The stimulus-response curve and motor unit variability in normal subjects and subjects with amyotrophic lateral sclerosis

The behavior and stability of motor units (MUs) in response to electrical stimulation of different intensities can be assessed with the stimulus-response curve, which is a graphical representation of the size of the compound muscle action potential (CMAP) in relation to stimulus intensity. To examine MU characteristics across the whole stimulus range, the variability of CMAP responses to electrical stimulation, and the differences that occur between normal and disease states, the curve was studied in 11 normal subjects and 16 subjects with amyotrophic lateral sclerosis (ALS). In normal subjects, the curve showed a gradual increase in CMAP size with increasing stimulus intensity, although one or two discrete steps were sometimes observed in the upper half of the curve, indicating the activation of large MUs at higher intensities. In ALS subjects, large discrete steps, due to loss of MUs and collateral sprouting, were frequently present. Variability of the CMAP responses was greater than baseline variability, indicating variability of MU responses, and at certain levels this variability was up to 100 mu Vms. The stimulus-response curve shows differences between normal and ALS subjects and provides information on MU activation and variability throughout the curve.

A novel conotoxin inhibitor of Kv1.6 channel and nAChR subtypes defines a new superfamily of conotoxins

Using assay-directed fractionation of the venom from the vermivorous cone snail Conus planorbis, we isolated a new conotoxin, designated p114a, with potent activity at both nicotinic acetylcholine receptors and a voltage-gated potassium channel subtype. p114a contains 25 amino acid residues with an amidated C-terminus, an elongated N-terminal tail (six residues), and two disulfide bonds (1-3, 2-4 connectivity) in a novel framework distinct from other conotoxins. The peptide was chemically synthesized, and its three-dimensional structure was demonstrated to be well-defined, with an R-helix and two 3(10)-helices present. Analysis of a cDNA clone encoding the prepropeptide precursor of p114a revealed a novel signal sequence, indicating that p114a belongs to a new gene superfamily, the J-conotoxin superfamily. Five additional peptides in the J-superfamily were identified. Intracranial injection of p114a in mice elicited excitatory symptoms that included shaking, rapid circling, barrel rolling, and seizures. Using the oocyte heterologous expression system, p114a was shown to inhibit both a K+ channel subtype (Kv1.6, IC50) 1.59 mu M) and neuronal (IC50 = 8.7 mu M for alpha 3 beta 4) and neuromuscular (IC50 = 0.54 mu M for alpha 1 beta 1 is an element of delta) subtypes of the nicotinic acetylcholine receptor ( nAChR). Similarities in sequence and structure are apparent between the middle loop of p114a and the second loop of a number of alpha-conotoxins. This is the first conotoxin shown to affect the activity of both voltage-gated and ligand-gated ion channels.

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.

Phosphoinositide regulation of neuroexocytosis: adding to the complexity

Exocytosis of neurotransmitter containing vesicles supports neuronal communication. The importance of molecular interactions involving specific lipids has become progressively more evident and the lipid composition of both the synaptic vesicle and the pre-synaptic plasma membrane at the active zone has significant functional consequences for neurotransmitter release. Several classes of lipids have been implicated in exocytosis including polyunsaturated fatty acids and phosphoinositides. This minireview will focus on recent developments regarding the role of phosphoinositides in neurosecretion.

Dynamic training volume: A construct of both time under tension and volume load

The purpose of this study was to investigate the effects of three different weight training protocols, that varied in the way training volume was measured, on acute muscular fatigue. Ten resistance-trained males performed all three protocols which involved dynamic constant resistance exercise of the elbow flexors. Protocol A provided a standard for the time the muscle group was under tension (TUT) and volume load (VL), expressed as the product of the total number of repetitions and the load that was lifted. Protocol B involved 40% of the TUT but the same VL compared to protocol A; protocol C was equated with protocol A for TUT but only involved 50% of the VL. Fatigue was assessed by changes in maximum voluntary isometric force and integrated electromyography (iEMG) between the pre- and post-training protocols. The results of the study showed that, when equated for VL, greater TUT produced greater overall muscular fatigue ( p

Effects of care pathways on stroke care practices at regional hospitals

Background: Our previous work identified deficiencies in stroke care practices at regional hospitals in comparison to standards suggested by published stroke care guidelines. These deficiencies might be improved by the implementation of clinical pathways. The aim of this study was to assess changes in acute stroke care practices following the implementation of stroke care pathways at four regional Queensland hospitals. Methods: The medical records of two cohorts of 120 patients with a discharge diagnosis of stroke or transient ischaemic attack were retrospectively audited before and after implementation of stroke care pathways to identify differences in the use of acute interventions, investigations and secondary prevention strategies. Results: Following pathway implementation there were clinically important, but not statistically significant, increases in the rates of swallow assessment, allied health assessment (significant for occupational therapy, P = 0.04) and use of deep vein thrombosis prevention strategies (also significant, P = 0.006). Fewer patients were discharged on no anti-thrombotic therapy (statistically significant in the subgroup of patients with atrial fibrillation, P = 0.02). Only 37% of the patients audited were actually enrolled on the pathway. Among this subgroup there were significant increases in the rates of swallow assessment (first 24 h, P = 0.01; any time during admission, P = 0.0001), allied health assessments (all P < 0.05), estimation of blood glucose level (P = 0.0015) and the use of deep vein thrombosis prevention strategies (P = 0.0003). Conclusion: Stroke care pathways appear to improve the process of care. Whether this influences outcomes such as mortality, functional and neurological recovery, the incidence of complications, length of stay or the cost of care was beyond the scope of this study and will require further examination.

Circadian blood pressure variation after acute stroke

We aimed to characterise the patterns of circadian blood pressure (BP) variation after acute stroke and determine whether any relationship exists between these patterns and stroke outcome. BP was recorded manually every 4 h for 48 h following acute stroke. Patients were classified according to the percentage fall in mean systolic BP (SBP) at night compared to during the day as: dippers (fall >= 10-= 20%); non-dippers (>= 0-

Computational methods for the detection of facial palsy

We are developing a telemedicine application which offers automated diagnosis of facial (Bell's) palsy through a Web service. We used a test data set of 43 images of facial palsy patients and 44 normal people to develop the automatic recognition algorithm. Three different image pre-processing methods were used. Machine learning techniques (support vector machine, SVM) were used to examine the difference between the two halves of the face. If there was a sufficient difference, then the SVM recognized facial palsy. Otherwise, if the halves were roughly symmetrical, the SVM classified the image as normal. It was found that the facial palsy images had a greater Hamming Distance than the normal images, indicating greater asymmetry. The median distance in the normal group was 331 (interquartile range 277-435) and the median distance in the facial palsy group was 509 (interquartile range 334-703). This difference was significant (P

Motor unit number estimation - A Bayesian approach

All muscle contractions are dependent on the functioning of motor units. In diseases such as amyotrophic lateral sclerosis (ALS), progressive loss of motor units leads to gradual paralysis. A major difficulty in the search for a treatment for these diseases has been the lack of a reliable measure of disease progression. One possible measure would be an estimate of the number of surviving motor units. Despite over 30 years of motor unit number estimation (MUNE), all proposed methods have been met with practical and theoretical objections. Our aim is to develop a method of MUNE that overcomes these objections. We record the compound muscle action potential (CMAP) from a selected muscle in response to a graded electrical stimulation applied to the nerve. As the stimulus increases, the threshold of each motor unit is exceeded, and the size of the CMAP increases until a maximum response is obtained. However, the threshold potential required to excite an axon is not a precise value but fluctuates over a small range leading to probabilistic activation of motor units in response to a given stimulus. When the threshold ranges of motor units overlap, there may be alternation where the number of motor units that fire in response to the stimulus is variable. This means that increments in the value of the CMAP correspond to the firing of different combinations of motor units. At a fixed stimulus, variability in the CMAP, measured as variance, can be used to conduct MUNE using the "statistical" or the "Poisson" method. However, this method relies on the assumptions that the numbers of motor units that are firing probabilistically have the Poisson distribution and that all single motor unit action potentials (MUAP) have a fixed and identical size. These assumptions are not necessarily correct. We propose to develop a Bayesian statistical methodology to analyze electrophysiological data to provide an estimate of motor unit numbers. Our method of MUNE incorporates the variability of the threshold, the variability between and within single MUAPs, and baseline variability. Our model not only gives the most probable number of motor units but also provides information about both the population of units and individual units. We use Markov chain Monte Carlo to obtain information about the characteristics of individual motor units and about the population of motor units and the Bayesian information criterion for MUNE. We test our method of MUNE on three subjects. Our method provides a reproducible estimate for a patient with stable but severe ALS. In a serial study, we demonstrate a decline in the number of motor unit numbers with a patient with rapidly advancing disease. Finally, with our last patient, we show that our method has the capacity to estimate a larger number of motor units.

A pathology of the animal spirits - the clinical neurology of Thomas Willis (1621-1675) Part I - Background, and disorders of intrinsically normal animal spirits

Thomas Willis (1621-1675), author of the classical work Cerebri Anatome (1664), was arguably the father of the modem era of neurology. As compared with his neuroanatomy, relatively little attention has been paid to Willis' clinical neurology, as described in his Pathologiae Cerebri (1667) and Do Anima Brutorum (1672), where he gave a structured account of disease of the nervous system as it was known in his day. His account was largely derived from personal observations and not from traditional authorities and was based around his concept of the animal spirits, a fictitious entity in many ways analogous to the present day idea of the nerve impulse. This concept allowed him to develop a pathology of the animal spirits which embraced the whole content of the clinical neurology and psychiatry of his times. The anatomical and physiological background to Willis! concepts of animal spirit dysfunction, and those disorders he regarded as due to disturbed function of intrinsically normal animal spirits (mainly headache, disorders of consciousness, apoplexy and palsy) are dealt with in the present paper. The disorders he attributed to inherently abnormal animal spirits are considered in a second part of the paper. (C) 2002 Elsevier Science Ltd. All eights reserved.

Identification and evaluation of agents isolated from traditionally used herbs against Ophiophagus hannah venom

The aim of this study was firstly to identify active molecules in herbs, that are traditionally used for the treatment of snake bite, such as Curcuma antinaia, Curcuma contravenenum, Andrographis paniculata, and Tanacetum parthenium; secondly to test similar structurally related molecules and finally to prepare and evaluate an efficient formulation against Ophiophagus hannah venom intoxification. Three labdane based compounds, including labdane dialdehyde, labdane lactone, and labdane trialdehyde and two lactones including 14-deoxy-11,12-didehydroandrographolide and parthenolide were isolated by column chromatography and characterised. Using the isolated rat phrenic nerve-hemidiaphragm preparation, the antagonistic effect of crude extracts, isolated compounds and prepared formulations were measured in vitro on the inhibition of the neuromuscular transmission. Inhibition on muscle contraction, produced by the 5 μg/mL venom, was reversed by test agents in organ bath preparations. A labdane trialdehyde, isolated from C. contravenenum, was identified as the best antagonising agent in the low micromolar range. Tests on formulations of the most potent C. contravenenum extract showed, that the suppository with witepsol H15 was an effective medicine against O. hannah venom. This study elucidated the active compounds, accounting for the antivenin activity of traditionally used herbs and suggested the most suitable formulation, which may help to develop potent medicines for the treatment of snake bite in the future.