Peroneal Fascicles Research Articles

Fascicle localisation within peripheral nerves through evoked activity recordings: A comparison between electrical impedance tomography and multi-electrode arrays

BackgroundThe lack of understanding of fascicular organisation in peripheral nerves limits the potential of vagus nerve stimulation therapy. Two promising methods may be employed to identify the functional anatomy of fascicles within the nerve: fast neural electrical impedance tomography (EIT), and penetrating multi-electrode arrays (MEA). These could provide a means to image the compound action potential within fascicles in the nerve. New methodWe compared the ability to localise fascicle activity between silicon shanks (SS) and carbon fibre (CF) multi-electrode arrays and fast neural EIT, with micro-computed tomography (MicroCT) as an independent reference. Fast neural EIT in peripheral nerves was only recently developed and MEA technology has been used only sparingly in nerves and not for source localisation. Assessment was performed in rat sciatic nerves while evoking neural activity in the tibial and peroneal fascicles. ResultsRecorded compound action potentials were larger with CF compared to SS (∼700 μV vs ∼300 μV); however, background noise was greater (6.3 μV vs 1.7 μV) leading to lower SNR. Maximum spatial discrimination between Centres-of-Mass of fascicular activity was achieved by fast neural EIT (402 ± 30 μm) and CF MEA (414 ± 123 μm), with no statistical difference between MicroCT (625 ± 17 μm) and CF (p > 0.05) and between CF and EIT (p > 0.05). Compared to CF MEAs, SS MEAs had a lower discrimination power (103 ± 51 μm, p < 0.05). Comparison with existing methodsEIT and CF MEAs showed localisation power closest to MicroCT. Silicon MEAs adopted in this study failed to discriminate fascicle location. Re-design of probe geometry may improve results. ConclusionsNerve EIT is an accurate tool for assessment of fascicular position within nerves. Accuracy of EIT and CF MEA is similar to the reference method. We give technical recommendations for performing multi-electrode recordings in nerves.

Optimization of the electrode drive pattern for imaging fascicular compound action potentials in peripheral nerve with fast neural electrical impedance tomography

Objective: The main objective of this study was to investigate which injection pattern led to the best imaging of fascicular compound activity in fast neural EIT of peripheral nerve using an external cylindrical 2 × 14-electrodes cuff. Specifically, the study addressed the identification of the optimal injection pattern and of the optimal region of the reconstructed volume to image fascicles. Approach: The effect of three different measurement protocol features (transversal/longitudinal injection, drive electrode spacing, referencing configuration) over imaging was investigated in simulation with the use of realistic impedance changes and noise levels. Image-based metrics were employed to evaluate the quality of the reconstructions over the reconstruction domain. The optimal electrode addressing protocol suggested by the simulations was validated in vivo on the tibial and peroneal fascicles of rat sciatic peripheral nerves (N = 3) against MicroCT reference images. Main results: Injecting current transversally, with spacing of ⩾4 electrodes apart (⩾100°) and single-ring referencing of measurements, led to the best overall localization when reconstructing on the edge of the electrode array closest to the reference. Longitudinal injection protocols led to a higher SNR of the reconstructed image but poorer localization. All in vivo EIT recordings had statistically significant impedance variations (p < 0.05). Overall, fascicle center-of-mass (CoM) localization error was estimated at 141 ± 56 µm (−26 ± 94 µm and 5 ± 29° in radial coordinates). Significant difference was found (p < 0.05) between mean angular location of the tibial and peroneal CoMs. Significance: This study gives the reader recommendations for performing fast neural EIT of fascicular compound activity using the most effective protocol features.

Influence of Anatomical Detail and Tissue Conductivity Variations in Simulations of Multi-Contact Nerve Cuff Recordings.

Accurate simulations of peripheral nerve recordings are needed to develop improved neuroprostheses. Previous models of peripheral nerves contained simplifications whose effects have not been investigated. We created a novel detailed finite element (FE) model of a peripheral nerve, and used it to carry out a sensitivity analysis of several model parameters. To construct the model, in vivo recordings were obtained in a rat sciatic nerve using an 8-channel nerve cuff electrode, after which the nerve was imaged using magnetic resonance imaging (MRI). The FE model was constructed based on the MRI data, and included progressive branching of the fascicles. Neural pathways were defined in the model for the tibial, peroneal and sural fascicles. The locations of these pathways were selected so as to maximize the correlations between the simulated and in vivo recordings. The sensitivity analysis showed that varying the conductivities of neural tissues had little influence on the ability of the model to reproduce the recording patterns obtained experimentally. On the other hand, the increased anatomical detail did substantially alter the recording patterns observed, demonstrating that incorporating fascicular branching is an important consideration in models of nerve cuff recordings. The model used in this study constitutes an improved simulation tool and can be used in the design of neural interfaces.

A Parylene Self-Locking Cuff Electrode for Peripheral Nerve Stimulation and Recording

The cuff electrode provides a stable interface with the peripheral nerve, which has been widely utilized in both basic research and clinical practice over the past few decades. In this paper, we present a microfabricated, parylene-based self-locking cuff electrode. The cuff diameter can be adjusted to accommodate the nerve properly during implantation. This type of cuff electrodes is easy to implant and the cuff was made of the thin, flexible, and biocompatible parylene substrate. Moreover, the integrated parylene cable and pads facilitate the connection with external circuits. Electrochemical properties of electrode sites were characterized by impedance spectroscopy and cyclic voltammetry. The average impedance magnitude and average charge delivery capacity of the Pt electrodes are 8.3 kQ (at 1 kHz) and 2.8 mC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. Using the proposed cuff electrodes, the evoked compound action potentials of the rat sciatic nerve were successfully recorded. Electrical stimulation tests proved the feasibility of selective stimulation of tibial and peroneal fascicles within the rat sciatic nerve. This type of cuff electrodes induced only a benign foreign body reaction and did not damage the axons within the rat sciatic nerve over 11 weeks of an implantation period.

Effect of conduit repair on aberrant motor axon growth within the nerve graft in rats

After peripheral nerve injury, minimizing axonal misdirection has been a matter of importance to obtain good functional outcomes. In general, it becomes more challenging as the nerve defect length is longer. As previous works suggested that a conduit repair leaving a short gap could induce some target-specific reinnervation, we expected that a distally placed conduit combined with nerve graft would enhance the specificity of reinnervation, especially in dealing with a long gap. To test this, a 14-mm-long gap was created in the rat sciatic nerves and repaired with either 1) whole nerve graft (WG), 2) interfascicular nerve grafts (FG), or 3) whole nerve graft combined with distally placed silicone tube leaving a 5-mm gap (TUBG). At the end of follow up, the extent of target specific reinnervation (measurement of the compound muscle action potentials evoked by stimulation of the sciatic nerve and its tibial and common peroneal fascicles) and the accuracy of motoneuronal projection (sequential retrograde labeling of the common peroneal motor pool) were assessed. Both assessments revealed that groups FG and TUBG had a similar selectivity, which was significantly higher than in group WG. Consistent with these results, the functional recovery as assessed by walking track analysis showed no significant difference between groups FG and TUBG, whereas those were significantly superior to group WG. In contrast, histomorphometric assessment of the regenerating axons and wet muscle weight showed no significant difference among the three groups. In conclusion, conduit repair would have some effects on reducing motor axonal misdirection, and it might be more effective when used in the management of a large defect in combination with nerve graft.

Functional evaluation of regenerated and misrouted low threshold mechanoreceptors and polymodal nociceptors in the skin of Rat hindfeet after crush lesions to the sciatic nerve

Tracer studies on motor axons after nerve crush injuries have indicated that misrouting may occur even when the endoneurium is intact. Misrouting of regenerated polymodal nociceptive C-fibres and low threshold mechanoreceptive axons have been studied functionally in 50 rats three months after unilateral crush lesions to the sciatic nerve. Two weeks before evaluation the tibial fascicle (or the peroneal fascicle) above the lesion was cut and tied off. In this way only functional regeneration of misrouted axons was tested. Misrouted low threshold mechanoreceptive axons and polymodal nociceptor C-fibres were found after regeneration in both glabrous and hairy skin. We conclude that functional misdirection of both myelinated and unmyelinated sensory axons innervating either glabrous or hairy skin can occur after a crush lesion to a peripheral nerve in rats.

Peripheral and Spinal Motor Reorganization after Nerve Injury and Repair

Functional recovery after peripheral nerve injury depends on the amount as well as on the accuracy of reinnervation by regenerative axons. In this study, the rat sciatic nerve was subjected to crush injury or complete transection repaired by either (1) straight nerve suture, (2) crossed nerve suture of tibial and peroneal fascicles, or (3) silicone tubulization leaving a gap of 4 mm. The compound muscle action potentials (CMAP) of gastrocnemius, tibialis anterior and plantar muscles were recorded 90 days post operation to assess functional reinnervation and Fast Blue, Fluoro Gold and DiI were applied to the nerve branches projecting into these muscles to quantify morphological reinnervation. The CMAP amplitude achieved in gastrocnemius, tibialis anterior and plantar muscles was higher after nerve crush (86%, 82%, 65% of control) than after any surgical nerve repair (straight suture: 49%, 53%, 32%; crossed suture: 56%, 50%, 31%; silicone tube: 42%, 44%, 25%). The total number of labeled motoneurons, however, did not significantly differ between groups (control: 1238 +/- 82, crush: 1048 +/- 49, straight suture: 1175 +/- 106, crossed suture: 1085 +/- 84, silicone tube: 1250 +/- 182). The volume occupied by labeled motoneurons within the spinal cord was larger after surgical nerve repair than in crush or normal control animals, and fewer neurons showed abnormal multiple projections after crush (2.5%) or straight suture (2.2%) than following crossed suture (5%) or silicone tube (6%). In conclusion, nerve repair with a silicone tube leaving a short gap does not increase accuracy of reinnervation.

O-20-293 - Repair of cervical nerve root avulsions using intercostal nerves in brachial plexus surgery

Dorsal horn projections from muscle innervated by the common peroneal branch of the rat sciatic nerve were studied in three experimental situations: after either epineurial or individual fascicular suture of the sciatic nerve, or after isolated severance and repair of the peroneal sciatic fascicle. Four months after surgery, the peroneal-innervated muscles were injected with a conjugate of horseradish peroxidase and wheatgerm agglutinin. Projections from these muscles, as well as from peroneal-innervated skin and the entire sciatic nerve, were also studied in normal controls. Rats were perfused forty-eight hours after enzyme exposure, and the presence of horseradish peroxidase demonstrated by reaction of spinal cord sections with H2O2 and tetramethylbenzidine.Injection of normal peroneal-innervated muscle labeled a sharply-defined area within the substantia gelatinosa of the ipsilateral dorsal horn. After regeneration from individual fascicular sciatic repair, or suture of the isolated peroneal fascicle, this projection was more widespread, resembling that from normal peroneal-innervated skin. The muscle projection was even wider and more variable following epineurial repair, yet always confined within the normal sciatic projection. The width and variability of muscle projections after epineurial suture probably reflect inter-fascicular misdirection of regenerating axons. The finding of expanded projections even after partial (individual fascicular) and total (isolated peroneal repair) elimination of this misdirection, and the similarity of these projections to those of peroneal-innervated skin, suggest confusion at the intra-fascicular level as well. Muscle could be reinnervated by peroneal nerve axons which previously served non-muscular structures, and which project to a wider area of the dorsal horn not originally labeled by muscle injection.These experiments demonstrate a substantial projection from muscle to the substantia gelatinosa, an area strongly implicated in the processing of nociceptive information. Reorganization of these projections might provide an anatomical substrate for abnormal pain perception after peripheral nerve injury, including confusion as to its tissue of origin. Furthermore, this reorganization is not eliminated by individual fascicular suture. This technique, which decreases the frequency with which regenerating axons cross from one fascicle to another, does not, therefore, prevent axon disorganization within the fascicle itself.

Regeneration across a partial defect in rat sciatic nerve encased in a silicone chamber.

Forty-four rat sciatic nerves with partial defects were repaired with a silicone chamber. Each partial defect was created by resecting a 10 mm segment from the tibial fascicle leaving the peroneal fascicle intact. The proximal and the distal stumps of the tibial fascicle together with the intact peroneal fascicle were encased in a single silicone chamber. After seven days a fibrin matrix had surrounded the peroneal fascicle and spanned the defect between the tibial stumps. This matrix was later invaded by non-neuronal cells and regenerating axons. Non-myelinated nerve fibres had almost regenerated across the defect by 16 days. The tetanic force of the gastrocnemius muscle 120 days after repair showed 80% recovery, which was no different from that of partial defects repaired with conventional nerve grafts. The results suggest that the silicone chamber technique could be applicable to the treatment of partially transected nerve trunks.

Dispersion of regenerating axons across enclosed neural gaps

Tubular prostheses support peripheral axon regeneration across gaps of up to 3 cm in the primate. However, the precision with which axons cross a gap and reinnervate the periphery remains controversial. These experiments use continuous tracing of regenerated rat sciatic nerve axons with HRP-WGA to examine the dispersion of axons as they cross a gap, and the effects on this dispersion of gap distance and fascicular orientation. Proximal and distal tibial and peroneal fascicles were precisely oriented about the longitudinal midplane of a silicon tube, with correct or reversed fascicular alignment and gaps of 2 mm and 5 mm. After 6 weeks of regeneration, HRP-WGA was applied to the distal peroneal fascicle to continuously label its reinnervating axons. These axons tended to grow straight across the tube, with dispersion increasing as a factor of distance when correct fascicular alignment was maintained. However, when fascicular alignment was reversed, axonal dispersion was determined by fascicular size rather than fascicular identity. These experiments provide no evidence for neurotropic interactions promoting "correct" fascicular reinnervation. Progressive axonal dispersion and the absence of factors to promote fascicular specificity should result in an increase of random reinnervation and functional disruption with larger gaps. An enclosed gap is not an acceptable substitute for nerve graft when reconstructing a nerve that serves multiple functions.

Functional evaluation of regenerated and misrouted axons to glabrous and hairy skin of the rat hind foot after sciatic neurotomy and suture

The function of misrouted regenerated polymodal nociceptor C-fibers and low-threshold mechanoreceptive axons in the lateral plantar nerve (LPN) and in the foot branch of the superficial peroneal nerve (fSPN) was evaluated 3 months after unilateral sciatic neurotomy and suture. Two weeks before evaluation the tibial fascicle (or the peroneal fascicle) above the neurotomy was cut and tied off. In this way only functional regeneration of misrouted axons was tested in the LPN (or the fSPN). In regenerated animals the glabrous skin area had no functional fSPN-related low-threshold mechanoreceptive axons. However, the hairy fSPN skin area showed function of misrouted LPN-related low-threshold mechanoreceptive axons. In both the glabrous skin domain innervated by the LPN and the hairy skin area supplied by the fSPN, functional regeneration of misrouted polymodal nociceptor C-fibers was found. We conclude that functional regeneration of misrouted axons related to polymodal nociceptive units and low-threshold mechanoreceptive units is more efficient in hairy skin of the rat foot whereas only misrouted polymodal nociceptor C-fibers recover function in glabrous skin.

Can sensory and motor collateral sprouting be induced from intact peripheral nerve by end-to-side anastomosis?

The possibility that collateral sprouting could occur from intact axons in an undamaged sciatic nerve was studied in the rat by suturing either a 7-day predegenerated or a fresh nerve segment in an end-to-side fashion to the sciatic nerve proper. Following a 14- or 35-day recovery period, the pinch reflex test was performed on the transplanted segment to demonstrate the presence of sensory axons. The majority of cases, using a predegenerated nerve segment but not a fresh segment, responded positively. Neurofilament staining and histological examination confirmed the presence of axons in the attached nerve segment. In another series of experiments, the proximal peroneal fascicle was ligated and cut. Following a 7-day predegeneration period the distal stump was sutured end-to-side to the ipsilateral tibial fascicle. After 90 days, stimulation of the tibial nerve proximal to the attached site induced substantial contraction in both the native gastrocnemius muscle and the foreign tibialis anterior muscle. These findings suggest that collateral sprouting may occur from intact axons, perhaps induced by factors emanating from the attached nerve segment, and subsequently make functional peripheral connections.

Reinnervation of muscles in rats after repair of transsected sciatic nerves with Y-shaped and X-shaped silicone tubes. Muscle reinnervation after nerve repair.

Reinnervation of the gastrocnemius and anterior tibial muscles was assessed by measurements of tetanic force after repair of sciatic nerves with Y-shaped or X-shaped silicone tubes in rats. The transsected proximal stump of either the tibial or the peroneal fascicle was introduced into the opening of a Y-shaped silicone tube, or both fascicles were introduced into an X-shaped tube. The distal tibial and peroneal fascicles were inserted into the distal outlets of the tubes leaving a gap of 4 mm between proximal and distal stumps. In the X-shaped tubes the proximal inserts were placed opposite or adjacent to their respective distal parts. Sixteen weeks later reinnervation was evaluated by measurements of tetanic force of the gastrocnemius and anterior tibial muscles after electrical stimulation of the fascicles. There was preferential reinnervation in both types of tubes. In Y-shaped tubes about 90% of the tetanic force could be recorded from both muscles after stimulation of the peroneal and tibial fascicles, respectively. Recovery was lower in the X-shaped tubes, amounting to about 75%. Contractions evoked by misrouted fibres were similar (roughly 40%) in both models. We conclude that motor axons preferentially, but not exclusively, selected a path to reinnervate their original target muscle.

Axonal projections and functional recovery following fascicular repair of the rat sciatic nerve with Y-tunnelled silicone chambers

The projection of regenerating axons and the specificity of motor reinnervation were studied after repair of the transected rat sciatic nerve with Y-tunnelled silicone chambers. This geometry was used experimentally to face either the proximal tibial or peroneal fascicle with two distal fascicular options usually the distal peroneal and tibial fascicle. A 4 mm gap separated the proximal and distal fascicles. Four weeks after the repair, preferential motor reinnervation could be demonstrated and there were always more axons projecting towards the distal homonymous fascicle. In contrast, if the distal stumps were disconnected from the target no fascicle specific projection of axons was observed. This was true even if segments from the median and ulnar nerve were used to replace either the distal tibial or peroneal segments. It appeared as though the size and not the type of fascicle determined the number of attracted axons. The results suggest that there is no fascicle specific guidance of regenerating nerve fibers.

Serotonin immunocytochemistry of physiologically characterized raphe magnus neurons : P. Mason A. Strassmaan and R. Maciewicz, Exp. Brain Res., 73 (1988) 1–7

Tubular prostheses support peripheral axon regeneration across gaps of up to 3 cm in the primate. However, the precision with which axons cross a gap and reinnervate the periphery remains controversial. These experiments use continuous tracing of regenerated rat sciatic nerve axons with HRP-WGA to examine the dispersion of axons as they cross a gap, and the effects on this dispersion of gap distance and fascicular orientation. Proximal and distal tibial and peroneal fascicles were precisely oriented about the longitudinal midplane of a silicon tube, with correct or reversed fascicular alignment and gaps of 2 mm and 5 mm. After 6 weeks of regeneration, HRP-WGA was applied to the distal peroneal fascicle to continuously label its reinnervating axons. These axons tended to grow straight across the tube, with dispersion increasing as a factor of distance when correct fascicular alignment was maintained. However, when fascicular alignment was reversed, axonal dispersion was determined by fascicular size rather than fascicular identity. These experiments provide noevidence for neurotropic interactions promoting “correct” fascicular reinnervation. Progressive axonal dispersion and the absence of factors to promote fascicular specificity should result in an increase of random reinnervation and functional disruption with larger gaps. An enclosed gap is not an acceptable substitute for nerve graft when reconstructing a nerve that serves multiple functions.

Chronic access to endoneurial space using an arterial autograft

A technique for direct chronic infusion of compounds onto peripheral axons has been investigated in the rat sciatic nerve. A 2 cm segment of the femoral artery was removed and one end inserted into the endoneurial space of the contralateral peroneal nerve fascicle of the same animal. The other end of the artery was connected to a catheter system to allow infusion into the endoneurium, thus bypassing the barrier that the perineurium presents to hydrophilic compounds. The patency of this arterial access system was evaluated by the ability of 20 μl of 2% lidocaine to inhibit the toe-spreading reflex. The results of the study were that the infusion system remained operational for 3–7 days after transplantation. There were histologic changes in the nerve but there were no functional deficits due to the surgery. Although a long-term endoneurial infusion was not achieved, the limited access time to the axons might be long enough for applications such as the delivery of nerve growth factors to injured nerve.

Evaluation of axonal specificity of the regenerating rat sciatic nerve using a fluorescent labeling technique.

A double-labeling technique using fluorescent compounds, i.e., diamidino yellow and true blue, is described, with the divided rat sciatic nerve model. Tibial and peroneal fascicles were transected, and each freshly cut nerve end was placed in a vial containing either the true blue or the diamidino yellow label. After a 10-15 day survival period, animals were systemically perfused with fixative, and the lumbar enlargement and dorsal root ganglia corresponding to sciatic nerve roots were removed. Serial sectioning and examination with ultraviolet fluorescence microscopy and counts of the labeled cells were performed. Diamidino yellow in labeled cells was found localized to the nucleus, whereas true blue was found localized to the cytoplasm and nucleolus (control group n = 5). Intermixing of these pools was noted, with yellow cells seen among blue labeled cells following nerve autograft repair of a 1 cm segment of the rat sciatic nerve (experimental group n = 5). Double-labeled cells displaying a yellow nucleus and a blue cytoplasmic label were also seen. We believe that the double-labeling technique described, using the fluorescent retrograde tracers diamidino yellow and true blue, is a useful monitoring method for assessing the specificity of regenerating axons in the rat sciatic nerve.

Target-specific nerve regeneration through a nerve guide in the rat.

Nerve regeneration across a gap in peripheral nerve has been achieved through various nonneural nerve guides in both lower and primate species. This technique can only be useful if the regenerated nerve cable grows specifically to and reinnervates the appropriate distal target. In this study, the proximal peroneal fascicle of rat sciatic nerve was inserted into the proximal limb of a Y-shaped nerve guide. Distal peroneal and tibial fascicles were placed within the two distal limbs of the same Y. The proximal peroneal nerve grew preferentially by a 2:1 ratio to the appropriate distal peroneal fascicle suggesting that target-specific reinnervation is possible through a nerve guide.

Responses in muscle sympathetic nerve activity to sustained hand-grips of different tensions in humans.

To clarify whether sympathetic nerve activity increases in relation to the tension of a sustained muscle contraction, muscle sympathetic nerve activity (MSA) was recorded directly from the peroneal nerve fascicle at the popliteal fossa by means of tungsten microelectrodes in five healthy male subjects. A sustained muscle contraction was performed by handgrip for two minutes in a supine position at tensions of 10, 30 and 45% of maximal grip strength (MGS). MSA, electrocardiogram (ECG) using bipolar electrodes from the chest and surface electromyogram (EMG) from the extensor pollicis longus were recorded simultaneously before and during the sustained handgrip. Arterial blood pressure was measured at the resting upper arm by auscultation. During handgrip with tensions of 10, 30 and 45% MGS, average MSA burst rate (bursts X min-1) increased to 122, 152 and 230% of the resting value, respectively. During the same experimental procedures with tensions of 10, 30 and 45% MGS, average heart rate increased to 105, 110 and 111% of the resting value. These results confirm that sympathetic outflow to a resting muscle is increased with elevation of tension in an active muscle. This process would promote perfusion pressure in the active muscle.

Sympathetic neural outflow in spinal man. A preliminary report

Microelectrode recordings were made from peroneal skin or muscle fascicles in 11 patients with traumatic spinal cord transection. Spontaneous neural activity was sparse. Both in skin and muscle nerve recordings pressure on the abdomen over the bladder, electrical skin stimulation and skin pinching below the level of the lesion gave rise to single bursts of multiunit impulse activity occurring after latencies of 0.5–1 s. Bursts were never evoked by sound stimuli or by skin stimuli applied above the level of the lesion. Bursts were unaffected by local anesthetic blocks of the nerve distal to the recording site but were abolished by proximal blocks. Conduction velocity of the bursts was approximately 0.7 m/s. After a latency of 2–5 s peroneal neural bursts were followed by cutaneous vasoconstriction and/or skin resistance reduction. Durations of vasoconstrictor responses were often much longer than in intact subjects. It is concluded that the activity was sympathetic and comprised of vasoconstrictor and sudomotor impulses of spinal origin. The parallel activation of bursts in skin and muscle fascicles suggests that sympathetic outflow from the isolated spinal cord is less differentiated than when supraspinal connections are intact. This, together with the long duration vasoconstrictor responses may contribute to the increased blood pressure during attacks of ‘autonomic hyperreflexia’.