Stochastic vagus nerve stimulation affects acute heart rate dynamics in rats

Direct vagus nerve stimulation: A new tool to control allergic airway inflammation through α7 nicotinic acetylcholine receptor

BACKGROUND AND PURPOSE

Asthma is characterized by airway inflammation, mucus hypersecretion, and airway hyperresponsiveness. The use of nicotinic agents to mimic the cholinergic anti-inflammatory pathway (CAP) controls experimental asthma. Yet, the effects of vagus nerve stimulation (VNS)-induced CAP on allergic inflammation remain unknown.

EXPERIMENTAL APPROACH

BALB/c mice were sensitized and challenged with house dust mite (HDM) extract and treated with active VNS (5 Hz, 0.5 ms, 0.05-1 mA). Bronchoalveolar lavage (BAL) fluid was assessed for total and differential cell counts and cytokine levels. Lungs were examined by histopathology and electron microscopy.

KEY RESULTS

In the HDM mouse asthma model, VNS at intensities equal to or above 0.1 mA (VNS 0.1) but not sham VNS reduced BAL fluid differential cell counts and alveolar macrophages expressing α7 nicotinic receptors (α7nAChR), goblet cell hyperplasia, and collagen deposition. Besides, VNS 0.1 also abated HDM-induced elevation of type 2 cytokines IL-4 and IL-5 and was found to block the phosphorylation of transcription factor STAT6 and expression level of IRF4 in total lung lysates. Finally, VNS 0.1 abrogated methacholine-induced hyperresponsiveness in asthma mice. Prior administration of α-bungarotoxin, a specific inhibitor of α7nAChR, but not propranolol, a specific inhibitor of β2-adrenoceptors, abolished the therapeutic effects of VNS 0.1.

CONCLUSION AND IMPLICATIONS

Our data revealed the protective effects of VNS on various clinical features in allergic airway inflammation model. VNS, a clinically approved therapy for depression and epilepsy, appears to be a promising new strategy for controlling allergic asthma.

Vagus Nerve Stimulation and Its Cardioprotective Abilities: A Systematic Review

Despite the vagus nerve stimulator (VNS) being used in neuroscience, it has recently been highlighted that it has cardioprotective functions. However, many studies related to VNS are not mechanistic in nature. This systematic review aims to focus on the role of VNS in cardioprotective therapy, selective vagus nerve stimulators (sVNS), and their functional capabilities. A systemic review of the current literature was conducted on VNS, sVNS, and their ability to induce positive effects on arrhythmias, cardiac arrest, myocardial ischemia/reperfusion injury, and heart failure. Both experimental and clinical studies were reviewed and assessed separately. Of 522 research articles retrieved from literature archives, 35 met the inclusion criteria and were included in the review. Literature analysis proves that combining fiber-type selectivity with spatially-targeted vagus nerve stimulation is feasible. The role of VNS as a tool for modulating heart dynamics, inflammatory response, and structural cellular components was prominently seen across the literature. The application of transcutaneous VNS, as opposed to implanted electrodes, provides the best clinical outcome with minimal side effects. VNS presents a method for future cardiovascular treatment that can modulate human cardiac physiology. However, continued research is needed for further insight.

Effects on heart rate from direct current block of the stimulated rat vagus nerve

Objective.Although electrical vagus nerve stimulation has been shown to augment parasympathetic control of the heart, the effects of electrical conduction block have been less rigorously characterized. Previous experiments have demonstrated that direct current (DC) nerve block can be applied safely and effectively in the autonomic system, but additional information about the system dynamics need to be characterized to successfully deploy DC nerve block to clinical practice.Approach.The dynamics of the heart rate (HR) from DC nerve block of the vagus nerve were measured by stimulating the vagus nerve to lower the HR, and then applying DC block to restore normal rate. DC block achieved rapid, complete block, as well as partial block at lower amplitudes.Main Results. Complete block was also achieved using lower amplitudes, but with a slower induction time. The time for DC to induce complete block was significantly predicted by the amplitude; specifically, the amplitude expressed as a percentage of the current required for a rapid, 60 s induction time. Recovery times after the cessation of DC block could occur both instantly, and after a significant delay. Both blocking duration and injected charge were significant in predicting the delay in recovery to normal conduction.Significance. While these data show that broad features such as induction and recovery can be described well by the DC parameters, more precise features of the HR, such as the exact path of the induction and recoveries, are still undefined. These findings show promise for control of the cardiac autonomic nervous system, with potential to expand to the sympathetic inputs as well.

Differential immunostaining patterns of transient receptor potential (TRP) ion channels in the rat nodose ganglion

Vagal afferents regulate numerous physiological functions including arterial blood pressure, heart rate, breathing, and nociception. Cell bodies of vagal afferents reside in the inferior vagal (nodose) ganglia and their stimulation by various means is being considered as a way to regulate cardiorespiratory responses and control pain sensations. Stimulation of the nodose by exposure to infrared light is recently being considered as a precise way to elicit responses. These responses would likely involve the activity of temperature-sensitive membrane-bound channels. While papers have been published to track the expression of these transient receptor potential ion channels (TRPs), further studies are warranted to determine the in situ expression of the endogenous TRP proteins in the nodose ganglia to fully understand their pattern of expression, subcellular locations, and functions in this animal model. TRP ion channels are a superfamily of Na⁺ /Ca²⁺ -channels whose members are temperature- and/or mechano-sensitive and therefore represent a potential set of proteins that will be activated directly or indirectly by infrared light. Here, we report the spatial localization of six TRP channels, TRPV1, TRPV4, TRPM3, TRPM8, TRPA1, and TRPC1, from nodose ganglia taken from juvenile male Sprague-Dawley rats. The channels were detected using immunohistology with fluorescent tags on cryosections and imaged using confocal microscopy. All six TRP channels were detected with different levels of intensity in neuronal cell bodies and some were also detected in axonal fibers and blood vessels. The TRP receptors differed in their prevalence, in their patterns of expression, and in subcellular expression/localization. More specifically, TRPV1, TRPV4, TRPA1, TRPM8, TRPC1, and TRPM3 were found in vagal afferent cell bodies with a wide range of immunostaining intensity from neuron to neuron. Immunostaining for TRPV1, TRPV4, and TRPA1 appeared as fine particles scattered throughout the cytoplasm of the cell body. Intense TRPV1 immunostaining was also evident in a subset of axonal fibers. TRPM8 and TRPC1 were expressed in courser particles suggesting different subcellular compartments than for TRPV1. The localization of TRPM3 differed markedly from the other TRP channels with an immunostaining pattern that was localized to the periphery of a subset of cell bodies, whereas a scattering or no immunostaining was detected within the bulk of the cytoplasm. TRPV4 and TRPC1 were also expressed on the walls of blood vessels. The finding that all six TRP channels (representing four subfamilies) were present in the nodose ganglia provides the basis for studies designed to understand the roles of these channels in sensory transmission within vagal afferent fibers and in the responses elicited by exposure of nodose ganglia to infrared light and other stimuli. Depending on the location and functionality of the TRP channels, they may regulate the flux of Na⁺ /Ca²⁺ -across the membranes of cell bodies and axons of sensory afferents, efferent (motor) fibers coursing through the ganglia, and in vascular smooth muscle.

Auricular Vagus Nerve Stimulation Attenuates Lipopolysaccharide-Induced Acute Lung Injury by Inhibiting Neutrophil Infiltration and Neutrophil Extracellular Traps Formation

ABSTRACT

Vagus nerve stimulation has been shown to exert anti-inflammation activities in sepsis. However, surgical implantation of stimulation devices is performed under general anesthesia, which limits its clinical application. Auricular vagus nerve stimulation (AVNS) is a minimal invasive technique that delivers electrical currents to the auricular branch of the vagus nerve. The purpose of this study was to determine the effects of AVNS on systemic inflammation, lung injury, neutrophil infiltration, and neutrophil extracellular traps (NETs) formation in the lung. In a LPS challenge lung-injury mice model, AVNS was applied to bilateral ears. Twelve hours after LPS administration, samples of blood, bronchoalveolar lavage fluid (BALF), and lung tissues were processed for investigations. We found that the treatment with AVNS significantly attenuated histopathological changes and neutrophil infiltration in the lung tissue, inhibited inflammatory cytokine elevations in serum and BALF, and decreased protein concentrations in BALF. Besides, AVNS decreased leukocyte and neutrophil accounts in BALF. Furthermore, colocalization of citrullination of histone H3 and myeloperoxidase expressions (highly specific marker of NETs) was reduced in AVNS mice. In conclusion, AVNS reduced systemic inflammation, attenuated lung edema, and inhibited neutrophil infiltration and NETs formation in the lung in LPS mice.

Advances in Cardiac Pacing: Arrhythmia Prediction, Prevention and Control Strategies

Cardiac arrhythmias constitute a tremendous burden on healthcare and are the leading cause of mortality worldwide. An alarming number of people have been reported to manifest sudden cardiac death as the first symptom of cardiac arrhythmias, accounting for about 20% of all deaths annually. Furthermore, patients prone to atrial tachyarrhythmias such as atrial flutter and fibrillation often have associated comorbidities including hypertension, ischemic heart disease, valvular cardiomyopathy and increased risk of stroke. Technological advances in electrical stimulation and sensing modalities have led to the proliferation of medical devices including pacemakers and implantable defibrillators, aiming to restore normal cardiac rhythm. However, given the complex spatiotemporal dynamics and non-linearity of the human heart, predicting the onset of arrhythmias and preventing the transition from steady state to unstable rhythms has been an extremely challenging task. Defibrillatory shocks still remain the primary clinical intervention for lethal ventricular arrhythmias, yet patients with implantable cardioverter defibrillators often suffer from inappropriate shocks due to false positives and reduced quality of life. Here, we aim to present a comprehensive review of the current advances in cardiac arrhythmia prediction, prevention and control strategies. We provide an overview of traditional clinical arrhythmia management methods and describe promising potential pacing techniques for predicting the onset of abnormal rhythms and effectively suppressing cardiac arrhythmias. We also offer a clinical perspective on bridging the gap between basic and clinical science that would aid in the assimilation of promising anti-arrhythmic pacing strategies.

Sex Differences in Vagus Nerve Stimulation Effects on Rat Cardiovascular and Immune Systems

Background

Investigations into the benefits of vagus nerve stimulation (VNS) through pre-clinical and clinical research have led to promising findings for treating several disorders. Despite proven effectiveness of VNS on conditions such as epilepsy and depression, understanding of off-target effects and contributing factors such as sex differences can be beneficial to optimize therapy design.

New Methods

In this article, we assessed longitudinal effects of VNS on cardiovascular and immune systems, and studied potential sex differences using a rat model of long-term VNS. Rats were implanted with cuff electrodes around the left cervical vagus nerve for VNS, and wireless physiological monitoring devices for continuous monitoring of cardiovascular system using electrocardiogram (ECG) signals. ECG morphology and heart rate variability (HRV) features were extracted to assess cardiovascular changes resulting from VNS in short-term and long-term timescales. We also assessed VNS effects on expression of inflammatory cytokines in blood during the course of the experiment. Statistical analysis was performed to compare results between Treatment and Sham groups, and between male and female animals from Treatment and Sham groups.

Results

Considerable differences between male and female rats in cardiovascular effects of VNS were observed in multiple cardiovascular features. However, the effects seemed to be transient with approximately 1-h recovery after VNS. While short-term cardiovascular effects were mainly observed in male rats, females in general showed more significant long-term effects even after VNS stopped. We did not observe notable changes or sex differences in systemic cytokine levels resulting from VNS.

Comparison With Existing Methods

Compared to existing methods, our study design incorporated wireless physiological monitoring and systemic blood cytokine level analysis, along with long-term VNS experiments in unanesthetized rats to study sex differences.

Conclusion

The contribution of sex differences for long-term VNS off-target effects on cardiovascular and immune systems was assessed using awake behaving rats. Although VNS did not change the concentration of inflammatory biomarkers in systemic circulation for male and female rats, we observed significant differences in cardiovascular effects of VNS characterized using ECG morphology and HRV analyses.

Analysis of serum gastrin-17 and Helicobacter pylori antibody in healthy Chinese population

BACKGROUND

Gastrin-17 (G-17) and Helicobacter pylori (H pylori) antibody are widely used in the screening of gastric diseases, especially in gastric cancer. In this study, we aimed to evaluate the value of G-17 and H pylori antibody in gastric disease screening.

METHODS

Healthy males and females (1368 and 1212, respectively) aged between 21-80 years were recruited for the study. Serum G-17 value was measured using ELISA, and H pylori antibodies were measured using Western blotting. Statistical analyses were performed using the chi-square, Mann-Whitney U, and Kruskal-Wallis H tests.

RESULTS

Serum G-17 level was higher in the H pylori-positive group than in the negative group. Serum G-17 level was higher in the type 1 H pylori-positive group than in the type 2 H pylori-positive group. Further, serum G-17 level was higher in females than in males and showed significant differences among different age-groups, with changes in trend proportional to the age. The positive rate of H pylori infection in all the subjects was 58.29% and did not show a significant difference between males and females. However, it showed significant differences among different age-groups, with the changing trend proportional to the age.

CONCLUSION

Analysis of serum G-17 level and H pylori antibody typing is valuable in gastric disease screening. Every laboratory should establish its own reference interval for G-17 level.

Anodal block permits directional vagus nerve stimulation

Vagus nerve stimulation (VNS) is a bioelectronic therapy for disorders of the brain and peripheral organs, and a tool to study the physiology of autonomic circuits. Selective activation of afferent or efferent vagal fibers can maximize efficacy and minimize off-target effects of VNS. Anodal block (ABL) has been used to achieve directional fiber activation in nerve stimulation. However, evidence for directional VNS with ABL has been scarce and inconsistent, and it is unknown whether ABL permits directional fiber activation with respect to functional effects of VNS. Through a series of vagotomies, we established physiological markers for afferent and efferent fiber activation by VNS: stimulus-elicited change in breathing rate (ΔBR) and heart rate (ΔHR), respectively. Bipolar VNS trains of both polarities elicited mixed ΔHR and ΔBR responses. Cathode cephalad polarity caused an afferent pattern of responses (relatively stronger ΔBR) whereas cathode caudad caused an efferent pattern (stronger ΔHR). Additionally, left VNS elicited a greater afferent and right VNS a greater efferent response. By analyzing stimulus-evoked compound nerve potentials, we confirmed that such polarity differences in functional responses to VNS can be explained by ABL of A- and B-fiber activation. We conclude that ABL is a mechanism that can be leveraged for directional VNS.

Moving beyond belief: A narrative review of potential biomarkers for transcutaneous vagus nerve stimulation

Transcutaneous vagus nerve stimulation (tVNS) is a non-invasive neurostimulation technique that is currently being tested as a potential treatment for a myriad of neurological and psychiatric disorders. However, the working mechanisms underlying tVNS are poorly understood and it remains unclear whether stimulation activates the vagus nerve for every participant. Finding a biological marker of tVNS is imperative, as it can help guide research on clinical applications and can inform researchers on optimal stimulation sites and parameters to further optimize treatment efficacy. In this narrative review, we discuss five potential biomarkers for tVNS and review currently available evidence for these markers for both invasive and tVNS. While some of these biomarkers hold promise from a theoretical perspective, none of the potential biomarkers provide clear and definitive indications that tVNS increases the vagal activity or augments activity in the locus coeruleus-noradrenaline network. We conclude the review by providing several recommendations for how to tackle the challenges and opportunities when researching potential biomarkers for the effects of tVNS.

Vagus Nerve Stimulation and the Cardiovascular System

The vagus nerve plays an important role in maintaining physiological homeostasis, which includes reflex pathways that regulate cardiac function. The link between vagus nerve activity and the high-frequency component of heart rate variability (HRV) has been well established, correlating with vagal tone. Recently, vagus nerve stimulation (VNS) has been investigated as a therapeutic for a multitude of diseases, such as treatment-resistant epilepsy, rheumatoid arthritis, Crohn's disease, and asthma. Because of the vagus nerve's innervation of the heart, VNS has been identified as a potential therapy for cardiovascular disorders, such as cardiac arrest, acute myocardial infarction, and stroke. Here, we review the current state of preclinical and clinical studies, as well as the potential application of VNS in relation to the cardiovascular system.

Electric vagal nerve stimulation inhibits inflammation and improves early postoperation cognitive dysfunction in aged rats

BACKGROUND

This study aimed to evaluate effects of electric vagal nerve stimulation on early postoperation cognitive dysfunction in aged rats.

METHODS

A total of 33 male Sprague Dawley rats were selected and assigned randomly to three groups, control group (C, n = 10), splenectomy group (S, n = 10) and splenectomy+vagal nerve stimulation group (SV, n = 13). Behavior and memory of rats were evaluated by Open Field Test and Morris Water Maze. Levels of TNF-α, IL-6 and IL-10 in serum were measured by ELISA. The level of TNF-α protein in hippocampus was assessed by Western blotting. rt-PCR was used to detect mRNA expression of NF-κB in hippocampus.

RESULTS

During anesthesia/operation, vital life signs of rats were stable. In SV group, vagal nerve stimulation decreased heart rate lower than 10% of basic level and kept it at a stable range by regulating stimulation intensity. After stimulation stop, heart rate returned to the basic level again. This indicated that the model of vagal nerve stimulation was successful. Serum levels of TNF-α and IL-6 increased by the operation/anesthesia, but they decreased with vagal nerve stimulation (all P < 0.05). TNF-α protein and mRNA expression of NF-κB in hippocampus were also eliminated by vagal nerve stimulation compared to S group (P < 0.05). Results of Morris Water Maze showed escape latency of postoperation in S group was significantly longer than C group (P < 0.05), and times of crossing platform in S group was lower than that of C group (P < 0.05). Although escape latency of postopration in SV group was shorter than that of S group, there was no significant difference between two groups. Meanwhile there were no significant differences of behavior test in Open Field test between three groups, although vagal nerve stimulation improved partly active explore behavior compared to S group.

CONCLUSION

The inflammation caused by operation and general anesthesia was an important reason of early postoperation cognitive dysfunction, and electric vagal nerve stimulation could inhibit the inflammation. Meanwhile, vagal nerve stimulation could ameliorate early postoperation cognitive dysfunction partly, but its protective effects were not enough and should be studied and improved in future.

A rodent model for long-term vagus nerve stimulation experiments

Aim: Investigations into the benefits of vagus nerve stimulation (VNS) using rodents have led to promising findings for treating clinical disorders. However, the majority of research has been limited to acute timelines. We developed a rodent model for longitudinal assessment of VNS and validated it with a long-term experiment incorporating continuous physiological monitoring. While the primary aim was not to investigate the effects of VNS on the cardiovascular system, we analyzed cardiovascular parameters to demonstrate the model's capabilities in a long-term stimulation-and-recording setup. Materials & methods: Rats were implanted with a cuff electrode around the cervical vagus nerve and electrocardiogram monitoring devices were implanted in the peritoneal cavity. We also designed a connector mount for seamless access to the cuff electrode for VNS in awake-behaving rats. Results & conclusion: Results signified easy-to-interface VNS system, electrode robustness and discernible physiological signals in a long-term setup. Analysis of the cardiovascular parameters revealed some transient effects during VNS. Our proposed model enables long-term VNS experiments along with physiological monitoring in unanesthetized rats.