Activation of XII motoneurons and premotor neurons during various oropharyngeal behaviors

Persistent Glossopharyngeal Nerve Respiratory Discharge Patterns after Ponto-Medullary Transection

Shape and size of the nasopharyngeal airway is controlled by muscles innervated facial, glossopharyngeal, vagal, and hypoglossal cranial nerves. Contrary to brainstem networks that drive facial, vagal and hypoglossal nerve activities (FNA, VNA, HNA) the discharge patterns and origins of glossopharyngeal nerve activity (GPNA) remain poorly investigated. Here, an in situ perfused brainstem preparation (n=19) was used for recordings of GPNA in relation to phrenic (PNA), FNA, VNA and HNA. Brainstem transections were performed (n=10/19) to explore the role of pontomedullary synaptic interactions in generating GPNA. GPNA generally mirrors FNA and HNA discharge patterns and displays pre-inspiratory activity relative to the PNA, followed by robust inspiratory discharge in coincidence with PNA. Postinspiratory (early expiratory) discharge was, contrary to VNA, generally absent in FNA, GPNA or HNA. As described previously FNA and HNA discharge was virtually eliminated after pontomedullary transection while an apneustic inspiratory motor discharge was maintained in PNA, VNA and GPNA. After brainstem transection GPNA displayed an increased tonic activity starting during mid-expiration and thus developed prolonged pre-inspiratory activity compared to control. In conclusion respiratory GPNA reflects FNA and HNA which implies similar function in controlling upper airway patency during breathing. That GPNA preserved its pre-inspiratory/inspiratory discharge pattern in relation PNA after pontomedullary transection suggest that GPNA premotor circuits may have a different anatomical distribution compared HNA and FNA and thus may therefore hold a unique role in in preserving airway patency.

Apnea behavior in early- and late-stage mouse models of Parkinson's disease: Cineradiographic analysis of spontaneous breathing, acute stress, and swallowing

This study aimed to evaluate the timing and frequency of spontaneous apneas during breathing and swallowing by using cineradiography on mouse models of early/initial or late/advanced Parkinson's disease (PD). C57BL/6 J mice received either 6-OHDA or vehicle injections into their right striatum, followed by respiratory movement recordings during spontaneous breathing and swallowing, and a stress challenge, two weeks later. Experimental group animals showed a significantly lower respiratory rate (158.66 ± 32.88 breaths/minute in late PD, 173.16 ± 25.19 in early PD versus 185.27 ± 25.36 in controls; p<0.001) and a significantly higher frequency of apneas (median 1 apnea/minute in both groups versus 0 in controls; p<0.001). Other changes included reduced food intake and the absence of swallow apneas in experimental mice. 6-OHDA-induced nigrostriatal degeneration in mice disrupted respiratory control, swallowing, stress responsiveness, and feeding behaviors, potentially hindering airway protection and elevating the risk of aspiration.

Altered tongue muscle contractile properties coincide with altered swallow function in the adult Ts65Dn mouse model of down syndrome

Purpose

Down syndrome (DS) is a developmental disability associated with difficulties in deglutition. The adult Ts65Dn mouse model of DS has been previously shown to have differences in measures of swallowing compared with euploid controls. However, the putative mechanisms of these differences in swallowing function are unclear. This study tested the hypothesis that the Ts65Dn genotype is associated with atypical measures of tongue muscle contractile properties, coinciding with atypical swallow function.

Methods

Adult (5-month-old) Ts65Dn (n = 15 female, 14 male) and euploid sibling controls (n = 16 female, 14 male) were evaluated through videofluoroscopy swallow studies (VFSS) to quantify measures of swallowing performance including swallow rate and inter-swallow interval (ISI). After VFSS, retrusive tongue muscle contractile properties, including measures of muscle fatigue, were determined using bilateral hypoglossal nerve stimulation.

Results

The Ts65Dn group had significantly slower swallow rates, significantly greater ISI times, significantly slower rates of tongue force development, and significantly greater levels of tongue muscle fatigue, with lower retrusive tongue forces than controls in fatigue conditions.

Conclusion

Tongue muscle contractile properties are altered in adult Ts65Dn and coincide with altered swallow function.

The integrated brain network that controls respiration

Respiration is a brain function on which our lives essentially depend. Control of respiration ensures that the frequency and depth of breathing adapt continuously to metabolic needs. In addition, the respiratory control network of the brain has to organize muscular synergies that integrate ventilation with posture and body movement. Finally, respiration is coupled to cardiovascular function and emotion. Here, we argue that the brain can handle this all by integrating a brainstem central pattern generator circuit in a larger network that also comprises the cerebellum. Although currently not generally recognized as a respiratory control center, the cerebellum is well known for its coordinating and modulating role in motor behavior, as well as for its role in the autonomic nervous system. In this review, we discuss the role of brain regions involved in the control of respiration, and their anatomical and functional interactions. We discuss how sensory feedback can result in adaptation of respiration, and how these mechanisms can be compromised by various neurological and psychological disorders. Finally, we demonstrate how the respiratory pattern generators are part of a larger and integrated network of respiratory brain regions.

Swallowing Dynamics and Breathing-Swallowing Coordination Are Altered in Patients with Mild Cognitive Impairment

INTRODUCTION

Postinspiratory activity, which is essential for laryngeal closure during swallowing to prevent aspiration of food into the airways, is reduced in a mouse model of tauopathy. Therefore, we hypothesized that patients at the stage of mild cognitive impairment (MCI) exhibit alterations in swallowing dynamics and coordination between swallowing and breathing.

METHODS

We examined breathing-swallowing coordination in patients with MCI. Patients who scored ≥24 on the Mini-Mental State Examination and <26 on the Japanese version of the Montreal Cognitive Assessment were recruited at Sumoto Itsuki Hospital. Parameters associated with breathing-swallowing coordination were assessed using a combination of two sensors: a respiratory flow sensor and a piezoelectric sensor attached to the skin surface of the anterior neck.

RESULTS

Nineteen patients met the criteria for MCI; 16 of these patients (79.5 ± 9.1 years old) scored <3 on the 10-item Eating Assessment Tool and were enrolled in the study. Their data were compared with those of an age-matched elderly cohort (79.9 ± 2.9 years old). The frequencies of swallowing during inspiration and swallowing immediately followed by inspiration in patients with MCI were 6.9% and 9.6%, respectively; these frequencies were not significantly different from those of the age-matched elderly cohort. However, the timing of swallowing in the respiratory cycle was significantly delayed in the MCI patients, and both time from the onset to the peak of laryngeal elevation and the duration between the onset of rapid laryngeal elevation and the time when the larynx returned to the resting position were significantly lengthened in this group.

CONCLUSION

At the stage of MCI, breathing-swallowing coordination has already started to decline.

Electrical Properties of Adult Mammalian Motoneurons

Motoneurons are the 'final common path' between the central nervous system (that intends, selects, commands, and organises movement) and muscles (that produce the behaviour). Motoneurons are not passive relays, but rather integrate synaptic activity to appropriately tune output (spike trains) and therefore the production of muscle force. In this chapter, we focus on studies of mammalian motoneurons, describing their heterogeneity whilst providing a brief historical account of motoneuron recording techniques. Next, we describe adult motoneurons in terms of their passive, transition, and active (repetitive firing) properties. We then discuss modulation of these properties by somatic (C-boutons) and dendritic (persistent inward currents) mechanisms. Finally, we briefly describe select studies of human motor unit physiology and relate them to findings from animal preparations discussed earlier in the chapter. This interphyletic approach to the study of motoneuron physiology is crucial to progress understanding of how these diverse neurons translate intention into behaviour.

Breathing disturbances in Rett syndrome

Rett Syndrome is an X-linked neurological disorder characterized by behavioral and neurological regression, seizures, motor deficits, and dysautonomia. A particularly prominent presentation includes breathing abnormalities characterized by breathing irregularities, hyperventilation, repetitive breathholding during wakefulness, obstructive and central apneas during sleep, and abnormal responses to hypoxia and hypercapnia. The condition and pathology of the respiratory system is further complicated by dysfunctions of breathing-motor coordination, which is reflected in dysphagia. The discovery of the X-linked mutations in the MECP2 gene has transformed our understanding of the cellular and molecular mechanisms that are at the root of various clinical phenotypes. However, the genotype-phenotype relationship is complicated by various factors which include not only X-inactivation but also consequences of the intermittent hypoxia and oxidative stress associated with the breathing abnormalities.

Assessment of the Use of Multi-Channel Organic Electrodes to Record ENG on Small Nerves: Application to Phrenic Nerve Burst Detection

Effective closed-loop neuromodulation relies on the acquisition of appropriate physiological control variables and the delivery of an appropriate stimulation signal. In particular, electroneurogram (ENG) data acquired from a set of electrodes applied at the surface of the nerve may be used as a potential control variable in this field. Improved electrode technologies and data processing methods are clearly needed in this context. In this work, we evaluated a new electrode technology based on multichannel organic electrodes (OE) and applied a signal processing chain in order to detect respiratory-related bursts from the phrenic nerve. Phrenic ENG (pENG) were acquired from nine Long Evans rats in situ preparations. For each preparation, a 16-channel OE was applied around the phrenic nerve’s surface and a suction electrode was applied to the cut end of the same nerve. The former electrode provided input multivariate pENG signals while the latter electrode provided the gold standard for data analysis. Correlations between OE signals and that from the gold standard were estimated. Signal to noise ratio (SNR) and ROC curves were built to quantify phrenic bursts detection performance. Correlation score showed the ability of the OE to record high-quality pENG. Our methods allowed good phrenic bursts detection. However, we failed to demonstrate a spatial selectivity from the multiple pENG recorded with our OE matrix. Altogether, our results suggest that highly flexible and biocompatible multi-channel electrode may represent an interesting alternative to metallic cuff electrodes to perform nerve bursts detection and/or closed-loop neuromodulation.

Sex-Specific Effects of Stress on Respiratory Control: Plasticity, Adaptation, and Dysfunction

As our understanding of respiratory control evolves, we appreciate how the basic neurobiological principles of plasticity discovered in other systems shape the development and function of the respiratory control system. While breathing is a robust homeostatic function, there is growing evidence that stress disrupts respiratory control in ways that predispose to disease. Neonatal stress (in the form of maternal separation) affects "classical" respiratory control structures such as the peripheral O₂ sensors (carotid bodies) and the medulla (e.g., nucleus of the solitary tract). Furthermore, early life stress disrupts the paraventricular nucleus of the hypothalamus (PVH), a structure that has emerged as a primary determinant of the intensity of the ventilatory response to hypoxia. Although underestimated, the PVH's influence on respiratory function is a logical extension of the hypothalamic control of metabolic demand and supply. In this article, we review the functional and anatomical links between the stress neuroendocrine axis and the medullary network regulating breathing. We then present the persistent and sex-specific effects of neonatal stress on respiratory control in adult rats. The similarities between the respiratory phenotype of stressed rats and clinical manifestations of respiratory control disorders such as sleep-disordered breathing and panic attacks are remarkable. These observations are in line with the scientific consensus that the origins of adult disease are often found among developmental and biological disruptions occurring during early life. These observations bring a different perspective on the structural hierarchy of respiratory homeostasis and point to new directions in our understanding of the etiology of respiratory control disorders. © 2021 American Physiological Society. Compr Physiol 11:1-38, 2021.

Constructing an adult orofacial premotor atlas in Allen mouse CCF

Premotor circuits in the brainstem project to pools of orofacial motoneurons to execute essential motor action such as licking, chewing, breathing, and in rodent, whisking. Previous transsynaptic tracing studies only mapped orofacial premotor circuits in neonatal mice, but the adult circuits remain unknown as a consequence of technical difficulties. Here, we developed a three-step monosynaptic transsynaptic tracing strategy to identify premotor neurons controlling vibrissa, tongue protrusion, and jaw-closing muscles in the adult mouse. We registered these different groups of premotor neurons onto the Allen mouse brain common coordinate framework (CCF) and consequently generated a combined 3D orofacial premotor atlas, revealing unique spatial organizations of distinct premotor circuits. We further uncovered premotor neurons that simultaneously innervate multiple motor nuclei and, consequently, are likely to coordinate different muscles involved in the same orofacial motor actions. Our method for tracing adult premotor circuits and registering to Allen CCF is generally applicable and should facilitate the investigations of motor controls of diverse behaviors.

The pontine Kölliker-Fuse nucleus gates facial, hypoglossal, and vagal upper airway related motor activity

The pontine Kölliker-Fuse nucleus (KFn) is a core nucleus of respiratory network that mediates the inspiratory-expiratory phase transition and gates eupneic motor discharges in the vagal and hypoglossal nerves. In the present study, we investigated whether the same KFn circuit may also gate motor activities that control the resistance of the nasal airway, which is of particular importance in rodents. To do so, we simultaneously recorded phrenic, facial, vagal and hypoglossal cranial nerve activity in an in situ perfused brainstem preparation before and after bilateral injection of the GABA-receptor agonist isoguvacine (50-70 nl, 10 mM) into the KFn (n = 11). Our results show that bilateral inhibition of the KFn triggers apneusis (prolonged inspiration) and abolished pre-inspiratory discharge of facial, vagal and hypoglossal nerves as well as post-inspiratory discharge in the vagus. We conclude that the KFn plays a critical role for the eupneic regulation of naso-pharyngeal airway patency and the potential functions of the KFn in regulating airway patency and orofacial behavior is discussed.

Respiratory pathology in the Optn-/- mouse model of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder that results in death due to respiratory failure. Many genetic defects are associated with ALS; one such defect is a mutation in the gene encoding optineurin (OPTN). Using an optineurin null mouse (Optn^-/-), we sought to characterize the impact of optineurin deficiency on respiratory neurodegeneration. Respiratory function was assessed at 6 and 12 mo of age using whole body plethysmography at baseline during normoxia (FiO₂: 0.21; N₂ balance) and during a respiratory challenge with hypoxia and hypercapnia (FiCO₂: 0.07, FiO₂: 0.10; N₂ balance). Histological analyses to assess motor neuron viability and respiratory nerve integrity were performed in the medulla, cervical spinal cord, hypoglossal nerve, and phrenic nerve. Minute ventilation, peak inspiratory flow, and peak expiratory flow are significantly reduced during a respiratory challenge in 6 mo Optn^-/-mice. By 12 mo, tidal volume is also significantly reduced in Optn^-/- mice. Furthermore, 12mo Optn^-/- mice exhibit hypoglossal motor neuron loss, phrenic and hypoglossal dysmyelination, and accumulated mitochondria in the hypoglossal nerve axons. Overall, these data indicate that Optn^-/- mice display neurodegenerative respiratory dysfunction and are a useful model to study the impact of novel therapies on respiratory function for optineurin-deficient ALS patients.

Quipazine Elicits Swallowing in the Arterially Perfused Rat Preparation: A Role for Medullary Raphe Nuclei?

Pharmacological neuromodulation of swallowing may represent a promising therapeutic option to treat dysphagia. Previous studies suggested a serotonergic control of swallowing, but mechanisms remain poorly understood. Here, we investigated the effects of the serotonergic agonist quipazine on swallowing, using the arterially perfused working heart-brainstem (in situ) preparation in rats. Systemic injection of quipazine produced single swallows with motor patterns and swallow-breathing coordination similar to spontaneous swallows, and increased swallow rate with moderate changes in cardiorespiratory functions. Methysergide, a 5-HT2 receptor antagonist, blocked the excitatory effect of quipazine on swallowing, but had no effect on spontaneous swallow rate. Microinjections of quipazine in the nucleus of the solitary tract were without effect. In contrast, similar injections in caudal medullary raphe nuclei increased swallow rate without changes in cardiorespiratory parameters. Thus, quipazine may exert an excitatory effect on raphe neurons via stimulation of 5-HT2A receptors, leading to increased excitability of the swallowing network. In conclusion, we suggest that pharmacological stimulation of swallowing by quipazine in situ represents a valuable model for experimental studies. This work paves the way for future investigations on brainstem serotonergic modulation, and further identification of neural populations and mechanisms involved in swallowing and/or swallow-breathing interaction.

Intralingual and Intrapleural AAV Gene Therapy Prolongs Survival in a SOD1 ALS Mouse Model

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that results in death from respiratory failure. No cure exists for this devastating disease, but therapy that directly targets the respiratory system has the potential to prolong survival and improve quality of life in some cases of ALS. The objective of this study was to enhance breathing and prolong survival by suppressing superoxide dismutase 1 (SOD1) expression in respiratory motor neurons using adeno-associated virus (AAV) expressing an artificial microRNA targeting the SOD1 gene. AAV-miRSOD1 was injected in the tongue and intrapleural space of SOD1G93A mice, and repetitive respiratory and behavioral measurements were performed until the end stage. Robust silencing of SOD1 was observed in the diaphragm and tongue as well as systemically. Silencing of SOD1 prolonged survival by approximately 50 days, and it delayed weight loss and limb weakness in treated animals compared to untreated controls. Histologically, there was preservation of the neuromuscular junctions in the diaphragm as well as the number of axons in the phrenic and hypoglossal nerves. Although SOD1 suppression improved breathing and prolonged survival, it did not ameliorate the restrictive lung phenotype. Suppression of SOD1 expression in motor neurons that underlie respiratory function prolongs survival and enhances breathing until the end stage in SOD1G93A ALS mice.

Kölliker-Fuse/Parabrachial complex mu opioid receptors contribute to fentanyl-induced apnea and respiratory rate depression

Overdoses caused by the opioid agonist fentanyl have increased exponentially in recent years. Identifying mechanisms to counter progression to fatal respiratory apnea during opioid overdose is desirable, but difficult to study in vivo. The pontine Kölliker-Fuse/Parabrachial complex (KF/PB) provides respiratory drive and contains opioid-sensitive neurons. The contribution of the KF/PB complex to fentanyl-induced apnea was investigated using the in situ arterially perfused preparation of rat. Systemic application of fentanyl resulted in concentration-dependent respiratory disturbances. At low concentrations, respiratory rate slowed and subsequently transitioned to an apneustic-like, 2-phase pattern. Higher concentrations caused prolonged apnea, interrupted by occasional apneustic-like bursts. Application of CTAP, a selective mu opioid receptor antagonist, directly into the KF/PB complex reversed and prevented fentanyl-induced apnea by increasing the frequency of apneustic-like bursting. These results demonstrate that countering opioid effects in the KF/PB complex is sufficient to restore phasic respiratory output at a rate similar to pre-fentanyl conditions, which could be beneficial in opioid overdose.

AAV Gene Therapy Utilizing Glycosylation-Independent Lysosomal Targeting Tagged GAA in the Hypoglossal Motor System of Pompe Mice

Pompe disease is caused by mutations in the gene encoding the lysosomal glycogen-metabolizing enzyme, acid-alpha glucosidase (GAA). Tongue myofibers and hypoglossal motoneurons appear to be particularly susceptible in Pompe disease. Here we used intramuscular delivery of adeno-associated virus serotype 9 (AAV9) for targeted delivery of an enhanced form of GAA to tongue myofibers and motoneurons in 6-month-old Pompe (Gaa -/- ) mice. We hypothesized that addition of a glycosylation-independent lysosomal targeting tag to the protein would result in enhanced expression in tongue (hypoglossal) motoneurons when compared to the untagged GAA. Mice received an injection into the base of the tongue with AAV9 encoding either the tagged or untagged enzyme; tissues were harvested 4 months later. Both AAV9 constructs effectively drove GAA expression in lingual myofibers and hypoglossal motoneurons. However, mice treated with the AAV9 construct encoding the modified GAA enzyme had a >200% increase in the number of GAA-positive motoneurons as compared to the untagged GAA (p < 0.008). Our results confirm that tongue delivery of AAV9-encoding GAA can effectively target tongue myofibers and associated motoneurons in Pompe mice and indicate that the effectiveness of this approach can be improved by addition of the glycosylation-independent lysosomal targeting tag.

Postnatal development of persistent inward currents in rat XII motoneurons and their modulation by serotonin, muscarine and noradrenaline

KEY POINTS

Persistent inward currents (PICs) in spinal motoneurons are long-lasting, voltage-dependent currents that increase excitability; they are dramatically potentiated by serotonin, muscarine, and noradrenaline (norepinephrine). Loss of these modulators (and the PIC) during sleep is hypothesized as a major contributor to REM sleep atonia. Reduced excitability of XII motoneurons that drive airway muscles and maintain airway patency is causally implicated in obstructive sleep apnoea (OSA), but whether XII motoneurons possess a modulator-sensitive PIC that could be a factor in the reduced airway tone of sleep is unknown. Whole-cell recordings from rat XII motoneurons in brain slices indicate that PIC amplitude increases ∼50% between 1 and 23 days of age, when potentiation of the PIC by 5HT₂ , muscarinic, or α₁ noradrenergic agonists peaks at <50%, manyfold lower than the potentiation observed in spinal motoneurons. α₁ noradrenergic receptor activation produced changes in XII motoneuron firing behaviour consistent with PIC involvement, but indicators of strong PIC activation were never observed; in vivo experiments are needed to determine the role of the modulator-sensitive PIC in sleep-dependent reductions in airway tone.

ABSTRACT

Hypoglossal (XII) motoneurons play a key role in maintaining airway patency; reductions in their excitability during sleep through inhibition and disfacilitation, i.e. loss of excitatory modulation, is implicated in obstructive sleep apnoea. In spinal motoneurons, 5HT₂ , muscarinic and α₁ noradrenergic modulatory systems potentiate persistent inward currents (PICs) severalfold, dramatically increasing excitability. If the PICs in XII and spinal motoneurons are equally sensitive to modulation, loss of the PIC secondary to reduced modulatory tone during sleep could contribute to airway atonia. Modulatory systems also change developmentally. We therefore characterized developmental changes in magnitude of the XII motoneuron PIC and its sensitivity to modulation by comparing, in neonatal (P1-4) and juvenile (P14-23) rat brainstem slices, the PIC elicited by slow voltage ramps in the absence and presence of agonists for 5HT₂ , muscarinic, and α₁ noradrenergic receptors. XII motoneuron PIC amplitude increased developmentally (from -195 ± 12 to -304 ± 19 pA). In neonatal XII motoneurons, the PIC was only potentiated by α₁ receptor activation (5 ± 4%). In contrast, all modulators potentiated the juvenile XII motoneurons PIC (5HT₂ , 5 ± 5%; muscarine, 22 ± 11%; α₁ , 18 ± 5%). These data suggest that the influence of the PIC and its modulation on XII motoneuron excitability will increase with postnatal development. Notably, the modulator-induced potentiation of the PIC in XII motoneurons was dramatically smaller than the 2- to 6-fold potentiation reported for spinal motoneurons. In vivo measurements are required to determine if the modulator-sensitive, XII motoneuron PIC is an important factor in sleep-state dependent reductions in airway tone.

Distribution of excitatory and inhibitory axon terminals on the rat hypoglossal motoneurons

Detailed information about the excitatory and inhibitory synapses on the hypoglossal motoneurons may help understand the neural mechanism for control of the hypoglossal motoneuron excitability and hence the precise and coordinated movements of the tongue during chewing, swallowing and licking. For this, we investigated the distribution of GABA-, glycine (Gly)- and glutamate (Glut)-immunopositive (+) axon terminals on the genioglossal (GG) motoneurons by retrograde tracing, electron microscopic immunohistochemistry, and quantitative analysis. Small GG motoneurons (< 400 μm² in cross-sectional area) had fewer primary dendrites, significantly higher nuclear/cytoplasmic ratio, and smaller membrane area covered by synaptic boutons than large GG motoneurons (> 400 μm²). The fraction of inhibitory boutons (GABA + only, Gly + only, and mixed GABA +/Gly + boutons) of all boutons was significantly higher for small GG motoneurons than for large ones, whereas the fraction of Glut + boutons was significantly higher for large GG motoneurons than for small ones. Almost all boutons (> 95%) on both small and large GG motoneurons were GABA + , Gly + or Glut + . The frequency of mixed GABA +/Gly + boutons was the highest among inhibitory boutons types for both small and large GG motoneurons. These findings may elucidate the anatomical substrate for precise regulation of the motoneuron firing required for the fine movements of the tongue, and also suggest that the excitability of small and large GG motoneurons may be regulated differently.

Development and Implementation of an Intraoral Device for Occlusal Stability during Sports Performance: A Case Report

INTRODUCTION

Sports dentistry assumes a clinical relevance, not only in the prevention of orofacial trauma by the use of mouthguards, but also with the development of intraoral devices that aim to provide greater occlusal stability, as well as a greater balance in the level of certain structures of the cranio-cervical-mandibular complex. In this way, the dentistry can have an intervention action on sports performance.

OBJECTIVES

The objective of this research was to verify the existence of a correlation between occlusal stability and an eventual balance of some facial structures during sports performance using a specially developed Occlusal Stability Sports Performance Device.

METHODOLOGY

An individualized mandibular intraoral device was manufactured and evaluated on an athlete canoeing. Infrared thermography was the complementary diagnostic method used for this purpose.

RESULTS

Greater symmetry of certain regions of interest of the cranio-cervico-mandibular complex was observed with the implementation of the Occlusal Stability Sports Performance Device. These areas were the anterior temporal muscle, the masseter muscle and the temporomandibular joint. No asymmetry decrease was found in the anterior triangle region of the neck.

CONCLUSION

The use of this type of intraoral devices may allow greater occlusal stability and consequent balance of anatomical structures constituting the cranio-cervical-mandibular complex. Infrared thermography is an effective diagnostic tool for studying the results of the intraoral device on the cranio-cervico-mandibular complex use during canoeing.

Sciatic nerve stimulation and its effects on upper airway resistance in the anesthetized rabbit model relevant to sleep apnea

Obstructive sleep apnea (OSA) is a disorder characterized by collapse of the velopharynx and/or oropharynx during sleep when drive to the upper airway is reduced. Here, we explore an indirect approach for activation of upper airway muscles that might affect airway dynamics, namely, unilateral electrical stimulation of the afferent fibers of the sciatic nerve, in an anesthetized rabbit model. A nerve cuff electrode was placed around the sciatic and hypoglossal nerves to deliver stimulus while airflow, air pressure, and alae nasi electromyogram (EMG) were monitored both before and after sciatic transection. Sciatic nerve stimulation increased respiratory effort, rate, and alae nasi EMG, which persisted for seconds after stimulation; however, upper airway resistance was unchanged. Hypoglossal stimulation reduced resistance without altering drive. Although sciatic nerve stimulation is not ideal for treating OSA, it remains a target for altering respiratory drive. NEW & NOTEWORTHY Previously, sciatic nerve stimulation has been shown to activate upper airway and chest wall muscles. The supposition that resistance through the upper airway would be reduced with this afferent reflex was disproven. Findings were in contrast with the effect of hypoglossal nerve stimulation, which was shown to decrease resistance without changing muscle activation or ventilatory drive.

Central Respiration and Mechanical Ventilation in the Gating of Swallow With Breathing

Swallow-breathing coordination safeguards the lower airways from tracheal aspiration of bolus material as it moves through the pharynx into the esophagus. Impaired movements of the shared muscles or structures of the aerodigestive tract, or disruptions in the interaction of brainstem swallow and respiratory central pattern generators (CPGs) result in dysphagia. To maximize lower airway protection these CPGs integrate respiratory rhythm generation signals and vagal afferent feedback to synchronize swallow with breathing. Despite extensive study, the roles of central respiratory activity and vagal feedback from the lungs as key elements for effective swallow-breathing coordination remain unclear. The effect of altered timing of bronchopulmonary vagal afferent input on swallows triggered during electrical stimulation of the superior laryngeal nerves or by injection of water into the pharyngeal cavity was studied in decerebrate, paralyzed, and artificially ventilated cats. We observed two types of single swallows that produced distinct effects on central respiratory-rhythm across all conditions: post-inspiratory type swallows disrupted central-inspiratory activity without affecting expiration, whereas expiratory type swallows prolonged expiration without affecting central-inspiratory activity. Repetitive swallows observed during apnea reset the E2 phase of central respiration and produced facilitation of swallow motor output nerve burst durations. Moreover, swallow initiation was negatively modulated by vagal feedback and was reset by lung inflation. Collectively, these findings support a novel model of reciprocal inhibition between the swallow CPG and inspiratory or expiratory cells of the respiratory CPG where lung distension and phases of central respiratory activity represent a dual peripheral and central gating mechanism of swallow-breathing coordination.

Expression of the transcription factor FOXP2 in brainstem respiratory circuits of adult rat is restricted to upper-airway pre-motor areas

Expression of the transcription factor FOXP2 is linked to brain circuits that control motor function and speech. Investigation of FOXP2 protein expression in respiratory areas of the ponto-medullary brainstem of adult rat revealed distinct rostro-caudal expression gradients. A high density of FOXP2 immunoreactive nuclei was observed within the rostral pontine Kölliker-Fuse nucleus, compared to low densities in caudal pontine and rostral medullary respiratory nuclei, including the: (i) noradrenergic A5 and parafacial respiratory groups; (ii) Bötzinger and pre-Bötzinger complex and; (iii) rostral ventral respiratory group. Moderate densities of FOXP2 immunoreactive nuclei were observed in the caudal ventral respiratory group and the nucleus retroambiguus, with significant density levels found in the caudal half of the dorsal respiratory group and the hypoglossal pre-motor area lateral around calamus scriptorius. FOXP2 immunoreactivity was absent in all cranial nerve motor nuclei. We conclude that FOXP2 expression in respiratory brainstem areas selectively delineates laryngeal and hypoglossal pre-motor neuron populations essential for the generation of sound and voice.

The Consequences of Preterm Birth and Chorioamnionitis on Brainstem Respiratory Centers: Implications for Neurochemical Development and Altered Functions by Inflammation and Prostaglandins

Preterm birth is a major cause for neonatal morbidity and mortality, and is frequently associated with adverse neurological outcomes. The transition from intrauterine to extrauterine life at birth is particularly challenging for preterm infants. The main physiological driver for extrauterine transition is the establishment of spontaneous breathing. However, preterm infants have difficulty clearing lung liquid, have insufficient surfactant levels, and underdeveloped lungs. Further, preterm infants have an underdeveloped brainstem, resulting in reduced respiratory drive. These factors facilitate the increased requirement for respiratory support. A principal cause of preterm birth is intrauterine infection/inflammation (chorioamnionitis), and infants with chorioamnionitis have an increased risk and severity of neurological damage, but also demonstrate impaired autoresuscitation capacity and prevalent apnoeic episodes. The brainstem contains vital respiratory centers which provide the neural drive for breathing, but the impact of preterm birth and/or chorioamnionitis on this brain region is not well understood. The aim of this review is to provide an overview of the role and function of the brainstem respiratory centers, and to highlight the proposed mechanisms of how preterm birth and chorioamnionitis may affect central respiratory functions.

Morphology of Dbx1 respiratory neurons in the preBötzinger complex and reticular formation of neonatal mice

The relationship between neuron morphology and function is a perennial issue in neuroscience. Information about synaptic integration, network connectivity, and the specific roles of neuronal subpopulations can be obtained through morphological analysis of key neurons within a microcircuit. Here we present morphologies of two classes of brainstem respiratory neurons. First, interneurons derived from Dbx1-expressing precursors (Dbx1 neurons) in the preBötzinger complex (preBötC) of the ventral medulla that generate the rhythm for inspiratory breathing movements. Second, Dbx1 neurons of the intermediate reticular formation that influence the motor pattern of pharyngeal and lingual movements during the inspiratory phase of the breathing cycle. We describe the image acquisition and subsequent digitization of morphologies of respiratory Dbx1 neurons from the preBötC and the intermediate reticular formation that were first recorded in vitro. These data can be analyzed comparatively to examine how morphology influences the roles of Dbx1 preBötC and Dbx1 reticular interneurons in respiration and can also be utilized to create morphologically accurate compartmental models for simulation and modeling of respiratory circuits.

Non-chemosensitive parafacial neurons simultaneously regulate active expiration and airway patency under hypercapnia in rats

KEY POINTS

Hypercapnia or parafacial respiratory group (pFRG) disinhibition at normocapnia evokes active expiration in rats by recruitment of pFRG late-expiratory (late-E) neurons. We show that hypercapnia simultaneously evoked active expiration and exaggerated glottal dilatation by late-E synaptic excitation of abdominal, hypoglossal and laryngeal motoneurons. Simultaneous rhythmic expiratory activity in previously silent pFRG late-E neurons, which did not express the marker of ventral medullary CO₂ -sensitive neurons (transcription factor Phox2b), was also evoked by hypercapnia. Hypercapnia-evoked active expiration, neural and neuronal late-E activities were eliminated by pFRG inhibition, but not after blockade of synaptic excitation. Hypercapnia produces disinhibition of non-chemosensitive pFRG late-E neurons to evoke active expiration and concomitant cranial motor respiratory responses controlling the oropharyngeal and upper airway patency.

ABSTRACT

Hypercapnia produces active expiration in rats and the recruitment of late-expiratory (late-E) neurons located in the parafacial respiratory group (pFRG) of the ventral medullary brainstem. We tested the hypothesis that hypercapnia produces active expiration and concomitant cranial respiratory motor responses controlling the oropharyngeal and upper airway patency by disinhibition of pFRG late-E neurons, but not via synaptic excitation. Phrenic nerve, abdominal nerve (AbN), cranial respiratory motor nerves, subglottal pressure, and medullary and spinal neurons/motoneurons were recorded in in situ preparations of juvenile rats. Hypercapnia evoked AbN active expiration, exaggerated late-E discharges in cranial respiratory motor outflows, and glottal dilatation via late-E synaptic excitation of abdominal, hypoglossal and laryngeal motoneurons. Simultaneous rhythmic late-E activity in previously silent pFRG neurons, which did not express the marker of ventral medullary CO₂ -sensitive neurons (transcription factor Phox2b), was also evoked by hypercapnia. In addition, hypercapnia-evoked AbN active expiration, neural and neuronal late-E activities were eliminated by pFRG inhibition, but not after blockade of synaptic excitation. On the other hand, pFRG inhibition did not affect either hypercapnia-induced inspiratory increases in respiratory motor outflows or CO₂ sensitivity of the more medial Phox2b-positive neurons in the retrotrapezoid nucleus (RTN). Our data suggest that neither RTN Phox2b-positive nor other CO₂ -sensitive brainstem neurons activate Phox2b-negative pFRG late-E neurons under hypercapnia to produce AbN active expiration and concomitant cranial motor respiratory responses controlling the oropharyngeal and upper airway patency. Hypercapnia produces disinhibition of non-chemosensitive pFRG late-E neurons in in situ preparations of juvenile rats to activate abdominal, hypoglossal and laryngeal motoneurons.

Dbx1 precursor cells are a source of inspiratory XII premotoneurons

All behaviors require coordinated activation of motoneurons from central command and premotor networks. The genetic identities of premotoneurons providing behaviorally relevant excitation to any pool of respiratory motoneurons remain unknown. Recently, we established in vitro that Dbx1-derived pre-Bötzinger complex neurons are critical for rhythm generation and that a subpopulation serves a premotor function (Wang et al., 2014). Here, we further show that a subpopulation of Dbx1-derived intermediate reticular (IRt) neurons are rhythmically active during inspiration and project to the hypoglossal (XII) nucleus that contains motoneurons important for maintaining airway patency. Laser ablation of Dbx1 IRt neurons, 57% of which are glutamatergic, decreased ipsilateral inspiratory motor output without affecting frequency. We conclude that a subset of Dbx1 IRt neurons is a source of premotor excitatory drive, contributing to the inspiratory behavior of XII motoneurons, as well as a key component of the airway control network whose dysfunction contributes to sleep apnea.

DOI:http://dx.doi.org/10.7554/eLife.12301.001

The Kölliker-Fuse nucleus: a review of animal studies and the implications for cranial nerve function in humans

To review the scientific literature on the relationship between Kölliker-Fuse nucleus (KF) and cranial nerve function in animal models, with view to evaluating the potential role of KF maturation in explaining age-related normal physiologic parameters and developmental and acquired impairment of cranial nerve function in humans. Medical databases (Medline and PubMed). Studies investigating evidence of KF activity responsible for a specific cranial nerve function that were based on manipulation of KF activity or the use of neural markers were included. Twenty studies were identified that involved the trigeminal (6 studies), vagus (9), and hypoglossal nerves (5). These pertained specifically to a role of the KF in mediating the dive reflex, laryngeal adductor control, swallowing function and upper airway tone. The KF acts as a mediator of a number of important functions that relate primarily to laryngeal closure, upper airway tone and swallowing. These areas are characterized by a variety of disorders that may present to the otolaryngologist, and hence the importance of understanding the role played by the KF in maintaining normal function.

Preparing the periphery for a subsequent behavior: motor neuronal activity during biting generates little force but prepares a retractor muscle to generate larger forces during swallowing in Aplysia

Some behaviors occur in obligatory sequence, such as reaching before grasping an object. Can the earlier behavior serve to prepare the musculature for the later behavior? If it does, what is the underlying neural mechanism of the preparation? To address this question, we examined two feeding behaviors in the marine mollusk Aplysia californica, one of which must precede the second: biting and swallowing. Biting is an attempt to grasp food. When that attempt is successful, the animal immediately switches to swallowing to ingest food. The main muscle responsible for pulling food into the buccal cavity during swallowing is the I3 muscle, whose motor neurons B6, B9, and B3 have been previously identified. By performing recordings from these neurons in vivo in intact, behaving animals or in vitro in a suspended buccal mass preparation, we demonstrated that the frequencies and durations of these motor neurons increased from biting to swallowing. Using the physiological patterns of activation to drive these neurons intracellularly, we further demonstrated that activating them using biting-like frequencies and durations, either alone or in combination, generated little or no force in the I3 muscle. When biting-like patterns preceded swallowing-like patterns, however, the forces during the subsequent swallowing-like patterns were significantly enhanced. Sequences of swallowing-like patterns, either with these neurons alone or in combination, further enhanced forces in the I3 muscle. These results suggest a novel mechanism for enhancing force production in a muscle, and may be relevant to understanding motor control in vertebrates.

Cortical innervation of the hypoglossal nucleus in the non-human primate (Macaca mulatta)

The corticobulbar projection to the hypoglossal nucleus was studied from the frontal, parietal, cingulate, and insular cortices in the rhesus monkey by using high-resolution anterograde tracers and stereology. The hypoglossal nucleus received bilateral input from the face/head region of the primary (M1), ventrolateral pre- (LPMCv), supplementary (M2), rostral cingulate (M3), and caudal cingulate (M4) motor cortices. Additional bilateral corticohypoglossal projections were found from the dorsolateral premotor cortex (LPMCd), ventrolateral proisocortical motor area (ProM), ventrolateral primary somatosensory cortex (S1), rostral insula, and pregenual region of the anterior cingulate gyrus (areas 24/32). Dense terminal projections arose from the ventral region of M1, and moderate projections from LPMCv and rostral part of M2, with considerably fewer hypoglossal projections arising from the other cortical regions. These findings demonstrate that extensive regions of the non-human primate cerebral cortex innervate the hypoglossal nucleus. The widespread and bilateral nature of this corticobulbar connection suggests recovery of tongue movement after cortical injury that compromises a subset of these areas, may occur from spared corticohypoglossal projection areas located on the lateral, as well as medial surfaces of both hemispheres. Since functional imaging studies have shown that homologous cortical areas are activated in humans during tongue movement tasks, these corticobulbar projections may exist in the human brain.

Inhibition of the pontine Kölliker-Fuse nucleus abolishes eupneic inspiratory hypoglossal motor discharge in rat

The pontine Kölliker-Fuse nucleus (KF) has established functions in the regulation of inspiratory-expiratory phase transition and the regulation of upper airway patency via laryngeal valving mechanisms. Here we studied the role of the KF in the gating and modulation of eupneic hypoglossal motor activity (HNA) using the in situ perfused brainstem preparation, which displays robust inspiratory HNA. Microinjection of glutamate into the KF area triggered complex and often biphasic modulation (excitation/inhibition or inhibition/excitation) of HNA. Subsequent transient pharmacological inhibition of KF by unilateral microinjection of GABA-A receptor agonist isoguvacine reduced HNA and while bilateral microinjections completely abolished HNA. Our results indicate that mixed and overlapping KF pre-motor neurons provide eupneic drive for inspiratory HNA and postinspiratory vagal nerve activity. Both motor activities have important functions in the regulation of upper airway patency during eupnea but also during various oro-pharyngeal behaviors. These results have potential implications in the contribution of state-dependent modulation of KF hypoglossal pre-motor neurons during sleep-wake cycle to obstructive sleep apnea.

The generation of pharyngeal phase of swallow and its coordination with breathing: interaction between the swallow and respiratory central pattern generators

Swallowing and breathing utilize common muscles and an anatomical passage: the pharynx. The risk of aspiration of ingested material is minimized not only by the laryngeal adduction of the vocal folds and laryngeal elevation but also by the precise coordination of swallows with breathing. Namely, swallows: (1) are preferentially initiated in the postinspiratory/expiratory phase, (2) are accompanied by a brief apnea, and (3) are often followed by an expiration and delay of the next breath. This review summarizes the expiratory evidence on the brainstem regions comprising the central pattern generator (CPG) that produces the pharyngeal stage of swallow, how the motor acts of swallowing and breathing are coordinated, and lastly, brainstem regions where the swallowing and respiratory CPGs may interact in order to ensure "safe" swallows.

Activity of respiratory neurons in the rostral medulla during vocalization, swallowing, and coughing in guinea pigs

To examine the relationship between the neuronal networks underlying respiration and non-respiratory behaviors such as vocalization and airway defensive reflexes, we compared the activity of respiratory neurons in the ventrolateral medulla during breathing with that during non-respiratory behaviors including vocalization, swallowing, and coughing in guinea pigs. During fictive vocalization the activity of augmenting expiratory neurons ceased, whereas the other types of expiratory neurons did not show a consistent tendency of increasing or decreasing activity. All inspiratory neurons discharged in synchrony with the phrenic nerve activity. Most of the phase-spanning neurons were activated throughout the vocal phase. During fictive swallowing, many expiratory and inspiratory neurons were silent, whereas many phase-spanning neurons were activated. During fictive coughing, many expiratory neurons were activated during the expiratory phase of coughing. Most inspiratory neurons discharged in parallel with the phrenic nerve activity during coughing. Many phase-spanning neurons were activated during the expiratory phase of coughing. These findings indicate that the medullary respiratory neurons help shape respiratory muscle nerve activity not only during breathing but also during these non-respiratory behaviors, and thus suggest that at least some of the respiratory neurons are shared among the neuronal circuits underlying the generation of breathing and non-respiratory behaviors.

TASK-2 channels contribute to pH sensitivity of retrotrapezoid nucleus chemoreceptor neurons

Phox2b-expressing glutamatergic neurons of the retrotrapezoid nucleus (RTN) display properties expected of central respiratory chemoreceptors; they are directly activated by CO2/H(+) via an unidentified pH-sensitive background K(+) channel and, in turn, facilitate brainstem networks that control breathing. Here, we used a knock-out mouse model to examine whether TASK-2 (K2P5), an alkaline-activated background K(+) channel, contributes to RTN neuronal pH sensitivity. We made patch-clamp recordings in brainstem slices from RTN neurons that were identified by expression of GFP (directed by the Phox2b promoter) or β-galactosidase (from the gene trap used for TASK-2 knock-out). Whereas nearly all RTN cells from control mice were pH sensitive (95%, n = 58 of 61), only 56% of GFP-expressing RTN neurons from TASK-2(-/-) mice (n = 49 of 88) could be classified as pH sensitive (>30% reduction in firing rate from pH 7.0 to pH 7.8); the remaining cells were pH insensitive (44%). Moreover, none of the recorded RTN neurons from TASK-2(-/-) mice selected based on β-galactosidase activity (a subpopulation of GFP-expressing neurons) were pH sensitive. The alkaline-activated background K(+) currents were reduced in amplitude in RTN neurons from TASK-2(-/-) mice that retained some pH sensitivity but were absent from pH-insensitive cells. Finally, using a working heart-brainstem preparation, we found diminished inhibition of phrenic burst amplitude by alkalization in TASK-2(-/-) mice, with apneic threshold shifted to higher pH levels. In conclusion, alkaline-activated TASK-2 channels contribute to pH sensitivity in RTN neurons, with effects on respiration in situ that are particularly prominent near apneic threshold.

Pontine mechanisms of respiratory control

Pontine respiratory nuclei provide synaptic input to medullary rhythmogenic circuits to shape and adapt the breathing pattern. An understanding of this statement depends on appreciating breathing as a behavior, rather than a stereotypic rhythm. In this review, we focus on the pontine-mediated inspiratory off-switch (IOS) associated with postinspiratory glottal constriction. Further, IOS is examined in the context of pontine regulation of glottal resistance in response to multimodal sensory inputs and higher commands, which in turn rules timing, duration, and patterning of respiratory airflow. In addition, network plasticity in respiratory control emerges during the development of the pons. Synaptic plasticity is required for dynamic and efficient modulation of the expiratory breathing pattern to cope with rapid changes from eupneic to adaptive breathing linked to exploratory (foraging and sniffing) and expulsive (vocalizing, coughing, sneezing, and retching) behaviors, as well as conveyance of basic emotions. The speed and complexity of changes in the breathing pattern of behaving animals implies that "learning to breathe" is necessary to adjust to changing internal and external states to maintain homeostasis and survival.

The respiratory neuromuscular system in Pompe disease

Pompe disease is due to mutations in the gene encoding the lysosomal enzyme acid α-glucosidase (GAA). Absence of functional GAA typically results in cardiorespiratory failure in the first year; reduced GAA activity is associated with progressive respiratory failure later in life. While skeletal muscle pathology contributes to respiratory insufficiency in Pompe disease, emerging evidence indicates that respiratory neuron dysfunction is also a significant part of dysfunction in motor units. Animal models show profound glycogen accumulation in spinal and medullary respiratory neurons and altered neural activity. Tissues from Pompe patients show central nervous system glycogen accumulation and motoneuron pathology. A neural mechanism raises considerations about the current clinical approach of enzyme replacement since the recombinant protein does not cross the blood-brain-barrier. Indeed, clinical data suggest that enzyme replacement therapy delays symptom progression, but many patients eventually require ventilatory assistance, especially during sleep. We propose that treatments which restore GAA activity to respiratory muscles, neurons and networks will be required to fully correct ventilatory insufficiency in Pompe disease.

Central neural circuits for coordination of swallowing, breathing, and coughing: predictions from computational modeling and simulation

The purpose of this article is to update the otolaryngologic community on recent developments in the basic understanding of how cough, swallow, and breathing are controlled. These behaviors are coordinated to occur at specific times relative to one another to minimize the risk of aspiration. The control system that generates and coordinates these behaviors is complex, and advanced computational modeling methods are useful tools to elucidate its function.

Activation of upper airway muscles during breathing and swallowing

The upper airway is a complex muscular tube that is used by the respiratory and digestive systems. The upper airway is invested with several small and anatomically peculiar muscles. The muscle fiber orientations and their nervous innervation are both extremely complex, and how the activity of the muscles is initiated and adjusted during complex behaviors is poorly understood. The bulk of the evidence suggests that the entire assembly of tongue and laryngeal muscles operate together but differently during breathing and swallowing, like a ballet rather than a solo performance. Here we review the functional anatomy of the tongue and laryngeal muscles, and their neural innervation. We also consider how muscular activity is altered as respiratory drive changes, and briefly address upper airway muscle control during swallowing.

The emerging role of the parabrachial complex in the generation of wakefulness drive and its implication for respiratory control

The parabrachial complex is classically seen as a major neural knot that transmits viscero- and somatosensory information toward the limbic and thalamic forebrain. In the present review we summarize recent findings that imply an emerging role of the parabrachial complex as an integral part of the ascending reticular arousal system, which promotes wakefulness and cortical activation. The ascending parabrachial projections that target wake-promoting hypothalamic areas and the basal forebrain are largely glutamatergic. Such fast synaptic transmission could be even more significant in promoting wakefulness and its characteristic pattern of cortical activation than the cholinergic or mono-aminergic ascending pathways that have been emphasized extensively in the past. A similar role of the parabrachial complex could also apply for its more established function in control of breathing. Here the parabrachial respiratory neurons may modulate and adapt breathing via the control of respiratory phase transition and upper airway patency, particularly during respiratory and non-respiratory behavior associated with wakefulness.

Contributions of the Kölliker-Fuse nucleus to coordination of breathing and swallowing

Herein we compare the effects of perturbations in the Kölliker-Fuse nucleus (KFN) and the lateral (LPBN) and medial (MPBN) parabrachial nuclei on the coordination of breathing and swallowing. Cannula was chronically implanted in goats through which ibotenic acid (IA) was injected while awake. Swallows in late expiration (E) always reset while swallows in early inspiration (I) never reset the respiratory rhythm. Before cannula implantation, all other E and I swallows did not reset the respiratory rhythm, and had small effects on E and I duration and tidal volume (VT). However, after cannula implantation in the MPBN and KFN, E and I swallows reset the respiratory rhythm and increased the effects on I and E duration and VT. Subsequent injection of IA into the KFN eliminated the respiratory phase resetting of swallows but exacerbated the effects on I and E duration and VT. We conclude that the KFN and to a lesser extent the MPBN contribute to coordination of breathing and swallowing.

Kölliker–Fuse neurons send collateral projections to multiple hypoxia-activated and nonactivated structures in rat brainstem and spinal cord

The Kölliker–Fuse nucleus (KFN) in dorsolateral pons has been implicated in many physiological functions via its extensive efferent connections. Here, we combine iontophoretic anterograde tracing with posthypoxia c-Fos immunohistology to map KFN axonal terminations among hypoxia-activated/nonactivated brain stem and spinal structures in rats. Using a set of stringent inclusion/exclusion criteria to align visualized axons across multiple coronal brain sections, we were able to unequivocally trace axonal trajectories over a long rostrocaudal distance perpendicular to the coronal plane. Structures that were both richly innervated by KFN axonal projections and immunopositive to c-Fos included KFN (contralateral side), ventrolateral pontine area, areas ventral to rostral compact/subcompact ambiguus nucleus, caudal (lateral) ambiguus nucleus, nucleus retroambiguus, and commissural–medial subdivisions of solitary tract nucleus. The intertrigeminal nucleus, facial and hypoglossal nuclei, retrotrapezoid nucleus, parafacial region and spinal cord segment 5 were also richly innervated by KFN axonal projections but were only weakly (or not) immunopositive to c-Fos. The most striking finding was that some descending axons from KFN sent out branches to innervate multiple (up to seven) pontomedullary target structures including facial nucleus, trigeminal sensory nucleus, and various parts of ambiguus nucleus and its surrounding areas. The extensive axonal fan-out from single KFN neurons to multiple brainstem and spinal cord structures("one-to-many relationship"’) provides anatomical evidence that KFN may coordinate diverse physiological functions including hypoxic and hypercapnic respiratory responses, respiratory pattern generation and motor output,diving reflex, modulation of upper airways patency,coughing and vomiting abdominal expiratory reflex, as well as cardiovascular regulation and cardiorespiratory coupling.

Regulation of hindbrain Pyy expression by acute food deprivation, prolonged caloric restriction, and weight loss surgery in mice

PYY is a gut-derived putative satiety signal released in response to nutrient ingestion and is implicated in the regulation of energy homeostasis. Pyy-expressing neurons have been identified in the hindbrain of river lamprey, rodents, and primates. Despite this high evolutionary conservation, little is known about central PYY neurons. Using in situ hybridization, PYY-Cre;ROSA-EYFP mice, and immunohistochemistry, we identified PYY cell bodies in the gigantocellular reticular nucleus region of the hindbrain. PYY projections were present in the dorsal vagal complex and hypoglossal nucleus. In the hindbrain, Pyy mRNA was present at E9.5, and expression peaked at P2 and then decreased significantly by 70% at adulthood. We found that, in contrast to the circulation, PYY-(1-36) is the predominant isoform in mouse brainstem extracts in the ad libitum-fed state. However, following a 24-h fast, the relative amounts of PYY-(1-36) and PYY-(3-36) isoforms were similar. Interestingly, central Pyy expression showed nutritional regulation and decreased significantly by acute starvation, prolonged caloric restriction, and bariatric surgery (enterogastroanastomosis). Central Pyy expression correlated with body weight loss and circulating leptin and PYY concentrations. Central regulation of energy metabolism is not limited to the hypothalamus but also includes the midbrain and the brainstem. Our findings suggest a role for hindbrain PYY in the regulation of energy homeostasis and provide a starting point for further research on gigantocellular reticular nucleus PYY neurons, which will increase our understanding of the brain stem pathways in the integrated control of appetite and energy metabolism.

Association of prepro-orexin polymorphism with obstructive sleep apnea/hypopnea syndrome

BACKGROUND

Because of the potential role of orexin neuronal circuitry in the regulation of sleep and wakefulness and arousal and breathing, it seems reasonable to speculate that abnormalities in the prepro-orexin gene could be relevant to studies of obstructive sleep apnea/hypopnea syndrome (OSAHS); and it might be a candidate gene in the pathogenesis of OSAHS.

OBJECTIVE

The present study investigated whether single nucleotide polymorphisms (SNPs) in the human prepro-orexin gene are associated with OSAHS in Han Chinese people.

METHODS

A total of 394 subjects (217 cases and 177 control subjects) were recruited from China. Diagnostic polysomnography was performed in all patients and control subjects. SNPs in potentially functional regions of the gene were identified; and genotypes, determined by direct sequencing.

RESULTS

By sequencing the promoter, 2 exons, and the exon-intron junctions of the prepro-orexin gene, the g11182C>T SNP was identified. Statistical analysis showed that there were significant differences in the genotype distribution between patients with OSAHS and the control group (χ(2)(2) = 6.437, P = .04). Variant allele T of the g1182C>T polymorphism was more commonly found in patients with OSAHS as compared with control subjects (χ(2)(1) = 5.648, P = .017; odds ratio, 1.449; 95% confidence interval, 1.0466-1.968).

CONCLUSIONS

Our results suggest that the prepro-orexin gene polymorphism g1182C>T is associated with susceptibility to OSAHS in Han Chinese. This study provides insights into the genetic information for future studies regarding this gene in OSAHS.

Perspective on the human cough reflex

This review dissects the complex human cough reflex and suggests hypotheses about the evolutionary basis for the reflex. A mechanosensory-induced cough reflex conveys through branches of myelinated Aδ nerve fibers is not chemically reactive (i.e., capsaicin, bradykinin); possibly, its evolution is to prevent the harmful effects of aspiration of gastric or particulate contents into the lungs. This became necessary as the larynx moves closer to the opening of the esophagus as human ancestors adapt phonation over olfaction beginning less than 10 million years ago. The second type of cough reflex, a chemosensory type, is carried by unmyelinated C fibers. Supposedly, its origin dates back when prehistoric humans began living in close proximity to each other and were at risk for infectious respiratory diseases or irritant-induced lung injury. The mechanism for the latter type of cough is analogous to induced pain after tissue injury; and, it is controlled by the identical transient receptor potential vanilloid cation channel (TRPV1). The airways do not normally manifest nociceptive pain from a stimulus but the only consistent response that capsaicin and lung inflammation provoke in healthy human airways is cough. TRPA1, another excitatory ion channel, has been referred to as the "irritant receptor" and its activation also induces cough. For both types of cough, the motor responses are identical and via coordinated, precisely-timed and sequential respiratory events orchestrated by complex neuromuscular networking of the diaphragm, chest and abdominal respiratory muscles, the glottis and parts of the brain.