Visualization of sleep influences on cerebellar and brainstem cardiac and respiratory control mechanisms

Exploring the brain with sleep-related injuries, and fixing it

The focus of my research efforts rests with determining dysfunctional neural systems underlying disorders of sleep, and identifying interventions to overcome those disorders. Aberrant central and physiological control during sleep exerts serious consequences, including disruptions in breathing, motor control, blood pressure, mood, and cognition, and plays a major role in sudden infant death syndrome, congenital central hypoventilation, and sudden unexpected death in epilepsy, among other concerns. The disruptions can be traced to brain structural injury, leading to inappropriate outcomes. Identification of failing systems arose from the assessment of single neuron discharge in intact, freely moving and state-changing human and animal preparations within multiple systems, including serotonergic action and motor control sites. Optical imaging of chemosensitive, blood pressure and other breathing regulatory areas, especially during development, were useful to show integration of regional cellular action in modifying neural output. Identification of damaged neural sites in control and afflicted humans through structural and functional magnetic resonance imaging procedures helped to identify the sources of injury, and the nature of interactions between brain sites that compromise physiological systems and lead to failure. Interventions to overcome flawed regulatory processes were developed, and incorporate noninvasive neuromodulatory means to recruit ancient reflexes or provide peripheral sensory stimulation to assist breathing drive to overcome apnea, reduce the frequency of seizures, and support blood pressure in conditions where a failure to perfuse can lead to death.

Association between auditory system pathology and sudden infant death syndrome (SIDS): a systematic review

OBJECTIVE

A theory has emerged, suggesting that abnormalities in the auditory system may be associated with sudden infant death syndrome (SIDS). However, current clinical evidence has never been systematically reviewed.

DESIGN

A systematic review was conducted according to the guideline of Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

DATA SOURCES

PubMed, Embase and Web of Science were systematically searched through 7 September 2020.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Only human studies with a reference group were included. Studies were eligible for inclusion if they examined infants exposed to otoacoustic emissions (OAEs), auditory brainstem response (ABR) or had autopsies with brainstem histology of the auditory system. SIDS was the primary outcome, while the secondary outcome was near-miss sudden infant death syndrome episodes.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers extracted data and assessed risk of bias, and the quality of evidence. Due to high heterogeneity, a narrative synthesis was conducted. Risk of bias and quality of evidence was assessed using the Newcastle-Ottawa Scale and Grading of Recommendations Assessment, Development and Evaluation.

RESULTS

Twelve case-control studies were included. Seven studies on OAEs or ABR had a high degree of inconsistency. Contrarily, four out of five studies reporting on brainstem histology found that auditory brainstem abnormalities were more prevalent in SIDS cases than in controls. However, the quality of evidence across all studies was very low.

CONCLUSION

This systematic review found no clear association between auditory system pathology and SIDS. The higher prevalence of histological abnormalities in the auditory system of SIDS may indicate an association. However, further studies of higher quality and larger study populations are needed to determine whether these findings are valid.

PROSPERO REGISTRATION NUMBER

CRD42020208045.

Brainstem atrophy in Gulf War Illness

BACKGROUND

Gulf War Illness (GWI) is a condition that affects about 30 % of veterans who served in the 1990-91 Persian Gulf War. Given its broad symptomatic manifestation, including chronic pain, fatigue, neurological, gastrointestinal, respiratory, and skin problems, it is of interest to examine whether GWI is associated with changes in the brain. Existing neuroimaging studies, however, have been limited by small sample sizes, inconsistent GWI diagnosis criteria, and potential comorbidity confounds.

OBJECTIVES

Using a large cohort of US veterans with GWI, we assessed regional brain volumes for their associations with GWI, and quantified the relationships between any regional volumetric changes and GWI symptoms.

METHODS

Structural magnetic resonance imaging (MRI) scans from 111 veterans with GWI (Age = 49 ± 6, 88 % Male) and 59 healthy controls (age = 51 ± 9, 78 % male) were collected at the California War Related Illness and Injury Study Center (WRIISC-CA) and from a multicenter study of the Parkinson's Progression Marker Initiative (PPMI), respectively. Individual MRI volumes were segmented and parcellated using FreeSurfer. Regional volumes of 19 subcortical, 68 cortical, and 3 brainstem structures were evaluated in the GWI cohort relative to healthy controls. The relationships between regional volumes and GWI symptoms were also assessed.

RESULTS

We found significant subcortical atrophy, but no cortical differences, in the GWI group relative to controls, with the largest effect detected in the brainstem, followed by the ventral diencephalon and the thalamus. In a subsample of 58 veterans with GWI who completed the Chronic Fatigue Scale (CFS) inventory of Centers for Disease Control and Prevention (CDC), smaller brainstem volumes were significantly correlated with increased severities of fatigue and depressive symptoms.

CONCLUSION

The findings suggest that brainstem volume may be selectively affected by GWI, and that the resulting atrophy could in turn mediate or moderate GWI-related symptoms such as fatigue and depression. Consequently, the brain stem should be carefully considered in future research focusing on GWI pathology.

Neuropathological Developments in Sudden Infant Death Syndrome

A wide variety of neuropathological abnormalities have been investigated in infants who have died of sudden infant death syndrome (SIDS). Issues which detracted from early studies included failure to use uniform definitions of SIDS and lack of appropriately matched control populations. Development of the triple risk model focused attention on the concept of an inherent susceptibility to unexpected death in certain infants, with research demonstrating a role for the neurotransmitter serotonin within the brainstem. However, it now appears that neuropathological abnormalities in SIDS infants are more complex than a simple serotonergic deficiency in certain medullary nuclei but instead could involve failure of an integrated network of neurochemical transmitters in a variety of subcortical locations. The following overview examines recent research developments looking particularly at the potential role of the peptide neurotransmitter substance P and its neurokinin-1 receptor in multiple nuclei within the brainstem, asymmetry and microdysgenesis of the hippocampus, and decreased orexin levels within dorsomedial, perifornical, and lateral levels in the hypothalamus. Whether such research will lead to identifiable biomarker for infants at risk of SIDS is yet to be established. Use of standardized and consistent methods of classifying and categorizing infant deaths will be pivotal in generating reproducible research results.

Delineation of Subregions in the Early Postnatal Human Cerebellum for Design-Based Stereologic Studies

Recent design-based stereologic studies have shown that the early postnatal (<1 year of age) human cerebellum is characterized by very high plasticity and may thus be very sensitive to external and internal influences during the first year of life. A potential weakness of these studies is that they were not separately performed on functionally relevant subregions of the cerebellum, as was the case in a few design-based stereologic studies on the adult human cerebellum. The aim of the present study was to assess whether it is possible to identify unequivocally the primary, superior posterior, horizontal, ansoparamedian, and posterolateral fissures in the early postnatal human cerebellum, based on which functionally relevant subregions could be delineated. This was tested in 20 human post mortem cerebellar halves from subjects aged between 1 day and 11 months by means of a combined macroscopic and microscopic approach. We found that the superior posterior, horizontal, and posterolateral fissures can be reliably identified on all of the specimens. However, reliable and reproducible identification of the primary and ansoparamedian fissures was not possible. Accordingly, it appears feasible to perform subregion-specific investigations in the early postnatal human cerebellum when the identification of subregions is restricted to crus I (bordered by the superior posterior and horizontal fissures) and the flocculus (bordered by the posterolateral fissure). As such, it is recommended to define the entire cerebellar cortex as the region of interest in design-based stereologic studies on the early postnatal human cerebellum to guarantee reproducibility of results.

Abnormalities in substance P neurokinin-1 receptor binding in key brainstem nuclei in sudden infant death syndrome related to prematurity and sex

Sudden infant death syndrome (SIDS) involves failure of arousal to potentially life threatening events, including hypoxia, during sleep. While neuronal dysfunction and abnormalities in neurotransmitter systems within the medulla oblongata have been implicated, the specific pathways associated with autonomic and cardiorespiratory failure are unknown. The neuropeptide substance P (SP) and its tachykinin neurokinin-1 receptor (NK1R) have been shown to play an integral role in the modulation of homeostatic function in the medulla, including regulation of respiratory rhythm generation, integration of cardiovascular control, and modulation of the baroreceptor reflex and mediation of the chemoreceptor reflex in response to hypoxia. Abnormalities in SP neurotransmission may therefore result in autonomic dysfunction during sleep and contribute to SIDS deaths. [¹²⁵I] Bolton Hunter SP autoradiography was used to map the distribution and density of the SP, NK1R to 13 specific nuclei intimately related to cardiorespiratory function and autonomic control in the human infant medulla of 55 SIDS and 21 control (non-SIDS) infants. Compared to controls, SIDS cases exhibited a differential, abnormal developmental profile of the SP/NK1R system in the medulla. Furthermore the study revealed significantly decreased NK1R binding within key medullary nuclei in SIDS cases, principally in the nucleus tractus solitarii (NTS) and all three subdivisions of the inferior portion of the olivo-cerebellar complex; the principal inferior olivary complex (PIO), medial accessory olive (MAO) and dorsal accessory olive (DAO). Altered NK1R binding was significantly influenced by prematurity and male sex, which may explain the increased risk of SIDS in premature and male infants. Abnormal NK1R binding in these medullary nuclei may contribute to the defective interaction of critical medullary mechanisms with cerebellar sites, resulting in an inability of a SIDS infant to illicit appropriate respiratory and motor responses to life threatening challenges during sleep. These observations support the concept that abnormalities in a multi-neurotransmitter network within key nuclei of the medullary homeostatic system may underlie the pathogenesis of a subset of SIDS cases.

Parasympathetic Concomitants of Habitual, Spontaneous, and Instructed Emotional Suppression

Abstract. The neurovisceral integration model proposes that different forms of self-regulation, including the emotional suppression, are characterized by the activation of neural network whose workings are also reflected in respiratory sinus arrhythmia (RSA). However, most of the previous studies failed to observe theoretically expected increases in RSA during emotional suppression. Even when such effects were observed, it was not clear whether they resulted from specific task demands, a decrease in muscle activity, or they were the consequence of more specific self-control processes. We investigated the relation between habitual or trait-like suppression, spontaneous, and instructed suppression with changes in RSA during negative emotion experience. A modest positive correlation between spontaneous situational and habitual suppression was observed across two experimental tasks. Furthermore, the results showed greater RSA increase among participants who experienced higher negative affect (NA) increase and reported higher spontaneous suppression than among those with higher NA increase and lower spontaneous suppression. Importantly, this effect was independent from the habitual suppression and observable facial expressions. The results of the additional task based on experimental manipulation, rather than spontaneous use of situational suppression, indicated a similar relation between suppression and RSA. Our results consistently demonstrate that emotional suppression, especially its self-regulation component, is followed by the increase in parasympathetic activity.

No changes in cerebellar microvessel length density in sudden infant death syndrome: implications for pathogenetic mechanisms

Sudden infant death syndrome (SIDS) is the leading cause of mortality in infants younger than 1 year in developed countries, but its primary cause remains unknown. Some studies suggest that there may be hypoxia in the cerebellum in SIDS subjects, but mean total Purkinje cell numbers in SIDS versus controls was recently found not to be different. Probably the best marker for chronic hypoxia in a brain region is the microvessel length per unit volume of tissue, that is, the microvessel length density (MLD). Here, we investigated MLDs using a rigorous design-based stereologic approach in all cell layers and white matter in postmortem cerebella from 9 SIDS cases who died between ages 2 and 10 months and from 14 control children, 9 of which were age- and sex- matched to the SIDS cases. We found no differences either in mean MLDs in the cerebellar layers between the SIDS cases and the controls or between controls with a low likelihood of hypoxia and those with a higher likelihood of hypoxia. Immunohistochemical detection of the astrocytosis marker glial fibrillary acidic protein showed no differences between the SIDS and the matched control cases. These data indicate that there is no association of chronic hypoxia in the cerebellum with SIDS.

Intact numbers of cerebellar purkinje and granule cells in sudden infant death syndrome: a stereologic analysis and critical review of neuropathologic evidence

Despite much research during recent decades, the etiology and pathogenesis of sudden infant death syndrome (SIDS) remain unknown. Because of the role of the cerebellum in respiratory and cardiovascular control, it has been proposed that it plays an important role in the pathogenesis of SIDS. To date, 5 postmortem studies on the cerebellum of SIDS cases have yielded conflicting results. Using a rigorous design-based stereologic approach, we investigated postmortem cerebella from 9 SIDS patients who died between 2 and 10 months of age and from 9 age- and sex-matched control children. Neither the volumes of the cerebellar external granule cell layer, molecular layer, internal granule cell layer (including the Purkinje cell layer), and white matter nor the total numbers of Purkinje cells, granule cells in the internal granule cell layer, and the number of granule cells per Purkinje cell showed statistically significant differences between the SIDS cases and the controls. Based on these observations, we conclude that structural alterations in cerebellar development are not involved in the etiology and pathogenesis of SIDS.

Acute cardiovascular responses in preterm infants at 34-39 weeks of gestational age

BACKGROUND

Premature infants demonstrate immature physiological control mechanisms; however their acute cardiovascular control has not yet been widely studied.

AIM

The aim of this study was to analyze heart rate (HR) and blood pressure (BP) control in preterm infants.

SUBJECTS

Twenty preterm infants with a mean gestational age of 31 ± 2.4 (26-34) weeks at birth were evaluated at a gestational age of 36 ± 1.5 (34-39) weeks. Results were compared to twenty, healthy, full-term, control infants studied at the age of 12 ± 3 weeks.

OUTCOME MEASURES

HR and BP responses to 45° head-up tilt and side motion tests during non-rapid eye movement sleep were analyzed. In addition, HR responses to spontaneous arousals from non-rapid eye movement sleep were evaluated.

RESULTS

Preterm infants showed significantly smaller initial HR and BP responses compared with controls in head-up tilt (HR p=0.0005, systolic BP p=0.02, diastolic BP p=0.01) and side motion tests (HR p=0.002, systolic BP p<0.0001, diastolic BP p<0.0001). Furthermore, in tilt tests, preterm infants presented with greater intersubject variability in BP responses than controls (systolic BP p=0.009, diastolic BP p=0005). Preterm HR responses to spontaneous arousals were similar to controls.

CONCLUSIONS

This study indicates immature vestibulo-mediated cardiovascular control in preterm infants compared with term infants. This is seen as attenuated BP responses to side motion test and more labile acute BP control to postural challenge.

Neonatal otoacoustic emission screening and sudden infant death syndrome

OBJECTIVE

Exploratory research findings have suggested that otoacoustic emission (OAE) recordings may be predictive for infants at risk of sudden infant death syndrome (SIDS). The present study aimed to investigate whether an actual SIDS prevalence rate was comparable to OAE-determined rates for "at risk" status.

METHODS

Previously collected OAE results from 521 infants in Hong Kong were used for analyses and OAE-determined "at risk" rate compared to the prevalence rate for SIDS in Hong Kong infants.

RESULTS

Results indicated that the OAE-determined rates were very much greater than the actual prevalence of SIDS in Hong Kong.

CONCLUSION

The use of OAE screening to identify infants at risk for SIDS is therefore not advisable, using present criteria, as false alarm rates would be very high and this may cause unnecessary parental anxiety and a considerable additional burden to the health care system.

Postnatal development of Na(+)-K(+)-2Cl(-) co-transporter 1 and K(+)-Cl(-) co-transporter 2 immunoreactivity in multiple brain stem respiratory nuclei of the rat

Previously, we reported that in rats, GABA(A) and glycine receptor immunoreactivity increased markedly in multiple brain stem respiratory nuclei around postnatal days (P) 12-13, a critical period when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory network and when the system is under greater inhibition than excitation. Since Na(+)-K(+)-2Cl(-) co-transporter 1 (NKCC1) and K(+)-Cl(-) co-transporter 2 (KCC2) play pivotal roles in determining the responses of GABA(A) and glycine receptors, we hypothesized that NKCC1 and KCC2 undergo significant changes during the critical period. An in-depth immunohistochemical and single neuron optical densitometric study of neurons in seven respiratory-related nuclei (the pre-Bötzinger complex [PBC], nucleus ambiguus [Amb], hypoglossal nucleus [XII], ventrolateral subnucleus of solitary tract nucleus [NTS(VL)], retrotrapezoid nucleus/parafacial respiratory group [retrotrapezoid nucleus/parafacial respiratory group (RTN/pFRG)], dorsal motor nucleus of the vagus nerve [dorsal motor nucleus of the vagus nerve (DMNX)], and inferior olivary nucleus [IO]) and a non-respiratory cuneate nucleus (CN, an internal control) was undertaken in P0-P21 rats. Our data revealed that (1) NKCC1 immunoreactivity exhibited a developmental decrease from P0 to P21 in all eight nuclei examined, being relatively high during the first 1½ postnatal weeks and decreased thereafter. The decrease was abrupt and statistically significant at P12 in the PBC, Amb, and XII; (2) KCC2 immunoreactivity in these eight nuclei showed a developmental increase from P0 to P21; and (3) the significant reduction in NKCC1 and the greater dominance of KCC2 around P12 in multiple respiratory nuclei of the brain stem may form the basis of an enhanced inhibition in the respiratory network during the critical period before the system stabilizes to a more mature state.

Positional circulatory control in the sleeping infant and toddler: role of the inner ear and arterial pulse pressure

Heart rate (HR) and arterial blood pressure (BP) are rapidly and reflexively adjusted as body position and the force/direction of gravity alters. Anomalies in these mechanisms may predispose to circulatory failure during sleep. We analysed the development of two key reflexes involved by undertaking a longitudinal (birth–1 year) comparison of instantaneous HR and BP changes evoked by abrupt upright, sideways or horizontal repositioning. Each manoeuvre triggered an identical rise in HR (tachycardia) followed by a slower rise in diastolic blood pressure (DBP)/systolic blood pressure (SBP) and variable pulse pressure (PP) change. We show that tachycardia is triggered by acceleration (vestibular) sensors located in the inner ear and slight changes in the pulsatile component of BP then signal to the arterial baroreceptors to reinforce or oppose these actions as needed. We also identified a PP anomaly in sleeping 1-year-olds of smokers that prematurely slows HR and is associated with mild positional hypotension. We conclude that positional circulatory compensation is initiated pre-emptively in a feed-forward manner and that feedback changes in vago-sympathetic drive to the heart (and perhaps blood vessels) by PP exert a slower but powerful modulating effect. An anomaly in either or both mechanisms may weaken positional compensation in some sleeping infants.

A brain MRI study of chronic fatigue syndrome: evidence of brainstem dysfunction and altered homeostasis

To explore brain involvement in chronic fatigue syndrome (CFS), the statistical parametric mapping of brain MR images has been extended to voxel-based regressions against clinical scores. Using SPM5 we performed voxel-based morphometry (VBM) and analysed T(1) - and T(2) -weighted spin-echo MR signal levels in 25 CFS subjects and 25 normal controls (NC). Clinical scores included CFS fatigue duration, a score based on the 10 most common CFS symptoms, the Bell score, the hospital anxiety and depression scale (HADS) anxiety and depression, and hemodynamic parameters from 24-h blood pressure monitoring. We also performed group × hemodynamic score interaction regressions to detect locations where MR regressions were opposite for CFS and NC, thereby indicating abnormality in the CFS group. In the midbrain, white matter volume was observed to decrease with increasing fatigue duration. For T(1) -weighted MR and white matter volume, group × hemodynamic score interactions were detected in the brainstem [strongest in midbrain grey matter (GM)], deep prefrontal white matter (WM), the caudal basal pons and hypothalamus. A strong correlation in CFS between brainstem GM volume and pulse pressure suggested impaired cerebrovascular autoregulation. It can be argued that at least some of these changes could arise from astrocyte dysfunction. These results are consistent with an insult to the midbrain at fatigue onset that affects multiple feedback control loops to suppress cerebral motor and cognitive activity and disrupt local CNS homeostasis, including resetting of some elements of the autonomic nervous system (ANS).

Down-regulation of V1a vasopressin receptors in the cerebellum after myocardial infarction

Vasopressin V1a receptors (V1aR) were found in the cerebellum but their functional role has not been determined. As V1aR are engaged in the central regulation of the cardiovascular system and anxiogenic behavior and their role increases in the heart failure and stress, we decided to find out whether expression of V1aR is altered after myocardial infarction and chronic stressing. RT-PCR and Western blot analysis were performed to determine V1aR mRNA and protein expression in the cerebellum of four groups of rats (control sham-operated, infarcted, chronically stressed and infarcted chronically stressed). The myocardial infarct was produced by left coronary artery ligation, and chronic stressing by exposing the rat for four weeks to different types of mild stressors. The rats were sacrificed four weeks after the myocardial surgery or sham operation. Expressions of V1aR mRNA and protein were significantly lower in the infarcted and infarcted chronically stressed rats than in the sham-operated controls and chronically stressed not infarcted rats. No significant differences were found between the sham-operated controls and chronically stressed rats and between the infarcted rats and infarcted rats exposed to chronic stressing. It is concluded that V1aR mRNA and protein expressions are significantly down-regulated in the rats with the post-infarct heart failure but they are not affected by mild chronic stressing.

The role of spiking and bursting pacemakers in the neuronal control of breathing

Breathing is controlled by a distributed network involving areas in the neocortex, cerebellum, pons, medulla, spinal cord, and various other subcortical regions. However, only one area seems to be essential and sufficient for generating the respiratory rhythm: the preBötzinger complex (preBötC). Lesioning this area abolishes breathing and following isolation in a brain slice the preBötC continues to generate different forms of respiratory activities. The use of slice preparations led to a thorough understanding of the cellular mechanisms that underlie the generation of inspiratory activity within this network. Two types of inward currents, the persistent sodium current (I(NaP)) and the calcium-activated non-specific cation current (I(CAN)), play important roles in respiratory rhythm generation. These currents give rise to autonomous pacemaker activity within respiratory neurons, leading to the generation of intrinsic spiking and bursting activity. These membrane properties amplify as well as activate synaptic mechanisms that are critical for the initiation and maintenance of inspiratory activity. In this review, we describe the dynamic interplay between synaptic and intrinsic membrane properties in the generation of the respiratory rhythm and we relate these mechanisms to rhythm generating networks involved in other behaviors.

Chapter 3--networks within networks: the neuronal control of breathing

Breathing emerges through complex network interactions involving neurons distributed throughout the nervous system. The respiratory rhythm generating network is composed of micro networks functioning within larger networks to generate distinct rhythms and patterns that characterize breathing. The pre-Bötzinger complex, a rhythm generating network located within the ventrolateral medulla assumes a core function without which respiratory rhythm generation and breathing cease altogether. It contains subnetworks with distinct synaptic and intrinsic membrane properties that give rise to different types of respiratory rhythmic activities including eupneic, sigh, and gasping activities. While critical aspects of these rhythmic activities are preserved when isolated in in vitro preparations, the pre-Bötzinger complex functions in the behaving animal as part of a larger network that receives important inputs from areas such as the pons and parafacial nucleus. The respiratory network is also an integrator of modulatory and sensory inputs that imbue the network with the important ability to adapt to changes in the behavioral, metabolic, and developmental conditions of the organism. This review summarizes our current understanding of these interactions and relates the emerging concepts to insights gained in other rhythm generating networks.

Effects of alcohol and smoking during pregnancy on infant autonomic control

Prenatal exposure to smoking and alcohol increases the risk for Sudden Infant Death Syndrome (SIDS). Physiological changes associated with these exposures are not well studied. Full-term infants were tested within the first 3 days of life. We hypothesized that maternal alcohol consumption and/or smoking during pregnancy would alter autonomic nervous system function. Newborns whose mothers smoked during pregnancy had lower beat-to-beat heart rate variability in quiet sleep. Infants whose mothers consumed alcohol had lower global heart rate variability, but only in active sleep. Unexposed infants demonstrated increases in heart rate with head-up tilt and decreases in heart rate with head-down tilt, but smoking and alcohol-exposed infants showed no significant responses. These results indicate that autonomic function is altered by prenatal exposure to alcohol and smoking. Such markers may provide early identification of infants at greatest risk for SIDS.

5-HT2A receptors are concentrated in regions of the human infant medulla involved in respiratory and autonomic control

The serotonergic (5-HT) system in the human medulla oblongata is well-recognized to play an important role in the regulation of respiratory and autonomic function. In this study, using both immunocytochemistry (n=5) and tissue section autoradiography with the radioligand (125)I-1-(2,5-dimethoxy-4-iodo-phenyl)2-aminopropane (n=7), we examine the normative development and distribution of the 5-HT(2A) receptor in the human medulla during the last part of gestation and first postnatal year when dramatic changes are known to occur in respiratory and autonomic control, in part mediated by the 5-HT(2A) receptor. High 5-HT(2A) receptor binding was observed in the dorsal motor nucleus of the vagus (preganglionic parasympathetic output) and hypoglossal nucleus (airway patency); intermediate binding was present in the nucleus of the solitary tract (visceral sensory input), gigantocellularis, intermediate reticular zone, and paragigantocellularis lateralis. Negligible binding was present in the raphé obscurus and arcuate nucleus. The pattern of 5-HT(2A) immunoreactivity paralleled that of binding density. By 15 gestational weeks, the relative distribution of the 5-HT(2A) receptor was similar to that in infancy. In all nuclei sampled, 5-HT(2A) receptor binding increased with age, with significant increases in the hypoglossal nucleus (p=0.027), principal inferior olive (p=0.044), and medial accessory olive (0.038). Thus, 5-HT(2A) receptors are concentrated in regions involved in autonomic and respiratory control in the human infant medulla, and their developmental profile changes over the first year of life in the hypoglossal nucleus critical to airway patency and the inferior olivary complex essential to cerebellar function.

QT interval prolongation in future SIDS victims: a polysomnographic study

OBJECTIVE

Previous data have suggested that a prolonged QTc interval during the first days of life can be associated with some cases of sudden infant death syndrome (SIDS). Analysis of heart rate variability during sleep in future SIDS victims has shown findings compatible with an imbalance in autonomic tone. We hypothesized that some future SIDS infants could have longer QTc intervals during sleep, compared with healthy control infants, and that this difference would correlate with the autonomic imbalance already found in these infants.

METHODS

QTc intervals and a heart rate autoregressive power spectral analysis were calculated during the same periods in the polysomnographic sleep recordings of 18 infants who eventually died of SIDS and of 18 control infants. The control infants were matched for sex, gestational age, postnatal age, birth weight, and sleep position. The median postnatal age was 8 weeks.

RESULTS

Compared with control infants, future SIDS victims were characterized by having longer QTc intervals during total sleep (P = 0.019), rapid eye movement sleep (P = 0.045) and non-rapid eye movement sleep (P = 0.029). When the night was divided into 3 equal parts, this difference was always present but was most marked during the last part of the night. There was, respectively, a negative and a positive correlation between parasympathetic activity and sympathovagal balance and median and maximum QTc interval values.

CONCLUSION

Compared with QTc intervals in matched control infants, QTc intervals were increased in future SIDS victims. Such a prolongation could be related to the autonomic dysfunction already reported in these patients.

Hyperventilation evoked by activation of the vicinity of the caudal inferior olivary nucleus depends on the fastigial nucleus in anesthetized rats

Several studies have demonstrated that cerebellar deep nuclei, particularly the rostral fastigial nucleus (FNr), are involved in respiratory modulation. These nuclei receive inputs from the contralateral caudal inferior olivary nuclei of the medulla. The objectives of this study were to determine whether electrical and chemical activation of the vicinity of the caudal inferior olivary nuclei (vIOc) affected respiration and, if true, whether the FNr was involved in the vIOc stimulation-evoked ventilatory responses. Experiments were conducted in 30 anesthetized and spontaneously breathing rats. Our results showed that 1) electrical (25 or 100 μA at 10 or 20 Hz for 10 s) and chemical (1 or 100 mM, 25–50 nl N-methyl-d-aspartate) stimulation of the vIOc augmented ventilation predominantly via increasing tidal volume; 2) the responses to the electrical stimulation were almost eliminated by lesion of the contralateral FNr via microinjection of ibotenic acid; and 3) the respiratory responses to electrical stimulation in the vicinity of the rostral IO were 65–70% smaller compared with that evoked by vIOc stimulation. These findings strongly suggest that vIOc neurons play a significant role in modulation of respiratory activity, largely depending on their projections to the FNr.

Newborn oto-acoustic emission hearing screening tests: preliminary evidence for a marker of susceptibility to SIDS

OBJECTIVE

To evaluate the newborn transient evoked otoacoustic emission (TEOAE) hearing screening tests of infants later diagnosed with the sudden infant death syndrome (SIDS).

STUDY DESIGN

In a case-controlled study, the newborn TEOAE hearing screens of 31 infants who subsequently died of SIDS were retrospectively compared to those of 31 newborn infants that survived the first year of life. SIDS cases were individually matched to surviving controls based on gender, term versus preterm age and NICU versus well baby nursery.

RESULTS

The TEOAE screens of SIDS infants demonstrated significantly decreased signal to noise ratios at 2000, 3000, and 4000 Hz (p<0.05) on the right side compared to healthy control infants.

CONCLUSION

Newborns at risk for SIDS are currently indistinguishable from other newborns and are only identified following a later fatal event. A unilateral difference in cochlear function is a unique finding that may offer the opportunity to identify infants at risk of SIDS during the early postnatal period with a simple non invasive hearing screen test. The ability to implement preventative measures well in advance of a potential critical incident would be an important breakthrough.

Sudden death due to central alveolar hypoventilation syndrome (Ondine's curse) in a 39-year-old woman with heterotopia of the inferior olive

Failure of automatic involuntary respiration with preservation of voluntary respiratory drive (Ondine's curse) is a rare occurrence which has been reported following a variety of morphologic lesions near respiratory centers in the lower brainstem. We report the case of a 39-year-old woman with a syndrome of fulminant respiratory failure with features of Ondine's curse in whom neuropathologic examination disclosed a preexisting malformation of the lower brainstem, as well as acute local subarachnoid bleeding. Mechanisms in the present case are discussed and a review of similar cases published so far is given. The necessity of sound investigation, including neuropathologic studies in cases of sudden unexplained death, is underlined.

Methodological issues in the quantification of respiratory sinus arrhythmia

Although respiratory sinus arrhythmia (RSA) is a commonly quantified physiological variable, the methods for quantification are not consistent. This manuscript questions the assumption that respiration frequency needs to be manipulated or monitored to generate an accurate measure of RSA amplitude. A review of recent papers is presented that contrast RSA amplitude with measures that use respiratory parameters to adjust RSA amplitude. In addition, data from two studies are presented to evaluate empirically both the relation between RSA amplitude and respiration frequency and the covariation between RSA frequency and respiration frequency. The literature review demonstrates similar findings between both classes of measures. The first study demonstrates, during spontaneous breathing without task demands, that there is no relation between respiration frequency and RSA amplitude and that respiration frequency can be accurately derived from the heart period spectrum (i.e., frequency of RSA). The second study demonstrates that respiration frequency is unaffected by atropine dose, a manipulation that systematically mediates the amplitude of RSA, and that the tight linkage between the RSA frequency and respiration frequency is unaffected by atropine. The research shows that the amplitude of RSA is not affected by respiration frequency under either baseline conditions or vagal manipulation via atropine injection. Respiration frequency is therefore unlikely to be a concern under these conditions. Research examining conditions that produce (causal) deviations from the intrinsic relation between respiratory parameters and the amplitude of RSA combined with appropriate statistical procedures for understanding these deviations are necessary.

Methodological issues in the quantification of respiratory sinus arrhythmia

Although respiratory sinus arrhythmia (RSA) is a commonly quantified physiological variable, the methods for quantification are not consistent. This manuscript questions the assumption that respiration frequency needs to be manipulated or monitored to generate an accurate measure of RSA amplitude. A review of recent papers is presented that contrast RSA amplitude with measures that use respiratory parameters to adjust RSA amplitude. In addition, data from two studies are presented to evaluate empirically both the relation between RSA amplitude and respiration frequency and the covariation between RSA frequency and respiration frequency. The literature review demonstrates similar findings between both classes of measures. The first study demonstrates, during spontaneous breathing without task demands, that there is no relation between respiration frequency and RSA amplitude and that respiration frequency can be accurately derived from the heart period spectrum (i.e., frequency of RSA). The second study demonstrates that respiration frequency is unaffected by atropine dose, a manipulation that systematically mediates the amplitude of RSA, and that the tight linkage between the RSA frequency and respiration frequency is unaffected by atropine. The research shows that the amplitude of RSA is not affected by respiration frequency under either baseline conditions or vagal manipulation via atropine injection. Respiration frequency is therefore unlikely to be a concern under these conditions. Research examining conditions that produce (causal) deviations from the intrinsic relation between respiratory parameters and the amplitude of RSA combined with appropriate statistical procedures for understanding these deviations are necessary.

Sudden cardiac arrest in an intubated premature infant with cerebellar and brainstem injury: is there a link?

The ventilated premature infant frequently exhibits unprovoked desaturation episodes accompanied by bradycardia. In most instances, these episodes are short-lived and recover spontaneously or with minimal interventions. However, in some infants these episodes may be more profound and require substantial interventions to restore cardiorespiratory status. Here we present the case of a ventilated premature infant who had experienced prolonged, multiple daily desaturation episodes accompanied by bradycardia that required significant interventions. Postoperatively, after placement of a tracheotomy and despite a patent airway, the infant developed acute bradycardia that progressed rapidly to sudden death. At autopsy, significant cerebellar and brainstem injury was noted. We hypothesize that the specific cerebellum and brainstem injury may have contributed to autonomic dysfunction and sudden death.

Medial vestibular nucleus mediates the cardiorespiratory responses to fastigial nuclear activation and hypercapnia

Electrical stimulation of the cerebellar fastigial nucleus (FN) evokes hyperventilation and hypertension responses that are similar to those induced by stimulation of the medial region of the vestibular nucleus (VNM). Because there are mutual projections between these two nuclei morphologically, we hypothesized that the FN-mediated cardiorespiratory responses were related to the integrity of the VNM. Experiments were conducted on 21 anesthetized, tracheotomized, and spontaneously breathing rats. Electrical stimulation (approximately 10 s) of the FN was used to evoke cardiorespiratory responses, and the same stimulus was repeated 30-45 min after bilateral lesions of the VNM by local microinjection of ibotenic acid (100 mM, 100 nl). We found that FN stimulation-induced hyperventilation and hypertension were attenuated significantly by the lesions. The role of the VNM in the ventilatory responses to chemical challenges was subsequently defined. The animals were exposed to hypercapnia (10% CO2) and hypoxia (10% O2) for 1-2 min randomly before and after VNM lesions. The results showed that VNM lesions significantly attenuated the cardiorespiratory responses to hypercapnia but not to hypoxia, with little effect on baseline respiratory variables. These findings suggest that the VNM is required for full expression of the cardiorespiratory responses to electrical stimulation of the FN as well as to hypercapnia. However, neurons within the VNM do not appear to be critical for maintaining eupneic breathing and the cardiorespiratory responses to hypoxia.

Postnatal developmental expressions of neurotransmitters and receptors in various brain stem nuclei of rats

Previously, we reported that the expression of cytochrome oxidase in a number of brain stem nuclei exhibited a plateau or reduction at postnatal day (P) 3-4 and a dramatic decrease at P12, against a general increase with age. The present study examined the expression of glutamate, N-methyl-D-aspartate receptor subunit 1 (NMDAR1), GABA, GABAB receptors, glycine receptors, and glutamate receptor subunit 2 (GluR2) in the ventrolateral subnucleus of the solitary tract nucleus, nucleus ambiguus, hypoglossal nucleus, medial accessory olivary nucleus, dorsal motor nucleus of the vagus, and cuneate nucleus, from P2 to P21 in rats. Results showed that 1) the expression of glutamate increased with age in a majority of the nuclei, whereas that of NMDAR1 showed heterogeneity among the nuclei; 2) GABA and GABAB expressions decreased with age, whereas that of glycine receptors increased with age; 3) GluR2 showed two peaks, at P3-4 and P12; and 4) glutamate and NMDAR1 showed a significant reduction, whereas GABA, GABAB receptors, glycine receptors, and GluR2 exhibited a concomitant increase at P12. These features were present but less pronounced in hypoglossal nucleus and dorsal motor nucleus of the vagus and were absent in the cuneate nucleus. These data suggest that brain stem nuclei, directly or indirectly related to respiratory control, share a common developmental trend with the pre-Botzinger complex in having a transient period of imbalance between inhibitory and excitatory drives at P12. During this critical period, the respiratory system may be more vulnerable to excessive exogenous stressors.

Genetics and early disturbances of breathing control

Early disturbances in breathing control, including apneas of prematurity and apparently life-threatening events, account for some cases of sudden infant death syndrome and for a rare disorder called congenital central hypoventilation syndrome (CCHS). Data suggesting a genetic basis for CCHS have been obtained. Recently, we found heterozygous de novo mutations of the PHOX2B gene in 18 of 29 individuals with CCHS. Most mutations consisted of five to nine alanine expansions within a 20-residue polyalanine tract, probably resulting from nonhomologous recombination. Other mutations, generally inherited from one of the parents, in the coding regions of genes involved in the endothelin and RET signaling pathways and in the brain-derived-neurotrophic factor (BDNF) gene have been found in a few CCHS patients. Interestingly, all these genes are involved in the development of neural crest cells. Targeted disruption of these genes in mice has provided information on the pathophysiological mechanisms underlying CCHS. Despite the identification of these genes involved in breathing control, none of the genetically engineered mice developed to date replicate the full human CCHS respiratory phenotype. Recent insights into the genetic basis for CCHS may shed light on the genetics of other early disturbances in breathing control, such as apnea of prematurity and sudden infant death syndrome.

24-Hour BP in Children With Congenital Central Hypoventilation Syndrome

OBJECTIVE

To study circadian BP patterns in patients with congenital central hypoventilation syndrome (CCHS).

DESIGN

Case-control study.

SETTING

Teaching hospital in Paris, France.

PATIENTS

Eleven patients with CCHS (median age, 13 years; range, 6 to 18 years) and 11 sex- and height-matched control subjects.

INTERVENTION

None.

METHODS

Each subject underwent 24-h ambulatory BP monitoring. Oxygen saturation and end-tidal PCO(2) were monitored noninvasively. Polysomnography was performed to determine sleep times. All patients with CCHS received mechanical ventilation during sleep. Mean values for systolic BP (SBP) and diastolic BP (DBP) during wakefulness and sleep were analyzed. Nocturnal BP "dipping" was defined as the difference in mean SBP (and/or DBP) between wakefulness and sleep, divided by individual waking mean values. BP "dippers" were defined as subjects showing at least 10% nocturnal dipping.

RESULTS

Patients with CCHS had BPs in the low normal range of normative data. As compared to control subjects, patients with CCHS had lower BP during wakefulness (p = 0.003 and p = 0.016 for SBP and DBP, respectively), and higher BP during sleep (p = 0.016 and p = 0.002). Nocturnal BP dipping was abnormally reduced in patients with CCHS (p = 0.000). Ten of the 11 patients with CCHS were BP nondippers, compared to none of the control subjects.

CONCLUSION

The abnormal circadian BP pattern observed in children and adolescents with CCHS may be related to autonomic nervous dysfunction. Lifelong cardiovascular follow-up is recommended for patients with CCHS.

Genes modulating chemical breathing control: lessons from mutant animals

Genetic factors influence breathing control. Respiratory phenotypes of mutant mice may help to better understand these factors. Congenital central hypoventilation syndrome (CCHS) is a rare disorder defined as failure of chemical control of breathing causing central alveolar hypoventilation, especially during sleep. A genetic basis for CCHS is supported by several arguments, mainly the identification, in a few CCHS patients, of heterozygous mutations of genes contributing to neural crest cell development, namely, genes involved in the endothelin and c-ret pathways. Furthermore, plethysmography studies of the respiratory phenotypes of newborn heterozygous mutant mice have shown that genes in both pathways are involved in breathing control at birth. Nevertheless, no single gene mutation in newborn mice reproduces the human CCHS phenotype. Avenues for future research into the genetics of CCHS include (i) testing of mutant newborn mice for genes in other pathways and (ii) use of microarrays to identify gene clusters that should be associated with abnormal chemical breathing control.

Depression of hypoxic arousal response in adolescent mice following antenatal vasoactive intestinal polypeptide blockade

Late-gestation blockade of vasoactive intestinal polypeptide (VIP) activity in pregnant mice produces discrete morphological abnormalities in the somatosensory cortex of offspring. We investigated the functional implications of this lesion on the behavioural arousal response to moderate hypoxia. Pregnant mice received twice-daily injections of 200 microl saline (control), or saline + 50 microg VIP antagonist (anti-VIP) on embryonic days 17 and 18. Offspring were studied unrestrained at 6-7 weeks after birth, in a bias-flow whole-body plethysmograph during behavioural quiet sleep. Arousal was defined by movement (MVT) lasting > or =1 s. Hypoxic ventilatory (HVR) and arousal responses were measured during a 5 min exposure to 10 % O(2)-3 % CO(2) (hypoxia); peripheral chemoreflex drive was estimated by transient hyperoxia administered at rest and end-hypoxia (Dejours-type test). MVTs increased in all mice during hypoxia, but in anti-VIP mice: (a) MVT onset was delayed (174 +/- 90 vs. 108 +/- 59 s from the start of hypoxia, anti-VIP vs. control; P = 0.008); and (b) MVTs were less frequent, and total MVT time in hypoxia was less (8 +/- 7 vs. 15 +/- 9 %; P = 0.03). The HVR, and peripheral drive at rest and end-hypoxia were comparable in control and anti-VIP mice. In conclusion, a significant arousal deficit was evident in anti-VIP mice. This was not associated with obviously deranged peripheral or brainstem-mediated responses to hypoxia during sleep. This may signal a general deficit in the way hypoxic distress is monitored and processed, and arousal initiated and sustained in these mice.

Role of central mineralocorticoid receptors in cardiovascular disease

Mineralocorticoids act directly through their receptors in specific centers in the central nervous system, kidneys, heart, and vascular smooth muscle to mediate hemodynamic homeostasis. These steroids also modulate renal and cardiovascular function indirectly through the autonomic nervous system. Complex homeostatic mechanisms under normal hormonal control become pathogenic when there is an excess of regulatory hormone. Experiments in which mineralocorticoid receptor antagonists or antisense oligodeoxynucleotides were administered centrally have clearly shown that centrally mediated effects on salt appetite, baroreceptor function, and autonomic drive to the renal and cardiovascular systems are crucial to the pathogenesis of hypertension and cardiovascular disease of hyperaldosteronism, and certain forms of genetic hypertension.