Increased oxidative stress is associated with chronic intermittent hypoxia-mediated brain cortical neuronal cell apoptosis in a mouse model of sleep apnea

[Obstructive sleep apnea syndrome: a cause of cognitive disorders in the elderly?]

Obstructive sleep apnea syndrome is a chronic disease characterized by repeated upper airway obstructions during sleep, resulting in fragmented sleep with arousals, nocturnal intermittent hypoxemia and diurnal dysfunctions. Despite its high prevalence in elderly, sleep apnea syndrome seems to be underestimated and difficult to be recognized because of the lack of clinical symptoms specificity in this population. Among the numerous consequences of the obstructive sleep apnea syndrome, cognitive impairment prevails on the attention, executive functions and memory. Neuroimaging studies in human and experimental models allowed to highlight neural correlates of these cognitive dysfunctions in obstructive sleep apnea syndrome. The obstructive sleep apnea syndrome with cognitive impairment shares some features with Alzheimer's disease, involving genetic predisposition ApoE4, hippocampus and synaptic plasticity abnormalities. In this context, the question arises whether obstructive sleep apnea syndrome is a possible etiological or aggravating factor of cognitive decline in elderly with mild cognitive impairment or Alzheimer's disease. Although there are conflicting results in studies evaluating therapeutic efficiency of continuous positive air pressure, obstructive sleep apnea syndrome seems nevertheless as a correctable factor, at least for its impact on some cognitive consequences. Looking for sleep apnea syndrome in elderly with cognitive decline should be considered in a global, diagnosis and therapeutic management.

Chronic nitric oxide synthase inhibition does not impair upper airway muscle adaptation to chronic intermittent hypoxia in the rat

Nitric oxide (NO) is an important modulator of striated muscle function. Nitric oxide synthase (NOS) expression and activity is altered by hypoxia and NO is implicated in respiratory muscle remodeling following chronic sustained hypoxia. We sought to determine if NO is implicated in upper airway dilator muscle adaptation to chronic intermittent hypoxia (CIH). Thirty-two adult male Wistar rats (284±13, mean±SD) were exposed to alternating bouts of hypoxia (90 s; 5% O2 at the nadir) and normoxia (210 s; 21% O2) for 12 cycles per hour, 8h/day for 3 weeks. Sham animals were exposed to normoxia in parallel. Half of the animals in both groups received the nNOS inhibitor-L-NNA (2mM) in the drinking water throughout the study (N=8 for all groups). Sternohyoid (pharyngeal dilator) muscle contractile and endurance properties were determined ex vivo. Sternohyoid muscle myosin heavy chain (MHC) isoform composition and cross-sectional area was determined by fluorescence microscopy. Chronic nNOS blockade did not alter sternohyoid muscle peak force or force-frequency relationship in sham or CIH-treated animals. In contrast, chronic nNOS blockade significantly decreased sternohyoid muscle endurance with equivalent effects in sham and CIH-treated rats. Our results suggest that NO is an important modulator of sternohyoid muscle endurance. However, our data provide no evidence to suggest that NO is implicated in upper airway muscle adaptation to CIH.

Pathological consequences of intermittent hypoxia in the central nervous system

Intermittent hypoxia (IH) is a frequent occurrence in clinical settings. In the last decades, evidence has emerged implicating the gas exchange alterations and sleep disruption associated with those disorders in the high prevalence of cognitive and behavioral deficits afflicting these patients. In an effort to better characterize the role of IH, and to identify potential mechanisms of IH-induced central nervous system (CNS) dysfunction, a large number of rodent models have been recently developed. The cumulative evidence confirms that IH indeed induces a heterotopic pattern of injury in the brain, particularly affecting cortical, subcortical, and hippocampal regions, ultimately leading to neuronal apoptosis and activation of microglia. These IH-induced deleterious processes exhibit substantial variability across the lifespan, are under substantial modulatory influences of diet, physical or intellectual activity, and genetic factors, and preferentially recruit oxidative stress and inflammatory pathways.

Chronic intermittent hypoxia exerts CNS region-specific effects on rat microglial inflammatory and TLR4 gene expression

Intermittent hypoxia (IH) during sleep is a hallmark of sleep apnea, causing significant neuronal apoptosis, and cognitive and behavioral deficits in CNS regions underlying memory processing and executive functions. IH-induced neuroinflammation is thought to contribute to cognitive deficits after IH. In the present studies, we tested the hypothesis that IH would differentially induce inflammatory factor gene expression in microglia in a CNS region-dependent manner, and that the effects of IH would differ temporally. To test this hypothesis, adult rats were exposed to intermittent hypoxia (2 min intervals of 10.5% O₂) for 8 hours/day during their respective sleep cycles for 1, 3 or 14 days. Cortex, medulla and spinal cord tissues were dissected, microglia were immunomagnetically isolated and mRNA levels of the inflammatory genes iNOS, COX-2, TNFα, IL-1β and IL-6 and the innate immune receptor TLR4 were compared to levels in normoxia. Inflammatory gene expression was also assessed in tissue homogenates (containing all CNS cells). We found that microglia from different CNS regions responded to IH differently. Cortical microglia had longer lasting inflammatory gene expression whereas spinal microglial gene expression was rapid and transient. We also observed that inflammatory gene expression in microglia frequently differed from that in tissue homogenates from the same region, indicating that cells other than microglia also contribute to IH-induced neuroinflammation. Lastly, microglial TLR4 mRNA levels were strongly upregulated by IH in a region- and time-dependent manner, and the increase in TLR4 expression appeared to coincide with timing of peak inflammatory gene expression, suggesting that TLR4 may play a role in IH-induced neuroinflammation. Together, these data indicate that microglial-specific neuroinflammation may play distinct roles in the effects of intermittent hypoxia in different CNS regions.

Effect of continuous positive airway pressure on regional cerebral blood flow during wakefulness in obstructive sleep apnea

BACKGROUND

The alteration of regional cerebral blood flow (rCBF) during wakefulness after the treatment for obstructive sleep apnea syndrome (OSA) using continuous positive airway pressure (CPAP) has not been elucidated. The aim of this study was to investigate rCBF characteristics and the effects of nasal CPAP in OSA patients.

METHODS

Fifteen severe OSA patients (apnea-hypopnea index, 62.7 ± 22.4/h), when awake, underwent Technetium-99m ethyl cysteinate dimer single photon emission computed tomography before and after CPAP treatment, and the findings were compared to those of nine healthy controls matched for age and sex.

RESULTS

Compared to controls, patients with OSA before CPAP treatment showed a significantly lower rCBF in the frontal lobe. After the treatment, no difference in rCBF was observed between the good CPAP compliance group and the controls. In the former group, there was a positive correlation between the 3% oxygen desaturation index on diagnostic polysomnogram and the increase of rCBF after CPAP treatment in the frontal lobe.

CONCLUSIONS

When awake, patients with severe OSA were shown to have reversible decreases in rCBF, especially in the frontal lobe, and an appropriate CPAP treatment was thought to improve rCBF in this area. Our results support the importance of appropriate CPAP treatment for severe OSA patients.

Mitochondrial dysfunction in epilepsy

Epilepsy is the most common neurologic disorder worldwide and is characterized by recurrent unprovoked seizures. The mitochondrial (mt) respiratory chain is the final common pathway for cellular energy production through the process of oxidative phosphorylation. As neurons are terminally differentiated cells that lack significant regenerative capacity and have a high energy demand, they are more vulnerable to mt dysfunction. Therefore, epileptic seizures have been well described in several diseases such as mt encephalomyopathy, lactic acidosis, and stroke-like episodes and myoclonic epilepsy and ragged red fibers, which are caused by gene mutations in mtDNA, among others. Mutations in nuclear DNA regulating mt function are also being described (eg, POLG gene mutation). The role of mitochondria (mt) in acquired epilepsies, which account for about 60% of all epilepsies, is equally important but less well understood. Oxidative stress is one of the possible mechanisms in the pathogenesis of epilepsy resulting from mt dysfunction gradually disrupting the intracellular Ca(2+) homeostasis, which modulates neuronal excitability and synaptic transmission, making neurons more vulnerable to additional stress, and leading to energy failure and neuronal loss in epilepsy. Antiepileptic drugs (AEDs) also affect mt function in several ways. There must be caution when treating epilepsy in patients with known mt disorders as some AEDs are toxic to the mt. This review summarizes our current knowledge of the effect of mt disorders on epilepsy, of epileptic seizures on mt, and of AEDs on mt function and the implications of all these interactions for the management of epilepsy in patients with or without mt disease.

Chronic intermittent hypoxia promotes expression of 3-mercaptopyruvate sulfurtransferase in adult rat medulla oblongata

The present experiments were carried out to investigate the expression of 3-mercaptopyruvate sulfurtransferase (3MST) in medulla oblongata of rats and effects of chronic intermittent hypoxia (CIH) on its expression. Sprague Dawley adult rats were randomly divided into two groups, including control (Con) group and CIH group. The endogenous production of hydrogen sulfide (H2S) in medulla oblongata tissue homogenates was measured using the methylene blue assay method, 3MST mRNA and protein expression were analyzed by RT-PCR and Western blotting, respectively, and the expression of 3MST in the neurons of respiratory-related nuclei in medulla oblongata of rats was investigated with immunohistochemical technique. CIH elevated the endogenous H2S production in rat medulla oblongata (P<0.01). The RT-PCR and Western blotting analyses showed that 3MST mRNA and protein were expressed in the medulla oblongata of rats and CIH promoted their expression (P<0.01). Immunohistochemical staining indicated that 3MST existed in the neurons of pre-Bötzinger complex (pre-BötC), hypoglossal nucleus (12N), ambiguous nucleus (Amb), facial nucleus (FN) and nucleus tractus solitarius (NTS) in the animals and the mean optical densities of 3MST-positive neurons in the pre-BötC, 12N and Amb, but not in FN and NTS, were significantly increased in CIH group (P<0.05). In conclusion, 3MST exists in the neurons of medullary respiratory nuclei and its expression can be up-regulated by CIH in adult rat, suggesting that 3MST-H2S pathway may be involved in regulation of respiration and protection on medullary respiratory centers from injury induced by CIH.

Growth hormone releasing hormone (GHRH) signaling modulates intermittent hypoxia-induced oxidative stress and cognitive deficits in mouse

Intermittent hypoxia (IH) during sleep, such as occurs in obstructive sleep apnea (OSA), leads to degenerative changes in the hippocampus, and is associated with spatial learning deficits in adult mice. In both patients and murine models of OSA, the disease is associated with suppression of growth hormone (GH) secretion, which is actively involved in the growth, development, and function of the central nervous system (CNS). Recent work showed that exogenous GH therapy attenuated neurocognitive deficits elicited by IH during sleep in rats. Here, we show that administration of the Growth Hormone Releasing Hormone (GHRH) agonist JI-34 attenuates IH-induced neurocognitive deficits, anxiety, and depression in mice along with reduction in oxidative stress markers such as MDA and 8-hydroxydeoxyguanosine, and increases in hypoxia inducible factor-1α DNA binding and up-regulation of insulin growth factor-1 and erythropoietin expression. In contrast, treatment with a GHRH antagonist (MIA-602) during intermittent hypoxia did not affect any of the IH-induced deleterious effects in mice. Thus, exogenous GHRH administered as the formulation of a GHRH agonist may provide a viable therapeutic intervention to protect IH-vulnerable brain regions from OSA-associated neurocognitive dysfunction. Sleep apnea, characterized by chronic intermittent hypoxia (IH), is associated with substantial cognitive and behavioral deficits. Here, we show that administration of a GHRH agonist (JI-34) reduces oxidative stress, increases both HIF-1α nuclear binding and downstream expression of IGF1 and erythropoietin (EPO) in hippocampus and cortex, and markedly attenuates water maze performance deficits in mice exposed to intermittent hypoxia during sleep.

Circulating adhesion molecules in obstructive sleep apnea and cardiovascular disease

Over 20 years of evidence indicates a strong association between obstructive sleep apnea (OSA) and cardiovascular disease. Although inflammatory processes have been heavily implicated as an important link between the two, the mechanism for this has not been conclusively established. Atherosclerosis may be one of the mechanisms linking OSA to cardiovascular morbidity. This review addresses the role of circulating adhesion molecules in patients with OSA, and how these may be part of the link between cardiovascular disease and OSA. There is evidence for the role of adhesion molecules in cardiovascular disease risk. Some studies, albeit with small sample sizes, also show higher levels of adhesion molecules in patients with OSA compared to controls. There are also studies that show that levels of adhesion molecules diminish with continuous positive airway pressure therapy. Limitations of these studies include small sample sizes, cross-sectional sampling, and inconsistent control for confounding variables known to influence adhesion molecule levels. There are potential novel therapies to reduce circulating adhesion molecules in patients with OSA to diminish cardiovascular disease. Understanding the role of cell adhesion molecules generated in OSA will help elucidate one mechanistic link to cardiovascular disease in patients with OSA.

Chronic intermittent hypoxia aggravates intrahepatic endothelial dysfunction in cirrhotic rats

Chronic intermittent hypoxia (CIH) occurs with obstructive sleep apnea syndrome (OSAS) and provokes systemic endothelial dysfunction, which is associated with oxidative stress and low nitric oxide (NO) bioavailability. Cirrhotic livers exhibit intrahepatic endothelial dysfunction, which is characterized by an impaired endothelium-dependent response to vasodilators and hyperresponse to vasoconstrictors. We hypothesized that CIH may also contribute to intrahepatic endothelial dysfunction in cirrhosis. Normal and cirrhotic rats were exposed for 14 days to repetitive cycles of CIH mimicking OSAS in humans, or caged with room air (handled controls [HC]). Hepatic endothelial function was assessed in isolated and perfused rat livers by dose-response curves to acetylcholine (ACh) and methoxamine (Mtx). In a group of cirrhotic rats, in vivo systemic and hepatic hemodynamic parameters were evaluated at baseline and after volume expansion. In addition, liver samples were obtained to assess endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), NO bioavailability, and nitrotyrosinated proteins as a marker of oxidative stress. Cirrhotic rats exposed to CIH exhibited an attenuated vasodilatory response to ACh and hyperresponse to Mtx compared with HC rats. During volume expansion, similar portal pressure increases were observed in CIH and HC rats, although the mean arterial pressure increase was lower after CIH. These functional responses were associated with the presence of increased hepatic oxidative stress without changes in p-eNOS after CIH exposure. In normal rats, no hemodynamic changes were found.

CONCLUSION

CIH exacerbates intrahepatic endothelial dysfunction in cirrhotic rats, which is associated with increased oxidative stress that may reduce NO bioavailability. Clinical studies are needed to assess whether OSAS contributes to endothelial impairment in human patients with cirrhosis.

Death by a thousand cuts in Alzheimer's disease: hypoxia--the prodrome

A wide range of clinical consequences may be associated with obstructive sleep apnea (OSA) including systemic hypertension, cardiovascular disease, pulmonary hypertension, congestive heart failure, cerebrovascular disease, glucose intolerance, impotence, gastroesophageal reflux, and obesity, to name a few. Despite this, 82 % of men and 93 % of women with OSA remain undiagnosed. OSA affects many body systems, and induces major alterations in metabolic, autonomic, and cerebral functions. Typically, OSA is characterized by recurrent chronic intermittent hypoxia (CIH), hypercapnia, hypoventilation, sleep fragmentation, peripheral and central inflammation, cerebral hypoperfusion, and cerebral glucose hypometabolism. Upregulation of oxidative stress in OSA plays an important pathogenic role in the milieu of hypoxia-induced cerebral and cardiovascular dysfunctions. Strong evidence underscores that cerebral amyloidogenesis and tau phosphorylation--two cardinal features of Alzheimer's disease (AD), are triggered by hypoxia. Mice subjected to hypoxic conditions unambiguously demonstrated upregulation in cerebral amyloid plaque formation and tau phosphorylation, as well as memory deficit. Hypoxia triggers neuronal degeneration and axonal dysfunction in both cortex and brainstem. Consequently, neurocognitive impairment in apneic/hypoxic patients is attributable to a complex interplay between CIH and stimulation of several pathological trajectories. The framework presented here helps delineate the emergence and progression of cognitive decline, and may yield insight into AD neuropathogenesis. The global impact of CIH should provide a strong rationale for treating OSA and snoring clinically, in order to ameliorate neurocognitive impairment in aged/AD patients.

Protective action of tetramethylpyrazine on the medulla oblongata in rats with chronic hypoxia

Tetramethylpyrazine (TMP), one of the active ingredients of the Chinese herb Lingusticum Wallichii Frantchat (Chuan Xiong), plays an important role in neuroprotection. However, the protective effect of TMP on the medulla oblongata, the most important region of the brain for cardiovascular and respiratory control, during chronic hypoxia remains unclear. In this study, we examined the neuroprotective effect of TMP on the medulla oblongata after chronic hypoxic injury in rats. Male Sprague-Dawley rats were randomly divided into four groups: control group, TMP group, chronic hypoxia group, and chronic hypoxia+TMP group. Rats were exposed to hypoxia (10% (v/v) O₂) or normoxia for 6 h daily for 14 days. TMP (80 mg/kg) or vehicle (saline) was injected intraperitoneally 30 min before experimentation. Loss of neurons in the pre-Bötzinger complex, the nucleus ambiguus, the nucleus tractus solitarius, the hypoglossal nucleus and the facial nucleus were evaluated by Nissl staining. Superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were measured, and apoptosis was monitored using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) method. The level of Bcl-2 mRNA and Bax mRNA was quantitatively measured by RT-PCR analysis. TMP protected Nissl bodies of neurons from injury in all nuclei observed, and reduced the loss of neurons in the nucleus ambiguus, the nucleus tractus solitarius, and the hypoglossal nucleus in rats subjected to chronic hypoxia. TMP upregulated SOD activity and inhibited the increase in MDA content in the medulla oblongata of hypoxic rats. In addition, TMP decreased the rate of apoptosis index (the percentage of apoptotic cells against the total number of cells) in all medullary structures examined, excepting the nucleus ambiguus and inhibited the decrease in Bcl-2 mRNA levels in the medulla oblongata following hypoxia. Our findings indicate that TMP may protect the medullary structures that are involved in cardiovascular and respiratory control from injury induced by chronic hypoxia in rats via its anti-oxidant and anti-apoptotic effects.

Repetitive acute intermittent hypoxia increases expression of proteins associated with plasticity in the phrenic motor nucleus

Acute intermittent hypoxia (AIH) initiates plasticity in respiratory motor control, including phrenic long term facilitation (pLTF). Since pLTF is enhanced by preconditioning with repetitive exposure to AIH (rAIH), we hypothesized that a rAIH protocol consisting of 3 AIH exposures per week for 10 weeks (3×wAIH; AIH: 10, 5-min episodes of 10.5% O(2); 5-min normoxic intervals) would enhance expression of molecules that play key roles in pLTF within the phrenic motor nucleus. Immunohistochemical analyses revealed that 3×wAIH for 10 weeks increased serotonin terminal density in the C4 phrenic motor nucleus and serotonin 2A (5-HT(2A)) receptor expression in presumptive phrenic motor neurons. Immunoreactive brain derived neurotrophic factor (BDNF) and its high affinity receptor (TrkB) also increased following 3×wAIH. 3×wAIH also increased expression of another hypoxia-sensitive growth factor known to elicit phrenic motor facilitation, vascular endothelial growth factor (VEGF), and its receptor (VEGFR-2). Kinases "downstream" from TrkB and VEGFR-2 were up-regulated in or near presumptive phrenic motor neurons, including phosphorylated extracellular-signal regulated kinase (p-ERK) and protein kinase B (p-AKT). Thus, 3×wAIH up-regulates neurochemicals known to be associated with phrenic motor plasticity. Since 3×wAIH upregulates pro-plasticity molecules without evidence for CNS pathology, it may be a useful therapeutic tool in treating disorders that cause respiratory insufficiency, such as spinal injury or motor neuron disease.

In vivo screening to determine neurological hazards of nitrogen dioxide (NO2) using Wistar rats

NO(2) is a well-known indoor and outdoor pollutant that may cause adverse health problems. Recently, accumulating but extremely limited evidences show that NO(2) possibly express neurotoxicity and is responsible for various neurological disorders. In the present study, neurological hazard of NO(2) and possible mechanisms were determined in rat pallium following a repetitive inhalation exposure with various concentrations (5, 10 and 20mg/m(3)). After 7-day exposure (6h/day), observable adverse effects were induced encompassing decreased ratio of brain to body weight, mild brain pathology, increased neuronal apoptosis, altered antioxidants (Cu/Zn-SOD, Mn-SOD, GPx and NO) activity and increasing formation of PCO. NO(2) inhalation also induced augment of oncogenes (c-fos, c-jun) levels, and deregulation of apoptosis-related genes (p53, bax and bcl-2) expression. With all above data, the present report provided essential information for the characterization of the neurotoxic hazard of NO(2) and related mechanisms, which is required in response to the general concern about the vulnerability of the neurological system to it.

Exogenous erythropoietin administration attenuates intermittent hypoxia-induced cognitive deficits in a murine model of sleep apnea

Background

In rodents, exposure to intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), is associated with neurobehavioral impairments, increased apoptosis in the hippocampus and cortex, as well as increased oxidant stress and inflammation. Such findings are markedly attenuated in rodents exposed to sustained hypoxia 9SH) of similar magnitude. The hypoxia-sensitive gene erythropoietin (EPO) has emerged as a major endogenous neuroprotectant, and could be involved in IH-induced neuronal dysfunction.

Methods and Results

IH induced only transiently increased expression of EPO mRNA in hippocampus, which was continued in (SH)-exposed mice. IH, but not SH, adversely affected two forms of spatial learning in the water maze, and increased markers of oxidative stress. However, on a standard place training task, mice treated with exogenously administered EPO displayed normal learning, and were protected from the spatial learning deficits observed in vehicle-treated (C) littermates exposed to IH. Moreover, anxiety levels were increased in IH as compared to normoxia, while no changes in anxiety emerged in EPO-treated mice. Additionally, C mice, but not EPO-treated IH-exposed mice had significantly elevated levels of NADPH oxidase expression, as well as increased MDA and 8-OHDG levels in cortical and hippocampal lysates.

Conclusions

The oxidative stress responses and neurobehavioral impairments induced by IH during sleep are mediated, at least in part, by imbalances between EPO expression and increased NADPH oxidase activity, and thus pharmacological agents targeting EPO expression in CNS may provide a therapeutic strategy in sleep-disordered breathing.

Sleep apnea syndrome and cognition

Obstructive sleep apnea (OSA) is a sleep-related breathing disorder characterized by repetitive episodes of airflow cessation resulting in brief arousals and intermittent hypoxemia. Several studies have documented significant daytime cognitive and behavioral dysfunction that seems to extend beyond that associated with simple sleepiness and that persists in some patients after therapeutic intervention. A still unanswered question is whether cognitive symptoms in OSA are primarily a consequence of sleep fragmentation and hypoxemia, or whether they coexist independently from OSA. Moreover, very little is known about OSA effects on cognitive performances in the elderly in whom an increased prevalence of OSA is present. In this review we will consider recent reports in the association between sleep apnea and cognition, with specific interest in elderly subjects, in whom sleep disturbances and age-related cognitive decline naturally occur. This will allow us to elucidate the behavioral and cognitive functions in OSA patients and to gain insight into age differences in the cognitive impairment. Clinically, these outcomes will aid clinicians in the evaluation of diurnal consequences of OSA and the need to propose early treatment.

Human apolipoprotein E4 targeted replacement in mice reveals increased susceptibility to sleep disruption and intermittent hypoxia

Intermittent hypoxia (IH) and sleep fragmentation (SF) are major manifestations of sleep apnea, a frequent condition in aging humans. Sleep perturbations are frequent in Alzheimer's disease (AD) and may underlie the progression of disease. We hypothesized that acute short-term IH, SF, and their combination (IH+SF) may reveal unique susceptibility in sleep integrity in a murine model of AD. The effects of acute IH, SF, and IH+SF on sleep architecture, delta power, sleep latency, and core body temperature were assessed in adult male human ApoE4-targeted replacement mice (hApoE4) and wild-type (WT) controls. Slow wave sleep (SWS) was significantly reduced, and rapid eye movement (REM) sleep was almost abolished during acute exposure to IH alone and IH+SF for 6 h in hApoE4, with milder effects in WT controls. Decreased delta power during SWS did not show postexposure rebound in hApoE4 unlike WT controls. IH and IH+SF induced hypothermia, which was more prominent in hApoE4 than WT controls. Mice subjected to SF also showed sleep deficits but without hypothermia. hApoE4 mice, unlike WT controls, exhibited increased sleep propensity, especially following IH and IH+SF, suggesting limited ability for sleep recovery in hApoE4 mice. These findings substantiate the potential impact of IH and SF in modulating sleep architecture and sleep homeostasis including maintenance of body temperature. Furthermore, the increased susceptibility and limited recovery ability of hApoE4 mice to sleep apnea suggests that early recognition and treatment of the latter in AD patients may restrict the progression and clinical manifestations of this frequent neurodegenerative disorder.

Ginkgo biloba protects against intermittent hypoxia-induced memory deficits and hippocampal DNA damage in rats

The aim of the present study was to explore the potential protective effect of Ginkgo biloba extract (EGb 761) on intermittent hypoxia (IH)-induced memory deficits and oxidative stress in rats.

METHODS

The passive avoidance reflex (PAR) test was employed to assess the effect of concurrent EGb 761 treatment in different dose levels on the memory deficits that were induced by concurrent long-term exposure to IH (21 days). The levels of hippocampal malondialdehyde (MDA), nitric oxide (NO), and intracellular glutathione (GSH) and the activity of glutathione peroxidase (GSH-Px) were estimated. In addition, serum and hippocampal 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were assessed to study the effect of EGb 761 on hippocampal oxidative DNA damage induced by IH.

RESULTS

Exposure to long-term IH in rats induced marked memory impairment that was indicated by a significant decrease in the retention latency in the PAR test. This effect was accompanied by a significant increase in hippocampal oxidative stress and DNA damage. EGb 761 that was administered in either 50- or 100-mg/kg doses per day reversed IH-induced memory deficits, an effect that was accompanied by a significant decrease in hippocampal MDA and NO levels. The antioxidant defence (GSH and GSH-Px) that was depressed by IH was significantly reactivated by EGb 761. Furthermore, serum and hippocampal levels of 8-OHdG that were elevated by IH were significantly reduced.

CONCLUSIONS

EGb 761 can protect against IH-induced memory impairment, oxidative stress and neuronal DNA damage, possibly through multiple mechanisms involving its potential anti-oxidative effect.

Repetitive intermittent hypoxia induces respiratory and somatic motor recovery after chronic cervical spinal injury

Spinal injury disrupts connections between the brain and spinal cord, causing life-long paralysis. Most spinal injuries are incomplete, leaving spared neural pathways to motor neurons that initiate and coordinate movement. One therapeutic strategy to induce functional motor recovery is to harness plasticity in these spared neural pathways. Chronic intermittent hypoxia (CIH) (72 episodes per night, 7 nights) increases synaptic strength in crossed spinal synaptic pathways to phrenic motoneurons below a C2 spinal hemisection. However, CIH also causes morbidity (e.g., high blood pressure, hippocampal apoptosis), rendering it unsuitable as a therapeutic approach to chronic spinal injury. Less severe protocols of repetitive acute intermittent hypoxia may elicit plasticity without associated morbidity. Here we demonstrate that daily acute intermittent hypoxia (dAIH; 10 episodes per day, 7 d) induces motor plasticity in respiratory and nonrespiratory motor behaviors without evidence for associated morbidity. dAIH induces plasticity in spared, spinal pathways to respiratory and nonrespiratory motor neurons, improving respiratory and nonrespiratory (forelimb) motor function in rats with chronic cervical injuries. Functional improvements were persistent and were mirrored by neurochemical changes in proteins that contribute to respiratory motor plasticity after intermittent hypoxia (BDNF and TrkB) within both respiratory and nonrespiratory motor nuclei. Collectively, these studies demonstrate that repetitive acute intermittent hypoxia may be an effective and non-invasive means of improving function in multiple motor systems after chronic spinal injury.

Poly (ADP-ribose) polymerase plays an important role in intermittent hypoxia-induced cell death in rat cerebellar granule cells

Background

Episodic cessation of airflow during sleep in patients with sleep apnea syndrome results in intermittent hypoxia (IH). Our aim was to investigate the effects of IH on cerebellar granule cells and to identify the mechanism of IH-induced cell death.

Methods

Cerebellar granule cells were freshly prepared from neonatal Sprague-Dawley rats. IH was created by culturing the cerebellar granule cells in the incubators with oscillating O₂ concentration at 20% and 5% every 30 min for 1-4 days. The results of this study are based on image analysis using a confocal microscope and associated software. Cellular oxidative stress increased with increase in IH. In addition, the occurrence of cell death (apoptosis and necrosis) increased as the duration of IH increased, but decreased in the presence of an iron chelator (phenanthroline) or poly (ADP-ribose) polymerase (PARP) inhibitors [3-aminobenzamide (3-AB) and DPQ]. The fluorescence of caspase-3 remained the same regardless of the duration of IH, and Western blots did not detect activation of caspase-3. However, IH increased the ratio of apoptosis-inducing factor (AIF) translocation to the nucleus, while PARP inhibitors (3-AB) reduced this ratio.

Results

According to our findings, IH increased oxidative stress and subsequently leading to cell death. This effect was at least partially mediated by PARP activation, resulting in ATP depletion, calpain activation leading to AIF translocation to the nucleus.

Conclusions

We suggest that IH induces cell death in rat primary cerebellar granule cells by stimulating oxidative stress PARP-mediated calpain and AIF activation.

Natural plant products and extracts that reduce immunoexcitotoxicity-associated neurodegeneration and promote repair within the central nervous system

Our understanding of the pathophysiological and biochemical basis of a number of neurological disorders has increased enormously over the last three decades. Parallel with this growth of knowledge has been a clearer understanding of the mechanism by which a number of naturally occurring plant extracts, as well as whole plants, can affect these mechanisms so as to offer protection against injury and promote healing of neurological tissues. Curcumin, quercetin, green tea catechins, balcalein, and luteolin have been extensively studied, and they demonstrate important effects on cell signaling that go far beyond their antioxidant effects. Of particular interest is the effect of these compounds on immunoexcitotoxicity, which, the authors suggest, is a common mechanism in a number of neurological disorders. By suppressing or affecting microglial activation states as well as the excitotoxic cascade and inflammatory mediators, these compounds dramatically affect the pathophysiology of central nervous system disorders and promote the release and generation of neurotrophic factors essential for central nervous system healing. We discuss the various aspects of these processes and suggest future directions for study.

Pathogenesis of cognitive dysfunction in patients with obstructive sleep apnea: a hypothesis with emphasis on the nucleus tractus solitarius

OSA is characterized by the quintessential triad of intermittent apnea, hypoxia, and hypoxemia due to pharyngeal collapse. This paper highlights the upstream mechanisms that may trigger cognitive decline in OSA. Three interrelated steps underpin cognitive dysfunction in OSA patients. First, several risk factors upregulate peripheral inflammation; these crucial factors promote neuroinflammation, cerebrovascular endothelial dysfunction, and oxidative stress in OSA. Secondly, the neuroinflammation exerts negative impact globally on the CNS, and thirdly, important foci in the neocortex and brainstem are rendered inflamed and dysfunctional. A strong link is known to exist between neuroinflammation and neurodegeneration. A unique perspective delineated here underscores the importance of dysfunctional brainstem nuclei in etiopathogenesis of cognitive decline in OSA patients. Nucleus tractus solitarius (NTS) is the central integration hub for afferents from upper airway (somatosensory/gustatory), respiratory, gastrointestinal, cardiovascular (baroreceptor and chemoreceptor) and other systems. The NTS has an essential role in sympathetic and parasympathetic systems also; it projects to most key brain regions and modulates numerous physiological functions. Inflamed and dysfunctional NTS and other key brainstem nuclei may play a pivotal role in triggering memory and cognitive dysfunction in OSA. Attenuation of upstream factors and amelioration of the NTS dysfunction remain important challenges.

Dysfunctional nucleus tractus solitarius: its crucial role in promoting neuropathogenetic cascade of Alzheimer's dementia--a novel hypothesis

The pathophysiological mechanism(s) underlying Alzheimer's disease (AD) still remain unclear, and no disease-modifying or prophylactic therapies are currently available. Unraveling the fundamental neuropathogenesis of AD is an important challenge. Several studies on AD have suggested lesions in a number of CNS areas including the basal forebrain, hippocampus, entorhinal cortex, amygdale/insula, and the locus coeruleus. However, plausible unifying studies on the upstream factors that involve these heterogeneous regions and herald the onset of AD pathogenesis are not available. The current article presents a novel nucleus tractus solitarius (NTS) vector hypothesis that underpins several disparate biological mechanisms and neural circuits, and identifies relevant hallmarks of major presumptive causative factor(s) linked to the NTS, in older/aging individuals. Aging, obesity, infection, sleep apnea, smoking, neuropsychological states, and hypothermia-all activate inflammatory cytokines and oxidative stress. The synergistic impact of systemic proinflammatory mediators activates microglia and promotes neuroinflammation. Acutely, the innate immune response is protective defending against pathogens/toxins; however, when chronic, it causes neuroinflammation and neuronal dysfunction, particularly in brainstem and neocortex. The NTS in the brainstem is an essential multiple signaling hub, and an extremely important central integration site of baroreceptor, chemoreceptor, and a multitude of sensory afferents from gustatory, gastrointestinal, cardiac, pulmonary, and upper airway systems. Owing to persistent neuroinflammation, the dysfunctional NTS exerts deleterious impact on nucleus ambiguus, dorsal motor nucleus of vagus, hypoglossal, parabrachial, locus coeruleus and many key nuclei in the brainstem, and the hippocampus, entorhinal cortex, prefrontal cortex, amygdala, insula, and basal forebrain in the neocortex. The neuronal and synaptic dysfunction emanating from the inflamed NTS may affect its interconnected pathways impacting almost the entire CNS--which is already primed by neuroinflammation, thus promoting cognitive and neuropsychiatric symptoms. The upstream factors discussed here may underpin the neuropathopgenesis of AD. AD pathology is multifactorial; the current perspective underscores the value of attenuating disparate upstream factors--in conjunction with anticholinesterase, anti-inflammatory, immunosuppressive, and anti-oxidant pharmacotherapy. Amelioration of the NTS pathology may be of central importance in countering the neuropathological cascade of AD. The NTS, therefore, may be a potential target of novel therapeutic strategies.

Chronic intermittent hypoxia-induced deficits in synaptic plasticity and neurocognitive functions: a role for brain-derived neurotrophic factor

Obstructive sleep apnea (OSA) is well known for its metabolic as well as neurobehavioral consequences. Chronic intermittent hypoxia (IH) is a major component of OSA. In recent years, substantial advances have been made in elucidating the cellular and molecular mechanisms underlying the effect of chronic IH on neurocognitive functions, many of which are based on studies in animal models. A number of hypotheses have been put forward to explain chronic IH-induced neurological dysfunctions. Among these, the roles of oxidative stress and apoptosis-related neural injury are widely accepted. Here, focusing on results derived from animal studies, we highlight a possible role of reduced expression of brain-derived neurotrophic factor (BDNF) in causing impairment in long-term synaptic plasticity and neurocognitive functions during chronic IH. The possible relationship between BDNF and previous findings on this subject will be elucidated.

Neurocognitive impairment in Chinese patients with obstructive sleep apnoea hypopnoea syndrome

BACKGROUND AND OBJECTIVE

Sleep-disordered breathing is known to be associated with impairment in cognitive function. The aim of this study was to characterize neurocognitive impairment in a cohort of Chinese patients with varying severities of obstructive sleep apnoea hypopnoea syndrome (OSAHS), and to develop a sensitive instrument for routine screening of cognitive impairment.

METHODS

Eligible patients (n = 394) were categorized into a primary snoring group, and mild, moderate and severe OSAHS groups, based on assessment of AHI. The Montreal Cognitive Assessment (MoCA) and the Mini-Mental State Examination (MMSE) questionnaires were administered to assess cognitive function, and the correlations between questionnaire scores and clinical and polysomnographic parameters were further evaluated by stepwise multivariate regression.

RESULTS

MoCA scores decreased progressively across the spectrum from primary snoring to severe OSAHS. Importantly, mild neurocognitive impairment as defined by a MoCA score <26 was more common in the moderate (38.6%) and severe (41.4%) OSAHS groups than in the mild OSAHS (25.0%) and primary snoring (15.2%) groups. In contrast, MMSE scores were largely normal and comparable among all four groups. Evaluation of MoCA subdomains further revealed selective reduction in memory/delayed recall, visuospatial and executive function, and attention span in the severe OSAHS group compared with the other groups. Stepwise multivariate regression analysis demonstrated that MoCA scores correlated significantly with lowest oxygen saturation (L-SaO(2) ) and years of education.

CONCLUSIONS

Neurocognitive impairment is common in patients with OSAHS. The MoCA is a brief and sensitive tool for the assessment of cognitive impairment in OSAHS patients, whose performance on the MMSE is in the normal range.

Increased EID1 nuclear translocation impairs synaptic plasticity and memory function associated with pathogenesis of Alzheimer's disease

Though loss of function in CBP/p300, a family of CREB-binding proteins, has been causally associated with a variety of human neurological disorders, such as Rubinstein-Taybi syndrome, Huntington's disease and drug addiction, the role of EP300 interacting inhibitor of differentiation 1 (EID1), a CBP/p300 inhibitory protein, in modulating neurological functions remains completely unknown. Through the examination of EID1 expression and cellular distribution, we discovered that there is a significant increase of EID1 nuclear translocation in the cortical neurons of Alzheimer's disease (AD) patient brains compared to that of control brains. To study the potential effects of EID1 on neurological functions associated with learning and memory, we generated a transgenic mouse model with a neuron-specific expression of human EID1 gene in the brain. Overexpression of EID1 led to an increase in its nuclear localization in neurons mimicking that seen in human AD brains. The transgenic mice had a disrupted neurofilament organization and increase of astrogliosis in the cortex and hippocampus. Furthermore, we demonstrated that overexpression of EID1 reduced hippocampal long-term potentiation and impaired spatial learning and memory function in the transgenic mice. Our results indicated that the negative effects of extra nuclear EID1 in transgenic mouse brains are likely due to its inhibitory function on CBP/p300 mediated histone and p53 acetylation, thus affecting the expression of downstream genes involved in the maintenance of neuronal structure and function. Together, our data raise the possibility that alteration of EID1 expression, particularly the increase of EID1 nuclear localization that inhibits CBP/p300 activity in neuronal cells, may play an important role in AD pathogenesis.

Cardiovascular consequences of sleep apnea

Sleep apnea is a common health concern that is characterized by repetitive episodes of asphyxia. This condition has been linked to serious long-term adverse effects such as hypertension, metabolic dysregulation, and cardiovascular disease. Although the mechanism for the initiation and aggravation of cardiovascular disease has not been fully elucidated, oxidative stress and subsequent endothelial dysfunction play major roles. Animal models, which have the advantage of being free of comorbidities and/or behavioral variables (that commonly occur in humans), allow invasive measurements under well-controlled experimental conditions, and as such are useful tools in the study of the pathophysiological mechanisms of sleep apnea. This review summarizes currently available information on the cardiovascular consequences of sleep apnea and briefly describes common experimental approaches useful to sleep apnea in different animal models.

Mouse intermittent hypoxia mimicking apnoea of prematurity: effects on myelinogenesis and axonal maturation

Premature babies are at high risk for both infantile apnoea and long-term neurobehavioural deficits. Recent studies suggest that diffuse structural changes in brain white matter are a positive predictor of poor cognitive outcomes. Since oligodendrocyte maturation, myelination, axon development, and synapse formation mainly occur in the third trimester of gestation and first postnatal year, infantile apnoea could lead to and/or exaggerate white matter impairments in preterm neonates. Therefore, we investigated oligodendroglia and axon development in a neonatal mouse model of intermittent hypoxia between postnatal days 2 and 10. During critical phases of central nervous system development, intermittent hypoxia induced hypomyelination in the corpus callosum, striatum, fornix, and cerebellum, but not in the pons or spinal cord. Intermittent hypoxia-elicited alterations in myelin-forming processes were reflected by decreased expression of myelin proteins, including MBP, PLP, MAG, and CNPase, possibly due to arrested maturation of oligodendrocytes. Ultrastructural abnormalities were apparent in the myelin sheath and axon. Immature oligodendrocytes were more vulnerable to neonatal intermittent hypoxia exposures than developing axons, suggesting that hypomyelination may contribute, at least partially, to axonal deficits. Insufficient neurofilament synthesis with anomalous components of neurofilament subunits, β-tubulin, and MAP2 isoforms indicated immaturity of axons in intermittent hypoxia-exposed mouse brains. In addition, down-regulation of synapsin I, synaptophysin, and Gap-43 phosphorylation suggested a potential stunt in axonogenesis and synaptogenesis. The region-selective and complex impairment in brain white matter induced by intermittent hypoxia was further associated with electrophysiological changes that may underlie long-term neurobehavioural sequelae.

Systemic inflammation impairs respiratory chemoreflexes and plasticity

Many lung and central nervous system disorders require robust and appropriate physiological responses to assure adequate breathing. Factors undermining the efficacy of ventilatory control will diminish the ability to compensate for pathology, threatening life itself. Although most of these same disorders are associated with systemic and/or neuroinflammation, and inflammation affects neural function, we are only beginning to understand interactions between inflammation and any aspect of ventilatory control (e.g. sensory receptors, rhythm generation, chemoreflexes, plasticity). Here we review available evidence, and present limited new data suggesting that systemic (or neural) inflammation impairs two key elements of ventilatory control: chemoreflexes and respiratory motor (versus sensory) plasticity. Achieving an understanding of mechanisms whereby inflammation undermines ventilatory control is fundamental since inflammation may diminish the capacity for natural, compensatory responses during pathological states, and the ability to harness respiratory plasticity as a therapeutic strategy in the treatment of devastating breathing disorders, such as during cervical spinal injury or motor neuron disease.

Inflammatory pathways in children with insufficient or disordered sleep

Sleep is not only an essential physiological function, but also serves important roles in promoting growth, maturation, and overall health of children and adolescents. There is increasing interest regarding the impact of sleep and its disorders on the regulation of inflammatory processes and end-organ morbidities, particularly in the context of metabolic and cardiovascular diseases (CVD) and their complications. Obstructive sleep apnea syndrome (OSAS) is an increasingly common health problem in children, and in the last decade, the emergence of increasing obesity rates has further led to remarkable increases in the prevalence of OSAS, along with more prominent neurocognitive, behavioral, cardiovascular and metabolic morbidities. Although the underlying mechanisms leading to OSAS-induced morbidities are likely multi-factorial, and remain to be fully elucidated, activation of inflammatory pathways by OSAS has emerged as an important pathophysiological component of the end-organ injury associated with this disorder. To this effect, it would appear that OSAS could be viewed as a chronic, low-grade inflammatory disorder. Furthermore, the concurrent presence of obesity and OSAS poses a theoretically increased risk of OSAS-related complications. In this review, we will critically review the current state of research regarding the impact of insufficient and disrupted sleep and OSAS on the immune processes and inflammatory pathways that underlie childhood OSAS as a distinctive systemic inflammatory condition in children, and will explore potential interactions between OSAS and obesity.

Losartan abolishes oxidative stress induced by intermittent hypoxia in humans

The aim of this study was to assess the role of the type 1 angiotensin II (AT(1)) receptor in the increase of oxidative stress and NO metabolism during a single 6 h exposure to intermittent hypoxia (IH). Nine healthy young men were exposed, while awake, to sham IH, IH with placebo medication, and IH with the AT(1) receptor antagonist, losartan, using a double-blind, placebo-controlled, randomized, crossover study design. In addition to blood pressure, oxidative stress, peroxynitrite activity, uric acid, global antioxidant status and the end-products of NO (NOx) metabolism were measured in plasma before and after 6 h of IH. Oxidative stress and peroxynitrite activity increased and NOx decreased during IH with placebo. In contrast, neither sham IH nor IH with losartan affected these parameters. With respect to each condition, blood pressure had the same profile as oxidative stress. These results demonstrate that blockade of AT(1) receptors prevented the increase in oxidative stress and peroxynitrite activity and the decrease in NO metabolism induced by IH. Finally, this study suggests that the renin-angiotensin system may participate in the overproduction of reactive oxygen species associated with IH by upregulation of the actions of angiotensin II.

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.

Intermittent hypoxia after transient focal ischemia induces hippocampal neurogenesis and c-Fos expression and reverses spatial memory deficits in rats

BACKGROUND

Memory impairment is a frequent complication of brain ischemia. Neurogenesis is implicated in learning and memory and is regulated by the transcription factor c-Fos. Preconditioning intermittent hypoxia (IH) attenuates ischemia-related memory impairments, but it is not known whether post-ischemia IH intervention has a similar effect. We investigated the effects of post-ischemia IH on hippocampal neurogenesis and c-Fos expression as well as spatial learning and memory in rats.

METHODOLOGY/PRINCIPAL FINDINGS

Focal cerebral ischemia was induced in some rats by middle cerebral artery occlusion (MCAO), while other rats received sham MCAO surgery. Beginning a week later, half of the rats of each group received IH interventions (12% oxygen concentration, 4 hrs/d, for 7 d) and half received sham IH sessions. An additional group of rats received MCAO, IH, and injections of the neurogenesis-impairing agent 3'-AZT. Spatial learning and memory was measured in the Morris water maze, and hippocampal neurogenesis and c-Fos expression were examined. Hypoxia-inducible factor 1α (HIF-1α) and phosphorylated mitogen-activated protein kinase (pMAPK) were considered as possible mediators of IH-induced changes in neurogenesis and c-Fos expression. IH intervention following MCAO resulted in recovered spatial memory, increased hippocampal neurogenesis, and increased expression of c-Fos in newborn hippocampal cells. These effects were blocked by 3'-AZT. IH intervention following MCAO also was associated with increased hippocampal pMAPK and HIF-1α expression.

CONCLUSIONS/SIGNIFICANCE

IH intervention following MCAO rescued ischemia-induced spatial learning and memory impairments, likely by inducing hippocampal neurogenesis and c-Fos expression through mediators including pMAPK and HIF-1α.

Exogenous growth hormone attenuates cognitive deficits induced by intermittent hypoxia in rats

Sleep disordered breathing (SDB), which is characterized by intermittent hypoxia (IH) during sleep, causes substantial cardiovascular and neurocognitive complications and has become a growing public health problem. SDB is associated with suppression of growth hormone (GH) secretion, the latter being integrally involved in the growth, development, and function of the CNS. Since GH treatment is able to attenuate neurocognitive deficits in a hypoxic-ischemic stroke model, GH, GH receptor (GHR) mRNA expression, and GH protein expression were assessed in rat hippocampus after exposures to chronic sustained hypoxia (CH, 10% O(2)) or IH (10% O(2) alternating with 21% O(2) every 90 s). In addition, the effect of GH treatment (50 μg/kg daily s.c. injection) on erythropoietin (EPO), vascular endothelial growth factor (VEGF), heme oxygenase-1 (HO-1), and GLUT-1 mRNA expression and neurobehavioral function was assessed. CH significantly increased GH mRNA and protein expression, as well as insulin-like growth factor-1 (IGF-1). In contrast, IH only induced a moderate increase in GH mRNA and a slight elevation in GH protein at day 1, but no increases in IGF-1. CH, but not IH, up-regulated GHR mRNA in the hippocampus. IH induced marked neurocognitive deficits compared with CH or room air (RA). Furthermore, exogenous GH administration increased hippocampal mRNA expression of IGF-1, EPO, and VEGF, and not only reduced IH-induced hippocampal injury, but also attenuated IH-induced cognitive deficits. Thus, exogenous GH may provide a viable therapeutic intervention to protect IH-vulnerable brain regions from SDB-associated neuronal loss and associated neurocognitive dysfunction.

The cognitive cost of sleep lost

A substantial body of literature supports the intuitive notion that a good night's sleep can facilitate human cognitive performance the next day. Deficits in attention, learning & memory, emotional reactivity, and higher-order cognitive processes, such as executive function and decision making, have all been documented following sleep disruption in humans. Thus, whilst numerous clinical and experimental studies link human sleep disturbance to cognitive deficits, attempts to develop valid and reliable rodent models of these phenomena are fewer, and relatively more recent. This review focuses primarily on the cognitive impairments produced by sleep disruption in rodent models of several human patterns of sleep loss/sleep disturbance. Though not an exclusive list, this review will focus on four specific types of sleep disturbance: total sleep deprivation, experimental sleep fragmentation, selective REM sleep deprivation, and chronic sleep restriction. The use of rodent models can provide greater opportunities to understand the neurobiological changes underlying sleep loss induced cognitive impairments. Thus, this review concludes with a description of recent neurobiological findings concerning the neuroplastic changes and putative brain mechanisms that may underlie the cognitive deficits produced by sleep disturbances.

Xanthine oxidase inhibition attenuates endothelial dysfunction caused by chronic intermittent hypoxia in rats

BACKGROUND

Xanthine oxidase is a major source of superoxide in the vascular endothelium. Previous work in humans demonstrated improved conduit artery function following xanthine oxidase inhibition in patients with obstructive sleep apnea.

OBJECTIVES

To determine whether impairments in endothelium-dependent vasodilation produced by exposure to chronic intermittent hypoxia are prevented by in vivo treatment with allopurinol, a xanthine oxidase inhibitor.

METHODS

Sprague-Dawley rats received allopurinol (65 mg/kg/day) or vehicle via oral gavage. Half of each group was exposed to intermittent hypoxia (FIO(2) = 0.10 for 1 min, 15×/h, 12 h/day) and the other half to normoxia. After 14 days, gracilis arteries were isolated, cannulated with micropipettes, and perfused and superfused with physiological salt solution. Diameters were measured before and after exposure to acetylcholine (10(-6)M) and nitroprusside (10(-4)M).

RESULTS

In vehicle-treated rats, intermittent hypoxia impaired acetylcholine-induced vasodilation compared to normoxia (+4 ± 4 vs. +21 ± 6 μm, p = 0.01). Allopurinol attenuated this impairment (+26 ± 6 vs. +34 ± 9 μm for intermittent hypoxia and normoxia groups treated with allopurinol, p = 0.55). In contrast, nitroprusside-induced vasodilation was similar in all rats (p = 0.43). Neither allopurinol nor intermittent hypoxia affected vessel morphometry or systemic markers of oxidative stress. Urinary uric acid concentrations were reduced in allopurinol- versus vehicle-treated rats (p = 0.02).

CONCLUSIONS

These data confirm previous findings that exposure to intermittent hypoxia impairs endothelium-dependent vasodilation in skeletal muscle resistance arteries and extend them by demonstrating that this impairment can be prevented with allopurinol. Thus, xanthine oxidase appears to play a key role in mediating intermittent hypoxia-induced vascular dysfunction.

Tissue oxygenation in brain, muscle, and fat in a rat model of sleep apnea: differential effect of obstructive apneas and intermittent hypoxia

STUDY OBJECTIVES

To test the hypotheses that the dynamic changes in brain oxygen partial pressure (PtO(2)) in response to obstructive apneas or to intermittent hypoxia differ from those in other organs and that the changes in brain PtO(2) in response to obstructive apneas is a source of oxidative stress.

DESIGN

Prospective controlled animal study.

SETTING

University laboratory.

PARTICIPANTS

98 Sprague-Dawley rats.

INTERVENTIONS

Cerebral cortex, skeletal muscle, or visceral fat tissues were exposed in anesthetized animals subjected to either obstructive apneas or intermittent hypoxia (apneic and hypoxic events of 15 s each and 60 events/h) for 1 h.

MEASUREMENTS AND RESULTS

Arterial oxygen saturation (SpO(2)) presented a stable pattern, with similar desaturations during both stimuli. The PtO(2) was measured by a microelectrode. During obstructive apneas, a fast increase in cerebral PtO(2) was observed (38.2 ± 3.4 vs. 54.8 ± 5.9 mm Hg) but not in the rest of tissues. This particular cerebral response was not found during intermittent hypoxia. The cerebral content of reduced glutathione was decreased after obstructive apneas (46.2% ± 15.2%) compared to controls (100.0% ± 14.7%), but not after intermittent hypoxia. This antioxidant consumption after obstructive apneas was accompanied by increased cerebral lipid peroxidation under this condition. No changes were observed for these markers in the other tissues.

CONCLUSIONS

These results suggest that cerebral cortex could be protected in some way from hypoxic periods caused by obstructive apneas. The increased cerebral PtO(2) during obstructive apneas may, however, cause harmful effects (oxidative stress). The obstructive apnea model appears to be more adequate than the intermittent hypoxia model for studying brain changes associated with OSA.

Regulation of oxidative stress and cardioprotection in diabetes mellitus

Analysis of the Framingham data has shown that the risk of heart failure is increased substantially among diabetic patients, while persons with the metabolic syndrome have an increased risk of both atherosclerosis and diabetes mellitus. Sleep apnea may be related to the metabolic syndrome and systemic inflammation through hypoxia, which might also cause the cardiac remodeling by increased oxidative stress. On the other hand, the renin-angiotensin system is activated in diabetes, and local angiotensin II production may lead to oxidative damage via the angiotensin II type 1 receptor. Basic and clinical data indicate that angiotensin II receptor blockers have the potential to preserve left ventricular function and prevent cardiac remodeling that is exaggerated by oxidative stress in patients with diabetes. Thus, alleviation of oxidative stress might be one possible strategy in the treatment of diabetic patients associated with sleep apnea.

Inhalation of hydrogen gas attenuates left ventricular remodeling induced by intermittent hypoxia in mice

Sleep apnea syndrome increases the risk of cardiovascular morbidity and mortality. We previously reported that intermittent hypoxia increases superoxide production in a manner dependent on nicotinamide adenine dinucleotide phosphate and accelerates adverse left ventricular (LV) remodeling. Recent studies have suggested that hydrogen (H(2)) may have an antioxidant effect by reducing hydroxyl radicals. In this study, we investigated the effects of H(2) gas inhalation on lipid metabolism and LV remodeling induced by intermittent hypoxia in mice. Male C57BL/6J mice (n = 62) were exposed to intermittent hypoxia (repetitive cycle of 1-min periods of 5 and 21% oxygen for 8 h during daytime) for 7 days. H(2) gas (1.3 vol/100 vol) was given either at the time of reoxygenation, during hypoxic conditions, or throughout the experimental period. Mice kept under normoxic conditions served as controls (n = 13). Intermittent hypoxia significantly increased plasma levels of low- and very low-density cholesterol and the amount of 4-hydroxy-2-nonenal-modified protein adducts in the LV myocardium. It also upregulated mRNA expression of tissue necrosis factor-α, interleukin-6, and brain natriuretic peptide, increased production of superoxide, and induced cardiomyocyte hypertrophy, nuclear deformity, mitochondrial degeneration, and interstitial fibrosis. H(2) gas inhalation significantly suppressed these changes induced by intermittent hypoxia. In particular, H(2) gas inhaled at the timing of reoxygenation or throughout the experiment was effective in preventing dyslipidemia and suppressing superoxide production in the LV myocardium. These results suggest that inhalation of H(2) gas was effective for reducing oxidative stress and preventing LV remodeling induced by intermittent hypoxia relevant to sleep apnea.

Intermittent hypoxia-induced cognitive deficits are mediated by NADPH oxidase activity in a murine model of sleep apnea

BACKGROUND

In rodents, exposure to intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), is associated with neurobehavioral impairments, increased apoptosis in the hippocampus and cortex, as well as increased oxidant stress and inflammation. Excessive NADPH oxidase activity may play a role in IH-induced CNS dysfunction.

METHODS AND FINDINGS

The effect of IH during light period on two forms of spatial learning in the water maze and well as markers of oxidative stress was assessed in mice lacking NADPH oxidase activity (gp91phox(_/Y)) and wild-type littermates. On a standard place training task, gp91phox(_/Y) displayed normal learning, and were protected from the spatial learning deficits observed in wild-type littermates exposed to IH. Moreover, anxiety levels were increased in wild-type mice exposed to IH as compared to room air (RA) controls, while no changes emerged in gp91phox(_/Y) mice. Additionally, wild-type mice, but not gp91phox(_/Y) mice had significantly elevated levels of NADPH oxidase expression and activity, as well as MDA and 8-OHDG in cortical and hippocampal lysates following IH exposures.

CONCLUSIONS

The oxidative stress responses and neurobehavioral impairments induced by IH during sleep are mediated, at least in part, by excessive NADPH oxidase activity, and thus pharmacological agents targeting NADPH oxidase may provide a therapeutic strategy in sleep-disordered breathing.

Decreased GABAB receptor function in the cerebellum and brain stem of hypoxic neonatal rats: role of glucose, oxygen and epinephrine resuscitation

Background-

Hypoxia during the first week of life can induce neuronal death in vulnerable brain regions usually associated with an impairment of cognitive function that can be detected later in life. The neurobiological changes mediated through neurotransmitters and other signaling molecules associated with neonatal hypoxia are an important aspect in establishing a proper neonatal care.

Methods-

The present study evaluated total GABA, GABA_B receptor alterations, gene expression changes in GABA_B receptor and glutamate decarboxylase in the cerebellum and brain stem of hypoxic neonatal rats and the resuscitation groups with glucose, oxygen and epinephrine. Radiolabelled GABA and baclofen were used for receptor studies of GABA and GABA_B receptors respectively and Real Time PCR analysis using specific probes for GABA_B receptor and GAD mRNA was done for gene expression studies.

Results-

The adaptive response of the body to hypoxic stress resulted in a reduction in total GABA and GABA_B receptors along with decreased GABA_B receptor and GAD gene expression in the cerebellum and brain stem. Hypoxic rats supplemented with glucose alone and with oxygen showed a reversal of the receptor alterations and changes in GAD. Resuscitation with oxygen alone and epinephrine was less effective in reversing the receptor alterations.

Conclusions-

Being a source of immediate energy, glucose can reduce the ATP-depletion-induced changes in GABA and oxygenation, which helps in encountering hypoxia. The present study suggests that reduction in the GABA_B receptors functional regulation during hypoxia plays an important role in central nervous system damage. Resuscitation with glucose alone and glucose and oxygen to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Pro-apoptotic activity of inhibitory PAS domain protein (IPAS), a negative regulator of HIF-1, through binding to pro-survival Bcl-2 family proteins

Inhibitory PAS (Per/Arnt/Sim) domain protein (IPAS) is a dominant negative transcription factor that represses hypoxia-inducible factor 1 (HIF-1) activity. In this study, we show that IPAS also functions as a pro-apoptotic protein through binding to pro-survival Bcl-2 family members. In a previous paper, we reported that NF-κB-dependent IPAS induction by cobalt chloride repressed the hypoxic response in PC12 cells. We found that prolonged incubation under the same conditions caused apoptosis in PC12 cells. Repression of IPAS induction protected cells from apoptosis. Furthermore, knockdown of IPAS recovered cell viability. EGFP-IPAS protein was localized in both the nucleus and the cytoplasm, with a large fraction associated with mitochondria. Mitochondrial IPAS induced mitochondria depolarization and caspase-3 activation. Immunoprecipitation assays revealed that IPAS is associated with Bcl-x(L), Bcl-w and Mcl-1. The association of IPAS with Bcl-x(L) was also observed in living cells by the FLIM-based FRET analysis, indicating direct binding between the two proteins. IPAS contributed to dysfunction of Bcl-x(L) by inhibiting the interaction of Bcl-x(L) with Bax. These results demonstrate that IPAS functions as a dual function protein involved in transcription repression and apoptosis.

Serotonin 2A and 2B receptor-induced phrenic motor facilitation: differential requirement for spinal NADPH oxidase activity

Acute intermittent hypoxia (AIH) facilitates phrenic motor output by a mechanism that requires spinal serotonin (type 2) receptor activation, NADPH oxidase activity and formation of reactive oxygen species (ROS). Episodic spinal serotonin (5-HT) receptor activation alone, without changes in oxygenation, is sufficient to elicit NADPH oxidase-dependent phrenic motor facilitation (pMF). Here we investigated: (1) whether serotonin 2A and/or 2B (5-HT2A/B) receptors are expressed in identified phrenic motor neurons, and (2) which receptor subtype is capable of eliciting NADPH-oxidase-dependent pMF. In anesthetized, artificially ventilated adult rats, episodic C4 intrathecal injections (3×6 μl injections, 5 min intervals) of a 5-HT2A (DOI) or 5-HT2B (BW723C86) receptor agonist elicited progressive and sustained increases in integrated phrenic nerve burst amplitude (i.e. pMF), an effect lasting at least 90 min post-injection for both receptor subtypes. 5-HT2A and 5-HT2B receptor agonist-induced pMF were both blocked by selective antagonists (ketanserin and SB206553, respectively), but not by antagonists to the other receptor subtype. Single injections of either agonist failed to elicit pMF, demonstrating a need for episodic receptor activation. Phrenic motor neurons retrogradely labeled with cholera toxin B fragment expressed both 5-HT2A and 5-HT2B receptors. Pre-treatment with NADPH oxidase inhibitors (apocynin and diphenylenodium (DPI)) blocked 5-HT2B, but not 5-HT2A-induced pMF. Thus, multiple spinal type 2 serotonin receptors elicit pMF, but they act via distinct mechanisms that differ in their requirement for NADPH oxidase activity.

Mechanisms of vascular damage in obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by repetitive apnea-hypopnea cycles during sleep, which are associated with oxygen desaturation and sleep disruption. Up to 30% of the adult population in Western countries are thought to be affected by asymptomatic OSA and approximately 2-4% by symptomatic OSA (also known as obstructive sleep apnea syndrome, or OSAS). Controlled trials have demonstrated that OSAS causes hypertension and prospective epidemiological studies have indicated that OSAS might be an independent risk factor for stroke and myocardial ischemia. Three biological mechanisms are thought to underpin the association of OSA with endothelial dysfunction and arterial disease: intermittent hypoxia leading to increased oxidative stress, systemic inflammation, and sympathetic activity; intrathoracic pressure changes leading to excessive mechanical stress on the heart and large artery walls; and arousal-induced reflex sympathetic activation with resultant repetitive blood-pressure rises. More clinical interventional trials are needed to determine the magnitude of the effect OSA has on cardiovascular damage and to enable a comparison with conventional vascular risk factors.