Spinal cord stimulation reduces ventricular arrhythmias during acute ischemia by attenuation of regional myocardial excitability

Comparing the Memory Effects of 50-Hz Low-Frequency and 10-kHz High-Frequency Thoracic Spinal Cord Stimulation on Spinal Neural Network in a Myocardial Infarction Porcine Model

OBJECTIVE

This study evaluated the effects of cessation of both conventional low-frequency (50 Hz) and high-frequency (10 kHz) spinal cord stimulation (SCS) on the cardiospinal neural network activity in pigs with myocardial infarction (MI). The objective is to provide an insight into the memory effect of SCS.

MATERIALS AND METHODS

In nine Yorkshire pigs, chronic MI was created by delivering microspheres to the left circumflex coronary artery. Five weeks after MI, anesthetized pigs underwent sternotomy to expose the heart for performing acute ischemia intervention, and laminectomy to expose the T1-T4 spinal regions for extracellular in vivo neural recording and SCS. Cardiac ischemic-sensitive neurons were identified by selective responsiveness to left anterior descending (LAD) coronary artery occlusion. SCS episodes were delivered in a random order between low- (50 Hz) and high- (10 kHz) frequency, for 1 minute, at 90% of the motor threshold current. Neural firing and synchrony of ischemic-sensitive spinal neurons were evaluated before vs after SCS.

RESULTS

Using a 64-channel microelectrode array, 2711 spinal neurons were recorded extracellularly. LAD ischemia excited 228 neurons that were labeled as ischemic-responsive neurons. The cessation of 50-Hz SCS caused a higher activation than did inhibition of ischemic-responsive neurons (41 activated vs 19 inhibited), whereas the cessation of 10-kHz SCS caused an opposite response with higher inhibition (11 activated vs 28 inhibited, p < 0.01 vs 50 Hz). Termination of low-frequency SCS caused an increase in ischemic-responsive neuronal firing rate compared with high-frequency SCS (50 Hz: 0.39 Hz ± 0.16 Hz, 10 kHz: -0.11 Hz ± 0.057 Hz, p < 0.01). In addition, SCS delivered at 50 Hz increased the number of synchronized pairs of neurons by 205 pairs, whereas high-frequency SCS decreased the number of synchronized pairs by 345 pairs (p < 0.01).

CONCLUSIONS

High-frequency (10 kHz) stimulation provides persistent suppression of the ischemia-sensitive neurons after termination of SCS. In contrast, the spinal neural network reverted to excitatory state after termination of low-frequency (50 Hz) stimulation.

Real-time in vivo thoracic spinal glutamate sensing during myocardial ischemia

In the spinal cord, glutamate serves as the primary excitatory neurotransmitter. Monitoring spinal glutamate concentrations offers valuable insights into spinal neural processing. Consequently, spinal glutamate concentration has the potential to emerge as a useful biomarker for conditions characterized by increased spinal neural network activity, especially when uptake systems become dysfunctional. In this study, we developed a multichannel custom-made flexible glutamate-sensing probe for the large-animal model that is capable of measuring extracellular glutamate concentrations in real time and in vivo. We assessed the probe's sensitivity and specificity through in vitro and ex vivo experiments. Remarkably, this developed probe demonstrates nearly instantaneous glutamate detection and allows continuous monitoring of glutamate concentrations. Furthermore, we evaluated the mechanical and sensing performance of the probe in vivo, within the pig spinal cord. Moreover, we applied the glutamate-sensing method using the flexible probe in the context of myocardial ischemia-reperfusion (I/R) injury. During I/R injury, cardiac sensory neurons in the dorsal root ganglion transmit excitatory signals to the spinal cord, resulting in sympathetic activation that potentially leads to fatal arrhythmias. We have successfully shown that our developed glutamate-sensing method can detect this spinal network excitation during myocardial ischemia. This study illustrates a novel technique for measuring spinal glutamate at different spinal cord levels as a surrogate for the spinal neural network activity during cardiac interventions that engage the cardio-spinal neural pathway.NEW & NOTEWORTHY In this study, we have developed a new flexible sensing probe to perform an in vivo measurement of spinal glutamate signaling in a large animal model. Our initial investigations involved precise testing of this probe in both in vitro and ex vivo environments. We accurately assessed the sensitivity and specificity of our glutamate-sensing probe and demonstrated its performance. We also evaluated the performance of our developed flexible probe during the insertion and compared it with the stiff probe during animal movement. Subsequently, we used this innovative technique to monitor the spinal glutamate signaling during myocardial ischemia and reperfusion that can cause fatal ventricular arrhythmias. We showed that glutamate concentration increases during the myocardial ischemia, persists during the reperfusion, and is associated with sympathoexcitation and increases in myocardial substrate excitability.

Thoracic Dorsal Root Ganglion Application of Resiniferatoxin Reduces Myocardial Ischemia-Induced Ventricular Arrhythmias

BACKGROUND

A myocardial ischemia/reperfusion (IR) injury activates the transient receptor potential vanilloid 1 (TRPV1) dorsal root ganglion (DRG) neurons. The activation of TRPV1 DRG neurons triggers the spinal dorsal horn and the sympathetic preganglionic neurons in the spinal intermediolateral column, which results in sympathoexcitation. In this study, we hypothesize that the selective epidural administration of resiniferatoxin (RTX) to DRGs may provide cardioprotection against ventricular arrhythmias by inhibiting afferent neurotransmission during IR injury.

METHODS

Yorkshire pigs (n = 21) were assigned to either the sham, IR, or IR + RTX group. A laminectomy and sternotomy were performed on the anesthetized animals to expose the left T2-T4 spinal dorsal root and the heart for IR intervention, respectively. RTX (50 μg) was administered to the DRGs in the IR + RTX group. The activation recovery interval (ARI) was measured as a surrogate for the action potential duration (APD). Arrhythmia risk was investigated by assessing the dispersion of repolarization (DOR), a marker of arrhythmogenicity, and measuring the arrhythmia score and the number of non-sustained ventricular tachycardias (VTs). TRPV1 and calcitonin gene-related peptide (CGRP) expressions in DRGs and CGRP expression in the spinal cord were assessed using immunohistochemistry.

RESULTS

The RTX mitigated IR-induced ARI shortening (-105 ms ± 13 ms in IR vs. -65 ms ± 11 ms in IR + RTX, p = 0.028) and DOR augmentation (7093 ms2 ± 701 ms2 in IR vs. 3788 ms2 ± 1161 ms2 in IR + RTX, p = 0.020). The arrhythmia score and VT episodes during an IR were decreased by RTX (arrhythmia score: 8.01 ± 1.44 in IR vs. 3.70 ± 0.81 in IR + RTX, p = 0.037. number of VT episodes: 12.00 ± 3.29 in IR vs. 0.57 ± 0.3 in IR + RTX, p = 0.002). The CGRP expression in the DRGs and spinal cord was decreased by RTX (DRGs: 6.8% ± 1.3% in IR vs. 0.6% ± 0.2% in IR + RTX, p < 0.001. Spinal cord: 12.0% ± 2.6% in IR vs. 4.5% ± 0.8% in IR + RTX, p = 0.047).

CONCLUSIONS

The administration of RTX locally to thoracic DRGs reduces ventricular arrhythmia in a porcine model of IR, likely by inhibiting spinal afferent hyperactivity in the cardio-spinal sympathetic pathways.

Spinal neuromodulation mitigates myocardial ischemia-induced sympathoexcitation by suppressing the intermediolateral nucleus hyperactivity and spinal neural synchrony

Introduction

Myocardial ischemia disrupts the cardio-spinal neural network that controls the cardiac sympathetic preganglionic neurons, leading to sympathoexcitation and ventricular tachyarrhythmias (VTs). Spinal cord stimulation (SCS) is capable of suppressing the sympathoexcitation caused by myocardial ischemia. However, how SCS modulates the spinal neural network is not fully known.

Methods

In this pre-clinical study, we investigated the impact of SCS on the spinal neural network in mitigating myocardial ischemia-induced sympathoexcitation and arrhythmogenicity. Ten Yorkshire pigs with left circumflex coronary artery (LCX) occlusion-induced chronic myocardial infarction (MI) were anesthetized and underwent laminectomy and a sternotomy at 4-5 weeks post-MI. The activation recovery interval (ARI) and dispersion of repolarization (DOR) were analyzed to evaluate the extent of sympathoexcitation and arrhythmogenicity during the left anterior descending coronary artery (LAD) ischemia. Extracellular in vivo and in situ spinal dorsal horn (DH) and intermediolateral column (IML) neural recordings were performed using a multichannel microelectrode array inserted at the T2-T3 segment of the spinal cord. SCS was performed for 30 min at 1 kHz, 0.03 ms, 90% motor threshold. LAD ischemia was induced pre- and 1 min post-SCS to investigate how SCS modulates spinal neural network processing of myocardial ischemia. DH and IML neural interactions, including neuronal synchrony as well as cardiac sympathoexcitation and arrhythmogenicity markers were evaluated during myocardial ischemia pre- vs. post-SCS.

Results

ARI shortening in the ischemic region and global DOR augmentation due to LAD ischemia was mitigated by SCS. Neural firing response of ischemia-sensitive neurons during LAD ischemia and reperfusion was blunted by SCS. Further, SCS showed a similar effect in suppressing the firing response of IML and DH neurons during LAD ischemia. SCS exhibited a similar suppressive impact on the mechanical, nociceptive and multimodal ischemia sensitive neurons. The LAD ischemia and reperfusion-induced augmentation in neuronal synchrony between DH-DH and DH-IML pairs of neurons were mitigated by the SCS.

Discussion

These results suggest that SCS is decreasing the sympathoexcitation and arrhythmogenicity by suppressing the interactions between the spinal DH and IML neurons and activity of IML preganglionic sympathetic neurons.

GABAergic Signaling during Spinal Cord Stimulation Reduces Cardiac Arrhythmias in a Porcine Model

BACKGROUND

Neuraxial modulation, including spinal cord stimulation, reduces cardiac sympathoexcitation and ventricular arrhythmogenesis. There is an incomplete understanding of the molecular mechanisms through which spinal cord stimulation modulates cardiospinal neural pathways. The authors hypothesize that spinal cord stimulation reduces myocardial ischemia-reperfusion-induced sympathetic excitation and ventricular arrhythmias through γ-aminobutyric acid (GABA)-mediated pathways in the thoracic spinal cord.

METHODS

Yorkshire pigs were randomized to control (n = 11), ischemia-reperfusion (n = 16), ischemia-reperfusion plus spinal cord stimulation (n = 17), ischemia-reperfusion plus spinal cord stimulation plus γ-aminobutyric acid type A (GABAA) or γ-aminobutyric acid type B (GABAB) receptor antagonist (GABAA, n = 8; GABAB, n = 8), and ischemia-reperfusion plus GABA transaminase inhibitor (GABAculine, n = 8). A four-pole spinal cord stimulation lead was placed epidurally (T1 to T4). GABA modulating pharmacologic agents were administered intrathecally. Spinal cord stimulation at 50 Hz was applied 30 min before ischemia. A 56-electrode epicardial mesh was used for high-resolution electrophysiologic recordings, including activation recovery intervals and ventricular arrhythmia scores. Immunohistochemistry and Western blots were performed to measure GABA receptor expression in the thoracic spinal cord.

RESULTS

Cardiac ischemia led to myocardial sympathoexcitation with reduction in activation recovery interval (mean ± SD, -42 ± 11%), which was attenuated by spinal cord stimulation (-21 ± 17%, P = 0.001). GABAA and GABAB receptor antagonists abolished spinal cord stimulation attenuation of sympathoexcitation (GABAA, -9.7 ± 9.7%, P = 0.043 vs. ischemia-reperfusion plus spinal cord stimulation; GABAB, -13 ± 14%, P = 0.012 vs. ischemia-reperfusion plus spinal cord stimulation), while GABAculine alone caused a therapeutic effect similar to spinal cord stimulation (-4.1 ± 3.7%, P = 0.038 vs. ischemia-reperfusion). The ventricular arrhythmia score supported these findings. Spinal cord stimulation during ischemia-reperfusion increased GABAA receptor expression with no change in GABAB receptor expression.

CONCLUSIONS

Thoracic spinal cord stimulation reduces ischemia-reperfusion-induced sympathoexcitation and ventricular arrhythmias through activation of GABA signaling pathways. These data support the hypothesis that spinal cord stimulation-induced release of GABA activates inhibitory interneurons to decrease primary afferent signaling from superficial dorsal horn to sympathetic output neurons in the intermediolateral nucleus.

EDITOR’S PERSPECTIVE

Real-time in vivo thoracic spinal glutamate sensing reveals spinal hyperactivity during myocardial ischemia

Myocardial ischemia-reperfusion (IR) can cause ventricular arrhythmias and sudden cardiac death via sympathoexcitation. The spinal cord neural network is crucial in triggering these arrhythmias and evaluating its neurotransmitter activity during IR is critical for understanding ventricular excitability control. To assess the real-time in vivo spinal neural activity in a large animal model, we developed a flexible glutamate-sensing multielectrode array. To record the glutamate signaling during IR injury, we inserted the probe into the dorsal horn of the thoracic spinal cord at the T2-T3 where neural signals generated by the cardiac sensory neurons are processed and provide sympathoexcitatory feedback to the heart. Using the glutamate sensing probe, we found that the spinal neural network was excited during IR, especially after 15 mins, and remained elevated during reperfusion. Higher glutamate signaling was correlated with the reduction in the cardiac myocyte activation recovery interval, showing higher sympathoexcitation, as well as dispersion of the repolarization which is a marker for increased risk of arrhythmias. This study illustrates a new technique for measuring the spinal glutamate at different spinal cord levels as a surrogate for the spinal neural network activity during cardiac interventions that engage the cardio-spinal neural pathway.

Graphical abstract

Thoracic dorsal root ganglion stimulation reduces acute myocardial ischemia induced ventricular arrhythmias

Background

Dorsal root ganglion stimulation (DRGS) may serve as a novel neuromodulation strategy to reduce cardiac sympathoexcitation and ventricular excitability.

Objective

In this pre-clinical study, we investigated the effectiveness of DRGS on reducing ventricular arrhythmias and modulating cardiac sympathetic hyperactivity caused by myocardial ischemia.

Methods

Twenty-three Yorkshire pigs were randomized to two groups, which was control LAD ischemia-reperfusion (CONTROL) or LAD ischemia-reperfusion + DRGS (DRGS) group. In the DRGS group (n = 10), high-frequency stimulation (1 kHz) at the second thoracic level (T2) was initiated 30 min before ischemia and continued throughout 1 h of ischemia and 2 h of reperfusion. Cardiac electrophysiological mapping and Ventricular Arrhythmia Score (VAS) were assessed, along with evaluation of cFos expression and apoptosis in the T2 spinal cord and DRG.

Results

DRGS decreased the magnitude of activation recovery interval (ARI) shortening in the ischemic region (CONTROL: -201 ± 9.8 ms, DRGS: -170 ± 9.4 ms, p = 0.0373) and decreased global dispersion of repolarization (DOR) at 30 min of myocardial ischemia (CONTROL: 9546 ± 763 ms2, DRGS: 6491 ± 636 ms2, p = 0.0076). DRGS also decreased ventricular arrhythmias (VAS-CONTROL: 8.9 ± 1.1, DRGS: 6.3 ± 1.0, p = 0.038). Immunohistochemistry studies showed that DRGS decreased % cFos with NeuN expression in the T2 spinal cord (p = 0.048) and the number of apoptotic cells in the DRG (p = 0.0084).

Conclusion

DRGS reduced the burden of myocardial ischemia-induced cardiac sympathoexcitation and has a potential to be a novel treatment option to reduce arrhythmogenesis.

Spinal Cord Stimulation Attenuates Neural Remodeling, Inflammation, and Fibrosis After Myocardial Infarction

OBJECTIVES

Spinal cord stimulation (SCS) is an established neuromodulation method that regulates the cardiac autonomic system. However, the biological mechanisms of the therapeutic effects of SCS after myocardial infarction (MI) remain unclear.

MATERIALS AND METHODS

Twenty-five rabbits were divided into five groups: SCS-MI (voltage: 0.5 v; pulse width: 0.2 ms; 50 Hz; ten minutes on and 30 minutes off; two weeks; n = 5), MI (n = 5), sham SCS-MI (voltage: 0 v; two weeks; n = 5), sham MI (n = 5), and blank control (n = 5) groups. MI was induced by permanent left anterior descending artery ligation. SCS-MI and sham SCS-MI rabbits received the corresponding interventions 24 hours after MI. Autonomic remodeling was evaluated using enzyme-linked immunosorbent assay and immunohistochemistry. Inflammation and myocardial fibrosis were assessed using immunohistochemistry, quantitative polymerase chain reaction, hematoxylin and eosin staining, Masson staining, and Western blot.

RESULTS

SCS improved the abnormal systemic autonomic activity. Cardiac norepinephrine decreased after MI (p < 0.01) and did not improve with SCS. Cardiac acetylcholine increased with SCS compared with the MI group (p < 0.05). However, no difference was observed between the MI and blank control groups. Growth-associated protein 43 (p < 0.001) and tyrosine hydroxylase (p < 0.001) increased whereas choline acetyltransferase (p < 0.05) decreased in the MI group compared with the blank control group. These changes were attenuated with SCS. SCS inhibited inflammation, decreased the ratio of phosphorylated-Erk to Erk (p < 0.001), and increased the ratio of phosphorylated-STAT3 to STAT3 (p < 0.001) compared with the MI group. Myocardial fibrosis was also attenuated by SCS.

CONCLUSIONS

SCS improved abnormal autonomic activity after MI, leading to reduced inflammation, reactivation of STAT3, and inhibition of Erk. Additionally, SCS attenuated myocardial fibrosis. Our results warrant future studies of biological mechanisms of the therapeutic effects of SCS after MI.

Porcine spinal cord injury model for translational research across multiple functional systems

Animal models are necessary to identify pathological changes and help assess therapeutic outcomes following spinal cord injury (SCI). Small animal models offer value in research in terms of their easily managed size, minimal maintenance requirements, lower cost, well-characterized genomes, and ability to power research studies. However, despite these benefits, small animal models have neurologic and anatomical differences that may influence translation of results to humans and thus limiting the success of their use in preclinical studies as a direct pipeline to clinical studies. Large animal models, offer an attractive intermediary translation model that may be more successful in translating to the clinic for SCI research. This is largely due to their greater neurologic and anatomical similarities to humans. The physical characteristics of pig spinal cord, gut microbiome, metabolism, proportions of white to grey matter, bowel anatomy and function, and urinary system are strikingly similar and provide great insight into human SCI conditions. In this review, we address the variety of existing porcine injury models and their translational relevance, benefits, and drawbacks in modeling human systems and functions for neurophysiology, cardiovascular, gastrointestinal and urodynamic functions.

Optical Activation of the Dorsal Horn of the Thoracic Spinal Cord Prevents Ventricular Arrhythmias in Acute Myocardial Ischemia-Reperfusion Rats

Background and Objectives

Spinal cord stimulation can prevent myocardial ischemia and reperfusion arrhythmias, but the relevant neurons and mechanisms remain unknown. Thus, this study applied optogenetic techniques to selectively activate glutamatergic neurons at the thoracic spinal cord (T1 segment) for examining the anti-arrhythmia effects during acute myocardial ischemic-reperfusion.

Methods

Adeno-associated viruses (AAVs) carrying channelrhodopsin-2 (ChR2, a blue-light sensitive ion channel) CaMKIIα-hChR2(H134R) or empty vector were injected into the dorsal horn of the T1 spinal cord. Four weeks later, optogenetic stimulation with a 473-nm blue laser was applied for 30 min. Then, the myocardial ischemia-reperfusion model was created by occlusion of the anterior descending coronary artery for ischemia (15 min) and reperfusion (30 min). Cardiac electrical activity and sympathetic nerve activity were assessed continuously.

Results

CaMKIIα-hChR2 viral transfection is primarily expressed in glutamatergic neurons in the spinal cord. Selective optical stimulation of the T1 dorsal horn in the ChR2 rat reduced the ventricular arrhythmia and arrhythmia score during myocardial ischemia-reperfusion, preventing the over-activation of cardiac sympathetic nerve activity. Additionally, optical stimulation also reduced the action potential duration at the 90% level (APD90) and APD dispersion.

Conclusion

Selective optical stimulation T1 glutamatergic neurons of dorsal horn prevent ischemia-reperfusion arrhythmias. The mechanism may be associated with inhibiting sympathetic nervous system overexcitation and increasing APD dispersion during myocardial ischemia-reperfusion.

Device-Based Sympathetic Nerve Regulation for Cardiovascular Diseases

Sympathetic overactivation plays an important role in promoting a variety of pathophysiological processes in cardiovascular diseases (CVDs), including ventricular remodeling, vascular endothelial injury and atherosclerotic plaque progression. Device-based sympathetic nerve (SN) regulation offers a new therapeutic option for some CVDs. Renal denervation (RDN) is the most well-documented method of device-based SN regulation in clinical studies, and several large-scale randomized controlled trials have confirmed its value in patients with resistant hypertension, and some studies have also found RDN to be effective in the control of heart failure and arrhythmias. Pulmonary artery denervation (PADN) has been clinically shown to be effective in controlling pulmonary hypertension. Hepatic artery denervation (HADN) and splenic artery denervation (SADN) are relatively novel approaches that hold promise for a role in cardiovascular metabolic and inflammatory-immune related diseases, and their first-in-man studies are ongoing. In addition, baroreflex activation, spinal cord stimulation and other device-based therapies also show favorable outcomes. This review summarizes the pathophysiological rationale and the latest clinical evidence for device-based therapies for some CVDs.

Autonomic modulation of ventricular electrical activity: recent developments and clinical implications

PURPOSE

This review aimed to provide a complete overview of the current stance and recent developments in antiarrhythmic neuromodulatory interventions, focusing on lifethreatening vetricular arrhythmias.

METHODS

Both preclinical studies and clinical studies were assessed to highlight the gaps in knowledge that remain to be answered and the necessary steps required to properly translate these strategies to the clinical setting.

RESULTS

Cardiac autonomic imbalance, characterized by chronic sympathoexcitation and parasympathetic withdrawal, destabilizes cardiac electrophysiology and promotes ventricular arrhythmogenesis. Therefore, neuromodulatory interventions that target the sympatho-vagal imbalance have emerged as promising antiarrhythmic strategies. These strategies are aimed at different parts of the cardiac neuraxis and directly or indirectly restore cardiac autonomic tone. These interventions include pharmacological blockade of sympathetic neurotransmitters and neuropeptides, cardiac sympathetic denervation, thoracic epidural anesthesia, and spinal cord and vagal nerve stimulation.

CONCLUSION

Neuromodulatory strategies have repeatedly been demonstrated to be highly effective and very promising anti-arrhythmic therapies. Nevertheless, there is still much room to gain in our understanding of neurocardiac physiology, refining the current neuromodulatory strategic options and elucidating the chronic effects of many of these strategic options.

Spinal Cord Stimulation Reduces Ventricular Arrhythmias by Attenuating Reactive Gliosis and Activation of Spinal Interneurons

OBJECTIVES

This study investigated spinal cord neuronal and glial cell activation during cardiac ischemia-reperfusion (IR)-triggered ventricular arrhythmias and neuromodulation therapy by spinal cord stimulation (SCS).

BACKGROUND

Myocardial ischemia induces changes in cardiospinal neural networks leading to sudden cardiac death. Neuromodulation with SCS decreases cardiac sympathoexcitation; however, the molecular mechanisms remain unknown.

METHODS

Yorkshire pigs (n = 16) were randomized to Control, IR, or IR+SCS groups. A 4-pole SCS lead was placed in the T1-T4 epidural space with stimulation for 30 minutes before IR (50 Hz, 0.4-ms duration, 90% motor threshold). Cardiac electrophysiological mapping and Ventricular Arrhythmia Score (VAS) were recorded. Immunohistochemistry of thoracic spinal sections was used to map and identify Fos-positive neuronal and glial cell types during IR with and without SCS.

RESULTS

IR increased cardiac sympathoexcitation and arrhythmias (VAS = 6.2 ± 0.9) that were attenuated in IR + SCS (VAS = 2.8 ± 0.5; P = 0.017). IR increased spinal cellular Fos expression (#Fos+ cells Control = 23 ± 2 vs IR = 88 ± 5; P < 0.0001) in T1-T4, with the greatest increase localized to T3, and the greatest %Fos+ cells being microglia and astrocytes. Fos expression was attenuated by IR + SCS (62 ± 4; P < 0.01), primarily though a reduction in Fos+ microglia and astrocytes, as SCS also led to increase in Fos+ neurons in deep dorsal laminae.

CONCLUSIONS

In a porcine model, cardiac IR was associated with astrocyte and microglial cell activation. Our results suggest that preemptive thoracic SCS decreased IR-induced cardiac sympathoexcitation and ventricular arrhythmias through attenuation of reactive gliosis and activation of inhibitory interneurons in the dorsal horn of spinal cord.

Electrical epidural stimulation of the cervical spinal cord: implications for spinal respiratory neuroplasticity after spinal cord injury

Traumatic cervical spinal cord injury (cSCI) can lead to damage of bulbospinal pathways to the respiratory motor nuclei and consequent life-threatening respiratory insufficiency due to respiratory muscle paralysis/paresis. Reports of electrical epidural stimulation (EES) of the lumbosacral spinal cord to enable locomotor function after SCI are encouraging, with some evidence of facilitating neural plasticity. Here, we detail the development and success of EES in recovering locomotor function, with consideration of stimulation parameters and safety measures to develop effective EES protocols. EES is just beginning to be applied in other motor, sensory, and autonomic systems; however, there has only been moderate success in preclinical studies aimed at improving breathing function after cSCI. Thus, we explore the rationale for applying EES to the cervical spinal cord, targeting the phrenic motor nucleus for the restoration of breathing. We also suggest cellular/molecular mechanisms by which EES may induce respiratory plasticity, including a brief examination of sex-related differences in these mechanisms. Finally, we suggest that more attention be paid to the effects of specific electrical parameters that have been used in the development of EES protocols and how that can impact the safety and efficacy for those receiving this therapy. Ultimately, we aim to inform readers about the potential benefits of EES in the phrenic motor system and encourage future studies in this area.

Spinal Anesthesia Reduces Myocardial Ischemia-triggered Ventricular Arrhythmias by Suppressing Spinal Cord Neuronal Network Interactions in Pigs

BACKGROUND

Cardiac sympathoexcitation leads to ventricular arrhythmias. Spinal anesthesia modulates sympathetic output and can be cardioprotective. However, its effect on the cardio-spinal reflexes and network interactions in the dorsal horn cardiac afferent neurons and the intermediolateral nucleus sympathetic neurons that regulate sympathetic output is not known. The authors hypothesize that spinal bupivacaine reduces cardiac neuronal firing and network interactions in the dorsal horn-dorsal horn and dorsal horn-intermediolateral nucleus that produce sympathoexcitation during myocardial ischemia, attenuating ventricular arrhythmogenesis.

METHODS

Extracellular neuronal signals from the dorsal horn and intermediolateral nucleus neurons were simultaneously recorded in Yorkshire pigs (n = 9) using a 64-channel high-density penetrating microarray electrode inserted at the T2 spinal cord. Dorsal horn and intermediolateral nucleus neural interactions and known markers of cardiac arrhythmogenesis were evaluated during myocardial ischemia and cardiac load-dependent perturbations with intrathecal bupivacaine.

RESULTS

Cardiac spinal neurons were identified based on their response to myocardial ischemia and cardiac load-dependent perturbations. Spinal bupivacaine did not change the basal activity of cardiac neurons in the dorsal horn or intermediolateral nucleus. After bupivacaine administration, the percentage of cardiac neurons that increased their activity in response to myocardial ischemia was decreased. Myocardial ischemia and cardiac load-dependent stress increased the short-term interactions between the dorsal horn and dorsal horn (324 to 931 correlated pairs out of 1,189 pairs, P < 0.0001), and dorsal horn and intermediolateral nucleus neurons (11 to 69 correlated pairs out of 1,135 pairs, P < 0.0001). Bupivacaine reduced this network response and augmentation in the interactions between dorsal horn-dorsal horn (931 to 38 correlated pairs out of 1,189 pairs, P < 0.0001) and intermediolateral nucleus-dorsal horn neurons (69 to 1 correlated pairs out of 1,135 pairs, P < 0.0001). Spinal bupivacaine reduced shortening of ventricular activation recovery interval and dispersion of repolarization, with decreased ventricular arrhythmogenesis during acute ischemia.

CONCLUSIONS

Spinal anesthesia reduces network interactions between dorsal horn-dorsal horn and dorsal horn-intermediolateral nucleus cardiac neurons in the spinal cord during myocardial ischemia. Blocking short-term coordination between local afferent-efferent cardiac neurons in the spinal cord contributes to a decrease in cardiac sympathoexcitation and reduction of ventricular arrhythmogenesis.

EDITOR’S PERSPECTIVE

Neuromodulation With Thoracic Dorsal Root Ganglion Stimulation Reduces Ventricular Arrhythmogenicity

Introduction: Sympathetic hyperactivity is strongly associated with ventricular arrhythmias and sudden cardiac death. Neuromodulation provides therapeutic options for ventricular arrhythmias by modulating cardiospinal reflexes and reducing sympathetic output at the level of the spinal cord. Dorsal root ganglion stimulation (DRGS) is a recent neuromodulatory approach; however, its role in reducing ventricular arrhythmias has not been evaluated. The aim of this study was to determine if DRGS can reduce cardiac sympathoexcitation and the indices for ventricular arrhythmogenicity induced by programmed ventricular extrastimulation. We evaluated the efficacy of thoracic DRGS at both low (20 Hz) and high (1 kHz) stimulation frequencies. Methods: Cardiac sympathoexcitation was induced in Yorkshire pigs (n = 8) with ventricular extrastimulation (S1/S2 pacing), before and after DRGS. A DRG-stimulating catheter was placed at the left T2 spinal level, and animals were randomized to receive low-frequency (20 Hz and 0.4 ms) or high-frequency (1 kHz and 0.03 ms) DRGS for 30 min. High-fidelity cardiac electrophysiological recordings were performed with an epicardial electrode array measuring the indices of ventricular arrhythmogenicity-activation recovery intervals (ARIs), electrical restitution curve (S_max), and Tpeak-Tend interval (Tp-Te interval). Results: Dorsal root ganglion stimulation, at both 20 Hz and 1 kHz, decreased S1/S2 pacing-induced ARI shortening (20 Hz DRGS -21±7 ms, Control -50±9 ms, P = 0.007; 1 kHz DRGS -13 ± 2 ms, Control -46 ± 8 ms, P = 0.001). DRGS also reduced arrhythmogenicity as measured by a decrease in S_max (20 Hz DRGS 0.5 ± 0.07, Control 0.7 ± 0.04, P = 0.006; 1 kHz DRGS 0.5 ± 0.04, Control 0.7 ± 0.03, P = 0.007), and a decrease in Tp-Te interval/QTc (20 Hz DRGS 2.7 ± 0.13, Control 3.3 ± 0.12, P = 0.001; 1 kHz DRGS 2.8 ± 0.08, Control; 3.1 ± 0.03, P = 0.007). Conclusions: In a porcine model, we show that thoracic DRGS decreased cardiac sympathoexcitation and indices associated with ventricular arrhythmogenicity during programmed ventricular extrastimulation. In addition, we demonstrate that both low-frequency and high-frequency DRGS can be effective neuromodulatory approaches for reducing cardiac excitability during sympathetic hyperactivity.

The autonomic nervous system and ventricular arrhythmias in myocardial infarction and heart failure

Ventricular arrhythmias (VA) can range in presentation from asymptomatic to cardiac arrest and sudden cardiac death (SCD). Sustained ventricular tachycardias/ventricular fibrillation (VT/VF) are a common cause of SCD in the setting of myocardial infarction (MI) and heart failure. A particularly arrhythmogenic cardiac syncytia in these conditions can be attributed to both sympathetic activation and parasympathetic dysfunction, while appropriate neuromodulation has the potential to reduce occurrence of VT/VF. In this review, we outline the components of the autonomic nervous system that play an important role in normal cardiac electrophysiology and function. In addition, we discuss changes that occur in the setting of cardiac disease including adverse neural remodeling and neurohormonal activation which significantly contribute to propensity for VT/VF. Finally, we review neuromodulation strategies to mitigate VT/VF which predominantly rely on increasing parasympathetic drive and blockade of sympathetic neurotransmission.

Endothelin receptors in the brain modulate autonomic responses and arrhythmogenesis during acute myocardial infarction in rats

AIMS

Endothelin has been implicated in various processes in the brain, including the modulation of sympathetic responses. The present study examined the pathophysiologic role of brain endothelin-receptors in the setting of acute myocardial infarction, characterized by high incidence of ventricular tachyarrhythmias.

MAIN METHODS

We investigated the effects of intracerebroventricular administration of antagonists of endothelin-receptors ET_A, ET_B, or both, during a 24 h-observation period post-coronary ligation in (n = 70) rats. Continuous recording was performed via implanted telemetry transmitters, followed by arrhythmia-analysis and calculation of autonomic indices derived from heart rate variability. The regional myocardial electrophysiologic properties were assessed by monophasic action potentials and multi-electrode recordings.

KEY FINDINGS

Sympathetic-activity was decreased and vagal-activity was enhanced after intracerebroventricular ET_A-receptor blockade, thus attenuating regional myocardial repolarization inhomogeneity. As a result, the incidence of ventricular tachyarrhythmias was markedly lower in this group. Such effects were also observed after intracerebroventricular blockade of ET_B-, or both, ET_A- and ET_B-receptors, although to a lesser extent.

SIGNIFICANCE

ET_A-receptors in the brain modulate sympathetic and vagal responses and alter arrhythmogenesis during evolving myocardial necrosis in rats. These findings provide insights into arrhythmogenic mechanisms during acute myocardial infarction and call for further investigation on the role of endothelin in the central autonomic network.

Alterations in amino acid levels and metabolite ratio of spinal cord in rat with myocardial ischemia-reperfusion injury by proton magnetic resonance spectroscopy

OBJECTIVES

The mechanism behind spinal metabolites and myocardial ischemia-reperfusion (IR) injury is not well understood. Proton magnetic resonance spectroscopic analysis of spinal cord extracts provides a quick evaluation of the specific metabolic activity in rats with myocardial IR injury. We investigated the relationship between the IR-related variables and the changes in spinal metabolites.

METHODS

Proton magnetic resonance spectroscopy (¹H-MRS) was used to assess the spinal metabolites of adult rats with and without myocardial IR injury (n = 6 per group). Myocardial IR injury was reproduced using intermittent occlusion of the left anterior descending coronary artery. We studied the relationship between the metabolite ratio measurement and IR-related variables. All rats underwent ¹H-MRS, with the ratio of interest placed in different spinal cord segments to measure levels of twelve metabolites including N-acetylaspartate (NAA), taurine (Tau), glutamate (Glu), gamma amino acid butyric acid (GABA), creatine (Cr), and myoinositol (MI), etc. Results: Rats with myocardial IR injury had higher concentration of Tau in the upper thoracic spinal cord (P < 0.05), and lower concentration of Gly and Glu in the cervical segment of the spinal cord (P < 0.05), when compared to the Control group. The ratios of glutamate/taurine (Glu/Tau), Glu/(GABA + Tau) and Glu/Total were significantly different between the IR group and the Control group in the upper thoracic spinal cord (P < 0.05). So were the ratios of Glu/(GABA + Tau) in the cervical segment (P < 0.05), and Glu/Tau and Glu/(GABA + Tau) in the lower thoracic spinal cord (P < 0.05).

CONCLUSIONS

These findings suggest that myocardial IR injury may be related to spinal biochemical alterations. It is speculated that these observed changes in the levels of spinal metabolites may be involved in the pathogenesis and regulation of myocardial IR injury.

Identification of lncRNA and mRNA expression profiles in rat spinal cords at various time‑points following cardiac ischemia/reperfusion

The identification of the expression patterns of long non-coding RNAs (lncRNAs) and mRNAs in the spinal cord under normal and cardiac ischemia/reperfusion (I/R) conditions is essential for understanding the genetic mechanisms underlying the pathogenesis of cardiac I/R injury. The present study used high-throughput RNA sequencing to investigate differential gene and lncRNA expression patterns in the spinal cords of rats during I/R-induced cardiac injury. Male Sprague Dawley rats were assigned to the following groups: i) Control; ii) 2 h (2 h post-reperfusion); and iii) 0.5 h (0.5 h post-reperfusion). Further mRNA/lncRNA microarray analysis revealed that the expression profiles of lncRNA and mRNA in the spinal cords differed markedly between the control and 2 h groups, and in total 7,980 differentially expressed (>2-fold) lncRNAs (234 upregulated, 7,746 downregulated) and 3,428 mRNAs (767 upregulated, 2,661 downregulated) were identified. Reverse transcription-quantitative polymerase chain reaction analysis was performed to determine the expression patterns of several lncRNAs. The results indicated that the expression levels of lncRNA NONRATT025386 were significantly upregulated in the 2 and 0.5 h groups when compared with those in the control group, whereas the expression levels of NONRATT016113, NONRATT018298 and NONRATT018300 were elevated in the 2 h group compared with those in the control group; however, there was no statistically significant difference between the 0.5 h and control groups. Furthermore, the expression of lncRNA NONRATT002188 was significantly downregulated in the 0.5 and 2 h groups when compared with the control group. The present study determined the expression pattern of lncRNAs and mRNAs in rat spinal cords during cardiac I/R. It was suggested that lncRNAs and mRNAs from spinal cords may be novel therapeutic targets for the treatment of I/R-induced cardiac injury.

Neuromodulation Approaches for Cardiac Arrhythmias: Recent Advances

PURPOSE OF REVIEW

This review aims to describe the latest advances in autonomic neuromodulation approaches to treating cardiac arrhythmias, with a focus on ventricular arrhythmias.

RECENT FINDINGS

The increasing understanding of neuronal remodeling in cardiac diseases has led to the development and improvement of novel neuromodulation therapies targeting multiple levels of the autonomic nervous system. Thoracic epidural anesthesia, spinal cord stimulation, stellate ganglion modulatory therapies, vagal stimulation, renal denervation, and interventions on the intracardiac nervous system have all been studied in preclinical models, with encouraging preliminary clinical data. The autonomic nervous system regulates all the electrical processes of the heart and plays an important role in the pathophysiology of cardiac arrhythmias. Despite recent advances in the clinical application of cardiac neuromodulation, our comprehension of the anatomy and function of the cardiac autonomic nervous system is still limited. Hopefully in the near future, more preclinical data combined with larger clinical trials will lead to further improvements in neuromodulatory treatment for heart rhythm disorders.

Autonomic Neuromodulation for Preventing and Treating Ventricular Arrhythmias

The cardiac autonomic nervous system (CANS) is associated with modulation of cardiac electrophysiology and arrhythmogenesis. In this mini review, we will briefly introduce cardiac autonomic anatomy and autonomic activity in ventricular arrhythmias (VAs) and discuss novel approaches of CANS modulation for treating VAs. Studies over the decades have provided a better understanding of cardiac autonomic innervation and revealed overwhelming evidence of the relationship between autonomic tone and VAs. A high sympathetic tone and low parasympathetic (vagal) tone are considered as the major triggers of VAs in patients with myocardial ischemia, which can cause sudden cardiac death. In recent years, novel methods of autonomic neuromodulation have been investigated to prevent VAs, and they have been verified as being beneficial for malignant VAs in animal models and humans. The clinical outcome of autonomic neuromodulation depends on the level of cardiac neuraxis, stimulation parameters, and patient's pathological status. Since autonomic modulation for VA treatment is still in the early stage of clinical application, more basic and clinical studies should be performed to clarify these mechanisms and optimize autonomic neuromodulation therapies for patients with VAs in the future.

Modulation of Ion Channels in the Superior Cervical Ganglion Neurons by Myocardial Ischemia and Fluvastatin Treatment

Background: The superior cervical ganglion (SCG) of the autonomic nervous system plays an important role in different cardiovascular diseases. In this study, we investigated the effects of ischemia and fluvastatin treatment on the ion channel characteristics of SCG neurons in a rabbit myocardial ischemia (MI) model. Methods: MI was induced by abdominal subcutaneous injections of isoproterenol (ISO). The properties of the delayed rectifier potassium channel current (IK ), sodium channel current (INa ), and action potential (APs) on isolated SCG neurons in the control, MI-7d, MI-14d, fluvastatin-7d (fluvastatin pretreated 14 days and treated 7 days after ISO-induced MI), and fluvastatin-14d (fluvastatin pretreated 14 days and treated 14 days after ISO-induced MI) groups were studied. In addition, the RNA expressions of KCNQ3 and SCN9A in the SCG tissue were determined by performing real-time PCR. Intracellular calcium concentration was monitored using laser scanning confocal microscopy. Results: Compared with the control group, the current amplitude of IK and INa were increased in the MI-7d and MI-14d groups. KCNQ3 RNA (corresponding to channel proteins of IK ) expression and SCN9A RNA (corresponding to channel proteins of INa ) expression were also increased in MI groups. Activation and inactivation curves for INa in the two MI groups shifted negatively compared with the control group. These changes were reversed by fluvastatin treatment. Intracellular calcium concentration in SCG neurons was not altered significantly by MI or fluvastatin treatment. By contrast, increased AP amplitude and shortened APD90 were observed in the MI-7d and MI-14d groups. These changes were reversed in the fluvastatin-treated MI group. Conclusion: Fluvastatin treatment partly reversed the characteristics of SCG neurons in MI. The ion channel of SCG neurons could be one of the potential targets of fluvastatin in treating coronary heart diseases.

Segmental innervation of the Göttingen minipig hind body. An electrophysiological study

The Göttingen minipig is being used increasingly in biomedical research. The anatomical structure of the porcine peripheral nervous system has been extensively characterized, but no equivalent to the dermatome map, which is so valuable in human neurophysiological research, has been created. We characterized the medullar segmental skin and muscle innervations of the minipig hind body, using neurophysiological methodology. Six adult minipigs underwent unilateral laminectomy from L2 to S3, exposing the nerve roots. The skin of the hind part of the body was divided into 36 predefined fields, based on anatomical landmarks for consistent reproducibility. We recorded the evoked potential in each exposed nerve root L2-S3 for cutaneous stimulation of each skin field, mapping the sensory innervation of the entire hind body. We subsequently recorded the motor response in seven predefined muscles during sequential stimulation of the L2-S3 nerve roots. We obtained a clear sensory evoked potential in the nerve roots during stimulation of the skin fields, allowing us to map the sensory innervation of the minipig hind body. Neurophysiological data from skin stimulation and muscle recordings enabled us to map the sensory innervation of the Göttingen minipig hind body and provide information about muscular innervation. The skin fields were sensory innervated by more than one root. The muscles each had one dominant root with minor contribution from neighboring roots. This is consistent with experimental data from human studies.

Statistical considerations in reporting cardiovascular research

The problem of inadequate statistical reporting is long standing and widespread in the biomedical literature, including in cardiovascular physiology. Although guidelines for reporting statistics have been available in clinical medicine for some time, there are currently no guidelines specific to cardiovascular physiology. To assess the need for guidelines, we determined the type and frequency of statistical tests and procedures currently used in the American Journal of Physiology-Heart and Circulatory Physiology. A PubMed search for articles published in the American Journal of Physiology-Heart and Circulatory Physiology between January 1, 2017, and October 6, 2017, provided a final sample of 146 articles evaluated for methods used and 38 articles for indepth analysis. The t-test and ANOVA accounted for 71% (212 of 300 articles) of the statistical tests performed. Of six categories of post hoc tests, Bonferroni and Tukey tests were used in 63% (62 of 98 articles). There was an overall lack in details provided by authors publishing in the American Journal of Physiology-Heart and Circulatory Physiology, and we compiled a list of recommended minimum reporting guidelines to aid authors in preparing manuscripts. Following these guidelines could substantially improve the quality of statistical reports and enhance data rigor and reproducibility.