Transient Reinnervation of Antagonistic Muscles by the Same Motoneuron

When reinnervation is allowed after a sciatic nerve cut in the adult rat, motoneuron axons may branch to innervate antagonistic muscles. This multiple innervation is widespread, but transient. Fourteen weeks after denervation isometric muscle contraction experiments and studies with anterograde transport of the fluorescent tracer Fast Blue showed that branches from the same motoneurons reached the distal part of the tibial nerve and either the soleus or the extensor digitorum longus muscles or both muscles. Retrogradely double-labeled motoneurons were found after injections of different fluorescent tracers into these muscles. Sixty-four to 88 weeks after the nerve cut, similar experiments showed that selective innervation was reestablished. The findings suggest a selective mechanism for axon withdrawal in an adult mammal.     

Innervation and Properties of the Rat FDSBQ Muscle: An Animal Model to Evaluate Voluntary Muscle Strength after Incomplete Spinal Cord Injury

Muscles innervated from spinal segments close to the site of a human spinal cord injury are often under voluntary control but are weak because they are partially paralyzed and partially denervated. Our objective was to develop an animal model of this clinical condition to evaluate strategies to improve voluntary muscle strength. To do so, we examined the spinal and peripheral innervation of the flexor digitorum superficialis brevis quinti (FDSBQ) muscle of the rat foot, characterized the muscle and motor unit properties, and located the FDSBQ motoneurons. Retrograde labeled motoneurons were in L4 to L6 spinal cord. Unilateral stimulation of L4 to S1 ventral roots and recording of evoked force showed that FDSBQ motor axons exited via two ventral roots (L5 and L6 or L6 and S1) in 38% of rats and via one ventral root in 62% of rats. FDSBQ motor axons traveled via two peripheral nerves, the lateral plantar (76% of axons) and sural nerves (24%). Each ventral root contributed motor axons to each nerve branch. Thus, by combining conduction block of one peripheral nerve to induce partial muscle paralysis and ventral root section to induce partial denervation, it is possible to produce in one rat muscle the consequences of many human cervical spinal cord injuries. FDSBQ muscles and motor units were mainly fast-twitch, fatigable, and composed of fast-type muscle fibers. The narrow range of motor unit forces (1-13 mN), the low mean twitch force (5.1 +/- 0.3 mN), and the large number of motoneurons (31 +/- 4) suggest that rat FDSBQ muscle is a good model of distal human musculature which is frequently influenced by spinal cord injury. We conclude that the FDSBQ muscle and its innervation provide a useful animal model in which to study the consequences of many spinal cord injuries which spare some descending inputs but also induce substantial motoneuron death near the lesion.     

Crossing dendrites may be a substrate for synchronized activation of penile motoneurons

The morphology of perineal and extensor hindlimb motoneurons in adult male rats was examined using retrograde labelling with wheat germ agglutinin and horseradish peroxidase. Bulbocavernosus and levator ani motoneurons, located in the spinal nucleus of the bulbocavernosus, were organized as distinct clusters of motoneurons in the medial ventral area of the lumbar (L6-L5) spinal cord and possessed prominent contralaterally projecting dendritic arborizations. In similar experiments, laterally located soleus and extensor digitorum longus motoneurons did not exhibit a similar organization. These findings are discussed with respect to their possible role in the synchronized bilateral activation of penile muscles.     

Motor, sympathetic and sensory innervation of rat skeletal muscles

This study reports on the location, number and size of motor, sympathetic and sensory neurons innervating the following muscles of rat: quadriceps femoris (QF), tibialis anterior (TA), extensor digitorum longus (EDL), peroneus longus (PL), gastrocnemius medius (GM) and soleus (SOL). Cells were labelled by application of horseradish peroxidase (HRP) to transected muscle nerves. Counts of neurons were compared with counts of myelinated (MF) and unmyelinated (UMF) fibers in normal, deafferented and chemically sympathectomized nerves. The topographical arrangement of spinal motor nuclei resembled that reported previously in other mammals and birds. Sensory somata were aggregated without precise somatotopic organization, preferentially in one of the lumbar dorsal root ganglia at a segmental level corresponding to that of the motor innervation. Because lumbar sympathetic ganglia were often poorly circumscribed, the segmental position of sympathetic ganglion cells could not be localized with certainty. Sensory and sympathetic somata demonstrated a unimodal size-frequency distribution, while QF, TA and PL motoneurons could be subdivided according to size in alpha and gamma cells. For all muscles except unsuccessfully deafferented QF, counts of motor fibers after deafferentation correlated closely with counts of labelled motoneurons. Similarly, estimates of sympathetic axons, averaging 30,7% of the UMF, in most instances exceeded only marginally the ganglion cell population. In contrast, the number of peripheral afferent fibers outnumbered markedly that of sensory cell bodies, with an average of 2.8 axons per ganglion cell.     

Survival, regeneration and functional recovery of motoneurons in adult rats by reimplantation of ventral root following spinal root avulsion

We investigated the functional recovery of motoneurons after reimplanting an avulsed ventral root in a rat model of traction injury. The eighth cervical root (C8) was avulsed by controlled traction and immediately reimplanted to the spinal cord. Spinal nerves from neighbouring segments (C5, C6, C7 and T1) were ligated and cut. After 12 or 20 weeks, the survival, regeneration and functional recovery of spinal motoneurons were evaluated by Nissl staining, retrograde labelling of motoneurons, NOS histochemistry, histological examination of muscle and nerve-muscle junction, electromyography and behavioural observation. In the control animals, about 14% or 11% of spinal motoneurons survived 12 or 20 weeks postinjury, respectively. By contrast, in animals with ventral root reimplantation, 62% and 55% of motoneurons survived at 12 or 20 weeks postinjury, respectively. Retrograde labelling and histological examination indicated that about 90% of the surviving motoneurons in the C8 segment regenerated axons into the reimplanted ventral root. Staining the muscles with silver and cholinesterase revealed new motor endplates in the reinnervated muscle. Functionally significant electromyographic responses in flexor digitorum superficialis and flexor carpi radialis were observed in experimental animals; however, the average latency of the motor action potentials was greater than normal control. The grasping test showed functional recovery of finger flexors and median nerve. In conclusion, our results indicate that spinal motoneurons can regenerate axons through reimplanted roots and reinnervate muscles to recover partial function.     

The effect of riluzole treatment in rats on the survival of injured adult and grafted embryonic motoneurons

The effect of riluzole on the survival of injured motoneurons was studied. The L4 ventral root was avulsed and reimplanted into the spinal cord. Immediately after the operation, 4 animals were treated with riluzole for 3 weeks while another 4 animals received no treatment after the operation. Three months later the fluorescent dyes, Fast Blue and Diamidino Yellow, were applied to the cut ventral ramus of the L4 spinal nerve, for retrograde labelling of neurons. Three days later, the spinal cords were processed to reveal the retrograde-labelled cells. In untreated animals, there were 20 +/- 2.1 labelled neurons (+/- SEM), while in animals treated with riluzole there were 723 +/- 26. Thus, treatment with riluzole dramatically enhanced the survival of injured motoneurons. In another series of experiments, after avulsion of the L4 ventral root and its reinsertion, embryonic spinal cord pieces were grafted into the host cord. Five animals received riluzole treatment and 4 were left untreated. In the untreated animals, 125 +/- 5.1 retrograde-labelled cells of both graft and host origin were detected. In rats treated with riluzole, 645 +/- 35.7 retrograde-labelled cells were seen and almost all of these were of host origin. Thus, treatment with riluzole enhanced the survival of injured host motoneurons, and by doing so, (i) reduced the ability of grafted neurons to extend their axons into the reimplanted L4 ventral root, and (ii) reduced the survival of the grafted cells.     

Fetal-type creatine kinase in rat fast and slow muscles during denervation and reinnervation

Creatine kinase (CK) has three forms of isozymes; CK-BB, CK-MB, and CK-MM. In adult rats they show a specific tissue distribution: the BB form in the brain, the MB form in the heart, and the MM form in skeletal muscle. In embryonic skeletal muscles only the BB and MB forms are found. Adult slow-twitch muscles contain more fetal type creatine kinase (CK-B) than do fast-twitch muscles. In the present experiment the effect of denervation and reinnervation on the CK-B concentration was investigated in rat fast (extensor digitorum longus)- and slow (soleus)-twitch muscles by a highly sensitive immunoassay. Denervation of these muscles produced a progressive increase in CK-B concentration in both muscles. When the sciatic nerve was cut and immediately sutured, the CK-B concentration in both muscles showed a gradual reduction after an initial increase. By the 34th postoperative week the CK-B concentration in the soleus was about one-half that of the contralateral control, whereas that in the extensor digitorum longus was nearly normal. After cross union of the nerves innervating the muscles, the CK-B concentration in the soleus was reduced at 35 weeks to about one-half normal, but that in the extensor digitorum longus was always higher than the control value. After self-reunion of the nerves, the CK-B concentration at the 20th week was approximately normal in the extensor digitorum longus and significantly increased in the soleus. We suggest that the motoneurons normally innervating the extensor digitorum longus have a greater capability in suppressing the production of CK-B than do the soleus motoneurons.     

Repeated injury to the sciatic nerve in immature rats causes motoneuron death and impairs muscle recovery

Injury to the sciatic nerve of newborn rats causes motoneuron death, while the same insult inflicted 5 days later does not. In this study the effects of prolonging the period of target deprivation and axonal regeneration were investigated by inflicting a second nerve crush 6 days after the first, just before reinnervation of the muscle occurred. Two to 4 months later the number of motoneurons supplying soleus, tibialis anterior, and extensor digitorum longus muscles was established by retrograde labeling with horseradish peroxidase injected into the muscle. After nerve injury at 5 days there was no significant loss of motoneurons to any muscle. However, when the injury was repeated, the number of labeled motoneurons was reduced, suggesting that a significant proportion had died. Motoneurons to soleus were affected more than those to the fast muscles, reflecting their lesser maturity. Moreover, motoneurons to soleus that survived both injuries to their axon failed to grow to their full size. The relative impairment of recovery of the muscles, indicated by weight and maximal tetanic tension, mirrored the loss of motoneurons in each case. Previous studies have suggested that repeated nerve injuries in adult animals can enhance reinnervation. However, the present results along with those of other recent studies suggest that immature motoneurons that are repeatedly induced to support growth of their axons are at greater risk of death and can result in poorer reinnervation of the muscles.     

Morphological relationships among extensor digitorum longus, tibialis anterior, and semitendinosus motor nuclei of the cat: an investigation employing the retrograde transport of multiple fluorescent tracers.

To determine the morphological relationships among extensor digitorum longus (EDL), tibialis anterior (TA), and semitendinosus (St) motor nuclei in the spinal cord of the cat, these nuclei were retrogradely labeled with three different fluorescent tracers. The fluorochromes--bisbenzimide, nuclear yellow, and propidium iodide--were applied by intramuscular injection or soaking the muscle nerve. The positions of the labeled motor nuclei were bilaterally symmetrical. The EDL and TA motoneurons were located in close proximity to one another, in the lateral regions of lamina IX in spinal segments L6 and L7. Although the boundaries of each nucleus were tightly opposed, the EDL and TA motor nuclei overlapped minimally, with the somata of EDL motoneurons positioned dorsal to those of TA. The St motor nucleus was located ventromedial to that of EDL and extended from the caudal portion of L6 through S1. Supplemental studies of the reflex effects evoked in EDL, TA, and St muscles by cutaneous nerve stimulation provided physiological observations that may be related to these anatomical results.     

Electrophysiologic mapping of the segmental anatomy of the muscles of the lower extremity.

Our knowledge of the specific root innervation of skeletal muscles is derived from accumulated clinical experience. While performing selective posterior rhizotomy for treatment of spasticity in children with cerebral palsy, we made direct electrophysiologic measurement of the root innervation of the lower extremity. We stimulated ventral roots from L2 to S2 while recording from all muscles simultaneously. The size of the evoked compound muscle action potential was used as an indication of the amount of innervation derived from stimulation of a given spinal root. We found the major root innervation for the 8 muscles studied to be: adductor longus, vastus medialis, and vastus lateralis, L3; tibialis anterior; L4; peroneus longus, L5; and medial gastrocnemius, lateral gastrocnemius, and gluteus maximus, S1. In general, each muscle received innervation from 3 or more roots. Prefixed or postfixed innervation patterns were found in 27.9% of legs examined, and there was asymmetry of innervation in 29.8%. We conclude that the segmental innervation of lower extremity muscles is broader than previously thought. Anomalous innervation occurs so frequently that caution should be used in attributing any pattern of clinical or EMG findings to a specific spinal level.     

Survival, regeneration and functional recovery of motoneurons after delayed reimplantation of avulsed spinal root in adult rat

We have established that extensive reinnervation and functional recovery follow immediate reimplantation of avulsed ventral roots in adult rats. In the present study, we examined the consequences of reimplantation delayed for 2 weeks after avulsion of the C6 spinal root. Twelve and 20 weeks after delayed reimplantation, 57% and 53% of the motoneurons in the injured spinal segment survived. More than 80% of surviving motoneurons regenerated axons into the reimplanted spinal root. Cholinesterase-silver staining revealed axon terminals on endplates in the denervated muscles. The biceps muscles in reimplanted animals had atrophied less than those in animals with avulsion only, as indicated by muscle wet weight and histological appearance. After electrical stimulation of the motor cortex or the C6 spinal root, typical EMG signals were recorded in biceps of reimplanted animals. The latency of the muscle potential at 20 weeks was similar to that of sham-operated controls. Behavioral recovery was demonstrated by a grooming test and ipsilateral forepaw movements were well coordinated in both voluntary and automatic activities. These results demonstrate that ventral root reimplantation can protect severed motoneurons, enable the severed motoneurons to regenerate axons, and enhance the recovery of forelimb function even when it is delayed for 2 weeks after avulsion.     

Transplantation of embryonic neurones to replace missing spinal motoneurones

Loss of spinal motoneurones results in severe functional impairment. The most successful way to replace missing motoneurones is the use of embryonic postmitotic motoneurone grafts. It has been shown that grafted motoneurones survive, differentiate and integrate into the host cord. If grafted motoneurones are provided with a suitable conduit for axonal regeneration (e.g. a reimplanted ventral root) the grafted cells are able to grow their axons along the whole length of the peripheral nerves to reach muscles in the limb and restore function. Grafted motoneurones show excellent survival in motoneurone-depleted adult host cords, but the developing spinal cord appears to be an unfavourable environment for these cells. The long term survival and maturation of the grafted neurones are dependent on the availability of a nerve conduit and one or more target muscles, no matter whether these are ectopic nerve-muscle implants or limb muscles in their original place. Thus, grafted and host motoneurones induce functional recovery of the denervated limb muscles when their axons regenerate into an avulsed and reimplanted ventral root. On the other hand, motoneurone-enriched embryonic grafts placed into a hemisection cavity in the cervical spinal cord induce axonal regeneration from great numbers of host motoneurones, possibly by the bridging effect of the grafts. In this case the regenerating host motoneurones reinnervate their original target muscles while the graft provides few axons for the reinnervation of muscles. These results suggest that reconstruction of the injured spinal cord with embryonic motoneurone-enriched spinal cord graft is a feasible method to improve severe functional motor deficits.     

A spatio-temporal analysis of motoneuron survival, axonal regeneration and neurotrophic factor expression after lumbar ventral root avulsion and implantation

Reimplantation of avulsed rat lumbar spinal ventral roots results in poor recovery of function of the denervated hind limb muscles. In contrast, reimplantation of cervical or sacral ventral roots is a successful repair strategy that results in a significant degree of regeneration. A possible explanation for this difference could be that following lumbar root avulsion, axons have to travel longer distances towards their target muscles, resulting in prolonged denervation of the distal nerve and a diminished capacity to support regeneration. Here we present a detailed spatio-temporal analysis of motoneuron survival, axonal regeneration and neurotrophic factor expression following unilateral avulsion and implantation of lumbar ventral roots L3, L4, and L5. Reimplantation prolongs the survival of motoneurons up to one month post-lesion. The first regenerating motor axons entered the reimplanted ventral roots during the first week and large numbers of fibers gradually enter the lumbar plexus between 2 and 4 weeks, indicating that axons enter the reimplanted roots and plexus over an extended period of time. However, motor axon counts show that relatively few axons reach the distal sciatic nerve in the 16 week post-lesion period. The observed initial increase and subsequent decline in expression of glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor correlate with the apparent spatio-temporal decline in the regenerative capacity of motor axons, indicating that the distal nerve is losing its capacity to support regenerating motor axons following prolonged denervation. These findings have important implications for future strategies to promote long-distance regeneration through distal, chronically denervated peripheral nerves.     

α-CGRP mRNA levels in motoneurons innervating specific rat muscles

Along with acetylcholine, motoneurons express several neuromodulatory peptides. The most extensively studied of these peptides is calcitonin gene-related peptide (CGRP). CGRP modulates the biochemical, physiological and metabolic properties of skeletal muscle primarily through activation of membrane receptors. Virtually all motor pool contain motoneurons that are immunoreactive for CGRP. The purpose of this study was to determine the proportions of motoneurons that express α-CGRP in motor pools innervating muscles with different motor unit compositions. These include the soleus, extensor digitorum longus, tensor fascia latae and the diaphragm muscles as well as the spinal nucleus of the bulbocavernosus. The spinal nucleus of the bulbocavernosus provides innervation to the bulbocavernosus/levator ani muscle complex and the external anal sphincter muscle. The spinal nucleus of the bulbocavernosus contained the greatest proportion of α-CGRP mRNA-positive motoneurons, followed in descending rank order by the tensor fascia latae, the extensor digitorum longus, the soleus and the diaphragm motor pools. In addition, significant differences between motor pools were observed in the mean relative α-CGRP mRNA level among those motoneurons expressing α-CGRP. The highest mean relative α-CGRP mRNA level was observed in soleus and the extensor digitorum longus motor pools; followed in descending rank order by the tensor fascia latae, the diaphragm and the spinal nucleus of the bulbocavernosus. We have previously shown that muscle contractile inactivity increases the number of motoneurons that express α-CGRP and in the relative mRNA levels. The results of the present study suggest that the proportion of motoneurons within a motor pool that express α-CGRP may be closely related to the contractile activity (i.e. activation history) of the target muscle.     

Neuroprotection and Axonal Regeneration After Lumbar Ventral Root Avulsion by Re-implantation and Mesenchymal Stem Cells Transplant Combined Therapy

Ventral spinal root avulsion causes complete denervation of muscles in the limb and also progressive death of segmental motoneurons (MN) leading to permanent paralysis. The chances for functional recovery after ventral root avulsion are very poor owing to the loss of avulsed neurons and the long distance that surviving neurons have to re-grow axons from the spinal cord to the corresponding targets. Following unilateral avulsion of L4, L5 and L6 spinal roots in adult rats, we performed an intraspinal transplant of mesenchymal stem cells (MSC) and surgical re-implantation of the avulsed roots. Four weeks after avulsion the survival of MN in the MSC-treated animals was significantly higher than in vehicle-injected rats (45 % vs 28 %). Re-implantation of the avulsed roots in the injured spinal cord allowed the regeneration of motor axons. By combining root re-implantation and MSC transplant the number of surviving MN at 28 days post-injury was higher (60 %) than in re-implantation alone animals (46 %). Electromyographic tests showed evidence of functional re-innervation of anterior tibialis and gastrocnemius muscles by the regenerated motor axons only in rats with the combined treatment. These results indicate that MSC are helpful in enhancing neuronal survival and increased the regenerative growth of injured axons. Surgical re-implantation and MSC grafting combined had a synergic neuroprotective effect on MN and on axonal regeneration and muscle re-innervation after spinal root avulsion.     

Time course of preferential motor unit loss in the SOD1 G93A mouse model of amyotrophic lateral sclerosis

Electromyographical analyses of pre-symptomatic motor unit loss in the SOD1 G93A transgenic mouse model of amyotrophic lateral sclerosis (ALS) have yielded contradictory findings as to the onset and time course. We recorded hindlimb muscle and motor unit isometric forces to determine motor unit number and size throughout the life span of the mice. Motor unit numbers in fast-twitch tibialis anterior, extensor digitorum longus and medial gastrocnemius muscles declined from 40 days of age, 50 days before reported overt symptoms and motoneuron loss. Motor unit numbers fell after overt symptoms in the slow-twitch soleus muscle. Muscle forces declined in parallel with motor unit numbers, indicating little or no functional compensation by sprouting. Early muscle-specific decline was due to selective preferential vulnerability of large, fast motor units, innervated by large motoneurons. Large motoneurons are hence the most vulnerable in ALS with die-back occurring prior to overt symptoms. We conclude that size of motoneurons, their axons, and their motor unit size are important determinants of motoneuron susceptibility in ALS.     

Colchicine-induced differential sprouting of the endplates on fast and slow muscle fibers in rat extensor digitorum longus, soleus and tibialis anterior muscles

The patterns of sprouting of motor endplates were examined in fast extensor digitorum longus and slow soleus muscles and in tibialis anterior muscles containing fast and slow muscle fiber types. A histochemical technique combining nerve silver impregnation and endplate cholinesterase staining was developed for this task. Temporal examination of the innervation was conducted 3, 7 and 10 days after either a 45 or 90 min application of the ipsilateral sciatic nerve with 5 mM colchicine. This dosage of drug did not cause detectable axon or muscle fiber degeneration, unlike 60 mM which was highly neurotoxic. At 3 days following treatment with the lower concentration, there were no significant differences in the percentages of intranodal, preterminal and ultraterminal sprouts between the normal (non-treated), sham-treated, contralateral systemic-control and drug-treated groups of muscles. By 7 and 10 days, the muscles on the drug-treated side exhibited significant increases in the 3 types of sprouts. Collateral sprouting was uncommon: most outgrowths remained on the muscle fibers innervated by the parent axons. Endplates in the tibialis anterior muscles of the control and drug-treated groups were classified Complex, Intermediate or Simple according to the relative degrees of branching of the terminal arbors. The occurrence of endplate classes and muscle fiber types was correlated in the superficial and deep regions of this muscle. Complex endplates innervated fast glycolytic fibers, Intermediate endplates supplied fast oxidative glycolytic fibers, and Simple endplates served slow oxidative fibers. In response to colchicine, the endplates of the slow muscles sprouted more than those of fast muscles while the innervation of slow fiber types sprouted less than that of fast fiber types. Furthermore, intranodal sprouts were more prevalent in slow muscles and ultraterminal sprouts more numerous in fast muscles whereas intranodal sprouts predominated on fast fiber types and ultraterminal sprouts were characteristic of slow fiber types. These apparently contradictory results were reconciled when it was noted that soleus endplates were mostly Complex and Intermediate, and the extensor digitorum longus contained more Simple endplates. Thus, consistency of sprouting patterns among endplate types of the 3 muscles was recognized when the pre-existing branching patterns were considered. This indicated that the patterns of sprouting were determined by the motor neurons rather than the muscle fibers. The observed sprouting responses supported the hypothesis that colchicine treatment of motor axons caused muscle fibers to elaborate a diffusible sprout-inducing factor.     

Changes in the distribution of the components of the troponin complex in muscle fibers after cross-innervation

Monospecific antibodies to the fast and slow skeletal muscle forms of the components of the troponin complex were used to follow the changes that occur in troponin I, troponin C, and troponin T during cross-innervation in rabbit skeletal muscles. During the period of transition after either soleus muscle was innervated by a fast nerve or when extensor digitorum longus and tibialis anterior muscles were innervated with slow nerves, most of the fibers contained both fast and slow forms of the components of the troponin complex. About 15 weeks after surgery the transformation of physiologic properties was complete in the soleus. The fully transformed soleus muscle consisted of about 10% of fibers containing only the slow troponin complex; the other 90% of fibers contained only the fast troponin complex. With extensor digitorum longus and tibialis anterior muscles transformation of fiber type was complete in 22 weeks when more than 90% of the innervated fibers contained only the slow troponin complex and the remaining fibers only the fast troponin complex. The results suggest that the synthesis of the forms of the components of the troponin complex appropriate to the activity resulting from the imposed innervation was under some type of coordinated control as was the degradation of the troponin components that were replaced as a consequence of the cross-innervation.     

Survival and regeneration of motoneurons in adult rats by reimplantation of ventral root following spinal root avulsion

The present study examines whether reimplantation of the ventral root could prevent motoneuron death after root avulsion. In the control animals about 65% or 39% of motoneurons survived at 3 or 6 weeks post-injury respectively. More than 60% of them expressed nitric oxide synthase (NOS). In contrast, in animals with ventral root reimplantation, nearly 90% or 80% of motoneurons survived at 3 or 6 weeks post-injury respectively. Expression of NOS due to root avulsion was significantly inhibited in these experimental animals. More interestingly, about 80% of the surviving motoneurons were found to regenerate their axons into the reimplanted ventral root, and all of these regenerating motoneurons were NOS negative. Results of the present study show that reimplantation of avulsed ventral root can greatly enhance motoneuron survival and the surviving motoneurons can regrow their axons into the original ventral root.