Long-COVID sequelae are associated with oxidative stress in hemodialysis patients

pathophysiology of long-COVID sequelae in the general population of SARS-CoV-2-infected patients has been shown to be strongly influenced by oxidative stress. However, the potential role of oxidative stress in the development of long-COVID sequelae in hemodialysis patients (HD) has never been investigated. The present study aimed to evaluate the oxidative status of HD patients 3.5 months after SARS-CoV-2 infection in relation to the presence of long-COVID sequelae and the severity of the acute phase COVID-19. Methods. This cross-sectional cohort study included 63 HD patients with a median age of 55 (43-62.5) years and a dialysis vintage of 42 (25-73) months who had been infected with COVID-19 at least 3 months before recruitment. Patients were divided into two groups according to the occurrence of long-COVID sequelae: Group 1 included 31 (49.2%) HD patients with sequelae, while Group 2 included 32 (50.8%) fully recovered individuals. At 3.5 (3.2-4.6) months after the acute phase of COVID-19, malondialdehyde (MDA) and erythrocyte levels (MDAe), sulfhydryl groups (SH -groups), serum catalase activity, transferrin, and ceruloplasmin were measured. A comparison of the obtained data was performed using the Student’s test or the Mann-Whitney test according to the data distribution. A correlation was evaluated with the Spearman test. Results. HD patients with persistent long-COVID sequelae had significantly higher concentrations of MDAs (p = 0.002), MDAe (p = 0.0006), and CTs (p = 0.02), and lower serum levels of SH-groups (p = 0.03) and ceruloplasmin (p = 0.03) compared with Group 2. The concentration of most studied indicators of pro- and antioxidant status did not depend on the severity of the acute phase COVID-19, and only catalase activity was statistically significantly related to the need for hospitalization (r = 0.59; p = 0.001), oxygen support (r = 0.44; p = 0.02), and the percentage of lung injury according to computed tomography (p = 0.03). Although the serum concentration of transferrin did not differ between the studied groups, the individual analysis showed that its value was statistically higher in HD patients with severe COVID-19 even 3.5 months after infection (p < 0.0001). Conclusions. Long-term COVID-19 sequelae in HD patients are associated with oxidative stress. High levels of catalase activity and serum transferrin 3.5 months after COVID-19 may be a consequence of the severe course of the acute phase of the disease. The obtained data suggest that the use of antioxidants may be one of the possible strategies to treat the long-term consequences of COVID in HD patients.  

ECONOMIC INSTRUMENTS OF STRATEGIC HOUSEHOLD WASTE MANAGEMENT

Introduction. The need to pursue more active government policy for the stimulation of waste processing is causedby the necessity to prevent those threats that arise unless an environment friendly and efficient waste management system is in place.Problem Statement. Ukraine demonstrates a low level of household waste recycling, which poses a hazard to theenvironment, quality of life, and health of the population of Ukraine. The measures identified in the National WasteManagement Strategy until 2030 can be implemented by combining the organization of separate collection of household waste with the revision of the existing incentives aiming at increasing the demand for secondary resources.Purpose. The purpose of this research is to generalize the causes of low amount and rates of processing ofhousehold waste and to develop a system of economic tools for the formation of supply and demand for household waste as main factors of effective strategic waste management.Material and Methods. Qualitative analysis and generalization of theoretical material, systematization ofeconomic tools of household waste management, economic and statistical analysis, and regression analysis have been used in this research. Results. A set of tools for strategic household waste management and changes in approaches to their formation have been proposed. The formation of waste management tariff should be based on the length of the waste management chain, the structure of the collected waste, the potential for its recycling, the revised methods for forming the tariff, organizing waste sorting, andamending the list of tax payers of environmental tax.Conclusions. The household waste management in Ukraine demonstrates certain stability of the waste processing structure and the absence of dynamic transformations in response to changes in the modern economy. It needs support, in particular, the revision of the set of economic tools for stimulating waste processing and organizational approaches to their implementation.

Multi-Level Regulation of Opioid-Induced Respiratory Depression

Opioids depress minute ventilation primarily by reducing respiratory rate. This results from direct effects on the preBötzinger Complex as well as from depression of the Parabrachial/Kölliker-Fuse Complex, which provides excitatory drive to preBötzinger Complex neurons mediating respiratory phase-switch. Opioids also depress awake drive from the forebrain and chemodrive.

Pharmacological disinhibition enhances paced breathing following complete spinal cord injury in rats

Respiratory dysfunction is one of the most devastating and life-threatening deficits that occurs following cervical spinal cord injury (SCI). Assisted breathing with mechanical ventilators is a necessary part of care for many cervical injured individuals, but it is also associated with increased risk of secondary complications such as infection, muscle atrophy and maladaptive plasticity. Pre-clinical studies with epidural stimulation (EDS) have identified it as an alternative/additional method to support adequate lung ventilation without mechanical assistance. The full potential of EDS, however, may be limited by spinal inhibitory mechanisms within the injured spinal cord. The goal of the present work is to assess the potential improvement for EDS in combination with pharmacological disinhibition of spinal circuits following complete high cervical SCI. All experiments were performed in decerebrate, unanesthetized, non-paralyzed (n = 13) and paralyzed (n = 8) adult Sprague-Dawley rats 6 h following a complete C1 transection. The combination of high-frequency EDS (HF-EDS) at the C4 spinal segment with intrathecal delivery of GABA and glycine receptors antagonists (GABAzine and strychnine, respectively) resulted in significantly increased phrenic motor output, tidal volume and amplitude of diaphragm electrical activity compared to HF-EDS alone. Thus, it appears that spinal fast inhibitory mechanisms limit phrenic motor output and present a new neuropharmacological target to improve paced breathing in individuals with cervical SCI.

Galenic Pial Arteriovenous Fistulas in Adults

BACKGROUND

Vein of Galen aneurysmal malformations (VOGMs) are pial arteriovenous fistulas possessing Galenic venous drainage most commonly presenting during the neonatal period and infancy, with initial discovery during adulthood quite rare.

OBJECTIVES AND METHODS

We conducted a literature survey of the PubMed database in order to identify Galenic pial arteriovenous fistulas (GPAVFs) with major manifestation or initial presentation during adulthood. Inclusionary criteria included pial AVFs with Galenic drainage with major manifestation or initial presentation at, or older than, 18 years. Exclusionary criteria included exclusive pediatric onset of symptomatology attributable to GPAVFs without a new onset major presentation during adulthood, exclusive or major dural arterial supply, arteriovenous malformations with Galenic drainage, developmental venous anomalies with Galenic drainage, isolated varices or anomalies of the vein of Galen, and any lesions with uncertainty regarding true GPAVF nature.

RESULTS

Our search generated 1589 articles. Excluding duplicates, 26 cases met criteria for evaluation. Mean age was 34.1 +/- 2.53 years. Clinical presentations of GPAVFs among adults included headache, intracranial hemorrhage, seizures, and focal neurologic deficits. Management strategies included observation (n = 5), emergent ventriculostomy or Torkildsen shunt (n = 3), cerebrospinal fluid diversion via ventriculoperitoneal shunting (n = 4), microsurgical obliteration or thrombectomy (n = 4), transarterial and/or transvenous embolotherapeutic obliteration (n = 7), and concurrent embolotherapy and radiosurgical irradiation (n = 1).

CONCLUSIONS

GPAVFs in adults often present with symptomatology of mild severity and may be effectively managed conservatively, though occasionally present catastrophically or may be treated via cerebrospinal fluid diversion, microsurgical obliteration, or endovascular embolization. Severity sufficient to require emergent intervention portended a poor outcome.

Structure and function of the perivascular fluid compartment and vertebral venous plexus: Illumining a novel theory on mechanisms underlying the pathogenesis of Alzheimer's, cerebral small vessel, and neurodegenerative diseases

Blood dynamically and richly supplies the cerebral tissue via microvessels invested in pia matter perforating the cerebral substance. Arteries penetrating the cerebral substance derive an investment from one or two successive layers of pia mater, luminally apposed to the pial-glial basal lamina of the microvasculature and abluminally apposed to a series of aquaporin IV-studded astrocytic end feet constituting the soi-disant glia limitans. The full investment of successive layers forms the variably continuous walls of the periarteriolar, pericapillary, and perivenular divisions of the perivascular fluid compartment. The pia matter disappears at the distal periarteriolar division of the perivascular fluid compartment. Plasma from arteriolar blood sequentially transudates into the periarteriolar division of the perivascular fluid compartment and subarachnoid cisterns in precession to trickling into the neural interstitium. Fluid from the neural interstitium successively propagates into the venules through the subarachnoid cisterns and perivenular division of the perivascular fluid compartment. Fluid fluent within the perivascular fluid compartment flows gegen the net direction of arteriovenular flow. Microvessel oscillations at the central tendency of the cerebral vasomotion generate corresponding oscillations of within the surrounding perivascular fluid compartment, interposed betwixt the abluminal surface of the vessels and internal surface of the pia mater. The precise microanatomy of this most fascinating among designable spaces has eluded the efforts of various investigators to interrogate its structure, though most authors non-consensusly concur the investing layers effectively and functionally segregate the perivascular and subarachnoid fluid compartments. Enlargement of the perivascular fluid compartment in a variety of neurological disorders, including senile dementia of the Alzheimer's type and cerebral small vessel disease, may alternately or coordinately constitute a correlative marker of disease severity and a possible cause implicated in the mechanistic pathogenesis of these conditions. Venular pressures modulating oscillatory dynamic flow within the perivascular fluid compartment may similarly contribute to the development of a variety among neurological disorders. An intimate understanding of subtle features typifying microanatomy and microphysiology of the investing structures and spaces of the cerebral microvasculature may powerfully inform mechanistic pathophysiology mediating a variety of neurovascular ischemic, neuroinfectious, neuroautoimmune, and neurodegenerative diseases.

Modulation of Respiratory System by Limb Muscle Afferents in Intact and Injured Spinal Cord

Breathing constantly adapts to environmental, metabolic or behavioral changes by responding to different sensory information, including afferent feedback from muscles. Importantly, not just respiratory muscle feedback influences respiratory activity. Afferent sensory information from rhythmically moving limbs has also been shown to play an essential role in the breathing. The present review will discuss the neuronal mechanisms of respiratory modulation by activation of peripheral muscles that usually occurs during locomotion or exercise. An understanding of these mechanisms and finding the most effective approaches to regulate respiratory motor output by stimulation of limb muscles could be extremely beneficial for people with respiratory dysfunctions. Specific attention in the present review is given to the muscle stimulation to treat respiratory deficits following cervical spinal cord injury.

Integration of Transplanted Neural Precursors with the Injured Cervical Spinal Cord

Cervical spinal cord injuries (SCI) result in devastating functional consequences, including respiratory dysfunction. This is largely attributed to the disruption of phrenic pathways, which control the diaphragm. Recent work has identified spinal interneurons as possible contributors to respiratory neuroplasticity. The present work investigated whether transplantation of developing spinal cord tissue, inherently rich in interneuronal progenitors, could provide a population of new neurons and growth-permissive substrate to facilitate plasticity and formation of novel relay circuits to restore input to the partially denervated phrenic motor circuit. One week after a lateralized, C3/4 contusion injury, adult Sprague-Dawley rats received allografts of dissociated, developing spinal cord tissue (from rats at gestational days 13-14). Neuroanatomical tracing and terminal electrophysiology was performed on the graft recipients 1 month later. Experiments using pseudorabies virus (a retrograde, transynaptic tracer) revealed connections from donor neurons onto host phrenic circuitry and from host, cervical interneurons onto donor neurons. Anatomical characterization of donor neurons revealed phenotypic heterogeneity, though donor-host connectivity appeared selective. Despite the consistent presence of cholinergic interneurons within donor tissue, transneuronal tracing revealed minimal connectivity with host phrenic circuitry. Phrenic nerve recordings revealed changes in burst amplitude after application of a glutamatergic, but not serotonergic antagonist to the transplant, suggesting a degree of functional connectivity between donor neurons and host phrenic circuitry that is regulated by glutamatergic input. Importantly, however, anatomical and functional results were variable across animals, and future studies will explore ways to refine donor cell populations and entrain consistent connectivity.

Paced breathing and phrenic nerve responses evoked by epidural stimulation following complete high cervical spinal cord injury in rats

Spinal cord injury (SCI) at the level of cervical segments often results in life-threatening respiratory complications and requires long-term mechanical ventilator assistance. Thus restoring diaphragm activity and regaining voluntary control of breathing are the primary clinical goals for patients with respiratory dysfunction following cervical SCI. Epidural stimulation (EDS) is a promising strategy that has been explored extensively for nonrespiratory functions and to a limited extent within the respiratory system. The goal of the present study is to assess the potential for EDS at the location of the phrenic nucleus (C₃-C₅) innervating the diaphragm: the main inspiratory muscle following complete C₁ cervical transection. To avoid the suppressive effect of anesthesia, all experiments were performed in decerebrate, C₁ cervical transection, unanesthetized, nonparalyzed ( n = 13) and paralyzed ( n = 7) animals. Our results show that C₄ segment was the most responsive to EDS and required the lowest threshold of current intensity, affecting tracheal pressure and phrenic nerve responses. High-frequency (200-300 Hz) EDS applied over C₄ segment (C₄-EDS) was able to maintain breathing with normal end-tidal CO₂ level and raise blood pressure. In addition, 100-300 Hz of C₄-EDS showed time- and frequency-dependent changes (short-term facilitation) of evoked phrenic nerve responses that may serve as a target mechanism for pacing of phrenic motor circuits. The present work provides the first report of successful EDS at the level of phrenic nucleus in a complete SCI animal model and offers insight into the potential therapeutic application in patients with high cervical SCI. NEW & NOTEWORTHY The present work offers the first demonstration of successful life-supporting breathing paced by epidural stimulation (EDS) at the level of the phrenic nucleus, following a complete spinal cord injury in unanesthetized, decerebrate rats. Moreover, our experiments showed time- and frequency-dependent changes of evoked phrenic nerve activity during EDS that may serve as a target mechanism for pacing spinal phrenic motor networks.

Spontaneous respiratory plasticity following unilateral high cervical spinal cord injury in behaving rats

Unilateral cervical C2 hemisection (C2Hx) is a classic model of spinal cord injury (SCI) for studying respiratory dysfunction and plasticity. However, most previous studies were performed under anesthesia, which significantly alters respiratory network. Therefore, the goal of this work was to assess spontaneous diaphragm recovery post-C2Hx in awake, freely behaving animals. Adult rats were chronically implanted with diaphragm EMG electrodes and recorded during 8 weeks post-C2Hx. Our results reveal that ipsilateral diaphragm activity partially recovers within days post-injury and reaches pre-injury amplitude in a few weeks. However, the full extent of spontaneous ipsilateral recovery is significantly attenuated by anesthesia (ketamine/xylazine, isoflurane, and urethane). This suggests that the observed recovery may be attributed in part to activation of NMDA receptors which are suppressed by anesthesia. Despite spontaneous recovery in awake animals, ipsilateral hemidiaphragm dysfunction still persists: i) Inspiratory bursts during basal (slow) breathing exhibit an altered pattern, ii) the amplitude of sighs - or augmented breaths - is significantly decreased, and iii) the injured hemidiaphragm exhibits spontaneous events of hyperexcitation. The results from this study offer an under-appreciated insight into spontaneous diaphragm activity and recovery following high cervical spinal cord injury in awake animals.

Supraspinal respiratory plasticity following acute cervical spinal cord injury

Impaired breathing is a devastating result of high cervical spinal cord injuries (SCI) due to partial or full denervation of phrenic motoneurons, which innervate the diaphragm - a primary muscle of respiration. Consequently, people with cervical level injuries often become dependent on assisted ventilation and are susceptible to secondary complications. However, there is mounting evidence for limited spontaneous recovery of respiratory function following injury, demonstrating the neuroplastic potential of respiratory networks. Although many studies have shown such plasticity at the level of the spinal cord, much less is known about the changes occurring at supraspinal levels post-SCI. The goal of this study was to determine functional reorganization of respiratory neurons in the medulla acutely (>4h) following high cervical SCI. Experiments were conducted in decerebrate, unanesthetized, vagus intact and artificially ventilated rats. In this preparation, spontaneous recovery of ipsilateral phrenic nerve activity was observed within 4 to 6h following an incomplete, C2 hemisection (C2Hx). Electrophysiological mapping of the ventrolateral medulla showed a reorganization of inspiratory and expiratory sites ipsilateral to injury. These changes included i) decreased respiratory activity within the caudal ventral respiratory group (cVRG; location of bulbospinal expiratory neurons); ii) increased proportion of expiratory phase activity within the rostral ventral respiratory group (rVRG; location of inspiratory bulbo-spinal neurons); iii) increased respiratory activity within ventral reticular nuclei, including lateral reticular (LRN) and paragigantocellular (LPGi) nuclei. We conclude that disruption of descending and ascending connections between the medulla and spinal cord leads to immediate functional reorganization within the supraspinal respiratory network, including neurons within the ventral respiratory column and adjacent reticular nuclei.

Enhancing neural activity to drive respiratory plasticity following cervical spinal cord injury

Cervical spinal cord injury (SCI) results in permanent life-altering sensorimotor deficits, among which impaired breathing is one of the most devastating and life-threatening. While clinical and experimental research has revealed that some spontaneous respiratory improvement (functional plasticity) can occur post-SCI, the extent of the recovery is limited and significant deficits persist. Thus, increasing effort is being made to develop therapies that harness and enhance this neuroplastic potential to optimize long-term recovery of breathing in injured individuals. One strategy with demonstrated therapeutic potential is the use of treatments that increase neural and muscular activity (e.g. locomotor training, neural and muscular stimulation) and promote plasticity. With a focus on respiratory function post-SCI, this review will discuss advances in the use of neural interfacing strategies and activity-based treatments, and highlights some recent results from our own research.

The role of spinal GABAergic circuits in the control of phrenic nerve motor output

While supraspinal mechanisms underlying respiratory pattern formation are well characterized, the contribution of spinal circuitry to the same remains poorly understood. In this study, we tested the hypothesis that intraspinal GABAergic circuits are involved in shaping phrenic motor output. To this end, we performed bilateral phrenic nerve recordings in anesthetized adult rats and observed neurogram changes in response to knocking down expression of both isoforms (65 and 67 kDa) of glutamate decarboxylase (GAD65/67) using microinjections of anti-GAD65/67 short-interference RNA (siRNA) in the phrenic nucleus. The number of GAD65/67-positive cells was drastically reduced on the side of siRNA microinjections, especially in the lateral aspects of Rexed's laminae VII and IX in the ventral horn of cervical segment C4, but not contralateral to microinjections. We hypothesize that intraspinal GABAergic control of phrenic output is primarily phasic, but also plays an important role in tonic regulation of phrenic discharge. Also, we identified respiration-modulated GABAergic interneurons (both inspiratory and expiratory) located slightly dorsal to the phrenic nucleus. Our data provide the first direct evidence for the existence of intraspinal GABAergic circuits contributing to the formation of phrenic output. The physiological role of local intraspinal inhibition, independent of descending direct bulbospinal control, is discussed.

Inhibition of A5 Neurons Facilitates the Occurrence of REM Sleep-Like Episodes in Urethane-Anesthetized Rats: A New Role for Noradrenergic A5 Neurons?

When rapid eye movement (REM) sleep occurs, noradrenergic cells become silent, with the abolition of activity in locus coeruleus (LC) neurons seen as a key event permissive for the occurrence of REM sleep. However, it is not known whether silencing of other than LC noradrenergic neurons contributes to the generation of REM sleep. In urethane-anesthetized rats, stereotyped REM sleep-like episodes can be repeatedly elicited by injections of the cholinergic agonist, carbachol, into a discrete region of the dorsomedial pons. We used this preparation to test whether inhibition of ventrolateral pontine noradrenergic A5 neurons only, or together with LC neurons, also can elicit REM sleep-like effects. To silence noradrenergic cells, we sequentially injected the α₂-adrenergic agonist clonidine (20–40 nl, 0.75 mM) into both A5 regions and then the LC. In two rats, successful bilateral clonidine injections into the A5 region elicited the characteristic REM sleep-like episodes (hippocampal theta rhythm, suppression of hypoglossal nerve activity, reduced respiratory rate). In five rats, bilateral clonidine injections into the A5 region and then into one LC triggered REM sleep-like episodes, and in two rats injections into both A5 and then both LC were needed to elicit the effect. In contrast, in three rats, uni- or bilateral clonidine injections only into the LC had no effect, and clonidine injections placed in another six rats outside of the A5 and/or LC regions were without effect. The REM sleep-like episodes elicited by clonidine had similar magnitude of suppression of hypoglossal nerve activity (by 75%), similar pattern of hippocampal changes, and similar durations (2.5–5.3 min) to the episodes triggered in the same preparation by carbachol injections into the dorsomedial pontine reticular formation. Thus, silencing of A5 cells may importantly enable the occurrence of REM sleep-like episodes, at least under anesthesia. This is a new role for noradrenergic A5 neurons.

Motoneuron firing patterns underlying fast oscillations in phrenic nerve discharge in the rat

Fast oscillations are ubiquitous throughout the mammalian central nervous system and are especially prominent in respiratory motor outputs, including the phrenic nerves (PhNs). Some investigators have argued for an epiphenomenological basis for PhN high-frequency oscillations because phrenic motoneurons (PhMNs) firing at these same frequencies have never been recorded, although their existence has never been tested systematically. Experiments were performed on 18 paralyzed, unanesthetized, decerebrate adult rats in which whole PhN and individual PhMN activity were recorded. A novel method for evaluating unit-nerve time-frequency coherence was applied to PhMN and PhN recordings. PhMNs were classified according to their maximal firing rate as high, medium, and low frequency, corresponding to the analogous bands in PhN spectra. For the first time, we report the existence of PhMNs firing at rates corresponding to high-frequency oscillations during eupneic motor output. The majority of PhMNs fired only during inspiration, but a small subpopulation possessed tonic activity throughout all phases of respiration. Significant time-varying PhMN-PhN coherence was observed for all PhMN classes. High-frequency, early-recruited units had significantly more consistent onset times than low-frequency, early/middle-recruited and medium-frequency, middle/late-recruited PhMNs. High- and medium-frequency PhMNs had significantly more consistent offset times than low-frequency units. This suggests that startup and termination of PhMNs with higher firing rates are more precisely controlled, which may contribute to the greater PhMN-PhN coherence at the beginning and end of inspiration. Our findings provide evidence that near-synchronous discharge of PhMNs firing at high rates may underlie fast oscillations in PhN discharge.

GABAAergic and Glycinergic Inhibition in the Phrenic Nucleus Organizes and Couples Fast Oscillations in Motor Output

One of the characteristics of respiratory motor output is the presence of fast synchronous oscillations, at rates far exceeding the basic breathing rhythm, within a given functional population. However, the mechanisms responsible for organizing phrenic output into two dominant bands in vivo, medium (MFO)- and high (HFO)-frequency oscillations, have yet to be elucidated. We hypothesize that GABAAergic and glycinergic inhibition within the phrenic motor nucleus underlies the specific organization of these oscillations. To test this, the phrenic nuclei (C4) of 14 unanesthetized, decerebrate adult male Sprague-Dawley rats were microinjected unilaterally with either 4 mM strychnine ( n = 7) or GABAzine ( n = 7) to block glycine or GABAA receptors, respectively. Application of GABAzine caused an increase in overall phrenic amplitude during all three phases of respiration (inspiration, postinspiration, and expiration), while the increases caused by strychnine were most pronounced during postinspiration. Neither antagonist produced changes in inspiratory duration or respiratory rate. Power spectral analysis of inspiratory phrenic bursts showed that blockade of inhibition caused significant reduction in the relative power of MFO (GABAA and glycine receptors) and HFO (GABAA receptors only). In addition, analysis of the coherence between the firing of the ipsi- and contralateral phrenic nerves revealed that HFO coupling was significantly reduced by both antagonists and that of MFO was significantly reduced only by strychnine. We conclude that both GABAA and glycine receptors play critical roles in the organization of fast oscillations into MFO and HFO bands in the phrenic nerve, as well as in their bilateral coupling.

Joint Probability-Based Neuronal Spike Train Classification

Neuronal spike trains are used by the nervous system to encode and transmit information. Euclidean distance-based methods (EDBMs) have been applied to quantify the similarity between temporally-discretized spike trains and model responses. In this study, using the same discretization procedure, we developed and applied a joint probability-based method (JPBM) to classify individual spike trains of slowly adapting pulmonary stretch receptors (SARs). The activity of individual SARs was recorded in anaesthetized, paralysed adult male rabbits, which were artificially-ventilated at constant rate and one of three different volumes. Two-thirds of the responses to the 600 stimuli presented at each volume were used to construct three response models (one for each stimulus volume) consisting of a series of time bins, each with spike probabilities. The remaining one-third of the responses where used as test responses to be classified into one of the three model responses. This was done by computing the joint probability of observing the same series of events (spikes or no spikes, dictated by the test response) in a given model and determining which probability of the three was highest. The JPBM generally produced better classification accuracy than the EDBM, and both performed well above chance. Both methods were similarly affected by variations in discretization parameters, response epoch duration, and two different response alignment strategies. Increasing bin widths increased classification accuracy, which also improved with increased observation time, but primarily during periods of increasing lung inflation. Thus, the JPBM is a simple and effective method performing spike train classification.

Temperature and state dependence of dynamic phrenic oscillations in the decerebrate juvenile rat

The aim of the present study was to determine characteristics of fast oscillations in the juvenile rat phrenic nerve (Ph) and to establish their temperature and state dependence. Two different age-matched decerebrate, baro- and chemodenervated rat preparations, in vivo and in situ arterially perfused models, were used to examine three systemic properties: 1) generation and dynamics of fast oscillations in Ph activity (both preparations), 2) responses to anoxia (both preparations), and 3) the effects of temperature on fast oscillations (in situ only). Both juvenile preparations generated power and coherence in two major bands analogous to adult medium- and high-frequency oscillations (HFO) at frequencies that increased with temperature but were lower than in adults. At < 28°C, however, Ph oscillations were confined primarily to one low-frequency band (20–45 Hz). During sustained anoxia, both preparations produced stereotypical state changes from eupnea to hyperpnea to transition bursting (a behavior present only in vivo during incomplete ischemia) to gasping. Thus the juvenile rat produces a sequential pattern of responses to anoxia that are intermediate forms between those produced by neonates and those produced by adults. Time-frequency analysis determined that fast oscillations demonstrated dynamics over the course of the inspiratory burst and a state dependence similar to that of adults in vivo in which hyperpnea (and transition) bursts are associated with increases in HFO, while gasping contains no HFO. Our results confirm that both the fast oscillations in Ph activity and the coherence between Ph pairs produced by the juvenile rat are profoundly state- and temperature-dependent.

Retention of lung distension information in pump cell spike trains

Respiratory control requires feedback signals from the viscera, including mechanoreceptors and chemoreceptors. We previously showed that typical pulmonary stretch receptor (PSR) spike trains provide the central nervous system with approximately 31% of the theoretical maximum information regarding the amplitude of lung distension. However, it is unknown whether the spatiotemporal convergence of many PSR inputs onto second-order neurons (e.g., pump cells) results in more, or less, information about the stimulus carried by second-order cell spike trains. We recorded pump cell activity in adult, anesthetized, paralyzed, artificially ventilated rabbits during continuous manipulation of ventilator rate and volume to test the hypothesis that less information is carried by spike trains of individual pump cells than PSRs. Using previously developed analytic methods, we quantified the information carried by the pump cell spike trains and compared it with the same values derived from PSR data. Our results provide evidence that rejects our hypothesis: pump cells as a group did not carry significantly less information about the lung distension stimulus than PSRs, although that trend was implied by the data. By comparing the response variances with the theoretical minimum, we discovered that the trend toward information loss depends on response strength, with higher mean responses associated with larger response variances in pump cells than in PSRs. Thus spatiotemporal integration may result in information loss within certain analytic/stimulus parameters, but this is counterbalanced by the consistency of pump cell responses during brief integration times and/or low stimulus amplitudes, resulting in retention of total information.

Time-frequency coherence analysis of phrenic and hypoglossal activity in the decerebrate rat during eupnea, hyperpnea, and gasping

Fast respiratory rhythms include medium- (MFO) and high-frequency oscillations (HFO), which are much faster than the fundamental breathing rhythm. According to previous studies, HFO is characterized by high coherence (Coh) in phrenic (Ph) nerve activity, thereby providing a means of distinguishing between these two types of oscillations. Changes in Coh between the Ph and hypoglossal (XII) nerves during the transition from normal eupnic breathing to gasping have not been characterized. Experiments were performed on nine unanesthetized, chemo- and barodenervated, decerebrate adult rats, in which sustained asphyxia elicited hyperpnea and gasping. A gated time-frequency Coh analysis was developed and applied to whole Ph and medial XII nerve recordings. The results showed dynamic Ph-Ph Coh during eupnea, including MFO and HFO. XII-XII Coh during eupnea was broadband and included four distinct peaks, with low-frequency Coh dominating the epochs preceding the onset of Ph activity. During gasping, only MFO-peaks were present in Ph-Ph Coh. Bilateral XII activity showed a significant reduction in Coh and a shift toward lower frequencies during gasping. In contrast, contralateral Ph-XII Coh progressively increased during state changes from eupnea to gasping, a tendency mirrored in the startup part of the Ph activity. These data suggest significant hypoxia/hypercapnia-induced alterations in synchronization between respiratory outputs during the transition from eupnea to gasping, reflecting a reconfiguration of the respiratory network and/or alterations in the circuitry associated with the motor pools, including dynamic coupling between outputs.

Selective loss of high-frequency oscillations in phrenic and hypoglossal activity in the decerebrate rat during gasping

Respiratory motor outputs contain medium-(MFO) and high-frequency oscillations (HFO) that are much faster than the fundamental breathing rhythm. However, the associated changes in power spectral characteristics of the major respiratory outputs in unanesthetized animals during the transition from normal eupneic breathing to hypoxic gasping have not been well characterized. Experiments were performed on nine unanesthetized, chemo- and barodenervated, decerebrate adult rats, in which asphyxia elicited hyperpnea, followed by apnea and gasping. A gated fast Fourier transform (FFT) analysis and a novel time-frequency representation (TFR) analysis were developed and applied to whole phrenic and to medial branch hypoglossal nerve recordings. Our results revealed one MFO and one HFO peak in the phrenic output during eupnea, where HFO was prominent in the first two-thirds of the burst and MFO was prominent in the latter two-thirds of the burst. The hypoglossal activity contained broadband power distribution with several distinct peaks. During gasping, two high-amplitude MFO peaks were present in phrenic activity, and this state was characterized by a conspicuous loss in HFO power. Hypoglossal activity showed a significant reduction in power and a shift in its distribution toward lower frequencies during gasping. TFR analysis of phrenic activity revealed the increasing importance of an initial low-frequency “start-up” burst that grew in relative intensity as hypoxic conditions persisted. Significant changes in MFO and HFO rhythm generation during the transition from eupnea to gasping presumably reflect a reconfiguration of the respiratory network and/or alterations in signal processing by the circuitry associated with the two motor pools.

Cardiovascular responses to chemical stimulation of the lateral tegmental field and adjacent medullary reticular formation in the rat

Relatively few studies have been done to characterize cardiovascular responses to the chemical stimulation of sites located in the medullary lateral tegmental field (LTF) and most of them have been carried out in anesthetized animals. Our experiments were carried out in decerebrated, artificially ventilated, adult male Wistar rats. In the LTF, two types of cardiovascular responses were elicited. One type consisted of pressor responses accompanied by bradycardia. Such responses were elicited from a region 0.4 mm caudal to 0.8 mm rostral to the calamus scriptorius (CS); maximum responses were elicited from a site 0.6 mm rostral to the CS, 1.2 mm lateral to the midline and 1.2 mm deep from the dorsal medullary surface. Another type consisted of pressor responses without any change in heart rate; such responses were elicited from a region 1-1.6 mm rostral to the CS. Nucleus ambiguus (nAmb) and dorsal motor nucleus of the vagus (nDMX) and the reticular formation surrounding these areas were the main sites from which bradycardia (accompanied by either no or small changes in BP) was elicited. In the nAmb, maximum bradycardia was elicited from a site 0.6 mm rostral to the CS, 1.8 mm lateral to the midline and 2.4 mm deep from the dorsal medullary surface. In the nDMX, most prominent bradycardic responses were elicited at 0-0.6 mm rostral to the CS, and 0.6 mm lateral to the midline and 1 mm deep from the dorsal medullary surface. Cardiovascular effects elicited from sites in other well-known areas, such as the rostral ventrolateral medullary pressor area (RVLM) and caudal ventrolateral medullary depressor area (CVLM), and the nucleus tractus solitarius (nTS) were also included for comparison of different responses. These results are expected to prove useful in studies in which the microinjection technique is used to characterize cardiovascular responses.

Respiratory cycle timing and fast inspiratory discharge rhythms in the adult decerebrate rat

In supracollicular decerebrate paralyzed adult rats, neural respiration was monitored by bilateral phrenic recordings. In the study of respiratory cycle timing, the effects of vagal afferent input (lung inflation) on respiratory phase durations resembled those seen in decerebrate cats. 1) Withholding lung inflation during neural inspiration (I) produced lengthening of I phase duration by 46% (mean, n = 11). 2) Maintaining lung inflation during neural expiration (E) produced lengthening of E phase duration by 112% (mean, n = 4). In the study of fast rhythms in inspiratory discharges, phrenic nerve autospectra and bilateral (left-right) phrenic coherences in 16 rats revealed two types of fast rhythm: 1) high-frequency oscillation (HFO), which had significant coherence peaks (n = 9, range 106-160 Hz, mean 132 Hz); and 2) medium-frequency oscillation (MFO), which had autospectral peaks but no distinct coherence peaks (n = 11, range 46-96 Hz, mean 66 Hz). These rhythms resembled MFOs and HFOs in the decerebrate cat, but the modal frequency range was about twice as large. In addition, these frequency values differed markedly from the 20-40 Hz of the rhythms found in earlier studies in neonatal in vitro preparations; the difference may be due to developmental immaturity.

A5 cells are silenced when REM sleep-like signs are elicited by pontine carbachol

The A5 noradrenergic neurons are considered important for cardiorespiratory regulation. We hypothesized that A5 cells are silenced during rapid eye movement (REM) sleep, thereby contributing to cardiorespiratory changes and suppression of hypoglossal (XII) motoneuronal activity. We used an anesthetized, paralyzed, and artificially ventilated rat in which pontine microinjections of carbachol trigger signs of REM sleep, including hippocampal theta rhythm, motor suppression, and silencing of locus coeruleus neurons. All 16 putative noradrenergic A5 cells recorded were strongly suppressed when the REM sleep-like episodes were elicited and also after intravenous clonidine. Antidromic mapping showed that none of six neurons tested projected to the XII nucleus, whereas three of five projected to the nucleus of the solitary tract and two of four to the rostral ventrolateral medulla. Bilateral microinjections of clonidine into the A5 regions did not alter XII nerve activity. These data suggest that A5 neurons are silenced during natural REM sleep. This will lead to decreased norepinephrine release and may alter synaptic transmission in the nucleus of the solitary tract and rostral ventrolateral medulla without, however, a detectable impact on XII motoneurons.

Different patterns of respiratory and cardiovascular responses elicited by chemical stimulation of dorsal medulla in the rat

Respiratory and cardiovascular responses to microinjections (10 nl) of L-glutamate (10 mM) into the dorsal medulla were studied in spontaneously breathing urethane-anesthetized, adult male Wistar rats. A total of 10 patterns of respiratory and cardiovascular responses were observed: (1) hypotension alone; (2) hypotension and bradycardia; (3) hypotension and apnea; (4) hypotension, bradycardia, and apnea; (5) apnea alone; (6) hypotension and fast and shallow breathing; (7) hypotension, bradycardia, and fast and shallow breathing; (8) fast and shallow breathing alone; (9) sighs; and (10) increase in BP and HR accompanied with fast and shallow breathing. The sites from which a combination of hypotension, bradycardia, and apnea was elicited, occupied a region in the medial subnucleus of nucleus tractus solitarius (nTS), the reticular formation just ventral to it, and the dorsal motor nucleus of vagus. The sites from which hypotension alone or a combination of hypotension and apnea were elicited occupied the margins of the medial subnucleus of nTS. The sites from which apnea alone was elicited were located in the ventrolateral part of nTS and the reticular formation just ventral to it. In the commissural subnucleus of nTS, the responses comparable to those elicited by peripheral chemoreceptor stimulation (i.e., increase in BP, HR, and respiratory rate) were located in a midline region just caudal to the calamus scriptorius, the sites from which sighs were elicited were located slightly lateral and deeper, the sites from which fast and shallow breathing were elicited were located in the dorsal portion, slightly lateral to the midline. These results are expected to prove useful in studies in which microinjection technique is used to identify transmitters/receptors involved in mediating respiratory and cardiovascular reflex responses.