Nimodipine promotes regeneration and functional recovery after intracranial facial nerve crush

Enhancement of nerve regeneration with nimodipine treatment after sciatic nerve injury

Peripheral nerve injuries (PNI/s) are common orthopedic conditions, characterized by motor and sensory deficits in the damaged region. There is growing evidence that the L-type calcium channel antagonist nimodipine has neuroprotective and neuroregenerative effects in animal models of neurological disorders. The efficacy of nimodipine on improving motor function and sensation following a sciatic nerve crush model was investigated in male Wistar rats as a model of PNI. At different time periods following damage, we evaluated motor function, sensory recovery, electrophysiology, histomorphometry, and gene expression. Moreover, we used histological and mass ratio analysis of the gastrocnemius muscle to assess atrophy. Our findings suggest that the nimodipine improves motor and sensory function more quickly in the damaged region 2, 4, and 6 weeks after 1 week of treatment. Nimodipine treatment also increased the number of myelinated fibers while decreasing their thickness, as shown by histomorphometry. Additionally, nimodipine treatment increases the mRNA levels of neurotrophic factors (BDNF and NGF), which are known to contribute to the regeneration of injured neurons. The impact of nimodipine in PNI recovery may be due to its stimulation of the CREB signaling pathway and suppression of pro-inflammatory factor production.

Treatment With Nimodipine or FK506 After Facial Nerve Repair Neither Improves Accuracy of Reinnervation Nor Recovery of Mimetic Function in Rats

Purpose

Nimodipine and FK506 (Tacrolimus) are drugs that have been reported to accelerate peripheral nerve regeneration. We therefore tested these substances aiming to improve the final functional outcome of motoric reinnervation after facial nerve injury.

Methods

In 18 female rats, the transected facial nerve was repaired by an artificial nerve conduit. The rats were then treated with either placebo, nimodipine, or FK506, for 56 days. Facial motoneurons were pre-operatively double-labeled by Fluoro-Gold and again 56 days post-operation by Fast-Blue to measure the cytological accuracy of reinnervation. The whisking motion of the vibrissae was analyzed to assess the quality of functional recovery.

Results

On the non-operated side, 93–97% of those facial nerve motoneurons innervating the vibrissae were double-labeled. On the operated side, double-labeling only amounted to 38% (placebo), 40% (nimodipine), and 39% (FK506), indicating severe misdirection of reinnervation. Regardless of post-operative drug or placebo therapy, the whisking frequency reached 83–100% of the normal value (6.0 Hz), but whisking amplitude was reduced to 33–48% while whisking velocity reached 39–66% of the normal values. Compared to placebo, statistically neither nimodipine nor FK506 improved accuracy of reinnervation and function recovery.

Conclusion

Despite previous, positive data on the speed and quantity of axonal regeneration, nimodipine and FK506 do not improve the final functional outcome of motoric reinnervation in rats.

Perioperative Nimodipine to Improve Cranial Nerve Function: A Systematic Review and Meta-Analysis

OBJECTIVE

Nimodipine has emerged as a promising strategy for protection of cranial nerves following vestibular schwannoma (VS) resections. Our goal was to conduct a comprehensive analysis of clinical studies to determine the therapeutic efficacy of nimodipine in improving facial nerve and cochlear nerve function.

DATABASE REVIEWED

We searched PubMed, Scopus, Cochrane Clinical Trial Registry, Clinicaltrials.gov, World Health Organization's International Clinical Trials Registry Platform, and EU Clinical Trials Registry to identify clinical studies up to May 11, 2020.

METHODS

We included studies evaluating perioperative administration of nimodipine as a strategy to prevent or treat facial nerve or cochlear nerve dysfunction following VS resections. Primary outcomes included preservation or recovery of House-Brackman scale for facial nerve function and Hearing and Equilibrium Guidelines for cochlear nerve function at the latest follow-up visit. Secondary outcomes included adverse events and administration strategies of nimodipine.

RESULTS

Nine studies (603 patients) met inclusion, of which seven studies (559 patients) were included in the quantitative analysis. Overall, nimodipine significantly increased the odds of cranial nerve recovery compared with controls (odds ratio [OR] 2.87, 95% confidence intervals [CI] [2.08, 3.95]; I2 = 0%). Subgroup analysis demonstrated that nimodipine was only effective for cochlear nerve preservation (OR 2.78, 95% CI [1.74, 4.45]; I2 = 0%), but not for facial nerve function (OR 4.54, 95% CI [0.25, 82.42]; I2 = 33%).

CONCLUSION

Although there is evidence supporting the perioperative role of nimodipine for VS resections, more studies are warranted to help clarify the effects of nimodipine therapy on cranial nerve preservation.

Effect of Nimodipine and Botulinum Toxin A on Peripheral Nerve Regeneration in Rats: A Pilot Study

BACKGROUND

Peripheral nerve damage is a frequent problem, with an estimated 2.8%-5.0% of trauma admissions involving peripheral nerve injury. End-to-end, tension-free microsurgical repair (neurorrhaphy) is the current gold standard treatment for complete transection (neurotmesis). While neurorrhaphy reapproximates the nerve, it does not address the complex molecular regenerative process. Evidence suggests that botulinum toxin A (BTX) and nimodipine (NDP) may improve functional recovery, but mechanisms of action remain unknown.

METHODS

This research investigates BTX and NDP for their novel capacity to improve neural regeneration in the setting of neurorrhaphy using a Lewis rat tibial nerve neurotmesis model. In a triple-masked, placebo-controlled, randomized study design, we compared functional (rotarod, horizontal ladder walk), electrophysiological (conduction velocity, duration), and stereological (axon count, density) outcomes of rats treated with: NDP+saline injection, BTX+NDP, Saline+placebo, and BTX+placebo. Additional controls included sham surgery +/- BTX.

RESULTS

NDP+saline outperformed other treatment groups in the ladder walk. This group had the fewest deep slips (15.07% versus 30.77% in BTX+NDP, P = 0.122), and the most correct steps (70.53% versus 55.58% in BTX+NDP, P = 0.149) in functional testing. NDP+saline also had the fastest nerve conduction velocity (0.811m/s versus 0.598m/s in BTX+NDP, P = 0.126) among treatment groups. BTX+NDP had the highest axon count (10,012.36 versus 7,738.18 in NDP+Saline, P = 0.009).

CONCLUSION

This study is the first to test NDP with BTX in a multimodal assessment of nerve recovery following neurotmesis and neurorrhaphy. NDP outperformed BTX+NDP functionally. Future work will focus on nimodipine in an effort to improve nerve recovery in trauma patients.

Nimodipine promotes neurite outgrowth and protects against neurotoxicity in PC12 cells

OBJECTIVES

Nimodipine is an L-type voltage-dependent calcium channel (VDCC) antagonist. However, the actions of nimodipine except calcium blocking are poorly understood. This study aimed to investigate the effect of nimodipine on neurite outgrowth and neuroprotection in vitro.

MATERIALS AND METHODS

After PC12 cells were treated with different concentrations of nimodipine, neurite outgrowth was estimated using the ImageJ software. Neuroprotective effects of nimodipine against H2O2 and calcium ionophore-induced neurotoxicity were investigated using (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In addition, the activation of extracellular signal-regulated kinase (ERK) and cyclic AMP-response element-binding protein (CREB) pathway was investigated for clarifying the action mechanism of nimodipine.

RESULTS

Nimodipine treatment at doses of higher than 10 µM induced neurite outgrowth in the cells. Additionally, VDCC knockdown by siRNA significantly suppressed the nimodipine-induced neurite outgrowth in PC12 cells, suggesting that the drug promotes neurite outgrowth by binding to VDCC. H2O2 and calcium ionophore induce oxidative and calcium stress in PC12 cells. Nimodipine exhibited neuroprotective effects against H2O2- and calcium ionophore-induced neurotoxicity by increasing the mRNA expression levels of neurotrophic factors, calcium-binding proteins, and antioxidants that are transcribed by CREB activation.

CONCLUSION

This is the first report that nimodipine induces neurite outgrowth and exerts its neuroprotective activity through the ERK/CREB signaling pathway in PC12 cells.

ANXA1 directs Schwann cells proliferation and migration to accelerate nerve regeneration through the FPR2/AMPK pathway

Many factors are involved in the process of nerve regeneration. Understanding the mechanisms regarding how these factors promote an efficient remyelination is crucial to deciphering the molecular and cellular processes required to promote nerve repair. Schwann cells (SCs) play a central role in the process of peripheral nerve repair/regeneration. Using a model of facial nerve crush injury and repair, we identified Annexin A1 (ANXA1) as the extracellular trigger of SC proliferation and migration. ANXA1 activated formyl peptide receptor 2 (FPR2) receptors and the downstream adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling cascade, leading to SC proliferation and migration in vitro. SCs lacking FPR2 or AMPK displayed a defect in proliferation and migration. After facial nerve injury (FNI), ANXA1 promoted the proliferation of SCs and nerve regeneration in vivo. Collectively, these data identified the ANXA1/FPR2/AMPK axis as an important pathway in SC proliferation and migration. ANXA1-induced remyelination and SC proliferation promotes FNI regeneration.

Facial nerve repair utilizing intraoperative repair strategies

OBJECTIVES

To determine whether functional and anatomical outcomes following suture neurorrhaphy are improved by the addition of electrical stimulation with or without the addition of polyethylene glycol (PEG).

METHODS

In a rat model of facial nerve injury, complete facial nerve transection and repair was performed via (a) suture neurorrhaphy alone, (b) neurorrhaphy with the addition of brief (30 minutes) intraoperative electrical stimulation, or (c) neurorrhaphy with the addition electrical stimulation and PEG. Functional recovery was assessed weekly for 16 weeks. At 16 weeks postoperatively, motoneuron survival, amount of regrowth, and specificity of regrowth were assessed by branch labeling and tissue analysis.

RESULTS

The addition of brief intraoperative electrical stimulation improved all functional outcomes compared to suturing alone. The addition of PEG to electrical stimulation impaired this benefit. Motoneuron survival, amount of regrowth, and specificity of regrowth were unaltered at 16 weeks postoperative in all treatment groups.

CONCLUSION

The addition of brief intraoperative electrical stimulation to neurorrhaphy in this rodent model shows promising neurological benefit in the surgical repair of facial nerve injury.

LEVEL OF EVIDENCE

Animal study.

Overexpression of Foxc1 regenerates crushed rat facial nerves by promoting Schwann cells migration via the Wnt/β-catenin signaling pathway

Facial paralysis can result in severe implications for patients. A good prognosis depends on the degree of nerve regeneration. Schwann cells (SCs) play an important role in facial nerve development and regeneration through migration. Forkhead box C1 (Foxc1), a member of the forkhead transcription factor family, is implicated in cell migration. However, the role of Foxc1 in the progression after facial nerve crush remains unknown. Our aim was to evaluate the effect of Foxc1 overexpression on SC migration and recovery of facial nerves after crush injury. The rat facial nerve crush injury model was established through the use of unilateral surgery. The results showed that the expression of Foxc1 was increased in the surgery group compared to that of the control group. SCs were isolated from the sciatic nerves and cultured. Foxc1, delivered by an adeno‐associated virus in vivo, or adenovirus in vitro, both induced overexpression of Foxc1, and increased the expression of CXCL12 and β‐catenin. After the transfection of Foxc1, the migration of SC was increased both in vitro and in vivo, was reduced by the inhibition of CXCL12 or β‐catenin. The facial nerve function and the nerve axon remyelination of the rats transfected with Foxc1 were significantly improved after nerve crush injury. Overall, the results demonstrated that overexpression of Foxc1 promoted SC migration by regulating CXCL12 via the Wnt/β‐catenin pathway, thus contributing to improved facial nerve function after crush injury.

Functional and Anatomical Outcomes of Facial Nerve Injury With Application of Polyethylene Glycol in a Rat Model

Importance

Functional and anatomical outcomes after surgical repair of facial nerve injury may be improved with the addition of polyethylene glycol (PEG) to direct suture neurorrhaphy. The application of PEG has shown promise in treating spinal nerve injuries, but its efficacy has not been evaluated in treatment of cranial nerve injuries.

Objective

To determine whether PEG in addition to neurorrhaphy can improve functional outcomes and synkinesis after facial nerve injury.

Design, Setting, and Subjects

In this animal experiment, 36 rats underwent right facial nerve transection and neurorrhaphy with addition of PEG. Weekly behavioral scoring was done for 10 rats for 6 weeks and 14 rats for 16 weeks after the operations. In the 16-week study, the buccal branches were labeled and tissue analysis was performed. In the 6-week study, the mandibular and buccal branches were labeled and tissue analysis was performed. Histologic analysis was performed for 10 rats in a 1-week study to assess the association of PEG with axonal continuity and Wallerian degeneration. Six rats served as the uninjured control group. Data were collected from February 8, 2016, through July 10, 2017.

Intervention

Polyethylene glycol applied to the facial nerve after neurorrhaphy.

Main Outcomes and Measures

Functional recovery was assessed weekly for the 16- and 6-week studies, as well as motoneuron survival, amount of regrowth, specificity of regrowth, and aberrant branching. Short-term effects of PEG were assessed in the 1-week study.

Results

Among the 40 male rats included in the study, PEG addition to neurorrhaphy showed no functional benefit in eye blink reflex (mean [SEM], 3.57 [0.88] weeks; 95% CI, -2.8 to 1.9 weeks; P = .70) or whisking function (mean [SEM], 4.00 [0.72] weeks; 95% CI, -3.6 to 2.4 weeks; P = .69) compared with suturing alone at 16 weeks. Motoneuron survival was not changed by PEG in the 16-week (mean, 132.1 motoneurons per tissue section; 95% CI, -21.0 to 8.4; P = .13) or 6-week (mean, 131.1 motoneurons per tissue section; 95% CI, -11.0 to 10.0; P = .06) studies. Compared with controls, neither surgical group showed differences in buccal branch regrowth at 16 (36.9 motoneurons per tissue section; 95% CI, -14.5 to 22.0; P = .28) or 6 (36.7 motoneurons per tissue section; 95% CI, -7.8 to 18.5; P = .48) weeks or in the mandibular branch at 6 weeks (25.2 motoneurons per tissue section; 95% CI, -14.5 to 15.5; P = .99). Addition of PEG had no advantage in regrowth specificity compared with suturing alone at 16 weeks (15.3% buccal branch motoneurons with misguided projections; 95% CI, -7.2% to 11.0%; P = .84). After 6 weeks, the number of motoneurons with misguided projections to the mandibular branch showed no advantage of PEG treatment compared with suturing alone (12.1% buccal branch motoneurons with misguided projections; 95% CI, -8.2% to 9.2%; P = .98). In the 1-week study, improved axonal continuity and muscular innervation were not observed in PEG-treated rats.

Conclusions and Relevance

Although PEG has shown efficacy in treating other nervous system injuries, PEG in addition to neurorraphy was not beneficial in a rat model of facial nerve injury. The addition of PEG to suturing may not be warranted in the surgical repair of facial nerve injury.

Level of Evidence

NA.

Nimodipine-Dependent Protection of Schwann Cells, Astrocytes and Neuronal Cells from Osmotic, Oxidative and Heat Stress Is Associated with the Activation of AKT and CREB

Clinical and experimental data assumed a neuroprotective effect of the calcium channel blocker nimodipine. However, it has not been proven which neuronal or glial cell types are affected by nimodipine and which mechanisms underlie these neuroprotective effects. Therefore, the aim of this study was to investigate the influence of nimodipine treatment on the in vitro neurotoxicity of different cell types in various stress models and to identify the associated molecular mechanisms. Therefore, cell lines from Schwann cells, neuronal cells and astrocytes were pretreated for 24 h with nimodipine and incubated under stress conditions such as osmotic, oxidative and heat stress. The cytotoxicity was measured via the lactate dehydrogenase (LDH) activity of cell culture supernatant. As a result, the nimodipine treatment led to a statistically significantly reduced cytotoxicity in Schwann cells and neurons during osmotic (p ≤ 0.01), oxidative (p ≤ 0.001) and heat stress (p ≤ 0.05), when compared to the vehicle. The cytotoxicity of astrocytes was nimodipine-dependently reduced during osmotic (p ≤ 0.01), oxidative (p ≤ 0.001) and heat stress (not significant). Moreover, a decreased caspase activity as well as an increased proteinkinase B (AKT) and cyclic adenosine monophosphate response element-binding protein (CREB) phosphorylation could be observed after the nimodipine treatment under different stress conditions. These results demonstrate a cell type-independent neuroprotective effect of the prophylactic nimodipine treatment, which is associated with the prevention of stress-dependent apoptosis through the activation of CREB and AKT signaling pathways and the reduction of caspase 3 activity.

Effect of Local Administration of Verapamil Combined with Chitosan Based Hybrid Nanofiber Conduit on Transected Sciatic Nerve in Rat

Objective:

To assess the effect of locally administered verapamil on transected peripheral nerve regeneration and functional recovery.

Methods:

Sixty male healthy white Wistar rats were divided into four experimental groups (n=15), randomly: In transected group (TC), left sciatic nerve was transected and stumps were fixed in the adjacent muscle. In treatment group defect was bridged using chitosan tube (CHIT/Verapamil) filled with 10 µL verapamil (100ng/mL). In chitosan conduit group (CHIT), the tube was filled with phosphate-buffered saline alone. In sham-operated group (SHAM), sciatic nerve was exposed and manipulated. The repair trend was examined based on behavioral and performance tests as well as the variations of the gastrocnemius muscle, morphometric indices, and immunohistochemical indices.

Results:

Sciatic nerve functional study, muscle mass and morphometric indices confirmed faster recovery of regenerated axons in CHIT/Verapamil than CHIT group (P = 0.001). When loaded in a chitosan tube verapamil accelerated and improved functional recovery and morphometric indices of sciatic nerve. Immunohistochemical analysis revealed the S-100 protein was vastly present in the transverse nerve sections and the myelin sheath. In the treatment group (chit/verapamil), the immunohistochemical susceptibility of the axons being repaired and the axons in the myelin sheath to S-100 protein was higher than the other groups.

Conclusion:

The present study demonstrated that a single local application of verapamil could accelerate functional recovery after transection of sciatic nerve.

Recovery of Voice After Reconstruction of the Recurrent Laryngeal Nerve and Adjuvant Nimodipine

Background

Transection injury to the recurrent laryngeal nerve (RLN) has been associated with permanent vocal fold palsy, and treatment has been limited to voice therapy or local treatment of vocal folds. Microsurgical repair has been reported to induce a better function. The calcium channel antagonist nimodipine improves functional recovery after experimental nerve injury and also after cranial nerve injury in patients. This study aims to present voice outcome in patients who underwent repair of the RLN and received nimodipine during regeneration.

Methods

From 2002–2016, 19 patients were admitted to our center with complete unilateral injury to the RLN and underwent microsurgical repair of the RLN. After nerve repair, patients received nimodipine for 2–3 months. Laryngoscopy was performed repeatedly up to 14 months postoperatively. The Voice Handicap Index (VHI) was administered, and patients’ maximum phonation time (MPT) was recorded during the follow-up.

Results

All patients recovered well after surgery, and nimodipine was well tolerated with no dropouts. None of the patients suffered from atrophy of the vocal fold, and some patients even showed a small ab/adduction of the vocal fold on the repaired side with laryngoscopy. During long-term follow-up (>3 years), VHI and MPT normalized, indicating a nearly complete recovery from unilateral RLN injury.

Conclusions

In this cohort study, we report the results of the first 19 consecutive cases at our center subjected to reconstruction of the RLN and adjuvant nimodipine treatment. The outcome of the current strategy is encouraging and should be considered after iatrogenic RLN transection injuries.

New Treatment in Facial Nerve Palsy Caused by Sagittal Split Ramus Osteotomy of Mandible

A 25-years-old woman with mandibular prognathism underwent a mandibular setback by way of mandibular sagittal split ramus osteotomy (MSSRO). After 2 days of operation, she developed difficulty of closing her right eye. The blink reflex test and motor nerve conduction study of the right orbicularis oris muscle were revealed right facial neuropathy of unknown origin and House-Brackmann facial nerve grading system (HBFNGS) grade V. For treatment, we initially prescribed oral prednisolone and nimodipine including physical therapy. The samples consisted of 11 facial nerve palsy patients caused by MSSRO and were analysed about onset of facial nerve palsy, postoperative HBFNGS, final HBFNGS, treatment method and recovery time. At 10 weeks of treatment of nimodipine, she had completely regained normal function (HBFNGS grade I) of the right facial nerve. The clinical results lead to assume a fast recovery of facial nerve function by the nimodipine medication, whereas average time of recovery is 16.32 weeks in references. Despite of the limited one patient treated, the result was very promising with respect to a faster recovery of the facial nerve function. Considering the use of nimodipine treatment for peripheral facial nerve palsy following a surgical approach with an anatomically preserved nerve can be recommended.

A small molecule screen identifies in vivo modulators of peripheral nerve regeneration in zebrafish

Adult vertebrates have retained the ability to regenerate peripheral nerves after injury, although regeneration is frequently incomplete, often leading to functional impairments. Small molecule screens using whole organisms have high potential to identify biologically relevant targets, yet currently available assays for in vivo peripheral nerve regeneration are either very laborious and/or require complex technology. Here we take advantage of the optical transparency of larval zebrafish to develop a simple and fast pectoral fin removal assay that measures peripheral nerve regeneration in vivo. Twenty-four hours after fin amputation we observe robust and stereotyped nerve regrowth at the fin base. Similar to laser mediated nerve transection, nerve regrowth after fin amputation requires Schwann cells and FGF signaling, confirming that the fin amputation assay identifies pathways relevant for peripheral nerve regeneration. From a library of small molecules with known targets, we identified 21 compounds that impair peripheral nerve regeneration. Several of these compounds target known regulators of nerve regeneration, further validating the fin removal assay. Twelve of the identified compounds affect targets not previously known to control peripheral nerve regeneration. Using a laser-mediated nerve transection assay we tested ten of those compounds and confirmed six of these compounds to impair peripheral nerve regeneration: an EGFR inhibitor, a glucocorticoid, prostaglandin D2, a retinoic acid agonist, an inhibitor of calcium channels and a topoisomerase I inhibitor. Thus, we established a technically simple assay to rapidly identify valuable entry points into pathways critical for vertebrate peripheral nerve regeneration.

Prophylactic nimodipine treatment and improvement in hearing outcome after vestibular schwannoma surgery: a combined analysis of a randomized, multicenter, Phase III trial and its pilot study

OBJECTIVE In clinical routines, neuroprotective strategies in neurosurgical interventions are still missing. A pilot study (n = 30) and an analogously performed Phase III trial (n = 112) pointed to a beneficial effect of prophylactic nimodipine and hydroxyethyl starch (HES) in vestibular schwannoma (VS) surgery. Considering the small sample size, the data from both studies were pooled. METHODS The patients in both investigator-initiated studies were assigned to 2 groups. The treatment group (n = 70) received parenteral nimodipine (1-2 mg/hour) and HES (hematocrit 30%-35%) from the day before surgery until the 7th postoperative day. The control group (n = 72) was not treated prophylactically. Facial and cochlear nerve functions were documented preoperatively, during the inpatient care, and 1 year after surgery. RESULTS Pooled raw data were analyzed retrospectively. Intent-to-treat analysis revealed a significantly lower risk for hearing loss (Class D) 12 months after surgery in the treatment group compared with the control group (OR 0.46, 95% CI 0.22-0.97; p = 0.04). After exclusion of patients with preoperative Class D hearing, this effect was more pronounced (OR 0.38, 95% CI 0.17-0.83; p = 0.016). Logistic regression analysis adjusted for tumor size showed a 4 times lower risk for hearing loss in the treatment group compared with the control group (OR 0.25, 95% CI 0.09-0.63; p = 0.003). Facial nerve function was not significantly improved with treatment. Apart from dose-dependent hypotension (p < 0.001), the study medication was well tolerated. CONCLUSIONS Prophylactic nimodipine is safe and may be recommended in VS surgery to preserve hearing. Prophylactic neuroprotective treatment in surgeries in which nerves are at risk seems to be a novel and promising concept. Clinical trial registration no.: DRKS 00000328 ( https://drks-neu.uniklinik-freiburg.de/drks_web/ ).

Nimodipine Improves Reinnervation and Neuromuscular Function after Injury to the Recurrent Laryngeal Nerve in the Rat

Objectives:

Injury of the recurrent laryngeal nerve (RLN) is associated with a high degree of neuronal survival, but leads to various levels of vocal fold motion impairment or laryngeal synkinesis, which has been attributed to misdirected reinnervation of the target muscles in the larynx or aberrant, competing reinnervation from adjacent nerve fibers. The aim of the present study was to evaluate the impact of the regeneration-promoting agent nimodipine on reinnervation and neuromuscular function following RLN crush injury.

Methods:

Sixty adult rats were randomized into nimodipine-treated or untreated groups and then underwent RLN crush injury. Reinnervation of the posterior cricoarytenoid muscle (PCA) was assessed by electrophysiological examination, retrograde tracing of lower motor neurons before and after injury, and quantification of neuromuscular junctions in the PCA muscle.

Results:

At 6 weeks after injury, the nimodipine-treated animals showed significantly enhanced neuromuscular function and also demonstrated a higher number of motor neurons in the brain stem that had reinnervated the PCA, compared to the untreated animals. The somatotopic organization of ambiguus motor neurons innervating the larynx was similar before injury and after reinnervation.

Conclusions:

Nimodipine improves regeneration and neuromuscular function following RLN injury in the adult rat, and could be of use in future strategies following RLN injury.

Surgery for sporadic vestibular schwannoma. Part IV. Predictive factors influencing facial nerve function after surgery

OBJECTIVE

To analyze the impact of various clinical, radiological and perioperative factors that could influence the facial nerve intraoperative disruption risk (CNVII-IDR) and its long-term function (CNVII-LTF) after vestibular schwannoma (VS) surgery.

MATERIAL AND METHODS

The study included 212 patients operated on for sporadic VS with no history of previous treatment for VS or CNVII palsy. The mean size of the tumor was 30 mm. Gross (210) or near-total (2) resections were carried out using the retrosigmoid (210) or translabyrinthine (2) approach. Correlation studies and multivariate regression analysis (RA) were performed.

RESULTS

In correlation studies, the CNVII-IDR was increased by: headaches and cerebellar ataxia if one of them was the first symptom of the tumor (33% and 29%, respectively, p=0.008); preoperative hydrocephalus (40% vs. 9%, p=0.01), tumor size >3 cm (18% vs. 5%, p<0.01), tumor volume >10 cm(3) (19% vs. 4%, p<0.01), right-sided location 15% vs. 6%, p=0.047), lateral "park-bench" position (19% vs. 5% for supine position, p<0.01) and the procedure order (16% for the first 106 procedures vs. 6% for the last 106 procedures, p<0.05). In RA the tumor volume (p=0.012), side of the tumor (p=0.028) and patient's position during surgery (p=0.016) independently affected the CNVII-IDR. The following factors correlated significantly with satisfactory CNVII-LTF (HB grades I-III): tumor stage <T4 (p=0.000), tumor size ≤3 cm (p=0.000), tumor volume ≤10 cm(3) (p=0.001), and left-sided location (p=0.048). Additional factors correlated significantly with very good CNVII-LTF (HB grades I-II): anterior CNVII displacement (p=0.044), nimodipine use (p=0.016), the absence of postoperative complications (p=0.019), CNVII responsive on final intraoperative EMG stimulation (p=0.000) and supine position during surgery (p=0.018). However, an independent impact on very good CNVII-LTF proved to be the tumor size (p=0.0000), side (p=0.0175), and nimodipine use (p=0.0349).

CONCLUSIONS

In our series, the factors related to size and side of the tumor confirmed an independent impact on CNVII-IDR and CNVIILTF. The significance of patient positioning may reflect the impact of learning curve as only the first 91 patients were operated on using the lateral "park-bench" position. An independent impact on CNVII-LTF was exerted by the perioperative use of nimodipine.

Prophylactic nimodipine treatment for cochlear and facial nerve preservation after vestibular schwannoma surgery: a randomized multicenter Phase III trial

OBJECTIVE

A pilot study of prophylactic nimodipine and hydroxyethyl starch treatment showed a beneficial effect on facial and cochlear nerve preservation following vestibular schwannoma (VS) surgery. A prospective Phase III trial was undertaken to confirm these results.

METHODS

An open-label, 2-arm, randomized parallel group and multicenter Phase III trial with blinded expert review was performed and included 112 patients who underwent VS surgery between January 2010 and February 2013 at 7 departments of neurosurgery to investigate the efficacy and safety of the prophylaxis. The surgery was performed after the patients were randomly assigned to one of 2 groups using online randomization. The treatment group (n = 56) received parenteral nimodipine (1-2 mg/hr) and hydroxyethyl starch (hematocrit 30%-35%) from the day before surgery until the 7th postoperative day. The control group (n = 56) was not treated prophylactically.

RESULTS

Intent-to-treat analysis showed no statistically significant effects of the treatment on either preservation of facial nerve function (35 [67.3%] of 52 [treatment group] compared with 34 [72.3%] of 47 [control group]) (p = 0.745) or hearing preservation (11 [23.4%] of 47 [treatment group] compared with 15 [31.2%] of 48 [control group]) (p = 0.530) 12 months after surgery. Since tumor sizes were significantly larger in the treatment group than in the control group, logistic regression analysis was required. The risk for deterioration of facial nerve function was adjusted nearly the same in both groups (OR 1.07 [95% CI 0.34-3.43], p = 0.91). In contrast, the risk for postoperative hearing loss was adjusted 2 times lower in the treatment group compared with the control group (OR 0.49 [95% CI 0.18-1.30], p = 0.15). Apart from dose-dependent hypotension (p < 0.001), no clinically relevant adverse reactions were observed.

CONCLUSIONS

There were no statistically significant effects of the treatment. Despite the width of the confidence intervals, the odds ratios may suggest but do not prove a clinically relevant effect of the safe study medication on the preservation of cochlear nerve function after VS surgery. Further study is needed before prophylactic nimodipine can be recommended in VS surgery.

Nimodipine-mediated re-myelination after facial nerve crush injury in rats

This study aimed to investigate the mechanism of nimodipine-mediated neural repair after facial nerve crush injury in rats. Adult Sprague-Dawley rats were divided into three groups: healthy controls, surgery alone, and surgery plus nimodipine. A facial nerve crush injury model was constructed. Immediately after surgery, the rats in the surgery plus nimodipine group were administered nimodipine, 6 mg/kg/day, for a variable numbers of days. The animals underwent electromyography (EMG) before surgery and at 3, 10, or 20 days after surgery. After sacrifice, nerve samples were stained with hematoxylin and eosin (H&E) and luxol fast blue. The EMG at 20 days revealed an apparent recovery of eletroconductivity, with the surgery plus nimodipine group having a higher amplitude and shorter latency time than the surgery only group. H&E staining showed that at 20 days, the rats treated with nimodipine had an obvious recovery of myelination and reduction in the number of infiltrating cells, suggesting less inflammation, compared with the rats in the surgery only group. Luxol fast blue staining was relatively even in the surgery plus nimodipine group, indicating a protective effect against injury-induced demyelination. Staining for S100 calcium-binding protein B (S-100β) was not evident in the surgery alone group, but was evident in the surgery plus nimodipine group, indicating that nimodipine reversed the damage of the crush injury. After a facial nerve crush injury, treatment with nimodipine for 20 days reduced the nerve injury by mediating remyelination by Schwann cells. The protective effect of nimodipine may include a reduction of inflammation and an increase in calcium-binding S-100β protein.

Recovery of laryngeal function after intraoperative injury to the recurrent laryngeal nerve

Loss of function in the recurrent laryngeal nerve (RLN) during thyroid/parathyroid surgery, despite a macroscopically intact nerve, is a challenge which highlights the sensitivity and complexity of laryngeal innervation. Furthermore, the uncertain prognosis stresses a lack of capability to diagnose the reason behind the impaired function. There is a great deal of literature considering risk factors, surgical technique and mechanisms outside the nerve affecting the incidence of RLN paresis during surgery. To be able to prognosticate recovery in cases of laryngeal dysfunction and voice changes after thyroid surgery, the surgeon would first need to define the presence, location, and type of laryngeal nerve injury. There is little data describing the events within the nerve and the neurobiological reasons for the impaired function related to potential recovery and prognosis. In addition, very little data has been presented in order to clarify any differences between the transient and permanent injury of the RLN. This review aims, from an anatomical and neurobiological perspective, to provide an update on the current understandings of surgically-induced injury to the laryngeal nerves.

Nimodipine enhances neurite outgrowth in dopaminergic brain slice co-cultures

Calcium ions (Ca(2+)) play important roles in neuroplasticity and the regeneration of nerves. Intracellular Ca(2+) concentrations are regulated by Ca(2+) channels, among them L-type voltage-gated Ca(2+) channels, which are inhibited by dihydropyridines like nimodipine. The purpose of this study was to investigate the effect of nimodipine on neurite growth during development and regeneration. As an appropriate model to study neurite growth, we chose organotypic brain slice co-cultures of the mesocortical dopaminergic projection system, consisting of the ventral tegmental area/substantia nigra and the prefrontal cortex from neonatal rat brains. Quantification of the density of the newly built neurites in the border region (region between the two cultivated slices) of the co-cultures revealed a growth promoting effect of nimodipine at concentrations of 0.1μM and 1μM that was even more pronounced than the effect of the growth factor NGF. This beneficial effect was absent when 10μM nimodipine were applied. Toxicological tests revealed that the application of nimodipine at this higher concentration slightly induced caspase 3 activation in the cortical part of the co-cultures, but did neither affect the amount of lactate dehydrogenase release or propidium iodide uptake nor the ratio of bax/bcl-2. Furthermore, the expression levels of different genes were quantified after nimodipine treatment. The expression of Ca(2+) binding proteins, immediate early genes, glial fibrillary acidic protein, and myelin components did not change significantly after treatment, indicating that the regulation of their expression is not primarily involved in the observed nimodipine mediated neurite growth. In summary, this study revealed for the first time a neurite growth promoting effect of nimodipine in the mesocortical dopaminergic projection system that is highly dependent on the applied concentrations.

Quantitative analysis of muscle histologic method in rodent facial nerve injury

OBJECTIVE

To describe denervation features of facial musculature following facial nerve injury in a rodent model.

METHODS

Six Wistar-Hannover rats underwent unilateral transection and immediate repair of the facial nerve. After 8 weeks, muscular bundles consisting of dilator naris and levator labii superioris from both sides were analyzed for mean muscle cell diameter and the percentage of muscle cell cross-sectional area using image processing software. The atrophic features of facial muscles were quantified and compared with the contralateral, healthy side of the face.

RESULTS

Weekly postoperative whisking assessment demonstrated the anticipated course of recovery. We observed significant differences between the normal side and the manipulated side, respectively, in the percentage of muscle specimen cross-sectional area attributable to muscle cell profiles (57% vs 29%; P = .006) and total fiber counts (1346 vs 794; P = .02). The mean cross-sectional area of individual muscle fibers was higher on the normal side (1129 vs 928 μm2; P = .39); however, this difference was statistically nonsignificant.

CONCLUSION

The objective, quantitative measures of muscle microstructure used in this report provide a valuable point of comparison for whisking function and electrophysiologic measures and can be used in future studies to assess muscle atrophic features associated with facial nerve injury and repair techniques.

Blocking the P2X7 receptor improves outcomes after axonal fusion

BACKGROUND

Activation of the P2X7 receptor on peripheral neurons causes the formation of pannexin pores, which allows the influx of calcium across the cell membrane. Polyethylene glycol (PEG) and methylene blue have previously been shown to delay Wallerian degeneration if applied during microsuture repair of the severed nerve. Our hypothesis is that by modulating calcium influx via the P2X7 receptor pathway, we could improve PEG-based axonal repair. The P2X7 receptor can be stimulated or inhibited using bz adenosine triphosphate (bzATP) or brilliant blue (FCF), respectively.

METHODS

A single incision rat sciatic nerve injury model was used. The defect was repaired using a previously described PEG methylene blue fusion protocol. Experimental animals were treated with 100 μL of 100 μM FCF solution (n = 8) or 100 μL of a 30 μM bzATP solution (n = 6). Control animals received no FCF, bzATP, or PEG. Compound action potentials were recorded prior to transection (baseline), immediately after repair, and 21 d postoperatively. Animals underwent behavioral testing 3, 7, 14, and 21 d postoperatively. After sacrifice, nerves were fixed, sectioned, and immunostained to allow for counting of total axons.

RESULTS

Rats treated with FCF showed an improvement compared with control at all time points (n = 8) (P = 0.047, 0.044, 0.014, and 0.0059, respectively). A statistical difference was also shown between FCF and bzATP at d 7 (P < 0.05), but not shown with d 3, 14, and 21 (P > 0.05).

CONCLUSIONS

Blocking the P2X7 receptor improves functional outcomes after PEG-mediated axonal fusion.

The impact of nimodipine administration combined with nerve-muscle pedicle implantation on long-term denervated rat thyroarytenoid muscle

OBJECTIVES/HYPOTHESIS

To evaluate the impact of nimodipineon reinnervation of the long-term denervated rat thyroarytenoid (TA) muscle following nerve-muscle pedicle flap (NMP) implantation.

STUDY DESIGN

Quantitative histologic and physiologic assessments.

METHODS

Using 120 Wistar rats, we performed NMP implantation at different times after transection of the left recurrent laryngeal nerve (RLN). Sixty animals received nimodipine treatment (NIMO [+] group), and the remaining 60 animals received no nimodipine treatment (NIMO [-] group). As a control, an additional 28 animals were subjected only to transection of the left RLN (DNV group). Subgroups were assigned based on the period after RLN transection (0 [immediate], 8, 16, and 32 weeks). In the DNV group, we assessed histologically the muscle area, axons, neuromuscular junctions (NMJs), and myosin heavy chains (MyHC) type IIA and IIB in the TA muscle. In the NIMO (-) and NIMO (+) groups, histologic assessments and evoked electromyography were performed on the TA muscle at 10 weeks post-NMP implantation.

RESULTS

In 8-week interval subgroups, the muscle fiber area and the number of NMJs in the NIMO (+) group were significantly greater than in the NIMO (-) group (P < 0.05, each). In the 0-week and 32-week interval subgroups, the muscle fiber subtype changed significantly, from IIA to IIB (P < 0.01 and P < 0.05, respectively); and, at all time-points the muscle fiber area, number of NMJs, and action potentials in the TA muscle tended to be greater in the NIMO (+) group than in the NIMO (-) group.

CONCLUSIONS

Nimodipine expedited the effects of NMP implantation on reinnervation of the long-term denervated TA muscle. Laryngoscope, 2012.

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.

Repair and rehabilitation of plexus and root avulsions in animal models and patients

PURPOSE OF REVIEW

This review will discuss recent progress in experimental and translational research related to surgical repair of proximal nerve root injuries, and emerging potential therapies, which may be combined with replantation surgeries to augment functional outcomes after brachial plexus and cauda equina injuries.

RECENT FINDINGS

Progress in experimental studies of root and peripheral nerve injuries has identified potential candidates for adjunctive therapies, which may be combined with surgical replantation of avulsed roots after brachial plexus and cauda equina injuries. We will discuss recent advances related to adjunctive neuroprotective strategies, neurotrophic factor delivery, and emerging cellular treatment strategies after extensive nerve root trauma. We will also provide an update on electrical stimulation to promote regenerative axonal growth and new insights on the recovery of sensory functions after root injury and repair.

SUMMARY

In the light of recent advances in experimental studies, we envision that future repair of brachial plexus and cauda equina injuries will include spinal cord surgery to restore motor and sensory trajectories and a variety of adjunctive therapies to augment the recovery of neurological function.

Nimodipine and acceleration of functional recovery of the facial nerve after crush injury

OBJECTIVE

To establish whether nimodipine, a calcium channel blocker, accelerates or otherwise improves functional recovery of whisking after facial nerve crush injury in the rat.

METHODS

Thirty rats underwent exposure of the left main trunk of the facial nerve followed by a standard crush injury and subsequent quantitative facial movement testing. Animals were randomized into an experimental group (n = 15) and a control group (n = 15). Four days prior to facial nerve manipulation, experimental animals underwent subcutaneous implantation of a nimodipine-secreting pellet. All animals were tested preoperatively and on postoperative days 2, 8 to 17, 20, 22, 24, and 31 using a validated, quantitative whisking kinematics apparatus. Whisks were analyzed for amplitude, velocity, and acceleration.

RESULTS

Animals receiving nimodipine demonstrated significantly better whisking on 5 days (postoperative days 9, 11 to 13, and 20) compared with control animals (P < .001, P = .003, P = .009, P = .009, and P = .009, respectively; 1-tailed ttest). Overall, the nimodipine-treated animals showed earlier recovery compared with the untreated animals.

CONCLUSIONS

We demonstrate that nimodipine improves recovery of whisking after facial nerve crush. This finding corroborates the semiquantitative findings of others, and provides complete whisking kinematic data on its effects. Given the low adverse effect profile of nimodipine, there may be clinical implications in its administration in patients experiencing facial nerve injury.

Rodent facial nerve recovery after selected lesions and repair techniques

BACKGROUND

Measuring rodent facial movements is a reliable method for studying recovery from facial nerve manipulation and for examining the behavioral correlates of aberrant regeneration. The authors quantitatively compared recovery of vibrissal and ocular function following three types of clinically relevant nerve injury.

METHODS

One hundred seventy-eight adult rats underwent facial nerve manipulation and testing. In the experimental groups, the left facial nerve was either crushed, transected, and repaired epineurially, or transected and the stumps suture-secured into a tube with a 2-mm gap between them. Facial recovery was measured for the ensuing 1 to 4 months. Data were analyzed for whisking recovery. Previously developed markers of co-contraction of the upper and midfacial zones (possible synkinesis markers) were also examined.

RESULTS

Animals in the crush groups recovered nearly normal whisking parameters within 25 days. The distal branch crush group showed improved recovery over the main trunk crush group for several days during early recovery. By week 9, the transection/repair groups showed evidence of recovery that trended further upward throughout the study period. The entubulation groups followed a similar recovery pattern, although they did not maintain significant recovery levels by the study conclusion. Markers of potential synkinesis increased in selected groups following facial nerve injury.

CONCLUSIONS

Rodent vibrissal function recovers in a predictable fashion following manipulation. Generalized co-contraction of the upper and midfacial zones emerges following facial nerve manipulation, possibly related to aberrant regeneration, polyterminal axons, or hypersensitivity of the rodent to sensory stimuli following nerve manipulation.

Intraoperative neurophysiological monitoring in vestibular schwannoma surgery: advances and clinical implications

OBJECT

Intraoperative neurophysiological monitoring has become an integral part of vestibular schwannoma surgery. The aim of this article was to review the different techniques of intraoperative neurophysiological monitoring in vestibular schwannoma surgery, identify the clinical impact of certain pathognomonic patterns on postoperative outcomes of facial nerve function and hearing preservation, and highlight the role of postoperative medications in improving delayed cranial nerve dysfunction in the different reported series.

METHODS

The authors performed a review of the literature regarding intraoperative monitoring in acoustic/vestibular schwannoma surgery. The different clinical series representing different monitoring techniques were reviewed. All the data from clinical series were analyzed in a comprehensive and comparative model.

RESULTS

Intraoperative brainstem auditory evoked potential monitoring, direct cochlear nerve action potential monitoring, and facial nerve electromyography are the main tools used to assess the functional integrity of an anatomically intact cranial nerve. The identification of pathognomonic brainstem auditory evoked potential and electromyography patterns has been correlated with postoperative functional outcome. Recently, perioperative administration of intravenous hydroxyethyl starch and nimodipine as vasoactive and neuroprotective agents was shown to improve vestibular schwannoma functional outcome in few reported studies.

CONCLUSIONS

Recent advances in electrophysiological technology have considerably contributed to improvement in functional outcome of vestibular neuroma surgery in terms of hearing preservation and facial nerve paresis. Perioperative intravenous nimodipine and hydroxyethyl starch may be valuable additions to surgery.

Diagnosis and Prognosis of Iatrogenic Injury of the Recurrent Laryngeal Nerve

Objectives:

Following perioperative injury to a macroscopically intact recurrent laryngeal nerve (RLN), there are two possible intraneural injury types: 1) axonal injury, including disruption of axons, and 2) conduction block, only affecting the Schwann cells and the nodes of Ranvier. In this study, it was hypothesized that the functional outcome after RLN injury may depend on the type of nerve injury.

Methods:

Fifteen patients with acute postoperative unilateral RLN paralysis were prospectively studied. Electrophysiological examination (laryngeal electromyography) was used to differentiate between the two types of nerve injury. Vocal fold motions were monitored by repeated laryngoscopy during the study period (up to 6 months). Three of the patients with axonal injury were treated with the regeneration-promoting agent nimodipine.

Results:

The patients with conduction block all recovered normal vocal fold motion, whereas patients with axonal injury within the nerve had a significantly worse outcome. The 3 patients who were treated with nimodipine all recovered normal or near-normal vocal fold mobility despite the more severe axonal injury.

Conclusions:

In contrast to previous reports, our results show that laryngeal electromyography is a reliable tool for diagnosing the type of injury within the injured RLN, making it possible to predict the functional outcome in these patients. On the basis of the results, a future randomized study on nimodipine treatment for RLN axonal injury is suggested.

Preserved Regeneration and Functional Recovery of the Injured Recurrent Laryngeal Nerve after Secondary Surgical Repair in Adult Rats

Objectives:

Transection of the recurrent laryngeal nerve (RLN) is accompanied by poor functional recovery, despite primary repair, because of regeneration difficulties. Nimodipine can promote regeneration, but it is not yet clear whether preoperative treatment is necessary. It is also not clear whether surgical repair following RLN injury may be performed in a second procedure, with preserved regeneration. This study investigated the time window for secondary surgical repair of the transected RLN and the need for preoperative administration of nimodipine.

Methods:

In adult rats, the left RLN was transected and repaired at time intervals up to 3 weeks after transection, in combination with nimodipine treatment starting either before or after the operation. Regeneration and neuromuscular recovery were assessed by electrophysiology, retrograde tracing, and immunohistochemistry.

Results:

Similar (whether 0, 2, or 7 days) regenerative results were obtained when the RLN was repaired up to 1 week after injury, given nimodipine administration, whereas fewer motor neurons managed to regenerate after nerve repair at 3 weeks after the initial transection. No beneficial effect was detected from preoperative nimodipine administration.

Conclusions:

Provided that nimodipine is administered, surgical reconstruction of the RLN can be performed within 1 week after the initial nerve trauma, with preserved neuromuscular function. Nimodipine may be administered at the time of RLN transection injury.

Relationship between ribosomal RNA gene transcription activity and motoneuron death: Observations of avulsion and axotomy of the facial nerve in rats

Motoneuron number and expression of cytoplasmic RNA and ribosomal RNA (rRNA) gene transcription activity in the facial nucleus were examined quantitatively and chronologically for up to 4 weeks in rats after facial nerve axotomy and avulsion in order to elucidate interrelationships in axonal changes. The right facial nerves of adult Fischer rats were avulsed at a portion of the outlet or axotomized at a portion of the foramen stylomastoideus. The number of large motoneurons in the facial nucleus was reduced by 40% 2 weeks after avulsion and by 70% 4 weeks after avulsion but displayed a 19% loss even 4 weeks after axotomy. The amount of cytoplasmic RNA decreased significantly and progressively from 1 day after avulsion. rRNA gene transcription activity in the large motoneurons of the facial nucleus decreased significantly beginning 30 min after both axotomy and avulsion, but the severity of the decrease was far more marked in the avulsion group, showing a 59% loss from the control value 4 weeks after avulsion. These findings indicate that rRNA gene transcription activity, expression of cytoplasmic RNA, and the number of motoneurons that survive are interrelated and that the decrease in rRNA gene transcription activity is a very early event in the phenomena observed in the axonal reactions of motoneurons.

The Influence of Prophylactic Vasoactive Treatment on Cochlear and Facial Nerve Functions after Vestibular Schwannoma Surgery

OBJECTIVE

Facial nerve paresis and hearing loss are common complications after vestibular schwannoma surgery. Experiments with facial nerves of the rat and retrospectively analyzed clinical studies showed a beneficial effect of vasoactive treatment on the preservation of facial and cochlear nerve functions. This prospective and open-label randomized pilot study is the first study of a prophylactic vasoactive treatment in vestibular schwannoma surgery.

METHODS

Thirty patients were randomized before surgery. One group (n = 14) received a vasoactive prophylaxis consisting of nimodipine and hydroxyethylstarch which was started the day before surgery and was continued until the seventh postoperative day. The other group (n = 16) did not receive preoperative medication. Intraoperative monitoring, including acoustic evoked potentials and continuous facial electromyelograms, was applied to all patients. However, when electrophysiological signs of a deterioration of facial or cochlear nerve function were detected in the group of patients without medication, vasoactive treatment was started immediately. Cochlear and facial nerve function were documented preoperatively, during the first 7 days postoperatively, and again after long-term observation.

RESULTS

Despite the limited number of patients, our results were significant using the Fisher's exact test (small no. of patients) for a better outcome after vestibular schwannoma surgery for both hearing (P = 0.041) and facial nerve (P = 0.045) preservation in the group of patients who received a prophylactic vasoactive treatment.

CONCLUSION

Prophylactic vasoactive treatment consisting of nimodipine and hydroxyethylstarch shows significantly better results concerning preservation of the facial and cochlear nerve function in vestibular schwannoma surgery. The prophylactic use is also superior to intraoperative vasoactive treatment.

The making of successful axonal regeneration: Genes, molecules and signal transduction pathways

Unlike its central counterpart, the peripheral nervous system is well known for its comparatively good potential for regeneration following nerve fiber injury. This ability is mirrored by the de novo expression or upregulation of a wide variety of molecules including transcription factors, growth-stimulating substances, cell adhesion molecules, intracellular signaling enzymes and proteins involved in regulating cell-surface cytoskeletal interactions, that promote neurite outgrowth in cultured neurons. However, their role in vivo is less known. Recent studies using neutralizing antibodies, gene inactivation and overexpression techniques have started to shed light on those endogenous molecules that play a key role in axonal outgrowth and the process of successful functional repair in the injured nervous system. The aim of the current review is to provide a summary on this rapidly growing field and the experimental techniques used to define the specific effects of candidate signaling molecules on axonal regeneration in vivo.

Preservation of Facial Nerve Function after Postoperative Vasoactive Treatment in Vestibular Schwannoma Surgery

OBJECTIVE:

Facial nerve paresis and hearing loss are common complications after vestibular schwannoma surgery. Experimental and clinical studies point to a beneficial effect of nimodipine and hydroxyethyl starch for preservation of cochlear nerve function. A retrospective analysis was undertaken to evaluate the effect of vasoactive treatment on facial nerve outcome.

PATIENTS AND METHODS:

Forty-five patients with vestibular schwannoma removal, intraoperative electromyographic monitoring, and postoperative deterioration of facial nerve function were evaluated. Twenty-five patients underwent vasoactive treatment consisting of nimodipine and hydroxyethyl starch for improvement of hearing outcome. Twenty patients did not receive such treatment. Facial nerve function was evaluated before and after surgery, as well as 1 year after the surgical procedure. Patients were comparable regarding age, tumor size, and preoperative facial nerve function.

RESULTS:

Long-term results of facial nerve function were significantly improved in those patients who experienced severe postoperative deterioration of facial nerve function and received vasoactive treatment as compared with patients who did not receive nimodipine and hydroxyethyl starch after surgery. Treated patients showed a significantly higher rate of complete recovery compared with patients without treatment.

CONCLUSION:

The study points to a potential effect of vasoactive treatment for facial nerve function after vestibular schwannoma surgery. In particular, patients with postoperative disfiguring facial nerve palsy clearly benefit from intravenous hydroxyethyl starch and nimodipine with respect to a long-term socially acceptable facial nerve function.

Nimodipine and Microsurgery Induced Recovery of the Vocal Cord after Recurrent Laryngeal Nerve Resection

Transection of the recurrent laryngeal nerve leads to permanent palsy of the vocal cord. Experimental studies have confirmed that nimodipine increases the pace of axonal regeneration. We present a case of a 19-year-old male, suffering a thyroid cancer disease, who was subjected to unilateral resection of the recurrent laryngeal nerve during surgery. The nerve was repaired with a nerve graft and the patient further treated with nimodipine for 3 months. Evaluation of the patient showed normalization of voice, movement of the vocal cord on the injured side, and electromyography evidence of reinnervation of the larynx muscles at 15 months after surgery.

Molecular mechanisms in successful peripheral regeneration

Peripheral nerve injury is normally followed by a robust regenerative response. Here we describe the early changes associated with injury from the initial rise in intracellular calcium and the subsequent activation of transcription factors and cytokines leading to an inflammatory reaction, and the expression of growth factors, cytokines, neuropeptides, and other secreted molecules involved in cell-to-cell communication promoting regeneration and neurite outgrowth. The aim of this review is to summarize the molecular mechanisms that play a part in executing successful regeneration.

Facial nerve recovery in bcl2 overexpression mice after crush injury

OBJECTIVES

To develop a mouse model for measuring facial nerve injury and recovery and to test the hypothesis that overexpression of the antiapoptotic gene, bcl2, enhances recovery of facial nerve function after peripheral crush injury.

DESIGN

Prospective analysis of recovery of function after facial nerve crush injury in mice at juvenile (postnatal day 7) and adult (postnatal day 30) ages with blind comparison of wild-type and transgenic bcl2 overexpression littermates at both ages and immunohistologic confirmation of overexpression of bcl2 in facial motoneurons in transgenic animals.

RESULTS

Adult wild-type mice demonstrated full recovery of facial nerve function (measured as eye blink and whisker movement) within 3 weeks of injury. Juvenile wild-type mice demonstrated diminished recovery of function. Juvenile transgenic bcl2 overexpression mice demonstrated more rapid and complete recovery of eye blink but not whisker movement in comparison with wild-type littermates.

CONCLUSIONS

Measurement of facial nerve function in mice after injury is feasible. Enhanced recovery of facial nerve function in adult mice and mice overexpressing bcl2 indicates that preservation of central motoneurons after injury may improve function after peripheral nerve injury.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Altered localization of Cav1.2 (L-type) calcium channels in nerve fibers, Schwann cells, odontoblasts, and fibroblasts of tooth pulp after tooth injury

We have determined the localization of Cav1.2 (L-Type) Ca2+ channels in the cells and nerve fibers in molars of normal or injured rats. We observed high levels of immunostaining of L-type Ca2+ channels in odontoblast cell bodies and their processes, in fibroblast cell bodies and in Schwann cells. Many Cav1.2-containing unmyelinated and myelinated axons were also present in root nerves and proximal branches in coronal pulp, but were usually missing from nerve fibers in dentin. Labeling in the larger fibers was present along the axonal membrane, localized in axonal vesicles, and in nodal regions. After focal tooth injury, there is a marked loss of Cav1.2 channels in injured teeth. Immunostaining of Cav1.2 channels was lost selectively in nerve fibers and local cells of the tooth pulp within 10 min of the lesion, without loss of other Cav channel or pulpal labels. By 60 min, Cav1.2 channels in odontoblasts were detected again but at levels below controls, whereas fibroblasts were labeled well above control levels, similar to upregulation of Cav1.2 channels in astrocytes after injury. By 3 days after the injury, Cav1.2 channels were again detected in nerve fibers and immunostaining of fibroblasts and odontoblasts had returned to control levels. These findings provide new insight into the localization of Cav1.2 channels in dental pulp and sensory fibers, and demonstrate unexpected plasticity of channel distribution in response to nerve injury.