Protective effects of intermittent hypoxia on brain and memory in a mouse model of apnea of prematurity

Differential expression of genes in the RhoA/ROCK pathway in the hippocampus and cortex following intermittent hypoxia and high-intensity interval training

Structural neuroplasticity such as neurite extension and dendritic spine dynamics is enhanced by brain-derived neurotrophic factor (BDNF) and impaired by types of inhibitory molecules that induce growth cone collapse and actin depolymerization, for example, myelin-associated inhibitors, chondroitin sulfate proteoglycans, and negative guidance molecules. These inhibitory molecules can activate RhoA/rho-associated coiled-coil containing protein kinase (ROCK) signaling (known to restrict structural plasticity). Intermittent hypoxia (IH) and high-intensity interval training (HIIT) are known to upregulate BDNF that is associated with improvements in learning and memory and greater functional recovery following neural insults. We investigated whether the RhoA/ROCK signaling pathway is also modulated by IH and HIIT in the hippocampus, cortex, and lumbar spinal cord of male Wistar rats. The gene expression of 25 RhoA/ROCK signaling pathway components was determined following IH, HIIT, or IH combined with HIIT (30 min/day, 5 days/wk, 6 wk). IH included 10 3-min bouts that alternated between hypoxia (15% O2) and normoxia. HIIT included 10 3-min bouts alternating between treadmill speeds of 50 cm·s-1 and 15 cm·s-1. In the hippocampus, IH and HIIT significantly downregulated Acan and NgR2 mRNA that are involved in the inhibition of neuroplasticity. However, IH and IH + HIIT significantly upregulated Lingo-1 and NgR3 in the cortex. This is the first time IH and HIIT have been linked to the modulation of plasticity-inhibiting pathways. These results provide a fundamental step toward elucidating the interplay between the neurotrophic and inhibitory mechanisms involved in experience-driven neural plasticity that will aid in optimizing physiological interventions for the treatment of cognitive decline or neurorehabilitation.NEW & NOTEWORTHY Intermittent hypoxia (IH) and high-intensity interval training (HIIT) enhance neuroplasticity and upregulate neurotrophic factors in the central nervous system (CNS). We provide evidence that IH and IH + HIIT also have the capacity to regulate genes involved in the RhoA/ROCK signaling pathway that is known to restrict structural plasticity in the CNS. This provides a new mechanistic insight into how these interventions may enhance hippocampal-related plasticity and facilitate learning, memory, and neuroregeneration.

Neurogenesis, A Potential Target for Intermittent Hypoxia Leading to Cognitive Decline

As a sleep breathing disorder, characterized by intermittent hypoxia (IH) and Obstructive sleep apnea (OSA), is believed to decrease the cognitive function of patients. Many factors are thought to be responsible for cognitive decline in OSA patients. Neurogenesis, a process by which neural stem cells (NSCs) differentiate into new neurons in the brain, is a major determinant affecting cognitive function. However, there is no clear relationship between IH or OSA and neurogenesis. In recent years, increasing numbers of studies on IH and neurogenesis are documented. Therefore, this review summarizes the effects of IH on neurogenesis; then discusses the influencing factors that may cause these effects and the potential signaling pathways that may exist. Finally, based on this impact, we discuss potential methods and future directions for improving cognition.

Does Perinatal Intermittent Hypoxia Affect Cerebrovascular Network Development?

Perinatal hypoxia is an inadequate delivery of oxygen to the fetus in the period immediately before, during, or after the birth process. The most frequent form of hypoxia occurring in human development is chronic intermittent hypoxia (CIH) due to sleep-disordered breathing (apnea) or bradycardia events. CIH incidence is particularly high with premature infants. During CIH, repetitive cycles of hypoxia and reoxygenation initiate oxidative stress and inflammatory cascades in the brain. A dense microvascular network of arterioles, capillaries, and venules is required to support the constant metabolic demands of the adult brain. The development and refinement of this microvasculature is orchestrated throughout gestation and in the initial weeks after birth, at a critical juncture when CIH can occur. There is little knowledge on how CIH affects the development of the cerebrovasculature. However, since CIH (and its treatments) can cause profound abnormalities in tissue oxygen content and neural activity, there is reason to believe that it can induce lasting abnormalities in vascular structure and function at the microvascular level contributing to neurodevelopmental disorders. This mini-review discusses the hypothesis that CIH induces a positive feedback loop to perpetuate metabolic insufficiency through derailment of normal cerebrovascular development, leading to long-term deficiencies in cerebrovascular function.

Honokiol improves depression-like behaviors in rats by HIF-1α- VEGF signaling pathway activation

Increasing evidence indicates that the pathogenesis of depression is closely linked to impairments in neuronal synaptic plasticity. Honokiol, a biologically active substance extracted from Magnolia Officinalis, has been proven to exert significant antidepressant effects. However, the specific mechanism of action remains unclear. In this study, PC12 cells and chronic unpredictable mild stress (CUMS) model rats were used to explore the antidepressant effects and potential mechanisms of honokiol in vitro and in rats. In vitro experiment, a cell viability detection kit was used to screen the concentration and time of honokiol administration. PC12 cells were administered with hypoxia-inducible factor-1α (HIF-1α) blocker, 2-methoxyestradiol (2-ME), and vascular endothelial growth factor receptor 2 (VEGFR-2) blocker, SU5416, to detect the expression of HIF-1α, VEGF, synaptic protein 1 (SYN 1), and postsynaptic density protein 95 (PSD 95) by western blotting. In effect, we investigated whether the synaptic plasticity action of honokiol was dependent on the HIF-1α-VEGF pathway. In vivo, behavioral tests were used to evaluate the reproducibility of the CUMS depression model and depression-like behaviors. Molecular biology techniques were used to examine mRNA and protein expression of the HIF-1α-VEGF signaling pathway and synaptic plasticity-related regulators. Additionally, molecular docking techniques were used to study the interaction between honokiol and target proteins, and predict their binding patterns and affinities. Experimental results showed that honokiol significantly reversed CUMS-induced depression-like behaviors. Mechanically, honokiol exerted a significant antidepressant effect by enhancing synaptic plasticity. At the molecular level, honokiol can activate the HIF-1α-VEGF signaling pathway in vitro and in vivo, as well as promote the protein expression levels of SYN 1 and PSD 95. Taken together, the results do not only provide an experimental basis for honokiol in the clinical treatment of depression but also suggest that the HIF-1α-VEGF pathway may be a potential target for the treatment of depression.

Neurobehavioral morbidity of pediatric mild sleep-disordered breathing and obstructive sleep apnea

STUDY OBJECTIVES

Obstructive sleep apnea is associated with neurobehavioral dysfunction, but the relationship between disease severity as measured by the apnea-hypopnea index and neurobehavioral morbidity is unclear. The objective of our study is to compare the neurobehavioral morbidity of mild sleep-disordered breathing versus obstructive sleep apnea.

METHODS

Children 3-12 years old recruited for mild sleep-disordered breathing (snoring with obstructive apnea-hypopnea index < 3) into the Pediatric Adenotonsillectomy Trial for Snoring were compared to children 5-9 years old recruited for obstructive sleep apnea (obstructive apnea-hypopnea 2-30) into the Childhood Adenotonsillectomy Trial. Baseline demographic, polysomnographic, and neurobehavioral outcomes were compared using univariable and multivariable analysis.

RESULTS

The sample included 453 participants with obstructive sleep apnea (median obstructive apnea-hypopnea index 5.7) and 459 participants with mild sleep-disordered breathing (median obstructive apnea-hypopnea index 0.5). By polysomnography, participants with obstructive sleep apnea had poorer sleep efficiency and more arousals. Children with mild sleep-disordered breathing had more abnormal executive function scores (adjusted odds ratio 1.96, 95% CI 1.30-2.94) compared to children with obstructive sleep apnea. There were also elevated Conners scores for inattention (adjusted odds ratio 3.16, CI 1.98-5.02) and hyperactivity (adjusted odds ratio 2.82, CI 1.83-4.34) in children recruited for mild sleep-disordered breathing.

CONCLUSIONS

Abnormal executive function, inattention, and hyperactivity were more common in symptomatic children recruited into a trial for mild sleep-disordered breathing compared to children recruited into a trial for obstructive sleep apnea. Young, snoring children with only minimally elevated apnea-hypopnea levels may still be at risk for deficits in executive function and attention.

TRIAL REGISTRATION

Pediatric Adenotonsillectomy for Snoring (PATS), NCT02562040; Childhood Adenotonsillectomy Trial (CHAT), NCT00560859.

Effects of early life adversities upon memory processes and cognition in rodent models

Exposure to stressors in early postnatal life induces long-lasting modifications in brainfunction.Thisplasticity,an essential characteristic of the brain that enables adaptation to the environment, may also induce impairments in some psychophysiological functions, including learning and memory. Early life stress (ELS) has long-term effects on thehypothalamic-pituitary-adrenal axisresponse to stressors, and has been reported to lead toneuroinflammation,altered levelsof neurotrophic factors, modifications inneurogenesis andsynaptic plasticity,with changes in neurotransmitter systems and network functioning. In this review, we focus on early postnatal stress in animal models and their effects on learning and memory.Many studies have reported ELS-induced impairments in different types of memories, including spatial memory, fear memory, recognition (both for objects and social) memory, working memory and reversal learning. Studies are not always in agreement, however, no effects, or sometimes facilitation, being reported, depending on the nature and intensity of the early intervention, as well as the age when the outcome was evaluated and the sex of the animals. When considering processes occurring after consolidation, related with memory maintenance or modification, there are a very reduced number of reports. Future studies addressing the mechanisms underlying memory changes for ELS should shed some light on the understanding of the different effects induced by stressors of different types and intensities on cognitive functions.

Behavioral and brain morphological analysis of non-inflammatory and inflammatory rat models of preterm brain injury

Investigations using preclinical models of preterm birth have much contributed, together with human neuropathological studies, for advances in our understanding of preterm brain injury. Here, we evaluated whether the neurodevelopmental and behavioral consequences of preterm birth induced by a non-inflammatory model of preterm birth using mifepristone would differ from those after inflammatory prenatal transient hypoxia-ischemia (TSHI) model. Pregnant Wistar rats were either injected with mifepristone, and pups were delivered on embryonic day 21 (ED21 group), or laparotomized on the 18th day of gestation for 60 min of uterine arteries occlusion. Rat pups were tested postnatally for characterization of developmental milestones and, after weaning, they were behaviorally tested for anxiety and for spatial learning and memory. One month later, brains were processed for quantification of doublecortin (DCX)- and neuropeptide Y (NPY)-immunoreactive cells, and cholinergic varicosities in the hippocampus. ED21 rats did not differ from controls with respect to neonatal developmental milestones, anxiety, learning and memory functions, and neurochemical parameters. Conversely, in TSHI rats the development of neonatal reflexes was delayed, the levels of anxiety were reduced, and spatial learning and memory was impaired; in the hippocampus, the total number of DCX and NPY cells was increased, and the density of cholinergic varicosities was reduced. With these results we suggest that a preterm birth, in a non-inflammatory prenatal environment, does not significantly change neonatal development and adult neurologic outcome. On other hand, prenatal hypoxia and ischemia (inflammation) modifies developmental trajectory, learning and memory, neurogenesis, and NPY GABAergic and cholinergic brain systems.

Repeated episodes of transient reduction of oxygen exposure simulating aircraft cabin conditions enhance resilience to stress in mice

Pilots and crew of domestic flights are exposed to transient periods of mild reductions of partial pressure of inspired oxygen each day, and this might have functional consequence on their performance in the long range. Here, we exposed mice to mild reductions of oxygen exposure (ROE) four times per day for 21 days by lowering oxygen partial pressure to levels corresponding to an altitude of about 2300 m, which is the quote of pressurization of the air cabin. Four groups of mice were studied: unstressed or stressed mice exposed to ROE or normoxic conditions. Mice were exposed to chronic unpredictable stress (CUS) for 28 days, and ROE was delivered in the last 21 days of CUS. In normoxic mice, CUS caused anhedonia in the sucrose preference test, anxiety-like behaviour in the open field test, learning impairment in the Morris water maze, reduced hippocampal neurogenesis, increased serum corticosterone levels and increased expression of depression-related genes (Pclo, Mthfr and Grm5) in the hippocampus. All these changes were reversed by ROE, which had little or no effect in unstressed mice. These findings suggest that ROE simulating air cabin conditions of domestic flights may enhance resilience to stress improving mood, anxiety and learning ability.

Stage-dependent effects of intermittent hypoxia influence the outcome of hippocampal adult neurogenesis

Over one billion adults worldwide are estimated to suffer from sleep apnea, a condition with wide-reaching effects on brain health. Sleep apnea causes cognitive decline and is a risk factor for neurodegenerative conditions such as Alzheimer’s disease. Rodents exposed to intermittent hypoxia (IH), a hallmark of sleep apnea, exhibit spatial memory deficits associated with impaired hippocampal neurophysiology and dysregulated adult neurogenesis. We demonstrate that IH creates a pro-oxidant condition that reduces the Tbr2⁺ neural progenitor pool early in the process, while also suppressing terminal differentiation of adult born neurons during late adult neurogenesis. We further show that IH-dependent cell-autonomous hypoxia inducible factor 1-alpha (HIF1a) signaling is activated in early neuroprogenitors and enhances the generation of adult born neurons upon termination of IH. Our findings indicate that oscillations in oxygen homeostasis, such as those found in sleep apnea, have complex stage-dependent influence over hippocampal adult neurogenesis.

Chronic Intermittent Hypobaric Hypoxia Restores Hippocampus Function and Rescues Cognitive Impairments in Chronic Epileptic Rats via Wnt/β-catenin Signaling

Epilepsy is a complex neurological disorder with frequent psychiatric, cognitive, and social comorbidities in addition to recurrent seizures. Cognitive impairment, one of the most common comorbidities, has severe adverse effects on quality of life. Chronic intermittent hypobaric hypoxia (CIHH) has demonstrated neuroprotective efficacy in several neurological disease models. In the present study, we examined the effects of CIHH on cognition and hippocampal function in chronic epileptic rats. CIHH treatment rescued deficits in spatial and object memory, hippocampal neurogenesis, and synaptic plasticity in pilocarpine-treated epileptic rats. The Wnt/β-catenin pathway has been implicated in neural stem cell proliferation and synapse development, and Wnt/β-catenin pathway inhibition effectively blocked the neurogenic effects of CIHH. Our findings indicate that CIHH rescues cognitive deficits in epileptic rats via Wnt/β-catenin pathway activation. This study establishes CIHH and Wnt/β-catenin pathway regulators as potential treatments for epilepsy- induced cognitive impairments.

Animal models for neonatal brain injury induced by hypoxic ischemic conditions in rodents

Neonatal hypoxia-ischemia and resulting encephalopathies are of significant concern. Intrapartum asphyxia is a leading cause of neonatal death globally. Among surviving infants, there remains a high incidence of hypoxic-ischemic encephalopathy due to neonatal hypoxic-ischemic brain injury, manifesting as mild conditions including attention deficit hyperactivity disorder, and debilitating disorders such as cerebral palsy. Various animal models of neonatal hypoxic brain injury have been implemented to explore cellular and molecular mechanisms, assess the potential of novel therapeutic strategies, and characterize the functional and behavioural correlates of injury. Each of the animal models has individual advantages and limitations. The present review looks at several widely-used and alternative rodent models of neonatal hypoxia and hypoxia-ischemia; it highlights their strengths and limitations, and their potential for continued and improved use.

Intermittent hypoxia enhances shear-mediated dilation of the internal carotid artery in young adults

We explored the effects of cyclic intermittent hypoxia (IH) on shear-mediated dilation of the internal carotid artery (ICA), a potential index of cerebral endothelial function, in young adults. Cyclic IH increased blood flow and shear rate in the ICA and, as a result, increased shear-mediated dilation of the ICA. These data suggest that cyclic IH could potentially be applied as a nonpharmacological therapy to optimize cerebral vascular health.

Potential beneficial effects of caffeine administration in the neonatal period of an animal model of schizophrenia

Obstetric complications, like maternal hypertension and neonatal hypoxia, disrupt brain development, leading to psychiatry disorders later in life, like schizophrenia. The exact mechanisms behind this risk are not yet well known. Spontaneously hypertensive rats (SHR) are a well-established model to study neurodevelopment of schizophrenia since they exhibit behavioral alterations mimicking schizophrenia that can be improved with antipsychotic drugs. SHR mothers are hypertensive, and the SHR offspring develop in preeclampsia-like conditions. Hypoxic conditions increase levels of adenosine, which play an important role in brain development. The enhanced levels of adenosine at birth could be related to the future development of schizophrenia. To investigate this hypothesis adenosine levels of brain neonatal Wistar rats and SHR were quantified. After that, caffeine, an antagonist of adenosinergic system, was administrated on PND (postnatal day) 7 (neurodevelopmental age similar to a human at delivery) and rats were observed at adolescent and adult ages. We also investigated the acute effects of caffeine at adolescent and adult ages. SHR control adolescent and adult groups presented behavioral deficits like hyperlocomotion, deficit in social interaction (SI), and contextual fear conditioning (CFC). In SHR, neonatal caffeine treatment on PND 7 normalized hyperlocomotion, improved SI, and CFC observed at adolescent period and adult ages, showing a beneficial effect on schizophrenia-like behaviors. Wistar rats neonatally treated with caffeine exhibited hyperlocomotion, deficit in SI and CFC when observed at adolescent and adult ages. Acutely caffeine treatment administrated at adolescent and adult ages increased locomotion and decreased SI time of Wistar rats and impair CFC in adult Wistars. No effects were observed in SHR. In conclusion, caffeine can be suggested as a useful drug to prevent behavioral deficits observed in this animal model of prenatal hypoxia-induced schizophrenia profile when specifically administered on PND 7.

FG-4592 Improves Depressive-Like Behaviors through HIF-1-Mediated Neurogenesis and Synapse Plasticity in Rats

Depression, plus the accompanying memory impairment, is one of the leading causes of disability worldwide. Thus, there is a critical need to develop new drugs based on distinct strategies. FG-4592, an inhibitor of prolyl hydroxylase, activates the hypoxia-inducible factor-1 (HIF-1) pathway, to produce multiple effects on cell properties. Here, we examined whether FG-4592 has antidepressant effects, using a chronic unpredictable mild stress (CUMS) procedure to establish rodent depression models. We found that FG-4592 not only reversed depressive behaviors but also improved CUMS-induced memory impairment. Mechanistically, FG-4592 could play an important role in promoting hippocampal neurogenesis and synaptic plasticity. At the molecular level, FG-4592 was found to activate HIF-1 and cAMP-responsive element-binding protein/brain-derived neurotrophic factor signaling pathways in vivo, as well as promote the expression of postsynaptic density (PSD) proteins, PSD95 and Homer1. An examination of primary hippocampal neurons showed that FG-4592 promoted dendritic growth. Taken together, our results not only provide an experimental basis for the future application of FG-4592 in clinical treatment of depression but also support the argument that the HIF-1 signaling pathway is a promising target for the treatment of depression.

Altered prepulse inhibition of the acoustic startle response in BDNF-deficient mice in a model of early postnatal hypoxia: implications for schizophrenia

The brain-derived neurotrophic factor (BDNF) is a major proliferative agent in the nervous system. Both BDNF-deficiency and perinatal hypoxia represent genetic/environmental risk factors for schizophrenia. Moreover, a decreased BDNF response to birth hypoxia was associated with the disease. BDNF expression is influenced by neuronal activity and environmental conditions such as hypoxia. Thus, it may partake in neuroprotective and reparative mechanisms in acute or chronic neuronal insults. However, the interaction of hypoxia and BDNF is insufficiently understood and the behavioral outcome unknown. Therefore, we conducted a battery of behavioral tests in a classical model of chronic early postnatal mild hypoxia (10% O₂), known to significantly impair brain development, in BDNF-deficient mice. We found selective deficits in measures associated with sensorimotor gating, namely enhanced acoustic startle response (ASR) and reduced prepulse inhibition (PPI) of ASR in BDNF-deficient mice. Unexpectedly, the alterations of sensorimotor gating were caused only by BDNF-deficiency alone, whereas hypoxia failed to evoke severe deficits and even leads to a milder phenotype in BDNF-deficient mice. As deficits in sensorimotor gating are present in schizophrenia and animal models of the disease, our results are of relevance regarding the involvement of BDNF in its pathogenesis. On the other hand, they suggest that the effect of perinatal hypoxia on long-term brain abnormalities is complex, ranging from protective to deleterious actions, and may critically depend on the degree of hypoxia. Therefore, future studies may refine existing hypoxia protocols to better understand neurodevelopmental consequences associated with schizophrenia.

Immediate and delayed decrease of long term potentiation and memory deficits after neonatal intermittent hypoxia

Apnea of prematurity is a common clinical condition that occurs in premature infants and results in intermittent hypoxia (IH) to brain and other organs. While short episodes of apnea are considered of no clinical significance, prolonged apnea with bradycardia and large oxygen desaturation is associated with adverse neurological and cognitive outcome. The mechanisms of cognitive deficits in IH are poorly understood. We hypothesized that brief but multiple episodes of severe oxygen desaturation accompanied by bradycardia may affect early and late synaptic plasticity and produce long-term cognitive deficits. C57BL/6 mouse pups were exposed to IH paradigm consisting of alternating cycles of 5% oxygen for 2.5 min and room air for 5-10 min, 2 h a day from P3 to P7. Long term potentiation (LTP) of synaptic strength in response to high frequency stimulation in hippocampal slices were examined 3 days and 6 weeks after IH. LTP was decreased in IH group relative to controls at both time points. That decrease was associated with deficits in spatial memory on Morris water maze and context fear conditioning test. Hypomyelination was observed in multiple gray and white matter areas on in vivo MRI using micromolecule proton fraction and ex vivo diffusion tensor imaging. No difference in caspase labeling was found between control and IH groups. We conclude that early changes in synaptic plasticity occurring during severe episodes of neonatal IH and persisting to adulthood may represent functional and structural substrate for long term cognitive deficits.

Low Cerebral Oxygenation in Preterm Infants Is Associated with Adverse Neurodevelopmental Outcome

OBJECTIVE

To assess whether high and low levels of cerebral oxygenation (regional cerebral oxygenation [rScO₂]) in infants born at <32 weeks of gestation were associated with adverse long-term outcome.

STUDY DESIGN

Observational cohort study including preterm infants born at <32 weeks of gestation at the Wilhelmina Children's Hospital, The Netherlands, between April 2006 and April 2013. The rScO₂ was continuously monitored for 72 hours after birth using near-infrared spectroscopy. Outcome was assessed at 15 and 24 months of corrected age by certified investigators. An unfavorable composite outcome was defined as an outcome score below -1 SD or death. Various rScO₂ thresholds were explored.

RESULTS

In total, 734 infants were eligible for analysis, 60 of whom died. Associations with an unfavorable cognitive outcome in multivariable analysis were comparable for time spent with a rScO₂ below 55% and -1.5 SD (according to published reference values), with an OR of 1.4 (CI 1.1-1.7) for 20% of time below either threshold. Results at 15 months were comparable with results at 24 months. Results were not statistically significant for thresholds defining high values of rScO₂. The composite motor outcome was not significantly related to either low or high values or rScO₂.

CONCLUSIONS

Low, but not high, rScO₂ was associated with an unfavorable cognitive outcome. This suggests the use of a threshold of rScO₂ <55% for future clinical studies when using adult near-infrared sensors (rScO₂ <65% for neonatal sensors, approximately).

Intermittent Hypoxia Activates Duration-Dependent Protective and Injurious Mechanisms in Mouse Lung Endothelial Cells

Intermittent hypoxia is a major factor in clinical conditions like the obstructive sleep apnea syndrome or the cyclic recruitment and derecruitment of atelectasis in acute respiratory distress syndrome and positive pressure mechanical ventilation. In vivo investigations of the direct impact of intermittent hypoxia are frequently hampered by multiple co-morbidities of patients. Therefore, cell culture experiments are important model systems to elucidate molecular mechanisms that are involved in the cellular response to alternating oxygen conditions and could represent future targets for tailored therapies. In this study, we focused on mouse lung endothelial cells as a first frontier to encounter altered oxygen due to disturbances in airway or lung function, that play an important role in the development of secondary diseases like vascular disease and pulmonary hypertension. We analyzed key markers for endothelial function including cell adhesion molecules, molecules involved in regulation of fibrinolysis, hemostasis, redox balance, and regulators of gene expression like miRNAs. Results show that short-time exposure to intermittent hypoxia has little impact on vitality and health of cells. At early timepoints and up to 24 h, many endothelial markers are unchanged in their expression and some indicators of injury are even downregulated. However, in the long-term, multiple signaling pathways are activated, that ultimately result in cellular inflammation, oxidative stress, and apoptosis.

Intermittent living; the use of ancient challenges as a vaccine against the deleterious effects of modern life - A hypothesis

Chronic non-communicable diseases (CNCD) are the leading cause of mortality in developed countries. They ensue from the sum of modern anthropogenic risk factors, including high calorie nutrition, malnutrition, sedentary lifestyle, social stress, environmental toxins, politics and economic factors. Many of these factors are beyond the span of control of individuals, suggesting that CNCD are inevitable. However, various studies, ours included, show that the use of intermittent challenges with hormetic effects improve subjective and objective wellbeing of individuals with CNCD, while having favourable effects on immunological, metabolic and behavioural indices. Intermittent cold, heat, fasting and hypoxia, together with phytochemicals in multiple food products, have widespread influence on many pathways related with overall health. Until recently, most of the employed challenges with hormetic effects belonged to the usual transient live experiences of our ancestors. Our hypothesis; we conclude that, whereas the total inflammatory load of multi-metabolic and psychological risk factors causes low grade inflammation and aging, the use of intermittent challenges, united in a 7-10 days lasting hormetic intervention, might serve as a vaccine against the deleterious effects of chronic low grade inflammation and it's metabolic and (premature) aging consequences.

Physiological and Biological Responses to Short-Term Intermittent Hypobaric Hypoxia Exposure: From Sports and Mountain Medicine to New Biomedical Applications

In recent years, the altitude acclimatization responses elicited by short-term intermittent exposure to hypoxia have been subject to renewed attention. The main goal of short-term intermittent hypobaric hypoxia exposure programs was originally to improve the aerobic capacity of athletes or to accelerate the altitude acclimatization response in alpinists, since such programs induce an increase in erythrocyte mass. Several model programs of intermittent exposure to hypoxia have presented efficiency with respect to this goal, without any of the inconveniences or negative consequences associated with permanent stays at moderate or high altitudes. Artificial intermittent exposure to normobaric hypoxia systems have seen a rapid rise in popularity among recreational and professional athletes, not only due to their unbeatable cost/efficiency ratio, but also because they help prevent common inconveniences associated with high-altitude stays such as social isolation, nutritional limitations, and other minor health and comfort-related annoyances. Today, intermittent exposure to hypobaric hypoxia is known to elicit other physiological response types in several organs and body systems. These responses range from alterations in the ventilatory pattern to modulation of the mitochondrial function. The central role played by hypoxia-inducible factor (HIF) in activating a signaling molecular cascade after hypoxia exposure is well known. Among these targets, several growth factors that upregulate the capillary bed by inducing angiogenesis and promoting oxidative metabolism merit special attention. Applying intermittent hypobaric hypoxia to promote the action of some molecules, such as angiogenic factors, could improve repair and recovery in many tissue types. This article uses a comprehensive approach to examine data obtained in recent years. We consider evidence collected from different tissues, including myocardial capillarization, skeletal muscle fiber types and fiber size changes induced by intermittent hypoxia exposure, and discuss the evidence that points to beneficial interventions in applied fields such as sport science. Short-term intermittent hypoxia may not only be useful for healthy people, but could also be considered a promising tool to be applied, with due caution, to some pathophysiological states.

Perinatal Hypoxia and Ischemia in Animal Models of Schizophrenia

Intrauterine or perinatal complications constitute a major risk for psychiatric diseases. Infants who suffered from hypoxia-ischemia (HI) are at twofold risk to develop schizophrenia in later life. Several animal models attempt to reproduce these complications to study the yet unknown steps between an insult in early life and outbreak of the disease decades later. However, it is very challenging to find the right type and severity of insult leading to a disease-like phenotype in the animal, but not causing necrosis and focal neurological deficits. By contrast, too mild, repetitive insults may even be protective via conditioning effects. Thus, it is not surprising that animal models of hypoxia lead to mixed results. To achieve clinically translatable findings, better protocols are urgently needed. Therefore, we compare widely used models of hypoxia and HI and propose future directions for the field.

Transient Hypoxemia Chronically Disrupts Maturation of Preterm Fetal Ovine Subplate Neuron Arborization and Activity

Preterm infants are at risk for a broad spectrum of neurobehavioral disabilities associated with diffuse disturbances in cortical growth and development. During brain development, subplate neurons (SPNs) are a largely transient population that serves a critical role to establish functional cortical circuits. By dynamically integrating into developing cortical circuits, they assist in consolidation of intracortical and extracortical circuits. Although SPNs reside in close proximity to cerebral white matter, which is particularly vulnerable to oxidative stress, the susceptibility of SPNs remains controversial. We determined SPN responses to two common insults to the preterm brain: hypoxia-ischemia and hypoxia. We used a preterm fetal sheep model using both sexes that reproduces the spectrum of human cerebral injury and abnormal cortical growth. Unlike oligodendrocyte progenitors, SPNs displayed pronounced resistance to early or delayed cell death from hypoxia or hypoxia-ischemia. We thus explored an alternative hypothesis that these insults alter the maturational trajectory of SPNs. We used DiOlistic labeling to visualize the dendrites of SPNs selectively labeled for complexin-3. SPNs displayed reduced basal dendritic arbor complexity that was accompanied by chronic disturbances in SPN excitability and synaptic activity. SPN dysmaturation was significantly associated with the level of fetal hypoxemia and metabolic stress. Hence, despite the resistance of SPNs to insults that trigger white matter injury, transient hypoxemia disrupted SPN arborization and functional maturation during a critical window in cortical development. Strategies directed at limiting the duration or severity of hypoxemia during brain development may mitigate disturbances in cerebral growth and maturation related to SPN dysmaturation.SIGNIFICANCE STATEMENT The human preterm brain commonly sustains blood flow and oxygenation disturbances that impair cerebral cortex growth and cause life-long cognitive and learning disabilities. We investigated the fate of subplate neurons (SPNs), which are a master regulator of brain development that plays critical roles in establishing cortical connections to other brain regions. We used a preterm fetal sheep model that reproduces key features of brain injury in human preterm survivors. We analyzed the responses of fetal SPNs to transient disturbances in fetal oxygenation. We discovered that SPNs are surprisingly resistant to cell death from low oxygen states but acquire chronic structural and functional changes that suggest new strategies to prevent learning problems in children and adults that survive preterm birth.

Newborn blood gas derangements of children born extremely preterm and neurocognitive dysfunctions at age 10 years

Among 740 children born extremely preterm, we evaluated the relationship between the highest and lowest quartiles of the distributions of PaO₂ and PaCO₂, as well as the lowest quartile of pH on one day, and separately on two days, and the risk of neurocognitive, language, and behavioral dysfunctions at age 10 years. Children who had hypoxemia, hyperoxemia, hypocapnia, hypercapnia, and acidemia, sometimes on only one day, and sometimes on two or more days, were more likely than others to have a high illness severity score (within the first 12 postnatal hours), and 10 years later to have multiple dysfunctions. The tendency of blood gas derangements to be associated with high illness severity scores and with multiple dysfunctions 10 years later is compatible with the possibility that blood gas derangements are indicators of physiologic instability/vulnerability/immaturity rather than contributors to brain damage.

An overview of maternal separation effects on behavioural outcomes in mice: Evidence from a four-stage methodological systematic review

Early life stress (ELS) developmental effects have been widely studied by preclinical researchers. Despite the growing body of evidence from ELS models, such as the maternal separation paradigm, the reported results have marked inconsistencies. The maternal separation model has several methodological pitfalls that could influence the reliability of its results. Here, we critically review 94 mice studies that addressed the effects of maternal separation on behavioural outcomes. We also discuss methodological issues related to the heterogeneity of separation protocols and the quality of reporting methods. Our findings indicate a lack of consistency in maternal separation effects: major studies of behavioural and biological phenotypes failed to find significant deleterious effects. Furthermore, we identified several specific variations in separation methodological procedures. These methodological variations could contribute to the inconsistency of maternal separation effects by producing different degrees of stress exposure in maternal separation-reared pups. These methodological problems, together with insufficient reporting, might lead to inaccurate and unreliable effect estimates in maternal separation studies.

Intermittent hypoxia initiated plasticity in humans: A multipronged therapeutic approach to treat sleep apnea and overlapping co-morbidities

Over the past three decades exposure to intermittent hypoxia (IH) has generally been considered a stimulus associated with a number of detrimental outcomes. However, there is sufficient evidence to link IH to many beneficial outcomes but they have largely been ignored, particularly in the field of sleep medicine in the United States. Recent reviews have postulated that this apparent contradiction is related to the severity and duration of exposure to IH; mild forms of IH initiate beneficial outcomes while severe forms of IH are coupled to detrimental consequences. In the present review we explore the role that IH has in initiating respiratory plasticity and the potential this form of plasticity has to mitigate obstructive sleep apnea (OSA) in humans. In taking this approach, we address the possibility that IH could serve as an adjunct therapy coupled with continuous positive airway pressure (CPAP) to treat OSA. Our working hypothesis is that exposure to mild IH leads to respiratory plasticity that manifests in increased stability of the upper airway, which could ultimately reduce the CPAP required to treat OSA. In turn, this reduction could increase CPAP compliance and extend the length of treatment each night, which might improve the magnitude of outcome measures. Improved treatment compliance coupled with the direct effect that IH has on numerous overlapping conditions (i.e. asthma, chronic obstructive pulmonary disease, spinal cord injury) may well lead to substantial improvements that exceed outcomes following treatment with CPAP alone. Overall, this review will consider evidence from the published literature which suggests that IH could serve as an effective multipronged therapeutic approach to treat sleep apnea and its overlapping co-morbidities.

Chronic intermittent hypoxia and obstructive sleep apnea: an experimental and clinical approach

Obstructive sleep apnea (OSA) is a prevalent sleep disorder considered as an independent risk factor for cardiovascular consequences, such as systemic arterial hypertension, ischemic heart disease, cardiac arrhythmias, metabolic disorders, and cognitive dysfunction. The pathogenesis of OSA-related consequence is assumed to be chronic intermittent hypoxia (IH) inducing alterations at the molecular level, oxidative stress, persistent systemic inflammation, oxygen sensor activation, and increase of sympathetic activity. Overall, these mechanisms have an effect on vessel permeability and are considered to be important factors for explaining vascular, metabolic, and cognitive OSA-related consequences. The present review attempts to examine together the research paradigms and clinical studies on the effect of acute and chronic IH and the potential link with OSA. We firstly describe the literature data on the mechanisms activated by acute and chronic IH at the experimental level, which are very helpful and beneficial to explaining OSA consequences. Then, we describe in detail the effect of IH in patients with OSA that we can consider "the human model" of chronic IH. In this way, we can better understand the specific pathophysiological mechanisms proposed to explain the consequences of IH in OSA.