bluuebunny/crossref_metadata_2025_split huggingface dataset:
CO2 Sensitivity of the Ventilatory Response to Muscle Metaboreflex Stimulation in Humans
Authors: White Michael , AlGaith Jassim , Balanos George 
Published: November 2023

The role of skeletal muscle metaboreceptive afferents in human cardiorespiratory control is isolated by using a period of post exercise circulatory occlusion (PECO). Previously we showed that the ventilatory response to a period of PECO is augmented in humans during concurrent hypercapnia, which elevated end tidal pCO2 by ~10mmHg above resting. In addition we found that this augmentation did not depend on peripheral chemoreflex involvement or local muscle hypercapnia. This suggested an interaction between central chemoreflex and muscle metaboreflex activation. We now aim to further examine this interaction by determining the lower level of end tidal pCO2 elevation required to cause the sustained elevation of ventilation during PECO.With local Ethical Committee approval, young healthy subjects performed 4 trials in which end tidal pCO2 was elevated by 1, 3, 7 or 10 mmHg above resting levels. In each trial subjects were seated in an isometric dynamometer designed to measure ankle plantar flexor force. Rest for 2 minutes in room air was followed by 15 minutes of exposure to one of the four levels of hypercapnia. During this hypercapnia phase, 5 minutes further rest was followed by 2 minutes of sustained isometric calf muscle contraction, at 50% of the previously determined maximal voluntary strength. Just prior to cessation of exercise, a cuff around the upper leg was inflated rapidly to 200mmHg. This remained inflated for 3 more minutes before deflation and a further 5 minutes of exposure to hypercapnia. Beat to beat blood pressure (Finapres) and heart rate (ECG) were measured throughout as was breath‐by‐breath ventilation (VE) and end tidal PCO2 using a computer controlled dynamic end tidal forcing system.PECO maintained mean blood pressure significantly above baseline by ~15 mmHg in all trials, indicating a consistent and well controlled level of muscle chemoreflex activation. However, ventilation during PECO was only sustained above baseline levels when end tidal pCO2 was maintained at or above 3 mmHg.These results suggest that metaboreflex activation plus this threshold level of end tidal CO2 elevation is required to cause the ventilatory response to PECO. This further supports the idea of a synergistic interaction between muscle afferent activation and central chemoreflex stimulation, resulting in additional respiratory neurone excitation and increased ventilation in man.
Opioid‐induced suppression of augmented breaths (‘sighs’) persists during extended morphine administration at sub‐analgesic dosage
Authors: Donkin Joshua D , Grzesek Kimberly , Gulick Cody J , Bernardo Magalie , Nickels Cooper R , Bell Harold James 
Published: November 2023

Our previous work has demonstrated that acute morphine administration causes powerful suppression of augmented breaths (ABs) at the low‐to‐mid dosage range for analgesia in adult rats. The present study was performed to determine the extent to which this suppression of ABs persists in the course of prolonged morphine administration. We studied breathing non‐invasively in adult rats in 2 separate experiments: Exp 1: animals were monitored immediately before, and repeatedly following s.c. bolus injections of morphine, 4 mg/kg loading dose and maintenance doses of 2 mg/kg given each hour for 8 consecutive hours (n=8). Exp 2: Animals were monitored immediately before and again repeatedly across 10 consecutive days of morphine treatment self‐administered via oral dosing in drinking water (n=7). Appropriate sham/control experiments were performed using saline injections and normal drinking water. In Exp 1, morphine injection caused a potent suppression of ABs, observed immediately upon first injection (6.0 ± 2.9 vs 0.5 ± 0.5 ABs/15 min, pre vs. post), and persisting throughout the 8 hours of study (P<0.001). This occurred despite there being no depression of minute ventilation. The prevalence of ABs in the sham injection condition remained unchanged across the 8 hours of study. In Exp 2, morphine concentration in drinking water was titrated up to 0.4 mg/mL across days 1 to 5, and remained constant at 0.4 mg/mL through day 10. This concentration was chosen so as to avoid taste aversion and drinking abstinence commonly seen when attempting to use higher concentrations of morphine. Animals self‐administered an average of 33.1 ± 6.9 mg/day (1.4 mg/kg/hr) on day 7 and 36.6 ± 3.4 mg/kg/day (1.5 mg/kg/hr) on day 10. This relatively low dosage was sub‐analgesic in efficacy as confirmed by lack of prolongation of tail flick latency. Despite the low dosage, continuously administered morphine caused significantly fewer ABs to be expressed on day 10 of morphine treatment (3.3 ± 1.5 ABs/15 min) compared to either pre‐treatment (7.0 ± 1.8) or day 10 of the control (6.3 ± 1.8) condition. No depression of minute ventilation was observed across the 10 days of treatment. These results confirm that the opioid‐induced suppression of ABs occurs rapidly and persists across extended treatment of at least 10 days. Moreover, this side effect occurs even in the sub‐analgesic dose range in the absence of any depression of minute ventilation.Support or Funding InformationThis work was supported by research funds provided by the Central Michigan University College of Medicine, and an Early Career Grant awarded by the Office of Research and Sponsored Programs at Central Michigan University.
Adaptive Mechanisms Governing Tracheobronchial Cough: In Vivo Experiments and Model Simulations
Authors: Musselwhite M. Nicholas , Pitts Teresa E. , Morris Kendall F. , Shen Tabitha Y. , Davenport Paul W. , Bolser Donald C. 
Published: November 2023

Repetitive coughing can be suppressed in a dose‐dependent manner in response to administration of cough suppressant drugs in anesthetized cats. Cough suppression by these drugs manifests as a reduction in cough number and expiratory motor drive. Cough phase durations and inspiratory motor drive are unaffected by these drugs in the cat. The mechanism by which antitussive drugs exert these effects is unknown. We speculated that depression of synaptic excitability at the first central synapse of cough receptor afferents could contribute to this effect. To test this hypothesis, we conducted simulations using a well‐established computational model of the peripheral afferents and the central circuit that is proposed to account for cough and breathing. Modulation of the conductance of the first central synapse and then the firing probability of cough receptors predicted inverse relationships between these parameters, and cough number and expiratory motor drive. However, these simulations also predicted that reductions in the magnitudes of these parameters would result in longer cough cycle times, with a greater impact of synaptic conductance on this relationship. These predictions are not consistent with the known action of antitussive drugs on the cough motor pattern. Similarities to the results of these simulations were observed between coordinated in vivo experiments in anesthetized spontaneously breathing cats. A repetitive cough protocol was conducted in which naïve animals were challenged with a sequence of trials in which the intrathoracic trachea was mechanically stimulated to elicit coughing. Cough number and expiratory motor drive decreased by approximately 50% over the course of 15–20 consecutive trials. Total cough cycle duration increased by 46% (p<0.02) accounting for the decreased number of coughs during the protocol. Significant prolongations of cough TI, E1, and E2 were also observed. The data support: (i) significant adaptive processes of naïve animals to a sequential cough stimulation protocol, (ii) a different phenotype of this adaptive process than that associated with cough suppressants, (iii) potential mechanisms for this adaptive process that could include reduced excitation of both peripheral afferents and their first synapse with a larger contribution of the central component to the adaptation.Support or Funding InformationSupported by HL 103415, HL 111215, HL 109025
Frequency Dependent Inhibitory Mechanisms Controlling the Laryngeal Adductor Response (LAR)
Authors: Shen Tabitha Y. , Gestreau Christian , Musselwhite M. Nicholas , Rose Melanie J. , Pitts Teresa E. , Morris Kendall F. , Lindsey Bruce G. , Davenport Paul W. , Bolser Donald C. 
Published: November 2023

Electrical stimulation of the superior laryngeal nerve (SLN) has been used to induce behaviors with airway protective components, such as the LAR. The LAR has both short (R1) and long latency (R2) peaks in response to stimulation, but the neuronal pathways that produce and modulate the LAR are not well understood. It has been reported that there exists a frequency‐dependent suppression of R2 for SLN stimulation frequencies above 2.5 Hz. The R1 can follow frequencies of electrical stimulation of the SLN approaching 200 Hz, suggesting a high fidelity of brainstem neuronal pathways, but to our knowledge there is no report on whether R1 exhibits frequency‐dependent depression. We hypothesized that the R1 would exhibit frequency‐dependent depression consistent with the existence of modulatory short latency inhibitory mechanisms. To test this hypothesis, we monitored EMG activity from the thyroarytenoid (TA) muscle and electrically stimulated the SLN unilaterally with a range of frequencies between 1 and 40 Hz. All frequencies employed induced both repetitive swallowing and LAR. The R1 peak of the LAR was time‐locked to each stimulus pulse (peak R1 latencies were 13.7±0.5 ms (5–10 Hz) and 14.2±0.6 ms (35–40 Hz)), and the R2 peak was not observed. Lower frequency stimulations (5–10 Hz) of the SLN elicited significantly higher LAR amplitudes (52.8 ±2.9 % max) than higher frequency stimulations (35–40 Hz; 36.8±3.2 % max). In other experiments, analysis of neuronal responses recorded in the ventral respiratory column revealed evidence of stimulus‐induced synchrony as well as disruption of concurrent functional relationships among respiratory‐modulated neurons. These observations suggest that more complex regulatory mechanisms exist in addition to frequency‐dependent depression of the LAR.Support or Funding InformationSupported by NIH HL 103415, HL 111215, HL109025.
Ventilatory Acclimatization to Hypoxia Requires Early Microglia Activation
Authors: Stokes Jennifer Ann , Arbogast Tara Elizabeth , Powell Frank L 
Published: November 2023

Ventilatory acclimatization to hypoxia (VAH) is the time‐dependent increase in ventilation, which persists upon return to normoxia, and involves plasticity in central nervous system (CNS) respiratory centers and peripheral chemoreceptors. Plasticity within the CNS increases ventilatory motor output for a given chemoreceptor input and the mechanisms of such plasticity in the CNS are unknown. It is clear from the literature that glial cells influence neuronal transmission and central respiratory control. Previously we showed a role for microglia in VAH (Stokes JA et al., 2015), where pharmacological blockade of microglia by minocycline inhibited VAH during a 7‐day chronic sustained hypoxia (CSH) exposure (10% O2). Building upon this work, we investigated the effect of timing of microglia inhibition on VAH. In this study rats were exposed to 7 days of CSH (10% O2) and administered minocycline (45mg/kg i.p.) in one of two regimes: 1) Early minocycline – minocycline days 0–3 of hypoxia exposure and saline days 4–7; 2) Late minocycline – saline days 0–3 of hypoxia and minocycline days 4–7. Ventilation was recorded using whole‐body plethysmography on day 4 (before treatment change) and on day 7, after final hypoxic day. Early minocycline administration initially blocked VAH on day 4, but after saline administration during the final days of hypoxia VAH was observed on day 7. Late minocycline administration was not able to reverse the VAH, which was observed on day 4 with early saline administration. These results show that microglial activation is required for the initial plasticity involved in acclimatization but once acclimatization is established, blocking microglia activation does not reverse the adaptation. To investigate possible mechanisms, we used RT‐PCR to assess cytokine production in the nucleus tractus solitarius (NTS) following initial hypoxia exposure, as activated microglia release cytokines which activate neighboring glial cells and subsequently neurons. After 24 hours of hypoxia, Il‐6 and TNF‐α mRNA expression increased in the NTS and this increase was blocked by minocycline. Taken together these results support a model for microglia activation and release of cytokines early in sustained hypoxia that induce neural plasticity in VAH, which is generally assumed to be a healthy response to hypoxia.Support or Funding InformationNIH RO1 HL‐081823 (FLP) and T32 5T32HL098062‐04 (JAS)
An Evaluation of the Cytotoxic and Pro‐inflammatory Effects of Various E‐cigarette Liquid Flavors on Monocytes and Macrophages
Authors: Stanley Corshe D. , Clapp Phillip W. , Jones Shannon Z. , Jaspers Ilona 
Published: November 2023

The usage of electronic cigarettes is becoming very popular in today's society. Although the popularity of these products is increasing, they are not currently regulated by the Food and Drug Administration and the long term health effects are still unknown. The objective of the present study was to identify the potential cytotoxic and inflammatory effects of various flavors of E‐cigarette liquids in THP‐1 monocytes and alveolar macrophages. THP‐1 cells and alveolar macrophages were used as experimental models because these cells are important components of our immune system and first line of defense against infections, especially in the lung. Alveolar macrophages are the most predominant resident immune cell in the healthy human lung. Macrophages and other immune cells use cytokines to communicate with other components of the immune system and to signal the onset of infections. In this project we challenged macrophages/THP‐1 cells with seven different flavors of e‐cigarette liquids. The cells were harvested 24 hours post‐challenge and examined for the secretion of IL‐6 and IL‐8 as markers of inflammation and immune responses. We also calculated cell viability following challenge, using trypan blue exclusion. Our hypothesis was that E‐cigarette liquids are pro‐inflammatory and potentially cytotoxic and thus potentially adversely affecting the ability of these cells to function properly. Our data suggest that of the seven E‐cigarette liquids tested, two induced significant cytotoxicity in THP‐1 monocytes, while one of the flavors had no effect on cytokine secretion or cell viability. It is important to note that the two most cytotoxic liquids contained the cinnamon‐flavoring chemical cinnamaldehyde. These results suggest that, individually, E‐cigarette liquids may contribute to inflammatory and cytotoxic responses.Support or Funding InformationUNC TCORS grant (5‐33779)
Compromised Lung Mechanics in Cigarette Smoke Exposed Mice with Inhibited Pulmonary VEGF Expression
Authors: Lee Jasmine H. , Fine Janelle , Gutierrez Alma , Witte Tyler , Wong Fiona , Bigby Timothy , Breen Ellen C. 
Published: November 2023

Cigarette smoke (CS) exposure is well known to lead to progressive lung destruction that is characterized by enlarged airspaces and a decrease in lung elastic recoil. We hypothesized that VEGF expression by airway cells may protect against the early onset of excessive lung damage. Adult VEGFLoxP mice (5 months of age) were exposed to daily periods (5 days/week) of “nose‐only” CS or remained in room air (RA) for 4 months. Half of the mice in each exposure group were instilled one month earlier with AAV‐Cre to delete the VEGF gene in airway cells or a control virus (AAV‐LacZ). An additional group of VEGF promoter/luciferase reporter mice were exposed to CS to monitor VEGF transcriptional activation by in vivo optical imaging. Static lung mechanics were characterized from pressure‐volume curves and oxygen saturation levels were measured in awake mice breathing 21% O2 or 10% O2 by a pulse oximeter. VEGF transcriptional activity in the lungs peaked at 7 days and returned towards baseline level by 14 days (Day 0, 1.14e7 ± 2.4e6 relative light units (RLU); Day 1, 3.46e7 ± 9.5e6 RLU, Day 7, 7.40e7 ± 1.9e7 RLU, Day 14, 3.10e7 ± 5.4e6 RLU, p=0.055). There was a progressive left shift and increased hysteresis of the P‐V relationship in mice from the RA‐LacZ < CS‐LacZ < RA‐Cre < CS‐Cre groups. At an average airway pressure of 20 cmH2O, lung volumes were 0.9 ml RA‐LacZ group, 1.0 ml CS‐LacZ group, 1.1 ml RA‐Cre group, and 1.2 ml CS‐Cre group. O2 saturation levels were not different among groups when breathing RA. In mice challenged with 10% O2, the oxygen saturation levels were lowest in the CS‐Cre group (RA‐LacZ, 71.0 ± 1.8%; CS‐LacZ, 75.2 ± 4.9%; RA‐Cre, 70.4 ± 3.9%; CS‐Cre, 62.6 ± 3.5%, p<0.05). These data suggest that airway epithelial VEGF is vital for maintaining lung function and when deleted from the airway, obstructive physiology develops. This pattern is further exacerbated by exposure to chronic cigarette smoke.Support or Funding InformationDepartment of Veterans Affairs
Heparan Sulfate is Shed into the Alveolus after Intratracheal Lung Injury and Facilitates Alveolar Epithelial Growth Factor Signaling and Lung Repair
Authors: Haeger Sarah , Yang Yimu , Zemans Rachel , Suflita Matt , Zhang Fuming , Linhardt Robert , Tuder Rubin , Schmidt Eric 
Published: November 2023

Heparan sulfate proteoglycans (HSPGs) are proteins covalently bound to heparan sulfate (HS), a linear highly‐sulfated polysaccharide, and are present in both the extracellular matrix and on cell surfaces. During tissue injury, HSPGs are thought to be shed from the injured cell surface; for example, the protein component of the cell membrane‐bound HSPG, syndecan‐1, has been shown to be shed from the respiratory epithelial cell surface into the airway during naphthalene lung injury. However, it remains unknown whether heparan sulfate (HS) is also shed into the airspace during intratracheal (IT) lung injury. Additionally, as HS is known to function as a scaffolding molecule for numerous growth factor ligands and receptors, facilitating ligand‐receptor binding and enhancing signaling, it is important to determine if HS is shed into the airspace during lung injury, as the shed HS may affect growth factor signaling and lung repair.To determine if HS is shed into the airspace during lung injury, we intratracheally instilled lipopolysaccharide (LPS) in mice and performed mass spectrometry for HS in bronchoalveolar (BAL) fluid collected from mice days 2, 4, 6, and 8 after IT LPS instillation. We detected increased BAL HS on days 2 (2.3 fold) and 4 (3.2 fold) after IT LPS instillation in comparison to animals instilled with PBS as control. To determine if the airspace HS enhances lung epithelial growth factor signaling and repair, we tested if exogenous HS enhances ERK signaling in alveolar type II (ATII) epithelial cells, progenitor cells that re‐epithelialize the alveolus after injury. We treated MLE‐12 cells (a mouse ATII cell line) with 0.5μg/ml HS and determined that, while HS inhibits ERK signaling in naïve MLE‐12 cells, HS permits ERK signaling in MLE‐12 cells that are enzymatically devoid of cell‐surface HS. This finding suggests that airspace HS may facilitate growth factor signaling in ATII cells that have shed their cell‐surface HS during injury. Finally, to determine if supplementation with exogenous HS enhances lung repair in vivo, we treated animals with intravenous HS on day 4 after IT LPS instillation and measured outcomes of lung injury. Twenty‐four hours after supplementation, HS reduced BAL total protein by 30%, indicating that exogenous HS supplementation may enhance alveolar epithelial barrier function and lung repair.Support or Funding InformationNHLBI RO1 HL125371
Resident Lung Macrophages Are Sparsely Amongst Alveoli
Authors: Li Li , Gusarova Galina A , Bhattacharya Jahar 
Published: November 2023

Lung macrophages are major determinants of pro‐ and anti‐inflammatory mechanisms underlying multiple lung diseases, including Acute Lung Injury (ALI). Our recent findings in optically imaged mouse lungs indicate that resident macrophages in alveoli adhere to the alveolar epithelium (Nature 2014). We called these cells sessile alveolar macrophages (SAMs) to distinguish them from non‐adherent macrophages that can be recovered in the bronchoalveolar lavage. Here we report new studies in which we determined distribution of SAMs by lung histology. We anesthetized mice, then exsanguinated them by cardiac puncture (n=3). Through a tracheal cannula we instilled tissue embedding compound (OCT, R&D Systems) diluted 1:1 in PBS to inflate the lungs at 25 cmH2O. After 20 min, we isolated the lungs, froze the lungs in dry ice, then stored the lungs overnight at −80°C. We obtained tissue blocks that we sectioned in a tissue microtome to obtain 8 micron sections at 100–200 microns below the pleural surface. For immunohistochemistry, we incubated the sections at 4°C overnight with primary antibodies against the lung macrophage markers, CD11c and Siglec‐F, and the primary antibody against the alveolar wall marker, connexin 43 (Cx43). Then after washing the sections, we further exposed them to secondary antibodies tagged with different fluorescent markers. We viewed the sections by fluorescence microscopy. We identified alveolar walls as Cx43 expressing cells (green), and SAMs as cells co‐expressing CD11c (cyan) and Siglec‐F (red). In each lung, we counted the number of SAMs in 100 alveoli in 7–8 imaging fields. Normalized for a single imaging field, our counts indicated that 5±2 SAMs were present in 14±5 alveoli, indicating that SAMs were distributed as approximately 1 per 3 alveoli. We conclude, SAMs are sparsely distributed in the parenchyma, suggesting that SAMs employ communicative strategies for pathogen detection in macrophage‐free alveoli (Support: HL57556).Support or Funding InformationSupport: HL57556