Development of the interscutularis model as an outcome measure for facial nerve surgery

Electroacupuncture Promotes Functional Recovery after Facial Nerve Injury in Rats by Regulating Autophagy via GDNF and PI3K/mTOR Signaling Pathway

OBJECTIVE

To explore the mechanism of electroacupuncture (EA) in promoting recovery of the facial function with the involvement of autophagy, glial cell line-derived neurotrophic factor (GDNF), and phosphatidylinositol-3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling pathway.

METHODS

Seventy-two male Sprague-Dawley rats were randomly allocated into the control, sham-operated, facial nerve injury (FNI), EA, EA+3-methyladenine (3-MA), and EA+GDNF antagonist groups using a random number table, with 12 rats in each group. An FNI rat model was established with facial nerve crushing method. EA intervention was conducted at Dicang (ST 4), Jiache (ST 6), Yifeng (SJ 17), and Hegu (LI 4) acupoints for 2 weeks. The Simone's 10-Point Scale was utilized to monitor the recovery of facial function. The histopathological evaluation of facial nerves was performed using hematoxylin-eosin (HE) staining. The levels of Beclin-1, light chain 3 (LC3), and P62 were detected by immunohistochemistry (IHC), immunofluorescence, and reverse transcription-polymerase chain reaction, respectively. Additionally, IHC was also used to detect the levels of GDNF, Rai, PI3K, and mTOR.

RESULTS

The facial functional scores were significantly increased in the EA group than the FNI group (P<0.05 or P<0.01). HE staining showed nerve axons and myelin sheaths, which were destroyed immediately after the injury, were recovered with EA treatment. The expressions of Beclin-1 and LC3 were significantly elevated and the expression of P62 was markedly reduced in FNI rats (P<0.01); however, EA treatment reversed these abnormal changes (P<0.01). Meanwhile, EA stimulation significantly increased the levels of GDNF, Rai, PI3K, and mTOR (P<0.01). After exogenous administration with autophagy inhibitor 3-MA or GDNF antagonist, the repair effect of EA on facial function was attenuated (P<0.05 or P<0.01).

CONCLUSIONS

EA could promote the recovery of facial function and repair the facial nerve damages in a rat model of FNI. EA may exert this neuroreparative effect through mediating the release of GDNF, activating the PI3K/mTOR signaling pathway, and further regulating the autophagy of facial nerves.

Axonal Regeneration Through Autologous Grafts: Does the Axonal Load Influence Regeneration?

INTRODUCTION

Two-stage free functional muscle transfers for long-standing facial palsy can yield unpredictable results. Earlier studies have demonstrated incomplete regeneration across neurorrhaphies in native nerve and higher donor axonal counts correlating with improved outcomes but axonal count in nerve grafts have not been as thoroughly reviewed. To investigate the impact of varying axonal counts in autologous grafts on functional outcomes of repair.

MATERIALS AND METHODS

Animals were allocated into three groups: Direct Nerve Repair (DNR, n = 50), Small Nerve Graft (SNG, n = 50), and Large Nerve Graft (LNG, n = 50). All grafts were inset into the Posterior Auricular Nerve with ear movement recovery (EMR) monitored as functional outcome. At various postoperative weeks (POWs), excised specimens were imaged with electron microscopy. Axonal counts were measured proximal to, distal (DAC) to, and within grafts. Total Success Ratio (TSR) was calculated.

RESULTS

In DNR, DAC was significantly lower than proximal axonal counts at all POWs, with maximum TSR of 80%. TSR for LNG and SNG were significantly lower at all POWs when compared to DNR, with maximums of 56% and 38%, respectively. LNG had a significantly larger DAC than SNG at POW12 and beyond. A direct relationship was present between DAC and EMR for all values.

CONCLUSIONS

Higher native axonal count of autologous nerve grafts resulted in higher percentage of regeneration across neurorrhaphies.

Facial Nerve Repair: Bioengineering Approaches in Preclinical Models

Injury to the facial nerve can occur after different etiologies and range from simple transection of the branches to varying degrees of segmental loss. Management depends on the extent of injury and options include primary repair for simple transections and using autografts, allografts, or conduits for larger gaps. Tissue engineering plays an important role to create artificial materials that are able to mimic the nerve itself without extra morbidity in the patients. The use of neurotrophic factors or stem cells inside the conduits or around the repair site is being increasingly studied to enhance neural recovery to a greater extent. Preclinical studies remain the hallmark for development of these novel approaches and translation into clinical practice. This review will focus on preclinical models of repair after facial nerve injury to help researchers establish an appropriate model to quantify recovery and analyze functional outcomes. Different bioengineered materials, including conduits and nerve grafts, will be discussed based on the experimental animals that were used and the defects introduced. Future directions to extend the applications of processed nerve allografts, bioengineered conduits, and cues inside the conduits to induce neural recovery after facial nerve injury will be highlighted.

Variability in the development of synkinesis in a rabbit facial nerve axotomy model

OBJECTIVE

Weakness and synkinesis (involuntary cocontraction of different muscle groups) are common sequelae after facial nerve injury. We describe a rabbit model of facial nerve axotomy and repair, which can be used to study such sequelae and propose a grading tool to assess the facial movement outcomes. Using this rabbit model, we assess the effect of delaying facial nerve repair on the quality of the clinical result.

METHODS

A total of 15 rabbits (30 facial halves) were divided into 4 groups: control, facial nerve main trunk axotomy and immediate repair, axotomy and repair at 2.5 weeks as well as axotomy, and repair at 2 months. Functional recovery was graded according to the observable criteria. We performed retrograde fluorescence labelling of the distal facial nerve branches and assessed the distribution of tracers in the facial nucleus.

RESULTS

A consistent model of weakness and synkinesis was produced in all rabbits after immediate axotomy and repair. A grading tool was used to clinically grade the quality of the recovery. The somatotopy of the facial nucleus was disrupted, with axons projecting from the facial nucleus to incorrect facial muscle groups. Varying the denervation time before repair affected the quality of the recovery. The worst result was noted when repair was delayed for 2 months. Subtle changes in the pattern and severity of synkinesis was noted among the different treatment groups.

CONCLUSION

A slight delay in nerve repair by 2.5 weeks as well as contralateral facial paralysis (analogous to botulinum toxin (BTX) injection) appear to improve eye recovery and reduce synkinesis. Because of the large size of the rabbit, such variability in synkinesis severity can be graded.

Transgenic models for investigating the nervous system: Currently available neurofluorescent reporters and potential neuronal markers

Recombinant DNA technologies have enabled the development of transgenic animal models for use in studying a myriad of diseases and biological states. By placing fluorescent reporters under the direct regulation of the promoter region of specific marker proteins, these models can localize and characterize very specific cell types. One important application of transgenic species is the study of the cytoarchitecture of the nervous system. Neurofluorescent reporters can be used to study the structural patterns of nerves in the central or peripheral nervous system in vivo, as well as phenomena involving embryologic or adult neurogenesis, injury, degeneration, and recovery. Furthermore, crucial molecular factors can also be screened via the transgenic approach, which may eventually play a major role in the development of therapeutic strategies against diseases like Alzheimer's or Parkinson's. This review describes currently available reporters and their uses in the literature as well as potential neural markers that can be leveraged to create additional, robust transgenic models for future studies.