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After multiple waves of the COVID-19 pandemic, it has become clear that the impact of SARS-CoV-2 will carry on for years to come. Acutely infected patients show a broad range of disease severity, depending on virus variant, vaccination status, age and the presence of underlying medical and physical conditions, including obesity. Additionally, a large number of patients who have been infected with the virus present with post-COVID syndrome. In September 2020, the International Society for the Advancement of Respiratory Psychophysiology organized a virtual interest meeting on ‘Respiratory research in the age of COVID-19’, which aimed to discuss how research in respiratory psychophysiology could contribute to a better understanding of psychophysiological interactions in COVID-19. In the resulting current paper, we propose an interdisciplinary research agenda discussing selected research questions on acute and long-term neurobiological, physiological and psychological outcomes and mechanisms related to respiration and the airways in COVID-19, as well as research questions on comorbidity and potential treatment options, such as physical rehabilitation.

Background: Leigh syndrome (LS) is a progressive neurodegenerative mitochondrial disease character-ized by necrotizing lesions affecting different parts of the central nervous system, especially in the brainstem and basal ganglia. Lesions in this area may involve respiratory and sleep centers, resulting in the clinically significant disturbances seendbut poorly characterizeddin LS. The purpose of the present study is to characterize and compare the physiologic responses to respiratory disturbances quantified by polysomnography metrics of children with LS with age -sex-and apnea-hypopnea index (AHI)-matched patients with obstructive sleep apnea (OSA), a common clinical population with similar burden of sleep -disordered breathing.Methods: Retrospective comparative study of polysomnographic data from six patients with LS were reviewed and compared with 18 age-sex-AHI-matched patients with OSA, with particular attention to cardiorespiratory and sleep architecture metrics.Results: Sleep architecture and stage duration were conserved in LS and OSA groups, but increased wake after sleep onset was seen among the first group. The LS group exhibited both obstructive and central sleep apnea. The group also had significantly greater values of heart rate, >= 3% oxygen desaturation index, and lower values of sleep efficiency, respiratory arousal index, and total sleep time when compared with the OSA group.Conclusions: Patients with LS exhibited significantly more sleep-related cardiorespiratory disturbances and sleep fragmentation when compared with neurotypical children with OSA. Given that these findings are plausibly detrimental to health and development, sleep evaluation in patients with similar conditions should be encouraged for early management.

We identified six novel de novo human KCNQ5 variants in children with motor/language delay, intellectual disability (ID), and/or epilepsy by whole exome sequencing. These variants, comprising two nonsense and four missense alterations, were functionally characterized by electrophysiology in HEK293/CHO cells, together with four previously reported KCNQ5 missense variants (Lehman A, Thouta S, Mancini GM, Naidu S, van Slegtenhorst M, McWalter K, Person R, Mwenifumbo J, Salvarinova R; CAUSES Study; EPGEN Study; Guella I, McKenzie MB, Datta A, Connolly MB, Kalkhoran SM, Poburko D, Friedman JM, Farrer MJ, Demos M, Desai S, Claydon T. Am J Hum Genet 101: 65–74, 2017). Surprisingly, all eight missense variants resulted in gain of function (GOF) due to hyperpolarized voltage dependence of activation or slowed deactivation kinetics, whereas the two nonsense variants were confirmed to be loss of function (LOF). One severe GOF allele (P369T) was tested and found to extend a dominant GOF effect to heteromeric KCNQ5/3 channels. Clinical presentations were associated with altered KCNQ5 channel gating: milder presentations with LOF or smaller GOF shifts in voltage dependence [change in voltage at half-maximal conduction (ΔV(50)) = ∼−15 mV] and severe presentations with larger GOF shifts in voltage dependence (ΔV(50) = ∼−30 mV). To examine LOF pathogenicity, two Kcnq5 LOF mouse lines were created with CRISPR/Cas9. Both lines exhibited handling- and thermal-induced seizures and abnormal cortical EEGs consistent with epileptiform activity. Our study thus provides evidence for in vivo KCNQ5 LOF pathogenicity and strengthens the contribution of both LOF and GOF mutations to global pediatric neurological impairment, including ID/epilepsy. NEW & NOTEWORTHY Six novel de novo human KCNQ5 variants were identified from children with neurodevelopmental delay, intellectual disability, and/or epilepsy. Expression of these variants along with four previously reported KCNQ5 variants from a similar cohort revealed GOF potassium channels, negatively shifted in V(50) of activation and/or delayed deactivation kinetics. GOF is extended to KCNQ5/3 heteromeric channels, making these the predominant channels affected in heterozygous de novo patients. Kcnq5 LOF mice exhibited seizures, consistent with in vivo pathogenicity.

Cellular and network properties must be capable of generating rhythmic activity that is both flexible and stable. This is particularly important for breathing, a rhythmic behavior that dynamically adapts to environmental, behavioral, and metabolic changes from the first to the last breath. The pre-Bötzinger complex (preBötC), located within the ventral medulla, is responsible for producing rhythmic inspiration. Its cellular properties must be tunable, flexible as well as stabilizing. Here, we explore the role of the hyperpolarization-activated, nonselective cation current (I(h)) for stabilizing PreBötC activity during opioid exposure and reduced excitatory synaptic transmission. Introducing I(h) into an in silico preBötC network predicts that loss of this depolarizing current should significantly slow the inspiratory rhythm. By contrast, in vitro and in vivo experiments revealed that the loss of I(h) minimally affected breathing frequency, but destabilized rhythmogenesis through the generation of incompletely synchronized bursts (burstlets). Associated with the loss of I(h) was an increased susceptibility of breathing to opioid-induced respiratory depression or weakened excitatory synaptic interactions, a paradoxical depolarization at the cellular level, and the suppression of tonic spiking. Tonic spiking activity is generated by nonrhythmic excitatory and inhibitory preBötC neurons, of which a large percentage express I(h). Together, our results suggest that I(h) is important for maintaining tonic spiking, stabilizing inspiratory rhythmogenesis, and protecting breathing against perturbations or changes in network state. NEW & NOTEWORTHY The I(h) current plays multiple roles within the preBötC. This current is important for promoting intrinsic tonic spiking activity in excitatory and inhibitory neurons and for preserving rhythmic function during conditions that dampen network excitability, such as in the context of opioid-induced respiratory depression. We therefore propose that the I(h) current expands the dynamic range of rhythmogenesis, buffers the preBötC against network perturbations, and stabilizes rhythmogenesis by preventing the generation of unsynchronized bursts.

We identified six novel de novo human KCNQ5 variants in children with motor/language delay, intellectual disability (ID), and/or epilepsy by whole exome sequencing. These variants, comprising two nonsense and four missense alterations, were functionally characterized by electrophysiology in HEK293/CHO cells, together with four previously reported KCNQ5 missense variants (Lehman A, Thouta S, Mancini GM, Naidu S, van Slegtenhorst M, McWalter K, Person R, Mwenifumbo J, Salvarinova R; CAUSES Study; EPGEN Study; Guella I, McKenzie MB, Datta A, Connolly MB, Kalkhoran SM, Poburko D, Friedman JM, Farrer MJ, Demos M, Desai S, Claydon T. Am J Hum Genet 101: 65-74, 2017). Surprisingly, all eight missense variants resulted in gain of function (GOF) due to hyperpolarized voltage dependence of activation or slowed deactivation kinetics, whereas the two nonsense variants were confirmed to be loss of function (LOF). One severe GOF allele (P369T) was tested and found to extend a dominant GOF effect to heteromeric KCNQ5/3 channels. Clinical presentations were associated with altered KCNQ5 channel gating: milder presentations with LOF or smaller GOF shifts in voltage dependence [change in voltage at half-maximal conduction (ΔV50) = ~-15 mV] and severe presentations with larger GOF shifts in voltage dependence (ΔV50 = ~30 mV). To examine LOF pathogenicity, two Kcnq5 LOF mouse lines were created with CRISPR/Cas9. Both lines exhibited handling- and thermal-induced seizures and abnormal cortical EEGs consistent with epileptiform activity. Our study thus provides evidence for in vivo KCNQ5 LOF pathogenicity and strengthens the contribution of both LOF and GOF mutations to global pediatric neurological impairment, including ID/epilepsy.

The generation of rhythmic activity is fundamental to the brain. Rhythmicity is critical for cognition, learning and memory, the generationof sleep and wakefulness, and the generation of rhythmic motor behaviors. Breathing is a highly integrated rhythmic behavior that playsmultiple roles through its interactions with the heart and various states of the brain and by controlling ventilation. Various experimentalapproaches led to identifying and manipulating rhythmogenic networks and neurons in the medulla that are critical for the generationof breathing. These rhythmogenic networks can reconfigure to generate different activity patterns that give rise to eupnea, sighs, andgasping. They contain excitatory and inhibitory neurons that are critical for rhythmogenesis, establishing the phase relationship andfrequency of respiratory activity. Rhythmogenic networks in the brainstem interact with multiple brain areas and the heart to establishthe true complexity of the breathing behavior that is essential for life.

Swallowing is a vital behavior that is coordinated with breathing involving rhythmogenic networks in the medulla, the preBötzinger complex (PreBötC) and postinspiratory complex (PiCo). These networks are critical for generating inspiratory and postinspiratory activity, respectively. Both areas also interact with neurons involved in autonomic control, which contributes to increased sympathetic drive after chronic intermittent hypoxia exposure (CIH) exposure.Prior studies have demonstrated that CIH, an experimental model of obstructive sleep apnea, has been associated with dysphagia. However, the contribution of the sympathetic activity to swallow function is unknown in both healthy and diseased models. In this study we investigated the cervical sympathetic response to water swallow stimulation as well as optogenetic stimulation of the brainstem in an in vivo mouse preparation under control and CIH conditions for 21 days (5% O2 – 80 bouts/day). Recordings of diaphragm (DIA), submental and laryngeal muscles complex, hypoglossal (HN), vagus (cVN), and cervical sympathetic nerves (cSN) were performed in spontaneously breathing, anaesthetized (Urethane 1.5mg/kg) adult mice in baseline conditions and during swallow stimulation by injecting 0.1cc of water into the mouth. We found that baseline cSN is enhanced after CIH exposure due to a blunted respiratory-sympathetic coupling. During swallow stimulation, cSN activity was increased in both groups, which was further increased in the CIH group, suggesting swallow triggers an excitatory vasomotor sympathetic pathway. In order to understand the mechanistic underpinning of these findings, we use optogenetic stimulation of PreBötC and PiCo neurons to explore the effects on sympathetic activity modulation during swallow-breathing coordination. NIH Grants: P01 HL090554, R01 HL126523, R01 HL144801, R01 HL151389 and FY22 24050162. This is the full abstract presented at the American Physiology Summit 2023 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.

Leigh Syndrome is a severe neurometabolic disorder and the most common form of mitochondrial disorder in the pediatric population. It has been linked to loss of function mutations in Ndufs4, the gene that codes for a subunit of the mitochondrial complex I. First signs of early-onset Leigh Syndrome (LS) include difficulty swallowing (dysphagia), suckling and feeding. These symptoms result in an inability to grow and gain weight, leading to a failure to thrive. Mice lacking Ndufs4 globally, constitutes as an excellent model of LS, mimicking several core symptoms of the disease in humans including seizures, ataxia, hypotonia, rigidity, weight loss, and failure to thrive. In our previous work, we demonstrated that excitatory and inhibitory neurons drive distinct phenotypes in the mouse model. Knock out (KO) of Ndufs4 in mice, specifically in glutamatergic ( Vglut2) neurons, reproduces motor dysfunctions associated with LS. Whereas KO of the gene in GABAergic neurons primarily lead to epilepsy. Here we uncovered that KO of Ndufs4 gene, specifically in the Vglut2 neurons, mimics swallow dysfunction seen in LS. Using freely breathing urethane anesthetized adult Vglut2/Ndufs4 KO mice, swallow was evoked by injection of water into the oral cavity. Swallow and respiratory activity was measured via monopolar suction electrodes of the hypoglossal (XII) and vagus (X) nerves as well as bipolar electromyogram (EMG) of the submental, laryngeal complex and costal diaphragm muscles. Post-hoc histological analysis of swallow and breathing related medullary areas was performed using IBA-1 for microglia and TMEM119 for macrophage analysis. This protocol was performed in Vglut2/Ndufs4 KO mice 1) exposed to room air and 2) exposed to 11% oxygen for 6 months. We found, mice exposed to chronic hypoxia (CH) no longer presented with symptoms such as: ataxia, hunched posture, unbalanced, clasping, weight loss, as seen in mice exposed to room air (RA). CH mice lived significantly longer than RA mice (225 ±6, 111±19, p= 0.000). CH mice weighed significantly more than RA mice (26 ±2g, 19±2g, p= 0.000). We also saw a discoordination in swallowing and breathing in RA mice with 1) swallows occurring during inspiration, 2) various abnormal swallow related phenotypes, 3) swallow induced apneas for more than 30s, and 4) variable reset of the respiratory rhythm. CH mice showed no evidence of the former disturbances, indicating CH rescues swallow-breathing coordination. CH exposure also suppressed inflammatory reaction in respiratory and swallow centers such as PiCo and NTS. This study gives first insights into possible mechanisms of LS and treatment for dysphagia in LS. F32 HL160102-01, P01 HL090554, R01 HL126523, R01 HL144801, R01 HL151389, R01 NIH/NS 102796 This is the full abstract presented at the American Physiology Summit 2023 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.

During wakefulness, breathing is frequently voluntarily modulated to facilitate various behaviors including vocalization, feeding, and whisking. Breathing also correlates highly with changes in behavioral arousal such as during sleep ( Physiol 36: 203, 2021) , periods of high emotionality ( Neuroimage 134: 305, 2016), or recovery from anesthesia ( Curr Biol 28: 2145, 2018). The medial prefrontal cortex (mPFC) alters voluntary executive function ( Brain Stimul 13: 582, 2020) and arousal ( Trends Neurosci 45: 722, 2022). Additionally, previous studies have shown that the mPFC has the capacity to modulate breathing ( Resp Physiol Neurobiol 303: 103924, 2022). This modulation occurs via top-down influence of cortical and subcortical nuclei and hinges on a balance of excitatory and inhibitory activity within the mPFC ( Int Rev Neurobiol 158: 337, 2021). Furthermore, there are direct and indirect connections from the mPFC to the pontine and ventral respiratory column (VRC) neurons that control breathing ( J Comp Neurol 492: 145, 2005). Taken together, these data suggest a tripartite relationship among the mPFC, behavioral arousal, and breathing, however, the exact neuronal mechanisms underlying the mPFC modulation of breathing are unknown. To address this gap, this study is testing the hypothesis that administration of the GABAA receptor antagonist gabazine into the mPFC of mice increases breathing and heart rate, as well as neuronal activity of the respiratory neurons in the VRC. All procedures were reviewed and approved by the SCRI Institutional Animal Care and Use Committee and adhered to the ARRIVE guidelines. We recorded diaphragmatic activity and heart rate in response to unilateral microinjection (50.6nL) of gabazine (0.13nmol, 47ng) into the mPFC of female and male, urethane (1.5mg/kg) anesthetized mice (n = 5, mean age: 20wks). In 1 of the 5 mice, a Neuropixel high-density electrode was inserted into the VRC along the rostro caudal axis to simultaneously record neuronal activity. Paired, two-tailed t-test revealed gabazine delivered to the mPFC significantly (p This work is funded by the National Institutes of Health R01-HL151389, R01-HL126523, R01-HL144801, P01-HL090554 This is the full abstract presented at the American Physiology Summit 2023 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.

Opioid induced respiratory depression (OIRD) is the major cause of death associated with opioid overdose. Within the brainstem, respiratory activity is generated within the ventrolateral medulla in an opioid-sensitive region known as the PreBötzinger Complex (PreBötC). Within the PreBötC a heterogenous network of neurons under continuous influence by excitatory and inhibitory neuromodulators culminate to form synchronized bursting that results in inspiratory activity. Additionally, the PreBötC network dynamically interacts with the physiological processes that give rise to ventilation. Understanding the interplay between neural and physiological states of the in-vivo system will be key to overcoming OIRD. Here, we tested whether increasing the excitatory state of the PreBötC in-vivo by non-specific K+ channel inhibition, or elevated norepinephrine destabilizes breathing, but creates a network state resistant to OIRD. Further, we tested whether the state of upper airway patency following opioid administration influences sensitivity of the PreBötC to OIRD. Following microdialysis into the PreBötC of the non-specific K+ channel antagonist, tetraethylammonium (TEA)(10mM), or 1mM norepinephrine ventilation increased and breathing became erratic with variable frequency and tidal volume. However, following 150mg/kg morphine, breathing re-stabilized and returned to near control levels. These results demonstrate that determining the neuromodulatory state of excitability within the PreBötC prior to opioid administration may help to better predict and prevent OIRD. To determine whether the physiological state of the upper-airway following opioid administration can affect sensitivity of the PreBötC to OIRD we tested the ventilatory response to opioids in both airway-intact and tracheostomized mice in-vivo. For these experiments we utilized fentanyl, due to it’s known effects on disrupting upper airway function. Following administration of 500μg/kg fentanyl airway in-tact mice displayed increased upper airway resistance with regular periods of obstructive apnea, severe hypoxemia and reduced breathing frequency that eventually resulted in complete cessation of respiratory activity. Conversely, mice receiving 500μg/kg fentanyl following tracheostomy showed significantly less respiratory suppression and no apneic periods, compared to airway in-tact mice. However, following administration of a hypoxic gas mixture (10% O2) tracheostomized mice experienced terminal apnea in the presence of 500μg/Kg fentanyl. These results demonstrate that hypoxemia experienced following fentanyl administration, which is exacerbated by upper airway constriction may increase the risk of fatal OIRD in-vivo. Together our data suggest that understanding OIRD within the in-vivo system requires the careful investigation of integrative mechanisms between the neural and physiological processes that give rise to overall ventilation. This work was supported by NIH grants: HL154558 (NJB), HL145004 (NEB), HL126523 (JMR), HL144801 (JMR) This is the full abstract presented at the American Physiology Summit 2023 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.

Distributed and diverse populations of neurons throughout the Ventral Respiratory Column (VRC) are involved in the generation and maintenance of breathing. We have recently shown that the network-wide dynamics of these populations evolve through rotational trajectories in a low-dimensional latent neural space. These rotations evolve continuously through both inspiration and expiration, and they target a low-dimensional inspiratory-off attractor. It remains unknown how these rotational dynamics respond to perturbations of specific subsets of VRC populations. Here we record from the rostrocaudal extent of the VRC using high-density Neuropixel probes in-vivo in anesthetized mice while optogenetically stimulating subsets of neurons by Cre-driven expression of channel rhodopsin. These stimulations cause both widespread activation and deactivation of recorded populations. We find that brainstem wide stimulation of inhibitory neurons perturbs low-dimensional population trajectories towards the inspiration-off attractor, regardless of trajectory location at the time of stimulation. After cessation of stimulation, all trajectories proceed inexorably toward the inspiration-off point, and the cycle resets. When inhibitory populations are stimulated during the expiratory period, the population dynamics are clamped close to the inspiration-off attractor. Stimulation of glutamatergic populations, in contrast, directs the trajectories to a different region near the center of the rotation. However, upon cessation of excitatory stimulation, the trajectories immediately relax to the closest point along the rotational manifold, and the cycle resumes. Stimulation of either GABA-ergic or glutamatergic populations perturbs the dynamics perpendicular to the ongoing rotations; however stimulation of either Dbx1+ or cholinergic populations perturbs the populations along the current heading of the trajectories. Together, these data highlight a critical role of inhibition in the procession of VRC population dynamics, and suggest that the inspiration-off attractor is targeted by inhibitory mechanisms. R01 HL151389; R01 HL126523; R01 HL144801; F32HL159904 This is the full abstract presented at the American Physiology Summit 2023 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.

Background. A variety of molecular targets for volatile anesthetics have been suggested including the anesthetic-sensitive K+ leak channel, TREK-1. Knockout of TREK-1 is reported to render mice resistant to volatile anesthetics, making TREK-1 channels compelling targets for anesthetic action. Spinal cord slices from mice, either wildtype or an anesthetic-hypersensitive mutant, Ndufs4, display an isoflurane-induced outward K+ leak that correlates with their minimum alveolar concentrations (MAC) and is blocked by norfluoxetine. We hypothesized that TREK-1 channels conveyed this current and contribute to the anesthetic hypersensitivity of Ndufs4. Our results led to evaluation of a second TREK channel, TREK-2, in control of anesthetic sensitivity. Methods. We measured anesthetic sensitivities of mice carrying knockout alleles of Trek-1 and Trek-2, the double knockout Trek-1;Trek-2, and Ndufs4;Trek-1. Neurons from spinal cord slices from each mutant were patch clamped to characterize isoflurane-sensitive currents. Norfluoxetine was used to identify TREK-dependent currents. Results. We compared mean values for MAC (+/- SD) between wildtype and two Trek-1 knockout alleles in mice (p-values, Trek-1 compared to wildtype). Wildtype: (MAC(Hal), 1.30%(0.10); MAC(Iso), 1.40%(0.11): Trek-1tm1Lex (MAC(Hal), 1.27%(0.11); p=0.387; MAC(Iso), 1.38%(0.09); p=0.268): Trek-1tm1Lzd (MAC(Hal); 1.27%(0.11); p=0.482: MAC(Iso); 1.41%(0.12); p=0.188). Neither allele was resistant for loss of righting reflex. The EC50s of Ndufs4;Trek-1tm1Lex did not differ from Ndufs4. Ndufs4: (EC50(Hal), 0.65%(0.05); EC50 (Iso), 0.63%(0.05): Ndufs4;Trek-1tm1Lex (EC50(Hal), 0.58%(0.07); p=0.004; EC50(Iso); 0.61%(.06); p=0.442). Loss of TREK-2 did not alter anesthetic sensitivity in a wildtype or Trek-1 genetic background. Loss of TREK-1 or TREK-2, or both, did not alter the isoflurane-induced currents in wildtype cells but did cause them to be norfluoxetine-insensitive. Conclusions. Loss of TREK channels did not alter anesthetic sensitivity in mice, nor did it eliminate isoflurane-induced transmembrane currents. However, the isoflurane-induced currents are norfluoxetine-resistant in Trek mutants indicating that other channels may function in this role when TREK channels are deleted.

There is increasing interest in the African spiny mouse (Acomys cahirinus) as a model organism because of its ability for regeneration of tissue after injury in skin, muscle, and internal organs such as the kidneys. A high-quality reference genome is needed to better understand these regenerative properties at the molecular level. Here, we present an improved reference genome forA. cahirinusgenerated from long Nanopore sequencing reads. We confirm the quality of our annotations using RNA sequencing data from four different tissues. Our genome is of higher contiguity and quality than previously reported genomes from this species and will facilitate ongoing efforts to better understand the regenerative properties of this organism.

Breathing needs to be tightly coordinated with upper airway behaviors, such as swallowing. Discoordination leads to aspiration pneumonia, the leading cause of death in neurodegenerative diseases. Here we study the role of the postinspiratory complex, (PiCo) in coordinating breathing and swallowing. Using optogenetic approaches in freely breathing-anesthetized ChATcre, Vglut2cre and co-transmission of ChATcre/Vglut2FlpO mice reveals this small brainstem microcircuit acts as a central gating mechanism for airway protective behaviors. Activation of PiCo during inspiration or the beginning of postinspiration triggers swallow behavior, while there is a higher probability for stimulating laryngeal activation when activated further into expiration, suggesting PiCo’s role in swallow-breathing coordination. PiCo triggers consistent swallow behavior and preserves physiologic swallow motor sequence, while stimulates laryngeal activation variable to stimulation duration. Sufficient bilateral PiCo activation is necessary for gating function since activation of only a few PiCo neurons or unilateral activation leads to blurred behavioral response. Viral tracing experiments reveal projections from the caudal nucleus of the solitary tract (cNTS), the presumed swallow pattern generator (SPG), to PiCo and vice versa. However, PiCo does not directly connect to laryngeal muscles. Investigating PiCo’s role in swallow and laryngeal coordination will aid in understanding discoordination in breathing and neurological diseases.

The coordination of swallowing with breathing, in particular inspiration, is essential for homeostasis in most organisms. While much has been learned about the neuronal network critical for inspiration in mammals, the pre–Bötzinger complex (preBötC), little is known about how this network interacts with swallowing. Here we activate within the preBötC excitatory neurons (defined asVglut2andSstneurons) and inhibitory neurons (defined asVgatneurons) and inhibit and activate neurons defined by the transcription factorDbx1to gain an understanding of the coordination between the preBötC and swallow behavior. We found that stimulating inhibitory preBötC neurons did not mimic the premature shutdown of inspiratory activity caused by water swallows, suggesting that swallow-induced suppression of inspiratory activity is not directly mediated by the inhibitory neurons in the preBötC. By contrast, stimulation of preBötCDbx1neurons delayed laryngeal closure of the swallow sequence. Inhibition ofDbx1neurons increased laryngeal closure duration and stimulation ofSstneurons pushed swallow occurrence to later in the respiratory cycle, suggesting that excitatory neurons from the preBötC connect to the laryngeal motoneurons and contribute to the timing of swallowing. Interestingly, the delayed swallow sequence was also caused by chronic intermittent hypoxia (CIH), a model for sleep apnea, which is 1) known to destabilize inspiratory activity and 2) associated with dysphagia. This delay was not present when inhibiting Dbx1 neurons. We propose that a stable preBötC is essential for normal swallow pattern generation and disruption may contribute to the dysphagia seen in obstructive sleep apnea.

Death from opioid overdose is typically caused by opioid-induced respiratory depression (OIRD). A particularly dangerous characteristic of OIRD is its apparent unpredictability. The respiratory consequences of opioids can be surprisingly inconsistent, even within the same individual. Despite significant clinical implications, most studies have focused on average dose–r esponses rather than individual variation, and there remains little insight into the etiology of this apparent unpredictability. The preBötzinger complex (preBötC) in the ventral medulla is an important site for generating the respiratory rhythm and OIRD. Here, using male and female C57-Bl6 micein vitro, we demonstrate that the preBötC can assume different network states depending on the excitability of the preBötC and the intrinsic membrane properties of preBötC neurons. These network states predict the functional consequences of opioids in the preBötC, and depending on network state, respiratory rhythmogenesis can be either stabilized or suppressed by opioids. We hypothesize that the dynamic nature of preBötC rhythmogenic properties, required to endow breathing with remarkable flexibility, also plays a key role in the dangerous unpredictability of OIRD.SIGNIFICANCE STATEMENTOpioids can cause unpredictable, life-threatening suppression of breathing. This apparent unpredictability makes clinical management of opioids difficult while also making it challenging to define the underlying mechanisms of OIRD. Here, we find in brainstem slices that the preBötC, an opioid-sensitive subregion of the brainstem, has an optimal configuration of cellular and network properties that results in a maximally stable breathing rhythm. These properties are dynamic, and the state of each individual preBötC network relative to the optimal configuration of the network predicts how vulnerable rhythmogenesis is to the effects of opioids. These insights establish a framework for understanding how endogenous and exogenous modulation of the rhythmogenic state of the preBötC can increase or decrease the risk of OIRD.

Opioid-induced respiratory depression (OIRD) represents the primary cause of death associated with therapeutic and recreational opioid use. Within the United States, the rate of death from opioid abuse since the early 1990s has grown disproportionally, prompting the classification as a nationwide “epidemic.” Since this time, we have begun to unravel many fundamental cellular and systems-level mechanisms associated with opioid-related death. However, factors such as individual vulnerability, neuromodulatory compensation, and redundancy of opioid effects across central and peripheral nervous systems have created a barrier to a concise, integrative view of OIRD. Within this review, we bring together multiple perspectives in the field of OIRD to create an overarching viewpoint of what we know, and where we view this essential topic of research going forward into the future.

A sigh is a distinct respiratory behavior with specific psychophysiological roles. In two accompanying reviews we will discuss the physiological and psychological functions of the sigh. The present review will focus on the psychological functions of the sigh. We discuss the regulatory effects of a sigh, and argue how these effects may become maladaptive when sighs occur excessively. The adaptive role of a sigh is discussed in the context of regulation of psychophysiological states. We propose that sighs facilitate transitions from one psychophysiological state to the next, and this way contribute to psychophysiological flexibility, via a hypothesized resetting mechanism. We discuss how a sigh resets respiration, by controlling mechanical and metabolic properties of respiration associated with respiratory symptoms. Next, we elaborate on a sigh resetting emotional states by facilitating emotional transitions. We attempt to explain the adaptive and maladaptive functions of a sigh in the framework of stochastic resonance, in which we propose occasional, spontaneous sighs to be noise contributing to psychophysiological regulation, while excessive sighs result in psychophysiological dysregulation. In this context, we discuss how sighs can contribute to therapeutic interventions, either by increasing sighs to improve regulation in case of a lack of sighing, or by decreasing sighs to restore regulation in case of excessive sighing. Finally, a research agenda on the psychology of sighs is presented.

Breathing is a critical, complex, and highly integrated behavior. Normal rhythmic breathing, also referred to as eupnea, is interspersed with different breathing related behaviors. Sighing is one of such behaviors, essential for maintaining effective gas exchange by preventing the gradual collapse of alveoli in the lungs, known as atelectasis. Critical for the generation of both sighing and eupneic breathing is a region of the medulla known as the preBötzinger Complex (preBötC). Efforts are underway to identify the cellular pathways that link sighing as well as sneezing, yawning, and hiccupping with other brain regions to better understand how they are integrated and regulated in the context of other behaviors including chemosensation, olfaction, and cognition. Unraveling these interactions may provide important insights into the diverse roles of these behaviors in the initiation of arousal, stimulation of vigilance, and the relay of certain behavioral states. This chapter focuses primarily on the function of the sigh, how it is locally generated within the preBötC, and what the functional implications are for a potential link between sighing and cognitive regulation. Furthermore, we discuss recent insights gained into the pathways and mechanisms that control yawning, sneezing, and hiccupping.

Aim To determine which factors are associated with sudden unexpected infant death (SUID) by time of day. Methods Data were analysed from the National Fatality Review Case Reporting System (2006‐2015). Out of 20 005 SUID deaths in 37 states, 12 191 (60.9%) deaths had a recorded nearest hour of discovery of the infant. We compared distribution patterns between time of death and 118 variables to determine which were significantly correlated with SUID time of death using advanced statistical modelling techniques. Results The 12‐hour time periods that were most different were 10:00 to 21:00 (daytime) and 22:00 to 09:00 (nighttime). The main features that were associated with nighttime SUID were bed sharing, younger infants, non‐white infants, placed supine to sleep and found supine, and caregiver was the parent. Daytime SUID was associated with older infants, day care, white infants, sleeping in an adult bed and prone sleep position. Factors not associated with time of death were sex of the infant, smoking and breastfeeding. Conclusion Sudden unexpected infant death deaths that occur at night are associated with a separate set of risk factors compared to deaths that occur during the day. However, to minimise risk, it is important to practice safe sleep guidelines during both nighttime and daytime sleep.

Aim This study aimed to systematically analyse the pregnancy, birth and demographic‐related factors associated with age of death in sudden unexpected infant death (SUID). Methods Data were analysed from the Centers for Disease Control and Prevention's Cohort Linked Birth/Infant Death data set (2011‐2013; 11 737 930 live births). SUID was defined as deaths from sudden infant death syndrome, ill‐defined causes, or accidental suffocation and strangulation in bed. There were 9668 SUID cases (7‐364 days; gestation >28 weeks; 0.82/1000 live births). The odds of death at different ages were compared to determine which variables significantly affect the SUID age of death. Results Forty‐three features indicated a significant change in age of death with two main patterns: (a) younger chronologic age at death was associated with maternal smoking and factors associated with lower socio‐economic status, and (b) older age was associated with low birthweight, prematurity and admission to the neonatal intensive care unit. However, when age was corrected for gestation, these factors were associated with younger age. Conclusion Factors that varied with age of death are well‐documented risk factors for SUID. The majority of these risk factors were associated with younger age at death after allowing for gestational age at birth.

Breathing is a vital rhythmic motor behavior incessant from the first to our last breath. Increasingly refined anatomical, physiological, and genetic methods identified critical neuronal structures for breathing in a rostro-caudally aligned column of discrete functional nuclei with distinct neuron types that constitute the Ventral Respiratory Column (VRC). However, the concept of such compartmentalized organization must be reconciled with the considerable neuronal heterogeneity distributed along the entire VRC. Using Neuropixel probes we record simultaneously from hundreds of neurons across the entire VRC in anesthetized, but otherwise intact, freely breathing mice. Combined with optogenetic tagging techniques, and 3D histological reconstruction we create a functional, anatomic, and genetic map of over 13,000 neurons in the VRC with single-unit and millisecond resolution. By applying recent neural population analyses we uncover that a highly constrained rotational latent dynamical mode governs normal breathing. Our data reveal that the offset of inspiration forms an attractor that resets the respiratory rhythm, suggesting that the respiratory cycle begins not at the onset of an inspiration, but its cessation. These trajectories are sensitive to metabolic and pharmacological manipulations. Opioid administration alters the latent timing, while hypoxia-induced gasping results in a discrete reconfiguration from rotational to ballistic dynamics. These data provide a novel look at an old problem. They conceptualize the constitutive components of respiratory neural activity not as being composed of the average activity of homogenous genetic cell-classes or single nuclei, but of the underlying low dimensional neural activity patterns (neural modes) which may be distributed across cells of a given genotype and/or anatomical location.

BackgroundRett syndrome is a severe neurological disorder with a range of disabling autonomic and respiratory symptoms and resulting predominantly from variants in the methyl-CpG binding protein 2 gene on the long arm of the X-chromosome. As basic research begins to suggest potential treatments, sensitive measures of the dynamic phenotype are needed to evaluate the results of these research efforts. Here we test the hypothesis that the physiological fingerprint of Rett syndrome in a naturalistic environment differs from that of controls, and differs among genotypes within Rett syndrome.MethodsA comprehensive array of heart rate variability, cardiorespiratory coupling and cardiac repolarisation measures were evaluated from an existing database of overnight and daytime inhome ambulatory recordings in 47 cases and matched controls.ResultsDifferences between girls with Rett syndrome and matched controls were apparent in a range of autonomic measures, and suggest a shift towards sympathetic activation and/or parasympathetic inactivation. Daily temporal trends analysed in the context of circadian rhythms reveal alterations in amplitude and phase of diurnal patterns of autonomic balance. Further analysis by genotype class confirms a graded presentation of the Rett syndrome phenotype such that patients with early truncating mutations were most different from controls, while late truncating and missense mutations were least different from controls.ConclusionsComprehensive autonomic measures from extensive inhome physiological measurements can detect subtle variations in the phenotype of girls with Rett syndrome, suggesting these techniques are suitable for guiding novel therapies.

Cholinergic transmission shapes the maturation of glutamatergic circuits, yet the developmental sources of acetylcholine have not been systematically explored. Here we have used Cre-recombinase mediated genetic labeling to identify and map both mature and developing CNS neurons that express choline acetyltransferase (ChAT). Correction of a significant problem with a widely used Chat(Cre) transgenic line ensures that this map does not contain expression artifacts. Chat(Cre) marks all known cholinergic systems in the adult brain, but also identifies several brain areas not usually regarded as cholinergic, including specific thalamic and hypothalamic neurons, the subiculum, the lateral parabrachial nucleus, the cuneate/gracilis nuclei, and the pontocerebellar system. This Chat(Cre) fate map suggests transient developmental expression of a cholinergic phenotype in areas important for cognition, motor control, and respiration. We therefore examined expression of ChAT and the vesicular acetylcholine transporter (VAChT) in the embryonic and early postnatal brain to determine the developmental timing of this transient cholinergic phenotype, and found that it mirrored the establishment of relevant glutamatergic projection pathways. We then used an intersectional genetic strategy combining Chat(Cre) with Vglut2(Flp) to show that these neurons adopt a glutamatergic fate in the adult brain. The transient cholinergic phenotype of these glutamatergic neurons suggests a homosynaptic source of acetylcholine for the maturation of developing glutamatergic synapses. These findings thus define critical windows during which specific glutamatergic circuits may be vulnerable to disruption by nicotine in utero, and suggest new mechanisms for pediatric disorders associated with maternal smoking, such as sudden infant death syndrome.