Neuromuscular Activity (neuromuscular + activity)

Distribution by Scientific Domains

Selected Abstracts

Vastus lateralis surface and single motor unit electromyography during shortening, lengthening and isometric contractions corrected for mode-dependent differences in force-generating capacity

T. M. Altenburg
Abstract Aim:, Knee extensor neuromuscular activity, rectified surface electromyography (rsEMG) and single motor unit EMG was investigated during isometric (60 knee angle), shortening and lengthening contractions (50,70, 10 s,1) corrected for force,velocity-related differences in force-generating capacity. However, during dynamic contractions additional factors such as shortening-induced force losses and lengthening-induced force gains may also affect force capacity and thereby neuromuscular activity. Therefore, even after correction for force,velocity-related differences in force capacity we expected neuromuscular activity to be higher and lower during shortening and lengthening, respectively, compared to isometric contractions. Methods:, rsEMG of the three superficial muscle heads was obtained in a first session [10 and 50% maximal voluntary contraction (MVC)] and additionally EMG of (46) vastus lateralis motor units was recorded during a second session (4,76% MVC). Using superimposed electrical stimulation, force-generating capacity for shortening and lengthening contractions was found to be 0.96 and 1.16 times isometric (Iso) force capacity respectively. Therefore, neuromuscular activity during submaximal shortening and lengthening was compared with isometric contractions of respectively 1.04Iso (=1/0.96) and 0.86Iso (=1/1.16). rsEMG and discharge rates were normalized to isometric values. Results:, rsEMG behaviour was similar (P > 0.05) during both sessions. Shortening rsEMG (1.30 0.11) and discharge rate (1.22 0.13) were higher (P < 0.05) than 1.04Iso values (1.05 0.05 and 1.03 0.04 respectively), but lengthening rsEMG (1.05 0.12) and discharge rate (0.90 0.08) were not lower (P > 0.05) than 0.86Iso values (0.76 0.04 and 0.91 0.07 respectively). Conclusion:, When force,velocity-related differences in force capacity were taken into account, neuromuscular activity was not lower during lengthening but was still higher during shortening compared with isometric contractions. [source]

Fish venom: pharmacological features and biological significance

Gisha Sivan
Abstract Nearly 1200 species of marine fish are venomous and they account for two-third of the population of venomous vertebrates. Fish venoms are focused as a potential source of pharmacological agents and physiological tools that have evolved to target vital processes in the human body that appear to have more electivity than many drugs. Fish venoms possess cardiovascular, neuromuscular, oedematic and cytolytic activity. Lethal toxins have been isolated and purified, with some having LD50 values comparable to that of snake venoms. Cardiovascular activity seems to be the dominant effect of fish venoms in experimental models. Piscine venom acts both pre- and post-junctionally to produce depolarization of cell membranes. Studies on cytolytic activity of fish venom found that it produces lysis by forming hydrophilic pores in cell membranes which then result in cell lysis. Almost all fish venoms with neuromuscular activity also possesses cytolytic activity, and it is very likely that the two activities are related. Fish venom is known to induce intense and sustained edematogenic response. As piscine venoms have evolved for the same purpose, they show a number of similarities pharmacologically and it seems likely that most of the biological activities of any given toxin can be traced back to its cytolytic activity. A variety of toxins have been isolated from piscine venom. Although there is a complex balance between the components present in the venom of different fish, all of them seem to share similar activity , functionally and pharmacologically as well as structurally. [source]

Evidence for Antinociceptive Activity of Botulinum Toxin Type A in Pain Management

HEADACHE, Issue 2003
K. Roger Aoki PhD
The neurotoxin, botulinum toxin type A, has been used successfully, in some patients, as an analgesic for myofascial pain syndromes, migraine, and other headache types. The toxin inhibits the release of the neurotransmitter, acetylcholine, at the neuromuscular junction thereby inhibiting striated muscle contractions. In the majority of pain syndromes where botulinum toxin type A is effective, inhibiting muscle spasms is an important component of its activity. Even so, the reduction of pain often occurs before the decrease in muscle contractions suggesting that botulinum toxin type A has a more complex mechanism of action than initially hypothesized. Current data points to an antinociceptive effect of botulinum toxin type A that is separate from its neuromuscular activity. The common biochemical mechanism, however, remains the same between botulinum toxin type A's effect on the motor nerve or the sensory nerve: enzymatic blockade of neurotransmitter release. The antinociceptive effect of the toxin was reported to block substance P release using in vitro culture systems.1 The current investigation evaluated the in vivo mechanism of action for the antinociceptive action of botulinum toxin type A. In these studies, botulinum toxin type A was found to block the release of glutamate. Furthermore, Fos, a product of the immediate early gene, c- fos, expressed with neuronal stimuli was prevented upon peripheral exposure to the toxin. These findings suggest that botulinum toxin type A blocks peripheral sensitization and, indirectly, reduces central sensitization. The recent hypothesis that migraine involves both peripheral and central sensitization may help explain how botulinum toxin type A inhibits migraine pain by acting on these two pathways. Further research is needed to determine whether the antinociceptive mechanism mediated by botulinum toxin type A affects the neuronal signaling pathways that are activated during migraine. [source]

Learning to Smile: The Neuroanatomic Basis for Smile Training

ABSTRACT This article demonstrates that although any layperson could recognize that the smile manifests mainly in the oral and periorbital regions, a comprehension of the neurologic and musculoskeletal elements lends the clinician insight into the many aspects of a smile. The neurologic control of a smile consists of a complex process involving many facets. As with any other complex neuromuscular activity, repetitions of the act can train the central nervous system, neural network, and muscular network in efficient performance of and correct musculoskeletal activation involved in the act itself. With functional knowledge of muscles dedicated to a pleasing full smile, together with a battery of easy and effortless exercises, the clinician is able to help the patient change behavior intended to camouflage perceived oral flaws. A patient needs reassurance that behind the guidance from the clinician lies medical evidence that such routine movement of muscles will indeed improve the smile. When asked why or how the exercise succeeds, the clinician can reassure the patient based on a working knowledge of the neurologic and muscular anatomy involved. CLINICAL SIGNIFICANCE A functional knowledge of muscles dedicated to a pleasing full smile, together with a battery of easy and effortless exercises, provides the clinician with the ability to assist the patient in altering years of behavior intended to camouflage perceived oral flaws. [source]

Inactivity-induced modulation of Hsp20 and Hsp25 content in rat hindlimb muscles

MUSCLE AND NERVE, Issue 1 2004
Kimberly A. Huey PhD
Abstract Denervation decreases small heat shock protein (HSP) content in the rat soleus muscle; however, it is unknown whether this change is due to inactivity or absence of a nerve,muscle connection. Spinal cord isolation (SI) is a model of inactivity with an intact neuromuscular connection. After 7 days of SI, Hsp20 and Hsp25 levels in the soleus, plantaris, and adductor longus muscles were lower than in control rats, whereas Hsp20 was unchanged and Hsp25 increased in the tibialis anterior. The results for the soleus indicate that these small HSPs respond to inactivity and that this response is not influenced by neural activity,independent factors. Furthermore, the data indicate that these HSPs are impacted to a greater degree in muscles that are predominantly slow or have an antigravity function than in flexor muscles. Understanding the regulation of these HSPs during chronic reductions in neuromuscular activity may have valuable applications for conditions such as spinal cord injury. Muscle Nerve 30: 95,101, 2004 [source]

Comparison of the in vitro neuromuscular activity of venom from three australian snakes (Hoplocephalus stephensi, Austrelaps superbus and Notechis scutatus): Efficacy of tiger snake antivenom

Wayne C Hodgson
Summary 1.,Tiger snake antivenom, raised against Notechis scutatus venom, is indicated not only for the treatment of envenomation by this snake, but also that of the copperhead (Austrelaps superbus) and Stephen's banded snake (Hoplocephalus stephensi). The present study compared the neuromuscular pharmacology of venom from these snakes and the in vitro efficacy of tiger snake antivenom. 2.,In chick biventer cervicis muscle and mouse phrenic nerve diaphragm preparations, all venoms (3,10 g/mL) produced inhibition of indirect twitches. In the biventer muscle, venoms (10 g/mL) inhibited responses to acetylcholine (1 mmol/L) and carbachol (20 mol/L), but not KCl (40 mmol/L). The prior (10 min) administration of 1 unit/mL antivenom markedly attenuated the neurotoxic effects of A. superbus and N. scutatus venoms (10 g/mL), but was less effective against H. stephensi venom (10 g/mL); 5 units/mL antivenom attenuated the neurotoxic activity of all venoms. 3.,Administration of 5 units/mL antivenom at t90 partially reversed, over a period of 3 h, the inhibition of twitches produced by N. scutatus (10 g/mL; 41% recovery), A. superbus (10 g/mL; 25% recovery) and H. stephensi (10 g/mL; 50% recovery) venoms. All venoms (10,100 g/mL) also displayed signs of in vitro myotoxicity. 4.,The results of the present study indicate that all three venoms contain neurotoxic activity that is effectively attenuated by tiger snake antivenom. [source]

In vitro neuromuscular activity of snake venoms

Wayne C Hodgson
Summary 1.,Snake venoms consist of a multitude of pharmacologically active components used for the capture of prey. Neurotoxins are particularly important in this regard, producing paralysis of skeletal muscles. These neurotoxins can be classified according to their site of action (i.e. pre- or post-synaptic). 2.,Presynaptic neurotoxins, which display varying phospholipase A2 activities, have been identified in the venoms of the four major families of venomous snakes (i.e. Crotalidae, Elapidae, Hydrophiidae and Viperidae). The blockade of transmission produced by these toxins is usually characterized by a triphasic effect on acetylcholine release. Considerable work has been directed at identifying the binding site(s) on the presynaptic nerve terminal for these toxins, although their mechanism of action remains unclear. 3.,Post-synaptic neurotoxins are antagonists of the nicotinic receptor on the skeletal muscle. Depending on their sequence, post-synaptic toxins are subdivided into short- and long-chain toxins. These toxins display different binding kinetics and different affinity for subtypes of nicotinic receptors. Post-synaptic neurotoxins have only been identified in venoms from the families Elapidae and Hydrophiidae. 4.,Due to the high cost of developing new antivenoms and the reluctance of many companies to engage in this area of research, new methodologies are required to test the efficacy of existing antivenoms to ensure their optimal use. While chicken eggs have proven useful for the examination of haemorrhagic venoms, this procedure is not suited to venoms that primarily display neurotoxic activity. The chick biventer cervicis muscle has proven useful for this procedure, enabling the rapid screening of antivenoms against a range of venoms. 5.,Historically, the lethality of snake venoms has been based on murine LD50 studies. Due to ethical reasons, these studies are being superseded by in vitro studies. Instead, the time taken to produce 90% inhibition of nerve-mediated twitches (i.e. t90) in skeletal muscle preparations can be determined. However, these two procedures result in different rank orders because they are measuring two different parameters. While murine LD50 determinations are based on ,quantity', t90 values are based on how ,quick' a venom acts. Therefore, knowledge of both parameters is still desirable. 6.,In vitro neuromuscular preparations have proven to be invaluable tools in the examination of snake venoms and isolated neurotoxins. They will continue to play a role in further elucidating the mechanism of action of these highly potent toxins. Further study of these toxins may provide more highly specific research tools or lead compounds for pharmaceutical agents. [source]