Severe hypoplasia of medullary arcuate nucleus: quantitative analysis in sudden infant death syndrome

Development of the human medullary arcuate nucleus from mid-gestation to the perinatal period: A morphometric study

INTRODUCTION

Development of the human medullary arcuate nucleus (AN) has not been sufficiently investigated. The present study provides morphometric data by examining the brains from preterm and perinatal infants.

MATERIALS AND METHODS

Nine brains were obtained from infants aged 21-43 postmenstrual weeks (PW). Serial celloidin sections were cut and stained using the Klüver-Barrera method. After microscopic observations, morphometric parameters [AN volume, numerical density (Nv) and total number (Nt) of neurons, and neuronal profile area (PA)] were analyzed.

RESULTS

The AN was found as a pair of neuronal masses on the ventral medullary surface at 21 PW. Caudally, it was ventrolateral to the pyramidal tract (PT), and rostrally, medial to the PT. In the middle, it was diminished in size or interrupted. The AN neurons were gradually enlarged with age, showing multiplicity in size and shape. The following findings had a marked asymmetry and individual variability: (1) complete or partial inclusion of the AN in the PT; (2) connection between the rostral AN and the pontine nuclei; (3) coexistence of pyknotic neurons. The AN volume increased exponentially with age, while the Nv decreased exponentially. The Nt changed along two phases (decrease-increase) after mid-gestation. The mean PA increased linearly with age. Asymmetry and/or individual variability were demonstrated in the AN volume, Nt, and mean PA.

CONCLUSIONS

Asymmetry and individual variability in the AN morphology are present in fetal period. The AN may undergo neuron death and neuroblasts production in tandem after mid-gestation.

Individual variability in the size and organization of the human arcuate nucleus of the medulla

The arcuate nucleus (Arc) of the medulla is found in almost all human brains and in a small percentage of chimpanzee brains. It is absent in the brains of other mammalian species including mice, rats, cats, and macaque monkeys. The Arc is classically considered a precerebellar relay nucleus, receiving input from the cerebral cortex and projecting to the cerebellum via the inferior cerebellar peduncle. However, several studies have found aplasia of the Arc in babies who died of SIDS (Sudden Infant Death Syndrome), and it was suggested that the Arc is the locus of chemosensory neurons critical for brainstem control of respiration. Aplasia of the Arc, however, has also been reported in adults, suggesting that it is not critical for survival. We have examined the Arc in closely spaced Nissl-stained sections in thirteen adult human cases to acquire a better understanding of the degree of variability of its size and location in adults. We have also examined immunostained sections to look for neurochemical compartments in this nucleus. Caudally, neurons of the Arc are ventrolateral to the pyramidal tracts (py); rostrally, they are ventro-medial to the py and extend up along the midline. In some cases, the Arc is discontinuous, with a gap between sections with the ventrolaterally located and the ventromedially located neurons. In all cases, there is some degree of left-right asymmetry in Arc position, size, and shape at all rostro-caudal levels. Somata of neurons in the Arc express calretinin (CR), neuronal nitric oxide synthase (nNOS), and nonphosphorylated neurofilament protein (NPNFP). Calbindin (CB) is expressed in puncta whereas there is no expression of parvalbumin (PV) in somata or puncta. There is also immunostaining for GAD and GABA receptors suggesting inhibitory input to Arc neurons. These properties were consistent among cases. Our data show differences in location of caudal and rostral Arc neurons and considerable variability among cases in the size and shape of the Arc. The variability in size suggests that "hypoplasia" of the Arc is difficult to define. The discontinuity of the Arc in many cases suggests that establishing aplasia of the Arc requires examination of many closely spaced sections through the brainstem.

Hypertrophy of the Anterior External Arcuate Fasciculus: A Rare Variant With Implications for the Development of the Arcuate Nucleus

A rare anatomic variant of a markedly enlarged anterior external arcuate fasciculus (AEAF) on the ventral medullary surface is reported and compared to two controls. The hypertrophic AEAF was nine times larger in diameter than normal, whereas the arcuate nucleus (AN) and inferior olivary nucleus (ION) appeared histologically normal in size and neuronal distribution, and morphometric analysis of the AN confirmed that it was within the normal range. Calbindin-2 (calretinin, CALB2) expression was identified in the AN and in the fibers of the normal AEAF. The hypertrophic AEAF did not contain calbindin-2–expressing fibers. CALB2 expression was also present in the ventrolateral portion of the ION, both in the index case and in one of the control cases. The origin of the additional fibers was not identified; however, the potential origin of these fibers and its implications for the development of the AEAF are discussed.

Perinatal Nicotine Reduces Chemosensitivity of Medullary 5-HT Neurons after Maturation in Culture

Perinatal exposure to nicotine produces ventilatory and chemoreflex deficits in neonatal mammals. Medullary 5-HT neurons are putative central chemoreceptors that innervate respiratory nuclei and promote ventilation, receive cholinergic input and express nicotinic acetylcholine receptors (nAChRs). Perforated patch clamp recordings were made from cultured 5-HT neurons dissociated from the medullary raphé of 0-3 day old mice expressing enhanced yellow fluorescent protein driven by the enhancer region for PET1 (ePet-EYFP). The effect of exposure to low (6 mg kg^-1day^-1) or high (60 mg kg^-1day^-1) doses of nicotine in utero (prenatal), in culture (postnatal), or both and the effect of acute nicotine exposure (10 μM), were examined on baseline firing rate (FR at 5% CO₂, pH = 7.4) and the change in FR with acidosis (9% CO₂, pH 7.2) in young (12-21 days in vitro, DIV) and older (≥22 DIV) acidosis stimulated 5-HT neurons. Nicotine exposed neurons exhibited ∼67% of the response to acidosis recorded in neurons given vehicle (p = 0.005), with older neurons exposed to high dose prenatal and postnatal nicotine, exhibiting only 28% of that recorded in the vehicle neurons (p < 0.01). In neurons exposed to low or high dose prenatal and postnatal nicotine, acute nicotine exposure led to a smaller increase in FR (∼+51% vs +168%, p = 0.026) and response to acidosis (+6% vs +67%, p = 0.014) compared to vehicle. These data show that exposure to nicotine during development reduces chemosensitivity of 5-HT neurons as they mature, an effect that may be related to the abnormal chemoreflexes reported in rodents exposed to nicotine in utero, and may cause a greater risk for sudden infant death syndrome (SIDS).

Cerebellar heterotopia of infancy in sudden infant death syndrome: an observational neuropathological study of four cases

Sudden infant death syndrome (SIDS) is the sudden unexpected death of an infant < 1 year of age that remains unexplained after comprehensive workup including complete autopsy and investigation of the circumstances of death. The triple risk hypothesis posits that SIDS results as a combination of both intrinsic and extrinsic factors on the background of a predisposing vulnerability. Neuropathological examination in the past has focussed mainly on the brainstem as the major player in respiratory control, where subtle findings have been linked to the chain of events leading to death in SIDS. The cerebellum has received less attention, probably due to an assumed negligible role in central cardiorespiratory control. We report four cases of SIDS in which neuropathological investigation revealed cerebellar heterotopia of infancy, a distinct malformation of the cerebellum, and discuss the potential impact of this condition on the aetiology and pathogenesis of SIDS.

Immunohistochemical expression of Napsin A in normal human fetal lungs at different gestational ages and in acquired and congenital pathological pulmonary conditions

Surfactant protein B (SP-B) is a key component of pulmonary surfactant. SP-B is processed to a mature, surface-active protein from a pro-peptide by two distinct cleavage events in its N-terminal and C-terminal regions. Napsin A, a protease expressed in type II pneumocytes, is responsible for the N-terminal cleavage event. Here, for the first time, we have evaluated the expression of Napsin A in normal fetal lungs at different gestational ages and in lungs from fetuses and neonates with congenital and acquired pathological pulmonary conditions. Lung samples were collected from fetal and neonatal autopsies at the Department of Medicine and Surgery's Pathology Unit of Parma University (Italy). Immunohistochemical analysis was performed using a primary anti-Napsin A (clone IP64 clone) monoclonal antibody. A section of lung adenocarcinoma was used as an external positive control. Napsin A was expressed early in normal fetal lungs throughout the epithelium of the distal pseudoglandular tracts. In fetuses at 30 weeks of gestation and term newborns, Napsin A was already expressed only in isolated cells within the alveolar epithelium, similar to adult subjects. Furthermore, increased expression of Napsin A compared with a control group was observed in lung tissue from fetuses and a newborn with pathological conditions (inflammatory diseases and pulmonary hypoplasia). In conclusion, this study demonstrates that Napsin A is produced early in fetal life, and that its production is increased in many diseases, presumably in an effort to remedy functional pulmonary failure.

Variability of the medullary arcuate nucleus in humans

INTRODUCTION

The arcuate nucleus is a component of the ventral medullary surface involved in chemoreception and breathing control. The hypoplasia of this nucleus is a very frequent finding in victims of sudden unexplained fetal and infant death (from the last weeks of pregnancy to the first year of life). On the contrary, this developmental alteration is rarely present in age-matched controls who died of defined causes. These observations lead to hypothesize that a well-developed and functional arcuate nucleus is generally required to sustain life. The aim of this study was to investigate whether the arcuate nucleus maintains the same supposed function throughout life.

METHODS

We carried out neuropathological examinations of brainstems obtained from 25 adult subjects, 18 males and 7 females, aged between 34 and 89 years, who died from various causes.

RESULTS

For almost half of the cases (44%) microscopic examinations of serial histological sections of medulla oblongata showed a normal cytoarchitecture of the arcuate nucleus, extending along the pyramids. For the remaining 56% of cases, various degrees of hypodevelopment of this nucleus were observed, validated through the application of quantitative morphometric investigations, from decreased area, neuron number and volume, to full aplasia.

CONCLUSIONS

These unexpected findings indicate that the involvement of the arcuate nucleus in chemoreception in adulthood is questionable, given the possibility of living until late age without this nucleus. This opens new perspectives for researchers on the role and function of the arcuate nucleus in humans from birth to old age.

Central and peripheral chemoreceptors in sudden infant death syndrome

The pathogenesis of sudden infant death syndrome (SIDS) has been ascribed to an underlying biological vulnerability to stressors during a critical period of development. This paper reviews the main data in the literature supporting the role of central (e.g. retrotrapezoid nucleus, serotoninergic raphe nuclei, locus coeruleus, orexinergic neurons, ventral medullary surface, solitary tract nucleus) and peripheral (e.g. carotid body) chemoreceptors in the pathogenesis of SIDS. Clinical and experimental studies indicate that central and peripheral chemoreceptors undergo critical development during the initial postnatal period, consistent with the age range of SIDS (<1 year). Most of the risk factors for SIDS (gender, genetic factors, prematurity, hypoxic/hyperoxic stimuli, inflammation, perinatal exposure to cigarette smoke and/or substance abuse) may structurally and functionally affect the developmental plasticity of central and peripheral chemoreceptors, strongly suggesting the involvement of these structures in the pathogenesis of SIDS. Morphometric and neurochemical changes have been found in the carotid body and brainstem respiratory chemoreceptors of SIDS victims, together with functional signs of chemoreception impairment in some clinical studies. However, the methodological problems of SIDS research will have to be addressed in the future, requiring large and highly standardized case series. Up-to-date autopsy protocols should be produced, involving substantial, and exhaustive sampling of all potentially involved structures (including peripheral arterial chemoreceptors). Morphometric approaches should include unbiased stereological methods with three-dimensional probes. Prospective clinical studies addressing functional tests and risk factors (including genetic traits) would probably be the gold standard, allowing markers of intrinsic or acquired vulnerability to be properly identified.

Metabolomic profiling of brain from infants who died from Sudden Infant Death Syndrome reveals novel predictive biomarkers

OBJECTIVE

Sudden Infant Death Syndrome (SIDS) is defined as the sudden death of an infant <1 year of age that cannot be explained following a thorough investigation. Currently, no reliable clinical biomarkers are available for the prediction of infants who will die of SIDS.

STUDY DESIGN

This study aimed to profile the medulla oblongata from postmortem human brain from SIDS victims (n=16) and compare their profiles with that of age-matched controls (n=7).

RESULTS

Using LC-Orbitrap-MS, we detected 12 710 features in electrospray ionization positive (ESI+) mode and 8243 in ESI- mode from polar extracts of brain. Five features acquired in ESI+ mode produced a predictive model for SIDS with an area under the receiver operating characteristic curve (AUC) of 1 (confidence interval (CI): 0.995-1) and a predictive power of 97.4%. Three biomarkers acquired in ESI- mode produced a predictive model with an AUC of 0.866 (CI: 0.767-0.942) and a predictive power of 77.6%. We confidently identified 5 of these features (l-(+)-ergothioneine, nicotinic acid, succinic acid, adenosine monophosphate and azelaic acid) and putatively identify another 4 out of the 15 in total.

CONCLUSIONS

This study underscores the potential value of metabolomics for studying SIDS. Further characterization of the metabolome of postmortem SIDS brains could lead to the identification of potential antemortem biomarkers for novel prevention strategies for SIDS.

Sudden Infant Death Syndrome - Role of Trigeminocardiac Reflex: A Review

Sudden infant death syndrome (SIDS) is an unexplained death in infants, which usually occurs during sleep. The cause of SIDS remains unknown and multifactorial. In this regard, the diving reflex (DR), a peripheral subtype of trigeminocardiac reflex (TCR), is also hypothesized as one of the possible mechanisms for this condition. The TCR is a well-established neurogenic reflex that manifests as bradycardia, hypotension, apnea, and gastric hypermotility. The TCR shares many similarities with the DR, which is a significant physiological adaptation to withstand hypoxia during apnea in many animal species including humans in clinical manifestation and mechanism of action. The DR is characterized by breath holding (apnea), bradycardia, and vasoconstriction, leading to increase in blood pressure. Several studies have described congenital anomalies of autonomic nervous system in the pathogenesis of SIDS such as hypoplasia, delayed neuronal maturation, or decreased neuronal density of arcuate nucleus, hypoplasia, and neuronal immaturity of the hypoglossal nucleus. The abnormalities of autonomic nervous system in SIDS may explain the role of TCR in this syndrome involving sympathetic and parasympathetic nervous system. We reviewed the available literature to identify the role of TCR in the etiopathogenesis of SIDS and the pathways and cellular mechanism involved in it. This synthesis will help to update our knowledge and improve our understanding about this mysterious, yet common condition and will open the door for further research in this field.

Hippocampal Formation Maldevelopment and Sudden Unexpected Death across the Pediatric Age Spectrum

Sudden infant death syndrome (SIDS) and sudden unexplained death in childhood (SUDC) are defined as sudden death in a child remaining unexplained despite autopsy and death scene investigation. They are distinguished from each other by age criteria, i.e. with SIDS under 1 year and SUDC over 1 year. Our separate studies of SIDS and SUDC provide evidence of shared hippocampal abnormalities, specifically focal dentate bilamination, a lesion classically associated with temporal lobe epilepsy, across the 2 groups. In this study, we characterized the clinicopathologic features in a retrospective case series of 32 children with sudden death and hippocampal formation (HF) maldevelopment. The greatest frequency of deaths was between 3 weeks and 3 years (81%, 26/32). Dentate anomalies were found across the pediatric age spectrum, supporting a common vulnerability that defies the 1-year age cutoff between SIDS and SUDC. Twelve cases (38%) had seizures, including 7 only with febrile seizures. Subicular anomalies were found in cases over 1 year of age and were associated with increased risk of febrile seizures. Sudden death associated with HF maldevelopment reflects a complex interaction of intrinsic and extrinsic factors that lead to death at different pediatric ages, and may be analogous to sudden unexplained death in epilepsy.

Synaptogenesis and Myelination in the Nucleus/Tractus Solitarius: Potential Role in Apnea of Prematurity, Congenital Central Hypoventilation, and Sudden Infant Death Syndrome

Fetuses as early as 15 weeks' gestation exhibit rhythmical respiratory movements shown by real-time ultrasonography. The nucleus/tractus solitarius is the principal brainstem respiratory center; other medullary nuclei also participate. The purpose was to determine temporal maturation of synaptogenesis. Delayed synaptic maturation may explain neurogenic apnea or hypoventilation of prematurity and some cases of sudden infant death syndrome. Sections of medulla oblongata were studied from 30 human fetal and neonatal brains 9 to 41 weeks' gestation. Synaptophysin demonstrated the immunocytochemical sequence of synaptogenesis. Other neuronal markers and myelin stain also were applied. The nucleus/tractus solitarius was similarly studied in fetuses with chromosomopathies, metabolic encephalopathies, and brain malformations. Synapse formation in the nucleus solitarius begins at about 12 weeks' gestation and matures by 15 weeks; myelination initiated at 33 weeks. Synaptogenesis was delayed in 3 fetuses with different conditions, but was not specific for only nucleus solitarius. Delayed synaptogenesis or myelination in the nucleus solitarius may play a role in neonatal hypoventilation, especially in preterm infants and in some sudden infant death syndrome cases.

The First 5-Year-Long Survey on Intrauterine Unexplained Sudden Deaths from the Northeast Italy

PURPOSE

Sudden intrauterine unexplained death syndrome (SIUDS) represents one of the main open issues in the scientific and social setting of the modern medicine, and our efforts have aimed to understand its possible causes and risk factors.

METHODS

A 43-case series of consecutive unexplained fetal deaths coming from Northeast Italy, collected in a 5-year period (2011-2015), has been submitted to an in-depth investigation, based on neuropathological and cardiopathological examinations, immunohistochemistry for neuronal nuclear antigen (NeuN), genetic characterization for the serotonin transporter (5-HTT) gene polymorphisms, and toxicological environmental analyses.

RESULTS

The overall survey from the neuropathological findings highlights one or more congenital morphological abnormalities of the autonomic nervous system in 77% of cases of sudden fetal deaths.

CONCLUSIONS

From our results emerges the need to perform a complete autopsy of all SIUDS victims with an in-depth examination of the neuronal centers of the brainstem, which modulate the vital functions.

Hypoxia at the heart of sudden infant death syndrome?

Sudden infant death syndrome (SIDS) is a significant clinical problem without an accepted pathological mechanism, but with multiple conflicting models. Mutations in a growing number of genes have been found postmortem in SIDS cases, notably genes encoding ion channels. This can only account for a minority of cases, however. Our recent work on a novel mouse model of SIDS suggests a potentially more widespread role for cardiac arrhythmia in SIDS without needing to invoke the inheritance of abnormal ion-channel genes. We propose a model for SIDS pathogenesis whereby postnatal hypoxia leads to delayed maturation of the cardiac conduction system and an increased risk of cardiac arrhythmia. Our model may integrate several epidemiological findings related to risks factors for SIDS, and agrees with previous work suggesting a common final pathological pathway in SIDS.

Loss of motoneurons in the ventral compartment of the rat hypoglossal nucleus following early postnatal exposure to alcohol

Perinatal alcohol exposure (AE) has multiple detrimental effects on cognitive and various behavioral outcomes, but little is known about its impact on the autonomic functions. In a rat model of fetal alcohol spectrum disorders (FASD), we investigated neurochemical and neuroanatomical alterations in two brainstem nuclei, the hypoglossal nucleus (XIIn) and the dorsal nucleus of the vagus nerve (Xdn). One group of male Sprague-Dawley rats (n=6) received 2.625 g/kg ethanol intragastrically twice daily on postnatal days (PD) 4-9, a period equivalent to the third trimester of human pregnancy, and another group (n=6) was sham-intubated. On PD 18-19, the rats were perfused and medullary sections were immunohistochemically processed for choline acetyltransferase (ChAT) or two aminergic receptors that mediate excitatory drive to motoneurons, α₁-adrenergic (α₁-R) and serotonin 2A (5-HT(2A)-R), and c-Fos. Based on ChAT labeling, AE rats had reduced numbers of motoneurons in the ventral XIIn (XIIn-v; 35.4±1.3 motoneurons per side and section vs. 40.0±1.2, p=0.022), but not in the dorsal XIIn or Xdn. Consistent with ChAT data, both the numbers of α₁-R-labeled motoneurons in the XIIn-v and the area of the XIIn-v measured using 5-HT(2A)-R staining were significantly smaller in AE rats (19.7±1.5 vs. 25.0±1.4, p=0.031 and 0.063 mm² ±0.002 vs. 0.074±0.002, p=0.002, respectively). Concurrently, both 5-HT(2A)-R and c-Fos staining tended to be higher in AE rats, suggesting an increased activation. Thus, postnatal AE causes motoneuronal loss in the XIIn-v. This may compromise upper airway control and contribute to increased risk of upper airway obstructions and sudden infant death in FASD victims.

Sudden infant death syndrome: an update and new perspectives of etiology

Sudden infant death syndrome (SIDS) is a condition in which an infant, usually in the early postnatal period and nearly always before 6 months of age, dies during sleep for unexplained reasons and the standard autopsy fails to disclose an etiology. Various physiological explanations of risk factors include the prone sleeping position, overheating by excessive bundling, viral upper respiratory tract infections, parental smoking at home, and birthing injury resulting in an insult to the inner ear and central chemoreceptor zone, an immaturity that involves CO2 chemoreceptors that regulate respiratory control. Neuropathological studies and theories implicate: (1) hypoplasia or defective transmitter function in the medullary arcuate nucleus, a derivative of the rhombencephalic lip of His; (2) synaptic or receptor immaturity of the nucleus of the fasciculus solitarius, the "pneumotaxic center"; and (3) functional impairment of the serotonergic raphé nuclei of the pontine and medullary ventral median septum and other serotonergic neurons of the brainstem. Additional neurological risk factors for SIDS include perinatal neuromuscular diseases, infantile epilepsies or status epilepticus, and genetic metabolic encephalopathies.

Expression of brain-derived neurotrophic factor and TrkB receptor in the sudden infant death syndrome brainstem

This study compared the expression of BDNF (proBDNF and rhBDNF forms) and its receptor TrkB, in the medulla of sudden infant death syndrome (SIDS) infants and infants who died from known causes (non-SIDS). This study also evaluated these markers in association with SIDS clinical risk factors including, sleep position, cigarette smoke exposure and gender. Brainstem tissue was immunohistochemically stained and quantitative analyses were made for eight nuclei of the caudal and rostral medulla. Compared to non-SIDS, SIDS infants had lower rhBDNF in the caudal nucleus of the solitary tract and higher TrkB in the caudal dorsal motor nucleus of the vagus. Within the SIDS cohort, prone sleep position was associated with lower rhBDNF in the caudal arcuate nucleus, and cigarette smoke exposure was associated with lower rhBDNF and TrkB in the inferior olivary nucleus. Abnormal expression of BDNF and TrkB suggests that neuroprotective functions of the BDNF/TrkB system may be reduced in respiratory-related nuclei of SIDS infants.

5HT1A receptors inhibit glutamate inputs to cardiac vagal neurons post-hypoxia/hypercapnia

Synaptic inputs to cardiac vagal neurons (CVNs) regulate parasympathetic activity to the heart. Previous work has shown insults such as hypoxia and hypercapnia (H/H) alter CVN activity by activating post-synaptic serotonergic, purinergic, and glutamatergic receptors in CVNs. This study examines the role of serotonergic 5HT1A receptors in modulating these excitatory neurotransmissions to CVNs during control conditions, H/H and recovery from H/H. Excitatory post-synaptic currents (EPSCs) were recorded from identified CVNs in vitro before, during and post H/H. The 5HT1A receptor antagonist WAY 100635 had no effect on EPSCs in CVNs before, and during H/H. However, during recovery from H/H inspiratory-related excitatory serotonergic and purinergic pathways were recruited to excite CVNs. However, when these serotonergic and purinergic pathways are blocked, the 5HT1A receptor antagonist WAY 100635 restores an excitatory glutamatergic neurotransmission to CVNs. This study indicates endogenous activation of serotonergic 5HT1A receptors diminishes glutamatergic neurotransmission to CVNs following H/H, likely via a presynaptic site of action.

Unexplained stillbirth versus SIDS: common congenital diseases of the autonomic nervous system--pathology and nosology

OBJECTIVE

To contribute to a more balanced assessment of the morphological substrates underlying unexplained perinatal death and SIDS.

METHODS

In-depth histological, immunohistochemical and genetic examinations were performed on the autonomic nervous and cardiac conduction systems in 95 unexpected perinatal deaths, 140 SIDS and 78 controls (44 infants and 34 perinatal death victims).

RESULTS

The study revealed the localization and the nature of a variety of specific congenital abnormalities of the autonomic nervous system, central and peripheral, and of the cardiac conduction system that represent the morphological substrates of the pathophysiological mechanism of sudden fetal death and SIDS.

CONCLUSIONS

The observation of similar anomalies of the autonomic nervous and the cardiac conduction systems in both unexplained perinatal deaths and SIDS indicates their common congenital nature. Therefore, the definitions of these deaths, currently nosographically distinct, should be unified.

Interleukin-6 and the serotonergic system of the medulla oblongata in the sudden infant death syndrome

Mild infection may trigger sudden death in the vulnerable infant by cytokine interactions with a compromised medullary serotonergic (5-HT) system, leading to disrupted cardiorespiratory regulation and sleep-related sudden death. The cytokine interleukin (IL)-6 is elevated in the cerebrospinal fluid in SIDS. We tested the hypothesis that the expression of IL-6 receptors (IL-6R) and/or gp130 (involved in IL-6R signaling) is altered in the medullary 5-HT system in SIDS. Immunohistochemistry of IL-6R and gp130 was performed on medullae from 25 SIDS infants, 20 infectious deaths, and 14 controls using a semi-quantitative grading system. In the SIDS cases, mean IL-6R intensity grade in the arcuate nucleus (major component of medullary 5-HT system) was significantly higher than in the control group (2.00 +/- 0.07 vs. 1.77 +/- 0.08, P = 0.04), with no other differences in IL-6R or gp130 expression at any other site. Arcuate 5-HT neurons expressed IL-6R, indicating a site of IL-6/5-HT interaction. In SIDS, IL-6R expression is abnormal in the arcuate nucleus, the putative human homolog of rodent ventral medullary chemosensitivity sites involving 5-HT. Aberrant interactions between IL-6 and the arcuate nucleus may contribute to impaired responses to hypercapnia generated by infection (hyper-metabolism) combined with rebreathing.

Brainstem mechanisms underlying the sudden infant death syndrome: evidence from human pathologic studies

The brainstem hypothesis is one of the leading hypotheses concerning the sudden infant death syndrome (SIDS). It states that SIDS, or an important subset of SIDS, is due to abnormal brainstem mechanisms in the control of respiration, chemosensitivity, autonomic regulation, and/or arousal which impairs the infant's response to life-threatening, but often occurring, stressors during sleep (e.g., hypoxia, hypercarbia, asphyxia, hyperthermia) and leads to sudden death in a vulnerable developmental period. In this review, we summarize neuropathologic evidence from SIDS cases that support this hypothesis, beginning with the seminal report of subtle brainstem gliosis three decades ago. We focus upon recent neurochemical studies in our laboratory concerning the neurotransmitter serotonin (5-HT) and its key role in mediating protective responses to homeostatic stressors via medullary circuits. The possible fetal origin of brainstem defects in SIDS is reviewed, including evidence for adverse effects of prenatal exposure to maternal cigarette smoking and alcohol upon the postnatal development of human brainstem 5-HT pathways.

The brainstem and serotonin in the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is the sudden death of an infant under one year of age that is typically associated with sleep and that remains unexplained after a complete autopsy and death scene investigation. A leading hypothesis about its pathogenesis is that many cases result from defects in brainstem-mediated protective responses to homeostatic stressors occurring during sleep in a critical developmental period. Here we review the evidence for the brainstem hypothesis in SIDS with a focus upon abnormalities related to the neurotransmitter serotonin in the medulla oblongata, as these are the most robust pathologic findings to date. In this context, we synthesize the human autopsy data with genetic, whole-animal, and cellular data concerning the function and development of the medullary serotonergic system. These emerging data suggest an important underlying mechanism in SIDS that may help lead to identification of infants at risk and specific interventions to prevent death.

Leptomeningeal neurons are a common finding in infants and are increased in sudden infant death syndrome

Developmental abnormalities of the brain, in particular, the brainstem potentially affecting centers for breathing, circulation and sleep regulation, are thought to be involved in the etiology of sudden infant death syndrome (SIDS). In order to investigate whether leptomeningeal neurons could serve as morphological indicators for a developmental failure or retardation in cerebral maturation, we evaluated the density of isolated leptomeningeal neurons (without associated glia) in 15 brain regions of 24 SIDS and 8 control cases, representing part of the German Study on sudden infant death. Leptomeningeal neurons were encountered in 79% of SIDS and 68% of control cases. More leptomeningeal neurons in SIDS versus control cases were found in lower pons (p = 0.002), upper pons (p = 0.016), cerebellar hemispheres (p = 0.012), lower medulla oblongata (p = 0.039), and temporal lobe (p = 0.041). Summarizing the data according to gross anatomical region of origin (i.e., brainstem, cerebellum or cerebrum), higher numbers of leptomeningeal neurons in SIDS cases were only found in the brainstem (p = 0.006 vs. 0.13 and 0.19, respectively). Our data show that single leptomeningeal neurons are present in most normal infantile brains. The age-dependent increase of leptomeningeal neurons among SIDS cases may either (a) represent a delayed maturation or retardation, i.e., a later or slower reduction of neurons or a delayed peak in occurrence (shift toward an older age), or (b) may be interpreted as a generally increased occurrence of leptomeningeal neurons among SIDS cases as a result of a diffuse developmental abnormality during central nervous system maturation.

Complexity measures of the central respiratory networks during wakefulness and sleep

Since sleep is known to influence respiratory activity we studied whether the sleep state would affect the complexity value of the respiratory network output. Specifically, we tested the hypothesis that the complexity values of the diaphragm EMG (EMGdia) activity would be lower during REM compared to NREM. Furthermore, since REM is primarily generated by a homogeneous population of neurons in the medulla, the possibility that REM-related respiratory output would be less complex than that of the awake state was also considered. Additionally, in order to examine the influence of neuron vulnerabilities within the rostral ventral medulla (RVM) on the complexity of the respiratory network output, we inhibited respiratory neurons in the RVM by microdialysis of GABA(A) receptor agonist muscimol. Diaphragm EMG, nuchal EMG, EEG, EOG as well as other physiological signals (tracheal pressure, blood pressure and respiratory volume) were recorded from five unanesthetized chronically instrumented intact piglets (3-10 days old). Complexity of the diaphragm EMG (EMGdia) signal during wakefulness, NREM and REM was evaluated using the approximate entropy method (ApEn). ApEn values of the EMGdia during NREM and REM sleep were found significantly (p < 0.05 and p < 0.001, respectively) lower than those of awake EMGdia after muscimol inhibition. In the absence of muscimol, only the differences between REM and wakefulness ApEn values were found to be significantly different.

Biopathology of the dentate-olivary complex in sudden unexplained perinatal death and sudden infant death syndrome related to maternal cigarette smoking

OBJECTIVES

The present study was aimed to evaluate the possible presence of cytohistologic and/or biologic modifications of the human dentate-olivary complex in sudden unexplained perinatal and infant deaths.

METHODS

We investigated the histologic morphology of the dentate and inferior olivary nuclei, the glial index, the c-fos and apoptotic immunopositivity, as well as the possible effects elicited by maternal cigarette smoking, in 44 cases of perinatal and infant death victims, aged from the 26th gestational week to 10 months of life.

RESULTS

We observed subtle alterations of both the medullary inferior olivary nucleus and of the cerebellar dentate nucleus, represented by a significant increase in the reactive astrocyte density and in the neuronal c-fos and apoptotic expression in unexplained death victims, compared with age-matched controls. These alterations were closely related to a maternal cigarette smoking habit.

DISCUSSION

We postulate that maternal smoking, besides inducing the previously demonstrated morpho-functional alterations of the autonomic central nervous system, could also exert an adverse influence on the dentate-olivary complex, leading to sudden death in vulnerable periods of perinatal development or early infancy.

Neuronal cell death in the arcuate nucleus of the medulla oblongata in stillbirth

The hypothesis that unexplained stillbirth arises in a similar manner as the sudden infant death syndrome (SIDS) is based in part on shared neuropathologic features between the two entities, including hypoxic-ischemic lesions such as white matter and brainstem gliosis, as well as aplasia or hypoplasia of the arcuate nucleus on the ventral surface of the medulla. The arcuate nucleus is the putative homologue of the respiratory chemosensory region at the ventral medullary surface in animals that is involved in central chemosensitivity. To determine arcuate nucleus pathology in stillbirth, and its co-occurrence with evidence of hypoxia-ischemia, we reviewed brain specimens from the archives of our hospitals from 22 consecutive stillbirths from 22 to 41 gestational weeks. Explained causes of death (n=17) included nuchal cord, acute chorioamnionitis, placental abruption, and fetal glomerulosclerosis; 5 cases were unexplained. In 12 brains, we observed nuclear karyorrhexis and/or pyknosis with cytoplasmic hypereosinophilia in neurons in the arcuate nucleus in both explained (n=8) and unexplained (n=4) cases (54.5% of total cases). Three additional cases had arcuate aplasia (n=1) or hypoplasia (n=2) (13.6% of total cases); one of the latter cases also had neuronal necrosis in the hypoplastic arcuate. The degree of gliosis in the region of the arcuate nucleus was variable across all cases, without statistically significant differences between groups with and without arcuate nucleus necrosis. Other lesions in association with (n=14) and without (n=8) arcuate nucleus abnormalities were diffuse cerebral white matter gliosis, periventricular leukomalacia (PVL), and neuronal necrosis in the hippocampus, basal ganglia, thalamus, basis pontis, and brainstem tegmentum. In 16/20 (80.0%) cases (with or without histologic necrosis of the arcuate), immunostaining with caspase-3 demonstrated positive neurons. Our findings suggest that neuronal pathology in the arcuate nucleus may be both developmental (13.6%) and acquired (54.5%). The association of neuronal necrosis and apoptosis in the arcuate nucleus with systemic entities involving fetal ischemia, and with other brain lesions consistent with ischemia, e.g., cerebral white matter gliosis, suggests that ischemia plays a role in the arcuate nucleus damage as well. Thus, the underpopulation of arcuate neurons detected postnatally in some SIDS infants may be secondary to an acquired insult in mid- or late gestation, and in other cases, a primary developmental lesion in early gestation, or both. The role of arcuate nucleus pathology in the pathogenesis of fetal demise remains to be determined.

Sudden infant death due to neurofibromatosis type I

Sudden infant death syndrome (SIDS) is the unexpected death of an infant under the age of 1 year, where a complete autopsy, including scene investigation, fails to reveal a cause of death. Although the frequency of SIDS has decreased almost 50% over the past 10 years, it remains the leading cause of death in infants aged 1 to 6 months. SIDS is a diagnosis of exclusion and requires the elimination of a wide range of possible causes, including asphyxia, poisoning, abuse, occult heart disease, and other natural disease processes. In this report, we describe the case of an infant death initially suspected to be a SIDS death in which autopsy revealed an optic pathway glioma (optic glioma or hypothalamic glioma) and other stigmata of neurofibromatosis type I.

Ontogenesis of human cerebellar cortex and biopathological characterization in sudden unexplained fetal and infant death

The aims of this study were to investigate in the human cerebellar cortex the structural and biological ontogenetic features, the possible presence of alterations in cases of sudden unexplained fetal and infant death, and the involvement of the maternal cigarette smoking in developmental abnormalities. We analyzed 52 brains of fetal and infant death victims, aged from the second gestational trimester to 12th postnatal month. In the cerebellar cortex we evaluated, besides the morphological aspects, the expression of several biomarkers implicated in proliferative processes (c-fos, proliferating cell nuclear antigen, and apoptosis) as well as the presence of the neurotransmitter somatostatin, which is strongly implicated in central nervous system differentiation, and of EN2 gene. The observed features of the cerebellar cortex, mainly confined to the transient external granular layer, were high proliferative activity and high expression of both somatostatin and EN2 gene in prenatal life and high apoptotic index after birth. In 41% of the sudden unexplained death victims, in the greater part with smoking mothers, we observed different biopathological alterations of the cerebellar cortex. Maternal smoking is increasingly being demonstrated to be one of the main contributors to developmental neurological alterations in the offspring.

Serotonergic and glutamatergic neurons at the ventral medullary surface of the human infant: Observations relevant to central chemosensitivity in early human life

Central chemoreception is the mechanism by which the brain detects the level of carbon dioxide (CO(2)) in the arterial blood and alters breathing accordingly in order to maintain it within physiological levels. The ventral surface of the medulla oblongata (VMS) of animals has long been recognized as a site of chemosensitivity, culminating in the recent identification of chemosensitive serotonergic (5-HT) and glutamatergic (Glut) neurons in this region. In this study, we analyzed the distribution of 5-HT and Glut neurons and their receptors in the arcuate nucleus (Arc) at the VMS of the human infant, using single-and double-label immunohistochemistry with specific antibodies. We also examined the expression of astrocytes, as experimental evidence suggests that astrocytes mediate, at least in part, central chemosensitivity via 5-HT and/or Glut receptors. We identified a small number of 5-HT neurons (approximately 5% of Arc neurons), distributed over the entire extent of the VMS, a large number of Glut neurons (approximately 95% of Arc neurons) that localized almost exclusively to the medial Arc, and a large number of astrocytes distributed across the entire extent of the VMS. The Arc also contained 5-HT(1A), kainate (GluR5), and 5-HT(2A) receptors, which localized predominantly to 5-HT neurons, glutamate neurons and astrocytes, respectively. Astrocytes also expressed the vesicular glutamate transporter 2 and low levels of 5-HT(1A) and kainate (GluR5) receptors, indicating that astrocytes may store and release glutamate, possibly in response to stimulation by 5-HT and/or Glut. These observations suggest that important functional interactions exist between 5-HT, glutamate, and astrocytes in the Arc. They also support the idea that the Arc is homologous to chemosensitive zones at the VMS in experimental animals. These data are important towards delineating the role of the human Arc in modulation of homeostasis, and its dysfunction in brainstem-associated pathologies such as the sudden infant death syndrome.

Involvement of the EN-2 gene in normal and abnormal development of the human arcuate nucleus

In this study, we wanted to evaluate whether the engrailed EN-2 gene, a homeobox gene with an essential role in the development of the rhombic lip derivatives in different species, is (1) expressed also in man in the differentiation process of the medullary arcuate nucleus (ArcN) and (2) involved in sudden unexplained perinatal and infant death, frequently related to developmental defects of the ArcN. We evaluated by means of the monoclonal antibody 4D9, exclusively recognizing engrailed-2 protein, the expression of the EN-2 gene in the ArcN on histological sections of the brainstems of 30 subjects aged from 17 gestational weeks to 10 postnatal months, who had died of known (17 cases) and unknown causes (13 cases). We observed in the greater number of the cases that the expression of the EN-2 gene is very high in the ArcN neurons from the 17th to the 22nd gestational week, then decreases up to the first days after birth and later disappears. Moreover, in eight of the 13 sudden deaths (61%), a hypoplasia of the ArcN was present. In almost all of these cases, EN-2 expression was negative. In conclusion, we support the role of the EN-2 gene in the normal neuronal development and in the anatomic organization of the human ArcN as well as the possible existence of EN-2 mutations related to hypoplasia of this nucleus.

Hypoplasia of the arcuate nucleus and maternal smoking during pregnancy in sudden unexplained perinatal and infant death

Maternal smoking during pregnancy is the most important risk factor for sudden perinatal and infant death in more industrialized countries. The frequent observation of hypoplasia of the arcuate nucleus in the brainstem of these victims prompted the verification of whether maternal cigarette smoking could be related to defective development of this nucleus during intrauterine life, by affecting the expression of specific genes involved in its developmental process. In serial sections of the brainstem of 54 cases of sudden and unexplained fetal and infant deaths (13 stillbirths, 7 neonatal deaths and 34 sudden infant death syndrome (SIDS) victims), morphological and morphometrical analysis was used to observe the different structural alterations of the arcuate nucleus (bilateral hypoplasia, monolateral hypoplasia, partial hypoplasia, delayed neuronal maturation and decreased neuronal density) detected in 24 cases (44%). Correlating this finding with smoking in pregnancy, a significantly increased incidence of cytoarchitectural alterations of the arcuate nucleus was found in stillborns and SIDS victims with smoker mothers compared to victims with non-smoker mothers. Moreover, the observation of a wide range of developing morphological defects of the arcuate nucleus related to maternal smoking led to the hypothesis that the constituents of the gas phase in cigarette smoke could directly affect the expression of genes involved in the development of this nucleus, such as the homeobox En-2 gene.

Analysis of the human locus coeruleus in perinatal and infant sudden unexplained deaths. Possible role of the cigarette smoking in the development of this nucleus

We investigated the immunohistochemical expression of the tyrosine hydroxylase (TH) enzyme and the morphometric parameters of the human locus coeruleus (LC) in the brainstems of 32 subjects aged from 17 gestational weeks to 12 postnatal month, died of unknown (sudden unexplained perinatal and infant deaths) and known causes. The goals of this study were: (1) to obtain basic information about the structure and physiology of the LC during the first phases of human nervous system development; (2) to evaluate whether there is altered expression of TH and/or structural alterations of the LC in cases of sudden perinatal and infant death; and (3) to verify if morphological and/or physiological abnormalities of the LC could be related to maternal cigarette smoking. Morphometric analysis showed homogeneous data in cases of sudden perinatal and infant death and in age-matched controls who had died of known aetiology. However, immunohistochemistry demonstrated in a wide subset of sudden and unexplained deaths a negativity or low positivity of TH. High distribution of TH protein were instead detectable in the LC neurons of foetuses aged 17-18 gestational weeks who had died of known causes. Therefore, we postulate the functional importance of the LC in the early phases of central nervous system development. Besides, the observation of a significant correlation between sudden unexplained death, negativity of TH staining and maternal smoking, prompted us to suppose a close relation between smoking in utero and a decrease of the noradrenergic activity of the LC, leading to sudden death in the last part of pregnancy and in the first year of life.

Glial and neuronal alterations in the nucleus tractus solitarii of sudden infant death syndrome victims

The factors underlying the sudden infant death syndrome (SIDS) are still unknown, but in recent years much attention has been focused on the central cardiorespiratory control system. In the present work we analyzed the nucleus tractus solitarii (nTS) of 23 SIDS victims and 17 age-matched control cases. We studied the functional and morphological alterations of neurons and glial cells to evaluate the results of possible hypoxic-ischemic injury that could have led to sudden death. Morphometric and immunohistochemical analyses were performed on medullary sections. In the nTS of SIDS victims we observed modifications of both neuronal and glial cells. Brain injury triggers the activation of both astrocytes and microglia, which respond to neuronal damage by characteristic changes that could explain our observations in the nTS of SIDS victims. In our investigation of the nTS of SIDS victims we found a significant increase of reactive astrocytes density, a significantly higher percentage of necrotic cells, an increase of reactive microglial cells density, a significantly higher expression of substance P and the presence of NMDA receptors immunoreactivity. Our results support the hypothesis that there is injury of the nTS neurons in SIDS victims, even if the causes of this damage are still unknown. This neuronal damage may explain why adequate ventilation is often not maintained during hypoxia. Such histological findings have never been thought sufficient to explain SIDS, but the tissue findings could be an indication of the impairment of several pathophysiological mechanisms which may underlie brainstem dysfunction, affecting cardiorespiratory control.

Study of the brainstem, particularly the arcuate nucleus, in sudden infant death syndrome (SIDS) and sudden intrauterine unexplained death (SIUD)

Complete examination of the brainstem involves transverse serial 5-microm sections made throughout the entire brainstem. The number of serial sections varies from 360 in sudden intrauterine unexplained death (SIUD) to 600 in term fetuses to over 1400 sections in sudden infant death syndrome (SIDS) victims. The procedure is not applicable in all histopathological laboratories, owing to the need for additional technical personnel. The simplified procedure allows a remarkable reduction of the number of sections. The brainstem is divided into 3 blocks. The first, cranial block, extends from the border between the medulla oblongata and pons up to the upper pole of the olivary nucleus. The second, intermediate block, corresponding to the submedian area of the inferior olivary nucleus, has as reference point the obex and extends 2 to 3 mm above and below the obex itself. The third, caudal block, includes the lower pole of the inferior olivary nucleus and the lower adjacent area of the medulla oblongata. Examinations of the brainstems from 106 SIDS victims, 30 controls, and 51 stillborns underlined a remarkable variability, particularly of the arcuate nucleus. The simplified examination of the brainstem makes it possible to evaluate the structures, examining 3 specific levels, defined by morphologic reference points.

Serotonergic brainstem abnormalities in Northern Plains Indians with the sudden infant death syndrome

The rate of the sudden infant death syndrome (SIDS) among American Indian infants in the Northern Plains is almost 6 times higher than in U.S. white infants. In a study of infant mortality among Northern Plains Indians, we tested the hypothesis that receptor binding abnormalities to the neurotransmitter serotonin (5-HT) in SIDS cases, compared with autopsied controls, occur in regions of the medulla oblongata that contain 5-HT neurons and that are critical for the regulation of cardiorespiration and central chemosensitivity during sleep, i.e. the medullary 5-HT system. Tritiated-lysergic acid diethylamide binding to 5-HT(1A-D) and 5-HT2 receptors was measured in 19 brainstem nuclei in 23 SIDS and 6 control infants using tissue receptor autoradiography. Binding in the arcuate nucleus, a part of the medullary 5-HT system along the ventral surface, in the SIDS infants (mean age-adjusted binding 7.1 +/- 0.8 fmol/mg tissue, n = 23) was significantly lower than in controls (mean age-adjusted binding 13.1 +/- 1.6 fmol/mg tissue, n = 5) (p = 0.003). Binding also demonstrated significant diagnosis x age interactions (p < 0.04) in 4 other nuclei that are components of the 5-HT system. These data suggest that medullary 5-HT dysfunction can lead to sleep-related, sudden death in affected SIDS infants, and confirm the same binding abnormalities reported by us in a larger dataset of non-American Indian SIDS and control infants. This study also links 5-HT abnormalities in the arcuate nucleus with exposure to adverse prenatal exposures, i.e. cigarette smoking (p = 0.011) and alcohol (p = 0.075), during the periconceptional period or throughout pregnancy. Prenatal exposure to cigarette smoke and/or alcohol may contribute to abnormal fetal medullary 5-HT development in SIDS infants.

Watershed infarcts in the fetal and neonatal brainstem. An aetiology of central hypoventilation, dysphagia, Möibius syndrome and micrognathia

Watershed zone infarcts of the human cerebral cortex at the overlapping junctions of the anterior and middle cerebral arterial territories are well known. Another watershed zone exists in the brainstem tegmentum, between the terminal perfusion zones of the paramedian penetrating and long circumferential arteries, which are paired segmental vessels arising from the basilar artery. The vertebrobasilar circulation achieves its mature configuration and caudorostral flow by 9 weeks gestation. Systemic hypotension and other conditions of reduced basilar perfusion in the fetus, either early or late in gestation, may result in symmetrical longitudinal columns of infarction in the midbrain and tegmentum of the pons and medulla oblongata and laminar necrosis of the midbrain tectum. Within this zone are cranial nerve nuclei III-XII, the nucleus and tractus solitarius or central pneumotaxic center, as well as the nucleus ambiguus and other somatic motor nuclei that subserve muscles of swallowing, mastication and tongue movement. Watershed infarcts in the human fetal and neonatal brainstem are clinically expressed as multiple cranial neuropathies, failure of central respiratory drive and apnea, dysphagia and aspiration, Möbius syndrome and Pierre Robin sequence. MRI is sometimes helpful, but most of the involved neuroanatomical structures are beneath the resolution of present imaging techniques, and the diagnosis during life depends upon clinical neurological examination of the neonate, sometimes supported by evoked potential studies. Postmortem examination confirms the diagnosis and dates the lesions, but also contributes to better understand transient or persistent vascular insufficiencies in the fetal and neonatal brainstem.

A review of functional and structural components of the respiratory center involved in the arousal response

State-dependent changes influencing both the central chemoreceptor and vagal inputs to respiratory neurons may provide useful markers to assess some intrinsic factors of the respiratory center. In this paper we discuss the following topics from our recent experiences, and their relevance to the assessment of sleep-related phenomena. (1) 'Post-sigh' apnea appears predominantly during non-REM sleep in control subjects, and is a potential marker of respiratory dysfunction during this stage of sleep. (2) The disarranged configuration of the arcuate nucleus in Fukuyama-type congenital muscular dystrophy may represent a disturbance in the tangential migration pathway in the brainstem, and may be related to the sudden death that is common in this disorder. The maldevelopment of the arcuate nucleus in the victims of sudden infant death syndrome (SIDS) may also be related to some abnormality in the differentiation and migration of this neuronal population. (3) The onset of hypoglossal nerve activity precedes inspiratory activity of the phrenic nerve, possibly representing a latent drive from the respiratory rhythm generator. These issues are not only related to respiratory rhythmogenesis itself, but are also important in understanding the pathological conditions of arousal responses.

Crib death: further support for the concept of fatal cardiac electrical instability as the final common pathway

This work intends to be a review of the current status of knowledge on the cardiac conduction system in the crib death as well as remaining challenges, including reflections upon authors' personal works as well as many studies by others. The cardiac conduction system findings of resorptive degeneration, His bundle dispersion, Mahaim fibers, cartilaginous meta-hyperplasia, persistent fetal dispersion, left sided His bundle, hemorrhage of the atrio-ventricular junction, septation of the bifurcation, atrio-ventricular node dispersion, sinus node hypoplasia, Zahn node, His bundle hypoplasia, atrio-ventricular node and His bundle dualism are hereby discussed by the authors. The cardiac hypotheses postulating that crib death could be due to lethal cardiac arrhythmias or heart block were considered of great interest in the 1970s. After a general abandon of the conduction studies in crib death, the cardiac concept of crib death is gathering a renewed interest, as well as the occurrence of infantile junctional tachycardia. Both the morphological and functional derangement underlying crib death remain poorly understood, assuring that it remains to be a major medical and social problem. Despite the non-specificity of most of the cardiac conduction findings in crib death, we believe that they, in association with altered neurovegetative stimuli, could underlie potentially malignant arrhythmias, providing a morphologic support for the cardiac concept of crib death.

Sudden infant death syndrome: a cybernetic etiology

The brain's processes, by hypothesis, involve information processing by an extraordinarily complex, highly sophisticated, self-organizing cybernetic system embedded in the central nervous system. This cybernetic system generates itself in successive stages. Breathing is, by default, an autonomous function, but breath control is learned. If there is not a smooth transfer of function at the time when a successor system (one that enables autonomous breathing to be overridden by voluntary control) takes over, breathing may cease, without any overt cause being detectable, even with a thorough postmortem examination. If conditions are such that, at that point, the infant's body lacks the strength to resume breathing again under autonomic control, Sudden Infant Death Syndrome may result. The theory explains why infants are at greater risk if they sleep face down.

Vertebral artery insufficiency as a possible mechanism for sudden infant death--in vivo evidence does not support findings from postmortem studies

Recent postmortem studies have suggested that sudden infant death syndrome (SIDS) might involve an underlying, gradual brain stem injury caused by repeated episodes of transiently compromised brain stem circulation. Autopsy studies have also reported that vertebral artery occlusion due to head rotations, such as occurs, e.g. during prone sleeping, would be a physiological phenomenon of infant atlantooccipital junction. The present study was undertaken to examine whether vertebral artery insufficiency does truly occur in live infants during such head rotations. We studied by transcranial doppler sonography the blood flow velocity of the basilar artery (BA) in 27 infants during head rotation from straight position to maximal rotation in three directions (left, right, dorsiflexion). No significant change in BA blood flow was seen between any head positions. Weight and gestational age, but not arterial pressure or hematocrit, of the infants were correlated with blood flow velocity. Our results suggest that brain stem circulation in live infants may not be compromised due to changing the head position, which is inconsistent with the postmortem findings showing insufficiency of brain stem circulation in both controls and those succumbed to SIDS. We hence propose that the brain stem pathology observed with SIDS is likely caused by other factors (e.g. systemic disturbance) rather than by mechanical obstruction of brain stem circulation.

Association between pulmonary hypoplasia and hypoplasia of arcuate nucleus in stillbirth

OBJECTIVE

To investigate lung development and to correlate pulmonary hypoplasia with hypoplasia of the arcuate nucleus in stillbirths.

STUDY DESIGN

We examined 26 stillbirths which occurred after 25 complete gestational weeks. The brainstem and the lung were the particular focus of this study. The brainstem was examined according to the protocol routinely followed in our Institute. As regards the lung examination, the development stage was evaluated on the basis of the correlation between lung and body weight (LW/BW), and according to microscopic parameters, that is, the presence of cartilaginous bronchi up to the distal level and the radial alveolar count (RAC). The normal reference values for the last 3 months of gestation correspond to >0.022 for LW/BW and from 2.2 to 4.4 for RAC.

RESULTS

In 17 cases (65%) pulmonary hypoplasia was observed, characterized by a LW/BW value below 0.022 and RAC below 2.2. In nine cases (35%), microscopic examination of brainstem serial sections showed varying degrees of hypoplasia of the arcuate nucleus (ARCn). In eight cases (31%) the pulmonary hypoplasia was associated with hypoplasia/agenesis of the ARCn.

CONCLUSIONS

This study demonstrated that in about a third of stillbirths there is a congenital hypodevelopment of both lung and arcuate nucleus. In these cases the ARCn hypoplasia would exert a negative effect on respiratory movements in utero and therefore on lung development. When the pulmonary hypoplasia is not accompanied by hypodevelopment of this nucleus the explanation could be a failure to block the inhibitory action of the Kölliker-Fuse nucleus.

Highly H+-sensitive neurons in the caudal ventrolateral medulla of the rat

The ventral surface of the caudal ventrolateral medulla (cVLM) has been shown to generate intense respiratory responses after surface acid-base stimulation. With respect to their chemosensitive characteristics, cVLM neurons have been less studied than other rostral-most regions of the brainstem. The purpose of these experiments was to determine the bioelectric responses of cVLM neurons to acidic stimuli and to determine their chemosensitive properties. Using extracellular and microiontophoretic techniques, we recorded electrical activities from 117 neurons in an area close to the ventral surface of the cVLM in anaesthetised rats. All neurons were tested for their sensitivity to H+. The fluorescent probe BCECF was used to measure extracellular pH changes produced by the microiontophoretic injection of H+ in brainstem slices. This procedure provided an estimation of the local changes in pH produced by microiontophoretic H+ application in the anaesthetised rat. Neurons coupled to the respiratory cycle, R (n = 51), were not responsive to direct stimulation with H+. Sixty-six neurons that did respond to H+ stimulation were uncoupled from respiration, and identified as NR neurons. These neurons presented distinct ranges of H+ sensitivity. The neuronal sensitivity to H+ was mainly assessed by the slope of the stimulus-response curve, where the steeper the slope, the higher the H+ sensitivity. On this basis, NR neurons were classed as being either weakly or highly sensitive to H+. NR neurons with a high H+ sensitivity (n = 12) showed an average value of 34.17 +/- 7.44 spikes s-1 (100 nC)-1 (mean +/- S.D.) for maximal slope and an EC50 of 126.76 +/- 33 nC. Suprathreshold H+ stimulation of highly sensitive NR neurons elicited bursting pattern responses coupled to the respiratory cycle. The bursting responses, which were synchronised with the inspiratory phase and the early expiratory phase of the respiratory cycle, lasted for several seconds before returning to the steady state firing pattern characteristic of the pre-stimulus condition. These NR neurons, which possess the capacity to detect distinct H+ concentrations in the extracellular microenvironment, are excellent candidates to serve in a chemoreceptor capacity in the caudal medulla.