The brain-heart axis: integrative cooperation of neural, mechanical and biochemical pathways

The neural and cardiovascular systems are pivotal in regulating human physiological, cognitive and emotional states, constantly interacting through anatomical and functional connections referred to as the brain-heart axis. When this axis is dysfunctional, neurological conditions can lead to cardiovascular disorders and, conversely, cardiovascular dysfunction can substantially affect brain health. However, the mechanisms and fundamental physiological components of the brain-heart axis remain largely unknown. In this Review, we elucidate these components and identify three primary pathways: neural, mechanical and biochemical. The neural pathway involves the interaction between the autonomic nervous system and the central autonomic network in the brain. The mechanical pathway involves mechanoreceptors, particularly those expressing mechanosensitive Piezo protein channels, which relay crucial information about blood pressure through peripheral and cerebrovascular connections. The biochemical pathway comprises many endogenous compounds that are important mediators of neural and cardiovascular function. This multisystem perspective calls for the development of integrative approaches, leading to new clinical specialties in neurocardiology.

Linking hearts and minds: understanding the cardiovascular impact of bipolar disorder

Bipolar disorder is a severe and recurring condition that has become a significant public health issue globally. Studies indicate a heightened risk and earlier onset of cardiovascular diseases among individuals with bipolar disorder, potentially increasing mortality rates. The chronic nature of bipolar disorder leads to disturbances across multiple systems, including autonomic dysfunction, over-activation of the hypothalamic-pituitary-adrenal axis and increased levels of peripheral inflammatory markers. These disruptions cause endothelial damage, the formation of plaques and blood clots, in addition to the medications used to treat bipolar disorder and genetic associations contributing to cardiovascular disease development. Understanding the complex interplay between bipolar disorder and cardiovascular events is essential for the prevention and effective management of cardiovascular conditions in individuals with bipolar disorder.

Nrf2-Keap1 in Cardiovascular Disease: Which Is the Cart and Which the Horse?

High levels of oxidant stress in the form of reactive oxidant species are prevalent in the circulation and tissues in various types of cardiovascular disease including heart failure, hypertension, peripheral arterial disease, and stroke. Here we review the role of nuclear factor erythroid 2-related factor 2 (Nrf2), an important and widespread antioxidant and anti-inflammatory transcription factor that may contribute to the pathogenesis and maintenance of cardiovascular diseases. We review studies showing that downregulation of Nrf2 exacerbates heart failure, hypertension, and autonomic function. Finally, we discuss the potential for using Nrf2 modulation as a therapeutic strategy for cardiovascular diseases and autonomic dysfunction.

Inhibition of Extracellular Signal-Regulated Kinase Activity Improves Cognitive Function in Mice Subjected to Myocardial Infarction

Cognitive impairment is a commonly observed complication following myocardial infarction; however, the underlying mechanisms are still not well understood. The most recent research suggests that extracellular signal-regulated kinase (ERK) plays a critical role in the development and occurrence of cognitive dysfunction-related diseases. This study aims to explore whether the ERK inhibitor U0126 targets the ERK/Signal Transducer and Activator of Transcription 1 (STAT1) pathway to ameliorate cognitive impairment after myocardial infarction. To establish a mouse model of myocardial infarction, we utilized various techniques including Echocardiography, Hematoxylin-eosin (HE) staining, Elisa, Open field test, Elevated plus maze test, and Western blot analysis to assess mouse cardiac function, cognitive function, and signal transduction pathways. For further investigation into the mechanisms of cognitive function and signal transduction, we administered the ERK inhibitor U0126 via intraperitoneal injection. Reduced total distance and activity range were observed in mice subjected to myocardial infarction during the open field test, along with decreased exploration of the open arms in the elevated plus maze test. However, U0126 treatment exhibited a significant improvement in cognitive decline, indicating a protective effect through the inhibition of the ERK/STAT1 signaling pathway. Hence, this study highlights the involvement of the ERK/STAT1 pathway in regulating cognitive dysfunction following myocardial infarction and establishes U0126 as a promising therapeutic target.

Electroacupuncture pretreatment mediates sympathetic nerves to alleviate myocardial ischemia-reperfusion injury via CRH neurons in the paraventricular nucleus of the hypothalamus

BACKGROUND

Myocardial ischemia-reperfusion can further exacerbate myocardial injury and increase the risk of death. Our previous research found that the paraventricular nucleus (PVN) of the hypothalamus plays a crucial role in the improvement of myocardial ischemia-reperfusion injury (MIRI) by electroacupuncture (EA) pretreatment, but its mechanism of action is still unclear. CRH neurons exhibit periodic concentrated expression in PVN, but further research is needed to determine whether they are involved in the improvement of MIRI by EA pretreatment. Meanwhile, numerous studies have shown that changes in sympathetic nervous system innervation and activity are associated with many heart diseases. This study aims to investigate whether EA pretreatment improves MIRI through sympathetic nervous system mediated by PVNCRH neurons.

METHODS

Integrated use of fiber-optic recording, chemical genetics and other methods to detect relevant indicators: ECG signals were acquired through Powerlab standard II leads, and LabChart 8 calculated heart rate, ST-segment offset, and heart rate variability (HRV); Left ventricular ejection fraction (LVEF), left ventricular short-axis shortening (LVFS), left ventricular end-systolic internal diameter (LVIDs) and interventricular septal thickness (IVSs) were measured by echocardiography; Myocardial infarct area (IA) and area at risk (AAR) were calculated by Evans-TTC staining. Pathological changes in cardiomyocytes were observed by HE staining; Changes in PVNCRH neuronal activity were recorded by fiber-optic photometry; Sympathetic nerve discharges were recorded for in vivo electrophysiology; NE and TH protein expression was assayed by Western blot.

RESULTS

Our data indicated that EA pretreatment can effectively alleviate MIRI. Meanwhile, we found that in the MIRI model, the number and activity of CRH neurons co labeled with c-Fos in the PVN area of the rat brain increased, and the frequency of sympathetic nerve discharge increased. EA pretreatment could reverse this change. In addition, the results of chemical genetics indicated that inhibiting PVNCRH neurons has a similar protective effect on MIRI as EA pretreatment, and the activation of PVNCRH neurons can counteract this protective effect.

CONCLUSION

EA pretreatment can inhibit PVNCRH neurons and improve MIRI by inhibiting sympathetic nerve, which offers fresh perspectives on the application of acupuncture in the management of cardiovascular disease.

Reduced Heartbeat-Evoked Responses in a Near-Death Case Report

BACKGROUND AND PURPOSE

Whether brain-heart communication continues under ventricular fibrillation (VF) remains to be determined. There is weak evidence of physiological changes in cortical activity under VF. Moreover, brain-heart communication has not previously been studied in this condition. We aimed to measure parallel changes in heart-rate variability (HRV), cortical activity, and brain-heart interactions in a patient who experienced VF.

METHODS

The EEG and EKG signals for the case report were acquired for approximately 20 h. We selected different 1-min-long segments based on the changes in the EKG waveform. We present the changes in heartbeat-evoked responses (HERs), HRV, and EEG power for each selected segment.

RESULTS

The overall physiological activity appeared to deteriorate as VF proceeded. Brain-heart interactions measured using HERs disappeared, with a few aberrant amplitudes appearing occasionally. The parallel changes in EEG and HRV were not pronounced, suggesting the absence of bidirectional neural control.

CONCLUSIONS

Our measurements of brain-heart interactions suggested that the evolving VF impairs communication between the central and autonomic nervous systems. These results may support that reduced brain-heart interactions reflect loss of consciousness and deterioration in the overall health state.

Time-varying information measures: an adaptive estimation of information storage with application to brain-heart interactions

Network Physiology is a rapidly growing field of study that aims to understand how physiological systems interact to maintain health. Within the information theory framework the information storage (IS) allows to measure the regularity and predictability of a dynamic process under stationarity assumption. However, this assumption does not allow to track over time the transient pathways occurring in the dynamical activity of a physiological system. To address this limitation, we propose a time-varying approach based on the recursive least squares algorithm (RLS) for estimating IS at each time instant, in non-stationary conditions. We tested this approach in simulated time-varying dynamics and in the analysis of electroencephalographic (EEG) signals recorded from healthy volunteers and timed with the heartbeat to investigate brain-heart interactions. In simulations, we show that the proposed approach allows to track both abrupt and slow changes in the information stored in a physiological system. These changes are reflected in its evolution and variability over time. The analysis of brain-heart interactions reveals marked differences across the cardiac cycle phases of the variability of the time-varying IS. On the other hand, the average IS values exhibit a weak modulation over parieto-occiptal areas of the scalp. Our study highlights the importance of developing more advanced methods for measuring IS that account for non-stationarity in physiological systems. The proposed time-varying approach based on RLS represents a useful tool for identifying spatio-temporal dynamics within the neurocardiac system and can contribute to the understanding of brain-heart interactions.

Large-field-of-view scanning electron microscopy of the paraventricular nucleus of the hypothalamus during diet-induced obesity

Dysregulation in the paraventricular nucleus of the hypothalamus (PVN) is associated with a variety of diseases including those related to obesity. Although most investigations have focused on molecular changes, structural alterations in PVN neurons can reveal underlying functional disruptions. Although electron microscopy (EM) can provide nanometer resolution of brain structures, an inherent limitation of traditional transmission EM is the single field of view nature of data collection. To overcome this, we used large-field-of-view high-resolution backscatter scanning electron microscopy (bSEM) of the PVN. By stitching high-resolution bSEM images, taken from normal chow and high-fat diet mice, we achieved interactive, zoomable maps that allow for low-magnification screening of the entire PVN and high-resolution analyses of ultrastructure at the level of the smallest cellular organelle. Using this approach, quantitative analysis across the PVN revealed marked electron-dense regions within neuronal nucleoplasm following high-fat diet feeding, with an increase in kurtosis, indicative of a shift away from a normal distribution. Furthermore, measures of skewness indicated a shift toward darker clustered electron-dense regions, potentially indicative of heterochromatin clusters. We further demonstrate the utility to map out healthy and altered neurons throughout the PVN and the ability to remotely perform bSEM imaging in situations that require social distancing, such as the COVID-19 pandemic. Collectively, these findings present an approach that allows for the precise placement of PVN cells within an overall structural and functional map of the PVN. Moreover, they suggest that obesity may disrupt PVN neuronal chromatin structure.NEW & NOTEWORTHY Paraventricular nucleus of the hypothalamus (PVN) alterations are linked to obesity-related conditions, but limited knowledge exists about neuroanatomical changes in this region. A large-field-of-view backscatter scanning electron microscopy (bSEM) method was used, which allowed the identification of up to 40 PVN neurons in individual samples. During obesity in mice, bSEM revealed changes in PVN neuronal nucleoplasm, possibly indicating chromatin clustering. This microscopy advancement offers valuable insights into neuroanatomy in both healthy and disease conditions.

Angiotensin II-Mediated Neuroinflammation in the Hippocampus Contributes to Neuronal Deficits and Cognitive Impairment in Heart Failure Rats

BACKGROUND

Heart failure (HF) is a debilitating disease affecting >64 million people worldwide. In addition to impaired cardiovascular performance and associated systemic complications, most patients with HF suffer from depression and substantial cognitive decline. Although neuroinflammation and brain hypoperfusion occur in humans and rodents with HF, the underlying neuronal substrates, mechanisms, and their relative contribution to cognitive deficits in HF remains unknown.

METHODS

To address this critical gap in our knowledge, we used a well-established HF rat model that mimics clinical outcomes observed in the human population, along with a multidisciplinary approach combining behavioral, electrophysiological, neuroanatomical, molecular and systemic physiological approaches.

RESULTS

Our studies support neuroinflammation, hypoperfusion/hypoxia, and neuronal deficits in the hippocampus of HF rats, which correlated with the progression and severity of the disease. An increased expression of AT1aRs (Ang II [angiotensin II] receptor type 1a) in hippocampal microglia preceded the onset of neuroinflammation. Importantly, blockade of AT1Rs with a clinically used therapeutic drug (Losartan), and delivered in a clinically relevant manner, efficiently reversed neuroinflammatory end points (but not hypoxia ones), resulting in turn in improved cognitive performance in HF rats. Finally, we show than circulating Ang II can leak and access the hippocampal parenchyma in HF rats, constituting a possible source of Ang II initiating the neuroinflammatory signaling cascade in HF.

CONCLUSIONS

In this study, we identified a neuronal substrate (hippocampus), a mechanism (Ang II-driven neuroinflammation) and a potential neuroprotective therapeutic target (AT1aRs) for the treatment of cognitive deficits in HF.

Complex Brain-Heart Mapping in Mental and Physical Stress

OBJECTIVE

The central and autonomic nervous systems are deemed complex dynamic systems, wherein each system as a whole shows features that the individual system sub-components do not. They also continuously interact to maintain body homeostasis and appropriate react to endogenous and exogenous stimuli. Such interactions are comprehensively referred to functional brain-heart interplay (BHI). Nevertheless, it remains uncertain whether this interaction also exhibits complex characteristics, that is, whether the dynamics of the entire nervous system inherently demonstrate complex behavior, or if such complexity is solely a trait of the central and autonomic systems. Here, we performed complexity mapping of the BHI dynamics under mental and physical stress conditions.

METHODS AND PROCEDURES

Electroencephalographic and heart rate variability series were obtained from 56 healthy individuals performing mental arithmetic or cold-pressure tasks, and physiological series were properly combined to derive directional BHI series, whose complexity was quantified through fuzzy entropy.

RESULTS

The experimental results showed that BHI complexity is mainly modulated in the efferent functional direction from the brain to the heart, and mainly targets vagal oscillations during mental stress and sympathovagal oscillations during physical stress.

CONCLUSION

We conclude that the complexity of BHI mapping may provide insightful information on the dynamics of both central and autonomic activity, as well as on their continuous interaction.

CLINICAL IMPACT

This research enhances our comprehension of the reciprocal interactions between central and autonomic systems, potentially paving the way for more accurate diagnoses and targeted treatments of cardiovascular, neurological, and psychiatric disorders.

Increased sympathetic outflow induced by emotional stress aggravates myocardial ischemia-reperfusion injury via activation of TLR7/MyD88/IRF5 signaling pathway

BACKGROUND AND OBJECTIVE

Emotional stress substantially increases the risk of ischemic cardiovascular diseases. Previous study indicates that sympathetic outflow is increased under emotional stress. We aim to investigate the role of increased sympathetic outflow induced by emotional stress in myocardial ischemia-reperfusion (I/R) injury, and explore the underlying mechanisms.

METHODS AND RESULTS

We used Designer Receptors Exclusively Activated by Designer Drugs technique to activate the ventromedial hypothalamus (VMH), a critical emotion-related nucleus. The results revealed that emotional stress stimulated by VMH activation increased sympathetic outflow, enhanced blood pressure, aggravated myocardial I/R injury, and exacerbated infarct size. The RNA-seq and molecular detection demonstrated that toll-like receptor 7 (TLR7), myeloid differentiation factor 88 (MyD88), interferon regulatory factor 5 (IRF5), and downstream inflammatory markers in cardiomyocytes were significantly upregulated. Emotional stress-induced sympathetic outflow further exacerbated the disorder of the TLR7/MyD88/IRF5 inflammatory signaling pathway. While inhibition of the signaling pathway partially alleviated myocardial I/R injury aggravated by emotional stress-induced sympathetic outflow.

CONCLUSION

Increased sympathetic outflow induced by emotional stress activates TLR7/MyD88/IRF5 signaling pathway, ultimately aggravating I/R injury.

SARS-CoV-2 and Hypertension: Evidence Supporting Invasion into the Brain Via Baroreflex Circuitry and the Role of Imbalanced Renin-Angiotensin-Aldosterone-System

Hypertension is considered one of the most critical risk factors for COVID-19. Evidence suggests that SARS-CoV-2 infection produces intense effects on the cardiovascular system by weakening the wall of large vessels via vasa-vasorum. In this commentary, we propose that SARS-CoV-2 invades carotid and aortic baroreceptors, leading to infection of the nucleus tractus solitari (NTS) and paraventricular hypothalamic nucleus (PVN), and such dysregulation of NTS and PVN following infection causes blood pressure alteration at the central level. We additionally explored the hypothesis that SARS-CoV-2 favors the internalization of membrane ACE2 receptors generating an imbalance of the renin-angiotensin-aldosterone system (RAAS), increasing the activity of angiotensin II (ANG-II), disintegrin, and metalloproteinase 17 domain (ADAM17/TACE), eventually modulating the integration of afferents reaching the NTS from baroreceptors and promoting increased blood pressure. These mechanisms are related to the increased sympathetic activity, which leads to transient or permanent hypertension associated with SARS-CoV-2 invasion, contributing to the high number of deaths by cardiovascular implications.

Microglia-derived PDGFB promotes neuronal potassium currents to suppress basal sympathetic tonicity and limit hypertension

Although many studies have addressed the regulatory circuits affecting neuronal activities, local non-synaptic mechanisms that determine neuronal excitability remain unclear. Here, we found that microglia prevented overactivation of pre-sympathetic neurons in the hypothalamic paraventricular nucleus (PVN) at steady state. Microglia constitutively released platelet-derived growth factor (PDGF) B, which signaled via PDGFRα on neuronal cells and promoted their expression of Kv4.3, a key subunit that conducts potassium currents. Ablation of microglia, conditional deletion of microglial PDGFB, or suppression of neuronal PDGFRα expression in the PVN elevated the excitability of pre-sympathetic neurons and sympathetic outflow, resulting in a profound autonomic dysfunction. Disruption of the PDGFB^MG-Kv4.3^Neuron pathway predisposed mice to develop hypertension, whereas central supplementation of exogenous PDGFB suppressed pressor response when mice were under hypertensive insult. Our results point to a non-immune action of resident microglia in maintaining the balance of sympathetic outflow, which is important in preventing cardiovascular diseases.

Venoconstrictor responses to activation of bradykinin-sensitive pericardial afferents involve the region of the hypothalamic paraventricular nucleus

Veins are important in the control of venous return, cardiac output, and cardiovascular homeostasis. However, the effector systems modulating venous function remain to be fully elucidated. We demonstrated that activation of bradykinin-sensitive pericardial afferents elicited systemic venoconstriction. The hypothalamic paraventricular nucleus (PVN) is an important site modulating autonomic outflow to the venous compartment. We tested the hypothesis that the PVN region is involved in the venoconstrictor response to pericardial injection of bradykinin. Rats were anesthetized with urethane/alpha chloralose and instrumented for recording arterial pressure, vena caval pressure, and mean circulatory filling pressure (MCFP), an index of venous tone. The rats were fitted with a pericardial catheter and PVN injector guide tubes. Mean arterial pressure (MAP), heart rate (HR), and MCFP responses to pericardial injection of bradykinin (1, 10 µg/kg) were recorded before and after PVN injection of omega conotoxin GVIA (200 ng/200 nl). Pericardial injection of saline produced no systematic effects on MAP, HR, or MCFP. In contrast, pericardial injection of bradykinin was associated with short latency increases in MAP (16 ± 4 to 18 ± 2 mm Hg) and MCFP 0.35 ± 0.19 to 1.01 ± 0.27 mm Hg. Heart rate responses to pericardial BK were highly variable, but HR was significantly increased (15 ± 9 bpm) at the higher BK dose. Conotoxin injection in the PVN region did not affect baseline values for these variables. However, injection of conotoxin into the area of the PVN largely attenuated the pressor (-1 ± 3 to 6 ± 3 mm Hg), MCFP (-0.19 ± 0.07 to 0.20 ± 0.18 mm Hg), and HR (4 ± 14 bpm) responses to pericardial bradykinin injection. We conclude that the PVN region is involved in the venoconstrictor responses to pericardial bradykinin injection.

Distinct Hypothalamic Paraventricular Nucleus Inputs to the Cingulate Cortex and Paraventricular Thalamic Nucleus Modulate Anxiety and Arousal

Insomnia and anxiety are two common clinical diseases that threaten people’s physical and mental health. Insomnia and anxiety may share some similar underlying neural circuit mechanisms in the brain. In this study, we combine techniques including chemo-fMRI, optogenetics, and chemogenetics to reveal that the glutamatergic neurons of the paraventricular hypothalamic nucleus (PVN) regulate both anxiety and arousal through two different downstream neural circuits. Optogenetic activation of the PVN-cingulate cortex (Cg) neural circuit triggers anxiety-like behaviors in mice without affecting the wakefulness, while optogenetic activation of the PVN-paraventricular thalamic nucleus (PVT) neural circuit promotes wakefulness in mice without affecting anxiety-like behaviors. Our research reveals that PVN is a key brain area for controlling anxiety and arousal behaviors. We also provide a neurological explanation for anxiety disorder and insomnia which may offer guidance for treatments including drugs or transcranial magnetic stimulation for the patients.

Cerebral derailment after myocardial infarct: mechanisms and effects of the signaling from the ischemic heart to brain

Myocardial infarction (MI) is the leading cause of death among ischemic heart diseases and is associated with several long-term cardiovascular complications, such as angina, re-infarction, arrhythmias, and heart failure. However, MI is frequently accompanied by non-cardiovascular multiple comorbidities, including brain disorders such as stroke, anxiety, depression, and cognitive impairment. Accumulating experimental and clinical evidence suggests a causal relationship between MI and stroke, but the precise underlying mechanisms have not yet been elucidated. Indeed, the risk of stroke remains a current challenge in patients with MI, in spite of the improvement of medical treatment among this patient population has reduced the risk of stroke. In this review, the effects of the signaling from the ischemic heart to the brain, such as neuroinflammation, neuronal apoptosis, and neurogenesis, and the possible actors mediating these effects, such as systemic inflammation, immunoresponse, extracellular vesicles, and microRNAs, are discussed.

Oral Supplementation With Butyrate Improves Myocardial Ischemia/Reperfusion Injury via a Gut-Brain Neural Circuit

Objective: Butyrate, a short-chain fatty acid (SCFA) produced by the intestinal microbiota, plays a protective role in cardiovascular diseases (CVDs), but the mechanisms involved in this process remain unelucidated. We aimed to explore the effect of butyrate on myocardial ischemia/reperfusion (I/R) injury through the gut-brain neural circuit.

Methods: Rats were randomly divided into four groups: sham group (sham), I/R group (I/R), I/R+ butyrate group (butyrate), and I/R+ butyrate+ vagotomy group (vagotomy). The rats were treated with sodium butyrate for 4 weeks, and the gut-brain neural circuit was investigated by subdiaphragmatic vagotomy.

Results: Butyrate treatment significantly reduced the infarct size and decreased the expression of creatine kinase (CK), creatine kinase myocardial isoenzyme (CK-MB), and lactate dehydrogenase (LDH) compared with the values found for the I/R group. In addition, the I/R-induced increases in inflammation, oxidative stress, and apoptosis were attenuated by butyrate. However, the above-mentioned protective effects were diminished by subdiaphragmatic vagotomy. The RNA sequencing results also revealed that the butyrate-induced protective changes at the cardiac transcription level were reversed by vagotomy. An analysis of the heart rate variability (HRV) and the detection of norepinephrine (NE) showed that butyrate significantly inhibited the I/R-induced autonomic imbalance, but this inhibition was not observed in the vagotomy group. Butyrate treatment also suppressed the neural activity of the paraventricular nucleus (PVN) and superior cervical ganglion (SCG), and both of these effects were lost after vagotomy.

Conclusions: Butyrate treatment significantly improves myocardial I/R injury via a gut-brain neural circuit, and this cardioprotective effect is likely mediated by suppression of the sympathetic nervous system.

The role of electroencephalography electrical reference in the assessment of functional brain-heart interplay: From methodology to user guidelines

BACKGROUND

The choice of EEG reference has been widely studied. However, the choice of the most appropriate re-referencing for EEG data is still debated. Moreover, the role of EEG reference in the estimation of functional Brain-Heart Interplay (BHI), together with different multivariate modelling strategies, has not been investigated yet.

METHODS

This study identifies the best methodology combining a proper EEG electrical reference and signal processing methods for an effective functional BHI assessment. The effects of the EEG reference among common average, mastoids average, Laplacian reference, Cz reference, and the reference electrode standardization technique (REST) were explored throughout different BHI methods including synthetic data generation (SDG) model, heartbeat-evoked potentials, heartbeat-evoked oscillations, and maximal information coefficient.

RESULTS

The SDG model exhibited high robustness between EEG references, whereas the maximal information coefficient method exhibited a high sensitivity. The common average and REST references for EEG showed a good consistency in the between-method comparisons. Laplacian, and Cz references significantly bias a BHI measurement.

COMPARISON WITH EXISTING METHODS

The use of EEG reference based on a common average outperforms on the use of other references for consistency in estimating directed functional BHI. We do not recommend the use of EEG references based on analytical derivations as the experimental conditions may not meet the requirements of their optimal estimation, particularly in clinical settings.

CONCLUSION

The use of a common average for EEG electrical reference is concluded to be the most appropriate choice for a quantitative, functional BHI assessment.

Paraventricular Nucleus P2X7 Receptors Aggravate Acute Myocardial Infarction Injury via ROS-Induced Vasopressin-V1b Activation in Rats

The present study was designed to investigate the mechanisms by which P2X7 receptors (P2X7Rs) mediate the activation of vasopressinergic neurons thereby increasing sympathetic hyperactivity in the paraventricular nucleus (PVN) of the hypothalamus of rats with acute myocardial ischemia (AMI). The left anterior descending branch of the coronary artery was ligated to induce AMI in rats. The rats were pretreated with BBG (brilliant blue G, a P2X7R antagonist), nelivaptan (a vasopressin V1b receptor antagonist), or diphenyleneiodonium (DPI) [an nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor]. Hemodynamic parameters of the heart were monitored. Myocardial injury and cardiomyocyte apoptosis were assessed. In the PVN of AMI rats, P2X7R mediated microglial activation, while reactive oxygen species (ROS) and NADPH oxidase 2 (NOX2) were higher than in the sham group. Intraperitoneal injection of BBG effectively reduced ROS production and vasopressin expression in the PVN of AMI rats. Moreover, both BBG and DPI pretreatment effectively reduced sympathetic hyperactivity and ameliorated AMI injury, as represented by reduced inflammation and apoptosis of cardiomyocytes. Furthermore, microinjection of nelivaptan into the PVN improved cardiac function and reduced the norepinephrine (AE) levels in AMI rats. Collectively, the results suggest that, within the PVN of AMI rats, P2X7R upregulation mediates microglial activation and the overproduction of ROS, which in turn activates vasopressinergic neuron-V1b receptors and sympathetic hyperactivity, hence aggravating myocardial injury in the AMI setting.

Organization of the neuroendocrine and autonomic hypothalamic paraventricular nucleus

A major function of the nervous system is to maintain a relatively constant internal environment. The distinction between our external environment (i.e., the environment that we live in and that is subject to major changes, such as temperature, humidity, and food availability) and our internal environment (i.e., the environment formed by the fluids surrounding our bodily tissues and that has a very stable composition) was pointed out in 1878 by Claude Bernard (1814-1878). Later on, it was indicated by Walter Cannon (1871-1945) that the internal environment is not really constant, but rather shows limited variability. Cannon named the mechanism maintaining this limited variability homeostasis. Claude Bernard envisioned that, for optimal health, all physiologic processes in the body needed to maintain homeostasis and should be in perfect harmony with each other. This is illustrated by the fact that, for instance, during the sleep-wake cycle important elements of our physiology such as body temperature, circulating glucose, and cortisol levels show important variations but are in perfect synchrony with each other. These variations are driven by the biologic clock in interaction with hypothalamic target areas, among which is the paraventricular nucleus of the hypothalamus (PVN), a core brain structure that controls the neuroendocrine and autonomic nervous systems and thus is key for integrating central and peripheral information and implementing homeostasis. This chapter focuses on the anatomic connections between the biologic clock and the PVN to modulate homeostasis according to the daily sleep-wake rhythm. Experimental studies have revealed a highly specialized organization of the connections between the clock neurons and neuroendocrine system as well as preautonomic neurons in the PVN. These complex connections ensure a logical coordination between behavioral, endocrine, and metabolic functions that helps the organism maintain homeostasis throughout the day.

The hypothalamus and its role in hypertension

For the majority of hypertensive patients, the etiology of their disease is unknown. The hypothalamus is a central structure of the brain which provides an adaptive, integrative, autonomic, and neuroendocrine response to any fluctuations in physiological conditions of the external or internal environment. Hypothalamic insufficiency leads to severe metabolic and functional disorders, including persistent increase in blood pressure. Here, we discuss alterations in the neurochemical organization of the paraventricular and suprachiasmatic nucleus in the hypothalamus of patients who suffered from essential hypertension and died suddenly due to acute coronary failure. The changes observed are hypothesized to contribute to the pathogenesis of disease.

Role of α2-Adrenoceptors in Hypertension: Focus on Renal Sympathetic Neurotransmitter Release, Inflammation, and Sodium Homeostasis

The kidney is extensively innervated by sympathetic nerves playing an important role in the regulation of blood pressure homeostasis. Sympathetic nerve activity is ultimately controlled by the central nervous system (CNS). Norepinephrine, the main sympathetic neurotransmitter, is released at prejunctional neuroeffector junctions in the kidney and modulates renin release, renal vascular resistance, sodium and water handling, and immune cell response. Under physiological conditions, renal sympathetic nerve activity (RSNA) is modulated by peripheral mechanisms such as the renorenal reflex, a complex interaction between efferent sympathetic nerves, central mechanism, and afferent sensory nerves. RSNA is increased in hypertension and, therefore, critical for the perpetuation of hypertension and the development of hypertensive kidney disease. Renal sympathetic neurotransmission is not only regulated by RSNA but also by prejunctional α2-adrenoceptors. Prejunctional α2-adrenoceptors serve as autoreceptors which, when activated by norepinephrine, inhibit the subsequent release of norepinephrine induced by a sympathetic nerve impulse. Deletion of α2-adrenoceptors aggravates hypertension ultimately by modulating renal pressor response and sodium handling. α2-adrenoceptors are also expressed in the vasculature, renal tubules, and immune cells and exert thereby effects related to vascular tone, sodium excretion, and inflammation. In the present review, we highlight the role of α2-adrenoceptors on renal sympathetic neurotransmission and its impact on hypertension. Moreover, we focus on physiological and pathophysiological functions mediated by non-adrenergic α2-adrenoceptors. In detail, we discuss the effects of sympathetic norepinephrine release and α2-adrenoceptor activation on renal sodium transporters, on renal vascular tone, and on immune cells in the context of hypertension and kidney disease.

An Inhomogeneous Point-process Model for the Assessment of the Brain-to-Heart Functional Interplay: a Pilot Study

We propose a novel computational framework for the estimation of functional directional brain-to-heart interplay in an instantaneous fashion. The framework is based on inhomogeneous point-process models for human heartbeat dynamics and employs inverse-Gaussian probability density functions characterizing the timing of R-peak events. The instantaneous estimation of the functional directional coupling is based on the definition of point-process transfer entropy, which is here retrieved from heart rate variability (HRV) and Electroencephalography (EEG) power spectral series gathered from 12 healthy subjects undergoing significant sympathovagal changes induced by a cold-pressor test. Results suggest that EEG oscillations dynamically influence heartbeat dynamics with specific time delays in the 30-60s and 90-120s ranges, and through a functional activity over specific cortical regions.

An Injectable Microparticle Formulation Provides Long-Term Inhibition of Hypothalamic ERK1/2 Activity and Sympathetic Excitation in Rats with Heart Failure

Sympathetic excitation contributes to clinical deterioration in systolic heart failure (HF). Significant inhibition of hypothalamic paraventricular nucleus (PVN) ERK1/2 signaling and a subsequent reduction of plasma norepinephrine (NE) levels in HF rats were achieved 2 weeks after a single subcutaneous injection of PD98059-loaded polymeric microparticles, without apparent adverse events, while blank microparticles had no effect. Similar reductions in plasma NE, a general indicator of sympathetic excitation, were previously achieved in HF rats by intracerebroventricular infusion of PD98059 or genetic knockdown of PVN ERK1/2 expression. This study presents a clinically feasible therapeutic approach to the central abnormalities contributing to HF progression.

Myocardial infarction-induced anxiety-like behavior is associated with epigenetic alterations in the hippocampus of rat

Epidemiological and experimental animal studies indicate that there is a high risk for the incidence of neuropsychiatric disorders suffering from cardiovascular diseases such as myocardial infarction (MI). However, the potential mechanism of this association remains largely unknown. This study sought to evaluate whether epigenetic alterations in the hippocampus is associated with MI-induced anxiety-like behavior in rats. MI was induced by occlusion of the left anterior descending artery in adult female rats. Anxiety-like behavior was examined by elevated plus maze, light-dark box, and open field test. Relative gene and protein levels expression in the hippocampus were tested by qRT-PCR and western blotting, respectively. We found that MI rats exhibited anxiety-like behavior compared with those in controls, and there is a positive correlation between MI and anxiety-like behavior. We also found that MI decreased KDM6B while increased SIRT1 expression in the hippocampus of MI rats relative to those in controls. In addition, MI not only increased levels of IL-1β, bax, and cleaved-caspase 3, but also increased Iba-1 and GFAP expression in the hippocampus, as compared to those in controls, suggesting a promotion of neuro-inflammation and apoptosis in hippocampus. Co-immunoprecipitation assay illustrated that H3K27me3 functioned by counteracting with YAP activation in the hippocampus of MI rats relative to those in controls. Together, these results suggest a potential role of hippocampal epigenetic signaling in MI-induced anxiety-like behavior in rats, and pharmacological targeting KDM6B or SIRT1 could be a strategy to ameliorate anxiety-like behavior induced by MI.

Three-dimensional morphometric analysis reveals time-dependent structural changes in microglia and astrocytes in the central amygdala and hypothalamic paraventricular nucleus of heart failure rats

BACKGROUND

Cardiovascular diseases, including heart failure, are the most common cause of death globally. Recent studies support a high degree of comorbidity between heart failure and cognitive and mood disorders resulting in memory loss, depression, and anxiety. While neuroinflammation in the hypothalamic paraventricular nucleus contributes to autonomic and cardiovascular dysregulation in heart failure, mechanisms underlying cognitive and mood disorders in this disease remain elusive. The goal of this study was to quantitatively assess markers of neuroinflammation (glial morphology, cytokines, and A1 astrocyte markers) in the central amygdala, a critical forebrain region involved in emotion and cognition, and to determine its time course and correlation to disease severity during the progression of heart failure.

METHODS

We developed and implemented a comprehensive microglial/astrocyte profiler for precise three-dimensional morphometric analysis of individual microglia and astrocytes in specific brain nuclei at different time points during the progression of heart failure. To this end, we used a well-established ischemic heart failure rat model. Morphometric studies were complemented with quantification of various pro-inflammatory cytokines and A1/A2 astrocyte markers via qPCR.

RESULTS

We report structural remodeling of central amygdala microglia and astrocytes during heart failure that affected cell volume, surface area, filament length, and glial branches, resulting overall in somatic swelling and deramification, indicative of a change in glial state. These changes occurred in a time-dependent manner, correlated with the severity of heart failure, and were delayed compared to changes in the hypothalamic paraventricular nucleus. Morphometric changes correlated with elevated mRNA levels of pro-inflammatory cytokines and markers of reactive A1-type astrocytes in the paraventricular nucleus and central amygdala during heart failure.

CONCLUSION

We provide evidence that in addition to the previously described hypothalamic neuroinflammation implicated in sympathohumoral activation during heart failure, microglia, and astrocytes within the central amygdala also undergo structural remodeling indicative of glial shifts towards pro-inflammatory phenotypes. Thus, our studies suggest that neuroinflammation in the amygdala stands as a novel pathophysiological mechanism and potential therapeutic target that could be associated with emotional and cognitive deficits commonly observed at later stages during the course of heart failure.

Angiotensin Type 1 Receptors and Superoxide Anion Production in Hypothalamic Paraventricular Nucleus Contribute to Capsaicin-Induced Excitatory Renal Reflex and Sympathetic Activation

Chemical stimulation of the kidney increases sympathetic activity and blood pressure in rats. The hypothalamic paraventricular nucleus (PVN) is important in mediating the excitatory renal reflex (ERR). In this study, we examined the role of molecular signaling in the PVN in mediating the capsaicin-induced ERR and sympathetic activation. Bilateral PVN microinjections were performed in rats under anesthesia. The ERR was elicited by infusion of capsaicin into the cortico-medullary border of the right kidney. The reflex was evaluated as the capsaicin-induced changes in left renal sympathetic nerve activity and mean arterial pressure. Blockade of angiotensin type 1 receptors with losartan or inhibition of angiotensin-converting enzyme with captopril in the PVN abolished the capsaicin-induced ERR. Renal infusion of capsaicin significantly increased NAD(P)H oxidase activity and superoxide anion production in the PVN, which were prevented by ipsilateral renal denervation or microinjection of losartan into the PVN. Furthermore, either scavenging of superoxide anions or inhibition of NAD(P)H oxidase in the PVN abolished the capsaicin-induced ERR. We conclude that the ERR induced by renal infusion of capsaicin is mediated by angiotensin type 1 receptor-related NAD(P)H oxidase activation and superoxide anion production within the PVN.

Neuroinflammation in heart failure: new insights for an old disease

Heart failure (HF) is a complex clinical syndrome affecting roughly 26 million people worldwide. Increased sympathetic drive is a hallmark of HF and is associated with disease progression and higher mortality risk. Several mechanisms contribute to enhanced sympathetic activity in HF, but these pathways are still incompletely understood. Previous work suggests that inflammation and activation of the renin-angiotensin system (RAS) increases sympathetic drive. Importantly, chronic inflammation in several brain regions is commonly observed in aged populations, and a growing body of evidence suggests neuroinflammation plays a crucial role in HF. In animal models of HF, central inhibition of RAS and pro-inflammatory cytokines normalizes sympathetic drive and improves cardiac function. The precise molecular and cellular mechanisms that lead to neuroinflammation and its effect on HF progression remain undetermined. This review summarizes the most recent advances in the field of neuroinflammation and autonomic control in HF. In addition, it focuses on cellular and molecular mediators of neuroinflammation in HF and in particular on brain regions involved in sympathetic control. Finally, we will comment on what is known about neuroinflammation in the context of preserved vs. reduced ejection fraction HF.

Sensory signals mediating high blood pressure via sympathetic activation: role of adipose afferent reflex

Blood pressure regulation in health and disease involves a balance between afferent and efferent signals from multiple organs and tissues. Although there are numerous reviews focused on the role of sympathetic nerves in different models of hypertension, few have revised the contribution of afferent nerves innervating adipose tissue and their role in the development of obesity-induced hypertension. Both clinical and basic research support the beneficial effects of bilateral renal denervation in lowering blood pressure. However, recent studies revealed that afferent signals from adipose tissue, in an adipose-brain-peripheral pathway, could contribute to the increased sympathetic activation and blood pressure during obesity. This review focuses on the role of adipose tissue afferent reflexes and briefly describes a number of other afferent reflexes modulating blood pressure. A comprehensive understanding of how multiple afferent reflexes contribute to the pathophysiology of essential and/or obesity-induced hypertension may provide significant insights into improving antihypertensive therapeutic approaches.

Contribution of DNA methylation in chronic stress-induced cardiac remodeling and arrhythmias in mice

It is recognized that stress can induce cardiac dysfunction, but the underlying mechanisms are not well understood. The present study aimed to test the hypothesis that chronic negative stress leads to alterations in DNA methylation of certain cardiac genes, which in turn contribute to pathologic remodeling of the heart. We found that mice that were exposed to chronic restraint stress (CRS) for 4 wk exhibited cardiac remodeling toward heart failure, as characterized by ventricular chamber dilatation, wall thinning, and decreased contractility. CRS also induced cardiac arrhythmias, including intermittent sinus tachycardia and bradycardia, frequent premature ventricular contraction, and sporadic atrioventricular conduction block. Circulating levels of stress hormones were elevated, and the cardiac expression of tyrosine hydroxylase, a marker of sympathetic innervation, was increased in CRS mice. Using reduced representation bisulfite sequencing, we found that although CRS did not lead to global changes in DNA methylation in the murine heart, it nevertheless altered methylation at specific genes that are associated with the dilated cardiomyopathy (DCM) (e.g., desmin) and adrenergic signaling of cardiomyocytes (ASPC) (e.g., adrenergic receptor-α1) pathways. We conclude that CRS induces cardiac remodeling and arrhythmias, potentially through altered methylation of myocardial genes associated with the DCM and ASPC pathways.-Zhang, P., Li, T., Liu, Y.-Q., Zhang, H., Xue, S.-M., Li, G., Cheng, H.-Y.M., Cao, J.-M. Contribution of DNA methylation in chronic stress-induced cardiac remodeling and arrhythmias in mice.

Intrathecal Administration of Losartan Reduces Directly Recorded Cardiac Sympathetic Nerve Activity in Ovine Heart Failure

Early and preferential activation of cardiac sympathetic nerve activity (CSNA) is one of the strongest prognostic markers of heart failure (HF) in patients. Our previous studies have implicated central angiotensin mechanisms as playing a critical role in generating this increase in cardiac sympathetic drive. However, it is unclear if inhibition of AT₁R (angiotensin type-1 receptors) in different neural groups in the sympathetic pathway to the heart, such as the sympathetic preganglionic neurons in the intermediolateral column of the spinal cord, can reduce cardiac sympathetic drive. We hypothesized that in HF, localized intrathecal administration of the AT₁R antagonist losartan, specifically into the T1-2 subarachnoid space, would decrease CSNA. In normal conscious sheep, intrathecal infusion of Ang II (angiotensin II; 3.0 nmol/mL per hour), significantly increased mean arterial pressure and CSNA; this effect was abolished by prior administration of losartan (1 mg/h). In an ovine rapid ventricular pacing model of HF, the resting levels of heart rate and CSNA were significantly elevated compared with normals. Intrathecal infusion of losartan (1 mg/h) in HF significantly reduced CSNA and heart rate but did not change arterial pressure. The AT₁R binding density in the spinal cord was also elevated in the HF group. Our data suggest that AT₁Rs within the spinal cord are responsible, in part, for the increased CSNA in HF and may represent a target for the selective reduction of CSNA in HF.

Gut microbe-derived metabolite trimethylamine N-oxide activates the cardiac autonomic nervous system and facilitates ischemia-induced ventricular arrhythmia via two different pathways

BACKGROUND

We previously demonstrated the gut microbes-derived metabolite trimethylamine N-oxide (TMAO) could activate the atrial autonomic ganglion plexus and promote atrial arrhythmia. The cardiac sympathetic nervous system (CSNS) play important roles in modulating ventricular arrhythmia (VA).

METHODS

Part 1: To test whether TMAO can directly activate the CSNS, we performed local injection of TMAO into the left stellate ganglion (LSG). Part 2: To test whether TMAO can indirectly activate the CSNS through the central nervous system, we performed intravenous injection of TMAO. Ventricular electrophysiology and LSG function and neural activity were measured before and after TMAO administration. Then, the left anterior descending coronary artery was ligated, and electrocardiograms were recorded for 1 h. At the end of the experiment, LSG and paraventricular nucleus (PVN) tissues were excised for molecular analyses.

FINDINGS

Compared with the control, both intravenous and local TMAO administration significantly increased LSG function and activity, shortened effective refractory period, and aggravated ischemia-induced VA. Proinflammatory markers and c-fos in the LSG were also significantly upregulated in both TMAO-treated groups. Particularly, c-fos expression in PVN was significantly increased in the systemic TMAO administration group but not the local TMAO administration group.

INTERPRETATION

The gut microbe-derived metabolite TMAO can activate the CSNS and aggravate ischemia-induced VA via the direct pathway through the LSG and the indirect pathway through central autonomic activation. FUND: This work was supported by the National Key R&D Program of China [2017YFC1307800], and the National Natural Science Foundation of China [81530011, 81770364, 81570463, 81871486, 81600395, 81600367 and 81700444].

GABAB receptors in the hypothalamic paraventricular nucleus mediate β-adrenoceptor-induced elevations of plasma noradrenaline in rats

In the brain, various neurotransmitters such as noradrenaline and GABA regulate peripheral sympathetic functions. Previously, it has been reported that both β-adrenoceptor activation and GABA_B receptor activation in the brain are involved in the elevation of plasma noradrenaline levels. However, it is unknown whether these pathways interact with each other. In the present study, we examined the relationship between the central actions of β-adrenoceptor activation and GABA_B receptor activation with regard to plasma noradrenaline responses using urethane-anesthetized rats. Intracerebroventricular pretreatment with the GABA_A receptor antagonist bicuculline did not affect the β-adrenoceptor agonist isoproterenol-induced elevation of plasma noradrenaline levels. In contrast, pretreatment with the GABA_B receptor antagonist CGP 35348 suppressed the isoproterenol-induced elevation of noradrenaline levels. Intracerebroventricular pretreatment with the β-adrenoceptor antagonist propranolol did not alter the GABA_B receptor agonist baclofen-induced elevation of plasma noradrenaline levels. We next examined the central effects of β-adrenoceptor activation on GABA release in the paraventricular hypothalamic nucleus (PVN), the major integrative center for sympathetic regulation in the brain. Intracerebroventricular administration of isoproterenol increased GABA content in PVN dialysates. In addition, baclofen microinjected unilaterally into the PVN resulted in elevated plasma levels of noradrenaline, but not adrenaline. Finally, unilateral blockade of GABA_B receptors in the PVN suppressed the isoproterenol-induced elevation of plasma noradrenaline level. Our results suggest that activation of β-adrenoceptors in the brain, likely in the PVN, induces GABA release in the PVN, which in turn activates GABA_B receptors in the PVN, leading to elevated plasma noradrenaline.

Exposure to antenatal corticosteroids and reduced respiratory sinus arrhythmia in adult survivors of extremely low birth weight

Purpose/aim: Antenatal corticosteroid (ACS) therapy has dramatically increased survival rates among extremely low birth weight (ELBW) infants. However, the long-term effects of ACS on autonomic nervous system function have not been explored. Using the world's oldest longitudinally followed cohort of ELBW infants we compared respiratory sinus arrhythmia (RSA) among ELBW survivors whose mothers received ACS (ELBW-S), those who did not (ELBW-NS) and normal birth weight (NBW) controls in their 20 and 30 s. Methods: Resting electrocardiogram (ECG) was recorded from ELBW-S (n = 28), ELBW-NS (n = 36), and matched NBW controls (n = 79) at 22-26 and 29-36 years. Resting RSA was compared across groups via analyses of covariance (ANCOVA), adjusting for sex, medication use, postnatal steroid exposure and the presence of chronic health conditions. RSA was also compared across assessments for each group. Results: At 29-36 years, resting RSA in ELBW-S was significantly lower than in NBW controls. RSA in the ELBW-NS group was intermediate between ELBW-S and NBW groups. Although the ELBW-S group also showed nominally reduced RSA compared to NBW controls at the 22-26-year visit, this difference was not statistically significant. Conclusions: ELBW survivors exposed to ACS had lower RSA than NBW controls during their 30 s, suggestive of a decline in parasympathetic input to heart. ELBW survivors who received ACS may be particularly vulnerable to cardiovascular problems in later life.

A neuro-inflammatory model can explain the onset, symptoms and flare-ups of myalgic encephalomyelitis/chronic fatigue syndrome

Abstract A neuro-inflammatory model is proposed to explain the onset, symptoms and perpetuation of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) via characteristic flare-ups (relapses). In this article, I explore the proposition that a range of triggers (intense physiological stressors such as severe viral infections, chemical toxin exposure or emotional trauma) in ME/CFS-predisposed people causes disruption in the neural circuitry of the hypothalamus (paraventricular nucleus), which induces a neuro-inflammatory reaction in the brain and central nervous system of ME/CFS patients, via over-active innate immune (glial) cells. Resulting dysfunction of the limbic system, the hypothalamus and consequently of the autonomic nervous system can then account for the diverse range of ME/CFS symptoms. Ongoing stressors feed into a compromised (inflamed) hypothalamus and if a certain (but variable) threshold is exceeded, a flare-up will ensue, inducing further ongoing neuro-inflammation in the central nervous system, thus perpetuating the disease indefinitely.

Functional Organization of the Sympathetic Pathways Controlling the Pupil: Light-Inhibited and Light-Stimulated Pathways

Pupil dilation is mediated by a sympathetic output acting in opposition to parasympathetically mediated pupil constriction. While light stimulates the parasympathetic output, giving rise to the light reflex, it can both inhibit and stimulate the sympathetic output. Light-inhibited sympathetic pathways originate in retina-receptive neurones of the pretectum and the suprachiasmatic nucleus (SCN): by attenuating sympathetic activity, they allow unimpeded operation of the light reflex. Light stimulates the noradrenergic and serotonergic pathways. The hub of the noradrenergic pathway is the locus coeruleus (LC) containing both excitatory sympathetic premotor neurones (SympPN) projecting to preganglionic neurones in the spinal cord, and inhibitory parasympathetic premotor neurones (ParaPN) projecting to preganglionic neurones in the Edinger-Westphal nucleus (EWN). SympPN receive inputs from the SCN via the dorsomedial hypothalamus, orexinergic neurones of the latero-posterior hypothalamus, wake- and sleep-promoting neurones of the hypothalamus and brain stem, nociceptive collaterals of the spinothalamic tract, whereas ParaPN receive inputs from the amygdala, sleep/arousal network, nociceptive spinothalamic collaterals. The activity of LC neurones is regulated by inhibitory α₂-adrenoceptors. There is a species difference in the function of the preautonomic LC. In diurnal animals, the α₂-adrenoceptor agonist clonidine stimulates mainly autoreceptors on SymPN, causing miosis, whereas in nocturnal animals it stimulates postsynaptic α₂-arenoceptors in the EWN, causing mydriasis. Noxious stimulation activates SympPN in diurnal animals and ParaPN in nocturnal animals, leading to pupil dilation via sympathoexcitation and parasympathetic inhibition, respectively. These differences may be attributed to increased activity of excitatory LC neurones due to stimulation by light in diurnal animals. This may also underlie the wake-promoting effect of light in diurnal animals, in contrast to its sleep-promoting effect in nocturnal species. The hub of the serotonergic pathway is the dorsal raphe nucleus that is light-sensitive, both directly and indirectly (via an orexinergic input). The light-stimulated pathways mediate a latent mydriatic effect of light on the pupil that can be unmasked by drugs that either inhibit or stimulate SympPN in these pathways. The noradrenergic pathway has widespread connections to neural networks controlling a variety of functions, such as sleep/arousal, pain, and fear/anxiety. Many physiological and psychological variables modulate pupil function via this pathway.

Regulation of sympathetic vasomotor activity by the hypothalamic paraventricular nucleus in normotensive and hypertensive states

The hypothalamic paraventricular nucleus (PVN) is a unique and important brain region involved in the control of cardiovascular, neuroendocrine, and other physiological functions pertinent to homeostasis. The PVN is a major source of excitatory drive to the spinal sympathetic outflow via both direct and indirect projections. In this review, we discuss the role of the PVN in the regulation of sympathetic output in normal physiological conditions and in hypertension. In normal healthy animals, the PVN presympathetic neurons do not appear to have a major role in sustaining resting sympathetic vasomotor activity or in regulating sympathetic responses to short-term homeostatic challenges such as acute hypotension or hypoxia. Their role is, however, much more significant during longer-term challenges, such as sustained water deprivation, chronic intermittent hypoxia, and pregnancy. The PVN also appears to have a major role in generating the increased sympathetic vasomotor activity that is characteristic of multiple forms of hypertension. Recent studies in the spontaneously hypertensive rat model have shown that impaired inhibitory and enhanced excitatory synaptic inputs to PVN presympathetic neurons are the basis for the heightened sympathetic outflow in hypertension. We discuss the molecular mechanisms underlying the presynaptic and postsynaptic alterations in GABAergic and glutamatergic inputs to PVN presympathetic neurons in hypertension. In addition, we discuss the ability of exercise training to correct sympathetic hyperactivity by restoring blood-brain barrier integrity, reducing angiotensin II availability, and decreasing oxidative stress and inflammation in the PVN.

Sex differences in depression-like behavior and neuroinflammation in rats post-MI: role of estrogens

Patients with heart failure (HF) have a high prevalence of depression associated with a worse prognosis, particularly in older women. The present study evaluated whether sex and estrogens affect depression-like behavior and associated neuroinflammation induced by myocardial infarction (MI) in rats. MI was induced by occlusion of the left anterior descending artery in young adult male and female Wistar rats or in ovariectomized (OVX) female rats without and with estrogen [17β-estradiol (E₂)] replacement. MI groups showed a comparable degree of cardiac dysfunction. Eight weeks post-MI, male rats with HF exhibited depression-like behaviors, including anhedonia and higher immobility in the sucrose preference and forced swim tests, which were not observed in female rats with HF. In the cued fear conditioning test, male but not female rats with HF froze more than sham rats. After OVX, female sham rats developed mild depression-like behaviors that were pronounced in OVX female rats post-MI and were largely prevented by E₂ replacement. Cytokine levels in the plasma and paraventricular nucleus increased in both sexes with HF, but only male rats with HF showed an increase in cytokine levels in the prefrontal cortex. OVX alone did not affect cytokine levels, but OVX-MI caused significant increases in the prefrontal cortex, which were shifted to an anti-inflammatory pattern by E₂ replacement. These results suggest that estrogens prevent depression-like behavior induced by HF post-MI in young adult female rats by inhibiting proinflammatory cytokine production and actions in the prefrontal cortex. NEW & NOTEWORTHY In contrast to male rats, female rats with heart failure after myocardial infarction do not develop depression-like behavior or increases in prefrontal cortex cytokines. However, after ovariectomy, female rats exhibit similar changes, which are prevented by 17β-estradiol replacement. Neuroinflammation in the prefrontal cortex in male subjects may contribute to depression-like behavior, whereas its estrogen-dependent absence in female subjects may protect against depression.

Ion Channels in the Paraventricular Hypothalamic Nucleus (PVN); Emerging Diversity and Functional Roles

The paraventricular nucleus of the hypothalamus (PVN) is critical for the regulation of homeostatic function. Although also important for endocrine regulation, it has been referred to as the "autonomic master controller." The emerging consensus is that the PVN is a multifunctional nucleus, with autonomic roles including (but not limited to) coordination of cardiovascular, thermoregulatory, metabolic, circadian and stress responses. However, the cellular mechanisms underlying these multifunctional roles remain poorly understood. Neurones from the PVN project to and can alter the function of sympathetic control regions in the medulla and spinal cord. Dysfunction of sympathetic pre-autonomic neurones (typically hyperactivity) is linked to several diseases including hypertension and heart failure and targeting this region with specific pharmacological or biological agents is a promising area of medical research. However, to facilitate future medical exploitation of the PVN, more detailed models of its neuronal control are required; populated by a greater compliment of constituent ion channels. Whilst the cytoarchitecture, projections and neurotransmitters present in the PVN are reasonably well documented, there have been fewer studies on the expression and interplay of ion channels. In this review we bring together an up to date analysis of PVN ion channel studies and discuss how these channels may interact to control, in particular, the activity of the sympathetic system.

Hypothalamic paraventricular nucleus neuronal nitric oxide synthase activity is a major determinant of renal sympathetic discharge in conscious Wistar rats

NEW FINDINGS

What is the central question of this study? Does chronic reduction of neuronally generated nitric oxide in the hypothalamic paraventricular nucleus affect the set-point regulation of blood pressure and sympathetic activity destined to the kidneys? What is the main finding and its importance? Within the hypothalamic paraventricular nucleus, nitric oxide generated by neuronal nitric oxide synthase plays a major constitutive role in suppressing long term the levels of both ongoing renal sympathetic activity and arterial pressure in conscious Wistar rats. This finding unequivocally demonstrates a mechanism by which the diencephalon exerts a tonic influence on sympathetic discharge to the kidney and may provide the basis for both blood volume and osmolality homeostasis.

ABSTRACT

The paraventricular nucleus (PVN) of the hypothalamus plays a crucial role in cardiovascular and neuroendocrine regulation. Application of nitric oxide donors to the PVN stimulates GABAergic transmission, and may suppress sympathetic nerve activity (SNA) to lower arterial pressure. However, the role of endogenous nitric oxide within the PVN in regulating renal SNA chronically remains to be established in conscious animals. To address this, we used our previously established lentiviral vectors to knock down neuronal nitric oxide synthase (nNOS) selectively in the PVN of conscious Wistar rats. Blood pressure and renal SNA were monitored simultaneously and continuously for 21 days (n = 14) using radio-telemetry. Renal SNA was normalized to maximal evoked discharge and expressed as a percentage change from baseline. The PVN was microinjected bilaterally with a neurone-specific tetracycline-controllable lentiviral vector, expressing a short hairpin miRNA30 interference system targeting nNOS (n = 7) or expressing a mis-sense as control (n = 7). Recordings continued for a further 18 days. The vectors also expressed green fluorescent protein, and successful expression in the PVN and nNOS knockdown were confirmed histologically post hoc. Knockdown of nNOS expression in the PVN resulted in a sustained increase in blood pressure (from 95 ± 2 to 104 ± 3 mmHg, P < 0.05), with robust concurrent sustained activation of renal SNA (>70%, P < 0.05). The study reveals a major role for nNOS-derived nitric oxide within the PVN in chronic set-point regulation of cardiovascular autonomic activity in the conscious, normotensive rat.

Exercise training to reduce sympathetic nerve activity in heart failure patients. A systematic review and meta-analysis

OBJECTIVE

To determine the effects of exercise training on sympathetic nerve activity in heart failure patients.

METHODS

A systematic review was performed. An electronic search of MEDLINE, ProQuest, SciELO, SPORTDiscus, Rehabilitation and Sport Medicine Source, Cumulative Index to Nursing and Allied Health Literature, Tripdatabase, Science Direct and PEDrO was performed from their inception to February 2017. Clinical trials and quasi-experimental studies were considered for primary article selection. The studies should include patients diagnosed with chronic heart failure that performed exercise training for at least 4 weeks. Sympathetic nerve activity should be measured by microneurography before and after the intervention. The Cochrane Collaboration's Risk of Bias Tool was used to evaluate risk of bias, and the quality of evidence was rated following the GRADE approach. Standardized mean differences (SMD) were calculated for control and experimental groups. Meta-analysis was performed using the random effects model.

RESULTS

Five trials were included. Overall, the trials had moderate risk of bias. The experimental group indicated a significant decrease in the number of bursts per minute (SMD -2.48; 95% CI -3.55 to -1.41) when compared to the control group. Meanwhile, a significant decrease was also observed in the prevalence of bursts per 100 beats in the experimental group when compared to the control group (SMD -2.66; 95% CI -3.64 to -1.69).

CONCLUSION

Exercise training could be effective in reducing sympathetic nerve activity in patients with heart failure. The quality of evidence across the studies was moderate. Future studies are necessary to confirm these results.

Kisspeptin innervation of the hypothalamic paraventricular nucleus: sexual dimorphism and effect of estrous cycle in female mice

The hypothalamic paraventricular nucleus (PVN) is the major autonomic output area of the hypothalamus and a critical regulatory center for energy homeostasis. The organism's energetic balance is very important for both the regular onset of puberty and regulation of fertility. Several studies have suggested a relationship among neural circuits controlling food intake, energy homeostasis and the kisspeptin peptide. The kisspeptin system is clustered in two main groups of cell bodies [the anterior ventral periventricular region (AVPV) and the arcuate nucleus (ARC)] projecting mainly to gonadotropin-releasing hormone (GnRH) neurons and to a few other locations, including the PVN. In the present study, we investigated the distribution of the kisspeptin fibers within the PVN of adult CD1 mice. We observed a significant sexual dimorphism for AVPV and ARC, as well as for the PVN innervation. Kisspeptin fibers showed a different density within the PVN, being denser in the medial part than in the lateral one; moreover, in female, the density changed, according to different phases of the estrous cycle (the highest density being in estrus phase). The presence of a profound effect of estrous cycle on the kisspeptin immunoreactivity in AVPV (with a higher signal in estrus) and ARC, and the strong co-localization between kisspeptin and NkB only in ARC and not in PVN suggested that the majority of the kisspeptin fibers found in the PVN might arise directly from AVPV.

c-Jun N-terminal Kinase mediates prostaglandin-induced sympathoexcitation in rats with chronic heart failure by reducing GAD1 and GABRA1 expression

AIM

Prostaglandin E2 mediates sympathoexcitation in chronic heart failure (CHF) through EP3 receptors (PTGER3) in the paraventricular nucleus (PVN). The aim of this study was to investigate the role of c-Jun N-terminal kinase (JNK) in expressional regulation of gamma-aminobutyric acid signalling in PVN in CHF rats.

METHODS

Chronic heart failure was induced by left coronary ligation in Wistar rats. Renal sympathetic nerve discharge (RSND) and mean arterial pressure (MAP) responses to the PVN infusion were determined in anaesthetized rats. Osmotic minipumps were used for chronic PVN infusion. PTGER3 expression was examined with immunofluorescence staining, quantitative real-time PCR and Western blot.

RESULTS

Chronic heart failure rats had increased JNK activation and decreased glutamate decarboxylase 1 (GAD1) and GABA_A receptor alpha 1 subunit (GABRA1) expression in the PVN. PVN infusion of the PTGER3 agonist SC-46275 caused sympathoexcitation in sham-operated control (Sham) rats and increased it further in CHF. The PTGER3 antagonist L798106 reduced sympathoexcitation and cardiac dysfunction in CHF. PVN infusion of EP1 receptor antagonist SC-19220, EP2 receptor antagonist AH6809 or EP4 receptor antagonist L-161982 had no effect on sympathoexcitation. The JNK inhibitor SP600125 normalized sympathoexcitation and GAD1 and GABRA1 expression in PVN in CHF rats. Both the p44/42 and p38 mitogen-activated protein kinase inhibitors PD98059 and SB203580 could not prevent the downregulation of GAD1 and GABRA1 expression in PVN in CHF. PTGER3 agonist activated JNK but downregulated GAD1 and GABRA1 expression in NG108 neuronal cells.

CONCLUSION

Prostaglandin signalling through upregulated PTGER3 activates JNK which reduces GAD1 and GABRA1 expression in the PVN, and contributes to sympathoexcitation in CHF.

Corticolimbic regulation of cardiovascular responses to stress

Cardiovascular disease, a leading cause of death worldwide, is frequently initiated or exacerbated by stress. In fact, chronic stress exposure and heightened reactions to acute psychological stress are both associated with increased cardiovascular morbidity. This brief review focuses on the mechanisms by which corticolimbic nuclei, critical for stress appraisal and emotional reactivity, regulate heart rate and blood pressure responses to psychological stress. Both human and rodent data are examined with a major emphasis on basic studies investigating prefrontal cortex, amygdala, and hippocampus. A detailed literature review reveals substantial limitations in our understanding of this circuitry, as well as significant opportunities for future investigation that may ultimately reduce the burden of cardiovascular illness.