Microneurography

Sympathetic nerve activity (SNA) is tightly coupled with the respiratory cycle. In healthy human males, respiratory modulation of SNA does not change with age. However, it is unclear how this modulation is affected by age in females. We investigated whether respiratory sympathetic modulation is altered in healthy postmenopausal (PMF) versus premenopausal female (YF), and younger male (YM) adults, and determined its relationship to resting blood pressure. Muscle SNA (MSNA; microneurography), respiration (transducer belt), ECG and continuous blood pressure were measured in 12 YF, 13 PMF and 12 YM healthy volunteers...

We conducted a meta-analysis to determine the effect of acute poikilocapnic, high-altitude, and acute isocapnia hypoxemia on muscle sympathetic nerve activity (MSNA) and cardiovascular function. A comprehensive search across electronic databases was performed until June 2021. All observational designs were included: population (healthy individuals); exposures (MSNA during hypoxemia); comparators (hypoxemia severity and duration); outcomes (MSNA; heart rate, HR; and mean arterial pressure, MAP). Sixty-one studies were included in the meta-analysis...

Bursts of muscle sympathetic nerve activity (MSNA) and the ensuing vasoconstriction are pivotal determinants of beat-by-beat blood pressure regulation. Although age and sex impact blood pressure regulation, how these factors affect the central and peripheral arcs of the baroreflex remains unclear. In 27 young (25[3] years) males (YM; n =14) and females (YF; n =13) and 23 older (71[5] years) males (OM; n =11) and females (OF; n =12) femoral artery blood flow, blood pressure and MSNA were recorded for 10 minutes of supine rest...

PURPOSE: Orthostatic hypotension is a common condition with heterogeneous and, in many cases, unclear underlying pathophysiology. Frequent symptoms are syncope and falls with a strong impact on daily life. A two-generation family with eight individuals segregating early-onset severe orthostatic hypotension with persistent tachycardia in upright position and repeated faints was identified. Our aim was to elucidate the underlying pathophysiology. METHODS: One severely affected individual underwent thorough investigation with neurophysiological and blood pressure (BP) measurements, including direct recording of baroreflex-governed sympathetic nerve signalling and induction of BP rise with phenylephrine...

INTRODUCTION: Previous studies show that COVID-19 survivors have elevated muscle sympathetic nerve activity (MSNA), endothelial dysfunction, and aortic stiffening. However, the neurovascular responses to mental stress and exercise are still unexplored. We hypothesized that COVID-19 survivors compared with age- and body mass index (BMI)-matched healthy controls exhibit abnormal neurovascular responses to mental stress and physical exercise. METHODS: Fifteen severe COVID-19 survivors (aged: 49±2 years, BMI: 30±1 kg/m2 ) and 15 well-matched control subjects (aged: 46±3 years, BMI: 29±1 kg/m2 ) were studied...

We tested the hypothesis that hyperandrogenemia in androgen excess polycystic ovary syndrome (AE-PCOS) is a primary driver in blood pressure (BP) dysregulation via altered sympathetic nervous system activity (SNSA), reduced integrated baroreflex gain and increased renin-angiotensin system (RAS) activation. We measured resting SNSA (microneurography), integrated baroreflex gain, and RAS with lower body negative pressure in obese insulin-resistant (IR) women with AE-PCOS [ n = 8, 23 ± 4 yr; body mass index (BMI) = 36...

Sudden, unexpected stimuli can induce a transient inhibition of sympathetic vasoconstriction to skeletal muscle, indicating a link to defense reactions. This phenomenon is relatively stable within, but differs between, individuals. It correlates with blood pressure reactivity which is associated with cardiovascular risk. Inhibition of muscle sympathetic nerve activity (MSNA) is currently characterized through invasive microneurography in peripheral nerves. We recently reported that brain neural oscillatory power in the beta spectrum (beta rebound) recorded with magnetoencephalography (MEG) correlated closely with stimulus-induced MSNA inhibition...

The sympathetic nervous system is important for cardiovascular regulation, particularly during acute stress. Efferent sympathetic outflow can be regulated in an organ-dependent manner, but whether renal and leg vasoconstriction is associated at rest or during sympathetic stressors is unknown. Therefore, we sought to determine the relationships between muscle sympathetic nerve activity (MSNA), leg vascular conductance (LVC), and renal vascular conductance (RVC) at rest and during common laboratory-based sympathoexcitatory stimuli in a cohort of young healthy adults...

Metadata standards are well-established for many types of electrophysiological methods but are still lacking for microneurographic recordings of peripheral sensory nerve fibers in humans. Finding a solution for daily work in the laboratory is a complex process. We have designed templates based on odML and odML-tables to structure and capture metadata and provided an extension to the existing GUI to enable database searching.

Since their initial discovery in cats, low-threshold C-fiber mechanoreceptors have become a central interest of scientists studying the affective aspects of touch. Their pursuit in humans, here termed C-tactile (CT) afferents, has led to the establishment of a research field referred to as "affective touch", which is differentiated from "discriminative touch". Presently, we review these developments based on an automated semantic analysis of more than 1000 published abstracts as well as empirical evidence and the solicited opinions of leading experts in the field...

Nociceptors are a class of primary afferent neurons that signal potentially harmful noxious stimuli. An increase in nociceptor excitability occurs in acute and chronic pain conditions. This produces abnormal ongoing activity or reduced activation thresholds to noxious stimuli. Identifying the cause of this increased excitability is required for the development and validation of mechanism-based treatments. Single-neuron electrical threshold tracking can quantify nociceptor excitability. Therefore, we have developed an application to allow such measurements and demonstrate its use in humans and rodents...

The impact of age on exercise pressor responses is equivocal, likely because of sex-specific neuro-cardiovascular changes with age. However, assessments of the interactive effects of age and sex on muscle sympathetic nerve activity (MSNA) responses to exercise are lacking. We tested the hypothesis that older females would exhibit exaggerated increases in blood pressure (BP) and MSNA discharge patterns during handgrip exercise compared with similarly aged males and young adults. Twenty-five young (25 (2) years; mean (SD)) males (YM; n = 12) and females (YF; n = 13) and 23 older (71 (5) years) males (OM; n = 11) and females (OF; n = 12) underwent assessments of BP, total peripheral resistance (TPR; Modelflow) and MSNA action potential (AP) discharge patterns (microneurography) during incremental rhythmic handgrip exercise and post-exercise circulatory occlusion (PECO)...

NEW FINDINGS: What is the topic of this review? Hereditary sensory and autonomic neuropathy type III (HSAN III). What advances does it highlight? In individuals with (HSAN III) functional muscle spindles appear to be absent throughout the body, though myelinated cutaneous afferents are present. The former may explain the poor proprioception at the knee joint, while the latter may explain why increasing cutaneous feedback improves proprioception at the knee. Reaching and lifting small objects was greatly compromised, arguing for an important role of muscles spindles in sensorimotor control...

BACKGROUND: Diabetic metabolism causes changes of the chemical milieu including accumulation of reactive carbonyl species, for example, methylglyoxal (MGO). MGO activates chemosensitive TRPA1 on nociceptors, but the contribution to neuronal pathophysiology causing pain and hyperalgesia in diabetic neuropathy is not fully understood. METHODS: We employed single-nerve-fiber recordings in type 2 diabetes patients with (spDN) and without cutaneous pain (DN) and in streptozotocin-diabetic and healthy mice...

Increased peripheral chemoreflex sensitivity is a pathogenic feature of human hypertension (HTN), while both central and peripheral chemoreflex sensitivities are reportedly augmented in animal models of HTN. Herein, we tested the hypothesis that both central and combined central and peripheral chemoreflex sensitivities are augmented in human hypertension (HTN). Fifteen HTN participants (68±5 years; mean±SD) and 13 normotensives (NT; 65±6 years) performed two modified rebreathing protocols where the partial pressure of end-tidal carbon dioxide (PET CO2 ) progressively increased while the partial pressure of end-tidal oxygen was clamped at either 150 mmHg (isoxic hyperoxia; central chemoreflex activation) or 50 mmHg (isoxic hypoxia; combined central and peripheral chemoreflex activation)...

Previous work demonstrates augmented muscle sympathetic nerve activity (MSNA) responses to the cold pressor test (CPT) in older women. Given its interindividual variability, however, the influence of baseline MSNA on CPT reactivity in older adults remains unknown. Sixty volunteers (60-83y; 30 women) completed testing where MSNA (microneurography), blood pressure (BP), and heart rate (HR) were recorded during baseline and a 2-min CPT (~4°C). Participant data were terciled by baseline MSNA (n=10/group); comparisons were made between the high baseline men (HM) and women (HW), and low baseline men (LM) and women (LW)...

The ulnar nerve is the second most commonly entrapped nerve after the median nerve. Although clinical evaluation and electrodiagnostic studies remain widely used for the evaluation of ulnar neuropathy, advancements in imaging have led to increased utilization of these newer / better imaging techniques in the overall management of ulnar neuropathy. Specifically, high-resolution ultrasonography of peripheral nerves as well as MRI has become quite useful in evaluating the ulnar nerve in order to better guide treatment...

This study tested the hypothesis that during fatiguing volitional exercise in humans, descending cortical signals and ascending skeletal muscle metaboreflex signals exert divergent control over baroreflex resetting of sympathetic action potential (AP) discharge. We quantified the baroreflex gain for sympathetic AP clusters within the muscle sympathetic nerve activity neurogram (peroneal microneurography and continuous wavelet transform) during baseline (BSL), the first 2-minutes of a 5-minute isometric handgrip (20% of maximal effort; IHG1), the last 2-minutes of IHG (IHG2), and during post-exercise circulatory occlusion (PECO) in seven healthy participants...

Peripheral neural signals recorded during neuromodulation therapies provide insights into local neural target engagement and serve as a sensitive biomarker of physiological effect. Although these applications make peripheral recordings important for furthering neuromodulation therapies, the invasive nature of conventional nerve cuffs and longitudinal intrafascicular electrodes (LIFEs) limit their clinical utility. Furthermore, cuff electrodes typically record clear asynchronous neural activity in small animal models but not in large animal models...

[This corrects the article DOI: 10.3389/fncom.2022.899584.].