is a major source of human suffering, and chronic low back pain (cLBP) is among the most prevalent, costly, and disabling of pain conditions. Due to the significant personal and societal burden and the complex and recurring nature of cLBP, self-management approaches that can be practiced at home are highly relevant to develop and test. The respiratory system is one of the most integrated systems of the body, and breathing is bidirectionally related with stress, emotion, and pain. Thus, the widespread physiological and psychological impact of breathing practices and breathwork interventions hold substantial promise as possible self-management strategies for chronic pain. The primary aim of the current randomized pilot study is to test the feasibility and acceptability of a conscious connected breathing with breath retention intervention compared to a sham control condition. METHODS The rationale and procedures for testing a 5-day conscious connected breathing with breath retention intervention, compared to a deep breathing sham control intervention, in 24 adults (18-65 years) with cLBP is described. Both interventions will be delivered using standardized audio recordings and practiced over 5 days (two times in-person and three times at-home), and both are described as Breathing and Attention Training to reduce possible expectancy and placebo effects common in pain research. The primary outcomes for this study are feasibility and acceptability. Feasibility will be evaluated by determining rates of participant recruitment, adherence, retention, and study assessment completion, and acceptability will be evaluated by assessing participants' satisfaction and helpfulness of the intervention. We will also measure other clinical pain, psychological, behavioral, and physiological variables that are planned to be included in a follow-up randomized controlled trial. DISCUSSION This will be the first study to examine the effects of a conscious connected breathing with breath retention intervention for individuals with chronic pain. The successful completion of this smaller-scale pilot study will provide data regarding the feasibility and acceptability to conduct a subsequent trial testing the efficacy of this breathing self-management practice for adults with cLBP. TRIAL REGISTRATION Clinicaltrials.gov, identifier NCT04740710 . Registered on 5 February 2021.
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Affiliation(s)
- Steven D Pratscher
- Department of Community Dentistry and Behavioral Science, University of Florida, Gainesville, FL, USA.
- Pain Research and Intervention Center of Excellence, University of Florida, Gainesville, FL, USA.
| | - Kimberly T Sibille
- Pain Research and Intervention Center of Excellence, University of Florida, Gainesville, FL, USA
- Department of Physical Medicine & Rehabilitation, University of Florida, Gainesville, FL, USA
| | - Roger B Fillingim
- Department of Community Dentistry and Behavioral Science, University of Florida, Gainesville, FL, USA
- Pain Research and Intervention Center of Excellence, University of Florida, Gainesville, FL, USA
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Nair J, Welch JF, Marciante AB, Hou T, Lu Q, Fox EJ, Mitchell GS. APOE4, Age & Sex Regulate Respiratory Plasticity Elicited By Acute Intermittent Hypercapnic-Hypoxia. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.06.522840. [PMID: 36711653 PMCID: PMC9881941 DOI: 10.1101/2023.01.06.522840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Rationale Acute intermittent hypoxia (AIH) is a promising strategy to induce functional motor recovery following chronic spinal cord injuries and neurodegenerative diseases. Although significant results are obtained, human AIH trials report considerable inter-individual response variability. Objectives Identify individual factors ( e.g. , genetics, age, and sex) that determine response magnitude of healthy adults to an optimized AIH protocol, acute intermittent hypercapnic-hypoxia (AIHH). Methods Associations of individual factors with the magnitude of AIHH (15, 1-min O 2 =9.5%, CO 2 =5% episodes) induced changes in diaphragm motor-evoked potential amplitude (MEP) and inspiratory mouth occlusion pressures (P 0.1 ) were evaluated in 17 healthy individuals (age=27±5 years) compared to Sham. Single nucleotide polymorphisms (SNPs) in genes linked with mechanisms of AIH induced phrenic motor plasticity ( BDNF, HTR 2A , TPH 2 , MAOA, NTRK 2 ) and neuronal plasticity (apolipoprotein E, APOE ) were tested. Variations in AIHH induced plasticity with age and sex were also analyzed. Additional experiments in humanized ( h ) ApoE knock-in rats were performed to test causality. Results AIHH-induced changes in diaphragm MEP amplitudes were lower in individuals heterozygous for APOE 4 ( i.e., APOE 3/4 ) allele versus other APOE genotypes (p=0.048). No significant differences were observed between any other SNPs investigated, notably BDNFval/met ( all p>0.05 ). Males exhibited a greater diaphragm MEP enhancement versus females, regardless of age (p=0.004). Age was inversely related with change in P 0.1 within the limited age range studied (p=0.007). In hApoE 4 knock-in rats, AIHH-induced phrenic motor plasticity was significantly lower than hApoE 3 controls (p<0.05). Conclusions APOE 4 genotype, sex and age are important biological determinants of AIHH-induced respiratory motor plasticity in healthy adults. ADDITION TO KNOWLEDGE BASE Acute intermittent hypoxia (AIH) is a novel rehabilitation strategy to induce functional recovery of respiratory and non-respiratory motor systems in people with chronic spinal cord injury and/or neurodegenerative diseases. Since most AIH trials report considerable inter-individual variability in AIH outcomes, we investigated factors that potentially undermine the response to an optimized AIH protocol, acute intermittent hypercapnic-hypoxia (AIHH), in healthy humans. We demonstrate that genetics (particularly the lipid transporter, APOE ), age and sex are important biological determinants of AIHH-induced respiratory motor plasticity.
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Affiliation(s)
- Jayakrishnan Nair
- Breathing Research and Therapeutics Center Department of Physical Therapy, University of Florida
- Current address: Department of Physical Therapy, Thomas Jefferson University, PA
| | - Joseph F. Welch
- Breathing Research and Therapeutics Center Department of Physical Therapy, University of Florida
- Current address: School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Alexandria B. Marciante
- Breathing Research and Therapeutics Center Department of Physical Therapy, University of Florida
| | - Tingting Hou
- Department of Biostatistics, University of Florida
| | - Qing Lu
- Department of Biostatistics, University of Florida
| | - Emily J. Fox
- Breathing Research and Therapeutics Center Department of Physical Therapy, University of Florida
- Brooks Rehabilitation, Jacksonville, Florida
| | - Gordon S. Mitchell
- Breathing Research and Therapeutics Center Department of Physical Therapy, University of Florida
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Seven YB, Allen LL, Ciesla MC, Smith KN, Zwick A, Simon AK, Holland AE, Santiago JV, Stefan K, Ross A, Gonzalez-Rothi EJ, Mitchell GS. Intermittent Hypoxia Differentially Regulates Adenosine Receptors in Phrenic Motor Neurons with Spinal Cord Injury. Neuroscience 2022; 506:38-50. [PMID: 36273657 DOI: 10.1016/j.neuroscience.2022.10.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 10/04/2022] [Accepted: 10/07/2022] [Indexed: 11/09/2022]
Abstract
Cervical spinal cord injury (cSCI) impairs neural drive to the respiratory muscles, causing life- threatening complications such as respiratory insufficiency and diminished airway protection. Repetitive "low dose" acute intermittent hypoxia (AIH) is a promising strategy to restore motor function in people with chronic SCI. Conversely, "high dose" chronic intermittent hypoxia (CIH; ∼8 h/night), such as experienced during sleep apnea, causes pathology. Sleep apnea, spinal ischemia, hypoxia and neuroinflammation associated with cSCI increase extracellular adenosine concentrations and activate spinal adenosine receptors which in turn constrains the functional benefits of therapeutic AIH. Adenosine 1 and 2A receptors (A1, A2A) compete to determine net cAMP signaling and likely the tAIH efficacy with chronic cSCI. Since cSCI and intermittent hypoxia may regulate adenosine receptor expression in phrenic motor neurons, we tested the hypotheses that: 1) daily AIH (28 days) downregulates A2A and upregulates A1 receptor expression; 2) CIH (28 days) upregulates A2A and downregulates A1 receptor expression; and 3) cSCI alters the impact of CIH on adenosine receptor expression. Daily AIH had no effect on either adenosine receptor in intact or injured rats. However, CIH exerted complex effects depending on injury status. Whereas CIH increased A1 receptor expression in intact (not injured) rats, it increased A2A receptor expression in spinally injured (not intact) rats. The differential impact of CIH reinforces the concept that the injured spinal cord behaves in distinct ways from intact spinal cords, and that these differences should be considered in the design of experiments and/or new treatments for chronic cSCI.
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Affiliation(s)
- Yasin B Seven
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Latoya L Allen
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Marissa C Ciesla
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Kristin N Smith
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Amanda Zwick
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Alec K Simon
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Ashley E Holland
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Juliet V Santiago
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Kelsey Stefan
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Ashley Ross
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Elisa J Gonzalez-Rothi
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and, McKnight Brain Institute, University of Florida, Gainesville, FL 32611, USA.
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Jia S, Rybalchenko N, Kunwar K, Farmer GE, Little JT, Toney GM, Cunningham JT. Chronic intermittent hypoxia enhances glycinergic inhibition in nucleus tractus solitarius. J Neurophysiol 2022; 128:1383-1394. [PMID: 36321700 PMCID: PMC9678432 DOI: 10.1152/jn.00241.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Chronic intermittent hypoxia (CIH), an animal model of sleep apnea, has been shown to alter the activity of second-order chemoreceptor neurons in the caudal nucleus of the solitary tract (cNTS). Although numerous studies have focused on excitatory plasticity, few studies have explored CIH-induced plasticity impacting inhibitory inputs to NTS neurons, and the roles of GABAergic and glycinergic inputs on heightened cNTS excitability following CIH are unknown. In addition, changes in astrocyte function may play a role in cNTS plasticity responses to CIH. This study tested the effects of a 7-day CIH protocol on miniature inhibitory postsynaptic currents (mIPSCs) in cNTS neurons receiving chemoreceptor afferents. Normoxia-treated rats primarily displayed GABA mIPSCs, whereas CIH-treated rats exhibited a shift toward combined GABA/glycine-mediated mIPSCs. CIH increased glycinergic mIPSC amplitude and area. This shift was not observed in dorsal motor nucleus of the vagus neurons or cNTS cells from females. Immunohistochemistry showed that strengthened glycinergic mIPSCs were associated with increased glycine receptor protein and were dependent on receptor trafficking in CIH-treated rats. In addition, CIH altered astrocyte morphology in the cNTS, and inactivation of astrocytes following CIH reduced glycine receptor-mediated mIPSC frequency and overall mIPSC amplitude. In cNTS, CIH produced changes in glycine signaling that appear to reflect increased trafficking of glycine receptors to the cell membrane. Increased glycine signaling in cNTS associated with CIH also appears to be dependent on astrocytes. Additional studies will be needed to determine how CIH influences glycine receptor expression and astrocyte function in cNTS.NEW & NOTEWORTHY Chronic intermittent hypoxia (CIH) has been used to mimic the hypoxemia associated with sleep apnea and determine how these hypoxemias influence neural function. The nucleus of the solitary tract is the main site for chemoreceptor input to the CNS, but how CIH influences NTS inhibition has not been determined. These studies show that CIH increases glycine-mediated miniature IPSCs through mechanisms that depend on protein trafficking and astrocyte activation.
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Affiliation(s)
- Shuping Jia
- 1Department of Physiology and Anatomy, University of Texas Health Science Center, Fort Worth, Texas
| | - Nataliya Rybalchenko
- 1Department of Physiology and Anatomy, University of Texas Health Science Center, Fort Worth, Texas
| | - Kishor Kunwar
- 2Microscopy Core, Division of Research and Innovation, University of Texas Health Science Center, Fort Worth, Texas
| | - George E. Farmer
- 1Department of Physiology and Anatomy, University of Texas Health Science Center, Fort Worth, Texas
| | - Joel T. Little
- 1Department of Physiology and Anatomy, University of Texas Health Science Center, Fort Worth, Texas
| | - Glenn M. Toney
- 3Department of Cellular & Integrative Physiology, University of Texas Health San Antonio, San Antonio, Texas
| | - J. Thomas Cunningham
- 1Department of Physiology and Anatomy, University of Texas Health Science Center, Fort Worth, Texas
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Marciante AB, Howard J, Kelly MN, Santiago Moreno J, Allen LL, Gonzalez-Rothi EJ, Mitchell GS. Dose-dependent phosphorylation of endogenous Tau by intermittent hypoxia in rat brain. J Appl Physiol (1985) 2022; 133:561-571. [PMID: 35861520 PMCID: PMC9448341 DOI: 10.1152/japplphysiol.00332.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 07/11/2022] [Accepted: 07/13/2022] [Indexed: 11/22/2022] Open
Abstract
Intermittent hypoxia, or intermittent low oxygen interspersed with normal oxygen levels, has differential effects that depend on the "dose" of hypoxic episodes (duration, severity, number per day, and number of days). Whereas "low dose" daily acute intermittent hypoxia (dAIH) elicits neuroprotection and neuroplasticity, "high dose" chronic intermittent hypoxia (CIH) similar to that experienced during sleep apnea elicits neuropathology. Sleep apnea is comorbid in >50% of patients with Alzheimer's disease-a progressive, neurodegenerative disease associated with brain amyloid and chronic Tau dysregulation (pathology). Although patients with sleep apnea present with higher Tau levels, it is unknown if sleep apnea through attendant CIH contributes to onset of Tau pathology. We hypothesized CIH characteristic of moderate sleep apnea would increase dysregulation of phosphorylated Tau (phospho-Tau) species in Sprague-Dawley rat hippocampus and prefrontal cortex. Conversely, we hypothesized that dAIH, a promising neurotherapeutic, has minimal impact on Tau phosphorylation. We report a dose-dependent intermittent hypoxia effect, with region-specific increases in 1) phospho-Tau species associated with human Tauopathies in the soluble form and 2) accumulated phospho-Tau in the insoluble fraction. The latter observation was particularly evident with higher CIH intensities. This important and novel finding is consistent with the idea that sleep apnea and attendant CIH have the potential to accelerate the progression of Alzheimer's disease and/or other Tauopathies.NEW & NOTEWORTHY Sleep apnea is highly prevalent in people with Alzheimer's disease, suggesting the potential to accelerate disease onset and/or progression. These studies demonstrate that intermittent hypoxia (IH) induces dose-dependent, region-specific Tau phosphorylation, and are the first to indicate that higher IH "doses" elicit both endogenous, (rat) Tau hyperphosphorylation and accumulation in the hippocampus. These findings are essential for development and implementation of new treatment strategies that minimize sleep apnea and its adverse impact on neurodegenerative diseases.
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Affiliation(s)
- Alexandria B Marciante
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - John Howard
- Department of Neuroscience, University of Florida, Gainesville, Florida
- Center for Translational Research in Neurodegenerative Diseases, University of Florida, Gainesville, Florida
| | - Mia N Kelly
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Juan Santiago Moreno
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Latoya L Allen
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Elisa J Gonzalez-Rothi
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Center, University of Florida, Gainesville, Florida
- Department of Physical Therapy, University of Florida, Gainesville, Florida
- McKnight Brain Institute, University of Florida, Gainesville, Florida
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Yu JJ, Non AL, Heinrich EC, Gu W, Alcock J, Moya EA, Lawrence ES, Tift MS, O'Brien KA, Storz JF, Signore AV, Khudyakov JI, Milsom WK, Wilson SM, Beall CM, Villafuerte FC, Stobdan T, Julian CG, Moore LG, Fuster MM, Stokes JA, Milner R, West JB, Zhang J, Shyy JY, Childebayeva A, Vázquez-Medina JP, Pham LV, Mesarwi OA, Hall JE, Cheviron ZA, Sieker J, Blood AB, Yuan JX, Scott GR, Rana BK, Ponganis PJ, Malhotra A, Powell FL, Simonson TS. Time Domains of Hypoxia Responses and -Omics Insights. Front Physiol 2022; 13:885295. [PMID: 36035495 PMCID: PMC9400701 DOI: 10.3389/fphys.2022.885295] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2022] [Accepted: 05/24/2022] [Indexed: 02/04/2023] Open
Abstract
The ability to respond rapidly to changes in oxygen tension is critical for many forms of life. Challenges to oxygen homeostasis, specifically in the contexts of evolutionary biology and biomedicine, provide important insights into mechanisms of hypoxia adaptation and tolerance. Here we synthesize findings across varying time domains of hypoxia in terms of oxygen delivery, ranging from early animal to modern human evolution and examine the potential impacts of environmental and clinical challenges through emerging multi-omics approaches. We discuss how diverse animal species have adapted to hypoxic environments, how humans vary in their responses to hypoxia (i.e., in the context of high-altitude exposure, cardiopulmonary disease, and sleep apnea), and how findings from each of these fields inform the other and lead to promising new directions in basic and clinical hypoxia research.
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Affiliation(s)
- James J. Yu
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Amy L. Non
- Department of Anthropology, Division of Social Sciences, University of California, San Diego, La Jolla, CA, United States,*Correspondence: Amy L. Non, Tatum S. Simonson,
| | - Erica C. Heinrich
- Division of Biomedical Sciences, School of Medicine, University of California, Riverside, CA, United States
| | - Wanjun Gu
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States,Herbert Wertheim School of Public Health and Longevity Sciences, University of California, San Diego, La Jolla, CA, United States
| | - Joe Alcock
- Department of Emergency Medicine, University of New Mexico, Albuquerque, MX, United States
| | - Esteban A. Moya
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Elijah S. Lawrence
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Michael S. Tift
- Department of Biology and Marine Biology, College of Arts and Sciences, University of North Carolina Wilmington, Wilmington, NC, United States
| | - Katie A. O'Brien
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States,Department of Physiology, Development and Neuroscience, Faculty of Biology, School of Biological Sciences, University of Cambridge, Cambridge, ENG, United Kingdom
| | - Jay F. Storz
- School of Biological Sciences, College of Arts and Sciences, University of Nebraska-Lincoln, Lincoln, IL, United States
| | - Anthony V. Signore
- School of Biological Sciences, College of Arts and Sciences, University of Nebraska-Lincoln, Lincoln, IL, United States
| | - Jane I. Khudyakov
- Department of Biological Sciences, University of the Pacific, Stockton, CA, United States
| | | | - Sean M. Wilson
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda, CA, United States
| | | | | | | | - Colleen G. Julian
- School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Lorna G. Moore
- Division of Reproductive Sciences, Department of Obstetrics and Gynecology, Aurora, CO, United States
| | - Mark M. Fuster
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Jennifer A. Stokes
- Department of Kinesiology, Southwestern University, Georgetown, TX, United States
| | - Richard Milner
- San Diego Biomedical Research Institute, San Diego, CA, United States
| | - John B. West
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Jiao Zhang
- Department of Medicine, UC San Diego School of Medicine, San Diego, CA, United States
| | - John Y. Shyy
- Department of Medicine, UC San Diego School of Medicine, San Diego, CA, United States
| | - Ainash Childebayeva
- Department of Archaeogenetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | - José Pablo Vázquez-Medina
- Department of Integrative Biology, College of Letters and Science, University of California, Berkeley, Berkeley, CA, United States
| | - Luu V. Pham
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, School of Medicine, Johns Hopkins Medicine, Baltimore, MD, United States
| | - Omar A. Mesarwi
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - James E. Hall
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Zachary A. Cheviron
- Division of Biological Sciences, College of Humanities and Sciences, University of Montana, Missoula, MT, United States
| | - Jeremy Sieker
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Arlin B. Blood
- Department of Pediatrics Division of Neonatology, School of Medicine, Loma Linda University, Loma Linda, CA, United States
| | - Jason X. Yuan
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Graham R. Scott
- Department of Pediatrics Division of Neonatology, School of Medicine, Loma Linda University, Loma Linda, CA, United States
| | - Brinda K. Rana
- Moores Cancer Center, UC San Diego, La Jolla, CA, United States,Department of Psychiatry, UC San Diego, La Jolla, CA, United States
| | - Paul J. Ponganis
- Center for Marine Biotechnology and Biomedicine, La Jolla, CA, United States
| | - Atul Malhotra
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Frank L. Powell
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Tatum S. Simonson
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States,*Correspondence: Amy L. Non, Tatum S. Simonson,
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Janssen Daalen JM, Meinders MJ, Giardina F, Roes KCB, Stunnenberg BC, Mathur S, Ainslie PN, Thijssen DHJ, Bloem BR. Multiple N-of-1 trials to investigate hypoxia therapy in Parkinson's disease: study rationale and protocol. BMC Neurol 2022; 22:262. [PMID: 35836147 PMCID: PMC9281145 DOI: 10.1186/s12883-022-02770-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 06/24/2022] [Indexed: 11/30/2022] Open
Abstract
Background Parkinson’s disease (PD) is a neurodegenerative disease, for which no disease-modifying therapies exist. Preclinical and clinical evidence suggest that hypoxia-based therapy might have short- and long-term benefits in PD. We present the contours of the first study to assess the safety, feasibility and physiological and symptomatic impact of hypoxia-based therapy in individuals with PD. Methods/Design In 20 individuals with PD, we will investigate the safety, tolerability and short-term symptomatic efficacy of continuous and intermittent hypoxia using individual, double-blind, randomized placebo-controlled N-of-1 trials. This design allows for dose finding and for including more individualized outcomes, as each individual serves as its own control. A wide range of exploratory outcomes is deployed, including the Movement Disorders Society Unified Parkinson’s Disease Rating scale (MDS-UPDRS) part III, Timed Up & Go Test, Mini Balance Evaluation Systems (MiniBES) test and wrist accelerometry. Also, self-reported impression of overall symptoms, motor and non-motor symptoms and urge to take dopaminergic medication will be assessed on a 10-point Likert scale. As part of a hypothesis-generating part of the study, we also deploy several exploratory outcomes to probe possible underlying mechanisms of action, including cortisol, erythropoietin and platelet-derived growth factor β. Efficacy will be assessed primarily by a Bayesian analysis. Discussion This evaluation of hypoxia therapy could provide insight in novel pathways that may be pursued for PD treatment. This trial also serves as a proof of concept for deploying an N-of-1 design and for including individualized outcomes in PD research, as a basis for personalized treatment approaches. Trial registration ClinicalTrials.gov Identifier: NCT05214287 (registered January 28, 2022).
Supplementary Information The online version contains supplementary material available at 10.1186/s12883-022-02770-7.
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Affiliation(s)
- Jules M Janssen Daalen
- Center of Expertise for Parkinson & Movement Disorders; Nijmegen, the Netherlands, Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Marjan J Meinders
- Center of Expertise for Parkinson & Movement Disorders; Nijmegen, the Netherlands, Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands.,IQ Healthcare, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Federica Giardina
- Department of Health Evidence, Radboud Institute for Health Sciences, Radboud University Medical Center, Section Biostatistics, Nijmegen, The Netherlands
| | - Kit C B Roes
- Department of Health Evidence, Radboud Institute for Health Sciences, Radboud University Medical Center, Section Biostatistics, Nijmegen, The Netherlands
| | - Bas C Stunnenberg
- Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands.,Department of Neurology, Rijnstate Hospital, Arnhem, Netherlands
| | | | - Philip N Ainslie
- Center for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, Canada
| | - Dick H J Thijssen
- Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Bastiaan R Bloem
- Center of Expertise for Parkinson & Movement Disorders; Nijmegen, the Netherlands, Department of Neurology, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands.
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38
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Mesquita RNO. Concurrent exposure to (acute intermittent) hypoxia and hypercapnia: A promising therapeutic cocktail for neuroplasticity? J Physiol 2022; 600:3017-3019. [PMID: 35603547 DOI: 10.1113/jp283215] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 05/19/2022] [Indexed: 11/08/2022] Open
Affiliation(s)
- Ricardo N O Mesquita
- School of Medical and Health Sciences, Edith Cowan University, Perth, Australia.,Neuroscience Research Australia, Sydney, Australia
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39
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Welch JF, Nair J, Argento PJ, Mitchell GS, Fox EJ. Acute intermittent hypercapnic-hypoxia elicits central neural respiratory motor plasticity in humans. J Physiol 2022; 600:2515-2533. [PMID: 35348218 DOI: 10.1113/jp282822] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2022] [Accepted: 03/25/2022] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The occurrence of respiratory long-term facilitation following acute exposure to intermittent hypoxia is believed to be dependent upon CO2 regulation - mechanisms governing the critical role of CO2 have seldom been explored. We tested the hypothesis that acute intermittent hypercapnic-hypoxia (AIHH) enhances cortico-phrenic neurotransmission in awake healthy humans. The amplitude of diaphragmatic motor-evoked potentials induced by transcranial magnetic stimulation was increased after AIHH, but not the amplitude of compound muscle action potentials evoked by cervical magnetic stimulation. Mouth occlusion pressure (P0.1 , indicator of neural respiratory drive) was also increased after AIHH, but not tidal volume or minute ventilation. Thus, moderate AIHH elicits central neural mechanisms of respiratory motor plasticity, without measurable ventilatory long-term facilitation in awake humans. ABSTRACT Acute intermittent hypoxia (AIH) elicits long-term facilitation (LTF) of respiration. Although LTF is observed when CO2 is elevated during AIH in awake humans, the influence of CO2 on corticospinal respiratory motor plasticity is unknown. Thus, we tested the hypotheses that acute intermittent hypercapnic-hypoxia (AIHH): 1) enhances cortico-phrenic neurotransmission (reflecting volitional respiratory control); and 2) elicits ventilatory LTF (reflecting automatic respiratory control). Eighteen healthy adults completed four study visits. Day 1 consisted of anthropometry and pulmonary function testing. On Days 2, 3 and 4, in a balanced alternating sequence, participants received: AIHH, poikilocapnic AIH, and normocapnic-normoxia (Sham). Protocols consisted of 15, 60-s exposures with 90-s normoxic intervals. Transcranial (TMS) and cervical (CMS) magnetic stimulation were used to induce diaphragmatic motor-evoked potentials and compound muscle action potentials, respectively. Respiratory drive was assessed via mouth occlusion pressure (P0.1 ), and minute ventilation measured at rest. Dependent variables were assessed at baseline and 30-60 min post-exposures. Increases in TMS-evoked diaphragm potential amplitudes were observed following AIHH versus Sham (+28 ± 41%, p = 0.003), but not after AIH. No changes were observed in CMS-evoked diaphragm potential amplitudes. Mouth occlusion pressure also increased after AIHH (+21 ± 34%, p = 0.033), but not after AIH. Ventilatory LTF was not observed after any treatment. We demonstrate that AIHH elicits central neural mechanisms of respiratory motor plasticity and increases resting respiratory drive in awake humans. These findings may have important implications for neurorehabilitation after spinal cord injury and other neuromuscular disorders compromising respiratory motor function. Abstract Figure Legend In a single-blind, cross-over, sham-controlled trial, 18 healthy adults received in a balanced alternating sequence: normocapnic-normoxia (Sham), poikilocapnic acute intermittent hypoxia (AIH), and acute intermittent hypercapnic-hypoxia (AIHH). The study tested the hypothesis that AIHH enhances cortico-phrenic neurotransmission and elicits ventilatory long-term facilitation. Note the increase in the mean amplitude of diaphragmatic motor-evoked potentials (MEP) induced by transcranial magnetic stimulation 60 min after AIHH only, whereas the amplitude of diaphragmatic compound muscle action potentials evoked by cervical (phrenic nerve) stimulation were unchanged after AIHH, AIH and Sham. Traces are composite averages of all participants. Mouth occlusion pressure (P0.1 ), an indicator of resting respiratory drive, was increased after AIHH, but not after AIH or Sham (see yellow shaded area). Traces are mouth pressure at the onset of an occluded inspiration during resting breathing. Finally, tidal volume (VT ) was unchanged 30-60 min after AIHH, AIH and Sham. Our results indicate that moderate AIHH elicits a central neural mechanism of respiratory motor plasticity and increases resting respiratory drive in awake humans, without measurable ventilatory long-term facilitation. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Joseph F Welch
- Breathing Research and Therapeutics Centre.,Department of Physical Therapy
| | - Jayakrishnan Nair
- Breathing Research and Therapeutics Centre.,Department of Physical Therapy.,Department of Physical Therapy, Thomas Jefferson University, Philadelphia, PA, USA
| | - Patrick J Argento
- Herbert Wertheim College of Engineering, University of Florida, Gainesville, FL, USA
| | - Gordon S Mitchell
- Breathing Research and Therapeutics Centre.,Department of Physical Therapy
| | - Emily J Fox
- Breathing Research and Therapeutics Centre.,Department of Physical Therapy.,Brooks Rehabilitation, Jacksonville, FL, USA
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Mitchell GS, Baker TL. Respiratory neuroplasticity: Mechanisms and translational implications of phrenic motor plasticity. HANDBOOK OF CLINICAL NEUROLOGY 2022; 188:409-432. [PMID: 35965036 DOI: 10.1016/b978-0-323-91534-2.00016-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Widespread appreciation that neuroplasticity is an essential feature of the neural system controlling breathing has emerged only in recent years. In this chapter, we focus on respiratory motor plasticity, with emphasis on the phrenic motor system. First, we define related but distinct concepts: neuromodulation and neuroplasticity. We then focus on mechanisms underlying two well-studied models of phrenic motor plasticity: (1) phrenic long-term facilitation following brief exposure to acute intermittent hypoxia; and (2) phrenic motor facilitation after prolonged or recurrent bouts of diminished respiratory neural activity. Advances in our understanding of these novel and important forms of plasticity have been rapid and have already inspired translation in multiple respects: (1) development of novel therapeutic strategies to preserve/restore breathing function in humans with severe neurological disorders, such as spinal cord injury and amyotrophic lateral sclerosis; and (2) the discovery that similar plasticity also occurs in nonrespiratory motor systems. Indeed, the realization that similar plasticity occurs in respiratory and nonrespiratory motor neurons inspired clinical trials to restore leg/walking and hand/arm function in people living with chronic, incomplete spinal cord injury. Similar application may be possible to other clinical disorders that compromise respiratory and non-respiratory movements.
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Affiliation(s)
- Gordon S Mitchell
- Breathing Research and Therapeutics Center, Department of Physical Therapy and McKnight Brain Institute, University of Florida, Gainesville, FL, United States.
| | - Tracy L Baker
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI, United States
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Editorial: Intermittent hypoxia. Exp Neurol 2021; 348:113951. [PMID: 34955452 DOI: 10.1016/j.expneurol.2021.113951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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