Adipose invasion of muscle in Wagyu cattle: Monitoring by histology and melting temperature.

Remarkably, Wagyu cattle progressively desaturate intramuscular and subcutaneous fat leading to melting temperatures (Tm) well below 38°C. In parallel, the adipose tissue expands, arborises and invades the muscle. The process is aggressive in that it leads to loss of myofibres resulting in much smaller fascicles and therefore fine marbling or snowflaking. The "Microscopic score" appears to be an excellent measure of marbling especially for lesser and greater degrees which are not quantified reliably by others methods. By comparing muscle groups, we conclude that the tailhead is a suitable site for sequential monitoring. Melting temperatures of intramuscular and subcutaneous tissue are also useful.

Cytokines in immune-mediated inflammatory myopathies: cellular sources, multiple actions and therapeutic implications.

The idiopathic inflammatory myopathies are a heterogeneous group of disorders characterised by diffuse muscle weakness and inflammation. A common immunopathogenic mechanism is the cytokine-driven infiltration of immune cells into the muscle tissue. Recent studies have further dissected the inflammatory cell types and associated cytokines involved in the immune-mediated myopathies and other chronic inflammatory and autoimmune disorders. In this review we outline the current knowledge of cytokine expression profiles and cellular sources in the major forms of inflammatory myopathy and detail the known mechanistic functions of these cytokines in the context of inflammatory myositis. Furthermore, we discuss how the application of this knowledge may lead to new therapeutic strategies for the treatment of the inflammatory myopathies, in particular for cases resistant to conventional forms of therapy.

Statin myotoxicity: a review of genetic susceptibility factors.

The 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase inhibitors (statins) are among the most common medications prescribed worldwide, but their efficacy and toxicity vary between individuals. One of the major factors contributing to intolerance and non-compliance are the muscle side-effects, which range from mild myalgia through to severe life-threatening rhabdomyolysis. One way to address this is pharmacogenomic screening, which aims to individualize therapy to maximize efficacy whilst avoiding toxicity. Genes encoding proteins involved in the metabolism of statins as well as genes known to cause inherited muscle disorders have been investigated. To-date only polymorphisms in the SLCO1B1 gene, which encodes the protein responsible for hepatic uptake of statins, and the COQ2 gene, important in the synthesis of coenzyme Q10, have been validated as being strongly associated with statin-induced myopathy. The aim of this review is to summarize studies investigating genetic factors predisposing to statin myopathy and myalgia, as the first step towards pharmacogenomic screening to identify at risk individuals.

Polymorphism in the TOMM40 gene modifies the risk of developing sporadic inclusion body myositis and the age of onset of symptoms.

A polyT repeat in an intronic polymorphism (rs10524523) in the TOMM40 gene, which encodes an outer mitochondrial membrane translocase involved in the transport of amyloid-ß and other proteins into mitochondria, has been implicated in Alzheimer's disease and APOE-TOMM40 genotypes have been shown to modify disease risk and age at onset of symptoms. Because of the similarities between Alzheimer's disease and sporadic inclusion body myositis (s-IBM), and the importance of amyloid-ß and mitochondrial changes in s-IBM, we investigated whether variation in poly-T repeat lengths in rs10524523 also influence susceptibility and age at onset in a cohort of 90 Caucasian s-IBM patients (55 males; age 69.1 ± 9.6). In carriers of APOE ε3/ε3 or ε3/ε4, genotypes with a very long (VL) poly-T repeat were under-represented in s-IBM compared to controls and were associated with a later age at symptom onset, suggesting that these genotypes may be protective. Our study is the first to suggest that polymorphisms in genes controlling mitochondrial function can influence susceptibility to s-IBM and have disease modifying effects. However, further studies in other s-IBM populations are needed to confirm these findings, as well as expression studies of different TOMM40 alleles in muscle tissue.

Comparing kinematic changes between a finger-tapping task and unconstrained finger flexion-extension task in patients with Parkinson's disease.

Repetitive finger tapping is a well-established clinical test for the evaluation of parkinsonian bradykinesia, but few studies have investigated other finger movement modalities. We compared the kinematic changes (movement rate and amplitude) and response to levodopa during a conventional index finger-thumb-tapping task and an unconstrained index finger flexion-extension task performed at maximal voluntary rate (MVR) for 20 s in 11 individuals with levodopa-responsive Parkinson's disease (OFF and ON) and 10 healthy age-matched controls. Between-task comparisons showed that for all conditions, the initial movement rate was greater for the unconstrained flexion-extension task than the tapping task. Movement rate in the OFF state was slower than in controls for both tasks and normalized in the ON state. The movement amplitude was also reduced for both tasks in OFF and increased in the ON state but did not reach control levels. The rate and amplitude of movement declined significantly for both tasks under all conditions (OFF/ON and controls). The time course of rate decline was comparable for both tasks and was similar in OFF/ON and controls, whereas the tapping task was associated with a greater decline in MA, both in controls and ON, but not OFF. The findings indicate that both finger movement tasks show similar kinematic changes during a 20-s sustained MVR, but that movement amplitude is less well sustained during the tapping task than the unconstrained finger movement task. Both movement rate and amplitude improved with levodopa; however, movement rate was more levodopa responsive than amplitude.

Evidence for high-fidelity timing-dependent synaptic plasticity of human motor cortex.

A single transcranial magnetic stimulation (TMS) pulse typically evokes a short series of spikes in corticospinal neurons [known as indirect (I)-waves] which are thought to arise from transynaptic input. Delivering a second pulse at inter-pulse intervals (IPIs) corresponding to the timing of these I-waves leads to a facilitation of the response, and if stimulus pairs are delivered repeatedly, a persistent LTP-like increase in excitability can occur. This has been demonstrated at an IPI of 1.5 ms, which corresponds to the first I-wave interval, in an intervention referred to as ITMS (I-wave TMS), and it has been argued that this may have similarities with timing-dependent plasticity models. Consequently, we hypothesized that if the second stimulus is delivered so as not to coincide with I-wave timing, it should lead to LTD. We performed a crossover study in 10 subjects in which TMS doublets were timed to coincide (1.5-ms IPI, ITMS(1.5)) or not coincide (2-ms IPI, ITMS(2)) with I-wave firing. Single pulse motor-evoked potential (MEP) amplitude, resting motor threshold (RMT), and short-interval cortical inhibition (SICI) were measured from the first dorsal interosseous (FDI) muscle. After ITMS(1.5) corticomotor excitability was increased by ~60% for 15 min (P < 0.05) and returned to baseline by 20 min. Increasing the IPI by just 500 µs to 2 ms reversed the aftereffect, and MEP amplitude was significantly reduced (~35%, P < 0.05) for 15 min before returning to baseline. This reduction was not associated with an increase in SICI, suggesting a reduction in excitatory transmission rather than an increase in inhibitory efficacy. RMT also remained unchanged, suggesting that these changes were not due to changes in membrane excitability. Amplitude-matching ITMS(2) did not modulate excitability. The results are consistent with timing-dependent synaptic LTP/D-like effects and suggest that there are plasticity mechanisms operating in the human motor cortex with a temporal resolution of the order of a few hundreds of microseconds.

Breakdown in central motor control can be attenuated by motor practice and neuro-modulation of the primary motor cortex.

The performance of a repetitive index finger flexion-extension task at maximal voluntary rate (MVR) begins to decline just a few seconds into the task and we have previously postulated that this breakdown has a central origin. To test this hypothesis, we have combined two objectives; to determine whether motor practice can lessen the performance deterioration in an MVR task, and whether further gains can be achieved with a transcranial magnetic stimulation (TMS) protocol that increases corticomotor excitability (CME). Eleven right-handed subjects participated in a randomized crossover study design that consisted of a 15-min interventional TMS at I-wave periodicity (ITMS) and single-pulsed Sham intervention prior to six 10-s practice sets of a repetitive finger flexion-extension task at MVR. Motor-evoked potentials (MEPs) were recorded from the first dorsal interosseous muscle. The starting movement rate, and the percentage decline in rate by the end of the MVR were quantitated. Training of the MVR task improved the sustainability of the task by reducing the decline in movement rate. CME increased steadily after each training bout, and this increase was maintained up to 20 min after the last bout. ITMS further increased CME, and was associated with an increase in both the starting rate of the MVR task and its sustainability, when compared to Sham. The results implicate central motor processes in the performance and sustainability of the MVR task, and indicate that MVR kinematics can improve with short-term training and with non-invasive neuro-modulation.

Co-regulation of survival of motor neuron and Bcl-xL expression: implications for neuroprotection in spinal muscular atrophy.

Spinal muscular atrophy (SMA), a fatal genetic motor disorder of infants, is caused by diminished full-length survival of motor neuron (SMN) protein levels. Normally involved in small nuclear ribonucleoprotein (snRNP) assembly and pre-mRNA splicing, recent studies suggest that SMN plays a critical role in regulating apoptosis. Interestingly, the anti-apoptotic Bcl-x isoform, Bcl-xL, is reduced in SMA. In a related finding, Sam68, an RNA-binding protein, was found to modulate splicing of SMN and Bcl-xL transcripts, promoting SMNΔ7 and pro-apoptotic Bcl-xS transcripts. Here we demonstrate that Bcl-xL expression increases SMN protein by ∼2-fold in SH-SY5Y cells. Conversely, SMN expression increases Bcl-xL protein levels by ∼6-fold in SH-SY5Y cells, and ∼2.5-fold in the brains of transgenic mice over-expressing SMN (PrP-SMN). Moreover, Sam68 protein levels were markedly reduced following SMN and Bcl-xL expression in SH-SY5Y cells, suggesting a feedback mechanism co-regulating levels of both proteins. We also found that exogenous SMN expression increased full-length SMN transcripts, possibly by promoting exon 7 inclusion. Finally, co-expression of SMN and Bcl-xL produced an additive anti-apoptotic effect following PI3-kinase inhibition in SH-SY5Y cells. Our findings implicate Bcl-xL as another potential target in SMA therapeutics, and indicate that therapeutic increases in SMN may arise from modest increases in total SMN.

Changes in corticomotor excitability and inhibition after exercise are influenced by hand dominance and motor demand.

Previous studies on handedness have often reported functional asymmetries in corticomotor excitability (CME) associated with voluntary movement. Recently, we have shown that the degree of post-exercise corticomotor depression (PED) and increase in short-interval cortical inhibition (SICI) after a repetitive finger movement task was less when the task was performed at a maximal voluntary rate (MVR) than when it was performed at a submaximal sustainable rate (SR). In the current study, we have compared the time course of PED and SICI in the dominant (DOM) and nondominant (NDOM) hands after an MVR and SR finger movement task to determine the influence of hand dominance and task demand. We tracked motor-evoked potential (MEP) amplitude from the first dorsal interosseous muscle of the DOM and NDOM hand for 20 min after a 10-s index finger flexion-extension task at MVR and SR. For all hand-task combinations, we report a period of PED and increased SICI lasting for up to 8 min. We find that the least demanding task, one that involved index finger movement of the DOM hand at SR, was associated with the greatest change in PED and SICI from baseline (63.6±5.7% and 79±2%, P<0.001, PED and SICI, respectively), whereas the most demanding task (MVR of the NDOM hand) was associated with the least change from baseline (PED: 88.1±3.6%, SICI: 103±2%; P<0.001). Our findings indicate that the changes in CME and inhibition associated with repetitive finger movement are influenced both by handedness and the degree of demand of the motor task and are inversely related to task demand, being smallest for an MVR task of the NDOM hand and greatest for an SR task of the DOM hand. The findings provide additional evidence for differences in neuronal processing between the dominant and nondominant hemispheres in motor control.

Post-exercise depression in corticomotor excitability after dynamic movement: a general property of fatiguing and non-fatiguing exercise.

Transcranial magnetic stimulation has been used to study changes in central excitability associated with motor tasks. Recently, we reported that a finger flexion-extension task performed at a maximal voluntary rate (MVR) could not be sustained and that this was not due to muscle fatigue, but was more likely a breakdown in central motor control. To determine the central changes that accompany this type of movement task, we tracked motor-evoked potential (MEP) amplitude from the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles of the dominant hand in normal subjects for 20 min after a 10 sec index finger flexion-extension task performed at MVR and at a moderate sustainable rate (MSR) and half the MSR (MSR(/2)). The FDI MEP amplitude was reduced for up to 6-8 min after each of the tasks but there was a greater and longer-lasting reduction after the MSR and MSR(/2) tasks compared to the MVR task. There was a similar reduction in the amplitude of the FDI MEP after a 10 sec cyclic index finger abduction-adduction task when the FDI was acting as the prime mover. The amplitude of the MEP recorded from the inactive APB was also reduced after the flexion-extension tasks, but to a lesser degree and for a shorter duration. Measurements of short-interval cortical inhibition revealed an increase in inhibition after all of the finger flexion-extension tasks, with the MSR task being associated with the greatest degree of inhibition. These findings indicate that a demanding MVR finger movement task is followed by a period of reduced corticomotor excitability and increased intracortical inhibition. However, these changes also occur with and are greater with slower rates of movement and are not specific for motor demand, but may be indicative of adaptive changes in the central motor pathway after a period of repetitive movement.

Update on toxic myopathies.

The toxic myopathies are a clinically and pathologically diverse group of disorders that can be caused by a variety of therapeutic agents used in clinical practice, as well as various venoms and other biological toxins. The most important iatrogenic causes are the statin and fibrate cholesterol-lowering agents that can cause a severe necrotizing myopathy and acute rhabdomyolysis and myoglobinuria. The current update focuses on the mechanisms of statin myotoxicity and the importance of genetic predisposing factors for statin myopathy, as well as the recently described form of necrotizing autoimmune myopathy, which is associated with antibodies to the 3-hydroxy-3-methylglutaryl-coenzyme A reductase enzyme and is responsive to aggressive immunotherapy. Mitochondrial myopathies associated with antiretroviral agents and the pyrimidine nucleoside analogue clevudine, and recent reports of myopathies caused by ingestion of red yeast rice and toxic species of mushrooms are also discussed.

The association of sporadic inclusion body myositis and Sjögren's syndrome in carriers of HLA-DR3 and the 8.1 MHC ancestral haplotype.

Sporadic inclusion body myositis (sIBM) usually occurs as an isolated condition, but it may occur in association with another autoimmune disorder such as Sjögren's syndrome. We reviewed sIBM cases with Sjögren's syndrome (sIBM/SS) from the Perth Inflammatory Myopathies Database to determine whether they are distinguishable from other sIBM cases. Six such cases were identified, representing 12% of all sIBM cases. Muscle biopsies confirmed the presence of an inflammatory myopathy with rimmed vacuoles and the characteristic muscle fibre inclusions of sIBM. Five of the six were females, contrasting with a 2:1 male preponderance in the rest of the sIBM cohort. The mean age-at-onset and the pattern of muscle weakness were similar in the two groups. Four out of five sIBM/SS patients treated with immune therapies had improvement in muscle strength lasting for 6-24 months, whereas only 27% of other sIBM patients improved. All 6 patients with sIBM/SS carried the HLA-DRB1*0301 allele, or its equivalent HLA-DR3 serological specificity, compared with 83% of other sIBM cases and all carried some or all of the major markers of the 8.1 MHC ancestral haplotype which is also associated with Sjögren's syndrome. Patients with sIBM/SS represent a subgroup of sIBM cases who are more likely to be female and carriers of HLA-DR3 and the 8.1 MHC ancestral haplotype, and are more likely to respond to treatment. The association of sIBM and Sjögren's syndrome is likely to be due to a common genetic predisposition linked to the MHC and supports the notion that sIBM has an autoimmune basis.

Survival of motor neuron protein over-expression prevents calpain-mediated cleavage and activation of procaspase-3 in differentiated human SH-SY5Y cells.

Spinal muscular atrophy (SMA), a neurodegenerative disorder primarily affecting motor neurons, is the most common genetic cause of infant death. This incurable disease is caused by the absence of a functional SMN1 gene and a reduction in full length survival of motor neuron (SMN) protein. In this study, a neuroprotective function of SMN was investigated in differentiated human SH-SY5Y cells using an adenoviral vector to over-express SMN protein. The pro-survival capacity of SMN was assessed in an Akt/PI3-kinase inhibition (LY294002) model, as well as an oxidative stress (hydrogen peroxide) and excitotoxic (glutamate) model. SMN over-expression in SH-SY5Y cells protected against Akt/phosphatidylinositol 3-kinase (PI3-kinase) inhibition, but not oxidative stress, nor against excitotoxicity in rat cortical neurons. Western analysis of cell homogenates from SH-SY5Y cultures over-expressing SMN harvested pre- and post-Akt/PI3-kinase inhibition indicated that SMN protein inhibited caspase-3 activation via blockade of calpain-mediated procaspase-3 cleavage. This study has revealed a novel anti-apoptotic function for the SMN protein in differentiated SH-SY5Y cells. Finally, the cell death model described herein will allow the assessment of future therapeutic agents or strategies aimed at increasing SMN protein levels.

Modulation of corticomotor excitability by an I-wave intervention delivered during low-level voluntary contraction.

Transcranial magnetic stimulation (TMS) interventions that modulate cortical plasticity may achieve a more functional benefit if combined with neuro-rehabilitation therapies. With a TMS protocol targeting I-wave dynamics, it is possible to deliver stimuli while a subject performs a motor task, and this may more effectively target functional networks related to the task. However, the efficacy of this intervention during a simple task such as a low-level voluntary contraction is not known. We delivered paired-pulse TMS at an inter-pulse interval (IPI) of 1.5 ms for 15 min while subjects performed a 10 ± 2.5% voluntary contraction of the first dorsal interosseous (FDI) muscle and made motor evoked potential (MEP) amplitude and short-interval intracortical facilitation (SICF) curve measurements. Pre-intervention SICF curves showed only a single peak at 1.3-1.5 ms IPI. During the intervention, MEP amplitude steadily increased (P < 0.001) to 137 ± 13% of its initial value. After the intervention, SICF curves were increased in amplitude (P < 0.001) and later peaks emerged at 2.8 and 4.3 ms IPIs. A control experiment, replacing paired-pulse stimulation with single-pulse stimulation showed no effect on MEP amplitude (P = 0.951). We conclude that the I-wave intervention can be administered concurrently with a simple motor task and that it acts by increasing trans-synaptic efficacy across a number of I-waves. The ability to perform a motor task simultaneously with a TMS intervention could confer a degree of specificity to the induced excitability changes and may be beneficial for functional neuro-rehabilitation programs built around motor learning and retraining.

Longitudinally extensive myelopathy in Caucasians: a West Australian study of 26 cases from the Perth Demyelinating Diseases Database.

OBJECTIVES: To characterise West Australian cases of longitudinally extensive myelopathy (LEM). METHODS: Twenty six patients with LEM were identified from a cohort of 983 patients with demyelinating disease. Clinical and MRI data and AQP4-IgG results were reviewed. RESULTS: LEM cases were classified as conventional MS (CMS) 13, neuromyelitis optica (NMO) 7, and isolated LEM 6. LEM was the initial presentation in 13/26 cases. In CMS cases lesions were mainly in the lower cervical cord (C4-C7) whereas in NMO and isolated LEM they were more often thoracic and were longer. The severity of disability was highly variable but was greater in the NMO than the CMS group. Only one of 20 patients tested was seropositive for AQP4-IgG. CONCLUSION: LEM occurred as part of CMS or NMO or in isolation. Patients with LEM had highly heterogeneous clinical characteristics and a low rate of AQP4-IgG seropositivity.

Raised corticomotor excitability of M1 forearm area following anodal tDCS is sustained during robotic wrist therapy in chronic stroke.

PURPOSE: Anodal transcranial direct current stimulation (tDCS) can transiently increase corticomotor excitability of intrinsic hand muscles and improve upper limb function in patients with chronic stroke. As a preliminary study, we tested whether increased corticomotor excitability would be similarly observed in muscles acting about the wrist, and remain present during robotic training involving active wrist movements, in six chronic stroke patients with residual motor deficit. METHODS: Transcranial magnetic stimulation (TMS) generated motor evoked potentials (MEP) in the flexor carpi radialis (FCR) and provided a measure of corticomotor excitability and short-interval cortical inhibition (SICI) before and immediately after a period of tDCS (1 mA, 20 min, anode and TMS applied to the lesioned hemisphere), and robotic wrist training (1hr). RESULTS: Following tDCS, the same TMS current strength evoked an increased MEP amplitude (mean 168 +/- 22%SEM; p < 0.05), that remained increased after robot training (166 +/- 23%; p < 0.05). Conditioned MEPs were of significantly lower amplitude relative to unconditioned MEPs prior to tDCS (62 +/- 6%, p < 0.05), but not after tDCS (89 +/- 14%, p = 0.40), or robot training (91 +/- 8%, p = 0.28), suggesting that the increased corticomotor excitability is associated with reduced intracortical inhibition. CONCLUSION: The persistence of these effects after robotic motor training, indicates that a motor learning and retraining program can co-exist with tDCS-induced changes in cortical motor excitability, and supports the concept of combining brain stimulation with physical therapy to promote recovery after brain injury.

Sporadic inclusion body myositis: variability in prevalence and phenotype and influence of the MHC.

Sporadic inclusion body myositis (sIBM) is the most common myopathy presenting over the age of 40 years but its prevalence varies considerably in different populations. Genetic factors play a part in the pathogenesis of sIBM and in Caucasians susceptibility has been linked to the HLA-DR3 allele and the 8.1 MHC ancestral haplotype (AH) which is also associated with other autoimmune diseases. The variable prevalence of sIBM in different populations may be related to differences in the population frequency of this haplotype. Our recent observations indicate that the clinical phenotype at presentation is also quite variable and that the influence of the MHC is more complex than previously appreciated with HLA alleles also having modifying effects on the age-at-onset, severity and rate of progression of the disease. Recent recombinant mapping studies of polymorphisms in the Class II/III regions of the MHC by our group have further refined the susceptibility region and have identified a number of candidate genes warranting further investigation. The significance of these findings for the pathogenesis of the disease is discussed.

Neuromodulation by paired-pulse TMS at an I-wave interval facilitates multiple I-waves.

Corticospinal excitability can be increased by a transcranial magnetic stimulation (TMS) intervention that delivers repeated paired TMS pulses at an I (indirect)-wave interval of 1.5 ms. This is thought to target excitatory synaptic events by reinforcing facilitatory I-wave interaction, however, it remains to be determined what effect this intervention has on the various I-wave components. In the present study we compared I-wave facilitation curves over a range of inter-pulse intervals (IPIs) encompassing the first three I-waves, before and after 15 min of a paired-pulse TMS intervention with an IPI of 1.5 ms. The three peaks in the I-wave facilitation curves occurred at the same IPIs pre- and post-intervention (1.3, 2.5 and 4.3 ms). The facilitation curves were increased in amplitude for all three I-wave peaks post-intervention (mean increase 33%), and the mean increase across all IPIs correlated with the post-intervention increase in single-pulse MEP amplitude (r = 0.77). Modelling showed that the changes in the post-intervention curves were consistent with an increase in amplitude and broadening of the individual I-wave peaks. We conclude that an iTMS intervention with an IPI of 1.5 ms is able to target multiple I-waves. The findings are consistent with existing models of I-wave generation and suggest that the intervention increases the efficacy of synaptic events associated with the generation of descending I-wave volleys.

Inflammatory muscle diseases.

The three major immune-mediated inflammatory myopathies, dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM), each have their own distinctive clinical features, underlying pathogenetic mechanisms and patterns of muscle gene expression. In DM a complement-dependent humoral process thought to be initiated by antibodies to endothelial cells results in a microangiopathy with secondary ischemic changes in muscles. On the other hand, in PM and IBM there is a T-cell response with invasion of muscle fibers by CD8+ lymphocytes and perforin-mediated cytotoxic necrosis. In IBM degenerative changes are also a feature and comprise autophagia with rimmed vacuole formation and inclusions containing beta-amyloid and other proteins whose accumulation may be linked to impaired proteasomal function. The relationship between the inflammatory and degenerative component remains unclear, as does the basis for the selective vulnerability of certain muscles and the resistance to conventional forms of immunotherapy in most cases of IBM. Patients with DM or PM usually respond to treatment with glucocorticoids and immunosuppressive agents but their use remains largely empirical. Intravenous immunoglobulin therapy can be used to achieve disease control in patients with severe weakness or dysphagia, or in patients with immunodeficiency, but its use is limited by expense. Emerging therapies for resistant cases include TNFalpha inhibitors (etanercept, infliximab) and monoclonal antibodies (rituximab, alemtuzumab). However, experience with these therapies is still limited and there is a need for randomized trials to test their efficacy and establish guidelines for their use in clinical practice.