A noninvasive functional evaluation following peripheral nerve repair with electromyography in a rat model

Translating morphology from bench side to bed side via neurophysiology: 8-min protocol for peripheral neuropathy research

BACKGROUND

Peripheral neuropathy treatment is not always satisfactory. To fill this gap, inferences from bench side are warranted, where morphological and pathogenetic determinations can be performed. Nerve conduction studies (NCS) are ideal to translate results from preclinical to clinical setting.

NEW METHODS

We propose a comprehensive 8-minute protocol for sensory-motor neurophysiological assessment, similar to routine clinical practice: sensory proximal and distal caudal nerves, motor caudal nerve, and sensory digital nerve recordings were used and tested in 2 different experimental settings. In Experiment 1 we compared control (CTRL) animals to a severe sensory-motor polyneuropathy (animals treated with vincristine [VCR]), and in Experiment 2 CTRL animals were compared to a mild sensory polyneuropathy (animals treated with oxaliplatin [OHP]). NCS were performed after 1-month of chemotherapy and matched with confirmatory neuropathological analyses.

RESULTS

VCR treated animals showed, at NCS, a relevant sensory-motor polyneuropathy ensued at the end of treatment; whereas, OHP animals showed a mild distal sensory neuropathy. These patterns were confirmed by neuropathological analysis.

COMPARISON WITH EXISTING METHODS

In literature, the majority of proposed neurophysiological protocols relies mainly on a single nerve testing, rather than a combination of them, and only a few studies tested both caudal and sciatic nerve branches, nevertheless not aiming at fully reproduce clinical protocols (e.g., seeking for length-dependency); to provide evidence of appropriateness of our protocol we applied a gold standard: neuropathology.

CONCLUSION

The simple and rapid protocol here presented can be suggested as a good translation outcome measure in preclinical setting.

Polymeric nanofibrous nerve conduits coupled with laminin for peripheral nerve regeneration

Artificial nerve guidance conduits (NGCs) are being investigated as an alternative to autografts, since autografts are limited in supply. A polycaprolactone (PCL)-based spiral NGC with crosslinked laminin on aligned nanofibers was evaluated in vivo post a successful in vitro assessment. PC-12 cell assays confirmed that the aligned nanofibers functionalized with laminin were able to guide and enhance neurite outgrowth. In the rodent model, the data demonstrated that axons were able to regenerate across the critical nerve gap, when laminin was present. Without laminin, the spiral NGC with aligned nanofibers group resulted in a random cluster of extracellular matrix tissue following injuries. The reversed autograft group performed best, showing the most substantial improvement based on nerve histological assessment and gastrocnemius muscle measurement. Nevertheless, the recovery time was too short to obtain meaningful data for the motor functional assessments. A full motor recovery may take up to years. An interesting observation was noted in the crosslinked laminin group. Numerous new blood capillary-like structures were found around the regenerated nerve. Owing to recent studies, we hypothesized that new blood vessel formation could be one of the key factors to increase the successful rate of nerve regeneration in the current study. Overall, these findings indicated that the incorporation of laminin into polymeric nerve conduits is a promising strategy for enhancing peripheral nerve regeneration. However, the best combination of contact-guidance cues, haptotactic cues, and chemotactic cues have yet to be realized. The natural sequence of nerve regeneration should be studied more in-depth before modulating any strategies.

Rabbit facial nerve anastomosis with fibrin glue: nerve conduction velocity evaluation

AIM

The aim of this study was to evaluate the use of fibrin glue on nerve anastomosis, and study conduction velocity obtained by surface electrodes.

METHODS

In this experimental model we evaluated nerve conduction velocity differences in the preoperative and postoperative periods, for the left facial nerve of 12 rabbits. Then, we evaluated whether there were correlations between conduction velocity and the number of postoperative regenerated axons. The sectioned nerves were anastomosed with fibrin glue. The muscle action potentials were obtained from surface electrodes. The stimulation electrode was placed immediately before the ear pinna (facial nerve trunk) and the recording surface electrode was placed on the quadratus labii inferioris muscle.

RESULTS

The facial nerve normal conduction velocity mean value was of 36.53 m/sec. On the postoperative period, the mean conduction velocity was approximately 81% of the normal mean value. A significant correlation was not observed between the postoperative conduction velocity and the number of regenerated axons (p=0.146).

CONCLUSION

The fibrin glue can be used on nerve anastomosis in this animal model and nerve.

A Novel Drug Therapy for Recurrent Laryngeal Nerve Injury Using T-588

OBJECTIVES/HYPOTHESIS

We have previously shown that gene therapy using Insulin-like growth factor (IGF)-I, glial cell line-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF), or a combination of these trophic factors, is a treatment option for recurrent laryngeal nerve (RLN) palsy. However, there remain some difficulties preventing this option from becoming a common clinical therapy for RLN injury. Thus, we need to develop novel treatment option that overcomes the problems of gene therapy.R(-)-1-(benzothiophen-5-yl)-2-[2-N,N-diethylamino]ethoxy]ethanol hydrochloride (T-588), a synthetic compound, is known to have neuroprotective effects on neural cells. In the present study, the possibility of new drug treatments using T-588 for RLN injury was assessed using rat models.

STUDY DESIGN

Animal study.

METHODS

Animals were administered T-588 for 4 weeks. The neuroprotective effects of T-588 administration after vagal nerve avulsion and neurofunctional recovery after recurrent laryngeal nerve crush were studied using motoneuron cell counting, evaluation of choline acetyltransferase immunoreactivity, the electrophysiologic examination, and the re-mobilization of the vocal fold.

RESULTS

T-588 administration successfully prevented motoneuron loss and ameliorated the choline acetyltransferase immunoreactivity in the ipsilateral nucleus ambiguus after vagal nerve avulsion. Significant improvements of motor nerve conduction velocity of the RLN and vocal fold movement were observed in the treatment group when compared to controls.

CONCLUSION

These results indicate that oral administration of T-588 might be a promising therapeutic option in treating peripheral nerve injury.

Gene therapy for laryngeal paralysis

OBJECTIVES

The surgical options for laryngeal paralysis only achieve static changes of vocal fold position. Laryngeal reinnervation procedures have had little impact on the return of dynamic laryngeal function. The development of a new treatment for laryngeal paralysis, aimed at the return of dynamic function and neurologic restoration and regeneration, is necessary.

METHODS

To assess the possibility of gene therapy for laryngeal paralysis aiming for the return of dynamic laryngeal function, we investigated the therapeutic effects of gene therapy using rat laryngeal paralysis models.

RESULTS

In a rat vagal nerve avulsion model, we transferred glial cell line-derived neurotrophic factor (GDNF) gene into the nucleus ambiguus using an adenovirus vector. Two and 4 weeks after the GDNF gene transfer, a significantly larger number of surviving motoneurons was observed. These neuroprotective effects of GDNF gene transfer were enhanced by simultaneous brain-derived neurotrophic factor gene transfer. In a rat recurrent laryngeal nerve crush model, we transferred GDNF gene into recurrent laryngeal nerve fibers after crush injury. Two and 4 weeks after GDNF gene transfer, we observed significantly faster nerve conduction velocity and better vocal fold motion recovery.

CONCLUSIONS

These results indicate that gene therapy could be a future treatment strategy for laryngeal paralysis. Further studies will be necessary to demonstrate the safety of the vector before clinical application.

Anastomose do nervo facial de coelhos com cola de fibrina: estudo da velocidade de condução nervosa

OBJETIVO: Este estudo tem o objetivo de avaliar através da velocidade de condução nervosa com eletrodos de superfície a utilização da cola de fibrina na anastomose nervosa. MÉTODOS: Neste experimento, foram avaliadas as diferenças entre as velocidades de condução nervosa pré e pós-operatória do nervo facial esquerdo de 12 coelhos. Foi verificada a existência de correlação entre a velocidade de condução nervosa e o número de axônios regenerados no pós-operatório. Os nervos transeccionados foram unidos com cola de fibrina. O potencial de ação motora foi obtido com o uso de eletrodos de superfície. O eletrodo de estimulação foi colocado imediatamente à frente do pavilhão auditivo (tronco do nervo facial) e o eletrodo de gravação foi colocado no músculo quadrado do lábio inferior. RESULTADOS: A média normal da velocidade de condução nervosa foi de 36,53 m/seg. Ao final do período, a velocidade de condução nervosa atingiu um valor de aproximadamente 81% do valor normal. Não foi observada correlação significativa entre a velocidade de condução nervosa pós-operatória e o número de axônios regenerados (p=0,146). CONCLUSÃO: A anastomose com cola de fibrina pode ser utilizada para anastomose nervosa no modelo animal e nervo estudados.

Adenoviral GDNF gene transfer enhances neurofunctional recovery after recurrent laryngeal nerve injury

To assess the possibility of gene therapy for recurrent laryngeal nerve (RLN) injury, we examined functional and histological recovery after glial cell line-derived neurotrophic factor (GDNF) gene transfer in a rat RLN crush model. Adenoviral vector encoding beta-galactosidase gene (AxCALacZ) or human GDNF gene (AxCAhGDNF) was injected into the crush site of the RLN. Neurons in the nucleus ambiguus on the crushed side were labeled with X-gal or GDNF immnohistochemistry after AxCALacZ or AxCAhGDNF injection. Reverse transcription-polymerase chain reaction analysis revealed expression of human GDNF mRNA transcripts in brainstem tissue containing the nucleus ambiguus on the crushed side after AxCAhGDNF injection. Animals injected with AxCAhGDNF displayed significantly improved motor nerve conduction velocity of the RLN and recovery rate of vocal fold movement at 2 and 4 weeks after treatment as compared to controls. AxCAhGDNF-injected animals showed a significantly larger axonal diameter and improved remyelination in crushed RLN as compared to controls. Adenoviral GDNF gene transfer may thus promote laryngeal function recovery after RLN injury. Inoculation of adenoviral vector containing the GDNF gene at the site of damage soon after nerve injury may assist patients with laryngeal paralysis caused by nerve injury during head and neck surgery.

Functional assessment of sciatic nerve recovery: biodegradable poly (DLLA-epsilon-CL) nerve guide filled with fresh skeletal muscle

The aim of this study was to compare functional peripheral nerve recovery in the rat sciatic nerve model after reconstruction of a 10-mm gap with a biodegradable poly (DLLA-epsilon-CL) nerve guide, as filled with either fresh skeletal muscle or phosphate-buffered saline (PBS). During 24 weeks of recovery, motor and sensory functional evaluation was tested by extensor postural thrust (EPT) and withdrawal reflex latency (WRL), respectively. At the end of the experiment, anesthetized animals were prepared for motor nerve conduction velocity (MNCV) studies, followed by gastrocnemius and soleus muscle weight measurement. Motor functional recovery was greater in the muscle-grafted group, and reached a significant difference from weeks 8-12 (P < 0.05). The results of this investigation suggest that filling a nerve guide with fresh skeletal muscle induces faster maturation of regenerated nerve fibers in comparison with traditional tubular repair.

Conduction velocity of the rabbit facial nerve: a noninvasive functional evaluation

The aim of this study was to evaluate standardized conduction velocity data for uninjured facial nerve and facial nerve repaired with autologous graft nerves and synthetic materials. An evaluation was made measuring the preoperative differences in the facial nerve conduction velocities on either side, and ascertaining the existence of a positive correlation between facial nerve conduction velocity and the number of axons regenerated postoperatively. In 17 rabbits, bilateral facial nerve motor action potentials were recorded pre- and postoperatively. The stimulation surface electrodes were placed on the auricular pavilion (facial nerve trunk) and the recording surface electrodes were placed on the quadratus labii inferior muscle. The facial nerves were isolated, transected and separated 10 mm apart. The gap between the two nerve ends was repaired with autologous nerve grafts and PTFE-e (polytetrafluoroethylene) or collagen tubes. The mean of maximal conduction velocity of the facial nerve was 41.10 m/s. After 15 days no nerve conduction was evoked in the evaluated group. For the period of 2 and 4 months the mean conduction velocity was approximately 50% of the normal value in the subgroups assessed. A significant correlation was observed between the conduction velocity and the number of regenerated axons. Noninvasive functional evaluation with surface electrodes can be useful for stimulating and recording muscle action potentials and for assessing the functional state of the facial nerve.

Effects of nerve growth factor on the neurotization of denervated muscles

Studies on surgical repair techniques of the peripheral nerve are still trying to improve the outcome. There are many studies on the effects of various neurotrophic factors on the transected peripheral nerve. Muscular neurotization, which is the direct implantation of the nerve to the target denervated skeletal muscle, is one of the techniques used when the primary repair of the peripheral nerves is not possible. The effects of nerve growth factor (NGF), which is one of the primary neurotrophic factors, on the reinnervation of denervated muscles by neurotization is investigated in this experimental study. The denervated soleus muscle was neurotized via peroneal nerve implantation (group 1), and NGF was administered to the neurotized muscle (group 2). All animals were evaluated at weeks 8, 10, and 12 using electromyography. Muscle contractility, muscle weight, and histological morphometric tests were performed at week 12. The experimental groups were compared with each other and normal control values. Electromyographically, group 2 (direct nerve implantation + NGF) demonstrated better reinnervation in all evaluations. The study of muscle weight showed that the muscle mass was 75% of the normal soleus muscle in group 1 and was 85% of the normal side in group 2 at the end of week 12. In group 1, the twitch force was 56% of the normal soleus muscle and was 71% in group 2. Tetanic force was 53% of the normal soleus muscle in group 1 and 68% in group 2. Histological morphometric studies revealed that there was a decrease in the density of the motor end plates in group 1, but there was no statistically significant difference between the normal soleus muscles and the NGF applied to group 2. The positive effects of NGF on the neurotization of denervated muscles seen in this study suggest that it may be useful for treating some difficult reconstructions caused by denervation.

Methods to evaluate functional nerve recovery in adult rats: walking track analysis, video analysis and the withdrawal reflex

The aim of this study was to compare different methods for the evaluation of functional nerve recovery. Three groups of adult male Wistar rats were studied. In group A, a 12-mm gap between nerve ends was bridged by an autologous nerve graft; in rats of group B we performed a crush lesion of the sciatic nerve and group C consisted of non-operated control rats. The withdrawal reflex, elicited by an electric stimulus, was used to evaluate the recovery of sensory nerve function. To investigate motor nerve recovery we analyzed the walking pattern. Three different methods were used to obtain data for footprint analysis: photographic paper with thickened film developer on the paws, normal white paper with finger paint, and video recordings. The footprints were used to calculate the sciatic function index (SFI). From the video recordings, we also analyzed stepcycles. The withdrawal reflex is a convenient and reproducible test for the evaluation of global sensory nerve recovery. Recording walking movements on video and the analysis of footplacing is a perfect although time-consuming method for the evaluation of functional aspects of motor nerve recovery.

Fabrication of Silicone Tubes in Experimental Nerve Surgery

A technique of fabricating silicone tubes to the desired dimensions from a silicone sheet is described. The fabricated tube was used successfully as a conduit for the rat tibial nerve defect. The advantages and disadvantages of fabricated tubes are discussed.