Creation of a biological sensorimotor interface for bionic reconstruction.

Neuromuscular control of bionic arms has constantly improved over the past years, however, restoration of sensation remains elusive. Previous approaches to reestablish sensory feedback include tactile, electrical, and peripheral nerve stimulation, however, they cannot recreate natural, intuitive sensations. Here, we establish an experimental biological sensorimotor interface and demonstrate its potential use in neuroprosthetics. We transfer a mixed nerve to a skeletal muscle combined with glabrous dermal skin transplantation, thus forming a bi-directional communication unit in a rat model. Morphological analyses indicate reinnervation of the skin, mechanoreceptors, NMJs, and muscle spindles. Furthermore, sequential retrograde labeling reveals specific sensory reinnervation at the level of the dorsal root ganglia. Electrophysiological recordings show reproducible afferent signals upon tactile stimulation and tendon manipulation. The results demonstrate the possibility of surgically creating an interface for both decoding efferent motor control, as well as encoding afferent tactile and proprioceptive feedback, and may indicate the way forward regarding clinical translation of biological communication pathways for neuroprosthetic applications.

Characterization, number, and spatial organization of nerve fibers in the human cervical vagus nerve and its superior cardiac branch.

BACKGROUND: Electrical stimulation of the vagus nerve (VN) is a therapy for epilepsy, obesity, depression, and heart diseases. However, whole nerve stimulation leads to side effects. We examined the neuroanatomy of the mid-cervical segment of the human VN and its superior cardiac branch to gain insight into the side effects of VN stimulation and aid in developing targeted stimulation strategies. METHODS: Nerve specimens were harvested from eight human body donors, then subjected to immunofluorescence and semiautomated quantification to determine the signature, quantity, and spatial distribution of different axonal categories. RESULTS: The right and left cervical VN (cVN) contained a total of 25,489 ± 2781 and 23,286 ± 3164 fibers, respectively. Two-thirds of the fibers were unmyelinated and one-third were myelinated. About three-quarters of the fibers in the right and left cVN were sensory (73.9 ± 7.5 % versus 72.4 ± 5.6 %), while 13.2 ± 1.8 % versus 13.3 ± 3.0 % were special visceromotor and parasympathetic, and 13 ± 5.9 % versus 14.3 ± 4.0 % were sympathetic. Special visceromotor and parasympathetic fibers formed clusters. The superior cardiac branches comprised parasympathetic, vagal sensory, and sympathetic fibers with the left cardiac branch containing more sympathetic fibers than the right (62.7 ± 5.4 % versus 19.8 ± 13.3 %), and 50 % of the left branch contained sensory and sympathetic fibers only. CONCLUSION: The study indicates that selective stimulation of vagal sensory and motor fibers is possible. However, it also highlights the potential risk of activating sympathetic fibers in the superior cardiac branch, especially on the left side.

Axonal mapping of the motor cranial nerves.

Basic behaviors, such as swallowing, speech, and emotional expressions are the result of a highly coordinated interplay between multiple muscles of the head. Control mechanisms of such highly tuned movements remain poorly understood. Here, we investigated the neural components responsible for motor control of the facial, masticatory, and tongue muscles in humans using specific molecular markers (ChAT, MBP, NF, TH). Our findings showed that a higher number of motor axonal population is responsible for facial expressions and tongue movements, compared to muscles in the upper extremity. Sensory axons appear to be responsible for neural feedback from cutaneous mechanoreceptors to control the movement of facial muscles and the tongue. The newly discovered sympathetic axonal population in the facial nerve is hypothesized to be responsible for involuntary control of the muscle tone. These findings shed light on the pivotal role of high efferent input and rich somatosensory feedback in neuromuscular control of finely adjusted cranial systems.

Nerve transfer reversal to treat co-contraction after anatomic brachial plexus reconstruction and Oberlin transfer: A case report.

Distal nerve transfers to restore elbow flexion have become standard of care in brachial plexus reconstruction. The purpose of this report is to draw attention to intractable co-contraction as a rare but significant adverse event of distal nerve transfers. Here we report of treatment of a disabling co-contraction of the brachialis muscle and wrist/finger flexors after median to brachialis fascicular transfer in a 61-year-old male patient. The primary injury was an postganglionic lesion of roots C5/C6 and a preganglionic injury of C7/C8 with intact root Th1 after a motor bicycle accident. After upper brachial plexus reconstruction (C5/C6 to suprascapular nerve and superior trunk) active mobility in the shoulder joint (supraspinatus, deltoid) could be restored. However, due to lacking motor recovery of elbow flexion the patient underwent additional median to brachialis nerve transfer. Shortly after, active elbow flexion commenced with rapid recovery to M4 at 9 months postoperatively. However, despite intensive EMG triggered physiotherapy the patient could not dissociate hand from elbow function and was debilitated by this iatrogenic co-contraction. After preoperative ultrasound-guided block resulted in preserved biceps function, the previously transferred median nerve fascicle was reversed. This was done by dissecting the previous nerve transfer of the median nerve fascicle to the brachialis muscle branch and adapting the fascicles to their original nerve. Postoperatively, the patient was followed up for 10 months without a complication and maintained M4 elbow flexion with independent strong finger flexion. Distal nerve transfers are an excellent option to restore function, however, in some patients cognitive limitations may prevent cortical reorganization and lead to disturbing co-contractions.

Axonal mapping of motor and sensory components within the ulnar nerve and its branches.

OBJECTIVE: Intrinsic function is indispensable for dexterous hand movements. Distal ulnar nerve defects can result in intrinsic muscle dysfunction and sensory deficits. Although the ulnar nerve's fascicular anatomy has been extensively studied, quantitative and topographic data on motor axons traveling within this nerve remain elusive. METHODS: The ulnar nerves of 14 heart-beating organ donors were evaluated. The motor branches to the flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP) muscles and the dorsal branch (DoBUN) as well as 3 segments of the ulnar nerve were harvested in 2-cm increments. Samples were subjected to double immunofluorescence staining using antibodies against choline acetyltransferase and neurofilament. RESULTS: Samples revealed more than 25,000 axons in the ulnar nerve at the forearm level, with a motor axon proportion of only 5%. The superficial and DoBUN showed high axon numbers of more than 21,000 and 9300, respectively. The axonal mapping of more than 1300 motor axons revealed an increasing motor/sensory ratio from the proximal ulnar nerve (1:20) to the deep branch of the ulnar nerve (1:7). The motor branches (FDP and FCU) showed that sensory axons outnumber motor axons by a ratio of 10:1. CONCLUSIONS: Knowledge of the detailed axonal architecture of the motor and sensory components of the human ulnar nerve is of the utmost importance for surgeons considering fascicular grafting or nerve transfer surgery. The low number of efferent axons in motor branches of the ulnar nerve and their distinct topographical distribution along the distal course of the nerve is indispensable information for modern nerve surgery.

Newly identified axon types of the facial nerve unveil supplemental neural pathways in the innervation of the face.

INTRODUCTION: Neuromuscular control of the facial expressions is provided exclusively via the facial nerve. Facial muscles are amongst the most finely tuned effectors in the human motor system, which coordinate facial expressions. In lower vertebrates, the extracranial facial nerve is a mixed nerve, while in mammals it is believed to be a pure motor nerve. However, this established notion does not agree with several clinical signs in health and disease. OBJECTIVES: To elucidate the facial nerve contribution to the facial muscles by investigating axonal composition of the human facial nerve. To reveal new innervation pathways of other axon types of the motor facial nerve. METHODS: Different axon types were distinguished using specific molecular markers (NF, ChAT, CGRP and TH). To elucidate the functional role of axon types of the facial nerve, we used selective elimination of other neuronal support from the trigeminal nerve. We used retrograde neuronal tracing, three-dimensional imaging of the facial muscles, and high-fidelity neurophysiological tests in animal model. RESULTS: The human facial nerve revealed a mixed population of only 85% motor axons. Rodent samples revealed a fiber composition of motor, afferents and, surprisingly, sympathetic axons. We confirmed the axon types by tracing the originating neurons in the CNS. The sympathetic fibers of the facial nerve terminated in facial muscles suggesting autonomic innervation. The afferent fibers originated in the facial skin, confirming the afferent signal conduction via the facial nerve. CONCLUSION: These findings reveal new innervation pathways via the facial nerve, support the sympathetic etiology of hemifacial spasm and elucidate clinical phenomena in facial nerve regeneration.

Spinal cord from body donors is suitable for multicolor immunofluorescence.

Immunohistochemistry is a powerful tool for studying neuronal tissue from humans at the molecular level. Obtaining fresh neuronal tissue from human organ donors is difficult and sometimes impossible. In anatomical body donations, neuronal tissue is dedicated to research purposes and because of its easier availability, it may be an alternative source for research. In this study, we harvested spinal cord from a single organ donor 2 h (h) postmortem and spinal cord from body donors 24, 48, and 72 h postmortem and tested how long after death, valid multi-color immunofluorescence or horseradish peroxidase (HRP) immunohistochemistry is possible. We used general and specific neuronal markers and glial markers for immunolabeling experiments. Here we showed that it is possible to visualize molecularly different neuronal elements with high precision in the body donor spinal cord 24 h postmortem and the quality of the image data was comparable to those from the fresh organ donor spinal cord. High-contrast multicolor images of the 24-h spinal cords allowed accurate automated quantification of different neuronal elements in the same sample. Although there was antibody-specific signal reduction over postmortem intervals, the signal quality for most antibodies was acceptable at 48 h but no longer at 72 h postmortem. In conclusion, our study has defined a postmortem time window of more than 24 h during which valid immunohistochemical information can be obtained from the body donor spinal cord. Due to the easier availability, neuronal tissue from body donors is an alternative source for basic and clinical research.

Autonomic nerve fibers aberrantly reinnervate denervated facial muscles and alter muscle fiber population.

The surgical redirection of efferent neural input to a denervated muscle via a nerve transfer can reestablish neuromuscular control after nerve injuries. The role of autonomic nerve fibers during the process of muscular reinnervation remains largely unknown. Here, we investigated the neurobiological mechanisms behind the spontaneous functional recovery of denervated facial muscles in male rodents. Recovered facial muscles demonstrated an abundance of cholinergic axonal endings establishing functional neuromuscular junctions. The parasympathetic source of the neuronal input was confirmed to be in the pterygopalatine ganglion. Furthermore, the autonomically reinnervated facial muscles underwent a muscle fiber change to a purely intermediate muscle fiber population (MHCIIa). Finally, electrophysiological tests revealed that the postganglionic parasympathetic fibers travel to the facial muscles via the sensory infraorbital nerve. Our findings demonstrated expanded neuromuscular plasticity of denervated striated muscles enabling functional recovery via alien autonomic fibers. These findings may further explain the underlying mechanisms of sensory protection implemented to prevent atrophy of a denervated muscle.SIGNIFICANCE STATEMENT:Nerve injuries represent significant morbidity and disability for patients. Rewiring motor nerve fibers to other target muscles have shown to be a successful approach in the restoration of motor function. This demonstrates the remarkable capacity of the central nervous system to adapt to the needs of the neuromuscular system. Yet, the capability of skeletal muscles being reinnervated by non-motor axons remains largely unknown. Here, we show that under deprivation of original efferent input, the neuromuscular system can undergo functional and morphological remodeling via autonomic nerve fibers. This may explain neurobiological mechanisms of the sensory protection phenomenon, which is due to parasympathetic reinnervation.

Proof of concept for multiple nerve transfers to a single target muscle.

Surgical nerve transfers are used to efficiently treat peripheral nerve injuries, neuromas, phantom limb pain, or improve bionic prosthetic control. Commonly, one donor nerve is transferred to one target muscle. However, the transfer of multiple nerves onto a single target muscle may increase the number of muscle signals for myoelectric prosthetic control and facilitate the treatment of multiple neuromas. Currently, no experimental models are available. This study describes a novel experimental model to investigate the neurophysiological effects of peripheral double nerve transfers to a common target muscle. In 62 male Sprague-Dawley rats, the ulnar nerve of the antebrachium alone (n=30) or together with the anterior interosseus nerve (n=32) was transferred to reinnervate the long head of the biceps brachii. Before neurotization, the motor branch to the biceps' long head was transected at the motor entry point. Twelve weeks after surgery, muscle response to neurotomy, behavioral testing, retrograde labeling, and structural analyses were performed to assess reinnervation. These analyses indicated that all nerves successfully reinnervated the target muscle. No aberrant reinnervation was observed by the originally innervating nerve. Our observations suggest a minimal burden for the animal with no signs of functional deficit in daily activities or auto-mutilation in both procedures. Furthermore, standard neurophysiological analyses for nerve and muscle regeneration were applicable. This newly developed nerve transfer model allows for the reliable and standardized investigation of neural and functional changes following the transfer of multiple donor nerves to one target muscle.

Selective Denervation of the Facial Dermato-Muscular Complex in the Rat: Experimental Model and Anatomical Basis.

The facial dermato-muscular system consists of highly specialized muscles tightly adhering to the overlaying skin and thus form a complex morphological conglomerate. This is the anatomical and functional basis for versatile facial expressions, which are essential for human social interaction. The neural innervation of the facial skin and muscles occurs via branches of the trigeminal and facial nerves. These are also the most commonly pathologically affected cranial nerves, often requiring surgical treatment. Hence, experimental models for researching these nerves and their pathologies are highly relevant to study pathophysiology and nerve regeneration. Experimental models for the distinctive investigation of the complex afferent and efferent interplay within facial structures are scarce. In this study, we established a robust surgical model for distinctive exploration of facial structures after complete elimination of afferent or efferent innervation in the rat. Animals were allocated into two groups according to the surgical procedure. In the first group, the facial nerve and in the second all distal cutaneous branches of the trigeminal nerve were transected unilaterally. All animals survived and no higher burden was caused by the procedures. Whisker pad movements were documented with video recordings 4 weeks after surgery and showed successful denervation. Whole-mount immunofluorescent staining of facial muscles was performed to visualize the innervation pattern of the neuromuscular junctions. Comprehensive quantitative analysis revealed large differences in afferent axon counts in the cutaneous branches of the trigeminal nerve. Axon number was the highest in the infraorbital nerve (28,625 ± 2,519), followed by the supraorbital nerve (2,131 ± 413), the mental nerve (3,062 ± 341), and the cutaneous branch of the mylohyoid nerve (343 ± 78). Overall, this surgical model is robust and reliable for distinctive surgical deafferentation or deefferentation of the face. It may be used for investigating cortical plasticity, the neurobiological mechanisms behind various clinically relevant conditions like facial paralysis or trigeminal neuralgia as well as local anesthesia in the face and oral cavity.

Effect of conventional and rapid-deployment aortic valve replacement on the distance from the aortic annulus to coronary arteries.

OBJECTIVES: This study aimed to compare the effect of surgical aortic valve replacement (SAVR) on coronary height in patients undergoing SAVR with rapid-deployment or SAVR with several standard sutured bioprostheses. This study may identify patients at higher risk of coronary obstruction during valve-in-valve procedures. METHODS: We analysed 112 patients [mean age 71 (9 SD) years] who underwent SAVR with either a rapid-deployment aortic bioprosthesis (EDWARDS INTUITY Elite Valve) or other standard sutured biological valves. The coronary heights were assessed by computed tomography scan with the Philips 3D HeartNavigator system. RESULTS: Two groups of patients were analysed: 51 (45.5%) patients implanted with an RD-AVR, which is a supra-annular valve that requires 3 anchoring sutures without the use of pledgets, and 61 (54.5%) patients implanted with a conventional supra-annular sutured bioprosthesis. The mean right and left coronary artery-to-annulus (RCAA and LCAA) heights at baseline were 16.9 (4.6 SD) and 14.2 (4.0 SD) mm in the standard sutured group and 16.3 (3.5 SD) and 12.8 (2.9 SD) mm in the RD-AVR group, respectively; a significantly shorter distance was observed for the left coronary artery in the rapid-deployment group (P = 0.420 for RCAA height and P = 0.044 for LCAA). Postoperatively, the mean RCAA and LCAA heights were significantly decreased in both groups compared to baseline. A mean of 11.5 (4.8 SD) mm for the RCAA and 7.9 (4.3 SD) mm for the LCAA in the standard sutured group as well as 14.4 (3.9 SD) mm for the RCAA and 9.0 (3.1 SD) mm for the LCAA in the RD-AVR group were observed (P < 0.001 for RCAA and LCAA in both the sutured and rapid-deployment groups). Despite the significant difference in the mean distance from the left coronary artery to annulus between the groups at baseline, the postoperative mean distance of the LCAA to the sewing ring was still higher in the RD-AVR group. CONCLUSIONS: A significantly shorter coronary artery-to-aortic annulus distance for both the right and left main coronary arteries was observed after AVR with different conventional sutured supra-annular bioprostheses compared to AVR with rapid-deployment valves. These findings might be relevant for bioprosthesis selection, especially for young patients.