Hypobaric hypoxia induces depression-like behavior in female Sprague-Dawley rats, but not in males

Kynurenines Dynamics in the Periphery and Central Nervous System Steers Behavioral Deficits in Rats under Hypobaric Hypoxia

People travel to high-altitude regions as tourists, workers, and military personnel on duty. Despite the consistent 21% oxygen content in the atmosphere, ascending to higher altitudes results in a decrease in the partial pressure of oxygen, inducing a state known as hypobaric hypoxia (HH). HH is an environmental stress that is responsible for neuroinflammation and behavioral deficits (anxiety, depression, mood disturbance, etc.), but little is known about its metabolic pathways. The kynurenine pathway (KP) is a promising candidate to uncover the mysteries of HH stress, as it is an important regulator of the immune system and is associated with behavioral deficits. To investigate the role of KP under HH, the levels of KP metabolites in the serum, cerebrospinal fluid (CSF), and brain tissue (prefrontal cortex-PFC, neocortex, and hippocampus) of male Sprague-Dawley rats exposed to HH at 7620 m for 1, 3, and 7 days were estimated utilizing high-performance liquid chromatography (HPLC). The behavioral analogs for anxiety-like and depression-like behavior were assessed using the open field test and forced swim test, respectively. Upon HH exposure, crosstalk between the periphery and central nervous system and KP metabolite region-dependent differential expression in the brain were observed. KP metabolites showed a positive correlation with behavioral parameters. The results of our study are indicative that KP can be proposed as the etiology of behavioral deficits, and KP metabolite levels in serum or CSF can be used as plausible markers for anxiety-like and depression-like behaviors under HH stress with a scope of targeted therapeutic interventions.

The Effect of High-Altitude Hypoxia on Neuropsychiatric Functions

Liu, Bo, Minlan Yuan, Mei Yang, Hongru Zhu, and Wei Zhang. The effect of high-altitude hypoxia on neuropsychiatric functions. High Alt Med Biol. 25:26-41, 2024. Background: In recent years, there has been a growing popularity in engaging in activities at high altitudes, such as hiking and work. However, these high-altitude environments pose risks of hypoxia, which can lead to various acute or chronic cerebral diseases. These conditions include common neurological diseases such as acute mountain sickness (AMS), high-altitude cerebral edema, and altitude-related cerebrovascular diseases, as well as psychiatric disorders such as anxiety, depression, and psychosis. However, reviews of altitude-related neuropsychiatric conditions and their potential mechanisms are rare. Methods: We conducted searches on PubMed and Google Scholar, exploring existing literature encompassing preclinical and clinical studies. Our aim was to summarize the prevalent neuropsychiatric diseases induced by altitude hypoxia, the potential pathophysiological mechanisms, as well as the available pharmacological and nonpharmacological strategies for prevention and intervention. Results: The development of altitude-related cerebral diseases may arise from various pathogenic processes, including neurovascular alterations associated with hypoxia, cytotoxic responses, activation of reactive oxygen species, and dysregulation of the expression of hypoxia inducible factor-1 and nuclear factor erythroid 2-related factor 2. Furthermore, the interplay between hypoxia-induced neurological and psychiatric changes is believed to play a role in the progression of brain damage. Conclusions: While there is some evidence pointing to pathophysiological changes in hypoxia-induced brain damage, the precise mechanisms responsible for neuropsychiatric alterations remain elusive. Currently, the range of prevention and intervention strategies available is primarily focused on addressing AMS, with a preference for prevention rather than treatment.

Exploring the Role of Drug Repurposing in Bridging the Hypoxia-Depression Connection

High levels of oxidative stress are implicated in hypoxia, a physiological response to low levels of oxygen. Evidence supports a connection between this response and depression. Previous studies indicate that tryptophan hydroxylase can be negatively affected in hypoxia, impairing serotonin synthesis and downstream pathways. Some studies also hypothesize that increasing hypoxia-inducible factor-1 (HIF-1) levels may be a new therapeutic modality for depression. Hence, this study delved into the influence of hypoxia on the cellular response to drugs designed to act in depression. By the induction of hypoxia in SH-SY5Y cells through a hypoxia incubator chamber or Cobalt Chloride treatment, the effect of Mirtazapine, an antidepressant, and other drugs that interact with serotonin receptors (TCB-2, Dextromethorphan, Ketamine, Quetiapine, Scopolamine, Celecoxib, and Lamotrigine) on SH-SY5Y cellular viability and morphology was explored. The selection of drugs was initially conducted by literature search, focusing on compounds with established potential for employment in depression therapy. Subsequently, we employed in silico approaches to forecast their ability to traverse the blood-brain barrier (BBB). This step was particularly pertinent as we aimed to assess their viability for inducing potential antidepressant effects. The effect of these drugs in hypoxia under the inhibition of HIF-1 by Echinomycin was also tested. Our results revealed that all the potential repurposed drugs promoted cell viability, especially when hypoxia was chemically induced. When combined with Echinomycin, all drugs decreased cellular viability, possibly by the inability to interact with HIF-1.

Sestrin-2 and hypoxia-ınducible factor-1 alpha levels in major depressive disorder and its subtypes

BACKGROUND

The objective of this study is to measure the levels of sestrin-2 (SESN2) and hypoxia-inducible factor-1 alpha (HIF-1α), which can be determinants in the relevant physiopathology and etiology, assessment of the clinical severity, and identification of new treatment targets in major depressive disorder (MDD) and its subtypes.

METHODS

A total of 230 volunteers, including 153 patients diagnosed with MDD according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), and 77 healthy controls, were included in the study. Of the MDD patients included in the study, 40 had melancholic features, 40 had anxious distress features, 38 had atypical features, and the remaining 35 had psychotic features. All participants were administered the Beck's Depression Inventory (BDI) and Clinical Global Impressions-Severity (CGI-S) scale. Serum SESN2 and HIF-1α levels of the participants were measured using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

The HIF-1α and SESN2 values of the patient group were found to be significantly lower than those of the control group (p < 0.05). The HIF-1α and SESN2 values were significantly lower in patients with melancholic, anxious distress, and atypical features compared to the control group (p < 0.05). The HIF-1α and SESN2 levels did not differ significantly between patients with psychotic features and the control group (p > 0.05).

CONCLUSION

The findings of the study suggested that knowledge of SESN2 and HIF-1α levels may contribute to the explanation of the etiology of MDD, objective assessment of the severity of the disease, and identification of new treatment targets.

Women's mood at high altitude. sexual dimorphism in hypoxic stress modulation by the tryptophan-melatonin axis

Sexual (and gender)-dimorphism in tolerance to hypobaric hypoxia increasingly matters for a differential surveillance of human activities at high altitude (HA). At low altitudes, the prevalence of anxiety and depression in women has already been found to double when compared with men; it could be expected to even increase on exposure to HA. In purposefully caring for the health of women at HA, the present work explores the potential involvement of the tryptophan (Trp)-melatonin axis in mood changes on exposure to hypobaric hypoxia. The present work highlights some already known anxiogenic effects of HA exposure. Hypoxia and insomnia reduce serotonin (5-HT) availability; the latter defect being expressed as failure of brown adipose tissue (BAT) activation and mood disorders. Rapid eye movement (REM) sleep organization and synapsis restoration that are additionally affected by hypoxia impair memory consolidation. Affective complaints may thus surge, evolving into anxiety and depression. Sex-related differences in neural network organization and hormonal changes during the menstrual cycle, and certainly also during the life cycle, underscore the possibility of 5-HT-related mood alterations, particularly in women on HA exposure. The mean brain rate of 5-HT synthesis at sea level is already 1.5-fold higher in males than in females. sexual dimorphism also evidences the overexpression effects of SERT, a 5-HT transporter protein. Gonadal and thyroid hormones, as influenced by HA exposure, further modulate 5-HT availability and its effects in women. Besides caring for adequate oxygenation and maintenance of one's body core temperature, special precautions concerning women sojourning at HA should include close observations of hormonal cycles and, perhaps, also trials with targeted antidepressants.

Disparities in the prevalence of screened depression at different altitudes in Peru: A retrospective analysis of the ENDES 2019

INTRODUCTION

Depression is a public health concern, nearing 1.5 million cases and accounting for 9.7% of years lost due to disability. Several factors, including altitude, contribute to its development. Altitude has become a topic for recent research, but its association with depressive symptoms has not been fully clarified. Therefore, this study aimed to determine the association between altitude and depressive symptoms in the Peruvian population.

METHODS

A retrospective, cross-sectional study of the 2019 Demographic and Family Health Survey (ENDES in Spanish) was conducted. The dependent variable, depressive symptoms, was measured using the Patient Health Questionnaire (PHQ-9) and the independent variable, altitude, was categorized into: <1500 meters above sea level (masl), 1500-2499 masl and ≥2500 masl. To evaluate the association between altitude and depressive symptoms, we used Poisson regression model, constructing crude and multiple models.

RESULTS

Of those living at 1500 to 2499 masl and ≥2500 masl, 7.23% and 7.12% had depressive symptoms, respectively. After adjusting for confounding variables, high altitude was found to be associated with depressive symptoms (prevalence ratio adjusted (aPR): 1.38, 95% confidence interval: 1.04-1.84; aPR 1.41, 95% CI: 1.20-1.66).

CONCLUSIONS

A statistically significant association was found between high altitude and depressive symptoms. This may be attributable to hypobaric hypoxia that occurs at high altitudes and its effects on brain function. This study's findings should be considered to identify the population at risk and expand the coverage of preventive and therapeutic measures in high-altitude areas of Peru with poor access to health services.

An Inexpensive Open-Source Chamber for Controlled Hypoxia/Hyperoxia Exposure

Understanding hypoxia/hyperoxia exposure requires either a high-altitude research facility or a chamber in which gas concentrations are precisely and reproducibly controlled. Hypoxia-induced conditions such as hypoxic-ischemic encephalopathy (HIE), obstructive or central apneas, and ischemic stroke present unique challenges for the development of models with acute or chronic hypoxia exposure. Many murine models exist to study these conditions; however, there are a variety of different hypoxia exposure protocols used across laboratories. Experimental equipment for hypoxia exposure typically includes flow regulators, nitrogen concentrators, and premix oxygen/nitrogen tanks. Commercial hypoxia/hyperoxia chambers with environmental monitoring are incredibly expensive and require proprietary software with subscription fees or highly expensive software licenses. Limitations exist in these systems as most are single animal systems and not designed for extended or intermittent hypoxia exposure. We have developed a simple hypoxia chamber with off-the-shelf components, and controlled by open-source software for continuous data acquisition of oxygen levels and other environmental factors (temperature, humidity, pressure, light, sound, etc.). Our chamber can accommodate up to two mouse cages and one rat cage at any oxygen level needed, when using a nitrogen concentrator or premixed oxygen/nitrogen tank with a flow regulator, but is also scalable. Our system uses a Python-based script to save data in a text file using modules from the sensor vendor. We utilized Python or R scripts for data analysis, and we have provided examples of data analysis scripts and acquired data for extended exposure periods (≤7 days). By using FLOS (Free-Libre and open-source) software and hardware, we have developed a low-cost and customizable system that can be used for a variety of exposure protocols. This hypoxia/hyperoxia exposure chamber allows for reproducible and transparent data acquisition and increased consistency with a high degree of customization for each experimenter’s needs.

Evaluation of the effects of altitude on biological signatures of inflammation and anxiety- and depressive-like behavioral responses

Over sixteen million people suffer from a depressive episode annually in the United States, with females affected at twice the rate of males. Little is known about the effects of exposure to high altitude on the risk of development of major depressive disorder, despite reports of higher suicide rates at higher altitudes. We hypothesize that exposure to hypobaric hypoxia at high altitude increases endophenotypes of self-directed suicidal violence, including biological signatures of chronic inflammation and vulnerability to anxiety-like and depressive-like behavioral responses in a sex-specific manner. Biological signatures of inflammation, including granulocyte:lymphocyte ratios, monocyte cell counts, and monocyte:lymphocyte ratios were assessed using complete blood count data, anhedonia, and anxiety- and depressive-like behavioral responses were evaluated. We assessed biological signatures of inflammation and behavioral responses in the open-field test, sucrose preference test, and modified Porsolt forced swim test in young adult male and female Long-Evans and Sprague Dawley rats. All tests were conducted near sea level (374 ft [114 m] elevation) and at moderate-high altitude (5430 ft [1655 m] elevation) during acclimation periods of one, two, three, four, and five weeks following shipment from a sea level animal breeding facility (N = 320, n = 8 per group). Exposure to moderate-high altitude induced a biological signature of increased inflammation, as evidenced by main effects of altitude for: 1) increased granulocyte:lymphocyte ratio; 2) increased count and relative abundance of circulating monocytes; and 3) increased monocyte:lymphocyte ratios. Exposure to moderate-high altitude also increased anhedonia as assessed in the sucrose preference test in both male and female rats, when data were collapsed across strain and time. Among male and female Long Evans rats, exposure to moderate-high altitude increased immobility in the forced swim test, without changing anxiety-like behaviors in the open-field test. Finally, granulocyte:lymphocyte ratios were correlated with anhedonia in the sucrose preference test. These data are consistent with the hypothesis that hypobaric hypoxia at moderate-high altitude induces persistent endophenotypes of self-directed suicidal violence including biological signatures of inflammation, anhedonia, and depressive-like behavioral responses.

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

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

Sex-based changes in rat brain serotonin and behavior in a model of altitude-related vulnerability to treatment-resistant depression

RATIONALE

Rates of depression and suicide increase with altitude. In our animal model, rats housed at moderate altitude vs. at sea level exhibit increased depressive symptoms in the forced swim test (FST) and lack of response to selective serotonin reuptake inhibitors (SSRIs). Depression and SSRI resistance are linked to disrupted serotonergic function, and hypobaric hypoxia may reduce the oxygen-dependent synthesis of serotonin. We therefore tested brain serotonin in rats housed at altitude.

METHODS

Sprague-Dawley rats were housed at altitude (4,500 ft, 10,000 ft) vs. sea level for 7-36 days. Brain serotonin was measured by ELISA, or behavior evaluated in the FST, sucrose preference (SPT), or open-field tests (OFT).

RESULTS

After 2 weeks at 4,500 ft or 10,000ft vs. sea level, serotonin levels decreased significantly at altitude in the female prefrontal cortex, striatum, hippocampus, and brainstem, but increased with altitude in the male hippocampus and brainstem. Female brain serotonin decreased from 7 to 36 days at 4,500 ft, but males did not vary. At 2 weeks and 24 days, females at altitude exhibit lower brain serotonin and increased depressive symptoms in the FST and SPT, with motor behavior unaltered. In males, serotonin, passive coping in the FST and OFT immobility increased with altitude at 2 weeks, but not at 24 days. Male SPT behavior did not change with altitude.

CONCLUSIONS

Females may be more vulnerable to depressive symptoms at altitude, while males may be resilient. Chronic hypoxic stress at altitudes as low as 4,500 ft may cause a brain serotonin imbalance to worsen vulnerability to depression and SSRI resistance, and potentially worsen suicide risk.

Effect of moderate altitude on human cerebral metabolite levels: A preliminary, multi-site, proton magnetic resonance spectroscopy investigation

Epidemiological studies show that altitude-of-residence is an independent risk factor for worsening rates of mood disorders, substance abuse, and suicide. Proton (1H) magnetic resonance spectroscopy (MRS) studies in rodent models of moderate-to-high altitude exposure have documented significant alterations in total creatine, glutamate, and myo-inositol, neurometabolites involved in bioenergetic homeostasis and neuronal/glial cell function. This preliminary study utilized 3 Tesla 1H MRS to study anterior cingulate cortex (ACC) and parietal-occipital cortex (POC) neurochemistry in healthy subjects residing in Utah (n = 19), Massachusetts (n = 10), and South Carolina (n = 10), to test the hypothesis that individuals residing at moderate altitude (Utah; 1,372 m) would show neurometabolite alterations vs. subjects living at sea level. Expressed as ratios to total N-acetyl aspartate (NAA), Utah participants showed lower ACC (p = 0.03) and POC (p < 0.01) total creatine, a trend towards lower ACC glutamate (p = 0.06), and lower POC myo-inositol (p = 0.02). Study limitations include small sample sizes and uncorrected multiple comparisons. To our knowledge, this is the first MRS investigation to identify potential neurochemical differences in individuals residing at moderate altitudes vs. sea level, warranting future 1H MRS studies in larger cohorts and across a range of altitudes-of-residence.

Sex-Based Impact of Creatine Supplementation on Depressive Symptoms, Brain Serotonin and SSRI Efficacy in an Animal Model of Treatment-Resistant Depression

Background: Rates of major depressive disorder (MDD) increase with living at altitude. In our model, rats housed at moderate altitude (in hypobaric hypoxia) exhibit increased depression-like behavior, altered brain serotonin and a lack of antidepressant response to most selective serotonin reuptake inhibitors (SSRIs). A forebrain deficit in the bioenergetic marker creatine is noted in people living at altitude or with MDD. Methods: Rats housed at 4500 ft were given dietary creatine monohydrate (CRMH, 4% w/w, 5 weeks) vs. un-supplemented diet, and impact on depression-like behavior, brain bioenergetics, serotonin and SSRI efficacy assessed. Results: CRMH significantly improved brain creatine in a sex-based manner. At altitude, CRMH increased serotonin levels in the female prefrontal cortex and striatum but reduced male striatal and hippocampal serotonin. Dietary CRMH was antidepressant in the forced swim test and anti-anhedonic in the sucrose preference test in only females at altitude, with motor behavior unchanged. CRMH improved fluoxetine efficacy (20 mg/kg) in only males at altitude: CRMH + SSRI significantly improved male striatal creatine and serotonin vs. CRMH alone. Conclusions: Dietary CRMH exhibits sex-based efficacy in resolving altitude-related deficits in brain biomarkers, depression-like behavior and SSRI efficacy, and may be effective clinically for SSRI-resistant depression at altitude. This is the first study to link CRMH treatment to improving brain serotonin.

Oxygen Enrichment Ameliorates Cardiorespiratory Alterations Induced by Chronic High-Altitude Hypoxia in Rats

Chronic high-altitude hypoxia (HAH) results in compensatory pathological adaptations, especially in the cardiorespiratory system. The oxygen enrichment technology can provide long-lasting oxygen supply and minimize oxygen toxicity, which has proven to be effective to increase oxygen saturation, decrease heart rate, and improve human exercise performance after ascending to high altitudes. Nevertheless, it remains unknown whether oxygen enrichment can resist chronic HAH-induced cardiorespiratory alterations. Thirty-six male rats were equally assigned to the normal control (NC), HAH, and HAH with oxygen enrichment (HAHO) groups. The HAH and HAHO rats were housed in a hypobaric hypoxia chamber equivalent to 5,000 m for 4 weeks. The HAHO rats were exposed to oxygen-enriched air for 8 h/day. We found that oxygen enrichment mitigated the augmented skin blood flow and improved the locomotor activity of HAH-exposed rats. Oxygen enrichment inhibited HAH-induced increase in the production of red blood cells (RBCs). The hemodynamic results showed that oxygen enrichment decreased right ventricular systolic pressure (RVSP) and mean pulmonary artery pressure (mPAP) in HAH-exposed rats. HAH-associated right ventricular hypertrophy and cardiomyocyte enlargement were ameliorated by oxygen enrichment. Oxygen enrichment inhibited HAH-induced excessive expression of cytokines associated with cardiac hypertrophy and myocardial fibrosis [angiotensin-converting enzyme (ACE)/angiotensin-converting enzyme 2 (ACE2), angiotensin II (Ang II), collagen type I alpha 1 (Col1α1), collagen type III alpha 1 (Col3α1), and hydroxyproline] in the right ventricle (RV). Oxygen enrichment inhibited medial thickening, stenosis and fibrosis of pulmonary arterioles, and cytokine expression related with fibrosis (Col1α1, Col3α1, and hydroxyproline) and pulmonary vasoconstriction [endothelin-1(ET-1)] in HAH-exposed rats. This study represents the first effort testing the efficacy of the oxygen enrichment technique on cardiopulmonary structure and function in chronic HAH animals, and we found oxygen enrichment has the capability of ameliorating chronic HAH-induced cardiopulmonary alterations.

The Association Between Hypoxia Improvement and Electroconvulsive Therapy for Major Depressive Disorder

BACKGROUND

The occurrence of depression was related with a state of mild hypoxia for a long time. Hypoxia-inducible factor-2α (HIF-2α) modulates the process from acute to chronic hypoxia, consequently regulating changes in inducible nitric oxide synthase (iNOS). Increasing levels of iNOS combined with major depressive disorder (MDD) have been associated with the concentration of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), which increase the severity of depression.

OBJECTIVE

The aim was to investigate whether depressive symptoms might be improved by regulating HIF-2α levels to decrease the degree of oxidative stress and inflammation using electroconvulsive therapy (ECT).

METHODS

In this observational study, 49 MDD patients were divided into the ECT group (n=32) and control group (n=17). The Hamilton Depression Rating Scale (HAMD) was used to evaluate depressive symptoms of patients at enrollment and after 2 weeks of treatment. The levels of HIF-2α, NOS, IL-6, and TNF-α in plasma were analyzed accordingly.

RESULTS

The total score in each dimension of HAMD decreased more efficiently in the ECT group than in the control group (p < 0.05). The plasma levels of IL-6 in the ECT group were notably decreased after the 2-week treatment (t = 3.596, p = 0.001). The decreased trend to statistical significance of HIF-2α was observed after treatment in the ECT group (p = 0.091).

CONCLUSION

The present study demonstrated that the therapeutic effects of long-term ECT therapy for MDD may further benefit from and contribute to the improvement of MDD-associated chronic hypoxia.

An analysis of the relationship between chronic obstructive pulmonary disease, smoking and depression in an integrated healthcare system

OBJECTIVE

Chronic Obstructive Pulmonary Disease (COPD) and smoking are highly associated with depression and hypoxia. There is limited knowledge about whether hypoxic conditions interact to cause depression.

METHOD

A population-based cohort study was conducted using the Veterans Affairs (VA) Corporate Data Warehouse. Patients must have accessed any healthcare at a VA facility between 2004 and 2014 and had a negative depression screen (Patient Health Questionnaire-2 (PHQ-2) score ≤ 2). Patients with COPD or a positive depression screen (PHQ-2 score: 3+) during or prior to the year with a negative depression screen were excluded. Logistic regression with annual observations was used to evaluate depression incidence based on COPD and smoking status. Models were adjusted for demographics and other comorbid conditions. A probability scale was used to examine interactions between COPD and smoking.

RESULTS

A total of 3,284,496 patients were included. Patients with COPD and current smokers were at increased risk for developing depression. There were minimal interaction effects between COPD and smoking. The odds of developing depression in a year varied from 1.4% among never smokers without COPD to 2.9.% among current smokers with COPD.

CONCLUSION

Smoking and COPD are independent risk factors for depression and interact to cause depression. Further research is needed to confirm whether hypoxia contributes to this association.

Brain diseases in changing climate

Climate change is one of the biggest and most urgent challenges for the 21st century. Rising average temperatures and ocean levels, altered precipitation patterns and increased occurrence of extreme weather events affect not only the global landscape and ecosystem, but also human health. Multiple environmental factors influence the onset and severity of human diseases and changing climate may have a great impact on these factors. Climate shifts disrupt the quantity and quality of water, increase environmental pollution, change the distribution of pathogens and severely impacts food production - all of which are important regarding public health. This paper focuses on brain health and provides an overview of climate change impacts on risk factors specific to brain diseases and disorders. We also discuss emerging hazards in brain health due to mitigation and adaptation strategies in response to climate changes.

Cerebral bioenergetic differences measured by phosphorus-31 magnetic resonance spectroscopy between bipolar disorder and healthy subjects living in two different regions suggesting possible effects of altitude

AIM

Increased oxidative stress in cerebral mitochondria may follow exposure to the systemic hypobaric hypoxia associated with residing at higher altitudes. Because mitochondrial dysfunction is implicated in bipolar disorder (BD) pathophysiology, this may impact the cerebral bioenergetics in BD. In this study, we evaluated the cerebral bioenergetics of BD and healthy control (HC) subjects at two sites, located at sea level and at moderate altitude.

METHODS

Forty-three veterans with BD and 33 HC veterans were recruited in Boston (n = 22) and Salt Lake City (SLC; n = 54). Levels of phosphocreatine, β nucleoside triphosphate (βNTP), inorganic phosphate, and pH over total phosphate (TP) were measured using phosphorus-31 magnetic resonance spectroscopy in the following brain regions: anterior cingulate cortex and posterior occipital cortex, as well as bilateral prefrontal and occipitoparietal (OP) white matter (WM).

RESULTS

A significant main effect of site was found in βNTP/TP (Boston > SLC) and phosphocreatine/TP (Boston < SLC) in most cortical and WM regions, and inorganic phosphate/TP (Boston < SLC) in OP regions. A main effect analysis of BD diagnosis demonstrated a lower pH in posterior occipital cortex and right OP WM and a lower βNTP/TP in right prefrontal WM in BD subjects, compared to HC subjects.

CONCLUSION

The study showed that there were cerebral bioenergetic differences in both BD and HC veteran participants at two different sites, which may be partly explained by altitude difference. Future studies are needed to replicate these results in order to elucidate the dysfunctional mitochondrial changes that occur in response to hypobaric hypoxia.

Creatine for the Treatment of Depression

Depressed mood, which can occur in the context of major depressive disorder, bipolar disorder, and other conditions, represents a serious threat to public health and wellness. Conventional treatments are not effective for a significant proportion of patients and interventions that are often beneficial for treatment-refractory depression are not widely available. There is, therefore, an immense need to identify novel antidepressant strategies, particularly strategies that target physiological pathways that are distinct from those addressed by conventional treatments. There is growing evidence from human neuroimaging, genetics, epidemiology, and animal studies that disruptions in brain energy production, storage, and utilization are implicated in the development and maintenance of depression. Creatine, a widely available nutritional supplement, has the potential to improve these disruptions in some patients, and early clinical trials indicate that it may have efficacy as an antidepressant agent.

Association between altitude, prescription opioid misuse, and fatal overdoses

OBJECTIVE

Prescription opioid misuse and fatal overdoses have increased significantly over the last two decades. Living at altitude has been linked to greater reward benefits of other drugs of abuse, and living at altitude may also exacerbate the respiratory depression linked to opioid use. Therefore, we examined the relationships between living at altitude, and prescription opioid misuse and fatal overdoses.

METHOD

State-level past year rates of prescription opioid misuse were retrieved from the Substance Abuse and Mental Health Services Administration. County-level overdose data were extracted from the Centers for Disease Control and Prevention. Multiple linear regression models were fit to determine the relationship between average state elevation and state rates of opioid misuse. Logistic regression models were fit to determine the relationship between county elevation and county-level fatal opioid overdose prevalence.

RESULTS

After controlling for state opioid prescribing rates and other confounders, we identified a significant positive association between mean state altitude and state-level opioid misuse rates for women, but not men. We also found a significant positive association between county-level altitude and prevalence of fatal opioid overdose.

CONCLUSIONS

Living at altitude is thus demographically associated with increasing rates of misuse of prescription opioids, as well as of cocaine and methamphetamine. Animal studies suggest that the hypobaric hypoxia exposure involved with living at altitude may disrupt brain neurochemistry, to increase reward benefits of drugs of abuse. This increased misuse of both stimulants and opioids may increase likelihood of overdose at altitude, with overdoses by opioid use also potentially facilitated by altitude-related hypoxia.

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.

Injury-Related Deaths according to Environmental, Demographic, and Lifestyle Factors

Background

Environmental, demographic, and lifestyle variables have been associated with injury-related deaths. The current study identifies the simultaneous association of selected environmental, demographic, and lifestyle variables with deaths from homicide, unintentional injuries, and suicide.

Materials and Methods

Analyses are based on county-level mortality data in the contiguous United States, 2011–15. Basic summary statistics and Poisson regression were used to evaluate the data.

Results

The selected causes of death were impacted differently by age, sex, and race: for homicide, mortality rates were greater in ages 20–39, males, and blacks; for unintentional injuries, the rates increased with age, most noticeably in the oldest age group, and were highest among males and whites; and for suicide, the rates tended to increase with age and were greater in males and whites. Mortality rates from homicide were positively associated with poverty, cigarette smoking, air temperature, and leisure-time physical inactivity. They were negatively associated with precipitation and sunlight. Mortality rates from unintentional injuries were positively associated with altitude, cigarette smoking, air temperature, poverty, obesity, and precipitation. They were negatively associated with population density. Mortality rates from suicides were positively associated with altitude, cigarette smoking, obesity, air temperature, and precipitation and negatively associated with population density.

Conclusion

The results confirm and extend previous research in which death from homicide, unintentional injuries, and suicide are distinctly associated with a combination of environmental, demographic, and lifestyle variables. The findings may be useful in developing strategies for reducing injury-related deaths.

Modeling the effects of atmospheric pressure on suicide rates in the USA using geographically weighted regression

Low atmospheric pressure may increase depression and suicide through inducing hypoxia. Previous studies have not evaluated the geographic variation of this relationship across the United States. Analyses were based on three groupings of age-adjusted completed suicide rates (all suicide, firearm-related suicide, non-firearm-related suicide) from 2286 counties in the United States. Multiple regression was used to determine the overall relationship between atmospheric pressure and completed suicide rates. Geographically weighted regression (GWR) models were used to obtain local coefficient estimates. A negative correlation between atmospheric pressure and completed suicide rates was observed for all three suicide groupings (p-value <0.0001). Significant, negative GWR coefficient estimates were located in the West and Northeast for the all suicides and firearm-related suicides, and in the Midwest for non-firearm-related suicides.

Association between vitamin D deficiency and depression in Nepalese population

Recent studies link vitamin D deficiency with depression; however evidences from the Nepalese population are scarce. The current study explored the association between vitamin D deficiency and depression among 300 adults of 18 years and above age residing in eastern Nepal. Validated Nepali version of the Beck Depression Inventory scale (BDI-Ia) was used to determine depressive symptoms and a BDI cutoff score of ≥20 was considered as clinically significant depression. Sociodemographic data were collected using semi-structured questionnaire. Blood samples were collected to measure serum 25‑hydroxy vitamin D (25(OH)D) and classify vitamin D status (deficient, insufficient and sufficient). We used Chi-square test to identify the association of sociodemographic variables and vitamin D status with clinically significant depression. We found a significant association of gender, geographical location of residence, marital status, religion and vitamin D status with clinically significant depression. Binary logistic regression model was used to examine the likelihood of clinically significant depression among vitamin D deficient individuals. Vitamin D deficiency was significantly associated with increased odds of clinically significant depression even after adjusting for confounding variables. This finding suggests Vitamin D deficient people have increased odds of having clinically significant depression.

Hypobaric hypoxia exposure in rats differentially alters antidepressant efficacy of the selective serotonin reuptake inhibitors fluoxetine, paroxetine, escitalopram and sertraline

Treatment-resistant depression, a chronic condition that affects 30% of depressed patients on antidepressants, is highly linked to suicidal behavior. Chronic hypoxia exposure via living at altitude (hypobaric hypoxia) or with chronic hypoxic diseases is demographically linked to increased risk for depression and suicide. We previously demonstrated that housing rats at altitude for a week incrementally increases depression-like behavior in the forced swim test (FST) in females, but not males. In animal models, high altitude exposure reduces brain serotonin, and selective serotonin reuptake inhibitors (SSRIs) can lose efficacy when brain serotonin levels are low. To address whether residence at moderate altitude is detrimental to SSRI function, we examined SSRI efficacy in the FST after a week of housing rats at altitudes of 4500 ft. or 10,000 ft. as compared to at sea level. In females, the tricyclic antidepressant desipramine (positive control) functioned well in all groups, increasing latency to immobility and decreasing immobility, by increasing climbing. However, the SSRIs fluoxetine, paroxetine and escitalopram were ineffective in females in all groups: only paroxetine improved swimming in the FST as expected of a SSRI, while all three unexpectedly reduced climbing. Fluoxetine was also ineffective in male rats. Sertraline was the only SSRI with antidepressant efficacy at altitude in both females and males, increasing swimming, climbing and latency to immobility, and reducing immobility. Hypobaric hypoxia thus appears to be detrimental to efficacy of the SSRIs fluoxetine, paroxetine and escitalopram, but not of sertraline. Unlike the other SSRIs, sertraline can improve both serotonergic and dopaminergic transmission, and may be less impacted by a hypoxia-induced serotonin deficit. A targeted approach may thus be necessary for successful antidepressant treatment in patients with depression who live at altitude or with chronic hypoxic diseases, and that sertraline may be the SSRI of choice for prescription for this population.

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.

Chronic respiratory disease and high altitude are associated with depressive symptoms in four diverse settings

SETTING

Depression is a prevalent comorbidity of chronic respiratory disease (CRD), and may indicate worse clinical outcomes. The relationship between depression and living with chronic hypoxia due to CRD or residence at altitude has received little attention in resource-poor settings.

OBJECTIVE

To investigate the association between CRD conditions and depressive symptoms in four settings in Peru.

DESIGN

We collected data on CRD and depressive symptoms in adults aged ⩾35 years. Depressive symptoms were measured according to the Center for Epidemiologic Studies Depression scale. Multivariable ordinal logistic regression was used to assess the adjusted odds of being in a higher category of depressive symptoms as a function of CRD.

RESULTS

We analyzed data from 2953 participants (mean age 55.3 years, 49% male). The prevalence of major depressive symptoms was 19%, with significant variation according to setting. Participants with at least one CRD (OR 1.34, 95%CI 1.06-1.69) and those living at altitude (OR 1.64, 95%CI 1.10-2.43) had an increased adjusted odds of being in a higher category of depressive symptoms.

CONCLUSION

We found a high prevalence of depressive symptoms, and a positive association between depressive symptoms with CRD and with living at altitude, both of which cause chronic hypoxia.

Increased Anxiety and Anhedonia in Female Rats Following Exposure to Altitude

Sheth, Chandni, Hendrik Ombach, Paul Olson, Perry F. Renshaw, and Shami Kanekar. Increased anxiety and anhedonia in female rats following exposure to altitude. High Alt Med Biol. 19:81-90, 2018.-Anxiety disorders are chronic, highly prevalent conditions, often comorbid with depression. Both anxiety and depression form major risk factors for suicide. Living at altitude is associated with higher rates of depression and suicide, leading us to address whether anxiety disorders may also be amplified at altitude. Using a novel translational animal model, we previously showed that depression-like behavior increases with altitude of housing in female, but not male rats. We now use this model to examine the effects of altitude on both anxiety-like behavior and anhedonia, a core symptom of depression. After housing for a week at sea level, 4500 or 10,000 ft, rats were evaluated for anxiety in the open-field test or the elevated plus maze, and anhedonia in the sucrose preference test. Another group was tested at baseline. Anxiety-like behavior increased in females housed at altitude. In females, lower sucrose preference was seen in those housed at 10,000 ft versus those at sea level. Males showed no change in anxiety or anhedonia across groups. These data suggest that living at moderate-high altitude may pose a risk factor for those vulnerable to anxiety disorders, with the potential to be particularly detrimental to females at altitude.

Animal models to improve our understanding and treatment of suicidal behavior

Worldwide, suicide is a leading cause of death. Although a sizable proportion of deaths by suicide may be preventable, it is well documented that despite major governmental and international investments in research, education and clinical practice suicide rates have not diminished and are even increasing among several at-risk populations. Although nonhuman animals do not engage in suicidal behavior amenable to translational studies, we argue that animal model systems are necessary to investigate candidate endophenotypes of suicidal behavior and the neurobiology underlying these endophenotypes. Animal models are similarly a critical resource to help delineate treatment targets and pharmacological means to improve our ability to manage the risk of suicide. In particular, certain pathophysiological pathways to suicidal behavior, including stress and hypothalamic-pituitary-adrenal axis dysfunction, neurotransmitter system abnormalities, endocrine and neuroimmune changes, aggression, impulsivity and decision-making deficits, as well as the role of critical interactions between genetic and epigenetic factors, development and environmental risk factors can be modeled in laboratory animals. We broadly describe human biological findings, as well as protective effects of medications such as lithium, clozapine, and ketamine associated with modifying risk of engaging in suicidal behavior that are readily translatable to animal models. Endophenotypes of suicidal behavior, studied in animal models, are further useful for moving observed associations with harmful environmental factors (for example, childhood adversity, mechanical trauma aeroallergens, pathogens, inflammation triggers) from association to causation, and developing preventative strategies. Further study in animals will contribute to a more informed, comprehensive, accelerated and ultimately impactful suicide research portfolio.