Name: facial nerve surgery in the rat model to study axonal inhibition and regeneration
Uploaded: 2020-05-05T12:30:00
Description: Watch this Scientific Journal Video about Facial Nerve Surgery in the Rat Model to Study Axonal Inhibition and Regeneration at JoVE.com

S.A.A. is funded by the American Academy of Facial Plastic and Reconstructive Surgery Leslie Bernstein Grants Program.

All interventions were performed in strict accordance with the National Institutes of Health (NIH) guidelines. The experimental protocol was approved by the University of Michigan&#39;s Institutional Animal Care &#38; Use Committee (IACUC) prior to implementation. Ten-week-old adult female Sprague-Dawley rats were utilized.
1. Prior to the operative day
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	<li>Ensure an appropriate stock of sterilized surgical instruments, analgesic medications, anesthetic medication, and oxygen prior to ...

The rat facial nerve injury model has emerged as the most versatile system for the evaluation of neurotrophic factors due to its surgical accessibility, branching pattern, and physiological significance27,29,33,34,35,36. The combination of video demonstration and application of transgenic animal data opens new possibilities f...

Cranial nerve injury in the head and neck region can be secondary to congenital, infectious, idiopathic, iatrogenic, traumatic, neurologic, oncologic, or systemic etiologies1. Cranial nerve VII, or the facial nerve, is commonly affected. The incidence of facial nerve dysfunction can be significant, as it affects 20 to 30 per 100,000 people each year2. The main motor branches of the facial nerve are the temporal, zygomatic, buccal, marginal mandibular, and cervical branches; depending on the branch involved, the consequences can include oral incompetence or drooling, corneal dryness, visual field obstruction secondary to ptosis, dysarthria, or facial asymmetry2,3. Long-term morbidity includes the phenomenon of synkinesis, or involuntary movement of one facial muscle group, with attempted voluntary contraction of a distinct facial muscle group. Ocular-oral synkinesis is the most common of the aberrant regeneration as a sequela of facial nerve injury and causes functional impairment, embarrassment, diminished self-esteem, and poor quality of life3. Injury to individual branches dictates the functions that are selectively compromised.
The clinical treatment of facial nerve injury is not well standardized and is in need of further research to improve outcomes. Steroids can alleviate acute facial nerve swelling, whereas Botox is useful for temporizing synkinetic movements; but, the primary reconstructive options in the practitioner&#39;s armamentarium involve surgical intervention through nerve repair, substitution, or reanimation3,4,5,6. Depending on the type of facial nerve injury sustained, the facial nerve surgeon may utilize a number of options. For simple transection, nerve reanastomosis is useful whereas cable-graft repair is better suited for a nerve defect; for a restoration of function, the surgeon may choose either static or dynamic facial reanimation procedures. In many cases of facial nerve injury and subsequent repair, even in the hands of experienced facial nerve surgeons, the best outcome still results in persistent facial asymmetry and functional compromise7.
These suboptimal outcomes have spurred extensive research on facial nerve regeneration. Broad topics of interest include perfecting and innovating nerve repair techniques, determining the effect of various nerve regeneration factors, and assessing the potential of specific neural inhibitors to help combat the long-term outcome of synkinesis8,9,10,11. While in vitro models can be used to assess some characteristics of pro-growth or inhibitory factors, true translational research on this subject matter is best accomplished via translatable animal models.
The decision of which animal model to utilize can be challenging, as researchers have utilized both large animals, such as sheep and small animal models, such as mice12,13. While large animal models offer ideal anatomic visualization, their use requires specialized equipment and personnel not readily or easily available. Furthermore, powering a study to demonstrate effect could be highly cost-prohibitive and potentially not within the feasible scope of many scientific centers. Thus, the small animal model is most frequently utilized. The mouse model can be utilized for assessing a number of outcomes related to facial nerve surgery; however, the limited length of the nerve can restrict the scientist&#39;s ability to model certain patterns, such as large-gap injury14.
Thus, the rat murine prototype has emerged as the workhorse model through which the scientist can perform innovative surgical procedures or utilize inhibitory or pro-growth factors and assess effect across a broad range of outcome parameters. The rat facial nerve anatomy is predictably and easily approached in a reproducible fashion. Its larger scale, in comparison to the mouse model, allows for modeling of a wide range of surgical defects, ranging from simple transection to 5 mm gaps15,16. This further allows for the application of complex interventions at the defect site, including the topical placement of factor, intraneural injections of factor, and the placement of isografts or bridges17,18,19,20,21,22,23.
The docile nature of the rat, its reliable anatomy, and its propensity for effective nerve regeneration allows for the collection of many outcome measures in response to the aforementioned surgical patterns of injury24. Via the rat model, the facial nerve scientist is able to assess electrophysiologic responses to injury, nerve and muscle histologic outcomes via immunohistochemistry, functional outcomes via tracking movement of the vibrissal pad and assessing eye closure, and micro- and macroscopic changes via fluorescent or confocal microscopy, among others11,22,23,25,26,27,28,29. Thus, the following protocol will outline a surgical approach to the rat facial nerve and the injury patterns that can be induced.

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facial nerve surgery in the rat model to study axonal inhibition and regeneration

This protocol describes consistent and reproducible methods to study axonal regeneration and inhibition in a rat facial nerve injury model. The facial nerve can be manipulated along its entire length, from its intracranial segment to its extratemporal course. There are three primary types of nerve injury used for the experimental study of regenerative properties: nerve crush, transection, and nerve gap. The range of possible interventions is vast, including surgical manipulation of the nerve, delivery of neuroactive reagents or cells, and either central or end-organ manipulations. Advantages of this model for studying nerve regeneration include simplicity, reproducibility, interspecies consistency, reliable survival rates of the rat, and an increased anatomic size relative to murine models. Its limitations involve a more limited genetic manipulation versus the mouse model and the superlative regenerative capability of the rat, such that the facial nerve scientist must carefully assess time points for recovery and whether to translate results to higher animals and human studies. The rat model for facial nerve injury allows for functional, electrophysiological, and histomorphometric parameters for the interpretation and comparison of nerve regeneration. It thereby boasts tremendous potential toward furthering the understanding and treatment of the devastating consequences of facial nerve injury in human patients.

Following the initial surgical procedure, there are two main types of outcome measures: serial measurements in the live animal and measurements that require sacrificing the animal. Examples of serial measurements include electrophysiological assays, such as a compound muscle action potential measurement30, assessments of facial muscle movement via laser-assisted or videography means9, or even repetitive live imaging of regrowth of the facial...

Watch this Scientific Journal Video about Facial Nerve Surgery in the Rat Model to Study Axonal Inhibition and Regeneration at JoVE.com

Facial Nerve Surgery in the Rat Model to Study Axonal Inhibition and Regeneration

This protocol describes a reproducible approach to facial nerve surgery in the rat model, including descriptions of various inducible patterns of injury.

This protocol describes consistent and reproducible methods to study axonal regeneration and inhibition in a rat facial nerve injury model. The facial ...

This protocol can help scientists study outcomes after facial nerve injury and methods to improve regeneration across many different parameters. The main advantage of this technique is that the rat anatomy allows easy access to the facial nerve, and its large scale allows us to study all of the relevant injury patterns. The applications of this technique extend toward the rehabilitation of the patients after facial nerve injury.As the regenerative potential the rat provides a reproducible and concise experimental model. And this method can provide insight into surgical and medical therapies for facial nerve paresis or paralysis. And it's translatable to other head and neck models or other peripheral nerves.Operating under a microscope using both hands can be challenging. I recommend practicing using binocular version under the microscope before attempting a facial nerve dissection. After confirming a lack of response to toe pinch, apply ointment to the eyes of the rat and shave the surgical area.Establish a method for rat identification and place a roll of gauze under the neck. Disinfect the exposed skin with three alternating chlorhexidine and 70%ethanol scrubs and place the rat under a stereo microscope. Manipulate the ipsilateral ear in an anterior-posterior direction to determine the natural folding of the postauricular skin.Use a number 15 blade to make a two to three millimeter incision in the postauricular crease. The planning and the placement of the incision are the most critical steps for ensuring reliable identification of the facial nerve while minimizing the wound size. Bluntly dissect through the immediate subcutaneous fascia and place a micro-Weitlaner retractor to enhance the tissue exposure.Identify the anterior digastric muscle as it travels in an inferior-to-superior direction toward its insertion along the skull base. Spread gently through the muscle belly along the muscle insertion point to reveal the tendon of the anterior digastric belly. The tendon will appear as a filmy white process emanating from the muscle with a solid insertion onto the skull base.After identification of the anterior digastric muscle and its tendon, adjust the Weitlaner retractor to further retract the muscle belly. The exposed region is the three-dimensional space in which the main trunk of the facial nerve lies. Dissect along the nerve in an inferior direction distally from the exit of the stylomastoid foramen.To induce a crush injury pattern, use smooth-surfaced jeweler's forceps to firmly grasp and compress the nerve applying constant and reproducible pressure for 30 seconds to ensure an appropriate crush injury. For a simple transection, grasp the immediate epineurium overlying the nerve with fine-toothed forceps, and use sharp microscissors to cleanly transect the nerve at the desired point with a single cut. For a nerve gap model, use adjustable calipers to set the desired nerve nerve gap length to ensure similar injury patterns between animals and transect the nerve as just demonstrated.After the experimental injury has been delivered, Irrigate the wound with sterile saline and dry the tissue with sterile gauze. before closing the skin incision according to institutional guidelines. Here, live imaging of the main trunk of the facial nerve with a crush injury approximately two to three millimeters distal to the branch point of the first PES in an adult transgenic Thy1-GFP rat is shown.Assessment of the gradual return of fluorescence at one, two, three, and four weeks post injury can be used as a marker for monitoring nerve regeneration in these transgenic animals. Histomorphometric analysis can be used to obtain cross-sectional images of the marginal mandibular division allowing quantification of the axonal diameter, amount of debris, nerve fiber, percentage of nerve, and density measurements. It is important to frequently adjust the placement of the retractor as needed to ensure that the relevant anatomic nerves are visible when identifying the facial nerve.Following this procedure the relevant nerves and muscles can be harvested for immunohistochemical analysis to assess the degree of regeneration relative to other experimental groups. Following its development, this technique has paved the way for researchers in studying the functional outcomes after facial nerve injury. Specifically, how to effect the phenomenon of synkinesis.

Research

JoVE Journal

Neuroscience

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The optic nerve can be ...

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The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

The Olfactory System as a Model to Study Axonal Growth Patterns and Morphology In Vivo

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In Vivo Electrophysiological Measurement of the Rat Ulnar Nerve with Axonal Excitability Testing

In Vivo Electrophysiological Measurement of the Rat Ulnar Nerve with Axonal Excitability Testing

Electrophysiology enables the objective assessment of peripheral nerve function in vivo. Traditional nerve conduction measures such as amplitude and ...

Screening of Axonal Degeneration in Carpal Tunnel Syndrome Using Ultrasonography and Nerve Conduction Studies

Axonal degeneration, indicative of surgical decompression, may coexist in carpal tunnel syndrome (CTS) as the disease progresses. However, the current ...

3D Kinematic Analysis for the Functional Evaluation in the Rat Model of Sciatic Nerve Crush Injury

Compared to the Sciatic Functional Index (SFI), kinematic analysis is a more reliable and sensitive method for performing functional evaluations of ...

Automated Gait Analysis to Assess Functional Recovery in Rodents with Peripheral Nerve or Spinal Cord Contusion Injury

Peripheral and central nerve injuries are mostly studied in rodents, especially rats, given the fact that these animal models are both cost-effective and ...