Cardiac autonomic imbalance by social stress in rodents: understanding putative biomarkers

Role of corticotropin-releasing factor neurotransmission in the lateral hypothalamus on baroreflex impairment evoked by chronic variable stress in rats

Despite the importance of physiological responses to stress in a short-term, chronically these adjustments may be harmful and lead to diseases, including cardiovascular diseases. The lateral hypothalamus (LH) has been reported to be involved in expression of physiological and behavioral responses to stress, but the local neurochemical mechanisms involved are not completely described. The corticotropin-releasing factor (CRF) neurotransmission is a prominent brain neurochemical system implicated in the physiological and behavioral changes induced by aversive threats. Furthermore, chronic exposure to aversive situations affects the CRF neurotransmission in brain regions involved in stress responses. Therefore, in this study, we evaluated the influence of CRF neurotransmission in the LH on changes in cardiovascular function and baroreflex activity induced by chronic variable stress (CVS). We identified that CVS enhanced baseline arterial pressure and impaired baroreflex function, which were followed by increased expression of CRF2, but not CRF1, receptor expression within the LH. Local microinjection of either CRF1 or CRF2 receptor antagonist within the LH inhibited the baroreflex impairment caused by CVS, but without affecting the mild hypertension. Taken together, the findings documented in this study suggest that LH CRF neurotransmission participates in the baroreflex impairment related to chronic stress exposure.

Anterior cingulate cortex, but not amygdala, modulates the anxiogenesis induced by living with conspecifics subjected to chronic restraint stress in male mice

Cohabitation with a partner undergoing chronic restraint stress (CRE) induces anxiogenic-like behaviors through emotional contagion. We hypothesized that the anterior cingulate cortex (ACC) and the amygdala would be involved in the modulation of this emotional process. This study investigated the role of the ACC and amygdala in empathy-like behavior (e.g., anxiety-like responses) induced by living with a mouse subjected to CRE. Male Swiss mice were housed in pairs for 14 days and then allocated into two groups: cagemate stress (one animal of the pair was subjected to 14 days of restraint stress) and cagemate control (no animal experienced stress). Twenty-four hours after the last stress session, cagemates had their brains removed for recording FosB labeling in the ACC and amygdala (Exp.1). In experiments 2 and 3, 24 h after the last stress session, the cagemates received 0.1 μL of saline or cobalt chloride (CoCl₂ 1 mM) into the ACC or amygdala, and then exposed to the elevated plus-maze (EPM) for recording anxiety. Results showed a decrease of FosB labeling in the ACC without changing immunofluorescence in the amygdala of stress cagemate mice. Cohabitation with mice subjected to CRE provoked anxiogenic-like behaviors. Local inactivation of ACC (but not the amygdala) reversed the anxiogenic-like effects induced by cohabitation with a partner undergoing CRE. These results suggest the involvement of ACC, but not the amygdala, in anxiety induced by emotional contagion.

Hypoactive Thalamic Crh+ Cells in a Female Mouse Model of Alcohol Drinking After Social Trauma

BACKGROUND

Comorbid stress-induced mood and alcohol use disorders are increasingly prevalent among female patients. Stress exposure can disrupt salience processing and goal-directed decision making, contributing to persistent maladaptive behavioral patterns; these and other stress-sensitive cognitive and behavioral processes rely on dynamic and coordinated signaling by midline and intralaminar thalamic nuclei. Considering the role of social trauma in the trajectory of these debilitating psychopathologies, identifying vulnerable thalamic cells may provide guidance for targeting persistent stress-induced symptoms.

METHODS

A novel behavioral protocol traced the progression from social trauma to the development of social defensiveness and chronically escalated alcohol consumption in female mice. Recent cell activation-measured as cFos-was quantified in thalamic cells after safe social interactions, revealing stress-sensitive corticotropin-releasing hormone-expressing (Crh+) anterior central medial thalamic (aCMT) cells. These cells were optogenetically stimulated during stress-induced social defensiveness and abstinence-escalated binge drinking.

RESULTS

Crh+ aCMT neurons exhibited substantial activation after social interactions in stress-naïve but not in stressed female mice. Photoactivating Crh+ aCMT cells dampened stress-induced social deficits, whereas inhibiting these cells increased social defensiveness in stress-naïve mice. Optogenetically activating Crh+ aCMT cells diminished abstinence-escalated binge alcohol drinking in female mice, regardless of stress history.

CONCLUSIONS

This work uncovers a role for Crh+ aCMT neurons in maladaptive stress-induced social interactions and in binge drinking after forced abstinence in female mice. This molecularly defined thalamic cell population may serve as a critical stress-sensitive hub for social deficits caused by exposure to social trauma and for patterns of excessive alcohol drinking in female populations.

Corticotropin-releasing factor neurotransmission in the lateral hypothalamus modulates the tachycardiac response during acute emotional stress in rats

The lateral hypothalamus (LH) is implicated in the physiological and behavioral responses during stressful events. However, the local neurochemical mechanisms related to control of stress responses by this hypothalamic area are not completely understood. Therefore, in this study we evaluated the involvement of CRFergic neurotransmission acting through the CRF₁ receptor within the LH in cardiovascular responses evoked by an acute session of restraint stress in rats. For this, we investigated the effect of bilateral microinjection of different doses (0.01, 0.1 and 1 nmol/100 nL) of the selective CRF₁ receptor antagonist CP376395 into the LH on arterial pressure and heart rate increases and decrease in tail skin temperature evoked by acute restraint stress. We found that all doses of the CRF₁ receptor antagonist microinjected into the LH decreased the restraint-evoked tachycardia, but without affecting the arterial pressure and tail skin temperature responses. Additionally, treatment of the LH with CP376395 at the doses of 0.1 and 1 nmol/100 nL increased the basal values of both heart rate and arterial pressure, whereas the dose of 0.1 nmol/100 nL decreased the skin temperature. Taken together, these findings indicate that CRFergic neurotransmission in the LH, acting through activation of local CRF₁ receptors, plays a facilitatory role in the tachycardia observed during aversive threats, but without affecting the pressor and tail skin temperature responses. Our results also provide evidence that LH CRFergic neurotransmission in involved in tonic maintenance of cardiovascular function.

The Moderating Role of Coping Style on Chronic Stress Exposure and Cardiovascular Reactivity Among African American Emerging Adults

Chronic stress exposure may contribute to dysregulation of cardiovascular functions and increase CVD risk among African Americans. This study investigated the direct and interactive effects of chronic stress exposure and coping styles on cardiovascular reactivity to acute stress. A sample of African American emerging adults (n = 277) completed a battery of self-report assessments and underwent the Trier Social Stress Test (TSST) across two time points. Prior chronic stress exposure was negatively associated with heart rate (HR) reactivity among females at 1-month follow-up. Task-oriented coping was positively associated with HR reactivity, while avoidance-oriented coping showed a negative association. Higher use of emotion-oriented coping moderated the relationship between chronic stress exposure and HR reactivity, resulting in more robust reactivity. Among females, but not males, lower use of avoidance-oriented coping moderated the relationship between prior chronic stress exposure and HR reactivity, also resulting in more robust reactivity. Prior chronic stress exposure and the use of maladaptive coping strategies may confer negative impacts on cardiovascular reactivity, particularly among African American females. Using adaptive coping styles may mitigate these effects and improve cardiovascular reactivity. These findings provide preliminary support for psychosocial determinants of health within a controlled laboratory experiment and highlight important gender differences to consider in prevention efforts for African American cardiovascular health disparities.

Prefrontal Cortex Regulates Chronic Stress-Induced Cardiovascular Susceptibility

Background The medial prefrontal cortex is necessary for appropriate appraisal of stressful information, as well as coordinating visceral and behavioral processes. However, prolonged stress impairs medial prefrontal cortex function and prefrontal-dependent behaviors. Additionally, chronic stress induces sympathetic predominance, contributing to health detriments associated with autonomic imbalance. Previous studies identified a subregion of rodent prefrontal cortex, infralimbic cortex (IL), as a key regulator of neuroendocrine-autonomic integration after chronic stress, suggesting that IL output may prevent chronic stress-induced autonomic imbalance. In the current study, we tested the hypothesis that the IL regulates hemodynamic, vascular, and cardiac responses to chronic stress. Methods and Results A viral-packaged small interfering RNA construct was used to knockdown vesicular glutamate transporter 1 (vGluT1) and reduce glutamate packaging and release from IL projection neurons. Male rats were injected with a vGluT1 small interfering RNA-expressing construct or GFP (green fluorescent protein) control into the IL and then remained as unstressed controls or were exposed to chronic variable stress. IL vGluT1 knockdown increased heart rate and mean arterial pressure reactivity, while chronic variable stress increased chronic mean arterial pressure only in small interfering RNA-treated rats. In another cohort, chronic variable stress and vGluT1 knockdown interacted to impair both endothelial-dependent and endothelial-independent vasoreactivity ex vivo. Furthermore, vGluT1 knockdown and chronic variable stress increased histological markers of fibrosis and hypertrophy. Conclusions Knockdown of glutamate release from IL projection neurons indicates that these cells are necessary to prevent the enhanced physiological responses to stress that promote susceptibility to cardiovascular pathophysiology. Ultimately, these findings provide evidence for a neurobiological mechanism mediating the relationship between stress and poor cardiovascular health outcomes.

The Effects of Submaximal and Maximal Exercise on Heart Rate Variability

The purpose of this study was to examine heart rate variability (HRV) at rest, and during submaximal (100 bpm) and maximal exercise in collegiate distance runners. We predicted there would be less HRV during exercise. Eight collegiate runners (19-22 yrs) were recruited for participation. The participants were equipped with a standard Lead II EKG to record HRV at rest. The participants then performed an incremental VO_2max test while running on a treadmill. EKG was recorded throughout the exercise test and HRV was later calculated during the submaximal and maximal exercise. To assess HRV the standard deviation of R-R intervals (SDNN) was calculated at rest and during submaximal and maximal exercise. A one-way ANOVA was used to determine HRV differences between these three states. The average R-R interval was 0.961 ± 0.155 s (64 bpm), 0.413 ± 0.018 s (146 bpm), and 0.321 ± 0.008 s (187 bpm) for rest, submaximal, and maximal exercise, respectively. There were significant differences in SDNN from rest to submaximal (0.108 ± 0.055 to 0.008 ± 0.002 s, p < 0.05), and from rest to maximal exercise (0.108 ± 0.055 to 0.006 ± 0.002 s, p < 0.05). When comparing HRV between the resting and exercise states it seems that the parasympathetic nervous system (PNS) influence at rest contributes to greater HRV, whereas the sympathetic nervous system (SNS) influence during both submaximal and maximal exercise corresponds to a reduced HRV. These effects may be related to the enhanced automaticity effects of norepinephrine acting on its B₁ receptor sites in the heart.

Novice Meditators of an Easily Learnable Audible Mantram Sound Self-Induce an Increase in Vagal Tone During Short-term Practice: A Preliminary Study

INTRODUCTION

The autonomic nervous system (ANS) plays a vital role in regulation of the physiological processes during normal and pathological conditions. Heart rate variability (HRV) is regarded as a major indicator of the self-regulatory strength and balance of parasympathetic nervous system (PNS) and sympathetic nerve system (SNS) impulses, as interpreted by the intrinsic nervous system of the heart. The present study focuses on the evaluation of the effects of audible and mindful practice of chanting meditation on HRV and on the cognitive disposition.

METHODOLOGY

The subjects were randomly assigned to 2 different sounds based on monotone repetition. One was the Hare Krishna Mantram (HKM-Sanskrit experimental sound) and the other was a concocted sound (Sanskrit placebo). Changes in vagal tone were measured with respect to both time domain and frequency domains. Five-min baseline and postmeditation measurements were obtained on different days over the next 6 wk. The subjects who chanted the placebo/sham sound switched to the experimental sound at the 4-wk mark for the next 2 wk. All subjects completed an experience survey.

RESULTS

Paired t test results for all HRV parameters achieved statistical significance in the test group. Statistical significance in all the aforementioned measures of HRV was also observed on switching the control group placebo sound chanting to the experimental sound. HRV wave forms showed relaxation, a pattern and experience survey suggests an increase in attributes associated with higher self-regulation.

CONCLUSION

This study suggests statistically significant efficacy data and that a larger randomized study is feasible to test the potential of the audible repetition of the HKM in clinical settings. It may therefore enable beneficial lifestyle for health creation and thus play a role in the prevention of chronic diseases. Further, large scale studies are required for a better perspective on the effect of mantram repetition on the HRV.

Neuroimmune Imbalances and Yin-Yang Dynamics in Stress, Anxiety, and Depression

Evidences from psychoneuroimmunology (PNI) and systems biology studies support a conceptual framework of "Yin-Yang dynamics" for understanding the "whole mind-body system." The Yin-Yang dynamical balances in the stress response networks may be critical for health and diseases, especially mental health and psychiatric disorders. Specifically, the neuroimmune imbalances have been found as the important features and potential biomarkers of stress, anxiety, depression, and systemic inflammation. At the system levels, factors such as psychosocial stress and obesity, especially a leaky gut, may result in the imbalance between regulatory and proinflammatory T cells. At the molecular and cellular levels, the imbalances in multiple networks including the cytokine and redox pathways, immune-kynurenine networks, HPA axis, and synaptic plasticity in the hypothalamus are the key factors in depression. The recognition of the neuroimmune imbalances and the restoration of the Yin-Yang dynamical balances need to become a high priority toward the development of dynamical systems medicine for psychiatric diseases including depression and schizophrenia.

Psychological and Physical Environmental Factors in the Development of Incontinence in Adults and Children: A Comprehensive Review

The aim of this review was to identify etiological environmental factors related to incontinence in children and adults. A variety of etiological environmental factors for the development of incontinence were identified. In children, these encompass stressful life events and trauma, family dysfunction, parental psychopathology, school-related stressors, toilet or "potty" training, fluid consumption habits, housing conditions, and the availability of toilets. In adults, physical exercise, obesity, working conditions, fluid intake, and the availability of toilets play a role. Intervening variables such as hormonal variations due to work shifts have also been identified as influencing the likelihood of incontinence. Current research suggests that environmental factors influence the development of incontinence in children and adults. The interactions between biological factors, the immediate environment, and intervening variables need to be explored in greater detail. Practical solutions to reduce barriers to adequate fluid intake and healthy toileting habits should be implemented in school and work settings.

Atrial Fibrillation: The Science behind Its Defiance

Atrial fibrillation (AF) is the most prevalent arrhythmia in the world, due both to its tenacious treatment resistance, and to the tremendous number of risk factors that set the stage for the atria to fibrillate. Cardiopulmonary, behavioral, and psychological risk factors generate electrical and structural alterations of the atria that promote reentry and wavebreak. These culminate in fibrillation once atrial ectopic beats set the arrhythmia process in motion. There is growing evidence that chronic stress can physically alter the emotion centers of the limbic system, changing their input to the hypothalamic-limbic-autonomic network that regulates autonomic outflow. This leads to imbalance of the parasympathetic and sympathetic nervous systems, most often in favor of sympathetic overactivation. Autonomic imbalance acts as a driving force behind the atrial ectopy and reentry that promote AF. Careful study of AF pathophysiology can illuminate the means that enable AF to elude both pharmacological control and surgical cure, by revealing ways in which antiarrhythmic drugs and surgical and ablation procedures may paradoxically promote fibrillation. Understanding AF pathophysiology can also help clarify the mechanisms by which emerging modalities aiming to correct autonomic imbalance, such as renal sympathetic denervation, may offer potential to better control this arrhythmia. Finally, growing evidence supports lifestyle modification approaches as adjuncts to improve AF control.

Individual differences in the locus coeruleus-norepinephrine system: Relevance to stress-induced cardiovascular vulnerability

Repeated exposure to psychosocial stress is a robust sympathomimetic stressor and as such has adverse effects on cardiovascular health. While the neurocircuitry involved remains unclear, the physiological and anatomical characteristics of the locus coeruleus (LC)-norepinephrine (NE) system suggest that it is poised to contribute to stress-induced cardiovascular vulnerability. A major theme throughout is to review studies that shed light on the role that the LC may play in individual differences in vulnerability to social stress-induced cardiovascular dysfunction. Recent findings are discussed that support a unique plasticity in afferent regulation of the LC, resulting in either excitatory or inhibitory input to the LC during establishment of different stress coping strategies. This contrasting regulation of the LC by either afferent regulation, or distinct differences in stress-induced neuroinflammation would translate to differences in cardiovascular regulation and may serve as the basis for individual differences in the cardiopathological consequences of social stress. The goal of this review is to highlight recent developments in the interplay between the LC-NE and cardiovascular systems during repeated stress in an effort to advance therapeutic treatments for the development of stress-induced cardiovascular vulnerability.

A Method for Psychosocial Stress-Induced Reinstatement of Cocaine Seeking in Rats

We describe a novel preclinical model of stress-induced relapse to cocaine use in rats using social defeat stress, an ethologically valid psychosocial stressor in rodents that closely resembles stressors that promote craving and relapse in humans. Rats self-administered cocaine for 20 days. On days 11, 14, 17, and 20, animals were subjected to social defeat stress or a nonstressful control condition following the session, with discrete environmental stimuli signaling the impending event. After extinction training, reinstatement was assessed following re-exposure to these discrete cues. Animals re-exposed to psychosocial stress-predictive cues exhibited increased serum corticosterone and significantly greater reinstatement of cocaine seeking than the control group, and active coping behaviors during social defeat episodes were associated with subsequent reinstatement magnitude. These studies are the first to describe an operant model of psychosocial stress-induced relapse in rodents and lay the foundation for future work investigating its neurobiological underpinnings.

The brain norepinephrine system, stress and cardiovascular vulnerability

Chronic exposure to psychosocial stress has adverse effects on cardiovascular health, however the stress-sensitive neurocircuitry involved remains to be elucidated. The anatomical and physiological characteristics of the locus coeruleus (LC)-norepinephrine (NE) system position it to contribute to stress-induced cardiovascular disease. This review focuses on cardiovascular dysfunction produced by social stress and a major theme highlighted is that differences in coping strategy determine individual differences in social stress-induced cardiovascular vulnerability. The establishment of different coping strategies and cardiovascular vulnerability during repeated social stress has recently been shown to parallel a unique plasticity in LC afferent regulation, resulting in either excitatory or inhibitory input to the LC. This contrasting regulation of the LC would translate to differences in cardiovascular regulation and may serve as the basis for individual differences in the cardiopathological consequences of social stress. The advances described suggest new directions for developing treatments and/or strategies for decreasing stress-induced cardiovascular vulnerability.

Distinctive cardiac autonomic dysfunction following stress exposure in both sexes in an animal model of PTSD

It is unclear whether the poor autonomic flexibility or dysregulation observed in patients with posttraumatic stress disorder (PTSD) represents a pre-trauma vulnerability factor or results from exposure to trauma. We used an animal model of PTSD to assess the association between the behavioral response to predator scent stress (PSS) and the cardiac autonomic modulation in male and female rats. The rats were surgically implanted with radiotelemetry devices to measure their electrocardiograms and locomotor activity (LMA). Following baseline telemetric monitoring, the animals were exposed to PSS or sham-PSS. Continuous telemetric monitoring (24h/day sampling) was performed over the course of 7days. The electrocardiographic recordings were analyzed using the time- and frequency-domain indexes of heart rate variability (HRV). The behavioral response patterns were assessed using the elevated plus maze and acoustic startle response paradigms for the retrospective classification of individuals according to the PTSD-related cut-off behavioral criteria. During resting conditions, the male rats had significantly higher heart rates (HR) and lower HRV parameters than the female rats during both the active and inactive phases of the daily cycle. Immediately after PSS exposure, both the female and male rats demonstrated a robust increase in HR and a marked drop in HRV parameters, with a shift of sympathovagal balance towards sympathetic predominance. In both sexes, autonomic system habituation and recovery were selectively inhibited in the rats whose behavior was extremely disrupted after exposure to PSS. However, in the female rats, exposure to the PSS produced fewer EBR rats, with a more rapid recovery curve than that of the male rats. PSS did not induce changes to the circadian rhythm of the LMA. According to our results, PTSD can be conceptualized as a disorder that is related to failure-of-recovery mechanisms that impede the restitution of physiological homeostasis.

Acute Stress Decreases but Chronic Stress Increases Myocardial Sensitivity to Ischemic Injury in Rodents

Cardiovascular disease (CVD) is the largest cause of mortality worldwide, and stress is a significant contributor to the development of CVD. The relationship between acute and chronic stress and CVD is well evidenced. Acute stress can lead to arrhythmias and ischemic injury. However, recent evidence in rodent models suggests that acute stress can decrease sensitivity to myocardial ischemia-reperfusion injury (IRI). Conversely, chronic stress is arrhythmogenic and increases sensitivity to myocardial IRI. Few studies have examined the impact of validated animal models of stress-related psychological disorders on the ischemic heart. This review examines the work that has been completed using rat models to study the effects of stress on myocardial sensitivity to ischemic injury. Utilization of animal models of stress-related psychological disorders is critical in the prevention and treatment of cardiovascular disorders in patients experiencing stress-related psychiatric conditions.