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Twitch
Terms modified by Twitch Selected AbstractsTwitch and nontwitch motoneuron subgroups in the oculomotor nucleus of monkeys receive different afferent projectionsTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2004Richard Wasicky Abstract Motoneurons in the primate oculomotor nucleus can be divided into two categories, those supplying twitch muscle fibers and those supplying nontwitch muscle fibers. Recent studies have shown that twitch motoneurons lie within the classical oculomotor nucleus (nIII), and nontwitch motoneurons lie around the borders. Nontwitch motoneurons of medial and inferior rectus are in the C group dorsomedial to nIII, whereas those of inferior oblique and superior rectus lie near the midline are in the S group. In this anatomical study, afferents to the twitch and nontwitch subgroups of nIII have been anterogradely labeled by injections of tritiated leucine into three areas and compared. 1) Abducens nucleus injections gave rise to silver grain deposits over all medial rectus subgroups, both twitch and nontwitch. 2) Laterally placed vestibular complex injections that included the central superior vestibular nucleus labeled projections only in twitch motoneuron subgroups. However, injections into the parvocellular medial vestibular nucleus (mvp), or Y group, resulted in labeled terminals over both twitch and nontwitch motoneurons. 3) Pretectal injections that included the nucleus of the optic tract (NOT), and the olivary pretectal nucleus (OLN), labeled terminals only over nontwitch motoneurons, in the contralateral C group and in the S group. Our study demonstrates that twitch and nontwitch motoneuron subgroups do not receive identical afferent inputs. They can be controlled either in parallel, or independently, suggesting that they have basically different functions. We propose that twitch motoneurons primarily drive eye movements and nontwitch motoneurons the tonic muscle activity, as in gaze holding and vergence, possibly involving a proprioceptive feedback system. J. Comp. Neurol. 479:117,129, 2004. © 2004 Wiley-Liss, Inc. [source] Effect of dopamine on rat diaphragm apoptosis and muscle performanceEXPERIMENTAL PHYSIOLOGY, Issue 4 2006Janet D. Pierce The purpose of this study was to determine whether dopamine (DA) decreases diaphragm apoptosis and attenuates the decline in diaphragmatic contractile performance associated with repetitive isometric contraction using an in vitro diaphragm preparation. Strenuous diaphragm contractions produce free radicals and muscle apoptosis. Dopamine is a free radical scavenger and, at higher concentrations, increases muscle contractility by simulating ,2 -adrenoreceptors. A total of 47 male Sprague,Dawley rats weighing 330,450 g were used in a prospective, randomized, controlled in vitro study. Following animal anaesthetization, diaphragms were excised, and muscle strips prepared and placed in a temperature-controlled isolated tissue bath containing Krebs,Ringer solution (KR) or KR plus 100 ,m DA. The solutions were equilibrated with oxygen (O2) at 10, 21 or 95% and 5% carbon dioxide, with the balance being nitrogen. Diaphragm isometric twitch and subtetanic contractions were measured intermittently over 65 min. The diaphragms were then removed and, using a nuclear differential dye uptake method, the percentages of normal, apoptotic and necrotic nuclei were determined using fluorescent microscopy. There were significantly fewer apoptotic nuclei in the DA group diaphragms than in the KR-only group diaphragms in 10 and 21% O2 following either twitch or subtetanic contractions. Dopamine at 100 ,m produced only modest increases in muscle performance in both 10 and 21% O2. The attenuation of apoptosis by DA was markedly greater than the effect of DA on muscle performance. Dopamine decreased diaphragmatic apoptosis, perhaps by preventing the activation of intricate apoptotic pathways, stimulating antiapoptotic mechanisms and/or scavenging free radicals. [source] Contractile Properties, Fatigue and Recovery are not Influenced by Short-Term Creatine Supplementation in Human MuscleEXPERIMENTAL PHYSIOLOGY, Issue 4 2000J. M. Jakobi There have been several studies on the effect of short-term creatine (Cr) supplementation on exercise performance, but none have investigated both voluntary and stimulated muscle contractions in the same experiment. Fourteen moderately active young men (19-28 years) were randomly assigned, in a double blind manner, to either a creatine (Cr) or placebo (P) group. The subjects supplemented their regular diet 4 times a day for 5 days with either 5 g Cr + 5 g maltodextrin (Cr group), or 5 g maltodextrin (P group). Isometric maximal voluntary contraction (MVC), muscle activation, as assessed using the modified twitch interpolation technique, electrically stimulated contractile properties, electromyography (EMG), endurance time and recovery from fatigue were measured in the elbow flexors. The fatigue protocol involved both voluntary and stimulated contractions. Following supplementation there was a significant weight gain in the Cr group (1.0 kg), whereas the P group did not change. For each group, pre-supplementation measures were not significantly different from post-supplementation for MVC, twitch and tetanic tensions at rest, time to peak tension, half-relaxation time and contraction duration. Prior to Cr supplementation time to fatigue was 10 ± 4 min (mean ± S.E.M.) for both groups, and following supplementation there was a non-significant increase of 1 min in each group. MVC force, muscle activation, EMG, stimulated tensions and durations were similar for the Cr and P groups over the course of the fatigue protocol and did not change after supplementation. Furthermore, recovery of MVC, stimulated tensions and contractile speeds did not differ as a result of Cr supplementation. These results indicate that short-term Cr supplementation does not influence isometric elbow flexion force, muscle activation, stimulated contractile properties, or delay time to fatigue or improve recovery. [source] Unidirectional startle responses and disrupted left,right co-ordination of motor behaviors in robo3 mutant zebrafishGENES, BRAIN AND BEHAVIOR, Issue 5 2009H. A. Burgess The Roundabout (Robo) family of receptors and their Slit ligands play well-established roles in axonal guidance, including in humans where horizontal gaze palsy with progressive scoliosis (HGPPS) is caused by mutations in the robo3 gene. Although significant progress has been made toward understanding the mechanism by which Robo receptors establish commissural projections in the central nervous system, less is known about how these projections contribute to neural circuits mediating behavior. In this study, we report cloning of the zebrafish behavioral mutant twitch twice and show that twitch twice encodes robo3. We show that in mutant hindbrains the axons of an identified pair of neurons, the Mauthner cells, fail to cross the midline. The Mauthner neurons are essential for the startle response, and in twitch twice/robo3 mutants misguidance of the Mauthner axons results in a unidirectional startle response. Moreover, we show that twitch twice mutants exhibit normal visual acuity but display defects in horizontal eye movements, suggesting a specific and critical role for twitch twice/robo3 in sensory-guided behavior. [source] Recessive mutations in RYR1 are a common cause of congenital fiber type disproportion,HUMAN MUTATION, Issue 7 2010Nigel F. Clarke Abstract The main histological abnormality in congenital fiber type disproportion (CFTD) is hypotrophy of type 1 (slow twitch) fibers compared to type 2 (fast twitch) fibers. To investigate whether mutations in RYR1 are a cause of CFTD we sequenced RYR1 in seven CFTD families in whom the other known causes of CFTD had been excluded. We identified compound heterozygous changes in the RYR1 gene in four families (five patients), consistent with autosomal recessive inheritance. Three out of five patients had ophthalmoplegia, which may be the most specific clinical indication of mutations in RYR1. Type 1 fibers were at least 50% smaller, on average, than type 2 fibers in all biopsies. Recessive mutations in RYR1are a relatively common causeof CFTD and can be associated with extreme fiber size disproportion. © 2010 Wiley-Liss, Inc. [source] Comparison of the contractile properties, oxidative capacities and fibre type profiles of the voluntary sphincters of continence in the ratJOURNAL OF ANATOMY, Issue 3 2010Maria Buffini Abstract The external urethral sphincter (EUS) and external anal sphincter (EAS) are the principal voluntary striated muscles that sustain continence of urine and faeces. In light of their common embryological origin, shared tonic sphincteric action and synchronized electrical activity in vivo, it was expected that they would exhibit similar physiological and structural properties. However, the findings of this study using paired observations of both sphincters isolated from the rat show clearly that this is not the case. The anal sphincter is much more fatigable than the urethral sphincter. On completion of a fatigue protocol, the amplitude of the last twitch of the EAS had declined to 42 ± 3% of the first twitch, whereas the last twitch of the EUS was almost identical to that of the first (95 ± 3%). Immunocytochemical detection of myosin heavy-chain isoforms showed that this difference was not due to the presence of more slow-twitch oxidative type 1 fibres in the EUS compared with the EAS (areal densities 4 ± 1% and 5 ± 1%, respectively; P = 0.35). In addition, the fatigue difference was not explained by a greater contribution to force production by fast oxidative type 2A fibres in the urethral sphincter. In fact, the anal sphincter contained a higher areal density of type 2A fibres (56 ± 5% vs. 37 ± 4% in the EUS, P = 0.017). The higher oxidative capacity of the EUS, measured histochemically, explained its fatigue resistance. These results were surprising because the fatigue-resistant urethral muscle exhibited faster single-twitch contraction times compared with the anal sphincter (56 ± 0.87 ms vs. 72.5 ± 1.16 ms, P < 0.001). Neither sphincter expressed the type 2X myosin isoform but the fast-twitch isoform type 2B was found exclusively in the EUS (areal density 16 ± 2%). The type 2B fibres of the EUS were small (diameter 19.5 ± 0.4 ,m) in comparison to typical type 2B fibres of other muscles. As a whole the EUS is a more oxidative than glycolytic muscle. In conclusion, analysis of the twitch mechanics and fatigue of two sphincters showed that the EUS contained more fatigue-resistant muscle fibres compared with the EAS. [source] Infusion requirements and reversibility of rocuronium at the corrugator supercilii and adductor pollicis musclesACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 10 2009T. SUZUKI Background: The aim of this study is to compare the infusion rates required to maintain a constant neuromuscular block and the reversibility of rocuronium at the corrugator supercilii muscle (CSM) and the adductor pollicis muscle (APM). Methods: We randomly allocated 30 female patients into two groups of 15 patients each to monitor neuromuscular block at either the CSM or the APM. After induction of anaesthesia and laryngeal mask insertion, contraction of the CSM to the facial nerve stimulation or that of the APM to the ulnar nerve stimulation was quantified using an acceleromyograph during 1.0,1.5% end-tidal sevoflurane anaesthesia. All the patients received a bolus of 1 mg/kg rocuronium. When the first twitch (T1) of train-of-four (TOF) recovered to 10% of the control, rocuronium infusion was commenced and maintained at T1 of 10% of the control at the CSM or APM for 120 min. Immediately after rocuronium infusion was discontinued, the time required for 0.04 mg/kg neostigmine-facilitated recovery to a TOF ratio of 0.9 was recorded. Results: Rocuronium infusion dose after a lapse of 120 min was significantly larger in the CSM than in the APM [7.1 (2.3) vs. 4.7 (2.6) ,g/kg/min; P=0.001]. The time for facilitated recovery was shorter in the CSM than in the APM [11.4 (3.8) vs. 16.2 (6.0) min; P=0.016]. Conclusion: A larger rocuronium infusion dose was required to maintain a constant neuromuscular block at the CSM. Neostigmine-mediated reversal was faster at the CSM. [source] Muscle fibre types and size distribution in sub-antarctic notothenioid fishesJOURNAL OF FISH BIOLOGY, Issue 6 2000D. A. Fernandez The presumptive tonic muscles fibres of Cottoperca gobio, Champsocephalus esox, Harpagifer bispinis, Eleginops maclovinus, Patagontothen tessellata, P. cornucola and Paranotothenia magellanica stained weakly or were unstained for glycogen, lipid, succinic dehydrogenase (SDHase) and myosin ATPase (mATPase) activity. Slow, intermediate and fast twitch muscle fibres, distinguished on the basis of the pH stability of their mATPases, showed intense, moderate and low staining activity for SDHase, respectively. Slow fibres were the major component of the pectoral fin adductor profundis muscle. The proportion of different muscle fibre types varied from the proximal to distal end of the muscle, but showed relatively little variation between species. The myotomes contained a lateral superficial strip of red muscle composed of presumptive tonic, slow twitch and intermediate fibres, thickening to a major wedge at the horizontal septum. All species also had characteristic secondary dorsal and ventral wedges of red muscle. The relative abundance and localization of muscle fibre types in the red muscle varied between species and with body size in the protandric hermaphrodite E. maclovinus. The frequency distribution of diameters for fast twitch muscle fibres, the major component of deep white muscle, was determined in fish of a range of body sizes. The absence of fibres <20 ,m diameter was used as a criterion for the cessation of muscle fibre recruitment. Fibre recruitment had stopped in P. tessellata of 13·8 cm LT and E. maclovinus of 32·8 cm LT, equivalent to 49 and 36·5% of their recorded maximum sizes respectively. As a result in 20-cm P. tessellata, the maximum fibre diameter was 300 ,m and 36% of fibres were in excess of 200 ,m. The unusually large maximum fibre diameter, the general arrangement of the red muscle layer and the extreme pH lability of the mATPase of fast twitch fibres are all common characters of the sub-Antarctic and Antarctic Notothenioids, including Cottoperca gobio, the suggested sister group to the Notothenidae. [source] Effects of Botox® and Neuronox® on muscle force generation in miceJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 12 2007Austin V. Stone Abstract The current study determined the dose,response relationship for inhibition of muscle force of two commercially available botulinum neurotoxin type-A (BoNTA) preparations (Botox® and Neuronox®) in a murine model and characterized the time course of recovery from the toxin-induced muscle paralysis. The effect of freezing reconstituted toxin on toxin potency was also determined. The gastrocnemius muscles in male CD-1 mice were injected with either saline or BoNTA (0.3,3.0 U/kg), and muscle force generation was examined following stimulation of the tibial nerve (single twitch and 15,200 Hz tetany). Botox and Neuronox produced nearly equivalent decrements in muscle force (30%,90%) at 4 days after toxin injection. At 28 days after injection (1 U/kg), muscle force had recovered from the effects of both toxin preparations. Maintaining reconstituted toxin at ,80°C for up to 5 months did not result in significant loss of toxin activity. The results of this study suggest that Botox and Neuronox produce equivalent responses in a murine model, and, in contrast to other models, muscle recovery is rapid with doses of toxin that produce less than maximal decrements in muscle force. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1658,1664, 2007 [source] Characterisation of the effects of potassium channel modulating agents on mouse intestinal smooth muscleJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 3 2002Chi-Kong Yeung The actions of agents which modulate ATP-sensitive potassium (KATP) channels in excitable cells were investigated in an in-vitro preparation of mouse ileum from which the mucosa was removed. A range of potassium channel openers of diverse structure, cromakalim (0.1,100 ,M), pinacidil (0.1,200 ,M) and its analogue P1060 (0.1,200 ,M), SDZ PCO400 ((-)-(3S,4R)-3,4-dihydro-3-hydroxy-2,2-dimethyl-4-(3-oxo-cyclopent-1-enyloxy)-2H -1-benzopyran-6-carbonitrile) (0.3,60 ,M), caused concentration-related reduction in twitch height of electrical field stimulated ileum. P1060 and SDZ PCO400 were the most potent agents; diazoxide (0.1,100 ,M) was without effect. The order of inhibitory potency, based on EC50 values (concentration of a relaxant producing 50% of the maximum inhibition of twitch) was: P1060 = SDZ PCO400 > cromakalim > pinacidil. The relaxant effect of the potassium channel openers was antagonised by the sulfonylureas glibenclamide (0.1-1.0 ,M) and glipizide (3,30 ,M) but the nature of the antagonism differed. Antagonism of P1060 and SDZ PCO400 by glibenclamide appeared to be competitive whereas the antagonism of relaxation induced by cromakalim and pinacidil was apparently not competitive. Both phentolamine (1,10 ,M) and tolbutamide (100,300 ,M) showed competitive antagonism of the actions of pinacidil while yohimbine (1,20 ,M) did not antagonise relaxation and appeared to have actions at sites other than the KATP channel in this preparation. The relative effectiveness of the antagonists on pinacidil-induced relaxation was found to be: glibenclamide >phentolamine >tolbutamide >yohimbine, which is in agreement with studies in other tissues. The results show that many structurally diverse potassium channel openers are potent relaxants of mouse ileum. These observations are consistent with the existence of ATP-dependent K+ channels in murine intestinal muscle which, however, differ somewhat in properties from those reported for vascular muscle and pancreatic ,-cells. [source] Practices and Outcome of Artificial Cardiac Pacing in 154 DogsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 3 2001Mark A. Oyama Artificial pacing (AP) is a treatment for symptomatic bradyarrhythmias unresponsive to medical therapy. This retrospective study was designed to define the practices and outcome of AP in dogs at 7 referral institutions participating in the Companion Animal Pacemaker Registry and Repository (CANPACERS). The indications, implantation techniques, complications, long-term outcome, and owner satisfaction were examined. One hundred fifty-four dogs were identified as undergoing AP from January 1, 1991, to January 1, 1996. Third-degree atrioventricular (AV) block (n = 91; 59%) and sinus node dysfunction (n = 45; 29%) were the most common indications for AP. Transvenous endocardial AP systems were implanted in 136 dogs (88%), and epicardial systems were implanted in 18 (12%). Complications associated with AP were reported in 84 dogs (55%). Major complications occurred in 51 dogs (33%), including dislodgement of the pacing lead (n = 15; 10%), generator failure (n = 10; 6%), cardiac arrest during implantation (n = 9; 6%), and infection (n = 7; 5%). Minor complications occurred in 47 dogs (31%), including seroma formation (n = 18; 12%), muscle twitch (n = 17; 11%), and inconsequential arrhythmias (n = 15; 10%). Fourteen dogs (9%) experienced both major and minor complications. Survival analysis revealed 1-, 2-, and 3-year survival rates of 70, 57, and 45%, respectively. Age and presence of preexisting congestive heart failure (CHF) had a negative effect on survival (P= .001). Sixty percent of dogs with preexisting CHF died within 1 year of implantation, whereas 25% of dogs without heart failure died during the same period. Owners rated their satisfaction with the procedure as high in 80% of the dogs. [source] Physiological assessment of muscle strength in vitro after direct injection of doxorubicin into rabbit sternocleidomastoid muscleMOVEMENT DISORDERS, Issue 4 2001Jon H. Falkenberg MS Abstract Doxorubicin chemomyectomy is a potent method for the permanent removal of a muscle or group of muscles after direct local injection, and has been used successfully to treat blepharospasm and hemifacial spasm patients. The efficacy of doxorubicin chemomyectomy on reducing muscle strength after direct injection of doxorubicin into rabbit sternocleidomastoid muscle was tested. One- and 6-month postinjection force assessment was performed in vitro to measure alterations in peak twitch and tetanic force generation, as well as fatigue responses for the treated muscles compared to control. There were significant reductions of both twitch and tetanic peak amplitudes in the doxorubicin-treated muscles. One month after treatment, the decreases in force were greater after 2 mg doxorubicin injections than after 1 mg doxorubicin. While there was a significant reduction in force generation after doxorubicin treatment, fatigue resistances for the doxorubicin-treated muscles were increased compared to the controls. There were significant reductions in muscle mass after doxorubicin treatment, and by 6 months, the myosin heavy chain isoform distribution was similar to normal sternocleidomastoid, except for an increase in slow myosin-positive fibers. Doxorubicin chemomyectomy resulted in a significant reduction in functional force generation in the treated sternocleidomastoid muscles. These findings suggest a potential clinical use of doxorubicin chemomyectomy to treat cervical dystonia patients. © 2001 Movement Disorder Society. [source] Influence of time of day on tendon compliance and estimations of voluntary activation levelsMUSCLE AND NERVE, Issue 6 2006Stephen J. Pearson PhD Abstract We investigated the importance of tendon stiffness on estimations of central activation capacity (CAC). Patella tendon,force elongation relationship, quadriceps torque, and response to 50-,s, 100-HZ electrical twitch doublets were studied at ,8:00 A.M. and ,6:00 P.M. in 8 healthy young men. Results show that in the evening, as compared with the morning, tendon stiffness decreased by 20.2 ± 9.5% (P = 0.03) and time to twitch peak (Ttp) increased by 55% (P = 0.04). Tendon stiffness and Ttp correlated significantly (r = 0.28, P < 0.05). Whereas the CAC, calculated as the ratio of force preceding the interpolated twitch (IT) to the total force at the peak of the IT, showed no change with time of day, calculations that used twitch ratios suggested CAC decrements (,10.3%, P = 0.03, unpotentiated; ,10%, P = 0.02, potentiated ratio) in the evening. This study shows that CAC estimations are invalid when tendon properties are not taken into account, an error that would have important implications in a clinical setting. Muscle Nerve, 2006 [source] Twitch and nontwitch motoneuron subgroups in the oculomotor nucleus of monkeys receive different afferent projectionsTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2004Richard Wasicky Abstract Motoneurons in the primate oculomotor nucleus can be divided into two categories, those supplying twitch muscle fibers and those supplying nontwitch muscle fibers. Recent studies have shown that twitch motoneurons lie within the classical oculomotor nucleus (nIII), and nontwitch motoneurons lie around the borders. Nontwitch motoneurons of medial and inferior rectus are in the C group dorsomedial to nIII, whereas those of inferior oblique and superior rectus lie near the midline are in the S group. In this anatomical study, afferents to the twitch and nontwitch subgroups of nIII have been anterogradely labeled by injections of tritiated leucine into three areas and compared. 1) Abducens nucleus injections gave rise to silver grain deposits over all medial rectus subgroups, both twitch and nontwitch. 2) Laterally placed vestibular complex injections that included the central superior vestibular nucleus labeled projections only in twitch motoneuron subgroups. However, injections into the parvocellular medial vestibular nucleus (mvp), or Y group, resulted in labeled terminals over both twitch and nontwitch motoneurons. 3) Pretectal injections that included the nucleus of the optic tract (NOT), and the olivary pretectal nucleus (OLN), labeled terminals only over nontwitch motoneurons, in the contralateral C group and in the S group. Our study demonstrates that twitch and nontwitch motoneuron subgroups do not receive identical afferent inputs. They can be controlled either in parallel, or independently, suggesting that they have basically different functions. We propose that twitch motoneurons primarily drive eye movements and nontwitch motoneurons the tonic muscle activity, as in gaze holding and vergence, possibly involving a proprioceptive feedback system. J. Comp. Neurol. 479:117,129, 2004. © 2004 Wiley-Liss, Inc. [source] Dihydrotestosterone activates the MAPK pathway and modulates maximum isometric force through the EGF receptor in isolated intact mouse skeletal muscle fibresTHE JOURNAL OF PHYSIOLOGY, Issue 3 2010M. M. Hamdi It is generally believed that steroid hormones have both genomic and non-genomic (rapid) actions. Although the latter form an important component of the physiological response of these hormones, little is known about the cellular signalling pathway(s) mediating these effects and their physiological functions in adult mammalian skeletal muscle fibres. Therefore, the primary aim of this study was to investigate the non-genomic actions of dihydrotestosterone (DHT) and their physiological role in isolated intact mammalian skeletal muscle fibre bundles. Our results show that treating the fibre bundles with physiological concentrations of DHT increases both twitch and tetanic contractions in fast twitch fibres. However, it decreases them in slow twitch fibres. These changes in force are accompanied by an increase in the phosphorylation of MAPK/ERK1/2 in both fibre types and that of regulatory myosin light chains in fast twitch fibres. Both effects were insensitive to inhibitors of Src kinase, androgen receptor, insulin-like growth factor 1 receptor and platelet-derived growth factor receptor. However, they were abolished by the MAPK/ERK1/2 kinase inhibitor PD98059 and the epidermal growth factor (EGF) receptor inhibitor tyrphostin AG 1478. In contrast, testosterone had no effect on force and increased the phosphorylation of ERK1/2 in slow twitch fibres only. From these results we conclude that sex steroids have non-genomic actions in isolated intact mammalian skeletal muscle fibres. These are mediated through the EGF receptor and one of their main physiological functions is the enhancement of force production in fast twitch skeletal muscle fibres. [source] Interpolated twitches in fatiguing single mouse muscle fibres: implications for the assessment of central fatigueTHE JOURNAL OF PHYSIOLOGY, Issue 11 2008Nicolas Place An electrically evoked twitch during a maximal voluntary contraction (twitch interpolation) is frequently used to assess central fatigue. In this study we used intact single muscle fibres to determine if intramuscular mechanisms could affect the force increase with the twitch interpolation technique. Intact single fibres from flexor digitorum brevis of NMRI mice were dissected and mounted in a chamber equipped with a force transducer. Free myoplasmic [Ca2+] ([Ca2+]i) was measured with the fluorescent Ca2+ indicator indo-1. Seven fibres were fatigued with repeated 70 Hz tetani until 40% initial force with an interpolated pulse evoked every fifth tetanus. Results showed that the force generated by the interpolated twitch increased throughout fatigue, being 9 ± 1% of tetanic force at the start and 19 ± 1% at the end (P < 0.001). This was not due to a larger increase in [Ca2+]i induced by the interpolated twitch during fatigue but rather to the fact that the force,[Ca2+]i relationship is sigmoidal and fibres entered a steeper part of the relationship during fatigue. In another set of experiments, we observed that repeated tetani evoked at 150 Hz resulted in more rapid fatigue development than at 70 Hz and there was a decrease in force (,sag') during contractions, which was not observed at 70 Hz. In conclusion, the extent of central fatigue is difficult to assess and it may be overestimated when using the twitch interpolation technique. [source] The time course of the motoneurone afterhyperpolarization is related to motor unit twitch speed in human skeletal muscleTHE JOURNAL OF PHYSIOLOGY, Issue 2 2003E. Roderich Gossen The relationship between the electrophysiological properties of motoneurones and their muscle units has been established in animal models. A functionally significant relationship exists whereby motoneurones with long post-spike afterhyperpolarizations (AHPs) innervate slow contracting muscle units. The purpose of this study was to determine whether the time course of the AHP as measured by its time constant is associated with the contractile properties of its muscle unit in humans. Using an intramuscular fine wire electrode, 46 motor units were recorded in eight subjects as they held a low force contraction of the first dorsal interosseus muscle for approximately 10 min. By applying a recently validated transform to the interspike interval histogram, the mean voltage versus time trajectory of the motoneurone AHP was determined. Spike-triggered averaging was used to extract the muscle unit twitch from the whole muscle force with strict control over force variability and motor unit discharge rate (interspike intervals between 120 and 200 ms). The AHP time constant was positively correlated to the time to half-force decay (,= 0.36, P < 0.05) and twitch duration (,= 0.57, P < 0.001); however, time to peak force failed to reach significance (,= 0.27, P < 0.07). These results suggest that a similar functional relationship exists in humans between the motoneurone AHP and the muscle unit contractile properties. [source] The use of sugammadex in a patient with myasthenia gravisANAESTHESIA, Issue 3 2010C. Unterbuchner Summary Myasthenia gravis, affecting neuromuscular transmission, leads to a large variability in sensitivity to depolarising and non-depolarising neuromuscular blocking drugs. We report the successful use of the modified ,-cyclodextrin sugammadex in a myasthenic patient to reverse a rocuronium-induced deep level of neuromuscular block. After spontaneous neuromuscular recovery of T2 (second twitch of the train-of-four series), we administered 2 mg.kg,1 of sugammadex intravenously, reversing neuromuscular blockade to a train-of-four ratio (T4/T1) > 90% within 210 s. Sugammadex, in combination with objective neuromuscular monitoring, can be used to reverse rocuronium-induced neuromuscular blockade in patients with myasthenia gravis, thereby avoiding the need for reversal with acetylcholinesterase inhibitors. [source] Antagonism of non-depolarising neuromuscular block: current practiceANAESTHESIA, Issue 2009A. F. Kopman Summary There is now mounting evidence that even small degrees of postoperative residual neuromuscular block increases the incidence of adverse respiratory events in the Post Anaesthesia Care Unit and may increase longer-term morbidity as well. In the absence of quantitative neuromuscular monitoring, residual block is easily missed. A very strong case can be made for the routine administration of a non-depolarising antagonist unless it can be objectively demonstrated that complete recovery has occurred spontaneously. However, the use of acetylcholinesterase inhibitors is associated with the potential for cardiovascular and respiratory side-effects, so there are cogent reasons for using low doses when the level of neuromuscular block is not intense. As little as 0.015,0.025 mg.kg,1 of neostigmine is required at a train-of-four count of four with minimal fade, whereas 0.04,0.05 mg.kg,1 is needed at a train-of-four count of two or three. If only a single twitch or none at all can be evoked, neostigmine should not be expected to promptly reverse neuromuscular block, and antagonism is best delayed till a train-of-four-count of two is achieved. [source] NERVE STIMULATION IN THYROID SURGERY: IS IT REALLY USEFUL?ANZ JOURNAL OF SURGERY, Issue 5 2007Thorbjorn J Loch-Wilkinson Background: Monitoring of the recurrent laryngeal nerve (RLN) has been claimed in some studies to reduce rates of nerve injury during thyroid surgery compared with anatomical dissection and visual identification of the RLN alone, whereas other studies have found no benefit. Continuous monitoring with endotracheal electrodes is expensive whereas discontinuous monitoring by laryngeal palpation with nerve stimulation is a simple and inexpensive technique. This study aimed to assess the value of nerve stimulation with laryngeal palpation as a means of identifying and assessing the function of the RLN and external branch of the superior laryngeal nerve (EBSLN) during thyroid surgery. Methods: This was a prospective case series comprising 50 consecutive patients undergoing total thyroidectomy providing 100 RLN and 100 EBSLN for examination. All patients underwent preoperative and postoperative vocal cord and voice assessment by an independent ear, nose and throat surgeon, laryngeal examination at extubation and all were asked to complete a postoperative dysphagia score sheet. Dysphagia scores in the study group were compared with a control group (n = 20) undergoing total thyroidectomy without nerve stimulation. Results: One hundred of 100 (100%) RLN were located without the use of the nerve stimulator. A negative twitch response occurred in seven (7%) RLN stimulated (two bilateral, three unilateral). Postoperative testing, however, only showed one true unilateral RLN palsy postoperatively (1%), which recovered in 7 weeks giving six false-positive and one true-positive results. Eighty-six of 100 (86%) EBSLN were located without the nerve stimulator. Thirteen of 100 (13%) EBSLN could not be identified and 1 of 100 (1%) was located with the use of the nerve stimulator. Fourteen per cent of EBSLN showed no cricothyroid twitch on EBSLN stimulation. Postoperative vocal function in these patients was normal. There were no instances of equipment malfunction. Dysphagia scores did not differ significantly between the study and control groups. Conclusion: Use of a nerve stimulator did not aid in anatomical dissection of the RLN and was useful in identifying only one EBSLN. Discontinuous nerve monitoring by stimulation during total thyroidectomy confers no obvious benefit for the experienced surgeon in nerve identification, functional testing or injury prevention. [source] The Characterization of Contractile and Myoelectric Activities in Paralyzed Tibialis Anterior Post Electrically Elicited Muscle FatigueARTIFICIAL ORGANS, Issue 4 2010Nan-Ying Yu Abstract This study aimed to understand the myoelectric and mechanical characteristics of muscle recovering from electrically elicited fatigue. A modified Burke fatigue protocol was delivered to activate the tibialis anterior of 13 spinal cord injured subjects for 4 min. Before and after the fatigue protocol, a series of pulse trains was delivered to induce three twitches and a fused contraction at 0, 1, 3, and 5 min and then followed every 5 min for 60 min. The recovery processes of the ankle dorsiflexion torque and the evoked electromyography (EMG) parameters were analyzed and characterized by a first-order exponential equation. The recovery process was found to be faster in regard to tetanic muscle contraction. Factors relating to low-frequency fatigue, postfatigue potentiation, and the quickly normalized relaxation rate were taken into account for the discussion of this result. During the recovery process, the disassociation was found not only between twitch and tetanic contractions but also between mechanical and myoelectric activities. After the complete normalization of EMG parameters from about 15 min post fatigue, the tetanic force recovered incompletely to an asymptotic level. [source] Differential effects of drugs interacting with autonomic transmitters on responses of rat vas deferens to field stimulationAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 2 2000C. Boselli 1 Frequency,response curves (0.1,30 Hz) were obtained in the epididymal portion of rat vas deferens. At low frequencies (0.1,1 Hz), the parameters evaluated were the first twitch and the fourth twitch at each frequency. The responses to trains of stimuli at intermediate (2,5 Hz) and high (10,30 Hz) frequencies were biphasic consisting of phase I (the first rapid phase of tetanus) and of phase II (the secondary slowly developing one). 2 Prazosin inhibited the first and the fourth twitch but not when the frequency was <1 Hz. Suramin inhibited the first twitch while substantially depressing the fourth one. The combination of prazosin and suramin almost completely abolished all the twitches evoked by a train of stimuli at low frequencies. Nifedipine left almost unaltered the first twitch while markedly depressing the fourth one, especially at relatively high frequency (1 Hz). Verapamil was devoid of any inhibitory action. Papaverine depressed the first twitch while only at the highest concentration used (1×10,4 m) markedly inhibited the fourth one. Chloroethylclonidine (CEC) depressed the first twitch and increased the fourth. 3 When intermediate (2,5 Hz) and high (10,30 Hz) frequencies are considered, prazosin and suramin partially inhibited both phase I and phase II, while in combination they almost completely abolished both phases. Nifedipine and verapamil selectively suppressed phase II, leaving phase I unaffected. Papaverine completely abolished both phase I and phase II. CEC was able to completely abolish phase I but increased phase II. 4 These results suggest that the response to the first twitch of a train at low frequency is prevailingly noradrenergic, prazosin-sensitive, while when the twitches are close enough (i.e. at 1 Hz) a summation of stimuli takes place and a predominant purinergic component, both suramin- and nifedipine-sensitive, becomes evident. 5 At high frequencies, both phases are due to the concomitant release of noradrenaline and adenosine triphosphate (ATP). The noradrenergic component of phase I is nifedipine-insensitive and CEC-sensitive, resembling the pharmacological profile of the endogenously released noradrenaline by single pulse, while that of phase II, nifedipine-sensitive and CEC-insensitive, is similar to that produced by exogenously applied noradrenaline. [source] The effect of strength training on the force of twitches evoked by corticospinal stimulation in humansACTA PHYSIOLOGICA, Issue 2 2009T. J. Carroll Abstract Aim:, Although there is considerable evidence that strength training causes adaptations in the central nervous system, many details remain unclear. Here we studied neuromuscular responses to strength training of the wrist by recording electromyographic and twitch responses to transcranial magnetic stimulation (TMS) and cervicomedullary stimulation of the corticospinal tract. Methods:, Seventeen participants performed 4 weeks (12 sessions) of strength training for the radial deviator (RD) muscles of the wrist (n = 8) or control training without external load (n = 9). TMS recruitment curves were constructed from stimuli at five to eight intensities ranging between 15% below resting motor threshold and maximal stimulator output, both at rest and during isometric wrist extension (EXT) and RD at 10% and 50% of maximal voluntary contraction (MVC). Responses to weak TMS and cervicomedullary stimulation (set to produce a response of 10% maximal M wave amplitude during 10% MVC EXT contraction) were also compared at contraction strengths ranging from 10% to 75% MVC. Results:, Isometric strength increased following strength training (10.7% for the RD MVC, 8.8% for the EXT MVC), but not control training. Strength training also significantly increased the amplitude of TMS- and cervicomedullary-evoked twitches during low-force contractions. Increases in the force-generating capacity of the wrist extensor muscles are unlikely to account for this finding because training did not affect the amplitude of twitches elicited by supra-maximal nerve stimulation. Conclusion:, The data suggest that strength training induces adaptations that increase the net gain of corticospinal-motor neuronal projections to the trained muscles. [source] Chronic facial twitches: when tracers reveal their statusEUROPEAN JOURNAL OF NEUROLOGY, Issue 8 2009F. Siclari No abstract is available for this article. [source] Monitoring of CBFV and time characteristics of oxygen-induced acute CNS toxicity in humansEUROPEAN JOURNAL OF NEUROLOGY, Issue 7 2008A. E. Koch Background:, Hyperbaric oxygen can cause central nervous system (CNS) toxicity with seizures. We tested the hypothesis that CNS toxicity could be predictable by cerebral blood flow velocity (CBFV) monitoring. Method:, We monitored 369 mandatory oxygen tolerance tests (30 min, 280 kPa O2) by video-documentation and since May 2005 by additional CBFV registration (n = 61). Results:, The onset of early manifestations of CNS toxicity was documented in 11 of 369 tests within 22 ± 3 min. These included twitches and/or agitation, 6 of 11 and tonic,clonic seizures in 5 of 11 cases. In both cases with CBFV monitoring, an increase in CBFV preceded symptom onset, once followed by seizure, once without seizure after timely oxygen reduction. Conclusions:, During exposure to 280 kPa oxygen at rest a constant delay of approximately 20 min precedes the onset of central nervous oxygen toxicity. An increase in CBFV may indicate the impending seizure. [source] Changes in contractile properties of motor units of the rat medial gastrocnemius muscle after spinal cord transectionEXPERIMENTAL PHYSIOLOGY, Issue 5 2006Jan Celichowski The effects of complete transection of the spinal cord at the level of Th9/10 on contractile properties of the motor units (MUs) in the rat medial gastrocnemius (MG) muscle were investigated. Our results indicate that 1 month after injury the contraction time (time-to-peak) and half-relaxation time were prolonged and the maximal tetanic force in most of the MUs in the MG muscle of spinal rats was reduced. The resistance to fatigue also decreased in most of the MUs in the MG of spinal animals. Moreover, the post-tetanic potentiation of twitches in MUs diminished after spinal cord transection. Criteria for the division of MUs into three types, namely slow (S), fast fatigue resistant (FR) and fast fatigable (FF), applied in intact animals, could not be directly used in spinal animals owing to changes in contractile properties of MUs. The ,sag' phenomenon observed in unfused tetani of fast units in intact animals essentially disappeared in spinal rats and it was only detected in few units, at low frequencies of stimulation only. Therefore, the MUs in spinal rats were classified as fast or slow on the basis of an adjusted borderline of 20 ms, instead of 18 ms as in intact animals, owing to a slightly longer contraction time of those fast motor units with the ,sag'. We conclude that all basic contractile properties of rat motor units in the medial gastrocnemius muscle are significantly changed 1 month after complete spinal cord transection, with the majority of motor units being more fatigable and slower than those of intact rats. [source] Behavioural responses of dairy cattle to the stable fly, Stomoxys calcitrans, in an open field environmentMEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2006B. A. Mullens Abstract., Individual cows (25 in each of four herds) were monitored 8,10 times weekly for 12 weeks (stable fly season) on a southern California dairy, with 100 observations per cow. The numbers of biting stable flies, Stomoxys calcitrans (L.) (Diptera: Muscidae) on the front legs and the frequencies of four fly-repelling behaviours per 2-min observation period [head throws, front leg stamps, skin twitches (panniculus reflex) and tail flicks] were recorded. Fly numbers varied, peaking at 3.0,3.5 flies per leg in week 9 (late May). Weekly herd mean frequencies of fly-repelling behaviours were highly dependent on fly numbers, with a linear regression r2 > 0.8. Head throws and stamps were less frequent than skin twitches and tail flicks. Individual cows differed in numbers of stable flies and behaviours. Behaviours were correlated with flies for individual cows, but at a lower level than were herd means (r = 0.3,0.7). Cows that stamped more within a herd tended to have lower fly counts; other fly-repelling behaviours were less effective. Cows maintained ranks within a herd with regard to fly numbers (r = 0.47), head throws (0.48), leg stamps (0.64), skin twitches (0.69) and tail flicks (0.64). Older cows tended to harbour higher fly numbers and to stamp less relative to younger adult cows. Ratios of leg stamps and head throws to fly numbers dropped significantly through time, suggesting habituation to pain associated with fly biting. Tail flicks were not effective for repelling Stomoxys, but were easiest to quantify and may help in monitoring pest intensity. At this low,moderate fly pressure, no consistent impacts on milk yield were detected, but methods incorporating cow behaviour are recommended for future studies of economic impact. [source] Interpolated twitches in fatiguing single mouse muscle fibres: implications for the assessment of central fatigueTHE JOURNAL OF PHYSIOLOGY, Issue 11 2008Nicolas Place An electrically evoked twitch during a maximal voluntary contraction (twitch interpolation) is frequently used to assess central fatigue. In this study we used intact single muscle fibres to determine if intramuscular mechanisms could affect the force increase with the twitch interpolation technique. Intact single fibres from flexor digitorum brevis of NMRI mice were dissected and mounted in a chamber equipped with a force transducer. Free myoplasmic [Ca2+] ([Ca2+]i) was measured with the fluorescent Ca2+ indicator indo-1. Seven fibres were fatigued with repeated 70 Hz tetani until 40% initial force with an interpolated pulse evoked every fifth tetanus. Results showed that the force generated by the interpolated twitch increased throughout fatigue, being 9 ± 1% of tetanic force at the start and 19 ± 1% at the end (P < 0.001). This was not due to a larger increase in [Ca2+]i induced by the interpolated twitch during fatigue but rather to the fact that the force,[Ca2+]i relationship is sigmoidal and fibres entered a steeper part of the relationship during fatigue. In another set of experiments, we observed that repeated tetani evoked at 150 Hz resulted in more rapid fatigue development than at 70 Hz and there was a decrease in force (,sag') during contractions, which was not observed at 70 Hz. In conclusion, the extent of central fatigue is difficult to assess and it may be overestimated when using the twitch interpolation technique. [source] Changes of Extremity and Laryngeal Muscle Electromyographic Amplitudes After Intravenous Administration of Vecuronium,THE LARYNGOSCOPE, Issue 12 2008Yongbing Shi MD Abstract Objectives: To compare electromyographic (EMG) amplitude changes in extremity and laryngeal muscles after vecuronium administration and study the effects of topical lidocaine on laryngeal EMG in a swine model. Study Design: Prospective animal study. Methods: Electrically evoked EMG activities were recorded from the vocalis muscles (directly and via an EMG endotracheal tube) and from the flexor digitorum muscles before and after intravenous vecuronium administration. EMG amplitudes were followed for 30 minutes after vecuronium injection together with monitoring of limb twitches to train-of-four stimulation. The testing was repeated after a 30-minute wash-out period and with topical lidocaine. Results: EMG amplitude recovery occurred sooner and more quickly in flexor digitorum muscle than in vocalis muscles. Reappearance of four twitches corresponded to EMG amplitude recovery to about 80% of the baseline in flexor digitorum muscles and to about half-baseline size in vocalis muscles. EMG amplitudes were generally lower at the start of the second round testing than the first round, with somewhat slower recovery in vocalis muscles. Conclusions: In contrast to reports by others in human studies, extremity muscles seem to be more resistant to vecuronium at 0.1 mg/kg than laryngeal muscles in the swine. Reappearance of four twitches corresponds to 50% of laryngeal EMG recovery and indicates adequate condition for monitoring electrically evoked laryngeal EMG activities. This study is inconclusive regarding the effects of topically applied lidocaine on laryngeal EMG amplitudes. Translation of these data to humans should be done with caution. [source] The Characterization of Contractile and Myoelectric Activities in Paralyzed Tibialis Anterior Post Electrically Elicited Muscle FatigueARTIFICIAL ORGANS, Issue 4 2010Nan-Ying Yu Abstract This study aimed to understand the myoelectric and mechanical characteristics of muscle recovering from electrically elicited fatigue. A modified Burke fatigue protocol was delivered to activate the tibialis anterior of 13 spinal cord injured subjects for 4 min. Before and after the fatigue protocol, a series of pulse trains was delivered to induce three twitches and a fused contraction at 0, 1, 3, and 5 min and then followed every 5 min for 60 min. The recovery processes of the ankle dorsiflexion torque and the evoked electromyography (EMG) parameters were analyzed and characterized by a first-order exponential equation. The recovery process was found to be faster in regard to tetanic muscle contraction. Factors relating to low-frequency fatigue, postfatigue potentiation, and the quickly normalized relaxation rate were taken into account for the discussion of this result. During the recovery process, the disassociation was found not only between twitch and tetanic contractions but also between mechanical and myoelectric activities. After the complete normalization of EMG parameters from about 15 min post fatigue, the tetanic force recovered incompletely to an asymptotic level. [source] | ||||||||||||||||||||||||||||