Facial motor nuclei cell loss with intratemporal facial nerve crush injuries in rats

Contemporary Perspectives in Pathophysiology of Facial Nerve Damage in Oto-Neurological and Skull Base Surgical Procedures: A Narrative Review

During the last decades, neuro-otological surgery has progressively reduced functional morbidity, including facial nerve damage. However, the occurrence of this sequela may significantly impact on patients' quality of life. The aim of this narrative review is to provide an update on the patho-physiological and clinical issues related to facial nerve damage in oto-neurological and skull base surgery, in the light of a comprehensive therapeutic and rehabilitative approach to iatrogenic disfunctions. The narrative review is based on a search in the PubMed, Scopus, and Web of Science databases. In this surgical setting, the onset of intraoperative facial nerve damage is related to various aspects, mainly concerning the anatomical relationship between tumor and nerve, the trajectory of the surgical corridor, and the boundaries of the resection margins. Mechanisms related to stretching, compression, devascularization, and heating may play a role in determining intraoperative facial nerve damage and provide the patho-physiological basis for possible nerve regeneration disorders. Most of the studies included in this review, dealing with the pathophysiology of surgical facial nerve injury, were preclinical. Future research should focus on the association between intraoperative trauma mechanisms and their clinical correlates in surgical practice. Further investigations should also be conducted to collect and record intraoperative data on nerve damage mechanisms, as well as the reports from neuro-monitoring systems.

Testosterone treatment restores vestibular function by enhancing neuronal survival in an experimental closed-head repetitive mild traumatic brain injury model

Repetitive mild traumatic brain injury (rmTBI) results in a myriad of symptoms, including vestibular impairment. The mechanisms underlying vestibular dysfunction in rmTBI patients remain poorly understood. Concomitantly, acute hypogonadism occurs following TBI and can persist chronically in many patients. Using a repetitive mild closed-head animal model of TBI, the role of testosterone on vestibular function was tested. Male Long Evans Hooded rats were randomly divided into sham or rmTBI groups. Significant vestibular deficits were observed both acutely and chronically in the rmTBI groups. Systemic testosterone was administered after the development of chronic vestibular dysfunction. rmTBI animals given testosterone showed improved vestibular function that was sustained for 175 days post-rmTBI. Significant vestibular neuronal cell loss was, however, observed in the rmTBI animals compared to Sham animals at 175 days post-rmTBI and testosterone treatment significantly improved vestibular neuronal survival. Taken together, these data demonstrate a critical restorative role of testosterone in vestibular function following rmTBI. This study has important clinical implications because it identifies testosterone treatment as a viable therapeutic strategy for the long-term recovery of vestibular function following TBI.

Clinical Studies and Pre-clinical Animal Models on Facial Nerve Preservation, Reconstruction, and Regeneration Following Cerebellopontine Angle Tumor Surgery-A Systematic Review and Future Perspectives

Background and purpose: Tumorous lesions developing in the cerebellopontine angle (CPA) get into close contact with the 1st (cisternal) and 2nd (meatal) intra-arachnoidal portion of the facial nerve (FN). When surgical damage occurs, commonly known reconstruction strategies are often associated with poor functional recovery. This article aims to provide a systematic overview for translational research by establishing the current evidence on available clinical studies and experimental models reporting on intracranial FN injury.

Methods: A systematic literature search of several databases (PubMed, EMBASE, Medline) was performed prior to July 2020. Suitable articles were selected based on predefined eligibility criteria following the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) guidelines. Included clinical studies were reviewed and categorized according to the pathology and surgical resection strategy, and experimental studies according to the animal. For anatomical study purposes, perfusion-fixed adult New Zealand white rabbits were used for radiological high-resolution imaging and anatomical dissection of the CPA and periotic skull base.

Results: One hundred forty four out of 166 included publications were clinical studies reporting on FN outcomes after CPA-tumor surgery in 19,136 patients. During CPA-tumor surgery, the specific vulnerability of the intracranial FN to stretching and compression more likely leads to neurapraxia or axonotmesis than neurotmesis. Severe FN palsy was reported in 7 to 15 % after vestibular schwannoma surgery, and 6% following the resection of CPA-meningioma. Twenty-two papers reported on experimental studies, out of which only 6 specifically used intracranial FN injury in a rodent (n = 4) or non-rodent model (n = 2). Rats and rabbits offer a feasible model for manipulation of the FN in the CPA, the latter was further confirmed in our study covering the radiological and anatomical analysis of perfusion fixed periotic bones.

Conclusion: The particular anatomical and physiological features of the intracranial FN warrant a distinguishment of experimental models for intracranial FN injuries. New Zealand White rabbits might be a very cost-effective and valuable option to test new experimental approaches for intracranial FN regeneration. Flexible and bioactive biomaterials, commonly used in skull base surgery, endowed with trophic and topographical functions, should address the specific needs of intracranial FN injuries.

Mechanisms of the Immunomodulation Effects of Bone Marrow-Derived Mesenchymal Stem Cells on Facial Nerve Injury in Sprague-Dawley Rats

Normal facial nerve (FN) function is very important for human being. However, if injured, FN function is difficult to restore completely. Recently, many studies reported the immune regulation function of stem cells (SCs). However, the immunomodulation function of SCs on FN injury is still unclear. Our study aims to explore the mechanism of immunomodulation effect of Sprague-Dawley rat bone marrow-derived SCs (BMSCs) on FN injury and specially focus on the regulation of Th17 and the protection effects of BMSCs on central facial motor neurons (FMNs). First, rat FNs were harvested. FN and BMSCs were cultured together or separately and levels of transforming growth factor (TGF)-β1, interleukin (IL)-6, hepatocyte growth factor (HGF), inducible nitric oxide synthase (iNOS), and prostaglandin E2 (PGE2) in supernatant were detected by enzyme-linked immunosorbent assay (ELISA). Then, after treating with or without local BMSCs injection, the proportion of Th17 in neck lymph nodes (LNs) was investigated in rat FN injury models. Furthermore, the apoptotic index of FMNs was studied in rat FN injury models that were treated with or without BMSCs. We found that BMSCs could secrete high levels of IL-6, HGF, PGE2, iNOS, and TGF-β1 in culture. The percentage of Th17 of neck LNs in BMSCs-treated group was significantly lower than that in the control group. The apoptotic index of FMNs in BMSCs-treated group was significantly lower than that in the control group. In conclusion, our research indicates BMSCs could independently secrete cytokines IL-6, HGF, PGE2, iNOS, and TGF-β1, and these cytokines could regulate the balance among subsets of CD4⁺ T cells and could protect FMNs by inhibiting neuron apoptosis.

Intracranial facial nerve crush injury and facial motor nuclei cell loss in rats

OBJECTIVES

The purpose of this study was to (1) assess the degree of motoneuron cell loss and (2) the combinatorial effects of electrical stimulation (ES) and testosterone propionate (TP) on cell survival following an intracranial facial nerve crush injury and (3) compare these results to distal injuries.

STUDY DESIGN

Prospective, randomized, controlled animal study.

METHODS

Sprague-Dawley rats were randomly divided into 3 groups: intracranial sham surgery or intracranial crush injury with or without ES and TP treatments. The intracranial sham group underwent exposure of the meatal segment of the right facial nerve. The intracranial crush groups underwent a crush of the meatal segment following exposure with or without ES and TP treatment immediately following the injury and followed for 8 weeks. Brain sections were thionin-stained, and facial motor nuclei (FMN) were counted using light microscopy. Results were compared to intratemporal and extracranial facial nerve crush injuries.

RESULTS

Intracranial crush injury resulted in a significant decrease in cell survival (n = 6) of 65.6% as compared to the sham group (99.4%; n = 9). The treatments increased cell survival to 93.8% (n = 2). The cell loss in the intracranial facial nerve injury is more substantial than the intratemporal (85.8%; n = 7) and extracranial (103.3%; n = 4) injuries.

CONCLUSIONS

Intracranial injury results in a more profound cell loss compared to the distal injuries. These data suggest a critical importance for the development of treatment modalities that can help improve cell survival following facial nerve injuries.

Neuroregeneration in the nucleus ambiguus after recurrent laryngeal nerve avulsion in rats

OBJECTIVES

The objective was to investigate neuroregeneration, the origins of newborn cells and the proliferation of neuronal and glial cells in the nucleus ambiguus (NA) after ipsilateral recurrent laryngeal nerve (RLN) avulsion.

METHODS

All of the animals received a CM-Dil injection in the left lateral ventricle. Forty-five adult rats were subjected to a left RLN avulsion injury, while 9 rats were used as controls. 5-Bromo-2-deoxyuridine (BrdU) was injected intraperitoneally. Neuron quantification and immunohistochemical analysis were performed in the brain stems at different time points after RLN injury.

RESULTS

After RLN avulsion, CM-Dil labeled neural progenitor cells (NPCs) migrated to the ipsilateral NA and differentiated into astrocytes but not into neurons. In the NA, the neuronal cells re-expressed nestin. Only a small number of neuronal and glial cells in the NA showed BrdU immunoreactivity.

CONCLUSIONS

After RLN avulsion, the NPCs in the ependymal layer of the fourth ventricle or central canal are activated, migrate to the lesion in the NA and differentiate exclusively into astrocytes. The newborn neural stem cells in the NA may arise from the mature region neurons. The presence of both cell types in the NA may play a role in repairing RLN injuries.

Transient changes in spinal cord glial cells following transection of preganglionic sympathetic axons

Following peripheral nerve injury, retrograde signals originating from the injury site may activate intrinsic factors in the injured neurons, possibly leading to regenerative growth. Retrograde influences from peripheral injury sites may lead to the activation of glial cells in the vicinity of the centrally located cell bodies of the injured neurons. Few studies have examined changes in the spinal cord intermediolateral cell column (IML), which houses sympathetic preganglionic cell bodies, following injury to distal axons in the cervical sympathetic trunk (CST). The goal of the present study was to determine if transection of the CST results in plasticity in glial cells in the IML. At 1 day following injury, changes in the expression of microglial marker Iba1 were observed and the typical oligodendrocyte-neuronal relationship was altered. By 7 days, astrogliosis, microglial aggregation, and increased numbers of oligodendrocytes, as well as enhanced glial-glial and glial-neuronal relationships were present. The majority of cases were similar to controls at 3 weeks following injury and no changes were observed in any cases at 10 weeks following the injury. These results revealed changes in astrocytes, microglia, oligodendrocytes in the spinal cord following transection of preganglionic axons comprising the CST, indicating their ability to respond to distal axonal injury.

A rat model for intracranial facial nerve crush injuries

OBJECTIVE

(1) Explain the need for an animal model to study intracranial injuries to the facial nerve. (2) Describe various techniques attempted to identify and crush the intracranial segment of the facial nerve in a rat model. (3) Describe in detail a successful rat model of intracranial facial nerve crush injury.

STUDY DESIGN

Randomized controlled animal study.

SETTING

Animal laboratory.

SUBJECTS AND METHODS

Multiple attempts at surgical approaches to the cerebellopontine angle were attempted on cadaveric rats. Once a successful approach was derived, this was used on 19 live rats under anesthesia. Fourteen rats had a 1-minute facial nerve crush performed, and 5 had a sham surgery with complete surgical exposure of the facial nerve but no crush. Rats were followed for a 12-week duration evaluating immediate postoperative facial nerve function, complications, and survival.

RESULTS

All 14 (100%) rats that underwent surgery with crush injury had complete facial paralysis postoperatively. Complete facial paralysis was defined as loss of eye-blink reflex, flat vibrissae, and lack of vibrissae movement. The 5 sham surgery rats had complete facial function postoperatively. Surgery was performed by 2 separate surgeons with no difference in outcome between the 2. Complications occurred in only 1 animal (1/19, 5.3%), which was a corneal abrasion requiring sacrifice.

CONCLUSION

Our group describes a consistent method for performing an intracranial crush injury in the rat. This new model and its applications in translational facial nerve research are promising, particularly with tumors or lesions at the cerebellopontine angle.