Heat stress-induced memory impairment is associated with neuroinflammation in mice

Coenzyme Q10 and vitamin E alleviate heat stress-induced mood disturbances in male mice: Modulation of inflammatory pathways and the HPA axis

Heat stress, as an environmental stressor, can lead to temperature dysregulation and neuroinflammation, causing depression and anxiety by disrupting brain physiology and functional connectivity. This study looked at how co-enzyme Q10 (Q10) and vitamin E (Vit E), alone and together, affected heat stress-caused anxiety and depression symptoms and inflammation in male mice. Five groups were utilized in the study: control, heat stress (NS), Q10, Vit E, and the combination group (Q10+Vit E). The mice were subjected for 15 min/day to a temperature of 43°C for 14 consecutive days, followed by daily treatments for two weeks with either normal saline, Q10 (500 mg/kg), Vit E (250 mg/kg), or their combination. The forced swimming test (FST) and tail suspension test (TST) were employed to evaluate despair behavior, whereas the elevated plus maze (EPM) and open field test (OFT) were used to assess anxious behaviors. Subsequently, the animals were sacrificed, and serum corticosterone levels, protein expression of inflammasome-related proteins, and hsp70 gene expression were evaluated in the prefrontal cortex (PFC). The study revealed that treatment with Vit E and Q10, alone or together, provided anxiolytic and antidepressant effects in the heat-stress-subjected animals. Also, giving Vit E and Q10 alone or together greatly lowered serum corticosterone levels. In the PFC, they also lowered the levels of hsp70 mRNA and NF-κB, caspase 1, NLRP3, and IL-1β proteins. It is speculated that treatment with Q10 and Vit E can attenuate heat stress-associated anxious and depressive responses by inhibiting the inflammatory pathways and modulating the hypothalamus-pituitary-adrenal axis.

Protective effects of taurine on heat Stress-Induced cognitive impairment through Npas4 and Lcn2

Heat stress (HS) induces various pathophysiological responses in the brain, encompassing neuroinflammation and cognitive impairments. Although taurine has been reported to possess anti-inflammatory and cognitive-enhancing properties, its role and mechanisms in HS-induced cognitive impairment remain unclear. This study supplemented mice exposed to HS with taurine to assess its effect on cognitive function in a HS-induced mouse model. The results revealed that taurine ameliorated cognitive deficits following HS in mice and mitigated HS-induced astrocyte and microglia activation as well as blood-brain barrier (BBB) damage in the hippocampus. Mechanistically, Mechanistically, transcriptome sequencing was employed to identify that taurine regulates neuronal PAS domain protein (Npas4) and lipocalin 2 (Lcn2) during HS. Taurine was found to modulate hippocampal inflammation and influence cognitive function by upregulating Npas4 and downregulating Lcn2 after HS. Subsequently, molecular docking and AnimalTFDB database calculations were conducted, revealing that taurine might regulate the expression of Npas4 and Lcn2 by modulating the regulatory transcription factors (TFs) RE1 silencing transcription factor (REST) and nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NFKB1). Our findings demonstrate that taurine enhances the recovery of cognitive function through Npas4 and Lcn2 following HS, providing a theoretical basis for the clinical application of taurine in preventing or treating HS-induced cognitive impairment.

Effects of Akkermansia muciniphila on Gut Morphology, Antioxidant Indices, and Gut Microbiome of Mice Under Heat Stress

Nutritional manipulations can reduce the detrimental effects of heat stress on animal health and production. Akkermansia muciniphila (AM) is an innovative beneficial bacteria and can be used for conventional use as dietary supplements and pharmaceutical application. This study aimed to investigate the effects of administering AM on gut morphology, antioxidant indices, and gut microbiome of mice during heat stress. A total of 24 BALB/c mice were randomly assigned to three groups including the control group (CON), heat stress group (HS), and AM administration under heat stress group (AM). Our results showed heat stress significantly increased the water consumption of mice. Administration of AM did not improve feed intake or weight gain. The serum levels of alanine aminotransferase and aspartate aminotransferase as well as antioxidant parameters were not different among the three groups. Heat stress decreased the jejunal villus height, and AM could reverse this effect. AM administration significantly increased the relative abundance of Verrucomicrobiota at the phylum level. At the genus level, heat stress and AM groups tended to have a lower abundance of Alloprevotella. In addition, AM tended to increase the relative abundance of [Eubacterium]_xylanophilum_group in comparison with the other two groups. In summary, administration of AM can alleviate the damage of heat stress to the jejunum. However, it has no effect on serum antioxidant parameters, and its effect on the cecal microbiota is limited.

Genetic patterning in hippocampus of rat undergoing impaired spatial memory induced by long-term heat stress

The organism's normal physiological function is greatly impacted in a febrile environment, leading to the manifestation of pathological conditions including elevated body temperature, dehydration, gastric bleeding, and spermatogenic dysfunction. Numerous lines of evidence indicate that heat stress significantly impacts the brain's structure and function. Previous studies have demonstrated that both animals and humans experience cognitive impairment as a result of exposure to high temperatures. However, there is a lack of research on the effects of prolonged exposure to high-temperature environments on learning and memory function, as well as the underlying molecular regulatory mechanisms. In this study, we examined the impact of long-term heat stress exposure on spatial memory function in rats and conducted transcriptome sequencing analysis of rat hippocampal tissues to identify the crucial molecular targets affected by prolonged heat stress exposure. It was found that the long-term heat stress impaired rats' spatial memory function due to the pathological damages and apoptosis of hippocampal neurons at the CA3 region, which is accompanied with the decrease of growth hormone level in peripheral blood. RNA sequencing analysis revealed the signaling pathways related to positive regulation of external stimulation response and innate immune response were dramatically affected by heat stress. Among the verified differentially expressed genes, the knockdown of Arhgap36 in neuronal cell line HT22 significantly enhances the cell apoptosis, suggesting the impaired spatial memory induced by long-term heat stress may at least partially be mediated by the dysregulation of Arhgap36 in hippocampal neurons. The uncovered relationship between molecular changes in the hippocampus and behavioral alterations induced by long-term heat stress may offer valuable insights for the development of therapeutic targets and protective drugs to enhance memory function in heat-exposed individuals.

New Insights into Sources, Bioavailability, Health-Promoting Effects, and Applications of Chitin and Chitosan

Chitin and chitosan are mostly derived from the exoskeletons of crustaceans, insects, and fungi. Chitin is the second most abundant biopolymer after cellulose, and it is a fibrous polysaccharide which resists enzymatic degradation in the stomach but undergoes microbial fermentation in the colon, producing beneficial metabolites. Chitosan, which is more soluble in the alkaline small intestine, is more susceptible to enzymatic action. Both biopolymers show limited absorption into the bloodstream, with smaller particles exhibiting better bioavailability. The health effects include anti-inflammatory properties, potential in immune system modulation, impacts on cholesterol levels, and antimicrobial effects, with a specific focus on implications for gut health. Chitin and chitosan exhibit anti-inflammatory properties by interacting with immune cells, influencing cytokine production, and modulating immune responses, which may benefit conditions characterized by chronic inflammation. These biopolymers can impact cholesterol levels by binding to dietary fats and reducing lipid absorption. Additionally, their antimicrobial properties contribute to gut health by controlling harmful pathogens and promoting beneficial gut microbiota. This review explores the extensive health benefits and applications of chitin and chitosan, providing a detailed examination of their chemical compositions, dietary sources, and applications, and critically assessing their health-promoting effects in the context of human well-being.

The Impact of High-Temperature Stress on Gut Microbiota and Reproduction in Siberian Hamsters (Phodopus sungorus)

Global warming has induced alterations in the grassland ecosystem, such as elevated temperatures and decreased precipitation, which disturb the equilibrium of these ecosystems and impact various physiological processes of grassland rodents, encompassing growth, development, and reproduction. As global warming intensifies, the repercussions of high-temperature stress on small mammals are garnering increased attention. Recently, research has highlighted that the composition and ratio of gut microbiota are not only shaped by environmental factors and the host itself but also reciprocally influence an array of physiological functions and energy metabolism in animals. In this research, we combined 16S rRNA high-throughput sequencing with conventional physiological assessments, to elucidate the consequences of high-temperature stress on the gut microbiota structure and reproductive capacity of Siberian hamsters (Phodopus sungorus). The results were as follows: 1. The growth and development of male and female hamsters in the high-temperature group were delayed, with lower body weight and reduced food intake. 2. High temperature inhibits the development of reproductive organs in both female and male hamsters. 3. High temperature changes the composition and proportion of gut microbiota, reducing bacteria that promote reproduction, such as Pseudobutyricoccus, Ruminiclostridium-E, Sporofaciens, UMGS1071, and CAG_353. Consequently, our study elucidates the specific impacts of high-temperature stress on the gut microbiota dynamics and reproductive health of Siberian hamsters, thereby furnishing insights for managing rodent populations amidst global climatic shifts. It also offers a valuable framework for understanding seasonal variations in mammalian reproductive strategies, contributing to the broader discourse on conservation and adaptation under changing environmental conditions.

Heat-related illness and dementia: a study integrating epidemiological and experimental evidence

BACKGROUND

Heat-related illness (HRI) is commonly considered an acute condition, and its potential long-term consequences are not well understood. We conducted a population-based cohort study and an animal experiment to evaluate whether HRI is associated with dementia later in life.

METHODS

The Taiwan National Health Insurance Research Database was used in the epidemiological study. We identified newly diagnosed HRI patients between 2001 and 2015, but excluded those with any pre-existing dementia, as the study cohort. Through matching by age, sex, and the index date with the study cohort, we selected individuals without HRI and without any pre-existing dementia as a comparison cohort at a 1:4 ratio. We followed each cohort member until the end of 2018 and compared the risk between the two cohorts using Cox proportional hazards regression models. In the animal experiment, we used a rat model to assess cognitive functions and the histopathological changes in the hippocampus after a heat stroke event.

RESULTS

In the epidemiological study, the study cohort consisted of 70,721 HRI patients and the comparison cohort consisted of 282,884 individuals without HRI. After adjusting for potential confounders, the HRI patients had a higher risk of dementia (adjusted hazard ratio [AHR] = 1.24; 95% confidence interval [CI]: 1.19-1.29). Patients with heat stroke had a higher risk of dementia compared with individuals without HRI (AHR = 1.26; 95% CI: 1.18-1.34). In the animal experiment, we found cognitive dysfunction evidenced by animal behavioral tests and observed remarkable neuronal damage, degeneration, apoptosis, and amyloid plaque deposition in the hippocampus after a heat stroke event.

CONCLUSIONS

Our epidemiological study indicated that HRI elevated the risk of dementia. This finding was substantiated by the histopathological features observed in the hippocampus, along with the cognitive impairments detected, in the experimental heat stroke rat model.

BHBA attenuates endoplasmic reticulum stress-dependent neuroinflammation via the gut-brain axis in a mouse model of heat stress

BACKGROUND

Heat stress (HS) commonly occurs as a severe pathological response when the body's sensible temperature exceeds its thermoregulatory capacity, leading to the development of chronic brain inflammation, known as neuroinflammation. Emerging evidence suggests that HS leads to the disruption of the gut microbiota, whereas abnormalities in the gut microbiota have been demonstrated to affect neuroinflammation. However, the mechanisms underlying the effects of HS on neuroinflammation are poorly studied. Meanwhile, effective interventions have been unclear. β-Hydroxybutyric acid (BHBA) has been found to have neuroprotective and anti-inflammatory properties in previous studies. This study aims to explore the modulatory effects of BHBA on neuroinflammation induced by HS and elucidate the underlying molecular mechanisms.

METHODS

An in vivo and in vitro model of HS was constructed under the precondition of BHBA pretreatment. The modulatory effects of BHBA on HS-induced neuroinflammation were explored and the underlying molecular mechanisms were elucidated by flow cytometry, WB, qPCR, immunofluorescence staining, DCFH-DA fluorescent probe assay, and 16S rRNA gene sequencing of colonic contents.

RESULTS

Heat stress was found to cause gut microbiota disruption in HS mouse models, and TM7 and [Previotella] spp. may be the best potential biomarkers for assessing the occurrence of HS. Fecal microbiota transplantation associated with BHBA effectively reversed the disruption of gut microbiota in HS mice. Moreover, BHBA may inhibit microglia hyperactivation, suppress neuroinflammation (TNF-α, IL-1β, and IL-6), and reduce the expression of cortical endoplasmic reticulum stress (ERS) markers (GRP78 and CHOP) mainly through its modulatory effects on the gut microbiota (TM7, Lactobacillus spp., Ruminalococcus spp., and Prevotella spp.). In vitro experiments revealed that BHBA (1 mM) raised the expression of the ERS marker GRP78, enhanced cellular activity, and increased the generation of reactive oxygen species (ROS) and anti-inflammatory cytokines (IL-10), while also inhibiting HS-induced apoptosis, ROS production, and excessive release of inflammatory cytokines (TNF-α and IL-1β) in mouse BV2 cells.

CONCLUSION

β-Hydroxybutyric acid may be an effective agent for preventing neuroinflammation in HS mice, possibly due to its ability to inhibit ERS and subsequent microglia neuroinflammation via the gut-brain axis. These findings lay the groundwork for future research and development of BHBA as a preventive drug for HS and provide fresh insights into techniques for treating neurological illnesses by modifying the gut microbiota.

Thrombomodulin Improves Cognitive Deficits in Heat-Stressed Mice

BACKGROUND

Thrombomodulin (TM) exerts anticoagulant and anti-inflammatory effects to improve the survival of patients with septic shock. Heat stroke resembles septic shock in many aspects. We tested whether TM would improve cognitive deficits and related causative factors in heat-stressed (HS) mice.

METHODS

Adult male mice were exposed to HS (33°C for 2 hours daily for 7 consecutive days) to induce cognitive deficits. Recombinant human soluble TM (1 mg/kg, i.p.) was administered immediately after the first HS trial and then once daily for 7 consecutive days. We performed the Y-maze, novel objective recognition, and passive avoidance tests to evaluate cognitive function. Plasma levels of lipopolysaccharide (LPS), high-mobility group box 1 (HMGB1), coagulation parameters, and both plasma and tissue levels of inflammatory and oxidative stress markers were biochemically measured. The duodenum and hippocampus sections were immunohistochemically stained. The intestinal and blood-brain barrier permeability were determined.

RESULTS

Compared with controls, HS mice treated with TM had lesser extents of cognitive deficits, exacerbated stress reactions, gut barrier disruption, endotoxemia, blood-brain barrier disruption, and inflammatory, oxidative, and coagulatory injury to heart, duodenum, and hippocampal tissues, and increased plasma HMGB1. In addition to reducing cognitive deficits, TM therapy alleviated all the abovementioned complications in heat-stressed mice.

CONCLUSIONS

The findings suggest that HS can lead to exacerbated stress reactions, endotoxemia, gut barrier disruption, blood-brain barrier disruption, hippocampal inflammation, coagulopathy, and oxidative stress, which may act as causative factors for cognitive deficits. TM, an anti-inflammatory, antioxidant, and anti-coagulatory agent, inhibited heat stress-induced cognitive deficits in mice.

Heat stress induces IL-1β and IL-18 overproduction via ROS-activated NLRP3 inflammasome: implication in neuroinflammation in mice with heat stroke

Heat stroke induced cerebral damage via neuroinflammation. This study aimed to approach whether heat stress would promote NOD-like receptor protein 3 (NLRP3) inflammasome via reactive oxygen species (ROS). The mice were randomly divided into the sham group, the heat stress group, and the heat stress + TEMPOL (ROS scavenger) group. And the NLRP3 -/- mice were applied and divided into the NLRP3 -/-  + sham group and the NLRP3 -/-  + heat stress group. Furthermore, the BV2 cells were divided into four groups following the intervention measures: the heat stress + TEMPOL group, the heat stress + Z-VAD-FMK (caspase-1 inhibitor) group, the heat stress group, and the control group. ROS levels were examined. The expression levels of NLRP3, caspase-1, IL-1β, and IL-18 were detected by western blotting and double immunofluorescence. We found that heat stress attack induced excessive ROS in microglia and subsequently activated NLRP3 inflammasome in both mice and BV2 cells. When ROS scavenged, the expression level of NLRP3 was downregulated. Furthermore, with NLRP3 inflammasome activation, the expression levels of caspase-1, IL-1β, and IL-18 were increased. In NLRP3 -/- mice, however, the caspase-1, IL-1β, and IL-18 were significantly declined. Further experiments showed that pretreatment of caspase-1 inhibitor decreased the expression levels of IL-1β and IL-18. These results suggest that heat stress attack caused neuroinflammation via excessive ROS activating the NLRP3 inflammasome in microglia cells.

Periodic heat waves-induced neuronal etiology in the elderly is mediated by gut-liver-brain axis: a transcriptome profiling approach

Heat stress exposure in intermittent heat waves and subsequent exposure during war theaters pose a clinical challenge that can lead to multi-organ dysfunction and long-term complications in the elderly. Using an aged mouse model and high-throughput sequencing, this study investigated the molecular dynamics of the liver-brain connection during heat stress exposure. Distinctive gene expression patterns induced by periodic heat stress emerged in both brain and liver tissues. An altered transcriptome profile showed heat stress-induced altered acute phase response pathways, causing neural, hepatic, and systemic inflammation and impaired synaptic plasticity. Results also demonstrated that proinflammatory molecules such as S100B, IL-17, IL-33, and neurological disease signaling pathways were upregulated, while protective pathways like aryl hydrocarbon receptor signaling were downregulated. In parallel, Rantes, IRF7, NOD1/2, TREM1, and hepatic injury signaling pathways were upregulated. Furthermore, current research identified Orosomucoid 2 (ORM2) in the liver as one of the mediators of the liver-brain axis due to heat exposure. In conclusion, the transcriptome profiling in elderly heat-stressed mice revealed a coordinated network of liver-brain axis pathways with increased hepatic ORM2 secretion, possibly due to gut inflammation and dysbiosis. The above secretion of ORM2 may impact the brain through a leaky blood-brain barrier, thus emphasizing intricate multi-organ crosstalk.

The firestorm within: A narrative review of extreme heat and wildfire smoke effects on brain health

Climate change is generating increased heatwaves and wildfires across much of the world. With these escalating environmental changes comes greater impacts on human health leading to increased numbers of people suffering from heat- and wildfire smoke-associated respiratory and cardiovascular impairment. One area of health impact of climate change that has received far less attention is the effects of extreme heat and wildfire smoke exposure on human brain health. As elevated temperatures, and wildfire-associated smoke, are increasingly experienced simultaneously over summer periods, understanding this combined impact is critical to management of human health especially in the elderly, and people with dementia, and other neurological disorders. Both extreme heat and wildfire smoke air pollution (especially particulate matter, PM) induce neuroinflammatory and cerebrovascular effects, oxidative stress, and cognitive impairment, however the combined effect of these impacts are not well understood. In this narrative review, a comprehensive examination of extreme heat and wildfire smoke impact on human brain health is presented, with a focus on how these factors contribute to cognitive impairment, and dementia, one of the leading health issues today. Also discussed is the potential impact of combined heat and wildfire smoke on brain health, and where future efforts should be applied to help advance knowledge in this rapidly growing and critical field of health research.

Effect of extreme high temperature on cognitive function at different time scales: A national difference-in-differences analysis

BACKGROUND

Mounting evidence has demonstrated that high temperature was associated with adverse health outcomes, especially morbidity and mortality. Nonetheless, the impact of extreme high temperature on cognitive performance, which is the fundamental capacity for interpreting one's surroundings, decision-making, and acquiring new abilities, has not been thoroughly investigated.

METHODS

We aimed to assess associations between extreme high temperature at different time scales and poor cognitive function. We used longitudinal survey data from the three waves of data from China Family Panel Study, providing an 8-year follow-up of 53,008 participants from China. We assessed temperature and extreme high temperature exposure for each participant based on the residential area and date of cognitive test. We defined the proportion of days/hours above 32 °C as the metric of the exposure to extreme high temperature. Then we used generalized additive model and difference-in-differences approach to explore the associations between extreme high temperature and cognitive function.

RESULTS

Our results demonstrated that either acute exposure or long-term exposure to extreme high temperature was associated with cognitive decline. At hourly level, 0-1 hour acute exposure to extreme high temperature would induce -0.93 % (95 % CI: -1.46 %, -0.39 %) cognitive change. At annual level, 10 percentage point increase in the hours proportion exceeding 32 °C in the past two years induced -9.87 % (95 % CI: -13.99 %, -5.75 %) cognitive change. Furthermore, subgroup analyses indicated adaptation effect: for the same 10 percentage increase in hours proportion exceeding 32 °C, people in warmer areas had cognitive change of -6.41 % (-11.22 %, -1.61 %), compared with -15.30 % (-21.07 %, -9.53 %) for people in cool areas.

CONCLUSION

Our results demonstrated that extreme high temperature was associated with reduced cognitive function at hourly, daily and annual levels, warning that people should take better measures to protect the cognitive function in the context of climate change.

Heat stroke-induced cerebral cortex nerve injury by mitochondrial dysfunction: A comprehensive multi-omics profiling analysis

In recent years, global warming has led to frequent instances of extremely high temperatures during summer, arousing significant concern about the adverse effects of high temperature. Among these, heat stroke is the most serious, which has detrimental effects on the all organs of human body, especially on brain. However, the comprehensive pathogenesis leading to brain damage remains unclear. In this study, we constructed a mouse model of heat stroke and conducted multi-omics profiling to identify relevant pathogenesis induced by heat stroke. The mice were placed in a constant temperature chamber at 42 °C with a humidity of 50 %, and the criteria for success in modeling were that the rectal temperature reached 42 °C and that the mice were trembling. Then the mice were immediately taken out for further experiments. Firstly, we conducted cFos protein localization and identified the cerebral cortex, especially the anterior cingulate cortex as the region exhibiting the most pronounced damage. Secondly, we performed metabolomics, transcriptomics, and proteomics analysis on cerebral cortex. This multi-omics investigation unveiled noteworthy alterations in proteins and metabolites within pathways associated with neurotransmitter systems, heatstroke-induced mitochondrial dysfunction, encompassing histidine and pentose phosphate metabolic pathways, as well as oxidative stress. In addition, the cerebral cortex exhibited pronounced Reactive Oxygen Species (ROS) production, alongside significant downregulation of the mitochondrial outer membrane protein Tomm40 and mitochondrial permeability transition pore, implicating cerebral cortex mitochondrial dysfunction as the primary instigator of neural impairment. This study marks a significant milestone as the first to employ multi-omics analysis in exploring the molecular mechanisms underlying heat stroke-induced damage in cerebral cortex neurons. It comprehensively identifies all potentially impacted pathways by heat stroke, laying a solid foundation for ensuing research endeavors. Consequently, this study introduces a fresh angle to clinical approaches in heatstroke prevention and treatment, as well as establishes an innovative groundwork for shaping future-forward environmental policies.

Thirty Risk Factors for Alzheimer's Disease Unified by a Common Neuroimmune-Neuroinflammation Mechanism

One of the major obstacles confronting the formulation of a mechanistic understanding for Alzheimer's disease (AD) is its immense complexity-a complexity that traverses the full structural and phenomenological spectrum, including molecular, macromolecular, cellular, neurological and behavioural processes. This complexity is reflected by the equally complex diversity of risk factors associated with AD. However, more than merely mirroring disease complexity, risk factors also provide fundamental insights into the aetiology and pathogenesis of AD as a neurodegenerative disorder since they are central to disease initiation and subsequent propagation. Based on a systematic literature assessment, this review identified 30 risk factors for AD and then extended the analysis to further identify neuroinflammation as a unifying mechanism present in all 30 risk factors. Although other mechanisms (e.g., vasculopathy, proteopathy) were present in multiple risk factors, dysfunction of the neuroimmune-neuroinflammation axis was uniquely central to all 30 identified risk factors. Though the nature of the neuroinflammatory involvement varied, the activation of microglia and the release of pro-inflammatory cytokines were a common pathway shared by all risk factors. This observation provides further evidence for the importance of immunopathic mechanisms in the aetiopathogenesis of AD.

High temperatures are associated with reduced cognitive performance in wild southern pied babblers

Global temperatures are increasing rapidly. While considerable research is accumulating regarding the lethal and sublethal effects of heat on wildlife, its potential impact on animal cognition has received limited attention. Here, we tested wild southern pied babblers (Turdoides bicolor) on three cognitive tasks (associative learning, reversal learning and inhibitory control) under naturally occurring heat stress and non-heat stress conditions. We determined whether cognitive performance was explained by temperature, heat dissipation behaviours, individual and social attributes, or proxies of motivation. We found that temperature, but not heat dissipation behaviours, predicted variation in associative learning performance. Individuals required on average twice as many trials to learn an association when the maximum temperature during testing exceeded 38°C compared with moderate temperatures. Higher temperatures during testing were also associated with reduced inhibitory control performance, but only in females. By contrast, we found no temperature-related decline in performance in the reversal learning task, albeit individuals reached learning criterion in only 14 reversal learning tests. Our findings provide novel evidence of temperature-mediated cognitive impairment in a wild animal and indicate that its occurrence depends on the cognitive trait examined and individual sex.

Heat exposure intervention, anxiety level, and multi-omic profiles: A randomized crossover study

BACKGROUND

Climate change has led to the frequent occurrence of high-temperature weather, which has various adverse effects on health, ranging from blood metabolism to systemic organ function. In particular, the sequelae of heat stress injury in most people are related to the nervous system. However, the mechanisms between heat stress and mental health conditions, especially heat stress and anxiety, remain unclear.

OBJECTIVE

We attempted to elucidate the effect of heat exposure intervention on anxiety levels in the population and its mechanism.

METHODS

We first carried out a randomized controlled trial in 20 college students in Beijing, China, to observe the results of the effects of heat exposure intervention on human anxiety. Then, we collected blood samples before and after heat exposure experiment and used metabolomic and transcriptomic approaches to quantify serum metabolites and ELISA measurements to explore the underlying mechanisms.

RESULTS

We found that even 1.5-hour heat exposure intervention significantly increased anxiety levels. Heat stress-induced anxiety was mediated by the activation of the HPA axis, inflammation, oxidative stress, and subsequently unbalanced neurotransmitters. Metabolites such as BDNF, GABA, and glucocorticoids released by the adrenal glands are biomarkers of heat stress-induced anxiety.

CONCLUSIONS

We have demonstrated a causal link between heat stress and anxiety, explored possible biological pathway between heat stress and anxiety. Heat stress can cause the activation of the HPA axis and lead to changes in the body's metabolism, resulting in a series of changes such as inflammation and oxidative stress, leading to anxiety. This study reveals hidden health cost of climate change that has been underexplored, and also reminds us the importance of immediate climate actions.

Impact of ocean warming on a coral reef fish learning and memory

Tropical ectotherms are highly sensitive to environmental warming, especially coral reef fishes, which are negatively impacted by an increase of a few degrees in ocean temperature. However, much of our understanding on the thermal sensitivity of reef fish is focused on a few traits (e.g., metabolism, reproduction) and we currently lack knowledge on warming effects on cognition, which may endanger decision-making and survival. Here, we investigated the effects of warming on learning and memory in a damselfish species, Acanthochromis polyacanthus. Fish were held at 28-28.5 °C (control group), 30-30.5 °C (moderate warming group) or 31.5-32 °C (high warming group) for 2 weeks, and then trained to associate a blue tag (cue) to the presence of a conspecific (reward). Following 20 training trials (5 days), fish were tested for associative learning (on the following day) and memory storage (after a 5-days interval). The control group A. polyacanthus showed learning of the task and memory retention after five days, but increasing water temperature impaired learning and memory. A thorough understanding of the effects of heat stress, cognition, and fitness is urgently required because cognition may be a key factor determining animals' performance in the predicted scenario of climate changes. Knowing how different species respond to warming can lead to better predictions of future community dynamics, and because it is species specific, it could pinpoint vulnerable/resilience species.

Insulin-like growth factor 1 in heat stress-induced neuroinflammation: novel perspective about the neuroprotective role of chromium

Heat stress (HS) can cause a series of stress responses, resulting in numerous negative effects on the body, such as the diminished food intake, carcass quality and reproductive capacity. In addition to the negative effects on the peripheral system, HS leads to central nervous system (CNS) disorders given its toll on neuroinflammation. This neuroinflammatory process is mainly mediated by microglia and astrocytes, which are involved in the activation of glial cells and the secretion of cytokines. While the regulation of inflammatory signaling has a close relationship with the expression of heat shock protein 70 (Hsp70), HS-induced neuroinflammation is closely related to the activation of the TLR4/NF-κB pathway. Moreover, oxidative stress and endoplasmic reticulum (ER) stress are key players in the development of neuroinflammation. Chromium (Cr) has been widely shown to have neuroprotective effects in both humans and animals, despite the lack of mechanistic evidence. Evidence has shown that Cr supplementation can increase the levels of insulin-like growth factor 1 (IGF-1), a major neurotrophic factor with anti-inflammatory and antioxidant effects. This review highlights recent advances in the attenuating effects and potential mechanisms of Cr-mediated IGF-1 actions on HS-induced neuroinflammation, providing presently existing evidence supporting the neuroprotective role of Cr.

Neural Progenitor Cells and the Hypothalamus

Neural progenitor cells (NPCs) are multipotent neural stem cells (NSCs) capable of self-renewing and differentiating into neurons, astrocytes and oligodendrocytes. In the postnatal/adult brain, NPCs are primarily located in the subventricular zone (SVZ) of the lateral ventricles (LVs) and subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). There is evidence that NPCs are also present in the postnatal/adult hypothalamus, a highly conserved brain region involved in the regulation of core homeostatic processes, such as feeding, metabolism, reproduction, neuroendocrine integration and autonomic output. In the rodent postnatal/adult hypothalamus, NPCs mainly comprise different subtypes of tanycytes lining the wall of the 3^rd ventricle. In the postnatal/adult human hypothalamus, the neurogenic niche is constituted by tanycytes at the floor of the 3^rd ventricle, ependymal cells and ribbon cells (showing a gap-and-ribbon organization similar to that in the SVZ), as well as suprachiasmatic cells. We speculate that in the postnatal/adult human hypothalamus, neurogenesis occurs in a highly complex, exquisitely sophisticated neurogenic niche consisting of at least four subniches; this structure has a key role in the regulation of extrahypothalamic neurogenesis, and hypothalamic and extrahypothalamic neural circuits, partly through the release of neurotransmitters, neuropeptides, extracellular vesicles (EVs) and non-coding RNAs (ncRNAs).

Involvement of brain-derived neurotrophic factor methylation in the prefrontal cortex and hippocampus induced by chronic unpredictable mild stress in male mice

Early life stress alters brain-derived neurotrophic factor (BDNF) promoter IV methylation and BDNF expression, which is closely related to the pathophysiological process of depression. However, the role of abnormal methylation of BDNF induced by stress during adolescence due to depression has not yet been clarified. In this study, adolescent mice were exposed to chronic unpredictable mild stress (CUMS). Depression-like behaviors, BDNF promoter IV methylation, expression of DNA methyltransferases (DNMTs), demethylation machinery enzymes, BDNF protein levels, and neuronal development in the prefrontal cortex (PFC) and hippocampus (HIP) were assessed in adolescent and adult mice. The DNMT inhibitor, 5-Aza-2-deoxycytidine (5-AzaD), was used as an intervention. Stress in adolescence induces behavioral dysfunction, elevated methylation levels of BDNF promoter IV, changes in the expression of DNMT, and demethylation machinery enzymes in adolescent and adult mice. Additionally, the stress in adolescence induced lower levels of BDNF and abnormal hippocampal doublecortin (DCX) expression in adolescent and adult mice. However, DNMT inhibitor treatment in adolescent-stressed mice relieved the abnormal behaviors, normalized the methylation level of BDNF promoter IV, BDNF protein expression, expression of DNMTs, and demethylation machinery enzymes, and improved the neuronal development of adult mice. These results suggest that stress in adolescence induces short- and long-term hypermethylation of BDNF promoter IV, which is regulated by DNMTs, and leads to the development of depression.

Lessons from evolution by natural selection: An unprecedented opportunity to use biomimetics to improve planetary health

Planetary health embraces the concept that long-term human welfare depends on the well-being of its ecological systems. Current practices, however, have often ignored this concept and have led to an anthropocentric world, with the consequence of increased greenhouse gas emissions, heat stress, lack of clean water and pollution, that are threatening the environment as well as the health and life of Homo sapiens and many other species. One consequence of environmental stressors has been the stimulation of inflammatory and oxidative stress that may not only promote common lifestyle diseases, but the ageing process. Despite the harshness of the current reality, treatment opportunities may exist 'in our backyard'. Biomimicry is an emerging field of research that explores how nature is structured and aims to mimic ingenious solutions that have evolved in nature for different applications that benefit human life. As nature always counteracts excesses from within, biodiversity could be a source of solutions that have evolved through the natural selection of animal species that have survived polluted, warm, and arid environments - i.e. the same presumptive changes that now threaten human health. One example from the emerging science suggests that animals use the cytoprotective Nrf2 antioxidant pathway to combat environmental stress and this may be a case example that we can apply to better human health. Learning from nature may provide opportunities for environmental management and solutions to the most challenging issue that face the future of the planet.

ZBP1 and heatstroke

Heatstroke, which is associated with circulatory failure and multiple organ dysfunction, is a heat stress-induced life-threatening condition characterized by a raised core body temperature and central nervous system dysfunction. As global warming continues to worsen, heatstroke is expected to become the leading cause of death globally. Despite the severity of this condition, the detailed mechanisms that underlie the pathogenesis of heatstroke still remain largely unknown. Z-DNA-binding protein 1 (ZBP1), also referred to as DNA-dependent activator of IFN-regulatory factors (DAI) and DLM-1, was initially identified as a tumor-associated and interferon (IFN)-inducible protein, but has recently been reported to be a Z-nucleic acid sensor that regulates cell death and inflammation; however, its biological function is not yet fully understood. In the present study, a brief review of the main regulators is presented, in which the Z-nucleic acid sensor ZBP1 was identified to be a significant factor in regulating the pathological characteristics of heatstroke through ZBP1-dependent signaling. Thus, the lethal mechanism of heatstroke is revealed, in addition to a second function of ZBP1 other than as a nucleic acid sensor.

Combined exposure of heat stress and ozone enhanced cognitive impairment via neuroinflammation and blood brain barrier disruption in male rats

BACKGROUND

Heat stress (HS) exposure has been linked to cognitive dysfunction. In reality, high temperature does not occur alone in environment, and ozone (O₃) and heatwaves usually co-exist in atmospheric environment. However, whether O₃ exposure exacerbates HS-induced cognitive impairment and the potential underlying mechanisms have not been explored experimentally. The aim of this study was to determine the co-effects and mechanisms of HS and O₃ on the cognitive dysfunction.

METHODS

48 Sprague Dawley male rats were randomly divided into 4 groups: control, HS, O₃ and HS plus O₃ (HO₃) groups. Rats in HS and HO₃ group were exposed to 40 °C every morning from 9:00 to 12:00 for 15 consecutive days. While rats in O₃ and HO₃ groups were exposed to 0.7 ppm O₃ the same day from 14:00 to 17:00 for 15 days. Cognitive performance was examined with Morris water maze test. Neurodegeneration, glial activation, neuroinflammation, blood brain barrier (BBB) disruption and apoptosis were evaluated by Western blot, Elisa, immunohistochemistry and immunofluorescence staining.

RESULTS

HS induced cognitive decline and neuronal damage in rats. Further studies showed that exposure of rats to HS could also induce glial activation, neuroinflammation and neuronal apoptosis in hippocampus, and decrease in the expressions of ZO-1, claudin-5 and occluding, indicative of BBB disruption. Impressively, the neuronal effects induced by HS, as depicted above, could be worsened by co-exposure to O₃ in rats.

CONCLUSIONS

Co-exposure to O₃ promotes HS-induced cognitive impairment in rats possibly through glial-mediated neuroinflammation and BBB disruption.

Effect of Heat Stress on Hippocampal Neurogenesis: Insights into the Cellular and Molecular Basis of Neuroinflammation-Induced Deficits

Heat stress is known to result in neuroinflammation, neuronal damage, and disabilities in learning and memory in animals and humans. It has previously been reported that cognitive impairment caused by neuroinflammation may at least in part be mediated by defective hippocampal neurogenesis, and defective neurogenesis has been linked to aberrantly activated microglial cells. Moreover, the release of cytokines within the brain has been shown to contribute to the disruption of cognitive functions in several conditions following neuroinflammation. In this review, we summarize evolving evidence for the current understanding of inflammation-induced deficits in hippocampal neurogenesis, and the resulting behavioral impairments after heat stress. Furthermore, we provide valuable insights into the molecular and cellular mechanisms underlying neuroinflammation-induced deficits in hippocampal neurogenesis, particularly relating to cognitive dysfunction following heat stress. Lastly, we aim to identify potential mechanisms through which neuroinflammation induces cognitive dysfunction, and elucidate how neuroinflammation contributes to defective hippocampal neurogenesis. This review may therefore help to better understand the relationship between hippocampal neurogenesis and heat stress.

Nanowired Delivery of Cerebrolysin with Mesenchymal Stem Cells Attenuates Heat Stress-Induced Exacerbation of Neuropathology Following Brain Blast Injury

Blast brain injury (bBI) following explosive detonations in warfare is one of the prominent causes of multidimensional insults to the central nervous and other vital organs injury. Several military personnel suffered from bBI during the Middle East conflict at hot environment. The bBI largely occurs due to pressure waves, generation of heat together with release of shrapnel and gun powders explosion with penetrating and/or impact head trauma causing multiple brain damage. As a result, bBI-induced secondary injury causes breakdown of the blood-brain barrier (BBB) and edema formation that further results in neuronal, glial and axonal injuries. Previously, we reported endocrine imbalance and influence of diabetes on bBI-induced brain pathology that was significantly attenuated by nanowired delivery of cerebrolysin in model experiments. Cerebrolysin is a balanced composition of several neurotrophic factors, and active peptide fragment is capable of neuroprotection in several neurological insults. Exposure to heat stress alone causes BBB damage, edema formation and brain pathology. Thus, it is quite likely that hot environment further exacerbates the consequences of bBI. Thus, novel therapeutic strategies using nanodelivery of stem cell and cerebrolysin may further enhance superior neuroprotection in bBI at hot environment. Our observations are the first to show that combined nanowired delivery of mesenchymal stem cells (MSCs) and cerebrolysin significantly attenuated exacerbation of bBI in hot environment and induced superior neuroprotection, not reported earlier. The possible mechanisms of neuroprotection with MSCs and cerebrolysin in bBI are discussed in the light of current literature.

Co-administration of Nanowired Oxiracetam and Neprilysin with Monoclonal Antibodies to Amyloid Beta Peptide and p-Tau Thwarted Exacerbation of Brain Pathology in Concussive Head Injury at Hot Environment

Environmental temperature adversely affects the outcome of concussive head injury (CHI)-induced brain pathology. Studies from our laboratory showed that animals reared at either cold environment or at hot environment exacerbate brain pathology following CHI. Our previous experiments showed that nanowired delivery of oxiracetam significantly attenuated CHI-induced brain pathology and associated neurovascular changes. Military personnel are the most susceptible to CHI caused by explosion, blasts, missile or blunt head trauma leading to lifetime functional and cognitive impairments affecting the quality of life. Severe CHI leads to instant death and/or lifetime paralysis. Military personnel engaged in combat operations are often subjected to extreme high or low environmental temperature zones across the globe. Thus, further exploration of novel therapeutic agents at cold or hot ambient temperatures following CHI are the need of the hour. CHI is also a major risk factor for developing Alzheimer's disease by enhancing amyloid beta peptide deposits in the brain. In this review, effect of hot environment on CHI-induced brain pathology is discussed. In addition, whether nanodelivery of oxiracetam together with neprilysin and monoclonal antibodies (mAb) to amyloid beta peptide and p-tau could lead to superior neuroprotection in CHI is explored. Our results show that co-administration of oxiracetam with neprilysin and mAb to AβP and p-tau significantly induced superior neuroprotection following CHI in hot environment, not reported earlier.

β-Hydroxybutyric acid improves cognitive function in a model of heat stress by promoting adult hippocampal neurogenesis

Heat stress has multiple potential effects on the brain, such as neuroinflammation, neurogenesis defects, and cognitive impairment. β-hydroxybutyric acid (BHBA) has been demonstrated to play neuroprotective roles in various models of neurological diseases. In the present study, we investigated the efficacy of BHBA in alleviating heat stress-induced impairments of adult hippocampal neurogenesis and cognitive function, as well as the underlying mechanisms. Mice were exposed to 43 ℃ for 15 min for 14 days after administration with saline, BHBA, or minocycline. Here, we showed for the first time that BHBA normalized memory ability in the heat stress-treated mice and attenuated heat stress-impaired hippocampal neurogenesis. Consistently, BHBA noticeably improved the synaptic plasticity in the heat stress-treated hippocampal neurons by inhibiting the decrease of synapse-associated proteins and the density of dendritic spines. Moreover, BHBA inhibited the expression of cleaved caspase-3 by suppressing endoplasmic reticulum (ER) stress, and increased the expression of brain-derived neurotrophic factor (BDNF) in the heat stress-treated hippocampus by activating the protein kinase B (Akt)/cAMP response element binding protein (CREB) and methyl-CpG binding protein 2 (MeCP2) pathways. These findings indicate that BHBA is a potential agent for improving cognitive functions in heat stress-treated mice. The action may be mediated by ER stress, and Akt-CREB-BDNF and MeCP2 pathways to improve adult hippocampal neurogenesis and synaptic plasticity.

Association between sequential extreme precipitation-heatwaves events and hospitalizations for schizophrenia: The damage amplification effects of sequential extremes

OBJECTIVES

In the context of frequent global extreme weather events, there are few studies on the effects of sequential extreme precipitation (EP) and heatwaves (HW) events on schizophrenia. We aimed to quantify the effects of the events on hospitalizations for schizophrenia and compare them with EP and HW alone to explore the amplification effect of successive extremes on health loss.

METHODS

A time-series Poisson regression model combined with a distributed lag non-linear model was applied to estimate the association between sequential EP and HW events (EP-HW) and schizophrenia hospitalizations. The effects of EP-HW with different intervals and intensities on the admission of schizophrenia were compared. In addition, we calculated the mean attributable fraction (AF) and attributable numbers (AN) per exposure of extreme events to reflect the amplification effect of sequential extreme events on health hazards compared with individual extreme events.

RESULTS

EP-HW increased the risk of hospitalization for schizophrenia, with significant effects lasting from lag0 (RR and 95% CI: 1.150 (1.041-1.271)) to lag11 (1.046 (1.000-1.094)). Significant associations were found in the subgroups of male, female, married people, and those aged≥ 40 years old. Shorter-interval (0-3days) or higher-intensity EP-HW (both precipitation ≥ P97.5 and mean temperature ≥ P97.5) had a longer lag effect compared to EP-HW with longer intervals or lower intensity. We found that the mean AF and AN caused by each exposure to EP-HW (AF: 0.074% (0.015%-0.123%); AN: 4.284 (0.862-7.118)) were higher than those induced by each exposure to HW occurring alone (AF:0.032% (0.004%-0.058%); AN:1.845 (0.220-3.329)).

CONCLUSIONS

Sequential extreme precipitation-heatwaves events significantly increase the risk of hospitalizations for schizophrenia, with greater impact and disease burden than independently occurring extremes. The impact of consecutive extremes is supposed to be considered in local sector early warning systems for comprehensive public health decision-making.

Neurodegenerative Diseases: Implications of Environmental and Climatic Influences on Neurotransmitters and Neuronal Hormones Activities

Neurodegenerative and neuronal-related diseases are major public health concerns. Human vulnerability to neurodegenerative diseases (NDDs) increases with age. Neuronal hormones and neurotransmitters are major determinant factors regulating brain structure and functions. The implications of environmental and climatic changes emerged recently as influence factors on numerous diseases. However, the complex interaction of neurotransmitters and neuronal hormones and their depletion under environmental and climatic influences on NDDs are not well established in the literature. In this review, we aim to explore the connection between the environmental and climatic factors to NDDs and to highlight the available and potential therapeutic interventions that could use to improve the quality of life and reduce susceptibility to NDDs.

Influence of Heat Stress on Intestinal Epithelial Barrier Function, Tight Junction Protein, and Immune and Reproductive Physiology

The potential threat of global warming in the 21^st century is on the ecosystem through many aspects, including the negative impact of rising global temperature on the health of humans and animals, especially domestic animals. The damage caused by heat stress to animals has been more and more significant as the worldwide climate continues to rise, along with the breeding industry's expanding scale and stocking density, and it has become the most important stress-causing factor in southern China. In this review, we described the effects of heat stress on animal immune organs and immune system. The much-debated topic is how hyperthermia affects the tight junction barrier. Heat stress also induces inflammation in the body of animals causing low body weight and loss of appetite. This review also discussed that heat stress leads to hepatic disorder, and it also damages the intestine. The small intestine experiences ischemia, and the permeability of the intestine increases. Furthermore, the oxidative stress and mitogen-activated protein kinase (MAPK) pathways have a significant role in stress-induced cellular and organ injury. The study has shown that MAPK activity in the small intestine was increased by heat stress. Heat stress caused extreme small intestine damage, enhanced oxidative stress, and activated MAPK signaling pathways.

Short-term exposure to heatwave-like temperatures affects learning and memory in bumblebees

Global warming has been identified as a key driver of bee declines around the world. While it is clear that elevated temperatures during the spring and summer months-the principal activity period of many bee species-is a factor in this decline, exactly how temperature affects bee survival is unknown. In vertebrates, there is clear evidence that elevated ambient temperatures impair cognition but whether and how heat affects the cognitive abilities of invertebrates remains unclear. Cognitive skills in bees are essential for their survival as, to supply the hive with nutrition, workers must be able to learn and remember the location of the most rewarding floral resources. Here, we investigate whether temperature-related cognitive impairments could be a driver of bee declines by exploring the effect of short-term increases in ambient temperature on learning and memory. We found that, in comparison to bees that were tested at 25°C (a temperature that they would typically experience in summer), bees that were exposed to 32°C (a temperature that they will becoming increasingly exposed to during heatwave events) were significantly worse at forming an association between a coloured light and a sucrose reward and that their capacity to remember this association after just 1 h was abolished. This study provides novel experimental evidence that even just a few hours of exposure to heatwave-like temperatures can severely impair the cognitive performance of insects. Such temperature-induced cognitive deficits could play an important role in explaining recent and future bee population declines.

The novel anti-neuroinflammatory functional food CCL01, a mixture of Cuscuta seed extracts and Lactobacillus paracasei NK112

Neuroinflammation, which occurs due to microglia, is related to the pathogenesis of neurodegenerative disorders. Recently, the development of functional foods that down-regulate over-activated microglial cells to prevent the progression of neurodegenerative disorders has been proposed, since over-activated microglia induce a chronic source of neurotoxic factors and reduce neuronal survival. Thus, the anti-neuroinflammatory effects of a functional food mixture (CCL01) including Cuscuta seeds and Lactobacillus paracasei NK112 on lipopolysaccharide (LPS)-induced experimental models were investigated. In LPS-induced in vitro models, the expression levels of inflammatory mediators (e.g., inducible nitric oxide synthase, cyclooxygenase-2, nitric oxide, and prostaglandin E2) and pro-inflammatory cytokines (e.g., tumor necrosis factor-α, interleukin (IL)-1β, and IL-6) were decreased upon CCL01 treatment. CCL01 showed an anti-neuroinflammatory effect in LPS-induced microglial cells via the inhibition of the mitogen-activated protein kinase (MAPK)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway and the activation of the nuclear factor erythroid-2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway. In the LPS-treated in vivo mouse models, the increased expression of ionized calcium binding adaptor molecule 1 (Iba-1), which indicates microglial activity, was markedly decreased upon treatment with CCL01 (50 and 200 mg kg^-1) in the hippocampus and cortex areas of the mouse brains in comparison with the LPS-injected group. In addition, the groups to which CCL01 was administered had significantly decreased plasma levels of tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 in the LPS-injected mouse models. Our data suggest that CCL01 may be a potential anti-neuroinflammatory agent that can prevent microglia overactivation, and it could be useful for developing functional foods.

The combination of HT-ac and HBET improves the cognitive and learning abilities of heat-stressed mice by maintaining mitochondrial function through the PKA-CREB-BDNF pathway

The aim was to investigate whether the combination of hydroxytyrosol acetate (HT-ac) and ethyl β-hydroxybutyrate (HBET) can improve the cognition of heat-stressed mice, meanwhile exploring the mechanism of action. Mice were divided into 5 groups: control, heat-stressed, HT-ac, HBET, and HT-ac + HBET. Mice were gavaged for 21 days and exposed to heat (42.5 ± 0.5 °C, RH 60 ± 10%, 1 h day^-1) on days 15-21, except for the control group. Results showed that the combination of HT-ac + HBET improved the cognitive and learning abilities of heat-stressed mice, which were tested by Morris water maze, shuttle box, and jumping stage tests. The combination of HT-ac + HBET maintained the integrity of neurons and mitochondria of heat-stressed mice. Likewise, this combination increased the mitochondrial membrane potential, the ATP content, the expression of phosphorylated PKA, BDNF, phosphorylated CREB and Bcl-2, and decreased the expression of Bax, caspase-3, and intracytoplasmic Cyt C in heat-stressed mice.

Effect of Cyclic Heat Stress on Hypothalamic Oxygen Homeostasis and Inflammatory State in the Jungle Fowl and Three Broiler-Based Research Lines

Heat stress (HS) is devastating to poultry production sustainability due its detrimental effects on performance, welfare, meat quality, and profitability. One of the most known negative effects of HS is feed intake depression, which is more pronounced in modern high-performing broilers compared to their ancestor unselected birds, yet the underlying molecular mechanisms are not fully defined. The present study aimed, therefore, to determine the hypothalamic expression of a newly involved pathway, hypoxia/oxygen homeostasis, in heat-stressed broiler-based research lines and jungle fowl. Three populations of broilers (slow growing ACRB developed in 1956, moderate growing 95RB from broilers available in 1995, and modern fast growing MRB from 2015) and unselected Jungle fowl birds were exposed to cyclic heat stress (36°C, 9 h/day for 4 weeks) in a 2 × 4 factorial experimental design. Total RNAs and proteins were extracted from the hypothalamic tissues and the expression of target genes and proteins was determined by real-time quantitative PCR and Western blot, respectively. It has been previously shown that HS increased core body temperature and decreased feed intake in 95RB and MRB, but not in ACRB or JF. HS exposure did not affect the hypothalamic expression of HIF complex, however there was a line effect for HIF-1α (P = 0.02) with higher expression in JF under heat stress. HS significantly up regulated the hypothalamic expression of hemoglobin subunits (HBA1, HBBR, HBE, HBZ), and HJV in ACRB, HBA1 and HJV in 95RB and MRB, and HJV in JF, but it down regulated FPN1 in JF. Additionally, HS altered the hypothalamic expression of oxygen homeostasis- up and down-stream signaling cascades. Phospho-AMPK^Thr172 was activated by HS in JF hypothalamus, but it decreased in that of the broiler-based research lines. Under thermoneutral conditions, p-AMPK^Thr172 was higher in broiler-based research lines compared to JF. Ribosomal protein S6K1, however, was significantly upregulated in 95RB and MRB under both environmental conditions. HS significantly upregulated the hypothalamic expression of NF-κB2 in MRB, RelB, and TNFα in ACRB, abut it down regulated RelA in 95RB. The regulation of HSPs by HS seems to be family- and line-dependent. HS upregulated the hypothalamic expression of HSP60 in ACRB and 95RB, down regulated HSP90 in JF only, and decreased HSP70 in all studied lines. Taken together, this is the first report showing that HS modulated the hypothalamic expression of hypoxia- and oxygen homeostasis-associated genes as well as their up- and down-stream mediators in chickens, and suggests that hypoxia, thermotolerance, and feed intake are interconnected, which merit further in-depth investigations.

Heat-Stress Preconditioning Attenuates Behavioral Responses to Psychological Stress: The Role of HSP-70 in Modulating Stress Responses

Exposure to high ambient temperature is a stressor that influences both biological and behavioral functions and has been previously shown to have an extensive impact on brain structure and function. Physiological, cellular and behavioral responses to heat-stress (HS) (40-41 °C, 2 h) were evaluated in adult male Sprague-Dawley rats. The effect of HS exposure before predator-scent stress (PSS) exposure (i.e., HS preconditioning) was examined. Finally, a possible mechanism of HS-preconditioning to PSS was investigated. Immunohistochemical analyses of chosen cellular markers were performed in the hippocampus and in the hypothalamic paraventricular nucleus (PVN). Plasma corticosterone levels were evaluated, and the behavioral assessment included the elevated plus-maze (EPM) and the acoustic startle response (ASR) paradigms. Endogenous levels of heat shock protein (HSP)-70 were manipulated using an amino acid (L-glutamine) and a pharmacological agent (Doxazosin). A single exposure to an acute HS resulted in decreased body mass (BM), increased body temperature and increased corticosterone levels. Additionally, extensive cellular, but not behavioral changes were noted. HS-preconditioning provided behavioral resiliency to anxiety-like behavior associated with PSS, possibly through the induction of HSP-70. Targeting of HSP-70 is an attractive strategy for stress-related psychopathology treatment.

β-Hydroxybutyric acid attenuates heat stress-induced neuroinflammation via inhibiting TLR4/p38 MAPK and NF-κB pathways in the hippocampus

Heat stress causes many pathophysiological responses in the brain, including neuroinflammation and cognitive deficits. β-Hydroxybutyric acid (BHBA) has been shown to have neuroprotective effects against inflammation induced by lipopolysaccharide. The aim of the present study was to evaluate the effects of BHBA on neuroinflammation induced by heat stress, as well as the underlying mechanisms. Mice were pretreated with vehicle, BHBA or minocycline (positive control group) and followed by heat exposure (43°C) for 15 min for 14 days. In mice subjected to heat stress, we found that treatment with BHBA or minocycline significantly decreased the level of serum cortisol, the expressions of heat shock protein 70 (HSP70), and the density of c-Fos⁺ cells in the hippocampus. Surprisingly, the ethological tests revealed that heat stress led to cognitive dysfunctions and could be alleviated by BHBA and minocycline administration. Further investigation showed that BHBA and minocycline significantly attenuated the activation of microglia and astrocyte induced by heat stress. Pro-inflammatory cytokines were attenuated in the hippocampus by BHBA and minocycline treatment. Importantly, compared with the heat stress group, mice in the BHBA treatment group and positive control group experienced a decrease in the expressions of toll-like receptor 4 (TLR4), phospho-p38 (p-p38), and nuclear factor kappa B (NF-κB). Our results elucidated that BHBA inhibits neuroinflammation induced by heat stress by suppressing the activation of microglia and astrocyte, and modulating TLR4/p38 MAPK and NF-κB pathways. This study provides new evidence that BHBA is a potential strategy for protecting animals from heat stress.

Evaluating the biological safety on mice at 16 T static magnetic field with 700 MHz radio-frequency electromagnetic field

OBJECTIVES

This study evaluated the associated biological effects of radio-frequency (RF) exposure at 16 T magnetic resonance imaging (MRI) on mice health.

MATERIAL AND METHODS

A total of 48 healthy 8-week-old male C57BL/6 mice were investigated. A 16 T high static magnetic field (HiSMF) was generated by a superconducting magnet, and a radiofrequency (RF) electromagnetic field for hydrogen resonance at 16 T (700 MHz) was transmitted via a homemade RF system. The mice were exposed inside the 16 T HiSMF with the 700 MHz RF field for 60 min, and the body weight, organ coefficients, histomorphology of major organs, and blood indices were analyzed for the basal state of the mice on day 0 and day 14. The Heat Shock Protein 70 (HSP70), cyclooxygenase 2 (COX2), and interleukin- 6 (IL-6) were used to evaluate the thermal effects on the brain. Locomotor activity, the open field test, tail suspension test, forced swimming test, and grip strength test were used to assess the behavioral characteristics of the mice.

RESULTS

The 16 T HiSMF with 700 MHz RF electromagnetic field exposure had no significant effects on body weight, organ coefficients, or histomorphology of major organs in the mice. On day 0, the expressions of HSP70 and COX2 in the brain were increased by 16 T HiSMF with 700 MHz RF electromagnetic field exposure. However, the expression of HSP70, COX2, and IL-6 had no significant difference compared with the sham group on day 14. Compared with the sham groups, the meancorpuscularvolume (MCV) on day 0 and the total protein (TP) on day 14 were increased significantly, whereas the other blood indices did not change significantly. The 16 T HiSMF with 700 MHz RF electromagnetic field exposure caused the mice to briefly circle tightly but had no effect on other behavioral indicators.

CONCLUSIONS

In summary, 16 T HiSMF with 700 MHz RF electromagnetic field exposure for 60 min did not have severe effects on mice.

Effect of chitosan on blood profile, inflammatory cytokines by activating TLR4/NF-κB signaling pathway in intestine of heat stressed mice

Heat stress can significantly affect the immune function of the animal body. Heat stress stimulates oxidative stress in intestinal tissue and suppresses the immune responses of mice. The protecting effects of chitosan on heat stress induced colitis have not been reported. Therefore, the aim of this study was to investigate the protective effects of chitosan on immune function in heat stressed mice. Mice were exposed to heat stress (40 °C per day for 4 h) for 14 consecutive days. The mice (C57BL/6J), were randomly divided into three groups including: control group, heat stress, Chitosan group (LD: group 300 mg/kg/day, MD: 600 mg/kg/day, HD: 1000 mg/kg/day). The results showed that tissue histology was improved in chitosan groups than heat stress group. The current study showed that the mice with oral administration of chitosan groups had improved body performance as compared with the heat stress group. The results also showed that in chitosan treated groups the production of HSP70, TLR4, p65, TNF-α, and IL-10 was suppressed on day 1, 7, and 14 as compared to the heat stress group. In addition Claudin-2, and Occludin mRNA levels were upregulated in mice receiving chitosan on day 1, 7, and 14 of heat stress. Furthermore, the IL-6, IL-10, and TNF-α plasma levels were down-regulated on day 1, 7, and 14 of heat stress in mice receiving the oral administration of chitosan. In conclusion, the results showed that chitosan has an anti-inflammatory ability to tolerate hot environmental conditions.

Climate change and neurodegenerative diseases

The climate change induced global warming, and in particular the increased frequency and intensity of heat waves, have been linked to health problems. Among them, scientific works have been reporting an increased incidence of neurological diseases, encompassing also neurodegenerative ones, such as Dementia of Alzheimer's type, Parkinson's Disease, and Motor Neuron Diseases. Although the increase in prevalence of neurodegenerative diseases is well documented by literature reports, the link between global warming and the enhanced prevalence of such diseases remains elusive. This is the main theme of our work, which aims to examine the connection between high temperature exposure and neurodegenerative diseases. Firstly, we evaluate the influence of high temperatures exposure on the pathophysiology of these disorders. Secondly, we discuss its effects on the thermoregulation, already compromised in affected patients, and its interference with processes of excitotoxicity, oxidative stress and neuroinflammation, all of them related with neurodegeneration. Finally, we investigate chronic versus acute stressors on body warming, and put forward a possible interpretation of the beneficial or detrimental effects on the brain, which is responsible for the incidence or progression of neurological disorders.

Terpinen4-ol inhibits heat stress induced inflammation in colonic tissue by Activating Occludin, Claudin-2 and TLR4/NF-κB signaling pathway

Heat stress has severe implications on the health of mice involving intestinal mucosal barrier damage and dysregulated mucosal immune response. This study was designed with long-term heat stress to detect the protective effect of terpinen4-ol on body weight, colon length, organ index, morphological structure, inflammatory cytokines expression, Claudin-2, Occludin, and TLR4 signaling pathway of colonic tissue in mice under heat stress. A study found that oral administration of terpinen4-ol helped against mortality and intestinal inflammation in a mouse model of acute colitis induced by heat stress (40 °C per day for 4 h) exposed for 14 consecutive days. The mice were divided into five groups including control, heat stress, terpinen4-ol low dose (TER LD: 5 mg/kg), medium dose (TER MD: 10 mg/kg), and high dose (TER HD: 20 mg/kg) group. Our study showed that the heat-stress terpinen4-ol group had improved body weight, colon length, and organ index, the number of white blood cells, lymphocytes, and neutrophils in the blood as compared to the heat stress group. In addition, results showed that heat stress upregulated the expression of TLR4, p65, TNF-α, and IL-10. While, in mice receiving the oral administration of terpinen4-ol, the production of TNF-α, IL-10, TLR4, and p65 was suppressed on day 1, 7, and 14 of heat stress. In addition Claudin-2, Occludin mRNA levels were upregulated in mice receiving terpinen4-ol on day 1, 7, and 14 of heat stress. Furthermore, the IL-6, IL-10, TNF-α serum levels were also upregulated in mice under heat stress, but in mice receiving the oral administration of terpinen4-ol, the IL-6, IL-10, TNF-α level was down-regulated on day 1, 7, and 14 of heat stress. Histomorphological examination found that as compared to the control group, the muscle layer thickness and villi height of mice in the heat stress group were significantly reduced, while the changes of the above indicators in the terpinene4-ol groups were improved than those in the heat stress group. In conclusion, the terpinen4-ol has a protective effect on colonic tissue damage induced by heat stress.

Cognitive impairment in obese rat model: role of glial cells

BACKGROUND

Obesity is a worldwide problem. Some studies revealed that it leads to deterioration of the cognitive function, regardless of age.

AIM OF THE STUDY

explore the effect of obesity on cognitive function in a rat model of obesity highlighting the role of glial cells.

MATERIALS AND METHODS

twenty adult male albino rats were assigned to two groups: group I: consumed normal diet, group II: consumed high-fat diet. Body Mass Index (BMI), serum glucose, insulin, HOMA IR and lipid profile were measured. Also, hippocampal expression of Brain derived neurotrophic factor (Bdnf), synapsin, Ionized calcium binding adaptor molecule 1 (Iba), nuclear factor erythroid -related factor 2 (Nrf2), Myelin basic protein (Mbp) were measured by real-time polymerase chain reaction. The Morris Water Maze is a test used to assess spatial learning and memory capacities of rats.

RESULTS

There was a high significant increase in lipid profile, serum glucose, insulin serum levels and HOMA-IR in obese groups with impaired Morris water maze performance compared to control group. There was a significant downregulation in hippocampal Bdnf and synapsin mRNA expression. In addition to decrease in Mbp mRNA expression (P < 0.001). This could be explained by oxidative stress through significant downregulation of Nrf2 mRNA, and inflammation observed in significant upregulation Iba mRNA gene expression in the obese group.

CONCLUSION

Many factors contribute to obesity associated cognitive impairment. In our study, we figured out the crucial roles of glial cells including microglial activation and oligodendrocytes affection with other underlying mechanisms including oxidative stress and hippocampal inflammation.

Sericin Alleviates Thermal Stress Induced Anxiety-Like Behavior and Cognitive Impairment Through Regulation of Oxidative Stress, Apoptosis, and Heat-Shock Protein-70 in the Hippocampus

Exposure to heat stress (HS) has adverse effects on brain function, leading to anxiety-like behavior and memory impairment. Sericin is a silk derived protein with various neurobiological activities. The present study has investigated the effects of sericin on anxiety and cognitive impairments, in HS-received mice. The adult male mice were exposed to HS (43 ºC, 15 min once a day for 14 days) and simultaneously treated with 100, 150, and 200 mg/kg/day of sericin through oral gavage. Elevated plus-maze and Lashley III Maze tests were used to evaluate anxiety and learning and memory, respectively. The hippocampal BAX, BCL-2, caspase3, caspase9 and heat-shock protein-70 (HSP-70) were evaluated by western blotting and oxidative stress markers including malondialdehyde (MDA), total antioxidant capacity (TAC), super oxide dismutase (SOD) as well as glutathione peroxidase (GPx) were evaluated by spectroscopy method. The serum was collected for the analysis of the corticosterone levels. Treatment with sericin in higher doses reversed anxiety-like behavior and cognitive deficit induced by HS. Moreover, heat exposure increased serum corticosterone, hippocampal MDA, apoptotic proteins and HSP-70 levels. Sericin administration decreased serum corticosterone and enhanced hippocampal antioxidant defense and attenuated apoptosis and HSP-70 levels. The results show that the protective effects of sericin against HS-mediated cognitive dysfunction and anxiety-like behavior is possibly through suppressing HSP-70, oxidative stress and apoptosis.

Effect of short- and long-term heat exposure on brain monoamines and emotional behavior in mice and rats

Heat exposure affects several physiological, neuronal, and emotional functions. Notably, monoaminergic neurotransmitters in the brain such as noradrenaline, dopamine, and serotonin, which regulate several basic physiological functions, such as thermoregulation, food intake, and energy balance, are affected by heat exposure and heat acclimation. Furthermore, cognition and emotional states are also affected by heat exposure and changes in brain monoamine levels. Short-term heat exposure has been reported to increase anxiety in some behavioral tests. In contrast, there is a possibility that long-term heat exposure decreases anxiety due to heat acclimation. These changes might be due to adaptation of the core body temperature and/or brain monoamine levels by heat exposure. In this review, we first outline the changes in brain monoamine levels and thereafter focus on changes in emotional behavior due to heat exposure and heat acclimation. Finally, we describe the relationships between emotional behavior and brain monoamine levels during heat acclimation.

Nanodelivery of traditional Chinese Gingko Biloba extract EGb-761 and bilobalide BN-52021 induces superior neuroprotective effects on pathophysiology of heat stroke

Military personnel often exposed to high summer heat are vulnerable to heat stroke (HS) resulting in abnormal brain function and mental anomalies. There are reasons to believe that leakage of the blood-brain barrier (BBB) due to hyperthermia and development of brain edema could result in brain pathology. Thus, exploration of suitable therapeutic strategies is needed to induce neuroprotection in HS. Extracts of Gingko Biloba (EGb-761) is traditionally used in a variety of mental disorders in Chinese traditional medicine since ages. In this chapter, effects of TiO2 nanowired EGb-761 and BN-52021 delivery to treat brain pathologies in HS is discussed based on our own investigations. We observed that TiO2 nanowired delivery of EGb-761 or TiO2 BN-52021 is able to attenuate more that 80% reduction in the brain pathology in HS as compared to conventional drug delivery. The functional outcome after HS is also significantly improved by nanowired delivery of EGb-761 and BN-52021. These observations are the first to suggest that nanowired delivery of EGb-761 and BN-52021 has superior therapeutic effects in HS not reported earlier. The clinical significance in relation to the military medicine is discussed.

Is cyclooxygenase-1 involved in neuroinflammation?

Purpose: Reactive microglia are an important hallmark of neuroinflammation. Reactive microglia release various inflammatory mediators, such as cytokines, chemokines, and prostaglandins, which are produced by enzymes like cyclooxygenases (COX). The inducible COX‐2 subtype has been associated with inflammation, whereas the constitutively expressed COX‐1 subtype is generally considered as a housekeeping enzyme. However, recent evidence suggests that COX‐1 can also be upregulated and may play a prominent role in the brain during neuroinflammation. In this review, we summarize the evidence that supports this involvement of COX‐1. Methods: Five databases were used to retrieve relevant studies that addressed COX‐1 in the context of neuroinflammation. The search resulted in 32 articles, describing in vitro, in vivo, post mortem, and in vivo imaging studies that specifically investigated the COX‐1 isoform under such conditions. Results: Reviewed literature generally indicated that the overexpression of COX‐1 was induced by an inflammatory stimulus, which resulted in an increased production of prostaglandin E2. The pharmacological inhibition of COX‐1 was shown to suppress the induction of inflammatory mediators like prostaglandin E2. Positron emission tomography (PET) imaging studies in animal models confirmed the overexpression of COX‐1 during neuroinflammation. The same imaging method, however, could not detect any upregulation of COX‐1 in patients with Alzheimer's disease. Conclusion: Taken together, studies in cultured cells and living rodents suggest that COX‐1 is involved in neuroinflammation. Most postmortem studies on human brains indicate that the concentration of COX‐1‐expressing microglial cells is increased near sites of inflammation. However, evidence for the involvement of COX‐1 in neuroinflammation in the living human brain is still largely lacking.

Heat stress aggravates oxidative stress, apoptosis, and endoplasmic reticulum stress in the cerebellum of male C57 mice

BACKGROUND

The current study was set to assess the effect of heat stress exposure on oxidative stress, apoptosis, and endoplasmic reticulum stress markers in the cerebellum of male mice.

METHODS

Fifty male C57BL/6 mice were assigned to five groups of (I) control, (II) heat stress (HS)7, (III) HS14, (IV) HS21, and (V) HS42 groups. Animals in the control group were not exposed to HS. Mice in the II-V groups were exposed to HS once a day over 7, 14, 21, and 42 days, respectively. Cerebellar reactive oxygen species (ROS) levels, expression of heat shock protein (HSP)70 and caspase 3 as well as endoplasmic reticulum stress-related proteins (PERK, p-PERK, CHOP, and Full-length ATF-6) expression were determined on the 7th, 14th, 21st, and 42nd days.

RESULTS

ROS levels and HSP70 expression increased following HS on the 14th, 21st, and 42nd days and the 7th, and 14th days with a peak level of expression on the 14th day following HS. HSP70 levels decreased afterward on the 21st and 42nd days compared with the control group. Besides, exposure to HS for 14, 21, and 42 days resulted in a significant increase in the CHOP and p-PERK levels in the cerebellum compared with the control group. Heat exposure also increased protein expression of cleaved caspase 3 and active ATF-6/Full-length ATF-6 on the 21st and 42nd days in the cerebellum compared with the control animals.

CONCLUSION

These findings indicated that chronic HS augmented oxidative stress, endoplasmic reticulum stress, and apoptosis pathways in the cerebellum of mice.