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Isabel Gamache, Marc-André Legault, Jean-Christophe Grenier, Rocio Sanchez, Eric Rhéaume, Samira Asgari, Amina Barhdadi, Yassamin Feroz Zada, Holly Trochet, Yang Luo, et al.
Published: 5 October 2021
Abstract:
Pharmacogenomic studies have revealed associations between rs1967309 in the adenylyl cyclase type 9 (ADCY9) gene and clinical responses to the cholesteryl ester transfer protein (CETP) modulator dalcetrapib, however, the mechanism behind this interaction is still unknown. Here, we characterized selective signals at the locus associated with the pharmacogenomic response in human populations and we show that rs1967309 region exhibits signatures of positive selection in several human populations. Furthermore, we identified a variant in CETP, rs158477, which is in long-range linkage disequilibrium with rs1967309 in the Peruvian population. The signal is mainly seen in males, a sex-specific result that is replicated in the LIMAA cohort of over 3400 Peruvians. Analyses of RNA-seq data further suggest an epistatic interaction on CETP expression levels between the two SNPs in multiple tissues, which also differs between males and females. We also detected interaction effects of the two SNPs with sex on cardiovascular phenotypes in the UK Biobank, in line with the sex-specific genotype associations found in Peruvians at these loci. We propose that ADCY9 and CETP coevolved during recent human evolution due to sex-specific selection, which points toward a biological link between dalcetrapib’s pharmacogene ADCY9 and its therapeutic target CETP.
Neetu Kushwah, Vishal Jain, Manisha Kadam, Rahul Kumar, Aastha Dheer, Dipti Prasad, Bhuvnesh Kumar,
Published: 12 July 2021
Frontiers in Pharmacology, Volume 12; https://doi.org/10.3389/fphar.2021.669701

Abstract:
Hypobaric hypoxia (HH) is a stressful condition, which is more common at high altitudes and can impair cognitive functions. Ginkgo biloba L. leaf extract (GBE) is widely used as herbal medicine against different disorders. Its ability to improve cognitive functions, reduce oxidative stress, and promote cell survival makes it a putative therapeutic candidate against HH. The present study has been designed to explore the effect of GBE on HH-induced neurodegeneration and memory impairment as well as possible signaling mechanisms involved. 220–250 gm (approximately 6- to 8-week-old) Sprague Dawley rats were randomly divided into different groups. GBE was orally administered to respective groups at a dose of 100 mg/kg/day throughout the HH exposure, i.e., 14 days. Memory testing was performed followed by hippocampus isolation for further processing of different molecular and morphological parameters related to cognition. The results indicated that GBE ameliorates HH-induced memory impairment and oxidative damage and reduces apoptosis. Moreover, GBE modulates the activity of the small conductance calcium-activated potassium channels, which further reduces glutamate excitotoxicity and apoptosis. The exploration of the downstream signaling pathway demonstrated that GBE administration prevents HH-induced small conductance calcium-activated potassium channel activation, and that initiates pro-survival machinery by activating extracellular signal–regulated kinase (ERK)/calmodulin-dependent protein kinase II (CaMKII) and the cAMP response element–binding protein (CREB) signaling pathway. In summary, the current study demonstrates the beneficial effect of GBE on conditions like HH and provides various therapeutic targets involved in the mechanism of action of GBE-mediated neuroprotection.
Isabel Gamache, , , Rocio Sanchez, Eric Rhéaume, , Amina Barhdadi, Yassamin Feroz Zada, , , et al.
Published: 14 May 2021
Abstract:
Pharmacogenomic studies have revealed associations between rs1967309 in the adenylyl cyclase type 9 (ADCY9) gene and clinical responses to the cholesteryl ester transfer protein (CETP) modulator dalcetrapib, however, the mechanism behind this interaction is still unknown. Here, we characterized selective signals at the locus associated with the pharmacogenomic response in human populations and we show that rs1967309 region exhibits signatures of positive selection in several human populations. Furthermore, we identified a variant in CETP, rs158477, which is in long-range linkage disequilibrium with rs1967309 in the Peruvian population. The signal is mainly seen in males, a sex-specific result that is replicated in the LIMAA cohort of over 3,400 Peruvians. Analyses of RNA-seq data further suggest an epistatic interaction on CETP expression levels between the two SNPs in multiple tissues, which also differs between males and females. We also detected interaction effects of the two SNPs with sex on cardiovascular phenotypes in the UK Biobank, in line with the sex-specific genotype associations found in Peruvians at these loci. We propose that ADCY9 and CETP coevolved during recent human evolution due to sex-specific selection, which points towards a biological link between dalcetrapib’s pharmacogene ADCY9 and its therapeutic target CETP.
Julie Deguil,
Published: 3 February 2021
Therapies, Volume 76, pp 87-99; https://doi.org/10.1016/j.therap.2021.02.001

The publisher has not yet granted permission to display this abstract.
Published: 17 September 2020
by MDPI
Biomolecules, Volume 10; https://doi.org/10.3390/biom10091328

Abstract:
Cognition is a crucial element of human functionality. Like any other physical capability, cognition is both enabled and limited by tissue biology. The aim of this study was to investigate whether oxygen is a rate-limiting factor for any of the main cognitive domains in healthy young individuals. Fifty-six subjects were randomly assigned to either increased oxygen supply using hyperbaric oxygen (two atmospheres of 100% oxygen) or to a “sham” treatment (a simulation of increased pressure in a chamber with normal air). While in the chamber, participants went through a battery of tests evaluating the major cognitive domains including information processing speed, episodic memory, working memory, cognitive flexibility, and attention. The results demonstrated that from all evaluated cognitive domains, a statistically significant improvement was found in the episodic memory of the hyper-oxygenized group. The hyper-oxygenized group demonstrated a better learning curve and a higher resilience to interference. To conclude, oxygen delivery is a rate-limiting factor for memory function even in healthy young individuals under normal conditions. Understanding the biological limitations of our cognitive functions is important for future development of interventional tools that can be used in daily clinical practice.
, Lara Phillips, Peter Inglis, Gabriel Lathrop, Jaclyn Gadbois, Katherine Rizzolo, N. Stuart Harris
High Altitude Medicine & Biology, Volume 21, pp 184-191; https://doi.org/10.1089/ham.2019.0111

Abstract:
Background: This study aimed to longitudinally quantify the prevalence of mild cognitive impairment (MCI) in individual trekkers at three different ascending altitudes (Site 1: ∼3500 m, Site 2: ∼4400 m, and Site 3: ∼5100 m). We correlated these findings with the presence of acute mountain sickness (AMS).Materials and Methods: We performed serial assays using the environmental quick mild cognitive impairment (eQMCI) score on 103 English-speaking 18- to 65-year-old volunteers trekking to Everest Base Camp in Nepal during spring 2016. We defined MCI as a score less than 67 (lower scores indicating more cognitive impairment). Additional data collected included the Lake Louise Score, demographics, and other possible confounders.Results: eQMCI scores significantly decreased with ascent from Site 1 to 2 (a score of 78.95 [SD = 7.96] to 74.67 [SD = 8.8] [Site 1–2 p = 0.04]), but then increased on ascent to Site 3 to 83.68 (SD = 8.67) (Site 1–3 p = <0.0001, Site 2–3 p = <0.0001). However, subjects who fulfilled eQMCI criteria for MCI increased despite the overall improvement in score: 6.8% (N = 7) at Site 1, 18.7% (N = 14) at Site 2, and 3.3% (N = 2) at Site 3. Incidence of AMS at Sites 1, 2, and 3 was 22.3% (N = 23), 21.3% (N = 16), and 48.3% (N = 29), respectively. Of those with MCI, 1.94% met criteria for AMS at Site 1 (p = 0.0017), 2.67% at Site 2 (p = 0.6949), and 3.33% at Site 3 (p = <0.0001).Conclusions: There is a significant incidence of MCI at high altitude, even in those without subjective findings of AMS. Interestingly, subjects with a decline in cognitive function show an increasing trend for developing AMS at higher altitude. Future research on the clinical impact of MCI on a subject's health, judgment, and performance remains to be elucidated.
Todd R. Seech, Matthew E. Funke, Richard F. Sharp, Gregory A. Light,
Published: 31 January 2020
Frontiers in Psychiatry, Volume 11; https://doi.org/10.3389/fpsyt.2020.00012

Abstract:
The ability to detect novelty in our environment is a critical sensory function. A reliable set of event-related potentials (ERP), known as the auditory deviance response (ADR), are elicited in the absence of directed attention and indexes functionally relevant networks. The ADR consists of three peaks: mismatch negativity (MMN), P3a, and reorienting negativity (RON) that are sequentially evoked in response to unattended changes in repetitive background stimulation. While previous studies have established the ADR’s sensitivity to a range of pharmacologic and nonpharmacologic interventions and are leading candidate biomarkers of perturbations of the central nervous system (CNS), here we sought to determine if ADR peaks are sensitive to decreases in breathable oxygen. Participants performed a visuomotor tracking task while EEG was recorded during two 27-min sessions. The two sessions differed in the amount of environmental oxygen available: 10.6% O2 (hypoxia) versus 20.4% O2 (normoxia). ERPs were measured while a series of identical, or “standard,” tones combined with occasional “oddball,” tones, were presented. MMN, P3a, and RON were assessed in response to the oddball compared to the standard stimuli. Behavioral impairment during hypoxia was demonstrated by a deficit in tracking performance compared to the normoxia condition. Whereas no changes were detected in the MMN or RON, the amplitude of the P3a component was significantly reduced during hypoxia compared to normoxia, within the first 9 min of exposure. To our knowledge, this is the first study to demonstrate the effect of low oxygen exposure on passively elicited neural measures of early sensory processing. This study demonstrates that passively elicited EEG measures, reflecting preattentive auditory processing, are disrupted by acute hypoxia. Results have implications for the development of biomarkers for the noninvasive assessment of CNS perturbations.
Koushik Ray, Krishna Kishore, , Debojyoti Bhattacharyya, Almaz Akunov, Abdirashit Maripov, Akpay Sarybaev, Shashi Bala Singh, Bhuvnesh Kumar
High Altitude Medicine & Biology, Volume 20, pp 236-244; https://doi.org/10.1089/ham.2018.0139

Abstract:
Ray, Koushik, Krishna Kishore, Praveen Vats, Debojyoti Bhattacharyya, Almaz Akunov, Abdirashit Maripov, Akpay Sarybaev, Shashi Bala Singh, and Bhuvnesh Kumar. A temporal study on learning and memory at high altitude in two ethnic groups. High Alt Med Biol 00:000–000, 2019. Introduction: Cognitive function has been compromised during high-altitude (HA) exposure due to slowing of mental processing. Materials and Methods: A total of 20 Indian and 20 Kyrgyz soldiers were studied at 4111 m to assess cognitive function in two different ethnic groups. Paired associate learning, pattern recognition memory, spatial span (SSP), spatial working memory (SWM), choice reaction time (CRT), and simple reaction time (SRT) were evaluated at sea level and on days 3, 7, 14, and 21 of HA stay and on day 3 of deinduction. Results: All the parameters were significantly affected at HA. Indian soldiers were acclimatized by 7 days but Kyrgyz soldiers required 21 days for acclimatization. A slow impairment in SWM, CRT, and SRT was observed in Kyrgyz soldiers than in Indian soldiers and it continues throughout 21 days of HA stay, but for Indian soldiers the deterioration was maximum on day 7 and improvement in SWM, CRT, and SRT was observed on day 14 and close to baseline value on day 21. After deinduction, although Indian soldiers attained the normal value, Kyrgyz soldiers had higher value than baseline in SSP, SWM, CRT, and SRT. Conclusion: Difference in the cognitive performances of Indian and Kyrgyz soldiers may be due to the ethnogenetic diversity of these two groups.
XiaoMing Chen, Hong Li, Qian Zhang, Jiye Wang, Wenbin Zhang, Jian Liu, Baojuan Li, Zhenlong Xin, Jie Liu, Hong Yin, et al.
Published: 17 June 2019
Human Brain Mapping, Volume 40, pp 4202-4212; https://doi.org/10.1002/hbm.24696

The publisher has not yet granted permission to display this abstract.
, Matea A. Djokic, Dillon Gilbertson, Pamela N. Deyoung, Naa-Oye Bosompra, Lu Wu, Cecilia Anza-Ramirez, , Frank L. Powell, Atul Malhotra, et al.
Published: 12 June 2019
Abstract:
Impairments in cognitive function, mood, and sleep quality occur following ascent to high altitude. Low oxygen (hypoxia) and poor sleep quality are both linked to impaired cognitive performance, but their independent contributions at high altitude remain unknown. Adaptive servoventilation (ASV) improves sleep quality by stabilizing breathing and preventing central apneas without supplemental oxygen. We compared the efficacy of ASV and supplemental oxygen sleep treatments for improving daytime cognitive function and mood in high-altitude visitors (N = 18) during acclimatization to 3,800 m. Each night, subjects were randomly provided with ASV, supplemental oxygen (SpO2 > 95%), or no treatment. Each morning subjects completed a series of cognitive function tests and questionnaires to assess mood and multiple aspects of cognitive performance. We found that both ASV and supplemental oxygen (O2) improved daytime feelings of confusion (ASV: p < 0.01; O2: p < 0.05) and fatigue (ASV: p < 0.01; O2: p < 0.01) but did not improve other measures of cognitive performance at high altitude. However, performance improved on the trail making tests (TMT) A and B (p < 0.001), the balloon analog risk test (p < 0.0001), and the psychomotor vigilance test (p < 0.01) over the course of three days at altitude after controlling for effects of sleep treatments. Compared to sea level, subjects reported higher levels of confusion (p < 0.01) and performed worse on the TMT A (p < 0.05) and the emotion recognition test (p < 0.05) on nights when they received no treatment at high altitude. These results suggest that stabilizing breathing (ASV) or increasing oxygenation (supplemental oxygen) during sleep can reduce feelings of fatigue and confusion, but that daytime hypoxia may play a larger role in other cognitive impairments reported at high altitude. Furthermore, this study provides evidence that some aspects of cognition (executive control, risk inhibition, sustained attention) improve with acclimatization.
Shahnawaz Alam, Koushik Ray, Vishal Jain, Meetu Wadhwa, Punita Kumari, Koustav Roy, Garima Chauhan, Krishna Kishore, Usha Panjwani,
Published: 6 March 2019
Behavioural Brain Research, Volume 366, pp 135-141; https://doi.org/10.1016/j.bbr.2019.03.016

The publisher has not yet granted permission to display this abstract.
, Alexandru Korotcov, Asamoah Bosomtwi, Xiufen Xu, Derek R. Holman, Kathleen Whiting, Scott Jones, Andrew Hoy, ,
Published: 13 October 2018
Experimental Neurology, Volume 311, pp 293-304; https://doi.org/10.1016/j.expneurol.2018.10.007

Abstract:
We sought to understand the mechanisms underlying cognitive deficits that are reported to affect non-native subjects following their prolonged stay and/or work at high altitude (HA). We found that mice exposed to a simulated environment of 5000 m exhibit deficits in hippocampal learning and memory accompanied by abnormalities in brain MR imaging. Exposure (1–8 months) to HA led to an increase in brain ventricular volume, a reduction in relative cerebral blood flow and changes in diffusion tensor imaging (DTI) derived parameters within the hippocampus and corpus callosum. Furthermore, neuropathological examination revealed significant expansion of the neurovascular network, microglia activation and demyelination within the corpus callosum. Electrophysiological recordings from the corpus callosum indicated that axonal excitabilities are increased while refractory periods are longer despite of a lack of change in action potential conduction velocities of both myelinated and unmyelinated fibers. Next generation RNA-sequencing identified alterations in hippocampal and amygdala transcriptome signaling pathways linked to angiogenesis, neuroinflammation and myelination. Our findings reveal that exposure to hypobaric-hypoxia triggers maladaptive responses inducing cognitive deficits and suggests potential mechanisms underlying the adverse impacts of staying or traveling at high altitude.
Jigni Mishra, Kshipra Misra
Management of High Altitude Pathophysiology pp 69-80; https://doi.org/10.1016/b978-0-12-813999-8.00004-5

The publisher has not yet granted permission to display this abstract.
Journal for Healthcare Quality, Volume 40, pp 9-18; https://doi.org/10.1097/jhq.0000000000000061

Abstract:
Although variation in-patient outcomes based on hospitals' geographic location has been studied, altitude of hospitals above sea level may also affect patient outcomes. Possibly, because of negative physical and psychological effects of altitude on hospital employees, hospital efficiency may decline at higher altitudes. Greater focus on hospital efficiency, despite decreasing efficiency at higher altitudes, could increase demands on hospital employees and further deteriorate patient outcomes. Using data envelopment analysis on a sample of 840 hospital-year observations representing 95,504 patients with acute myocardial infarction (AMI) in the United States, and controlling for patient, hospital, and county characteristics and controlling for hospital, state, and year fixed effects, we find support for the negative association between hospital altitude and efficiency; for 1 percentage point increase in efficiency and every 1,000 feet increase in altitude above the sea level, the mortality of patients with AMI increases by 0.66 percentage points. The findings have implications for hospital performance at increasing geographic elevation and introduces to the literature the notion of “health economics of elevation,” to suggest that elevation of a hospital may be an important criterion for consideration for policy makers and insurance firms.
Lara Phillips, , Yuchiao Chang, Erik R. Swenson, N. Stuart Harris
High Altitude Medicine & Biology, Volume 18, pp 121-127; https://doi.org/10.1089/ham.2016.0001

Abstract:
Phillips, Lara, Buddha Basnyat, Yuchiao Chang, Erik R. Swenson, and N. Stuart Harris. Findings of cognitive impairment at high altitude: relationships to acetazolamide use and acute mountain sickness. High Alt Med Biol. 18:121–127, 2017. Objective: Acute mountain sickness (AMS) is defined by patient-reported symptoms using the Lake Louise Score (LLS), which provides limited insight into any possible underlying central nervous system (CNS) dysfunction. Some evidence suggests AMS might coexist with altered neural functioning. Cognitive impairment (CI) may go undetected unless a sensitive test is applied. Our hypothesis was that a standardized test for mild CI would provide an objective measure of CNS dysfunction, which may correlate with the symptoms of AMS and so provide a potential new tool to better characterize altitude-related CNS dysfunction. We compared a cognitive screening tool with the LLS to see if it correlated with CNS dysfunction. Methods: Adult native English-speaking subjects visiting Himalayan Rescue Association aid stations in Nepal at 3520 m (11,548 ft) and 4550 m (14,927 ft) were recruited. Subjects were administered the LLS and a slightly modified version of the environmental Quick mild cognitive impairment screen (eQmci). Medication use for altitude illness was recorded. Scores were compared using the Spearman's correlation coefficient. Data also included medication use. Results: Seventy-nine subjects were enrolled. A cut-off of three or greater was used for the LLS to diagnose AMS and 67 or less for the eQmci to diagnose CI. There were 22 (28%) subjects who met criteria for AMS and 17 (22%) subjects who met criteria for CI. There was a weak correlation (r2 = 0.06, p = 0.04) between eQmci score and LLS. In matched subjects with identical LLS, recent acetazolamide use was associated with significantly more CI. Conclusion: Field assessment of CI using a rapid standardized tool demonstrated that a substantial number of subjects were found to have mild CI following rapid ascent to 3520–4550 m (11,548–14,927 ft). The weak correlation between the LLS and eQmci suggests that AMS does not result in CI. Use of acetazolamide appears to be associated with CI at all levels of AMS severity.
, Satya Narayan Deep, , Narayanappa Amruta, Dipti Prasad,
Published: 1 June 2017
Physiology & Behavior, Volume 175, pp 56-65; https://doi.org/10.1016/j.physbeh.2017.03.035

The publisher has not yet granted permission to display this abstract.
Entesar Yaseen Abdo Qaid, , S F Sulaiman, Nurul Aiman Mohd Yusof, N Shafin, , , Cb Abd Aziz
Human & Experimental Toxicology, Volume 36, pp 1315-1325; https://doi.org/10.1177/0960327116689714

Abstract:
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.
XiaoMing Chen, Xinqin Liu, Bin Li, Qian Zhang, Jiye Wang, Wenbin Zhang, Wenjing Luo, Jingyuan Chen
International Journal of Biological Sciences, Volume 13, pp 518-531; https://doi.org/10.7150/ijbs.17800

Abstract:
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.
Qinghai Shi, Xin Liu, Ning Wang, Xinchuan Zheng, Jihua Ran, Zhengxiang Liu, Jianfeng Fu, Jiang Zheng
Published: 22 November 2016
Behavioural Brain Research, Volume 319, pp 188-199; https://doi.org/10.1016/j.bbr.2016.11.039

The publisher has not yet granted permission to display this abstract.
Glutamate and ATP at the Interface of Metabolism and Signaling in the Brain, Volume 12, pp 307-321; https://doi.org/10.1007/978-3-319-28383-8_16

The publisher has not yet granted permission to display this abstract.
Sheng Li Hu, Wei Xiong, Zhi Qiang Dai, Heng Li Zhao,
Published: 5 January 2016
Abstract:
Hypersensitive C-reaction protein (hsCRP) may be a risk factor for cognitive impairment resulting from Alzheimer’s disease (AD), stroke, and vascular dementia. This study explored the correlation of peripheral blood hsCRP level with cognitive decline due to high altitude exposure. The study was conducted on 100 male military participants who had never been to high altitude. Cerebral oxygen saturation monitoring, event related potentials (P300, N200) detection, and neurocognitive assessment was performed and total hsCRP, interleukin-6 (IL-6), and homocysteine was estimated at 500m altitude, 3650m altitude, 3day, 1, and 3 month post arriving at the base camp (4400m), and 1 month after coming back to the 500m altitude. High altitude increased brain oxygen saturation, prolonged P300 and N200 latencies, injured cognitive functions, and raised plasma hsCRP levels. But they all recovered in varying degrees at 1 and 3 month post arriving at the base camp (4400m). P300 latencies and hsCRP levels were strongly correlated to cognitive performances. These results suggested that cognitive deterioration occurred during the acute period of exposure to high altitude and may recover probably owning to acclimatization after extended stay at high altitude. Plasma hsCRP is inversely correlated to neurological cognition and it may be a potential biomarker for the prediction of high altitude induced cognitive dysfunction.
Juan C. López-Ramos, , Agnès Gruart, Joan J. Guinovart,
Frontiers in Cellular Neuroscience, Volume 9; https://doi.org/10.3389/fncel.2015.00431

Abstract:
Although glycogen is the only carbohydrate reserve of the brain, its overall contribution to brain functions remains unclear. It has been proposed that glycogen participates in the preservation of such functions during hypoxia. Several reports also describe a relationship between brain glycogen and susceptibility to epilepsy. To address these issues, we used our brain-specific Glycogen Synthase knockout (GYS1Nestin-KO) mouse to study the functional consequences of glycogen depletion in the brain under hypoxic conditions and susceptibility to epilepsy. GYS1Nestin-KO mice presented significantly different power spectra of hippocampal local field potentials (LFPs) than controls under hypoxic conditions. In addition, they showed greater excitability than controls for paired-pulse facilitation evoked at the hippocampal CA3-CA1 synapse during experimentally induced hypoxia, thereby suggesting a compensatory switch to presynaptic mechanisms. Furthermore, GYS1Nestin-KO mice showed greater susceptibility to hippocampal seizures and myoclonus following the administration of kainate and/or a brief train stimulation of Schaffer collaterals. We conclude that brain glycogen could play a protective role both in hypoxic situations and in the prevention of brain seizures.
Published: 6 October 2015
BMC Neuroscience, Volume 16, pp 1-11; https://doi.org/10.1186/s12868-015-0199-6

Abstract:
It is well documented that the nitric oxide (NO) might be directly involved in brain response to hypobaric hypoxia, and could contribute to memory deficiencies. Recent studies have shown that melatonin could attenuate hypoxia or ischemia-induced nerve injuries by decreasing the production of free radicals. The present study, using immunohistochemical and immunoblot methods, aimed to explore whether melatonin treatment may affect the expression of nitric oxide system and protein nitration, and provide neuroprotection in the rat hippocampus injured by hypobaric hypoxia. Prior to hypoxic treatment, adult rats were pretreated with melatonin (100 mg/kg, i.p.) before they were exposed to the altitude chamber with 48 Torr of the partial oxygen concentration (pO2) for 7 h to mimic the ambience of being at 9000 m in height. They were then sacrificed after 0 h, 1, and 3 days of reoxygenation. The results obtained from the immunohistochemical and immunoblotting analyses showed that the expressions of neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), nitrotyrosine (Ntyr) and Caspase 3 in the hypoxic hippocampus were increased from 0 h to 3 days of reoxygenation. Interestingly, the hypoxia-induced increase of nNOS, eNOS, iNOS, Ntyr and Caspase 3 protein expression was significantly depressed in the hypoxic rats treated with melatonin. Activation of the nitric oxide system and protein nitration constitutes a hippocampal response to hypobaric hypoxia and administration of melatonin could provide new therapeutic avenues to prevent and/or treat the symptoms produced by hypobaric hypoxia.
Vijay K. Sharma, Saroj K. Das, Priyanka Dhar, Kalpana B. Hota, Bidhu B. Mahapatra, Vivek Vashishtha, Ashish Kumar, , Tsering Norboo,
Published: 2 July 2014
Abstract:
Though acute exposure to hypobaric hypoxia is reported to impair cognitive performance, the effects of prolonged exposure on different cognitive domains have been less studied. The present study aimed at investigating the time dependent changes in cognitive performance on prolonged stay at high altitude and its correlation with electroencephalogram (EEG) and plasma homocysteine. The study was conducted on 761 male volunteers of 25–35 years age who had never been to high altitude and baseline data pertaining to domain specific cognitive performance, EEG and homocysteine was acquired at altitude ≤240 m mean sea level (MSL). The volunteers were inducted to an altitude of 4200–4600 m MSL and longitudinal follow-ups were conducted at durations of 03, 12 and 18 months. Neuropsychological assessment was performed for mild cognitive impairment (MCI), attention, information processing rate, visuo-spatial cognition and executive functioning. Total homocysteine (tHcy), vitamin B12 and folic acid were estimated. Mini Mental State Examination (MMSE) showed temporal increase in the percentage prevalence of MCI from 8.17% on 03 months of stay at high altitude to 18.54% on 18 months of stay. Impairment in visuo-spatial executive, attention, delayed recall and procedural memory related cognitive domains were detected following prolonged stay in high altitude. Increase in alpha wave amplitude in the T3, T4 and C3 regions was observed during the follow-ups which was inversely correlated (r = −0.68) to MMSE scores. The tHcy increased proportionately with duration of stay at high altitude and was correlated with MCI. No change in vitamin B12 and folic acid was observed. Our findings suggest that cognitive impairment is progressively associated with duration of stay at high altitude and is correlated with elevated tHcy in the plasma. Moreover, progressive MCI at high altitude occurs despite acclimatization and is independent of vitamin B12 and folic acid.
Gang Zhang, Si-Min Zhou, Chao Yuan, Huai-Jun Tian, Peng Li,
High Altitude Medicine & Biology, Volume 14, pp 338-341; https://doi.org/10.1089/ham.2012.1091

Abstract:
Zhang, Gang, Si-Min Zhou, Chao Yuan, Huai-Jun Tian, Peng Li, and Yu-Qi Gao. The effects of short-term and long-term exposure to a high altitude hypoxic environment on neurobehavioral function. High Alt Med Biol 14:338–341, 2013.—Aims: Examined the change in neurobehavioral function of individuals acclimated to high altitudes and those native to high altitudes. Methods: A neurobehavioral core test battery approved by the WHO (WHO-NCTB) was used to evaluate the effects of high altitude hypoxia on neurobehavioral function. The WHO-NCTB is composed of seven individual tests: a mood state profile, simple reaction time test, digit span test, Santa Ana manual dexterity test, digit symbol test, Benton visual retention test, and pursuit aiming test. Results: The values from the Santa Ana manual dexterity test, digit symbol test, and pursuit aiming test from sea-level subjects acclimated for 5 days at 3700 m were significantly decreased when compared with the same subjects at sea level. The values from the digit span, Santa Ana manual dexterity, digit symbol, Benton visual retention and pursuit aiming tests in subjects native to high altitudes of 3700, 4500, and 5100 m were significantly decreased when compared with subjects at sea level and compared with sea-level subjects acclimated for 5 days at 3700 m. Conclusions: These results demonstrate that high altitude hypoxia induces damage to neurobehavioral functions, and the long-term deficit in neurobehavioral function was more severe than the short-term changes.
H. Kauser, Surajit Sahu, S. Kumar,
Published: 30 October 2013
Physiology & Behavior, Volume 123, pp 187-192; https://doi.org/10.1016/j.physbeh.2013.10.028

The publisher has not yet granted permission to display this abstract.
H. Kauser, S. Sahu, S. Kumar,
Published: 18 September 2013
Neuroscience, Volume 254, pp 110-119; https://doi.org/10.1016/j.neuroscience.2013.09.023

The publisher has not yet granted permission to display this abstract.
R. Guerra-Narbona, J. M. Delgado-Garcia,
Journal of Applied Physiology, Volume 114, pp 1705-1716; https://doi.org/10.1152/japplphysiol.01298.2012

Abstract:
The aim of this work was to reveal a hypothetical improvement of cognitive abilities in animals acclimatized to altitude and performing under ground level conditions, when looking at submaximal performance, once seen that it was not possible when looking at maximal scores. We modified contrasted cognitive tasks (object recognition, operant conditioning, eight-arm radial maze, and classical conditioning of the eyeblink reflex), increasing their complexity in an attempt to find performance differences in acclimatized animals vs. untrained controls. In addition, we studied, through immunohistochemical quantification, the expression of choline acetyltransferase and acetyl cholinesterase, enzymes involved in the synthesis and degradation of acetylcholine, in the septal area, piriform and visual cortexes, and the hippocampal CA1 area of animals submitted to acute hypobaric hypoxia, or acclimatized to this simulated altitude, to find a relationship between the cholinergic system and a cognitive improvement due to altitude acclimatization. Results showed subtle improvements of the cognitive capabilities of acclimatized animals in all of the tasks when performed under ground-level conditions (although not before 24 h), in the three tasks used to test explicit memory (object recognition, operant conditioning in the Skinner box, and eight-arm radial maze) and (from the first conditioning session) in the classical conditioning task used to evaluate implicit memory. An imbalance of choline acetyltransferase/acetyl cholinesterase expression was found in acclimatized animals, mainly 24 h after the acclimatization period. In conclusion, altitude acclimatization improves cognitive capabilities, in a process parallel to an imbalance of the cholinergic system.
J. Deguil, L. Ravasi, A. Auffret, , , V. Bragulat, C. Cassé-Perrot, V. Colavito, M.T. Herrero Ezquerro, Y. Lamberty, et al.
Drug Discovery Today: Technologies, Volume 10; https://doi.org/10.1016/j.ddtec.2013.03.003

The publisher has not yet granted permission to display this abstract.
Peng Li, Gang Zhang, Hai-Yan You, Ran Zheng,
Published: 1 June 2012
Physiology & Behavior, Volume 106, pp 439-445; https://doi.org/10.1016/j.physbeh.2012.03.002

The publisher has not yet granted permission to display this abstract.
M. Udayabanu, D. Kumaran, A. Katyal
Published: 27 January 2012
Neuroscience, Volume 202, pp 434-445; https://doi.org/10.1016/j.neuroscience.2011.11.022

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Xiaodan Yan, , , Xuchu Weng
Published: 31 October 2011
Brain and Cognition, Volume 77, pp 53-59; https://doi.org/10.1016/j.bandc.2011.06.002

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Matthew S. Ganio, , Douglas J. Casa, Brendon P. McDermott, Elaine C. Lee, Linda M. Yamamoto, Stefania Marzano, , Liliana Jimenez, Laurent Le Bellego, et al.
British Journal of Nutrition, Volume 106, pp 1535-1543; https://doi.org/10.1017/s0007114511002005

Abstract:
The present study assessed the effects of mild dehydration on cognitive performance and mood of young males. A total of twenty-six men (age 20·0 (sd0·3) years) participated in three randomised, single-blind, repeated-measures trials: exercise-induced dehydration plus a diuretic (DD; 40 mg furosemide); exercise-induced dehydration plus placebo containing no diuretic (DN); exercise while maintaining euhydration plus placebo (EU; control condition). Each trial included three 40 min treadmill walks at 5·6 km/h, 5 % grade in a 27·7°C environment. A comprehensive computerised six-task cognitive test battery, the profile of mood states questionnaire and the symptom questionnaire (headache, concentration and task difficulty) were administered during each trial. Pairedttests compared the DD and DN trials resulting in >1 % body mass loss (mean 1·59 (sd0·42) %) with the volunteer's EU trial (0·01 (sd0·03) %). Dehydration degraded specific aspects of cognitive performance: errors increased on visual vigilance (P = 0·048) and visual working memory response latency slowed (P = 0·021). Fatigue and tension/anxiety increased due to dehydration at rest (P = 0·040 and 0·029) and fatigue during exercise (P = 0·026). Plasma osmolality increased due to dehydration (P< 0·001) but resting gastrointestinal temperature was not altered (P = 0·238). In conclusion, mild dehydration without hyperthermia in men induced adverse changes in vigilance and working memory, and increased tension/anxiety and fatigue.
, Jean Krieger, , Christine Erhardt, Myriam Maumy, Patricia Tassi
Published: 28 February 2011
Brain and Cognition, Volume 75, pp 39-50; https://doi.org/10.1016/j.bandc.2010.10.003

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Sangu Muthuraju, Panchanan Maiti, Preeti Solanki, Alpesh Kumar Sharma, Amitabh, Shashi Bala Singh, Dipti Prasad,
Published: 12 October 2009
Behavioural Brain Research, Volume 203, pp 1-14; https://doi.org/10.1016/j.bbr.2009.03.026

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, Shashi B. Singh, Birendranath Mallick, Sangu Muthuraju, Govindasami Ilavazhagan
Published: 31 December 2008
Journal of Chemical Neuroanatomy, Volume 36, pp 227-238; https://doi.org/10.1016/j.jchemneu.2008.07.003

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M. Udayabanu, D. Kumaran, R. Unnikrishnan Nair, P. Srinivas, Neeta Bhagat, R. Aneja, Anju Katyal
Published: 16 September 2008
Brain Research, Volume 1230, pp 138-149; https://doi.org/10.1016/j.brainres.2008.06.081

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Sunil K. Hota, Kalpana Barhwal, Koushik Ray, Shashi B. Singh,
Neurobiology of Learning and Memory, Volume 89, pp 522-532; https://doi.org/10.1016/j.nlm.2008.01.003

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K. Jayalakshmi, S.B. Singh, B. Kalpana, M. Sairam, S. Muthuraju, G. Ilavazhagan
Published: 23 November 2007
Physiology & Behavior, Volume 92, pp 643-650; https://doi.org/10.1016/j.physbeh.2007.05.051

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, P. J. Yi, L. Eleore, N. Madronal, A. Rueda, J. M. Delgado-Garcia
Journal of Applied Physiology, Volume 103, pp 1479-1487; https://doi.org/10.1152/japplphysiol.00384.2007

Abstract:
This work attempts to evaluate the cognitive aspects of the acclimatization ability of mice submitted to simulated altitude. Critical altitudes were detected by evaluating open field activity, combined or not with object recognition tasks, at different acute simulated altitudes. Results showed impaired cognitive abilities at ≈3,733 m and above. To evaluate acclimatization capabilities, mice submitted to hypobaric hypoxia at ≈5,000 m for 1 wk were tested for learning and memory performances with classical eyeblink conditioning at the same altitude or at land altitude. Results showed total acclimatization in mice conditioned at ≈5,000 m but no improved performance in those conditioned at land altitudes compared with controls. Selected brain sites of conditioned animals were analyzed by immunohistochemistry to detect expression of the protein product of the protooncogene c-fos (Fos) in relation to both motor learning processes and hypobaric conditions. In the nucleus of the solitary tract, a higher expression of Fos was found in the acute hypobaric conditioned animals than in control conditioned and nonconditioned animals. Similar patterns between groups were found in the other brain areas, mainly in the piriform cortex and area 1 of the cingulate cortex and in the hippocampus. Differences between hemispheres were detected only in acute hypobaric animals. The present results show that acclimatization to high altitude prevents the impairment of classical eyeblink conditioning evoked by hypobaric hypoxic conditions but does not improve this task when acquired under land conditions, although it could diminish the activation requirements for its performance.
A.D.J. Titus, , H.N. Harsha, K. Ramkumar, , S.B. Singh, S. Chattarji,
Published: 2 March 2007
Neuroscience, Volume 145, pp 265-278; https://doi.org/10.1016/j.neuroscience.2006.11.037

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, Xing-Jiang Lu, Xiao-Chuan Wang, Wang Li, Ji-Zeng Du
Journal of Neuroscience Research, Volume 84, pp 228-235; https://doi.org/10.1002/jnr.20860

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Guo Shao, Ran Zhang, Zhan-Li Wang, Cui-Ying Gao, ,
Published: 1 January 2006
Neurosignals, Volume 15, pp 314-321; https://doi.org/10.1159/000121368

Abstract:
Although it has been reported in a lot of studies that hypoxic preconditioning could protect the brain from hypoxic/ischemic injury, it is not clear whether hypoxic preconditioning could affect brain functions such as cognitive ability. This work aims at investigating the effect of hypoxic preconditioning on spatial cognitive ability in mice after acute and repeated hypoxic exposures. The mice were randomly divided into 3 groups: a control group in which mice were not exposed to hypoxia (H0) and experimental groups in which mice encountered hypoxia either once (H1) or 4 times (H4). Neural cell adhesion molecule (NCAM) expression, long-term potentiation (LTP) recording and Morris water maze test were used to measure the animals' cognitive ability. The tolerance time was progressively prolonged as exposure went on. The expression of both NCAM mRNA and NCAM protein as well as the LTP induction rate decreased in group H1, but recovered to control level in group H4. The performance of mice in the maze test was improved in H4 in comparison with that in both H1 and H0. These findings may indicate that spatial cognitive ability is improved in adult mice by their hypoxic preconditioning.
Jia-Xing Zhang, Xue-Qun Chen, Ji-Zeng Du, Qing-Mei Chen, Chao-Yang Zhu
Published: 1 October 2005
Journal of Neurobiology, Volume 65, pp 72-84; https://doi.org/10.1002/neu.20174

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