Hypobaric hypoxia damages the hippocampal pyramidal neurons in the rat brain

Lipidomics and Mass Spectrometry Imaging unveil Alterations in Mice Hippocampus Lipid Composition exposed to Hypoxia

Lipids are components of cytomembranes that are involved in various biochemical processes. High-altitude hypoxic environments not only affect the body's energy metabolism, but these environments can also cause abnormal lipid metabolism involved in the hypoxia-induced cognitive impairment. Thus, comprehensive lipidomic profiling of the brain tissue is an essential step toward understanding the mechanism of cognitive impairment induced by hypoxic exposure. In the present study, mice showed reduced new-object recognition and spatial memory when exposed to hypobaric hypoxia for 1 day. Histomorphological staining revealed significant morphological and structural damage to the hippocampal tissue, along with prolonged exposure to hypobaric hypoxia. Dynamic lipidomics of the mouse hippocampus showed a significant shift in both the type and distribution of phospholipids, as verified by spatial lipid mapping. Collectively, these results have provided new insights into the cognitive decline induced by high altitude, in which alterations in lipid metabolism may be an important contributing factor.

Selective vulnerability of hippocampal CA1 and CA3 pyramidal cells: What are possible pathomechanisms and should more attention be paid to the CA3 region in future studies?

Transient ischemia and reperfusion selectively damage neurons in brain, with hippocampal pyramidal cells being particularly vulnerable. Even within hippocampus, heterogeneous susceptibility is evident, with higher vulnerability of CA1 versus CA3 neurons described for several decades. Therefore, numerous studies have focused exclusively on CA1. Pediatric cardiac surgery is increasingly focusing on studies of hippocampal structures, and a negative impact of cardiopulmonary bypass on the hippocampus cannot be denied. Recent studies show a shift in selective vulnerability from neurons of CA1 to CA3. This review shows that cell damage is increased in CA3, sometimes stronger than in CA1, depending on several factors (method, species, age, observation period). Despite a highly variable pattern, several markers illustrate greater damage to CA3 neurons than previously assumed. Nevertheless, the underlying cellular mechanisms have not been fully deciphered to date. The complexity is reflected in possible pathomechanisms discussed here, with numerous factors (NMDA, kainate and AMPA receptors, intrinsic oxidative stress potential and various radicals, AKT isoforms, differences in vascular architecture, ratio of pro- and anti-apoptotic Bcl-2 factors, vulnerability of interneurons, mitochondrial dysregulation) contributing to either enhanced CA1 or CA3 vulnerability. Furthermore, differences in expressed genome, proteome, metabolome, and transcriptome in CA1 and CA3 appear to influence differential behavior after damaging stimuli, thus metabolomics-, transcriptomics-, and proteomics-based analyses represent a viable option to identify pathways of selective vulnerability in hippocampal neurons. These results emphasize that future studies should focus on the CA3 field in addition to CA1, especially with regard to improving therapeutic strategies after ischemic/hypoxic brain injury.

Histological and cytochemical analysis of the brain under conditions of hypobaric hypoxia-induced oxygen deficiency in albino rats

High altitude sickness is a life-threatening disease that occurs among acclimatized individuals working or living at a high altitude accompanied by hypobaric hypoxia exposure. The prolonged influence of hypobaric hypoxia on the brain may trigger neuronal damage and cell death due to an oxygen deficiency. The purpose of the current study was to investigate the histomorphological changes in the hippocampus, cerebral cortex, cerebellar cortex, and striatum of the rat's brain following chronic hypobaric hypoxia. Fourteen albino rats were used for this investigation. The animals were exposed to chronic hypobaric hypoxia in the special decompression chamber at an altitude of 7000 m for 7 days. The histological analysis was conducted via toluidine staining and silver impregnation. DNA damage and cell apoptosis were assessed via Feulgen staining. The histochemical assessment revealed increased dark neurons in the hippocampus with cell swelling. Silver impregnation showed increased argyrophilic neurons in the cerebellar cortex, striatum, CA1 subfield of the hippocampus, and cerebral cortex. The cytochemical analysis determined the increased apoptotic cells with hyperchromatic condensation and pyknosis in the hippocampus subfields and cerebral cortex. In addition, it has been observed that hypoxia has resulted in small hemorrhages and perivascular edema within the cerebellar and cerebral cortex. The results indicate brain injury observed in the various parts of the brain towards hypobaric hypoxia, however, the hippocampus showed greater vulnerability against hypoxic exposure in comparison to the striatum, cerebellum, and cerebral cortex. These changes support our insights regarding brain intolerance under conditions of hypoxia-induced oxygen deficiency and its histomorphological manifestations.

Mild hypoxia-induced structural and functional changes of the hippocampal network

Hypoxia causes structural and functional changes in several brain regions, including the oxygen-concentration-sensitive hippocampus. We investigated the consequences of mild short-term hypoxia on rat hippocampus in vivo. The hypoxic group was treated with 16% O2 for 1 h, and the control group with 21% O2. Using a combination of Gallyas silver impregnation histochemistry revealing damaged neurons and interneuron-specific immunohistochemistry, we found that somatostatin-expressing inhibitory neurons in the hilus were injured. We used 32-channel silicon probe arrays to record network oscillations and unit activity from the hippocampal layers under anaesthesia. There were no changes in the frequency power of slow, theta, beta, or gamma bands, but we found a significant increase in the frequency of slow oscillation (2.1-2.2 Hz) at 16% O2 compared to 21% O2. In the hilus region, the firing frequency of unidentified interneurons decreased. In the CA3 region, the firing frequency of some unidentified interneurons decreased while the activity of other interneurons increased. The activity of pyramidal cells increased both in the CA1 and CA3 regions. In addition, the regularity of CA1, CA3 pyramidal cells' and CA3 type II and hilar interneuron activity has significantly changed in hypoxic conditions. In summary, a low O2 environment caused profound changes in the state of hippocampal excitatory and inhibitory neurons and network activity, indicating potential changes in information processing caused by mild short-term hypoxia.

Mechanism, prevention and treatment of cognitive impairment caused by high altitude exposure

Hypobaric hypoxia (HH) characteristics induce impaired cognitive function, reduced concentration, and memory. In recent years, an increasing number of people have migrated to high-altitude areas for work and study. Headache, sleep disturbance, and cognitive impairment from HH, severely challenges the physical and mental health and affects their quality of life and work efficiency. This review summarizes the manifestations, mechanisms, and preventive and therapeutic methods of HH environment affecting cognitive function and provides theoretical references for exploring and treating high altitude-induced cognitive impairment.

High-altitude exposure duration dependent global and regional gray matter volume decrease in healthy immigrants: a cross-sectional study

BACKGROUND

The correlation between brain injury and high-altitude (HA) exposure duration (Dur_HA) as well as peripheral oxygen saturation (SpO₂) remains unclear.

PURPOSE

To evaluate the global and regional brain volume differences between HA immigrants and sea-level residents, and the relationship between brain volume with Dur_HA and SpO₂.

MATERIAL AND METHODS

Structural magnetic resonance imaging (MRI) scans were acquired in 33 healthy male HA immigrants (HA group) and 33 matched sea-level male residents (SL group). Differences in global gray matter volume (GMV), white matter volume (WMV), brain parenchyma volume (BV), total intracranial volume (TIV), and the volume-fraction (the ratio of GMV/TIV, WMV/TIV, BV/TIV) were assessed. Regional gray matter differences were investigated using voxel-based morphology analysis. The volume of clusters with GM loss were calculated as the volume of volume of interest (V_VOI). Student's t-test and partial correlation were adopted for statistic calculation.

RESULTS

Compared to the SL group, the HA immigrants had larger WMV (P = 0.015), smaller ratio of GMV/WMV (P = 0.022), and regional gray matter loss in bilateral basal ganglion, limbic system, midbrain, and vermis (cluster size >100 voxels, family-wise error corrected at P = 0.01). The global GMV, BV, and V_VOI confined to vermis had negative correlations with the Dur_HA (r = -0.369, P = 0.049; r = -0.380, P = 0.042; and r = -0.471, P = 0.010. Neither global nor regional brain volume correlated with SpO₂.

CONCLUSION

Global and regional brain are affected by long-term HA exposure, and global and regional gray matter have a time-dependent volume loss.

A bibliometric analysis of the studies in high-altitude induced sleep disturbances and cognitive impairment research

Background: The two main symptoms at high altitude, sleep abnormalities and cognitive impairments, interact with each other. These two dysfunctions are also closely related to systemic multisystem diseases, including cerebrovascular diseases, psychiatric disorders, and immune regulatory diseases. Purpose: To systematically analyze and visualize research on sleep disturbances and cognitive impairment at high altitudes using a bibliometrics method, and to determine future research directions by analyzing research trends and the latest hotspots. Methods: Publications from 1990 to 2022 on sleep disturbances and cognitive impairment at high altitudes were retrieved from the Web of Science. Using the R Bibliometrix software and Microsoft Excel, all data were examined statistically and qualitatively. For network visualization, the data were later exported into VOSviewer 1.6.17 and CiteSpace 6.1.R6. Results: A total of 487 articles in this area were published from 1990 to 2022. In this period, there was an overall increase in the number of publications. The United States has shown considerable importance in this sector. Bloch Konrad E was the most prolific and valuable author. The most prolific journal was High Altitude Medicine & Biology, and it has been the first choice for publishing in this field in recent years. Analysis of keyword co-occurrences suggested that research interest in the clinical manifestations of sleep disturbances and cognitive impairment caused by altitude hypoxia was mainly focused on "acute mountain-sickness," "insomnia," "apnea syndrome," "depression," "anxiety," "Cheyne-strokes respiration," and "pulmonary hypertension." The mechanisms of disease development related to "oxidative stress," "inflammation," "hippocampus," "prefrontal cortex," "neurodegeneration," and "spatial memory" in the brain have been the focus of recent research. According to burst detection analysis, "mood" and "memory impairment," as terms with high strength, are expected to remain hot topics in the coming years. High-altitude-induced pulmonary hypertension is also in the emerging stage of research, and the treatments will continue to receive attention in the future. Conclusion: More attention is being focused on sleep disturbances and cognitive impairment at high altitudes. This work will serve as a useful reference for the clinical development of treatments for sleep disturbances and cognitive impairment induced by hypobaric hypoxia at high altitudes.

Hippocampal adaptation to high altitude: a neuroanatomic profile of hippocampal subfields in Tibetans and acclimatized Han Chinese residents

The hippocampus is highly plastic and vulnerable to hypoxia. However, it is unknown whether and how it adapts to chronic hypobaric hypoxia in humans. With a unique sample of Tibetans and acclimatized Han Chinese individuals residing on the Tibetan plateau, we aimed to build a neuroanatomic profile of the altitude-adapted hippocampus by measuring the volumetric differences in the whole hippocampus and its subfields. High-resolution T1-weighted magnetic resonance imaging was performed in healthy Tibetans (TH, n = 72) and healthy Han Chinese individuals living at an altitude of more than 3,500 m (HH, n = 27). In addition, healthy Han Chinese individuals living on a plain (HP, n = 72) were recruited as a sea-level reference group. Whereas the total hippocampal volume did not show a significant difference across groups when corrected for age, sex, and total intracranial volume, subfield-level differences within the hippocampus were found. Post hoc analyses revealed that Tibetans had larger core hippocampal subfields (bilateral CA3, right CA4, right dentate gyrus); a larger right hippocampus–amygdala transition area; and smaller bilateral presubiculum, right subiculum, and bilateral fimbria, than Han Chinese subjects (HH and/or HP). The hippocampus and all its subfields were found to be slightly and non-significantly smaller in HH subjects than in HP subjects. As a primary explorational study, our data suggested that while the overall hippocampal volume did not change, the core hippocampus of Tibetans may have an effect of adaptation to chronic hypobaric hypoxia. However, this adaptation may have required generations rather than mere decades to accumulate in the population.

Taurine ameliorates volatile organic compounds-induced cognitive impairment in young rats via suppressing oxidative stress, regulating neurotransmitter and activating NMDA receptor

Long-term exposure to volatile organic compounds (VOCs) in children leads to intellectual and cognitive impairment. Taurine is an essential nutritional amino acid for children, which can improve neurological development in children. However, the neuroprotective effect of taurine on VOCs-induced cognitive impairment in children remains unclear. The aim of this study was to investigate the neuroprotective effects of taurine on VOCs-induced cognitive impairment in young rats. The rats were nose-only exposed to VOCs for a period of 4 weeks to create a model of cognitive impairment, and 0.5% and 1% taurine in tap water were administered throughout the trial period, respectively. Our results showed that young rats adjusted the recovery of their physiological functions by voluntarily increasing the intake of taurine in tap water when exposed to excessive VOCs by inhalation. In addition, taurine enhanced grasp, shortened the latency period of escape, and improved the learning and memory function of young rats. Moreover, taurine decreased malondialdehyde (MDA), γ-aminobutyric acid (GABA), Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), Urea, Creatinine (CREA) and injury biomarker level, enhanced superoxide dismutase (SOD), reduced glutathione (GSH) and glutamic acid (Glu) activities, up-regulated the protein expression of brain derived neurotrophic factor (BDNF) and N-Methyl-d-aspartate receptor 1 (NMDAR1) in model rats, and in most of cases 1% but not 0.5%, ameliorated the defects induced by VOCs. Collectively, these findings suggested that taurine protected against VOCs-induced cognitive-behavioral impairment in young rats through inhibiting oxidative stress and regulating neurotransmitter homeostasis. In addition, taurine were capable of restoring abilities of learning and memory in young rats exposed to VOCs by activating the N-Methyl-d-aspartate (NMDA) receptor. The findings suggest taurine as a potential novel drug for the treatment of cognitive behavioral disorders in children.

The human brain in a high altitude natural environment: A review

With the advancement of in vivo magnetic resonance imaging (MRI) technique, more detailed information about the human brain at high altitude (HA) has been revealed. The present review aimed to draw a conclusion regarding changes in the human brain in both unacclimatized and acclimatized states in a natural HA environment. Using multiple advanced analysis methods that based on MRI as well as electroencephalography, the modulations of brain gray and white matter morphology and the electrophysiological mechanisms underlying processing of cognitive activity have been explored in certain extent. The visual, motor and insular cortices are brain regions seen to be consistently affected in both HA immigrants and natives. Current findings regarding cortical electrophysiological and blood dynamic signals may be related to cardiovascular and respiratory regulations, and may clarify the mechanisms underlying some behaviors at HA. In general, in the past 10 years, researches on the brain at HA have gone beyond cognitive tests. Due to the sample size is not large enough, the current findings in HA brain are not very reliable, and thus much more researches are needed. Moreover, the histological and genetic bases of brain structures at HA are also needed to be elucidated.

The role of sex and ovarian hormones in hippocampal damage and cognitive deficits induced by chronic exposure to hypobaric hypoxia

Purpose

This study aims to investigate the role of sex and ovarian hormones in hippocampal damage and cognitive deficits and behavioral dysfunction in rats induced by chronic exposure to hypobaric hypoxia.

Methods

Six-week-old male and female SD rats were housed for 3 months either in a real altitude (4,250 m) environment as the model of chronic hypobaric-hypoxia (CHH) or in a plain as controls. The animal behavioral and hippocampal neurons at subcellular, molecular, and ultrastructural levels were characterized after CHH exposure.

Results

After 3 months of CHH exposure, (1) male CHH rats’ serum testosterone level was lower than male controls’ whereas female CHH rats’ serum estradiol level was higher than female controls’; (2) Morris water maze test finds that male rats showed more learning and spatial memory deficits than female rats; (3) male rats showed more severe hippocampal damage, hippocampal inflammation, oxidative stress and decreased hippocampal integrity (neurogenesis and dendritic spine density) than female rats; (4) Western blot analysis shows that, compared with the male control group, in male CHH group’s hippocampus, expression of nNOS, HO-1, and Bax protein increased whereas that of Bcl-2 protein decreased; (5) Expression of PON2 protein in male rats (CHH and controls) was lower than female rats (CHH and controls). In addition, CHH exposure decreased the expression of PON2 protein in both male and female rats; (6) qPCR analysis reveals that CHH exposure reduced the gene expression of N-methyl-D-aspartate receptor NR2A and NR2B subunits in male rats’ hippocampus. In addition, compared with the sham CHH group, the expression level of PON2 protein decreased in the OVX-CHH group’s hippocampus whereas oxidative stress, neuroinflammation, and degeneration of hippocampal neurons increased in the OVX-CHH group’s hippocampus.

Conclusion

After CHH exposure, male rats were significantly more likely than female rats to develop hippocampal damage, hippocampal neuroinflammation, and cognitive decline and deficits, suggesting that sex and ovarian hormones were significantly involved in regulating the rats’ susceptibility to CHH exposure-induced hippocampal damage.

Hypobaric Hypoxia Induces Deficits in Adult Neurogenesis and Social Interaction via Cyclooxygenase-1/ EP1 Receptor Pathway Activating NLRP3 Inflammasome

Low oxygen environments, like hypobaric hypoxia (HH), are common nodes in a number of diseases characterized by neuroinflammation, which is detrimental to the structural and functional aspects of hippocampal circuitry. Hypoxic conditions lead to elevation of inflammasome-mediated inflammation that may contribute to cognitive deficits. However, a systematic investigation of the impact of inflammasome-mediated neuroinflammation on the components of neurogenic niche during HH remains to be elusive. Cerebral hypoxia was induced in adult male Sprague Dawley rats via decreasing partial pressure of oxygen. The effect of HH (1, 3, and 7 days at 25,000 ft) on social memory, anxiety, adult neurogenesis, and NLRP3- (NLR family pyrin domain containing 3) mediated neuroinflammation in the dentate gyrus (DG) was explored in detail. Furthermore, we explored the therapeutic efficacy of cyclooxygenase-1 inhibitor (valeryl salicylate, 5 mg/kg/day, i.p.) and EP1 receptor (EP1R) antagonist (SC19220, 1 mg/kg/day, i.p.) on HH-induced deficits. Seven days of HH exposure induced alteration in social and anxiety-like behavior along with perturbation in adult neurogenesis. Elevation in NLRP3, caspase-1, and IL-1β levels was observed during HH from day 1. A notable increase in the COX-1/EP1R pathway in activated glial cells in DG was evident during HH. COX-1 inhibitor and EP1R antagonist mitigated the detrimental effects of HH on social memory, adult neurogenesis via blunting NLRP3-mediated inflammation. Our data showed induction of the COX-1/EP1R pathway in the glial cells, which is detrimental to neurogenesis and social memory, opening up the possibility that the COX-1/EP1R pathway is a plausible target for inflammasome-related neurogenesis impairments.

Preservation of dendritic spine morphology and postsynaptic signaling markers after treatment with solid lipid curcumin particles in the 5xFAD mouse model of Alzheimer's amyloidosis

BACKGROUND

Synaptic failure is one of the principal events associated with cognitive dysfunction in Alzheimer's disease (AD). Preservation of existing synapses and prevention of synaptic loss are promising strategies to preserve cognitive function in AD patients. As a potent natural anti-oxidant, anti-amyloid, and anti-inflammatory polyphenol, curcumin (Cur) shows great promise as a therapy for AD. However, hydrophobicity of natural Cur limits its solubility, stability, bioavailability, and clinical utility for AD therapy. We have demonstrated that solid lipid curcumin particles (SLCP) have greater therapeutic potential than natural Cur in vitro and in vivo models of AD. In the present study, we have investigated whether SLCP has any preservative role on affected dendritic spines and synaptic markers in 5xFAD mice.

METHODS

Six- and 12-month-old 5xFAD and age-matched wild-type mice received oral administration of SLCP (100 mg/kg body weight) or equivalent amounts of vehicle for 2 months. Neuronal morphology, neurodegeneration, and amyloid plaque load were investigated from prefrontal cortex (PFC), entorhinal cortex (EC), CA1, CA3, and the subicular complex (SC). In addition, the dendritic spine density from apical and basal branches was studied by Golgi-Cox stain. Further, synaptic markers, such as synaptophysin, PSD95, Shank, Homer, Drebrin, Kalirin-7, CREB, and phosphorylated CREB (pCREB) were studied using Western blots. Finally, cognitive and motor functions were assessed using open-field, novel object recognition (NOR) and Morris water maze (MWM) tasks after treatment with SLCP.

RESULTS

We observed an increased number of pyknotic and degenerated cells in all these brain areas in 5xFAD mice and SLCP treatment partially protected against those losses. Decrease in dendritic arborization and dendritic spine density from primary, secondary, and tertiary apical and basal branches were observed in PFC, EC, CA1, and CA3 in both 6- and 12-month-old 5xFAD mice, and SLCP treatments partially preserved the normal morphology of these dendritic spines. In addition, pre- and postsynaptic protein markers were also restored by SLCP treatment. Furthermore, SLCP treatment improved NOR and cognitive function in 5xFAD mice.

CONCLUSIONS

Overall, these findings indicate that use of SLCP exerts neuroprotective properties by decreasing amyloid plaque burden, preventing neuronal death, and preserving dendritic spine density and synaptic markers in the 5xFAD mice.

Comparative study of oral and intranasal puerarin for prevention of brain injury induced by acute high-altitude hypoxia

Human activities in the areas of high altitude have increased significantly recently. Brain is highly sensitive to changing of oxygen pressure due to high altitude, and this physiological response may lead to serious brain injury, such as learning and memory disabilities. Puerarin is a phytoestrogen with many pharmacological activities, such as treatment of neurological disorders. However, most of current drugs can not easily enter brain through the blood-brain barrier (BBB). The nose-to-brain route can bypass BBB for brain-targeting. Here, thermosensitive in situ hydrogels (TISGs) of puerarin were prepared with poloxamers 407, poloxamers 188 and propylene glycol to improve bioavailability and brain targeting. In vitro drug release in simulated nasal fluids, rheological properties and cilia toxicity of puerarin TISGs were explored. The pharmacodynamics and pharmacokinetics of puerarin by intranasal (i.n.) and oral (p.o.) administrations were also evaluated. The viscosity of puerarin TISGs tended to increase obviously with increased temperature. The puerarin release profile and transmucosal process of puerarin TISGs could be described with the first-order kinetics equation, depending on drug diffusion. The cilia toxicity of puerarin TISGs was not obvious. Rat models of hypobarism/hypoxia-induced brain injury were established with a hypobaric simulation chamber. Morris water maze and open filed tests indicated that puerarin TISGs improved the spatial memory and spontaneous exploratory behavior of the rats suffering from hypoxia-induced brain injury. Furthermore, puerarin TISGs decreased the level of oxidative stress cytokines (malondialdehyde (MDA) and glutathione (GSH)) in the peripheral circulation, alleviated the cerebral histological lesions, and relieved the expression of hypoxia-inducible factor-1α (HIF-1α). Intranasal puerarin TISGs were absorbed quickly with a shorter T_max (10.0 ± 5.7 min) compared to that of oral puerarin (36 ± 13.4 min). In addition, the relative bioavailability of i.n. puerarin TISGs was high to 300% compared to oral administration of puerarin. The area under the curve (AUC) of brain after i.n. administration of puerarin TISGs was 954.5 ± 335.1 h.ng/mL, while no puerarin was detected in the brain after oral administration. Therefore, i.n. puerarin TISGs led to excellent brain targeting effect. Puerarin TISGs are an effective neuroprotector formulation for prevention of brain injury induced by acute high-altitude hypoxia.

Ameliorative Properties of Boronic Compounds in In Vitro and In Vivo Models of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by amyloid (Aβ) aggregation, hyperphosphorylated tau, neuroinflammation, and severe memory deficits. Reports that certain boronic compounds can reduce amyloid accumulation and neuroinflammation prompted us to compare trans-2-phenyl-vinyl-boronic-acid-MIDA-ester (TPVA) and trans-beta-styryl-boronic-acid (TBSA) as treatments of deficits in in vitro and in vivo models of AD. We hypothesized that these compounds would reduce neuropathological deficits in cell-culture and animal models of AD. Using a dot-blot assay and cultured N₂a cells, we observed that TBSA inhibited Aβ42 aggregation and increased cell survival more effectively than did TPVA. These TBSA-induced benefits were extended to C. elegans expressing Aβ42 and to the 5xFAD mouse model of AD. Oral administration of 0.5 mg/kg dose of TBSA or an equivalent amount of methylcellulose vehicle to groups of six- and 12-month-old 5xFAD or wild-type mice over a two-month period prevented recognition- and spatial-memory deficits in the novel-object recognition and Morris-water-maze memory tasks, respectively, and reduced the number of pyknotic and degenerated cells, Aβ plaques, and GFAP and Iba-1 immunoreactivity in the hippocampus and cortex of these mice. These findings indicate that TBSA exerts neuroprotective properties by decreasing amyloid plaque burden and neuroinflammation, thereby preventing neuronal death and preserving memory function in the 5xFAD mice.

Exercise-Induced Elevated BDNF Level Does Not Prevent Cognitive Impairment Due to Acute Exposure to Moderate Hypoxia in Well-Trained Athletes

Exposure to acute hypoxia causes a detrimental effect on the brain which is also manifested by a decrease in the ability to perform psychomotor tasks. Conversely, brain-derived neurotrophic factor (BDNF), whose levels are elevated in response to exercise, is a well-known factor in improving cognitive function. Therefore, the aim of our study was to investigate whether the exercise under hypoxic conditions affects psychomotor performance. For this purpose, 11 healthy young athletes performed a graded cycloergometer exercise test to volitional exhaustion under normoxia and acute mild hypoxia (FiO₂ = 14.7%). Before, immediately after exercise and after a period of recovery, choice reaction time (CRT) and number of correct reactions (NCR) in relation to changes in serum BDNF were examined. Additionally, other selected factors which may modify BDNF production, i.e., cortisol (C), nitrite, catecholamines (adrenalin-A, noradrenaline-NA, dopamine-DA, serotonin-5-HT) and endothelin-1 (ET-1), were also measured. Exercise in hypoxic conditions extended CRT by 13.8% (p < 0.01) and decreased NCR (by 11.5%) compared to rest (p < 0.05). During maximal workload, NCR was lower by 9% in hypoxia compared to normoxia (p < 0.05). BDNF increased immediately after exercise in normoxia (by 29.3%; p < 0.01), as well as in hypoxia (by 50.0%; p < 0.001). There were no differences in BDNF between normoxia and hypoxia. Considering the fact that similar levels of BDNF were seen in both conditions but cognitive performance was suppressed in hypoxia, acute elevation of BDNF did not compensate for hypoxia-induced cognition impairment. Moreover, neither potentially negative effects of C nor positive effects of A, DA and NO on the brain were observed in our study.

Abnormal brain activity in rats with sustained hypobaric hypoxia exposure: a resting-state functional magnetic resonance imaging study

Background:

Hypobaric hypoxia (HH) exposure at high altitudes can result in a decline in cognitive function, which may have a serious impact on the daily life of people who migrate to high altitudes. However, the specific HH-induced changes in brain function remain unclear. This study explored changes in brain activity in rats exposed to a sustained HH environment using functional magnetic resonance imaging (fMRI).

Methods:

Healthy male rats (8 weeks old) were randomly divided into a model group and a control group. A rat model of cognitive impairment induced by sustained HH exposure was established. The control and model groups completed training and testing in the Morris water maze (MWM). A two-sample t-test for between-group difference comparisons was performed. Repeated measures analyses of variance for within-group comparisons were performed and post-hoc comparisons were made using the Tukey test. Between-group differences in spontaneous brain activity were assessed using a voxel-wise analysis of resting-state fMRI (rs-fMRI), combined with analyses of the fractional amplitude of low frequency fluctuations (fALFF) in statistical parametric mapping.

Results:

In the MWM test, the escape latencies of the model group were significantly longer compared with those of the control group (control group vs. model group, day 1: 21.6 ± 3.3 s vs. 40.5 ± 3.4 s, t = –11.282; day 2: 13.5 ± 2.2 s vs. 28.7 ± 5.3 s, t = –7.492; day 3: 10.5 ± 2.8 s vs. 22.6 ± 6.1 s, t = –5.099; day 4: 9.7 ± 2.5 s vs. 18.6 ± 5.2 s, t = –4.363; day 5: 8.8 ± 2.7 s vs. 16.7 ± 5.0 s, t = –3.932; all P < 0.001). Within both groups, the escape latency at day 5 was significantly shorter than those at other time points (control group: F = 57.317, P < 0.001; model group: F = 50.718, P < 0.001). There was no within-group difference in average swimming speed (control group, F = 1.162, P = 0.956; model group, F = 0.091, P = 0.880). Within the model group, the time spent within the original platform quadrant was significantly shorter (control group vs. model group: 36.1 ± 5.7 s vs. 17.8 ± 4.3 s, t = 7.249, P < 0.001) and the frequency of crossing the original platform quadrant was significantly reduced (control group vs. model group: 6.4 ± 1.9 s vs. 2.0 ± 0.8 s, t = 6.037, P < 0.001) compared with the control group. In the rs-fMRI study, compared with the control group, rats in the model group showed widespread reductions in fALFF values throughout the brain.

Conclusions:

The abnormalities in spontaneous brain activity indicated by the fALFF measurements may reflect changes in brain function after HH exposure. This widespread abnormal brain activity may help to explain and to provide new insights into the mechanism underlying the impairment of brain function under sustained exposure to high altitudes.

The effects of repeated propofol anesthesia on spatial memory and long-term potentiation in infant rats under hypoxic conditions

Propofol is widely used as an intravenous drug for induction and maintenance in general anesthesia. Hypoxemia is a common complication during perianesthesia. We want to know the effect of propofol on spatial memory and LTP (Long-term potentiation) under hypoxic conditions. In this study, 84 seven-day-old Sprague–Dawley rats were randomly assigned into six groups (n = 14)-four control groups: lipid emulsion solvent + 50% oxygen (CO), lipid emulsion solvent + room air (CA), lipid emulsion solvent + 18% oxygen (CH), and propofol + 50% oxygen (propofol–oxygen, PO); and two experiment groups: propofol + room air (propofol–air, PA), and propofol + 18% oxygen (propofol–hypoxia, PH). After receiving propofol (50 mg/kg) or the same volume of intralipid intraperitoneal (5.0 ml/kg), injected once per day for seven consecutive days, the rats were exposed to 18% oxygen, 50% oxygen and air, until recovery of the righting reflex. We found that the apoptotic index and activated caspase-3 increased in the PH group (P < 0.05) compared with the PA group, fEPSP (field excitatory postsynaptic) potential and success induction rate of LTP reduced in all propofol groups (P < 0.05). Compared with the PO group, the fEPSP and success induction rate of LTP reduced significantly in the PA and PH groups (P < 0.05). Moreover, compared with CH group, the average time of escape latency was longer, and the number of platform location crossings was significantly reduced in the PH group (P < 0.05). Thus, we believe that adequate oxygen is very important during propofol anesthesia.

The role of mTOR signalling pathway in hypoxia-induced cognitive impairment

Hypoxia has been associated with cognitive impairment. Many studies have investigated the role of mTOR signalling pathway in cognitive functions but its role in hypoxia-induced cognitive impairment remains controversial. This review aimed to elucidate the role of mTOR in the mechanisms of cognitive impairment that may pave the way towards the mechanistic understanding and therapeutic intervention of hypoxia-induced cognitive impairment. mTORC1 is normally regulated during mild or acute hypoxic exposure giving rise to neuroprotection, whereas it is overactivated during severe or chronic hypoxia giving rise to neuronal cells death. Thus, it is worth exploring the possibility of maintaining normal mTORC1 activity and thereby preventing cognitive impairment during severe or chronic hypoxia.

Association between CIRP expression and hypoxic-ischemic brain injury in neonatal rats

The role of cold inducible RNA-binding protein (CIRP) in mediating ischemic brain injury in neonatal rats under chronic hypobaric hypoxia was investigated. The neonatal rat model of chronic hypobaric hypoxia and the cell culture model of SH-SY5Y cells exposed to hypoxia (1% O₂) were constructed. The expression of CIRP and hypoxia-inducible factor-1α (HIF-1α) was detected after hypoxic exposure, and the apoptosis-related proteins were analyzed via terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) and western blot analysis to detect neuronal apoptosis. Moreover, the effects of CIRP overexpression on HIF-1α and neuronal apoptosis were identified. Chronic hypobaric hypoxia can lead to HIF-1α expression and neuronal apoptosis in the body. CIRP was induced at early exposure (3 d/7 d). However, the CIRP level in the hypoxic group was obviously lower than that in the control group with the prolongation of exposure time (21 d). In addition, the knockdown of HIF-1α significantly reduced the neuronal apoptosis under hypoxic conditions, indicating that HIF-1α may promote apoptosis during exposure. The overexpression of CIRP significantly inhibited the upregulation of HIF-1α during hypoxia and the HIF-1α-mediated neuronal apoptosis. Results of the current study showed that, CIRP is involved in the ischemic brain injury induced by chronic hypoxia through downregulation of HIF-1α expression.

Reduced expression of Kalirin-7 contributes to working memory deficit during chronic hypobaric hypoxia exposure

Hypobaric hypoxia (HH) is an environmental stress encountered at high altitude. It has been shown that HH resulted in spine atrophy and working memory deficits. Kalirin-7, a postsynaptic density protein, plays an important and key role in regulating spine dynamics and its plasticity. Spine atrophy is implicated in HH induced memory deficits but role of Kalirin-7 in this phenomenon is not studied. Present study is therefore designed to investigate the effect of chronic HH exposure on Kalirin-7 expression in hippocampus and its role in spatial working memory deficits. Adult rats (n = 12, 3 months old) were exposed to a simulated altitude of 25,000 feet for 7 days. Following HH exposure, spatial working memory was assessed with Radial arm maze and T maze. Hippocampal expression of Kalrin-7 was estimated at mRNA and protein levels. Results of behavioural experiments showed that HH causes significant decrease in the spatial working memory. There was a significant reduction in the protein expression of Kalirin-7 in the hippocampus of hypoxia exposed rats (43.89 ± 7.43) as compared to the control (69.54 ± 10.99). The mRNA expression of Kalrin-7 also exhibits significant reduction (0.59 ± 0.05) in the exposed group as compared to the control (0.98 ± 0.07). Immunohistochemistry showed that Kalirin-7 is decreased significantly in CA1, CA3 and DG regions of the hippocampus. Moreover, memory deficits are significantly correlated with decreased immunoreactivity of the hippocampal Kalirin-7. In conclusion, it can be said therefore, that change in Kalirin-7 expression in the hippocampus is associated with HH induced working memory deficit.

Transplantation of mesenchymal stem cells overexpressing interleukin-10 induces autophagy response and promotes neuroprotection in a rat model of TBI

Autophagy, including mitophagy, is critical for neuroprotection in traumatic brain injury (TBI). Transplantation of mesenchymal stem cells (MSCs) provides neuroprotection and induces autophagy by increasing anti‐inflammatory cytokines, such as interleukin‐10 (IL‐10). To evaluate these effects of IL10 that are released by MSCs, we genetically engineered MSCs to overexpress IL10 and compared their effects to unaltered MSCs following transplantation near the site of induced TBIs in rats. Adult, male Sprague‐Dawley rats were divided into four groups: Sham + vehicle, TBI + vehicle, TBI + MSCs‐IL‐10 and TBI + MSCs‐GFP. Thirty‐six hours post‐TBI, the first two groups received vehicle (Hanks balance salt solution), whereas last two groups were transplanted with MSCs‐IL‐10 or MSCs‐GFP. Three weeks after transplantation, biomarkers for neurodegenerative changes, autophagy, mitophagy, cell death and survival markers were measured. We observed a significant increase in the number of dead cells in the cortex and hippocampus in TBI rats, whereas transplantation of MSCs‐IL‐10 significantly reduced their numbers in comparison to MSCs alone. MSCs‐IL‐10 rats had increased autophagy, mitophagy and cell survival markers, along with decreased markers for cell death and neuroinflammation. These results suggest that transplantation of MSCs‐IL‐10 may be an effective strategy to protect against TBI‐induced neuronal damage.

Living High and Feeling Low: Altitude, Suicide, and Depression

After participating in this activity, learners should be better able to:• Assess epidemiologic evidence that increased altitude of residence is linked to increased risk of depression and suicide• Evaluate strategies to address hypoxia-related depression and suicidal ideation ABSTRACT: Suicide and major depressive disorder (MDD) are complex conditions that almost certainly arise from the influences of many interrelated factors. There are significant regional variations in the rates of MDD and suicide in the United States, suggesting that sociodemographic and environmental conditions contribute. Here, we review epidemiological evidence that increases in the altitude of residence are linked to the increased risk of depression and suicide. We consider the possibility that chronic hypobaric hypoxia (low blood oxygen related to low atmospheric pressure) contributes to suicide and depression, which is suggested by animal models, short-term studies in humans, and the effects of hypoxic medical conditions on suicide and depression. We argue that hypobaric hypoxia could promote suicide and depression by altering serotonin metabolism and brain bioenergetics; both of these pathways are implicated in depression, and both are affected by hypoxia. Finally, we briefly examine treatment strategies to address hypoxia-related depression and suicidal ideation that are suggested by these findings, including creatine monohydrate and the serotonin precursors tryptophan and 5-hydroxytryptophan.

Hypobaric hypoxia impairs cued and contextual fear memory in rats

Fear memory is essential for survival, and its dysregulation leads to disorders. High altitude hypobaric hypoxia (HH) is known to induce cognitive decline. However, its effect on fear memory is still an enigma. We aimed to investigate the temporal effect of HH on fear conditioning and the underlying mechanism. Adult male Sprague-Dawley rats were trained for fear conditioning and exposed to simulated HH equivalent to 25,000 ft for different durations (1, 3, 7, 14 and 21 days). Subsequently, rats were tested for cued and contextual fear conditioning. Neuronal morphology, apoptosis and DNA fragmentation were studied in the medial prefrontal cortex (mPFC), hippocampus and basolateral amygdala (BLA). We observed significant deficit in cued and contextual fear acquisition (at 1, 3 and 7 days) and consolidation (cued at 1 and 3 days and contextual fear at 1, 3 and 7 days) under HH. HH exposure with retraining showed the earlier restoration of contextual fear memory. Further, we found a gradual increase in the number of pyknotic and apoptotic neurons together with the increase in DNA fragmentation in mPFC, hippocampus, and BLA up to 7 days of HH exposure. The present study concludes that HH exposure equivalent to 25,000 ft induced cued and contextual fear memory deficit (acquisition and consolidation) which is found to be correlated with the neurodegenerative changes in the limbic brain regions.

Solid lipid curcumin particles provide greater anti-amyloid, anti-inflammatory and neuroprotective effects than curcumin in the 5xFAD mouse model of Alzheimer's disease

BACKGROUND

Neuroinflammation and the presence of amyloid beta protein (Aβ) and neurofibrillary tangles are key pathologies in Alzheimer's disease (AD). As a potent anti-amyloid and anti-inflammatory natural polyphenol, curcumin (Cur) could be potential therapies for AD. Unfortunately, poor solubility, instability in physiological fluids, and low bioavailability limit its clinical utility. Recently, different lipid modifications in the formulae of Cur have been developed that would enhance its therapeutic potential. For example, we have reported greater permeability and neuroprotection with solid lipid curcumin particles (SLCP) than with natural Cur in an in vitro model of AD. In the present study, we compared the Aβ aggregation inhibition, anti-amyloid, anti-inflammatory responses of Cur and or SLCP in both in vitro and in vivo models of AD. One-year-old 5xFAD-and age-matched wild-type mice were given intraperitoneal injections of Cur or SLCP (50 mg/kg body weight) for 2- or 5-days. Levels of Aβ aggregation, including oligomers and fibril formation, were assessed by dot blot assay, while Aβ plaque load and neuronal morphology in the pre-frontal cortex (PFC) and hippocampus were assayed by immunolabeling with Aβ-specific antibody and cresyl violet staining, respectively. In addition, neuroinflammation was assessed the immunoreactivity (IR) of activated astrocytes (GFAP) and microglia (Iba-1) in different brain areas. Finally, comparisons of solubility and permeability of Cur and SLCP were made in cultured N2a cells and in primary hippocampal neurons derived from E16 pups of 5xFAD mice.

RESULTS

We observed that relative to Cur, SLCP was more permeable, labeled Aβ plaques more effectively, and produced a larger decrease in Aβ plaque loads in PFC and dentate gyrus (DG) of hippocampus. Similarly, relative to Cur, SLCP produced a larger decrease of pyknotic, or tangle-like, neurons in PFC, CA1, and CA3 areas of hippocampus after 5 days of treatment. Both Cur and or SLCP significantly reduced GFAP-IR and Iba-1-IR in PFC, in the striatum as well as CA1, CA3, DG, subicular complex of hippocampus, and the entorhinal cortex in the 5xFAD mice after 5 days of treatment.

CONCLUSIONS

The use of SLCP provides more anti-amyloid, anti-inflammatory, and neuroprotective outcomes than does Cur in the 5xFAD mouse model of AD.

Cold Inducible RNA Binding Protein Is Involved in Chronic Hypoxia Induced Neuron Apoptosis by Down-Regulating HIF-1α Expression and Regulated By microRNA-23a

Background: Neuron apoptosis mediated by hypoxia inducible factor 1α (HIF-1α) in hippocampus is one of the most important factors accounting for the chronic hypobaric hypoxia induced cognitive impairment. As a neuroprotective molecule that is up-regulated in response to various environmental stress, CIRBP was reported to crosstalk with HIF-1α under cellular stress. However, its function under chronic hypobaric hypoxia remains unknown. Objective: In this study, we tried to identify the role of CIRBP in HIF-1α mediated neuron apoptosis under chronic hypobaric hypoxia and find a possible method to maintain its potential neuroprotective in long-term high altitude environmental exposure. Methods: We established a chronic hypobaric hypoxia rat model as well as a tissue culture model where SH-SY5Y cells were exposed to 1% hypoxia. Based on these models, we measured the expressions of HIF-1α and CIRBP under hypoxia exposure and examined the apoptosis of neurons by TUNEL immunofluorescence staining and western blot analysis of apoptosis related proteins. In addition, by establishing HIF-1α shRNA and pEGFP-CIRBP plasmid transfected cells, we confirmed the role of HIF-1α in chronic hypoxia induced neuron apoptosis and identified the influence of CIRBP over-expression upon HIF-1α and neuron apoptosis in the process of exposure. Furthermore, we measured the expression of the reported hypoxia related miRNAs in both models and the influence of miRNAs' over-expression/knock-down upon CIRBP in the process of HIF-1α mediated neuron apoptosis. Results: HIF-1α expression as well as neuron apoptosis was significantly elevated by chronic hypobaric hypoxia both in vivo and in vitro. CIRBP was induced in the early stage of exposure (3d/7d); however as the exposure was prolonged (21d), CIRBP level of the hypoxia group became significantly lower than that of control. In addition, HIF-1α knockdown significantly decreased neuron apoptosis under hypoxia, suggesting HIF-1α may be pro-apoptotic in the process of exposure. CIRBP over-expression significantly suppressed HIF-1α up-regulation in hypoxia and inhibited HIF-1α mediated neuron apoptosis. Interestingly, miR-23a was also induced by hypoxia exposure and showed the same changing tendency with CIRBP (increasing in 3d/7d, decreasing in 21d). In addition, over-expressing miR-23a up-regulated CIRBP, down-regulated HIF-1α and attenuated neuron apoptosis. Conclusion: Cold inducible RNA binding protein is involved in chronic hypoxia induced neuron apoptosis by down-regulating HIF-1α expression, and MiR-23a may be an important tool to maintain CIRBP level and function.

Oxidative stress and apoptosis after acute respiratory hypoxia and reoxygenation in rat brain

Acute hypoxia increases the formation of reactive oxygen species (ROS) in the brain. However, the effect of reoxygenation, unavoidable to achieve full recovery of the hypoxic organ, has not been clearly established. The aim of the present study was to evaluate the effects of exposition to acute severe respiratory hypoxia followed by reoxygenation on the evolution of oxidative stress and apoptosis in the brain. We investigated the effect of in vivo acute severe normobaric hypoxia (rats exposed to 7% O₂ for 6 h) and reoxygenation in normoxia (21% O₂ for 24 h or 48 h) on oxidative stress markers, the antioxidant system and apoptosis in the brain. After respiratory hypoxia we found increased levels of HIF-1α expression, lipid peroxidation, protein oxidation and nitric oxide in brain extracts. Antioxidant defence systems such as superoxide dismutase (SOD), reduced glutathione (GSH) and glutathione peroxidase (GPx) and the reduced/oxidized glutathione (GSH/GSSG) ratio were significantly decreased in the brain. After 24 h of reoxygenation, oxidative stress parameters and the anti-oxidant system returned to control values. Regarding the apoptosis parameters, acute hypoxia increased cytochrome c, AIF and caspase 3 activity in the brain. The apoptotic effect is greatest after 24 h of reoxygenation. Immunohistochemistry suggests that CA3 and dentate gyrus in the hippocampus seem more susceptible to hypoxia than the cortex. Severe acute hypoxia increases oxidative damage, which in turn could activate apoptotic mechanisms. Our work is the first to demonstrate that after 24 h of reoxygenation oxidative stress is attenuated, while apoptosis is maintained mainly in the hippocampus, which may, in fact, be the cause of impaired brain function.

Insight into potential mechanisms of hypobaric hypoxia-induced learning and memory deficit - Lessons from rat studies

Impairment of memory is one of the most frequently reported symptoms during sudden hypoxia exposure in human. Cortical atrophy has been linked to the impaired memory function and is suggested to occur with chronic high-altitude exposure. However, the precise molecular mechanism(s) of hypoxia-induced memory impairment remains an enigma. In this work, we review hypoxia-induced learning and memory deficit in human and rat studies. Based on data from rat studies using different protocols of continuous hypoxia, we try to elicit potential mechanisms of hypobaric hypoxia-induced memory deficit.

Reversible Brain Abnormalities in People Without Signs of Mountain Sickness During High-Altitude Exposure

A large proportion of lowlanders ascending to high-altitude (HA) show no signs of mountain sickness. Whether their brains have indeed suffered from HA environment and the persistent sequelae after return to lowland remain unknown. Thirty-one sea-level college students, who had a 30-day teaching on Qinghai-Tibet plateau underwent MRI scans before, during, and two months after HA exposure. Brain volume, cortical structures, and white matter microstructure were measured. Besides, serum neuron-specific enolase (NSE), C-reactive protein, and interleukin-6 and neuropsychiatric behaviors were tested. After 30-day HA exposure, the gray and white matter volumes and cortical surface areas significantly increased, with cortical thicknesses and curvatures changed in a wide spread regions; Anisotropy decreased with diffusivities increased in multiple sites of white matter tracts. Two months after HA exposure, cortical measurements returned to basal level. However, increased anisotropy with decreased diffusivities was observed. Behaviors and serum inflammatory factor did not significant changed during three time-point tests. NSE significantly decreased during HA but increased after HA exposure. Results suggest brain swelling occurred in people without neurological signs at HA, but no negative sequelae in cortical structures and neuropsychiatric functions were left after the return to lowlands. Reoxygenation changed white matter microstructure.

Neuroprotective Role of Intermittent Hypobaric Hypoxia in Unpredictable Chronic Mild Stress Induced Depression in Rats

Hypoxic exposure results in several pathophysiological conditions associated with nervous system, these include acute and chronic mountain sickness, loss of memory, and high altitude cerebral edema. Previous reports have also suggested the role of hypoxia in pathogenesis of depression and related psychological conditions. On the other hand, sub lethal intermittent hypoxic exposure induces protection against future lethal hypoxia and may have beneficial effect. Therefore, the present study was designed to explore the neuroprotective role of intermittent hypobaric hypoxia (IHH) in Unpredictable Chronic Mild Stress (UCMS) induced depression like behaviour in rats. The IHH refers to the periodic exposures to hypoxic conditions interrupted by the normoxic or lesser hypoxic conditions. The current study examines the effect of IHH against UCMS induced depression, using elevated plus maze (EPM), open field test (OFT), force swim test (FST), as behavioural paradigm and related histological and molecular approaches. The data indicated the UCMS induced depression like behaviour as evident from decreased exploration activity in OFT with increased anxiety levels in EPM, and increased immobility time in the FST; whereas on providing the IHH (5000m altitude, 4hrs/day for two weeks) these behavioural changes were ameliorated. The morphological and molecular studies also validated the neuroprotective effect of IHH against UCMS induced neuronal loss and decreased neurogenesis. Here, we also explored the role of Brain-Derived Neurotrophic Factor (BDNF) in anticipatory action of IHH against detrimental effect of UCMS as upon blocking of BDNF-TrkB signalling the beneficial effect of IHH was nullified. Taken together, the findings of our study demonstrate that the intermittent hypoxia has a therapeutic potential similar to an antidepressant in animal model of depression and could be developed as a preventive therapeutic option against this pathophysiological state.

Hypobaric Hypoxia Imbalances Mitochondrial Dynamics in Rat Brain Hippocampus

Brain is predominantly susceptible to oxidative stress and mitochondrial dysfunction during hypobaric hypoxia, and therefore undergoes neurodegeneration due to energy crisis. Evidences illustrate a high degree of association for mitochondrial fusion/fission imbalance and mitochondrial dysfunction. Mitochondrial fusion/fission is a recently reported dynamic mechanism which frequently occurs among cellular mitochondrial network. Hence, the study investigated the temporal alteration and involvement of abnormal mitochondrial dynamics (fusion/fission) along with disturbed mitochondrial functionality during chronic exposure to hypobaric hypoxia (HH). The Sprague-Dawley rats were exposed to simulated high altitude equivalent to 25000 ft for 3, 7, 14, 21, and 28 days. Mitochondrial morphology, distribution within neurons, enzyme activity of respiratory complexes, Δψ m , ADP: ATP, and expression of fission/fusion key proteins were determined. Results demonstrated HH induced alteration in mitochondrial morphology by damaged, small mitochondria observed in neurons with disturbance of mitochondrial functionality and reduced mitochondrial density in neuronal processes manifested by excessive mitochondrial fragmentation (fission) and decreased mitochondrial fusion as compared to unexposed rat brain hippocampus. The study suggested that imbalance in mitochondrial dynamics is one of the noteworthy mechanisms occurring in hippocampal neurons during HH insult.

Investigation of prolonged hypobaric hypoxia-induced change in rat brain using T2 relaxometry and diffusion tensor imaging at 7T

The present study examines the change in water diffusion properties of the corpus callosum (CC) and the hippocampus, in response to prolonged hypobaric hypoxia (HH) stress, using in vivo magnetic resonance imaging (MRI) modalities such as T2 relaxometry and diffusion tensor imaging (DTI). Three groups of rats (n=7/group) were exposed to a simulated altitude of 6700m above sea level for the duration of 7, 14 and 21days, respectively. Data were acquired pre-exposure, post-exposure and after 1week of normoxic follow-up in each group. The increment in T2 values with no apparent diffusion coefficient (ADC) change in the CC after 7 and 14days of HH exposure indicated mixed (vasogenic and cytotoxic) edema formation. After 1week of normoxia, 7-day HH-exposed rats showed a decrease in ADC values in the CC, probably due to cytotoxic edema. A delayed decrease in ADC values was observed in the hippocampus after 1week normoxic follow-up in 7- and 14-day HH groups giving an insight of cytotoxic edema formation. Interestingly, 21-day HH-exposed rats did not show change in ADC values. The decrease in T2 values after 14 and 21days in the hippocampal region depicts iron deposition, which was confirmed by histopathology. This study successfully demonstrated the use of MRI modality to trace water diffusion changes in the brain due to prolonged HH exposure.

The protective effects of Cyperus rotundus on behavior and cognitive function in a rat model of hypoxia injury

CONTEXT

Hypoxia injury (HI) with its long-term neurological complications is one of the leading causes of morbidity and mortality in the world. Currently, the treatment regimens for hypoxia are aimed only at ameliorating the damage without complete cure. The need, therefore, for novel therapeutic drugs to treat HI continues.

OBJECTIVE

This study investigates the protective effects of the ethanol extract of Cyperus rotundus L. (Cyperaceae) (EECR), a medicinal plant used in Ayurvedic traditional medicine against sodium nitrite-induced hypoxia in rats.

MATERIALS AND METHODS

We have evaluated the protective effect of 200 and 400 mg/kg of EECR against sodium nitrite-induced hypoxia injury in rats by assessing the cognitive functions, motor, and behavioral effects of EECR treatment along with the histological changes in the brain. By comparing the protective effects of standard drugs galantamine, a reversible cholinesterase inhibitor and pyritinol, an antioxidant nootropic drug against sodium nitrite-induced hypoxia in rats, we have tested the protective ability of EECR.

RESULTS

EECR at doses of 200 and 400 mg/kg was able to protect against the cognitive impairments, and the locomotor activity and muscular coordination defects, which are affected by sodium nitrite-induced hypoxia injury in rats.

CONCLUSION

Based on our results, we suggest that the medicinal herb C. rotundus possesses a protective effect against sodium nitrite-induced hypoxia in rats. Further studies on these protective effects of EECR may help in designing better therapeutic regimes for hypoxia injury.

CoCl2-induced biochemical hypoxia down regulates activities and expression of super oxide dismutase and catalase in cerebral cortex of mice

Hypoxia-induced oxidative stress is one of the major hallmark reasons underlying brain dysfunction. In the present manuscript, we have used CoCl2-induced hypoxic mice to investigate alterations in the activities of chief antioxidative stress enzymes- superoxide dismutase (SOD) and catalase (CAT) and expression of their genes Sod1 and Cat in the cerebral cortex as this model has not been routinely used for carrying out such study. Hypoxia mimetic mice model was accordingly developed by oral CoCl2 administration to mice and validated by analyzing alterations in the expression of the hypoxia inducible factor gene Hif-1α and its immediate responsive genes. Our Western blot data demonstrated that a dose of 40 mg/kg BW of CoCl2 was able to generate hypoxia like condition in mice in which Hif-1α and its immediate responsive genes-glutamate transporter-1 (Slc2a1) and erythropoietin (Epo) expression were up regulated. Our in-gel assay data indicated that SOD and CAT activities significantly declined and it was associated with significant down regulation of Sod1 and Epo expression as evident from our semi quantitative RT-PCR and Western blot data, which might be correlated with up regulation of Hif-1α expression in the cerebral cortex of the CoCl2-treated hypoxic mice. Our findings suggest that CoCl2-induced hypoxic mouse model is useful for studying alterations in the anti oxidative enzymes and biochemical/molecular/neurobiological analysis of hypoxia-induced alterations in brain function.

Fatty acid biosynthesis from glutamate and glutamine is specifically induced in neuronal cells under hypoxia

Hypoxia is involved in many neuronal and non-neuronal diseases, and defining the mechanisms for tissue adaptation to hypoxia is critical for the understanding and treatment of these diseases. One mechanism for tissue adaptation to hypoxia is increased glutamine and/or glutamate (Gln/Glu) utilization. To address this mechanism, we determined incorporation of Gln/Glu and other lipogenic substrates into lipids and fatty acids in both primary neurons and a neuronal cell line under normoxic and hypoxic conditions and compared this to non-neuronal primary cells and non-neuronal cell lines. Incorporation of Gln/Glu into total lipids was dramatically and specifically increased under hypoxia in neuronal cells including both primary (2.0- and 3.0-fold for Gln and Glu, respectively) and immortalized cultures (3.5- and 8.0-fold for Gln and Glu, respectively), and 90% to 97% of this increase was accounted for by incorporation into fatty acids (FA) depending upon substrate and cell type. All other non-neuronal cells tested demonstrated decreased or unchanged FA synthesis from Gln/Glu under hypoxia. Consistent with these data, total FA mass was also increased in neuronal cells under hypoxia that was mainly accounted for by the increase in saturated and monounsaturated FA with carbon length from 14 to 24. Incorporation of FA synthesized from Gln/Glu was increased in all major lipid classes including cholesteryl esters, triacylglycerols, diacylglycerols, free FA, and phospholipids, with the highest rate of incorporation into triacylglycerols. These results indicate that increased FA biosynthesis from Gln/Glu followed by esterification may be a neuronal specific pathway for adaptation to hypoxia. We identified a novel neuronal specific pathway for adaptation to hypoxia through increased fatty acid biosynthesis from glutamine and glutamate (Gln/Glu) followed by esterification into lipids. All other non-neuronal cells tested demonstrated decreased or unchanged lipid synthesis from Gln/Glu under hypoxia. Incorporation of other lipogenic substrates into lipids was decreased under hypoxia in neuronal cells. We believe that this finding will provide a novel strategy for treatment of oxygen and energy deficient conditions in the neuronal system.

Enriched environment prevents hypobaric hypoxia induced memory impairment and neurodegeneration: role of BDNF/PI3K/GSK3β pathway coupled with CREB activation

Adverse environmental conditions such as hypobaric hypoxia (HH) cause memory impairment by affecting cellular machinery leading to neurodegeneration. Providing enriched environment (EE) is found to be beneficial for curing several neurodegenerative disorders. The protective role of EE in preventing HH induced neuronal death has been reported previously but the involved mechanism is still not clearly understood. The present study is an attempt to verify the impact of EE on spatial memory during HH and also to explore the possible role of neurotrophin in EE mediated neuroprotection. Signaling mechanism involved in neuroprotection was also explored. Male Sprague Dawley rats were simulated to HH condition in an Animal Decompression Chamber at an altitude of 25000 feet in standard and enriched cages for 7 days. Spatial memory was assessed through Morris Water Maze. Role of different neurotrophins was explored by gene silencing and inhibitors for their respective receptors. Further, using different blockers signaling pathway was also explored. Finding of the present study suggested that EE prevents HH mediated memory impairment and neurodegeneration. Also brain-derived neurotrophic factor (BDNF) plays a major role in EE mediated neuroprotection and it effectively prevented neurodegeneration by activating PI3K/AKT pathway resulting in GSK3β inactivation which further inhibits apoptosis. Moreover GSK3β phosphorylation and hence its inactivation upregulates CREB phosphorylation which may also accounts for activation of survival machinery in cells and provides neuroprotection. From these observations it can be postulated that EE has a therapeutic potential in amelioration of HH induced memory impairment and neurodegeneration. Hence it may be used as a non invasive and non pharmacological intervention against various neurological disorders.

Long-term results of enriched environment and erythropoietin after hypobaric hypoxia in rats

After global cerebral hypoxia, many patients are severely disabled even after intensive neurorehabilitation. Secondary mechanisms of brain injury as a result of biochemical and physiological events occur within a period of hours to months, and provide a window of opportunity for therapeutic intervention. Erythropoietin (EPO) has been shown to be neuroprotective in the brain subjected to a variety of injuries. Fifty-nine 3-month-old male Wistar rats were randomly distributed to experimental groups with respect to the housing (enriched environment - EE, standard housing - SH), to hypoxia exposure, and to EPO treatment. An acute mountain sickness model was used as a hypobaric hypoxia simulating an altitude of 8000 m. One half of the animals received erythropoietin injections, while the others were injected saline. Spatial memory was tested in a Morris water maze (MWM). The escape latency and the path length were measured. Better spatial learning in MWM was only seen in the group that received erythropoietin together with enriched environment. EPO administration itself had no influence on spatial memory. The results were very similar for both latencies and path lengths. These results support the idea that after brain injuries, the recovery can be potentiated by EPO administration combined with neurorehabilitation.

Withania somnifera root extract ameliorates hypobaric hypoxia induced memory impairment in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Withania somnifera (WS) root extract has been used traditionally in ayurvedic system of medicine as a memory enhancer and anti-stress agent.

AIM OF THE STUDY

To evaluate the neuroprotective and prophylactic potential of WS root extract in ameliorating hypobaric hypoxia (HH) induced memory impairment and to explore the underlying molecular mechanism.

MATERIALS AND METHODS

WS root extract was administered to male Sprague Dawley rats during a period of 21 days pre-exposure and 07 days exposure to a simulated altitude of 25,000 ft. Spatial memory was assessed by Morris Water Maze. Neurodegeneration, corticosterone, acetylcholine (Ach) levels, acetylcholine esterase (AchE) activity, oxidative stress markers and nitric oxide (NO) concentration were assessed in the hippocampus. Synaptic and apoptotic markers were also investigated by immunoblotting. To study the role of NO in regulating corticosterone mediated signaling, the neuronal nitric oxide synthase (n-NOS) inhibitor, L-Nitro-arginine methyl ester (L-Name) and NO agonist sodium nitroprusside (SNP) were administered from 3rd to 7th day of hypoxic exposure.

RESULTS

Administration of WS root extract prevented HH induced memory impairment and neurodegeneration along with decreased NO, corticosterone, oxidative stress and AchE activity in hippocampal region. Inhibition of NO synthesis by administration of L-Name reduced corticosterone levels in hippocampus during hypoxic exposure while co-administration of corticosterone increased neurodegeneration. Administration of sodium nitroprusside (SNP) along with WS root extract supplementation during hypoxic exposure increased corticosterone levels and increased the number of pyknotic cells.

CONCLUSION

WS root extract ameliorated HH induced memory impairment and neurodegeneration in hippocampus through NO mediated modulation of corticosterone levels.