Relationships between hippocampal activity and breathing patterns

Proteostasis failure exacerbates neuronal circuit dysfunction and sleep impairments in Alzheimer's disease

Failed proteostasis is a well-documented feature of Alzheimer's disease, particularly, reduced protein degradation and clearance. However, the contribution of failed proteostasis to neuronal circuit dysfunction is an emerging concept in neurodegenerative research and will prove critical in understanding cognitive decline. Our objective is to convey Alzheimer's disease progression with the growing evidence for a bidirectional relationship of sleep disruption and proteostasis failure. Proteostasis dysfunction and tauopathy in Alzheimer's disease disrupts neurons that regulate the sleep-wake cycle, which presents behavior as impaired slow wave and rapid eye movement sleep patterns. Subsequent sleep loss further impairs protein clearance. Sleep loss is a defined feature seen early in many neurodegenerative disorders and contributes to memory impairments in Alzheimer's disease. Canonical pathological hallmarks, β-amyloid, and tau, directly disrupt sleep, and neurodegeneration of locus coeruleus, hippocampal and hypothalamic neurons from tau proteinopathy causes disruption of the neuronal circuitry of sleep. Acting in a positive-feedback-loop, sleep loss and circadian rhythm disruption then increase spread of β-amyloid and tau, through impairments of proteasome, autophagy, unfolded protein response and glymphatic clearance. This phenomenon extends beyond β-amyloid and tau, with interactions of sleep impairment with the homeostasis of TDP-43, α-synuclein, FUS, and huntingtin proteins, implicating sleep loss as an important consideration in an array of neurodegenerative diseases and in cases of mixed neuropathology. Critically, the dynamics of this interaction in the neurodegenerative environment are not fully elucidated and are deserving of further discussion and research. Finally, we propose sleep-enhancing therapeutics as potential interventions for promoting healthy proteostasis, including β-amyloid and tau clearance, mechanistically linking these processes. With further clinical and preclinical research, we propose this dynamic interaction as a diagnostic and therapeutic framework, informing precise single- and combinatorial-treatments for Alzheimer's disease and other brain disorders.

Perspectives on the basis of seizure-induced respiratory dysfunction

Epilepsy is an umbrella term used to define a wide variety of seizure disorders and sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in epilepsy. Although some SUDEP risk factors have been identified, it remains largely unpredictable, and underlying mechanisms remain poorly understood. Most seizures start in the cortex, but the high mortality rate associated with certain types of epilepsy indicates brainstem involvement. Therefore, to help understand SUDEP we discuss mechanisms by which seizure activity propagates to the brainstem. Specifically, we highlight clinical and pre-clinical evidence suggesting how seizure activation of: (i) descending inhibitory drive or (ii) spreading depolarization might contribute to brainstem dysfunction. Furthermore, since epilepsy is a highly heterogenous disorder, we also considered factors expected to favor or oppose mechanisms of seizure propagation. We also consider whether epilepsy-associated genetic variants directly impact brainstem function. Because respiratory failure is a leading cause of SUDEP, our discussion of brainstem dysfunction focuses on respiratory control.

Inappropriate Ventilatory Homeostatic Responses in Hospitalized COVID-19 Patients

Background

The clinical presentation of COVID-19 suggests altered breathing control - tachypnoea, relative lack of dyspnoea, and often a discrepancy between severity of clinical and radiological findings. Few studies characterize and analyse the contribution of breathing drivers and their ventilatory and perceptual responses.

Aim

To establish the prevalence of inappropriate ventilatory and perceptual response in COVID-19, by characterizing the relationships between respiratory rate (RR), dyspnoea and arterial blood gas (ABG) in a cohort of COVID-19 patients at presentation to hospital, and their post-Covid respiratory sequelae at follow-up.

Methods

We conducted a retrospective cohort study including consecutive adult patients admitted to hospital with confirmed COVID-19 between 1st March 2020 and 30th April 2020. In those with concurrent ABG, RR and documented dyspnoea status on presentation, we documented patient characteristics, disease severity, and outcomes at hospital and 6-week post-discharge.

Results

Of 492 admissions, 194 patients met the inclusion criteria. Tachypnoea was present in 75% pronounced (RR>30) in 36%, and persisted during sleep. RR correlated with heart rate (HR) (r = 0.2674), temperature (r = 0.2824), CRP (r = 0.2561), Alveolar-arterial (A-a) gradient (r = 0.4189), and lower PaO₂/FiO₂ (PF) ratio (r = −0.3636). RR was not correlated with any neurological symptoms. Dyspnoea was correlated with RR (r = 0.2932), A-a gradient (r = 0.1723), and lower PF ratio (r = −0.1914), but not correlated with PaO₂ (r = −0.1095), PaCO₂ (r = −0.0598) or any recorded neurological symptom except for altered consciousness. Impaired ventilatory homeostatic control of pH/PaCO₂ [tachypnoea (RR>20), hypocapnia (PaCO₂ <4.6 kPa), and alkalosis (pH>7.45)] was observed in 29%. This group, of which 37% reported no dyspnoea, had more severe respiratory disease (A-a gradient 38.9 vs. 12.4 mmHg; PF ratio 120 vs. 238), and higher prevalence of anosmia (21 vs. 15%), dysgeusia (25 vs. 12%), headache (33 vs. 23%) and nausea (33 vs. 14%) with similar rates of new anxiety/depression (26 vs. 23%), but lower incidence of past neurological or psychiatric diagnoses (5 vs. 21%) compared to appropriate responders. Only 5% had hypoxia sufficiently severe to drive breathing (i.e. PaO₂ <6.6 kPa). At 6 weeks post-discharge, 24% (8/34) showed a new breathing pattern disorder with no other neurological findings, nor previous respiratory, neurological, or psychiatric disorder diagnoses.

Conclusions

Impaired homeostatic control of ventilation i.e., tachypnoea, despite hypocapnia to the point of alkalosis appears prevalent in patients admitted to hospital with COVID-19, a finding typically accompanying more severe disease. Tachypnoea prevalence was between 12 and 29%. Data suggest that excessive tachypnoea is driven by both peripheral and central mechanisms, but not hypoxia. Over a third of patients with impaired homeostatic ventilatory control did not experience dyspnoea despite tachypnoea. A subset of followed-up patients developed post-covid breathing pattern disorder.

Limbic and paralimbic respiratory modulation: from inhibition to enhancement

OBJECTIVE

Increased understanding of the role of cortical structures in respiratory control may help the understanding of seizure-induced respiratory dysfunction that leads to sudden death in epilepsy (SUDEP). The aim of this study was to characterize respiratory responses to electrical stimulation (ES), including inhibition and enhancement of respiration.

METHODS

We prospectively recruited 19 consecutive patients with intractable epilepsy undergoing stereotactic EEG evaluation from June 2015 to June 2018. Inclusion criteria were patients ≥18 years and in whom ES was indicated for clinical mapping of ictal onset or eloquent cortex as part of the presurgical evaluation. ES was carried out at 50 Hz, 0.2 ms and 1-10 mA current intensity. Common brain regions sampled across all patients were- amygdala (AMY), hippocampus (HG), anterior cingulate gyrus (CING), orbitofrontal cortex (OrbF), temporal neocortex (TNC), temporal pole (TP) and entorhinal cortex (ERC). 755 stimulations were conducted. Quantitative analysis of breathing signal i.e., changes in breathing rate (BR), depth (TV), and minute ventilation (MV) was carried out during ES using the BreathMetrics breathing waveform analysis toolbox. Electrocardiogram, arterial oxygen saturation, end-tidal and transcutaneous carbon dioxide, nasal airflow, and abdominal and thoracic plethysmography were continuously monitored during stimulations.

RESULTS

Electrical stimulation of TP and CING (at lower current strengths <3mA) increased TV and MV. At 7-10mA, CING decreased TV and MV. On the other hand, decreased TV and MV occurred with stimulation of mesial temporal structures such as AMY and HG. Breathing changes were dependent on stimulation intensity. Lateral temporal, entorhinal, and orbitofrontal cortices did not affect breathing either way.

SIGNIFICANCE

These findings suggest that breathing responses other than apnea can be induced by ES. Identification of two regions, the temporal pole and anterior cingulate gyrus, for enhancement of breathing may be important in paving the way to future development of strategies for prevention of SUDEP.

Protocol of controlled odorant stimulation for reducing apnoeic episodes in premature newborns: a randomised open-label Latin-square study with independent evaluation of the main endpoint (PREMODEUR)

INTRODUCTION

Apnoea affects 85% of premature infants under 34 weeks of age and would be an important risk factor for subsequent neuropsychological disorders. Currently, premature children with life-threatening apnoeas receive stimulants such as methylxanthines (mainly, caffeine) or doxapram (an analeptic unlicensed in children under 15). However, these products have undesirable effects (hyperarousal, irritability, sleep disorders, tachycardia) and are not always effective because apnoea does persist in some premature newborns. Previous studies have indicated that odorant stimulation, a non-invasive intervention, may stimulate the respiratory rhythm. The objective of the present protocol is to reduce the occurrence of apnoeic episodes in premature newborns by controlled odorant stimulation added to current pharmacological treatments.

METHODS AND ANALYSIS

The project is a randomised open-label Latin-square trial with independent evaluation of the main endpoint. It will include 60 preterm neonates from two university hospital neonatal intensive care units over 2 years (2021-2023). Each newborn will receive no (S0), sham (S1) or real olfactory stimulation (S2) in random order. During S2, three distinct odorants (mint, grapefruit and vanilla) will be delivered successively, in puffs, over 24 hours. Mint and grapefruit odours stimulate the main and the trigeminal olfactory pathways, whereas vanilla odour stimulates only the main olfactory pathway. A statistical analysis will compare the incidence of apnoeic episodes during S1 versus S2 using a mixed effects Poisson model.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Comité de Protection des Personnes Île-de-France XI (# 2017-AO13-50-53). The results will be disseminated through various scientific meetings, specialised peer-reviewed journals and, whenever possible, posted on appropriate public websites.

TRIAL REGISTRATION NUMBER

NCT02851979; Pre-results.

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.

Peri-ictal hypoxia is related to extent of regional brain volume loss accompanying generalized tonic-clonic seizures

OBJECTIVES

Hypoxia, or abnormally low blood-oxygen levels, often accompanies seizures and may elicit brain structural changes in people with epilepsy which contribute to central processes underlying sudden unexpected death in epilepsy (SUDEP). The extent to which hypoxia may be related to brain structural alterations in this patient group remains unexplored.

METHODS

We analyzed high-resolution T1-weighted magnetic resonance imaging (MRI) to determine brain morphometric and volumetric alterations in people with generalized tonic-clonic seizures (GTCS) recorded during long-term video-electroencephalography (VEEG), recruited from two sites (n = 22), together with data from age- and sex-matched healthy controls (n = 43). Subjects were sub-divided into those with mild/moderate (GTCS-hypox-mild/moderate, n = 12) and severe (GTCS-hypox-severe, n = 10) hypoxia, measured by peripheral oxygen saturation (SpO2 ) during VEEG. Whole-brain voxel-based morphometry (VBM) and regional volumetry were used to assess group comparisons and correlations between brain structural measurements as well as the duration and extent of hypoxia during GTCS.

RESULTS

Morphometric and volumetric alterations appeared in association with peri-GTCS hypoxia, including volume loss in the periaqueductal gray (PAG), thalamus, hypothalamus, vermis, cerebellum, parabrachial pons, and medulla. Thalamic and PAG volume was significantly reduced in GTCS patients with severe hypoxia compared with GTCS patients with mild/moderate hypoxia. Brainstem volume loss appeared in both hypoxia groups, although it was more extensive in those with severe hypoxia. Significant negative partial correlations emerged between thalamic and hippocampal volume and extent of hypoxia, whereas vermis and accumbens volumes declined with increasing hypoxia duration.

SIGNIFICANCE

Brain structural alterations in patients with GTCS are related to the extent of hypoxia in brain sites that serve vital functions. Although the changes are associative only, they provide evidence of injury to regulatory brain sites related to respiratory manifestations of seizures.

Obstructive sleep apnea, cognition and Alzheimer's disease: A systematic review integrating three decades of multidisciplinary research

Increasing evidence links cognitive-decline and Alzheimer's disease (AD) to various sleep disorders, including obstructive sleep apnea (OSA). With increasing age, there are substantial differences in OSA's prevalence, associated comorbidities and phenotypic presentation. An important question for sleep and AD researchers is whether OSA's heterogeneity results in varying cognitive-outcomes in older-adults compared to middle-aged adults. In this review, we systematically integrated research examining OSA and cognition, mild cognitive-impairment (MCI) and AD/AD biomarkers; including the effects of continuous positive airway pressure (CPAP) treatment, particularly focusing on characterizing the heterogeneity of OSA and its cognitive-outcomes. Broadly, in middle-aged adults, OSA is often associated with mild impairment in attention, memory and executive function. In older-adults, OSA is not associated with any particular pattern of cognitive-impairment at cross-section; however, OSA is associated with the development of MCI or AD with symptomatic patients who have a higher likelihood of associated disturbed sleep/cognitive-impairment driving these findings. CPAP treatment may be effective in improving cognition in OSA patients with AD. Recent trends demonstrate links between OSA and AD-biomarkers of neurodegeneration across all age-groups. These distinct patterns provide the foundation for envisioning better characterization of OSA and the need for more sensitive/novel sleep-dependent cognitive assessments to assess OSA-related cognitive-impairment.

Hippocampal modulation of cardiorespiratory function

Changes in cardiorespiratory control accompany the expression of complex emotions, indicative of limbic brain inputs onto bulbar autonomic pathways. Previous studies have focussed on the role of the prefrontal cortex in autonomic regulation. However, the role of the hippocampus, also important in limbic processing, has not been addressed in detail. Anaesthetised, instrumented rats were used to map the location of hippocampal sites capable of evoking changes in cardiorespiratory control showing that stimulation of discrete regions within the CA1 fields of both the dorsal and ventral hippocampus potently alter breathing and cardiovascular activity. Additionally, tracing of the neuroanatomical tracts and pharmacological inactivation studies were used to demonstrate a role of the basomedial amygdala in hippocampal evoked responses. Collectively, these data support the existence of a hippocampal-amygdala neural circuit capable of modulating bulbar cardiorespiratory control networks and may suggest a role for this circuit in the top-down regulation of breathing and autonomic outflow necessary for the expression of complex emotions.

Breathing above the brain stem: volitional control and attentional modulation in humans

Whereas the neurophysiology of respiration has traditionally focused on automatic brain stem processes, higher brain mechanisms underlying the cognitive aspects of breathing are gaining increasing interest. Therapeutic techniques have used conscious control and awareness of breathing for millennia with little understanding of the mechanisms underlying their efficacy. Using direct intracranial recordings in humans, we correlated cortical and limbic neuronal activity as measured by the intracranial electroencephalogram (iEEG) with the breathing cycle. We show this to be the direct result of neuronal activity, as demonstrated by both the specificity of the finding to the cortical gray matter and the tracking of breath by the gamma-band (40-150 Hz) envelope in these structures. We extend prior observations by showing the iEEG signal to track the breathing cycle across a widespread network of cortical and limbic structures. We further demonstrate a sensitivity of this tracking to cognitive factors by using tasks adapted from cognitive behavioral therapy and meditative practice. Specifically, volitional control and awareness of breathing engage distinct but overlapping brain circuits. During volitionally paced breathing, iEEG-breath coherence increases in a frontotemporal-insular network, and during attention to breathing, we demonstrate increased coherence in the anterior cingulate, premotor, insular, and hippocampal cortices. Our findings suggest that breathing can act as an organizing hierarchical principle for neuronal oscillations throughout the brain and detail mechanisms of how cognitive factors impact otherwise automatic neuronal processes during interoceptive attention. NEW & NOTEWORTHY Whereas the link between breathing and brain activity has a long history of application to therapy, its neurophysiology remains unexplored. Using intracranial recordings in humans, we show neuronal activity to track the breathing cycle throughout widespread cortical/limbic sites. Volitional pacing of the breath engages frontotemporal-insular cortices, whereas attention to automatic breathing modulates the cingulate cortex. Our findings imply a fundamental role of breathing-related oscillations in driving neuronal activity and provide insight into the neuronal mechanisms of interoceptive attention.

Sigh rate during emotional transitions: More evidence for a sigh of relief

Evidence suggests that sighs regulate stress and emotions, e.g. by facilitating relief. This study aimed to investigate sigh rates during relief. In addition, links between sighs, anxiety sensitivity and HPA-axis activity were explored. Healthy volunteers (N=29) were presented cues predicting the valence of subsequent stimuli. By sequencing cues that predicted pleasant or unpleasant stimuli with or without certainty, transitions to certain pleasantness (relief) or to certain unpleasantness (control) were created and compared to no transitions. Salivary cortisol, anxiety sensitivity and respiration were measured. Sigh frequency was significantly higher during relief than during control transitions and no transition states, and higher during control transitions than during no transition states. Sigh frequency increased with steeper cortisol declines for high anxiety sensitive persons. Results confirm a relationship between sighs and relief. In addition, results suggest that sigh frequency is importantly related to HPA-axis activity, particularly in high anxiety sensitive persons.

Obstructive sleep apnea and its controversial effects on cognition

Obstructive sleep apnea syndrome is a sleep disorder that may affect many brain functions. We are interested in the cognitive consequences of the condition with regard to the quality of life of individuals with this disorder. A debate is still underway as to whether cognitive difficulties caused by obstructive sleep apnea actually induce a "pseudodementia" pattern. This work provides a brief overview of the main controversies currently surrounding this issue. We report findings and opinions on structural and cognitive brain changes in individuals affected by obstructive sleep apnea by highlighting the involvement of executive functions and the possible reversibility of signs following-treatment with continuous positive airway pressure. Much research has been done on this issue but, to the best of our knowledge, a review of the present state of the literature evaluating different points of view has not yet been carried out.

Neuronal control of breathing: sex and stress hormones

There is a growing public awareness that hormones can have a significant impact on most biological systems, including the control of breathing. This review will focus on the actions of two broad classes of hormones on the neuronal control of breathing: sex hormones and stress hormones. The majority of these hormones are steroids; a striking feature is that both groups are derived from cholesterol. Stress hormones also include many peptides which are produced primarily within the paraventricular nucleus of the hypothalamus (PVN) and secreted into the brain or into the circulatory system. In this article we will first review and discuss the role of sex hormones in respiratory control throughout life, emphasizing how natural fluctuations in hormones are reflected in ventilatory metrics and how disruption of their endogenous cycle can predispose to respiratory disease. These effects may be mediated directly by sex hormone receptors or indirectly by neurotransmitter systems. Next, we will discuss the origins of hypothalamic stress hormones and their relationship with the respiratory control system. This relationship is 2-fold: (i) via direct anatomical connections to brainstem respiratory control centers, and (ii) via steroid hormones released from the adrenal gland in response to signals from the pituitary gland. Finally, the impact of stress on the development of neural circuits involved in breathing is evaluated in animal models, and the consequences of early stress on respiratory health and disease is discussed.

Respiratory cycle entrainment of septal neurons mediates the fast coupling of sniffing rate and hippocampal theta rhythm

Memory for odour information may result from temporal coupling between the olfactory and hippocampal systems. Respiration defines the frequency of olfactory perception, but how the respiratory rate affects hippocampal oscillations remains poorly understood. The afferent connectivity of the medial septum/diagonal band of Broca complex (MS/DB) proposes this region as a crossroads between respiratory and limbic pathways. Here we investigate if the firing rates of septal neurons integrate respiratory rate signals. We demonstrate that approximately 50% of MS/DB neurons are temporally correlated with sniffing frequency. Moreover, a group of slow-spiking septal neurons are phase-locked to the sniffing cycle. We show that inter-burst intervals of MS/DB theta cells relate to the sniff rate. Intranasal odour infusion evokes sniff phase preference for the activity of fast-spiking MS/DB neurons. Concurrently, the infusion augments the correlation between sniffing and limbic theta oscillations. During periods of sniffing–theta correlation, CA1 place cells fired preferentially during the inhalation phase, suggesting the theta cycle as a coherent time frame for central olfactory processing. Furthermore, injection of the GABAergic agonist muscimol into medial septum induces a parallel decrease of sniffing and theta frequencies. Our findings provide experimental evidence that MS/DB does not merely generate theta rhythm, but actively integrates sensorimotor stimuli that reflect sniffing rate. Such integration may provide temporal oscillatory synchronisation of MS/DB-innervated limbic structures with the sniffing cycle.

Respiratory variability and sighing: a psychophysiological reset model

Whereas respiratory psychophysiological research has mainly studied respiratory time and volume, variability in these parameters has been largely disregarded, even though it may provide important information about respiratory regulation. The present paper reviews the literature on respiratory variability and elaborates on the importance of assessing various components of respiratory variability when studying the interrelationships between emotions and breathing. A model is proposed that predicts specific action tendencies related to emotions to disturb the balance between various respiratory variability components depending on valence by arousal and control dimensions. The central focus of the paper is sighing. The causes and consequences of sighing are reviewed and integrated in the proposed model in which sighing is hypothesized to function as a resetter in the regulation of both breathing and emotions, because it restores a balance in respiratory variability fractions and causes relief.

Concentrations of opiates and psychotropic agents in polydrug overdoses: a surprising correlation between morphine and antidepressants

The relationship between postmortem concentrations of morphine and co-detected psychoactive drugs in fatal overdoses is examined. Morphine and other drugs were detected in 161 medicolegal autopsy cases. Subsets of these morphine-positive cases based on drug class were established, including opioids, antidepressants, ethanol, benzodiazepines, and "other." Each subset was split into high or low concentration groups based on median drug concentrations. Morphine concentrations of the [high] and [low] groups were compared, with no significant difference in morphine concentration identified in the opioid, ethanol, or benzodiazepine subsets. The "other" drug class was too heterogeneous for statistical assessment. Morphine concentrations did show a significant direct relationship (p = 0.01) with antidepressants, namely increased concentrations of antidepressant drugs are associated with an increased concentration of morphine. This trend probably remains even after excluding cocaine-positive cases. The unsuspected finding that postmortem concentrations of antidepressants positively correlate with morphine levels may be important in the treatment of depression in drug addicts.

Relationship between respiratory, endocrine, and cognitive-emotional factors in response to a pharmacological panicogen

BACKGROUND

The cholecystokinin agonist pentagastrin has been used to study panic attacks in the laboratory and to investigate hypothalamic-pituitary-adrenal axis activity. Its mechanism of panicogenesis remains unclear. Data from other models suggest that respiratory stimulation itself may induce panic, but pentagastrin's effects on respiration are not well established. Data from another model also suggest links between respiratory and HPA axis reactivity and cognitive modulation of both. To further explore these phenomena, we added respiratory measures to a study of cognitive modulation of HPA and anxiety responses to pentagastrin.

METHODS

Healthy subjects received pentagastrin and placebo injections, with measurement of cortisol and subjective responses, on two different laboratory visits. They were randomly assigned to receive standard instructions or one of two versions of previously studied cognitive interventions (to either facilitate coping or increase sense of control), given before each visit. Capnograph measures of heart rate (HR), respiratory rate (RR), and end-tidal pCO(2) were obtained on 24 subjects.

RESULTS

Relative to placebo, pentagastrin induced a significant decline in pCO(2) with no change in RR. Cortisol and HR increased, as expected. Cognitive intervention reduced the hyperventilatory response to pentagastrin.

CONCLUSIONS

Pentagastrin stimulates respiration, likely via increases in tidal volume. Respiratory stimulation could play a role in its panicogenic potency, though perhaps indirectly. As with HPA axis responses, higher-level brain processes may be capable of modulating pentagastrin-induced hyperventilation. This model may be useful for further study of cortical/cognitive control of interacting emotional, respiratory, and neuroendocrine sensitivities, with potential relevance to panic pathophysiology.

HPA axis, respiration and the airways in stress--a review in search of intersections

Given clear connections between respiratory distress and subjective anxiety, it is not surprising that respiratory psychophysiologists have been interested in the psychobiology of anxiety. Given parallel links between anxiety and stress, it is not surprising that the hypothalamic-pituitary adrenal (HPA) stress system has also been a focus in anxiety research. However, despite extensive work in respiratory psychophysiology and stress neuroendocrinology--and evidence that these systems are jointly dysregulated in anxiety disorders--direct studies of their interactions are rare. This paper reviews evidence for scientific intersections, providing an overview of the HPA axis, its psychobiology, and shared neural substrates for HPA and respiratory control. We examine HPA hormone effects on respiration, immune/inflammatory mediators, and lung maturation. We also examine respiratory/dyspnea effects on HPA axis. There are clear points of intersection in the neuroscience of respiration and stress. Given the importance of both systems to an organism's ability to survive and adapt in challenging and changing environments, further study of their interactions is needed.

Theta oscillations and sensorimotor performance

Performance and cognitive effort in humans have recently been related to amplitude and multisite coherence of alpha (7-12 Hz) and theta (4-7 Hz) band electroencephalogram oscillations. I examined this phenomenon in rats by using theta band oscillations of the local field potential to signify sniffing as a sensorimotor process. Olfactory bulb (OB) theta oscillations are coherent with those in the dorsal hippocampus (HPC) during odor sniffing in a two-odor olfactory discrimination task. Coherence is restricted to the high-frequency theta band (6-12 Hz) associated with directed sniffing in the OB and type 1 theta in the HPC. Coherence and performance fluctuate on a time scale of several minutes. Coherence magnitude is positively correlated with performance in the two-odor condition but not in extended runs of single odor conditional-stimulus-positive trials. Simultaneous with enhanced OB-HPC theta band coherence during odor sniffing is a significant decrease in lateral entorhinal cortex (EC)-HPC and OB-EC coherence, suggesting that linkage of the olfactory and hippocampal theta rhythms is not through the synaptic relay from OB to HPC in the lateral EC. OB-HPC coupling at the sniffing frequency is proposed as a mechanism underlying olfactory sensorimotor effort as a cognitive process.

Structural mechanisms underlying autonomic reactions in pediatric arousal

Arousal provides an essential means to restore homeostasis following a system perturbation during a quiescent state. The classic definition of 'arousal' includes a constellation of cardiovascular, respiratory and somatic muscle characteristics, together with activation of the electrocorticogram (ECoG). At least two ascending activating systems, a ventral cholinergic and a serotonergic ascending system, both interacting with other regional neurotransmitter processes, contribute to electrocortical activation, with separate behaviors mediated by each system. A number of 'arousal' processes essential for survival operate at local levels, and interact with the systems that mediate cortical activation. These processes include cerebellar compensatory mechanisms which respond to extreme cardiovascular challenges, and limbic structures which respond to hypoxia or hypercarbia and the resultant dyspnea. The local processes show exceptional cortical arousing properties upon recruitment of some structures, such as the amygdala, which has major projections to ascending arousal systems. Components of arousal can emerge without ECoG activation and can be mediated at local levels which interact with ascending systems.

Millivolt-scale DC shifts in the human scalp EEG: evidence for a nonneuronal generator

Slow shifts in the human scalp-recorded EEG, including those related to changes in brain CO(2) levels, have been generally assumed to result from changes in the level of tonic excitation of apical dendrites of cortical pyramidal neurons. We readdressed this issue using DC-EEG shifts elicited in healthy adult subjects by hypo- or hypercapnia. A 3-min period of hyperventilation resulted in a prompt negative shift with a rate of up to 10 microV/s at the vertex (Cz) and an extremely steep dependence (up to 100 microV/mmHg) on the end-tidal Pco(2). This shift had a maximum of up to -2 mV at Cz versus the temporal derivations (T3/T4). Hyperventilation-like breathing of 5% CO(2)-95% O(2), which does not lead to a significant hypocapnia, resulted in a near-complete block of the negative DC shift at Cz. Hypoventilation, or breathing 5% CO(2) in air at normal respiratory rate, induced a positive shift. The high amplitude of the voltage gradients on the scalp induced by hyperventilation is not consistent with a neuronal origin. Instead, the present data suggest that they are generated by extracortical volume currents driven by a Pco(2)-dependent potential difference across epithelia separating the cerebrospinal fluid and blood. Since changes in respiratory patterns and, hence, in the level of brain Pco(2), are likely to occur under a number of experimental conditions in which slow EEG responses have been reported (e.g., attention shifts, preparatory states, epileptic seizures, and hypoxic episodes), the present results call for a thorough reexamination of the mechanisms underlying scalp-recorded DC-EEG responses.

To breathe, perchance to sleep: sleep-disordered breathing and chronic insomnia among trauma survivors

Standard psychiatric classification (DSM-IV-TR) traditionally attributes post-traumatic sleep disturbance to a secondary or symptomatic feature of a primary psychiatric disorder. The DSM-IV-TR paradigm, however, has not been validated with objective sleep assessment technology, incorporated nosological constructs from the field of sleep disorders medicine, or adequately addressed the potential for post-traumatic stress disorder (PTSD) sleep problems to manifest as primary, physical disorders, requiring independent medical assessments and therapies. This paradigm may limit understanding of sleep problems in PTSD by promulgating such terms as "insomnia related to another mental disorder," a.k.a. "psychiatric insomnia." Emerging evidence invites a broader comorbidity perspective, based on recent findings that post-traumatic sleep disturbance frequently manifests with the combination of insomnia and a higher-than-expected prevalence of sleep-disordered breathing (SDB). In this model of complex sleep disturbance, the underlying sleep pathophysiology interacts with PTSD and related psychiatric distress; and this relationship appears very important as demonstrated by improvement in insomnia, nightmares, and post-traumatic stress with successful SDB treatment, independent of psychiatric interventions. Continuous positive airway pressure treatment in PTSD patients with SDB reduced electroencephalographic arousals and sleep fragmentation, which are usually attributed to central nervous system or psychophysiological processes. Related findings and clinical experience suggest that other types of chronic insomnia may also be related to SDB. We hypothesize that an arousal-based mechanism, perhaps initiated by post-traumatic stress and/or chronic insomnia, may promote the development of SDB in a trauma survivor and perhaps other patients with chronic insomnia. We discuss potential neurohormonal pathways and neuroanatomatical sites that may be involved in this proposed interaction between insomnia and SDB.

Brain morphology associated with obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by repeated occurrences of hypoxic, hypercapnic, and transient blood pressure elevation episodes that may damage or alter neural structures. Underdeveloped structures or pre-existing damage in brain areas may also contribute to the genesis of the syndrome. Brain morphology in 21 patients with OSA and in 21 control subjects was assessed using high-resolution T1-weighted magnetic resonance imaging. Three-dimensional brain images were obtained with voxels of approximately 1 mm3. Images were spatially normalized and segmented into gray matter, white matter, and cerebrospinal fluid. For each segment, regional volumetric differences were determined relative to age, handedness, and group (patients with OSA versus control subjects), using voxel-based morphometry, with OSA effects weighted by disease severity. A significant age effect on total gray matter was found in control subjects but not in patients with OSA. Diminished regional and often unilateral gray matter loss was apparent in multiple sites of the brain in patients with OSA, including the frontal and parietal cortex, temporal lobe, anterior cingulate, hippocampus, and cerebellum. Unilateral loss in well-perfused structures suggests onset of neural deficits early in the OSA syndrome. The gray matter loss occurs within sites involved in motor regulation of the upper airway as well as in areas contributing to cognitive function.

Postnatal development of rat hippocampal gamma rhythm in vivo

Network oscillations in the gamma-frequency band (20-100 Hz) may have a central role in the timing and coordination of neural activity in the adult brain, yet their appearance in the course of development has remained unexplored. Moreover, electroencephalogram (EEG)-based classification of the vigilance states [active sleep (AS), quiet sleep (QS), or awake (W)] has been thought to be possible only after the second postnatal week. We now report the presence of spontaneous hippocampal gamma oscillations in the area CA3 of freely moving rats at postnatal days (P) 5-10. Initially, at P5, the gamma oscillations were seen in time-frequency analyses of intrahippocampal EEG recordings as brief (<500 ms) bursts at 20-30 Hz. The early gamma rhythmicity was most pronounced during periods of AS but was occasionally detected also during QS. Toward P10, the gamma oscillations gained amplitude and extended also to higher (<or=60 Hz) frequencies. In parallel, the gamma oscillations were progressively more and more confined to AS. To further consolidate these findings, we compared amplitude spectra averaged within the behavioral categories. AS was characterized by the appearances of gamma (20-30 Hz) and theta (3-5 Hz) peaks at P6 and at P8, respectively. QS, on the other hand, had considerably smoother amplitude distributions between 1 and 100 Hz for P5-P10, with no peaks in gamma or theta bands. Hippocampal gamma rhythm thus seems to hallmark early AS. Our data provide the first in vivo evidence for both the presence and the behavioral correlate of spontaneous gamma oscillations in the newborn rat.

Persistent respiratory irregularity in patients with panic disorder

BACKGROUND

Dysregulated respiratory control may play a role in the pathophysiology of panic disorder. This could be due to abnormalities in brain stem respiratory nuclei or to dysregulation at higher brain levels. Results from previous studies using the doxapram model of panic have yielded an unclear picture. A brief cognitive manipulation reduced doxapram-induced hyperventilation in patients, suggesting that higher level inputs can substantially alter their respiratory patterns. However, respiratory abnormalities persisted, including a striking irregularity in breathing patterns.

METHODS

To directly study respiratory irregularity, breath-by-breath records of tidal volume (V(t)) and frequency (f) from previously studied subjects were obtained. Irregularity was quantified using von Neumann's statistic and calculation of "sigh" frequency in 16 patients and 16 matched control subjects. Half of each group received a standard introduction to the study and half received a cognitive intervention designed to reduce anxiety/distress responses to the doxapram injection.

RESULTS

Patients had significantly greater V(t) irregularity relative to control subjects. Neither the cognitive intervention nor doxapram-induced hyperventilation produced significant changes in V(t) irregularity. The V(t) irregularity was attributable to a sighing pattern of breathing that was characteristic of panic patients but not control subjects. Patients also had somewhat elevated f irregularity relative to control subjects.

CONCLUSIONS

The irregular breathing patterns in panic patients appear to be intrinsic and stable, uninfluenced by induced hyperventilation or cognitive manipulation. Further study of V(t) irregularity and sighs are warranted in efforts to localize dysregulated neural circuits in panic to brain stem or midbrain levels.

Geophysical variables and behavior: LXXXV. Sudden infant death, bands of geomagnetic activity, and pc1 (0.2 to 5 HZ) geomagnetic micropulsations

Pc1s (continuous pulsations) within the geomagnetic field, whose durations are about 30 minutes but which can reoccur several times nightly, are observed during periods when global geomagnetic activity is very low (less than 10 nT). The hypothesis that these 0.2 to 5 Hz synchronized micropulsations or hydromagnetic emissions might stimulate physical chemical cascades within the brain that precipitate the sudden death in infants was tested by correlational analysis for a two-year period (1960-1961) for Ontario. Results were consistent with the hypothesis that the monthly incidences of these unexpected deaths, pcl micropulsations and geomagnetic activity less than 10 nT displayed a shared source of variance. Implications are discussed.