Nimodipine-induced improved survival rate of facial motor neurons following intracranial transection of the facial nerve in the adult rat

Central Facial Nervous System Biomolecules Involved in Peripheral Facial Nerve Injury Responses and Potential Therapeutic Strategies

Peripheral facial nerve injury leads to changes in the expression of various neuroactive substances that affect nerve cell damage, survival, growth, and regeneration. In the case of peripheral facial nerve damage, the injury directly affects the peripheral nerves and induces changes in the central nervous system (CNS) through various factors, but the substances involved in these changes in the CNS are not well understood. The objective of this review is to investigate the biomolecules involved in peripheral facial nerve damage so as to gain insight into the mechanisms and limitations of targeting the CNS after such damage and identify potential facial nerve treatment strategies. To this end, we searched PubMed using keywords and exclusion criteria and selected 29 eligible experimental studies. Our analysis summarizes basic experimental studies on changes in the CNS following peripheral facial nerve damage, focusing on biomolecules that increase or decrease in the CNS and/or those involved in the damage, and reviews various approaches for treating facial nerve injury. By establishing the biomolecules in the CNS that change after peripheral nerve damage, we can expect to identify factors that play an important role in functional recovery from facial nerve damage. Accordingly, this review could represent a significant step toward developing treatment strategies for peripheral facial palsy.

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.

Nimodipine Exerts Time-Dependent Neuroprotective Effect after Excitotoxical Damage in Organotypic Slice Cultures

During injuries in the central nervous system, intrinsic protective processes become activated. However, cellular reactions, especially those of glia cells, are frequently unsatisfactory, and further exogenous protective mechanisms are necessary. Nimodipine, a lipophilic L-type calcium channel blocking agent is clinically used in the treatment of aneurysmal subarachnoid haemorrhage with neuroprotective effects in different models. Direct effects of nimodipine on neurons amongst others were observed in the hippocampus as well as its influence on both microglia and astrocytes. Earlier studies proposed that nimodipine protective actions occur not only via calcium channel-mediated vasodilatation but also via further time-dependent mechanisms. In this study, the effect of nimodipine application was investigated in different time frames on neuronal damage in excitotoxically lesioned organotypic hippocampal slice cultures. Nimodipine, but not nifedipine if pre-incubated for 4 h or co-applied with NMDA, was protective, indicating time dependency. Since blood vessels play no significant role in our model, intrinsic brain cell-dependent mechanisms seems to strongly be involved. We also examined the effect of nimodipine and nifedipine on microglia survival. Nimodipine seem to be a promising agent to reduce secondary damage and reduce excitotoxic damage.

Targeting microglia L-type voltage-dependent calcium channels for the treatment of central nervous system disorders

Calcium (Ca²⁺ ) is a ubiquitous mediator of a multitude of cellular functions in the central nervous system (CNS). Intracellular Ca²⁺ is tightly regulated by cells, including entry via plasma membrane Ca²⁺ permeable channels. Of specific interest for this review are L-type voltage-dependent Ca²⁺ channels (L-VDCCs), due to their pleiotropic role in several CNS disorders. Currently, there are numerous approved drugs that target L-VDCCs, including dihydropyridines. These drugs are safe and effective for the treatment of humans with cardiovascular disease and may also confer neuroprotection. Here, we review the potential of L-VDCCs as a target for the treatment of CNS disorders with a focus on microglia L-VDCCs. Microglia, the resident immune cells of the brain, have attracted recent attention for their emerging inflammatory role in several CNS diseases. Intracellular Ca²⁺ regulates microglia transition from a resting quiescent state to an "activated" immune-effector state and is thus a valuable target for manipulation of microglia phenotype. We will review the literature on L-VDCC expression and function in the CNS and on microglia in vitro and in vivo and explore the therapeutic landscape of L-VDCC-targeting agents at present and future challenges in the context of Alzheimer's disease, Parkinson's disease, Huntington's disease, neuropsychiatric diseases, and other CNS disorders.

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.

[Neuroprotective medication in vestibular schwannoma surgery]

BACKGROUND

Except for glucocorticoids there is a lack of neuroprotective medication in neurosurgical interventions.

OBJECTIVE

An overview of clinical trials investigating administration of the calcium antagonist nimodipine and hydroxyethyl starch (HES) in vestibular schwannoma (VS) surgery is given. Basic research is addressed and potential neuroprotective effect mechanisms are discussed, as are perspectives for application of the concept to other types of surgery with a risk postoperative impairment of nerve function.

MATERIALS AND METHODS

A selective PubMed search was performed and all 10 clinical trials corresponding to the search criteria were included.

RESULTS

Four trials with an intraoperative start of the medication showed a positive effect for the preservation of facial nerve function and hearing preservation. A pilot study showed superiority of prophylactic treatment over intraoperative application. There were no significant results in a prospective multicenter phase III trial. After 1 year, postoperative facial nerve preservation rates were excellent in both groups. However, the risk of hearing loss was twice as high in the control group. A combined analysis of the phase III trial with its pilot study showed significant results for better hearing preservation rates in the treatment group (probably by increasing the case load).

CONCLUSION

Prophylactic nimodipine can be recommended in VS surgery in patients with good preoperative hearing. The effect mechanisms of nimodipine and modifications to prophylaxis should be clarified in basic research.

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/ ).

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.

Calcium dysregulation via L-type voltage-dependent calcium channels and ryanodine receptors underlies memory deficits and synaptic dysfunction during chronic neuroinflammation

Background

Chronic neuroinflammation and calcium (Ca⁺²) dysregulation are both components of Alzheimer’s disease. Prolonged neuroinflammation produces elevation of pro-inflammatory cytokines and reactive oxygen species which can alter neuronal Ca⁺² homeostasis via L-type voltage-dependent Ca⁺² channels (L-VDCCs) and ryanodine receptors (RyRs). Chronic neuroinflammation also leads to deficits in spatial memory, which may be related to Ca⁺² dysregulation.

Methods

The studies herein use an in vivo model of chronic neuroinflammation: rats were infused intraventricularly with a continuous small dose of lipopolysaccharide (LPS) or artificial cerebrospinal fluid (aCSF) for 28 days. The rats were treated with the L-VDCC antagonist nimodipine or the RyR antagonist dantrolene.

Results

LPS-infused rats had significant memory deficits in the Morris water maze, and this deficit was ameliorated by treatment with nimodipine. Synaptosomes from LPS-infused rats had increased Ca⁺² uptake, which was reduced by a blockade of L-VDCCs either in vivo or ex vivo.

Conclusions

Taken together, these data indicate that Ca⁺² dysregulation during chronic neuroinflammation is partially dependent on increases in L-VDCC function. However, blockade of the RyRs also slightly improved spatial memory of the LPS-infused rats, demonstrating that other Ca⁺² channels are dysregulated during chronic neuroinflammation. Ca⁺²-dependent immediate early gene expression was reduced in LPS-infused rats treated with dantrolene or nimodipine, indicating normalized synaptic function that may underlie improvements in spatial memory. Pro-inflammatory markers are also reduced in LPS-infused rats treated with either drug. Overall, these data suggest that Ca⁺² dysregulation via L-VDCCs and RyRs play a crucial role in memory deficits resulting from chronic neuroinflammation.

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.

The L-type voltage-gated calcium channel modulates microglial pro-inflammatory activity

Under pathological conditions, microglia, the resident CNS immune cells, become reactive and release pro-inflammatory cytokines and neurotoxic factors. We investigated whether this phenotypic switch includes changes in the expression of the L-type voltage-gated calcium channel (VGCC) in a rat model of N-methyl-D-aspartate-induced hippocampal neurodegeneration. Double immunohistochemistry and confocal microscopy evidenced that activated microglia express the L-type VGCC. We then analyzed whether BV2 microglia express functional L-type VGCC, and investigated the latter's role in microglial cytokine release and phagocytic capacity. Activated BV2 microglia express the CaV1.2 and CaV1.3 subunits of the L-type VGCC determined by reverse transcription-polymerase chain reaction, Western blot and immunocytochemistry. Depolarization with KCl induced a Ca2+ entry facilitated by Bay k8644 and partially blocked with nifedipine, which also reduced TNF-α and NO release by 40%. However, no nifedipine effect on BV2 microglia viability or phagocytic capacity was observed. Our results suggest that in CNS inflammatory processes, the L-type VGCC plays a specific role in the control of microglial secretory activity.

Hyperbaric oxygen versus steroid in facial nerve injury: an experimental animal study

OBJECTIVE

The aim of this experimental study was to evaluate the effects of hyperbaric oxygen, methylprednisolone and combined hyperbaric oxygen-methylprednisolone treatments on traumatic facial nerve regeneration in rats.

SUBJECTS AND METHODS

After exposure to facial nerve injury, four groups of rats were created with five subjects in each group: Group 1 (hyperbaric oxygen), group 2 (control), group 3 (combined hyperbaric oxygen-methylprednisolone), group 4 (methylprednisolone). Facial nerve specimens from sacrificed animals were examined for axonal degeneration, vascular congestion, macro vacuolization, axon diameter and thickness of myelin sheath.

RESULTS

There were significant differences with regard to axonal degeneration, vascular congestion and axon diameter between group 3 and the control group. In addition to lower axonal degeneration and vascular congestion, a larger diameter of axons was observed in group 3. There were significant differences with regard to vascular congestion and axon diameter between group 4 and the control group. We observed thicker myelin and lower axonal degeneration in group 3 compared with group 4.

CONCLUSION

The combination therapy with hyperbaric oxygen and methylprednisolone had an additive beneficial effect on regeneration of the facial nerve and may provide better treatment outcomes than methylprednisolone or hyperbaric oxygen therapy alone.

Inhibition of human astrocyte and microglia neurotoxicity by calcium channel blockers

We examined the effects of L-type calcium channel blockers (CCBs) on toxicity exerted by activated human astrocytes and microglia towards SH-SY5Y human neuronal cells. The CCBs nimodipine (NDP) and verapamil (VPM) both significantly suppressed toxic secretions from human astrocytes and astrocytoma U-373 MG cells that were induced by interferon (IFN)-γ. NDP also inhibited neurotoxic secretions of human microglia and monocytic THP-1 cells that were induced by the combination of lipopolysaccharide and IFN-γ. In human astrocytes, both NDP and VPM reduced IFN-γ-induced phosphorylation of signal transducer and activator of transcription (STAT) 3. They also inhibited the astrocytic production of IFN-γ-inducible T cell α chemoattractant (I-TAC). These results suggest that CCBs attenuate IFN-γ-induced neurotoxicity of human astrocytes through inhibition of the STAT3 signaling pathway. L-type CCBs, especially NDP, might be a useful treatment option for a broad spectrum of neurodegenerative diseases, including Alzheimer disease, where the pathology is believed to be exacerbated by neurotoxic glial activation.

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.

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.

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.

Modelo experimental comportamental e histológico da regeneração do nervo facial em ratos

O estabelecimento de modelos experimentais é o passo inicial para estudos de regeneração neural. OBJETIVO: Estabelecer modelo experimental de regeneração do nervo facial. MATERIAIS E MÉTODOS: Ratos Wistar com secção completa e sutura do tronco do nervo facial extratemporal, com análise comportamental e histológica até 9 semanas. FORMA DE ESTUDO: Estudo prospectivo experimental. RESULTADOS: Progressiva recuperação clínica e histológica dos animais. CONCLUSÃO: Estabelecemos um método aceitável para o estudo de regeneração do nervo facial em ratos.

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.

Padronização das técnicas de secção do nervo facial e de avaliação da mímica facial em ratos

OBJETIVOS: Padronização da técnica de secção do nervo facial extratemporal em ratos e elaboração de uma escala de avaliação da mímica facial desses animais antes e após essa secção. TIPO DE ESTUDO: Experimental. MÉTODO: Vinte ratos Wistar foram anestesiados com xilasina e ketamina e submetidos à secção do nervo facial próximo à sua emergência pelo forame mastóideo na pele. Todos os animais foram avaliados. Foram observados: fechamento ocular, reflexo de piscamento, movimentação e posicionamento das vibrissas, e foi elaborada uma escala de avaliação e graduação destes parâmetros. RESULTADOS: O tronco do nervo facial foi encontrado entre a margem tendinosa do músculo clavotrapézio e a cartilagem auricular. O tronco foi seccionado proximal à sua saída pelo forame mastóideo e os cotos foram suturados com nylon 9-0. Foi elaborada uma escala de avaliação e graduação da mímica facial independente para olho e vibrissa e a somatória dos parâmetros, como forma de avaliar a face paralisada. A ausência de piscamento e de fechamento ocular recebeu valor 1; a presença de contração do músculo orbicular, sem reflexo de piscamento, valor 2; fechamento ocular de 50% através de reflexo de piscamento, valor 3, o fechamento de 75%, valor 4. A presença de reflexo de piscamento com fechamento ocular completo recebeu valor 5. A ausência de movimento e posição posterior das vibrissas recebeu pontuação 1; tremor leve e posição posterior, pontuação 2; tremor maior e posição posterior, pontuação 3 e movimento normal com posição posterior, pontuação 4. A movimentação simétrica das vibrissas, com posição anterior recebeu pontuação 5. CONCLUSÃO: O rato apresenta anatomia que permite fácil acesso ao nervo facial extratemporal, possibilitando secção e sutura desse nervo de forma padronizada. Também foi possível estabelecer uma escala de avaliação e graduação da mímica facial dos ratos com paralisia facial a partir da observação clínica desses animais.

Standardization of techniques used in facial nerve section and facial movement evaluation in rats

Aim

standardization of the technique to section the extratemporal facial nerve in rats and creation of a scale to evaluate facial movements in these animals before and after surgery.

Study design

Experimental.

Method

twenty Wistar rats were anesthetized with ketamine xylazine and submitted to sectioning of the facial nerve near its emergence through the mastoid foramen. Eye closure and blinking reflex, vibrissae movement and positioning were observed in all animals and a scale to evaluate these parameters was then created.

Results

The facial nerve trunk was found between the tendinous margin of the clavotrapezius muscle and the auricular cartilage. The trunk was proximally sectioned as it exits the mastoid foramen and the stumps were sutured with a 9-0-nylon thread. An evaluation and graduation scale of facial movements, independent for eye and vibrissae, was elaborated, together with a sum of the parameters, as a means to evaluate facial palsy. Absence of eye blinking and closure scored 1; the presence of orbicular muscle contraction, without blinking reflex, scored 2; 50% of eye closure through blinking reflex, scored 3, 75% of closure scored 4. The presence of complete eye closure and blinking reflex scored 5. The absence of movement and posterior position of the vibrissae scored 1; slight shivering and posterior position scored 2; greater shivering and posterior position, scored 3 and normal movement with posterior position, scored 4; symmetrical movement of he vibrissae, with anterior position, scored 5.

Conclusion

The rat anatomy allows easy access to the extratemporal facial nerve, allowing its sectioning and standardized suture. It was also possible to establish an evaluation and graduation scale of the rat facial movements with facial palsy based on the clinical observation of these animals.

Motor neuronal and glial apoptosis in the adult facial nucleus after intracranial nerve transection

Object

Intracranial lesions affecting the facial nerve are usually associated with significant morbidity and poor functional restitution, despite the fact that a peripheral nerve injury normally recovers well. Mechanistic explanations are needed to direct future therapies. Although neonatal motor neurons are known to die as a result of apoptosis after axotomy, this cell death mechanism has not been explicitly demonstrated after peripheral cranial nerve transection in adult mammals.

Methods

The authors induced substantial retrograde neuronal death in the adult rodent by transecting the facial nerve during its intracranial course. Neuronal apoptosis was demonstrated as shrunken facial motor neurons, retrogradely labeled with fluorogold and with nuclei positively labeled by terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick–end labeling (TUNEL). Glial apoptosis was demonstrated by double labeling with respect to cell type.

On postinjury Days 7 and 14, the intracranial axotomy led to neuronal apoptosis, corresponding to a neuronal loss that was observed quantitatively in cresyl violet–stained tissue sections obtained using a stereological method. In contrast, no neuronal apoptosis was observed after creating a distal lesion of the facial nerve, which causes less neuronal loss. In addition, glial apoptosis was seen in the facial nucleus after both distal and proximal axotomy. Whereas the proximal intracranial axotomy led to TUNEL-positive nuclei in cells showing markers for oligodendrocytes and microglia, only the latter glial cell population was double labeled with TUNEL-positive nuclei after distal lesioning.

Conclusions

These findings may ultimately lead to new therapeutic strategies in patients suffering from facial nerve palsy due to an intracranial lesion.

Nimodipine and TMB-8 potentiate the AMPA-induced lesion in the basal ganglia

Acute injection of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) into the rat globus pallidus leads to calcium precipitation, neuronal death and gliosis. In order to determine whether L-type calcium channels and/or release of Ca(2+) from intracellular stores contribute to the effects of AMPA, nimodipine and 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8) were administered in combination with AMPA. Nimodipine, but not TMB-8, tended to exacerbate the calcification process initiated by AMPA; the AMPA/nimodipine/TMB-8 combination produced much more calcium deposition than AMPA (+62%, P<0.05). AMPA alone induced a slight but not significant astroglial reaction. Nimodipine slightly enhanced the astroglial reaction triggered by AMPA, whereas TMB-8 doubled it (P<0.001 versus AMPA). These data suggest that blockade of L-type calcium channels by nimodipine enhances calcium imbalance triggered by AMPA, and the calcium release from the endoplasmic reticulum does not participate in the AMPA-induced calcification.

Nimodipine ameliorates trauma-induced cochlear neuronal death

Excessive entry of Ca2+ into injured cochlear neurons activates various Ca(2+)-activated enzymes and subsequent spiral ganglion cell death. Therefore, preventing intracellular calcium overload by using Ca2+ channel antagonists may become an important countermeasure to spiral ganglion cell death. We experimentally investigated whether an L-type Ca2+ channel blocker (nimodipine) can rescue traumatized cochlear neurons from degeneration. A group of rats (n = 6) was pre-operatively treated with nimodipine for one week and compression injury was applied to the cerebellopontine angle portion of the cochlear nerve in a highly quantitative fashion. The rats from the compression with nimodipine treatment groups were post-operatively treated with nimodipine for 10 days and killed for histological examination. The histological analysis of the temporal bones revealed that the spiral ganglion cells in the basal turn of the cochlea where the magnitude of traumatic impact had been the least in our experimental condition were rescued in a statistically significant fashion in the compression with nimodipine treatment group. The results of the present study indicate that nimodipine may become an intra- and post-operative important adjunct to raise the rate of hearing preservation in vestibular schwannoma excision or other cerebellopontine angle surgical interventions.

Spinal cord regeneration induced by a voltage-gated calcium channel agonist

Regeneration in the central nervous system (CNS) is prohibitive. This is likely due to an interplay of cellular (gene expression, growth factors) and environmental (inhibition by CNS myelin) factors. Calcium supports various intracellular functions, and multiple in vitro studies have shown a role of calcium in axonal growth. In this study, we examine the role of a calcium agonist, S(-)-Bay K 8644, in promoting or impeding CNS growth in vivo, in an effort to understand further the relationship between the voltage-gated L type calcium channel and regeneration. Using a well-established rat spinal cord model of regeneration, we have injected various doses of S(-)-Bay K 8644 (30-240 M) around the injured spinal cord. Our results demonstrate that S(-)-Bay K 8644 enhances regeneration in a dose-dependent fashion. In addition, at very specific concentrations, the same agonist has no effect on or even inhibits regeneration. We conclude that spinal regeneration is highly dependent on intracellular calcium concentration. Furthermore, depending on the dose used, the effect of calcium agonist supplementation on spinal regeneration can be supportive or inhibitory.

Properties of motoneurons underlying their regenerative capacity after axon lesions in the ventral funiculus or at the surface of the spinal cord

Spinal motoneurons represent neurons with axons located in both the central (CNS) and peripheral (PNS) nervous systems. Following a lesion to their axons in the PNS, motoneurons are able to regenerate. The regenerative capacity of these neurons is seen also after lesion in the ventral funiculus of the spinal cord, i.e. within the CNS compartment. Thus, after an axotomy within the ventral funiculus, motoneurons respond with a changing polarity towards production of axons, sometimes even from the dendritic tree. This capacity can be used in cases of ventral root avulsion (VRA) lesions, if a conduit for outgrowing axons is presented in the form of replanted ventral roots. In human cases, this procedure may accomplish return of function in denervated muscles. The strong regenerative capacity of motoneurons provides the basis for studies of the response in motoneurons with regard to their contents of substances related to survival and regeneration. Such studies have shown that, of the large number of receptors for neurotrophic substances and extracellular matrix molecules, mRNAs for receptors or receptor components for neurotrophin-3 (NT-3), ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) are strongly downregulated after VRA, while receptors for glial cell line-derived neurotrophic factor (GDNF) and laminins are profoundly upregulated. These results should be considered in the design of combined pharmacological and surgical approaches to lesions of motor axons at or close to the CNS-PNS interface.

Survival-promoting activity of nimodipine and nifedipine in rat motoneurons: implications of an intrinsic calcium toxicity in motoneurons

L-type calcium channel antagonists, nimodipine and nifedipine, were tested for effects on the survival of purified rat motoneurons in culture. They showed significant activity, with maximum survival at 30 microm after 3 days in culture as high as 75%, which was comparable to the maximum effect obtained with brain-derived neurotrophic factor, a potent neurotrophic factor for rat motoneurons. It was also found that depolarizing conditions with a high potassium concentration (30 mm) were toxic to motoneurons. This toxicity was blocked by co-treatment with nimodipine. These results implicate a pre-existing calcium burden through calcium channels in motoneurons; they may offer further insights into understanding the selective death of motoneurons and have therapeutic implications in amyotrophic lateral screlosis.

Vasoactive treatment for hearing preservation in acoustic neuroma surgery

OBJECT

Delayed hearing loss following surgery for acoustic neuroma indicates anatomical and functional preservation of the cochlear nerve and implies that a pathophysiological mechanism is initiated during surgery and continues thereafter. Intraoperative brainstem auditory evoked potentials (BAEPs) typically demonstrate gradual reversible loss of components in these patients.

METHODS

Based on this BAEP pattern, a consecutive series of 41 patients with unilateral acoustic neuromas was recruited into a prospective randomized study to investigate hearing outcomes following the natural postoperative course and recuperation after vasoactive medication. Both groups were comparable in patient age, tumor size, and preoperative hearing level. Twenty patients did not receive postoperative medical treatment. In 70% of these patients anacusis was documented and in 30% hearing was preserved. Twenty-one patients were treated with hydroxyethyl starch and nimodipine for an average of 9 days. In 66.6% of these patients hearing was preserved and in 33.3% anacusis occurred.

CONCLUSIONS

These results are statistically significant (p < 0.05, chi2 = 5.51) and provide evidence that these surgically treated patients suffer from a disturbed microcirculation that causes delayed hearing loss following removal of acoustic neuromas.

Nimodipine promotes regeneration and functional recovery after intracranial facial nerve crush

The calcium flow inhibitor, nimodipine, has been shown to promote motor neuron survival in the facial nucleus after intracranial facial nerve transection. However, it has not been known whether the neuroprotective effects primarily involve survival of nerve cell bodies or outgrowth and/or myelination of nerve fibers. Here, we studied the effects of nimodipine in a different injury model in which the facial nerve was unilaterally crushed intracranially. This lesion caused complete anterograde degeneration and partial retrograde degeneration that were studied with a combination of several stereological methods. Nimodipine did not attenuate the modest lesion-induced neuronal loss (13%) but accelerated the time course of functional recovery and axonal regrowth, inducing increased numbers and sizes of myelinated axons in the facial nerve. It is interesting to note that nimodipine also enlarged the axons and the myelin sheaths in the nonlesioned facial nerve, which points to the possibility of using this substance for new clinical applications to promote axonal growth and remyelination.

Approaches permitting and enhancing motoneuron regeneration after spinal cord, ventral root, plexus and peripheral nerve injuries

The motoneuron has a strong ability to regenerate after injury. However, the problems of nerve cell survival after a proximal axotomy, difficulty in axonal elongation after intraspinal lesion and the lack of target specificity during nerve fibre regrowth interfere with a good functional restitution. Current research has addressed these impediments. New approaches for the management of complicated as well as intraspinal lesions and peripheral nerve trunk injuries are described.

The novel pyrrolopyrimidine PNU-101033-E improves facial motor neuron survival following intracranial axotomy of the facial nerve in the adult rat

Neuronal survival is important to functional restitution following axotomy. Proximal lesions of the facial nerve, due to head trauma or tumor growth, for example, may cause long-standing or even permanent facial nerve palsy. Betamethasone has been used by several neurosurgical clinics for the treatment of postoperative facial nerve palsy; however, this practice is based only on clinical experience. The aim of the present study was to explore the putative effect on facial motor neuron survival of a novel lazaroid (pyrrolopyrimidine, PNU-101033-E) and furthermore to compare the effects with those of betamethasone, following intracranial transection of the facial nerve in adult rats. Both agents are known to inhibit lipid peroxidation by free radical scavenging. The lesion model used has recently been reported to induce massive neuronal cell death with a relative survival of 26.8 +/- 11.3% 1 month after lesion. Oral administration of lazaroids or daily injections of betamethasone followed surgery for 1 month, after which quantification of motor neuronal profiles was performed in the facial nucleus. Lazaroid-treated animals showed a significantly enhanced neuronal survival (68.0 +/- 9.8%), whereas no significant difference was found in betamethasone-treated animals (33.1 +/- 11.7%). The microglial and astrocytic responses in the facial nucleus were intense on the operated sides in betamethasone-treated as well as lazaroid-treated animals, and no differences in comparison with untreated animals were found. In conclusion, we found that the novel pyrrolopyrimidine PNU-101033-E, but not betamethasone, significantly enhanced nerve cell survival. This agent may therefore serve as a useful neuroprotective agent following intracranial trauma to the facial nerve and should be further evaluated for clinical use.