Summary

Il nervo del perone Metodo Injury: Un test affidabile di individuare e testare i fattori che Repair neuromuscolari giunzioni

Published: August 11, 2016
doi:

Summary

We have developed a nerve injury method to reliably examine muscle reinnervation, and thus regeneration of neuromuscular junctions in mice. This technique involves injuring the common fibular nerve via a simple and highly reproducible surgery. Muscle reinnervation in then assessed by whole-mounting the extensor digitorum longus muscle.

Abstract

La giunzione neuromuscolare (NMJ) subisce cambiamenti strutturali e funzionali deleteri a causa di invecchiamento, lesioni e malattie. Pertanto, è indispensabile per capire i cambiamenti cellulari e molecolari coinvolti nella manutenzione e riparazione NMJs. A questo scopo, abbiamo sviluppato un metodo per affidabile e coerente esaminare rigenerante NMJs nei topi. Questo metodo comporta la lesione del nervo schiacciamento del nervo peroneo comune che passa sopra la testa laterale del tendine del muscolo gastrocnemio vicino al ginocchio. Utilizzando vecchi topi di sesso femminile di 70 giorni, dimostriamo che assoni motori cominciano a Reinnervate precedenti obiettivi post-sinaptici entro 7 giorni post-cotta. Essi rioccupano completamente le loro precedenti zone sinaptiche da 12 giorni. Per determinare l'affidabilità di questo metodo di infortunio, abbiamo confrontato i tassi di reinnervazione tra i singoli vecchi topi femmina 70 al giorno. Abbiamo scoperto che il numero di siti post-sinaptici reinnervated era simile tra i topi a 7, 9, e 12 giorni post-cotta. Per determinare sequesto test lesione può essere utilizzato anche per confrontare cambiamenti molecolari nei muscoli, abbiamo esaminato livelli di gamma-subunità del recettore nicotinico muscolare (gamma-AChR) e la chinasi muscolo-specifica (MuSK). La subunità gamma-AChR e muschio di sono altamente sovraregolati dopo denervazione e tornare a livelli normali seguenti reinnervazione di NMJs. Abbiamo trovato una stretta relazione tra i livelli di trascrizione di questi geni e lo stato innervazione dei muscoli. Noi crediamo che questo metodo accelererà la nostra comprensione dei cambiamenti cellulari e molecolari coinvolti nella riparazione del NMJ e altre sinapsi.

Introduction

In young adult and healthy animals, the neuromuscular junction (NMJ) is a highly stable connection between the presynapse, the nerve ending of an α-motor axon, and the postsynapse, the specialized region of an extrafusal muscle fiber where nicotinic acetylcholine receptors (AChRs) selectively aggregate1. The nearly perfect apposition of the pre- and post-synaptic apparatuses is necessary for proper neurotransmission, survival of α-motor neurons and muscle fibers and motor function. Unfortunately, the function of the NMJ is adversely affected by aging, diseases such as amyotrophic lateral sclerosis (ALS), autoimmune diseases and injury to muscles and peripheral nerves2-5. These insults often result in degeneration of presynaptic nerve endings, leaving muscles denervated and significantly altering motor skills. For this reason, the identification of molecules that function to maintain and repair the NMJ has become a priority. Because peripheral nerves regenerate and reinnervate targets, peripheral nerve injury models have been used to identify molecular changes associated with regenerating NMJs.

Peripheral nerve injury models often involve either completely cutting or crushing specific nerve branches6. Following a cut, the endoneurial tube has to be reformed, delaying axonal regeneration and reinnervation of target cells and tissues. The severity of this type of injury also causes axons to meander away from their original path, resulting in their failure to reach original targets. This is in contrast to nerves injured via crush where the endoneurium remains contiguous, providing a path for efficient and proper regrowth of regenerating axons. It also allows axons to find and reinnervate their original muscle fiber partners. Irrespective of injury model, there are a number of cellular and molecular changes that must occur for axons to regenerate and reinnervate targets. After an injury, the nerve segment proximal to the target is broken down and removed via a process termed Wallerian Degeneration7. This process involves reprogramming and de-differentiation of Schwann cells into non-myelinating cells that secrete regenerative factors, clear myelin, and recruit macrophages to the site of injury8. Macrophages in turn complete the clearance of myelin and axonal debris, which would otherwise impede growth of the regenerating axon9. In parallel, motor and sensory neurons activate mechanisms needed to promote regeneration of their severed axons. Once the regenerating axon reaches the target, it must transform from a growth cone to a nerve ending capable of properly transmitting (for motor axons) or receiving (for sensory axons) information10. In this regard, alpha-motor axons undergo a series of well-orchestrated changes that culminate in their growth cone differentiating into a fully functional presynaptic nerve ending that nearly perfectly opposes the post-synaptic site on the target muscle fiber11.

The sciatic, tibial and accessory nerves have been the primary choices for studying axonal and NMJ regeneration12-14. However, there are a number of drawbacks when using these models to examine cellular and molecular changes associated with regenerating NMJs between animals and under different conditions. Firstly, the sciatic nerve supplies the majority of the muscles of the hind limb, with injury significantly limiting both movement and sensation. It is therefore not possible to use this method to study the impact of exercise alone or in combination with other factors. Additionally, the sciatic nerve is a rather thick structure and thus requires a large amount of compressive force to fully injure all axons. This in turn may result in complete transection of the more superficial axons while leaving the endoneurial tube of deeper lying axons intact, introducing significant variability in the rate and fidelity of regeneration among these axons. Complete transection of this nerve is even less desirable given that many axons will fail to reconnect with the same muscle fibers. Complicating matters, the sciatic nerve possesses intrinsic anatomic variability, both in the number and site of origin of its terminal nerve branches. It is therefore very difficult to lesion the same site. While the tibial nerve is smaller and more amenable to crush injuries, there is also no readily available landmark to serve as a lesion site for this nerve branch.

The accessory nerve branch (part of cranial nerve XI) that supplies the sternocleidomastoid muscle has also been used to study regeneration of NMJs15. This nerve is particularly attractive because NMJs in the sternocleidomastoid muscle can be more readily imaged in live animals compared to NMJs in other muscles. But similar to the sciatic and tibial nerves, there is no specific landmark that can be used to injure this nerve in the same location, limiting it as a model for comparing regeneration of NMJs among individual animals of an experimental cohort. An inconsistent lesion site introduces variability in the rates of NMJ reinnervation. Due to these shortcomings, the procedure presented here utilizes the injury of a different peripheral nerve branch to examine regenerating NMJs.

The common fibular nerve, also called the common peroneal nerve, contains many features that make it a reliable nerve to examine regeneration of NMJs between animals and across different treatments. The common fibular nerve has a predictable anatomic course as it runs over the tendon of the lateral head of the gastrocnemius muscle in the knee, the intersection serving as a stable landmark for lesions. The nerve is accessed through a small and minimally invasive incision near but anatomically segregated from the muscles of interest. The findings presented here demonstrate that regenerating motor axons begin to reform NMJs in the extensor digitorum longus (EDL) muscle 8 days after crushing the fibular nerve in 70 days old young adult female mice. Importantly, the pattern and rate of reinnervation is consistent among animals of the same age and sex and therefore provide a reliable injury model that will significantly hasten our understanding of the cellular and molecular changes required to maintain and repair NMJs.

Protocol

Tutti gli esperimenti sono stati eseguiti secondo le linee guida NIH e protocolli animali approvati dal Comitato di Virginia Tech Istituzionale Animal Care e Usa. 1. Gli animali prepara per la chirurgia Anestetizzare topi con una miscela di ketamina (90 mg / kg) e xilazina (10 mg / kg) mediante iniezione sottocutanea con inguinale sterile 1 ml siringa da insulina. soluzione Carrier contiene una miscela di soluzione fisiologica 0,9%, 17,4 mg / ml ketamina e 2,6 mg / ml xilazina. Me…

Representative Results

Il nervo peroneale comune, chiamato anche il nervo peroneo comune, nasce dal nervo sciatico di sopra della fossa poplitea, dove si oscilla intorno alla testa del perone alla faccia anteriore della gamba (Figura 1A). Ci si dirama nei nervi peroneale superficiali e profondi, insieme fornendo i flessori dorsali del piede e dita del piede (tibiale anteriore, estensore lungo delle dita e brevis, e alluci estensori muscoli longus), e le everters del piede (muscoli peronei). Qu…

Discussion

Il metodo presentato in questo manoscritto fornisce opportunità uniche per identificare i meccanismi coinvolti nella riparazione di giunzioni neuromuscolari (NMJ). Questo metodo comporta la frantumazione del nervo peroneo comune che passa sopra il gastrocnemio tendine vicino al ginocchio. Abbiamo dimostrato che dopo soli 5 secondi di compressione del nervo con una pinza, completa degenerazione è notato da 4 giorni dopo l'infortunio. Nei topi giovani adulti, gli assoni alfa-motori cominciano a Reinnervate precedent…

Disclosures

The authors have nothing to disclose.

Acknowledgements

The authors thank members of the Valdez laboratory for intellectual input on experiments and comments on the manuscript.

Materials

Ketamine VetOne  501072 
Xylazine Lloyd Inc.  003437 
Buprenorphine  Zoopharm 1Z-73000-150910 
Nair Nair
Kim-wipes Kimtech 34155
Electric Razor Braintree Scientific CLP-64800
80% EtOH/H20
10% Proviodine
1 mL Insulin Syringe
Spring Scissors Vannas 91500-09
No. 15 scalpel Braintree Scientific SSS 15
#5 Forceps Dumont 11252-00
6-0 silk suture on reverse cutting needle  Suture Express 752B 
Rodent Heating Pad Braintree Scientific AP-R-18.5
Alexa 555 conjugated alpha-BTX Molecular Probes B35451
Vectashield Vector Labs H-1000
Olympus Stereo Zoom Microscope Olympus 562037192
Zeiss 700 Confocal Microscope Zeiss
Variable-flow peristaltic perfusion pump Fisher Scientific 13-876-3
Aurum Total RNA Mini Kit Bio-Rad 7326820
Bio-Rad iScript RT Supermix Bio-Rad 1708840
SsoFast Evagreen Supermix Bio-Rad 1725200
Bio-Rad CFX96 Bio-Rad 1855196
Puralube vet ointment Puralube 1621
Synaptotagmin-2 antibody Antibodies-Online ABIN401605
Neurofilament antibody Antibodies-Online ABIN2475842

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Cite This Article
Dalkin, W., Taetzsch, T., Valdez, G. The Fibular Nerve Injury Method: A Reliable Assay to Identify and Test Factors That Repair Neuromuscular Junctions. J. Vis. Exp. (114), e54186, doi:10.3791/54186 (2016).

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