Muscle Afferents (muscle + afferent)

Distribution by Scientific Domains
Distribution within Life Sciences


Selected Abstracts


Induction of prolonged tenderness in patients with tension-type headache by means of a new experimental model of myofascial pain

EUROPEAN JOURNAL OF NEUROLOGY, Issue 3 2003
H. Mørk
Tenderness is the most prominent abnormal finding in patients with tension-type headache (TTH). Recently we developed a model of myofascial tenderness using intramuscular infusion of a combination of bradykinin, serotonin, histamine and prostaglandin E2. We aimed to examine tenderness after this combination in patients with episodic TTH (ETTH). Fifteen patients and 15 healthy controls completed the study. Participants received the combination into the non-dominant trapezius muscle in a randomized, double-blinded and placebo-controlled design. Local tenderness and stimulus,response functions, mechanical pain thresholds (PPDT) in the temporal region and on the finger, and total tenderness score (TTS) were recorded. A local, prolonged, and mild to moderate tenderness was reported both in patients (P = 0.001) and in controls (P = 0.001) after the combination compared with the placebo. The response to the combination tended to be increased in patients. The stimulus,response function was leftward shifted after the combination, compared with baseline in both groups. No changes in PPDT or TTS were found after the infusions, whereas baseline PPDTs were decreased in ETTH compared with controls (PPDTfinger: P = 0.033; PPDTtemporal: P = 0.015). Intramuscular infusion of a combination of endogenous substances induced prolonged tenderness in both patients with episodic TTH and healthy subjects. The present results suggest an increased excitability of peripheral muscle afferents in TTH. [source]


Functional subdivision of feline spinal interneurons in reflex pathways from group Ib and II muscle afferents; an update

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2010
Elzbieta Jankowska
Abstract A first step towards understanding the operation of a neural network is identification of the populations of neurons that contribute to it. Our aim here is to reassess the basis for subdivision of adult mammalian spinal interneurons that mediate reflex actions from tendon organs (group Ib afferents) and muscle spindle secondary endings (group II afferents) into separate populations. Re-examining the existing experimental data, we find no compelling reasons to consider intermediate zone interneurons with input from group Ib afferents to be distinct from those co-excited by group II afferents. Similar patterns of distributed input have been found in subpopulations that project ipsilaterally, contralaterally or bilaterally, and in both excitatory and inhibitory interneurons; differences in input from group I and II afferents to individual interneurons showed intra- rather than inter-population variation. Patterns of reflex actions evoked from group Ib and II afferents and task-dependent changes in these actions, e.g. during locomotion, may likewise be compatible with mediation by premotor interneurons integrating information from both group I and II afferents. Pathological changes after injuries of the central nervous system in humans and the lineage of different subclasses of embryonic interneurons may therefore be analyzed without need to consider subdivision of adult intermediate zone interneurons into subpopulations with group Ib or group II input. We propose renaming these neurons ,group I/II interneurons'. [source]


The changes in neuromuscular excitability with normobaric hyperoxia in humans

EXPERIMENTAL PHYSIOLOGY, Issue 1 2010
Christelle Brerro-Saby
Based on previous observations in hyperbaric hyperoxia, we hypothesized that normobaric hyperoxia, often used during general anaesthesia and resuscitation, might also induce a neuromuscular excitability. In heathy volunteers, we studied the consequences of a 50 min period of pure oxygen breathing on the neuromuscular conduction time (CT), the amplitude of the compound evoked muscle potential (M-wave), the latency and amplitude of the Hoffman reflex (H reflex) and the electromyographic tonic vibratory response (TVR) of the flexor digitorum superficialis muscle to explore the proprioceptive reflex loop. Hyperoxia-induced oxidative stress was measured by the changes in blood markers of lipid peroxidation (thiobarbituric acid reactive substances, TBARS) and antioxidant response (reduced ascorbic acid, RAA). During hyperoxia, the M-wave amplitude increased, both CT and H reflex latency were shortened, and the H reflex amplitude increased. By contrast, TVR significantly decreased. Concomitantly, an oxidative stress was assessed by increased TBARS and decreased RAA levels. This study shows the existence of dual effects of hyperoxia, which facilitates the muscle membrane excitability, nerve conduction and spinal reflexes, but reduces the gain of the proprioceptive reflex loop. The activation of the group IV muscle afferents by hyperoxia and the resulting oxidative stress might explain the TVR depression. [source]


Muscle afferent contributions to the cardiovascular response to isometric exercise

EXPERIMENTAL PHYSIOLOGY, Issue 6 2004
James P. Fisher
The cardiovascular response to isometric exercise is governed by both central and peripheral mechanisms. Both metabolic and mechanical stresses on the exercising skeletal muscle produce cardiovascular change, yet it is often overlooked that the afferent signal arising from the muscle can be modified by factors other than exercise intensity. This review discusses research revealing that muscle fibre type, muscle mass and training status are important factors in modifying this peripheral feedback from the active muscles. Studies in both animals and humans have shown that the pressor response resulting from exercise of muscle with a faster contractile character and isomyosin content is greater than that from a muscle of slower contractile character. Athletic groups participating in training programmes that place a high anaerobic load on skeletal muscle groups show attenuated muscle afferent feedback. Similarly, longitudinal studies have shown that specific local muscle training also blunts the pressor response to isometric exercise. Thus it appears that training may decrease the metabolic stimulation of muscle afferents and in some instances chronic exposure to the products of anaerobic metabolism may blunt the sensitivity of the muscle metaboreflex. There may be surprising parallels between the local muscle conditions induced in athletes training for longer sprint events (e.g. 400 m) and by the low-flow conditions in, for example, the muscles of chronic heart failure patients. Whether their similar attenuations in muscle afferent feedback during exercise are due to decreased metabolite accumulation or to a desensitization of the muscle afferents is not yet known. [source]


The role of cutaneous sensation in the motor function of the hand

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2004
Ayman M. Ebied
Abstract We studied the effect of abolishing cutaneous sensation (by infiltrating local anaesthetic around the median nerve at the wrist) on the ability of 10 healthy volunteers (a) to maintain a submaximal isometric pinch-grip force for 30 s without visual feedback, and (b) to perform a fine finger-manipulation ,handwriting" task. Blocking cutaneous sensation had no effect on ability to maintain pinch force, suggesting that muscle afferents have the major role in force-control feedback. However, a near-linear fall in force, present with or without block (mean slope = ,1.3 ± 0.2% s,1), which cannot be attributed to motor fatigue, reveals a shortcoming of the afferent feedback system. Blocking cutaneous sensation did impair ability to perform the more demanding writing task, as judged by an 18 ± 6% increase in the length of the path between target points, a 22 ± 9% increase in the duration of the movement and a 63 ± 24% in ,normalised averaged rectified jerk", an averaged time-derivative of acceleration (all significantly nonzero, P < 0.04). These experiments demonstrate the relative importance of muscular and cutaneous afferent feedback on two aspects of hand performance, and provide a way to quantify the deficit resulting from the lack of cutaneous sensation. © 2003 Published by Elsevier Ltd. on behalf of Orthopaedic Research Society. All rights reserved. [source]


Glial cell line-derived neurotrophic factor-responsive and neurotrophin-3-responsive neurons require the cytoskeletal linker protein dystonin for postnatal survival

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2001
Julie A. Carlsten
Abstract We have investigated the fate of different neurotrophin-responsive subpopulations of dorsal root ganglion neurons in dystonia musculorum (dt) mice. These mice have a null mutation in the cytoskeletal linker protein, dystonin. Dystonin is expressed by all sensory neurons and cross links actin filaments, intermediate filaments, and microtubules. The dt mice undergo massive sensory neurodegeneration postnatally and die at around 4 weeks of age. We assessed the surviving and degenerating neuronal populations by comparing the dorsal root ganglion (DRG) neurons and central and peripheral projections in dt mice and wildtype mice. Large, neurofilament-H-positive neurons, many of which are muscle afferents and are neurotrophin-3 (NT-3)-responsive, were severely decreased in number in dt DRGs. The loss of muscle afferents was correlated with a degeneration of muscle spindles in skeletal muscle. Nerve growth factor (NGF)-responsive populations, which were visualized using calcitonin gene-related peptide and p75, appeared qualitatively normal in the lumbar spinal cord, DRG, and hindlimb skin. In contrast, glial cell line-derived neurotrophic factor (GDNF)-responsive populations, which were visualized using the isolectin B-4 and thiamine monophosphatase, were severely diminished in the lumbar spinal cord, DRG, and hindlimb skin. Analysis of NT-3, NGF, and GDNF mRNA levels using semiquantitative reverse transcriptase-polymerase chain reaction revealed normal trophin synthesis in the peripheral targets of dt mice, arguing against decreased trophic synthesis as a possible cause of neuronal degeneration. Thus, the absence of dystonin results in the selective survival of NGF-responsive neurons and the postnatal degeneration of many NT-3- and GDNF-responsive neurons. Our results reveal that the loss of this ubiquitously expressed cytoskeletal linker has diverse effects on sensory subpopulations. Moreover, we show that dystonin is critical for the maintenance of certain DRG neurons, and its function may be related to neurotrophic support. J. Comp. Neurol. 432:155,168, 2001. © 2001 Wiley-Liss, Inc. [source]


Gadolinium inhibits group III but not group IV muscle afferent responses to dynamic exercise

THE JOURNAL OF PHYSIOLOGY, Issue 4 2009
Shawn G. Hayes
Dynamic exercise has been shown to stimulate rapidly both group III and IV muscle afferents. The often rapid (i.e. 2 s) onset latencies of the group IV afferents is particularly surprising because these unmyelinated afferents are thought to respond to the gradual accumulation of metabolites signalling a mismatch between blood/oxygen demand and supply in exercising muscles. One explanation for the rapid onset to exercise by group IV afferents is that they are mechanosensitive, a concept that has been supported by the finding that these afferents were stimulated by vasodilatation induced by injection of vasoactive drugs. We therefore examined in decerebrated cats the effect of gadolinium, a blocker of mechanogated channels, on the responses of group III and IV muscle afferents to dynamic exercise induced by electrical stimulation of the mesencephalic locomotor region. We found that gadolinium (10 mm; 1 ml) injected into the abdominal aorta had no significant effect (P > 0.05) on the responses of 11 group IV afferents to dynamic exercise. In contrast, gadolinium markedly attenuated the responses of 11 group III afferents to exercise (P < 0.05). Our findings suggest that group IV afferents are not responding to a mechanical stimulus during exercise. Instead their rapid response to dynamic exercise might be caused by a chemical substance whose concentration is directly proportional to blood flow, which increases in the skeletal muscles when they are dynamically exercising. [source]


Excitability of human muscle afferents studied using threshold tracking of the H reflex

THE JOURNAL OF PHYSIOLOGY, Issue 2 2002
Cindy S.-Y.
In human peripheral nerves, physiological evidence has been presented for a number of biophysical differences between cutaneous afferents and , motor axons. The differences in strength-duration properties for cutaneous afferents and motor axons in the median nerve have been attributed to greater expression of a persistent Na+ conductance (INa,P) on cutaneous afferents. However, it is unclear whether the biophysical properties of human group Ia afferents differ from those of cutaneous afferents. The present studies were undertaken to determine whether the properties of human group Ia afferents can be studied indirectly using ,threshold tracking' to measure the excitability changes in the H reflex, and to determine whether the excitability of group Ia afferents differs from that of cutaneous afferents. The strength-duration properties of the soleus H reflex and soleus motor axons were measured at rest and during sustained voluntary contractions. Similar experiments were performed on the median nerve at the wrist to study the strength-duration properties of cutaneous afferents, , motor axons and H reflex of the thenar muscles. In addition, the technique of ,latent addition' was used to determine whether there was a difference in a low-threshold conductance on soleus Ia afferent and motor axons. The present findings indicate that the strength-duration time constant (,SD) for the H reflex is longer than that for , motor axons, but similar to that for cutaneous afferents. There were no differences in ,SD for the soleus H reflex at rest and during contractions, suggesting that ,SD for the H reflex is largely unaffected by changes in synaptic or motoneurone properties. Finally, the difference in latent addition suggests that the longer ,SD of the soleus H reflex may indeed be due to greater activity of a persistent Na+ conductance on Ia afferents than on soleus , motor axons. [source]