Individual differences in plasma catecholamine and corticosterone stress responses of wild-type rats: relationship with aggression

The catecholamine response to graded high-altitude flight in yellow-rumped warblers (Setophaga coronata)

Chronic exposure to low oxygen (hypoxia) leads to amplification of the hypoxic chemoreflex, increasing breathing and sympathetic nervous system (SNS) activation. Prolonged SNS activation redistributes blood to hypoxia-sensitive tissues away from muscles. Recent tracking studies have shown that migratory songbirds can fly 5,000 m or higher above sea level, leading us to hypothesize that migratory birds may have a blunted hypoxic chemoreflex to maintain blood flow to muscles during migratory flight at high altitudes. To test this hypothesis, we used a hypobaric wind tunnel and measured circulating plasma catecholamines after maximal altitude flight, flight at 75% of maximal altitude, flight at ground level (∼250 m), and after rest at 75% of maximal altitude and ground level in migratory myrtle yellow-rumped warblers (Setophaga coronata). Yellow-rumped warblers were capable of flying above 4,000 m simulated altitude above sea level (average maximum altitude of ∼3,600 m) and would maintain flights at 75% of individual maximum altitudes (∼2,700 m). Circulating dopamine and noradrenaline were similar between resting and flight conditions at ground level and with exposure to 75% of maximal altitude, whereas adrenaline significantly increased with flight, but did not change further with flight at 75% of maximal altitude. In contrast, both adrenaline and noradrenaline concentrations increased after maximum altitude flights compared with 75% and ground-level flights. Our findings show that exercise increases plasma adrenaline in migratory songbirds and suggest that warblers flying at high altitudes below their maximum altitude may be minimally hypoxic, allowing them to maintain oxygen transport to flight muscles.NEW & NOTEWORTHY Yellow-rumped warblers, a small songbird that conducts migratory flights, were found to fly to altitudes above 4,000 m above sea level in simulated flights using a hypobaric wind tunnel. Circulating adrenaline suggests that warblers flying at 75% of individual maximum altitudes are not experiencing arterial hypoxia, allowing them to maintain aerobically demanding migratory flight at high altitudes.

Effects of Excessive Sucrose Intake on Aggressive Behavior and Peripheral Stress-Related Hormone and Catecholamines in BALB/c Mice during Adolescent Development

As binge eating and unbalanced diets increase the prevalence of obesity and metabolic disorders, it has been noted that the increase in psychiatric disorders is also a consequence of diet. The present study examined aggressive behavior and peripheral stress-related hormone and catecholamine levels in BALB/c mice fed a high-sucrose diet during adolescent development. BALB/c mice are rarely used in research assessing the effect of diet, but were used for ethnic and personal differences and as a new experimental model. BALB/c mice were fed a diet in which all carbohydrate components were replaced with sucrose for 4 wk and were subjected to the resident-intruder and social dominance tube test. Plasma insulin, corticosterone, and catecholamine levels were also compared to mice fed a control diet. The high-sucrose diet did not alter body weight, glucose tolerance, and plasma insulin levels in BALB/c mice, indicating that the diet was resilient to obesity. Mice fed a high-sucrose diet exhibited increased aggressive behaviors in the resident-intruder test and had a significantly higher win rate in the tube test. Increases in adrenal weight and plasma corticosterone as well as noradrenaline and adrenaline levels were exhibited in mice fed a high-sucrose diet. In particular, this is the first evidence of increased social dominance and hyperplasia of the adrenal glands by a sucrose diet. Sucrose diet intake increased aggression in mice and caused elevated peripheral hormones involving the HPA axis and the sympathetic nervous system, indicating that this may be a central nervous system-mediated effect of excess sucrose.

Intraoperative Takotsubo Cardiomyopathy: A Case Report

Takotsubo cardiomyopathy (TTC) is a rare condition associated with transient akinesia of apical segments and hyperkinesia of basal segments of the heart. Although several mechanisms have been proposed to cause direct and indirect myocardial damage owing to catecholamine excess, the underlying pathophysiology remains unknown. An 18-year-old female was referred to our otorhinolaryngology outpatient clinic for a septorhinoplasty. Apart from the fear of surgery, the patient had no other health issues. After the administration of local anesthesia (lidocaine and epinephrine mix), tachycardia storms occurred and soon ended with cardiac collapse. Further evaluation revealed TTC. TTC should be considered, especially in cases of treatment-resistant hemodynamic problems after cardiac resuscitation, and nurses can play a crucial role during the preanesthetic period in helping the patient cope with the stress factors related to the upcoming surgery.

The impact of sciatic nerve injury and social interactions testing on glucocorticoid receptor expression in catecholaminergic medullary cell populations

Paradoxically, while acute pain leads to transiently elevated corticosterone, chronic pain does not result in persistently elevated corticosterone. In the sciatic nerve chronic constriction injury (CCI) model of chronic pain, we have shown that the same nerve injury produces a range of behavioural outcomes, each associated with distinctive adaptations to the HPA-axis to achieve stable plasma corticosterone levels. We also demonstrated that CRF and GR expression in the paraventricular hypothalamus (PVH) was increased in rats that showed persistent changes to their social behaviours during Resident-Intruder testing ('Persistent Effect' rats) when compared to rats that showed no behavioural changes ('No Effect' rats). In this study, we investigated whether these changes were driven in part by altered sensitivity of the brainstem catecholaminergic pathways (known to regulate the PVH) to glucocorticoids. GR expression in adrenergic (C1,C2) and noradrenergic (A1,A2) cells was determined using immunohistochemistry in behaviourally tested CCI rats and in uninjured controls. We found no differences between Persistent Effect and No Effect rats in (1) the glucocorticoid sensitivity of these cells, or (2) the numbers of adrenergic and noradrenergic cells in each region. However, we discovered an overall reduction in GR expression in the non-catecholaminergic cells of these regions in both experimental groups when compared to uninjured controls, most likely attributable to the repeated Resident-Intruder testing. Taken together, these data suggest strongly that brainstem mechanisms are unlikely to play a key role in the rebalancing of the HPA-axis triggered by CCI, increasing the probability that these changes are driven by supra-hypothalamic regions.

Preclinical Models of Chronic Stress: Adaptation or Pathology?

The experience of prolonged stress changes how individuals interact with their environment and process interoceptive cues, with the end goal of optimizing survival and well-being in the face of a now-hostile world. The chronic stress response includes numerous changes consistent with limiting further damage to the organism, including development of passive or active behavioral strategies and metabolic adjustments to alter energy mobilization. These changes are consistent with symptoms of pathology in humans, and as a result, chronic stress has been used as a translational model for diseases such as depression. While it is of heuristic value to understand symptoms of pathology, we argue that the chronic stress response represents a defense mechanism that is, at its core, adaptive in nature. Transition to pathology occurs only after the adaptive capacity of an organism is exhausted. We offer this perspective as a means of framing interpretations of chronic stress studies in animal models and how these data relate to adaptation as opposed to pathology.

Effects of the social environment on vertebrate fitness and health in nature: Moving beyond the stress axis

Social interactions are a ubiquitous feature of the lives of vertebrate species. These may be cooperative or competitive, and shape the dynamics of social systems, with profound effects on individual behavior, physiology, fitness, and health. On one hand, a wealth of studies on humans, laboratory animal models, and captive species have focused on understanding the relationships between social interactions and individual health within the context of disease and pathology. On the other, ecological studies are attempting an understanding of how social interactions shape individual phenotypes in the wild, and the consequences this entails in terms of adaptation. Whereas numerous studies in wild vertebrates have focused on the relationships between social environments and the stress axis, much remains to be done in understanding how socially-related activation of the stress axis coordinates other key physiological functions related to health. Here, we review the state of our current knowledge on the effects that social interactions may have on other markers of vertebrate fitness and health. Building upon complementary findings from the biomedical and ecological fields, we identify 6 key physiological functions (cellular metabolism, oxidative stress, cellular senescence, immunity, brain function, and the regulation of biological rhythms) which are intimately related to the stress axis, and likely directly affected by social interactions. Our goal is a holistic understanding of how social environments affect vertebrate fitness and health in the wild. Whereas both social interactions and social environments are recognized as important sources of phenotypic variation, their consequences on vertebrate fitness, and the adaptive nature of social-stress-induced phenotypes, remain unclear. Social flexibility, or the ability of an animal to change its social behavior with resulting changes in social systems in response to fluctuating environments, has emerged as a critical underlying factor that may buffer the beneficial and detrimental effects of social environments on vertebrate fitness and health.

Neuroinflammation and Mitochondrial Dysfunction Link Social Stress to Depression

Major depressive disorder is a debilitating mental illness and a leading cause of global disease burden. While many etiological factors have been identified, social stress is a highly prevalent causative factor for the onset of depression. Unfortunately, rates of depression continue to increase around the world, and the recent COVID-19 pandemic has further exacerbated this mental health crisis. Though several therapeutic strategies are available, nearly 50% of patients who receive treatment never reach remission. The exact mechanisms by which social stress exposure promotes the development of depression are unclear, making it challenging to develop novel and more effective therapeutics. However, accumulating evidence points to a role for stress-induced neuroinflammation, particularly in treatment-resistant patients. Moreover, recent evidence has expanded the concept of the pathogenesis of depression to mitochondrial dysfunction, suggesting that the combined effects of social stress on mitochondria and inflammation may synergize to facilitate stress-related depression. In this chapter, we review evidence for neuroinflammation and mitochondrial dysfunction in the pathogenesis of social stress-induced depression and discuss these in the context of novel therapeutic targets for the treatment of depression.

Ethanol enhanced MDPV- and cocaine-induced aggressive behavior in mice: Forensic implications

BACKGROUND

Reports concerning the causal link between aggressive behavior and use and abuse of different substances (i.e., alcohol, MDPV) can be found in the literature. Nonetheless, the topic concerning the effects of acute ethanol administration on MDPV and cocaine induced aggressive behavior has yet to be thoroughly investigated. The aim of this study was to investigate such synergistic effects.

MATERIALS AND METHODS

A total of 360 male mice were employed in the study. Ethanol was diluted with saline solution and administered 10 min before MDPV or cocaine injection via oral gavage needles. Similarly, MDPV and cocaine were dissolved in saline solution and administered by intraperitoneal injection. Different associations of specific drug doses were then tested. To investigate the acute effects of MDPV and cocaine and their interaction with ethanol on aggression in mice, a resident-intruder test was used.

RESULTS

Ethanol alone was ineffective at dosages of 0.05 g/kg and 0.25 g/kg but increased the aggressiveness of the mice at 0.125 g/kg. Similarly, the injection of both cocaine alone and MDPV alone did not significantly increase the aggressiveness of the mice; conversely, the combination of ethanol and cocaine and ethanol and MDPV enhanced aggression at specific ethanol dosages (0.05 g/kg and 0.125 g/kg).

CONCLUSION

This study demonstrated that acute ethanol administration enhances MDPV- and cocaine-induced aggressive behavior in mice. This aggressive response is particularly enhanced when MDVP and cocaine are coupled with specific ethanol dosages, proving that psychostimulant drugs may act synergistically under certain conditions.

Inter-individual variability in habituation of anxiety-related responses within three mouse inbred strains

Inter-individual variability in behavioral and physiological response has become a well-established phenomenon in animal models of anxiety and other disorders. Such variability is even demonstrated within mouse inbred strains. A recent study showed that adaptive and non-adaptive anxiety phenotypes (measured as habituation and/or sensitization of anxiety responses) may differ within cohorts of 129 mice. This variability was expressed across both anxiety- and activity-related behavioral dimensions. These findings were based however on re-analysis of previously published data. The present study therefore aimed to empirically validate these findings in 129 mice. In addition, we assessed such inter-individuality in two other strains: BALB/c and C57BL/6. Males of three mouse inbred strains (BALB/c, C57BL/6 and 129S2) were behaviorally characterized through repeated exposure to a mild aversive stimulus (modified Hole Board, 4 consecutive trials). Behavioral observations were supplemented with assessment of circulating corticosterone levels. Clustering the individual response trajectories of behavioral and endocrine responses yielded two multidimensional response types of different adaptive value. Interestingly, these response types were displayed by individuals of all three strains. The response types differed significantly on anxiety and activity related behavioral dimensions but not on corticosterone concentrations. This study empirically confirms that adaptive capacities may differ within 129 cohorts. In addition, it extends this inter-individual variability in behavioral profiles to BALB/c and C57BL/6. Whether these two sub-types constitute differential anxiety phenotypes may differ per strain and requires further study.

Evolution of stress responses refine mechanisms of social rank

Social rank functions to facilitate coping responses to socially stressful situations and conditions. The evolution of social status appears to be inseparably connected to the evolution of stress. Stress, aggression, reward, and decision-making neurocircuitries overlap and interact to produce status-linked relationships, which are common among both male and female populations. Behavioral consequences stemming from social status and rank relationships are molded by aggressive interactions, which are inherently stressful. It seems likely that the balance of regulatory elements in pro- and anti-stress neurocircuitries results in rapid but brief stress responses that are advantageous to social dominance. These systems further produce, in coordination with reward and aggression circuitries, rapid adaptive responding during opportunities that arise to acquire food, mates, perch sites, territorial space, shelter and other resources. Rapid acquisition of resources and aggressive postures produces dominant individuals, who temporarily have distinct fitness advantages. For these reasons also, change in social status can occur rapidly. Social subordination results in slower and more chronic neural and endocrine reactions, a suite of unique defensive behaviors, and an increased propensity for anxious and depressive behavior and affect. These two behavioral phenotypes are but distinct ends of a spectrum, however, they may give us insights into the troubling mechanisms underlying the myriad of stress-related disorders to which they appear to be evolutionarily linked.

Acute stress counteracts framing-induced generosity boosts in social discounting in young healthy men

Most individuals are willing to forego resources for the benefit of others, but their willingness to do so typically declines as a function of social distance between the donor and recipient, a phenomenon termed social discounting. We recently showed that participants were more altruistic towards strangers when a costly generous choice was framed as preventing a monetary loss to the other rather than granting them a gain. Here, we asked if acute stress would diminish this frame effect on social discounting. To test this hypothesis, 102 male participants engaged in either the Maastricht Acute Stress Task, or a matched, non-stressful control procedure. They subsequently played a two-frame dictator game version of the social discounting paradigm. Whereas both frame conditions were economically equivalent, in the give frame, participants were asked how much money they would share with other persons on variable social distance levels, and in the take frame, they decided on how much money to take away from the others. While non-stressed control participants showed increased generosity toward strangers in the take compared to the give frame, similar to previous findings of our group, stress attenuated this frame effect on social discounting by reducing generosity toward strangers in the take frame. These findings confirm that stress can corrupt prosocial motives and social norm compliance, diminishing prosocial tendencies toward unfamiliar others.

Social defeat stress induces myocardial injury by modulating inflammatory factors

OBJECTIVES

We investigated the endoplasmic reticulum (ER) stress markers C/EBP homologous protein (CHOP) and glucose-regulated protein (GRP) 78, as well as the inflammatory factors nuclear factor (NF)-κB and IκBα, to assess how social defeat stress induces myocardial injury. Furthermore, we evaluated the protective effects of the ER stress inhibitor 4-phenylbutyric acid (PBA) on myocardial injury in mice.

METHODS

Adult mice were divided into control, control + PBA, social defeat, and social defeat + PBA groups. The social defeat and social defeat + PBA groups were exposed to social defeat stress for 10 days. Cardiac tissues from all groups were analyzed after social defeat stress. H₉C₂ cells were used to detect the role of the ER stress agonist thapsigargin on expression of ER stress and inflammatory markers.

RESULTS

Social defeat stress promoted apoptosis of cardiomyocytes, increased CHOP, NF-κB and, phospho-NF-κB protein expression, and decreased GRP78 and IκBα protein expression. Moreover, PBA significantly reversed these changes and attenuated thapsigargin-induced increased expression of CHOP and phospho-NF-κB, and decreased IκBα expression in H₉C₂ cells.

CONCLUSIONS

Social defeat stress initiates ER stress, promotes expression of inflammatory factors, and induces myocardial injury. Inhibiting ER stress could protect the myocardium from social defeat stress-induced myocardial injury.

Febrile and sleep responses to an immune challenge are affected by trait aggressiveness in rats

Sleep is altered in response to an immune challenge: non-rapid eye movement (NREM) sleep is increased and fragmented, REM sleep is inhibited. Sleep and immune response are affected by stress: several stressors inhibit sleep and increase waking time; stress-induced cortisol secretion affects the immune response, with immunosuppressive effects. Different levels of trait aggressiveness are associated with specific patterns of neuroendocrine and autonomic stress responsiveness. Aim of this study was to test the hypothesis that trait aggressiveness, by affecting response to stressors, modifies sleep alterations induced by the activation of the immune response. To this aim, rats were selected on the basis of their latency time to attack a male intruder in the resident-intruder test. Animals were instrumented for chronic recordings of sleep-wake activity and injected, intraperitoneally, with an immune challenge (250 μg/kg lipopolysaccharide - LPS, a component of gram-negative bacterial cell wall). Here we report that high aggressive (HA) rats responded to an immune challenge with a 24-h long increase in cortical brain temperature. During the first 12 post-injection hours, HA rats also responded with a prolonged increase in NREM sleep amount, and a 5-h long and continuous inhibition of REM sleep. In HA rats, the LPS-induced increase in the amount of time spent in NREM sleep was due to an increase in the number of episodes of this sleep phase, without any change in the bout duration. The LPS-induced REM sleep inhibition observed in HA rats was due to a decrease in both the number and duration of REM sleep bouts. In HA rats, during REM sleep, LPS administration significantly reduced the power of the EEG theta band. In non-aggressive (NA) rats, in response to LPS administration, cortical brain temperature was increased only for two hours, NREM sleep was unaffected, and REM sleep inhibition was scattered along the first 8 post-injection hours. The LPS-induced changes in the number of NREM sleep bouts of NA rats were limited to few and scattered hours, with a change in bout duration only in a single hour. A combination of decreases, in few hours, in both REM sleep bouts and their duration contributed to the REM sleep inhibition observed in NA rats. In NA rats, the power of EEG theta band was not modified, during REM sleep, by LPS administration. Gross motor activity was inhibited in both HA and NA rats. Results of this study show that trait aggressiveness affects febrile and sleep responses to an immune challenge.

Coping Style of Pigs Is Associated With Different Behavioral, Neurobiological and Immune Responses to Stressful Challenges

Based on the animal’s reaction to environmental challenges, consistent but different coping styles can be identified, which in turn may have consequences for health and welfare. Therefore, profound knowledge of the complex interrelationships between individual behavioral response patterns, underlying neurobiological mechanisms and immunological effects is required. The aim of this study was to examine whether pigs with different coping styles exhibit distinct behavioral, neurobiological and immune responses to stressful situations. Therefore, pigs (n = 40) were classified as proactive, reactive or intermediate animals according to a repeatedly-performed backtest, and behavioral, neuroendocrine and immune alterations were analyzed without any stress before weaning on day 28 and after a stress treatment on day 32. Our results show that the behavioral responses in an open-field/novel-object test characterized proactive pigs as more active. There were no significant differences in adrenocorticotropic hormone and cortisol concentrations between pigs with different coping characteristics. However, we found that proactive pigs displayed significantly increased plasma noradrenaline levels in response to stress, which may reflect a higher sympathetic reactivity of these animals. Furthermore, the present study revealed coping style differences in mRNA expression of mineralocorticoid, glucocorticoid, oxytocin and arginine vasopressin receptors and the immediate early gene c-fos in stress-related brain regions. While proactive pigs responded to stress with higher mRNA expression of arginine vasopressin, mineralocorticoid and glucocorticoid receptors, reactive pigs displayed higher oxytocin receptor and c-fos mRNA expression, indicating different neurobiological mechanisms of distinct coping styles in response to stressful challenges. Moreover, we also found humoral immune differences between proactive, intermediate and reactive animals. Proactive pigs had a higher total serum IgA concentration before and after stress treatment, with a significant increase in response to stress compared to reactive and intermediate pigs. In contrast, stress-induced IgM concentrations only increased in reactive and intermediate animals, suggesting that the effects of coping style on humoral immunity may differ depending on the specific function of the immunoglobulin classes. In conclusion, this multidisciplinary study expands the concept of coping style in farm animals, particularly in terms of individual stress reactivity and disease susceptibility, and thus contributes to the understanding of the biology of animal welfare.

Zebrafish models for personalized psychiatry: Insights from individual, strain and sex differences, and modeling gene x environment interactions

Currently becoming widely recognized, personalized psychiatry focuses on unique physiological and genetic profiles of patients to best tailor their therapy. However, the role of individual differences, as well as genetic and environmental factors, in human psychiatric disorders remains poorly understood. Animal experimental models are a valuable tool to improve our understanding of disease pathophysiology and its molecular mechanisms. Due to high reproduction capability, fully sequenced genome, easy gene editing, and high genetic and physiological homology with humans, zebrafish (Danio rerio) are emerging as a novel powerful model in biomedicine. Mounting evidence supports zebrafish as a useful model organism in CNS research. Robustly expressed in these fish, individual, strain, and sex differences shape their CNS responses to genetic, environmental, and pharmacological manipulations. Here, we discuss zebrafish as a promising complementary translational tool to further advance patient-centered personalized psychiatry.

Contingency Training Alters Neurobiological Components of Emotional Resilience in Male and Female Rats

Prior research with a rat model of behavioral therapy [i.e., effort-based reward (EBR) contingency training] suggests that strengthened associations between physical effort and desired outcomes enhance neurobiological indices of resilience. In the current study, male and female Long-Evans rats were exposed to either six weeks of EBR training or noncontingent training prior to 10 days of exposure to chronic unpredictable stress (CUS). Subsequently, all animals were exposed to a problem-solving task and then trained in a spatial learning/foraging task, the Dry Land Maze (DLM). Following habituation training and test trials, rats were assessed in a probe trial that generated a prediction error (cognitive uncertainty). Results indicated that, during CUS exposure, contingency-training enhanced dehydroepiandrosterone/corticosterone ratios (consistent with healthier stress responses), especially in male rats. Additionally, contingency training increased exploratory behaviors in the probe trial as well as differentially influenced on-task problem-solving performance in males and females. Following the probe trial, brains were exposed to histological analyses to determine the effects of sex and contingency training on various neurobiological markers. Contingency training decreased BDNF-immunoreactivity (ir) in the hippocampus CA1 and lateral habenula, implicating differential neuroplasticity responses in the training groups. Further, coordinated fos-ir activation in areas associated with emotional resilience (i.e., motivation-regulation) was observed in contingent-trained animals. In sum, the current findings confirm that behavioral training is associated with neurobiological markers of emotional resilience; however, further assessments are necessary to more accurately determine the therapeutic potential for the EBR contingency training model.

Regulation of divergent cortisol responsiveness in European sea bass, Dicentrarchus labrax L

Mechanisms regulating differences in cortisol responsiveness between low (LR) and high response (HR) individuals have been poorly studied. In this context, we aimed to study key regulatory processes in cortisol dynamics at the head kidneys of LR and HR European sea bass. To do so, resting plasma cortisol and ACTH concentrations were quantified in these fish. Additionally, the head kidneys of these individuals were superfused through an in vitro superfusion system and stimulated with the same amount of ACTH to assess their cortisol biosynthetic capacity. Moreover, the expression of important genes in cortisol regulation was assessed. Results showed that LR fish had lower resting cortisol concentrations than HR, although no differences existed in the circulating levels of ACTH. Additionally, the biosynthetic capacity of HR was higher than that of LR fish when in vitro stimulated with ACTH. At the molecular level, a statistically significant 3.4-fold higher expression of the ACTH receptor, mc2r, and a 2.3-fold, though not significant, higher expression of 11β-hydroxylase (cyp11b1), an enzyme involved in cortisol biosynthesis, was observed in the HR fish. Finally, a statistically significant 1.3-fold lower expression of 11β-hydroxysteroid dehydrogenase 2 (hsd11b2), an enzyme involved in cortisol inactivation, was observed in HR when compared to LR fish. Therefore, it was for the first time indicated that cortisol dynamics can also be regulated at the post-production level in the head kidney. Collectively, our results highlight the crucial role of the interrenal tissue in the regulation of differences in cortisol response between LR and HR sea bass individuals.

Age-Related Decrease in Stress Responsiveness and Proactive Coping in Male Mice

Coping is a strategic approach to dealing with stressful situations. Those who use proactive coping strategies tend to accept changes and act before changes are expected. In contrast, those who use reactive coping are less flexible and more likely to act in response to changes. However, little research has assessed how coping style changes with age. This study investigated age-related changes in coping strategies and stress responsiveness and the influence of age on the processing of conditioned fear memory in 2-, 12- and 23-month-old male mice. Coping strategy was measured by comparing the escape latency in an active avoidance test and by comparing responses to a shock prod. The results showed that proactivity in coping response gradually decreased with age. Stress responsiveness, measured by stress-induced concentration of corticosterone, was also highest in 2-month-old mice and decreased with age. Consolidation of fear memory was highest in 12-month-old mice and was negatively correlated with the degree of stress responsiveness and proactivity in coping. Fear extinction did not differ among age groups and was not correlated with stress responsiveness or the proactivity of coping. However, the maintenance of extinct fear memory, which was best in 2-month-old mice and worst in 12-month-old mice, was negatively correlated with stress responsiveness but not with coping style. Age-dependent changes in the expression of glucocorticoid receptor (GR) and its regulatory co-chaperones, which are accepted mechanisms for stress hormone stimulation, were measured in the hippocampus. The expression of GR was increased at 12 months compared to other age groups. There were no differences in Hsp70 and BAG1 expression by age. These results can be summarized as follows: (1) stress responsiveness and proactivity in coping decreased with age class; (2) consolidation of fear memory was negatively correlated with both stress responsiveness and proactivity; however, maintenance of extinct fear memory was negatively correlated with stress responsiveness only; and (3) consolidation and maintenance of extinct fear memory appeared to be more influenced by factors other than stress reactivity and proactivity in coping, such as the amount of hippocampal glucocorticoid expression.

Developmental stress and social phenotypes: integrating neuroendocrine, behavioural and evolutionary perspectives

The social world is filled with different types of interactions, and social experience interacts with stress on several different levels. Activation of the neuroendocrine axis that regulates the response to stress can have consequences for innumerable behavioural responses, including social decision-making and aspects of sociality, such as gregariousness and aggression. This is especially true for stress experienced during early life, when physiological systems are developing and highly sensitive to perturbation. Stress at this time can have persistent effects on social behaviours into adulthood. One important question remaining is to what extent these effects are adaptive. This paper initially reviews the current literature investigating the complex relationships between the hypothalamic-pituitary-adrenal (HPA) axis and other neuroendocrine systems and several aspects of social behaviour in vertebrates. In addition, the review explores the evidence surrounding the potential for 'social programming' via differential development and activation of the HPA axis, providing an insight into the potential for positive effects on fitness following early life stress. Finally, the paper provides a framework from which novel investigations could work to fully understand the adaptive significance of early life effects on social behaviours.This article is part of the themed issue 'Physiological determinants of social behaviour in animals'.

Coping Style Modifies General and Affective Autonomic Reactions of Domestic Pigs in Different Behavioral Contexts

Based on individual adaptive strategies (coping), animals may react differently to environmental challenges in terms of behavior and physiology according to their emotional perception. Emotional valence as well as arousal may be derived by measuring vagal and sympathetic tone of the autonomic nervous system (ANS). We investigated the situation-dependent autonomic response of 16 domestic pigs with either a reactive or a proactive coping style, previously selected according to the backtest which is accepted in piglets to assess escape behavior. At 11 weeks of age, the pigs were equipped with an implantable telemetric device, and heart rate (HR), blood pressure (BP) and their respective variabilities (HRV, BPV) were recorded for 1 h daily over a time period of 10 days and analyzed in four behavioral contexts (resting, feeding, idling, handling). Additionally, the first minute of feeding and handling was used for a short-term analysis of these parameters in 10-s intervals. Data from day 1-3 (period 1) and day 8-10 (period 2) were grouped into two separate periods. Our results revealed general differences between the coping styles during feeding, resting and handling, with proactive pigs showing higher HR compared to reactive pigs. This elevated HR was based on either lower vagal (resting) or elevated sympathetic activation (feeding, handling). The short-term analysis of the autonomic activation during feeding revealed a physiological anticipation reaction in proactive pigs in period 1, whereas reactive pigs showed this reaction only in period 2. Food intake was characterized by sympathetic arousal with concurrent vagal withdrawal, which was more pronounced in proactive pigs. In contrast, neither coping style resulted in an anticipation reaction to handling. Vagal activation increased in reactive pigs during handling, while proactive pigs showed an increase in sympathetically driven arousal in period 2. Our findings confirm significant context-related differences in the general autonomic reaction of pigs with different coping styles. Additionally, the two coping styles differ in their affective appraisal over the time course of the experiment, underlining the importance of taking individual differences into account when studying affect and emotion in humans and animals.

ANIMAL BEHAVIOR AND WELL-BEING SYMPOSIUM: Interaction between coping style/personality, stress, and welfare: Relevance for domestic farm animals

This paper will argue that understanding animal welfare and the individual vulnerability to stress-related disease requires a fundamental understanding of functional individual variation as it occurs in nature as well as the underlying neurobiology and neuroendocrinology. Ecological studies in feral populations of mice, fish, and birds start to recognize the functional significance of phenotypes that individually differ in their behavioral and neuroendocrine response to environmental challenge. Recent studies indicate that the individual variation within a species may buffer the species for strong fluctuations in the natural habitat. Similarly, evolutionary ancient behavioral trait characteristics have now been identified in a range of domestic farm animals including cattle, pigs, and horses. Individual variation in behavior can be summarized in a 3-dimensional model with coping style, emotionality, and sociality as independent dimensions. These dimensions can be considered trait characteristics that are stable over time and across situations within the individual. This conceptual model has several consequences. First, the coping style dimension is strongly associated with differential stress vulnerability. Social stress studies show that proactive individuals are resilient under stable environmental conditions but vulnerable when outcome expectancies are violated. Reactive individuals are, in fact, rather flexible and seem to adapt more easily to a changing environment. A second consequence relates to genetics and breeding. Genetic selection for one trait usually implies selection for other traits as well. It is discussed that a more balanced breeding program that takes into account biologically functional temperamental traits will lead to more robust domestic farm animals. Finally, the relationship between temperamental traits, animal production, fitness, and welfare is discussed.

Repeatability of cortisol stress response in the European sea bass (Dicentrarchus labrax) and transcription differences between individuals with divergent responses

Understanding the stress responses of organisms is of importance in the performance and welfare of farmed animals, including fish. Especially fish in aquaculture commonly face stressors, and better knowledge of their responses may assist in proper husbandry and selection of breeding stocks. European sea bass (Dicentrarchus labrax), a species with high cortisol concentrations, is of major importance in this respect. The main objectives of the present study were to assess the repeatability and consistency of cortisol stress response and to identify differences in liver transcription profiles of European sea bass individuals, showing a consistent low (LR) or high (HR) cortisol response. The progeny of six full sib families was used, and sampled for plasma cortisol after an acute stress challenge once per month, for four consecutive months. Results suggest that cortisol responsiveness was a repeatable trait with LR and HR fish showing low or high resting, free and post-stress cortisol concentrations respectively. Finally, the liver transcription profiles of LR and HR fish showed some important differences, indicating differential hepatic regulation between these divergent phenotypes. These transcription differences were related to various metabolic and immunological processes, with 169 transcripts being transcribed exclusively in LR fish and 161 exclusively in HR fish.

Putting the "Biology" Back into "Neurobiology": The Strength of Diversity in Animal Model Systems for Neuroscience Research

Current trends in neuroscience research have moved toward a reliance on rodent animal models to study most aspects of brain function. Such laboratory-reared animals are highly inbred, have been disengaged from their natural environments for generations and appear to be of limited predictive value for successful clinical outcomes. In this Perspective article, we argue that research on a rich diversity of animal model systems is fundamental to new discoveries in evolutionarily conserved core physiological and molecular mechanisms that are the foundation of human brain function. Analysis of neural circuits across phyla will reveal general computational solutions that form the basis for adaptive behavioral responses. Further, we stress that development of ethoexperimental approaches to improve our understanding of behavioral nuance will help to realign our research strategies with therapeutic goals and improve the translational validity of specific animal models. Finally, we suggest that neuroscience has a role in environmental conservation of habitat and fauna that will preserve and protect the ecological settings that drive species-specific behavioral adaptations. A rich biodiversity will enhance our understanding of human brain function and lead in unpredicted directions for development of therapeutic treatments for neurological disorders.

Effects of prenatal restraint stress on hypothalamic-pituitary-adrenocortical and sympatho-adrenomedullary axis in neonatal pigs

Studies in rodents and primates strongly indicate that prenatal stress affects the survival, behaviour and physiology of the offspring. Stressful stimuli during gestation may have a direct or hormone mediated effect on the development of stress systems in the foetal organism, resulting in an altered coping during stressful situations. The present study was conducted to elucidate prenatal stress effects in domestic pigs on the responses of the hypothalamicpituitary- adrenocortical (HPA) axis and the sympatho-adrenomedullary (SAM) system as well as on morbidity, mortality and growth of the offspring. Pregnant sows were subjected to a restraint stress for five minutes daily during the last five weeks of gestation. Endocrine reactions of the piglets were tested at 3, 7, 21 and 35 days of age using an immobilization test and an ACTH challenge test. Prenatally stressed piglets showed lower basal plasma cortisol and increased corticosteroid binding globulin (CBG) concentrations at 3 days of age, indicating decreased free cortisol concentrations after birth. Cortisol levels after ACTH stimulation and catecholamine levels after immobilization were not affected by the stress treatment of the sows. Piglets from stressed sows tended to have lower noradrenaline : adrenaline ratios at three days of age compared with the control piglets. In addition, stressed sows tended to have lower litter weights after birth. The morbidity and mortality during the suckling period was higher in the prenatally stressed litters, as shown by a higher frequency of diseased and perished piglets per litter. We suppose that prenatal stress during late gestation in pigs alters the development of the HPA system and impairs the vitality of the offspring.

Acute and long term effects of chronic intermittent noise stress on hypothalamic-pituitary-adrenocortical and sympatho-adrenomedullary axis in pigs

Noise is a potential environmental stressor and has also been identified as an aversive stimulus during animal housing. The impact of a 4-week chronic intermittent noise exposure on plasma adrenaline, noradrenaline, ACTH, cortisol and behaviour was studied in 24 male castrated German Landrace pigs. Three treatment groups were formed: N1 animals were subjected to a daily stimulation with broad-band noise (2 h, 90 dB(Lin)), N2 animals were subjected to the same stimulus three times a week and control animals were equally handled but experienced no noise exposure. Blood was serially sampled once a week via jugular vein catheters before, during and after a noise session. Behavioural observations of focal animals were performed by video technique. The first noise exposure of the animals caused no significant changes of stress hormone levels compared with the controls despite indices for more locomotion and less lying at the beginning of the noise stimulation, indicating that this noise stimulus is a rather mild stressor compared with other stimuli. The chronic intermittent noise stimulation, however, caused an increase of plasma ACTH and cortisol concentrations in the N1 animals after 4 days. The cortisol response of the N2 animals was unchanged compared to the controls at day 4, increased thereafter and at day 11 and 18 these animals tended to have higher cortisol levels compared with the controls. The noradrenaline/adrenaline ratio was significantly increased in N1 animals after 11 days and thereafter, whereas this ratio was unchanged in N2 animals until day 18, but also increased at day 25. In tendency, chronic intermittent noise exposure tended to reduce social behaviour and increase lying behaviour in both noise groups. In addition, the growth performance of pigs was negatively affected by the daily noise stimulation. In a second experiment with 16 male castrated German Landrace pigs, the impact of the daily intermittent noise exposure (N1) on the endocrine response to an acute stressor (restraint) and on the adrenocortical sensitivity to an ACTH challenge was studied. The time course of cortisol levels during the ACTH test indicated alterations in the time dynamics of the adrenocortical response with a more rapid response in the N1 animals. The results show that chronic intermittent noise exposure causes time-dependent alterations of the adrenocortical and sympathetic neural systems and may lead to behavioural suppression and growth retardation in pigs. Thus, repeated exposure of animals to noise levels over 90 dB should be avoided in pig husbandry to sustain productivity and animal welfare.

Hypothalamic-pituitary-adrenal and cardiac autonomic responses to transrectal examination differ with behavioral reactivity in dairy cows

Behavior, hypothalamic-pituitary-adrenal axis, and cardiac autonomic nervous system (ANS) activity were evaluated in response to transrectal examination in nonlactating Holstein-Friesian cows with different behavioral reactivity. According to behavioral reactions shown to the procedure of fixing the heart rate (HR) monitors, the 20 cows with the highest and the 20 cows with the lowest behavioral reactivity were involved in the study (high responder, n=20; and low responder, n=20, respectively). Activity of the ANS was assessed by HR and HR variability parameters. Blood and saliva were collected at 5 min before (baseline) and 0, 5 10, 15, 20, 30, 40, 60, and 120 min after the examination to determine cortisol concentrations. The examination lasted for 5 min. Cardiac parameters included HR, the root mean square of successive differences between the consecutive interbeat intervals, the high frequency (HF) component of heart rate variability, and the ratio between the low frequency (LF) and HF parameter (LF/HF). Following the examination, peak plasma and saliva cortisol levels and the amplitude of the plasma and saliva cortisol response were higher in high responder cows than in low responders. Areas under the plasma and saliva cortisol response curves were greater in high responder cows. Plasma and salivary cortisol levels correlated significantly at baseline (r=0.91), right after examination (r=0.98), and at peak levels (r=0.96). Area under the HR response curve was higher in low responder cows; however, maximum HR and the amplitude of the HR response showed no differences between groups. Minimum values of both parameters calculated for the examination were higher in high responders. Following the examination, response parameters of root mean square of successive differences and HF did not differ between groups. The maximum and the amplitude of LF/HF response and area under the LF/HF response curve were lower in low responder cows, suggesting a lower sympathetic activation of the ANS. Although changes in behaviors indicated that the procedure was painful for the animals, no differences were observed either in vocalization or in attendant behavior between groups during the examination. Our results demonstrate that behaviorally more reactive animals exhibit increased plasma and salivary cortisol concentrations and higher cardiac autonomic responsiveness to transrectal examination than less reactive cows. Salivary cortisol may substitute for plasma cortisol when assessing response of cattle to stress.

Non-invasive genetic sampling reveals diet shifts, but little difference in endoparasite richness and faecal glucocorticoids, in Belizean felids inside and outside protected areas

Many Neotropical felids are threatened with extinction due to direct effects of habitat destruction and/or human persecution. However, indirect and synergistic effects of human-felid conflict remain under-studied and potentially include increased stress and diet shifts that may negatively impact felid health. We hypothesized that faecal glucocorticoid metabolites (FGM) and endoparasite species richness (ESR) would be higher, and diet would shift, for felids outside protected areas where conflict occurs. In north-western Belize, a scat-detector dog located 336 faecal samples, identified to species and individual using DNA analyses. DNA amplification success was substantially higher within protected areas than outside. We detected jaguar, puma, ocelot, jaguarundi and domestic cat. FGMs were higher in puma and jaguarundi than in other felids, while ESR was similar across felids with domestic cats exhibiting the highest number of genera. Diet partitioning occurred among felids, but domestic cats may compete with ocelot and jaguarundi for small prey. Outside of protected areas, large cats shifted their diet to smaller prey and livestock remains were not found. Contrary to our hypotheses, FGM and ESR did not differ inside versus outside protected areas, but sample sizes were low in human-modified areas. We provide a baseline on wild felid adrenal activity, endoparasites and diet and suggest improvements to increase sample sizes outside protected areas. Our research provides a template for expanding non-invasive sampling approaches more widely across the range of Neotropical felids.

Neuroinflammation at the interface of depression and cardiovascular disease: Evidence from rodent models of social stress

A large body of evidence has emerged linking stressful experiences, particularly from one's social environment, with psychiatric disorders. However, vast individual differences emerge in susceptibility to developing stress-related pathology which may be due to distinct differences in the inflammatory response to social stress. Furthermore, depression is an independent risk factor for cardiovascular disease, another inflammatory-related disease, and results in increased mortality in depressed patients. This review is focused on discussing evidence for stress exposure resulting in persistent or sensitized inflammation in one individual while this response is lacking in others. Particular focus will be directed towards reviewing the literature underlying the impact that neuroinflammation has on neurotransmitters and neuropeptides that could be involved in the pathogenesis of comorbid depression and cardiovascular disease. Finally, the theme throughout the review will be to explore the notion that stress-induced inflammation is a key player in the high rate of comorbidity between psychosocial disorders and cardiovascular disease.

Key role of 5-HT3 receptors in the nucleus tractus solitarii in cardiovagal stress reactivity

Serotonin plays a modulatory role in central control of the autonomic nervous system (ANS). The nucleus tractus solitarii (NTS) in the medulla is an area of viscerosomatic integration innervated by both central and peripheral serotonergic fibers. Influences from different origins therefore trigger the release of serotonin into the NTS and exert multiple influences on the ANS. This major influence on the ANS is also mediated by activation of several receptors in the NTS. In particular, the NTS is the central zone with the highest density of serotonin₃ (5-HT₃) receptors. In this review, we present evidence that 5-HT₃ receptors in the NTS play a key role in one of the crucial homeostatic responses to acute and chronic stress: inhibitory modulation of the parasympathetic component of the ANS. The possible functional interactions of 5-HT₃ receptors with GABA_A and NK₁ receptors in the NTS are also discussed.

Resilience to the effects of social stress: evidence from clinical and preclinical studies on the role of coping strategies

The most common form of stress encountered by people stems from one's social environment and is perceived as more intense than other types of stressors. One feature that may be related to differential resilience or vulnerability to stress is the type of strategy used to cope with the stressor, either active or passive coping. This review focuses on models of social stress in which individual differences in coping strategies produce resilience or vulnerability to the effects of stress. Neurobiological mechanisms underlying these individual differences are discussed. Overall, the literature suggests that there are multiple neural mechanisms that underlie individual differences in stress-induced resilience and vulnerability. How these mechanisms interact with one another to produce a resilient or vulnerable phenotype is not understood and such mechanisms have been poorly studied in females and in early developmental periods. Finally, we propose that resilience may be stress context specific and resilience phenotypes may need to be fine-tuned to suit a shifting environment.

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Resilience is considered positive adaptation in the face of adversity.

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Coping strategy impacts one's susceptibility to social stress-induced psychopathology.

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Neurobiological substrates such as CRF, NPY and DA may impact stress susceptibility.

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Individual differences within females and during adolescence are poorly understood.

The effect of aging on the specialized conducting system: a telemetry ECG study in rats over a 6 month period

Advanced age alone appears to be a risk factor for increased susceptibility to cardiac arrhythmias. We previously observed in the aged rat heart that sinus rhythm ventricular activation is delayed and characterized by abnormal epicardial patterns although conduction velocity is normal. While these findings relate to an advanced stage of aging, it is not yet known when and how ventricular electrical impairment originates and which is the underlying substrate. To address these points, we performed continuous telemetry ECG recordings in freely moving rats over a six-month period to monitor ECG waveform changes, heart rate variability and the incidence of cardiac arrhythmias. At the end of the study, we performed in-vivo multiple lead epicardial recordings and histopathology of cardiac tissue. We found that the duration of ECG waves and intervals gradually increased and heart rate variability gradually decreased with age. Moreover, the incidence of cardiac arrhythmias gradually increased, with atrial arrhythmias exceeding ventricular arrhythmias. Epicardial multiple lead recordings confirmed abnormalities in ventricular activation patterns, likely attributable to distal conducting system dysfunctions. Microscopic analysis of aged heart specimens revealed multifocal connective tissue deposition and perinuclear myocytolysis in the atria. Our results demonstrate that aging gradually modifies the terminal part of the specialized cardiac conducting system, creating a substrate for increased arrhythmogenesis. These findings may open new therapeutic options in the management of cardiac arrhythmias in the elderly population.

Resident intruder paradigm-induced aggression relieves depressive-like behaviors in male rats subjected to chronic mild stress

Background

Accumulating epidemiological evidence shows that life event stressors are major vulnerability factors for psychiatric diseases such as major depression. It is also well known that the resident intruder paradigm (RIP) results in aggressive behavior in male rats. However, it is not known how resident intruder paradigm-induced aggression affects depressive-like behavior in isolated male rats subjected to chronic mild stress (CMS), which is an animal model of depression.

Material/Methods

Male Wistar rats were divided into 3 groups: non-stressed controls, isolated rats subjected to the CMS protocol, and resident intruder paradigm-exposed rats subjected to the CMS protocol.

Results

In the sucrose intake test, ingestion of a 1% sucrose solution by rats in the CMS group was significantly lower than in control and CMS+RIP rats after 3 weeks of stress. In the open-field test, CMS rats had significantly lower open-field scores compared to control rats. Furthermore, the total scores given the CMS group were significantly lower than in the CMS+RIP rats. In the forced swimming test (FST), the immobility times of CMS rats were significantly longer than those of the control or CMS+RIP rats. However, no differences were observed between controls and CMS+RIP rats.

Conclusions

Our data show that aggressive behavior evoked by the resident intruder paradigm could relieve broad-spectrum depressive-like behaviors in isolated adult male rats subjected to CMS.

Effects of social defeat on sleep and behaviour: importance of the confrontational behaviour

We studied the short- and long-term effects of a double social defeat (SD) on sleep parameters, EEG power, behaviour in the open field emergence test, corticosterone responsiveness, and acoustic startle responses. Pre-stress levels of corticosterone were assessed before all rats were surgically implanted with telemetric transmitters for sleep recording, and allowed 3weeks of recovery. Rats in the SD group (n=10) were exposed to 1hour SD on two consecutive days, while control rats (n=10) were left undisturbed. Telemetric sleep recordings were performed before SD (day -1), day 1 post SD, and once weekly for 3weeks thereafter. The open field emergence test was performed on day 9 and weekly for 2weeks thereafter. Blood samples for measures of corticosterone responsiveness were drawn after the last emergence test (day 23). Acoustic startle responses were tested on day 24 post SD. Overall, SD rats as a group were not affected by the social conflict. Effects of SD seemed, however, to vary according to the behaviours that the intruder displayed during the social confrontation with the resident. Compared to those SD rats showing quick submission (SDS, n=5), SD rats fighting the resident during one or both SD confrontations before defeat (SDF, n=5) showed more fragmented slow wave sleep, both in SWS1 and SWS2. They also showed longer latency to leave the start box and spent less time in the open field arena compared to SDS rats. In the startle test, SDF rats failed to show response decrement at the lowest sound level. Our results indicate that how animals behave during a social confrontation is more important than exposure to the SD procedure itself, and that rapid submission during a social confrontation might be more adaptive than fighting back.

Corticosterone responses and personality in birds: Individual variation and the ability to cope with environmental changes due to climate change

Birds can respond to an internal or external stimulus with activation of the HPA axis and secretion of corticosterone. There is considerable individual variation in corticosterone responses, and individual responses can be very different from the mean response for a group of birds. Corticosterone responses and behavioural responses to environmental stimuli are determined by individual characteristics called personality. It is proposed that birds with low corticosterone responses and proactive personalities are likely to be more successful (have greater fitness) in constant or predictable conditions, whilst birds with reactive personalities and high corticosterone responses will be more successful in changing or unpredictable conditions. The relationship between corticosterone responses and fitness thus depends on the prevailing environmental conditions, so birds with either low or high corticosterone responses can have the greatest fitness and be most successful, but in different situations. It is also proposed that birds with reactive personalities and high corticosterone responses will be better able to cope with environmental changes due to climate change than birds with proactive personalities and relatively low corticosterone responses. Phenotypic plasticity in corticosterone responses can be quantified using a reaction norm approach, and reaction norms can be used to determine the degree of plasticity in corticosterone responses of individual birds, and mean levels of plasticity in responses of species of birds. Individual corticosterone responses and personality, and reaction norms for corticosterone responses, can in future be used to predict the ability of birds to cope with environmental changes due to climate change.

An animal model of stress-induced cardiomyopathy utilizing the social defeat paradigm

Stress-induced cardiomyopathy (SIC) is a form of acute heart disease triggered by extreme psychological stress. In patients who develop SIC, the outward symptoms are almost indistinguishable from acute myocardial infarction (AMI). However, some important criteria differentiate patients with SIC from those with AMI. Patients with SIC: (1) experience some form of extreme psychological stress from minutes to hours before developing heart disease, (2) do not suffer from atherosclerosis or coronary artery obstruction, and 3) exhibit abnormal ballooning of the left ventricle. In the present study, the resident-intruder (RI) social defeat test was investigated as a potential rat model for stressed-induced cardiomyopathy. Adult Long-Evans rats were implanted with a biotelemetry transmitter for ECG recordings and habituated for two weeks. An intruder rat was placed in the cage of a resident rat behind a wire-mesh partition for 5 min. The partition was then removed for 5 min to allow direct contact between the intruder and resident rats. After this interval, the wire-mesh partition was replaced and the intruder rat remained behind the partition for an additional 50 min. Behavioral responses were noted and ECG recordings were collected during the entire 60-min testing period. Upon completion of the test, the intruder rat was removed from the cage of the resident rat and sacrificed. The heart was examined and blood was collected. Heart weight/body weight ratio, left ventricle/body weight ratio, heart length, plasma corticosterone levels, and plasma troponin I levels of intruder rats were significantly higher as compared to control rats. Intruder rats significantly increased their heart rate during the first 5 min of the RI test. It is concluded that the RI test to induce social defeat is a novel rodent paradigm for modeling stress-induced cardiomyopathy in the human.