Behavioral Responses To Stress Research Articles

Effects of developmental exposure to arsenic species on behavioral stress responses in larval zebrafish and implications for stress-related disorders.

Arsenic (As) is globally detected in drinking water and food products at levels repeatedly surpassing regulatory thresholds. Several neurological and mental health risks linked to arsenic exposure are proposed; however, the nature of these effects and their association with the chemical forms of arsenic are not fully understood. Gaining a clear understanding of the etiologies and characteristics of these effects is crucial, particularly in association with developmental exposures where the nervous system is most vulnerable. In this study, we investigated the effects of early developmental exposure (6-120 hours post fertilization (hpf)) of larval zebrafish to environmentally relevant concentrations of arsenic species-trivalent/pentavalent, inorganic/organic forms-on developmental, behavioral, and molecular endpoints to determine their effect on stress response and their potential association with stress-related disorders. At 120-hpf, the developing larvae were assessed for a battery of endpoints including survival, developmental malformities, background activity, and behavioral responses to acute visual and acoustic stimuli. Pooled larval samples were analyzed for alterations in the transcript levels of genes associated with developmental neurotoxicity and stress-related disorders. Developmental exposures at target concentrations did not significantly alter survival, overall development or background activity, and had minor effects on developmental morphology. Sodium arsenate and monomethylarsonic acid exaggerated the behavioral responses of larval zebrafish, while sodium arsenite depressed them. Sodium arsenate induced significant effects on molecular biomarkers. This study highlights the effects of developmental exposure to arsenicals on the behavioral stress response, the role chemical formulation plays in exerting toxicological effects, and the possible association with stress-related disorders.

Failure of senolytic treatment to prevent cognitive decline in a female rodent model of aging.

There are sex differences in vulnerability and resilience to the stressors of aging and subsequent age-related cognitive decline. Cellular senescence occurs as a response to damaging or stress-inducing stimuli. The response includes a state of irreversible growth arrest, the development of a senescence-associated secretory phenotype, and the release of pro-inflammatory cytokines associated with aging and age-related diseases. Senolytics are compounds designed to eliminate senescent cells. Our recent work indicates that senolytic treatment preserves cognitive function in aging male F344 rats. The current study examined the effect of senolytic treatment on cognitive function in aging female rats. Female F344 rats (12 months) were treated with dasatinib (1.2 mg/kg) + quercetin (12 mg/kg) or ABT-263 (12 mg/kg) or vehicle for 7 months. Examination of the estrus cycle indicated that females had undergone estropause during treatment. Senolytic treatment may have increased sex differences in behavioral stress responsivity, particularly for the initial training on the cued version of the watermaze. However, pre-training on the cue task reduced stress responsivity for subsequent spatial training and all groups learned the spatial discrimination. In contrast to preserved memory observed in senolytic-treated males, all older females exhibited impaired episodic memory relative to young (6-month) females. We suggest that the senolytic treatment may not have been able to compensate for the loss of estradiol, which can act on aging mechanisms for anxiety and memory independent of cellular senescence.

Social buffering of behavioural stress response in two fish species, Nile tilapia (Oreochromis niloticus) and koi carp (Cyprinus carpio)

AbstractThe presence of conspecifics plays a crucial role in mitigating stress responses in social teleost species and holds potential for enhancing welfare in captive fish. While studies on social buffering effects have typically focussed on single species, marked interspecific differences can exist. Here, we conducted an analysis of social buffering of stress response in two of the most extensively farmed fish, the Nile tilapia and the koi carp. Subjects were exposed to a behavioural stress response assay (open‐field test) in three conditions simulating increasing levels of social enrichment: isolation, pairs, or shoals of five fish. We obtained five stress indicators from the assay: thigmotaxis, freezing, activity, erratic movements and interindividual distance in conditions with more than one fish. In both species, erratic movements significantly decreased with increasing levels of social enrichment, suggesting a similar social buffering effect. However, other indicators revealed species differences. Koi carp, but not Nile tilapia, showed a socially‐mediated reduction in thigmotaxis, whereas Nile tilapia, but not Koi carp, showed a socially‐mediated reduction in freezing behaviour. Furthermore, social enrichment determined opposite effects on the activity of the two species: Nile tilapia were more active as group size increased, whereas the opposite trend was found in koi carp. Finally, Nile tilapia showed increased interindividual distance with increasing social group size, whereas no changes were observed for koi carp. Our study indicates that the buffering effects of social enrichment on the behavioural stress response do not completely overlap between different fish species, highlighting the importance of developing finely‐tuned species‐specific enrichments and welfare indicators.

Effects of developmental exposure to individual and combined PFAS on development and behavioral stress responses in larval zebrafish

Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic chemicals known for their widespread use and persistence in the environment. Laboratory and epidemiological studies investigating these compounds have signaled their neurotoxic and endocrine-disrupting propensities, prompting further research into their effects on behavioral stress responses and their potential role as risk factors for stress-related disorders such as anxiety and depression. This study elucidates the ramifications of early developmental exposures to individual and combined PFAS on the development and behavioral stress responses of larval zebrafish (Danio rerio), an established model in toxicological research. Wild-type zebrafish embryos were enzymatically dechorionated and exposed to PFOS, PFOA, PFHxS, and PFHxA between 6 and 120 h post-fertilization (hpf). We targeted environmentally relevant concentrations stemming from the USEPA 2016 Hazard Advisory Limit (HAL, 0.07 μg/L) and folds higher (0.35, 0.7, 1.75, and 3.5 μg/L). Evaluations at 120 hpf encompassed mortality, overall development, developmental defects, and larval activity both at baseline stress levels and following exposure to acute stressors (acoustic and visual). Larval exposure to PFOA, PFOS, or PFHxS (0.07 μg/L or higher) elicited significant increases in mortality rates, which capped at 23.1%. Exposure to individual chemicals resulted in limited effects on overall development but increased the prevalence of developmental defects in the body axis, swim bladder, pigmentation, and eyes, as well as the prevalence of yolk sac and pericardial edemas. Larval activity at baseline stress levels and following exposure to acute stimuli was significantly altered. Combined exposure to all four chemicals intensified the breadth of developmental and behavioral alterations, suggesting possible additive or synergistic effects. Our findings shed light on the developmental and neurobehavioral disturbances associated with developmental exposure to PFAS at environmentally relevant concentrations, the added risks of combined exposures to these chemicals, and their possible role as environmental risk factors for stress-related disorders.

Androgen regulation of behavioral stress responses and the hypothalamic-pituitary-adrenal axis

Testosterone is a powerful steroid hormone that can impact the brain and behavior in various ways, including regulating behavioral and neuroendocrine (hypothalamic-pituitary-adrenal (HPA) axis) stress responses. Early in life androgens can act to alter development of brain regions associated with stress regulation, which ultimately impacts the display of stress responses later in life. Adult circulating androgens can also influence the expression of distinct genes and proteins that regulate stress responses. These changes in the brain are hypothesized to underlie the potent effects of androgens in regulating behaviors related to stress and stress-induced activation of the HPA axis. Androgens can induce alterations in these functions through direct binding to the androgen receptor (AR) or following conversion to estrogens and subsequent binding to estrogen receptors including estrogen receptor alpha (ERα), beta (ERβ), and G protein-coupled estrogen receptor 1 (GPER1). In this review, we focus on the role of androgens in regulating behavioral and neuroendocrine stress responses at different stages of the lifespan and the sex hormone receptors involved in regulating these effects. We also review the specific brain regions and cell phenotypes upon which androgens are proposed to act to regulate stress responses with an emphasis on hypothalamic and extended amygdala subregions. This knowledge of androgen effects on these neural systems is critical for understanding how sex hormones regulate stress responses.

Gonadotropin-inhibitory hormone and its receptors in teleosts: Physiological roles and mechanisms of actions

Gonadotropin-inhibitory hormone (GnIH) was the first reported hypothalamic neuropeptide inhibiting reproduction in vertebrates. Since its discovery in the quail brain, its orthologs have been identified in a variety of vertebrate species and even protochordates. Depending on the species, the GnIH precursor polypeptides comprise two, three or four mature peptides of the RFamide family. It has been well documented that GnIH inhibits reproduction at the brain-pituitary–gonadal levels and participates in metabolism, stress response, and social behaviors in birds and mammals. However, most studies in fish have mainly been focused on the physiological roles of GnIH in the control of reproduction and results obtained are in some cases conflicting, leaving aside its potential roles in the regulation of other functions. In this manuscript we summarize the information available in fish with respect to the structural diversity of GnIH peptides and functional roles of GnIH in reproduction and other physiological processes. We also highlight the molecular mechanisms of GnIH actions on target cells and possible interactions with other neuroendocrine factors.

Alterations in Blaood Profiles and Spleen Tissue Following Purple Sweet Pota-to Anthocyanin Extract Treatment in Restraint-Stressed Mice

Stress is associated with broad changes in blood and immune cell dysfunction, which are correlated with the spleen as a secondary lymphoid organ. Anthocyanin, a plant bioactive compound from purple sweet potatoes, has previously been reported to have a beneficial effect on stress response behavior. However, the limited studies evaluated anthocyanin's effect on blood profiles and spleen tissue under stress. Therefore, this study aimed to explore the effect of total anthocyanin extract (ANC) from purple sweet potatoes (PSP) on the blood profiles and spleen tissue of restraint stressed mice. A total of 20 male adult BALB/c mice were divided into control (CTRL), stress (STR), stress + ANC 10 mg/kgBW (STR+ANC10), stress + ANC 20 mg/kgBW (STR+ANC20), and stress + ANC 40 mg/kgBW (STR+ANC10). Restraint stress was applied two hours/day for 14 days. An automatic blood analyzer was used for blood profiling. Immunoblotting of caspase-3 and hematoxylin-eosin-stained histological slides were observed for spleen tissue analysis. Combination of STR and ANC treatment reduced the erythrocyte count, hemoglobin level, and leucocyte count. The ANC-treated groups had a higher percentage of lymphocytes and a lower percentage of granulocytes. The expression of caspase-3 declined among ANC-treated groups. Spleen extramedullary erythropoiesis, vacuolization, and white pulp involution were demonstrated in stress and ANC-treated animals. In summary, restraint stress modified the blood cell profiles and spleen tissue in the mice model. Further research is necessary to evaluate the mechanism of ANC during stress on blood cells and splenic tissue repair enhancement

Maternal contact and positive human interactions during lactation impacts piglet performance and behaviour during lactation

IntroductionEarly life interactions with the sow or humans can have lifelong consequences on welfare and performance in pigs. It was hypothesised that piglets that received increased maternal contact and positive human contact would display improved responses to stressful events and improved performance.MethodsNinety-eight litters were allocated to a 2 x 2 factorial design for maternal contact (MC+)/restricted maternal contact (MC-); and positive human contact (HC+)/no additional human contact (HC-). Modified farrowing crates were used to restrict maternal contact (MC-) and litters in the HC+ treatment received five minutes of daily positive human interaction (stroking). Behavioural and physiological responses were assessed during processing at three days of age and during a behaviour test in which piglets were introduced to an empty arena, novel object, human hand and human standing in the arena at 18 days of age. Observations of behaviour in the home pen and growth and survival of piglets to weaning were also assessed.ResultsAt processing, MC- piglets had more squeals (P = 0.015), tended to have more grunts (P = 0.063) and struggle attempts (P = 0.079), and had increased plasma cortisol concentrations (P = 0.009) after processing than MC+ piglets. During the behaviour test, HC+ piglets were more active (P = 0.014) and had more vocalisations (P < 0.05) in the empty arena than HC piglets. Furthermore, HC+ piglets were more likely to approach a human standing in the arena (P = 0.006) than HC- piglets. MC- piglets were less active (P = 0.008) and were less likely to approach the novel object (P = 0.049) than MC+ piglets. MC+ piglets tended to have higher weaning weights (P = 0.055) and more MC+ piglets were successfully weaned (P = 0.022) than MC- piglets. There was no significant effect of HC on piglet performance.DiscussionWhile positive handling did not affect behavioural and physiological stress response to processing, HC+ reduced fear of novelty and humans. These findings highlight the importance of early life experiences has on stress resilience early in life.

GxE interaction effects of HCRTR2 single nucleotide polymorphism and adverse childhood experiences on methamphetamine use disorder

ABSTRACT Background: Methamphetamine use disorder (MUD) is a worldwide health concern. The hypothalamic orexin system regulates stress response and addictive behaviors. The genetic variation in the hypocretin receptor 2 (HCRTR2), rs2653349, is associated with substance use disorder. Objectives: We explored the gene-environment (GxE) interaction of rs2653349 and adverse childhood experiences (ACEs) associated with MUD susceptibility. Methods: Four hundred and one individuals (336 males, 65 females) with MUD and 348 healthy controls (288 males, 60 females) completed a self-report questionnaire evaluating ACEs, encompassing childhood abuse and household dysfunction categories, and were genotyped for SNP rs2653349. Methamphetamine use variables were collected using the Diagnostic Interview for Genetic Studies. We used regression analyses to assess the GxE effect on MUD risk. Results: The MUD group had a comparable genotypic distribution for rs2653349 to the control group, albeit with a higher prevalence and number of types of ACEs, correlating with an increased MUD risk (p < .05). No significant genetic impact of rs2653349 on MUD risk was found. However, we observed a GxE interaction effect between the minor allele of rs2653349 and the number of childhood abuse or household dysfunction types, correlating with a reduced MUD risk (OR = -0.71, p = .04, Benjamini-Hochberg adjusted p = .08 and OR = -0.59, p = .045, Benjamini-Hochberg adjusted p = .09, respectively). Conclusion: HCRTR2 SNP rs2653349 has no significant impact on MUD risk, but ACEs may increase this risk. GxE results suggest that rs2653349 could offer protection against developing MUD in individuals experiencing multiple types of ACEs.

Effects of Rumen Fermentation Characteristics on Stress-Related Hormones and Behavior in Sheep

This study investigated the relationship between rumen fermentation, stress-related hormones, and behavior in sheep with the aim of providing insights for improving animal welfare and feed management practices. Eight lambs were assigned to either a high concentration or control group. Blood samples were collected for hormone analysis, and an open field test was conducted to observe behavioral stress responses. The results showed that diet composition may affect the behavior of ruminants in response to stressors and novel situations, as evidenced by the higher number of escape attempts in the high-concentration group. In addition, analyses of individual volatile fatty acids (VFAs) showed a significant positive correlation between the acetic acid/propionic acid ratio and sniffing behavior of the novel object (p &lt; 0.05, ρ = −0.414). These findings have important implications for animal welfare and feed management practices. Overall, this study provides insights into the potential impact of diet composition on the behavior of ruminants in response to stressors and novel situations, highlighting the importance of improving animal welfare through feed management practices. Further research is needed to fully elucidate the mechanisms underlying the complex relationship between rumen fermentation, stress-related hormones, and behavior in ruminant animals.

Transcriptomic analysis reveals mitochondrial pathways associated with distinct adolescent behavioral phenotypes and stress response

Adolescent individuals exhibit great variability in cortical dynamics and behavioral outcomes. The developing adolescent brain is highly sensitive to social experiences and environmental insults, influencing how personality traits emerge. A distinct pattern of mitochondrial gene expression in the prefrontal cortex (PFC) during adolescence underscores the essential role of mitochondria in brain maturation and the development of mental illnesses. Mitochondrial features in certain brain regions account for behavioral differences in adulthood. However, it remains unclear whether distinct adolescent behavioral phenotypes and the behavioral consequences of early adolescent stress exposure in rats are accompanied by changes in PFC mitochondria-related genes and mitochondria respiratory chain capacity. We performed a behavioral characterization during late adolescence (postnatal day, PND 47–50), including naïve animals and a group exposed to stress from PND 31–40 (10 days of footshock and 3 restraint sessions) by z-normalized data from three behavioral domains: anxiety (light–dark box tests), sociability (social interaction test) and cognition (novel-object recognition test). Employing principal component analysis, we identified three clusters: naïve with higher-behavioral z-score (HBZ), naïve with lower-behavioral z-score (LBZ), and stressed animals. Genome-wide transcriptional profiling unveiled differences in the expression of mitochondria-related genes in both naïve LBZ and stressed animals compared to naïve HBZ. Genes encoding subunits of oxidative phosphorylation complexes were significantly down-regulated in both naïve LBZ and stressed animals and positively correlated with behavioral z-score of phenotypes. Our network topology analysis of mitochondria-associated genes found Ndufa10 and Cox6a1 genes as central identifiers for naïve LBZ and stressed animals, respectively. Through high-resolution respirometry analysis, we found that both naïve LBZ and stressed animals exhibited a reduced prefrontal phosphorylation capacity and redox dysregulation. Our findings identify an association between mitochondrial features and distinct adolescent behavioral phenotypes while also underscoring the detrimental functional consequences of adolescent stress on the PFC.

Short-term effects of standard procedures associated with surgical transmitter implantation on a benthic shark species requiring anaesthesia

Surgical implantation of acoustic transmitters is a widely used method to study the movement ecology and eco-physiology of sharks. Nevertheless, the impact of surgical implantation on the behaviour of the target species is seldom separated from the capture stress. Pyjama catsharks (Poroderma africanum) is a small benthic shark species endemic to South Africa. For this species, tonic immobility is insufficient to achieve adequate sedation for surgical implantation of internal transmitters and a combination of tonic immobility and anaesthetic is needed. Therefore, behavioural responses to surgical implantation of internal transmitters were quantified in pyjama catsharks using tri-axial accelerometers in a controlled captive environment for a 24-h period after capture and a 24-h period after surgery. A 2-state hidden Markov model was developed to investigate the sharks’ activity patterns, as well as the related possible effects of the treatment type (capture vs surgery and surgery vs non surgery) and time of day. The results showed that the sharks which went through surgery (treatment group) spent significantly more time (58.7 % of their time) in a lower activity state, which we believe relates to higher stress levels, following surgery compared to following capture. Furthermore, sharks in the treatment group spent roughly 20 % more time in the lower activity state compared to the control group (without surgical implantation). These results could be related to the sedating effect of the anaesthetic, and/or suggest short-term behavioural stress response to the surgical implantation of transmitter, related to either biochemical stress or anatomical discomfort. Furthermore, the sharks changed their behavioural state more frequently in the three hours after the surgery and spent more time in a lower activity state. This emphasises the importance of allowing the sharks enough time to recover from the combination of anaesthesia and surgery before being released into the ocean.

Sex differences in androgen receptor, estrogen receptor alpha, and c-Fos co-expression with corticotropin releasing factor expressing neurons in restrained adult mice

Gonadal hormone actions through androgen receptor (AR) and estrogen receptor alpha (ERα) regulate sex differences in hypothalamic-pituitary-adrenal (HPA) axis responsivity and stress-related behaviors. Here we tested whether corticotropin releasing factor (CRF) expressing neurons, which are widely known to regulate neuroendocrine and behavioral stress responses, co-express AR and ERα as a potential mechanism for gonadal hormone regulation of these responses. Using Crh-IRES-Cre::Ai9 reporter mice we report high co-localization of AR in CRF neurons within the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BST), medial amygdala (MeA), and ventromedial hypothalamus (VMH), moderate levels within the central amygdala (CeA) and low levels in the paraventricular hypothalamus (PVN). Sex differences in CRF/AR co-expression were found in the principal nucleus of the BST (BSTmpl), CeA, MeA, and VMH (males>females). CRF co-localization with ERα was generally lower relative to AR co-localization. However, high co-expression was found within the MPOA, AVPV, and VMH, with moderate co-expression in the arcuate nucleus (ARC), BST, and MeA and low levels in the PVN and CeA. Sex differences in CRF/ERα co-localization were found in the BSTmpl and PVN (males>females). Finally, we assessed neural activation of CRF neurons in restraint-stressed mice and found greater CRF/c-Fos co-expression in females in the BSTmpl and periaqueductal gray, while co-expression was higher in males within the ARC and dorsal CA1. Given the known role of CRF in regulating behavioral stress responses and the HPA axis, AR/ERα co-expression and sex-specific activation of CRF cell groups indicate potential mechanisms for modulating sex differences in these functions.

Effect of Benson's relaxation technique versus music intervention on physiological parameters and stress of children with thalassemia during blood transfusions: A randomized controlled trial

BackgroundChildren with thalassemia are generally dependent on blood transfusions and face a lot of stress and alteration in their physiological parameters through the procedure. AimThis study aimed to investigate the effect of Benson's relaxation technique versus music intervention on physiological parameters and stress of children with thalassemia during blood transfusions. DesignA randomized, controlled trial with three parallel groups. MethodsOne hundred and twenty preschool-age children with thalassemia who underwent blood transfusions were randomly assigned to three groups. Children of the control group received only routine hospital care through blood transfusions. Music intervention group children listened to recorded Mozart's music and children of Benson's relaxation group received relaxation intervention before and during the blood transfusions. Outcome measures were physiological parameters and behavioral distress levels. SettingHematology outpatient clinic of the Children's University Hospital at El-Shatby in Alexandria from October 2022 to February 2023. ResultsThe mean total score of children's behavioral responses to stress before the blood transfusions procedure was 19.32 ± 4.08, 14.20 ± 0.93, and 16.92 ± 4.74 in the control, music, and Benson groups, respectively. Beyond that, there was a decline in their physiological parameters and behavioral stress response during and after procedure among groups of study (P = 0.005 & <0.001, respectively). ConclusionMusic and Benson's relaxation interventions had a helpful effect on stabilizing the physiological parameters and reducing behavioral distress levels in children with thalassemia undergoing blood transfusions. Practice implicationsThis study directs paediatric nurses to apply Benson's relaxation and music interventions for children with thalassemia to enhance their responses.

Responses to Reduced Feeding Frequency in Captive-Born Cheetahs (Acinonyx jubatus): Implications for Behavioural and Physiological Stress and Gastrointestinal Health.

Unnatural diet composition and frequent feeding regimes may play an aetiological role in the multiple diseases prevalent in captive cheetahs. This study investigated the responses of captive-born (hand-reared) cheetahs (n = 6) to a reduced feeding frequency schedule distinguished by offering larger quantities of food less frequently. The study cheetahs were fed four once-daily meals per week during the 3-week treatment period, followed by a 3-week control period in which they were fed two daily rations six days a week. Total weekly food intake was maintained throughout the study. Variations in behaviour, faecal consistency score (FCS), and faecal glucocorticoid metabolite concentration were measured. Less frequent feeding resulted in higher FCS (p < 0.01) and locomotory behaviour (p < 0.05) among the studied cheetahs. Faecal glucocorticoid metabolite concentration demonstrated an initial acute stress response to the change in feeding frequency (p < 0.05) and subsequent adaptation. The results of the FCS analysis suggest that the more natural feeding pattern could have benefited the studied cheetahs' gastrointestinal health without a significant behavioural or physiological stress response overall to the change in feeding frequency.

Not so fast: Paradoxically increased variability in the glucose tolerance test due to food withdrawal in continuous glucose-monitored mice

ObjectiveThis study was performed to determine the effect of fasting on reproducibility of the glucose tolerance test. Due to individual variation in animal feeding behaviors, fasting animals prior to metabolic and behavioral experiments is widely held to reduce inter-subject variation in glucose and metabolic parameters of preclinical rodent models. Reducing variability is especially important for studies where initial metabolite levels can influence the magnitude of experimental interventions, but fasting also imposes stress that may distort the variables of interest. One such intervention is the glucose tolerance test (GTT) which measures the maximum response and recovery following a bolus of exogenous glucose. We sought to investigate how fasting affects the response of individual mice to a GTT. MethodsUsing simultaneous continuous glucose monitoring (CGM) and indirect calorimetry, we quantified blood glucose, physical activity, body temperature, metabolic rates, and food consumption levels on a minute-to-minute basis in adult male mice for 4 weeks. We tested the effects of a 4-h or 18-h fast on the GTT to examine the effect of food withdrawal in light or dark photoperiods. Studies were also performed with 4-h fasting in additional mice without implanted CGM probes. ResultsContrary to our expectations, a 4-h fast during the light photoperiod promotes a paradoxical increase in inter-animal variation in metabolic rate, physical activity, body temperature, glycemia, and glucose tolerance. This hyperglycemic and hyper-metabolic phenotype promotes increased corticosterone levels and is consistent with a behavioral stress response to food deprivation, even in well-fed mice. We find that mice undergoing an 18-h fast entered torpor, a hibernation-like state. In addition to low body temperature and metabolic rate, torpor is also associated with glucose levels 56 mg/dl lower than those seen in mice with ad libitum access to food. Moreover, the time spent in torpor affects the response to a GTT. ConclusionOur results suggest fasting mice before glucose tolerance testing, and perhaps other experiments, can have the opposite of the intended effect where fasting can increase, rather than decrease, experimental variability.

Network alteration of cyclically loaded elastomers mediated by dynamic bonds

Elastomers and hydrogels with dynamic network structures have received considerable research interest due to their high strength and toughness, and self-healing ability. While the general mechanical responses of dynamic polymer networks have been investigated, the study on their fatigue behaviors is still in its infancy. In this work, we employ experimental and theoretical approaches to gain a comprehensive understanding of the mechanical response of an elastomer with physical crosslinkers under fatigue tests up to 10,000 cycles. The constitutive model characterizes the network configuration using the density distribution function of the polymer chains, which is represented by a state variable denoting the stress-free configuration of each individual chain. The model takes into account the reversible dissociation/association of dynamic bonding facilitated by the physical crosslinkers. As a result, polymer chains can repeatedly release the involved strain energy and transform between different stress-free configurations. A multi-dispersed reaction process is further employed to describe the state transition of polymer chains, enabling the model to elucidate the progressive damage in long-term relaxation and fatigue tests by recording and updating the density distribution function of chain state. In addition, the reversible transition of the polymer chain between different state configurations enables the model to capture the rate-dependent stress response and relaxation behaviors of physically crosslinked elastomers and gels. Remarkably, our microscopic model, which requires only five parameters, offers an efficient approach to describe the mechanical responses of elastomers and gels with dynamic bonds.

Investigation on the fatigue behavior of 7075 aluminum alloy at different aging states

To study the effect of the aging state on the low-cycle fatigue (LCF) performance of 7075 Al alloy, LCF experiments with different strain amplitudes (Δε/2 = 0.5%- Δε/2 = 0.9%) were conducted for underaged (UA), peak-aging (PA) and overaged (OA) states with similar tensile properties in this work. The effect of the aging state on the cyclic stress response behavior and the LCF lives of 7075 Al alloy was revealed by observing the dislocation configuration after LCF. The microcrack orientation on the surface of LCF samples was observed by the electron backscatter diffraction (EBSD) technique, and the results showed that the soft orientation inside the coarse grains was the main cause of fatigue cracking. Combined with the previous studies, we summarized the dominant factors for the LCF and high-cycle fatigue (HCF) properties of 7075 Al alloys at different aging states, i.e., the LCF properties were determined by tensile properties, while the HCF properties were dominated by dislocation slip mode.

Habitat complexity and predator odours impact on the stress response and antipredation behaviour in coral reef fish.

Mass coral bleaching events coupled with local stressors have caused regional-scale loss of corals on reefs globally. Following the loss of corals, the structural complexity of these habitats is often reduced. By providing shelter, obscuring visual information, or physically impeding predators, habitat complexity can influence predation risk and the perception of risk by prey. Yet little is known on how habitat complexity and risk assessment interact to influence predator-prey interactions. To better understand how prey's perception of threats may shift in degraded ecosystems, we reared juvenile Pomacentrus chrysurus in environments of various habitat complexity levels and then exposed them to olfactory risk odours before simulating a predator strike. We found that the fast-start escape responses were enhanced when forewarned with olfactory cues of a predator and in environments of increasing complexity. However, no interaction between complexity and olfactory cues was observed in escape responses. To ascertain if the mechanisms used to modify these escape responses were facilitated through hormonal pathways, we conducted whole-body cortisol analysis. Cortisol concentrations interacted with habitat complexity and risk odours, such that P. chrysurus exhibited elevated cortisol levels when forewarned with predator odours, but only when complexity levels were low. Our study suggests that as complexity is lost, prey may more appropriately assess predation risk, likely as a result of receiving additional visual information. Prey's ability to modify their responses depending on the environmental context suggests that they may be able to partly alleviate the risk of increased predator-prey interactions as structural complexity is reduced.

The Role of Combined Modifiable Lifestyle Behaviors between Stressful Life Events and Allostatic Load in Australian Adults

Behavioral stress response is a proposed pathway that links exposure to stressors to elevated allostatic load, yet there is little empirical evidence. We tested the role of combined modifiable lifestyle behaviors in the mechanistic pathway between stressful life events and allostatic load among Australian adults. A latent profile analysis was performed to identify latent subgroups with distinct behavioral clusters based on five modifiable lifestyle behaviors (smoking, sedentary behaviour, physical activity, alcohol consumption, and diet quality). Subsequently, a path analysis was applied using a sequential mediational model to test the mediating effect of behavioral clusters in the associations between stressful life events and three measures of allostatic load (high-risk quartiles, high-risk deciles, and system risk index). The indirect effects via behavioral clusters were estimated using the product of coefficient approach. Three behavioral clusters: "least healthy lifestyle", "moderately healthy lifestyle", and "most healthy lifestyle" emerged from our analytic sample. Compared to the "moderately healthy lifestyle" group, the "most healthy lifestyle" participants had significantly lower allostatic load (p<0.01). Mediation analyses revealed non-significant indirect associations via the "least healthy lifestyle" and "most healthy lifestyle" clusters compared to the "moderately healthy lifestyle" group. Findings were consistent across allostatic load indices. This study confirms previous findings on the salutary effect of healthy lifestyle behaviors on allostatic load. The behavioural clusters did not explain the association between stressful life events and allostatic load. Future analyses should consider the optimal measurement intervals, moderating role of social support, and account for the time-varying nature of lifestyle behaviours.