Biology subjects

Shivkumar, K.

Publications and source records attributed to Shivkumar, K..

10 recordsLinked to original sources

bioRxiv2026

An Implantable Wireless Battery-Free Selective Vagus Nerve Stimulator

Objective. Vagus nerve stimulation (VNS) is an established clinical therapy for drug-resistant epilepsy and other inflammatory conditions. However, off-target stimulation can produce unwanted side effects that limit therapeutic stimulation and hinder the development of new neuromodulation therapies. Selective VNS (sVNS) offers a strategy to reduce off-target organ activation; however, this approach is not available in humans, and no implantable or portable devices exist to trial sVNS in the clinical setup. This work aimed to design, manufacture, and validate an implantable wireless, battery-free stimulator with a selectively addressable output stage for targeted current delivery to specific regions of the human vagus nerve (VN). Approach. We developed a near-field communication-controlled, wirelessly powered, battery-free, temporary implantable multichannel stimulation device, compatible with a 15-channel sVNS cuff electrode (14 selective electrode pairs and one circumferential whole-nerve channel). The device was encapsulated for short-term implantation and evaluated through benchtop characterisation, accelerated ageing, and validation in an acute porcine and a pilot human study. Main result. The sVNS device was evaluated in a porcine (n = 4) trial and a first-in-human pilot study (n = 1). Selective bradycardia of 23.28 {+/-} 12.91% was observed in pigs and 7.5% in the human participant. In the human, a clear separation of bradycardic and tachycardic effects was observed, with additional selectivity in laryngeal activity. Cardiac and laryngeal responses were separated by 231{degrees} around the circumference of the nerve. Significance. This work demonstrates the feasibility of wireless battery-free sVNS for cardiac applications using a temporary implantable device. Geometrically selective stimulation has the potential to improve therapeutic efficacy while reducing stimulation-related side effects, and may facilitate future therapies for heart failure and other autonomic disorders.

bioengineering↗

bioRxiv2025

Neuropeptide Y regulation of L-type Ca2+ channel activity is altered following chronic myocardial infarction

Neuropeptide Y (NPY) is a co-transmitter released from sympathetic neurons along with norepinephrine (NE). It has been observed that cardiac NPY levels are significantly elevated following myocardial infarction (MI), and this has been linked to an increase in ventricular arrhythmogenicity associated with elevated sympathetic tone. However, the effects that NPY has on the electrical activity of ventricular myocytes remain poorly understood. Previous studies have examined the influence of NPY alone on cardiac ion channel function, but not in the presence of NE, which is the situation expected in vivo. Furthermore, no one has examined the effects of NPY on ion channel activity following MI. The present study explored the impact of NPY on the L-type Ca2+ current in ventricular myocytes isolated from the hearts of normal healthy pigs and pigs subjected to MI. We found that NPY alone has a stimulatory effect on the Ca2+ current in myocytes isolated from healthy pigs. However, in the presence of NE, the effect of NPY was inhibitory. The stimulatory effect of NPY alone was blocked by the Y1 receptor antagonist BIBO3304, while the inhibitory effect observed in the presence of NE was blocked by the Y2 receptor antagonist BIIE0246. When the effects of NPY were examined using hearts from pigs following recovery from MI, the stimulatory effect of NPY was absent in myocytes obtained from both remote and border zone areas of infarcted hearts. The inhibitory effect of NPY observed in the presence of NE was also absent in myocytes from remote areas of the infarcted heart. However, the inhibitory effect of NPY observed in the presence of NE was intact in border zone cells. The implications of these results are discussed as they relate to the potential arrhythmogenic effects of NPY following MI. Graphical Abstract. NPY exerts bimodular, context dependent effects on LTCC. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=91 SRC="FIGDIR/small/690298v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@fb248borg.highwire.dtl.DTLVardef@1c3cd9org.highwire.dtl.DTLVardef@1def5b3org.highwire.dtl.DTLVardef@d4bfd5_HPS_FORMAT_FIGEXP M_FIG C_FIG Proposed signaling pathways for diverse effects of NPY in ventricular cardiac myocytes. Norepinephrine (NE) and neuropeptide Y (NPY) co-application results in a Y2/Gi-mediated reduction in {beta}-adrenergic ({beta}AR)/Gs enhanced ICaL, while NPY alone modestly enhances the current via Y1/Gq mechanism. These pathways are regionally altered following chronic MI.

pharmacology and toxicology↗

bioRxiv2025

Adrenergic Hypersensitivity Drives Ventricular Arrhythmias Following Loss of Plexin-Mediated Cardiac Innervation

BackgroundVentricular arrhythmias (VAs) are a leading cause of death and arise from a combination of cardiac muscle injury and dysfunction of the intramyocardial sympathetic nerves that control cardiac electrophysiology. The adrenergic mechanisms by which intramyocardial nerves contribute to arrhythmogenesis are poorly understood. Semaphorin-plexin signaling pathways are responsible for developmental guidance of sympathetic nerves onto the heart and have previously been associated with VAs in humans. ObjectiveTo investigate adrenergic control of arrhythmogenesis, we probed the cardiac electrophysiology of a Plexin-A3/-A4 double knockout mouse with loss of cardiac adrenergic nerves. MethodsWe studied cardiac structure and function using tissue clearing, immunohistochemistry, and echocardiography. We utilized ECG and optical mapping of action potentials to evaluate electrophysiologic responses to pharmacologic beta ({beta})-adrenergic stimulation and blockade. We measured circulating catecholamines and quantified {beta}-adrenergic receptor ({beta}AR) density in cardiac membranes. Finally, we performed a phenome-wide association study utilizing data from the UK Biobank to search for associations between PLXNA4 and human arrhythmias. ResultsMice with loss of plexin-dependent cardiac innervation had structurally normal hearts but displayed spontaneous VAs driven by adrenergic hypersensitivity, as well as increased cardiac {beta}AR density. Several human PLXNA4 variants were associated with arrhythmia phenotypes. ConclusionThese data establish a model of VAs driven by enhanced adrenergic receptor signaling, in the absence of structural heart disease, which can be used to investigate adrenergic mechanisms of arrhythmogenesis and to identify novel antiarrhythmic targets.

physiology↗

bioRxiv2025

Methadone blockade of IK1 promotes both long QT and Brugada-like arrhythmias: Mechanistic insights from computational modeling

BackgroundMethadone is widely used for chronic pain relief and in the maintenance therapy of opioid use disorder, however, it also increases the risk of ventricular arrhythmias and sudden cardiac death. Methadone blocks several ionic currents with different half-maximal inhibitory concentrations (IC50), including the rapid component of the delayed rectifier potassium current (IKr), the inward rectifier potassium current (IK1), the L-type calcium current (ICa,L), and the late component of the sodium current (INaL). Despite the well-known proarrhythmic effect of IKr blockade, the effects of blocking other ionic currents on arrhythmogenesis remain less well understood. MethodsComputer simulations were used to explore the proarrhythmic effects of methadone by investigating how its blocking effects on ionic currents act alone or together in arrhythmogenesis. ResultsThe major findings are: 1) blocking IK1 potentiates QT prolongation-related arrhythmogenesis by enhancing a tissue-scale dynamical instability for the spontaneous genesis of ectopic excitations. Blocking IK1 and IKr together results in a synergistic effect, greatly increasing the arrhythmia propensity, much larger than that of blocking either one alone; 2) blocking IK1 in combination with lowering ICa,L potentiates phase-2 reentry caused by spike-and-dome action potential morphology, an arrhythmia mechanism of Brugada syndrome. Blocking IKr exhibits little effect for this mechanism of arrhythmias; and 3) hypoxia, often comorbid in methadone populations, can potentiate QT prolongation-related arrhythmias at high sympathetic activity and phase-2 reentry at low or basal sympathetic activity, mainly via its effect on ICa,L. ConclusionsThese simulation results provide mechanistic insights into the genesis of QT prolongation-related Torsades de Pointes and Brugada-like ECG related arrhythmias caused by methadone use.

pharmacology and toxicology↗

bioRxiv2024

Anatomical and functional organization of cardiac fibers in the porcine cervical vagus nerve allows spatially selective efferent neuromodulation

Cardiac disease progression reflects the dynamic interaction between adversely remodeled neurohumoral control systems and an abnormal cardiac substrate. Vagal nerve stimulation (VNS) is an attractive neuromodulatory option to dampen this dynamic interaction; however, it is limited by off-target effects. Spatially-selective VNS (sVNS) offers a promising solution to induce cardioprotection while mitigating off-target effects by specifically targeting pre-ganglionic parasympathetic efferent cardiac fibers. This approach also has the potential to enhance therapeutic outcomes by eliminating time-consuming titration required for optimal VNS. Recent studies have demonstrated the independent modulation of breathing rate, heart rate, and laryngeal contraction through sVNS. However, the spatial organization of afferent and efferent cardiac-related fibers within the vagus nerve remains unexplored. By using trial-and-error sVNS in vivo in combination with ex vivo micro-computed tomography fascicle tracing, we show the significant spatial separation of cardiac afferent and efferent fibers (179{+/-}55{degrees} SD microCT, p<0.05 and 200{+/-}137{degrees} SD, p<0.05 sVNS - degrees of separation across a cross-section of nerve) at the mid-cervical level. We also show that cardiac afferent fibers are located in proximity to pulmonary fibers consistent with recent findings of cardiopulmonary convergent neurons and circuits. We demonstrate the ability of sVNS to selectively elicit desired scalable heart rate decrease without stimulating afferent-related reflexes. By elucidating the spatial organization of cardiac-related fibers within the vagus nerve, our findings pave the way for more targeted neuromodulation, thereby reducing off-target effects and eliminating the need for titration. This, in turn, will enhance the precision and efficacy of VNS therapy in treating cardiac pathology, allowing for improved therapeutic efficacy. Condensed AbstractSpatially-selective vagus nerve stimulation (sVNS) presents a promising approach for addressing chronic heart disease with enhanced precision. Our study reveals significant spatial separation between cardiac afferent and efferent fibers in the vagus nerve, particularly at the mid-cervical level. Utilizing trial-and-error sVNS in vivo and micro-computed tomography fascicle tracing, we demonstrate the potential for targeted neuromodulation, achieving therapeutic effects like scalable heart rate decrease without stimulating afferent-related reflexes. This spatial understanding opens avenues for more effective VNS therapy, minimizing off-target effects and eliminating the need for titration, thereby expediting therapeutic outcomes in myocardial infarction and related conditions. TweetWith functional and structural imaging, we found organization of vagal efferent & afferent cardiac regions. We can selectively activate only cardiac efferents to achieve bradycardia; desired to reduce the effects of sympathetic overactivation associated with heart disease #VNS #Cardiac #VagusNerve Key PointsO_LISpatially-selective vagus nerve stimulation (sVNS) presents a promising approach for addressing chronic heart disease with enhanced precision. C_LIO_LIOur study reveals significant spatial separation between cardiac afferent and efferent fibers in the vagus nerve, particularly at the mid-cervical level. C_LIO_LIUtilizing trial-and-error sVNS in vivo and micro-computed tomography fascicle tracing, we demonstrate the potential for targeted neuromodulation, achieving therapeutic effects like scalable heart rate decrease without stimulating afferent-related reflexes. C_LIO_LIThis spatial understanding opens avenues for more effective VNS therapy, minimizing off-target effects and eliminating the need for titration, thereby expediting therapeutic outcomes in myocardial infarction and related conditions. C_LI

neuroscience↗

bioRxiv2020

Innervation and Neuronal Control of the Mammalian Sinoatrial Node: A Comprehensive Atlas

Cardiac function is under exquisite intrinsic cardiac neural control. Neuroablative techniques to modulate control of cardiac function are currently being studied in patients, albeit with variable and sometimes deleterious results. Recognizing the major gaps in our understanding of cardiac neural control, we sought to evaluate neural regulation of impulse initiation in the sinoatrial node as an initial discovery step. Here, we report an in-depth, multi-scale structural and functional characterization of the innervation of the sinoatrial node (SAN) by the right atrial ganglionated plexus (RAGP) in porcine and human hearts. Combining intersectional strategies including tissue clearing, immunohistochemical and ultrastructural techniques, we have delineated a comprehensive neuroanatomic atlas of the RAGP-SAN complex. The RAGP shows significant phenotypic diversity of neurons while maintaining predominant cholinergic innervation. Cellular and tissue-level electrophysiologic mapping and ablation studies demonstrate interconnected ganglia with synaptic convergence within the RAGP to modulate SAN automaticity, atrioventricular (AV) conduction and left ventricular (LV) contractility. For the first time, we demonstrate that intrinsic cardiac neurons influence the pacemaking site in the heart. This provides an experimental demonstration of a discrete neuronal population controlling a specific geographic region of the heart (SAN) that can serve as a framework for further exploration of other parts of the intrinsic cardiac nervous system (ICNS) in mammalian hearts and for developing targeted therapies.

neuroscience↗

bioRxiv2020

A spatially-tracked single cell transcriptomics map of neuronal networks in the intrinsic cardiac nervous system

We developed a spatially-tracked single neuron transcriptomics map of an intrinsic cardiac ganglion - the right atrial ganglionic plexus (RAGP) that is a critical mediator of vagal control of the sinoatrial node (SAN) activity. We developed a 3D representation of RAGP with extensive mapping of neurons and used neuronal tracing to identify the spatial distribution of the subset of neurons that project to the SAN. RNAseq of laser capture microdissected neurons revealed a distinct composition of RAGP neurons compared to CNS neuronal subtypes. High-throughput qPCR of hundreds of laser capture microdissected single neurons led to a surprising finding that cholinergic and catecholaminergic neuronal markers Th and Chat were correlated, suggesting multipotential phenotypes that can drive neuroplasticity within RAGP. Interestingly, no single gene or module was an exclusive marker of RAGP neuronal connectivity to SAN. Neuropeptide-receptor coexpression analysis revealed a combinatorial paracrine neuromodulatory network within RAGP, informing follow-on studies on the vagal control of RAGP to regulate cardiac function in health and disease.

neuroscience↗

bioRxiv2020

Selective Modulation of Heart and Respiration by Optical Control of Vagus Nerve Axons Innervating the Heart

Targeting specifics subsets of peripheral pathways of the autonomic nervous system will enable new avenues to study organ control and develop new disease therapies. Vagus nerve stimulation (VNS) has shown many therapeutic benefits but current approaches involve imprecise electrical stimulation that gives rise to adverse effects, and the functionally relevant pathways are poorly understood. One method to overcome these limitations is the use of optogenetic techniques, which facilitate highly specific neural communication with light-sensitive actuators (opsins). Opsins can be targeted to cell populations of interest based on the location of viral delivery and genetic control of expression. Here, we tested whether holographic photostimulation of subsets of axons of the cervical vagus nerve that innervate the heart can be used to modulate cardiac function. Viral injection of retrograde adeno-associated virus (rAAV2-retro) in the heart resulted in robust, primarily afferent, opsin reporter expression in the vagus nerve, nodose ganglion, and brainstem. Selective holographic photostimulation of axons resulted in changes in heart rate, surface cardiac electrogram, and respiratory responses that were different from responses elicited by whole nerve photostimulation.Competing Interest StatementThe authors have declared no competing interest.View Full Text

bioengineering↗

bioRxiv2018

Identification of peripheral neural circuits that regulate heart rate using optogenetic and viral vector strategies

Heart rate is under the precise control of the autonomic nervous system. However, the wiring of peripheral neural circuits that regulate heart rate is poorly understood. Here, we developed a clearing-imaging-analysis pipeline to visualize innervation of intact hearts in 3D and employed a multi-technique approach to map parasympathetic and sympathetic neural circuits that control heart rate in mice. We anatomically and functionally identify cholinergic neurons and noradrenergic neurons in an intrinsic cardiac ganglion and the stellate ganglia, respectively, that project to the sinoatrial node. We also report that the heart rate response to optogenetic versus electrical stimulation of the vagus nerve displays different temporal characteristics and that vagal afferents enhance parasympathetic and reduce sympathetic tone to the heart via central mechanisms. Our findings provide new insights into neural regulation of heart rate, and our methodology to study cardiac circuits can be readily used to interrogate neural control of other visceral organs.

neuroscience↗

bioRxiv2018

Widespread and targeted gene expression by systemic AAV vectors: Production, purification, and administration

We recently developed novel AAV capsids for efficient and noninvasive gene transfer across the central and peripheral nervous systems. In this protocol, we describe how to produce and systemically administer AAV-PHP viruses to label and/or genetically manipulate cells in the mouse nervous system and organs including the heart. The procedure comprises three separate stages: AAV production, intravenous delivery, and evaluation of transgene expression. The protocol spans eight days, excluding the time required to assess gene expression, and can be readily adopted by laboratories with standard molecular and cell culture capabilities. We provide guidelines for experimental design and choosing the capsid, cargo, and viral dose appropriate for the experimental aims. The procedures outlined here are adaptable to diverse biomedical applications, from anatomical and functional mapping to gene expression, silencing, and editing.

neuroscience↗