Motion control of the ankle joint with a multiple contact nerve cuff electrode: a simulation study

The flat interface nerve electrode (FINE) has demonstrated significant capability for fascicular and subfascicular stimulation selectivity. However, due to the inherent complexity of the neuromuscular skeletal systems and nerve–electrode interface, a trajectory tracking motion control algorithm of musculoskeletal systems for functional electrical stimulation using a multiple contact nerve cuff electrode such as FINE has not yet been developed. In our previous study, a control system was developed for multiple-input multiple-output (MIMO) musculoskeletal systems with little prior knowledge of the system. In this study, more realistic computational ankle/subtalar joint model including a finite element model of the sciatic nerve was developed. The control system was tested to control the motion of ankle/subtalar joint angles by modulating the pulse amplitude of each contact of a FINE placed on the sciatic nerve. The simulation results showed that the control strategy based on the separation of steady state and dynamic properties of the system resulted in small output tracking errors for different reference trajectories such as sinusoidal and filtered random signals. The proposed control method also demonstrated robustness against external disturbances and system parameter variations such as muscle fatigue. These simulation results under various circumstances indicate that it is possible to take advantage of multiple contact nerve electrodes with spatial selectivity for the control of limb motion by peripheral nerve stimulation even with limited individual muscle selectivity. This technology could be useful to restore neural function in patients with paralysis.     

Rat sciatic nerve crush injury and recovery tracked by plantar test and immunohistochemistry analysis

An experimental crush injury to the sciatic nerve, with a crush force of 49.2 N (pressure p=1.98x10(8) Pa), was inflicted in 30 male rats (Wistar). A control group (sham), with the same number of rats, was also operated upon exactly as the experimental group but without the crush injury. We tested the sensory and motor recovery of the sciatic nerve with Hargreaves method, using an apparatus from Ugo Basile, Italy. Testing was continued for both legs of each rat, injured and uninjured, starting preoperatively (0 day), and then 1, 7, 14, 21, and 28 days postoperatively. The same experiment was run simultaneously with the sham group. The Plantar test showed recovery of the sensory and motor function of the sciatic nerve, though not complete recovery, by 28 days. An immunohistochemical experiment was run in parallel with the plantar test on L3-L6 segments of the spinal cord from where the sciatic nerve extends. We used antibodies for Myelin-associated glycoprotein (MAG), and gangliosides GD1a and GT1b on the aforesaid part of the spinal cord. The immunohistochemical methods showed changes in sensory and motor axons in the spinal cord segment L3-L6 which suggest correspondence with the results of the Plantar test, in terms of recovery of the sensory and motor function after injury of the sciatic nerve. The immunohistochemical results also show ipsilateral and contralateral changes following injury. Results of the plantar test are suggestive that the rat shows compensation for an injury in its contralateral leg.     

Electrical conduction through nerve and DNA

The aim of the present study was to analyse electric resistivity at different ambient temperatures between 300 to 20K in the frog sciatic nerve and salmon sperm DNA. When the electrical contacts were leaned just into the sciatic nerve, an increase of the sciatic nerve resistivity was observed for 240 K < T < 300 K and a rise of electrical conductivity was apparent below 240 K. This dependence is generally associated with a semiconductor behaviour. Once the sciatic nerve temperature was driven below 250K, the resistivity abruptly decreased and then at temperatures lower than 234 K, it remained constant and close to one tenth of its ambient temperature value. By contrast, when the electrical contacts were leaned into Salmon sperm DNA, the resistivity remained constant between 300K to 20K, showing a high electrical stability at low temperature. Thus, we report the existence of a new form of electric conductivity in the sciatic nerve at low ambient temperature, which in turn has many electric similarities with inorganic or organic superconductors, whereas temperature failed to alter DNA electrical properties until 20K.     

Comparison of age-related peripheral nerve changes in mice housed in either plastic cages with sawdust-covered solid flooring or wire-mesh-floor cages.

A comparative histologic survey was conducted on the dorsal root, sciatic, tibial and medial plantar nerves of 90- and 110-week-old B6C3F1 female mice reared in either solid-floor cages covered in sawdust or wire-mesh-floor cages. Age-related peripheral nerve lesions, characterized by axonal degeneration and remyelination, were present in all nerves surveyed, and were especially prominent in the sciatic and medial plantar nerves at 110 weeks of age but, there were no differences associated with the type of cage floor in clinical signs, grasping power of the fore- and hind-limbs, motor nerve conduction velocity or histopathologic findings at these ages.     

Multielectrode spiral cuff for ordered and reversed activation of nerve fibres

In this paper we present the modelling, design, and experimental testing of a nerve cuff multielectrode system for selective activation of fibres in superficial peripheral nerve trunk regions which is capable of activating fibres in physiological order. The multielectrode system consists of 45 platinum electrodes embedded within a self-curling spiral silicone sheet organized in fifteen longitudinal groups consisting of three electrodes spaced equidistally around the circumference of the cuff. Electrodes in the centre band acted as stimulating cathodes while the two electrodes of the same group in the two outer bands were connected together and corresponded to the position of a particular cathode, serving as anodes to block the nascent action potentials by membrane hyperpolarization. The interpolar distance was 6 mm on both sides, resulting in a total cuff length of about 20 mm. The cuff was constructed with a diameter to fit the size of the dog sciatic nerve. Preliminary animal testing of the nerve cuff was performed on the sciatic nerve of a Bigley female dog. In the 45-electrode stimulation system, biphasic cathodic first pulses with quasitrapezoidal-shaped cathodic and square anodic parts were delivered through the particular group of tripolar electrodes to effect both selective stimulation of motor axons within the gastrocnemius muscle fascicle, and differential block by membrane hyperpolarization. The test was repeated using rectangular cathodic first biphasic current pulses delivered monopolarly on the central electrode of the same group while connected anodes were replaced by a common anode situated elsewhere in the surrounding tissue. In both experiments an isometric torque in the ankle joint elicited by the gastrocnemius muscle was measured and compared. It was shown that tripolar activation with quasitrapezoidal stimulation pulses elicited an isometric torque with a peak value of 0.83 Nm in 65 ms after onset of delivering stimulating pulses in comparison to the monopolar activation with rectangular biphasic pulses where the peak of the same value was observed in 45 ms after onset. Thus, the multipolar cuff stimulating monopolarly provided an effective means of activating motor axons selectively within the gastrocnemius muscle fascicle, while more physiological recruitment of the muscle fibres was evident when stimulating tripolarly.     

Microglial activation in different models of peripheral nerve injury of the rat

Pain and pain modulation has been viewed as being mediated entirely by neurons. However, new research implicates spinal cord glia as key players in the creation and maintenance of pathological pain. Sciatic nerve lesions are one of the most commonly studied pain-related injuries. In our study we aimed to characterize changes in microglial activation in the rat spinal cord after axotomy and chronic constriction injury of the sciatic nerve and to evaluate this activation in regard to pain behavior in injured and control groups of rats. Microglial activation was observed at ipsilateral side of lumbar spinal cord in all experimental groups. There were slight differences in the level and extent of microglial activation between nerve injury models used, however, differences were clear between nerve-injured and sham animals in accordance with different level of pain behavior in these groups. It is known that activated microglia release various chemical mediators that can excite pain-responsive neurons. Robust microglial activation observed in present study could therefore contribute to pathological pain states observed following nerve injury.     

Bilateral activation of STAT3 by phosphorylation at the tyrosine-705 (Y705) and serine-727 (S727) positions and its nuclear translocation in primary sensory neurons following unilateral sciatic nerve injury

Unilateral sciatic nerve compression (SNC) or complete sciatic nerve transection (CSNT), both varying degrees of nerve injury, induced activation of STAT3 bilaterally in the dorsal root ganglia (DRG) neurons of lumbar (L4-L5) as well as cervical (C6–C8) spinal cord segments. STAT3 activation was by phosphorylation at the tyrosine-705 (Y705) and serine-727 (S727) positions and was followed by their nuclear translocation. This is the first evidence of STAT3(S727) activation together with the well-known activation of STAT3(Y705) in primary sensory neurons upon peripheral nerve injury. Bilateral activation of STAT3 in DRG neurons of spinal segments anatomically both associated as well as non-associated with the injured nerve indicates diffusion of STAT3 activation inducers along the spinal cord. Increased levels of IL-6 protein in the CSF following nerve injury as well as activation and nuclear translocation of STAT3 in DRG after intrathecal injection of IL-6 shows that this cytokine, released into the subarachnoid space can penetrate the DRG to activate STAT3. Previous results on increased bilateral IL-6 synthesis and the present manifestation of STAT3 activation in remote DRG following unilateral sciatic nerve injury may reflect a systemic reaction of the DRG neurons to nerve injury.     

Biophysical mechanisms of transient optical stimulation of peripheral nerve

A new method for in vivo neural activation using low-intensity, pulsed infrared light exhibits advantages over standard electrical means by providing contact-free, spatially selective, artifact-free stimulation. Here we investigate the biophysical mechanism underlying this phenomenon by careful examination of possible photobiological effects after absorption-driven light-tissue interaction. The rat sciatic nerve preparation was stimulated in vivo with a Holmium:yttrium aluminum garnet laser (2.12 microm), free electron laser (2.1 microm), alexandrite laser (750 nm), and prototype solid-state laser nerve stimulator (1.87 microm). We systematically determined relative contributions from a list of plausible interaction types resulting in optical stimulation, including thermal, pressure, electric field, and photochemical effects. Collectively, the results support our hypothesis that direct neural activation with pulsed laser light is induced by a thermal transient. We then present data that characterize and quantify the spatial and temporal nature of this required temperature rise, including a measured surface temperature change required for stimulation of the peripheral nerve (6 degrees C-10 degrees C). This interaction is a photothermal effect from moderate, transient tissue heating, a temporally and spatially mediated temperature gradient at the axon level (3.8 degrees C-6.4 degrees C), resulting in direct or indirect activation of transmembrane ion channels causing action potential generation.     

Investigation of the mechanisms for wireless nerve stimulation without active electrodes

Electric-field stimulation of neuronal activity can be used to improve the speed of regeneration for severed and damaged nerves. Most techniques, however, require invasive electronic circuitry which can be uncomfortable for the patient and can damage surrounding tissue. A recently suggested technique uses a graft-antenna—a metal ring wrapped around the damaged nerve—powered by an external magnetic stimulation device. This technique requires no electrodes and internal circuitry with leads across the skin boundary or internal power, since all power is provided wirelessly. This paper examines the microscopic basic mechanisms that allow the magnetic stimulation device to cause neural activation via the graft-antenna. A computational model of the system was created and used to find that under magnetic stimulation, diverging electric fields appear at the metal ring's edges. If the magnetic stimulation is sufficient, the gradients of these fields can trigger neural activation in the nerve. In-vivo measurements were also performed on rat sciatic nerves to support the modeling finding that direct contact between the antenna and the nerve ensures neural activation given sufficient magnetic stimulation. Simulations also showed that the presence of a thin gap between the graft-antenna and the nerve does not preclude neural activation but does reduce its efficacy.     

Lentiviral-mediated transfer of CDNF promotes nerve regeneration and functional recovery after sciatic nerve injury in adult rats

Peripheral nerve injury is often followed by incomplete and unsatisfactory functional recovery and may be associated with sensory and motor impairment of the affected limb. Therefore, a novel method is needed to improve the speed of recovery and the final functional outcome after peripheral nerve injuries. This report investigates the effect of lentiviral-mediated transfer of conserved dopamine neurotrophic factor (CDNF) on regeneration of the rat peripheral nerve in a transection model in vivo. We observed notable overexpression of CDNF protein in the distal sciatic nerve after recombinant CDNF lentiviral vector application. We evaluated sciatic nerve regeneration after surgery using light and electron microscopy and the functional recovery using the sciatic functional index and target muscle weight. HE staining revealed better ordered structured in the CDNF-treated group at 8 weeks post-surgery. Quantitative analysis of immunohistochemistry of NF200 and S-100 in the CDNF group revealed significant improvement of axonal and Schwann cell regeneration compared with the control groups at 4 weeks and 8 weeks after injury. The thickness of the myelination around the axons in the CDNF group was significantly higher than in the control groups at 8 weeks post-surgery. The CDNF group displayed higher muscle weights and significantly increased sciatic nerve index values. Our findings suggest that CDNF gene therapy could provide durable and stable CDNF protein concentration and has the potential to enhance peripheral nerve regeneration, morphological and functional recovery following nerve injury, which suggests a promising strategy for peripheral nerve repair.     

Walking track analysis: a long-term assessment of peripheral nerve recovery.

Functional recovery following sciatic, tibial, and peroneal nerve injury was assessed over a 1-year period using walking track analysis in the rat. Internal neurolysis did not affect nerve function. Crush injury induced a temporary, but complete, loss of function that recovered to control levels by 4 weeks. Nerve transection resulted in complete loss of function without any evidence of recovery. After nerve repair, functional recovery occurred, reaching near-optimal recovery by 12 weeks. The degree of functional recovery varied with the specific nerve involved. The sciatic nerve recovered 41 percent of function, whereas the tibial nerve recovered 54 percent of function. The peroneal nerve exhibited the highest degree of recovery, achieving functional levels similar to control values. Assessment of neural regeneration using walking track analysis appears to be a valuable addition to the traditional methods of histology and electrophysiology.     

Increased occurrence of PGP 9.5-immunoreactive epidermal Langerhans cells in rat plantar skin after sciatic nerve injury

This study examines the occurrence and distribution of epidermal dendritic cells (DCs) in cryostate sections from plantar skin in normal rats and in rats with a crush injury or neurotomy and suture of the sciatic nerve. The dendritic cells were visualized with antibodies against protein-gene product 9.5 (PGP 9.5). Counts under the fluorescence microscope showed that the occurrence of dendritic cells is increased and that the proportion of dendritic cells in the basal layer is elevated 3 months after sciatic neurotomy and suture but not after a crush lesion. The countings also revealed that the number of cells is elevated as soon as 1 week after neurotomy and suture. Labelling with specific antibodies showed that the dendritic cells examined represent Langerhans cells (LCs). These observations show that there is a neural influence on the occurrence and distribution of PGP 9.5-immunoreactive epidermal Langerhans cells. Whether this influence is direct or indirect remains to be ascertained.     

Relation of ATP and creatine phosphate to fast axoplasmic transport in mammalian nerve

—ATP and creatine phosphate (CP) levels in cat sciatic nerve maintained in vitro were measured. Anoxia produced by N₂ or NaCN or the uncoupling of phosphorylation with DNP reduced the combined levels of ATP + CP to approximately one-half of control levels within 15 min. These agents also blocked fast axoplasmic transport in vitro within 15 min. A block of glycolysis with iodoacetic acid (IAA) reduced the combined levels of ATP + CP to approximately one half of control levels within 1.5–2 h and exposure of nerve in vitro to IAA caused a block of fast axoplasmic transport within the same interval. The correlation of the time at which block of transport occurred with the fall in the level of high-energy phosphates is consistent with the hypothesis that ATP supplies the energy required by the mechanism underlying fast exoplasmic transport.     

Adrenergic nerve fibers in the human fetal sciatic nerve.

The adrenergic innervation was studied in the human sciatic nerve at the gestational age of 16, 17, 18 and 21 weeks. Formaldehyde-induced catecholamine fluorescence, tyrosine hydroxylase (TH) and neuropeptide Y (NPY) peroxidase-antiperoxidase immunohistochemistry methods were used. At the gestational age of 16, 17 and 18 weeks no adrenergic or NPY-positive nerve fibers were seen. At 21 weeks both fluorescence microscopy and TH immunohistochemistry showed adrenergic nerve fibers around arterioles in the epiperineurium and single nerve fibers in the endoneurium not related to blood vessels. The number of adrenergic nerve fibers appeared to be higher in the sciatic than in the tibial segment of the nerve. At this age, as at earlier stages of gestation, no NPY-positive nerve fibers were seen either in the epiperineurium or in the endoneurium. The results suggest that adrenergic nerve fibers may be associated with the epiperineurial blood vessels in the human sciatic nerve, and that the innervation starts to develop between 18 and 21 weeks of gestational age.     

Joint kinetic response during unexpectedly reduced plantar flexor torque provided by a robotic ankle exoskeleton during walking

During human walking, plantar flexor activation in late stance helps to generate a stable and economical gait pattern. Because plantar flexor activation is highly mediated by proprioceptive feedback, the nervous system must modulate reflex pathways to meet the mechanical requirements of gait. The purpose of this study was to quantify ankle joint mechanical output of the plantar flexor stretch reflex response during a novel unexpected gait perturbation. We used a robotic ankle exoskeleton to mechanically amplify the ankle torque output resulting from soleus muscle activation. We recorded lower-body kinematics, ground reaction forces, and electromyography during steady-state walking and during randomly perturbed steps when the exoskeleton assistance was unexpectedly turned off. We also measured soleus Hoffmann- (H-) reflexes at late stance during the two conditions. Subjects reacted to the unexpectedly decreased exoskeleton assistance by greatly increasing soleus muscle activity about 60 ms after ankle angle deviated from the control condition (p<0.001). There were large differences in ankle kinematic and electromyography patterns for the perturbed and control steps, but the total ankle moment was almost identical for the two conditions (p=0.13). The ratio of soleus H-reflex amplitude to background electromyography was not significantly different between the two conditions (p=0.4). This is the first study to show that the nervous system chooses reflex responses during human walking such that invariant ankle joint moment patterns are maintained during perturbations. Our findings are particularly useful for the development of neuromusculoskeletal computer simulations of human walking that need to adjust reflex gains appropriately for biomechanical analyses.     

Histologic assessment of nerve regeneration in the rat

This study reports the degree of spontaneous regeneration that will occur in the sciatic nerve of a rat 5 months after complete resection of the nerve. In 30 animals, the sciatic nerve was excised. Histological assessment at 5 months revealed evidence of regeneration for a variable distance (mean 23.7 mm +/- 6.4 mm). Histological sections were studied at 1-cm intervals along the length of the nerve. Evidence of compartmentation with "minifascicle" formation was noted. The orientation of the nerve fibers was parallel to the long axis of the nerve. This study assessing spontaneous regeneration is meant to serve as a control for other studies evaluating the effect of factors that may influence nerve regeneration in the rat model.     

Increased expression of Gem after rat sciatic nerve injury

Gem belongs to the Rad/Gem/Kir subfamily of Ras-related GTPases, whose expression is induced in several cell types upon activation by extracellular stimuli. Two functions of Gem have been demonstrated, including regulation of voltage-gated calcium channel activity and inhibition of Rho kinase-mediated cytoskeletal reorganization, such as stress fiber formation and neurite retraction. Because of the essential relationship between actin reorganization and peripheral nerve regeneration, we investigated the spatiotemporal expression of Gem in a rat sciatic nerve crush (SNC) model. After never injury, we observed that Gem had a significant up-regulation from 1 day, peaked at day 5 and then gradually decreased to the normal level. At its peak expression, Gem expressed mainly in Schwann cells (SCs) and macrophages of the distal sciatic nerve segment, but had few colocalization in axons. In addition, the peak expression of Gem was in parallel with PCNA, and numerous SCs expressing Gem were PCNA positive. Thus, all of our findings suggested that Gem may be involved in the pathophysiology of sciatic nerve after SNC.     

Bidirectional axonal transport of 16S acetylcholinesterase in rat sciatic nerve

Axonal transport of the 16S Molecular form of acetylcholinesterase (16S-AChE) in doubly ligated rat sciatic nerves was studied by means of velocity sedimentation analysis on sucrose gradients. This form of AChE was selectively confined to motor, and not to sensory, fibers in the sciatic nerve, where it represented 3--4% of total AChE. Its activity increased linearly with time (4--20 hr) in nerve segments (7 mm) proximal to the central ligature (4.5 mU/24hr) and distal to the peripheral ligature (2.0 mU/24 hr). From the linear rates of accumulation of 16S-AChE, we conclude that the enzyme is conveyed by anterograde and retrograde axonal transport at velocities close to those previously defined for the movement of total AChE (410 mm/day, anterograde; 220 mm/day, retrograde). The transport of AChE molecular forms, other than the 16S form, could not be resolved presumably due to their presence in blood as well as at extraaxonal sites. The present findings are consistent with the view that in rat sciatic nerve most, if not all, of the small portion of total AChE (approximately 3%) which is transported may be accounted for by 16S-AChE.     

The neuromuscular demands of toe walking: a forward dynamics simulation analysis

Toe walking is a gait deviation with multiple etiologies and often associated with premature and prolonged ankle plantar flexor electromyographic activity. The goal of this study was to use a detailed musculoskeletal model and forward dynamical simulations that emulate able-bodied toe and heel-toe walking to understand why, despite an increase in muscle activity in the ankle plantar flexors during toe walking, the internal ankle joint moment decreases relative to heel-toe walking. The simulations were analyzed to assess the force generating capacity of the plantar flexors by examining each muscle's contractile state (i.e., the muscle fiber length, velocity and activation). Consistent with experimental measurements, the simulation data showed that despite a 122% increase in soleus muscle activity and a 76% increase in gastrocnemius activity, the peak internal ankle moment in late stance decreased. The decrease was attributed to non-optimal contractile conditions for the plantar flexors (primarily the force-length relationship) that reduced their ability to generate force. As a result, greater muscle activity is needed during toe walking to produce a given muscle force level. In addition, toe walking requires greater sustained plantar flexor force and moment generation during stance. Thus, even though toe walking requires lower peak plantar flexor forces that might suggest a compensatory advantage for those with plantar flexor weakness, greater neuromuscular demand is placed on those muscles. Therefore, medical decisions concerning whether to reduce equinus should consider not only the impact on the ankle moment, but also the expected change to the plantar flexor's force generating capacity.     

急性神经损伤引起脊髓背角C-纤维诱发电位长时程增强

神经损伤引起神经病性疼痛,表现为持续性痛超敏和痛觉过敏。目前对神经病性疼痛的机制尚缺乏了解。我们以往的工作表明强直电刺激坐骨神经可引起脊髓背角C-纤维诱发电位的长时程增强(long-term potentiation,LTP),该LTP被认为是病理性疼痛的突触模型。本研究的目的在于探讨急性神经损伤是否能在完整动物的脊髓背角诱发出C-纤维诱发电位LTP。在以测试刺激(10～20V,0．5ms)电刺激坐骨神经的同时在脊髓背角用微电极记录C一纤维诱发电位。分别用强直刺激、剪断或夹捏坐骨神经诱导LTP。结果发现：(1)剪断或夹捏坐骨神经都可以诱导脊髓背角C-纤维诱发电位的LTP,该LTP可持续到实验结束(3～9h),在剪断神经前10min用利多卡因局部阻滞坐骨神经则可完全阻断LTP的产生;(2)神经损伤诱导的LTP可被NMDA受体阻断剂AP5所阻断;(3)用单次强直刺激引起LTP后,切断坐骨神经可使LTP的幅度进一步增大,而用多次强直电刺激使LTP饱和后,损伤神经则不能使LTP进一步增大。切断神经引起LTP后,强直电刺激也不能使LTP进一步增大。这些结果表明,急性神经损伤可以诱导脊髓背角C纤维诱发电位LTP,且切断神经能更有效地诱导LTP。该试验进一步支持我们的设想,即脊髓背角C-纤维诱发电位LTP可能在病理性疼痛的形成中起重要作用。