Muscle-specific mutations accumulate with aging in critical human mtDNA control sites for replication.

The recently discovered aging-dependent large accumulation of point mutations in the human fibroblast mtDNA control region raised the question of their occurrence in postmitotic tissues. In the present work, analysis of biopsied or autopsied human skeletal muscle revealed the absence or only minimal presence of those mutations. By contrast, surprisingly, most of 26 individuals 53 to 92 years old, without a known history of neuromuscular disease, exhibited at mtDNA replication control sites in muscle an accumulation of two new point mutations, i.e., A189G and T408A, which were absent or marginally present in 19 individuals younger than 34 years. These two mutations were not found in fibroblasts from 22 subjects 64 to 101 years of age (T408A), or were present only in three subjects in very low amounts (A189G). Furthermore, in several older individuals exhibiting an accumulation in muscle of one or both of these mutations, they were nearly absent in other tissues, whereas the most frequent fibroblast-specific mutation (T414G) was present in skin, but not in muscle. Among eight additional individuals exhibiting partial denervation of their biopsied muscle, four subjects >80 years old had accumulated the two muscle-specific point mutations, which were, conversely, present at only very low levels in four subjects <or =40 years old. The striking tissue specificity of the muscle mtDNA mutations detected here and their mapping at critical sites for mtDNA replication strongly point to the involvement of a specific mutagenic machinery and to the functional relevance of these mutations.

Neostigmine antagonism of rocuronium block during anesthesia with sevoflurane, isoflurane or propofol

Purpose: To examine the influence of continuing administration of sevoflurane or isoflurane during reversal of rocuronium induced neuromuscular block with neostigmine. Methods: One hundred and twenty patients, divided into three equal groups, were randomly allocated to maintenance of anesthesia with sevoflurane, isoflurane or propofol. Neuromuscular block was induced with rocuronium and monitored using train-of-four (TOF) stimulation of the ulnar nerve and recording the force of contraction of the adductor pollicis muscle. Neostigmine was administered when the first response in TOF had recovered to 25%. At this time the volatile agent administration was stopped or propofol dosage reduced in half the patients in each group (n = 20 in each group). The times to attain TOF ratio of 0.8, and the number of patients attaining this end point within 15 min were recorded. Results: The times (mean ± SD) to recovery of the TOF ratio to 0.8 were 12.0 ± 5.5 and 6.8 ± 2.3 min in the sevoflurane continued and sevoflurane stopped groups, 9.0 ± 8.3 and 5.5 ± 3.0 min in the isoflurane continued and isoflurane stopped groups, and 5.2 ± 2.8 and 4.7 ±1.5 min in the propofol continued and propofol stopped groups (P <0.5- 01). Only 9 and 15 patients in the sevoflurane and isoflurane continued groups respectively had attained a TOF ratio of 0.8 within 15 min (P <0.001 for sevoflurane). Conclusions: The continued administration of sevoflurane, and to a smaller extent isoflurane, results in delay in attaining adequate antagonism of rocuronium induced neuromuscular block.

Getting to the root of neuronal signalling in plant-parasitic nematodes using RNA interference

A variety of genes expressed in preparasitic second-stage juveniles (J2) of plant-parasitic nematodes appear to be vulnerable to RNA interference (RNAi) in vitro by coupling double-stranded (ds)RNA soaking with the artificial stimulation of pharyngeal pumping. Also, there is mounting evidence that the in planta generation of nematode-specific double-stranded RNAs (dsRNAs) has real utility in the control of these pests. Although neuronally-expressed genes in Caenorhabditis elegans are commonly refractory to RNAi, we have discovered that neuronally-expressed genes in plant-parasitic nematodes are highly susceptible to RNAi and that silencing can be induced by simple soaking procedures without the need for pharyngeal stimulation. Since most front-line anthelmintics that are used for the control of nematode parasites of animals and humans act to disrupt neuromuscular coordination, we argue that intercellular signalling processes associated with neurons have much appeal as targets for transgenic plant-based control strategies for plant-parasitic nematodes. FMRFamide-like peptides (FLPs) are a large family of neuropeptides which are intimately associated with neuromuscular regulation, and our studies on flp gene function in plant-parasitic nematodes have revealed that their expression is central to coordinated locomotory activities. We propose that the high level of conservation in nervous systems across nematodes coupled with the RNAi-susceptibility of neuronally-expressed genes in plant-parasitic nematodes provides a valuable research tool which could be used to interrogate neuronal signalling processes in nematodes.

Influence of predominant patterns of coordination on the exploitation of interaction torques in a two-joint rhythmic arm movement

In this study we investigate the coordination between rhythmic flexion-extension (FE) and supination-pronation (SP) movements at the elbow joint-complex, while manipulating the intersegmental dynamics by means of a 2-degrees of freedom (df) robot arm. We hypothesized that constraints imposed by the structure of the neuromuscular-skeletal system would (1) result in predominant pattern(s) of coordination in the absence of interaction torques and (2) influence the capabilities of participants to exploit artificially induced interaction torques. Two experiments were conducted in which different conditions of interaction torques were applied on the SP-axis as a function of FE movements. These conditions promoted different patterns of coordination between the 2-df. Control trials conducted in the absence of interaction torques revealed that both the in-phase (supination synchronized with flexion) and the anti-phase (pronation synchronized with flexion) patterns were spontaneously established by participants. The predominance of these patterns of coordination is explained in terms of the mechanical action of bi-articular muscles acting at the elbow joint-complex, and in terms of the reflexes that link the activity of the muscles involved. Results obtained in the different conditions of interaction torques revealed that those neuromuscular-skeletal constraints either impede or favor the exploitation of intersegmental dynamics depending on the context. Interaction torques were indeed found to be exploited to a greater extent in conditions in which the profiles of interaction torques favored one of the two predominant patterns of coordination (i.e., in-phase or anti-phase) as opposed to other patterns of coordination (e.g., 90 degrees or 270 degrees). Those results are discussed in relation to recent studies reporting exploitation of interaction torques in the context of rhythmic movements.

The consequences of resistance training for movement control in older adults

Older adults who undertake resistance training are typically seeking to maintain or increase their muscular strength with the goal of preserving or improving their functional capabilities. The extent to which resistance training adaptations lead to improved performance on tasks of everyday living is not particularly well understood. Indeed, studies examining changes in functional task performance experienced by older adults following periods of resistance training have produced equivocal findings. A clear understanding of the principles governing the transfer of resistance training adaptations is therefore critical in seeking to optimize the prescription of training regimes that have as their aim the maintenance and improvement of functional movement capacities in older adults. The degenerative processes that occur in the aging motor system are likely to influence heavily any adaptations to resistance training and the subsequent transfer to functional task performance. The resulting characteristics of motor behavior, such as the substantial decline in the rate of force development and the decreased steadiness of force production, may entail that specialized resistance training strategies are necessary to maximize the benefits for older adults. In this review, we summarize the alterations in the neuromuscular system that are responsible for the declines in strength, power, and force control, and the subsequent deterioration in the everyday movement capabilities of older adults. We examine the literature concerning the neural adaptations that older adults experience in response to resistance training, and consider the readiness with which these adaptations will improve the functional movement capabilities of older adults.

Haptic information stabilizes and destabilizes coordination dynamics

Goal-directed, coordinated movements in humans emerge from a variety of constraints that range from 'high-level' cognitive strategies based oil perception of the task to 'low-level' neuromuscular-skeletal factors such as differential contributions to coordination from flexor and extensor muscles. There has been a tendency in the literature to dichotomize these sources of constraint, favouring one or the other rather than recognizing and understanding their mutual interplay. In this experiment, subjects were required to coordinate rhythmic flexion and extension movements with an auditory metronome, the rate of which was systematically increased. When subjects started in extension on the beat of the metronome, there was a small tendency to switch to flexion at higher rates, but not vice versa. When subjects: were asked to contact a physical stop, the location of which was either coincident with or counterphase to the auditor) stimulus, two effects occurred. When haptic contact was coincident with sound, coordination was stabilized for both flexion and extension. When haptic contact was counterphase to the metronome, coordination was actually destabilized, with transitions occurring from both extension to flexion on the beat and from flexion to extension on the beat. These results reveal the complementary nature of strategic and neuromuscular factors in sensorimotor coordination. They also suggest the presence of a multimodal neural integration process-which is parametrizable by rate and context - in which intentional movement, touch and sound are bound into a single, coherent unit.

A randomised, controlled trial of conventional versus automated weaning from mechanical ventilation using SmartcareTM/PS

Objective
Preliminary assessment of an automated weaning system (SmartCare™/PS) compared to usual management of weaning from mechanical ventilation performed in the absence of formal protocols.


Design and setting
A randomised, controlled pilot study in one Australian intensive care unit.


Patients
A total of 102 patients were equally divided between SmartCare/PS and Control.

Interventions
The automated system titrated pressure support, conducted a spontaneous breathing trial and provided notification of success (“separation potential”).

Measurements and results
The median time from the first identified point of suitability for weaning commencement to the state of “separation potential” using SmartCare/PS was 20 h (interquartile range, IQR, 2–40) compared to 8 h (IQR 2–43) with Control (log-rank P = 0.3). The median time to successful extubation was 43 h (IQR 6–169) using SmartCare/PS and 40 (14–87) with Control (log-rank P = 0.6). Unadjusted, the estimated probability of reaching “separation potential” was 21% lower (95% CI, 48% lower to 20% greater) with SmartCare/PS compared to Control. Adjusted for other covariates (age, gender, APACHE II, SOFAmax, neuromuscular blockade, corticosteroids, coma and elevated blood glucose), these estimates were 31% lower (95% CI, 56% lower to 9% greater) with SmartCare/PS. The study groups showed comparable rates of reintubation, non-invasive ventilation post-extubation, tracheostomy, sedation, neuromuscular blockade and use of corticosteroids.

Conclusions
Substantial reductions in weaning duration previously demonstrated were not confirmed when the SmartCare/PS system was compared to weaning managed by experienced critical care specialty nurses, using a 1:1 nurse-to-patient ratio. The effect of SmartCare/PS may be influenced by the local clinical organisational context.

FMRFamide-like peptides (FLPs) enhance voltage-gated calcium currents to elicit muscle contraction in the human parasite Schistosoma mansoni.

Schistosomes are amongst the most important and neglected pathogens in the world, and schistosomiasis control relies almost exclusively on a single drug. The neuromuscular system of schistosomes is fertile ground for therapeutic intervention, yet the details of physiological events involved in neuromuscular function remain largely unknown. Short amidated neuropeptides, FMRFamide-like peptides (FLPs), are distributed abundantly throughout the nervous system of every flatworm examined and they produce potent myoexcitation. Our goal here was to determine the mechanism by which FLPs elicit contractions of schistosome muscle fibers. Contraction studies showed that the FLP Tyr-Ile-Arg-Phe-amide (YIRFamide) contracts the muscle fibers through a mechanism that requires Ca2+ influx through sarcolemmal voltage operated Ca2+ channels (VOCCs), as the contractions are inhibited by classical VOCC blockers nicardipine, verapamil and methoxyverapamil. Whole-cell patch-clamp experiments revealed that inward currents through VOCCs are significantly and reversibly enhanced by the application of 1 µM YIRFamide; the sustained inward currents were increased to 190% of controls and the peak currents were increased to 180%. In order to examine the biochemical link between the FLP receptor and the VOCCs, PKC inhibitors calphostin C, RO 31–8220 and chelerythrine were tested and all produced concentration dependent block of the contractions elicited by 1 µM YIRFamide. Taken together, the data show that FLPs elicit contractions by enhancing Ca2+ influx through VOCC currents using a PKC-dependent pathway.

Fasciolicides: Efficacy, actions, resistance and its management

The modes of action of fasciolicides are described. Closantel and other salicylanilides interfere with energy metabolism by uncoupling oxidative phosphorylation in the fluke. Other fasciolicides are believed to have a metabolic action-halogenated phenols (via uncoupling) and clorsulon (via inhibition of glycolysis)-but direct evidence is lacking. Benzimidazoles (in particular, riclabendazole) bind to fluke tubulin and disrupt microtubule-based processes. Diamphenethide inhibits protein synthesis in the fluke. Other potential drug actions may contribute to overall drug efficacy. In particular, a number of fasciolicides-salicylanilides, phenols, diamphenethide-induce a rapid paralysis of the fluke, so their action may have a neuromuscular basis, although the actions remain ill-defined. Resistance to salicylanilides and triclabendazole has been detected in the field, although drug resistance does not appear to be a major problem yet. Strategies to minimize the development of resistance include the use of synergistic drug combinations, together with the design of integrated management programmes and the search for alternatives to drugs, in particular, vaccines. (C) 1999 Harcourt Publishers Ltd.

Pharmacological effects of nematode FMRFamide-related peptides (FaRPs) on muscle contractility of the trematode, Fasciola hepatica

The physiological effects of synthetic replicates of the nematode FaRPs, AF1 (KNEFIRFamide), AF2 (KHEYLRFamide), PF1 (SDPNFLRFamide), PF2 (SADPNFLRFamide), AF8/PF3 (KSAYMRFamide) and PF4 (KPNFIRFamide) were examined on muscle preparations of the liver fluke, Fasciola hepatica. Changes in contractility following the addition of the test compound were recorded using a photo-optic transducer system. Unlike the varied effects these peptides have on nematode somatic musculature, all were found to induce excitatory responses in the muscle activity of F. hepatica. While qualitative effects of the nematode peptides were similar in that they induced increases in both the amplitude and frequency of F. hepatica muscle contractions, they varied considerably in the potency of their excitatory effects. The threshold activity for each peptide was as follows: 10 mu M, PF1 and PF2; 3 mu M, AF1 and PF3; 1 mu M, AF2; and 30 nM, PF4. The results demonstrate, for the first time, the cross-phyla activity of nematode neuropeptides on the neuromuscular activity of a trematode.

The pharmacology of nematode FMRFamide-related peptides

FMRFamide-related peptides (FaRPs) are the largest known family of invertebrate neuropeptides. Immunocytochemical screens of nematode tissues using antisera raised to these peptides have localized extensive FaRP-immunostaining to their nervous systems. Although 21 FaRPs have been isolated and sequenced from extracts of free-living and parasitic nematodes, available evidence indicates that other FaRPs await discovery. While our knowledge of the pharmacology of these native nematode neuropeptides is extremely limited, reports on their physiological activity in nematodes are ever increasing. All the nematode FaRPs examined so far have been found to have potent and varied actions on nematode neuromuscular activity. It is only through the extensive pharmacological and physiological assessment of the tissue, cell and receptor interactions of these peptidic messengers that an understanding of their activity on nematode neuromusculature will be possible. In this review, Aaron Maule and colleagues examine the current understanding of the pharmacology of nematode FaRPs.

PLATYHELMINTH FMRFAMIDE-RELATED PEPTIDES (FARPS) CONTRACT SCHISTOSOMA-MANSONI (TREMATODA, DIGENEA) MUSCLE-FIBERS IN-VITRO

Molluscan FMRFamide and two recently discovered platyhelminth FMRFamide-related peptides (FaRPs), GNFFRFamide from the cestode Moniezia expansa and RYIRFamide from the terrestrial turbellarian Artioposthia triangulata, cause dose-dependent contractions of individual muscle fibres from Schistosoma mansoni in vitro. The most potent FaRP tested was the turbellarian peptide RYIRFamide, which produced a concentration-dependent effect between 10(-9) and 10(-7) M. FMRFamide and GNFFRFamide were less potent, inducing contractions between 10(-8)-10(-6) M and 10(-7)-10(-5) M respectively. The contractile effect of each of these peptides was blocked by the presence of 1 mu M FMR-D-Famide. FMRF free acid did not elicit contraction of the muscle fibres. The FaRP-induced contractions did not occur if the Ca2+ was omitted and 0.5 mu M EGTA. was added to the extracellular medium. The FaRP-induced contractions were not blocked by the Ca2+ channel blockers nicardipine, verapamil or diltiazem, although high Kf-induced contractions of these fibres were blocked by nicardipine. These data indicate the presence of FaRP receptors on schistosome muscle fibres and demonstrate their ability to mediate muscle contraction. The action of these endogenous flatworm peptides on schistosome muscle is the first demonstration of a direct excitatory effect of any putative neurotransmitter on the muscle of a flatworm, and establishes a role for FaRPs in neuromuscular transmission in trematodes. In addition, it provides the first evidence that the peptidergic nervous system is a rational target for chemotherapeutic attack in parasitic platyhelmiths.

Investigation of physiological properties of nerves and muscles using electromyography.

The measurement and representation of the electrical activity of muscles [electromyography (EMG)] have a long history from the Victorian Era until today. Currently, EMG has uses both as a research tool, in noninvasively recording muscle activation, and clinically in the diagnosis and assessment of nerve and muscle disease and injury as well as in assessing the recovery of neuromuscular function after nerve damage. In the present report, we describe the use of a basic EMG setup in our teaching laboratories to demonstrate some of these current applications. Our practical also illustrates some fundamental physiological and structural properties of nerves and muscles. Learning activities include 1) displaying the recruitment of muscle fibers with increasing force development; 2) the measurement of conduction velocity of motor nerves; 3) the assessment of reflex delay and demonstration of Jendrassik's maneuver; and 4) a Hoffman reflex experiment that illustrates the composition of mixed nerves and the differential excitability thresholds of fibers within the same nerve, thus aiding an understanding of the reflex nature of muscle control. We can set up the classes at various levels of inquiry depending on the needs/professional requirements of the class. The results can then provide an ideal platform for a discovery learning session/tutorial on how the central nervous system controls muscles, giving insights on how supraspinal control interacts with reflexes to give smooth, precise muscular activation.