The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

Neurological Manifestations Associated with Exercise at Altitude

PURPOSE OF REVIEW

The effects that exercise at altitude has on the neurological system are diverse and still not well studied, and range from metabolic adaptations to modification of cerebral blood flow and neurotransmitters. In this review we summarise changes with exercise intensity, the implications of ascent, cognitive impairment, psychosis-like symptoms, the role of exercise in the development and prevention of AMS, and use of free radical scavengers to enhance sports performance and acclimatization.

RECENT FINDINGS

We discuss the impact of oxidative stress in hypobaric hypoxia and reactive oxygen species (ROS) production and its consequences, with special focus on exercise at altitude. Finally we consider how moderate intensity exercise could help prevent AMS, and the necessity of research on high intensity exercise with elevated rate of ascent, the development of specific tools of cognitive assessment, and the role of free-radical scavengers in the prevention of AMS and neurological symptoms.

Oxygen metabolism abnormalities and high-altitude cerebral edema

Hypobaric hypoxia is widely recognized as a prominent risk factor for high-altitude cerebral edema (HACE), which contributes to the exacerbation of multiple pathological mechanisms, including oxidative stress, mitochondrial dysfunction, disruption of blood-;brain barrier integrity, neuroinflammation, and neuronal apoptosis. Among these mechanisms, abnormalities in oxygen metabolism, including hypoxia, oxidative stress, and mitochondrial dysfunction, play pivotal roles in the pathophysiology of HACE. In this review, our objective is to enhance our comprehension of the underlying molecular mechanisms implicated in HACE by investigating the potential involvement of oxygen metabolism. Addressing aberrations in oxygen metabolism holds promise for providing innovative therapeutic strategies for managing HACE.

Lactobacillus johnsonii HL79 modulates the microbiota-gut-brain axis to protect cognitive function in mice chronically exposed to high altitude

Introduction

High-altitude environments have significant effects on brain function, particularly a decline in cognitive function, due to insufficient oxygen supply. The microbiome-gut-brain axis (MGBA) plays an important role in regulating cognitive function, but its specific mechanism of action in high-altitude environments is unclear. Therefore, the aim of this study was to investigate whether the probiotic Lactobacillus johnsonii HL79 could alleviate high altitude-induced cognitive dysfunction in mice by modulating the gut microbiota.

Methods and results

Sixty C57BL/6 mice aged 8 weeks were randomly divided into four groups: control, high altitude exposure (HA), HL79-treated (P), and high altitude exposure plus HL79-treated (HAP). the HA and HAP groups were exposed to a low-pressure oxygen chamber at a simulated altitude of 3,500-4,000 m for 20 weeks, while the Control and P groups were maintained at the normal barometric pressure level. Probiotic HL79 was given daily by gavage in the P and HAP groups, while saline gavage was given daily in the other two groups. The cognitive functions of the mice were assessed by new object recognition test and elevated plus maze test. The results showed that HL79 treatment significantly improved the working memory abilities of high altitude exposed mice. In addition, HL79 treatment improved antioxidant capacity, decreased malondialdehyde (MDA) content, and increased superoxide dismutase (SOD) and catalase (CAT) activities in serum and whole brain tissue. Gut microbiota analysis showed that HL79 was able to modulate the structure of gut microbiota and increase the relative abundance of beneficial flora in high altitude environment.

Conclusion

Lactobacillus johnsonii HL79 significantly ameliorated cognitive dysfunction in high altitude-exposed mice by modulating the gut microbiota and antioxidant capacity, further confirming the important role of MGBA in high altitude environment.

A finer-grained high altitude EEG dataset for hypoxia levels assessment

The study reports on a high-altitude EEG dataset comprising 64-channel EEG signals from 23 subjects, aiming at achieving a finer-grained assessment of hypoxia levels. Four hypoxia levels were induced by creating a gradient of oxygen partial pressure through changes in altitude and external hypoxia stimulation. The dataset was collected in a hypoxic chamber that simulates altitude changes, allowing for a refined classification of different hypoxia levels based on ranges of oxygen saturation. The total recorded EEG data amounts to approximately 10.25 hours. Validation results indicate that the four hypoxia levels can be effectively recognized using EEG signals. Compared to binary classification, our fine-grained dataset allows for more precise detection of hypoxia levels. This dataset is anticipated to have significant research and practical value in developing accurate methods for identifying hypoxia levels. As a valuable and standardized resource, it will enable extensive analysis and comparison for researchers in the field of high-altitude hypoxia.

Cognitive Impairment Mechanisms in High-Altitude Exposure: Proteomic and Metabolomic Insights

High-altitude exposure can adversely affect neurocognitive functions; however, the underlying mechanisms remain elusive. Why and how does high-altitude exposure impair neurocognitive functions, particularly sleep? This study seeks to identify the molecular markers and mechanisms involved, with the goal of forming prevention and mitigation strategies for altitude sickness. Using serum proteomics and metabolomics, we analyzed blood samples from 23 Han Chinese plain dwellers before and after six months of high-altitude work in Tibet. The correlation analysis revealed biomarkers associated with cognitive alterations. Six months of high-altitude exposure significantly compromised cognitive function, notably, sleep quality. The key biomarkers implicated include SEPTIN5, PCBP1, STIM1, UBE2L3/I/N, amino acids (l/d-aspartic acid and l-glutamic acid), arachidonic acid, and S1P. Immune and neural signaling were suppressed, with sex-specific differences observed. This study innovatively identified GABA, arachidonic acid, l-glutamic acid, 2-arachidonoyl glycerol, and d-aspartic acid as biomarkers and elucidated the underlying mechanisms contributing to high-altitude-induced neurocognitive decline with a particular focus on sleep disruption. These findings pave the way for developing preventive measures and enhancing adaptation strategies. This study underscores the physiological significance of high-altitude adaptation, raising new questions about sex-specific responses and long-term consequences. It sets the stage for future research exploring individual variability and intervention efficacy.

Reduced Violence-Related Burden and Mortality at Higher Altitudes: Examining the Association between High Altitude Living and Homicide Rates in Ecuador

Ortiz-Prado, Esteban, Juan Sebastian Izquierdo-Condoy, María G. Dávila-Rosero, Jorge Vásconez-González, Ana M. Diaz, Carla E. Moyano, Vanessa Arcos-Valle, Ginés Viscor, and Joshua H. West. Reduced violence-related burden and mortality at higher altitudes: examining the association between high altitude living and homicide rates in Ecuador. High Alt Med Biol. 25:295-307, 2024. Background: Homicides are a major public health concern and a leading cause of preventable deaths worldwide. The relationship between altitude and homicides remains unclear, and evidence of the possible effects of living at high altitudes on homicide rates is limited. This research aimed to investigate the mortality rates resulting from various types of aggression that culminated in homicides in Ecuador and to explore potential differences associated with altitude. Methods: An ecological analysis of homicide rates in Ecuador was conducted from 2001 to 2022. Homicide cases and the population at risk were categorized based on their place of residence according to two altitude classifications: a binary classification of low (<2,500 m) and high altitude (>2,500 m), and a detailed classification according to criteria by the International Society for Mountain Medicine, which includes low (<1,500 m), moderate (1,500-2,500 m), high (2,500-3,500 m), and very high altitude (3,500-5,500 m) categories. Both crude and directly age-sex standardized mortality rates were calculated for each altitude category. Results: We analyzed a total of 40,708 deaths attributed to aggressions (ICD-10 codes X85-Y09). The total homicide rate for men was 21.29 per 100,000 (95% confidence interval [CI]: 9.55-32.37), whereas for women, it was 2.46 per 100,000 (95% CI: 1.44-3.27). Average rates across the 22 analyzed years were higher at low altitudes (men: 13.2/100,000 and women: 1.33/100,000) as compared with high altitudes (men: 5.79/100,000 and women: 1.05/100,000). Notably, the male-to-female rate difference was more pronounced at low altitudes (898%) than at high altitudes (451%). Conclusions: Our study revealed a higher prevalence of homicides in certain provinces and significant disparities in mortality rates between men and women. Although we cannot establish a direct relationship between altitude and homicide rates, further research is needed to explore potential confounding factors and a better understanding of the underlying causes for these variations.

The effects of real vs simulated high altitude on associative memory for emotional stimuli

INTRODUCTION

This study aimed to investigate the effects of normobaric hypoxia (NH) and hypobaric hypoxia (HH) on associative memory performance for emotionally valenced stimuli.

METHODS

Two experiments were conducted. In Study 1, n = 18 undergraduates performed an associative memory task under three NH conditions (FiO2= 20.9 %, 15.1 %, 13.6 %) using a tent with a hypoxic generator. In Study 2, n = 20 participants were assessed in a field study at various altitudes on the Himalayan mountains, including the Pyramid Laboratory (5000 m above sea level), using functional Near-Infrared Spectroscopy (fNIRS) and behavioral assessments.

RESULTS

Study 1 revealed no significant differences in recognition accuracy across NH conditions. However, Study 2 showed a complex relationship between altitude and memory for emotionally valenced stimuli. At lower altitudes, participants more accurately recognized emotional stimuli compared to neutral ones, a trend that reversed at higher altitudes. Brain oxygenation varied with altitude, indicating adaptive cognitive processing, as revealed by fNIRS measurements.

CONCLUSIONS

These findings suggest that hypoxia affects associative memory and emotional processing in an altitude-dependent manner, highlighting adaptive cognitive mechanisms. Understanding the effects of hypobaric hypoxia on cognition and memory can help develop strategies to mitigate its impact in high-altitude and hypoxic environments.

[Body Function Changes and Prevention Strategies in High-Altitude Environment]

In high-altitude regions, the unique challenges posed by the low-oxygen environment exert significant stress on the physiological functions of the human body. Currently, there is an urgent need to develop a deeper understanding of the pathogenesis, prevention and treatment strategies, as well as effective interventions, of altitude sickness. In this paper, we explored the self-regulatory mechanisms of the human body in such extreme environments, elaborating on the adaptive mechanisms at the molecular level and the process of acclimatization to high altitudes. Furthermore, we summarized the historical background and distinctive advantages of hypoxic preconditioning in the prevention and treatment of altitude diseases. Additionally, we reviewed various adaptation strategies employed by populations in different high-altitude regions, along with the extensive use of Western medication, single-herb traditional Chinese medicine remedies, and compound formulas and composite formulations of traditional Chinese medicine in these regions. Through this paper, we intend to provide a theoretical foundation for the health maintenance of high-altitude populations and to improve survival strategies under extreme environmental conditions. Our goal is also to provide a theoretical reference for improving the physiological adaptability of newcomers to high altitude areas and for deepening our understanding of the mechanisms of human adaptation to high-altitude environments.

Mechanisms underlying the health benefits of intermittent hypoxia conditioning

Intermittent hypoxia (IH) is commonly associated with pathological conditions, particularly obstructive sleep apnoea. However, IH is also increasingly used to enhance health and performance and is emerging as a potent non-pharmacological intervention against numerous diseases. Whether IH is detrimental or beneficial for health is largely determined by the intensity, duration, number and frequency of the hypoxic exposures and by the specific responses they engender. Adaptive responses to hypoxia protect from future hypoxic or ischaemic insults, improve cellular resilience and functions, and boost mental and physical performance. The cellular and systemic mechanisms producing these benefits are highly complex, and the failure of different components can shift long-term adaptation to maladaptation and the development of pathologies. Rather than discussing in detail the well-characterized individual responses and adaptations to IH, we here aim to summarize and integrate hypoxia-activated mechanisms into a holistic picture of the body's adaptive responses to hypoxia and specifically IH, and demonstrate how these mechanisms might be mobilized for their health benefits while minimizing the risks of hypoxia exposure.

[Amplitude-integrated electroencephalography monitoring results of hospitalized neonates in plateau areas]

OBJECTIVES

To investigate the amplitude-integrated electroencephalography (aEEG) monitoring results of hospitalized neonates in plateau areas.

METHODS

A retrospective analysis was conducted on 5 945 neonates who were admitted to the Department of Neonatology, Kunming Children's Hospital, and received aEEG monitoring from January 2020 to December 2022. According to the aEEG monitoring results, they were divided into a normal aEEG group and an abnormal aEEG group. The incidence rate of aEEG abnormalities was analyzed in neonates with various systemic diseases, as well as the manifestations of aEEG abnormalities and the consistency between aEEG abnormalities and clinical abnormalities.

RESULTS

Among the 5 945 neonates, the aEEG abnormality rate was 19.28% (1 146/5 945), with an abnormality rate of 29.58% (906/3 063) in critically ill neonates and 8.33% (240/2 882) in non-critically ill neonates (P<0.05). The children with inherited metabolic diseases showed the highest aEEG abnormality rate of 60.77% (79/130), followed by those with central nervous system disorders [42.22% (76/180)] and preterm infants [35.53% (108/304)]. Compared with the normal aEEG group, the abnormal aEEG group had significantly lower age and gestational age, as well as a significantly lower birth weight of preterm infants (P<0.05). Among the 1 146 neonates with aEEG abnormalities, the main types of aEEG abnormalities were sleep cycle disorders in 597 neonates (52.09%), background activity abnormalities in 294 neonates (25.65%), and epileptiform activity in 255 neonates (22.25%), and there were 902 neonates (78.71%) with abnormal clinical manifestations. The sensitivity and specificity of aEEG monitoring for brain function abnormalities were 33.51% and 92.50%, respectively.

CONCLUSIONS

In plateau areas, there is a relatively high rate of aEEG abnormalities among hospitalized neonates, particularly in critically ill neonates and those with smaller gestational ages and younger ages, suggesting a high risk of brain injury. Therefore, routine aEEG monitoring for the hospitalized neonates can help with the early detection of brain function abnormalities, the decision-making in treatment, and the formulation of brain protection strategies.

[Cerebral oxygen metabolism and brain electrical activity of healthy full-term neonates in high-altitude areas: a multicenter clinical research protocol]

Further evidence is needed to explore the impact of high-altitude environments on the neurologic function of neonates. Non-invasive techniques such as cerebral near-infrared spectroscopy and amplitude-integrated electroencephalography can provide data on cerebral oxygenation and brain electrical activity. This study will conduct multiple cerebral near-infrared spectroscopy and amplitude-integrated electroencephalography monitoring sessions at various time points within the first 3 days postpartum for healthy full-term neonates at different altitudes. The obtained data on cerebral oxygenation and brain electrical activity will be compared between different altitudes, and corresponding reference ranges will be established. The study involves 6 participating centers in the Chinese High Altitude Neonatal Medicine Alliance, with altitude gradients divided into 4 categories: 800 m, 1 900 m, 2 400 m, and 3 500 m, with an anticipated sample size of 170 neonates per altitude gradient. This multicenter prospective cohort study aims to provide evidence supporting the impact of high-altitude environments on early brain function and metabolism in neonates.

The Hypoxia Response Pathway: A Potential Intervention Target in Parkinson's Disease?

Parkinson's disease (PD) is a progressive neurodegenerative disorder for which only symptomatic treatments are available. Both preclinical and clinical studies suggest that moderate hypoxia induces evolutionarily conserved adaptive mechanisms that enhance neuronal viability and survival. Therefore, targeting the hypoxia response pathway might provide neuroprotection by ameliorating the deleterious effects of mitochondrial dysfunction and oxidative stress, which underlie neurodegeneration in PD. Here, we review experimental studies regarding the link between PD pathophysiology and neurophysiological adaptations to hypoxia. We highlight the mechanistic differences between the rescuing effects of chronic hypoxia in neurodegeneration and short-term moderate hypoxia to improve neuronal resilience, termed "hypoxic conditioning". Moreover, we interpret these preclinical observations regarding the pharmacological targeting of the hypoxia response pathway. Finally, we discuss controversies with respect to the differential effects of hypoxia response pathway activation across the PD spectrum, as well as intervention dosing in hypoxic conditioning and potential harmful effects of such interventions. We recommend that initial clinical studies in PD should focus on the safety, physiological responses, and mechanisms of hypoxic conditioning, as well as on repurposing of existing pharmacological compounds. © 2023 International Parkinson and Movement Disorder Society.

Comparative Study of Complete Blood Count Between High-Altitude and Sea-Level Residents in West Saudi Arabia

The reduction in oxygen partial pressure at high altitudes leads to diminished oxygen saturation in the arteries, stimulating erythropoietin production and erythropoiesis to restore appropriate oxygenation. While many studies have explored acclimatization to high altitude and its effects on complete blood count (CBC) parameters, our research uniquely examined both male and female healthy individuals, emphasizing the novelty of gender-specific observations. We analyzed 1,160 individuals in Taif (Al Hada), east Saudi Arabia, a high-altitude region, and compared them to 1,044 counterparts in Jeddah, at sea level. Our results revealed significant variations in CBC parameters, including white blood count, red blood count, hemoglobin, hematocrit, platelets, neutrophils, lymphocytes, monocytes, eosinophils, and basophils, reflecting the body's hypoxic response. These variations were observed in both genders, with specific differences noted between males and females. For example, NEU (neutrophils), representing the absolute count of a type of white blood cell essential in the immune system's defense, showed significant variations for males. The male results show that the variation in males between the sea level and high altitudes indicated significant p-values for all CBC parameters except NEU between at sea level (Jeddah city), whose p-value was 0.8696, and at high altitude (Taif city, Al Hada). In contrast, MONO (monocytes), another type of white blood cell involved in immune response, and RBC (red blood cells), responsible for oxygen transport, were mentioned but did not show significant variations for females. The full results for females showed significant results (P<0.0001) for BASO, HCT, HGB, MCH, MCHC, MPV, PLT, RDW, and WBC between the sea-level altitude and high altitude for females. Also, EOS and LYM showed significant P-values of 0.0002 and 0.0001, respectively, while MONO, NEU, and RBC indicated no significance between the sea-level altitude and high altitude for females. The p-values of MONO, NEU, and RBC, respectively, were 0.1907, 0.1259, and 0.0677. The results for both genders combined showed significant variations of all CBC parameters (P<0.0001) between the sea-level altitude and high altitude except for MONO, NEU, and RBC, which were not significant for both males and females, with p-values of 0.1589, 0.2911, and 0.0595, respectively. All unhealthy individuals were excluded from the study with any condition that would cause significant changes in CBC parameters and would skew the results, ensuring a focus on physiological adaptations in healthy subjects. By comparing healthy individuals and examining each gender separately, this study contributes valuable insights into high-altitude acclimatization, enhancing our understanding of physiological adaptations and potentially guiding health management in such environments within the normal range.