Marc Bolliger

Changes in spinal reflex and locomotor activity after a complete spinal cord injury: a common mechanism?

Locomotor activity and spinal reflexes (SRs) show common features in different mammals, including humans. Here we report the time-course of the development of locomotor activity and SRs after a complete spinal cord injury in humans. SRs evoked by tibial nerve stimulation were studied, as was the leg muscle electromyography activity evoked by mechanically assisted locomotion (Lokomat) in biceps femoris, rectus femoris, tibialis anterior and gastrocenmius medialis. Around 8 weeks after the injury, an early SR component (latency 60-120 ms) appeared, as in healthy subjects, and a well-organized leg muscle activity was present during assisted locomotion. At around 6 months after injury an additional, late reflex component (latency 120-450 ms) appeared, which remained even 15 years after the spinal cord injury. In contrast, the early component had markedly decreased at 18 months after injury. These changes in SR were associated with a loss of electromyography activity and a successively stronger electromyography exhaustion (i.e. decline of electromyography amplitude), when comparing the level of electromyography activity at 2 and 10 min, respectively, during assisted locomotion. These changes in electromyography activity affected mainly the biceps femoris, gastrocenmius medialis and tibialis anterior but less so the rectus femoris. When the amplitude relationship of the early to late SR component was calculated, there was a temporal relationship between the decrease of the early component and an increase of the late component and the degree of exhaustion of locomotor activity. In chronic, severely affected but sensori-motor incomplete spinal cord injury subjects a late SR component, associated with an electromyography exhaustion, was present in subjects who did not regularly perform stepping movements. Our data are consistent with the proposal of a common mechanism underlying the changes in SR activity and locomotor activity after spinal cord injury. These findings should be taken into consideration in the development of novel rehabilitation schemes and programs to facilitate regeneration-inducing therapies in spinal cord injury subjects.

Down‐regulation of occludin expression in astrocytes by tumour necrosis factor (TNF) is mediated via TNF type‐1 receptor and nuclear factor‐κB activation

Tight junctions form the diffusion barrier of brain microcapillary endothelial cells and support cell polarity. Also astrocytes express tight junction components such as occludin, claudin‐1, ZO‐1 and ZO‐2, but do not establish a permeability barrier. However, little is known about the function and regulation of these molecules in astrocytes. We studied the impact of tumour necrosis factor (TNF) on occludin and ZO‐1 expression in astrocytes. TNF decreased occludin, but not ZO‐1 expression. In brain microcapillary endothelial cells, as well as in epithelial cells, occludin expression was not influenced by TNF. Removal of TNF from astrocytes restored the basal level of occludin. Down‐regulation was inhibited by caffeic acid phenethyl ester, a specific inhibitor of nuclear factor‐κB (NF‐κB) activation. Exposure of astrocytes isolated from mice deficient in either TNF type‐1 receptor (TNFR1), TNF type‐2 receptor (TNFR2), or both, respectively, revealed that down‐regulation was mediated entirely by TNFR1. ZO‐1, which can interact with occludin, was found to co‐precipitate connexin43, but not occludin. These findings demonstrate that TNF selectively down‐regulates occludin in astrocytes, but not in cells forming established tight junctions, through TNFR1 and suggest that NF‐κB is involved as a negative regulator.

Destabilization of the neuromuscular junction by proteolytic cleavage of agrin results in precocious sarcopenia

Etiology and pathogenesis of sarcopenia, the progressive decline in skeletal muscle mass and strength that occurs with aging, are still poorly understood. We recently found that overexpression of the neural serine protease neurotrypsin in motoneurons resulted in the degeneration of their neuromuscular junctions (NMJ) within days. Therefore, we wondered whether neurotrypsin‐dependent NMJ degeneration also affected the structure and function of the skeletal muscles. Using histological and functional analyses of neurotrypsin‐overexpressing and neurotrypsin‐deficient mice, we found that overexpression of neurotrypsin in motoneurons installed the full sarcopenia phenotype in young adult mice. Characteristic muscular alterations included a reduced number of muscle fibers, increased heterogeneity of fiber thickness, more centralized nuclei, fiber‐type grouping, and an increased proportion of type I fibers. As in age‐dependent sarcopenia, excessive fragmentation of the NMJ accompanied the muscular alterations. These results suggested the destabilization of the NMJ through proteolytic cleavage of agrin at the onset of a pathogenic pathway ending in sarcopenia. Studies of neurotrypsin‐deficient and agrin‐overexpressing mice revealed that old‐age sarcopenia also develops without neurotrypsin and is not prevented by elevated levels of agrin. Our results define neurotrypsin‐ and age‐dependent sarcopenia as the common final outcome of 2 etiologically distinct entities.—Bütikofer, L., Zurlinden, A., Bolliger, M. F., Kunz, B., Sonderegger, P. Destabilization of the neuromuscular junction by proteolytic cleavage of agrin results in precocious sarcopenia. FASEB J. 25, 4378–4393 (2011). www.fasebj.org

Computerized Visual Feedback: An Adjunct to Robotic-Assisted Gait Training

Background and Purpose: Robotic devices for walking rehabilitation allow new possibilities for providing performance-related information to patients during gait training. Based on motor learning principles, augmented feedback during robotic-assisted gait training might improve the rehabilitation process used to regain walking function. This report presents a method to provide visual feedback implemented in a driven gait orthosis (DGO). The purpose of the study was to compare the immediate effect on motor output in subjects during robotic-assisted gait training when they used computerized visual feedback and when they followed verbal instructions of a physical therapist. Subjects: Twelve people with neurological gait disorders due to incomplete spinal cord injury participated. Methods: Subjects were instructed to walk within the DGO in 2 different conditions. They were asked to increase their motor output by following the instructions of a therapist and by observing visual feedback. In addition, the subjects’ opinions about using visual feedback were investigated by a questionnaire. Results: Computerized visual feedback and verbal instructions by the therapist were observed to result in a similar change in motor output in subjects when walking within the DGO. Subjects reported that they were more motivated and concentrated on their movements when using computerized visual feedback compared with when no form of feedback was provided. Discussion and Conclusion: Computerized visual feedback is a valuable adjunct to robotic-assisted gait training. It represents a relevant tool to increase patients’ motor output, involvement, and motivation during gait training, similar to verbal instructions by a therapist.

Characterization of neurological recovery following traumatic sensorimotor complete thoracic spinal cord injury

Study design:Retrospective, longitudinal analysis of sensory, motor and functional outcomes from individuals with thoracic (T2–T12) sensorimotor complete spinal cord injury (SCI).Objectives:To characterize neurological changes over the first year after traumatic thoracic sensorimotor complete SCI.Methods:A dataset of 399 thoracic complete SCI subjects from the European Multi-center study about SCI (EMSCI) was examined for neurological level, sensory levels and sensory scores (pin-prick and light touch), lower extremity motor score (LEMS), ASIA Impairment Scale (AIS) grade, and Spinal Cord Independence Measure (SCIM) over the first year after SCI.Results:AIS grade conversions were limited. Sensory scores exhibited minimal mean change, but high variability in both rostral and caudal directions. Pin-prick and light touch sensory levels, as well as neurological level, exhibited minor changes (improvement or deterioration), but most subjects remained within one segment of their initial injury level after 1 year. Recovery of LEMS occurred predominantly in subjects with low thoracic SCI. The sensory zone of partial preservation (ZPP) had no prognostic value for subsequent recovery of sensory levels or LEMS. However, after mid or low thoracic SCI, ⩾3 segments of sensory ZPP correlated with an increased likelihood for AIS grade conversion.Conclusion:The data suggest that a sustained deterioration of three or more thoracic sensory levels or loss of upper extremity motor function are rare events and may be useful for tracking the safety of a therapeutic intervention in early phase acute SCI clinical trials, if a significant proportion of study subjects exhibit such an ascent.

Specific proteolytic cleavage of agrin regulates maturation of the neuromuscular junction

During the initial stage of neuromuscular junction (NMJ) formation, nerve-derived agrin cooperates with muscle-autonomous mechanisms in the organization and stabilization of a plaque-like postsynaptic specialization at the site of nerve–muscle contact. Subsequent NMJ maturation to the characteristic pretzel-like appearance requires extensive structural reorganization. We found that the progress of plaque-to-pretzel maturation is regulated by agrin. Excessive cleavage of agrin via transgenic overexpression of an agrin-cleaving protease, neurotrypsin, in motoneurons resulted in excessive reorganizational activity of the NMJs, leading to rapid dispersal of the synaptic specialization. By contrast, expression of cleavage-resistant agrin in motoneurons slowed down NMJ remodeling and delayed NMJ maturation. Neurotrypsin, which is the sole agrin-cleaving protease in the CNS, was excluded as the physiological agrin-cleaving protease at the NMJ, because NMJ maturation was normal in neurotrypsin-deficient mice. Together, our analyses characterize agrin cleavage at its proteolytic α- and β-sites by an as-yet-unspecified protease as a regulatory access for relieving the agrin-dependent constraint on endplate reorganization during NMJ maturation.

Increasing patient engagement during virtual reality-based motor rehabilitation.

OBJECTIVE To investigate the influence of different design characteristics of virtual reality exercises on engagement during lower extremity motor rehabilitation. DESIGN Correlational study. SETTING Spinal cord injury (SCI) rehabilitation center. PARTICIPANTS Subjects with SCI (n=12) and control subjects (n=10). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Heart rate and electromyographic activity from both legs at the tibialis anterior, the gastrocnemius medialis, the rectus femoris, and the biceps femoris were recorded. RESULTS Interactivity (ie, functionally meaningful reactions to motor performance) was crucial for the engagement of subjects. No significant differences in engagement were found between exercises that differed in feedback frequency, explicit task goals, or aspects of competition. CONCLUSIONS Functional feedback is highly important for the active participation of patients during robotic-assisted rehabilitation. Further investigations on the design characteristics of virtual reality exercises are of great importance. Exercises should thoroughly be analyzed regarding their effectiveness, while user preferences and expectations should be considered when designing virtual reality exercises for everyday clinical motor rehabilitation.

Modulation of spinal neuronal excitability by spinal direct currents and locomotion after spinal cord injury

OBJECTIVE Spinal neuronal function is impaired after a severe spinal cord injury (SCI) and can be assessed by the analysis of spinal reflex (SR) behavior. We applied transcutaneous spinal direct current stimulation (tsDCS) and locomotor activity, to determine whether the excitability of spinal neuronal circuitries underlying locomotion can be modulated after motor complete SCI. METHOD SRs were evoked by non-noxious electrical stimulation of the tibial nerve. SR behavior was assessed before, immediately after, and 20 min after four different interventions (anodal, cathodal, sham tsDCS, or locomotion) in subjects with motor complete SCI and healthy subjects. RESULTS SR amplitudes in SCI subjects were increased after anodal tsDCS by 84% (p < 0.05). Cathodal, sham tsDCS and locomotion had no influence on SR amplitudes. In addition, reflex threshold was lower after anodal tsDCS and locomotion in SCI subjects (p < 0.05). CONCLUSION Anodal tsDCS is able to modulate spinal neuronal circuitries after SCI. SIGNIFICANCE This novel, noninvasive approach might be used as a tool to excite spinal neuronal circuitries. If applied repetitively within a training approach, anodal tsDCS might prevent adverse alterations in spinal reflex function in severely affected SCI subjects, i.e., a manifestation of a spinal neuronal dysfunction taking part below the level of a spinal lesion.

Controlling patient participation during robot-assisted gait training.

BackgroundThe overall goal of this paper was to investigate approaches to controlling active participation in stroke patients during robot-assisted gait therapy. Although active physical participation during gait rehabilitation after stroke was shown to improve therapy outcome, some patients can behave passively during rehabilitation, not maximally benefiting from the gait training. Up to now, there has not been an effective method for forcing patient activity to the desired level that would most benefit stroke patients with a broad variety of cognitive and biomechanical impairments.MethodsPatient activity was quantified in two ways: by heart rate (HR), a physiological parameter that reflected physical effort during body weight supported treadmill training, and by a weighted sum of the interaction torques (WIT) between robot and patient, recorded from hip and knee joints of both legs. We recorded data in three experiments, each with five stroke patients, and controlled HR and WIT to a desired temporal profile. Depending on the patients cognitive capabilities, two different approaches were taken: either by allowing voluntary patient effort via visual instructions or by forcing the patient to vary physical effort by adapting the treadmill speed.ResultsWe successfully controlled patient activity quantified by WIT and by HR to a desired level. The setup was thereby individually adaptable to the specific cognitive and biomechanical needs of each patient.ConclusionBased on the three successful approaches to controlling patient participation, we propose a metric which enables clinicians to select the best strategy for each patient, according to the patients physical and cognitive capabilities. Our framework will enable therapists to challenge the patient to more activity by automatically controlling the patient effort to a desired level. We expect that the increase in activity will lead to improved rehabilitation outcome.

Profiling locomotor recovery: comprehensive quantification of impairments after CNS damage in rodents

Rodents are frequently used to model damage and diseases of the central nervous system (CNS) that lead to functional deficits. Impaired locomotor function is currently evaluated by using scoring systems or biomechanical measures. These methods often suffer from limitations such as subjectivity, nonlinearity and low sensitivity, or focus on a few very restricted aspects of movement. Thus, full quantitative profiles of motor deficits after CNS damage are lacking. Here we report the detailed characterization of locomotor impairments after applying common forms of CNS damage in rodents. We obtained many objective and quantitative readouts from rats with either spinal cord injuries or strokes and from transgenic mice (Epha4−/−) during skilled walking, overground walking, wading and swimming, resulting in model-specific locomotor profiles. Our testing and analysis method enables comprehensive assessment of locomotor function in rodents and has broad application in various fields of life science research.