Comparison of extratemporal and intratemporal facial nerve injury models

Rat Facial Nerve Regeneration with Human Immature Dental Pulp Stem Cells

Facial paralysis can result in severe implications for the patients. However, stem cell biology has become an important field in regenerative medicine since the discovery and characterization of mesenchymal stem cells. Our aim was to evaluate the regeneration after facial nerve crush injury and application of human immature dental pulp stem cells (iDPSC). For this study 70 Wistar rats underwent a unilateral facial nerve crush injury and were divided into two groups: Group I (GI): Crushed; Group II (GII): Crushed and iDPSC, and distributed into study periods of 3, 7, 14, 21, and 42 postoperative days. Facial nerve regeneration was analyzed via functional recovery of whisker movement, histomorphometric analysis, and immunoblotting assay. The results show that GII had complete functional recovery at 14 days, while GI recovered after 42 days. Also, regarding the facial nerve trunk, GII presented histological improvement, evidencing better axonal and structural organization of the myelin sheath, and exhibited statistically higher values for the outer and inner perimeters and g-ratio. Nevertheless, GI exhibited statistically higher values for the thickness of myelin sheath. In the buccal branch, no differences were observed for all parameters between groups. At 42 days, both groups GI and GII were close to the levels observed for the control group. Concerning nerve growth factor expression, GII exhibited statistically greater values (p < 0.05) compared with the control group at 7 days. In summary, a single injection of human iDPSC promoted a positive effect on regeneration of the facial nerve trunk after 14 days and provided an alternative to support regeneration following peripheral nerve injury.

The Effects of MESNA on the Facial Nerve, an Experimental Animal Study

OBJECTIVE

MESNA (Sodium-2-mercaptoethanesulfonate) is a mucolytic substance that is used for chemically assisted tissue dissection in various surgical operations. The aim of this study was to address the issue of possible neurotoxicity from topical administration of MESNA solution on the facial nerve. We used different concentrations of MESNA solution and evaluated their effects on facial nerve by histopathological and functional analysis.

MATERIALS AND METHODS

These groups were the saline administered group (control) (3 rats, 6 facial nerves), the 25% MESNA solution group (3 rats, 6 facial nerves), and the 100% MESNA solution group (3 rats, 6 facial nerves). Under general anesthesia (ketamine 150 mg/kg, xylocaine 4 mg/kg), the bilateral facial nerves of rats were dissected. The saline, 25% MESNA, and 100% MESNA solutions. Facial nerve functions of the rats were evaluated using mustachewhisker and blink reflex scores at day 20 days. On day 20, the rats were sacrificed and the buccal and marginal mandibular branches of the facial nerve were removed. The specimens were examined in terms of inflammation, granulation tissue, and foreign body reaction formation around the nerve. The functional and histopathological changes on facial nerves were compared between groups.

RESULTS

Mustache and blink reflex scores of the rats were 5 (normal) in both the control and study groups. There were no statistically significant differences between the three groups in terms of facial nerve functions (p=1.00). On histopathologic examination, the 25% and 100% MESNA groups had significantly more inflammation compared with the control group (p=0.038 and p=0.007, respectively). There were no statistically significant differences between the 25% and 100% MESNA groups in term of inflammation (p > 0.05). There were no statistically significant differences between the three groups in terms of foreign body reaction formation (p > 0.05).

CONCLUSION

Topical administration of MESNA solution onto the facial nerve causes increased inflammation in both the 25% and 100% concentrations. Nevertheless, it does not cause any facial nerve dysfunction.

Macroscopic in vivo imaging of facial nerve regeneration in Thy1-GFP rats

IMPORTANCE

Facial nerve injury leads to severe functional and aesthetic deficits. The transgenic Thy1-GFP rat is a new model for facial nerve injury and reconstruction research that will help improve clinical outcomes through translational facial nerve injury research.

OBJECTIVE

To determine whether serial in vivo imaging of nerve regeneration in the transgenic rat model is possible, facial nerve regeneration was imaged under the main paradigms of facial nerve injury and reconstruction.

DESIGN, SETTING, AND PARTICIPANTS

Fifteen male Thy1-GFP rats, which express green fluorescent protein (GFP) in their neural structures, were divided into 3 groups in the laboratory: crush-injury, direct repair, and cross-face nerve grafting (30-mm graft length). The distal nerve stump or nerve graft was predegenerated for 2 weeks. The facial nerve of the transgenic rats was serially imaged at the time of operation and after 2, 4, and 8 weeks of regeneration. The imaging was performed under a GFP-MDS-96/BN excitation stand (BLS Ltd).

INTERVENTION OR EXPOSURE

Facial nerve injury.

MAIN OUTCOME AND MEASURE

Optical fluorescence of regenerating facial nerve axons.

RESULTS

Serial in vivo imaging of the regeneration of GFP-positive axons in the Thy1-GFP rat model is possible. All animals survived the short imaging procedures well, and nerve regeneration was followed over clinically relevant distances. The predegeneration of the distal nerve stump or the cross-face nerve graft was, however, necessary to image the regeneration front at early time points. Crush injury was not suitable to sufficiently predegenerate the nerve (and to allow for degradation of the GFP through Wallerian degeneration). After direct repair, axons regenerated over the coaptation site in between 2 and 4 weeks. The GFP-positive nerve fibers reached the distal end of the 30-mm-long cross-face nervegrafts after 4 to 8 weeks of regeneration.

CONCLUSIONS AND RELEVANCE

The time course of facial nerve regeneration was studied by serial in vivo imaging in the transgenic rat model. Nerve regeneration was followed over clinically relevant distances in a small number of experimental animals, as they were subsequently imaged at multiple time points. The Thy1-GFP rat model will help improve clinical outcomes of facial reanimation surgery through improving the knowledge of facial nerve regeneration after surgical procedures.

LEVEL OF EVIDENCE

NA.

CD4 + T Cells and Neuroprotection: Relevance to Motoneuron Injury and Disease

We have established a physiologically relevant mechanism of CD4+ T cell-mediated neuroprotection involving axotomized wildtype (WT) mouse facial motoneurons (FMN) with significance in the treatment of amyotrophic lateral sclerosis (ALS), a fatal MN disease. Use of the transgenic mouse model of ALS involving expression of human mutant superoxide dismutase genes (SOD1(G93A); abbreviated here as mSOD1) has accelerated basic ALS research. Superimposition of facial nerve axotomy (FNA) on the mSOD1 mouse during pre-symptomatic stages indicates that they behave like immunodeficient mice in terms of increased FMN loss and decreased functional recovery, through a mechanism that, paradoxically, is not inherent within the MN itself, but, instead, involves a defect in peripheral immune: CNS glial cell interactions. Our goal is to utilize our WT mouse model of immune-mediated neuroprotection after FNA as a template to elucidate how a malfunctioning peripheral immune system contributes to motoneuron cell loss in the mSOD1 mouse. This review will discuss potential immune defects in ALS, as well as provide an up-to-date understanding of how the CD4+ effector T cells provide neuroprotection to motoneurons through regulation of the central microglial and astrocytic response to injury. We will discuss an IL-10 cascade within the facial nucleus that requires a functional CD4+ T cell trigger for activation. The review will discuss the role of T cells in ALS, and our recent reconstitution experiments utilizing our model of T cell-mediated neuroprotection in WT vs mSOD1 mice after FNA. Identification of defects in neural:immune interactions could provide targets for therapeutic intervention in ALS.

Intracranial supramaximal facial nerve stimulation: a murine model

PURPOSE

Supramaximal facial nerve stimulation is an applied current sufficient to evoke a maximal electromyographic response of facial musculature. It is used during cerebellopontine angle surgery for prognostication of postoperative nerve function. We utilized a rat model to examine safe parameters for intracranial electrical stimulation.

MATERIALS AND METHODS

Intracranial facial nerve stimulation with electromyographic monitoring of 14 rats was performed. Supramaximal current level was determined and 50 additional pulses of supramaximal (4 rats), 3 times supramaximal (4), 10 times supramaximal (3), or zero (3) current were applied. To monitor progression of facial nerve injury, video recordings of vibrissae movements and eye closure were captured at 1, 3 and 28 days after surgery; animals were sacrificed on day 28, when nerve morphometry was performed.

RESULTS

One rat in the supramaximal stimulation group (of 4), and one rat in the 10 times supramaximal stimulation group (of 3) demonstrated persistent impairment of facial nerve function as evidenced by decreased amplitude of vibrissae sweeping and eye closure impairment. The remainder of rats in all experimental groups demonstrated symmetric and normal facial nerve function at all time points.

CONCLUSIONS

A novel animal model for supramaximal stimulation of the rat intracranial facial nerve is described. A small proportion of animals demonstrated functional evidence of nerve injury postoperatively. Function was preserved in some animals after stimulation with current order of magnitude higher than supramaximal levels. Further study with this model is necessary to definitively isolate the effects of surgical trauma from those of supramaximal electrical stimulation.

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.

Combinatorial treatments enhance recovery following facial nerve crush

OBJECTIVES/HYPOTHESIS

To investigate the effects of various combinatorial treatments, consisting of a tapering dose of prednisone (P), a brief period of nerve electrical stimulation (ES), and systemic testosterone propionate (TP) on improving functional recovery following an intratemporal facial nerve crush injury.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

After a right intratemporal facial nerve crush, adult male Sprague-Dawley rats were divided into the following eight treatment groups: 1) no treatment, 2) P only, 3) ES only, 4) ES + P, 5) TP only, 6) TP + P, 7) ES + TP, and 8) ES + TP + P. For each group n = 4-8. Recovery of the eyeblink reflex and vibrissae orientation and movement were assessed. Changes in peak amplitude and latency of evoked response, in response to facial nerve stimulation, was also recorded weekly.

RESULTS

: Brief ES of the proximal nerve stump most effectively accelerated the initiation of functional recovery. Also, ES or TP treatments enhanced recovery of some functional parameters more than P treatment. When administered alone, none of the three treatments improved recovery of complete facial function. Only the combinatorial treatment of ES + TP, regardless of the presence of P, accelerated complete functional recovery and return of normal motor nerve conduction.

CONCLUSIONS

Our findings suggest that a combinatorial treatment strategy of using brief ES and TP together promises to be an effective therapeutic intervention for promoting regeneration following facial nerve injury. Administration of P neither augments nor hinders recovery.