The Rabbit Brachial Plexus as a Model for Nerve Repair Surgery-Histomorphometric Analysis

Comparison of Different In Vivo Animal Models of Brachial Plexus Avulsion and Its Application in Pain Study

Brachial plexus injuries (BPIs) are high-energy trauma that can result in serious functional problems in the affected upper extremities, and brachial plexus avulsion (BPA) could be considered the most severe type of them. The booming occurrence rate of BPA brings up devastating impact on patients' life. Complications of muscle atrophy, neuropathic pain, and denervation-associated psychological disorders are major challenges in the treatment of BPA. Animal models of BPA are good vehicles for this kind of research. Full understanding of the current in vivo BPA models, which could be classified into anterior approach avulsion, posterior approach avulsion, and closed approach avulsion groups, could help researchers select the appropriate type of models for their studies. Each group of the BPA model has its distinct merits and demerits. An ideal BPA model that can inherit the advantages and make up for the disadvantages is still required for further exploration.

GDNF Gene Therapy to Repair the Injured Peripheral Nerve

A spinal root avulsion is the most severe proximal peripheral nerve lesion possible. Avulsion of ventral root filaments disconnects spinal motoneurons from their target muscles, resulting in complete paralysis. In patients that undergo brachial plexus nerve repair, axonal regeneration is a slow process. It takes months or even years to bridge the distance from the lesion site to the distal targets located in the forearm. Following ventral root avulsion, without additional pharmacological or surgical treatments, progressive death of motoneurons occurs within 2 weeks (Koliatsos et al., 1994). Reimplantation of the avulsed ventral root or peripheral nerve graft can act as a conduit for regenerating axons and increases motoneuron survival (Chai et al., 2000). However, this beneficial effect is transient. Combined with protracted and poor long-distance axonal regeneration, this results in permanent function loss. To overcome motoneuron death and improve functional recovery, several promising intervention strategies are being developed. Here, we focus on GDNF gene-therapy. We first introduce the experimental ventral root avulsion model and discuss its value as a proxy to study clinical neurotmetic nerve lesions. Second, we discuss our recent studies showing that GDNF gene-therapy is a powerful strategy to promote long-term motoneuron survival and improve function when target muscle reinnervation occurs within a critical post-lesion period. Based upon these observations, we discuss the influence of timing of the intervention, and of the duration, concentration and location of GDNF delivery on functional outcome. Finally, we provide a perspective on future research directions to realize functional recovery using gene therapy.

Critical analysis of the value of the rabbit median nerve model for biomedical research on peripheral nerve grafts

The rabbit has been proposed to represent an animal model that allows studying peripheral nerve regeneration across extended gap lengths. We describe here our experiences with the rabbit median nerve model and the obstacles it comes along with. This short communication is meant to inform the community and to prevent other researcher from investing time and animal lives in a model with low translational power.

Brachial plexus nerve injury and repair in a rabbit model part II: Does middle trunk injury result in loss of biceps function while repair results in recovery of biceps function

INTRODUCTION

There is conflicting anatomic and innervation data regarding the rabbit brachial plexus injury model. This study aims to validate a rabbit brachial plexus injury model. We hypothesize the middle trunk (C6, C7) is the primary innervation of the biceps, and when cut and unrepaired, would demonstrate lack of recovery and when repaired would demonstrate evidence of recovery.

MATERIALS AND METHODS

Twenty two male New Zealand white rabbits (3-4 kg) underwent unilateral surgical division of the middle trunk. Five rabbits were randomly assigned to the "no-repair" group while the remaining 17 rabbits underwent direct coaptation ("repair" group). Rabbits were followed for 12 weeks, with ultrasound measurement of biceps cross-sectional area performed preoperatively, and at 4, 8, and 12 weeks postoperatively. At a euthanasia procedure, bilateral compound muscle action potential (CMAP) and isometric tetanic force (ITF) were measured. Bilateral biceps muscles were harvested and wet muscle weight was recorded. The operative side was expressed as a percentage of the non-operated side, and differences between the no repair and repair rabbits were statistically compared.

RESULTS

The repair group demonstrated significantly higher CMA (23.3 vs. 0%, p < .05), ITF (25.6 vs. 0%, p < .05), and wet muscle weight (65.8 vs. 52.0%, p < .05) as compared to the unrepaired group. At 4 weeks postoperatively, ultrasound-measured cross-sectional area of the biceps demonstrated atrophy in both groups. At 12 weeks, the repair group had a significantly larger cross-sectional area as compared to the no-repair group (89.1 vs. 59.3%, p < .05).

CONCLUSIONS

This injury model demonstrated recovery with repair and lack of function without repair. Longer survival time is recommended for future investigations.

Validation of Isometric Tetanic Force as a Measure of Muscle Recovery After Nerve Injury in the Rabbit Biceps

PURPOSE

The purpose of this study was to describe and validate a technique for measurement of isometric tetanic force (ITF) in the rabbit biceps muscle.

MATERIALS AND METHODS

Eighteen New Zealand White rabbits were randomized to test either the right side or the left side first. Under propofol anesthesia, the brachial plexus and biceps brachii were exposed. The middle trunk (C6, C7) was secured in a bipolar electrode. Compound muscle action potential (CMAP) was measured. The proximal, tendinous portion of the biceps was severed at the shoulder and clamped in a custom-made force transducer. Muscle preload and electrical stimulation variables were optimized to obtain the highest tetanic muscle contraction. Wet muscle weight (WMW) and nerve histomorphometry were analyzed. Statistical analysis was performed to determine side-to-side equivalence.

RESULTS

The rabbit biceps muscle force demonstrated side-to-side equivalence with overlapping 95% confidence intervals (95% CI). The right side, expressed as a percentage of the left, averaged 99.69% (95% CI, 88.89%-110.5%). The WMW of the right expressed as a percentage of the left was 98.9% (95% CI, 95.8%-102%).

CONCLUSIONS

The ITF is equivalent from side to side in the rabbit as demonstrated by the high degree of overlap in the 95% CIs for each side. The width of the 95% CI implies that there is more variability in the rabbit upper extremity than for the lower extremity of the rabbit or rat models, and researchers should take this into account when performing sample size estimates in pre-experimental planning.

CLINICAL RELEVANCE

The rabbit biceps muscle ITF measurements can be used to measure motor recovery in a rabbit model of brachial plexus injury and compared with the contralateral uninjured side.