Measurement of forelimb function by digital video motion analysis in rat nerve transection models

Retrograde peripheral nerve regeneration from sensory to motor pathways in rats: a new experimental concept in nerve repair

BACKGROUND

The polarity of nerve grafts does not interfere with axon growth. Our goal was to investigate whether axons can regenerate in a retrograde fashion within sensory pathways and then extend into motor pathways, leading to muscle reinnervation.

METHODS

Fifty-four rats were randomized into four groups. In Group 1, the ulnar nerve was connected end-to-end to the superficial radial nerve after neurectomy of the radial nerve in the axilla. In Group 2, the ulnar nerve was connected end-to-end to the radial nerve distal to the humerus; the radial nerve then was divided in the axilla. In Group 3, the radial nerve was divided in the axilla, but no nerve reconstruction was performed. In Group 4, the radial nerve was crushed in the axilla. Over 6 months, we behaviorally assessed the recovery of toe spread in the right operated-upon forepaw by lifting the rat by its tail and lowering it onto a flat surface. Six months after surgery, rats underwent reoperation, nerve transfers were tested electrophysiologically, and the posterior interosseous nerve (PIN) was removed for histological evaluation.

RESULTS

Rats in the crush group recovered toe spread between 5 and 8 days after surgery. Rats with nerve transfers demonstrated electrophysiological and histological findings of nerve regeneration but no behavioral recovery.

CONCLUSIONS

Ulnar nerve axons regrew into the superficial radial nerve and then into the PIN to reinnervate the extensor digitorum communis. We were unable to demonstrate behavioral recovery because rats cannot readapt to cross-nerve transfer.

Evaluation of motor and sensory neuron populations in a mouse median nerve injury model

BACKGROUND

Peripheral nerves can regenerate and restore function after injury but this process is hindered by many factors including chronic denervation, motor end-plate resorption and Schwann cell senescence. Forelimb injury models in rodents are becoming increasingly popular as they more accurately reflect the physiology and biomechanics of upper extremity nerve injuries. However several aspects of this surgical model remain poorly characterized.

NEW METHOD

C57Bl/6 mice underwent enumeration of median nerve motor and sensory neuron pools using retrograde labeling with or without nerve transection. Distal histomorphometry of uninjured mouse median nerves was also examined. Baseline reference values of volitional forelimb grip strength measurements were determined and the rate of neural elongation was also estimated.

RESULTS

We identified 1363 ± 165 sensory and 216 ± 16 motor neurons within the uninjured dorsal root ganglia (DRG) and ventral spinal cord, respectively. Eight days following injury, approximately 34% of motoneurons had elongated a distance of 5 mm beyond the repair site 8 days following injury. Volitional grip strength decreased 50% with unilateral median nerve transection and was negligible with contralateral flexor tendon tenotomy.

COMPARISON WITH EXISTING METHOD

Our spinal cord and DRG harvesting technique presented here was technically straightforward and reliable. Estimates of motor and sensory neuron numbers for the mouse median nerve compared favourably with studies using intramuscular injection of retrograde neurotracer. Histomorphometry data was consistent with and reinforced reference values in the literature.

CONCLUSIONS

This study provides data that further develops an increasingly popular surgical model for studying peripheral nerve injury and repair.

Modeling Complex Orthopedic Trauma in Rodents: Bone, Muscle and Nerve Injury and Healing

Orthopedic injury can occur from a variety of causes including motor vehicle collision, battlefield injuries or even falls from standing. Persistent limb pain is common after orthopedic injury or surgery and presents a unique challenge, as the initiating event may result in polytrauma to bone, muscle, and peripheral nerves. It is imperative that we understand the tissue-specific and multicellular response to this unique type of injury in order to best develop targeted treatments that improve healing and regeneration. In this Mini Review we will first discuss current rodent models of orthopedic trauma/complex orthotrauma. In the second section, we will focus on bone-specific outcomes including imaging modalities, biomechanical testing and immunostaining for markers of bone healing/turnover. In the third section, we will discuss muscle-related pathology including outcome measures of fibrosis, muscle regeneration and tensile strength measurements. In the fourth section, we will discuss nervous system-related pathology including outcome measures of pain-like responses, both reflexive and non-reflexive. In all sections we will consider parallels between preclinical outcome measures and the functional and mechanistic findings of the human condition.

Evaluation of Functional Recovery in Rats After Median Nerve Resection and Autograft Repair Using Computerized Gait Analysis

Computerized gait analysis is a common evaluation method in rat models of hind limb nerve injuries, but its use remains unpublished in models of segmental nerve injury of the forelimb. It was the aim of this work to investigate if computerized gait analysis is a feasible evaluation method in a rat model of segmental median nerve injury and autograft repair. Ten male Lewis rats underwent 7-mm resection of the right median nerve with immediate autograft repair. The left median nerve was resected without repair and served as an internal control. Animals were assessed for 12 weeks after surgery via CatWalk (CW) gait analysis every 2 weeks. Evaluation of motor recovery by means of the grasping test was performed weekly while electrophysiological measurements were performed at the end of the observation period. CW data were correlated with grasping strength at each post-operative time point. CW data were also correlated with electrophysiology using linear regression analysis. Principal component analysis was performed to identify clusters of outcome metrics. Recovery of motor function was observable 4 weeks after surgery, but grasping strength was significantly reduced (p < 0.01) compared to baseline values until post-operative week 6. In terms of sensory recovery, the pain-related parameter Duty Cycle showed significant (p < 0.05) recovery starting from post-operative week 8. The Print Area of the right paw was significantly (p < 0.05) increased compared to the left side starting from post-operative week 10. Various parameters of gait correlated significantly (p < 0.05) with mean and maximum grasping strength. However, only Stand Index showed a significant correlation with compound muscle action potential (CMAP) amplitude (p < 0.05). With this work, we prove that computerized gait analysis is a valid and feasible method to evaluate functional recovery after autograft repair of the rat median nerve. We were able to identify parameters such as Print Area, Duty Cycle, and Stand Index, which allow assessment of nerve regeneration. The course of these parameters following nerve resection without repair was also assessed. Additionally, external paw rotation was identified as a valid parameter to evaluate motor reinnervation. In summary, computerized gait analysis is a valuable additional tool to study nerve regeneration in rats with median nerve injury.

The Median Nerve Injury Model in Pre-clinical Research - A Critical Review on Benefits and Limitations

The successful introduction of innovative treatment strategies into clinical practise strongly depends on the availability of effective experimental models and their reliable pre-clinical assessment. Considering pre-clinical research for peripheral nerve repair and reconstruction, the far most used nerve regeneration model in the last decades is the sciatic nerve injury and repair model. More recently, the use of the median nerve injury and repair model has gained increasing attention due to some significant advantages it provides compared to sciatic nerve injury. Outstanding advantages are the availability of reliable behavioural tests for assessing posttraumatic voluntary motor recovery and a much lower impact on the animal wellbeing. In this article, the potential application of the median nerve injury and repair model in pre-clinical research is reviewed. In addition, we provide a synthetic overview of a variety of methods that can be applied in this model for nerve regeneration assessment. This article is aimed at helping researchers in adequately adopting this in vivo model for pre-clinical evaluation of peripheral nerve reconstruction as well as for interpreting the results in a translational perspective.

Activation of Intrinsic Growth State Enhances Host Axonal Regeneration into Neural Progenitor Cell Grafts

Axonal regeneration after spinal cord injury (SCI) can be enhanced by activation of the intrinsic neuronal growth state and, separately, by placement of growth-enabling neural progenitor cell (NPC) grafts into lesion sites. Indeed, NPC grafts support regeneration of all host axonal projections innervating the normal spinal cord. However, some host axons regenerate only short distances into grafts. We examined whether activation of the growth state of the host injured neuron would elicit greater regeneration into NPC grafts. Rats received NPC grafts into SCI lesions in combination with peripheral "conditioning" lesions. Six weeks later, conditioned host sensory axons exhibited a significant, 9.6-fold increase in regeneration into the lesion/graft site compared with unconditioned axons. Regeneration was further enhanced 1.6-fold by enriching NPC grafts with phenotypically appropriate sensory neuronal targets. Thus, activation of the intrinsic host neuronal growth state and manipulation of the graft environment enhance axonal regeneration after SCI.

Exercise Ameliorates Motor Deficits and Improves Dopaminergic Functions in the Rat Hemi-Parkinson's Model

To determine the influences of exercise on motor deficits and dopaminergic transmission in a hemiparkinson animal model, we measured the effects of exercise on the ambulatory system by estimating spatio-temporal parameters during walking, striatal dopamine (DA) release and reuptake and synaptic plasticity in the corticostriatal pathway after unilateral 6-OHDA lesions. 6-OHDA lesioned hemiparkinsonian rats were exercised on a fixed speed treadmill for 30 minutes per day. Controls received the same lesion but no exercise. Animals were subsequently analyzed for behavior including gait analysis, rotarod performance and apomorphine induced rotation. Subsequently, in vitro striatal dopamine release was analyzed by using FSCV and activity-dependent plasticity in the corticostriatal pathway was measured in each group. Our data indicated that exercise could improve motor walking speed and increase the apomorphine-induced rotation threshold. Exercise also ameliorated spatiotemporal impairments in gait in PD animals. Exercise increased the parameters of synaptic plasticity formation in the corticostriatal pathway of PD animals as well as the dynamics of dopamine transmission in PD animals. Fixed speed treadmill training 30 minutes per day could ameliorate spatial-temporal gait impairment, improve walking speed, dopamine transmission as well as corticostriatal synaptic plasticity in the unilateral 6-OHDA lesioned rat model.

Reflex-based grasping, skilled forelimb reaching, and electrodiagnostic evaluation for comprehensive analysis of functional recovery-The 7-mm rat median nerve gap repair model revisited

INTRODUCTION

The rat median nerve injury and repair model gets increasingly important for research on novel bioartificial nerve grafts. It allows follow-up evaluation of the recovery of the forepaw functional ability with several sensitive techniques. The reflex-based grasping test, the skilled forelimb reaching staircase test, as well as electrodiagnostic recordings have been described useful in this context. Currently, no standard values exist, however, for comparison or comprehensive correlation of results obtained in each of the three methods after nerve gap repair in adult rats.

METHODS

Here, we bilaterally reconstructed 7-mm median nerve gaps with autologous nerve grafts (ANG) or autologous muscle-in-vein grafts (MVG), respectively. During 8 and 12 weeks of observation, functional recovery of each paw was separately monitored using the grasping test (weekly), the staircase test, and noninvasive electrophysiological recordings from the thenar muscles (both every 4 weeks). Evaluation was completed by histomorphometrical analyses at 8 and 12 weeks postsurgery.

RESULTS

The comprehensive evaluation detected a significant difference in the recovery of forepaw functional motor ability between the ANG and MVG groups. The correlation between the different functional tests evaluated precisely displayed the recovery of distinct levels of forepaw functional ability over time.

CONCLUSION

Thus, this multimodal evaluation model represents a valuable preclinical model for peripheral nerve reconstruction approaches.

Median and ulnar nerve injuries reduce volitional forelimb strength in rats

INTRODUCTION

Peripheral nerve injuries (PNI) are among the leading causes of physical disability in the United States. The majority of injuries occur in the upper extremities, and functional recovery is often limited. Robust animal models are critical first steps for developing effective therapies to restore function after PNI.

METHODS

We developed an automated behavioral assay that provides quantitative measurements of volitional forelimb strength in rats. Multiple forelimb PNI models involving the median and ulnar nerves were used to assess forelimb function for up to 13 weeks postinjury.

RESULTS

Despite multiple weeks of task-oriented training following injury, rats exhibit significant reductions in multiple quantitative parameters of forelimb function, including maximal pull force and speed of force generation.

DISCUSSION

This study demonstrates that the isometric pull task is an effective method of evaluating forelimb function following PNI and may aid in development of therapeutic interventions to restore function. Muscle Nerve 56: 1149-1154, 2017.

Functional evaluation of peripheral nerve regeneration and target reinnervation in animal models: a critical overview

Peripheral nerve injuries usually lead to severe loss of motor, sensory and autonomic functions in the patients. Due to the complex requirements for adequate axonal regeneration, functional recovery is often poorly achieved. Experimental models are useful to investigate the mechanisms related to axonal regeneration and tissue reinnervation, and to test new therapeutic strategies to improve functional recovery. Therefore, objective and reliable evaluation methods should be applied for the assessment of regeneration and function restitution after nerve injury in animal models. This review gives an overview of the most useful methods to assess nerve regeneration, target reinnervation and recovery of complex sensory and motor functions, their values and limitations. The selection of methods has to be adequate to the main objective of the research study, either enhancement of axonal regeneration, improving regeneration and reinnervation of target organs by different types of nerve fibres, or increasing recovery of complex sensory and motor functions. It is generally recommended to use more than one functional method for each purpose, and also to perform morphological studies of the injured nerve and the reinnervated targets.

Gait cycle analysis: parameters sensitive for functional evaluation of peripheral nerve recovery in rat hind limbs

BACKGROUND

Video-assisted gait kinetics analysis has been a sensitive method to assess rat sciatic nerve function after injury and repair. However, in conduit repair of sciatic nerve defects, previously reported kinematic measurements failed to be a sensitive indicator because of the inferior recovery and inevitable joint contracture.

OBJECTIVE

This study aimed to explore the role of physiotherapy in mitigating joint contracture and to seek motion analysis indices that can sensitively reflect motor function.

METHODS

Data were collected from 26 rats that underwent sciatic nerve transection and conduit repair. Regular postoperative physiotherapy was applied. Parameters regarding step length, phase duration, and ankle angle were acquired and analyzed from video recording of gait kinetics preoperatively and at regular postoperative intervals.

RESULTS

Stride length ratio (step length of uninjured foot/step length of injured foot), percent swing of the normal paw (percentage of the total stride duration when the uninjured paw is in the air), propulsion angle (toe-off angle subtracted by midstance angle), and clearance angle (ankle angle change from toe off to midswing) decreased postoperatively comparing with baseline values. The gradual recovery of these measurements had a strong correlation with the post-nerve repair time course.

CONCLUSIONS

Ankle joint contracture persisted despite rigorous physiotherapy. Parameters acquired from a 2-dimensional motion analysis system, that is, stride length ratio, percent swing of the normal paw, propulsion angle, and clearance angle, could sensitively reflect nerve function impairment and recovery in the rat sciatic nerve conduit repair model despite the existence of joint contractures.

The sciatic nerve injury model in pre-clinical research

In the pre-clinical view, the study of peripheral nerve repair and regeneration still needs to be carried out in animal models due to the structural complexity of this organ which can be only partly simulated in vitro. The far most used experimental model is based on the injury of the sciatic nerve, the largest nerve trunk in mammals. In this paper, the potential application of the sciatic nerve injury model in pre-clinical research is critically reviewed. This paper is aimed at helping researchers in properly employing this in vivo model for the study of nerve repair and regeneration as well as interpreting the results in a clinical translation perspective.

The optimal distance between two electrode tips during recording of compound nerve action potentials in the rat median nerve

The distance between the two electrode tips can greatly influence the parameters used for recording compound nerve action potentials. To investigate the optimal parameters for these recordings in the rat median nerve, we dissociated the nerve using different methods and compound nerve action potentials were orthodromically or antidromically recorded with different electrode spacings. Compound nerve action potentials could be consistently recorded using a method in which the middle part of the median nerve was intact, with both ends dissociated from the surrounding fascia and a ground wire inserted into the muscle close to the intact part. When the distance between two stimulating electrode tips was increased, the threshold and supramaximal stimulating intensity of compound nerve action potentials were gradually decreased, but the amplitude was not changed significantly. When the distance between two recording electrode tips was increased, the amplitude was gradually increased, but the threshold and supramaximal stimulating intensity exhibited no significant change. Different distances between recording and stimulating sites did not produce significant effects on the aforementioned parameters. A distance of 5 mm between recording and stimulating electrodes and a distance of 10 mm between recording and stimulating sites were found to be optimal for compound nerve action potential recording in the rat median nerve. In addition, the orthodromic compound action potential, with a biphasic waveform that was more stable and displayed less interference (however also required a higher threshold and higher supramaximal stimulus), was found to be superior to the antidromic compound action potential.

Granulocyte colony-stimulating factor (G-CSF) positive effects on muscle fiber degeneration and gait recovery after nerve lesion in MDX mice

BACKGROUND

G-CSF has been shown to decrease inflammatory processes and to act positively on the process of peripheral nerve regeneration during the course of muscular dystrophy.

AIMS

The aims of this study were to investigate the effects of treatment of G-CSF during sciatic nerve regeneration and histological analysis in the soleus muscle in MDX mice.

METHODS

Six-week-old male MDX mice underwent left sciatic nerve crush and were G-CSF treated at 7 days prior to and 21 days after crush. Ten and twenty-one days after surgery, the mice were euthanized, and the sciatic nerves were processed for immunohistochemistry (anti-p75(NTR) and anti-neurofilament) and transmission electron microscopy. The soleus muscles were dissected out and processed for H&E staining and subsequent morphologic analysis. Motor function analyses were performed at 7 days prior to and 21 days after sciatic crush using the CatWalk system and the sciatic nerve index.

RESULTS

Both groups treated with G-CSF showed increased p75(NTR) and neurofilament expression after sciatic crush. G-CSF treatment decreased the number of degenerated and regenerated muscle fibers, thereby increasing the number of normal muscle fibers.

CONCLUSIONS

The reduction in p75(NTR) and neurofilament indicates a decreased regenerative capacity in MDX mice following a lesion to a peripheral nerve. The reduction in motor function in the crushed group compared with the control groups may reflect the cycles of muscle degeneration/regeneration that occur postnatally. Thus, G-CSF treatment increases motor function in MDX mice. Nevertheless, the decrease in baseline motor function in these mice is not reversed completely by G-CSF.

Challenges Facing Quantification of Rat Locomotion along Beams of Varying Widths

Optoelectronic motion capture systems have been widely used to investigate temporal gait parameters in humans and animals in order to understand function and behavioural attributes of different pathologies, e.g. Parkinson's disease (PD). The aim of the present paper was to investigate the practicality of utilising this system to investigate the effects of a unilateral 6-hydroxydopamine (6-OHDA) lesion on rat locomotion while walking on beams of varying widths (graduated, narrow, and wide). Temporal gait parameters of ten male Lister Hooded rats (five controls and five hemiparkinsonian) were observed using passive markers placed in locations that were representative of their four limbs and their body axis. The results demonstrate that marker-based motion capture can provide an effective and simple approach to quantifying temporal gait parameters for rat models of PD. They also reveal how the width of the path affects the locomotion in both experimental cohorts. Such measurements can be compared with human motion analysis to explore correlations between the animal model and human behaviour, which is an important step for translational medicine.

Quantitative evaluation of movement and strength of the upper limb after transection of the C-7 nerve: is it possible in an animal model?

Object

Contralateral C-7 nerve transfer has been used clinically for more than 20 years. The increased interest in studies of transfer effectiveness at different target muscles, posttransfer cocontraction, and brain plasticity has prompted the need for an animal model. In addition to the conventional electrophysiological, histomorphometric, and biomechanical evaluation modalities, quantitative functional and behavioral evaluation will be crucial in applying this kind of model. The aim of this study was to establish a C-7 transection animal model and quantify the changes in upper-limb joint movement and muscle power.

Methods

A C-7 nerve transection model was created in Sprague-Dawley rats, the brachial plexus of which resembles the human brachial plexus. The impact of C-7 transection on donor limb function—namely, strength, movement, and coordination—was evaluated in 6 rats. Muscle strength (power reported in g) was measured as a grasping task. The active range of motion (ROM; angle reported in °) of the elbow, wrist, and metacarpophalangeal joints was quantified by computerized video motion analysis. Antiresistance coordinated movement (speed reported in seconds) was assessed by the vertical rope-climbing test. These tests were carried out before surgery and at 2, 4, 6, 8, 10, 14, 21, and 28 days after C-7 transection. Repeated-measures 1-way analysis of variance was applied for statistical analysis. When the overall probability value was < 0.05, the Dunnett multiple-comparison posttest was used to compare postoperative values with preoperative baseline values.

Results

Immediately after C-7 transection, the mean ± SD grip strength declined from 378.50 ± 20.55 g to 297.77 ± 15.04 g. Active elbow extension was impaired, as shown by a significant decrease of the elbow extension angle. The speed of vertical rope climbing was also reduced. Elbow flexion, wrist flexion and extension, and metacarpophalangeal joint flexion and extension were not impaired. Fast recovery of motor function was observed thereafter. Grip strength, range of active elbow extension, and speed of rope climbing returned to baseline values at postoperative Days 4, 8, and 8, respectively.

Conclusions

The ROM and muscle strength of the upper limb in rats can be measured quantitatively in studies that simulate clinical situations. Application of these functional evaluation modalities in a C-7 nerve transection rat model confirmed that transection of C-7 causes only temporary functional dysfunction to the donor limb. The results obtained in this animal model mimic those seen in humans who undergo contralateral C-7 nerve harvesting.

Functional and morphological assessment of a standardized crush injury of the rat median nerve

The availability of effective experimental models for investigating nerve regeneration and designing new strategies for promoting this unique repair process is important. The aim of this study was to standardize a rat median nerve crush injury model using a non-serrated clamp exerting a compression force of 17.02 MPa for a duration of 30s. Results showed that functional recovery, evaluated by grasping test, was already detectable at day-12 and progressively increased until day-28 after which animal performance plateaued until the end of testing (day-42), reaching a range of 75-80% of pre-operative values. Morphological analysis on the median nerve segments, distal to the crush lesion, which were withdrawn at the end of the experiment showed that regenerated nerve fibers are significantly more numerous and densely packed; they are also smaller and have a thinner myelin sheath compared to controls. Together, these results provide a baseline characterization of the crush median nerve injury experimental model for its employment in the investigation of nerve regeneration research, especially when a reproducible regeneration process is required, such as for the study of biological mechanisms of peripheral nerve fiber regeneration or development of new therapeutic agents for promoting posttraumatic nerve repair.

Chapter 7: Methods and protocols in peripheral nerve regeneration experimental research: part IV-kinematic gait analysis to quantify peripheral nerve regeneration in the rat

Functional recovery is one of the primary goals of therapeutic intervention in peripheral nerve research. The number and diversity of tests which have been used to assess functional recovery after experimental interventions often makes it difficult to recommend any particular indicator of nerve regeneration. Functional assessment after sciatic nerve lesion has long been focused on walking track analysis; however, it is important to note that the validity of the sciatic functional index has been questioned by several researchers. In the last decade, several authors have designed a series of sensitive quantitative methods to assess the recovery of locomotor function using computerized rat gait analysis. The objective of the present review is to provide a helpful tool for the peripheral nerve investigator, by integrating the most important gait kinematic measures described in the literature that can be gathered with this technology.

Electrophysiologic findings and grip strength after nerve injuries in the rat forelimb

We developed electrophysiologic methods for testing the three major forelimb nerves as a tool to evaluate motor and sensory recovery in rats. Median, ulnar, or radial nerves were transected and repaired in Sprague-Dawley rats. Compound muscle action potentials (CMAPs) and somatosensory evoked potentials (SSEPs) were recorded preoperatively and at various postoperative intervals. Correlation between grip strength and CMAPs was investigated. Reliable CMAPs were recorded for all three nerves. Median- or ulnar-nerve-derived SSEPs were reliably recorded; radial SSEPs could not be recorded. CMAPs followed typical regeneration patterns after nerve repair. SSEPs showed a consistent peak latency but fluctuating amplitude. Grip strength and median CMAP amplitude correlated positively. We conclude that it is possible to conduct minimally invasive electrophysiologic testing in rat forelimbs. The CMAP is a valid parameter that shows the typical time course of nerve regeneration and reinnervation.