Deirdre Edge

Prenatal stress-induced alterations in major physiological systems correlate with gut microbiota composition in adulthood

Early-life adverse experiences, including prenatal stress (PNS), are associated with a higher prevalence of neurodevelopmental, cardiovascular and metabolic disorders in affected offspring. Here, in a rat model of chronic PNS, we investigate the impact of late gestational stress on physiological outcomes in adulthood. Sprague-Dawley pregnant dams were subjected to repeated restraint stress from embryonic day 14 to day 20, and their male offspring were assessed at 4 months of age. PNS induced an exaggeration of the hypothalamic-pituitary-adrenal (HPA) axis response to stress, as well as an elevation of blood pressure and impairment of cognitive function. Altered respiratory control was also observed, as demonstrated by increased variability in basal respiratory frequency and abnormal frequency responses to both hypoxic and hypercapnic challenges. PNS also affected gastrointestinal neurodevelopment and function, as measured by a decrease in the innervation density of distal colon and an increase in the colonic secretory response to catecholaminergic stimulation. Finally, PNS induced long lasting alterations in the intestinal microbiota composition. 16S rRNA gene 454 pyrosequencing revealed a strong trend towards decreased numbers of bacteria in the Lactobacillus genus, accompanied by elevated abundance of the Oscillibacter, Anaerotruncus and Peptococcus genera in PNS animals. Strikingly, relative abundance of distinct bacteria genera significantly correlated with certain respiratory parameters and the responsiveness of the HPA axis to stress. Together, these findings provide novel evidence that PNS induces long-term maladaptive alterations in the gastrointestinal and respiratory systems, accompanied by hyper-responsiveness to stress and alterations in the gut microbiota.

Tempol Ameliorates Pharyngeal Dilator Muscle Dysfunction in a Rodent Model of Chronic Intermittent Hypoxia

Respiratory muscle dysfunction is implicated in the pathophysiology of obstructive sleep apnea syndrome (OSAS), an oxidative stress disorder prevalent in men. Pharmacotherapy for OSAS is an attractive option, and antioxidant treatments may prove beneficial. We examined the effects of chronic intermittent hypoxia (CIH) on breathing and pharyngeal dilator muscle structure and function in male and female rats. Additionally, we tested the efficacy of antioxidant treatment in preventing (chronic administration) or reversing (acute administration) CIH-induced effects in male rats. Adult male and female Wistar rats were exposed to alternating cycles of normoxia and hypoxia (90 s each; Fi(O(2)) = 5% O(2) at nadir; Sa(O(2)) ∼ 80%) or sham treatment for 8 h/d for 9 days. Tempol (1 mM, superoxide dismutase mimetic) was administered to subgroups of sham- and CIH-treated animals. Breathing was assessed by whole-body plethysmography. Sternohyoid muscle contractile and endurance properties were examined in vitro. Muscle fiber type and cross-sectional area and the activity of key metabolic enzymes were determined. CIH decreased sternohyoid muscle force in male rats only. This was not attributable to fiber transitions or alterations in oxidative or glycolytic enzyme activity. Muscle weakness after CIH was prevented by chronic Tempol supplementation and was reversed by acute antioxidant treatment in vitro. CIH increased normoxic ventilation in male rats only. Sex differences exist in the effects of CIH on the respiratory system, which may contribute to the higher prevalence of OSAS in male subjects. Antioxidant treatment may be beneficial as an adjunct OSAS therapy.

Reactive oxygen species mediated diaphragm fatigue in a rat model of chronic intermittent hypoxia.

What is the central question of this study? The effects of chronic intermittent hypoxia (CIH) on respiratory muscles are relatively underexplored. It is speculated that muscle dysfunction and other key morbidities associated with sleep apnoea are the result of CIH‐induced oxidative stress. We sought to investigate the putative role of CIH‐induced reactive oxygen species in the development of respiratory muscle dysfunction. What is the main finding and its importance? The CIH‐induced diaphragm muscle fatigue is time and intensity dependent and is associated with a modest oxidative stress. Supplementation with N‐acetyl cysteine prevents CIH‐induced diaphragm muscle dysfunction, suggesting that antioxidant supplementation may have therapeutic value in respiratory muscle disorders characterized by CIH, such as obstructive sleep apnoea.

Respiratory control and sternohyoid muscle structure and function in aged male rats: Decreased susceptibility to chronic intermittent hypoxia

Obstructive sleep apnoea syndrome (OSAS) is a common respiratory disorder characterized by chronic intermittent hypoxia (CIH). We have shown that CIH causes upper airway muscle dysfunction in the rat due to oxidative stress. Ageing is an independent risk factor for the development of OSAS perhaps due to respiratory muscle remodelling and increased susceptibility to hypoxia. We sought to examine the effects of CIH on breathing and pharyngeal dilator muscle structure and function in aged rats. Aged (18-20 months), male Wistar rats were exposed to alternating cycles of normoxia and hypoxia (90 s each; F(I)O(2)=5% O(2) at nadir) or sham treatment for 8h/day for 9 days. Following CIH exposure, breathing was assessed by whole-body plethysmography. In addition, sternohyoid muscle contractile and endurance properties were examined in vitro. Muscle fibre type and cross-sectional area, and the activity of key oxidative and glycolytic enzymes were determined. CIH had no effect on basal breathing or ventilatory responses to hypoxia or hypercapnia. CIH did not alter succinate dehydrogenase or glycerol phosphate dehydrogenase enzyme activities, myosin heavy chain fibre areal density or cross-sectional area. Sternohyoid muscle force and endurance were unaffected by CIH exposure. Since we have established that this CIH paradigm causes sternohyoid muscle weakness in adult male rats, we conclude that aged rats have decreased susceptibility to CIH-induced stress. We suggest that structural remodelling with improved hypoxic tolerance in upper airway muscles may partly compensate for impaired neural regulation of the upper airway and increased propensity for airway collapse in aged mammals.

Respiratory Control in the mdx Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a genetic disease caused by defects in the dystrophin gene resulting in loss of the structural protein dystrophin. Patients have reduced diaphragm functional capacity due to progressive muscle weakness. Respiratory morbidity in DMD is further characterised by hypoxaemic periods due to hypoventilation. DMD patients die prematurely due to respiratory and cardiac failure. In this study, we examined respiratory function in young adult male mdx (dystrophin deficient) mice (C57BL/10ScSn-Dmd(mdx)/J; n = 10) and in wild-type controls (WT; C57BL/10ScSnJ; n = 11). Breathing was assessed in unrestrained, unanaesthetised animals by whole-body plethysmography. Ventilatory parameters were recorded during air breathing and during exposure to acute hypoxia (F(i)O(2) = 0.1, 20 min). Data for the two groups of animals were compared using Students t tests. During normoxic breathing, mdx mice had reduced breathing frequency (p = 0.011), tidal volume (p = 0.093) and minute ventilation (p = 0.033) compared to WT. Hypoxia increased minute ventilation in WT and mdx animals. Mdx mice had a significantly increased ventilatory response to hypoxia which manifest as an elevated % change from baseline for minute ventilation (p = 0.0015) compared to WT. We conclude that mdx mice have impaired normoxic ventilation suggestive of hypoventilation. Furthermore, mdx mice have an enhanced hypoxic ventilatory response compared to WT animals which we speculate may be secondary to chronic hypoxaemia. Our results indicate that a significant respiratory phenotype is evident as early as 8 weeks in the mdx mouse model of DMD.

Biodistribution and pharmacokinetic studies of SPION using particle electron paramagnetic resonance, MRI and ICP-MS

AIM Superparamagnetic iron oxide nanoparticles (SPIONs) may play an important role in nanomedicine by serving as drug carriers and imaging agents. In this study, we present the biodistribution and pharmacokinetic properties of SPIONs using a new detection method, particle electron paramagnetic resonance (pEPR). MATERIALS & METHODS The pEPR technique is based on a low-field and low-frequency electron paramagnetic resonance. pEPR was compared with inductively coupled plasma mass spectrometry and MRI, in in vitro and in vivo. RESULTS The pEPR, inductively coupled plasma mass spectrometry and MRI results showed a good correlation between the techniques. CONCLUSION The results indicate that pEPR can be used to detect SPIONs in both preclinical and clinical studies.

Chronic Intermittent Hypoxia Alters Genioglossus Motor Unit Discharge Patterns in the Anaesthetized Rat

The respiratory control system is subject to diverse and considerable plasticity in health and disease. Intermittent hypoxia elicits expression of intrinsic plasticity within sensory and motor pathways involved in the control of breathing with potentially adaptive and maladaptive consequences for respiratory homeostasis. We and others have shown that chronic intermittent hypoxia (CIH) - a major feature of sleep-disordered breathing - has deleterious effects on rat upper airway dilator muscle contractile function and motor control. In the present study, we sought to test the hypothesis that CIH alters genioglossus (pharyngeal dilator) motor unit properties during basal breathing and obstructive airway events. Adult male Wistar rats were exposed to 20 cycles of normoxia and hypoxia (5% O(2) at nadir; SaO(2) ∼ 80%) per hour, 8 h a day for 7 days (CIH, N = 5). The sham group (N = 5) were subject to alternating cycles of air under identical experimental conditions in parallel. Following gas treatments, rats were anaesthetized with an i.p injection of urethane (1.5 g/kg; 20% w/v). Fine concentric needle electrodes were inserted into the genioglossus and the costal diaphragm. Genioglossus motor unit potentials, together with arterial blood pressure, tracheal pressure and arterial O(2) saturation were recorded during quiet basal breathing and nasal airway occlusion. During basal breathing, the amplitude of genioglossus motor units was significantly different in sham vs. CIH-treated rats (313 ± 32 μV vs. 430 ± 46 μV; mean ± SEM, Students t test, p = 0.0415). The most common instantaneous firing frequency of individual units determined from auto correlograms was also significantly different in the two groups (53 ± 6 Hz vs. 37 ± 3 Hz; sham vs. CIH p = 0.0318). In addition, the amplitude of motor units recruited during airway obstruction was significantly decreased in CIH-treated rats (939 ± 102 μV vs. 619 ± 75 μV; sham vs. CIH p = 0.0267). Our results indicate that CIH causes remodelling in the central respiratory motor network with potentially maladaptive consequences for the physiological control of upper airway patency. We conclude that CIH could serve to exacerbate and perpetuate obstructive events in patients with sleep-disordered breathing.

Responses of iliac conduit artery and hindlimb resistance vessels to luminal hyperfructosemia in the anaesthetized pig

High fructose levels are found in diabetes mellitus, associated with high corn syrup diets, and have been claimed to cause hypertension. As the direct effects on conduit and resistance arteries have not been previously reported, we measured these in vivo in the anaesthetized pig with instrumented iliac arteries.

Respiratory Plasticity in the Behaving Rat Following Chronic Intermittent Hypoxia

Chronic intermittent hypoxia (CIH), a feature of obstructive sleep apnoea (OSA) has been shown to have myriad effects on the respiratory control system. The effects on breathing are of great clinical significance for the sleep apnoea patient. We sought to determine the effect of CIH on normoxic ventilation. Both male and female adult Wistar rats were studied due to the evident sex difference in the prevalence of OSA. A role for oxidative stress in respiratory modifications was also explored. Adult male (n = 30) and female (n = 16) rats were exposed to alternating periods of N(2) and O(2) for 90 s each, bringing the ambient oxygen concentration to 5% at nadir (CIH) group. Sham groups were subject to cycles of air/air under identical experimental conditions. A subset of male rats (8 controls, 8 CIH) had free access to water containing 1 mM Tempol (SOD-mimetic) at all times. Treatments were carried out for 8 hours a day for 9 days. Following treatment, normoxic ventilation was assessed by whole body plethysmography in sleeping animals. Baseline normoxic ventilation was increased in both male and female treated rats but this did not achieve statistical significance. However, ventilatory drive (V(T)/Ti) was significantly increased in male rats. Chronic treatment with Tempol abolished this effect. Conversely, CIH had no significant effect on VT/Ti in female rats. Our results indicate subtle effects of intermittent hypoxia on breathing in conscious behaving rats. We speculate the increased ventilatory drive following CIH represents a form a neural plasticity - a ROS dependent phenomenon - with sexual dimorphism.

Effect of chronic intermittent hypoxia on the reflex recruitment of the genioglossus during airway obstruction in the anesthetized rat.

We sought to test the hypothesis that chronic intermittent hypoxia (CIH)-a feature of sleep-disordered breathing in humans-impairs reflex recruitment of the genioglossus (GG, pharyngeal dilator) during obstructive airway events. Adult male Wistar rats were exposed to 20 cycles of normoxia and hypoxia (5% O2 at nadir) per hour, 8h a day for 7 days (CIH, N=7). The sham group (N=7) were exposed to normoxia in parallel. Following gas treatments, rats were anesthetized with an i.p. injection of urethane (1.5g/kg; 20%, w/v). Fine concentric needle electrodes were inserted into the GG and the costal diaphragm. Discriminated GG motor unit potentials and whole electromyograph (EMG), together with arterial blood pressure and arterial O2 saturation, were recorded during quiet basal breathing and during nasal airway occlusion. Airway occlusion significantly increased GG EMG activity in all animals; but there was no difference in the reflex response to airway occlusion between sham and CIH-treated animals (+105±22% vs. +105±17%, mean±SEM for area under the curve of integrated GG EMG, % increase from baseline, p=0.99). Occluded breaths were characterized by a significant increase in the firing frequency of phasically active units and the recruitment of large motor units that were quiescent under basal conditions. Though there are reports of impaired control of the upper airway following CIH in the rat, we conclude that reflexly evoked motor discharge to the GG is not affected by 7 days of CIH, a paradigm that we have shown increases apnea index in sleeping rats.