Anatomical Registration of Implanted Sensors Improves Accuracy of Trunk Tilt Estimates with a Networked Neuroprosthesis.

For individuals with spinal cord injuries (SCIs) above the midthoracic level, a common complication is the partial or complete loss of trunk stability in the seated position. Functional neuromuscular stimulation (FNS) can restore seated posture and other motor functions after paralysis by applying small electrical currents to the peripheral motor nerves. In particular, the Networked Neuroprosthesis (NNP) is a fully implanted, modular FNS system that is also capable of capturing information from embedded accelerometers for measuring trunk tilt for feedback control of stimulation. The NNP modules containing the accelerometers are located in the body based on surgical constraints. As such, their exact orientations are generally unknown and cannot be easily assessed. In this study, a method for estimating trunk tilt that employed the Gram-Schmidt method to reorient acceleration signals to the anatomical axes of the body was developed and deployed in individuals with SCI using the implanted NNP system. An anatomically realistic model of a human trunk and five accelerometer sensors was developed to verify the accuracy of the reorientation algorithm. Correlation coefficients and root mean square errors (RMSEs) were calculated to compare target trunk tilt estimates and tilt estimates derived from simulated accelerometer signals under a variety of conditions. Simulated trunk tilt estimates with correlation coefficients above 0.92 and RMSEs below 5° were achieved. The algorithm was then applied to accelerometer signals from implanted sensors installed in three NNP recipients. Error analysis was performed by comparing the correlation coefficients and RMSEs derived from trunk tilt estimates calculated from implanted sensor signals to those calculated via motion capture data, which served as the gold standard. NNP-derived trunk tilt estimates exhibited correlation coefficients between 0.80 and 0.95 and RMSEs below 13° for both pitch and roll in most cases. These findings suggest that the algorithm is effective at estimating trunk tilt with the implanted sensors of the NNP system, which implies that the method may be appropriate for extracting feedback signals for control systems for seated stability with NNP technology for individuals who have reduced control of their trunk due to paralysis.

Exploring Structural Requirements for Sigma-1 Receptor Linear Ligands: Experimental and Computational Approaches.

Sigma-1 receptor (S1R) is involved in a large array of biological functions due to its ability to interact with various proteins and ion channels. Crystal structures of human S1R revealed the trimeric organization for which each protomer comprises the ligand binding pocket. This study applied a multistep computational procedure to develop a pharmacophore model obtained from molecular dynamics simulations of available cocrystal structures of well-known S1R ligands. Apart from the well-established positive ionizable and hydrophobic features, the obtained model included an additional specific hydrophobic feature and different excluded volumes, thus increasing the selectivity of the model as well as a more detailed determination of the distance between two essential features. The obtained pharmacophore model passed the validation test by receiver operating characteristic (ROC) curve analysis of active and inactive S1R ligands. Finally, the pharmacophoric performance was experimentally investigated through the synthesis and binding assay of new 4-phenylpiperazine-based compounds. The most active new ligand 2-(3-methyl-1-piperidyl)-1-(4-phenylpiperazin-1-yl)ethanone (3) showed an S1R affinity close to the reference compound haloperidol (Ki values of 4.8 and 2.6 nM, respectively). The proposed pharmacophore model can represent a useful tool to design and discover new potent S1R ligands.

Anti-Aggregative and Protective Effects of Vicenin-2 on Heat and Oxidative Stress-Induced Damage on Protein Structures.

Vicenin-2, a flavonoid categorized as a flavones subclass, exhibits a distinctive and uncommon C-glycosidic linkage. Emerging evidence challenges the notion that deglycosylation is not a prerequisite for the absorption of C-glycosyl flavonoid in the small intestine. Capitalizing on this experimental insight and considering its biological attributes, we conducted different assays to test the anti-aggregative and antioxidant capabilities of vicenin-2 on human serum albumin under stressful conditions. Within the concentration range of 0.1-25.0 µM, vicenin-2 effectively thwarted the heat-induced HSA fibrillation and aggregation of HSA. Furthermore, in this study, we have observed that vicenin-2 demonstrated protective effects against superoxide anion and hydroxyl radicals, but it did not provide defense against active chlorine. To elucidate the underlying mechanisms, behind this biological activity, various spectroscopy techniques were employed. UV-visible spectroscopy revealed an interaction between HSA and vicenin-2. This interaction involves the cinnamoyl system found in vicenin-2, with a peak of absorbance observed at around 338 nm. Further evidence of the interaction comes from circular dichroism spectrum, which shows that the formation of bimolecular complex causes a reduction in α-helix structures. Fluorescence and displacement investigations indicated modifications near Trp214, identifying Sudlow's site I, similarly to the primary binding site. Molecular modeling revealed that vicenin-2, in nonplanar conformation, generated hydrophobic interactions, Pi-pi stacking, and hydrogen bonds inside Sudlow's site I. These findings expand our understanding of how flavonoids bind to HSA, demonstrating the potential of the complex to counteract fibrillation and oxidative stress.

Stabilizing leaning postures with feedback controlled functional neuromuscular stimulation after trunk paralysis.

Spinal cord injury (SCI) can cause paralysis of trunk and hip musculature that negatively impacts seated balance and ability to lean away from an upright posture and interact fully with the environment. Constant levels of electrical stimulation of peripheral nerves can activate typically paralyzed muscles and aid in maintaining a single upright seated posture. However, in the absence of a feedback controller, such seated postures and leaning motions are inherently unstable and unable to respond to perturbations. Three individuals with motor complete SCI who had previously received a neuroprosthesis capable of activating the hip and trunk musculature volunteered for this study. Subject-specific muscle synergies were identified through system identification of the lumbar moments produced via neural stimulation. Synergy-based calculations determined the real-time stimulation parameters required to assume leaning postures. When combined with a proportional, integral, derivative (PID) feedback controller and an accelerometer to infer trunk orientation, all individuals were able to assume non-erect postures of 30-40° flexion and 15° lateral bending. Leaning postures increased forward reaching capabilities by 10.2, 46.7, and 16 cm respectively for each subject when compared with no stimulation. Additionally, the leaning controllers were able to resist perturbations of up to 90 N, and all subjects perceived the leaning postures as moderately to very stable. Implementation of leaning controllers for neuroprostheses have the potential of expanding workspaces, increasing independence, and facilitating activities of daily living for individuals with paralysis.

Computational methods to analyze and predict the binding mode of inhibitors targeting both human and mushroom tyrosinase.

Tyrosinase, a copper-containing enzyme critical in melanin biosynthesis, is a key drug target for hyperpigmentation and melanoma in humans. Testing the inhibitory effects of compounds using tyrosinase from Agaricus bisporus (AbTYR) has been a common practice to identify potential therapeutics from synthetic and natural sources. However, structural diversity among human tyrosinase (hTYR) and AbTYR presents a challenge in developing drugs that are therapeutically effective. In this study, we combined retrospective and computational analyses with experimental data to provide insights into the development of new inhibitors targeting both hTYR and AbTYR. We observed contrasting effects of Thiamidol™ and our 4-(4-hydroxyphenyl)piperazin-1-yl-derivative (6) on both enzymes; based on this finding, we aimed to investigate their binding modes in hTYR and AbTYR to identify residues that significantly improve affinity. All the information led to the discovery of compound [4-(4-hydroxyphenyl)piperazin-1-yl](2-methoxyphenyl)methanone (MehT-3, 7), which showed comparable activity on AbTYR (IC50 = 3.52 µM) and hTYR (IC50 = 5.4 µM). Based on these achievements we propose the exploitation of our computational results to provide relevant structural information for the development of newer dual-targeting molecules, which could be preliminarily tested on AbTYR as a rapid and inexpensive screening procedure before being tested on hTYR.

Discovery and computational studies of piperidine/piperazine-based compounds endowed with sigma receptor affinity.

Herein, we describe our efforts to identify sigma receptor 1 (S1R) ligands through a screening campaign on our in-house collection of piperidine/piperazine-based compounds. Our investigations led to the discovery of the potent compound 2-[4-(benzyl)-1-piperidin-1-yl]-1-4-(4-phenylpiperazin-1-yl)ethanone (1) with high affinity toward S1R (Ki value of 3.2 nM) that was comparable to reference compound haloperidol (Ki value of 2.5 nM). Functional assay revealed that compound 1 acted as S1R agonist. To decipher the binding mode of this promising S1R ligand as a starting point for further structure-based optimization, we analysed the docking pose by using a S1R-structure derived from cocrystal structures of potent ligands in complex with target protein. The computational study was enriched with molecular dynamic simulations that revealed the crucial amino acid residues that interacted with the most interesting compound 1.

Leveraging the 3-Chloro-4-fluorophenyl Motif to Identify Inhibitors of Tyrosinase from Agaricus bisporus.

Tyrosinase (EC 1.14.18.1) is implicated in melanin production in various organisms. There is a growing body of evidence suggesting that the overproduction of melanin might be related to several skin pigmentation disorders as well as neurodegenerative processes in Parkinson's disease. Based on this consideration, the development of tyrosinase inhibitors represents a new challenge to identify new agents in pharmaceutical and cosmetic applications. With the goal of identifying tyrosinase inhibitors from a synthetic source, we employed a cheap and facile preliminary assay using tyrosinase from Agaricus bisporus (AbTYR). We have previously demonstrated that the 4-fluorobenzyl moiety might be effective in interactions with the catalytic site of AbTYR; moreover, the additional chlorine atom exerted beneficial effects in enhancing inhibitory activity. Therefore, we planned the synthesis of new small compounds in which we incorporated the 3-chloro-4-fluorophenyl fragment into distinct chemotypes that revealed the ability to establish profitable contact with the AbTYR catalytic site. Our results confirmed that the presence of this fragment is an important structural feature to improve the AbTYR inhibition in these new chemotypes as well. Furthermore, docking analysis supported the best activity of the selected studied compounds, possessing higher potency when compared with reference compounds.

Mindset and Reflection-How to Sustainably Improve Intra- and Interpersonal Competences in Medical Education.

Intra- and interpersonal competences (IICs) are essential for medical expertise. However, the effects of current medical curricula seem to not be sustainable enough, even though poorly trained IICs have negative effects on medical practice. A defensive attitude towards openly addressing personal-professional challenges seems to hinder a sustainable implementation of IICs training. Therefore, this study asks about the changeability of IICs and target factors of their implementation in medical education. The aim was to detect factors for the sustainable implementation of IICs in medical education from medical and non-medical perspectives. For this purpose, a total of 21 experts were interviewed. The interview material was analysed according to grounded theory principles to generate core categories to answer the research questions. As a first result, analysis revealed that IICs are changeable and developable, not in all, but in many students. It also showed four central prerequisites for successful implementation: the longitudinal integration of reflection and feedback in medical education and practice; a clear framework and individual path of education; the students' mindset to develop themselves on a personal level; as well as the superiors' mindset to openly deal with personal challenges in low hierarchies. Contrasting Carol Dweck's mindset concept with our findings supports our theory that the development of a mindset which allows an open approach to personal deficits and challenges seems to be of central importance for both students and teachers. Two key factors in this process might be teaching about the impact of mindsets on learning and the willingness of superiors to openly address their personal challenges. To improve IICs in medical professionals, it seems helpful to pay more attention to the development of mindsets. Educating teachers and superiors about targeting factors could be a feasible direction for sustainable implementation.

Facilitation of dependent transfers with functional neuromuscular stimulation: a computer simulation study.

A two-part simulation process was developed to investigate the facilitation of vertical patient lifts with functional neuromuscular stimulation (FNS) in individuals with spinal cord injury (SCI). First, external lifting forces representing caregiver assistance were applied to a 3D musculoskeletal model representing the patient and optimized to enforce a specific lifting trajectory during a forward dynamic simulation. The process was repeated with and without the activation of the knee, hip, and trunk extensor muscles of the patient model to represent contractions of the paralyzed muscles generated via FNS. Secondly, the spinal compression experienced by a caregiver at the L5/S1 joint while generating these external lifting forces was estimated using a second musculoskeletal model representing the caregiver. Simulation without muscle activation predicted spinal compression in the caregiver model approximately 1.3 × the National Institute for Occupational Safety and Health (NIOSH) recommended "Action Limit." Comparatively, simulations with two unique patterns of muscle activation both predicted caregiver spinal compressions below NIOSH recommendations. These simulation results support the hypothesis that FNS activation of a patient's otherwise paralyzed muscles would lower the force output required of a caregiver during a dependent transfer, thus lowering the spinal compression and risk of injury experienced by a caregiver.

Design, Synthesis, and in Vitro Evaluation of 4-(4-Hydroxyphenyl)piperazine-Based Compounds Targeting Tyrosinase.

Melanin biosynthesis is enzymatically regulated by tyrosinase (TYR, EC 1.14.18.1), which is efficiently inhibited by natural and synthetic phenols, demonstrating potential therapeutic application for the treatment of several human diseases. Herein we report the inhibitory effects of a series of (4-(4-hydroxyphenyl)piperazin-1-yl)arylmethanone derivatives, that were designed, synthesised and assayed against TYR from Agaricus bisporus (AbTYR). The best inhibitory activity was predominantly found for compounds bearing selected hydrophobic ortho-substituents on the aroyl moiety (IC50 values in the range of 1.5-4.6 µM). They proved to be more potent than the reference compound kojic acid (IC50 =17.8 µM) and displayed competitive mechanism of inhibition of diphenolase activity of AbTYR. Docking simulation predicted their binding mode into the catalytic cavities of AbTYR and the modelled human TYR. In addition, these compounds displayed antioxidant activity combined with no cytotoxicity in MTT tests. Notably, the best inhibitor affected tyrosinase activity in α-MSH-stimulated B16F10 cells, thus demonstrating anti-melanogenic activity.

Motorless cadence control of standard and low duty cycle-patterned neural stimulation intensity extends muscle-driven cycling output after paralysis.

BACKGROUND: Stimulation-driven exercise is often limited by rapid fatigue of the activated muscles. Selective neural stimulation patterns that decrease activated fiber overlap and/or duty cycle improve cycling exercise duration and intensity. However, unequal outputs from independently activated fiber populations may cause large discrepancies in power production and crank angle velocity among pedal revolutions. Enforcing a constant cadence through feedback control of stimulus levels may address this issue and further improve endurance by targeting a submaximal but higher than steady-state exercise intensity. METHODS: Seven participants with paralysis cycled using standard cadence-controlled stimulation (S-Cont). Four of those participants also cycled with a low duty cycle (carousel) cadence-controlled stimulation scheme (C-Cont). S-Cont and C-Cont patterns were compared with conventional maximal stimulation (S-Max). Outcome measures include total work (W), end power (Pend), power fluctuation (PFI), charge accumulation (Q) and efficiency (η). Physiological measurements of muscle oxygenation (SmO2) and heart rate were also collected with select participants. RESULTS: At least one cadence-controlled stimulation pattern (S-Cont or C-Cont) improved Pend over S-Max in all participants and increased W in three participants. Both controlled patterns increased Q and η and reduced PFI compared with S-Max and prior open-loop studies. S-Cont stimulation also delayed declines in SmO2 and increased heart rate in one participant compared with S-Max. CONCLUSIONS: Cadence-controlled selective stimulation improves cycling endurance and increases efficiency over conventional stimulation by incorporating fiber groups only as needed to maintain a desired exercise intensity. Closed-loop carousel stimulation also successfully reduces power fluctuations relative to previous open-loop efforts, which will enable neuroprosthesis recipients to better take advantage of duty cycle reducing patterns.

Development and deployment of cyclical focal muscle vibration system to improve walking performance in multiple sclerosis.

Vibration, a potent mechanical stimulus for activating muscle spindle primary afferents, may improve gait performance in persons with multiple sclerosis (MS), but has yet to be developed and deployed for multiple leg muscles with application during walking training. This study explored the development of a cyclic focal muscle vibration (FMV) system, and the deployment feasibility to correct MS walking swing phase deficits in order to determine whether this intervention warrants comprehensive study. The system was deployed during twelve, two-hour sessions of walking with cyclic FMV over six weeks. Participants served as their own control. Blood pressure, heart rate, walking speed, kinematics (peak hip, knee and ankle angles during swing), toe clearance, and step length were measured before and after deployment with blood pressure and heart rate monitored during deployment. During system deployment, there were no untoward sensations and physiological changes in blood pressure and heart rate, and volitional improvements were found in walking speed, improved swing phase kinematics, toe clearance and step length. This FMV training system was developed and deployed to improve joint flexion during walking in those with MS, and it demonstrated feasibility and benefits. Further study will determine the most effective vibration frequency and dose, carryover effects, and those most likely to benefit from this intervention.

Sudden stop detection and automatic seating support with neural stimulation during manual wheelchair propulsion.

Objective: Wheelchair safety is of great importance since falls from wheelchairs are prevalent and often have devastating consequences. We developed an automatic system to detect destabilizing events during wheelchair propulsion under real-world conditions and trigger neural stimulation to stiffen the trunk to maintain seated postures of users with paralysis.Design: Cross-over interventionSetting: Laboratory and community settingsParticipants: Three able-bodied subjects and three individuals with SCI with previously implanted neurostimulation systemsInterventions: An algorithm to detect wheelchair sudden stops was developed. This was used to randomly trigger trunk extensor stimulation during sudden stops eventsOutcome Measures: Algorithm success and false positive rates were determined. SCI users rated each condition on a seven-point Usability Rating Scale to indicate safety.Results: The system detected sudden stops with a success rate of over 93% in community settings. When used to trigger trunk neurostimulation to ensure stability, the implant recipients consistently reported feeling safer (P<.05 for 2/3 subjects) with the system while encountering sudden stops as indicated by a 1-3 point change in safety rating.Conclusion: These preliminary results suggest that this system could monitor wheelchair activity and only apply stabilizing neurostimulation when appropriate to maintain posture. Larger scale, unsupervised and longer-term trials at home and in the community are indicated. This system could be generalized and applied to individuals without an implanted stimulation by utilizing surface stimulation, or by actuating a mechanical restraint when necessary, thus allowing unrestricted trunk movements and only restraining the user when necessary to ensure safety.Trial Registration: NCT01474148.

Selective neural stimulation methods improve cycling exercise performance after spinal cord injury: a case series.

BACKGROUND: Exercise after paralysis can help prevent secondary health complications, but achieving adequate exercise volumes and intensities is difficult with loss of motor control. Existing electrical stimulation-driven cycling systems involve the paralyzed musculature but result in rapid force decline and muscle fatigue, limiting their effectiveness. This study explores the effects of selective stimulation patterns delivered through multi-contact nerve cuff electrodes on functional exercise output, with the goal of increasing work performed and power maintained within each bout of exercise. METHODS: Three people with spinal cord injury and implanted stimulation systems performed cycling trials using conventional (S-Max), low overlap (S-Low), low duty cycle (C-Max), and/or combined low overlap and low duty cycle (C-Low) stimulation patterns. Outcome measures include total work (W), end power (Pend), power fluctuation indices (PFI), charge accumulation (Q), and efficiency (η). Mann-Whitney tests were used for statistical comparisons of W and Pend between a selective pattern and S-Max. Welch's ANOVAs were used to evaluate differences in PFIs among all patterns tested within a participant (n ≥ 90 per stimulation condition). RESULTS: At least one selective pattern significantly (p < 0.05) increased W and Pend over S-Max in each participant. All selective patterns also reduced Q and increased η compared with S-Max for all participants. C-Max significantly (p < 0.01) increased PFI, indicating a decrease in ride smoothness with low duty cycle patterns. CONCLUSIONS: Selective stimulation patterns can increase work performed and power sustained by paralyzed muscles prior to fatigue with increased stimulation efficiency. While still effective, low duty cycle patterns can cause inconsistent power outputs each pedal stroke, but this can be managed by utilizing optimized stimulation levels. Increasing work and sustained power each exercise session has the potential to ultimately improve the physiological benefits of stimulation-driven exercise.

A closed-loop self-righting controller for seated balance in the coronal and diagonal planes following spinal cord injury.

Spinal cord injury (SCI) often results in loss of the ability to keep the trunk erect and stable while seated. Functional neuromuscular stimulation (FNS) can cause muscles paralyzed by SCI to contract and assist with trunk stability. We have extended the results of a previously reported threshold-based controller for restoring upright posture using FNS in the sagittal plane to more challenging displacements of the trunk in the coronal plane. The system was applied to five individuals with mid-thoracic or higher SCI, and in all cases the control system successfully restored upright sitting. The potential of the control system to maintain posture in forward-sideways (diagonal) directions was also tested in three of the subjects. In all cases, the controller successfully restored posture to erect. Clinically, these results imply that a simple, threshold based control scheme can restore upright sitting from forward, lateral or diagonal leaning without a chest strap; and that removal of barriers to upper extremity interaction with the surrounding environment could potentially allow objects to be more readily retrieved from around the wheelchair. Technical performance of the system was assessed in terms of three variables: response time, recovery time and percent maximum deviation from erect. Overall response and recovery times varied widely among subjects in the coronal plane (415±213 ms and 1381±883 ms, respectively) and in the diagonal planes (530±230 ms and 1800±820 ms, respectively). Average response time was significantly lower (p < 0.05) than the recovery time in all cases. The percent maximum deviation from erect was of the order of 40% or less for 9 out of 10 cases in the coronal plane and 5 out of 6 cases in diagonal directions.

Walking after incomplete spinal cord injury with an implanted neuromuscular electrical stimulation system and a hinged knee replacement: a single-subject study.

STUDY DESIGN: Single-subject repeated measures study. OBJECTIVES: Neuromuscular electrical stimulation (NMES) can enhance walking for people with partial paralysis from incomplete spinal cord injury (iSCI). This single-subject study documents an individual's experience who both received an experimental implanted NMES system and underwent clinical bilateral hinged total knee arthroplasty (TKA). She walked in the community with knee pain prior to either intervention. Walking performance improved with an implanted NMES system. Knee pain and instability continued to worsen over time and eventually required TKA. This study evaluates the effects of these interventions. SETTING: Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland OH, USA. METHODS: The differential and combined effects of NMES and hinged knee replacement were assessed in terms of walking speed, toe clearance, knee angle, and participant perceptions with and without stimulation assistance both before and after TKA. RESULTS: The combined approach both reduced pain and restored walking ability to levels achieved prior to developing significant knee pain that prevented walking without NMES. There was an interaction effect between NMES and TKA on walking speed. Toe clearance consistently improved with stimulation assistance and TKA prevented significant knee hyperextension. The greatest impact was on endurance. Knee replacement re-enabled long distance walking with the addition of stimulation again more than doubling her maximum walking distance from 214 to 513 m. CONCLUSIONS: These data support further research of combined implantable interventions that may benefit people with iSCI. Furthermore, joint laxity and pain may not necessarily be contraindications to NMES if addressed with conventional clinical treatments.

Oxygen Consumption While Walking With Multijoint Neuromuscular Electrical Stimulation After Stroke.

This case study evaluated the effect of implanted multijoint neuromuscular electrical stimulation gait assistance on oxygen consumption relative to walking without neuromuscular electrical stimulation after stroke. The participant walked slowly with an asymmetric gait pattern after stroke. He completed repeated 6-min walk tests at a self-selected walking speed with and without hip, knee, and ankle stimulation assistance. His walking speed with neuromuscular electrical stimulation more than doubled from 0.28 ± 0.01 m/sec to 0.58 ± 0.04 m/sec, whereas average step length and cadence increased by 0.12 m and 24 steps/min, respectively. As a result, energy cost of walking with neuromuscular electrical stimulation decreased by 0.19 ml O2/kg per meter as compared with walking without stimulation while oxygen consumption increased by 1.1 metabolic equivalent of tasks (3.9 ml O2/kg per minute). These metabolic demands are similar to those reported for stroke survivors capable of walking at equivalent speeds without stimulation, suggesting the increase in oxygen consumption and decreased energy cost result from improved efficiency of faster walking facilitated by neuromuscular electrical stimulation. Although the effect of neuromuscular electrical stimulation on gait economy has implications for community walking within the user's metabolic reserves, this case study's results should be interpreted with caution and the hypothesis that multijoint neuromuscular electrical stimulation improves metabolic efficiency should be tested in a wide population of stroke survivors with varied deficits.

Estimating total maximum isometric force output of trunk and hip muscles after spinal cord injury.

Functional neuromuscular stimulation (FNS) can be used to restore seated trunk function in individuals paralyzed due to spinal cord injury (SCI). Musculoskeletal models allow for the design and tuning of controllers for use with FNS; however, these models often use aggregated estimates for parameters of the musculotendon elements, the most significant of which is maximum isometric force (MIF). Stimulated MIF for individuals with SCI is typically assumed to be approximately 50% of the values exhibited by able-bodied muscles, which itself varies between studies and individuals. A method for estimating subject-specific MIF during dynamic motions in individuals with SCI produced by electrical stimulation has been developed to test this assumption and obtained more accurate estimates for biomechanical analysis and controller design. A simple on-off controller was applied to individuals with SCI seated in the workspace of a motion capture system to record joint angles of three types of trunk motions: forward flexion, left and right lateral bending followed by returning, un-aided, to upright posture via neural stimulation delivered to activate the muscles of the hips and trunk. System identification was used with a musculoskeletal model to find the optimal MIF values that reproduced the experimentally observed motions. Experiments with five volunteers with SCI indicate that an MIF of the 50% able-bodied values commonly used is significantly lower than the identified estimates in 33 of 44 muscle groups tested. This suggests that the strengths of paralyzed muscles when stimulated with FNS have been underestimated in many situations and their true force outputs may be higher than the values suggested for use in simulation studies with musculoskeletal models. These findings indicate that subject-specific musculoskeletal models can more closely mimic the motions of subjects by using individualized estimates of MIF, which may allow the design and tuning of controllers while reducing the time spent with subjects in the loop.

Isoform-specific NF1 mRNA levels correlate with disease severity in Neurofibromatosis type 1.

BACKGROUND: Neurofibromatosis type 1 (NF1) is characterized by an extreme clinical variability both within and between families that cannot be explained solely by the nature of the pathogenic NF1 gene mutations. A proposed model hypothesizes that variation in the levels of protein isoforms generated via alternative transcript processing acts as modifier and contributes to phenotypic variability. RESULTS: Here we used real-time quantitative PCR to investigate the levels of two major NF1 mRNA isoforms encoding proteins differing in their ability to control RAS signaling (isoforms I and II) in the peripheral blood leukocytes of 138 clinically well-characterized NF1 patients and 138 aged-matched healthy controls. As expected, expression analysis showed that NF1 isoforms I and II levels were significantly lower in patients than controls. Notably, these differences were more evident when patients were stratified according to the severity of phenotype. Moreover, a correlation was identified when comparing the levels of isoform I mRNA and the severity of NF1 features, with statistically significant lower levels associated with a severe phenotype (i.e., occurrence of learning disability/intellectual disability, optic gliomas and/or other neoplasias, and/or cerebrovascular disease) as well as in patients with cognitive impairment. CONCLUSIONS: The present findings provide preliminary evidence for a role of circuits controlling NF1 transcript processing in modulating NF1 expressivity, and document an association between the levels of neurofibromin isoform I mRNA and the severity of phenotype and cognitive impairment in NF1.