All peroneal motoneurons of the rat survive crush injury but some fail to reinnervate their original targets

Serum neurofilament light chain measurements following nerve trauma

BACKGROUND

Optimal functional recovery following peripheral nerve injuries (PNIs) is dependent upon early recognition and prompt referral to specialist centres for appropriate surgical intervention. Technologies which facilitate the early detection of PNI would allow faster referral rates and encourage improvements in patient outcomes. Serum Neurofilament light chain (NfL) measurements are cheaper to perform, easier to access and interpret than many conventional methods used for nerve injury diagnosis, such as electromyography and/or magnetic resonance imaging assessments, but changes in serum NfL levels following traumatic PNI have not been investigated. This pre-clinical study aimed to determine whether serum NfL levels can: (1) detect the presence of a nerve trauma and (2) delineate between different severities of nerve trauma.

METHODS

A rat sciatic nerve crush and common peroneal nerve crush were implemented as controlled animal models of nerve injury. At 1-, 3-, 7- and 21-days post-injury, serum samples were retrieved for analysis using the SIMOA® NfL analyser kit. Nerve samples were also retrieved for histological analysis. Static sciatic index (SSI) was measured at regular time intervals following injury.

RESULTS

Significant 45-fold and 20-fold increases in NfL serum levels were seen 1-day post-injury following sciatic and common peroneal nerve injury, respectively. This corresponded with an eightfold higher volume of axons injured in the sciatic compared to the common peroneal nerve (p < .001). SSI measurements post-injury revealed greater reduction in function in the sciatic crush group compared with the common peroneal crush group.

CONCLUSIONS

NfL serum measurements represent a promising method for detecting traumatic PNI and stratifying their severity. Clinical translation of these findings could provide a powerful tool to improve the surgical management of nerve-injured patients.

Exercise attenuates age-associated changes in motoneuron number, nucleocytoplasmic transport proteins and neuromuscular health

Life expectancy continues to extend, although frailty caused by loss of skeletal muscle mass continues unimpeded. Muscle atrophy caused by withdrawal of motor nerves is a feature of old age, as it is in amyotrophic lateral sclerosis (ALS) in which skeletal muscle denervation results from motoneuron death. In ALS, direct links have been established between motoneuron death and altered nucleocytoplasmic transport, so we ask whether similar defects accompany motoneuron death in normal ageing. We used immunohistochemistry on mouse tissues to explore potential links between neuromuscular junction (NMJ) degeneration, motoneuron death and nucleocytoplasmic transport regulatory proteins. Old age brought neuromuscular degeneration, motoneuron loss and reductions in immunodetectable levels of key nucleocytoplasmic transport proteins in lumbar motoneurons. We then asked whether exercise inhibited these changes and found that active elderly mice experienced less motoneuron death, improved neuromuscular junction morphology and retention of key nucleocytoplasmic transport proteins in lumbar motoneurons. Our results suggest that emergent defects in nucleocytoplasmic transport may contribute to motoneuron death and age-related loss of skeletal muscle mass, and that these defects may be reduced by exercise.

Variation in nerve autograft length increases fibre misdirection and decreases pruning effectiveness. An experimental study in the rat median nerve

OBJECTIVES

In the clinical set, autologus nerve grafts are the current option for reconstruction of nerve tissue losses. The length of the nerve graft has been suggested to affect outcomes. Experiments were performed in the rat in order to test this assumption and to detect a possible mechanism to explain differences in recovery.

METHODS

The rat median nerve was repaired by ulnar nerve grafts of different lengths. Rats were evaluated for 12 months by behavioural assessment and histological studies, including ATPase myofibrillary histochemistry and retrograde neuronal labelling.

RESULTS

It was demonstrated that graft length interferes in behavioural functional recovery that here correlates to muscle weight recovery. Short nerve grafts recovered faster and better. Reinnervation was not specific either at the trunk level or in the muscle itself. The normal mosaic pattern of Type I muscle fibres was never restored and their number remained largely augmented. An increment in the number of motor fibres was observed after the nerve grafting in a predominantly sensory branch in all groups. This increment was more pronounced in the long graft group. In the postoperative period, about a 20% reduction in the number of misdirected motor fibres occurred in the short nerve graft group only.

CONCLUSION

Variation in the length of nerve grafts interferes in behavioural recovery and increases motor fibres misdirection. Early recovery onset was related to a better outcome, which occurs in the short graft group.

Return of motor function after segmental nerve loss in a rat model: comparison of autogenous nerve graft, collagen conduit, and processed allograft (AxoGen)

BACKGROUND

An effective alternative to nerve autograft is needed to minimize morbidity and solve limited-availability issues. We hypothesized that the use of processed allografts and collagen conduits would allow recovery of motor function that is equivalent to that seen after the use of autografts.

METHODS

Sixty-five Lewis rats were divided into three experimental groups. In each group, a unilateral 10-mm sciatic nerve defect was repaired with nerve autograft, allograft treated by AxoGen Laboratories, or a 2.0-mm-inner-diameter collagen conduit. The animals were studied at twelve and sixteen weeks postoperatively. Evaluation included bilateral measurement of the tibialis anterior muscle force and muscle weight, electrophysiology, assessment of ankle contracture, and peroneal nerve histomorphometry. Muscle force was measured with use of our previously described and validated method. Results were expressed as a percentage of the values on the contralateral side. Two-way analysis of variance (ANOVA) corrected by the Ryan-Einot-Gabriel-Welsch multiple range test was used for statistical investigation (α = 0.05).

RESULTS

At twelve weeks, the mean muscle force (and standard deviation), as compared with that on the contralateral (control) side, was 45.2% ± 15.0% in the autograft group, 43.4% ± 18.0% in the allograft group, and 7.0% ± 9.2% in the collagen group. After sixteen weeks, the recovered muscle force was 65.5% ± 14.1% in the autograft group, 36.3% ± 15.7% in the allograft group, and 12.1% ± 16.0% in the collagen group. Autograft was statistically superior to allograft and the collagen conduit at sixteen weeks with regard to all parameters except histomorphometric characteristics (p < 0.05). The collagen-group results were inferior. All autograft-group outcomes improved from twelve to sixteen weeks, with the increase in muscle force being significant.

CONCLUSIONS

The use of autograft resulted in better motor recovery than did the use of allograft or a collagen conduit for a short nerve gap in rats. A longer evaluation time of sixteen weeks after segmental nerve injuries in rats would be beneficial as more substantial muscle recovery was seen at that time.

A rat model for intracranial facial nerve crush injuries

OBJECTIVE

(1) Explain the need for an animal model to study intracranial injuries to the facial nerve. (2) Describe various techniques attempted to identify and crush the intracranial segment of the facial nerve in a rat model. (3) Describe in detail a successful rat model of intracranial facial nerve crush injury.

STUDY DESIGN

Randomized controlled animal study.

SETTING

Animal laboratory.

SUBJECTS AND METHODS

Multiple attempts at surgical approaches to the cerebellopontine angle were attempted on cadaveric rats. Once a successful approach was derived, this was used on 19 live rats under anesthesia. Fourteen rats had a 1-minute facial nerve crush performed, and 5 had a sham surgery with complete surgical exposure of the facial nerve but no crush. Rats were followed for a 12-week duration evaluating immediate postoperative facial nerve function, complications, and survival.

RESULTS

All 14 (100%) rats that underwent surgery with crush injury had complete facial paralysis postoperatively. Complete facial paralysis was defined as loss of eye-blink reflex, flat vibrissae, and lack of vibrissae movement. The 5 sham surgery rats had complete facial function postoperatively. Surgery was performed by 2 separate surgeons with no difference in outcome between the 2. Complications occurred in only 1 animal (1/19, 5.3%), which was a corneal abrasion requiring sacrifice.

CONCLUSION

Our group describes a consistent method for performing an intracranial crush injury in the rat. This new model and its applications in translational facial nerve research are promising, particularly with tumors or lesions at the cerebellopontine angle.

Facial motor nuclei cell loss with intratemporal facial nerve crush injuries in rats

OBJECTIVES/HYPOTHESIS

Injuries of cranial nerves that are distal to but near the motor nucleus might result in retrograde motoneuron cell death. The hypothesis of this article is that an intratemporal crush injury of the facial nerve in rats can cause facial motor nuclei cell death.

STUDY DESIGN

Prospective, randomized, controlled animal study.

METHODS

Sprague-Dawley rats were randomly divided into four groups: intratemporal sham, intratemporal crush injury, extratemporal crush injury, and extratemporal sham. The intratemporal (n = 9) and extratemporal crush injury (n = 4) groups underwent a 60-second crush of the nerve at the facial nerve tympanic segment or main facial nerve trunk distal to the stylomastoid foramen, respectively. The intratemporal sham group (n = 4) underwent identical exposure to the intratemporal crush without subsequent injury. Both sham groups and the extratemporal crush group were sacrificed at 4 weeks. The intratemporal crush group was subdivided into 4- (n = 4) and 8-week (n = 5) postinjury groups. Brain sections were stained with thionin and facial motor nuclei were counted under magnification. The contralateral uninjured facial motor nucleus was used to compare motor nucleus cell survival.

RESULTS

Intratemporal crush injury resulted in increased cell loss at 4 (89.43% ± 8.57% standard error of mean) and 8 weeks (85.78% ± 3.15%) after injury compared to sham injury (119.09% ± 13.35%) (P <.05). No significant change in cell survival was noted between the distal crush (103.29% ± 6.34%) and sham group (111.71% ± 3.24%) (P >.05).

CONCLUSIONS

A rat intratemporal crush injury resulted in approximately 15% facial motor nuclei cell loss compared to an intratemporal sham injury. An extratemporal crush injury did not lead to any significant facial motor nuclei cell loss. This might have future translational implications in humans with intratemporal facial nerve injuries.

Facial nerve schwannoma

PURPOSE OF REVIEW

The purpose of this review is to summarize the current literature on facial nerve schwannoma and make practical recommendations based on best practices for the management of this difficult but benign neoplasm.

RECENT FINDINGS

Facial nerve schwannoma can be asymptomatic or can present with progressive or acute facial nerve palsy. Associated otological symptoms such as conductive and/or sensorineural hearing loss can occur. The tumor is usually slow-growing and can involve multiple segments of the nerve. Radiographic imaging and facial nerve electrical testing can be helpful in treatment planning. Options for management can include observation, decompression, stripping, resection with grafting, and possibly radiotherapy. Future adjunctive therapies to improve facial nerve function may include electrical stimulation, steroid hormones, and possibly stem cell therapy.

SUMMARY

Treatment of facial schwannoma is individualized based on patient symptoms, history, and clinicoradiographic evaluation. Not all patients require surgery. As the tumor can involve multiple segments of the nerve, the surgeon attempting removal should be familiar with modern neurotological surgical techniques. Ongoing translational research will hopefully allow us to decrease facial nerve morbidity in these patients.

Treatment of a segmental nerve defect in the rat with use of bioabsorbable synthetic nerve conduits: a comparison of commercially available conduits

BACKGROUND

The use of biodegradable synthetic nerve conduits for the reconstruction of segmental nerve defects has been extensively reported in both animal and human studies, with a majority of studies evaluating sensory nerve recovery. However, few studies have compared these nerve conduits for functional motor recovery. The purpose of this study was to compare three commercially available, synthetic, bioabsorbable nerve conduits and autograft with respect to compound muscle action potentials, maximum isometric tetanic force, wet muscle weight, and nerve histomorphometry.

METHODS

Eighty Lewis rats were divided into four groups according to the type of repair of a 10-mm excision of the sciatic nerve: group I had a reversed autograft; group II, a poly-DL-lactide-epsilon-caprolactone conduit; group III, a type-I collagen conduit; and group IV, a polyglycolic acid conduit. All results were compared with the contralateral side. At twelve weeks, the rats underwent bilateral measurements of the compound muscle action potentials of the tibialis anterior and flexor digiti quinti brevis muscles, isometric tetanic force and muscle weight of the tibialis anterior, and peroneal nerve histomorphometry.

RESULTS

At twelve weeks, no difference in the percentage of recovery between the autograft and the poly-DL-lactide-epsilon-caprolactone conduit was observed with respect to compound muscle action potentials, isometric muscle force, muscle weight, and axon count measurements. The poly-DL-lactide-epsilon-caprolactone and collagen conduits remained structurally stable at twelve weeks, while the polyglycolic acid conduits had completely collapsed. The polyglycolic acid conduit had the poorest results, with a recovery rate of 15% for compound muscle action potentials and 29% for muscle force.

CONCLUSIONS

The functional outcome in this rat model was similar for the autograft and the poly-DL-lactide-epsilon-caprolactone conduits when they were used to reconstruct a 10-mm sciatic nerve defect. Functional recovery following the use of the polyglycolic acid conduit was the poorest.

Evidence for a detrimental role of nitric oxide synthesized by endothelial nitric oxide synthase after peripheral nerve injury

Physical injury to a nerve is the most common cause of acquired peripheral neuropathy. Identification of molecules involved in degenerative and regenerative processes is a key step toward development of therapeutic tools in order to accelerate motor, sensory and/or autonomic function recovery. We have studied the role of nitric oxide (NO) using as a model the severe crushing of a motor nerve in adult rats. This type of injury up-regulates the three isoforms of nitric oxide synthase (NOS) in the affected nerve. Chronic systemic inhibition of NOS accelerated the onset of functional muscle reinnervation evaluated by the recording of compound muscle action potential evoked by electrical stimulation of the injured nerve. Besides, it increased the number of back-labeled motoneurons by application, 2 days after injury, of a retrograde marker 10 mm distal to the crushing site. These effects were mimicked by chronic specific inhibition of the endothelial isoform of nitric oxide synthase (eNOS), but not by specific inhibitors of the neuronal or inducible isoform. Next, we intraneurally injected a replication-deficient adenoviral vector directing the expression of a dominant negative mutant of eNOS (Ad-TeNOS). A single injection of Ad-TeNOS on the day of crushing significantly accelerated functional recovery of neuromuscular junction and increased axonal regeneration. Moreover, Ad-TeNOS did not compromise motoneuron viability or stability of reestablished neuromuscular junctions. Taken together, these results suggest that NO of endothelial origin slows down muscle reinnervation by means of detrimental actions on axonal regeneration after peripheral nerve injury. These experiments identify eNOS as a potential therapeutic target for treatment of traumatic nerve injuries and highlight the potential of gene therapy in treating injuries of this type using viral vectors to suppress the activity of eNOS.

Misdirection of regenerating motor axons after nerve injury and repair in the rat sciatic nerve model

Misdirection of regenerating axons is one of the factors that can explain the poor results often found after nerve injury and repair. In this study, we quantified the degree of misdirection and the effect on recovery of function after different types of nerve injury and repair in the rat sciatic nerve model; crush injury, direct coaptation, and autograft repair. Sequential tracing with retrograde labeling of the peroneal nerve before and 8 weeks after nerve injury and repair was performed to quantify the accuracy of motor axon regeneration. Digital video analysis of ankle motion was used to investigate the recovery of function. In addition, serial compound action potential recordings and nerve and muscle morphometry were performed. In our study, accuracy of motor axon regeneration was found to be limited; only 71% (+/-4.9%) of the peroneal motoneurons were correctly directed 2 months after sciatic crush injury, 42% (+/-4.2%) after direct coaptation, and 25% (+/-6.6%) after autograft repair. Recovery of ankle motion was incomplete after all types of nerve injury and repair and demonstrated a disturbed balance of ankle plantar and dorsiflexion. The number of motoneurons from which axons had regenerated was not significantly different from normal. The number of myelinated axons was significantly increased distal to the site of injury. Misdirection of regenerating motor axons is a major factor in the poor recovery of nerves that innervate different muscles. The results of this study can be used as basis for developing new nerve repair techniques that may improve the accuracy of regeneration.

Concepts of nerve regeneration and repair applied to brachial plexus reconstruction

Brachial plexus injury is a serious condition that usually affects young adults. Progress in brachial plexus repair is intimately related to peripheral nerve surgery, and depends on clinical and experimental studies. We review the rat brachial plexus as an experimental model, together with its behavioral evaluation. Techniques to repair nerves, such as neurolysis, nerve coaptation, nerve grafting, nerve transfer, fascicular transfer, direct muscle neurotization, and end-to-side neurorraphy, are discussed in light of the authors' experimental studies. Intradural repair of the brachial plexus by graft implants into the spinal cord and motor rootlet transfer offer new possibilities in brachial plexus reconstruction. The clinical experience of intradural repair is presented. Surgical planning in root rupture or avulsion is proposed. In total avulsion, the authors are in favor of the reconstruction of thoraco-brachial and abdomino-antebrachial grasping, and on the transfer of the brachialis muscle to the wrist extensors if it is reinnervated. Surgical treatment of painful conditions and new drugs are also discussed.

Distribution and immunohistochemical characterization of primary afferent neurons innervating the levator ani muscle of the female squirrel monkey

OBJECTIVE

This study was undertaken to examine the neurofilament and neurochemical composition of subpopulations of primary afferent neurons innervating the levator ani muscle by combining retrograde tracing and triple labeling immunofluorescence in the female squirrel monkey.

STUDY DESIGN

Cholera toxin B subunit (CTB) was injected unilaterally into the levator ani muscle of 3 monkeys to identify primary sensory neurons in the dorsal root ganglia (DRG) and their central projections in the spinal cord. L7-S2 DRG were processed for dual or triple labeling immunofluorescence 3 days after injection to examine labeling of the 200 kD neurofilament marker RT97 (a marker of myelinated neurons), calcitonin gene-related peptide (CGRP; a marker of peptidergic neurons), isolectin B4 (IB4; a marker of small, unmyelinated neurons), and nerve growth factor receptor (TrkA) in CTB-positive neurons.

RESULTS

RT97-negative (C-fiber) neurons were more numerous (74% of total CTB-labeled neurons) and smaller in size than RT97-positive (A-fiber) afferent neurons (26% of CTB-labeled neurons). IB4 labeling was almost exclusively found in RT97-negative afferent neurons. Approximately 43% of all CTB-labeled DRG neurons expressed CGRP, and the majority of these were small. The distribution and sizes of CTB-labeled TrkA-positive DRG neurons were similar to those of CTB-labeled CGRP-positive DRG neurons.

CONCLUSION

The levator ani muscle is innervated by 3 major subpopulations of primary afferent neurons consisting of cells with large, neurofilament-rich soma and A fibers (putative proprioceptive neurons) and those with small, peptidergic or nonpeptidergic, neurofilament-poor soma and C fibers (putative nociceptive, mechanoreceptive, ergoreceptive, and thermoreceptive neurons). Future investigation is needed to elucidate the relationship between primary sensory neuron subpopulations and changes in neuropeptide and neurotrophin expression on experimental levator ani nerve damage, childbirth, and aging.

Correlation between target reinnervation and distribution of motor axons in the injured rat sciatic nerve

Peripheral nerve injuries are rarely followed by complete return of function. Deficits are particularly important for motor function, resulting in paralysis and muscle atrophy. In different groups, the sciatic nerve was either crushed or transected and repaired by direct suture or by tube repair using silicone or collagen tubes. After 60 days, nerve regeneration was assessed by electrophysiological and functional tests, nerve morphology and immunohistochemistry against choline acetyltransferase (ChAT) for labeling motor axons. Suture and tube repair resulted in similar levels of muscle reinnervation, but significantly lower than after nerve crush. Recovery of walking track pattern was poor in all groups after nerve section. The numbers of regenerated myelinated fibers and of ChAT+ fibers were similar to control values after nerve crush, but increased after section and repair. The normal fascicular architecture and grouping of ChAT+ fibers were maintained after nerve crush, but lost after section and repair, where motor fibers were scattered within small regenerated fascicles throughout the nerve. The loss of fascicular organization was related to the deficient recovery of locomotor function. Thus, labeling of motor axons by ChAT immunohistochemistry provides useful information for the study of the degree and specificity of nerve regeneration.

Recovery of contractile and metabolic phenotypes in regenerating slow muscle after notexin-induced or crush injury

The recovery of metabolic pathways after muscle damage has been poorly studied. We investigated the myosin heavy chain (MHC) isoform transitions and the recovery of citrate synthase (CS) activity, isoform distribution of lactate dehydrogenase (LDH) and creatine kinase (CK) in slow muscles after two types of injury. Muscle degeneration was induced in left soleus muscles of male Wistar rats by either notexin injection or crushing and the regenerative process was examined from 2 to 56 days after injury. Myosin transition occurred earlier after notexin than after crush injury. Fast-type IIx and more particularly type IIa MHC isoform disappeared by day 28 after notexin inoculation, while they were still detected long after in crushed muscles. A full recovery of both the CS activity and the specific activity of the H-LDH subunit was observed from day 42 in notexin-treated muscles, while values measured in crushed muscles remained significantly lower than in non-injured muscles (P < 0.05). The activity of the mitochondrial isoform of CK (mi-CK) was markedly affected by the type of injury (P < 0.001), and failed to reach normal levels after crush injury (P < 0.05). The results of this study show that the relatively rapid MHC transitions during regeneration contrasts with the slow recovery in the oxidative capacity. The recovery of the oxidative capacity remained incomplete after crush injury, a model of injury known to lead to disruption of the basal lamina and severe interruption of the vascular and nerve supply.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Dead-ended autologous connective tissue chambers in peripheral nerve repair--early observations

The effects of the repair of nerve gap injuries are still unsatisfactory, despite the great progress in microsurgery. Until now, there is no effective method to induce the regeneration of the transected peripheral nerve when its distal stump is missing. The aim of this work was to examine whether the implantation of dead-ended connective tissue chambers can promote the outgrowth of injured peripheral neurites. This method differs from all previous nerve guides because it totally eliminates the distal part of the nerve and restricts the influence of surrounding tissues. We have also tried to establish whether some neurotrophic factors can be applied by means of these chambers. The results of this work show that dead-ended autologous connective tissue chambers can be a useful tool in peripheral nerve injuries treatment, even when the distal part of the nerve is missing.

Effects of insulin-like growth factor-1 gene transfer on myosin heavy chains in denervated rat laryngeal muscle

OBJECTIVES/HYPOTHESIS

To determine whether the myotrophic activity of human insulin-like growth factor (hIGF)-1 promotes restoration of normal myosin heavy chain (MHC) composition after nerve injury, MHC composition was analyzed after hIGF-1 gene transfer in denervated rat laryngeal muscle.

STUDY DESIGN

Animal model to study effects of gene transfer on laryngeal paralysis.

METHODS

In anesthetized rats, the left recurrent and superior laryngeal nerves are cut and suture ligated. A midline thyrotomy is performed, and the thyroarytenoid muscle is injected with a polyvinyl-based formulation containing a muscle specific expression system and hIGF-1 DNA (treatment group) or saline (control group). After 30 days, animals were killed, and the thyroarytenoid muscle was removed and processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Densitometric measurements were obtained to determine composition of MHCs.

RESULTS

As previously described, MHC composition in denervated laryngeal muscle was characterized by a decrease in type IIB and IIL and up-regulation of IIA/IIX. Compared with controls, hIGF-1 treated animals demonstrated a significant increase in expression of type IIB and IIL and a significant decrease in expression of type IIA/X.

CONCLUSIONS

These findings suggest that the myotrophic effect of hIGF-1 gene transfer results in normalization of MHC composition in denervated muscle, with suppression of type IIA/X MHC and promotion of type IIL expression.

Long interpositional nerve graft consistently induces incomplete motor and sensory recovery in the rat

Motor and sensory regeneration was studied in a 40 mm long graft interposed between the sectioned stumps of the rat median nerve. Animals were behaviorally assessed from 1 to 720 days after surgery by the grasping and modified Randall-Sellito tests. Rats recovered grasping function 43.7 (S.D. +/- 2.6) days after surgery. Grasping strength attained 50 and 65% of the normal control group, 280 and 360 days after surgery, respectively. From 90 to 360 days after surgery, sensory nociceptive recovery was only 30% of the normal control group. The results indicate that motor and sensory neurons were capable of regenerating additional axonal length, but functional return was clearly better in the motor system. This model of deficient reinnervation might prove to be of interest in testing of new strategies for the enhancement of nerve recovery.

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.

Ankle kinematics to evaluate functional recovery in crushed rat sciatic nerve

Peripheral nerve researchers frequently use the rat sciatic nerve crush model in order to test different therapeutic approaches. The purpose of this study was to determine the sequence of changes after an axonotmetic injury by means of a biomechanical model of the foot and ankle, and compare them with walking track analysis, over a fixed period of time. A kinematic analysis program was used to acquire ankle motion data for further analysis. Although repeated measures analysis of variance showed significant cumulative changes induced by the crush lesion for both ankle kinematic parameters and sciatic functional index, post-hoc multiple comparisons by the Student-Neuman-Keuls test revealed significant differences between week 0 and week 8 only for ankle kinematics. These results are of importance in showing the superiority of ankle kinematics in detecting small biomechanical deficits related to hyperexcitability of the plantarflexor muscles, in contrast with walking track analysis, which showed full motor functional recovery 8 weeks after the crush lesion.

Yasargil-Phynox aneurysm clip: a simple and reliable device for making a peripheral nerve injury

A great number of devices were used to make a peripheral nerve injury. In the scientific literature, experimental crush injuries have been usually created using forceps or hemostatic forceps, neither of which allows quantitative or standard application of compression. Therefore, we used a Yasargil-Phynox aneurysm clip to make a reliable and standardized peripheral nerve injury. The advantages and disadvantages of this clip were discussed. In particular, we think that standardization of the compression is necessary to compare interlaboratory results.

H reflex restitution and facilitation after different types of peripheral nerve injury and repair

This study addresses the restitution of monosynaptic H reflex after nerve injuries and their role in the recovery of walking. Adult rats were submitted to sciatic crush, complete section repaired by aligned or crossed fascicular suture, or an 8-mm resection repaired by autograft or tube repair. The sciatic nerve was stimulated proximal to the injury site and the M and H waves were recorded from gastrocnemius (GCm) and plantar (PLm) muscles at monthly intervals during 3 months postoperation. Walking track tests were also carried out and the sciatic functional index (SFI) calculated to assess gait recovery. The M and H waves reappeared in all the animals at the end of the follow-up. The H/M amplitude ratio increased during the first stages of regeneration and tended to decrease to control values as muscle reinnervation progressed. However, final values of the H/M ratio for the PLm remained significantly higher in all the groups except that with a nerve crush. The walking track pattern showed an appreciable recovery only after crush injury. Final SFI values correlated positively with the M wave amplitude and negatively with the H/M ratio. In conclusion, H reflex is facilitated after peripheral nerve injury and regeneration and tends to return to normal excitability with time. Changes in the H reflex circuitry and excitability correlated positively with the deficient recovery of walking pattern after severe nerve injury.

Nimodipine promotes regeneration and functional recovery after intracranial facial nerve crush

The calcium flow inhibitor, nimodipine, has been shown to promote motor neuron survival in the facial nucleus after intracranial facial nerve transection. However, it has not been known whether the neuroprotective effects primarily involve survival of nerve cell bodies or outgrowth and/or myelination of nerve fibers. Here, we studied the effects of nimodipine in a different injury model in which the facial nerve was unilaterally crushed intracranially. This lesion caused complete anterograde degeneration and partial retrograde degeneration that were studied with a combination of several stereological methods. Nimodipine did not attenuate the modest lesion-induced neuronal loss (13%) but accelerated the time course of functional recovery and axonal regrowth, inducing increased numbers and sizes of myelinated axons in the facial nerve. It is interesting to note that nimodipine also enlarged the axons and the myelin sheaths in the nonlesioned facial nerve, which points to the possibility of using this substance for new clinical applications to promote axonal growth and remyelination.

Modulation of myosin heavy chains in rat laryngeal muscle

OBJECTIVES

To test the hypothesis that myosin heavy chain (MHC) composition is a biological marker indicative of appropriate and functional reinnervation.

STUDY DESIGN

Age-matched adult rats were randomized for prospective study under three experimental conditions.

METHODS

In adult rats, three experimental conditions were surgically created, including transient recurrent laryngeal nerve (RLN) crush injury, RLN transection and repair, and cricoarytenoid joint fixation with intact RLN. Animals were survived for 30, 90, and 180 days. At each interval, vocal fold mobility was assessed by rigid microlaryngoscopy. Laryngeal electromyography (EMG) was performed before euthanasia. The thyroarytenoid and posterior cricoarytenoid muscles were then excised, each muscle was processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and MHC composition was determined.

RESULTS

Thirty days after nerve crush injury, three of six animals regained vocal fold mobility and normal MHC composition. Impaired vocal fold motion in three of six animals was associated with MHC composition characteristic of denervation. At 90 and 180 days, normal vocal fold motion and normal MHC composition were observed in all animals. Following nerve transection and repair, impaired vocal fold motion and MHC composition characteristic of denervation were observed in all animals, despite evidence of reinnervation on EMG. Following joint fixation, alteration in MHC composition consistent with denervation was observed only at 30 days, as was evident in the nerve crush model.

CONCLUSION

Temporary injury and vocal fold immobilization result in transient shifts in MHC composition. Nerve transection and repair result in persistent alteration of MHC composition and vocal fold dysfunction. The expression of normal MHC composition is dependent on the condition of appropriate neural contact and functional reinnervation.

Spinal cord atrophy and reorganization of motoneuron connections following long-standing limb loss in primates

Primates with long-standing therapeutic amputations of a limb at a young age were used to investigate the possibility that deefferented motor nerves sprout to new muscle targets. Injections of anatomical tracers into the muscles proximal to the amputated stump labeled a larger extent of motoneurons than matched injections on the intact side or in normal animals, including motoneurons that would normally supply only the missing limb muscles. Although the total numbers of distal limb motoneurons remained normal, some distal limb motoneurons on the amputated side were smaller in size and simpler in form. These results suggest that deprived motoneurons survive and retain function by reinnervating new muscle targets. The sprouted motor efferents may account for some of the reorganization of primary motor cortex that follows long-standing amputation.

Effects of pudendal nerve injury in the female rat

To test a neurogenic hypothesis for external urethral sphincter (EUS) dysfunction associated with urinary incontinence, the proximal pudendal nerve was crushed in anesthetized retired breeder female rats (n = 5) and compared with a sham lesion group (n = 4). Outcome measures included concentric needle electromyograms (EMGs) from the target EUS, voiding patterns during a 2-hour dark period, and micturition data over a 24-hour period. Fast Blue (FB) was introduced to the crush site at the time of injury and Diamidino Yellow (DY) to the EUS at the time the rats were killed (3 months post-operative), when histological analysis of the nerve and urethra was also performed. EMG records indicated the EUS motor units undergo typical denervation changes followed by regeneration and recovery. Voiding patterns from the crush group show a significant increase of small urine marks in the front third of the cage. At 1-2 weeks post-op, the frequency of voids was significantly increased in the crush group compared to pre-op and late post-op time periods. The mean volume voided in the light phase at the early post-op time was significantly increased in the sham group. Light and electron microscopic patterns seen in nerve and muscle suggest the regenerating motor units maintain a structural integrity. Motoneurons in the lower lumbar cord were labeled with either DY (14. 5 +/- 6.8), FB (31.7 +/- 23.7), or both (35.0 +/- 17.5) tracers, indicating approximately 54% of the crushed pudendal neurons regenerated to the EUS. In conclusion, several measures suggest this reversible crush lesion induces mild urinary incontinence. This animal model is promising for further development of hypotheses regarding neural injury, the pathogenesis of incontinence, and strategies aimed at prevention and treatment. Neurourol. Urodynam. 19:53-69, 2000.

Extensive neuronal cell death following intracranial transection of the facial nerve in the adult rat

The aim of the present study is to examine the neuronal degeneration and the glial response following intracranial transection of the facial nerve close to the brainstem and furthermore to compare the results with a distal nerve injury. The facial nerve was cut either intracranially in the posterior cranial fossa or further distally, where it passes the parotid gland, in adult rats. Intracranial axotomy caused a massive loss of neuronal profiles. Only 26.8+/-11.3% of facial motor neuronal profiles were found ipsilateral to the nerve injury when compared to the contralateral side, following intracranial axotomy. This was statistically significant in comparison to the distal injury (72.4+/-9.5%), 4 weeks post-lesion. Reactive microglial cells expressed ED1 immunoreactivity following the intracranial axotomy but not following the distal nerve injury. In conclusion, there was a large discrepancy in neuronal degeneration as well as presence of phagocytic (ED1 positive) microglia between the two lesions. The intracranial lesion model used in the present study generates a massive neuronal cell death and should therefore be a useful tool for studies on proximal cranial nerve injuries and in particular mechanisms causing cell death, which may occur following, for example, head trauma.

Recovery of C-fiber-induced extravasation following peripheral nerve injury in the rat

Peripheral nerve injury leads to substantial alterations in injured sensory neurons. These include cell death, phenotypic modifications, and regeneration. Primary sensory neurons have recently been shown not to die until a time beyond 4 months following a nerve crush or ligation and this loss is, moreover, limited to cells with unmyelinated axons, the C-fibers. The late loss of C-fibers may be due to a lack of target reinnervation during the regenerative phase. In order to investigate this, we have used a particular peripheral function, unique to C-fibers, as a measure of peripheral reinnervation: an increase in capillary permeability on antidromic activation of C-fibers, i.e., neurogenic extravasation. This was investigated in rats that had received a nerve crush injury 1 to 50 weeks earlier. Some recovery of the capacity of C-fibers to generate extravasation was detected at 8-10 weeks, which increased further at 12-14 weeks, and then plateaued at this level with no further recovery at 30 or 50 weeks. In intact and damaged sciatic nerves, A beta-fibers never induced extravasation. These findings are compatible with the hypothesis that those C-fibers which make it back to their peripheral targets do not subsequently die and those that do not, may die.

Motor versus sensory neuron regeneration through collagen tubules

Differences in regeneration of sensory and motor nerves were studied in rats to determine the effects of entubulation with collagen conduits. The rat sciatic nerve was repaired either with a 10-mm saline-filled gap or with a no-gap end-to-end repair cuffed within collagen tubules. These repairs were compared with the standard epineurial repairs. The populations of regenerated motor and sensory neurons in the peroneal nerves of all repairs were compared against the populations of normal peroneal neurons using horseradish peroxidase retrograde labeling. The epineurial repair resulted in regeneration of 65 percent (409 +/- 150) of motor neurons and 79 percent (2127 +/- 516) of sensory neurons (n = 6). The no-gap end-to-end repair in a collagen tubule resulted in regeneration of 53 percent (338 +/- 203) of motor and 70 percent (1893 +/- 794) of sensory neurons (n = 7). In the 10-mm gap repair, only 6.2 percent (39 +/- 18) of motor neurons but 63 percent (1710 +/- 557) of sensory neurons regenerated (n = 5). These results show that collagen entubulation supports nerve regeneration in end-to-end nerve repairs comparably to standard epineurial suture repairs. With the 10-mm gap repairs in collagen tubules, sensory neurons regenerated consistently better than motor neurons in the same environment. Therefore, intrinsic differences exist between motor and sensory neuron regeneration in the same nerve.

Simulation of motor unit recruitment and microvascular unit perfusion: spatial considerations

Muscle fiber activity is the principal stimulus for increasing capillary perfusion during exercise. The control elements of perfusion, i.e., microvascular units (MVUs), supply clusters of muscle fibers, whereas the control elements of contraction, i.e., motor units, are composed of fibers widely scattered throughout muscle. The purpose of this study was to examine how the discordant spatial domains of MVUs and motor units could influence the proportion of open capillaries (designated as perfusion) throughout a muscle cross section. A computer model simulated the locations of perfused MVUs in response to the activation of up to 100 motor units in a muscle with 40,000 fibers and a cross-sectional area of 100 mm2. The simulation increased contraction intensity by progressive recruitment of motor units. For each step of motor unit recruitment, the percentage of active fibers and the number of perfused MVUs were determined for several conditions: 1) motor unit fibers widely dispersed and motor unit territories randomly located (which approximates healthy human muscle), 2) regionalized motor unit territories, 3) reversed recruitment order of motor units, 4) densely clustered motor unit fibers, and 5) increased size but decreased number of motor units. The simulations indicated that the widespread dispersion of motor unit fibers facilitates complete capillary (MVU) perfusion of muscle at low levels of activity. The efficacy by which muscle fiber activity induced perfusion was reduced 7- to 14-fold under conditions that decreased the dispersion of active fibers, increased the size of motor units, or reversed the sequence of motor unit recruitment. Such conditions are similar to those that arise in neuromuscular disorders, with aging, or during electrical stimulation of muscle, respectively.

Functional recovery following neurorrhaphy of the rat sciatic nerve by epineurial repair compared with tubulization

Recovery of motor function is often poor following transection injuries to peripheral nerves. The purpose of this study was to measure and compare functional recovery of the sciatic nerve in the rat following transection and neurorrhaphy with the use of a nerve guide tube and with traditional end-to-end epineurial repair. Muscle recovery was also evaluated following a crush injury, a model of an axonotmetic lesion. Recovery was assessed at 8, 16, and 32 weeks after injury by measuring the isometric contractile properties of the soleus muscle and at 8 and 16 weeks by measuring the conduction properties of the sciatic nerve. The mean conduction velocity of the sciatic nerve in the crush group and both transection groups was significantly slower than that of controls at both 8 and 16 weeks. Following a transection injury, the soleus became a significantly faster muscle as measured by time to peak twitch tension. By 32 weeks, the maximum isometric tension of the soleus muscle recovered to 90% that of the control group following a crush injury and to less than 70% following a transection injury and repair. Recovery was better in the epineurial repair group than in the tube repair group at 8 weeks, but no difference was found between the groups at 16 or 32 weeks. These results demonstrate that nerve guide tubes are a potential alternative to epineurial repair. The poor motor recovery following repair of transection injuries may be related to poor specificity of reinnervation.

A differential and time-dependent decrease in AMPA-type glutamate receptor subunits in spinal motoneurons after sciatic nerve injury

After sciatic transection a strong decrease in immunoreactivity occurred, starting at 2 days. After 6, 10, 14, and 20 days survival only 5% of the sciatic motoneurons were strongly labeled for GluR2/3 against 80% in the control situation. From Day 20, GluR2/3 labeling started to increase again, reaching near normal levels at Day 80 after sciatic transection. In contrast, after sciatic crush, the decrease in GluR2/3 labeling in motoneurons was less pronounced and returned to normal in 30 days. In all animals, the GluR1 and GluR4 labeling of motoneurons remained unchanged after sciatic transection or crush. It is concluded that sciatic nerve injury leads to a strong, time-dependent decrease in the expression of GluR2 and 3 subunits in the corresponding motoneurons. As a consequence, AMPA receptors with a different subunit composition may be assembled, leading to a change in the functional properties of these receptors. Moreover, if they lack the GluR2 subunit, they may become calcium permeable.

Inaccurate projection of rat soleus motoneurons: a comparison of nerve repair techniques

The objectives of this study were 1) to determine the degree to which soleus motoneurons find their appropriate target following crush and transection injuries to the sciatic nerve, and 2) to determine whether repair of a transected nerve with a silicone tube leads to greater specificity of reinnervation and recovery of muscle function than the standard epineurial suture repair method. Sixty adult female Sprague-Dawley rats were randomly assigned to one of three sciatic nerve injury groups: crush injury, transection with epineurial suture repair, or transection with a silicone tube repair. The degree to which soleus motoneurons were able to find their appropriate target following a sciatic nerve injury was examined using a double labeling dye technique in which the original soleus motor pool was labeled with fast blue and reinnervating motoneurons were labeled with Dil. Soleus motoneurons were able to find their appropriate target following a crush injury. The accuracy of reinnervation following a transection injury and repair, however, was relatively poor. Only 14% of the original soleus motoneurons found the correct target following a transection injury. Repair of a lesioned nerve with a silicone tube and a 5-mm gap as opposed to epineurial sutures did not increase the specificity of reinnervation or the degree of muscle recovery.

Nerve regeneration across a 25-mm gap bridged by a polyglycolic acid-collagen tube: a histological and electrophysiological evaluation of regenerated nerves

In the study reported here we have examined the nerve regeneration that occurs over a 25-mm gap using a novel biodegradable nerve guide tube. The tube was a composite of polyglycolic acid (PGA) mesh coated with collagen which was filled with neurotrophic factors. The left sciatic nerve of ten adult cats was dissected. The stumps were connected by the tube, and fixed gap. Histological examinations carried out 4-16 months after implantation of the tube revealed regeneration of well vascularized nerve tissue. Regeneration of both myelinated, unmyelinated axons and Schwann cells was confirmed by electron microscopy 5 months after surgery. Following injection of horseradish peroxidase (HRP) into a site peripheral to the regenerated segment of the sciatic nerves, motoneurons in the ventral horn of the spinal cord, afferent terminals in the medial portion of the dorsal column of the medulla oblongata, and sensory afferent nerve terminals in the dorsal horn of the spinal cord were labelled. Electrophysiological examinations revealed restoration of evoked electromyograms and sensory evoked potentials (SEPs) recorded from the cerebral cortex as well as the spinal cord. We also found that some of the regenerated motor axons exhibited branching in the regenerated segments. In two cases, a single motoneuronal axon from the regenerated side projected to both flexors and extensors, simultaneously. Our results indicate that the PGA-collagen composite tube is a promising tool for use as a nerve guide tube in peripheral nerve regeneration.

Time course of muscle atrophy and recovery following a phenol-induced nerve block

Clinically, phenol is used often as a neurolytic agent to treat pain and spasticity. The purpose of this study was to examine the time course of denervation and recovery in several hindlimb muscles following application of a 5% aqueous solution of phenol to the sciatic nerve. Phenol was applied to the sciatic nerve of adult female rats either by intraneural or perineural injection. Axonal degeneration was evident within the sciatic nerve 2 days following phenol application, although variable amounts of damage were observed. By 2 weeks, the soleus and tibialis anterior had atrophied to 63% and 51% of control. Reinnervation of hindlimb muscles occurred between 2 and 4 weeks following the nerve block. Following denervation, the soleus became slower in that all of the fibers expressed the slow myosin heavy chain (MHC). At 5 months, maximum tension of the soleus was 74% of control and the muscle consisted of more fast fibers on average, some of which expressed IIx MHC. These data suggest that 5% phenol causes an injury to the nerve that is more severe than a crush injury, and that reinnervation of denervated muscles may be by motoneurons other than those that originally innervated the muscles.

Biotin-dextran: fast retrograde tracing of sciatic nerve motoneurons

We present evidence that biotin-dextran (BD) provides good fast retrograde tracing in the rat sciatic nerve. Using BD injected distal to a crush injury of either tibial or common peroneal nerves, spinal cord motoneuron counts after 48 h compare favorably with counts obtained using horseradish peroxidase. Advantages of BD include fine staining of the soma and its branches, increasing the reliability of motoneuron counting, as well as good staining of sciatic nerve axons 30 mm away from the crush site. BD, already demonstrated to be a good anterograde tracer in the central nervous system, is shown to be a good retrograde tracer in a peripheral nervous system model.

Most dorsal root ganglion neurons of the adult rat survive nerve crush injury

Severe crush of the rat sciatic nerve does not result in any significant cell death among motor neurons (Swett et al., 1991a). The present study reports on the survival of the dorsal root ganglion (DRG) neurons in the same experiments. From 15 to 187 days after crush of the left sciatic nerve, the common peroneal or sural nerve was cut and labeled distal to the injury with a mixture of horseradish peroxidase (HRP) and its wheatgerm agglutinin conjugate (WGA:HRP). In other cases, the crush injury was made far enough distally on a peroneal or sural branch to permit labeling several millimeters proximal to the injury. The procedures for reconstructing the regenerated DRG neuron populations were identical to those used in an earlier study describing the normal sciatic DRG neuron populations in the rat (Swett et al., 1991b). The normal peroneal nerve contains 2699 +/- 557 DRG neurons. When the peroneal nerve was crushed near its point of origin from the sciatic and labeled 10 mm distal to the injury, 2186 +/- 163 DRG neurons were counted, suggesting a decrease of about 19% (p < 0.01). However, when the entire sciatic nerve was crushed, distal labeling of the peroneal nerve revealed a mean number of 2578 +/- 291 DRG neurons, an insignificant reduction (p > 0.2). When the peroneal nerve was labeled proximal to a peroneal crush site, a similar number of DRG neurons (2563 +/- 412) was counted. Results following sural nerve crush were similar. The sural nerve normally contains 1675 +/- 316 DRG neurons. When the nerve was labeled distal to the injury, 1558 +/- 64 DRG neurons were counted--a number almost identical to that found (1529 +/- 240) when this nerve was labeled proximal to the injury. The results demonstrate that within 6 months of severe crush injury of the rat sciatic nerve, the vast majority of DRG neurons survive and regenerate new axons distally beyond the injury site, presumably to reinnervate their original targets.

Long-term effects of deprivation of cell support in the distal stump on peripheral nerve regeneration

The distal stump of an injured peripheral nerve supports regenerating axons by offering a favourable growth substratum and several cell-produced growth factors. Deprivation of cellular factors alone has been shown not to prevent fairly rapid axonal elongation after nerve injury if the growth substratum was preserved. The present study examined possible long-term untoward effects of cell support deprivation during an early phase of nerve regeneration. Rat sciatic nerve was crushed and a 25 mm long distal nerve segment was made acellular by freezing-thawing, while the integrity of the growth substratum for the regenerating axons was preserved. Toe-spreading reflex and skin sensitivity to pinch in the foot were monitored to follow recovery of motor and sensory function, respectively. The number of myelinated axons was determined in the sciatic nerve proximally to the lesion site, and distally in the predominantly sensory sural nerve as well as in the mixed motor nerve to the soleus muscle. Except for a short delay in the onset of recovery, explainable by the reduced elongation rate of axons growing through the acellular nerve segment, we found no deleterious effect of cell support deprivation on sensory or motor function recovery after nerve crush. Most of regenerating sensory neurons did not critically depend on the distal stump cell support. However, a 15% and 25% loss of myelinated axons both proximally to the lesion and distally in the sensory sural nerve, respectively, indicated that a corresponding minor loss of injured sensory neurons occurred when they were deprived of such cell support even if provided with a favourable growth substratum for successful regeneration.(ABSTRACT TRUNCATED AT 250 WORDS)

The resolution of neuropathic hyperalgesia following motor and sensory functional recovery in sciatic axonotmetic mononeuropathies

Nerve lesions producing extensive axonal loss can induce painful hyperalgesic states in man. The affect of axonal regeneration and end-organ reinnervation on hyperalgesia and pain is controversial. This study used two axonotmetic models, the sciatic crush injury (CI) and the sciatic chronic constrictive injury (CCI), to investigate the affects of nerve regeneration and reinnervation on hyperalgesia and presumed painful behavior in rats. The sciatic CI resulted in a transient loss of both sciatic motor function and the withdrawal response to pinch and heat in the sciatic distribution. Extensive recovery of motor function, pinch and heat response occurred over days 23-38 post-crush injury. This temporally corresponded with a plateau in the hindpaw autotomy score and a resolution of the saphenous-mediated pressure and heat hyperalgesia (adjacent neuropathic hyperalgesia; ANH) which developed over the medial dorsum of the hindpaw following the sciatic CI. In contrast, with sciatic transection and distal stump excision, no motor recovery occurs, large areas of the hindpaw remain unresponsive to heat and pinch, and the saphenous mediated ANH fails to resolve over a period of 3 months. When sciatic CI was compared to contralateral sciatic transection within the same rat, the bilateral saphenous-mediated pressure and heat thresholds were initially identical, but by 23-27 days post-crush, the crush side thresholds became hypoalgesic relative to the section side. This demonstrates an attenuation of the crush-induced ANH which temporally corresponds to the recovery of motor and sensory function. When the sciatic nerve was proximally crushed and distally transected (3 cm below the crush site), the saphenous-mediated pressure and heat threshold changes were identical (over 6 weeks of serial testing) to those produced by a contralateral sciatic transection within the same rat. This indicates that the microenvironments surrounding the regenerating axon tips did not differentially affect the development of ANH following sciatic CI or transection. The sciatic CCI resulted in a transient loss of hindpaw motor function without the loss of pinch or heat withdrawal responses in the sciatic distribution. Motor function recovery occurred primarily over days 23-59 post-ligature. During this prolonged period of motor function recovery there was a resolution of the sciatic-mediated plantar surface heat hyperalgesia and the saphenous-mediated heat ANH. The above data support the hypothesis that the successful regeneration of distal axons after axonotmetic lesions can initiate the resolution of neuropathic hyperalgesia.

Location and completeness of reinnervation by two types of neurons at a single target: the feline muscle spindle

Muscle spindles from the tenuissimus muscle of the cat were examined microscopically to assess the precision and completeness of reinnervation of intrafusal muscle fibers by efferent and afferent neurons. Positions of motor and sensory nerve terminals were charted relative to the cross-sectional area enclosed by the outer capsule of the spindle. Profiles of nerve endings were measured for normally innervated and reinnervated spindles. The tenuissimus was deprived of innervation by freezing its nerve, sometimes in conjunction with either spinal ganglion removal or ventral rhizotomy. Sensory and motor terminals occupied separate locales along the length of normal muscle spindles. Nerve terminals of efferent and afferent neurons were located in appropriate positions along the length of spindles when axons of both types of neurons regrew together and when either category of axon regenerated alone. Precise reinnervation of muscle spindles occurred in spite of a diminished diameter of intrafusal fibers. Repopulation of the spindle with motor endings was less complete than that by sensory endings, based on the proportion and size of the regenerated terminals. We conclude that under optimal conditions for axonal regrowth, efferent and afferent neurons reinnervate their respective regions along intrafusal muscle fibers but motor lags sensory reinnervation within the spindle. The mechanism by which positional specificity happens during reinnervation of intrafusal fibers requires neither an interaction between terminals of the two types of neurons nor target cells of normal bulk.

Neonatal nerve injury causes long-term changes in growth and distribution of motoneuron dendrites in the rat

Disruption of neuromuscular contact by nerve-crush during the early postnatal period results in the death of a large proportion of affected motoneurons. Increased activity and abnormal reflex responses are evident in those that survive. We have studied the aberrant dendritic morphology of surviving cells and have attempted to correlate the observed alterations in morphology with the above experimental findings. Motoneurons supplying the extensor hallucis longus muscles of the rat were retrogradely labelled with cholera toxin subunit-B conjugated to horseradish peroxidase. The dendritic tree of labelled cells was analysed in adult animals having undergone unilateral sciatic nerve-crush at birth. Unoperated control animals were also examined. Following nerve-crush at birth, total visible dendritic length was more than 30% smaller than control cells in the transverse plane. This decrease was confined largely to the medially directed segments of the dendritic field and appeared to be due to a reduction in dendritic branching combined with a failure to achieve the correct branch length. There was no overall change in total visible dendritic length in the longitudinal plane, but a reorientation of dendrites in favour of rostrodorsal regions was observed. There was no alteration in dendritic length in cells contralateral to the nerve injury. These results show that nerve injury during early postnatal development produces lasting changes in the distribution of motoneuron dendrites. The localized nature of these changes may explain the altered activity and induced death of motoneurons seen after neonatal nerve-crush.

Impaired motor axon regeneration in the C57BL/Ola mouse

The delayed Wallerian degeneration which occurs in the C57BL/Ola mouse is associated with impaired motor axon regeneration. Following sciatic nerve crush, recovery of the sciatic functional index was delayed and incomplete when compared with recovery in C57BL/6J mice. After facial nerve crush, recovery of whisker movement in Ola mice was also delayed, and there was a prolonged period of partial recovery, not seen in 6J mice. Regeneration rate of the motor axons was measured by the axonal transport technique in sciatic nerve and was approximately 0.7 mm/d for Ola mice, and 4.0 mm/d for 6J mice. Combining these results from our previous work, we conclude that regeneration of both sensory and motor axons is impaired when Wallerian degeneration does not follow its usual time course after injury.

Modification of the dystrophic phenotype after transient neonatal denervation: role of MHC isoforms

While it recently has been demonstrated that it is possible to modify the phenotypic expression of murine dystrophy (dy/dy) (i.e., prevent myofiber loss) by subjecting the extensor digitorum longus (EDL) muscle of 14-day-old dy/dy mice to transient neonatal denervation (Moschella and Ontell, 1987), the mechanism responsible for this phenomenon has not been determined. Since it has been suggested that the effects of dystrophy vary according to fiber type, the fiber type frequency in 100-day-old normal (+/+) and dy/dy EDL muscles subjected to transient neonatal denervation has been determined by immunohistochemical analysis of their myosin heavy chain (MHC) composition. This frequency has been compared with that found in the EDL muscles of 14- and 100-day-old unoperated +/+ and dy/dy mice, in order to determine whether the reinnervation of transiently denervated neonatal muscle results in a preponderance of fibers of the type that might be spared dystrophic deterioration. In unoperated dy/dy muscle there is a progressive decrease in the frequency and in the absolute number of fibers that express MHC2B, with 100-day-old dy/dy muscles having approximately 32% of the number of myofibers fibers containing MHC2B as is found in age-matched +/+ muscles. The number of fibers containing the other fast isoforms (MHC2A and MHC2X) is similar in +/+ and dy/dy muscles at this age, indicating that fibers with MHC2B are most affected by the dystrophic process. Reinnervation following transient neonatal denervation of both the +/+ and the dy/dy EDL muscles results in a similar decrease (approximately 62%) in the number of myofibers containing MHC2B and an increase in myofibers containing the other fast MHC isoforms (MHC2A and MHC2X). The selective effect of dy/dy on fibers containing MHC2B and the sparing of myofibers in transiently denervated dy/dy muscle (which contains a reduced frequency of fibers containing MHC2B) are consistent with, although not direct proof of, the hypothesis that alterations in the fiber type may play a role in the failure of myofibers in transiently denervated dy/dy muscles to undergo dystrophic deterioration. Evidence is presented suggesting that neurons that supply myofibers containing MHC2B may be at a selective disadvantage in their ability to reinnervate neonatally denervated muscles.

A time course analysis of the changes in spontaneous and evoked behaviour in a rat model of neuropathic pain

We have previously demonstrated that scratching was significantly increased in a rat model of polyarthritis and that this could be reversed by morphine and electrical stimulation of pain-modulating brain areas. We therefore proposed that scratching might represent a parameter of chronic pain. In this study, we examined the spontaneous behaviour of rats in a model of peripheral neuropathy induced by loosely tying 4 ligatures around the right common sciatic nerve. In half of the animals (N = 7), the ligatures were made with resorbable sutures and, in the other half (N = 7), with non-resorbable sutures of the same size. Postoperatively, scratching was significantly increased at the ligated side. This increase was already observed on the first postoperative day, and maximal effects were reached on the 3rd day. We also observed a qualitative change in the scratching behaviour; postoperatively, scratching was often a vibratory-like shaking of the hind paw in the air. The time course of the increased scratching was time-locked with the development of allodynia to thermal stimulation. No differences were found either in the time course of the increased scratching behaviour or in the time course of the thermal allodynia between the rats ligated with resorbable and with non-resorbable sutures. However, a difference in the walking pattern, as measured by the sciatic functional index (SFI), was observed between the two groups: whereas the SFI normalized after 4 weeks in rats ligated with resorbable sutures, it remained disturbed until the end of the 16-week observation period in the rats ligated with non-resorbable sutures. Morphine 1, 2 and 5 mg/kg dose-dependently reduced the increased scratching behaviour. This was not due to a general depressant effect on the rats' behaviour. This finding is discussed in light of the debate on opioid sensitivity of neuropathic pain. The present results add new evidence that scratching is a possible sign of chronic pain in the animal.

Electrical field effects on crushed nerve regeneration

The delivery of an electrical field to a transected nerve has been shown to enhance the regeneration. This study examined the effects of such fields on the regeneration of crushed rat sciatic nerve during the first postoperative month. The treated (T) nerve group received a battery implant delivering 10 microA with the cathode at the distal stump. The recovery was compared to an untreated (UT) group and unoperated controls (C). The loss of locomotion behavior and partial recovery (SFI) was identical for the T and UT groups. The index of motor recovery (twitch tension) was also similar (T/C = 48%, UT/C = 53%), but a "window" of enhancement occurred 2-4 days earlier in the T group. Qualitative histology at 28 days suggested a more healthy and normal-appearing nerve in the T group. Morphometric analysis indicated that the nerve area, fiber density, and fiber number in the T group were more similar to those in the control group than to those in the UT group. There were no group differences in the number of HRP-labeled motoneurons, but the enlarged endoneurial space was significantly reduced in the T group compared to the UT group. In conclusion, electrical fields appeared to have a small effect on some aspects of nerve regeneration following crush injury.

Sensory neurons of the rat sciatic nerve

Experiments have been undertaken in this laboratory over recent years to accurately determine the numbers and sizes of somatic neurons which contribute to the normal sciatic nerve, at mid-thigh levels, of the adult, albino rat. This article is concerned with the dorsal root ganglion (DRG) neuron population of the sciatic nerve whose cell bodies were identified through retrograde labeling of cut branches of the sciatic with horseradish peroxidase (HRP) and/or its wheat germ conjugate (WGA-HRP). It is essential to understand the neuronal composition of the normal rat sciatic nerve if the consequences of aging, nerve injury, and surgical repair to improve functional regeneration are to be properly evaluated. Neuron counts were determined from camera-lucida paper drawings of all labeled profiles in DRGs L3-L6 at 100 x magnification. The profiles, obtained by labeling individual branches of the sciatic nerve (sural, lateral sural, tibial, peroneal, medial, and lateral gastrocnemius/soleus nerves) were traced from 40-microns-thick, serial, frozen sections. The sizes of the perikarya, areas and diameters, were determined by tracing the perimeters of the drawn profiles on a digitizing tablet. The tablet's output was inputted directly into a specially designed computer spreadsheet which contained a mathematical table for correcting the split-cell error inherent to the sectioning process. Afferents from any given branch of the sciatic normally occupied two to three adjacent ganglia. Sciatic DRG neurons were normally located in lumbar ganglia L3-L6. Nearly 98-99% of all sciatic DRG perikarya resided in the L4 and L5 DRGs. The L6 DRG, traditionally regarded as an important contributor to the rat sciatic, contained merely 0.4% of its afferent neurons while the L3 ganglion, frequently overlooked as a contributor, contained 1.2% of the mid-thigh sciatic afferents. The mean size of rat DRG neurons was about 29 microns (550-600 microns2). The corrected counts revealed that the normal sciatic nerve (at mid-thigh levels), in rats between 2 and 12 months of age, contained a mean, total DRG neuron population of about 10,500 neurons. This is probably an underestimate by 3-5% of the true number due to occasional unreliable labeling of some of the small DRG neurons. It is estimated that the normal, mean number of sciatic DRG neurons of young to middle-aged rats lies somewhere between 10,500 and 11,000 +/- 2000. The data suggest that nearly 20% of all DRG neurons in the sciatic nerve supply muscle afferents. The vast majority of the remaining neurons are involved with innervation of the skin.(ABSTRACT TRUNCATED AT 400 WORDS)