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.

Age-related increases in cardiac excitability, refractoriness and impulse conduction favor arrhythmogenesis in male rats.

The effects of excitability, refractoriness, and impulse conduction have been independently related to enhanced arrhythmias in the aged myocardium in experimental and clinical studies. However, their combined arrhythmic effects in the elderly are not yet completely understood. Hence, the aim of the present work is to relate relevant cardiac electrophysiological parameters to enhanced arrhythmia vulnerability in the in vivo senescent heart. We used multiple-lead epicardial potential mapping in control (9-month-old) and aged (24-month-old) rat hearts. Cardiac excitability and refractoriness were evaluated at numerous epicardial test sites by means of the strength-duration curve and effective refractory period, respectively. During sinus rhythm, durations of electrogram intervals and waves were prolonged in the senescent heart, compared with control, demonstrating a latency in tissue activation and recovery. During ventricular pacing, cardiac excitability, effective refractory period, and dispersion of refractoriness increased in the aged animal. This scenario was accompanied by impairment of impulse propagation. Moreover, both spontaneous and induced arrhythmias were increased in senescent cardiac tissue. Histopathological evaluation of aged heart specimens revealed connective tissue deposition and perinuclear myocytolysis in the atria, while scattered microfoci of interstitial fibrosis were mostly present in the ventricular subendocardium. This work suggests that enhanced arrhythmogenesis in the elderly is a multifactorial process due to the joint increase in excitability and dispersion of refractoriness in association with enhanced conduction inhomogeneity. The knowledge of these electrophysiological changes will possibly contribute to improved prevention of the age-associated increase in cardiac arrhythmias.

Nocturnal Heart Rate Variability Might Help in Predicting Severe Obstructive Sleep-Disordered Breathing.

Obstructive sleep apnea (OSA) can have long-term cardiovascular and metabolic effects. The identification of OSA-related impairments would provide diagnostic and prognostic value. Heart rate variability (HRV) as a measure of cardiac autonomic regulation is a promising candidate marker of OSA and OSA-related conditions. We took advantage of the Physionet Apnea-ECG database for two purposes. First, we performed time- and frequency-domain analysis of nocturnal HRV on each recording of this database to evaluate the cardiac autonomic regulation in patients with nighttime sleep breathing disorders. Second, we conducted a logistic regression analysis (backward stepwise) to identify the HRV indices able to predict the apnea-hypopnea index (AHI) categories (i.e., "Severe OSA", AHI ≥ 30; "Moderate-Mild OSA", 5 ≥ AHI < 30; and "Normal", AHI < 5). Compared to the "Normal", the "Severe OSA" group showed lower high-frequency power in normalized units (HFnu) and higher low-frequency power in normalized units (LFnu). The standard deviation of normal R-R intervals (SDNN) and the root mean square of successive R-R interval differences (RMSSD) were independently associated with sleep-disordered breathing. Our findings suggest altered cardiac autonomic regulation with a reduced parasympathetic component in OSA patients and suggest a role of nighttime HRV in the characterization and identification of sleep breathing disorders.

The duration of successive epileptic seizures is monotonically correlated in neonates.

OBJECTIVE: Prolonged neonatal seizures are often due to severe acute brain injuries and are known to be harmful to the brain. No predictors have yet been identified to distinguish at an early time-point between brief and long seizures. We investigated the duration of seizures in neonates to determine the relationship between the duration of a seizure and that of subsequent seizures. METHODS: We retrospectively reviewed video-electroencephalogram confirmed seizures of 30 preterm and 36 full-term neonates selected from patients admitted to the neonatal intensive care unit of Parma University Hospital. The duration and relationship between successive seizures were investigated. Statistical models were performed to evaluate the risk of long-lasting ictal events among neonates with seizures. RESULTS: A positive monotonic relationship between the duration of successive seizures was identified. Most seizures were brief. No significant differences in seizure duration were found between preterm and full-term neonates, although a borderline significance emerged. CONCLUSION: Neonatal seizures are usually brief, and as the seizure duration increases, the duration of the subsequent seizures tends to increase. We also suggest that full-term neonates could be at higher risk of experiencing long seizures compared to preterm neonates. In summary, estimating the seizure duration is critical to evaluating the optimal timing of therapeutic interventions and can help to predict how seizures evolve.

Heart rate variability in neonatal seizures: Investigation and implications for management.

Many factors acting during the neonatal period can affect neurological development of the infant. Neonatal seizures (NS) that frequently occur in the immature brain may influence autonomic maturation and lead to detectable cardiovascular signs. These autonomic manifestations can also have significant diagnostic and prognostic value. The analysis of Heart Rate Variability (HRV) represents the most used and feasible method to evaluate cardiac autonomic regulation. This narrative review summarizes studies investigating HRV dynamics in newborns with seizures, with the aim of highlighting the potential utility of HRV measures for seizure detection and management. While HRV analysis in critically ill newborns is influenced by many potential confounders, we suggest that it can enhance the ability to better diagnose seizures in the clinical setting. We present potential applications of the analysis of HRV, which could have a useful future role, beyond the research setting.

Exposure to nanoparticles derived from diesel particulate filter equipped engine increases vulnerability to arrhythmia in rat hearts.

Air pollution is well recognized as a central player in cardiovascular disease. Exhaust particulate from diesel engines (DEP) is rich in nanoparticles and may contribute to the health effects of particulate matter in the environment. Moreover, diesel soot emitted by modern engines denotes defective surfaces alongside chemically-reactive sites increasing soot cytotoxicity. We recently demonstrated that engineered nanoparticles can cross the air/blood barrier and are capable to reach the heart. We hypothesize that DEP nanoparticles are pro-arrhythmogenic by direct interaction with cardiac cells. We evaluated the internalization kinetics and the effects of DEP, collected from Euro III (DEPe3, in the absence of Diesel Particulate Filter, DPF) and Euro IV (DEPe4, in the presence of DPF) engines, on alveolar and cardiac cell lines and on in situ rat hearts following DEP tracheal instillation. We observed significant differences in DEP size, metal and organic compositions derived from both engines. DEPe4 comprised ultrafine particles (<100 nm) and denoted a more pronounced toxicological outcome compared to DEPe3. In cardiomyocytes, particle internalization is fastened for DEPe4 compared to DEPe3. The in-vivo epicardial recording shows significant alteration of EGs parameters in both groups. However, the DEPe4-instilled group showed, compared to DEPe3, a significant increment of the effective refractory period, cardiac conduction velocity, and likelihood of arrhythmic events, with a significant increment of membrane lipid peroxidation but no increment in inflammation biomarkers. Our data suggest that DEPe4, possibly due to ultrafine nanoparticles, is rapidly internalized by cardiomyocytes resulting in an acute susceptibility to cardiac electrical disorder and arrhythmias that could accrue from cellular toxicity. Since the postulated transfer of nanoparticles from the lung to myocardial cells has not been investigated it remains open whether the effects on the cardiovascular function are the result of lung inflammatory reactions or due to particles that have reached the heart.

Right ventricular functional recovery depends on timing of pulmonary valve replacement in tetralogy of Fallot: a video kinematic study.

OBJECTIVES: Indications for and timing of pulmonary valve replacement (PVR) after tetralogy of Fallot repair are controversial. Among magnetic resonance imaging indices proposed to time valve replacement, a right ventricular (RV) end-diastolic volume index greater than 160 ml/m2 is often used. Recent evidence suggests that this value may still identify patients with irreversible RV dysfunction, thus hindering recovery. Our goal was to define, using intraoperative video kinematic evaluation, whether a relationship exists between timing of PVR and early functional recovery after surgery. METHODS: Between November 2016 and November 2018, a total of 12 consecutive patients aged 27.1 ± 19.1 years underwent PVR on average 22.2 ± 13.3 years after tetralogy of Fallot repair. Mean RV end-diastolic volume evident on the magnetic resonance images was 136.9 ± 35.7 ml/m2. Intraoperative cardiac kinematics were assessed by video kinematic evaluation via a high-speed camera acquiring videos at 200 fps before and after valve replacement. RESULTS: Patients presenting with RV end-diastolic volume <147 ml/m2 were significantly younger (11.2 ± 5.0 vs 38.4 ± 17.0; P = 0.005) and had a shorter time interval to valve replacement (11.0 ± 5.2 vs 30.1 ± 11.3; P = 0.03). The entire population showed a moderate correlation among energy expenditure, cardiac fatigue, perimeter of contraction and preoperative RV end-diastolic volume index. Both groups showed a reduction in all kinematic parameters after PVR, but those with end-diastolic volume >147 ml/m2 showed an unpredictable outcome. CONCLUSIONS: Video kinematic evaluation provides insight into intraoperative RV recovery in patients with tetralogy of Fallot undergoing PVR. Accordingly, functional recovery can be expected in patients with preoperative end-diastolic volume <147 ml/m2.

Bionic for Training: Smart Framework Design for Multisensor Mechatronic Platform Validation.

Home monitoring supports the continuous improvement of the therapy by sharing data with healthcare professionals. It is required when life-threatening events can still occur after hospital discharge such as neonatal apnea. However, multiple sources of external noise could affect data quality and/or increase the misdetection rate. In this study, we developed a mechatronic platform for sensor characterizations and a framework to manage data in the context of neonatal apnea. The platform can simulate the movement of the abdomen in different plausible newborn positions by merging data acquired simultaneously from three-axis accelerometers and infrared sensors. We simulated nine apnea conditions combining three different linear displacements and body postures in the presence of self-generated external noise, showing how it is possible to reduce errors near to zero in phenomena detection. Finally, the development of a smart 8Ws-based software and a customizable mobile application were proposed to facilitate data management and interpretation, classifying the alerts to guarantee the correct information sharing without specialized skills.

Antidepressant-like effects of pharmacological inhibition of FAAH activity in socially isolated female rats.

Pharmacological inhibition of the enzyme fatty acid amide hydrolase (FAAH), which terminates signaling of the endocannabinoid N-arachidonoylethanolamine (or anandamide, AEA), exerts favourable effects in rodent models of stress-related depression. Yet although depression seems to be more common among women than men and in spite of some evidence of sex differences in treatment efficacy, preclinical development of FAAH inhibitors for the pharmacotherapy of stress-related depression has been predominantly conducted in male animals. Here, adult female rats were exposed to six weeks of social isolation and, starting from the second week, treated with the FAAH inhibitor URB694 (0.3 mg/kg/day, i.p.) or vehicle. Compared to pair-housed females, socially isolated female rats treated with vehicle developed behavioral (mild anhedonia, passive stress coping) and physiological (reduced body weight gain, elevated plasma corticosterone levels) alterations. Moreover, prolonged social isolation provoked a reduction in brain-derived neurotrophic factor (BDNF) and AEA levels within the hippocampus. Together, these changes are indicative of an increased risk of developing a depressive-like state. Conversely, pharmacological inhibition of FAAH activity with URB694 restored both AEA and BDNF levels within the hippocampus of socially isolated rats and prevented the development of behavioral and physiological alterations. These results suggest a potential interplay between AEA-mediated signaling and hippocampal BDNF in the pathogenesis of depression-relevant behaviors and physiological alterations and antidepressant action of FAAH inhibition in socially isolated female rats.

Bifidobacterial Transfer from Mother to Child as Examined by an Animal Model.

Bifidobacteria commonly constitute the most abundant group of microorganisms in the healthy infant gut. Their intestinal establishment is believed to be maternally driven, and their acquisition has even been postulated to occur during pregnancy. In the current study, we evaluated bifidobacterial mother-to infant transmission events in a rat model by means of quantitative PCR (qPCR), as well as by Internally Transcribed Spacer (ITS) bifidobacterial profiling. The occurrence of strains supplied by mothers during pregnancy to their corresponding newborns was observed and identified by analysis immediately following C-section delivery. These findings provide intriguing support for the existence of an unknown route to facilitate bifidobacterial transfer during the very early stages of life.

Exploring the effects of COLOSTRONONI on the mammalian gut microbiota composition.

COLOSTRONONI is a dietary supplement consisting of bovine colostrum and Morinda citrifolia fruit (Noni). In this study, we tested the capability of COLOSTRONONI to influence gut microbiota composition using an in vivo evaluation in rats. Furthermore, we analyzed the effect of COLOSTRONONI on the systemic inflammatory responses as well as on the gut permeability of the animals. Altogether, our analyses supported the concept of COLOSTRONONI as a natural food supplement that doesn't affect (neither negatively nor positively) gut microbiota homeostasis in healthy conditions. Moreover, COLOSTRONONI highlighted a lower effect in the expression of genes coding for IL-10, Il-12 and TNF-α response allowing us to hypothesize an immunomodulatory activity of this dietary supplement.

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 ß-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 ß-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.

Ability of bifidobacteria to metabolize chitin-glucan and its impact on the gut microbiota.

Chitin-glucan (CG) represents a natural carbohydrate source for certain microbial inhabitants of the human gut and may act as a prebiotic for a number of bacterial taxa. However, the bifidogenic activity of this substrate is still unknown. In the current study, we evaluated the ability of chitin-glucan to influence growth of 100 bifidobacterial strains belonging to those species commonly identified within the bifidobacterial communities residing in the infant and adult human gut. Such analyses were coupled with transcriptome experiments directed to explore the transcriptional effects of CG on Bifidobacterium breve 2L, which was shown to elicit the highest growth performance on this natural polysaccharide. In addition, an in vivo trial involving a rat model revealed how the colonization efficiency of this bifidobacterial strain was enhanced when the animals were fed with a diet containing CG. Altogether our analyses indicate that CG is a valuable novel prebiotic compound that may be added to the human diet in order to re-establish/reinforce bifidobacteria colonization in the mammalian gut.

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

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

Heart rate variability in neonatal patients with seizures.

OBJECTIVE: Seizures are frequently observed in neurological conditions affecting newborns. Since autonomic alterations are commonly associated with neonatal seizures (NS), we investigated the utility of heart rate variability (HRV) indexes of cardiac autonomic regulation for NS detection. METHODS: HRV analysis was conducted on ECG tracings recorded during video-EEG monitoring in newborns with NS and matched-controls. The effects of gestational age on HRV were also evaluated. RESULTS: Newborns with NS showed lower resting state HRV compared to controls. Moreover, seizure episodes were characterized by a short-lasting increase in vagal indexes of HRV. Pre-term newborns with NS had a lower HRV than full-term at rest. In pre-term newborns, no changes in HRV were observed before and during NS. On the contrary, full-term newborns showed significantly higher HRV before and during NS compared to the respective baseline values. CONCLUSION: Our data point to resting autonomic impairment in newborns with NS. In addition, an increment in HRV has been observed during NS only in full term newborns. SIGNIFICANCE: Although these findings do not allow validation of HRV measures for NS prediction and detection, they suggest that a putative protective vagal mechanism might be adopted when an advanced maturation of autonomic nervous system is achieved.

The Utility of Rodent Models of Stress for Disentangling Individual Vulnerability to Depression and Cardiovascular Comorbidity.

PURPOSE OF REVIEW: This review offers a perspective of the utility of rodent models of stress for identifying sources of individual vulnerability to depression and cardiovascular disease comorbidity. RECENT FINDINGS: Differential stress susceptibility is found in rodents exposed to repeated social defeat as a function of their coping style. Specifically, passive coping rodents show an increase in inflammatory processes within the brain that favour the development of depressive-like symptoms and cardiovascular abnormalities. Similarly, only a sub-group of rats develops depressive-like symptoms following chronic mild stress exposure. Cardiovascular changes differ depending on individual stress susceptibility and may be related to an imbalance in the autonomic regulation of cardiac function in stress vulnerable subjects. Rodent models of stress that take into account individual phenotypic variations are useful for a better understanding of the role of neuroinflammatory and autonomic processes in the development of comorbid depression and cardiovascular disease under stressful conditions.

How to Feed the Mammalian Gut Microbiota: Bacterial and Metabolic Modulation by Dietary Fibers.

The composition of the gut microbiota of mammals is greatly influenced by diet. Therefore, evaluation of different food ingredients that may promote changes in the gut microbiota composition is an attractive approach to treat microbiota disturbances. In this study, three dietary fibers, such as inulin (I, 10%), resistant starch (RS, 10%), and citrus pectin (3%), were employed as supplements to normal chow diet of adult male rats for 2 weeks. Fecal microbiota composition and corresponding metabolite profiles were assessed before and after prebiotics supplementation. A general increase in the Bacteroidetes phylum was detected with a concurrent reduction in Firmicutes, in particular for I and RS experiments, while additional changes in the microbiota composition were evident at lower taxonomic levels for all the three substrates. Such modifications in the microbiota composition were correlated with changes in metabolic profiles of animals, in particular changes in acetate and succinate levels. This study represents a first attempt to modulate selectively the abundance and/or metabolic activity of various members of the gut microbiota by means of dietary fiber.

Social stress contagion in rats: Behavioural, autonomic and neuroendocrine correlates.

The negative emotional consequences associated with life stress exposure in an individual can affect the emotional state of social partners. In this study, we describe an experimental rat model of social stress contagion and its effects on social behaviour and cardiac autonomic and neuroendocrine functions. Adult male Wistar rats were pair-housed and one animal (designated as "demonstrator" (DEM)) was submitted to either social defeat stress (STR) by an aggressive male Wild-type rat in a separate room or just exposed to an unfamiliar empty cage (control condition, CTR), once a day for 4 consecutive days. We evaluated the influence of cohabitation with a STR DEM on behavioural, cardiac autonomic and neuroendocrine outcomes in the cagemate (defined "observer" (OBS)). After repeated social stress, STR DEM rats showed clear signs of social avoidance when tested in a new social context compared to CTR DEM rats. Interestingly, also their cagemate STR OBSs showed higher levels of social avoidance compared to CTR OBSs. Moreover, STR OBS rats exhibited a higher heart rate and a larger shift of cardiac autonomic balance toward sympathetic prevalence (as indexed by heart rate variability analysis) immediately after the first reunification with their STR DEMs, compared to the control condition. This heightened cardiac autonomic responsiveness habituated over time. Finally, STR OBSs showed elevated plasma corticosterone levels at the end of the experimental protocol compared to CTR OBSs. These findings demonstrate that cohabitation with a DEM rat, which has experienced repeated social defeat stress, substantially disrupts social behaviour and induces short-lasting cardiac autonomic activation and hypothalamic-pituitary-adrenal axis hyperactivity in the OBS rat, thus suggesting emotional state-matching between the OBS and the DEM rats. We conclude that this rodent model may be further exploited for investigating the neurobiological bases of negative affective sharing between social partners under chronic social stress conditions.

Rodent models of depression-cardiovascular comorbidity: Bridging the known to the new.

Numerous epidemiological studies have demonstrated a close and bidirectional association between depression and cardiovascular disorders (CVD). This comorbidity places a significant burden on individuals and the healthcare system. Not surprisingly, in the last two decades preclinical research in the field of depression and CVD has rapidly progressed. Multiple studies have demonstrated that aspects of human depression/cardiovascular comorbidity can be modeled in rodents exposed to chronic stress paradigms and that a depressive-like syndrome can be induced in rodent models of CVD. This research has provided insights into neural, autonomic, humoral, immune and circulatory mechanisms linking co-occurring mood and CVD. Recent investigations have started to address gender and individual differences in the vulnerability to both disorders and have begun to explore the efficacy of novel pharmacological interventions for the treatment of these comorbid conditions. This review discusses relatively well-established findings and the latest discoveries from rodent models of depression and CVD, with the aim of providing an up-to-date reference which may guide future studies of the relationship between mood and cardiovascular disturbances.

Reduced NPY Y1 receptor hippocampal expression and signs of decreased vagal modulation of heart rate in mice.

Central neuropeptide Y (NPY) signaling participates in the regulation of cardiac autonomic outflow, particularly via activation of NPY-Y1 receptors (Y1Rs). However, the specific brain areas and neural pathways involved have not been completely identified yet. Here, we evaluate the role of hippocampal Y1Rs in the modulation of the autonomic control of cardiac function using a conditional knockout mouse model. Radiotelemetric transmitters were implanted in 4-month-old male mice exhibiting reduced forebrain expression (rfb) of the Y1R (Npy1rrfb, n=10) and their corresponding controls (Npy1r2lox, n=8). ECG signals were recorded (i) during resting conditions, (ii) under selective pharmacological manipulation of cardiac vagal activity, and (iii) during acute and chronic psychosocial stress challenges, and analyzed via time- and frequency-domain analysis of heart rate variability. Npy1rrfb mice showed a lower Npy1r mRNA density in the dentate gyrus and in the CA1 region of the hippocampus. Under resting undisturbed conditions, Npy1rrfb mice exhibited (i) a higher heart rate, (ii) a reduced overall heart rate variability, and (iii) lower values of the indices of vagal modulation compared to Npy1r2lox counterparts. Following pharmacological vagal inhibition, heart rate was higher in control but not in Npy1rrfb mice compared to their respective baseline values, suggesting that tonic vagal influences on heart rate were reduced in Npy1rrfb mice. The magnitude of the heart rate response to acute stressors was smaller in Npy1rrfb mice compared to Npy1r2lox counterparts, likely due to a concurrent lower vagal withdrawal. These findings suggest that reduced Y1R expression leads to a decrease in resting vagal modulation and heart rate variability, which, in turn, may determine a reduced cardiac autonomic responsiveness to acute stress challenges.