Electrode positioning for reliable telemetry ECG recordings during social stress in unrestrained rats

Protective effects of exercise on responses to combined social and environmental stress in prairie voles

The combination of social and environmental stressors significantly influences psychological and physical health in males and females, and contributes to both depression and cardiovascular diseases. Animal models support these findings. Voluntary exercise may protect against some forms of stress; however, the protective effects of exercise against social stressors require further investigation. This study evaluated the influence of exercise on the impact of combined social and environmental stressors in socially monogamous prairie voles. Following a period of social isolation plus additional chronic environmental stress, prairie voles were either allowed access to a running wheel in a larger cage for 2 weeks or remained in sedentary conditions. A behavioral stress task was conducted prior to and following exercise or sedentary conditions. Heart rate (HR) and HR variability were evaluated after exercise or sedentary conditions. Group-based analyses indicated that exercise prevented elevated resting HR and promoted autonomic control of the heart. Exercise was also effective against social and environmental stress-induced forced swim test immobility. Some minor sex differences in behavior were observed in response to exercise intensity. This research informs our understanding of the protective influence of physical exercise against social and environmental stressors in male and female humans.

Sex-specific behavioral, cardiac, and neuroendocrine responses to repeated witness social stress in adult rats

In humans, sex disparities exist in the prevalence of social stress-related disorders, yet our understanding of the predisposing factors and underlying mechanisms is still elusive. Also at the preclinical level, the investigation of sex differences in social stress responses is limited. In this study, adult male and female wild-type Groningen rats were repeatedly exposed to witness social defeat stress (WS) to assess sex-specific behavioral, neuroendocrine, and cardiac responses to the same social stress paradigm. Male and female rats bore witness to an aggressive social defeat episode between two males for nine consecutive days or were exposed to a control (CTR) procedure. Stress-related parameters were assessed in correspondence to the first and last WS/CTR exposure and also during subsequent exposure to the stress context alone in the absence of social defeat. During WS, rats of both sexes displayed larger amounts of burying behavior and smaller amounts of rearing and grooming behaviors, but with a greater extent in female witnesses. Cardiac autonomic responses to WS were similar between the sexes, yet only females displayed higher plasma corticosterone levels after the first WS exposure compared to CTRs, and had a larger corticosterone increase than male witnesses upon repeated WS. Exposure to the stress context alone (i.e., without the presence of the aggressive resident rat) elicited greater amount of burying behavior and more pronounced and persistent tachycardic responses in females than males with a history of WS. Our findings suggest sex-disparities in the response of adult rats to WS at multiple behavioral, cardiac, and neuroendocrine levels, highlighting the utility of this social stress paradigm for investigating predisposing factors and pathophysiological mechanisms underlying sex-specific vulnerabilities to stress-related pathologies.

The latency to awake from induced-obstructive sleep apnea is reduced in rats with chronic epilepsy

OSA is known to increase the risk for SUDEP in persons with epilepsy, but the relationship between these two factors is not clear. Also, there is no study showing the acute responses to obstructive apnea in a chronic epilepsy model. Therefore, this study aimed to characterize cardiorespiratory responses to obstructive apnea and chemoreceptor stimulation in rats. In addition, we analyzed respiratory centers in the brain stem by immunohistochemistry. Epilepsy was induced with pilocarpine. About 30-60 days after the first spontaneous seizure, tracheal and thoracic balloons, and electrodes for recording the electroencephalogram, electromyogram, and electrocardiogram were implanted. Intermittent apneas were made by inflation of the tracheal balloon during wakefulness, NREM sleep, and REM sleep. During apnea, respiratory effort increased, and heart rate fell, especially with apneas made during wakefulness, both in control rats and rats with epilepsy. Latency to awake from apnea was longer with apneas made during REM than NREM, but rats with epilepsy awoke more rapidly than controls with apneas made during REM sleep. Rats with epilepsy also had less REM sleep. Cardiorespiratory responses to stimulation of carotid chemoreceptors with cyanide were similar in rats with epilepsy and controls. Immunohistochemical analysis of Phox2b, tryptophan hydroxylase, and NK1 in brain stem nuclei involved in breathing and sleep (retrotrapezoid nucleus, pre-Bötzinger complex, Bötzinger complex, and caudal raphe nuclei) revealed no differences between control rats and rats with epilepsy. In conclusion, our study showed that rats with epilepsy had a decrease in the latency to awaken from apneas during REM sleep, which may be related to neuroplasticity in some other brain regions related to respiratory control, awakening mechanisms, and autonomic modulation.

Sepsis-induced inflammatory demyelination in medullary visceral zone and cholinergic anti-inflammatory pathway: Insights from a Rat's model study

Background

Our previous studies have demonstrated that the activated Cholinergic Anti-inflammatory Pathway (CAP) effectively suppresses systemic inflammation and immunity in early sepsis. Some parameters of Heart Rate Variability (HRV) could be used to reflect the regulatory activity of CAP. However, in the early stages of severe sepsis of some patients, the inflammatory storm can still result in multiple organs dysfunction and even death, suggesting they lose CAP's modulation ability. Since CAP is part of the vagus nerve and is directly innervated by the Medullary Visceral Zone (MVZ), we can reasonably concluded that pathological changes induced by MVZ's neuroinflammation should be responsible for CAP's dysfunction in modulating systemic inflammation in early sepsis.

Methods

We conducted two independent septic experiments, the sepsis model rats were prepared by cecum ligation and puncture (CLP) method. In the first experiment, A total of 64 adult male Sprague-Dawley rats were included. Under the condition of sepsis and CAP's pharmacological activation or blockade, we investigated the MVZ's pathological changes, the functional state of key neurons including catecholaminergic and cholinergic neurons, key genes' expression such as Oligodendrocyte Transcription Factor 2 (Olig-2) mRNA, glial fibrillary acidic protein (GFAP) mRNA, and matrix metalloprotein (MMP) -9 mRNA, and CAP's activities reflected by HRV. The second experiment involved in 56 rats, through central anti-inflammation by feeding with 10 mg/ml minocycline sucrose solution as the only water source, or right vagus transection excepting for central anti-inflammation as a mean of the CAP's functional cancel, we confirmed that the neuroinflammation in MVZ affected systemic inflammation through CAP in sepsis.

Results

In the first experiment, cholinergic and catecholaminergic neurons showed significant apoptosis with reduced expressions of TH, but the expression of CHAT remained relatively unaffected in MVZ in sepsis. HRV parameters representing the tone of the vagus nerve, such as SDNN, RMSSD, HF, SD1, and SD2, did not show significant differences among the three Septic Groups, although they all decreased significantly compared to the Control Group. The expressions of GFAP mRNA and MMP-9 mRNA were up-regulated, while the expression of Olig-2 mRNA was down-regulated in the Septic Groups. Intervention of CAP had a significant effect on cholinergic and catecholaminergic neurons' apoptosis, as well as the expressions of TH/CHAT and these key genes, but had little effect on HRV in sepsis. In the second experiment, the levels of TNF-α, IL-6, in serum and MVZ were significantly increased in sepsis. Central anti-inflammatory treatment reversed these changes. However, right vagotomy abolished the central anti-inflammatory effect.

Conclusions

Our study uncovered that MVZ's neuroinflammation may play a crucial role in the uncontrolled systemic inflammation through inflammatory demyelination in MVZ, which disrupts CAP's modulation on the systemic inflammation in early sepsis.

Chronic Partial Sleep Deprivation Increased the Incidence of Atrial Fibrillation by Promoting Pulmonary Vein and Atrial Arrhythmogenesis in a Rodent Model

Sleep deprivation (SD) is a recognized risk factor for atrial fibrillation (AF), yet the precise molecular and electrophysiological mechanisms behind SD-induced AF are unclear. This study explores the electrical and structural changes that contribute to AF in chronic partial SD. We induced chronic partial SD in Wistar rats using a modified multiple-platform method. Echocardiography demonstrated impaired systolic and diastolic function in the left ventricle (LV) of the SD rats. The SD rats exhibited an elevated heart rate and a higher low-frequency to high-frequency ratio in a heart-rate variability analysis. Rapid transesophageal atrial pacing led to a higher incidence of AF and longer mean AF durations in the SD rats. Conventional microelectrode recordings showed accelerated pulmonary vein (PV) spontaneous activity in SD rats, along with a heightened occurrence of delayed after-depolarizations in the PV and left atrium (LA) induced by tachypacing and isoproterenol. A Western blot analysis showed reduced expression of G protein-coupled receptor kinase 2 (GRK2) in the LA of the SD rats. Chronic partial SD impairs LV function, promotes AF genesis, and increases PV and LA arrhythmogenesis, potentially attributed to sympathetic overactivity and reduced GRK2 expression. Targeting GRK2 signaling may offer promising therapeutic avenues for managing chronic partial SD-induced AF. Future investigations are mandatory to investigate the dose-response relationship between SD and AF genesis.

The rat telemetry assay and venous catheter access buttons for use in cardiovascular safety pharmacology assessments - Surgical methods, refinements and colony maintenance

INTRODUCTION

Rat telemetry is the assay of choice to assess the potential effects of novel drug candidates on cardiovascular parameters during early drug discovery. Telemetry device implantation can be combined with venous catheter and access button implantation when intravenous administration of the drug substance is required.

METHODS

Rats (Sprague Dawley or Han Wistar) were implanted with telemetry devices for arterial blood pressure measurement using either direct aortic catheterisation (n = 131) or aortic catheterisation via the femoral artery (n = 17). Bipolar leads for ECG recording were also implanted in some of the animals (n = 102). Femoral vein catheters and access buttons were implanted as a separate surgery after the initial telemetry implantation (n = 43).

RESULTS

128 animals (86%) were implanted successfully with telemetry devices without any notable surgical or post-surgical problems. When considering the 2 different catheterisation methods separately, the success rate of the direct aortic approach was 88% compared to 76% with the aortic placement via the femoral artery. Lameness was the most common post-surgical problem. Blood loss during surgery and ischaemic patches on the tail were also observed at a low incidence with the direct aortic approach. Catheter pull-out occurred in some rats before the first signal check reducing the overall success rate for blood pressure measurement using the direct aortic approach to 85%. A 95% success rate was observed for catheter and access button implantation.

DISCUSSION

A high success rate is possible when implanting telemetry devices in rats with and without venous catheters and access buttons. We have attempted to provide solutions to problems and describe refinements to the procedure which may further improve surgical outcomes.

Maladaptive cardiac and behavioral reactivity to repeated vicarious stress exposure in socially bonded male prairie vole siblings

Behaviors, emotions, and cardiovascular functions are influenced by stress. But these detrimental effects are not exclusive to an individual that directly experiences stress. Stress is also experienced vicariously through observation of another individual undergoing stress. The current study used the strong social bonds in socially monogamous prairie voles to determine effects of repeated vicarious stress on cardiac and behavioral outcomes. Male prairie voles were exposed to either a 5-minute open field chamber alone [separate (control)] or while concurrently witnessing their sibling undergo a tail-suspension stressor [concurrent (experimental)], repeated across 4 sessions. Cardiac responses in animals in the open field were evaluated for heart rate and heart rate variability prior to, during, and after each test session, and behaviors were evaluated for motion, exploration, stress reactivity, and anxiety-relevant behaviors during each test session. The concurrent condition (versus separate) displayed increased heart rate and reduced heart rate variability during repeated test sessions, and impaired recovery of these parameters following the test sessions. The pattern of disturbances suggests that both increased sympathetic and reduced parasympathetic influence contributed to the cardiac responses. Animals in the concurrent condition (versus separate) displayed disrupted rearing, grooming, and motion; reduced duration of center section exploration; and increased freezing responses across repeated test sessions. Collectively, cardiac and behavioral stress reactivity are increased as a function of vicarious stress in prairie voles, which are evident across repeated experiences of stress. These results inform our understanding of the experience of vicarious stress in social species, including humans.

Lack of the transcription factor Nfix causes tachycardia in mice sinus node and rats neonatal cardiomyocytes

AIMS

Nfix is a transcription factor belonging to the Nuclear Factor I (NFI) family comprising four members (Nfia, b, c, x). Nfix plays important roles in the development and function of several organs. In muscle development, Nfix controls the switch from embryonic to fetal myogenesis by promoting fast twitching fibres. In the adult muscle, following injury, lack of Nfix impairs regeneration, inducing higher content of slow-twitching fibres. Nfix is expressed also in the heart, but its function has been never investigated before. We studied Nfix role in this organ.

METHODS

Using Nfix-null and wild type (WT) mice we analyzed: (1) the expression pattern of Nfix during development by qPCR and (2) the functional alterations caused by its absence, by in vivo telemetry and in vitro patch clamp analysis.

RESULTS AND CONCLUSIONS

Nfix expression start in the heart from E12.5. Adult hearts of Nfix-null mice show a hearts morphology and sarcomeric proteins expression similar to WT. However, Nfix-null animals show tachycardia that derives form an intrinsic higher beating rate of the sinus node (SAN). Molecular and functional analysis revealed that sinoatrial cells of Nfix-null mice express a significantly larger L-type calcium current (Cacna1d + Cacna1c). Interestingly, downregulation of Nfix by sh-RNA in primary cultures of neonatal rat ventricular cardiomyocytes induced a similar increase in their spontaneous beating rate and in ICaL current. In conclusion, our data provide the first demonstration of a role of Nfix that, increasing the L-type calcium current, modulates heart rate.

Sex differences in heart rate and heart rate variability in rats: Implications for translational research

The present study aimed to investigate sex differences in measures of cardiac chronotropy and heart rate variability (HRV) in 132 young adult wild-type Groningen rats (n = 45 females). Electrocardiographic signals were recorded for 48 h in freely moving rats to quantify heart rate (HR) and inter-beat interval (IBI) as measures of cardiac chronotropy, and time- and frequency-domain HRV parameters as physiological readouts of cardiac vagal modulation. Females showed greater vagally-mediated HRV despite having higher HR and shorter IBI than males during undisturbed conditions. Such differences were evident i) at any given level of HRV, and ii) both during the 12-h light/inactive and 12-h dark/active phase of the daily cycle. These findings replicate the paradoxical cardiac chronotropic control reported by human meta-analytic findings, since one would expect greater vagally-mediated HRV to be associated with lower HR and longer IBI. Lastly, the association between some HRV measures and HR was stronger in female than male rats. Overall, the current study in young adult rats provides data illustrating a sex-dependent association between vagally-mediated HRV and indexes of cardiac chronotropy. The current results i) are in line with human findings, ii) suggest to always consider biological sex in the analysis and interpretation of HRV data in rats, and iii) warrant the use of rats for investigating the neuro-hormonal basis and temporal evolution of the impact of sex on the association between vagally-mediated HRV and cardiac chronotropy, which could inform the human condition.

Whole body vibration, an alternative for exercise to improve recovery from surgery?

Although exercise is usually associated with beneficial effects on physical and mental health, patients recovering from surgery may be hampered to perform active exercise. Whole body vibration (WBV) is suggested a passive alternative for physical training. Aim of the present study was to explore the therapeutic potential of WBV compared to physical exercise during early post-surgery recovery.

Male three months old Wistar rats underwent major abdominal surgery. Starting the day after surgery, rats were subjected to either daily WBV or exercise (treadmill running) for 15 consecutive days. Control rats underwent pseudo treatment. During the first week after surgery, effects of interventions were obtained from continuous recording of hemodynamic parameters, body temperature and activity (via an implanted transducer). Behavioral tests were performed during the second post-surgical week to evaluate anxiety-like behavior, short and long-term memory functions, cognitive flexibility and motor performance. Animals were sacrificed 15 days after surgery and brain tissue was collected for analysis of hippocampal neuroinflammation and neurogenesis.

Surgery significantly impacted all parameters measured during the first post-surgery week, irrespective of the type of surgery. Effect on cognitive performance was limited to cognitive flexibility; both WBV and exercise prevented the surgery-induced decline. Exercise, but not WBV increased anxiety-like behavior and grip strength. WBV as well as exercise prevented the surgery-induced declined neurogenesis, but surgery-associated hippocampal neuroinflammation was not affected.

Our results indicated that active exercise and WBV share similar therapeutic potentials in the prevention of surgery induced decline in cognitive flexibility and hippocampal neurogenesis. In contrast to exercise, WBV did not increase anxiety-like behavior. Since neither intervention affected hippocampal neuroinflammation, other mechanisms and/or brain areas may be involved in the behavioral effects. Taken together, we conclude that WBV may provide a relevant alternative to active exercise during the early stage of post-operative recovery.

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Both whole body vibration (WBV) and running exercise restored the reduced cognitive flexibility caused by surgery.

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WBV as well as active exercise prevented surgery-induced declined neurogenesis.

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Active exercise, but not WBV, induced anxiety-like behavior after surgery.

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Neither WBV nor active exercise affected surgery-induced neuroinflammation.

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Neither WBV nor active exercise influenced hemodynamic recovery from surgery.

Decline of cardiomyocyte contractile performance and bioenergetic function in socially stressed male rats

Chronic social stress has been epidemiologically linked to increased risk for cardiovascular disease, yet the underlying pathophysiological mechanisms are still largely elusive. Mitochondrial (dys)function represents a potential intersection point between social stress exposure and (mal)adaptive cardiac responses. In this study, we used a rodent model of social stress to study the extent to which alterations in the cellular mechanical properties of the heart were associated with changes in indexes of mitochondrial function. Male adult rats were exposed to repeated episodes of social defeat stress or left undisturbed (controls). ECG signals were recorded during and after social defeat stress. Twenty-four hours after the last social defeat, cardiomyocytes were isolated for analyses of mechanical properties and intracellular Ca²⁺ dynamics, mitochondrial respiration, and ATP content. Results indicated that social defeat stress induced potent cardiac sympathetic activation that lasted well beyond stress exposure. Moreover, cardiomyocytes of stressed rats showed poor contractile performance (e.g., slower contraction and relaxation rates) and intracellular Ca²⁺ derangement (e.g., slower Ca²⁺ clearing), which were associated with indexes of reduced reserve respiratory capacity and decreased ATP production. In conclusion, this study suggests that repeated social stress provokes impaired cardiomyocyte contractile performance and signs of altered mitochondrial bioenergetics in the rat heart. Future studies are needed to clarify the causal link between cardiac and mitochondrial functional remodeling under conditions of chronic social stress.

Acute cardiovascular effects of inhaled ambient particulate matter: Chemical composition-related oxidative stress, endothelin-1, blood pressure, and ST-segment changes in Wistar rats

Short-term increases in particulate matter (PM) are associated with heightened morbidity and mortality from cardiovascular causes. Inhalation of PM is known to increase endothelin (ET)-1 levels. Yet, less is known about particle composition-related changes at the molecular level including the endothelinergic system and relationship with cardiovascular function changes. In this work, adult Wistar male rats were exposed for 4 h by nose-only inhalation to clean air, Ottawa urban particles (EHC-93, 48 mg/m³) and water-leached (EHC-93L, 49 mg/m³) particles, to examine the effect of particle compositional changes on oxidative stress, circulating ETs, blood pressure, and heart electrophysiology. Particle deposition in the respiratory compartment was estimated at 85 μg (25 ng/cm²). Lung cell proliferation was low in both treatment groups, indicating absence of acute injury. Inhalation of EHC-93 caused statistically significant elevations (p < 0.05) of oxidative stress markers, ET-1, ET-3, blood pressure, and a decrease of ST-segment duration in the ECG at 1.5 days post-exposure. Leached particles (EHC-93L) caused rapid but transient elevation (p < 0.05) of oxidative stress, ET-1, ET-2, and ET-3 at earlier time points, with no changes in blood pressure or ST-segment. These results demonstrate that inhalation of urban particles at an internal dose inadequate to cause acute lung injury can induce oxidative stress, enhance vasoactive endothelins, leading to vasopressor response, affecting cardiac electrophysiology in Wistar rats, consistent with the cardiovascular impacts of ambient particles in human populations. Change in particle potency after removal of soluble species, notably cadmium, zinc and polar organics suggests that the toxicodynamics of cardiovascular effects can be modified by physicochemical properties of particles.

Social isolation and oxytocin antagonism increase emotion-related behaviors and heart rate in female prairie voles

Social isolation influences depression- and anxiety-related disorders and cardiac function. Oxytocin may mediate these conditions through interactions with social behavior, emotion, and cardiovascular function, via central and/or peripheral mechanisms. The present study investigated the influence of oxytocin antagonism using L-368,899, a selective oxytocin receptor antagonist that crosses the blood-brain barrier, on depression- and anxiety-related behaviors and heart rate in prairie voles. This rodent species has translational value for investigating interactions of social stress, behavior, cardiac responses, and oxytocin function. Adult female prairie voles were socially isolated or co-housed with a sibling for 4 weeks. A subset of animals in each housing condition was subjected to 4 sessions of acute L-368,899 (20 mg/kg, ip) or saline administration followed by a depression- or anxiety-related behavioral assessment. A subset of co-housed animals was evaluated for cardiac function following acute administration of L-368,899 (20 mg/kg, ip) and during behavioral assessments. Social isolation (vs. co-housing) increased depression- and anxiety-related behaviors. In isolated animals, L-368,899 (vs. vehicle) did not influence anxiety-related behaviors but exacerbated depression-related behaviors. In co-housed animals, L-368,899 exacerbated depression-related behaviors and increased heart rate at baseline and during behavioral tests. Social isolation produces emotion-related behaviors in prairie voles; central and/or peripheral oxytocin antagonism exacerbates these behavioral signs. Oxytocin antagonism induces depression-relevant behaviors and increases basal and stressor-reactive heart rate in co-housed prairie voles, similar to the consequences of social isolation demonstrated in this model. These results provide translational value for humans who experience behavioral and cardiac consequences of loneliness or social stress.

Alamandine but not angiotensin-(1-7) produces cardiovascular effects at the rostral insular cortex

Experiments aimed to evaluate the tissue distribution of Mas-related G protein-coupled receptor D (MrgD) revealed the presence of immunoreactivity for the MrgD protein in the rostral insular cortex (rIC), an important area for autonomic and cardiovascular control. To investigate the relevance of this finding, we evaluated the cardiovascular effects produced by the endogenous ligand of MrgD, alamandine, in this brain region. Mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in urethane anesthetized rats. Unilateral microinjection of equimolar doses of alamandine (40 pmol/100 nL), angiotensin-(1-7), angiotensin II, angiotensin A, and Mas/MrgD antagonist d-Pro7-Ang-1-7 (50 pmol/100 nL), Mas antagonist A779 (100 pmol/100 nL), or vehicle (0.9% NaCl) were made in different rats (n = 4-6/group) into rIC. To verify the specificity of the region, a microinjection of alamandine was also performed into intermediate insular cortex (iIC). Microinjection of alamandine in rIC produced an increase in MAP (Δ = 15 ± 2 mmHg), HR (Δ = 36 ± 4 beats/min), and RSNA (Δ = 31 ± 4%), but was without effects at iIC. Strikingly, an equimolar dose of angiotensin-(1-7) at rIC did not produce any change in MAP, HR, and RSNA. Angiotensin II and angiotensin A produced only minor effects. Alamandine effects were not altered by A-779, a Mas antagonist, but were completely blocked by the Mas/MrgD antagonist d-Pro7-Ang-(1-7). Therefore, we have identified a brain region in which alamandine/MrgD receptor but not angiotensin-(1-7)/Mas could be involved in the modulation of cardiovascular-related neuronal activity. This observation also suggests that alamandine might possess unique effects unrelated to angiotensin-(1-7) in the brain.

Elevated miR-34a expression and altered transcriptional profile are associated with adverse electromechanical remodeling in the heart of male rats exposed to social stress

This study investigated epigenetic risk factors that may contribute to stress-related cardiac disease in a rodent model. Experiment 1 was designed to evaluate the expression of microRNA-34a (miR-34a), a known modulator of both stress responses and cardiac pathophysiology, in the heart of male adult rats exposed to a single or repeated episodes of social defeat stress. Moreover, RNA sequencing was conducted to identify transcriptomic profile changes in the heart of repeatedly stressed rats. Experiment 2 was designed to assess cardiac electromechanical changes induced by repeated social defeat stress that may predispose rats to cardiac dysfunction. Results indicated a larger cardiac miR-34a expression after repeated social defeat stress compared to a control condition. This molecular modification was associated with increased vulnerability to pharmacologically induced arrhythmias and signs of systolic left ventricular dysfunction. Gene expression analysis identified clusters of differentially expressed genes in the heart of repeatedly stressed rats that are mainly associated with morphological and functional properties of the mitochondria and may be directly regulated by miR-34a. These results suggest the presence of an association between miR-34a overexpression and signs of adverse electromechanical remodeling in the heart of rats exposed to repeated social defeat stress, and point to compromised mitochondria efficiency as a potential mediator of this link. This rat model may provide a useful tool for investigating the causal relationship between miR-34a expression, mitochondrial (dys)function, and cardiac alterations under stressful conditions, which could have important implications in the context of stress-related cardiac disease.

Chronic apnea during REM sleep increases arterial pressure and sympathetic modulation in rats

STUDY OBJECTIVES

Obstructive sleep apnea can induce hypertension. Apneas in REM may be particularly problematic: they are independently associated with hypertension. We examined the role of sleep stage and awakening on acute cardiovascular responses to apnea. In addition, we measured cardiovascular and sympathetic changes induced by chronic sleep apnea in REM sleep.

METHODS

We used rats with tracheal balloons and electroencephalogram and electromyogram electrodes to induce obstructive apnea during wakefulness and sleep. We measured the electrocardiogram and arterial pressure by telemetry and breathing effort with a thoracic balloon.

RESULTS

Apneas induced during wakefulness caused a pressor response, intense bradycardia, and breathing effort. On termination of apnea, arterial pressure, heart rate, and breathing effort returned to basal levels within 10 s. Responses to apnea were strongly blunted when apneas were made in sleep. Post-apnea changes were also blunted when rats did not awake from apnea. Chronic sleep apnea (15 days of apnea during REM sleep, 8 h/day, 13.8 ± 2 apneas/h, average duration 12 ± 0.7 s) reduced sleep time, increased awake arterial pressure from 111 ± 6 to 118 ± 5 mmHg (p < 0.05) and increased a marker for sympathetic activity. Chronic apnea failed to change spontaneous baroreceptor sensitivity.

CONCLUSION

Our results suggest that sleep blunts the diving-like response induced by apnea and that acute post-apnea changes depend on awakening. In addition, our data confirm that 2 weeks of apnea during REM causes sleep disruption and increases blood pressure and sympathetic activity.

Age-Related Changes in Cardiac Autonomic Modulation and Heart Rate Variability in Mice

Objective

The aim of this study was to assess age-related changes in cardiac autonomic modulation and heart rate variability (HRV) and their association with spontaneous and pharmacologically induced vulnerability to cardiac arrhythmias, to verify the translational relevance of mouse models for further in-depth evaluation of the link between autonomic changes and increased arrhythmic risk with advancing age.

Methods

Heart rate (HR) and time- and frequency-domain indexes of HRV were calculated from Electrocardiogram (ECG) recordings in two groups of conscious mice of different ages (4 and 19 months old) (i) during daily undisturbed conditions, (ii) following peripheral β-adrenergic (atenolol), muscarinic (methylscopolamine), and β-adrenergic + muscarinic blockades, and (iii) following β-adrenergic (isoprenaline) stimulation. Vulnerability to arrhythmias was evaluated during daily undisturbed conditions and following β-adrenergic stimulation.

Results

HRV analysis and HR responses to autonomic blockades revealed that 19-month-old mice had a lower vagal modulation of cardiac function compared with 4-month-old mice. This age-related autonomic effect was not reflected in changes in HR, since intrinsic HR was lower in 19-month-old compared with 4-month-old mice. Both time- and frequency-domain HRV indexes were reduced following muscarinic, but not β-adrenergic blockade in younger mice, and to a lesser extent in older mice, suggesting that HRV is largely modulated by vagal tone in mice. Finally, 19-month-old mice showed a larger vulnerability to both spontaneous and isoprenaline-induced arrhythmias.

Conclusion

The present study combines HRV analysis and selective pharmacological autonomic blockades to document an age-related impairment in cardiac vagal modulation in mice which is consistent with the human condition. Given their short life span, mice could be further exploited as an aged model for studying the trajectory of vagal decline with advancing age using HRV measures, and the mechanisms underlying its association with proarrhythmic remodeling of the senescent heart.

Design and optimisation of dendrimer-conjugated Bcl-2/xL inhibitor, AZD0466, with improved therapeutic index for cancer therapy

Dual Bcl-2/Bcl-x_L inhibitors are expected to deliver therapeutic benefit in many haematological and solid malignancies, however, their use is limited by tolerability issues. AZD4320, a potent dual Bcl-2/Bcl-x_L inhibitor, has shown good efficacy however had dose limiting cardiovascular toxicity in preclinical species, coupled with challenging physicochemical properties, which prevented its clinical development. Here, we describe the design and development of AZD0466, a drug-dendrimer conjugate, where AZD4320 is chemically conjugated to a PEGylated poly-lysine dendrimer. Mathematical modelling was employed to determine the optimal release rate of the drug from the dendrimer for maximal therapeutic index in terms of preclinical anti-tumour efficacy and cardiovascular tolerability. The optimised candidate is shown to be efficacious and better tolerated in preclinical models compared with AZD4320 alone. The AZD4320-dendrimer conjugate (AZD0466) identified, through mathematical modelling, has resulted in an improved therapeutic index and thus enabled progression of this promising dual Bcl-2/Bcl-x_L inhibitor into clinical development.

Claire Patterson et al. present the design and development of AZD0466, a drug-dendrimer conjugate, and use preclinical and mathematical models to determine the optimal release rate of the drug from the dendrimer carrier for maximal therapeutic index in terms of anti-tumour efficacy and cardiovascular tolerability. This study identifies this promising dual Bcl-2/Bcl-x_L inhibitor for progression to clinical development.

The hydroxypropyl-β-cyclodextrin-minoxidil inclusion complex improves the cardiovascular and proliferative adverse effects of minoxidil in male rats: Implications in the treatment of alopecia

The efficacy of minoxidil (MXD) ethanolic solutions (1%-5% w/v) in the treatment of androgenetic alopecia is limited by adverse reactions. The toxicological effects of repeated topical applications of escalating dose (0.035%-3.5% w/v) and of single and twice daily doses (3.5% w/v) of a novel hydroxypropyl-β-cyclodextrin MXD GEL formulation (MXD/HP-β-CD) and a MXD solution were investigated in male rats. The cardiovascular effects were evaluated by telemetric monitoring of ECG and arterial pressure in free-moving rats. Ultrasonographic evaluation of cardiac morphology and function, and histopathological and biochemical analysis of the tissues, were performed. A pharmacovigilance investigation was undertaken using the EudraVigilance database for the evaluation of the potential cancer-related effects of topical MXD. Following the application of repeated escalating doses of MXD solution, cardiac hypertrophy, hypotension, enhanced serum natriuretic peptides and K+ -ion levels, serum liver biomarkers, and histological lesions including renal cancer were observed. In addition, the administration of a twice daily dose of MXD solution, at SF rat vs human = 311, caused reductions in the systolic, diastolic, and mean blood pressure of the rats (-30.76 ± 3%, -28.84 ± 4%, and -30.66 ± 5%, respectively, vs the baseline; t test P < .05). These effects were not reversible following washout of the MXD solution. Retrospective investigation showed 32 cases of cancer associated with the use of topical MXD in humans. The rats treated with MXD HP-β-CD were less severely affected. MXD causes proliferative adverse effects. The MXD HP-β-CD inclusion complex reduces these adverse effects.

A pharmacological characterization of electrocardiogram PR and QRS intervals in conscious telemetered rats

INTRODUCTION

The conscious telemetered rat is widely used as an early in vivo screening model for assessing the cardiovascular safety of novel pharmacological agents. The current study aimed to identify its utility in assessing electrocardiogram (ECG) PR and QRS interval changes.

METHOD

Male Han-Wistar rats (~250 g) were implanted with radio-telemetry devices for the recording of ECG and haemodynamic parameters. Animals (n = 4-8) were treated with single doses of calcium (nifedipine, diltiazem or verapamil; CCBs) or sodium channel blockers (quinidine or flecainide; SCBs) or their corresponding vehicles in an ascending dose design. Data was recorded continuously up to 24 h post-dose. Pharmacokinetic analysis of blood samples was performed to allow comparison of effects to published data in other species.

RESULTS

Of the CCBs, only diltiazem (300 mg/kg) prolonged the PR interval (49 ± 2 versus vehicle: 43 ± 1 ms), although this was not statistically significant (p = .11). QA interval decreased with nifedipine (30 ± 1 versus 24 ± 0 ms) and diltiazem (34 ± 1 versus 27 ± 1 ms) but increased with verapamil (30 ± 0 versus 37 ± 1 ms) demonstrating pharmacological activity of each agent. Both SCBs, caused statistically significant (p < .05) increases in both intervals - quinidine (100 mg/kg; PR: 50 ± 2 versus 43 ± 1 ms; QRS: 22 ± 2 versus 18 ± 1 ms) and flecainide (9 mg/kg; PR: 56 ± 1 versus 46 ± 1 ms; QRS: 27 ± 1 versus 21 ± 1 ms). Drug plasma exposure was confirmed in all animals.

DISCUSSION

At similar plasma concentrations to other species, the conscious telemetered rat demonstrates limited utility in assessing PR interval prolongation by CCBs, despite significant contractility effects being observed. However, results with SCBs demonstrate a potential application for evaluating drug-induced QRS prolongation.

Subchronic exposure to titanium dioxide nanoparticles modifies cardiac structure and performance in spontaneously hypertensive rats

BACKGROUND

Non-communicable diseases, intended as the results of a combination of inherited, environmental and biological factors, kill 40 million people each year, equivalent to roughly 70% of all premature deaths globally. The possibility that manufactured nanoparticles (NPs) may affect cardiac performance, has led to recognize NPs-exposure not only as a major Public Health concern, but also as an occupational hazard. In volunteers, NPs-exposure is problematic to quantify. We recently found that inhaled titanium dioxide NPs, one of the most produced engineered nanomaterials, acutely increased cardiac excitability and promoted arrhythmogenesis in normotensive rats by a direct interaction with cardiac cells. We hypothesized that such scenario can be exacerbated by latent cardiovascular disorders such as hypertension.

RESULTS

We monitored cardiac electromechanical performance in spontaneously hypertensive rats (SHRs) exposed to titanium dioxide NPs for 6 weeks using a combination of cardiac functional measurements associated with toxicological, immunological, physical and genetic assays. Longitudinal radio-telemetry ECG recordings and multiple-lead epicardial potential mapping revealed that atrial activation times significantly increased as well as proneness to arrhythmia. At the third week of nanoparticles administration, the lung and cardiac tissue encountered a maladaptive irreversible structural remodelling starting with increased pro-inflammatory cytokines levels and lipid peroxidation, resulting in upregulation of the main pro-fibrotic cardiac genes. At the end of the exposure, the majority of spontaneous arrhythmic events terminated, while cardiac hemodynamic deteriorated and a significant accumulation of fibrotic tissue occurred as compared to control untreated SHRs. Titanium dioxide nanoparticles were quantified in the heart tissue although without definite accumulation as revealed by particle-induced X-ray emission and ultrastructural analysis.

CONCLUSIONS

The co-morbidity of hypertension and inhaled nanoparticles induces irreversible hemodynamic impairment associated with cardiac structural damage potentially leading to heart failure. The time-dependence of exposure indicates a non-return point that needs to be taken into account in hypertensive subjects daily exposed to nanoparticles.

Cardiovascular alterations in rats with Parkinsonism induced by 6-OHDA and treated with Domperidone

After Alzheimer, Parkinson disease (PD) is the most frequently occurring progressive, degenerative neurological disease. It affects both sympathetic and parasympathetic nervous systems in a variable fashion. Cardiovascular symptoms are present in almost all stages of PD and narrower heart rate variability is the earliest sign. Administration of Levodopa to PD patients has proven to provide some degree of neurological protection. This drug, however, causes side effects including nausea and vomiting, lessened by the administration of domperidone. Autopsies in PD patients led some researchers to suggest the involvement of the ventricular arrhythmia induced by domperidone. The aim of the present study was to determine the impact of the adjusted human maximal dose of domperidone, on cardiological features of Wistar rats. domperidone was administered to both 6-hydroxydopamine Parkinsonism models and regular Wistar rats. Quantitative analysis of ranges of heart beat variation showed significant abnormal distribution in both groups receiving domperidone as compared with respective sham counterparts. However, qualitative analysis of Poincaré plots showed that 6-hydroxydopamine Parkinsonism models receiving domperidone had the narrowest full range of heart beat and the worst distribution heart beat ranges as compared with all study groups corroborating with previous suggestion that domperidone administration to PD patients is likely to play a role in sudden unexpected death in this group of patients.

Long-term cardiovascular effects of vandetanib and pazopanib in normotensive rats

Vandetanib and pazopanib are clinically available, multi-targeted inhibitors of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor tyrosine kinases. Short-term VEGF receptor inhibition is associated with hypertension in 15%-60% of patients, which may limit the use of these anticancer therapies over the longer term. To evaluate the longer-term cardiovascular implications of treatment, we investigated the "on"-treatment (21 days) and "off"-treatment (10 days) effects following daily administration of vandetanib, pazopanib, or vehicle, in conscious rats. Cardiovascular variables were monitored in unrestrained Sprague-Dawley rats instrumented with radiotelemetric devices. In Study 1, rats were randomly assigned to receive either daily intraperitoneal injections of vehicle (volume 0.5 mL; n = 5) or vandetanib 25 mg/kg/day (volume 0.5 mL; n = 6). In Study 2, rats received either vehicle (volume 0.5 mL; n = 4) or pazopanib 30 mg/kg/day (volume 0.5 mL; n = 7), dosed once every 24 hours for 21 days. All solutions were in 2% Tween, 5% propylene glycol in 0.9% saline solution. Vandetanib caused sustained increases in mean arterial pressure (MAP), systolic blood pressure (SBP), and diastolic blood pressure (DBP) compared to baseline and vehicle. Vandetanib also significantly altered the circadian cycling of MAP, SBP, and DBP. Elevations in SBP were detectable 162 hours after the last dose of vandetanib. Pazopanib also caused increases in MAP, SBP, and DBP. However, compared to vandetanib, these increases were of slower onset and a smaller magnitude. These data suggest that the cardiovascular consequences of vandetanib and pazopanib treatment are sustained, even after prolonged cessation of drug treatment.

Resting Heart Rate Variability Predicts Vulnerability to Pharmacologically-Induced Ventricular Arrhythmias in Male Rats

The electrical stability of the myocardium is dependent on the dynamic balance between sympathetic and parasympathetic influences on the heart, which is reflected by heart rate variability (HRV). Reduced HRV is a proposed predictor of sudden death caused by ventricular tachyarrhythmias in cardiac patients. However, the link between individual differences in HRV and ventricular tachyarrhythmic risk in populations without known pre-existing cardiac conditions is less well explored. In this study we investigated the extent to which individual differences in resting state HRV predict susceptibility to spontaneous and pharmacologically-induced ventricular arrhythmias in healthy rats. Radiotelemetric transmitters were implanted in 42 adult male Wild-type Groningen rats. ECG signals were recorded during 24-h resting conditions and under β-adrenoceptor pharmacological stimulation with isoproterenol and analyzed by means of time- and frequency-domain indexes of HRV. No significant association was found between individual differences in resting measures of HRV and spontaneous incidence of ventricular arrhythmias. However, lower resting values of HRV predicted a higher number of ventricular ectopic beats following β-adrenergic pharmacological stimulation with isoproterenol (0.02 mg/kg). Moreover, after isoproterenol administration, one rat with low resting HRV developed sustained ventricular tachycardia that led to death. The present results might be indicative of the potential utility of HRV measures of resting cardiac autonomic function for the prediction of ventricular arrhythmias, particularly during conditions of strong sympathetic activation, in populations without known cardiac disease.

Behavioral effects evoked by the beta globin-derived nonapeptide LVV-H6

LVV-hemorphin-6 (LVV-h6) is bioactive peptide and is a product of the degradation of hemoglobin. Since LVV-h6 effects are possibly mediated by opioid or AT4/IRAP receptors, we hypothesized that LVV-h6 would modify behavior. We evaluated whether LVV-h6 affects: i) anxiety-like behavior and locomotion; ii) depression-like behavior; iii) cardiovascular and neuroendocrine reactivity to emotional stress. Male Wistar rats ( ± 300 g) received LVV-h6 (153 nmol/kg i.p.) or vehicle (NaCl 0.9% i.p.). We used: i) open field (OF) test for locomotion; ii) elevated plus maze (EPM) for anxiety-like behavior; iii) forced swimming test (FST) for depression-like behavior and iv) air jet for cardiovascular and neuroendocrine reactivity to stress. Diazepam (2 mg/kg i.p.) and imipramine (15 mg/kg i.p.) were used as positive control for EPM and FST, respectively. To evaluate the LVV-h6 mechanisms, we used: the antagonist of oxytocin (OT) receptors (atosiban - ATS 1 and 0.1 mg/kg i.p.); the inhibitor of tyrosine hydroxylase (Alpha-methyl-p-tyrosine - AMPT 200 mg/kg i.p.) to investigate the involvement of catecholaminergic paths; and the antagonist of opioid receptors (naltrexone - NTX 0.3 mg/kg s.c.). We found that LVV-h6: i) evoked anxiolytic-like effect; ii) evoked antidepressant-like effect in the FST; and iii) did not change the locomotion, neuroendocrine and cardiovascular responses to stress. The LVV-h6 anxiolytic-like effect was not reverted by ATS and AMPT. However, the antidepressant effects were reverted only by NTX. Hence, our findings demonstrate that LVV-h6 modulates anxiety-like behavior by routes that are not oxytocinergic, catecholaminergic or opioid. The antidepressant-like effects of LVV-h6 rely on opioid pathways.

Low vagal tone in two rat models of psychopathology involving high or low corticosterone stress responses

The two stress-responsive physiological systems, autonomic nervous system (ANS) and hypothalamus-pituitary-adrenal (HPA) axis exert complementary and interrelated actions in the organism. Individuals that suffer stress-related psychopathologies frequently present simultaneous alterations -i.e., either low or high- responsiveness- in both systems. However, there is scarce evidence establishing whether a priori alterations in these systems -i.e., independent of previous stress exposure- may predispose to the development of psychopathologies possibly due to the lack of animal models simultaneously involving aberrant HPA and SNS responses. In this study, we describe two animal models selectively bred according to their differential (either high, 'High', or low, 'Low') glucocorticoid responsiveness to stress, in comparison to a third line of rats that displays intermediate ('Inter') glucocorticoid responses. The two extreme lines may be considered distinct models of psychopathology; the High line representing a model of constitutive mood alterations while the Low line a model of vulnerability to develop stress-induced psychopathologies. We recorded the electrocardiogram in rats from the three lines and quantified heart rate variability and vagal tone indexes during rest and stress challenges. Rats from both High and Low lines displayed higher heart rate and lower basal vagal tone than the Inter group, both at resting and following stress exposure. Specific pharmacological manipulations probing the relative contribution of sympathetic and parasympathetic components on HR modulation confirmed a relative lower vagal tone in High and Low lines and discarded differences in the sympathetic regulation of heart rate between the lines. Therefore, the two genetically-selected High and Low glucocorticoid rat lines emerge as two valuable preclinical models of psychopathology involving two key risk factors for psychiatric and cardiovascular disorders, namely dysregulations in the HPA axis and cardiac vagal functioning.

Coronary vasodilation impairment in pilocarpine model of epilepsy

We investigated the coronary arteries reactivity alterations in rats with epilepsy induced by pilocarpine. To do so, male Wistar rats weighing between 250 g and 300 g were used. Status epilepticus (SE) was induced in rats using 385 mg/kg (i.p.) of pilocarpine. After 60 days from the first spontaneous seizure, rats were submitted to heart rate measurements and then, one day after, euthanized, and the heart was dissected and submitted to constant flow Langendorff approaches to evaluate coronary reactivity. Rats with epilepsy showed higher resting heart rate and impairment of coronary vasodilation induced by bradykinin. Endothelial nitric oxide synthase (eNOS) and superoxide dismutase (SOD) presented a reduced staining in coronary arteries, and eNOS expression was also reduced in the left ventricle of rats with epilepsy. Our findings demonstrated, for the first time, that epilepsy can cause impairment of coronary arteries reactivity, probably because of an endothelial dependent mechanism.

A companion to the preclinical common data elements for physiologic data in rodent epilepsy models. A report of the TASK3 Physiology Working Group of the ILAE/AES Joint Translational Task Force

The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force created the TASK3 working groups to create common data elements (CDEs) for various aspects of preclinical epilepsy research studies, which could help improve standardization of experimental designs. This article concerns the parameters that can be measured to assess the physiologic condition of the animals that are used to study rodent models of epilepsy. Here we discuss CDEs for physiologic parameters measured in adult rats and mice such as general health status, temperature, cardiac and respiratory function, and blood constituents. We provide detailed CDE tables and case report forms (CRFs), and with this companion manuscript we discuss the monitoring of different aspects of physiology of the animals. The CDEs, CRFs, and companion paper are available to all researchers, and their use will benefit the harmonization and comparability of translational preclinical epilepsy research. The ultimate hope is to facilitate the development of biomarkers and new treatments for epilepsy.

Cardiac and behavioral effects of social isolation and experimental manipulation of autonomic balance

Improved understanding of how depression and social isolation interact to increase cardiac morbidity and mortality will improve public health. This experiment evaluated the effect of pharmacological autonomic blockade on cardiac and behavioral reactivity following social isolation in prairie voles. Experiment 1 validated the dose and time course of pharmacological autonomic antagonism of peripheral β-adrenergic (atenolol) and muscarinic cholinergic receptors (atropine methyl nitrate), and Experiment 2 used a novel protocol to investigate behavioral responses in the tail suspension test during pharmacological autonomic blockade as a function of social isolation (vs. paired control). Prairie voles isolated for 4 weeks (vs. paired) displayed significantly elevated heart rate and reduced heart rate variability. Autonomic receptor antagonism by atenolol led to exaggerated reductions in heart rate and standard deviation of normal-to-normal intervals, and lower amplitude of respiratory sinus arrhythmia in the isolated group (vs. paired). Administration of atropine led to an attenuated increase in heart rate in the isolated group (vs. paired), and similar near-zero levels of respiratory sinus arrhythmia amplitude in both groups. During the tail suspension test, isolated animals (vs. paired) displayed significantly greater immobility. In paired animals, atenolol administration did not influence immobility; atropine administration increased the duration of immobility (vs. vehicle). In isolated animals, atenolol administration increased the duration of immobility; atropine did not influence immobility duration (vs. vehicle). The current study contributes to our understanding of differential effects of social isolation and autonomic imbalance on cardiac and behavioral reactivity.

Electrocardiogram Delineation in a Wistar Rat Experimental Model

Background and Objectives

The extensive use of electrocardiogram (ECG) recordings during experimental protocols using small rodents requires an automatic delineation technique in the ECG with high performance. It has been shown that the wavelet transform (WT) based ECG delineator is a suitable tool to delineate electrocardiographic waveforms. The aim of this work is to implement and evaluate the ECG waves delineation in Wistar rats applying WT. We also describe the ECG signal of the Wistar rats giving the characteristics of its spectrum among other useful information.

Methods

We evaluated a delineator based on WT in a Wistar rat electrocardiograms database which was annotated manually by experienced observers.

Results

The delineation showed an “overall performance” such as sensitivity and a positive predictive value of 99.2% and 83.9% for P-wave, 100% and 99.9% for QRS complex, and 100% and 99.8% for T-wave, respectively. We also compared temporal analysis based ECG delineator with the WT based ECG delineator in RR interval, QRS duration, QT interval, and T-wave peak-to-end duration. The results showed that WT outperforms the temporal delineation technique in all parameters analyzed.

Conclusions

Finally, we propose a WT based ECG delineator as a methodology to implement in a wide diversity of experimental ECG analyses using Wistar rats.

The hemoglobin derived peptide LVV-hemorphin-7 evokes behavioral effects mediated by oxytocin receptors

LVV-hemorphin-7 (LVV-h7) is bioactive peptide resulting from degradation of hemoglobin β-globin chain. LVV-h7 is a specific agonist of angiotensin IV receptor. This receptor belongs to the class of insulin-regulated aminopeptidases (IRAP), which displays oxytocinase activity. Herein, our aims were to assess whether: i) LVV-h7 modifies centrally organized behavior and cardiovascular responses to stress and ii) mechanisms underlying LVV-h7 effects involve activation of oxytocin (OT) receptors, probably as result of reduction of IRAP proteolytic activity upon OT. Adult male Wistar rats (270-370g) received (i.p.) injections of LVV-h7 (153nmol/kg), or vehicle (0.1ml). Different protocols were used: i) open field (OP) test for locomotor/exploratory activities; ii) Elevated Plus Maze (EPM) for anxiety-like behavior; iii) forced swimming test (FST) test for depression-like behavior and iv) air jet for cardiovascular reactivity to acute stress exposure. Diazepam (2mg/kg) and imipramine (15mg/kg) were used as positive control for EPM and FST, respectively. The antagonist of OT receptors (OTr), atosiban (1 and 0,1mg/kg), was used to determine the involvement of oxytocinergic paths. We found that LVV-h7: i) increased the number of entries and the time spent in open arms of the maze, an indicative of anxiolysis; ii) provoked antidepressant effect in the FS test; and iii) increased the exploration and locomotion; iv) did not change the cardiovascular reactivity and neuroendocrine responses to acute stress. Also, increases in locomotion and the antidepressant effects evoked by LVV-h7 were reverted by OTr antagonist. We conclude that LVV-h7 modulates behavior, displays antidepressant and anxiolytic effects that are mediated in part by oxytocin receptors.

Noninvasive recording of electrocardiogram in conscious rat: A new device

Aim:

Electrocardiogram (ECG) is an important tool for the study of cardiac electrophysiology both in human beings and experimental animals. Existing methods of ECG recording in small animals like rat have several limitations and ECG recordings of the anesthetized rat lack validity for heart rate (HR) variability analysis. The aim of the present study was to validate the ECG data from new device with ECG of anesthetized rat.

Materials and Methods:

The ECG was recorded on student's physiograph (BioDevice, Ambala) and suitable coupler and electrodes in six animals first by the newly developed device in conscious state and second in anesthetized state (stabilized technique).

Results:

The data obtained were analyzed using unpaired t-test showed no significant difference (P < 0.05) in QTc, QRS, and HR recorded by new device and established device in rats.

Conclusion:

No previous study describes a similar ECG recording in conscious state of rats. Thus, the present method may be a most physiological and inexpensive alternative to other methods. In this study, the animals were not restrained; they were just secured and represent a potential strength of the study.

Improving animal welfare using continuous nalbuphine infusion in a long-term rat model of sepsis

Background

Sepsis research relies on animal models to investigate the mechanisms of the dysregulated host response to infection. Animal welfare concerns request the use of potent analgesics for the Refinement of existing sepsis models, according to the 3Rs principle. Nevertheless, adequate analgesia is often missing, partly because the effects of analgesics in this particular condition are unknown. We evaluated the use of nalbuphine, an opioid with kappa agonistic and mu antagonistic effects, in rats with and without experimental sepsis.

Methods

Male Wistar rats were anesthetized with isoflurane and instrumented with a venous line for drug administration. Arterial cannulation allowed for blood pressure measurements and blood sampling in short-term experiments of non-septic animals. Nalbuphine (or placebo) was administered intravenously at a dose of 1 mg/kg/h. Long-term (48 h) experiments in awake septic animals included repetitive clinical scoring with the Rat Grimace Scale and continuous heart rate monitoring by telemetry. Sepsis was induced by intraperitoneal injection of faecal slurry. Nalbuphine plasma levels were measured by liquid chromatography—high resolution mass spectrometry.

Results

In anesthetized healthy animals, nalbuphine led to a significant reduction of respiratory rate, heart rate, and mean arterial pressure during short-term experiments. In awake septic animals, a continuous nalbuphine infusion did not affect heart rate but significantly improved the values of the Rat Grimace Scale. Nalbuphine plasma concentrations remained stable between 4 and 24 h of continuous infusion in septic rats.

Conclusions

In anaesthetised rats, nalbuphine depresses respiratory rate, heart rate, and blood pressure. In awake animals, nalbuphine analgesia improves animal welfare during sepsis.

Autonomic changes induced by provocative motion in rats bred for high (HAB) and low (LAB) anxiety-related behavior: Paradoxical responses in LAB animals

In humans, associations between anxiety and nausea (including motion-induced) are reported but the underlying mechanisms are not known. Hypothermia is proposed to be an index of nausea in rats. Utilising hypothermia and heart rate as outcome measures we investigated the response to provocative motion in rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviors and in non-selected (NAB) rats to further elucidate the potential relationship between hypothermia and nausea-like state. Core temperature and electrocardiogram were monitored in each group (n=10 per group) using telemetry, with or without circular motion (40min; 0.75Hz) and vehicle or diazepam (2mg/kg, i.p.) pre-treatment. Heart rate and time- and frequency-domain parameters of heart rate variability were derived from the electrocardiogram. There was no baseline difference in core temperature between the three groups (mean 38.0±0.1°C), but HAB animals had a significantly lower resting heart rate (330±7bpm) compared to LAB (402±5bpm) and NAB (401±9bpm). Animals in all groups exhibited hypothermia during motion (HAB: 36.3±0.1°C; NAB: 36.4±0.1°C; LAB: 34.9±0.2°C) with the magnitude (area under the curve, AUC) of the response during 40-min motion being greater in LAB compared to NAB and HAB rats, and this was also the case for the motion-induced bradycardia. Diazepam had minimal effects on baseline temperature and heart rate in all groups, but significantly reduced the hypothermia response (AUC) to motion in all groups by ~30%. Breeding for extremes in anxiety-related behavior unexpectedly selects animals with low trait anxiety that have enhanced bradycardia and hypothermic responses to motion; consequently, this animal model appears to be not suitable for exploring relationships between anxiety and autonomic correlates of nausea. Thermal and cardiovascular responses to motion were little different between HAB and NAB rats indicating that either hypothermia is not an index of a nausea-like state in rats, or that the positive correlation between anxiety and nausea demonstrated in humans does not exist in rats. The mechanism underlying the enhanced physiological responses in LAB requires more detailed study and may provide a novel model to investigate factors modulating motion sensitivity.

Long-lasting bradypnea induced by repeated social defeat

Repeated social defeat in the rat induces long-lasting cardiovascular changes associated with anxiety. In this study, we investigated the effects of repeated social defeat on breathing. Respiratory rate was extracted from the respiratory sinus arrhythmia (RSA) peak frequency of the ECG in rats subjected to social defeat for 4 consecutive days. Respiratory rate was recorded under anesthesia 6 days (D+10) or 26 days (D+30) after social defeat. At D+10, defeated (D) rats spent less time in the open arms of the elevated plus maze test, had heavier adrenal glands, and displayed bradypnea, unlike nondefeated animals. At D+30, all signs of anxiety had disappeared. However, one-half of the rats still displayed bradypnea (DL rats, for low respiratory rate indicated by a lower RSA frequency), whereas those with higher respiratory rate (DH rats) had recovered. Acute blockade of the dorsomedial hypothalamus (DMH) or nucleus tractus solitarii (NTS) 5-HT3 receptors reversed bradypnea in all D rats at D+10 and in DL rats at D+30. Respiratory rate was also recorded in conscious animals implanted with radiotelemetric ECG probes. DH rats recovered between D+10 and D+18, whereas DL rats remained bradypneic until D+30. In conclusion, social stress induces sustained chronic bradypnea mediated by DMH neurons and NTS 5-HT3 receptors. These changes are associated with an anxiety-like state that persists until D+10, followed by recovery. However, bradypnea may persist in one-half of the population up until D+30, despite apparent recovery of the anxiety-like state.

Association of exercise training and angiotensin-converting enzyme 2 activator improves baroreflex sensitivity of spontaneously hypertensive rats

The present study sought to determine cardiovascular effects of aerobic training associated with diminazene aceturate (DIZE), an activator of the angiotensin converting enzyme 2, in spontaneously hypertensive rats (SHRs). Male SHRs (280–350 g) were either subjected to exercise training or not (sedentary group). The trained group was subjected to 8 weeks of aerobic training on a treadmill (five times a week, lasting 60 min at an intensity of 50–60% of maximum aerobic speed). In the last 15 days of the experimental protocol, these groups were redistributed into four groups: i) sedentary SHRs with daily treatment of 1 mg/kg DIZE (S+D1); ii) trained SHRs with daily treatment of 1 mg/kg DIZE (T+D1); iii) sedentary SHRs with daily treatment of vehicle (S+V); and iv) trained SHRs with daily treatment of vehicle (T+V). After treatment, SHRs were anesthetized and subjected to artery and femoral vein cannulation prior to the implantation of ECG electrode. After 24 h, mean arterial pressure (MAP) and heart rate (HR) were recorded; the baroreflex sensitivity and the effect of double autonomic blockade (DAB) were evaluated in non-anesthetized SHRs. DIZE treatment improved baroreflex sensitivity in the T+D1 group as compared with the T+V and S+D1 groups. The intrinsic heart rate (IHR) and MAP were reduced in T+D1 group as compared with T+V and S+D1 groups. Hence, we conclude that the association of exercise training with DIZE treatment improved baroreflex function and cardiovascular regulation.

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.

Antiarrhythmic effect of growth factor-supplemented cardiac progenitor cells in chronic infarcted heart

c-Kit(pos) cardiac progenitor cells (CPCs) represent a successful approach in healing the infarcted heart and rescuing its mechanical function, but electrophysiological consequences are uncertain. CPC mobilization promoted by hepatocyte growth factor (HGF) and IGF-1 improved electrogenesis in myocardial infarction (MI). We hypothesized that locally delivered CPCs supplemented with HGF + IGF-1 (GFs) can concur in ameliorating electrical stability of the regenerated heart. Adult male Wistar rats (139 rats) with 4-wk-old MI or sham conditions were randomized to receive intramyocardial injection of GFs, CPCs, CPCs + GFs, or vehicle (V). Enhanced green fluorescent protein-tagged CPCs were used for cell tracking. Vulnerability to stress-induced arrhythmia was assessed by telemetry-ECG. Basic cardiac electrophysiological properties were examined by epicardial multiple-lead recording. Hemodynamic function was measured invasively. Hearts were subjected to anatomical, morphometric, immunohistochemical, and molecular biology analyses. Compared with V and at variance with individual CPCs, CPCs + GFs approximately halved arrhythmias in all animals, restoring cardiac anisotropy toward sham values. GFs alone reduced arrhythmias by less than CPCs + GFs, prolonging ventricular refractoriness without affecting conduction velocity. Concomitantly, CPCs + GFs reactivated the expression levels of Connexin-43 and Connexin-40 as well as channel proteins of key depolarizing and repolarizing ion currents differently than sole GFs. Mechanical function and anatomical remodeling were equally improved by all regenerative treatments, thus exhibiting a divergent behavior relative to electrical aspects. Conclusively, we provided evidence of distinctive antiarrhythmic action of locally injected GF-supplemented CPCs, likely attributable to retrieval of Connexin-43, Connexin-40, and Cav1.2 expression, favoring intercellular coupling and spread of excitation in mended heart.

Assessment of anxiety in open field and elevated plus maze using infrared thermography

Due to their direct inaccessibility, affective states are classically assessed by gathering concomitant physiological and behavioral measures. Although such a dual approach to assess emotional states is frequently used in different species including humans, the invasiveness of procedures for physiological recordings particularly in smaller-sized animals strongly restricts their application. We used infrared thermography, a non-invasive method, to assess physiological arousal during open field and elevated plus maze tests in mice. By measuring changes in surface temperature indicative of the animals' emotional response, we aimed to improve the inherently limited and still controversial information provided by behavioral parameters commonly used in these tests. Our results showed significant and consistent thermal responses during both tests, in accordance with classical physiological responses occurring in stressful situations. Besides, we found correlations between these thermal responses and the occurrence of anxiety-related behaviors. Furthermore, initial temperatures measured at the start of each procedure (open field, elevated plus maze), which can be interpreted as a measure of the animals' initial physiological arousal, predicted the levels of activity and of anxiety-related behaviors displayed during the tests. Our results stress the strong link between physiological correlates of emotions and behaviors expressed during unconditioned fear tests.

Cardioprotective effects of fatty acid amide hydrolase inhibitor URB694, in a rodent model of trait anxiety

In humans, chronic anxiety represents an independent risk factor for cardiac arrhythmias and sudden death. Here we evaluate in male Wistar rats bred for high (HAB) and low (LAB) anxiety-related behavior, as well as non-selected (NAB) animals, the relationship between trait anxiety and cardiac electrical instability and investigate whether pharmacological augmentation of endocannabinoid anandamide-mediated signaling exerts anxiolytic-like and cardioprotective effects. HAB rats displayed (i) a higher incidence of ventricular tachyarrhythmias induced by isoproterenol, and (ii) a larger spatial dispersion of ventricular refractoriness assessed by means of an epicardial mapping protocol. In HAB rats, acute pharmacological inhibition of the anandamide-degrading enzyme, fatty acid amide hydrolase (FAAH), with URB694 (0.3 mg/kg), (i) decreased anxiety-like behavior in the elevated plus maze, (ii) increased anandamide levels in the heart, (iii) reduced isoproterenol-induced occurrence of ventricular tachyarrhythmias, and (iv) corrected alterations of ventricular refractoriness. The anti-arrhythmic effect of URB694 was prevented by pharmacological blockade of the cannabinoid type 1 (CB₁), but not of the CB₂, receptor. These findings suggest that URB694 exerts anxiolytic-like and cardioprotective effects in HAB rats, the latter via anandamide-mediated activation of CB₁ receptors. Thus, pharmacological inhibition of FAAH might be a viable pharmacological strategy for the treatment of anxiety-related cardiac dysfunction.

Doxorubicin: Comparison between 3-h continuous and bolus intravenous administration paradigms on cardio-renal axis, mitochondrial sphingolipids and pathology

Doxorubicin (DOX) is a potent and effective broad-spectrum anthracycline antitumor agent, but its clinical usefulness is restricted by cardiotoxicity. This study compared pharmacokinetic, functional, structural and biochemical effects of single dose DOX bolus or 3-h continuous iv infusion (3-h iv) in the Han–Wistar rat to characterize possible treatment-related differences in drug safety over a 72 h observation period. Both DOX dosing paradigms significantly altered blood pressure, core body temperature and QA interval (indirect measure of cardiac contractility); however, there was no recovery observed in the bolus iv treatment group. Following the 3-h iv treatment, blood pressures and QA interval normalized by 36 h then rose above baseline levels over 72 h. Both treatments induced biphasic changes in heart rate with initial increases followed by sustained decreases. Cardiac injury biomarkers in plasma were elevated only in the bolus iv treatment group. Tissue cardiac injury biomarkers, cardiac mitochondrial complexes I, III and V and cardiac mitochondrial sphingolipids were decreased only in the bolus iv treatment group. Results indicate that each DOX dosing paradigm deregulates sinus rhythm.However, slowing the rate of infusion allows for functional compensation of blood pressure and may decrease the likelihood of cardiac myocyte necrosis via a mechanism associated with reduced mitochondrial damage.

In rats the duration of diabetes influences its impact on cardiac autonomic innervations and electrophysiology

Diabetic cardiac autonomic neuropathy (DCAN) may cause fatal ventricular arrhythmias and increase mortality in diabetics. However, limited data are available with regard to the precise changes in cardiac autonomic denervation after diabetes onset. In this study, we dynamically observed the progression of DCAN and its relationship with the inducibility of ventricular arrhythmias in diabetic rats. Rats were randomly divided into normal control and diabetes mellitus (DM) groups. The rats were sacrificed at 3 or 6 months post-treatment. Heart rate variability and programmed electrical stimulation were used to assess the electrophysiological characteristics and the inducibility of ventricular arrhythmias in the animals. Immunohistochemistry and real-time RT-PCR were used to measure choline acetyltransferase and tyrosine hydroxylase-positive nerve fibers and the corresponding mRNA expression levels in the proximal and distal regions of the left ventricle. Short-term diabetes resulted in distal myocardial parasympathetic denervation with sparing of the proximal myocardium. By 6 months, both parasympathetic and sympathetic denervation were further aggravated. Moreover, electrophysiological experiments demonstrated a sympatho-parasympathetic imbalance and an increase in ventricular arrhythmia inducibility in the diabetic rats. These results suggest that DM causes cardiac nerve denervation, relative sympathetic hyperinnervation and inhomogeneous neural innervations, which may be associated with an increase in the induction of ventricular arrhythmia in diabetic rats.

Respiratory sinus arrhythmia as a surrogate measure of respiratory frequency: validity and robustness to activity in rats

Recording of breathing frequency is a basic requirement for respiratory physiology. Usual techniques are invasive and constraining. Respiratory sinus arrhythmia (RSA) has recently been demonstrated to be a simple way to obtain respiration frequency at rest. In this study, we investigated whether this correlation is also observed during activity. We first compared RSA to the respiration frequency obtained in anesthetized rats using a pneumotachograph connected to the trachea (TRF). Data analyses using Passing and Bablok regression confirmed the absence of bias and proportional differences. Accordingly, the Bland-Altman plot did not show any significant differences in data sets. In a second experiment, we compared RSA to the respiration frequency obtained in freely moving rats using a subpleurally inserted telemetric catheter (PRF). Comparisons between RSA and PRF revealed no significant difference in determination of respiratory rate with the two methods, although the bias and confidence interval were greater when activity increased. This was, however, not the case during short episodes of sniffing-like tachypnea, during which no matching RSA peaks were observed. In conclusion, RSA frequency reflected regular respiration frequency independently of the level of activity and appears to be a good surrogate to usual techniques.

Signs of cardiac autonomic imbalance and proarrhythmic remodeling in FTO deficient mice

In humans, variants of the fat mass and obesity associated (FTO) gene have recently been associated with obesity. However, the physiological function of FTO is not well defined. Previous investigations in mice have linked FTO deficiency to growth retardation, loss of white adipose tissue, increased energy metabolism and enhanced systemic sympathetic activation. In this study we investigated for the first time the effects of global knockout of the mouse FTO gene on cardiac function and its autonomic neural regulation. ECG recordings were acquired via radiotelemetry in homozygous knockout (n = 12) and wild-type (n = 8) mice during resting and stress conditions, and analyzed by means of time- and frequency-domain indexes of heart rate variability. In the same animals, cardiac electrophysiological properties (assessed by epicardial mapping) and structural characteristics were investigated. Our data indicate that FTO knockout mice were characterized by (i) higher heart rate values during resting and stress conditions, (ii) heart rate variability changes (increased LF to HF ratio), (iii) larger vulnerability to stress-induced tachyarrhythmias, (iv) altered ventricular repolarization, and (v) cardiac hypertrophy compared to wild-type counterparts. We conclude that FTO deficiency in mice leads to an imbalance of the autonomic neural modulation of cardiac function in the sympathetic direction and to a potentially proarrhythmic remodeling of electrical and structural properties of the heart.

Vagal modulation of resting heart rate in rats: the role of stress, psychosocial factors, and physical exercise

In humans, there are large individual differences in the levels of vagal modulation of resting heart rate (HR). High levels are a recognized index of cardiac health, whereas low levels are considered an important risk factor for cardiovascular morbidity and mortality. Several factors are thought to contribute significantly to this inter-individual variability. While regular physical exercise seems to induce an increase in resting vagal tone, chronic life stress, and psychosocial factors such as negative moods and personality traits appear associated with vagal withdrawal. Preclinical research has been attempting to clarify such relationships and to provide insights into the neurobiological mechanisms underlying vagal tone impairment/enhancement. This paper focuses on rat studies that have explored the effects of stress, psychosocial factors and physical exercise on vagal modulation of resting HR. Results are discussed with regard to: (i) individual differences in resting vagal tone, cardiac stress reactivity and arrhythmia vulnerability; (ii) elucidation of the neurobiological determinants of resting vagal tone.

Low vagally-mediated heart rate variability and increased susceptibility to ventricular arrhythmias in rats bred for high anxiety

In humans, there is a documented association between anxiety disorders and cardiovascular disease. Putative underlying mechanisms may include an impairment of the autonomic nervous system control of cardiac function. The primary objective of the present study was to characterize cardiac autonomic modulation and susceptibility to arrhythmias in genetic lines of rats that differ largely in their anxiety level. To reach this goal, electrocardiographic recordings were performed in high-anxiety behavior (HAB, n=10) and low-anxiety behavior (LAB, n=10) rats at rest, during stressful stimuli and under autonomic pharmacological manipulations, and analyzed by means of time- and frequency-domain indexes of heart rate variability. During resting conditions, HAB rats displayed a reduced heart rate variability, mostly in terms of lower parasympathetic (vagal) modulation compared to LAB rats. In HAB rats, this relatively low cardiac vagal control was associated with smaller heart rate responsiveness to acute stressors compared to LAB counterparts. In addition, beta-adrenergic pharmacological stimulation induced a larger incidence of ventricular tachyarrhythmias in HABs compared to LABs. At sacrifice, a moderate increase in heart-body weight ratio was observed in HAB rats. We conclude that high levels of anxiety-related behavior in rats are associated with signs of i) impaired autonomic modulation of heart rate (low vagally-mediated heart rate variability), ii) poor adaptive heart rate responsiveness to stressful stimuli, iii) increased arrhythmia susceptibility, and iv) cardiac hypertrophy. These results highlight the utility of the HAB/LAB model for investigating the mechanistic basis of the comorbidity between anxiety disorders and cardiovascular disease.

Central activation of the A1 adenosine receptor (A1AR) induces a hypothermic, torpor-like state in the rat

Since central activation of A1 adenosine receptors (A1ARs) plays an important role in the induction of the hypothermic and hypometabolic torpid state in hibernating mammals, we investigated the potential for the A1AR agonist N6-cyclohexyladenosine to induce a hypothermic, torpor-like state in the (nonhibernating) rat. Core and brown adipose tissue temperatures, EEG, heart rate, and arterial pressure were recorded in free-behaving rats, and c-fos expression in the brain was analyzed, following central administration of N6-cyclohexyladenosine. Additionally, we recorded the sympathetic nerve activity to brown adipose tissue; expiratory CO2 and skin, core, and brown adipose tissue temperatures; and shivering EMGs in anesthetized rats following central and localized, nucleus of the solitary tract, administration of N6-cyclohexyladenosine. In rats exposed to a cool (15°C) ambient temperature, central A1AR stimulation produced a torpor-like state similar to that in hibernating species and characterized by a marked fall in body temperature due to an inhibition of brown adipose tissue and shivering thermogenesis that is mediated by neurons in the nucleus of the solitary tract. During the induced hypothermia, EEG amplitude and heart rate were markedly reduced. Skipped heartbeats and transient bradycardias occurring during the hypothermia were vagally mediated since they were eliminated by systemic muscarinic receptor blockade. These findings demonstrate that a deeply hypothermic, torpor-like state can be pharmacologically induced in a nonhibernating mammal and that recovery of normothermic homeostasis ensues upon rewarming. These results support the potential for central activation of A1ARs to be used in the induction of a hypothermic, therapeutically beneficial state in humans.