Role of cardiac vagal C-fibers in cardiovascular control

The effect of microvascular decompression of the CN IX-X root entry/exit zone and the ventrolateral medulla in neurogenic hypertension involving the vertebral/basilar artery

Introduction

Neurogenic hypertension (HTN) is a type of HTN characterized by increased activity of the sympathetic nervous system. Vascular compression is one of the pathogenic mechanisms of neurogenic HTN. Despite Jannetta's solid anatomical and physiological arguments in favor of neurogenic HTN in the 1970's, the treatment for essential HTN by microvascular decompression (MVD) still lacks established selection criteria. Therefore, the subjects selected for our center were limited to patients with primary trigeminal neuralgia (TN) and primary hemifacial spasm (HFS) of the vertebral/basilar artery (VA/BA) responsible vessel type coexisting with neurogenic HTN who underwent MVD of the brainstem to further explore possible indications for MVD in the treatment of neurogenic HTN.

Methods

A retrospective analysis of 63 patients who were diagnosed with neurogenic HTN had symptoms of HFS and TN cranial nerve disease. Patients were treated at our neurosurgery department from January 2018 to January 2023. A preoperative magnetic resonance examination of the patients revealed the presence of abnormally located vascular compression in the rostral ventrolateral medulla (RVLM) and the root entry zone (REZ) of the IX and X cranial nerves (CN IX- X).

Results

There was no significant difference between the two groups in terms of gender, age, course of HFS, course of TN, course of HTN, degree of HTN, or preoperative blood pressure. Based on the postoperative blood pressure levels, nine out of 63 patients were cured (14.28%), eight cases (12.70%) showed a marked effect, 16 cases (25.40%) were effective, and 30 cases were invalid (47.62%). The overall efficacy was 52.38%. However, 39 cases of combined cranial nerve disease were on the left side of the efficacy rate (66.67%) and 24 cases of combined cranial nerve disease were on the right side of the efficacy rate (29.16%).

Discussion

Over the last few decades, many scholars have made pioneering progress in the clinical retrospective study of MVD for neurogenic hypertension, and our study confirms the efficacy of MVD in treating vertebral/basilar artery-type neurogenic hypertension by relieving the vascular pressure of RVLM. In the future, with the development and deepening of pathological mechanisms and clinical observational studies, MVD may become an important treatment for neurogenic hypertension by strictly grasping the surgical indications.

Conclusion

MVD is an effective treatment for neurogenic HTN. Indications may include the following: left-sided TN or HFS combined with neurogenic HTN; VA/BA compression in the left RVLM and REZ areas on MRI; and blood pressure in these patients cannot be effectively controlled by drugs.

Subacute Exposure to Gaseous Pollutants from Diesel Engine Exhaust Attenuates Capsaicin-Induced Cardio-Pulmonary Reflex Responses Involving Oxidant Stress Mechanisms in Adult Wistar Rats

Intravenous injection of capsaicin produces vagal-mediated protective cardio-pulmonary (CP) reflexes manifesting as tachypnea, bradycardia, and triphasic blood pressure (BP) response in anesthetized rats. Particulate matter from diesel engine exhaust has been reported to attenuate these reflexes. However, the effects of gaseous constituents of diesel exhaust are not known. Therefore, the present study was designed to investigate the effects of gaseous pollutants in diesel exhaust, on capsaicin-induced CP reflexes in rat model. Adult male rats were randomly assigned to three groups: Non-exposed (NE) group, filtered diesel exhaust-exposed (FDE) group and N-acetyl cysteine (NAC)-treated FDE group. FDE group of rats (n = 6) were exposed to filtered diesel exhaust for 5 h a day for 5 days (D1-D5), and were taken for dissection on day 6 (D6), while NE group of rats (n = 6) remained unexposed. On D6, rats were anesthetized, following which jugular vein was cannulated for injection of chemicals, and femoral artery was cannulated to record the BP. Lead II electrocardiogram and respiratory movements were also recorded. Results show that intravenous injection of capsaicin (0.1 ml; 10 µg/kg) produced immediate tachypneic, hyperventilatory, hypotensive, and bradycardiac responses in both NE and FDE groups of rats. However, these capsaicin-induced CP responses were significantly attenuated in FDE group as compared to the NE group of rats. Further, FDE-induced attenuation of capsaicin-evoked CP responses were diminished in the N-acetyl cysteine-treated FDE rats. These findings demonstrate that oxidant stress mechanisms could possibly be involved in inhibition of CP reflexes by gaseous pollutants in diesel engine exhaust.

Infrared light elicits endothelium-dependent vasodilation in isolated occipital arteries of the rat via soluble guanylyl cyclase-dependent mechanisms

The left and right occipital arteries provide blood supply to afferent cell bodies in the ipsilateral nodose and petrosal ganglia. This supply is free of an effective blood-ganglion barrier, so changes in occipital artery blood flow directly affect the access of circulating factors to the afferent cell bodies. The application of infrared (IR) light to modulate neural and other cell processes has yielded information about basic biological processes within tissues and is gaining traction as a potential therapy for a variety of disease processes. To address whether IR can directly modulate vascular function, we performed wire myography studies to determine the actions of IR on occipital arteries isolated from male Sprague-Dawley rats. Based on our previous research that functionally-important differences exist between occipital artery segments close to their origin at the external carotid artery (ECA) and those closer to the nodose ganglion, the occipital arteries were dissected into two segments, one closer to the ECA and the other closer to the nodose ganglion. Segments were constricted with 5-hydroxytryptamine to a level equal to 50% of the maximal response generated by the application of a high (80 mM) concentration of K+ ions. The direct application of pulsed IR (1,460 nm) for 5 s produced a rapid vasodilation in occipital arteries that was significantly more pronounced in segments closest to the ECA, although the ECA itself was minimally responsive. The vasodilation remained for a substantial time (at least 120 s) after cessation of IR application. The vasodilation during and following cessation of the IR application was markedly diminished in occipital arteries denuded of the endothelium. In addition, the vasodilation elicited by IR in endothelium-intact occipital arteries was substantially reduced in the presence of a selective inhibitor of the nitric oxide-sensitive guanylate cyclase, 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one (ODQ). It appears that IR causes endothelium-dependent, nitric-oxide-mediated vasodilation in the occipital arteries of the rat. The ability of IR to generate rapid and sustained vasodilation may provide new therapeutic approaches for restoring or improving blood flow to targeted tissues.

Differential contributions of cardiac, coronary and pulmonary artery vagal mechanoreceptors to reflex control of the circulation

Distinct populations of stretch‐sensitive mechanoreceptors attached to myelinated vagal afferents are found in the heart and adjoining coronary and pulmonary circulations. Receptors at atrio‐venous junctions appear to be involved in control of intravascular volume. These atrial receptors influence sympathetic control of the heart and kidney, but contribute little to reflex control of systemic vascular resistance. Baroreceptors at the origins of the coronary circulation elicit reflex vasodilatation, like feedback control from systemic arterial baroreceptors, as well as having characteristics that could contribute to regulation of mean pressure. In contrast, feedback from baroreceptors in the pulmonary artery and bifurcation is excitatory and elicits a pressor response. Elevation of pulmonary arterial pressure resets the vasomotor limb of the systemic arterial baroreflex, which could be relevant for control of sympathetic vasoconstrictor outflow during exercise and other states associated with elevated pulmonary arterial pressure. Ventricular receptors, situated mainly in the inferior posterior wall of the left ventricle, and attached to unmyelinated vagal afferents, are relatively inactive under basal conditions. However, a change to the biochemical environment of cardiac tissue surrounding these receptors elicits a depressor response. Some ventricular receptors respond, modestly, to mechanical distortion. Probably, ventricular receptors contribute little to tonic feedback control; however, reflex bradycardia and hypotension in response to chemical activation may decrease the work of the heart during myocardial ischaemia. Overall, greater awareness of heterogeneous reflex effects originating from cardiac, coronary and pulmonary artery mechanoreceptors is required for a better understanding of integrated neural control of circulatory function and arterial blood pressure.

Characterization of endothelium-dependent and -independent processes in occipital artery of the rat: Relevance to control of blood flow to nodose sensory cells

Circulating factors access cell bodies of vagal afferents in nodose ganglia (NG) via the occipital artery (OA). Constrictor responses of OA segments closer in origin from the external carotid artery (ECA) differ from segments closer to NG. Our objective was to determine the role of endothelium in this differential vasoreactivity in rat OA segments. Vasoreactivity of OA segments (proximal segments closer to ECA, distal segments closer to NG) were examined in wire myographs. We evaluated (a) vasoconstrictor effects of 5-hydroxytryptamine (5-HT) in intact and endothelium-denuded OA segments in absence/presence of soluble guanylate cyclase (SGC) inhibitor ODQ, (b) vasodilator responses elicited by NO-donor MAHMA NONOate in intact or endothelium-denuded OA segments in absence/presence of ODQ, and (c) vasodilator responses elicited by endothelium-dependent vasodilator, acetylcholine (ACh), in intact OA segments in absence/presence of ODQ. Intact distal OA responded more to 5-HT than intact proximal OA. Endothelium denudation increased 5-HT potency in both OA segments, especially proximal OA. ODQ increased maximal responses of 5HT in both segments, particularly proximal OA. ACh similarly relaxed both OA segments, effects abolished by endothelial denudation and attenuated by ODQ. MAHMA NONOate elicited transient vasodilation in both segments. Effects of ODQ against ACh were segment-dependent whereas those against MAHMA NONOate were not. The endothelium regulates OA responsiveness in a segment-dependently fashion. Endothelial cells at the OA-ECA junction more strongly influence vascular tone than those closer to NG. Differential endothelial regulation of OA tone may play a role in controlling blood flow and access of circulating factors to NG.

Air Pollution-Induced Autonomic Modulation

Air pollutants pose a serious worldwide health hazard, causing respiratory and cardiovascular morbidity and mortality. Pollutants perturb the autonomic nervous system, whose function is critical to cardiopulmonary homeostasis. Recent studies suggest that pollutants can stimulate defensive sensory nerves within the cardiopulmonary system, thus providing a possible mechanism for pollutant-induced autonomic dysfunction. A better understanding of the mechanisms involved would likely improve the management and treatment of pollution-related disease.

Microvascular decompression for trigeminal neuralgia caused by vertebrobasilar dolichoectasia: interposition technique versus transposition technique

BACKGROUND

Various techniques of microvascular decompression have been proposed for trigeminal neuralgia (TN) caused by vertebrobasilar dolichoectasia (VBD) with two main modalities: interposition and transposition. This retrospective study compares the outcomes of two techniques belonging to different modalities for VBD-associated TN.

METHODS

From January 2011 to April 2017, 39 patients underwent MVD for VBD-associated TN. The transposition method chosen was the biomedical glue sling technique. Patients were divided into the interposition group (n = 16) and the transposition group (n = 23). The radiologic data, intraoperative findings, complications, and outcomes were analyzed.

RESULTS

The 1-, 3-, and 5-year pain-free (BNI class I) maintenance rates were 100.0, 91.1, and 91.1%, respectively, in the transposition group and 87.5, 74.5, and 58.7% in the interposition group (p = 0.032). Postoperative complications were similar in both groups, but there was a trend for higher incidence of postoperative facial hypoesthesia using the interposition technique (p = 0.06).

CONCLUSION

In cases of VBD-associated TN, the transposition technique using biomedical glue was superior to the traditional interposition technique in maintaining a pain-free status, with no increase in the incidence of complication.

The Bezold-Jarisch Reflex in a Patient With Stanford Type A Acute Aortic Dissection

BACKGROUND

The Bezold-Jarisch reflex is a depressor reflex of the heart due to the preferential distribution of vagal nerves in the inferior wall of the left ventricle. We report a case of Stanford type A acute aortic dissection, in which coronary spastic angina caused the Bezold-Jarisch reflex in the acute phase.

CASE REPORT

A 53-year-old man presented with left chest pain and cold sweating. An electrocardiogram was normal and the high-sensitivity cardiac troponin T level was negative. A diagnosis of Stanford type A acute aortic dissection was made based on computed tomography (CT); there was no evidence of ischemic heart disease on coronary CT angiogram obtained simultaneously. While waiting for emergency surgical repair, chest pain worsened, followed by bradycardia and hypotension, along with ST-segment elevations in the inferior leads, all of which were resolved by conservative treatment. During surgery, no evidence to suggest an extension of the dissection to the ostium of the right coronary artery was observed. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: The present case highlights the importance of recognizing the Bezold-Jarisch reflex because this depressor reflex may require different management than other conditions.

The Bezold-Jarisch reflex in a patient with coronary spastic angina

Acute inferior myocardial damage can induce transient bradycardia and hypotension—the Bezold–Jarisch reflex, which is explained by the preferential distribution of vagal nerves in the inferior wall of the left ventricle. We report a 76‐year‐old man who showed a perfusion defect in the inferior wall with redistribution on exercise scintigraphy with thallium‐201. Of note, during exercise at an intensity of 100 watts, the patient's heart rate transiently decreased from 122 to 95 bpm in sinus rhythm, accompanied by ST‐segment depression. A diagnosis of coronary spastic angina was made since no stenotic lesions were observed on conventional coronary angiography.

Mapping of Sensory Nerve Subsets within the Vagal Ganglia and the Brainstem Using Reporter Mice for Pirt, TRPV1, 5-HT3, and Tac1 Expression

Vagal afferent sensory nerves, originating in jugular and nodose ganglia, are composed of functionally distinct subsets whose activation evokes distinct thoracic and abdominal reflex responses. We used Cre-expressing mouse strains to identify specific vagal afferent populations and map their central projections within the brainstem. We show that Pirt is expressed in virtually all vagal afferents; whereas, 5-HT3 is expressed only in nodose neurons, with little expression in jugular neurons. Transient receptor potential vanilloid 1 (TRPV1), the capsaicin receptor, is expressed in a subset of small nodose and jugular neurons. Tac1, the gene for tachykinins, is expressed predominantly in jugular neurons, some of which also express TRPV1. Vagal fibers project centrally to the nucleus tractus solitarius (nTS), paratrigeminal complex, area postrema, and to a limited extent the dorsal motor nucleus of the vagus. nTS subnuclei preferentially receive projections by specific afferent subsets, with TRPV1⁺ fibers terminating in medial and dorsal regions predominantly caudal of obex, whereas TRPV1⁻ fibers terminate in ventral and lateral regions throughout the rostral–caudal aspect of the medulla. Many vagal Tac1⁺ afferents (mostly derived from the jugular ganglion) terminate in the nTS. The paratrigeminal complex was the target of multiple vagal afferent subsets. Importantly, lung-specific TRPV1⁺ and Tac1⁺ afferent terminations were restricted to the caudal medial nTS, with no innervation of other medulla regions. In summary, this study identifies the specific medulla regions innervated by vagal afferent subsets. The distinct terminations provide a neuroanatomic substrate for the diverse range of reflexes initiated by vagal afferent activation.

Impact of Cardiovascular Neurohormones on Onset of Vasovagal Syncope Induced by Head-up Tilt

Background

Vasovagal reflex is the most common form of syncope, but the pathophysiological mechanisms that initiate the reflex are not well understood. We aimed to study supine and early orthostatic levels of the neurohormones involved in control of circulatory homeostasis in relation to the onset of tilt‐induced vasovagal syncope (VVS).

Methods and Results

A total of 827 patients who were investigated for unexplained syncope with head‐up tilt test (HUT) and optional nitroglycerin provocation (Italian protocol) had blood samples collected while supine and after 3‐minutes of HUT. Of these, 173 (20.9%) patients developed VVS during drug‐free HUT, 161 of whom (males 44.7%; age 45±21 years) had complete data. We analyzed levels of epinephrine, norepinephrine, C‐terminal pro–arginine vasopressin, C‐terminal endothelin‐1, and midregional fragments of pro–atrial natriuretic peptide and pro‐adrenomedullin in relation to time from tilt‐up to onset of VVS. We applied a linear regression model adjusted for age and sex. The mean time to syncope was 11±7 minutes. Older age (β=0.13; SE=0.03, P<0.001), higher supine systolic blood pressure (β=0.06; SE=0.03, P=0.02), and higher supine midregional fragment of pro‐adrenomedullin predicted longer time to syncope (β=2.31; SE=0.77, P=0.003), whereas supine levels of other neurohormones were not associated with time to syncope. Among 151 patients who developed VVS later than 3 minutes of HUT, increase in epinephrine (β=−3.24; SE=0.78, P<0.001) and C‐terminal pro–arginine vasopressin (β=−2.07; SE=0.61, P=0.001) at 3 minutes of HUT were related to shorter time to syncope.

Conclusions

Older age, higher blood pressure, and higher level of pro‐adrenomedullin are associated with later onset of VVS during tilt testing, whereas greater increase of tilt‐induced epinephrine and vasopressin release correlate with shorter time to syncope.

See Editorial Williford et al

Swimming exercise demonstrates advantages over running exercise in reducing proteinuria and glomerulosclerosis in spontaneously hypertensive rats

Experimental studies in animal models have described the benefits of physical exercise (PE) to kidney diseases associated with hypertension. Land- and water-based exercises induce different responses in renal function. Our aim was to evaluate the renal alterations induced by different environments of PE in spontaneously hypertensive rats (SHRs). The SHRs were divided into sedentary (S), swimming exercise (SE), and running exercise (RE) groups, and were trained for 8 weeks under similar intensities (60 min/day). Arterial pressure (AP) and heart rate (HR) were recorded. The renal function was evaluated through urinary volume at each week of training; sodium and potassium excretions, plasma and urinary osmolarities, glomerular filtration rate (GFR), levels of proteinuria, and renal damage were determined. SE and RE rats presented reduced mean AP, systolic blood pressure, and HR in comparison with S group. SE and RE rats showed higher urine osmolarity compared with S. SE rats showed higher free water clearance (P < 0.01), lower urinary density (P < 0.0001), and increased weekly urine volume (P < 0.05) in comparison with RE and S groups. GFR was increased in both SE and RE rats. The proteinuria of SE (7.0 ± 0.8 mg/24 h) rats was decreased at the 8th week of the PE in comparison with RE (9.6 ± 0.8 mg/24 h) and S (9.8 ± 0.5 mg/24 h) groups. The glomerulosclerosis was reduced in SE rats (P < 0.02). SE produced different response in renal function in comparison with RE, in which only swimming-trained rats had better profile for proteinuria and glomerulosclerosis.

Successful Cardiopulmonary Resuscitation in a Sevoflurane Anaesthetized Horse That Suffered Cardiac Arrest at Recovery

A 17-year-old mare undergoing dental surgery suffered a cardiac arrest while being transferred from the surgical theatre to the recovery box. This complication was diagnosed early, thus allowing a prompt start to the cardiopulmonary resuscitation maneuvers. External thoracic compressions, intermittent positive pressure ventilation, and adrenaline administration were at the core of this successful resuscitation. Although it was not possible to confirm the cause of cardiac arrest in this horse, a Bezold-Jarisch reflex due to potential decrease on venous return because of postural change and drug interactions was hypothesized. Based on this report, it appears advisable to smoothly change the position of anaesthetized patient; furthermore, the administration of drugs affecting cardiovascular hemodynamics or sympatho-vagal balance to animals while changing their recumbency should be avoided.

Clinical analysis and surgical treatment of trigeminal neuralgia caused by vertebrobasilar dolichoectasia: A retrospective study

BACKGROUND

Trigeminal neuralgia (TN) caused by vertebrobasilar dolichoectasia (VBD) is rare and needs further exploration. The purpose of this study is to investigate the clinical features and surgical treatment of TN caused by VBD.

METHODS

15 patients with TN caused by VBD were included in our study. The patient data regarding clinical characteristics, neuroimaging presentations, intraoperative findings and treatment outcomes were analyzed retrospectively. Moreover, the previous relevant literature was reviewed simultaneously. Simple MVD was performed in 13 cases and MVD plus trigeminal nerve selective partial posterior rhizotomy (SPPR) was conducted in 2 patients.

RESULTS

Of all patients, 7 cases were female and 8 were male. The average age at operation was 60.8 years old (range, 35yrs-75yrs). 13 patients suffered from hypertension and 7 had a history of stoke. The extended and ectatic vetebrobasilar artery (VBA) was preliminarily identified in preoperative imaging presentations and finally confirmed during surgical procedure. The facial neuralgia disappeared immediately after surgery in all patients. All patients were relieved of pain (BNI score I) with an average of 29.8 months follow-up.

CONCLUSIONS

Our results suggest that simple MVD is effective for TN caused by VBD. MVD plus SPPR can be cautiously performed if patient has advanced age and is susceptible to numbness.

Brainstem and Autonomic Nervous System Dysfunction: A Neurosurgical Point of View

Central autonomic control nuclei and pathways are mainly integrated within the brainstem, especially in the medulla oblongata. Lesions within these structures can lead to central dysautonomia.Central autonomic control structures can be damaged by tumors, during surgery, or by other neurosurgical pathologies. These may elicit clinical or subclinical autonomic complications that can constitute a serious clinical problem.The authors present a broad review of the central autonomic nervous system, its possible dysfunctions, and the relation between neurosurgery and this "not-well-known system". Preliminary results of an autonomic study of brainstem lesions that is currently being carried out by the authors are also shown.

Hypovolemic men and women regulate blood pressure differently following exposure to artificial gravity

PURPOSE

In addition to serious bone, vestibular, and muscle deterioration, space flight leads to cardiovascular dysfunction upon return to gravity. In seeking a countermeasure to space flight-induced orthostatic intolerance, we previously determined that exposure to artificial gravity (AG) training in a centrifuge improved orthostatic tolerance of ambulatory subjects. This protocol was more effective in men than women and more effective when subjects exercised.

METHODS

We now determine the orthostatic tolerance limit (OTL) of cardiovascularly deconditioned (furosemide) men and women on one day following 90 min of AG compared to a control day (90 min of head-down bed rest, HDBR).

RESULTS

There were three major findings: a short bout of artificial gravity improved orthostatic tolerance of hypovolemic men (30 %) and women (22 %). Men and women demonstrated different mechanisms of cardiovascular regulation on AG and HDBR days; women maintained systolic blood pressure the same after HDBR and AG exposure while men's systolic pressure dropped (11 ± 2.9 mmHg) after AG. Third, as presyncopal symptoms developed, men's and women's cardiac output and stroke volume dropped to the same level on both days, even though the OTL test lasted significantly longer on the AG day, indicating cardiac filling as a likely variable to trigger presyncope.

CONCLUSIONS

(1) Even with gender differences, AG should be considered as a space flight countermeasure to be applied to astronauts before reentry into gravity, (2) men and women regulate blood pressure during an orthostatic stress differently following exposure to artificial gravity and (3) the trigger for presyncope may be cardiac filling.

The implication of protein malnutrition on cardiovascular control systems in rats

The malnutrition in early life is associated with metabolic changes and cardiovascular impairment in adulthood. Deficient protein intake-mediated hypertension has been observed in clinical and experimental studies. In rats, protein malnutrition also increases the blood pressure and enhances heart rate and sympathetic activity. In this review, we discuss the effects of post-weaning protein malnutrition on the resting mean arterial pressure and heart rate and their variabilities, cardiovascular reflexes sensitivity, cardiac autonomic balance, sympathetic and renin-angiotensin activities and neural plasticity during adult life. These insights reveal an interesting prospect on the autonomic modulation underlying the cardiovascular imbalance and provide relevant information on preventing cardiovascular diseases.

Myocardial Performance Index in Neurocardiogenic Syncope Patients

BACKGROUND

Many syncopes resulting from neural reflexes in various conditions are called neurocardiogenic syncope (NCS). We aimed to investigate the presence of left ventricular (LV) myocardial performance index (MPI) in patients with NCS, which was diagnosed with head-up tilt table test (HUTT), and the accurateness of the test in order to use it as a method in patients with NCS. Assuming the MPI as a potential cause of syncope, we assessed the Tei index with non-invasive tissue Doppler echocardiography method.

METHODS

Consecutive outpatients with a history of recurrent unexplained syncope underwent HUTT. Twenty-nine HUTT (+) patients (24 female and five male, mean age: 30 ± 15 years) as the study group and HUTT (-) 23 healthy patients (six female and 17 male, mean age: 34 ± 16 years) as the control group were included into the study. Conventional and tissue Doppler echocardiography was performed to both groups. The MPI was determined by using PW Doppler. Measurements of Doppler time intervals, according to Tei index ((isovolumic contraction time + isovolumic relaxation time)/ejection time) is calculated as (a - b/b), where "a" is the interval between cessation and onset of the mitral inflow, and "b" is the ejection time (ET) at the LV outflow.

RESULTS

When comparing the groups in terms of MPI and ET, there was significant difference between groups. Patients with NCS had significantly longer ET and lower MPI value than control group (284 ± 24 ms vs. 260 ± 24 ms, P < 0.001, respectively and 0.44 ± 0.7 vs. 0.52 ± 0.8, P < 0.001, respectively). There was no significant difference in ejection fraction between groups.

CONCLUSION

In the present study, LV MPI value decreases in patients with NCS.

Sympathetic dysfunction in vasovagal syncope and the postural orthostatic tachycardia syndrome

Orthostatic intolerance is the inability to tolerate the upright posture and is relieved by recumbence. It most commonly affects young women and has a major impact on quality of life and psychosocial well-being. Several forms of orthostatic intolerance have been described. The most common one is the recurrent vasovagal syncope (VVS) phenotype which presents as a transient and abrupt loss of consciousness and postural tone that is followed by rapid recovery. Another common type of orthostatic intolerance is the postural orthostatic tachycardia syndrome (POTS) which is characterized by an excessive rise in heart rate upon standing and is associated with symptoms of presyncope such as light-headedness, fatigue, palpitations, and nausea. Maintenance of arterial pressure under condition of reduced central blood volume during the orthostasis is accomplished in large part through sympathetic efferent nerve traffic to the peripheral vasculature. Therefore sympathetic nervous system (SNS) dysfunction is high on the list of possible contributors to the pathophysiology of orthostatic intolerance. Investigations into the role of the SNS in orthostatic intolerance have yielded mixed results. This review outlines the current knowledge of the function of the SNS in both VVS and POTS.

Cardiorespiratory coupling of sympathetic outflow in humans: a comparison of respiratory and cardiac modulation of sympathetic nerve activity to skin and muscle

NEW FINDINGS

What is the central question of this study?Muscle sympathetic nerve activity (MSNA) is well known to be modulated by the arterial baroreceptors and respiration, but what are the magnitudes of cardiac and respiratory modulation of skin sympathetic nerve activity (SSNA), which primarily subserves thermoregulation?What is the main finding and what is its importance?Using direct microelectrode recordings of MSNA and SSNA in awake humans, we show that the magnitude of respiratory modulation of SSNA is identical to that of MSNA, the primary difference between the two sources of sympathetic outflow being the greater cardiac modulation of MSNA. This emphasises the role of the baroreceptors in entraining sympathetic outflow to muscle. It is well known that microelectrode recordings of skin sympathetic nerve activity (SSNA) in awake human subjects reveal spontaneous bursts of activity with no overt modulation by changes in blood pressure or respiration, in contrast to the clear cardiac and respiratory modulation of muscle sympathetic nerve activity (MSNA). However, cross-correlation analysis has revealed that, like individual muscle vasoconstrictor neurones, the firing of individual cutaneous vasoconstrictor neurones is temporally coupled to both the cardiac and respiratory rhythms during cold-induced cutaneous vasoconstriction, and the same is true of single sudomotor neurones during heat-induced sweating. Here, we used cross-correlation analysis to determine whether SSNA exhibits cardiac and respiratory modulation in thermoneutral conditions and to compare respiratory and cardiac modulation of SSNA with that of MSNA. Oligounitary recordings of spontaneous SSNA (n = 20) and MSNA (n = 18) were obtained during quiet, unrestrained breathing. Respiration was recorded by a strain-gauge transducer around the chest and ECG recorded by surface electrodes. Respiratory and cardiac modulation of SSNA and MSNA were quantified by fitting polynomial equations to the cross-correlation histograms constructed between the sympathetic spikes and respiration or ECG. The amplitude of the respiratory modulation (52.5 ± 3.4%) of SSNA was not significantly different from the amplitude of the cardiac modulation (46.6 ± 3.2%). Both were comparable to the respiratory modulation of MSNA (47.7 ± 4.2%), while cardiac modulation of MSNA was significantly higher (89.8 ± 1.5%). We conclude that SSNA and MSNA share similar levels of respiratory modulation, the primary difference between the two sources of sympathetic outflow being the marked cardiac modulation of MSNA provided by the baroreceptors.

The unsilent majority-TRPV1 drives "spontaneous" transmission of unmyelinated primary afferents within cardiorespiratory NTS

Cranial primary afferent sensory neurons figure importantly in homeostatic control of visceral organ systems. Of the two broad classes of visceral afferents, the role of unmyelinated or C-type class remains poorly understood. This review contrasts key aspects of peripheral discharge properties of C-fiber afferents and their glutamate transmission mechanisms within the solitary tract nucleus (NTS). During normal prevailing conditions, most information arrives at the NTS through myelinated A-type nerves. However, most of visceral afferent axons (75-90%) in NTS are unmyelinated, C-type axons. Centrally, C-type solitary tract (ST) afferent terminals have presynaptic transient receptor potential vanilloid type 1 (TRPV1) receptors. Capsaicin activation of TRPV1 blocks phasic or synchronous release of glutamate but facilitates release of glutamate from a separate pool of vesicles. This TRPV1-operated pool of vesicles is active at normal temperatures and is responsible for actively driving a 10-fold higher release of glutamate at TRPV1 compared with TRPV1- terminals even in the absence of afferent action potentials. This novel TRPV1 mechanism is responsible for an additional asynchronous release of glutamate that is not present in myelinated terminals. The NTS is rich with presynaptic G protein-coupled receptors, and the implications of TRPV1-operated glutamate offer unique targets for signaling in C-type sensory afferent terminals from neuropeptides, inflammatory mediators, lipid metabolites, cytokines, and cannabinoids. From a homeostatic view, this combination could have broad implications for integration in chronic pathological disturbances in which the numeric dominance of C-type endings and TRPV1 would broadly disturb multisystem control mechanisms.

Age-dependence of relative change in circulating epinephrine and norepinephrine concentrations during tilt-induced vasovagal syncope

BACKGROUND

Although vasovagal syncope (VVS) is preceded by a surge of circulating catecholamines (epinephrine [Epi] and norepinephrine [NE]) of adrenal/renal and synaptic origin, prevention of VVS with β-adrenergic blockade has been ineffective except in "older" VVS patients.

OBJECTIVE

We hypothesized that age-related differences of β-blocker effect may be due in part to differences in the relative magnitudes of Epi and NE release during an evolving faint, specifically, greater Epi/NE ratio in younger fainters compared to older patients. To assess this hypothesis, we measured changes in Epi/NE ratios in younger (<40 years) vs older (≥40 years) patients during head-up tilt-table test-induced VVS.

METHODS

The study comprised 29 patients (12 patients ≥40 years [mean 56 ± 10.7 years] and 17 patients <40 years mean 25 ± 5.7 years]) with recurrent suspected VVS in whom 70° head-up tilt testing reproduced symptoms. Arterial Epi and NE concentrations were measured at baseline (supine), 2 minutes of head-up tilt, and syncope.

RESULTS

Baseline Epi and NE concentrations and the Epi/NE ratio did not differ in younger and older groups (Epi: 90 ± 65 pg/mL vs 70 ± 32 pg/mL; NE: 226 ± 122 pg/mL vs 244 ± 183 pg/mL). However, Epi/NE ratio increased to a greater extent in younger fainters during head-up tilt and tended to be greater in younger patients at both 2 minutes (<40: 1.02 ± 1.29 vs ≥40: 0.40 ± 0.27, P = .11) and at symptoms (<40: 2.6 ± 1.26 vs ≥40: 1.6 ± 0.71, P = .03). At symptoms, Epi/NE ratio ≥2.5 was observed in 9 of 17 younger patients vs 1 of 12 older patients (P = .02).

CONCLUSION

Epi/NE ratios tend to be greater in younger fainters, a finding that may account in part for the observation that β-blocker therapy is less effective in reducing VVS susceptibility in younger individuals.

Unprovoked atrial tachyarrhythmias in aging spontaneously hypertensive rats: the role of the autonomic nervous system

Experimental models of unprovoked atrial tachyarrhythmias (AT) in conscious, ambulatory animals are lacking. We hypothesized that the aging, spontaneously hypertensive rat (SHR) may provide such a model. Baseline ECG recordings were acquired with radiotelemetry in eight young (14-wk-old) and eight aging (55-wk-old) SHRs and in two groups of four age-matched Wistar-Kyoto (WKY) rats. Quantification of AT and heart rate variability (HRV) analysis were performed based on 24-h ECG recordings in unrestrained rats. All animals were submitted to an emotional stress protocol (air-jet). In SHRs, carbamylcholine injections were also performed. Spontaneous AT episodes were observed in all eight aging SHRs (median, 91.5; range, 4-444 episodes/24 h), but not in young SHRs or WKY rats. HRV analysis demonstrated significantly decreased low frequency components in aging SHRs compared with age-matched WKY rats (P < 0.01) and decreased low/high frequency ratios in both young (P < 0.01) and aging (P = 0.01) SHRs compared with normotensive controls. In aging SHRs, emotional stress significantly reduced the number of arrhythmic events, whereas carbamylcholine triggered AT and significantly increased atrial electrical instability. This study reports the occurrence of unprovoked episodes of atrial arrhythmia in hypertensive rats, and their increased incidence with aging. Our results suggest that autonomic imbalance with relative vagal hyperactivity may be responsible for the increased atrial arrhythmogenicity observed in this model. We also provide evidence that, in this model, the sympatho-vagal imbalance preceded the occurrence of arrhythmia. These results indicate that aging SHRs may provide valuable insight into the understanding of atrial arrhythmias.

GABA(B)-mediated inhibition of multiple modes of glutamate release in the nucleus of the solitary tract

In the caudal portions of the solitary tract (ST) nucleus, primary sensory afferents fall into two broad classes based on the expression of transient receptor potential vanilloid type 1 (TRPV1) receptors. Both afferent classes (TRPV1+/-) have indistinguishable glutamate release mechanisms for ST-evoked excitatory postsynaptic currents (EPSCs). However, TRPV1+ terminals release additional glutamate from a unique, TRPV1-operated vesicle pool that is temperature sensitive and facilitated by ST activity to generate asynchronous EPSCs. This study tested whether presynaptic γ-aminobutyric acid (GABA)(B) receptors inhibit both the evoked and TRPV1-operated release mechanisms on second-order ST nucleus neurons. In horizontal slices, shocks activated single ST axons and evoked the time-invariant (latency jitter <200 μs), glutamatergic EPSCs, which identified second-order neurons. Gabazine eliminated GABA(A) responses in all recordings. The GABA(B) agonist baclofen inhibited the amplitude of ST-EPSCs from both TRPV1+ and TRPV1- afferents with a similar EC(50) (∼1.2 μM). In TTX, GABA(B) activation decreased miniature EPSC (mEPSC) rates but not amplitudes, suggesting presynaptic actions downstream from terminal excitability. With calcium entry through voltage-activated calcium channels blocked by cadmium, baclofen reduced mEPSC frequency, indicating that GABA(B) reduced vesicle release by TRPV1-dependent calcium entry. GABA(B) activation also reduced temperature-evoked increases in mEPSC frequency, which relies on TRPV1. Our studies indicate that GABA(B) G protein-coupled receptors are uniformly distributed across all ST primary afferent terminals and act at multiple stages of the excitation-release cascades to suppress both action potential-triggered and TRPV1-coupled glutamate transmission pathways. Moreover, the segregated release cascades within TRPV1+ ST primary afferents represent independent, potential targets for differential modulation.

Bezold-Jarisch reflex in sino-aortic denervated malnourished rats

In this study we assessed the role of Bezold-Jarisch reflex (BJR) in the regulation of blood pressure (BP) of malnourished (MN) and control rats (CN) with sino-aortic denervation (SAD). Fischer rats were fed diets containing either 6% (MN) or 15% (CN) protein for 35 days after weaning. These rats underwent sham or SAD and catheterization of femoral artery and vein for BP measurements and drug injection. Phenylbiguanide (PBG 5 μg/kg, i.v.) for activation BJR, produced bradycardia (-317±22 bpm for CN vs. -372±16 bpm for MN) and hypotension (-57±4 mm Hg for CN vs. -54±6 mm Hg for MN. After SAD, MN rats had reduced hypotensive (-37±7 mm Hg for MN vs. -82±6 mm Hg for CN) and bradycardic (-124±17 for MN vs. -414±20 bpm CN) responses to BJR activation. To evaluate the contribution of the parasympathetic component due to BJR for the fall in BP, methyl atropine bromide, was given between two injections of PBG (5 μg/kg) separated by 10 min each other. Both bradycardic (-216±21 bpm before and -4±3 bpm after for CN -226±43 bpm before and -9±20 bpm after for MN) and hypotensive (-42±4 mm Hg before and -6±1 mm Hg after for CN -33±9 mm Hg before and -5±2 mm Hg after for MN) responses were abolished in CN and MN groups. These data indicate that dietary protein malnutrition changes the relation between baroreflex and BJR required for maintenance of the BP during malnourishment.

Cardiovascular effects induced by N-(4'-dihydro)-piperoylthiomorpholine in normotensive rats

Objectives

We have tested the cardiovascular effects of N-(4′-dihydro)-piperoylthiomorpholine (LASSBio 365) on rats using an in-vivo and in-vitro approach.

Methods

LASSBio 365 (0.025, 0.05, 0.1, 0.25, 0.5 or 1 mg/kg, randomly injected) was administered to conscious unrestrained rats and the mean arterial pressure and heart rate were measured. The effects of LASSBio 365 (3 × 10−6–3 × 10−4m) on rat isolated aortic rings with and without endothelium were investigated.

Key findings

LASSBio 365 induced a dose-dependent decrease in mean arterial pressure and heart rate (ED50 = 158 ± 53 µg/kg). The effects evoked by LASSBio 365 (0.5 mg/kg) were inhibited by pretreatment with atropine. In anaesthetized rats, electrocardiogram recordings revealed second/third degree sinoatrial and atrioventricular blockade induced by the compound, which were completely inhibited after cardiac muscarinic blockade or cervical bilateral vagotomy. In rat isolated aortic rings, LASSBio 365 (3 × 10−6–3 × 10−4m) was capable of antagonizing the contractile effects induced by phenylephrine (1 µm) or KCl (80 mm) (IC50 = 107 ± 6; 92 ± 6 µm, respectively). This effect was not inhibited after removal of the vascular endothelium (IC50 = 84 ± 4; 92 ± 10 µm, respectively). LASSBio 365 (10−6–10−4m) antagonized CaCl2-induced contractions in a concentration-dependent manner. Furthermore, LASSBio 365 (98 µm) inhibited contractions produced by noradrenaline (1 µm), but not those induced by caffeine (20 mm).

Conclusions

These results suggested that LASSBio 365 produced negative chronotropism and reduced peripheral resistance that were probably due to the stimulation of cardiac muscarinic pathways. Peripheral vasodilation was probably linked to voltage-dependent Ca2+-channel blockade and/or specific inhibition of Ca2+ release from noradrenaline-sensitive intracellular stores.

Microvascular Decompression in the Treatment of Trigeminal Neuralgia Caused by Vertebrobasilar Ectasia

BACKGROUND

Vertebrobasilar ectasia (VBE) is a rare cause of trigeminal neuralgia (TN). It occurs in about 2% of all patients.

OBJECTIVE

This study reviewed the clinical features, radiological concomitants, and surgical findings of VBE and evaluate the microsurgical decompression procedure as a surgical line of treatment of the associated TN.

METHODS

Ten patients with TN caused by VBE and treated by microvascular decompression are the subject of this study. The study consisted of 6 men and 4 women with a mean age of 54 years. The mean duration of symptoms was 4.5 years. TN was the only symptom in 6 patients; it was associated with hemifacial spasm in 4. Arterial hypertension was present in 6 patients. Multiplanar high-resolution magnetic resonance imaging showed the accurate location and course of the ectatic vessel. Magnetic resonance angiography and digital subtraction angiography confirmed the diagnosis. Surgery demonstrated fifth nerve compression by an ectatic and tortuous vertebrobasilar artery in all cases and seventh nerve compression in 4 cases. Teflon felt was placed between the ectatic artery and compressed nerves.

RESULTS

There was complete resolution of TN in 8 patients (80%) and hemifacial spasm in 3 (75%) without medication. Four of 6 hypertensive patients (66.7%) achieved normotension without medication. There was no recurrence of symptoms in the mean follow-up period of 7.8 years.

CONCLUSION

Microvascular decompression is recommended for the treatment of TN caused by VBE if medical treatment has failed, if the patient is suitable for general anesthesia, and if there is evidence of vascular compression of the trigeminal nerve on magnetic resonance imaging.

Effect of carotid and aortic baroreceptors on cardiopulmonary reflex: the role of autonomic function

We determined the sympathetic and parasympathetic control of heart rate (HR) and the sensitivity of the cardiopulmonary receptors after selective carotid and aortic denervation. We also investigated the participation of the autonomic nervous system in the Bezold-Jarish reflex after selective removal of aortic and carotid baroreceptors. Male Wistar rats (220-270 g) were divided into three groups: control (CG, N = 8), aortic denervation (AG, N = 5) and carotid denervation (CAG, N = 9). AG animals presented increased arterial pressure (12%) and HR (11%) compared with CG, while CAG animals presented a reduction in arterial pressure (16%) and unchanged HR compared with CG. The sequential blockade of autonomic effects by atropine and propranolol indicated a reduction in vagal function in CAG (a 50 and 62% reduction in vagal effect and tonus, respectively) while AG showed an increase of more than 100% in sympathetic control of HR. The Bezold-Jarish reflex was evaluated using serotonin, which induced increased bradycardia and hypotension in AG and CAG, suggesting that the sensitivity of the cardiopulmonary reflex is augmented after selective denervation. Atropine administration abolished the bradycardic responses induced by serotonin in all groups; however, the hypotensive response was still increased in AG. Although the responses after atropine were lower than the responses before the drug, indicating a reduction in vagal outflow after selective denervation, our data suggest that both denervation procedures are associated with an increase in sympathetic modulation of the vessels, indicating that the sensitivity of the cardiopulmonary receptors was modulated by baroreceptor fibers.