Brainstem Respiratory Centers Research Articles

SARS-CoV-2 Decreases Neuronal Activity in Brainstem Respiratory Centers in C57BI6/J Mice

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), also called COVID-19, targets the respiratory system, leading to symptoms such as cough, fever, and diffculty breathing. As the mechanisms behind SARS-CoV-2 infections continues to be studied, understanding of how this virus targets specific tissues becomes more apparent. Angiotensin-converting enzyme-2 (ACE2), the target of SARS-CoV infections and a functional receptor for SARS-CoV-2 invasions, is highly expressed in many tissues throughout the body, including the lungs, kidneys, and brain. Notably, our group previously reported that neurons are the main cells within the brain expressing ACE2. Accordingly, we hypothesized that neuronal infection of brainstem respiratory centers by SARS-CoV-2 could contribute to respiratory symptoms associated with COVID-19, specifically respiratory failure. C57BI6/J mice were mock infected or received SARS-CoV-2 (7.5x103 or 1.5x104) intranasally in a BSL-3 facility (University of Texas in Galveston) and were euthanized by CO2 hypoxia after 5 days post infection. The heads were harvested and immersed in formalin for 3 days before being transferred to LSU Health-NO for processing. Brains were carefully dissected out and preserved in optimal cutting temperature (OCT) before sectioning on a cryostat. Sections (30 μm) containing the retrotrapezoid nucleus (RTN) were selected as its neurons are part of the pontomedullary regions that generate the respiratory rhythm and pattern. Immunohistochemistry for c-Fos, a marker of neuronal activity, was used to assess neuronal activity in the RTN. Sections were incubated overnight with a primary monoclonal antibody (rabbit anti c-Fos, 1:1000) followed with a secondary goat antirabbit fluorescent IgG (GFP, 1:200, 1h) antibody. Sections were then mounted to slides in the dark to preserve the fluorescence and observed under the microscope. Images of neurons present in the RTN were captured and neurons were then hand counted and averaged. Neuronal activity in the RTN was decreased with the dose of SARS-CoV-2 used to infect cells in the brain. The greater the dose of SARS-CoV-2, the lower the number of c-Fos-positive neurons was detected in the RTN. Mock brains had the greatest number of neurons and brains infected with 1.5x104 SARS-CoV-2 had the lowest number of neurons in the RTN. This was demonstrated by counting neurons at 3 different intervals and taking the average. We conclude that SARS-CoV-2 targets neurons in respiratory centers, possibly contributing to impaired respiratory function in infected patients. NIH/NHLBI HL163814. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Changes in Tryptophan Hydroxylase 2 and 5HT1A Receptor Density May Contribute to Developmental Variation in Response to Serotonin in the in vitro Bullfrog Brainstem

Bullfrog, Lithobates catesbeiana, is a vertebrate animal model that can be used to study toxicology and developmental physiology. Our research is focused on better understanding vulnerability to brainstem respiratory centers in the pathology of sudden infant death syndrome (SIDS). We propose that a link between nicotine exposure during development leads to changes in the serotonergic signaling cascades of respiratory coordinating neurons. Caudal raphe neurons send serotonergic fibers that arborize and terminate directly on or near respiratory neurons in the brainstem. In bullfrogs, serotonin elicits a developmentally dependent effect on respiratory motor output. Late metamorphic tadpoles demonstrate an increase in lung burst activity with exposure to low concentrations of serotonin (≤ 0.5μM 5-hydroxytryptamine; 5-HT) mediated in part by 5-HT1a receptor (5HT1aR) activation. This developmental change in activity may be due to changes in the number of serotonergic fibers and/or 5-HT1a receptor density. Using the NIH Basic Local Alignment Search Tool (BLAST) we compared human and bullfrog 5HT1aR and tryptophan hydroxylase 2 (TH2) protein sequences and found a 34 and 65 percent identity match respectively. Quantitative western blot analysis of both proteins indicates developmental shifts in the serotonergic network during metamorphosis. These results were supported by immunohistochemical staining of 5HT1aR and TH2 in caudal raphe containing brainstem sections from pre-metamorphic tadpoles and post-metamorphic frogs. Impairments in the maturation of this serotonergic network may underlie the toxidrome associated with developmental nicotine exposure and further support the increased risk of SIDS following that exposure. This research was supported by the University of Wisconsin- La Crosse (UWL) through support from the UWL College of Science and Health, two UWL Undergraduate Research Creative Grants and a UWL FY23/24 Faculty Research Grant. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Mechanical ventilation induces brainstem inflammation in preterm fetal sheep.

Preterm infants have immature respiratory drive and often require prolonged periods of mechanical ventilation. Prolonged mechanical ventilation induces systemic inflammation resulting in ventilation-induced brain injury, however its effect on brainstem respiratory centers is unknown. We aimed to determine the effects of 24 h of mechanical ventilation on inflammation and injury in brainstem respiratory centres of preterm fetal sheep. Preterm fetal sheep at 110 ± 1 days (d) gestation were instrumented to provide mechanical ventilation in utero. At 112 ± 1 d gestation, fetuses received either mechanical ventilation (VENT; n = 7; 3 ml/kg) for 24 h, or no ventilation (CONT; n = 6). At post-mortem, fetal brainstems were collected for assessment of mRNA and histological markers of inflammation and injury. In utero ventilation (IUV) did not alter any blood-gas parameters. IUV significantly increased systemic IL-6 and IL-8 concentrations over the 24 h period compared to CONT. The number of ameboid microglia within the nucleus tractus solitarius and the raphe nucleus increased in VENT fetuses (p < 0.05 for both vs. control). The % area fraction of GFAP + staining was not significantly higher within the preBötzinger complex (p = 0.067) and retrotrapezoid nucleus and parafacial respiratory group (p = 0.057) in VENT fetuses compared to CONT. Numbers of caspase-3 and TUNEL-positive cells were similar between groups. Gene expression (mRNA) levels of inflammation, injury, cell death and prostaglandin synthesis within the brainstem were similar between groups. Mechanical ventilation induces a systemic inflammatory response with only moderate inflammatory effects within the brainstem respiratory centres of preterm fetal sheep.

Transgenic NADH dehydrogenase restores oxygen regulation of breathing in mitochondrial complex I-deficient mice

The hypoxic ventilatory response (HVR) is a life-saving reflex, triggered by the activation of chemoreceptor glomus cells in the carotid body (CB) connected with the brainstem respiratory center. The molecular mechanisms underlying glomus cell acute oxygen (O2) sensing are unclear. Genetic disruption of mitochondrial complex I (MCI) selectively abolishes the HVR and glomus cell responsiveness to hypoxia. However, it is unknown what functions of MCI (metabolic, proton transport, or signaling) are essential for O2 sensing. Here we show that transgenic mitochondrial expression of NDI1, a single-molecule yeast NADH/quinone oxidoreductase that does not directly contribute to proton pumping, fully recovers the HVR and glomus cell sensitivity to hypoxia in MCI-deficient mice. Therefore, maintenance of mitochondrial NADH dehydrogenase activity and the electron transport chain are absolutely necessary for O2-dependent regulation of breathing. NDI1 expression also rescues other systemic defects caused by MCI deficiency. These data explain the role of MCI in acute O2 sensing by arterial chemoreceptors and demonstrate the optimal recovery of complex organismal functions by gene therapy.

Reverse Triggering during Controlled Ventilation: From Physiology to Clinical Management.

Reverse triggering dyssynchrony is a frequent phenomenon recently recognized in sedated critically ill patients under controlled ventilation. It occurs in at least 30-55% of these patients and often occurs in the transition from fully passive to assisted mechanical ventilation. During reverse triggering, patient inspiratory efforts start after the passive insufflation by mechanical breaths. The most often referred mechanism is the entrainment of the patient's intrinsic respiratory rhythm from the brainstem respiratory centers to periodic mechanical insufflations from the ventilator. However, reverse triggering might also occur because of local reflexes without involving the respiratory rhythm generator in the brainstem. Reverse triggering is observed during the acute phase of the disease, when patients may be susceptible to potential deleterious consequences of injurious or asynchronous efforts. Diagnosing reverse triggering might be challenging and can easily be missed. Inspection of ventilator waveforms or more sophisticated methods, such as the electrical activity of the diaphragm or esophageal pressure, can be used for diagnosis. The occurrence of reverse triggering might have clinical consequences. On the basis of physiological data, reverse triggering might be beneficial or injurious for the diaphragm and the lung, depending on the magnitude of the inspiratory effort. Reverse triggering can cause breath-stacking and loss of protective lung ventilation when triggering a second cycle. Little is known about how to manage patients with reverse triggering; however, available evidence can guide management on the basis of physiological principles.

Constitutive Expression of Hif2α Confers Acute O2 Sensitivity to Carotid Body Glomus Cells.

Acute oxygen (O2) sensing and adaptation to hypoxia are essential for physiological homeostasis. The prototypical acute O2 sensing organ is the carotid body, which contains chemosensory glomus cells expressing O2-sensitive K+ channels. Inhibition of these channels during hypoxia leads to cell depolarization, transmitter release, and activation of afferent sensory fibers terminating in the brain stem respiratory and autonomic centers. Focusing on recent data, here we discuss the special sensitivity of glomus cell mitochondria to changes in O2 tension due to Hif2α-dependent expression of several atypical mitochondrial electron transport chain subunits and enzymes. These are responsible for an accelerated oxidative metabolism and the strict dependence of mitochondrial complex IV activity on O2 availability. We report that ablation of Epas1 (the gene coding Hif2α) causes a selective downregulation of the atypical mitochondrial genes and a strong inhibition of glomus cell acute responsiveness to hypoxia. Our observations indicate that Hif2α expression is required for the characteristic metabolic profile of glomus cells and provide a mechanistic explanation for the acute O2 regulation of breathing.

Electrocution- post-mortem presentations, problems and pitfalls.

Deaths due to electrocution occur when there has been passage of an electric current through the body. Lethal mechanisms may involve the heart with ventricular fibrillation, or the respiratory muscles or brainstem respiratory centres with respiratory paralysis/cessation. The size of the current that flows through the body is directly dependent on the potential difference of the circuit and the resistance of the tissues. The majority of deaths are accidental, with suicides being less common and homicides being very rare. Problems arising in the evaluation of cases include situations where electrocution has clearly occurred from the scene findings, but no injuries are detectable at autopsy, or when electrical burns are found at autopsy with no defective equipment/circuitry identified at the death scene.

Functional MRI Correlates of Carbon Dioxide Chemosensing in Persons With Epilepsy.

ObjectivesSudden unexpected death in epilepsy (SUDEP) is a catastrophic epilepsy outcome for which there are no reliable premortem imaging biomarkers of risk. Percival respiratory depression is seen in monitored SUDEP and near SUDEP cases, and abnormal chemosensing of raised blood carbon dioxide (CO2) is thought to contribute. Damage to brainstem respiratory control and chemosensing structures has been demonstrated in structural imaging and neuropathological studies of SUDEP. We hypothesized that functional MRI (fMRI) correlates of abnormal chemosensing are detectable in brainstems of persons with epilepsy (PWE) and are different from healthy controls (HC).MethodsWe analyzed fMRI BOLD activation and brain connectivity in 10 PWE and 10 age- and sex-matched HCs during precisely metered iso-oxic, hypercapnic breathing challenges. Segmented brainstem responses were of particular interest, along with characterization of functional connectivity metrics between these structures. Regional BOLD activations during hypercapnic challenges were convolved with hemodynamic responses, and the resulting activation maps were passed on to group-level analyses. For the functional connectivity analysis, significant clusters from BOLD results were used as seeds. Each individual seed time-series activation map was extracted for bivariate correlation coefficient analyses to study changes in brain connectivity between PWE and HCs.Results(1) Greater brainstem BOLD activations in PWE were observed compared to HC during hypercapnic challenges in several structures with respiratory/chemosensing properties. Group comparison between PWE vs. HC showed significantly greater activation in the dorsal raphe among PWE (p < 0.05) compared to HCs. (2) PWE had significantly greater seed-seed connectivity and recruited more structures during hypercapnia compared to HC.SignificanceThe results of this study show that BOLD responses to hypercapnia in human brainstem are detectable and different in PWE compared to HC. Increased dorsal raphe BOLD activation in PWE and increased seed-seed connectivity between brainstem and adjacent subcortical areas may indicate abnormal chemosensing in these individuals. Imaging investigation of brainstem respiratory centers involved in respiratory regulation in PWE is an important step toward identifying suspected dysfunction of brainstem breathing control that culminates in SUDEP and deserve further study as potential imaging SUDEP biomarkers.

Alterations in brainstem respiratory centers following peripheral inflammation: A systematic review

Immune mediators upregulated in peripheral to central immune communication can modulate respiratory function by direct action on brainstem respiratory circuits. In this systematic review we consolidated findings from independent studies examining the relationship between peripheral and neuro- inflammation within brainstem respiratory centres. Microglia and astrocytes modulate brainstem neuroinflammation in response to peripheral immune mediators which then regulates neuronal activity and ultimately respiratory behaviours. Overall, respiratory brainstem nuclei showed increases in several key immune factors, and glia showed an increased response following peripheral inflammation. However, the functional impact of this neuroinflammation remains unclear.

Mechanisms of opioid-induced respiratory depression.

Opioid-induced respiratory depression (OIRD), the primary cause of opioid-induced death, is the neural depression of respiratory drive which, together with a decreased level of consciousness and obstructive sleep apnea, cause ventilatory insufficiency. Variability of responses to opioids and individual differences in physiological and neurological states (e.g., anesthesia, sleep-disordered breathing, concurrent drug administration) add to the risk. Multiple sites can independently exert a depressive effect on breathing, making it unclear which sites are necessary for the induction of OIRD. The generatorof inspiratoryrhythm is the preBötzinger complex (preBötC) in the ventrolateral medulla. Other important brainstem respiratory centres includethe pontine Kölliker-Fuse and adjacent parabrachial nuclei (KF/PBN) in the dorsal lateral pons, and the dorsal respiratory group in the medulla. Deletion of μ opioid receptors from neurons showed that the preBötC and KF/PBN contribute to OIRD with the KF as a respiratory modulator and the preBötC as inspiratory rhythm generator. Glutamatergic neurons expressing NK-1R and somatostatin involved in the autonomic function of breathing, and modulatory signal pathways involvingGIRK and KCNQ potassium channels, remain poorly understood. Reversal of OIRD has relied heavily on naloxone which also reverses analgesia but mismatches between the half-lives of naloxone and opioids can make it difficult to clinically safely avoid OIRD. Maternal opioid use, which is rising, increases apneas and destabilizes neonatal breathing but opioid effects on maternal and neonatal respiratory circuits in neonatal abstinence syndrome (NAS) are not well understood. Methadone, administered to alleviate symptoms of NAS in humans, desensitizes rats to RD.

SARS-CoV-2 entry sites are present in all structural elements of the human glossopharyngeal and vagal nerves: Clinical implications.

SummaryBackgroundSevere acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infections result in the temporary loss of smell and taste in about one third of confirmed cases.MethodsWe used immunohistochemistry to confirm the presence of ACE2, NRP1 and TMPRSS2 in two cranial nerves (IX and X) that mediate taste where they leave/join the medulla. Samples from three (two paraffin embedded and one frozen) postmortem samples were studied (facial (VII) nerve was not available). We also performed immunohistochemistry using the same antibodies in two human cell lines (oligodendrocytes and fibroblasts), and we isolated RNA from one nerve and performed PCR to confirm the presence of the mRNAs that encode the proteins visualized.FindingsAll three of the proteins (ACE-2, NRP1 and TMPRSS2) required for SARS-CoV-2 infections appear to be present in all cellular components (Schwann cells, axons, vascular endothelium, and connective tissue) of the human IXth and Xth nerves near the medulla. We also found their mRNAs in the nerve and in human oligodendrocytes and fibroblasts which were stained by antibodies directed at the three proteins examined.InterpretationInfection of the IXth and Xth nerves by the SARS-CoV-2 virus is likely to cause the loss of taste experienced by many Covid patients. Migration of the virus from the oral cavity through these nerves to brainstem respiratory centers might contribute to the problems that patients experience.FundingThis study was supported by the Intramural Research Program of the National Institute of Dental and Craniofacial Research (NIDCR), NIH (intramural project no. ZDE000755-01), and the Human Brain Tissue Bank, Semmelweis University, Budapest, Hungary from the Hungarian Brain Research Program (2017-1.2.1-NKP-2017-00002).

Increased Prostaglandin E2 in Brainstem Respiratory Centers Is Associated With Inhibition of Breathing Movements in Fetal Sheep Exposed to Progressive Systemic Inflammation.

BackgroundPreterm newborns commonly experience apnoeas after birth and require respiratory stimulants and support. Antenatal inflammation is a common antecedent of preterm birth and inflammatory mediators, particularly prostaglandin E2 (PGE2), are associated with inhibition of vital brainstem respiratory centers. In this study, we tested the hypothesis that exposure to antenatal inflammation inhibits fetal breathing movements (FBMs) and increases inflammation and PGE2 levels in brainstem respiratory centers, cerebrospinal fluid (CSF) and blood plasma.MethodsChronically instrumented late preterm fetal sheep at 0.85 of gestation were randomly assigned to receive repeated intravenous saline (n = 8) or lipopolysaccharide (LPS) infusions (experimental day 1 = 300 ng, day 2 = 600 ng, day 3 = 1200 ng, n = 8). Fetal breathing movements were recorded throughout the experimental period. Sheep were euthanized 4 days after starting infusions for assessment of brainstem respiratory center histology.ResultsLPS infusions increased circulating and cerebrospinal fluid PGE2 levels, decreased arterial oxygen saturation, increased the partial pressure of carbon dioxide and lactate concentration, and decreased pH (p < 0.05 for all) compared to controls. LPS infusions caused transient reductions in the % of time fetuses spent breathing and the proportion of vigorous fetal breathing movements (P < 0.05 vs. control). LPS-exposure increased PGE2 expression in the RTN/pFRG (P < 0.05 vs. control) but not the pBÖTC (P < 0.07 vs. control) of the brainstem. No significant changes in gene expression were observed for PGE2 enzymes or caspase 3. LPS-exposure reduced the numbers of GFAP-immunoreactive astrocytes in the RTN/pFRG, NTS and XII of the brainstem (P < 0.05 vs. control for all) and increased microglial activation in the RTN/pFRG, preBÖTC, NTS, and XII brainstem respiratory centers (P < 0.05 vs. control for all).ConclusionChronic LPS-exposure in late preterm fetal sheep increased PGE2 levels within the brainstem, CSF and plasma, and was associated with inhibition of FBMs, astrocyte loss and microglial activation within the brainstem respiratory centers. Further studies are needed to determine whether the inflammation-induced increase in PGE2 levels plays a key role in depressing respiratory drive in the perinatal period.

Chapter 10 - Stroke and breathing

Stroke remains a leading cause of neurologic disability with wide ranging effects, including a variety of respiratory abnormalities. Stroke may influence the central control of the respiratory drive and breathing pattern, airway protection and maintenance, and the respiratory mechanics of inspiration and expiration. In the acute phase of stroke, the central control of breathing is affected by changes in consciousness, cerebral edema, and direct damage to brainstem respiratory centers, resulting in abnormalities in respiratory pattern and loss of airway protection. Common acute complications related to respiratory dysfunction include dysphagia, aspiration, and pneumonia. Respiratory control centers are located in the brainstem, and brainstem stroke causes specific patterns of respiratory dysfunction. Depending on the exact location and extent of stroke, respiratory failure may occur. While major respiratory abnormalities often improve over time, sleep-disordered breathing remains common in the subacute and chronic phases and worsens outcomes. Respiratory mechanics are impaired in hemiplegic or hemiparetic stroke, contributing to worse cardiopulmonary health in stroke survivors. Interventions to address the respiratory complications are under researched, and further investigation in this area is critical to improving outcomes among stroke survivors.

The neurologic complications of COVID-19

Human infection with SARS-CoV-2, the agent of COVID-19, affects both the central nervous system (CNS) and the peripheral nervous system (PNS) including the muscle (Román GC, SpencerPS, Reis J, et al. The Neurology of COVID-19 Revisited. J Neurol Sci 414 (2020) 116884). This virus is neurogenic and invades the CNS via cranial nerve I, progressing into rhinencephalon and brainstem respiratory centers resulting in irreversible respiratory failure responsible for most of the 6.9 million excess deaths due to this coronavirus (Institute for Health Metrics and Evaluation, University of Washington [www.healthdata.org]).

Histamine Activates Chemosensitive Neurons in the Retrotrapezoid Nucleus

Histaminergic neurons of the posterior hypothalamic tuberomammillary nucleus (TMN) are pH-sensitive and contribute to CO2/H+-dependent behaviors including arousal and respiratory activity. Considering histaminergic neurons project to several brainstem respiratory centers including the retrotrapezoid nucleus (RTN), and since chemosensitive RTN neurons are an important source of CO2/H+-dependent respiratory drive, we wondered whether and how histamine contributes to RTN chemoreception at the cellular level and in anesthetized rats. In brain slices obtained from rat pups (7-12 days old), chemosensitive RTN neurons were identified in cell-attached voltage-clamp mode by their characteristic firing response to CO2 (≥ 0.8 Hz increase in activity in response to 10% CO2). We found that most chemosensitive RTN neurons showed a dose dependent increase in activity in response to bath application of histamine dihydrochloride (HD: 1-25 μM). The increased activity of RTN neurons by HD (25 mM) was blunted by bath application of the H1 receptor antagonist DPH (diphenhydramine hydrochloride; 100 µM) (1.1 ± 0.1 Hz to -0.06 ± 0.2 Hz; n = 7) or the H2 receptor antagonist ranitidine (ranitidine hydrochloride; 10 µM) (1.0 ± 0.2 Hz to 0.3 ± 0.3 Hz; n = 5). At the whole animal level, we measured mean arterial pressure (MAP) and diaphragm muscle activity (DIAEMG) in urethane-anaesthetized, vagotomized and artificial ventilated male Wistar rats. Unilateral injection of HD (25 mM - 50 nl) into the RTN increased DIAEMG amplitude (17.41 ± 3.8 vs. saline: 0.55 ± 1.9%) and DIAEMG frequency (4.72 ± 1.7 vs -1.8 ± 1.5) without changes MAP. Bilateral injections of DPH (0.5 mM) into the RTN decreased DIAEMG amplitude (-62.6 ± 14.5. vs. saline: -1.1 ± 1.3%), DIAEMG frequency (-66.4 ± 13.4 vs. saline: -1.5 ± 1.9%) and MAP (-43.67 ± 8,4 vs. saline: -3.2 ± 1.7 mmHg). Despite the strong inhibitory effect of DPH on baseline breathing, the hypercapnic ventilatory response was preserved in urethane-anesthetized rats under these experimental conditions. These results suggest histamine signaling via H1 and H2 receptors modulates activity of RTN neurons and respiratory activity.

Isoflurane inhibits a Kir4.1/5.1-like conductance in neonatal rat brainstem astrocytes and recombinant Kir4.1/5.1 channels in a heterologous expression system.

All inhalation anesthetics used clinically including isoflurane can suppress breathing; since this unwanted side effect can persist during the postoperative period and complicate patient recovery, there is a need to better understand how isoflurane affects cellular and molecular elements of respiratory control. Considering that astrocytes in a brainstem region known as the retrotrapezoid nucleus (RTN) contribute to the regulation of breathing in response to changes in CO2/H+ (i.e., function as respiratory chemoreceptors), and astrocytes in other brain regions are highly sensitive to isoflurane, we wanted to determine whether and how RTN astrocytes respond to isoflurane. We found that RTN astrocytes in slices from neonatal rat pups (7-12 days postnatal) respond to clinically relevant levels of isoflurane by inhibition of a CO2/H+-sensitive Kir4.1/5.1-like conductance [50% effective concentration (EC50) = 0.8 mM or ~1.7%]. We went on to confirm that similar levels of isoflurane (EC50 = 0.53 mM or 1.1%) inhibit recombinant Kir4.1/5.1 channels but not homomeric Kir4.1 channels expressed in HEK293 cells. We also found that exposure to CO2/H+ occluded subsequent effects of isoflurane on both native and recombinant Kir4.1/5.1 currents. These results identify Kir4.1/5.1 channels in astrocytes as novel targets of isoflurane. These results suggest astrocyte Kir4.1/5.1 channels contribute to certain aspects of general anesthesia including altered respiratory control.NEW & NOTEWORTHY An unwanted side effect of isoflurane anesthesia is suppression of breathing. Despite this clinical significance, effects of isoflurane on cellular and molecular elements of respiratory control are not well understood. Here, we show that isoflurane inhibits heteromeric Kir4.1/5.1 channels in a mammalian expression system and a Kir4.1/5.1-like conductance in astrocytes in a brainstem respiratory center. These results identify astrocyte Kir4.1/5.1 channels as novel targets of isoflurane and potential substrates for altered respiratory control during isoflurane anesthesia.

Postictal brainstem hypoperfusion and risk factors for sudden unexpected death in epilepsy.

Since the strongest risk factor for sudden unexpected death in epilepsy (SUDEP) is frequent bilateral tonic-clonic seizures (BTCS), our aim was to determine whether postictal hypoperfusion in brainstem respiratory centers (BRCs) is more common following tonic-clonic seizures. We studied 21 patients with focal epilepsies who underwent perfusion imaging with arterial spin labeling MRI. Subtraction maps of cerebral blood flow were obtained from the postictal and baseline scans. We identified 6 regions of interest in the brainstem that contain key BRCs. Patients were considered to have postictal BRC hypoperfusion if any of the 6 regions of interest were significantly hypoperfused. All 6 patients who experienced BTCS during the study had significant clusters of postictal hypoperfusion in BRCs compared to 7 who had focal impaired awareness seizures (7/15). The association between seizure type studied and the presence of BRC hypoperfusion was significant. Duration of epilepsy and frequency of BTCS were not associated with postictal brainstem hypoperfusion despite also being associated with risk for SUDEP. Postictal hypoperfusion in brainstem respiratory centers occurs more often following BTCS than other seizure types, providing a possible explanation for the increased risk of SUDEP in patients who regularly experience BTCS.

Validation and Development of a Cell‐based Model of Acute Oxygen Sensing

Located at the bifurcation of the carotid artery, the carotid body senses a decrease in blood oxygen to increase breathing within seconds. This chemosensory organ is important for physiological adaptation to low oxygen (hypoxia), and its activity is increased in chronic diseases like sleep‐disordered breathing, chronic heart failure, and metabolic syndrome. In the carotid body, neuroendocrine cells called glomus cells respond to hypoxia to stimulate afferent nerves that signal to brainstem respiratory centers. Several important steps of the response of glomus cells to hypoxia have been identified, including the inhibition of oxygen‐sensitive potassium currents, membrane depolarization, intracellular calcium increase, and neurotransmitter release. However, the exact oxygen sensor(s) and how it integrates with these downstream steps remains controversial. A major limitation in studying glomus cell sensory signaling is poor recovery of primary glomus cells from tissue, and a significant fraction of cultured glomus cells are not responsive to hypoxia. We are exploring whether the PC12 cell line, derived from a rat pheochromocytoma, can serve as a model for carotid body oxygen sensing. Previously, other labs demonstrated that PC12 cells have similar acute responses to hypoxia as glomus cells, and more recent gene expression studies show that PC12 cells express some key signaling components implicated in carotid body oxygen sensing. Here, we confirm that hypoxia inhibits potassium currents and causes membrane depolarization in PC12 cells and describe the subtypes of potassium channels found in PC12. We hope to develop the PC12 cell line as a more tractable cell‐based model of acute oxygen sensing and to study the interactions of putative oxygen sensors with downstream signaling through ion channels and neurotransmitter release using this model.

Brainstem ventilatory dysfunction: A plausible mechanism for dyspnea in Parkinson's Disease?

Dyspnea is an under-recognized and debilitating symptom that is reported in up to 40% of patients with Parkinson's disease and may have multiple origins. Despite its frequency, it is poorly researched, and there is a general lack of understanding of the pathophysiology of dyspnea and respiratory dysfunction in PD. Consequently, a number of PD patients are labelled as having "unexplained dyspnea." Studies to date have focused mainly on evaluating ventilatory capacity and lung volumes, and little is known about the effects of the disease on the medullary and pontine ventilatory control centers within the brainstem. This is of particular relevance in view of neuropathological studies demonstrating early involvement of the dorsal medulla and other brainstem structures by the disease process. The possibility that impaired brainstem ventilatory control is a contributory mechanism for dyspnea and could be a premotor manifestation in some PD patients therefore warrants further attention. This review focuses on clinical, pathological, and experimental evidence for the involvement of brainstem respiratory centers in PD. We highlight the need for further research, particularly in PD patients with unexplained dyspnea. © 2020 International Parkinson and Movement Disorder Society.

Brainstem Dysfunction in SARS-COV-2 Infection can be a Potential Cause of Respiratory Distress.

A terrible pandemic, Covid-19, has captivated scientists to investigate if SARS-CoV-2 virus infects the central nervous system (CNS). A crucial question is if acute respiratory distress syndrome (ARDS), the main cause of death in this pandemic, and often refractory to treatments, can be explained by respiratory center dysfunction. To discuss that ARDS can be caused by SARS-CoV-2 infection of the respiratory center in the brainstem. I reviewed literature about SARS-CoV-2 mechanisms to infect the respiratory center in the brainstem. An increasing amount of reports demonstrates that neurotropism is a common feature of coronavirus, which have been found in the brains of patients and experimental models, where the brainstem was severely infested. Recent studies have provided tremendous indication of the incidence of acute respiratory failure due to SARS-CoV-2 infection of the brainstem. SARS-CoV-2 might infect the CNS through the olfactory bulb, spreading from the olfactory nerves to the rhinencephalon, and finally reaching the brainstem. Hence, the virus infection causes respiratory center dysfunctions, leading to ARDS in COVID-19 patients. I conclude that acute ARDS in Covid-19 can be caused by SARS-CoV-2 invasion of brainstem respiratory center, suggesting the needs of more specific and aggressive treatments, with the direct participation of neurologists and neurointensivists.