Reinnervation of denervated skeletal muscle by central neurons regenerating via ventral roots implanted into the spinal cord

Motor recovery and the breathing arm after brachial plexus surgical repairs, including re-implantation of avulsed spinal roots into the spinal cord

Forty-four patients with severe traction brachial plexus avulsion injuries were studied following surgical repairs. In eight patients, re-implanting avulsed spinal roots directly to the spinal cord was performed with other repairs and motor recovery in the proximal limb was similar to that achieved by conventional nerve grafts and transfers when assessed using the MRC clinical grades, Narakas scores, EMG and Transcranial Magnetic Stimulation (TMS). Thirty-four of the 37 patients had co-contractions of agonist and antagonist muscle groups. Spontaneous contractions of limb muscles in synchrony with respiration, the "breathing arm", were noted in 26 of 37 patients: in three patients, the source of the breathing arm was from spinal cord re-connection, providing evidence of regeneration from the CNS to the periphery. Our study shows that re-connection of avulsed spinal roots can produce good motor recovery and provides a clinical model for developing new treatments which may enhance nerve regeneration.

Acute implantation of an avulsed lumbosacral ventral root into the rat conus medullaris promotes neuroprotection and graft reinnervation by autonomic and motor neurons

Trauma to the conus medullaris and cauda equina may result in autonomic, sensory, and motor dysfunctions. We have previously developed a rat model of cauda equina injury, where a lumbosacral ventral root avulsion resulted in a progressive and parallel death of motoneurons and preganglionic parasympathetic neurons, which are important for i.e. bladder control. Here, we report that an acute implantation of an avulsed ventral root into the rat conus medullaris protects preganglionic parasympathetic neurons and motoneurons from cell death as well as promotes axonal regeneration into the implanted root at 6 weeks post-implantation. Implantation resulted in survival of 44+/-4% of preganglionic parasympathetic neurons and 44+/-4% of motoneurons compared with 22% of preganglionic parasympathetic neurons and 16% of motoneurons after avulsion alone. Retrograde labeling from the implanted root at 6 weeks showed that 53+/-13% of surviving preganglionic parasympathetic neurons and 64+/-14% of surviving motoneurons reinnervated the graft. Implantation prevented injury-induced atrophy of preganglionic parasympathetic neurons and reduced atrophy of motoneurons. Light and electron microscopic studies of the implanted ventral roots demonstrated a large number of both myelinated axons (79+/-13% of the number of myelinated axons in corresponding control ventral roots) and unmyelinated axons. Although the diameter of myelinated axons in the implanted roots was significantly smaller than that of control roots, the degree of myelination was appropriate for the axonal size, suggesting normal conduction properties. Our results show that preganglionic parasympathetic neurons have the same ability as motoneurons to survive and reinnervate implanted roots, a prerequisite for successful therapeutic strategies for autonomic control in selected patients with acute conus medullaris and cauda equina injuries.

Novel repair strategies to restore bladder function following cauda equina/conus medullaris injuries

Trauma to the thoracolumbar junction or lumbosacral spine may result in a conus medullaris or cauda equina syndrome. In both conditions, symptoms typically include paraparesis or paraplegia, sensory impairment, pain, as well as bladder, bowel, and sexual dysfunctions. We present in this review a series of neural repair strategies that have been developed to address the unique features and challenges of subjects with a conus medullaris or cauda equina syndrome. We address, in particular, neural repair strategies that may have a translational research potential to restore bladder function. Recent animal injury models have suggested that a progressive retrograde death of both autonomic and motor neurons may contribute to the neurological deficits in subjects with conus medullaris and cauda equina injuries. For subjects with acute injuries, we present novel strategies to promote neuroprotection, axonal regeneration, and functional reinnervation of the lower urinary tract. For subjects with chronic injuries, we discuss new approaches to replace lost autonomic and motor neurons. A brief discussion on a variety of outcome measures that may be suitable to evaluate the function of the lower urinary tract in rodent neural repair models is also provided.

A single re-implanted ventral root exerts neurotropic effects over multiple spinal cord segments in the adult rat

Spinal cord injuries, particularly traumatic injuries to the conus medullaris and cauda equina, are typically complex and involve multiple segmental levels. Implantation of avulsed ventral roots into the spinal cord as a repair strategy has been shown to be neuroprotective and promote axonal regeneration by spinal cord neurons into an implanted root. However, it is not well known over what distance in the spinal cord an implanted ventral root can exert its neurotropic effect. Here, we investigated whether an avulsed L6 ventral root acutely implanted into the rat spinal cord after a four level (L5-S2) unilateral ventral root avulsion injury may exert neurotropic effects on autonomic and motor neurons over multiple spinal cord segments at 6 weeks postoperatively. Using retrograde labeling techniques and stereological quantification methods, we demonstrate that autonomic and motor neurons from all four lesioned spinal cord segments, spanning more than an 8 mm rostro-caudal distance, reinnervated the one implanted root. The rostro-caudal distribution suggested a gradient of neurotropism, where the axotomized neurons closest to the implanted site had the highest probability of root reinnervation. These results suggest that implantation of a single ventral root may provide neurotropic effects to injured neurons at the site of lesion as well as in the adjacent spinal cord segments. Our findings may be of translational research interest for the development of surgical repair strategies after multi-level conus medullaris and cauda equina injuries, in which fewer ventral roots than spinal cord segments may be available for implantation.

Spinal cord implantation with acidic fibroblast growth factor as a treatment for root avulsion in obstetric brachial plexus palsy

Nerve root avulsion carries the worst prognosis among brachial plexus injuries and remains a great challenge for surgeons to repair. In this case, a boy with complete avulsion of the left-side C6 root presented with flaccid paralysis of the left arm after birth. As there was no significant spontaneous recovery, the patient underwent operation when he was 6 months old. One end of the nerve graft from the sural nerve was anastomosed with the avulsed C6 root, and the other end was implanted into the ventrolateral aspect of the spinal cord with fibrin glue containing acidic fibroblast growth factor. After 2 years of follow-up, there has been significant improvement in motor function and in electrophysiologic studies over the left upper limb.

Management of infant brachial plexus injuries

Management of brachial plexus injuries is geared toward normalization of limb function, primarily through optimization of nerve regeneration and mechanical increase in elbow flexion and shoulder stabilization. Changes in the skeletal muscles and the osteous structures of the upper extremity are ongoing throughout the course of treatment, mandating continual assessment and aggressive rehabilitation. In patients who present too late for microsurgical intervention, irreversible changes take place in skeletal muscles, highlighting the importance of early referral. However, secondary procedures have been shown to be beneficial in older patients and in those whose primary procedures failed. Further advances in bionics and stem cell therapy may help replace the dynamic functional deficits of obstetric brachial plexus palsy.

Spinal nerve root repair and reimplantation of avulsed ventral roots into the spinal cord after brachial plexus injury

OBJECT

The authors review the first series of 10 cases in which injured intraspinal brachial plexus were surgically repaired. They describe the technique of spinal cord implantation or repair of ruptured nerve roots, as well as patient outcome.

METHODS

Spinal root repair/implantation was performed from 10 days to 9 months postinjury. There were nine male patients and one female patient. Postoperatively in most cases, regeneration of motor neurons from the spinal cord to denervated muscles could be demonstrated. The first signs of regeneration were noted approximately 9 to 12 months postoperatively. Useful function with muscle power of at least Medical Research Council Grade 3 occurred in three of 10 cases. Magnetic brain stimulation studies revealed a normal amplitude and latency from the cortex to reinnervated muscles on surgically treated and control sides. A certain degree of cocontraction between antagonistic muscles (for example, biceps-triceps) compromised function. With time there was a reduction of cocontractions, probably due to spinal cord plasticity. In these cases there was also, surprisingly, a return of sensory function, although the mechanism by which this occurred is uncertain. Sensory stimulation (thermal and mechanical) within the avulsed dermatomes was perceived abnormally and/or experienced at remote sites. There was some return of patients' sense of joint position.

CONCLUSIONS

A short time lag between the accident and the surgery was recognized as a significant factor for a successful outcome. Reimplantation of avulsed nerve roots may be combined with other procedures such as nerve transfers in severe cases of brachial plexus injury.

Selective restoration of sensation by peripheral nerve grafts directly implanted into the contralateral C7 dorsal root ganglion: an experimental study in rat brachial plexus

OBJECTIVE

In brachial plexus injuries, when the dorsal root ganglion (DRG) is avulsed from the spinal cord there is no possibility of direct repair. Therefore, in the present report the median nerve was connected directly to the contralateral C7 DRG, to restore forepaw sensation.

METHODS

The ulnar nerve was sectioned, and a 15-mm segment of nerve was removed. The median nerve was sectioned, transposed dorsally, and repaired using a sural nerve graft directly implanted into the C7 contralateral DRG. Rats were then assessed 6 and 12 months later by behavioral, histological, and plasma extravasion techniques.

RESULTS

All animals recovered sensation in the forepaw. Retrogradely labeled sensory neurons were demonstrated in the C7 DRG, and the whole forepaw was labeled after plasma extravasion induction by median nerve antidromic stimulation. Several myelinated and positively neurofilament-stained fibers were demonstrated in the grafted median nerve.

CONCLUSION

The surgical strategy proposed might be a useful alternative to selective sensory repair in the emerging field of brachial plexus reconstruction by direct spinal cord surgery.

Dorsal root repair by means of an autologous nerve graft: experimental study in the rat

Rat dorsal root regeneration was studied after 6th and 7th cervical root surgical removal and replacement with an autologous graft of peripheral nerve harvested from the surval nerve from dorsal root ganglion to dorsal horn. Histological studies showed axonal regeneration within the grafts. When the distal end of the graft was placed inside the posterior horn of the spinal cord by use of a myelotomy, axonal sprouts (revealed by the transganglionic staining method of horseradish peroxidase or HSP) reached the neurones of the posterior horn in a limited fashion.

Nerve fibre regeneration across the peripheral-central transitional zone

Neurons cannot negotiate an elongation across the peripheral (PNS)-central nervous system (CNS) transitional zone and grow into or out of the spinal cord in the mature mammal. The astrocytic rich CNS part of the spinal nerve root is most effective in preventing regeneration even of nerve fibres from transplanted embryonic ganglion cells. Regeneration of severed nerve fibres into the spinal cord occurs when the transition zone is absent as in the immature animal. Before the establishment of a transition zone there is also new growth of neuronal processes from dorsal horn neurons distally to the injured dorsal root. Thus the experimental strategy to reestablish spinal cord to peripheral nerve connectivity has been to delete the transitional region and implant severed ventral or dorsal roots into the spinal cord. Dorsal root implantation resulted in reestablished afferent connectivity by new neuronal processes from secondary sensory neurons in the dorsal horn of the spinal cord extending into the PNS. The ability for plasticity in these cells allowed for a concurrent retention of their original rostral projection. Ventral root implantation into the spinal cord corrected deficit motor function. In a long series of experiments performed in different species, the functional restitution was demonstrated to depend on an initial regrowth of motor neuron axons through spinal cord tissue (CNS). These findings have led to the design of a new surgical strategy in cases of traumatic spinal nerve root injuries.

Improved motor function of denervated rat hindlimb muscles induced by embryonic spinal cord grafts

Loss of motoneurons results in a decrease in force production by skeletal muscles and paralysis. Although it has been shown that missing motoneurons of rats can be replaced by embryonic homotopic neurons, attempts to guide their axons to their target muscles that have lost their innervation have been unsuccessful. In this study attempts were made to guide axons from grafted embryonic motoneurons to their target via a reimplanted ventral root. Adult hosts that received an embryonic graft prelabelled with 5-bromo-2'-deoxyuridine had their L4 ventral root avulsed and reimplanted into the spinal cord. Three to six months later, neurons that had their axons in the L4 ventral ramus were retrogradely labelled with fast blue and diamidino yellow. In five animals that had received an embryonic graft 116 +/- 16 cells were retrogradely labelled, and of these at least 15% were of graft origin, since they were positive for 5-bromo-2'-deoxyuridine. In five animals that had their L4 ventral root reimplanted but did not receive a graft, only 12 +/- 1.3 cells were retrogradely labelled. However, meaningful functional recovery could be achieved only if the regenerating axons of embryonic motoneurons found in the L4 ventral ramus were able to reverse the loss of force of muscles that had lost their innervation. This study shows that axons of embryonic motoneurons grafted into an adult rat spinal cord, as well as some axons of host origin, can be guided to denervated hindlimb muscles via reimplanted lumbar ventral roots. In normal rats approximately 30 motor axons innervated the extensor digitorum longus and 60 innervated the tibialis anterior via the L4 ventral root. In rats that did not receive a graft only 3.7 +/- 1.2 axons reached the extensor digitorum longus and 3.5 +/- 0.4 reached the tibialis anterior muscle via the implanted L4 ventral root. In animals that had an embryonic graft, 7.6 +/- 0.5 axons innervated the extensor digitorum longus and 8.5 +/- 0.5 reached the tibialis anterior muscle via the implanted root. In rats without a transplant the maximum tetanic tension elicited by stimulating the implanted L4 root was 16 +/- 7 g for the extensor digitorum longus and 53 +/- 36 g for the tibialis anterior muscle, whereas the corresponding muscles in animals that had an embryonic graft developed 82 +/- 16 and 281 +/- 95 g respectively. Thus it appears that the grafted motoneurons contributed to the innervation and functional recovery of the denervated muscles.

Functional recovery in primates with brachial plexus injury after spinal cord implantation of avulsed ventral roots

Intraspinal replantation of avulsed spinal nerve roots as a surgical treatment for motor deficits after severe brachial plexus injury was investigated in primates. Under general anaesthesia hemi-laminectomy was performed in cynomolgus monkeys (Macaca fascicularis). Ventral roots within the brachial plexus were then avulsed by traction and subsequently implanted into the ventrolateral aspect of the spinal cord. No dysfunction in the long fibre tracts was seen following surgery. Postoperatively there was a flaccid paralysis of the arm on the lesioned side. Severe atrophy developed within 5-7 weeks in the muscles supplied by the avulsed roots and EMG revealed denervation activity. Two to three months after surgery there were EMG signs of reinnervation, which were shortly followed by evidence of clinical recovery. A gradual improvement in the function of the affected arm occurred and the animals' motor behaviour normalised. One year after surgery there was a full range of motion in the arm, but the EMG activity in the reinnervated muscles at maximal force was reduced. Tracing of regenerated motor neurons with horseradish peroxidase (HRP) injected into the biceps muscle revealed retrogradely labelled motor neurons confined to the ipsilateral ventral horn. It was concluded that intraspinal replantation of avulsed ventral roots in primates significantly promotes motor recovery in the muscles supplied by the lesioned spinal cord segments.

Reimplantation of ventral rootlets into the cervical spinal cord after their avulsion: an anterior surgical approach

Root avulsions from the cervical spinal cord due to traction injuries are beyond repair up to the present day. An anterior surgical approach has been developed in cats for reimplantation of the ventral rootlets into the site of avulsion. The consecutive surgical steps towards exposure of the ventral surface of the cervical cord are given in detail. The morphological relations during the operative procedure are explained in the text and by illustrations. In this study the surgery related mortality rate was 16% and the overall mortality rate amounted to 21%. Loss of blood, initially a major problem, was coped with by increasing technical experience and the infusion of plasma expanding fluid. In 2 animals with survival times of 209 and 293 days respectively, many ventral horn motoneurons were found HRP-positive after retrograde HRP transport through the site of reimplantation. The findings provide evidence that the axonal continuity between reimplanted ventral roots and their motoneurons may be restored.

Novel surgical strategies to correct neural deficits following experimental spinal nerve root lesions

In attempts to correct neural deficits following avulsion trauma, novel experimental strategies were developed. In rats, spinal roots were replanted superficially in the dorsal horn following dorsal root avulsion and concomitant denervation by ganglionectomy. Outgrowth from cord neurons in the dorsal horn into the implanted dorsal root was demonstrated by means of retrograde HRP labeling. Double labeling experiments showed that some of these neurons had retained their central projections while extending new processes into the implanted root. After dorsal root avulsion, sensory pathways might be reconstructed by substituting the lost input from damaged primary sensory neurons with induced peripheral outgrowths from secondary neurons. In primates, intraspinal replantation of avulsed ventral nerve roots was investigated as a surgical treatment for motor deficits that develop after severe brachial plexus injury. Two to 3 months after surgery there were EMG signs of reinnervation in previously denervated muscles, which were shortly followed by evidence of clinical recovery. A gradual improvement in the function of the affected arm occurred and motor behavior became normalized, although the EMG activity in the reinnervated muscles at maximal contraction was still reduced. The outcome of these experimental studies indicates that reconstructive surgery applied to the brachial plexus might be of value to restore functional deficits induced by traumatic spinal nerve root avulsions also in man.