Sympathetic and afferent neurones projecting into forelimb and trunk nerves and the anatomical organization of the thoracic sympathetic outflow of the rat

Skin Sympathetic Nerve Activity and the Short-Term QT Interval Variability in Patients With Electrical Storm

Background: Skin sympathetic nerve activity (SKNA) and QT interval variability are known to be associated with ventricular arrhythmias. However, the relationship between the two remains unclear.

Objective: The aim was to test the hypothesis that SKNA bursts are associated with greater short-term variability of the QT interval (STVQT) in patients with electrical storm (ES) or coronary heart disease without arrhythmias (CHD) than in healthy volunteers (HV).

Methods: We simultaneously recorded the ECG and SKNA during sinus rhythm in patients with ES (N = 10) and CHD (N = 8) and during cold-water pressor test in HV (N = 12). The QT and QTc intervals were manually marked and calculated within the ECG. The STVQT was calculated and compared to episodes of SKNA burst and non-bursting activity.

Results: The SKNA burst threshold for ES and HV was 1.06 ± 1.07 and 1.88 ± 1.09 μV, respectively (p = 0.011). During SKNA baseline and burst, the QT/QTc intervals and STVQT for ES and CHD were significantly higher than those of the HV. In all subjects, SKNA bursts were associated with an increased STVQT (from 6.43 ± 2.99 to 9.40 ± 5.12 ms, p = 0.002 for ES; from 9.48 ± 4.40 to 12.8 ± 5.26 ms, p = 0.016 for CHD; and from 3.81 ± 0.73 to 4.49 ± 1.24 ms, p = 0.016 for HV). The magnitude of increased STVQT in ES (3.33 ± 3.06 ms) and CHD (3.34 ± 2.34 ms) was both higher than that of the HV (0.68 ± 0.84 ms, p = 0.047 and p = 0.020).

Conclusion: Compared to non-bursting activity, SKNA bursts were associated with a larger increase in the QTc interval and STVQT in patients with heart disease than in HV.

Organization of sympathetic innervation of interscapular brown adipose tissue in the mouse

The interscapular brown adipose tissue (iBAT) is under sympathetic control, and recent studies emphasized the importance of efferent sympathetic and afferent sensory or humoral feedback systems to regulate adipose tissue function and overall metabolic health. However, functional studies of the sympathetic nervous system in the mouse are limited, because details of anatomy and fine structure are lacking. Here, we used reporter mice for tyrosine hydroxylase expressing neurons (TH:tomato mice), iDISCO tissue clearance, confocal, lightsheet, and electron microscopy to clarify that (a) iBAT receives sympathetic input via dorsal rami (instead of often cited intercostal nerves); (b) dorsal rami T1-T5 correspond to the postganglionic input from sympathetic chain ganglia (stellate/T1-T5); (c) dorsal rami serve as conduits for sympathetic axons that branch off in finer nerve bundles to enter iBAT; (d) axonal varicosities show strong differential innervation of brown (dense innervation) versus white (sparse innervation) adipocytes, that surround the core iBAT in the mouse and are intermingled in human adipose tissues, (e) axonal varicosities can form neuro-adipocyte junctions with brown adipocytes. Taken together, we demonstrate that sympathetic iBAT innervation is organized by specific nerves and terminal structures that can be surgically and genetically accessed for neuromodulatory purposes.

SK4 calcium-activated potassium channels activated by sympathetic nerves enhances atrial fibrillation vulnerability in a canine model of acute stroke

Background

New-onset atrial fibrillation (AF) is common in patients with acute stroke (AS). Studies have shown that intermediate-conductance calcium-activated potassium channel channels (SK4) play an important role in cardiomyocyte automaticity. The aim of this study was to investigate the effects of SK4 on AF vulnerability in dogs with AS.

Experimental

Eighteen dogs were randomly divided into a control group, AS group and left stellate ganglion ablation (LSGA) group. In the control group, dogs received craniotomy without right middle cerebral artery occlusion (MCAO). AS dogs were established using a cerebral ischemic model with right MCAO. LSGA dogs underwent MCAO, and LSGA was performed.

Results

Three days later, the dispersion of the effective refractory period (dERP) and AF vulnerability in the AS group were significantly increased compared with those in the control group and LSGA group. However, no significant difference in dERP and AF vulnerability was found between the control group and the LSGA group. The SK4 inhibitor (TRAM-34) completely inhibited the inducibility of AF in AS dogs. SK4 expression and levels of noradrenaline (NE), β1-AR, p38 and c-Fos in the atrium were higher in the AS dogs than in the control group or LSGA group. However, no significant difference in SK4 expression or levels of NE, β1-AR, p38 and c-Fos in the left atrium was observed between the control group and LSGA group.

Conclusion

SK4 plays a key role in AF vulnerability in a canine model with AS. The effects of LSGA on AF vulnerability were associated with the p38 signaling pathways.

Role of intermediate-conductance calcium-activated potassium channels in atrial fibrillation in canines with rapid atrial pacing

PURPOSE

The aim of the present study was to explore the role of intermediate-conductance Ca²⁺-activated K⁺ (SK4) in atrial fibrillation (AF) inducibility in canines with rapid atrial pacing.

METHODS

Eighteen dogs were divided into the control group, the pacing group and the stellate ganglion ablation (SGA) + pacing group. In the pacing group, dogs were subjected to rapid atrial pacing, and the atrial effective refractory period (AERP) and AF inducibility were measured. After cessation of 7-h pacing, SK4 inhibitor (TRAM-34) was administered. After SGA, the SGA + pacing group received the same procedure of pacing and electrophysiological measurement as the pacing group. The expression of SK4 was measured in the left atrium (LA) and the right atrium (RA) in the three groups.

RESULTS

The duration of the AERP decreased, while the number of AF episodes, the duration of induced AF, and the amplitude of stellate ganglion neural activity all increased after rapid atrial pacing. TRAM-34 completely inhibited AF induction in the pacing group. There was no significant difference in AERP shortening or AF vulnerability between the SGA + pacing group and the control group. The expression of SK4 in the LA and RA was higher in the pacing group than in the control and SGA + pacing groups. However, there was no significant difference in the expression of SK4 in the LA or the RA between the SGA + pacing group and the control group.

CONCLUSION

The higher expression of SK4 plays an important role in AF induction and the increased expression of SK4 in the atrium is related to SG activity during rapid atrial pacing.

Antiarrhythmic and proarrhythmic effects of subcutaneous nerve stimulation in ambulatory dogs

BACKGROUND

High output subcutaneous nerve stimulation (ScNS) remodels the stellate ganglia and suppresses cardiac arrhythmia.

OBJECTIVE

The purpose of this study was to test the hypothesis that long duration low output ScNS causes cardiac nerve sprouting and increases plasma norepinephrine concentration and the duration of paroxysmal atrial tachycardia (PAT) in ambulatory dogs.

METHODS

We prospectively randomized 22 dogs (11 males and 11 females) into 5 different output groups for 2 months of ScNS: 0 mA (sham) (n = 6), 0.25 mA (n = 4), 1.5 mA (n = 4), 2.5 mA (n = 4), and 3.5 mA (n = 4).

RESULTS

As compared with baseline, the changes in the durations of PAT episodes per 48 hours were significantly different among different groups (sham, -5.0 ± 9.5 seconds; 0.25 mA, 95.5 ± 71.0 seconds; 1.5 mA, -99.3 ± 39.6 seconds; 2.5 mA, -155.3 ± 87.8 seconds; and 3.5 mA, -76.3 ± 44.8 seconds; P < .001). The 3.5 mA group had a greater reduction in sinus heart rate than did the sham group (-29.8 ± 15.0 beats/min vs -14.5 ± 3.0 beats/min; P = .038). Immunohistochemical studies showed that the 0.25 mA group had a significantly increased while 2.5 mA and 3.5 mA stimulation had significantly reduced growth-associated protein 43 nerve densities in both atria and ventricles. The plasma norepinephrine concentrations in the 0.25 mA group was 5063.0 ± 4366.0 pg/mL, which was significantly higher than that in the other groups of dogs (739.3 ± 946.3; P = .009). There were no significant differences in the effects of simulation between males and females.

CONCLUSION

In ambulatory dogs, low output ScNS causes cardiac nerve sprouting and increases plasma norepinephrine concentration and the duration of PAT episodes while high output ScNS is antiarrhythmic.

Chronic median nerve modulation reduces ventricular arrhythmia and improves ventricular function in a postmyocardial infarction rabbit model

AIM

Median nerve stimulation (MNS) is a novel neuromodulation approach for treatment of ventricular arrhythmia, but little is known about its chronic effects. The aim of this study was to investigate the effects of chronic MNS on ventricular arrhythmia and ventricular dysfunction postmyocardial infarction (MI).

METHOD

Two weeks after MI, 12 rabbits were randomly divided into control and MNS groups, and chronic MNS was performed in MNS group for 2 weeks. Ventricular function and arrhythmias; sympathetic innervation and activity; and interleukin-1 β (IL-1 β) and norepinephrine (NE) levels were analyzed.

RESULTS

Both the total number of premature ventricular complex and episodes of ventricular tachycardia were lower in MNS group than in control group (20 560 ± 10 314 beats vs 70 079 ± 37 184 beats, P = .021, and 115 ± 63 episodes vs 307 ± 164 episodes, P = .034, respectively). Compared with control group, MNS decreased the cardiac sympathetic nerve density and level of circulating NE in MNS group (1798.42 ± 644.07 μm² /mm² vs 1003.79 ± 453.00 μm² /mm²_, P = .041, and 20.86 ± 4.54 pg/mL vs 11.07 ± 1.43 pg/mL, P = .002, respectively). MNS also improved the left ventricular ejection fraction (59.07 ± 1.91% vs 49.77 ± 3.47%, P = .003) and inhibited the level of IL-1 β in serum (69.19 ± 4.71 pg/mL vs 85.93 ± 12.80 pg/mL, P = .013).

CONCLUSION

Chronic MNS appears to protect against ventricular arrhythmia and improves ventricular function post-MI, which may be mediated by suppressing cardiac sympathetic activity and anti-inflammatory effects.

Effects of Stellate Ganglion Cryoablation on Subcutaneous Nerve Activity and Atrial Tachyarrhythmias in a Canine Model of Pacing-Induced Heart Failure

OBJECTIVES

This study aimed to test the hypothesis that subcutaneous nerve activity (SCNA) can adequately estimate the cardiac sympathetic tone and the effects of cryoablation of the stellate ganglion in dogs with pacing-induced heart failure (HF).

BACKGROUND

Recording of SCNA is a new method to estimate sympathetic tone in dogs. HF is known to increase sympathetic tone and atrial arrhythmias.

METHODS

Twelve dogs with pacing-induced HF were studied using implanted radiotransmitters to record the stellate ganglia nerve activity (SGNA), vagal nerve activity, and SCNA. Of these, 6 dogs (ablation group) underwent bilateral stellate ganglia cryoablation before the rapid ventricular pacing; the remaining 6 dogs (control group) had rapid ventricular pacing only. In both groups, SCNA was compared with SGNA and the occurrence of arrhythmias.

RESULTS

SCNA invariably increased before the 360 identified atrial tachyarrhythmia episodes in the 6 control dogs before and after HF induction. SCNA and SGNA correlated in all dogs with an average correlation coefficient of 0.64 (95% confidence interval: 0.58 to 0.70). Cryoablation of bilateral stellate ganglia significantly reduced SCNA from 0.34 ± 0.033 μV to 0.25 ± 0.028 μV (p = 0.03) and eliminated all atrial tachyarrhythmias.

CONCLUSIONS

SCNA can be used to estimate cardiac sympathetic tone in dogs with pacing-induced HF. Cryoablation of the stellate ganglia reduced SCNA and arrhythmia vulnerability.

Left cervical vagal nerve stimulation reduces skin sympathetic nerve activity in patients with drug resistant epilepsy

BACKGROUND

We recently reported that skin sympathetic nerve activity (SKNA) can be used to estimate sympathetic tone in humans. In animal models, vagal nerve stimulation (VNS) can damage the stellate ganglion, reduce stellate ganglion nerve activity, and suppress cardiac arrhythmia. Whether VNS can suppress sympathetic tone in humans remains unclear.

OBJECTIVE

The purpose of this study was to test the hypothesis that VNS suppresses SKNA in patients with drug-resistant epilepsy.

METHODS

ECG patch electrodes were used to continuously record SKNA in 26 patients with drug-resistant epilepsy who were admitted for video electroencephalographic monitoring. Among them, 6 (2 men, age 40 ± 11 years) were previously treated with VNS and 20 (7 men, age 37 ± 8 years) were not. The signals from ECG leads I and II were filtered to detect SKNA.

RESULTS

VNS had an on-time of 30 seconds and off-time of 158 ± 72 seconds, with output of 1.92 ± 0.42 mA at 24.17 ± 2.01 Hz. Average SKNA during VNS off-time was 1.06 μV (95% confidence interval [CI] 0.93-1.18) in lead I and 1.13 μV (95% CI 0.99-1.27) in lead II, which was significantly lower than 1.38 μV (95% CI 1.01-1.75; P = .036) and 1.38 μV (95% CI 0.98-1.78; P = .035) in the control group, respectively. Heart rate was 65 bpm (95% CI 59-71) in the VNS group, which was significantly lower than 77 bpm (95% CI 71-83) in the control group.

CONCLUSION

Patients with VNS had significantly lower SKNA than those without VNS.

Recording sympathetic nerve activity from the skin

Sympathetic tone is important in cardiac arrhythmogenesis; however, methods to estimate sympathetic tone are either invasive or require proper sinus node function that may be abnormal in disease states. Because of the direct and extensive connections among various nerve structures, it is possible for the sympathetic nerves in the various structures to activate simultaneously. Therefore, we hypothesized that nerve activity can be recorded from the skin and it can be used to estimate the cardiac sympathetic tone. Preclinical studies in canines demonstrated that nerve activity is detectable using conventional ECG electrodes and can be used to estimate cardiac sympathetic tone. Subsequent clinical studies further supported this concept. In addition to studying the autonomic mechanisms of cardiac arrhythmia, these new methods may have broad application in studying both cardiac and non-cardiac diseases.

Therapeutic potential of stellate ganglion block in orofacial pain: a mini review

Orofacial pain is a common complaint of patients that causes distress and compromises the quality of life. It has many etiologies including trauma, interventional procedures, nerve injury, varicella-zoster (shingles), tumor, and vascular and idiopathic factors. It has been demonstrated that the sympathetic nervous system is usually involved in various orofacial pain disorders such as postherpetic neuralgia, complex regional pain syndromes, and atypical facial pain. The stellate sympathetic ganglion innervates the head, neck, and upper extremity. In this review article, the effect of stellate ganglion block and its mechanism of action in orofacial pain disorders are discussed.

Simultaneous noninvasive recording of skin sympathetic nerve activity and electrocardiogram

BACKGROUND

Sympathetic nerve activity is important to cardiac arrhythmogenesis.

OBJECTIVE

The purpose of this study was to develop a method for simultaneous noninvasive recording of skin sympathetic nerve activity (SKNA) and electrocardiogram (ECG) using conventional ECG electrodes. This method (neuECG) can be used to adequately estimate sympathetic tone.

METHODS

We recorded neuECG signals from the skin of 56 human subjects. The signals were low-pass filtered to show the ECG and high-pass filtered to show nerve activity. Protocol 1 included 12 healthy volunteers who underwent cold water pressor test and Valsalva maneuver. Protocol 2 included 19 inpatients with epilepsy but without known heart diseases monitored for 24 hours. Protocol 3 included 22 patients admitted with electrical storm and monitored for 39.0 ± 28.2 hours. Protocol 4 included 3 patients who underwent bilateral stellate ganglion blockade with lidocaine injection.

RESULTS

In patients without heart diseases, spontaneous nerve discharges were frequently observed at baseline and were associated with heart rate acceleration. SKNA recorded from chest leads (V₁-V₆) during cold water pressor test and Valsalva maneuver (protocol 1) was invariably higher than during baseline and recovery periods (P < .001). In protocol 2, the average SKNA correlated with heart rate acceleration (r = 0.73 ± 0.14, P < .05) and shortening of QT interval (P < .001). Among 146 spontaneous ventricular tachycardia episodes recorded in 9 patients of protocol 3, 106 episodes (73%) were preceded by SKNA within 30 seconds of onset. Protocol 4 showed that bilateral stellate ganglia blockade by lidocaine inhibited SKNA.

CONCLUSION

SKNA is detectable using conventional ECG electrodes in humans and may be useful in estimating sympathetic tone.

The Adaptor Protein CD2AP Is a Coordinator of Neurotrophin Signaling-Mediated Axon Arbor Plasticity

Growth of intact axons of noninjured neurons, often termed collateral sprouting, contributes to both adaptive and pathological plasticity in the adult nervous system, but the intracellular factors controlling this growth are largely unknown. An automated functional assay of genes regulated in sensory neurons from the rat in vivo spared dermatome model of collateral sprouting identified the adaptor protein CD2-associated protein (CD2AP; human CMS) as a positive regulator of axon growth. In non-neuronal cells, CD2AP, like other adaptor proteins, functions to selectively control the spatial/temporal assembly of multiprotein complexes that transmit intracellular signals. Although CD2AP polymorphisms are associated with increased risk of late-onset Alzheimer's disease, its role in axon growth is unknown. Assessments of neurite arbor structure in vitro revealed CD2AP overexpression, and siRNA-mediated knockdown, modulated (1) neurite length, (2) neurite complexity, and (3) growth cone filopodia number, in accordance with CD2AP expression levels. We show, for the first time, that CD2AP forms a novel multiprotein complex with the NGF receptor TrkA and the PI3K regulatory subunit p85, with the degree of TrkA:p85 association positively regulated by CD2AP levels. CD2AP also regulates NGF signaling through AKT, but not ERK, and regulates long-range signaling though TrkA(+)/RAB5(+) signaling endosomes. CD2AP mRNA and protein levels were increased in neurons during collateral sprouting but decreased following injury, suggesting that, although typically considered together, these two adult axonal growth processes are fundamentally different. These data position CD2AP as a major intracellular signaling molecule coordinating NGF signaling to regulate collateral sprouting and structural plasticity of intact adult axons.

SIGNIFICANCE STATEMENT

Growth of noninjured axons in the adult nervous system contributes to adaptive and maladaptive plasticity, and dysfunction of this process may contribute to neurologic pathologies. Functional screening of genes regulated during growth of noninjured axons revealed CD2AP as a positive regulator of axon outgrowth. A novel association of CD2AP with TrkA and p85 suggests a distinct intracellular signaling pathway regulating growth of noninjured axons. This may also represent a novel mechanism of generating specificity in multifunctional NGF signaling. Divergent regulation of CD2AP in different axon growth conditions suggests that separate mechanisms exist for different modes of axon growth. CD2AP is the first signaling molecule associated with adult sensory axonal collateral sprouting, and this association may offer new insights for NGF/TrkA-related Alzheimer's disease mechanisms.

Central Sympathetic Inhibition: a Neglected Approach for Treatment of Cardiac Arrhythmias?

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. Overactivation of the sympathetic nervous system (SNS) plays an important role in the pathogenesis of comorbidities related to AF such as hypertension, congestive heart failure, obesity, insulin resistance, and obstructive sleep apnea. Methods that reduce sympathetic drive, such as centrally acting sympatho-inhibitory agents, have been shown to reduce the incidence of spontaneous or induced atrial arrhythmias, suggesting that neuromodulation may be helpful in controlling AF. Moxonidine acts centrally to reduce activity of the SNS, and clinical trials indicate that this is associated with a decreased AF burden in hypertensive patients with paroxysmal AF and reduced post-ablation recurrence of AF in patients with hypertension who underwent pulmonary vein isolation (PVI). Furthermore, device-based approaches to reduce sympathetic drive, such as renal denervation, have yielded promising results in the prevention and treatment of cardiac arrhythmias. In light of these recent findings, targeting elevated sympathetic drive with either pharmacological or device-based approaches has become a focus of clinical research. Here, we review the data currently available to explore the potential utility of sympatho-inhibitory therapies in the prevention and treatment of cardiac arrhythmias.

Transcriptional changes in sensory ganglia associated with primary afferent axon collateral sprouting in spared dermatome model

Primary afferent collateral sprouting is a process whereby non-injured primary afferent neurons respond to some stimulus and extend new branches from existing axons. Neurons of both the central and peripheral nervous systems undergo this process, which contributes to both adaptive and maladaptive plasticity (e.g., [1], [2], [3], [4], [5], [6], [7], [8], [9]). In the model used here (the “spared dermatome” model), the intact sensory neurons respond to the denervation of adjacent areas of skin by sprouting new axon branches into that adjacent denervated territory. Investigations of gene expression changes associated with collateral sprouting can provide a better understanding of the molecular mechanisms controlling this process. Consequently, it can be used to develop treatments to promote functional recovery for spinal cord injury and other similar conditions. This report includes raw gene expression data files from microarray experiments in order to study the gene regulation in spared sensory ganglia in the initiation (7 days) and maintenance (14 days) phases of the spared dermatome model relative to intact (“naïve”) sensory ganglia. Data has been deposited into GEO (GSE72551).

[Neurobiology of visceral pain]

Visceral pain is diffusely localized, referred into other tissues, frequently not correlated with visceral traumata, preferentially accompanied by autonomic and somatomotor reflexes, and associated with strong negative affective feelings. It belongs together with the somatic pain sensations and non-painful body sensations to the interoception of the body. (1) Visceral pain is correlated with the excitation of spinal (thoracolumbar, sacral) visceral afferents and (with a few exceptions) not with the excitation of vagal afferents. Spinal visceral afferents are polymodal and activated by adequate mechanical and chemical stimuli. All groups of spinal visceral afferents can be sensitized (e.g., by inflammation). Silent mechanoinsensitive spinal visceral afferents are recruited by inflammation. (2) Spinal visceral afferent neurons project into the laminae I, II (outer part IIo) and V of the spinal dorsal horn over several segments, medio-lateral over the whole width of the dorsal horn and contralateral. Their activity is synaptically transmitted in laminae I, IIo and deeper laminae to viscero-somatic convergent neurons that receive additionally afferent synaptic (mostly nociceptive) input from the skin and from deep somatic tissues of the corresponding dermatomes, myotomes and sclerotomes. (3) The second-order neurons consist of excitatory and inhibitory interneurons (about 90 % of all dorsal horn neurons) and tract neurons activated monosynaptically in lamina I by visceral afferent neurons and di- or polysynaptically in deeper laminae. (4) The sensitization of viscero-somatic convergent neurons (central sensitization) is dependent on the sensitization of spinal visceral afferent neurons, local spinal excitatory and inhibitory interneurons and supraspinal endogenous control systems. The mechanisms of this central sensitization have been little explored. (5) Viscero-somatic tract neurons project through the contralateral ventrolateral tract and presumably other tracts to the lower and upper brain stem, the hypothalamus and via the thalamus to various cortical areas. (6) Visceral pain is presumably (together with other visceral sensations and nociceptive as well as non-nociceptive somatic body sensations) primarily represented in the posterior dorsal insular cortex (primary interoceptive cortex). This cortex receives in primates its spinal synaptic inputs mainly from lamina I tract neurons via the ventromedial posterior nucleus of the thalamus. (7) The transmission of activity from visceral afferents to second-order neurons in spinal cord is modulated in an excitatory and inhibitory way by endogenous anti- and pronociceptive control systems in the lower and upper brain stem. These control systems are under cortical control. (8) Visceral pain is referred to deep somatic tissues, to the skin and to other visceral organs. This referred pain consists of spontaneous pain and mechanical hyperalgesia. The mechanisms underlying referred pain and the accompanying tissue changes have been little explored.

Using skin sympathetic nerve activity to estimate stellate ganglion nerve activity in dogs

BACKGROUND

Stellate ganglion nerve activity (SGNA) is important in cardiac arrhythmogenesis. However, direct recording of SGNA requires access to the thoracic cavity. Skin of upper thorax is innervated by sympathetic nerve fibers originating from the stellate ganglia and is easily accessible.

OBJECTIVE

The purpose of this study was to test the hypothesis that thoracic skin nerve activity (SKNA) can be used to estimate SGNA.

METHODS

We recorded SGNA and SKNAs using surface electrocardiogram leads in 5 anesthetized and 4 ambulatory dogs. Apamin injected into the right stellate ganglion abruptly increased both right SGNA and SKNA in 5 anesthetized dogs. We integrated nerve activities and averaged heart rate in each 1-minure window over 10 minutes. We implanted a radiotransmitter to record left SGNA in 4 ambulatory dogs (2 normal, 1 with myocardial infarction, 1 with intermittent rapid atrial pacing). After 2 weeks of recovery, we simultaneously recorded the SKNA and left SGNA continuously for 30 minutes when the dogs were ambulatory.

RESULTS

There was a positive correlation [average r = 0.877, 95% confidence interval (CI) 0.732-1.000, P <.05 for each dog] between integrated skin nerve activity (iSKNA) and SGNA (iSGNA) and between iSKNA and heart rate (average r = 0.837, 95% CI 0.752-0.923, P <.05). Similar to that found in the anesthetized dogs, there was a positive correlation (average r = 0.746, 95% CI 0.527-0.964, P <.05) between iSKNA and iSGNA and between iSKNA and heart rate (average r = 0.706, 95% CI 0.484-0.927, P <.05).

CONCLUSION

SKNAs can be used to estimate SGNA in dogs.

Subcutaneous nerve activity and spontaneous ventricular arrhythmias in ambulatory dogs

BACKGROUND

Stellate ganglion nerve activity (SGNA) is important in ventricular arrhythmogenesis. However, because thoracotomy is needed to access the stellate ganglion, it is difficult to use SGNA for risk stratification.

OBJECTIVE

The purpose of this study was to test the hypothesis that subcutaneous nerve activity (SCNA) in canines can be used to estimate SGNA and predict ventricular arrhythmia.

METHODS

We implanted radiotransmitters to continuously monitor left stellate ganglion and subcutaneous electrical activities in 7 ambulatory dogs with myocardial infarction, complete heart block, and nerve growth factor infusion to the left stellate ganglion.

RESULTS

Spontaneous ventricular tachycardia (VT) or ventricular fibrillation (VF) was documented in each dog. SCNA preceded a combined 61 episodes of VT and VF, 61 frequent bigeminy or couplets, and 61 premature ventricular contractions within 15 seconds in 70%, 59%, and 61% of arrhythmias, respectively. Similar incidence of 75%, 69%, and 62% was noted for SGNA. Progressive increase in SCNA [48.9 (95% confidence interval [CI] 39.3-58.5) vs 61.8 (95% CI 45.9-77.6) vs 75.1 (95% CI 57.5-92.7) mV-s] and SGNA [48.6 (95% CI 40.9-56.3) vs 58.5 (95% CI 47.5-69.4) vs 69.0 (95% CI 53.8-84.2) mV-s] integrated over 20-second intervals was demonstrated 60 seconds, 40 seconds, and 20 seconds before VT/VF (P <.05), respectively. The Pearson correlation coefficient for integrated SCNA and SGNA was 0.73 ± 0.18 (P <.0001 for all dogs, n = 5). Both SCNA and SGNA exhibited circadian variation.

CONCLUSION

SCNA can be used as an estimate of SGNA to predict susceptibility to VT and VF in a canine model of ventricular arrhythmia and sudden cardiac death.

Estimating sympathetic tone by recording subcutaneous nerve activity in ambulatory dogs

INTRODUCTION

We tested the hypothesis that subcutaneous nerve activity (SCNA) of the thorax correlates with the stellate ganglion nerve activity (SGNA) and can be used to estimate the sympathetic tone.

METHODS AND RESULTS

We implanted radio transmitters in 11 ambulatory dogs to record left SGNA, left thoracic vagal nerve activity (VNA), and left thoracic SCNA, including 3 with simultaneous video monitoring and nerve recording. Two additional dogs were studied under general anesthesia with apamin injected into the right stellate ganglion while the right SGNA and the right SCNA were recorded. There was a significant positive correlation between integrated SGNA (iSGNA) and integrated SCNA (iSCNA) in the first 7 ambulatory dogs, with correlation coefficient of 0.70 (95% confidence interval [CI] 0.61-0.84, P < 0.05 for each dog). Tachycardia episodes (heart rate exceeding 150 bpm for ≥3 seconds) were invariably preceded by SGNA and SCNA. There was circadian variation of both SCNA and SGNA. Crosstalk was ruled out because SGNA, VNA, and SCNA bursts had different timing and activation patterns. In an eighth dog, closely spaced bipolar subcutaneous electrodes also recorded SCNA, but with reduced signal to noise ratio. Video monitoring in additional 3 dogs showed that movement was not a cause of high frequency SCNA. The right SGNA correlated strongly with right SCNA and heart rate in 2 anesthetized dogs after apamin injection into the right stellate ganglion.

CONCLUSIONS

SCNA recorded by bipolar subcutaneous electrodes correlates with the SGNA and can be used to estimate the sympathetic tone.

Role of the autonomic nervous system in atrial fibrillation: pathophysiology and therapy

Autonomic nervous system activation can induce significant and heterogeneous changes of atrial electrophysiology and induce atrial tachyarrhythmias, including atrial tachycardia and atrial fibrillation (AF). The importance of the autonomic nervous system in atrial arrhythmogenesis is also supported by circadian variation in the incidence of symptomatic AF in humans. Methods that reduce autonomic innervation or outflow have been shown to reduce the incidence of spontaneous or induced atrial arrhythmias, suggesting that neuromodulation may be helpful in controlling AF. In this review, we focus on the relationship between the autonomic nervous system and the pathophysiology of AF and the potential benefit and limitations of neuromodulation in the management of this arrhythmia. We conclude that autonomic nerve activity plays an important role in the initiation and maintenance of AF, and modulating autonomic nerve function may contribute to AF control. Potential therapeutic applications include ganglionated plexus ablation, renal sympathetic denervation, cervical vagal nerve stimulation, baroreflex stimulation, cutaneous stimulation, novel drug approaches, and biological therapies. Although the role of the autonomic nervous system has long been recognized, new science and new technologies promise exciting prospects for the future.

[Primary hyperhidrosis. Current status of surgical treatment]

Primary hyperhidrosis-PH is an excessive sweating without known etiology. The PH is more frequent in women and in palms, soles and axillae. Medical treatment is not effective. The objective of the surgery is to remove or to disconnect sympathetic ganglia T2 (craniofacial PH or facial blushing), T3 (palmar PH) and T3-T4 (axillary PH). The surgical techniques are mainly resection/transection, ablation with electrocoagulation, sympathetic block by clipping and radiofrequency. Anhidrosis is achieved in 95% of the patients. The overall rate of complications is less than 5% and these are minor complications. The most important unwanted effect is reflex sweating, presented in 48% of the patients. Reflex sweating is more frequent in back, thorax and abdomen and it appears independently of the surgical technique. Ninety percent of the patients are very satisfied after surgery. Nowadays, thoracic sympathetic surgery is the gold standard for primary hyperhidrosis.

A lateral percutaneous technique for stellate ganglion blockade in rats

BACKGROUND

In the present study, we describe and show the efficacy of a lateral approach to stellate ganglion block (SGB) in rats.

METHODS

Twenty-one rats were randomized into three groups: the posterior technique group (n = 7), the lateral technique group (n = 7), and the control group (n = 7). Thiopental was administered intraperitonally as 5 mg per 100 g of each rat's weight for sedation during the procedure. In the posterior technique group, SGB was performed by a posterior percutaneous approach as described previously. In the lateral technique and control groups, the cervical vertebrae was fixed between the left first and third fingers of the physician's left hand while palpating the C7 process with the second finger. The study drug was 0.2 mL 0.25% plain bupivacaine for the two percutaneous treatment groups, and 0.2 mL saline in the controls.

RESULTS

Two animals in the posterior technique group died immediately after local anesthetic injection (P < 0.01). There were no deaths in the new technique group or in the controls. Ptosis appeared at 300 +/- 120 s in the posterior group, whereas it was seen almost immediately after withdrawing the needle in the lateral technique group (6 +/- 4 s) (P < 0.001). Ptosis did not occur in the control group. There was no statistically significant difference in heart rate among groups (P > 0.069).

CONCLUSION

The lateral approach to SGB does not require the induction of general anesthesia. The approach is associated with early development of ptosis and may be associated with a lower mortality rate compared to the conventional posterior approach.

Sensory nerves have altered function contralateral to a monoarthritis and may contribute to the symmetrical spread of inflammation

Rheumatoid arthritis (RA) and rat models of RA exhibit symmetrical mirror-image spread. Many studies have sought to understand the underlying mechanisms and have reported contralateral effects that are manifested in many different forms. It is now well accepted that neurogenic mechanisms contribute to the symmetrical spread of inflammation. However, very few investigators have directly assessed changes in contralateral nerve function and there is a paucity of data. In the present study our aim was to investigate whether there are changes, in particular in the nervous system but also in the vascular system contralateral to an inflamed rat knee joint, that might precede overt inflammation and symmetrical spread. Three to five days following Complete Freund's Adjuvant (CFA) injection we found spontaneous antidromic (away from the CNS) activity in the homologous sensory nerve contralateral to the inflamed joint. Antidromic activity of this nature is known to result in the peripheral release of pro-inflammatory and vasoactive neuropeptides. Importantly, this activity was modulated by systemic analgesic treatment. Furthermore, levels of Evans blue dye extravasation were significantly increased in the joint contralateral to inflammation, indicating altered vascular function. These data suggest that contralateral increases in sensory neural activity and vascular function may account for the symmetrical spread of RA, and that early analgesic treatment may prevent or delay the spread of this debilitating disease.

Activation and retrograde transport of protein kinase G in rat nociceptive neurons after nerve injury and inflammation

Nerve injury elicits both universal and limited responses. Among the former is regenerative growth, which occurs in most peripheral neurons, and among the latter is the long-term hyperexcitability that appears selectively in nociceptive sensory neurons. Since positive injury signals communicate information from the site of an injury to the cell body, we hypothesize that a nerve injury activates both universal and limited positive injury signals. Studies in Aplysia indicate that protein kinase G is a limited signal that is responsible for the induction of long-term hyperexcitability. Given that long-term hyperexcitability contributes to chronic pain after axotomy in rodent neuropathic pain models, we investigated its underlying basis in the rat peripheral nervous system. Using biochemical assays, Western blots, and immunocytochemistry we found that the Type 1alpha protein kinase G is the predominant isoform in the rat periphery. It is present primarily in axons and cell bodies of nociceptive neurons, including populations that are isolectin B4-positive, isolectin B4-negative, and those that express transient receptor potential vanilloid receptor-1. Surprisingly, protein kinase G is not present in the facial nerve, which overwhelmingly contains axons of motor neurons. Crushing the sciatic nerve or a cutaneous sensory nerve activates protein kinase G in axons and results in its retrograde transport to the neuronal somata in the DRG. Preventing the activation of protein kinase G by injecting Rp-8-pCPT-cGMPS into the crush site abolished the transport. The protein kinase A inhibitor Rp-8-pCPT-cAMPS had no effect. Extracellular signal-related kinases 42/44 are also activated and transported after nerve crush, but in both motor and sensory axons. Chronic pain has been linked to long-term hyperexcitability following a nerve inflammation in several rodent models. We therefore injected complete Freund's adjuvant into the hindpaw to induce an inflammation and found that protein kinase G was activated in the sural nerve and transported to the DRG. In contrast, the extracellular signal-related kinases in the sensory axons were not activated by the complete Freund's adjuvant. These studies support the idea that the extracellular signal-related kinases are universal positive axonal signals and that protein kinase G is a limited positive axonal signal. They also establish the association between protein kinase G, the induction of long-term hyperexcitability, and chronic pain in rodents.

A novel technique for experimental stellate ganglion block in rats

A stellate ganglion block (SGB) is routinely performed in a clinical setting for the treatment of sympathetically maintained pain syndromes. However, the cardiovascular effects of SGB have not been well defined. The purpose of the present study was to develop a new technique of SGB in a rat model. Our new technique of SGB is a posterior percutaneous approach and uses the cartilaginous process of the C7 spinous process as a landmark. Twenty-six Sprague-Dawley female rats were divided into six groups. Group I (n = 4) underwent right sided SGB, Group II (n = 5) underwent left-sided SGB, and Group III (n = 5) underwent bilateral SGB using bupivacaine 0.25%. Three additional sham groups (n = 4 in each group) served as controls to each of the three treatment groups. Ipsilateral eyelid droop (ptosis) was observed in all animals that underwent SGB with bupivacaine. Heart rate decreased significantly for up to 45 min after bilateral SGB compared with control groups. However, this value did not change in rats after unilateral SGB. In 9 additional rats, we evaluated the accuracy of SGB by injecting methylene blue to stain the right (n = 3), left (n = 3), and bilateral SGB (n = 3). At autopsy, 11 of 12 SG were stained post-methylene blue injection. We conclude from our study that our new approach, posterior percutaneous SGB is a reliable technique that can be used for further studies.

IMPLICATIONS

We describe a new technique for stellate ganglion block in rats that may be used in future studies to investigate the role of cervical sympathetic nervous system (especially the stellate ganglion) in regulating sympathetically maintained pain and myocardial function.

Evaluation of Sympathetic Blockade after Intrathecal and Epidural Lidocaine in Rats by Laser Doppler Perfusion Imaging

The widespread use of neuraxial anaesthesia increases the need for animal models to evaluate therapeutic prospects, mechanisms and risks of this technique. As a methodological prerequisite, we characterised the sympathetic blockade after different modes of neuraxial anaesthesia with regard to segments supplying the splanchnic region. Under haemodynamic monitoring, lidocaine 2% or saline were infused via intrathecal (10 microl), lumbar epidural (10 and 30 microl) or thoracic epidural (10 and 30 microl) catheters. Segmental spread of neuraxially infused local anaesthetic was assessed using methylene blue. Mean arterial blood pressure decreased more severely after neuraxial lidocaine in thoracic epidural (10 and 30 microl) compared to high-volume (30 microl anaesthesia animals. Determination of the sympathetic blockade by means of laser Doppler perfusion imaging was restricted to the paws due to a higher density of subcutaneous blood vessels as compared to the abdominal wall (mean +/- SD: 3.93 +/- 0.06 vs. 1.35 +/- 0.05/384 mm(2), p < 0.05). Only high-volume (30 microl) lumbar and thoracic epidural anaesthesia (10 and 30 microl) increased skin perfusion in both hind and front paws. This extensive sympathetic blockade was demonstrated to include splanchnic segments using thermography. Segmental spread of methylene blue did not closely correspond to laser Doppler findings and should be interpreted as minimum rather than exact epidural spread of local anaesthetic.

Distribution of sensory neurons of ventral and dorsal cervical cutaneous nerves in dorsal root ganglia of adult rat--a double-label study using DiO and DiI

To examine distribution of sensory neurons of ventral and dorsal cervical cutaneous nerves in dorsal root ganglia (DRGs), DiO and DiI tracers were applied at the proximal section of nerves (transverse superficial cervical and anterior supraclavicular nerves were selected as ventral cervical cutaneous nerves; dorsal cutaneous branches of second, third and fourth cervical nerves were selected as dorsal cervical cutaneous nerves). Located distributions were observed in DRGs of C2, C3, and C4 (25/46 DRGs). Sensory neurons of the ventral cervical cutaneous nerves were distributed in dorso-lateral or dorso-medial portions; neurons of dorsal cervical cutaneous nerves were distributed in ventro-medial or ventro-lateral portions of DRGs. Moreover, sensory neurons of transverse superficial cervical and anterior supraclavicular nerves were mainly distributed from the caudal half of C2 to whole part of C4 DRGs. Results show that there is a tendency for located distribution in two group sensory neurons; also, sensory neurons of ventral cervical cutaneous nerves have a segmental distribution, which has been verified in the brachial and lumbar plexus.

Sympathetic efferent pathways projecting bilaterally to the vas deferens in the rat

BACKGROUND

The laterality of the signals passing through the splanchnic nerves to the vas deferens has not been well studied.

METHODS

The present study was designed to determine the bilateral distribution of sympathetic nerves to the rat vasa deferentia by measuring intravasal pressure (VP) responses to electrical stimulation of left lumbar splanchnic nerves (LSN) following consecutive transections of more distal nerves.

RESULTS

L2-L6 LSN stimulation increased VP bilaterally. Left VP responses decreased slightly (< 20%) after section of the right hypogastric nerve (HGN) and then were abolished by subsequent section of branches (B-M-APG) between the left major pelvic (MPG) and accessory pelvic ganglia (APG). Left VP responses were decreased by > 80% after section of left HGN, not changed further by subsequent section of commissural branches (CB-MPG) between the MPG, and completely eliminated by section of commissural branches between the APG (CB-APG). Right VP responses were decreased slightly (< 20%) by section of the left HGN and then abolished by section of the right B-M-APG. These responses were also decreased by > 70% by section of right HGN, not changed by section of CB-MPG, but then completely eliminated by section of CB-APG.

CONCLUSIONS

These results indicate that the left lumbar sympathetic pathway to the vas deferens is distributed bilaterally and exhibits two crossing points at the level of the inferior mesenteric ganglion and APG.

Sympathetic efferent pathways projecting to the bladder neck and proximal urethra in the rat

The sympathetic innervation of the rat bladder neck and proximal urethra (BN/PU) was investigated by measuring BN/PU pressure responses to electrical stimulation of a left lumbar splanchnic nerve (LSN) following consecutive transections of more distal nerves. L2-L6 LSN stimulation increased BN/PU pressure. BN/PU pressure responses did not change after section of the right hypogastric nerve (HGN) but significantly decreased after subsequent sectioning of the commissural branches (CB-MPG) between the right and left major pelvic ganglia (MPG) (22%) and the commissural branches (CB-APG) between right and left accessory pelvic ganglia (APG) (30%). In other animals BN/PU pressure responses were slightly decreased (< 11%) after sectioning the left HGN and then significantly decreased by subsequent sectioning of the CB-MPG (< 21%) and CB-APG (< 36%). BN/PU pressure responses were decreased by sectioning the branches from the MPG to the APG (25%) or postganglionic nerves (MPG-PN) from the MPG to the BN/PU (37%). When the HGN on one side and all branches from the MPG on the contralateral side except for the CB-MPG were transected, increases in BN/PU intraluminal pressure were still elicited by LSN stimulation but were eliminated by transection of the CB-MPG. These results indicate that the left lumbar sympathetic pathway to the BN/PU passes through multiple crossing points at the level of the inferior mesenteric ganglion, MPG and APG and that this pathway could maintain closure of the internal urethral sphincter following various unilateral neural injuries.