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Na V 1.7 plays a crucial role in inducing and conducting action potentials in pain-transducing sensory nociceptor fibres, suggesting that Na V 1.7 blockers could be effective non-opioid analgesics. While SCN9A is expressed in both sensory and autonomic neurons, its functional role in the autonomic system remains less established. Our single neuron rt-PCR analysis revealed that 82% of sympathetic neurons isolated from guinea-pig stellate ganglia expressed Na V 1.7 mRNA, with Na V 1.3 being the only other tetrodotoxin-sensitive channel expressed in approximately 50% of neurons. We investigated the role of Na V 1.7 in conducting action potentials in postganglionic sympathetic nerves and in the sympathetic adrenergic contractions of blood vessels using selective Na V 1.7 inhibitors. Two highly selective Na V 1.7 blockers, GNE8493 and PF 05089771, significantly inhibited postganglionic compound action potentials by approximately 70% (P < 0.01), with residual activity being blocked by the Na V 1.3 inhibitor, ICA 121431. Electrical field stimulation (EFS) induced rapid contractions in guinea-pig isolated aorta, pulmonary arteries, and human isolated pulmonary arteries via stimulation of intrinsic nerves, which were inhibited by prazosin or the Na V 1 blocker tetrodotoxin. Our results demonstrated that blocking Na V 1.7 with GNE8493, PF 05089771, or ST2262 abolished or strongly inhibited sympathetic adrenergic responses in guinea-pigs and human vascular smooth muscle. These findings support the hypothesis that pharmacologically inhibiting Na V 1.7 could potentially reduce sympathetic and parasympathetic function in specific vascular beds and airways. KEY POINTS: 82% of sympathetic neurons isolated from the stellate ganglion predominantly express Na V 1.7 mRNA. Na V 1.7 blockers inhibit action potential conduction in postganglionic sympathetic nerves. Na V 1.7 blockade substantially inhibits sympathetic nerve-mediated adrenergic contractions in human and guinea-pig blood vessels. Pharmacologically blocking Na V 1.7 profoundly affects sympathetic and parasympathetic responses in addition to sensory fibres, prompting exploration into the broader physiological consequences of Na V 1.7 mutations on autonomic nerve activity., (© 2024 The Authors. The Journal of Physiology © 2024 The Physiological Society.)

Recent work demonstrated that sympathetic neurons innervate the skeletal muscle near the neuromuscular junction (NMJ), and muscle sympathectomy and sympathomimetic agents strongly influence motoneuron synaptic vesicle release ex vivo. Moreover, reports attest that the pontine nucleus locus coeruleus (LC) projects to preganglionic sympathetic neurons and regulates human mobility and skeletal muscle physiology. Thus, we hypothesized that peripheral and central sympathetic neurons projecting directly or indirectly to the skeletal muscle regulate NMJ transmission. The aim of this study was to define the specific neuronal groups in the peripheral and central nervous systems that account for such regulation in adult mice in vivo by using optogenetics and NMJ transmission recordings in 3-5-month-old, male and female ChR2(H134R/EYFP)/TH-Cre mice. After detecting ChR2(H134R)/EYFP fluorescence in the paravertebral ganglia and LC neurons, we tested whether optostimulating the plantar nerve near the lumbricalis muscle or LC neurons effectively modulates motor nerve terminal synaptic vesicle release in living mice. Nerve optostimulation increased motor synaptic vesicle release in vitro and in vivo, while the presynaptic adrenoceptor blockers propranolol (β1/β2) and atenolol (β1) prevented this outcome. The effect is primarily presynaptic since miniature end-plate potential (MEPP) kinetics remained statistically unmodified after stimulation. In contrast, optostimulation of LC neurons did not regulate NMJ transmission. In summary, we conclude that postganglionic sympathetic neurons, but not LC neurons, increased NMJ transmission by acting on presynaptic β1-adrenergic receptors in vivo., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Rationale: After cardiac damage, excessive neurite outgrowth (sympathetic hyperinnervation) can occur, which is related to ventricular arrhythmias/sudden cardiac death. Post-damage reactivation of epicardium causes epicardium-derived cells (EPDCs) to acquire a mesenchymal character, contributing to cardiac regeneration. Whether EPDCs also contribute to cardiac re/hyperinnervation, is unknown., Aim: To investigate whether mesenchymal EPDCs influence cardiac sympathetic innervation., Methods and Results: Sympathetic ganglia were co-cultured with mesenchymal EPDCs and/or myocardium, and neurite outgrowth and sprouting density were assessed. Results showed a significant increase in neurite density and directional (i.e. towards myocardium) outgrowth when ganglia were co-cultured with a combination of EPDCs and myocardium, as compared to cultures with EPDCs or myocardium alone. In absence of myocardium, this outgrowth was not directional. Neurite differentiation of PC12 cells in conditioned medium confirmed these results via a paracrine effect, in accordance with expression of neurotrophic factors in myocardial explants co-cultured with EPDCs. Of interest, EPDCs increased the expression of nerve growth factor (NGF) in cultured, but not in fresh myocardium, possibly due to an "ischemic state" of cultured myocardium, supported by TUNEL and Hif1α expression. Cardiac tissues after myocardial infarction showed robust NGF expression in the infarcted, but not remote area., Conclusion: Neurite outgrowth and density increases significantly in the presence of EPDCs by a paracrine effect, indicating a new role for EPDCs in the occurrence of sympathetic re/hyperinnervation after cardiac damage., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Beneficial effects of sesame lignans, especially antioxidative effects, have been widely reported; however, its potential effects on autonomic nerves have not yet been investigated. Therefore, the current study aimed to investigate the effect of sesame lignans on the autonomic nervous system. The sympathetic nerve activity in rat skeletal muscle was measured using electrophysiological approaches, with blood flow determined using the laser Doppler method. Sesame lignans were administered intragastrically at 2 and 20 mg/kg, and after 60 min, the sympathetic nerve activity was observed to increase by 45.2% and 66.1%, respectively. A significant increase in blood flow (39.6%) was also observed for the 20-mg/kg dose when measured at 55 min after administration. These sympathomimetic effects were completely prevented by subdiaphragmatic vagotomy, and the increase in blood flow was eliminated in the presence of the beta2-adrenergic receptor inhibitor butoxamine. Thus, it is proposed that sesame lignans can increase the blood flow of skeletal muscle, possibly by exciting sympathetic nerve activity through the afferent vagal nerve.

Introduction: Forearm QSWEAT recordings are occasionally absent in females, likely due to high skin resistance., Methods: We identified consecutive subjects with no sudomotor abnormalities but absent/markedly reduced QSWEAT forearm volume, and repeated QSWEAT at the same site after gentle abrasion., Results: QSWEAT volumes were absent for 4 subjects and markedly reduced for the other 4 (median 0.01, IQR 0-0.03). After gentle skin abrasion, repeat volumes were significantly higher for all subjects and became normal in 7 of 8 subjects., Discussion: Skin abrasion restores QSWEAT volumes in previously absent/markedly reduced site suggesting that skin preparation using abrasion is more effective., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Thoracic paravertebral sympathetic postganglionic neurons (tSPNs) comprise the final integrative output of the distributed sympathetic nervous system controlling vascular and thermoregulatory systems. Considered a non-integrating relay, what little is known of tSPN intrinsic excitability has been determined by sharp microelectrodes with presumed impalement injury. We thus undertook the first electrophysiological characterization of tSPN cellular properties using whole-cell recordings and coupled results with a conductance-based model to explore the principles governing their excitability in adult mice of both sexes. Recorded membrane resistance and time constant values were an order of magnitude greater than values previously obtained, leading to a demonstrable capacity for synaptic integration in driving recruitment. Variation in membrane resistivity was the primary determinant controlling cell excitability with vastly lower currents required for tSPN recruitment. Unlike previous microelectrode recordings in mouse which observed inability to sustain firing, all tSPNs were capable of repetitive firing. Computational modeling demonstrated that observed differences are explained by introduction of a microelectrode impalement injury conductance. Overall, tSPNs largely linearly encoded injected current magnitudes over a broad frequency range with distinct subpopulations differentiable based on repetitive firing signatures. Thus, whole-cell recordings reveal tSPNs have more dramatically amplified excitability than previously thought, with greater intrinsic capacity for synaptic integration and with the ability for maintained firing to support sustained actions on vasomotor tone and thermoregulatory function. Rather than acting as a relay, these studies support a more responsive role and possible intrinsic capacity for tSPNs to drive sympathetic autonomic function., (Copyright © 2019 McKinnon et al.)

Key Points: The mechanisms affecting recruitment patterns of postganglionic sympathetic nerves remain unclear. The divergent and convergent preganglionic innervation patterns of postganglionic neurons and the presence of differently sized postganglionic nerves suggest that the ganglia may participate in modifying the discharge patterns of single sympathetic postganglionic neurons innervating the skeletal muscle circulation. Whether the ganglia affect the ordered behaviour of varying sized postganglionic sympathetic neurons in humans has not been studied. Trimethaphan infusion produced an ordered pattern of action potential (AP) de-recruitment whereby the firing of larger, low probability APs present at baseline was abolished first, followed by progressive decreased probability of smaller APs. Although integrated sympathetic bursts were no longer detected after several minutes of trimethaphan, firing of the smallest APs was detected. These data suggest the ganglia affect the distribution of firing probabilities exhibited by differently sized sympathetic neurons. The ganglia may contribute to sympathetic neural emission patterns involved in homeostatic regulation., Abstract: Do the ganglia contribute to the ordered behaviour of postganglionic neuronal discharge within the sympathetic nervous system? To further understand the functional organization of the sympathetic nervous system we employed the microneurographic approach to record muscle sympathetic nerve activity (MSNA) and a continuous wavelet transform to study postganglionic action potential (AP) behaviour during nicotinic blockade at the ganglia (trimethaphan camsylate, 1-7 mg min -1 ) in seven females (37 ± 5 years). Trimethaphan elicited a progressive reduction in sympathetic outflow characterized by fewer integrated bursts with decaying amplitude. Underlying trimethaphan-mediated attenuations in integrated MSNA were reductions in AP incidence (186 ± 101 to 29 ± 31 AP (100 beats) -1 ) and AP content per integrated burst (7 ± 2 to 3 ± 1 APs burst -1 ) (both P < 0.01) in the final minute of detectable bursting activity in the trimethaphan condition, compared to baseline. We observed an ordered de-recruitment of larger to smaller AP clusters active at baseline (14 ± 3 to 8 ± 2 active AP clusters, P < 0.01). Following cessation of integrated bursts in the trimethaphan condition, the smallest 6 ± 2 sympathetic AP clusters persisted to fire in an asynchronous pattern (49 ± 41 AP (100 beats) -1 ) in all participants. Valsalva's manoeuvre did not increase the incidence of these persistent APs (60 ± 42 AP (100 beats) -1 , P = 0.52), or recruit any larger APs in six of seven participants (6 ± 1 total AP clusters, P = 0.30). These data suggest that the ganglia participate in the ordered recruitment of differently sized postganglionic sympathetic nerves., (© 2018 The Authors. The Journal of Physiology © 2018 The Physiological Society.)

It has long been known from microneurographic recordings in human subjects that the activity of postganglionic sympathetic axons occurs as spontaneous bursts, with muscle sympathetic nerve activity (MSNA) exhibiting strong cardiac rhythmicity via the baroreflex and skin sympathetic nerve activity showing much weaker cardiac modulation. Here we review the firing properties of single sympathetic neurons, obtained using highly selective microelectrodes. Individual vasoconstrictor neurons supplying muscle or skin, or sudomotor neurons supplying sweat glands, always discharge with a low firing probability (~30%) and at very low frequencies (~0.5 Hz). Moreover, they usually fire only once per cardiac interval but can fire greater than four times within a burst. Modeling has shown that this pattern can best be explained by individual neurons being driven by, on average, two preganglionic inputs. Unitary recordings of muscle vasoconstrictor neurons have been made in several pathophysiological states, including heart failure, hypertension, obstructive sleep apnea, bronchiectasis, chronic obstructive pulmonary disease, depression, and panic disorder. The augmented MSNA in each of these diseases features an increase in firing probability and discharge frequency of individual muscle vasoconstrictor neurons above that seen in healthy subjects, yet firing rates rarely exceed 1 Hz. However, unlike patients with heart failure, all patients with respiratory disease or panic disorder, and patients with hyperhidrosis, exhibited an increase in multiple within-burst firing, which emphasizes the different modes by which the sympathetic nervous system grades its output in pathophysiological states of high sympathetic nerve activity.

Key Points: Cardiac sympathetic afferents are considered to be essential pathways for transmission of cardiac nociception to the central nervous system during myocardial ischaemia. However, a potential contribution of the CSAR control of cardiac dysfunction in both normal and chronic heart failure (CHF) states remains unknown. We found that activation of the CSAR evokes little increase in cardiac contractility with an exaggerated peripheral vasoconstriction in the CHF state. CSAR inhibition by epicardial lidocaine decreased cardiac contractility to a greater extent in CHF rats than sham rats. Furthermore, we also found that epicardial lidocaine paradoxically decreased left ventricular end-diastolic pressure (LVEDP) and left ventricular end-diastolic volume (preload) in CHF rats, which was not observed in sham rats. Chronic ablation of the CSAR by epicardial application of the afferent neurotoxin, RTX, selectively lowered diastolic blood pressure CHF rats. The observation suggests that CSAR has a differential effect on cardiac function in normal and CHF states. CSAR activation in normal state causes significant increase in cardiac contractility and cardiac output., Abstract: The enhanced 'cardiac sympathetic afferent reflex' (CSAR) critically contributes to the exaggerated global sympathetic tone in chronic heart failure (CHF). However, a potential contribution of the cardio-cardiac reflex control of cardiac function in both normal and CHF states remains unknown. In this study, we evaluated the effects of direct activation or inhibition of the CSAR on cardiac function by pressure-volume (P-V) loop analysis in ∼12-week sham-operated and myocardial infarcted (MI) rats. In sham rats, acute CSAR activation by epicardial application of bradykinin (BK) increased heart rate (HR), left ventricular systolic pressure (LVSP), the maximum first derivative of left ventricular pressure (dp/dt max ), and the slope of the end-systolic P-V relationship (ESPVR), suggesting that acute CSAR activation in the normal state enhances myocardial contractility. CSAR activation also decreased left ventricular (LV) systolic and diastolic volumes with little effect on LV end-diastolic pressure (LVEDP) or the end-diastolic P-V relationship (EDPVR) in sham rats. Compared to sham, CHF rats exhibit a reduced increase in the slope of the ESPVR and dp/dt max in response to BK, indicating a poor contractile response to CSAR activation. Interestingly, BK application in CHF rats increased cardiac systolic and diastolic volumes and further increased the elevated LVEDP, neither of which was seen in sham rats. Following CSAR inhibition by epicardial lidocaine, blood pressure, HR, LVSP, dp/dt, LVEDP and ESPVR decreased in CHF rats whereas lidocaine had little effect in sham rats, indicating that the CSAR is tonically active in CHF and contributes to cardiac dysfunction. Furthermore, we found that epicardial lidocaine paradoxically decreased LV end-diastolic volume (preload) in CHF rats, which was not observed in sham rats. The decreased preload by lidocaine in CHF rats may be due to a reduction in peripheral vascular resistance since epicardial lidocaine significantly lowered peripheral (renal) sympathetic nerve activity in CHF rats but not in sham rats. Furthermore, chronic ablation of CSAR by epicardial application of a selective afferent neurotoxin, resiniferatoxin, selectively lowered diastolic blood pressure both at daytime and night-time with less effect on systolic blood pressure in CHF rats. Our data suggest that there is an imbalance between cardiac and peripheral responses to CSAR in CHF animals compared to sham-operated controls., (© 2017 The Authors. The Journal of Physiology © 2017 The Physiological Society.)

Key Points: Peripheral chemoreflex sensitization is a feature of renovascular hypertension. Carotid sinus nerve denervation (CSD) has recently been shown to relieve hypertension and reduce sympathetic activity in other rat models of hypertension. We show that CSD in renovascular hypertension halts further increases in blood pressure. Possible mechanisms include improvements in baroreceptor reflex sensitivity and renal function, restoration of cardiac calcium signalling towards control levels, and reduced neural inflammation. Our data suggest that the peripheral chemoreflex may be a viable therapeutic target for renovascular hypertension., Abstract: The peripheral chemoreflex is known to be hyper-responsive in both spontaneously hypertensive (SHR) and Goldblatt hypertensive (two kidney one clip; 2K1C) rats. We have previously shown that carotid sinus nerve denervation (CSD) reduces arterial blood pressure (ABP) in SHR. In the present study, we show that CSD ameliorates 2K1C hypertension and reveal the potential underlying mechanisms. Adult Wistar rats were instrumented to record ABP via telemetry, and then underwent CSD (n = 9) or sham CSD (n = 9) 5 weeks after renal artery clipping, in comparison with normal Wistar rats (n = 5). After 21 days, renal function was assessed, and tissue was collected to assess sympathetic postganglionic intracellular calcium transients ([Ca 2+ ] i ) and immune cell infiltrates. Hypertensive 2K1C rats showed a profound elevation in ABP (Wistar: 98 ± 4 mmHg vs. 2K1C: 147 ± 8 mmHg; P < 0.001), coupled with impairments in renal function and baroreflex sensitivity, increased neuroinflammatory markers and enhanced [Ca 2+ ] I in stellate neurons (P < 0.05). CSD reduced ABP in 2K1C+CSD rats and prevented the further progressive increase in ABP seen in 2K1C+sham CSD rats, with a between-group difference of 14 ± 2 mmHg by week 3 (P < 0.01), which was accompanied by improvements in both baroreflex control and spectral indicators of cardiac sympatho-vagal balance. Furthermore, CSD improved protein and albuminuria, decreased [Ca 2+ ] i evoked responses from stellate neurons, and also reduced indicators of brainstem inflammation. In summary, CSD in 2K1C rats reduces the hypertensive burden and improves renal function. This may be mediated by improvements in autonomic balance, functional remodelling of post-ganglionic neurons and reduced inflammation. Our results suggest that the peripheral chemoreflex may be considered as a potential therapeutic target for controlling renovascular hypertension., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)

A full description of the terminal architecture of sympathetic axons innervating the gastrointestinal (GI) tract has not been available. To label sympathetic fibers projecting to the gut muscle wall, dextran biotin was injected into the celiac and superior mesenteric ganglia (CSMG) of rats. Nine days postinjection, animals were euthanized and stomachs and small intestines were processed as whole mounts (submucosa and mucosa removed) to examine CSMG efferent terminals. Myenteric neurons were counterstained with Cuprolinic Blue; catecholaminergic axons were stained immunohistochemically for tyrosine hydroxylase. Essentially all dextran-labeled axons (135 of 136 sampled) were tyrosine hydroxylase-positive. Complete postganglionic arbors (n = 154) in the muscle wall were digitized and analyzed morphometrically. Individual sympathetic axons formed complex arbors of varicose neurites within myenteric ganglia/primary plexus and, concomitantly, long rectilinear arrays of neurites within circular muscle/secondary plexus or longitudinal muscle/tertiary plexus. Very few CSMG neurons projected exclusively (i.e., ∼100% of an arbor's varicose branches) to myenteric plexus (∼2%) or smooth muscle (∼14%). With less stringent inclusion criteria (i.e., ≥85% of an axon's varicose branches), larger minorities of neurons projected predominantly to either myenteric plexus (∼13%) or smooth muscle (∼27%). The majority (i.e., ∼60%) of all individual CSMG postganglionics formed mixed, heterotypic arbors that coinnervated extensively (>15% of their varicose branches per target) both myenteric ganglia and smooth muscle. The fact that ∼87% of all sympathetics projected either extensively or even predominantly to smooth muscle, while simultaneously contacting myenteric plexus, is consistent with the view that these neurons control GI muscle directly, if not exclusively. J. Comp. Neurol. 524:2577-2603, 2016. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Purpose: Cutaneous sympathetic pathophysiology in complex regional pain syndrome type 1 (CRPS-1) is not yet completely understood. To evaluate cutaneous sympathetic dysfunction in CRPS-1, we evaluated sympathetic sweat response (SSwR) and skin vasomotor reflex (SkVR) in CRPS-1 patients., Methods: We studied 10 CRPS-1 patients (age 41 ± 13 years; 5 females and 5 males; disease duration 20 ± 22 months) and 10 healthy subjects (age 44 ± 13 years; 3 females and 7 males). SkVRs and SSwRs to several sympathetic activating procedures were recorded on the palms of the CRPS-1 patients (affected side) and controls (right side)., Results: There were no significant differences in the baselines of sweat output and skin blood flow between the CRPS-1 and control groups. SSwR and SkVR amplitudes were significantly lower in the CRPS-1 group than in the control group. There was no significant correlation between disease duration and SSwR or SkVR amplitudes among the patients., Conclusions: The reduced SSwRs and SkVRs in the affected limb of our CRPS-1 patients may reflect underlying damage to the sympathetic postganglionic fibres.

Background: Novel pulse photoplethysmographic-derived indices have been proposed as tools to measure autonomic nervous system (ANS) modulation in anesthetized and awake patients, but nowadays their experimental validation is lacking. The authors aimed to investigate the ability of pulse photoplethysmographic amplitude (PPGA), ANS state (ANSS), and ANSS index (ANSSi) to measure changes of ANS modulation in response to sympathetic stimulation., Methods: Ten awake healthy volunteers underwent two passive head-up tilts at 45° and 90°. The heart rate variability (HRV) and systolic arterial pressure variability were analyzed in the frequency domain as a measure of ANS modulation directed to the heart and the vessels. HRV, baroreflex sensitivity, and pulse photoplethysmographic indices were measured at baseline and after tilt maneuvers. The agreement between HRV-derived indices and pulse photoplethysmographic indices was assessed using Bland-Altman plots., Results: PPGA, ANSS, and ANSSi changed significantly during the study protocol. Head-up tilt decreased PPGA and ANSS and increased ANNSi. There was a good agreement between ANSSi and baroreflex sensitivity explored in the high-frequency band (bias, 0.23; 95% CI, -22.7 to 23.2 normalized units) and between ANSSi and the sympathovagal modulation directed to the heart (bias, 0.96; 95% CI, -8.7 to 10.8 normalized units)., Conclusions: In controlled experimental conditions, novel pulse plethysmographic indices seem to estimate the changes of the sympathetic outflow directed to the vessels and the sympathovagal balance modulating heart rate. These indices might be useful in the future to monitor the fluctuation of sympathetic activity in anesthetized patients.

Several articles have dealt with the importance and mechanisms of the sympathetic nervous system alterations in experimental animal models of hypertension. This review addresses the role of the sympathetic nervous system in the pathophysiology and therapy of human hypertension. We first discuss the strengths and limitations of various techniques for assessing the sympathetic nervous system in humans, with a focus on heart rate, plasma norepinephrine, microneurographic recording of sympathetic nerve traffic, and measurements of radiolabeled norepinephrine spillover. We then examine the evidence supporting the importance of neuroadrenergic factors as promoters and amplifiers of human hypertension. We expand on the role of the sympathetic nervous system in 2 increasingly common forms of secondary hypertension, namely hypertension associated with obesity and with renal disease. With this background, we examine interventions of sympathetic deactivation as a mode of antihypertensive treatment. Particular emphasis is given to the background and results of recent therapeutic approaches based on carotid baroreceptor stimulation and radiofrequency ablation of the renal nerves., (© 2015 American Heart Association, Inc.)

Background: Muscle sympathetic activation in heart failure with reduced ejection fraction (HFrEF) has been attributed, on the basis of multiunit recordings, to attenuated inhibitory feedback from stretch-sensitive cardiopulmonary mechanoreceptors. However, such preparations integrate 2 populations of single units exhibiting directionally opposite firing when atrial pressure is perturbed. We tested the hypothesis that the proportion of single units firing paradoxically when filling pressure increases is augmented in HFrEF., Methods and Results: Muscle sympathetic nerve activity and estimated central venous pressure were recorded during nonhypotensive lower body negative pressure (LBNP; -10 mm Hg) and nonhypertensive positive pressure (LBPP; +10 mm Hg) in 11 treated HFrEF (left ventricular ejection fraction 25 ± 6% [mean ± standard deviation]) patients and 14 similarly aged controls. Single-unit muscle sympathetic nerve activity discharge was termed either anticipated, if firing frequency exhibited classic negative-feedback responses, or paradoxical. LBNP and LBPP had no heart rate, stroke volume, or blood pressure effects (P>0.05). Estimated central venous pressure decreased with LBNP (P<0.05), increased with LBPP (P<0.05), and was consistently higher in HFrEF (P<0.05). During LBNP, the ratio of single units with anticipated and paradoxical discharge was similar in HFrEF (18:7) and controls (27:5), whereas LBPP elicited paradoxical reflex excitation in a greater proportion of HFrEF single units (7:18 versus 24:6; P=0.0001). Consequently, LBPP increased mean single-unit firing frequency (P<0.05) and did not inhibit multiunit muscle sympathetic nerve activity of HFrEF subjects (P<0.05 versus controls). Firing of 12/18 HFrEF (but no control) single units increased during both LBPP and LBNP., Conclusion: These findings provide the first evidence in human HFrEF for an augmented excitatory cardiopulmonary-muscle sympathetic nerve activity reflex response to increased preload, incorporating 2 distinct single-unit populations with differing firing properties., (© 2014 American Heart Association, Inc.)

The segmental origins of cardiac sympathetic nerve activity (CSNA) were investigated in 8 urethane-anesthetized, artificially ventilated rats. The left upper thoracic sympathetic chain was exposed retropleurally after removing the heads of the second to fourth ribs. The preganglionic inputs to the chain from segments T1-T3 and the trunk distal to T3 were marked for later sectioning. CSNA was recorded conventionally, amplified, rectified and smoothed. Its mean level was quantified before and after each preganglionic input was cut, usually in rostro-caudal sequence. The level after all inputs were cut (i.e. noise and residual ECG pickup) was subtracted from previous measurements. The signal decrement from cutting each preganglionic input was then calculated as a percentage. CSNA in all rats depended on preganglionic drive from two or more segments, which were not always contiguous. Over the population, most preganglionic drive came from T3 and below, while the least came from T1. But there was striking inter-individual variation, such that the strongest drive to CSNA in any one rat could come from T1, T2, T3, or below T3. These findings provide new functional data on the segmental origins of CSNA in rats., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Despite the well documented and very effective non pharmacologic and pharmacologic therapies, hypertension remains often poorly controlled. There is still room for improvements in blood pressure control and recent technological advances have generated a regained interest in the physiopathology of renal sympathetic innervation in hypertension. In this article we review the evidence that renal sympathetic activity is increased in essential hypertension. The postganglionic sympathetic fibers are directed to the afferent and efferent renal arterioles, the juxtaglomerular apparatus, the proximal renal tubule, the loop of Henle, as well as the distal renal tubule and are under the control of many reflex loops, which are summarized in a most comprehensive manner for an unfamiliar reader within this field of research. Studies on renal denervation have provided further insights on the role of the sympathetic system in the kidneys, however their proper interpretation requires a special attention to the experimental protocols, as is explained in the text. Last, the possibility of kidney reinnervation is discussed, as well as the emerging evidence that the kidney is also a sensory organ. In summary, this review article provides a strong scientific background to understand not only the mechanisms of the hypotensive effects, but also those of possible pitfalls, of renal denervation.

Purpose: To evaluate directly recorded efferent sympathetic nerve traffic in patients with stress-induced cardiomyopathy (SIC)., Background: SIC is a syndrome affecting mostly postmenopausal women following severe emotional stress. Though the precise pathophysiology is not well understood, a catecholamine overstimulation of the myocardium is thought to underlie the pathogenesis., Methods: Direct recordings of multiunit efferent postganglionic muscle sympathetic nerve activity (MSNA) were obtained from 12 female patients, 5 in the acute (24-48 h) and 7 in the recovery phase (1-6 months), with apical ballooning pattern and 12 healthy matched controls. MSNA was expressed as burst frequency (BF), burst incidence (BI) and relative median burst amplitude (RMBA %). One of the twelve patients in this study was on beta blockade treatment due to a different illness, at time of onset of SIC. All patients were investigated with ongoing medication., Results: MSNA was lower in patients with SIC as compared to matched controls, but did not differ between the acute and recovery phase of SIC. RMBA %, blood pressure and heart rate did not differ between the groups., Conclusion: MSNA is shown to be lower in patients with SIC compared to healthy controls, suggesting that sympathetic neuronal outflow is rapidly reduced following the initial phase of SIC. A distension of the ventricular myocardium, due to excessive catecholamine release over the heart in the acute phase, may increase the firing rate of unmyelinated cardiac c-fibre afferents resulting in widespread sympathetic inhibition. Such a mechanism may underlie the lower MSNA reported in our patients.

Using low-frequency (0.08-0.18 Hz) sinusoidal galvanic vestibular stimulation (sGVS), we recently showed that two peaks of modulation of muscle sympathetic nerve activity (MSNA) and skin sympathetic nerve activity (SSNA) occurred for each cycle of stimulation: a large peak associated with the positive peak of the sinusoid (defined as the primary peak) and a smaller peak (defined as the secondary peak) related to the negative peak of the sinusoid. However, these recordings were only made from the left common peroneal nerve, so to investigate lateralisation of vestibulosympathetic reflexes, concurrent recordings were made from both sides of the body. Tungsten microelectrodes were inserted into muscle or cutaneous fascicles of the left and right common peroneal nerves in 17 healthy individuals. Bipolar binaural sinusoidal GVS (±2 mA, 100 cycles) was applied to the mastoid processes at 0.08 Hz. Cross-correlation analysis revealed that vestibular modulation of MSNA (10 bilateral recordings) and SSNA (6 bilateral recordings) on the left side was expressed as a primary peak related to the positive phase of the sinusoid and a secondary peak related to the negative phase of the sinusoid. Conversely, on the right side, the primary and secondary peaks were reversed: the secondary peak on the right coincided with the primary peak on the left and vice versa. Moreover, differences in pattern of outflow were apparent across sides. We believe the results support the conclusion that the left and right vestibular nuclei send both an ipsilateral and contralateral projection to the left and right medullary output nuclei from which MSNA and SSNA originate. This causes a "flip-flop" patterning between the two sympathetic outflows: when vestibular modulation of a burst is high on the left, it is low on the right, and when modulation is low on the left, it is high on the right.

Hyperthermia is defined as an elevated body temperature due to failed thermoregulation. It can occur under physiological conditions such as intense exercise or due to pathology such as malignant hyperthermia and heat stroke. It has also been implicated as a cause for sudden infant death syndrome. High temperatures are also used in medical interventions - hyperthermic chemotherapy or radiofrequency ablation, for example, which have serious side effects. The effect of hyperthermia on the central nervous system has not been fully researched, but even less is known on the effects of hyperthermia on the peripheral autonomic nervous system. In this review we discuss how conditions such as malignant or therapeutic hyperthermia affect the central and peripheral components of the autonomic nervous system, smooth muscle, skeletal muscle and cardiac muscle. We conclude that there is sufficient evidence for the detrimental effect of hyperthermia on central nerves, and that these effects are long lasting, although the major mechanism for this remains unknown. Similarly, the direct damage of hyperthermia to the enteric nerves also seems to be long lasting. In contrast, the reduced contractility of cardiac muscle and gastrointestinal smooth muscle when exposed to hyperthermia is short-lived. The consensus is that inadequate calcium handling is the mechanism of heat damage to cardiac and skeletal muscle. There is no such consensus when dealing with smooth muscle. The mechanism of hyperthermic damage to autonomic end organs such as the gastrointestinal tract has yet to be elucidated and further research into both central and peripheral hyperthermia is necessary., (Copyright © 2012 Elsevier B.V. All rights reserved.)

After oral challenge of the pathological prion protein, the pathogen was first detected in the distal ileum and then deposited in the brain. The present study aims determining the possible neuronal transport pathways from the small intestine to the brain in the cattle and sheep using a tracer protein. After horseradish peroxidase was injected into the wall in the duodenum of the calf and lamb and in the ileum of the lamb, the greater part of labeled neurons was detected in the celiac and cranial mesenteric ganglion complex. In the dorsal root ganglia T3 to L4 of both animals, some sensory neurons were always found to be labeled. Some parasympathetic preganglionic neurons were labeled in the dorsal motor nucleus of the vagus nerve after injections into the duodenum of the cattle and sheep, but extremely a small number of them were labeled after ileal application. The number of labeled sensory neurons in the nodose ganglion after duodenal injections of the sheep was much greater than that after duodenal application of the cattle. After ileal injections in the sheep, practically no labeled sensory neurons were found in the nodose ganglion. These results suggest that the pathological prion protein is mainly transported to the spinal cord and brain via the sympathetic nervous system and partially via the sensory neurons in the dorsal root ganglia. The vagus nerve seems to contribute to the transport of the pathogen not from the ileum, but from the duodenum., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Other than efferent sympathetic innervation, the kidney has peptidergic afferent fibers expressing TRPV1 receptors and releasing substance P. We tested the hypothesis that stimulation of afferent renal nerve activity with the TRPV1 agonist capsaicin inhibits efferent renal sympathetic nerve activity tonically by a neurokinin 1 receptor-dependant mechanism. Anesthetized Sprague-Dawley rats were instrumented as follows: (1) arterial and venous catheters for recording of blood pressure and heart rate and drug administration; (2) left-sided renal arterial catheter for selective intrarenal administration of the TRPV1 agonist capsaicin (3.3, 6.6, 10, 33*10(-7) m; 10 μL; after 15, 30, 45, and 60 minutes, respectively) to stimulate afferent renal nerve activity; (3) right-sided bipolar electrode for continuous renal sympathetic nerve recording; and (4) specialized renal pelvic and renal artery catheters to separate pelvic from intrarenal afferent activity. Before and after intrarenal capsaicin application, increasing intravenous doses of the neurokinin 1 receptor blocker RP67580 were given. Intrarenal capsaicin decreased integrated renal sympathetic activity from 65.4±13.0 mV*s (baseline) to 12.8±3.2 mV*s (minimum; P<0.01). This sustained renal sympathetic inhibition reached its minimum within 70 minutes and was not directly linked to the transient electric afferent response to be expected with intrarenal capsaicin. Suppressed renal sympathetic activity transiently but completely recovered after intravenous administration of the neurokinin 1 blocker (maximum: 120.3±19.4 mV*s; P<0.01). Intrarenal afferent activity could be unequivocally separated from pelvic afferent activity. For the first time we provide direct evidence that afferent intrarenal nerves provide a tonically acting sympathoinhibitory system, which seems to be rather mediated by neurokinin release acting via neurokinin 1 receptor pathways rather than by electric afferent effects on central sympathetic outflow.

Sympathetic efferent and peptidergic afferent renal nerves likely influence hypertensive and inflammatory kidney disease. Our recent investigation with confocal microscopy revealed that in the kidney sympathetic nerve endings are colocalized with afferent nerve fibers (Ditting T, Tiegs G, Rodionova K, Reeh PW, Neuhuber W, Freisinger W, Veelken R. Am J Physiol Renal Physiol 297: F1427-F1434, 2009; Veelken R, Vogel EM, Hilgers K, Amman K, Hartner A, Sass G, Neuhuber W, Tiegs G. J Am Soc Nephrol 19: 1371-1378, 2008). However, it is not known whether renal afferent nerves are influenced by sympathetic nerve activity. We tested the hypothesis that norepinephrine (NE) influences voltage-gated Ca(2+) channel currents in cultured renal dorsal root ganglion (DRG) neurons, i.e., the first-order neuron of the renal afferent pathway. DRG neurons (T11-L2) retrogradely labeled from the kidney and subsequently cultured, were investigated by whole-cell patch clamp. Voltage-gated calcium channels (VGCC) were investigated by voltage ramps (-100 to +80 mV, 300 ms, every 20 s). NE and appropriate adrenergic receptor antagonists were administered by microperfusion. NE (20 μM) reduced VGCC-mediated currents by 10.4 ± 3.0% (P < 0.01). This reduction was abolished by the α-adrenoreceptor inhibitor phentolamine and the α(2)-adrenoceptor antagonist yohimbine. The β-adrenoreceptor antagonist propranolol and the α(1)-adrenoceptor antagonist prazosin had no effect. The inhibitory effect of NE was abolished when N-type currents were blocked by ω-conotoxin GVIA, but was unaffected by other specific Ca(2+) channel inhibitors (ω-agatoxin IVA; nimodipine). Confocal microscopy revealed sympathetic innervation of DRGs and confirmed colocalization of afferent and efferent fibers within in the kidney. Hence NE released from intrarenal sympathetic nerve endings, or sympathetic fibers within the DRGs, or even circulating catecholamines, may influence the activity of peptidergic afferent nerve fibers through N-type Ca(2+) channels via an α(2)-adrenoceptor-dependent mechanism. However, the exact site and the functional role of this interaction remains to be elucidated.

The heart receives both a left and right sympathetic innervation. Currently there is no description of an in vitro whole heart preparation for comparing the influence of each sympathetic supply on cardiac function. The aim was to establish the viability of using an in vitro model to investigate the effects of left and right sympathetic chain stimulation (LSS/RSS). For this purpose the upper sympathetic chain on each side was isolated and bipolar stimulating electrodes were attached between T2-T3 and electrically insulated from surrounding tissue in a Langendorff innervated rabbit heart preparation (n=8). Heart rate (HR) was investigated during sinus rhythm, whilst dromotropic, inotropic and ventricular electrophysiological effects were measured during constant pacing (250 bpm). All responses exhibited linear increases with increases in stimulation frequency (2-10 Hz). The change in HR was larger during RSS than LSS (P<0.01), increasing by 78±9 bpm and 49±8 bpm respectively (10 Hz, baseline; 145±7 bpm). Left ventricular pressure was increased from a baseline of 50±4 mmHg, by 22±5 mmHg (LSS, 10 Hz) and 4±1 mmHg (RSS, 10 Hz) respectively (P<0.001). LSS, but not RSS, caused a shortening of basal and apical monophasic action potential duration (MAPD90). We demonstrate that RSS exerts a greater effect at the sinoatrial node and LSS at the left ventricle. The study confirms previous experiments on dogs and cats, provides quantitative data on the comparative influence of right and left sympathetic nerves and demonstrates the feasibility of isolating and stimulating the ipsilateral cardiac sympathetic supply in an in vitro innervated rabbit heart preparation., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Inflammation can profoundly alter the structure and function of the nervous system. Interleukin (IL)-17 has been implicated in the pathogenesis of several inflammatory diseases associated with nervous system plasticity. However, the effects of IL-17 on the nervous system remain unexplored. Cell and explant culture techniques, immunohistochemistry, electrophysiology, and Ca2+ imaging were used to examine the impact of IL-17 on adult mouse sympathetic neurons. Receptors for IL-17 were present on postganglionic neurons from superior mesenteric ganglia (SMG). Supernatant from activated splenic T lymphocytes, which was abundant in IL-17, dramatically enhanced axonal length of SMG neurons. Importantly, IL-17-neutralizing antiserum abrogated the neurotrophic effect of splenocyte supernatant, and incubation of SMG neurons in IL-17 (1 ng/ml) significantly potentiated neurite outgrowth. The neurotrophic effect of IL-17 was accompanied by inhibition of voltage-dependent Ca2+ influx and was recapitulated by incubation of neurons in a blocker of N-type Ca2+ channels (ω-conotoxin GVIA; 30 nM). IL-17-induced neurite outgrowth in vitro appeared to be independent of glia, as treatment with a glial toxin (AraC; 5 μM) did not affect the outgrowth response to IL-17. Moreover, application of the cytokine to distal axons devoid of glial processes enhanced neurite extension. An inhibitor of the NF-κB pathway (SC-514; 20 μM) blocked the effects of IL-17. These data represent the first evidence that IL-17 can act on sympathetic somata and distal neurites to enhance neurite outgrowth, and identify a novel potential role for IL-17 in the neuroanatomical plasticity that accompanies inflammation.

Activation of cardiac sympathetic nerves alters ventricular repolarization; however, these changes remain poorly characterized. The goal of this study was to examine effects of sympathetic stimulation on repolarization to identify electrocardiographic markers of sympathetic activation. Pigs underwent median sternotomy and bilateral thoracotomy to expose the stellate ganglia. Changes in T-wave duration, amplitude, repolarization vector, and time from peak to end (Tp-Te) were continuously monitored. Within 15 seconds of unilateral left or right stellate ganglion (LSG/RSG) stimulation, T-wave amplitude increased 6- and 4.5-fold, respectively, in lead aVF. T-wave duration and Tp-Te both increased 200% during LSG stimulation but only 50% and 30%, respectively, with RSG stimulation. During LSG stimulation, frontal and horizontal T-wave vectors, respectively, changed from 1.9° ± 22.8° and 333.8° ± 9.7° at baseline to 83.4° ± 3.9° (inferiorly) and 306.7° ± 1.8° (posteriorly). During RSG stimulation, frontal and horizontal T-wave vectors changed from 348.2° ± 21.6° and 333.8° ± 10.3° before stimulation to 280.7° ± 4.6° (superiorly) and 118.1° ± 5.6° (anteriorly). During stellate stimulation, T-wave vectors are displaced to angles specific for LSG activation (posteroinferiorly) or RSG activation (anterosuperiorly); T-wave amplitude, duration, and Tp-Te increase; and ST-duration decreases. Displaced repolarization vector and changes in T-wave morphometrics provide a novel marker of unilateral sympathetic nerve stimulation., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The aim is to verify whether glabella electrical stimulation evokes sympathetic skin responses (SSR) without inter-side differences in latency and area of the responses and is more useful in mononeuropathies than peripheral nerve stimulation. SSRs were recorded in 25 healthy subjects from right palm, third (M3SSR) and fifth fingers and contralateral third finger. The inter-side differences of grand mean area and mean of largest area of M3SSR were significant only by ulnar nerve and not by glabella stimulation. Therefore glabella stimulation may be used in mononeuropathies comparing SSR area recorded from affected side with respect to contralateral healthy side., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The effect of aging on the number, size, conduction velocity, and vasoconstrictive function of unmyelinated fibers in ovarian nerve accompanying the ovarian artery was studied in adult (4-7mo) and aged (28-31mo) rats. Morphological observation by electron microscopy showed that the ovarian nerve contains mainly unmyelinated fibers with only a small percentage (less than 4%) of myelinated fibers in either age group. The number of unmyelinated fibers tended to decrease in aged rats (717±59) compared to adult rats (801±48), especially in fibers of smaller diameter, although this difference was not statistically significant. The maximum conduction velocity of unmyelinated fibers within the ovarian nerve was similar when compared between adult (1.05±0.04m/s) and aged (1.02±0.05m/s) rats. Under anesthesia, electrical stimulation of the distal portion of a severed ovarian nerve reduced ovarian blood flow, as measured by laser Doppler flowmetry, when the stimulus intensity was above the threshold for unmyelinated C fibers. Stimulation of the ovarian nerve with supra-maximum intensity (10V) at 2-20Hz frequencies produced frequency-dependent reductions in ovarian blood flow in both adult and aged rats. There were no significant differences in magnitude of the reduction in ovarian blood flow with comparable frequencies of electrical stimulation of the ovarian nerve between adult and aged rats. Collectively, these data indicate that unmyelinated C fibers in ovarian nerve are maintained in number, size, conduction ability, and vasoconstrictor function in aged rats., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Studies previously performed in our laboratory have shown that sinusoidal galvanic vestibular stimulation (sGVS), a means of selectively modulating vestibular input without affecting other inputs, can cause partial entrainment of muscle sympathetic nerve activity (MSNA) at frequencies ranging from 0.2 to 2.0 Hz. Here we test the effect of sGVS on sympathetic outflow when stimulating the vestibular system at lower frequencies. MSNA was recorded via tungsten microelectrodes inserted into the left common peroneal nerve in 12 awake, seated subjects. Bipolar binaural sinusoidal GVS (±2 mA, 100 cycles) was applied to the mastoid processes at 0.08, 0.13 and 0.18 Hz. Cross-correlation analysis revealed two bursts of modulation of MSNA for each cycle of stimulation. We believe the primary peak is related to the positive phase of the sinusoid, in which the right vestibular nerve is hyperpolarised and the left vestibular nerve depolarised. Furthermore, we believe the secondary peak is related to the negative phase of the sinusoid (depolarisation of the right vestibular nerve and hyperpolarisation of the left vestibular nerve). This was never observed at higher frequencies of stimulation, presumably because at such frequencies there is insufficient time for a second peak to be expressed. The incidence of double peaks of MSNA was highest at 0.08 Hz and lowest at 0.18 Hz. These observations emphasise the role of the vestibular apparatus in the control of blood pressure, and further suggest convergence of bilateral inputs from vestibular nuclei onto the output nuclei from which MSNA originates, the rostral ventrolateral medulla (RVLM).

Baroreflex dysfunction contributes to increased cardiovascular risk in cigarette smokers. Given the importance of adenosinergic pathways in baroreflex control, the hypothesis was tested that defective central adenosinergic modulation of cardiac autonomic activity mediates the nicotine-baroreflex interaction. Baroreflex curves relating changes in heart rate (HR) to increases or decreases in blood pressure (BP) evoked by i.v. doses (1-16μg/kg) of phenylephrine (PE) and sodium nitroprusside (SNP), respectively, were constructed in conscious rats; slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (25 and 100μg/kg i.v.) dose-dependently reduced BRS(SNP) in contrast to no effect on BRS(PE). BRS(SNP) was also attenuated after intracisternal (i.c.) administration of nicotine. Similar reductions in BRS(SNP) were observed in rats pretreated with atropine or propranolol. The combined treatment with nicotine and atropine produced additive inhibitory effects on BRS, an effect that was not demonstrated upon concurrent exposure to nicotine and propranolol. BRS(SNP) was reduced in preparations treated with i.c. 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A(2A) antagonist), or VUF5574 (A(3) antagonist). In contrast, BRS(SNP) was preserved after blockade of A(1) (DPCPX) or A(2B) (alloxazine) receptors or inhibition of adenosine uptake by dipyridamole. CSC or 8-PT abrogated the BRS(SNP) depressant effect of nicotine whereas other adenosinergic antagonists were without effect. Together, nicotine preferentially impairs reflex tachycardia via disruption of adenosine A(2A) receptor-mediated facilitation of reflex cardiac sympathoexcitation. Clinically, the attenuation by nicotine of compensatory sympathoexcitation may be detrimental in conditions such as hypothalamic defense response, posture changes, and ventricular rhythms., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Aims: To verify whether spectral components of atrial electrograms (AE) during sinus rhythm (SR) correlate with cardiac ganglionated plexus (GP) sites., Methods and Results: Thirteen patients undergoing atrial fibrillation (AF) ablation were prospectively enrolled. Prior to radio frequency application, endocardial AE were recorded with a sequential point-by-point approach. Electrical stimuli were delivered at 20 Hz, amplitude 100 V, and pulse width of 4 ms. A vagal response was defined as a high-frequency stimulation (HFS) evoked atrioventricular block or a prolongation of RR interval. Spectral analysis was performed on single AE during SR, sampling rate of 1000 Hz, Hanning window. Overall, 1488 SR electrograms were analysed from 186 different left atrium sites, 129 of them corresponding to negative vagal response sites, and 57 to positive response sites. The electrogram duration and the number of deflections were similar in positive and negative response sites. Spectral power density of sites with vagal response was lower between 26 and 83 Hz and higher between 107 and 200 Hz compared with negative response sites. The area between 120 and 170 Hz normalized to the total spectrum area was tested as a diagnostic parameter. Receiver operating characteristic curve analysis demonstrated that an area 120-170/area(total) value >0.14 identified vagal sites with 70.9% sensitivity and 72.1% specificity., Conclusion: Spectral analysis of AE during SR in sites that correspond to the anatomical location of the GP is feasible and may be a simpler method of mapping the cardiac autonomic nervous system, compared with the HFS technique.

Sympathetic baroreflex sensitivity (BRS) is greater during decreasing compared to increasing diastolic blood pressure (DBP) in young men and women. In older men and women there is no difference in sympathetic BRS to increasing and decreasing DBP. We investigated whether the sensitivity of the central nervous system to increasing and decreasing DBP is dependent upon baseline muscle sympathetic nerve activity (MSNA). We hypothesised that the difference in sympathetic BRS between falling and rising segments of DBP would be positively related to baseline MSNA in 30 young men, 21 young women, 14 older men and 14 postmenopausal women. MSNA was measured using peroneal microneurography and BRS was measured using the spontaneous baroreflex threshold technique. On average, sympathetic BRS was greater during decreasing compared to increasing DBP in young men (P <0.05) and women (P <0.05). In older men and women, mean sympathetic BRS was similar in response to increasing and decreasing DBP. The difference (delta) between the falling and rising BRS correlated with baseline MSNA in young (r =0.58, P <0.05) and older men (r =0.66, P <0.05) and postmenopausal women (r =0.74, P <0.05). Thus, all men, and older women, with higher BRS to falling DBP had lower baseline MSNA. This relationship was not observed in young women (r =0.14, P >0.05). In summary, baseline MSNA plays a role in determining sympathetic BRS to falling and rising DBP in young and older men and postmenopausal women, but not in young women. This relationship is consistent with a decreased potential for sympathoexcitation in people with higher resting MSNA. Furthermore, the lack of relationship in young women suggests important contributions of sex hormones to differential responses of MSNA to falling and rising pressures.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a peptidergic neurotransmitter that is highly expressed in the nervous system. We have previously reported that a central injection of PACAP leads to changes in the autonomic nervous system tones including sympathetic excitation and parasympathetic inhibition. An anatomical study revealed that melanocortin and PACAP are colocalized in some hypothalamic nuclei. Here, we investigated the possible role of the melanocortin system in autonomic control by PACAP using SHU9119, an antagonist of the melanocortin receptors (MC3-R/MC4-R). Pretreatment with SHU-9119 did not affect the activating neural responses of adrenal, renal, and lumbar sympathetic nerves following a PACAP injection However, SHU9119 significantly eliminated the suppressing effect of a PACAP injection on gastric vagal nerve activity and excitation effects on liver and brown adipose tissue sympathetic nerve activities. These results suggest that the brain melanocortin system might play a key role in the control of thermogenic sympathetic outflows and digestive parasympathetic outflow by PACAP, but this system does not participate in the central effects of PACAP on cardiovascular function and neural activities of renal, adrenal, and lumbar sympathetic nerves., (Copyright © 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.)

Earlier examination reported that central injection of nesfatin-1 elevated blood pressure and suppressed food intake in conscious rats. In this study, we analyzed the effects of the intracerebroventricular injection of nesfatin-1 on the sympathetic nerve outflow to the kidney in urethane-anesthetized rats. An intracerebroventricular injection of nesfatin-1 significantly stimulated renal sympathetic nerve activity and blood pressure in a dose-dependent manner. Moreover, we examined the role of the melanocortin system on the sympathoexcitation caused by the nesfatin-1 injection. Pretreatment with the melanocortin-3/4 receptor antagonist, SHU9119, abolished the increase in nerve activity and blood pressure induced by nesfatin-1. Thus, the stimulating effects of nesfatin-1 administration on the sympathetic nerve activity of the kidney may depend on the central melanocortin system.

Strychnine-sensitive glycine receptors and glycine-immunoreactive fibers are expressed in the hypothalamic paraventricular nucleus (PVN), yet the functional significance of this innervation is unclear. Therefore, these studies examined the changes in cardiovascular and renal function and renal sympathetic nerve activity (RSNA) produced by the microinjection of glycine (5 and 50 nmol) into the PVN of conscious Sprague-Dawley rats. Microinjection of glycine into, but not outside of, the PVN dose-dependently increased urine flow rate and urinary sodium excretion and decreased RSNA. At the higher dose, PVN glycine also decreased heart rate; neither 5 nor 50 nmol PVN glycine altered mean arterial pressure. The glycine (50 nmol)-evoked diuresis and natriuresis were abolished in rats continuously infused intravenously with [Arg(8)]-vasopressin. Furthermore, chronic bilateral renal denervation prevented the bradycardia and diuresis to PVN glycine and blunted the natriuresis. In other studies, unilateral PVN pretreatment with the glycine receptor antagonist strychnine (1.6 nmol) prevented the effects of PVN glycine (50 nmol) on heart rate, RSNA, and renal excretory function. When microinjected bilaterally, PVN strychnine (1.6 nmol per site) evoked a significant increase in heart rate and RSNA without altering renal excretory function. These findings demonstrate that in conscious rats glycine acts in the PVN to enhance the renal excretion of water and sodium and decrease central sympathetic outflow to the heart and kidneys. Although endogenous PVN glycine inputs elicit a tonic control of heart rate and RSNA, the renal excretory responses to PVN glycine seem to be caused primarily by the inhibition of arginine vasopressin secretion.

The ventrolateral pons contains the A5 group of noradrenergic neurons which regulate the circulation and probably breathing. The present experiments were designed to identify these neurons definitively in vivo, to examine their response to chemoreceptor stimuli (carotid body stimulation and changes in brain pH) and to determine their effects on sympathetic outflow. Bulbospinal A5 neurons, identified by juxtacellular labelling in anaesthetized rats, had a slow regular discharge, were vigorously activated by peripheral chemoreceptor stimulation with cyanide, but only mildly activated by hyperoxic hypercapnia (central chemoreceptor stimulation). The caudal end of the A5 region also contained neurons with properties reminiscent of retrotrapezoid neurons. These cells lacked a spinal axon and were characterized by a robust response to CO2. The pH sensitivity of A5 neurons, examined in brain slices from neonatal (postnatal days 6–10) tyrosine hydroxylase (TH)-GFP transgenic mice, was about 10 times smaller than that of similarly recorded retrotrapezoid neurons. Selective stimulation of the A5 neurons in rats using channelrhodopsin optogenetics (A5 TH neurons represented 66% of transfected cells) produced fivefold greater activation of the renal nerve than the lumbar sympathetic chain. In summary, adult A5 noradrenergic neurons are vigorously activated by carotid body stimulation. This effect presumably contributes to the increase in visceral sympathetic nerve activity elicited by acute hypoxia. A5 neurons respond weakly to hypercapnia in vivo or to changes in pH in slices suggesting that their ability to sense local variations in brain pH or Pco₂ is limited.

Chemically-induced quantitative sudomotor axon reflex test (QSART) and quantitative sensory testing (QST) are established clinical tools to assess thin fiber function in humans. We investigated stimulus-response functions to transcutaneous electrical stimuli of different current intensity (3.75 to 10mA) and pulse frequency (5 to 100Hz) comparing sweat output (ml/h/m(2)) and pain intensity (numeric rating scale [NRS], 0-10). Efferent sudomotor and afferent nociceptive responses were recorded after a 30s electrical stimulation period of distal (hand and foot) and proximal (forearm and thorax) body sites with 3 repetitive measures per body site. Sweat responses increased intensity dependently and peaked (~100ml/h/m(2)) at highest currents (10mA) that had been administered. Similarly, pain ratings increased with an escalating current intensity. At a constant stimulus intensity of 7.5mA, sudomotor activity was highest (~75ml/h/m(2)) at a stimulus frequency of 20Hz without further increase at 50 or 100Hz. In contrast, pain ratings increased frequency dependently and reached NRS 7 at 100Hz. Sudomotor activity, but not pain ratings, was significantly different between the body sites (p<0.05, ANOVA) with maximum sweat responses obtained at the ventral forearm. Varying response patterns for higher stimulation frequencies between sweating (peak maximum at 20Hz) and pain (maximum at 100Hz) might indicate differential axonal properties of sympathetic efferent and nociceptive afferent fibers. Electrically induced QSART could be a useful explorative and clinical method to indirectly study characteristics of frequency-dependent axonal excitability changes of sudomotor fibers., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The location of sympathetic, somatic and sensory neurons projecting to the cranial tibial muscle of the pig hindlimb was studied with the neuronal non-transynaptic tracer Fast Blue. Additionally, the number and the size of these neurons were determinated. The Fast blue, randomly applied to the cranial tibial muscle belly of 3 pigs, labelled sympathetic neurons in the ipsilateral L5-S3 and contralateral S1 sympathetic trunk ganglia and in the prevertebral caudal mesenteric ganglia of both sides. The somatic motoneurons were identified in the ipsilateral ventral horn of the S1 segment of spinal cord, while the sensory neurons were located in the ipsilateral L7-S1 spinal ganglia. The diameter of the multipolar sympathetic neurons oscillated between 26 and 46 microm in the sympathetic trunk ganglia and between 18 and 42 microm in the caudal mesenteric ganglia. The size of the multipolar spinal motoneurons oscillated between 33 and 102 microm. The size of the pseudounipolar sensory neurons oscillated between 23 and 67 microm. In all ganglia, the labelled neurons were localized at random and did not show a somatotopic distribution. Our results document a conspicuous autonomic innervation projecting to the "classic" skeletal cranial tibial muscle. Probably this innervation is destined to the muscle vessels.

We tested the hypothesis that vestibular and cardiac rhythms compete to modulate muscle sympathetic nerve activity (MSNA) in human subjects. Sinusoidal galvanic vestibular stimulation was applied across the mastoid processes at each subject's cardiac frequency and at ±0.1, ±0.2, ±0.3 and ±0.6 Hz. Cyclic modulation of MSNA was weakest at this central frequency (44.8±2.3%; n=8); significantly lower than when delivered 0.1 Hz lower (57.7±3.3%) or 0.1 Hz higher (56.3±3.3%) than this frequency. We conclude that vestibular inputs compete with baroreceptor inputs operating at the cardiac rhythm, with vestibular modulation of MSNA being lowest when competition with the baroreceptors is highest., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Background: Pure autonomic failure (PAF) and multiple system atrophy (MSA) are both characterised by chronic dysautonomia although presenting different disability and prognosis. Skin autonomic function evaluation by indirect tests has revealed conflicting results in these disorders. Here, the authors report the first direct analysis of skin sympathetic fibres including structure and function in PAF and MSA to ascertain different underlying autonomic lesion sites which may help differentiate between the two conditions., Methods: The authors studied eight patients with probable MSA (mean age 60±5 years) and nine patients fulfilling diagnostic criteria for PAF (64±8 years). They underwent head-up tilt test (HUTT), extensive microneurographic search for muscle and skin sympathetic nerve activities from peroneal nerve and punch skin biopsies from finger, thigh and leg to evaluate cholinergic and adrenergic autonomic dermal annexes innervation graded by a semiquantitative score presenting a high level of reliability., Results: MSA and PAF patients presented a comparable neurogenic orthostatic hypotension during HUTT and high failure rate of microneurographic trials to record sympathetic nerve activity, suggesting a similar extent of chronic dysautonomia. In contrast, they presented different skin autonomic innervation in the immunofluorescence analysis. MSA patients showed a generally preserved skin autonomic innervation with a significantly higher score than PAF patients showing a marked postganglionic sympathetic denervation. In MSA patients with a long disease duration, morphological abnormalities and/or a slightly decreased autonomic score could be found in the leg reflecting a mild postganglionic involvement., Conclusion: Autonomic innervation study of skin annexes is a reliable method which may help differentiate MSA from PAF.

Is there an ordered pattern in the recruitment of postganglionic sympathetic neurones? Using new multi-unit action potential detection and analysis techniques we sought to determine whether the activation of sympathetic vasomotor neurones during stress is governed by the size principle of recruitment. Multi-unit postganglionic sympathetic activity (fibular nerve) was collected from five male subjects at rest and during periods of elevated sympathetic stress (end-inspiratory apnoeas; 178 ± 37 s(mean ± S.D.)). Compared to baseline (0.24 ± 0.04 V), periods of elevated stress resulted in augmented sympathetic burst size (1.34 ± 0.38 V, P < 0.05). Increased burst size was directly related to both the number of action potentials within a multi-unit burst of postganglionic sympathetic activity (r = 0.88 ± 0.04, P < 0.001 in all subjects), and the amplitude of detected action potentials (r = 0.88 ± 0.06, P < 0.001 in all subjects). The recruitment of larger, otherwise silent, neurons accounted for approximately 74% of the increase in detected action potentials across burst sizes. Further, action potential conduction velocities (inverse of latencies) were increased as a function of action potential size (R² = 0.936, P = 0.001). As axon diameter is positively correlated with action potential size and conduction velocity, these data suggest that the principle of ordered recruitment based on neuronal size applies to postganglionic sympathetic vasomotor neurones. This information may be pertinent to our understanding of reflex-specific recruitment strategies in postganglionic sympathetic nerves, patterns of vasomotor control during stress, and the malleability of sympathetic neuronal properties and recruitment in health and disease.

Apnea divers increase intrathoracic pressure voluntarily by taking a deep breath followed by glossopharyngeal insufflation. Because apnea divers sometimes experience hypotension and syncope during the maneuver, they may serve as a model to study the mechanisms of syncope. We recorded changes in hemodynamics and sympathetic vasomotor tone with microneurography during breath holding with glossopharyngeal insufflation. Five men became hypotensive and fainted during breath holding with glossopharyngeal insufflation within the first minute. In four divers, heart rate dropped suddenly to a minimum of 38 ± 4 beats/min. Therefore, cardioinhibitory syncope was more common than low cardiac output syncope.

The distribution and co-localisation patterns of dopamine-beta-hydroxylase (DβH), neuropeptide Y (NPY), somatostatin (SOM) and galanin (GAL) were investigated by use of retrograde neuronal tracing and double-labelling immunofluorescence techniques in the caudal mesenteric ganglion (CaMG) neurons supplying the ovary of adult pigs. The existence and density of nerve fibres that are immunoreactive (IR) for the above-mentioned neuroactive substances were also evaluated. Injections of a fluorescent tracer (Fast Blue; FB) into the ovaries revealed the presence of small- (76.38%) and large-sized (23.62%) FB-positive postganglionic neurons in the CaMG. Noradrenergic FB-positive cells were simultaneously NPY- (43.38%), SOM- (18.77%) and GAL- (18.31%) IR. Of the examined FB-positive neurons, 53.49% were DβH-IR but NPY-immunonegative (IN), 79.06% were DβH-IR but SOM-IN, and 77.16% were DβH-IR but GAL-IN. Small- or large-sized subsets of traced neurons were supplied by only one or a few nerve fibres, exhibiting DβH-, NPY-, SOM- and/or GAL-IR. Our data show the specific morphological as well as immunochemical structural organisation of the sympathetic neurons in the CaMG in adult gilts. The occurrence of an abundant population of noradrenergic perikarya in the CaMG may suggest their important physiological role in the regulation of gonadal function(s) in these animals.

Cocaine and amphetamine-regulated transcript peptide (CART) is present in a subset of sympathetic preganglionic neurons in the rat. We examined the distribution of CART-immunoreactive terminals in rat stellate and superior cervical ganglia and adrenal gland and found that they surround neuropeptide Y-immunoreactive postganglionic neurons and noradrenergic chromaffin cells. The targets of CART-immunoreactive preganglionic neurons in the stellate and superior cervical ganglia were shown to be vasoconstrictor neurons supplying muscle and skin and cardiac-projecting postganglionic neurons: they did not target non-vasoconstrictor neurons innervating salivary glands, piloerector muscle, brown fat, or adrenergic chromaffin cells. Transneuronal tracing using pseudorabies virus demonstrated that many, but not all, preganglionic neurons in the vasoconstrictor pathway to forelimb skeletal muscle were CART immunoreactive. Similarly, analysis with the confocal microscope confirmed that 70% of boutons in contact with vasoconstrictor ganglion cells contained CART, whereas 30% did not. Finally, we show that CART-immunoreactive cells represented 69% of the preganglionic neuron population expressing c-Fos after systemic hypoxia. We conclude that CART is present in most, although not all, cardiovascular preganglionic neurons but not thoracic preganglionic neurons with non-cardiovascular targets. We suggest that CART immunoreactivity may identify the postulated "accessory" preganglionic neurons, whose actions may amplify vasomotor ganglionic transmission.

Cholinergic innervation of hippocampus and cortex is required for some forms of learning and memory. Several reports have shown that activation of muscarinic m1 receptors induces a long-term depression (mLTD) at glutamate synapses in hippocampus and in several areas of cortex, including perirhinal and visual cortices. This plasticity likely contributes to cognitive function dependent upon the cholinergic system. In rodent models, degeneration of hippocampal cholinergic innervation following lesion of the medial septum stimulates sprouting of adrenergic sympathetic axons, originating from the superior cervical ganglia (SCG), into denervated hippocampal subfields. We previously reported that this adrenergic sympathetic sprouting occurs simultaneously with a reappearance of cholinergic fibers in hippocampus and rescue of mLTD at CA3-CA1 synapses. Because cholinergic neurons throughout basal forebrain degenerate in aging and Alzheimer's disease, it is critical to determine if this compensatory sprouting occurs in other regions impacted by cholinergic cell loss. To this end, we investigated whether lesion of the nucleus basalis magnocellularis (NbM) to cholinergically denervate cortex stimulates adrenergic sympathetic sprouting and the accompanying increase in cholinergic innervation. Further, we assessed whether the presence of sprouting positively correlates with the ability of glutamate synapses in acute visual cortex slices to express mLTD and low frequency stimulation induced LTD (LFS LTD), another cholinergic dependent form of plasticity in visual cortex. We found that both mLTD and LFS LTD are absent in animals when NbM lesion is combined with bilateral removal of the SCG to prevent possible compensatory sprouting. In contrast, when the SCG remain intact to permit sprouting in animals with NbM lesion, cholinergic fiber density is increased concurrently with adrenergic sympathetic sprouting, and mLTD and LFS LTD are preserved. Our findings suggest that autonomic compensation for central cholinergic degeneration is not specific to hippocampus, but is a general repair mechanism occurring in other brain regions important for normal cognitive function., (Copyright 2010 IBRO. Published by Elsevier Ltd. All rights reserved.)

Mechanisms responsible for neuropathic pain are still unclear. By using microneurography we have been able to record from single C-nociceptive and sympathetic fibers in patients and attempted to uncover possible abnormal functional properties of these fibers of relevance for pain. In two previously published studies conducted on patients with erythromelalgia and patients with diabetic neuropathy, some of the major findings were: (1) spontaneous activity in nociceptive fibers, (2) sensitization of mechano-insensitive C-fibers, and (3) an altered distribution of C-afferent nerve fibers with a reversal of the proportion of the two main subtypes of C-nociceptive fibers, indicating a loss of function of polymodal nociceptors. Although some degree of spontaneous activity and sensitization also was found in patients without pain, these mechanisms may still be of importance for the development and maintenance of neuropathic pain. A change in the distribution of C-nociceptive fibers in the skin as shown in the patients with diabetic neuropathy may help to reveal mechanisms responsible for small-fiber dysfunction.

The aim of this study was to examine whether multifibrenal sympathetic nerve activity (RSNA) of conscious rats contains frequency components of biological interest at frequencies above 25Hz. RSNA was recorded in 10 conscious Sprague-Dawley rats under baseline conditions and during infusion of vasoactive drugs that reflexly altered the mean RSNA level. The RSNA signal was band-pass filtered (300-3000Hz) before being sampled at 10,000Hz. The analytic envelope of this raw signal was then extracted using the Hilbert transform, and 132-s periods were submitted to Fourier transform analysis. Spectral power was computed from 0 to 25Hz and from 25 to 3000Hz (P(25-3000)). P(25-3000) was reduced by about 80% after either ganglionic blockade or euthanasia, which indicated that it was of biological origin and derived from the activity of postganglionic sympathetic neurons. After subtraction of post-mortem spectral power, basal P(25-3000) contributed 59.8+/-2.4% of total power. P(25-3000) was strongly barosensitive and thus, accounted for a major part of the reflex changes in total power. In each of the 10 rats, P(25-3000) was linearly correlated with the mean RSNA level (0.984+/-0.003) and even more so with the spectral power in the 0-25Hz frequency range (0.994+/-0.001). In conclusion, the RSNA of conscious rats contains very high frequency components that account for about 60% of the total spectral power and are modulated by the baroreceptor reflex. A reasonable approximation of this power can be obtained by computing spectra up to 25Hz.

Neurons in the dorsomedial hypothalamus (DMH) play a key role in mediating tachycardia elicited by emotional stress. DMH activation by microinjections of the GABA(A) antagonist evokes tachycardia and physiological changes typically seen in experimental stress. DMH inhibition abolishes the tachycardia evoked by stress. Based on anatomic evidences for lateralization in the pathways from DMH, we investigated a possible inter-hemispheric difference in DMH-evoked cardiovascular responses. In anesthetized rats we compared changes in heart rate (HR), renal sympathetic activity (RSNA), mesenteric blood flow (MBF) and tail vascular conductance produced by activation of right (R) and left (L) sides of the DMH. We also evaluated the tachycardia produced by air jet stress after inhibition of R or L DMH. There were always greater increases in RSNA when bicuculline was injected ipsilaterally to the side where these parameters were recorded (average DeltaRSNA: L=+50% and R=+26%; P<0.05). Compared to pre-injection values, right DMH activation caused pronounced decrease (0.87+/-0.1% vs. 0.4+/-0.11%/mm Hg; P<0.05), whereas bicuculline methiodide (BMI) into left DMH produced no significant changes (0.95+/-0.09% vs. 1.04+/-0.25%/mm Hg) in tail vascular conductance. R or L DMH disinhibition produced decreases in MBF, but no differences in the range of these changes were observed. Activation of the right DMH caused greater tachycardia compared to the left DMH activation (average DeltaHR: R=+92 bpm; L=+48 bpm; P<0.05). Tachycardia evoked by air jet stress was smallest after right DMH inhibition (average DeltaHR: R=+57 bpm and L=+134 bpm; P<0.05). These results indicate that the descending cardiovascular pathways from DMH are predominantly lateralized and the right DMH might exert a prominent control on heart rate changes during emotional stress.