Reversal of hypertonic co-contraction after bilateral pallidal stimulation in generalised dystonia: a clinical and electromyogram case study

Mass Spectrometry-Based Proteomics to Unveil the Non-coding RNA World

The interaction between non-coding RNAs (ncRNAs) and proteins is crucial for the stability, localization and function of the different classes of ncRNAs. Although ncRNAs, when embedded in various ribonucleoprotein (RNP) complexes, control the fundamental processes of gene expression, their biological functions and mechanisms of action are still largely unexplored. Mass Spectrometry (MS)-based proteomics has emerged as powerful tool to study the ncRNA world: on the one hand, by identifying the proteins interacting with distinct ncRNAs; on the other hand, by measuring the impact of ncRNAs on global protein levels. Here, we will first provide a concise overview on the basic principles of MS-based proteomics for systematic protein identification and quantification; then, we will recapitulate the main approaches that have been implemented for the screening of ncRNA interactors and the dissection of ncRNA-protein complex composition. Finally, we will describe examples of various proteomics strategies developed to characterize the effect of ncRNAs on gene expression, with a focus on the systematic identification of microRNA (miRNA) targets.

Current and emerging strategies for treatment of childhood dystonia

Childhood dystonia is a movement disorder characterized by involuntary sustained or intermittent muscle contractions causing twisting and repetitive movements, abnormal postures, or both (Sanger et al, 2003). Dystonia is a devastating neurological condition that prevents the acquisition of normal motor skills during critical periods of development in children. Moreover, it is particularly debilitating in children when dystonia affects the upper extremities such that learning and consolidation of common daily motor actions are impeded. Thus, the treatment and rehabilitation of dystonia is a challenge that continuously requires exploration of novel interventions. This review will initially describe the underlying neurophysiological mechanisms of the motor impairments found in childhood dystonia followed by the clinical measurement tools that are available to document the presence and severity of symptoms. Finally, we will discuss the state-of-the-art of therapeutic options for childhood dystonia, with particular emphasis on emergent and innovative strategies.

Definition and classification of hyperkinetic movements in childhood

Hyperkinetic movements are unwanted or excess movements that are frequently seen in children with neurologic disorders. They are an important clinical finding with significant implications for diagnosis and treatment. However, the lack of agreement on standard terminology and definitions interferes with clinical treatment and research. We describe definitions of dystonia, chorea, athetosis, myoclonus, tremor, tics, and stereotypies that arose from a consensus meeting in June 2008 of specialists from different clinical and basic science fields. Dystonia is a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. Chorea is an ongoing random-appearing sequence of one or more discrete involuntary movements or movement fragments. Athetosis is a slow, continuous, involuntary writhing movement that prevents maintenance of a stable posture. Myoclonus is a sequence of repeated, often nonrhythmic, brief shock-like jerks due to sudden involuntary contraction or relaxation of one or more muscles. Tremor is a rhythmic back-and-forth or oscillating involuntary movement about a joint axis. Tics are repeated, individually recognizable, intermittent movements or movement fragments that are almost always briefly suppressible and are usually associated with awareness of an urge to perform the movement. Stereotypies are repetitive, simple movements that can be voluntarily suppressed. We provide recommended techniques for clinical examination and suggestions for differentiating between the different types of hyperkinetic movements, noting that there may be overlap between conditions. These definitions and the diagnostic recommendations are intended to be reliable and useful for clinical practice, communication between clinicians and researchers, and for the design of quantitative tests that will guide and assess the outcome of future clinical trials.

Dysregulation of striatal dopamine release in a mouse model of dystonia

Dystonia is a neurological disorder characterized by involuntary movements. We examined striatal dopamine (DA) function in hyperactive transgenic (Tg) mice generated as a model of dystonia. Evoked extracellular DA concentration was monitored with carbon-fiber microelectrodes and fast-scan cyclic voltammetry in striatal slices from non-Tg mice, Tg mice with a positive motor phenotype, and phenotype-negative Tg littermates. Peak single-pulse evoked extracellular DA concentration was significantly lower in phenotype-positive mice than in non-Tg or phenotype-negative mice, but indistinguishable between non-Tg and phenotype-negative mice. Phenotype-positive mice also had higher functional D2 DA autoreceptor sensitivity than non-Tg mice, which would be consistent with lower extracellular DA concentration in vivo. Multiple-pulse (phasic) stimulation (five pulses, 10-100 Hz) revealed an enhanced frequency dependence of evoked DA release in phenotype-positive versus non-Tg or phenotype-negative mice, which was exacerbated when extracellular Ca(2+) concentration was lowered. Enhanced sensitivity to phasic stimulation in phenotype-positive mice was reminiscent of the pattern seen with antagonism of nicotinic acetylcholine receptors. Consistent with a role for altered cholinergic regulation, the difference in phasic responsiveness among groups was lost when nicotinic receptors were blocked by mecamylamine. Together, these data implicate compromised DA release regulation, possibly from cholinergic dysfunction, in the motor symptoms of this dystonia model.

Cortically evoked long-lasting inhibition of pallidal neurons in a transgenic mouse model of dystonia

Dystonia is a neurological disorder characterized by sustained or repetitive involuntary muscle contractions and abnormal postures. To understand the pathophysiology of dystonia, neurophysiological analyses were performed on hyperkinetic transgenic mice generated as a model of DYT1 dystonia. Abnormal muscle activity, such as coactivation of agonist and antagonist muscles and sustained muscle activation, was frequently observed in these mice. Recording of neuronal activity in the awake state revealed reduced spontaneous activity with bursts and pauses in both the external and internal segments of the globus pallidus. Motor cortical stimulation evoked responses composed of excitation and subsequent long-lasting inhibition in both pallidal segments, which were never observed in the normal mice. In addition, the somatotopic arrangements in both pallidal segments were disorganized. Long-lasting inhibition induced by cortical inputs in the internal pallidal segment may disinhibit thalamic and cortical activity, resulting in the motor hyperactivity observed in the transgenic mice.

The sensory and motor representation of synchronized oscillations in the globus pallidus in patients with primary dystonia

In 15 patients with primary dystonia (six cervical and nine generalized dystonias) who were treated with bilateral chronic pallidal stimulation, we investigated the sensorimotor modulation of the oscillatory local field potentials (LFPs) recorded from the pallidal electrodes. We correlated these with the surface electromyograms in the affected muscles. The effects of involuntary, passive and voluntary movement and muscle-tendon vibration on frequency ranges of 0-3 Hz, theta (3-8 Hz), alpha (8-12 Hz), low (12-20 Hz) and high beta (20-30 Hz), and low (30-60 Hz) and high gamma (60-90 Hz) power were recorded and compared between cervical and generalized dystonia groups. Significant decreases in LFP synchronization at 8-20 Hz occurred during the sensory modulation produced by voluntary or passive movement or vibration. Voluntary movement also caused increased gamma band activity (30-90 Hz). Dystonic involuntary muscle spasms were specifically associated with increased theta, alpha and low beta (3-18 Hz). Furthermore, the increase in the frequency range of 3-20 Hz correlated with the strength of the muscle spasms and preceded them by approximately 320 ms. Differences in modulation of pallidal oscillation between cervical and generalized dystonias were also revealed. This study yields new insights into the pathophysiological mechanisms of primary dystonias and their treatment using pallidal deep brain stimulation.

Intraoperative neurophysiological assessment of disabling symptoms in DBS surgery

INTRODUCTION

Neurophysiological assessment can provide quantitative measures for the selected motor signs that have been targeted for surgery and may be helpful in predicting the therapeutic effects of deep brain stimulation (DBS) on pathological tremor, motor performance, and rigidity.

OBJECTIVE

To present a survey and demonstrate the contribution of neurophysiological assessment of side effects and effects on disabling motor symptoms at various steps of DBS surgery, and to confirm its role for optimal target localization, as an adjuvant to anatomic imaging.

MATERIAL AND METHODS

The data result from 192 nuclei in 118 procedures on patients with Parkinson's disease (84), essential tremor (24), Hallenvorder Spatz dystonia (4), multiple sclerosis (4), and Holmes tremor (2). The intraoperative neurophysiological monitoring (IOM) protocol consists of semimicroelectrode recording (for subthalamic nuclei), whereas accelerotransducers and spectral analysis allow assessment of tremor, finger tapping (FT), diadochokinesis (DDK), and determination of the distance between DBS electrodes and internal capsule (IC). Rigidity is assessed by surface EMG recordings in combination with a goniometer.

RESULTS

The determination of the functional distance between the DBS electrode and the IC is based on the activation functions of axons in the IC. We show the high sensitivity of accelerometers for tremor over a large part of the body, the relationship between clinical scores and spectral frequencies of FT and DDK. Parkinsonian rigidity can be assessed from surface EMG (sEMG) by means of a balance coefficient, which can detect negative rigidity, for low unified Parkinson's disease rating scale (UPDRS) scores (0-2) and quantified EMG when negative rigidity is excluded.

CONCLUSION

Accelerometer and sEMG recording have shown their value for intraoperative assessment of disabling motor symptoms and side effects during surgery, to optimize the target position electrodes for DBS. The combination with contemporary signal analyzing techniques permit intraoperative monitoring without a significant delay. IONM improves sensitivity and adds objective neurophysiological data.

Use of surface electromyography to assess and select patients with idiopathic dystonia for bilateral pallidal stimulation

OBJECT

The object of this study was to identify a preoperative physiological index by using surface electromyography (EMG) signals that would correlate with clinical outcome in dystonic patients following bilateral pallidal stimulation.

METHODS

In 14 patients with spasmodic torticollis, generalized dystonia, and myoclonic dystonia, surface EMG signals were recorded from the most affected muscle groups. Although the dystonia affected different body segments, the EMG signals in all patients could be decomposed into bursting and sustained components. Subsequently, a ratio of the EMG amplitude was calculated between the two components and then correlated with clinical outcome. Patients who experienced rapid improvement following bilateral pallidal stimulation had a significantly higher EMG ratio compared with those who did not. Furthermore, a significant correlation was found between the EMG ratio and clinical improvement during the 12-month period following pallidal stimulation.

CONCLUSIONS

The authors concluded that surface EMG studies could be used to predict the clinical outcome of and to select patients for pallidal stimulation for dystonia.

A dominant bursting electromyograph pattern in dystonic conditions predicts an early response to pallidal stimulation

Although chronic pallidal deep brain stimulation (DBS) is effective in the treatment of medically intractable dystonia, there is no way of predicting the variations in clinical outcome, partly due to our limited understanding of the pathophysiological mechanisms underlying this condition. We recorded electromyographic (EMG) activity from the most severely affected muscle groups in seven dystonia patients before and after pallidal DBS. Patient EMG recordings could be classified into two groups: one consisting of patients who at rest demonstrated a dominant low frequency component of activity on power spectral analysis (ranging from 2 to 5 Hz), and one group in which this dominant pattern was absent. Early postoperative improvements (within 2-3 days) were observed in the former group, whereas the latter group benefited more gradually (over several months). Analysis of EMG activity may provide a sensitive means of identifying dystonic patients who are likely to be most responsive to functional neurosurgical intervention.

Neurophysiologic intervention in deep brain stimulation treatment for movement disorders: a practical framework

Clinical neurophysiology has always played an important interventional role throughout the perioperative stages in functional neurosurgery. On the one hand, some neurophysiologic procedures have become an integrated part of neurosurgery. On the other hand, in deep brain stimulation, although the surgical electrode implantation is an essential step, the therapeutic effects are actually produced by electrically modulating the physiologic activity of the brain. We review the topic of neurophysiologic intervention in the deep brain stimulation for movement disorders by presenting the evidence derived from our own experiences based on an integrated group located at two hospitals in London and Oxford, UK, and mainly covering tremor caused by multiple sclerosis, Parkinson's disease and dystonia.

Different mechanisms may generate sustained hypertonic and rhythmic bursting muscle activity in idiopathic dystonia

Despite that deep brain stimulation (DBS) of the globus pallidus internus (GPi) is emerging as the favored intervention for patients with medically intractable dystonia, the pathophysiological mechanisms of dystonia are largely unclear. In eight patients with primary dystonia who were treated with bilateral chronic pallidal stimulation, we correlated symptom-related electromyogram (EMG) activity of the most affected muscles with the local field potentials (LFPs) recorded from the globus pallidus electrodes. In 5 dystonic patients with mobile involuntary movements, rhythmic EMG bursts in the contralateral muscles were coherent with the oscillations in the pallidal LFPs at the burst frequency. In contrast, no significant coherence was seen between EMG and LFPs either for the sustained activity separated out from the compound EMGs in those 5 cases, or in the EMGs in 3 other cases without mobile involuntary movements and rhythmic EMG bursts. In comparison with the resting condition, in both active and passive movements, significant modulation in the GPi LFPs was seen in the range of 8-16 Hz. The finding of significant coherence between GPi oscillations and rhythmic EMG bursts but not sustained tonic EMG activity suggests that the synchronized pallidal activity may be directly related to the rhythmic involuntary movements. In contrast, the sustained hypertonic muscle activity may be represented by less synchronized activity in the pallidum. Thus, the pallidum may play different roles in generating different components of the dystonic symptom complex.

Extracting burst and tonic components from surface electromyograms in dystonia using adaptive wavelet shrinkage

The compound surface electromyograms (EMGs) recorded from patients with dystonia commonly contains superimposed bursting and tonic activity representing various motor symptoms. It is desirable to differentially extract them from the compound EMGs so that different symptoms can be more specifically investigated and different mechanisms revealed. A non-linear denoising approach based on wavelet transformation was investigated by applying soft thresholding to the wavelet coefficients. Thresholds were determined according to three different principles and two models. Different techniques for wavelet shrinkage were investigated for separating burst and tonic activity in the compound EMGs. The combination of Stein's unbiased risk estimate principle with a non-white noise model proved optimal for separating burst and tonic activity. These turned out to be exponentially related; and the temporal relationships between antagonist muscle contractions could now be seen clearly. We conclude that adaptive soft-thresholding wavelet shrinkage provides effective separation of burst and tonic activity in the compound EMG in dystonia. This separation should improve our understanding of the pathophysiology of dystonia.