The effect of prenatal maternal infection on respiratory function in mouse offspring: evidence for enhanced chemosensitivity

Central respiratory command and microglia: An early-life partnership

Microglia, brain-resident macrophages, are key players in brain development, regulating synapse density, shaping neural circuits, contributing to plasticity, and maintaining nervous tissue homeostasis. These functions are ensured from early prenatal development until maturity, in normal and pathological states of the central nervous system. Microglia dysfunction can be involved in several neurodevelopmental disorders, some of which are associated with respiratory deficits. Breathing is a rhythmic motor behavior generated and controlled by hindbrain neuronal networks. The operation of the central respiratory command relies on the proper development of these rhythmogenic networks, formation of their appropriate interactions, and their lifelong constant adaptation to physiological needs. This review, focusing exclusively on the perinatal period, outlines recent advances obtained in rodents in determining the roles of microglia in the establishment and functioning of the respiratory networks and their involvement in certain pathologies.

Perinatal inflammation and gestational intermittent hypoxia disturbs respiratory rhythm generation and long-term facilitation in vitro: partial protection by acute minocycline

Perinatal inflammation triggers breathing disturbances early in life and affects the respiratory adaptations to challenging conditions, including the generation of amplitude long-term facilitation (LTF) by acute intermittent hypoxia (AIH). Some of these effects can be avoided by anti-inflammatory treatments like minocycline. Since little is known about the effects of perinatal inflammation on the inspiratory rhythm generator, located in the preBötzinger complex (preBötC), we tested the impact of acute lipopolysaccharide (LPS) systemic administration (sLPS), as well as gestational LPS (gLPS) and gestational chronic IH (gCIH), on respiratory rhythm generation and its long-term response to AIH in a brainstem slice preparation from neonatal mice. We also evaluated whether acute minocycline administration could influence these effects. We found that perinatal inflammation induced by sLPS or gLPS, as well as gCIH, modulate the frequency, signal-to-noise ratio and/or amplitude (and their regularity) of the respiratory rhythm recorded from the preBötC in the brainstem slice. Moreover, all these perinatal conditions inhibited frequency LTF and amplitude long-term depression (LTD); gCIH even induced frequency LTD of the respiratory rhythm after AIH. Some of the alterations were not observed in slices pre-treated in vitro with minocycline, when compared with slices obtained from naïve pups, suggesting that ongoing inflammatory conditions affect respiratory rhythm generation and its plasticity. Thus, it is likely that alterations in the inspiratory rhythm generator and its adaptive responses could contribute to the respiratory disturbances observed in neonates that suffered from perinatal inflammatory challenges.

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

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

The relationship between intermittent hypoxemia events and neural outcomes in neonates

This brief review examines 1) patterns of intermittent hypoxemia in extremely preterm infants during early postnatal life, 2) the relationship between neonatal intermittent hypoxemia exposure and outcomes in both human and animal models, 3) potential mechanistic pathways, and 4) future alterations in clinical care that may reduce morbidity. Intermittent hypoxemia events are pervasive in extremely preterm infants (<28 weeks gestation at birth) during early postnatal life. An increased frequency of intermittent hypoxemia events has been associated with a range of poor neural outcomes including language and cognitive delays, motor impairment, retinopathy of prematurity, impaired control of breathing, and intraventricular hemorrhage. Neonatal rodent models have shown that exposure to short repetitive cycles of hypoxia induce a pathophysiological cascade. However, not all patterns of intermittent hypoxia are deleterious and some may even improve neurodevelopmental outcomes. Therapeutic interventions include supplemental oxygen, pressure support and pharmacologic drugs but prolonged hyperoxia and pressure exposure have been associated with cardiopulmonary morbidity. Therefore, it becomes imperative to distinguish high risk from neutral and/or even beneficial patterns of intermittent hypoxemia during early postnatal life. Identification of such patterns could improve clinical care with targeted interventions for high-risk patterns and minimal or no exposure to treatment modalities for low-risk patterns.

The potential role of the carotid body in COVID-19

The carotid body (CB) plays a contributory role in the pathogenesis of various respiratory, cardiovascular, renal, and metabolic diseases through reflex changes in ventilation and sympathetic output. On the basis of available data about peripheral arterial chemoreception and severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), a potential involvement in the coronavirus disease 2019 (COVID-19) may be hypothesized through different mechanisms. The CB could be a site of SARS-CoV-2 invasion, due to local expression of its receptor [angiotensin-converting enzyme (ACE) 2] and an alternative route of nervous system invasion, through retrograde transport along the carotid sinus nerve. The CB function could be affected by COVID-19-induced inflammatory/immune reactions and/or ACE1/ACE2 imbalance, both at local or systemic level. Increased peripheral arterial chemosensitivity and reflex sympatho-activation may contribute to the increased morbidity and mortality in COVID-19 patients with respiratory, cardiovascular, renal, or metabolic comorbidities.

Effects of inflammation on the developing respiratory system: Focus on hypoglossal (XII) neuron morphology, brainstem neurochemistry, and control of breathing

Breathing is fundamental to life and any adverse change in respiratory function can endanger the health of an organism or even be fatal. Perinatal inflammation is known to adversely affect breathing in preterm babies, but lung infection/inflammation impacts all stages of life from birth to death. Little is known about the role of inflammation in respiratory control, neuronal morphology, or neural function during development. Animal models of inflammation can provide understanding and insight into respiratory development and how inflammatory processes alter developmental phenotype in addition to providing insight into new treatment modalities. In this review, we focus on recent work concerning the development of neurons, models of perinatal inflammation with an emphasis on two common LPS-based models, inflammation and its impact on development, and current and potential treatments for inflammation within the respiratory control circuitry of the mammalian brainstem. We have also discussed models of inflammation in adults and have specifically focused on hypoglossal motoneurons (XII) and neurons of the nucleus tractus solitarii (nTS) as these nuclei have been studied more extensively than other brainstem nuclei participating in breathing and airway control. Understanding the impact of inflammation on the developmental aspects of respiratory control and breathing pattern is critical to addressing problems of cardiorespiratory dysregulation in disease and this overview points out many gaps in our current knowledge.

All roads lead to inflammation: Is maternal immune activation a common culprit behind environmental factors impacting offspring neural control of breathing?

Despite numerous studies investigating how prenatal exposures impact the developing brain, there remains very little known about how these in utero exposures impact the life-sustaining function of breathing. While some exposures such as alcohol and drugs of abuse are well-known to alter respiratory function, few studies have evaluated other common maternal environmental stimuli, such as maternal infection, inhalation of diesel exhaust particles prevalent in urban areas, or obstructive sleep apnea during pregnancy, just to name a few. The goals of this review article are thus to: 1) highlight data on gestational exposures that impair respiratory function, 2) discuss what is known about the potential role of inflammation in the effects of these maternal exposures, and 3) identify less studied but potential in utero exposures that could negatively impact CNS regions important in respiratory motor control, perhaps by impacting maternal or fetal inflammation. We highlight gaps in knowledge, summarize evidence related to the possible contributions of inflammation, and discuss the need for further studies of life-long offspring respiratory function both at baseline and after respiratory challenge.

Postnatal morphological lung development of wild type and CD26/DPP4 deficient rat pups in dependency of LPS exposure

BACKGROUND

Rodents are born with morphological immature lungs and an intact surfactant system. CD26/DPP4 is a multifactorial transmembrane integral type II protein, which is involved in physiological and pathophysiological processes and is already expressed during development. CD26/DPP4, called CD26 in the following, is able to enhance or dampen differently triggered inflammation. LPS exposure often used to simulate perinatal infection delays lung development.

OBJECTIVE

A perinatal LPS rat model was used to test the hypothesis that CD26 deficiency modulates LPS-induced retardation in morphological lung development.

METHODS

New born Fischer CD26 positive (CD26⁺) and deficient (CD26^-) rats were exposed to LPS on postnatal day (day post partum, dpp) 3 and 5. Morphological parameters of lung development were determined stereologically. Lung development was analysed in 7, 10 14 and 21day old rats.

RESULTS

Compared to controls LPS application resulted (1) in a mild inflammation independent of the strain, (2) in significantly lower total surface and volume of alveolar septa combined with significantly higher total volume of airspaces and alveolar size on dpp 7 in both substrains. However, compared to controls in LPS treated CD26^- rats significant lower values of total septal surface and volume combined with higher values of total parenchymal airspaces and alveolar size were found until the end of classical alveolarization (dpp14). In LPS treated CD26⁺ rat pups the retardation was abolished already on dpp 10.

CONCLUSION

In absence of CD26, LPS enhances the delay of morphological lung development. Morphological recovery was slower after the end of LPS exposure in CD26 deficient lungs.

Rodent models of respiratory control and respiratory system development-Clinical significance

The newborn infant's respiratory system must rapidly adapt to extra-uterine life. Neonatal rat and mouse models have been used to investigate early development of respiratory control and reactivity in both health and disease. This review highlights several rodent models of control of breathing and respiratory system development (including pulmonary function), discusses their translational strengths and limitations, and underscores the importance of creating clinically relevant models applicable to the human infant.

Novel and de novo mutations in pediatric refractory epilepsy

Pediatric refractory epilepsy is a broad phenotypic spectrum with great genetic heterogeneity. Next-generation sequencing (NGS) combined with Sanger sequencing could help to understand the genetic diversity and underlying disease mechanisms in pediatric epilepsy. Here, we report sequencing results from a cohort of 172 refractory epilepsy patients aged 0-14 years. The pathogenicity of identified variants was evaluated in accordance with the American College of Medical Genetics and Genomics (ACMG) criteria. We identified 43 pathogenic or likely pathogenic variants in 40 patients (23.3%). Among these variants, 74.4% mutations (32/43) were de novo and 60.5% mutations (26/43) were novel. Patients with onset age of seizures ≤12 months had higher yields of deleterious variants compared to those with onset age of seizures > 12 months (P = 0.006). Variants in ion channel genes accounted for the greatest functional gene category (55.8%), with SCN1A coming first (16/43). 81.25% (13/16) of SCN1A mutations were de novo and 68.8% (11/16) were novel in Dravet syndrome. Pathogenic or likely pathogenic variants were found in the KCNQ2, STXBP1, SCN2A genes in Ohtahara syndrome. Novel deleterious variants were also found in West syndrome, Doose syndrome and glucose transporter type 1 deficiency syndrome patients. One de novo MECP2 mutation were found in a Rett syndrome patient. TSC1/TSC2 variants were found in 60% patients with tuberous sclerosis complex patients. Other novel mutations detected in unclassified epilepsy patients involve the SCN8A, CACNA1A, GABRB3, GABRA1, IQSEC2, TSC1, VRK2, ATP1A2, PCDH19, SLC9A6 and CHD2 genes. Our study provides novel insights into the genetic origins of pediatric epilepsy and represents a starting-point for further investigations into the molecular pathophysiology of pediatric epilepsy that could eventually lead to better treatments.

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.

Effect of maternal dyslipidaemia on the cardiorespiratory physiology and biochemical parameters in male rat offspring

The present study evaluated the effects of maternal dyslipidaemia on blood pressure (BP), cardiorespiratory physiology and biochemical parameters in male offspring. Wistar rat dams were fed either a control (CTL) or a dyslipidaemic (DLP) diet during pregnancy and lactation. After weaning, both CTL and DLP offspring received standard diet. On the 30th and 90th day of life, blood samples were collected for metabolic analyses. Direct measurements of BP, respiratory frequency (RF), tidal volume (VT) and ventilation (VE) under baseline condition, as well as during hypercapnia (7 % CO2) and hypoxia (KCN, 0·04 %), were recorded from awake 90-d-old male offspring. DLP dams exhibited raised serum levels of total cholesterol (TC) (4·0-fold), TAG (2·0-fold), VLDL+LDL (7·7-fold) and reduced HDL-cholesterol (2·4-fold), insulin resistance and hepatic steatosis at the end of lactation. At 30 d of age, the DLP offspring showed an increase in the serum levels of TC (P<0·05) and VLDL+LDL (P<0·05) in comparison with CTL offspring. At 90 d of age, DLP offspring exhibited higher mean arterial pressure (MAP, approximately 34 %). In the spectral analysis, the DLP group showed augmented low-frequency (LF) power and LF:high-frequency (HF) ratio when compared with CTL offspring. In addition, the DLP animals showed a larger delta variation in arterial pressure after administration of the ganglionic blocker (P=0·0003). We also found that cardiorespiratory response to hypercapnia and hypoxia was augmented in DLP offspring. In conclusion, the present data show that maternal dyslipidaemia alters cardiorespiratory physiology and may be a predisposing factor for hypertension at adulthood.

Before the first breath: prenatal exposures to air pollution and lung development

Various environmental contaminants are known to impair the growth trajectories of major organs, indirectly (gestational exposure) or directly (postnatal exposure). Evidence associates pre-gestational and gestational exposure to air pollutants with adverse birth outcomes (e.g., low birth weight, prematurity) and with a wide range of diseases in childhood and later in life. In this review, we explore the way that pre-gestational and gestational exposure to air pollution affects lung development. We present results in topics underlining epidemiological and toxicological evidence. We also provide a summary of the biological mechanisms by which air pollution exposure possibly leads to adverse respiratory outcomes. We conclude that gestational and early life exposure to air pollutants are linked to alterations in lung development and function and to other negative respiratory conditions in childhood (wheezing, asthma) that may last into adulthood. Plausible mechanisms encompass changes in maternal physiology (e.g., hypoxia, oxidative stress and inflammation) and DNA alterations in the fetus. Evidence for pre-gestational and gestational effects on the lung is scarce compared with that on early life exposure and further studies are needed. However, the suggested mechanisms are credible and the evidence of pre-gestational and gestational air pollution exposure is robust for adverse birth outcomes. Air pollutants might change lung developmental trajectories of the unborn child predisposing it to diseases later in life highlighting the urgent need for controls on urban air pollution levels worldwide.

Lipopolysaccharide exposure during the early postnatal period adversely affects the structure and function of the developing rat carotid body

The carotid body (CB) substantially influences breathing in premature infants by affecting the frequency of apnea and periodic breathing. In adult animals, inflammation alters the structure and chemosensitivity of the CB, yet it is not known if this pertains to neonates. We hypothesized that early postnatal inflammation leads to morphological and functional changes in the developing rat CB, which persists for 1 wk after the initial provoking insult. To test our hypothesis, we exposed rat pups at postnatal day 2 (P2) to lipopolysaccharide (LPS; 100 μg/kg) or saline (SAL) intraperitoneally. At P9-10 (1 wk after treatment), LPS-exposed animals had significantly more spontaneous intermittent hypoxic (IH) events, attenuated ventilatory responses to changes in oxygen tension (measured by whole body plethysmography), and attenuated hypoxic chemosensitivity of the carotid sinus nerve (measured in vitro), compared with SAL-exposed controls. These functional changes were associated with the following: 1) increased inflammatory cytokine mRNA levels; 2) decreased volume of supportive type II cells; and 3) elevated dopamine levels (a major inhibitory neuromodulator) within the CB. These findings suggest that early postnatal inflammation in newborn rats adversely affects the structure and function of the CB and is associated with increased frequency of intermittent desaturations, similar to the phenomenon observed in premature infants. Furthermore, this is the first newborn model of spontaneous intermittent desaturations that may be used to understand the mechanisms contributing to IH events in newborns.