Expression of sodium channel SNS/PN3 and ankyrin(G) mRNAs in the trigeminal ganglion after inferior alveolar nerve injury in the rat

Trigeminal Traumatic Neuroma: a Comprehensive Review of the Literature Based On a Rare Case

PURPOSE OF REVIEW

Traumatic neuromas in general, and trigeminal traumatic neuromas in particular, are relatively rare entities originating from a damage to a corresponding nerve or its branches. This manuscript is a comprehensive review of the literature on trigeminal traumatic neuromas based on an interesting and challenging case of bilateral intraoral lesions.

RECENT FINDINGS

The diagnosis for this patient was bilateral trigeminal traumatic neuromas. It is possible that these patients have a genetic predisposition to the development of these lesions. It is a neuropathic pain condition and may mimic dental and other trigeminal pain entities. Topical treatment with lidocaine gel, utilizing a custom-made neurosensory stent, rendered the patient significant and sustained pain relief. Trigeminal traumatic neuromas present a diagnostic challenge even to a seasoned clinician, due to the complex clinical features that may mimic other entities. Topical medications such as local anesthetics may be a good viable alternative to systemic medications to manage the pain associated with the condition. Early identification of the lesion and the associated pain helps in the succinct management of symptomatic trigeminal traumatic neuromas.

Mechanisms Underlying the Selective Therapeutic Efficacy of Carbamazepine for Attenuation of Trigeminal Nerve Injury Pain

Different peripheral nerve injuries cause neuropathic pain through distinct mechanisms. Even the site of injury may impact underlying mechanisms, as indicated by the clinical finding that the antiseizure drug carbamazepine (CBZ) relieves pain because of compression injuries of trigeminal but not somatic nerves. We leveraged this observation in the present study hypothesizing that because CBZ blocks voltage-gated sodium channels (VGSCs), its therapeutic selectivity reflects differences between trigeminal and somatic nerves with respect to injury-induced changes in VGSCs. CBZ diminished ongoing and evoked pain behavior in rats with chronic constriction injury (CCI) to the infraorbital nerve (ION) but had minimal effect in rats with sciatic nerve CCI. This difference in behavior was associated with a selective increase in the potency of CBZ-induced inhibition of compound action potentials in the ION, an effect mirrored in human trigeminal versus somatic nerves. The increase in potency was associated with a selective increase in the efficacy of the Na_V1.1 channel blocker ICA-121431 and Na_V1.1 protein in the ION, but no change in Na_V1.1 mRNA in trigeminal ganglia. Importantly, local ICA-121431 administration reversed ION CCI-induced hypersensitivity. Our results suggest a novel therapeutic target for the treatment of trigeminal neuropathic pain.SIGNIFICANCE STATEMENT This study is based on evidence of differences in pain and its treatment depending on whether the pain is above (trigeminal) or below (somatic) the neck, as well as evidence that voltage-gated sodium channels (VGSCs) may contribute to these differences. The focus of the present study was on channels underlying action potential propagation in peripheral nerves. There were differences between somatic and trigeminal nerves in VGSC subtypes underlying action potential propagation both in the absence and presence of injury. Importantly, because the local block of Na_V1.1 in the trigeminal nerve reverses nerve injury-induced mechanical hypersensitivity, the selective upregulation of Na_V1.1 in trigeminal nerves suggests a novel therapeutic target for the treatment of pain associated with trigeminal nerve injury.

Topical Ambroxol 20% for the Treatment of Classical Trigeminal Neuralgia - A New Option? Initial Clinical Case Observations

BACKGROUND

Trigeminal neuralgia is difficult to treat and shows upregulation of sodium channels. The expectorant ambroxol acts as a strong local anesthetic, about 40 times stronger than lidocaine. It preferentially inhibits the channel subtype Na_v 1.8, expressed especially in nociceptive C-fibers. It seemed reasonable to try ambroxol for the treatment with neuropathic facial pain unresponsive to other standard options.

MATERIAL AND METHODS

Medical records of patients suffering from classical trigeminal neuralgia (n = 5) and successful pain reduction following topical ambroxol 20% cream in addition to standard treatment are reported.

RESULTS

All patients reported pain attacks with pain intensity between 4 and 10 NRS (numeric pain scale). In all cases they could be triggered, 3 patients reported additional spontaneous pain. Attacks were reduced in all 5 patients. Pain reduction achieved following ambroxol 20% cream was 2-8 points (NRS) earliest within 15-30 minutes and lasted for 4-6 hours mostly. This was reproducible in all cases; in one case pain was eliminated after 1 week. No patient reported side effects or skin changes; oral medication was reduced in 2 patients.

CONCLUSION

For the first time, a clinically significant pain relief following topical ambroxol 20% cream in patients with trigeminal neuralgia is reported. In view of the positive side effect profile, topical ambroxol for patients with such a highly impaired quality of life should be investigated further as a matter of urgency.

Sodium channels and pain: from toxins to therapies

Voltage-gated sodium channels (NaV channels) are essential for the initiation and propagation of action potentials that critically influence our ability to respond to a diverse range of stimuli. Physiological and pharmacological studies have linked abnormal function of NaV channels to many human disorders, including chronic neuropathic pain. These findings, along with the description of the functional properties and expression pattern of NaV channel subtypes, are helping to uncover subtype specific roles in acute and chronic pain and revealing potential opportunities to target these with selective inhibitors. High-throughput screens and automated electrophysiology platforms have identified natural toxins as a promising group of molecules for the development of target-specific analgesics. In this review, the role of toxins in defining the contribution of NaV channels in acute and chronic pain states and their potential to be used as analgesic therapies are discussed.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

Correlation of Nav1.8 and Nav1.9 sodium channel expression with neuropathic pain in human subjects with lingual nerve neuromas

Background

Voltage-gated sodium channels Nav1.8 and Nav1.9 are expressed preferentially in small diameter sensory neurons, and are thought to play a role in the generation of ectopic activity in neuronal cell bodies and/or their axons following peripheral nerve injury. The expression of Nav1.8 and Nav1.9 has been quantified in human lingual nerves that have been previously injured inadvertently during lower third molar removal, and any correlation between the expression of these ion channels and the presence or absence of dysaesthesia investigated.

Results

Immunohistochemical processing and quantitative image analysis revealed that Nav1.8 and Nav1.9 were expressed in human lingual nerve neuromas from patients with or without symptoms of dysaesthesia. The level of Nav1.8 expression was significantly higher in patients reporting pain compared with no pain, and a significant positive correlation was observed between levels of Nav1.8 expression and VAS scores for the symptom of tingling. No significant differences were recorded in the level of expression of Nav1.9 between patients with or without pain.

Conclusions

These results demonstrate that Nav1.8 and Nav1.9 are present in human lingual nerve neuromas, with significant correlations between the level of expression of Nav1.8 and symptoms of pain. These data provide further evidence that changes in expression of Nav1.8 are important in the development and/or maintenance of nerve injury-induced pain, and suggest that Nav1.8 may be a potential therapeutic target.

Incidence of atypical acute nerve hyperexcitability symptoms in oxaliplatin-treated patients with colorectal cancer

CONTEXT

Peripheral, acute or chronic, neurotoxicity is one of the main dose-limiting adverse effects of oxaliplatin (OXA). Acute neurotoxicity is typically characterized by distal and perioral cold-induced paresthesias and dysesthesias, but other uncommon symptoms might also be present.

OBJECTIVES

The aim of this post hoc analysis of data extracted from a prospective, multicenter study was to assess the incidence of uncommon acute OXA neurotoxicity symptoms in patients undergoing OXA-based chemotherapy.

METHODS

One hundred chemotherapy-naïve patients (62 males, 38 females, aged 64.7 ± 8.7 years) with colorectal cancer scheduled to receive OXA-based therapy (FOLFOX-4, FOLFOX-6, and XELOX) underwent neurologic evaluation after the 1st infusion and then after 3 and 6 months of OXA-based chemotherapy (after 6th or 4th and 12th or 8th cycles, respectively, according to regimen). At evaluation, patients were asked to report the presence and characteristics of acute hyperexcitability symptoms.

RESULTS

Eighty-two patients presented typical symptoms of acute OXA neurotoxicity in the form of cold-induced paresthesias and dysesthesias. In 45/82 (54.9 %) of patients, uncommon symptoms were also present; shortness of breath (32 %), jaw spasm (26 %), fasciculations (25 %), cramps (20 %), and difficulty in swallowing (18 %) were more frequently reported, while voice (4 %) and visual changes, ptosis and pseudolaryngospasm (1 %) occurred rarely. No significant correlation was disclosed between acute OXA neurotoxicity and chemotherapy regimen, cumulative dose of OXA or patients' age.

CONCLUSIONS

A high percentage of patients treated with OXA-based chemotherapy develop acute neurotoxicity also with uncommon manifestations. Since OXA acute neurotoxicity might be related to the onset of chronic neurotoxicity, these patients should be closely monitored to avoid this dose-limiting adverse effect.

Nav1.7 sodium channel expression in human lingual nerve neuromas

OBJECTIVE

Peripheral branches of the trigeminal nerve are often damaged during the removal of lower third molar teeth, and a small proportion of patients who sustain an injury develop persistent chronic pain. The cause of the pain is not clear and there are no satisfactory methods of treatment. The aim of the present study was to examine the expression of the sodium channel subtype Na(v)1.7 in damaged human lingual nerves, and to identify any association between Na(v)1.7 expression and reported symptoms of dysaesthesia.

METHODS

Eleven neuromas-in-continuity (NICs) and 11 nerve-end neuromas (NENs) were studied, and were all obtained at the time of surgical repair of the damaged lingual nerve. Specimens were categorised as being obtained from patients with symptoms or without symptoms, according to the degree of pain, tingling or discomfort that had been experienced. The tissue was prepared and processed for indirect immunofluorescence, and image analysis was used to quantify the percentage area of PGP 9.5-labelled tissue that also contained Na(v)1.7.

RESULTS

The results demonstrated that sodium channel Na(v)1.7 was expressed in human lingual nerve neuromas. There was no direct relationship between the level of expression of Na(v)1.7 and the patients' symptoms of dysaesthesia. However, in NICs there was found to be an inverse correlation between Na(v)1.7 and macrophage expression, and in symptomatic NICs a direct correlation was found between Na(v)1.7 expression and axonal apposition.

CONCLUSIONS

These data suggest that Na(v)1.7 expression alone does not play a primary role in initiating the painful symptoms of dysaesthesia. The development of neuropathic pain may involve complex interactions including changes in ultrastructure and ion channel density.

Peripheral mechanisms of odontogenic pain

In this article, we review the key basic mechanisms associated with this phenomena and more recently identified mechanisms that are current areas of interest. Although many of these pain mechanisms apply throughout the body, we attempt to describe these mechanisms in the context of trigeminal pain.

Behavioral changes and trigeminal ganglion sodium channel regulation in an orofacial neuropathic pain model

We used a photochemical method to generate a partial ischemic injury to the infraorbital branch of the trigeminal nerve in rats. Following injury, rats developed a bilateral persistent hypersensitivity to mechanical stimulation in the territory innervated by the infraorbital nerve. In addition, spread of mechanical hypersensitivity beyond the facial region was noted. Heat hypersensitivity was also present, although to a lesser extent and of a shorter duration. In some rats, excessive facial grooming/scratching were observed. Morphological examination revealed a graded damage to the irradiated portion of the infraorbital nerve that was related to the duration of laser irradiation. Investigations of gene expression changes in injured trigeminal ganglion neurons of animals with behavioral signs of neuropathic pain demonstrated that the sodium channel alpha-subunit Na(v)1.3-absent in sham-operated animals-was expressed to a limited extent. mRNAs for Na(v)1.8 and Na(v)1.9 were reduced both with respect to proportions of expressing neurons and to intensities, whereas the beta 3 subunit was markedly upregulated. mRNA levels of p11, a regulatory factor that facilitates the surface expression of Na(v)1.8, were unchanged. Previous findings have shown that injury to the trigeminal nerve branches may elicit responses that differ from those of segmental spinal nerves. Despite this we conclude that the key sodium channel regulations that are reported as consequences of nerve damage in the dorsal root ganglia seem to appear also in the trigeminal ganglion. Thus, novel analgesic drugs designed to target the sodium channel subtypes involved could be of use for the treatment of orofacial pain.

The effects of axotomy on neurons and satellite glial cells in mouse trigeminal ganglion

Damage to peripheral nerves induces ectopic firing in sensory neurons, which can contribute to neuropathic pain. As most of the information on this topic is on dorsal root ganglia we decided to examine the influence of infra-orbital nerve section on cells of murine trigeminal ganglia. We characterized the electrophysiological properties of neurons with intracellular electrodes. Changes in the coupling of satellite glial cells (SGCs) were monitored by intracelluar injection of the fluorescent dye Lucifer yellow. Electrophysiology of SGCs was studied with the patch-clamp technique. Six to eight days after axotomy, the percentage of neurons that fire spontaneously increased from 1.6 to 12.8%, the membrane depolarized from -51.1 to -45.5 mV, the percentage of cells with spontaneous potential oscillations increased from 19 to 37%, the membrane input resistance decreased from 44.4 to 39.5 MOmega, and the threshold for firing an action potential decreased from 0.61 to 0.42 nA. These changes are consistent with increased neuronal excitability. SGCs were mutually coupled around a given neuron in 21% of the cases, and to SGCs around neighboring neurons in only 4.8% of the cases. After axotomy these values increased to 37.1 and 25.8%, respectively. After axotomy the membrane resistance of SGCs decreased from 101 MOmega in controls to 40 MOmega, possibly due to increased coupling among these cells. We conclude that axotomy affects both neurons and SGCs in the trigeminal ganglion. The increased neuronal excitability and ectopic firing may play a major role in neuropathic pain.

No blocking effects of the pentapeptide QYNAD on Na+ channel subtypes expressed in Xenopus oocytes or action potential conduction in isolated rat sural nerve

Reversible block of Na(+) channels by endogenous pentapeptide QYNAD has been reported to account for the fast relapses and remissions seen in autoimmune demyelinating disorders. Here it is shown that, in contrast to previous reports, synthetic QYNAD (10-100 microM) applied to Na(+) channels (Na(v)1.6 and 1.8) expressed in Xenopus oocytes was unable to block the peak current or inhibit channel kinetics. Furthermore, QYNAD (100 microM) applied to five isolated rat sural nerve in vitro did not demonstrate any change in the amplitude of compound nerve action potential or latency. The reason for the ineffectiveness of QYNAD has not been elucidated; it was apparently not related to a problem in the synthesis of the pentapeptide. Our experiments raise significant concerns about the suggestion that QYNAD peptide is a Na(+) channel blocker or modulator. However, in a protein library search the amino acid sequence of QYNAD was found to be related to ankyrin-G, which plays a role in Na(+) channel clustering in the node of Ranvier.

Effects and consequences of nerve injury on the electrical properties of sensory neurons

Nociceptive pain alerts the body to potential or actual tissue damage. By contrast, neuropathic or "noninflammatory" pain, which results from injury to the nervous system, serves no useful purpose. It typically continues for years after the original injury has healed. Sciatic nerve lesions can invoke chronic neuropathic pain that is accompanied by persistent, spontaneous activity in primary afferent fibers. This activity, which reflects changes in the properties and functional expression of Na+, K+, and Ca2+ channels, initiates a further increase in the excitability of second-order sensory neurons in the dorsal horn. This change persists for many weeks. The source of origin of the pain thus moves from the peripheral to the central nervous system. We hypothesize that this centralization of pain involves the inappropriate release of peptidergic neuromodulators from primary afferent fibers. Peptides such as substance P, neuropeptide Y (NPY), calcitonin-gene-related peptide (CGRP), and brain-derived neurotrophic factor (BDNF) may promote enduring changes in excitability as a consequence of neurotrophic actions on ion channel expression in the dorsal horn. Findings that form the basis of this hypothesis are reviewed. Study of the neurotrophic control of ion channel expression by spinal peptides may thus provide new insights into the etiology of neuropathic pain.

Painful neuromas: a potential role for a structural transmembrane protein, ankyrin G

OBJECT

Severe nerve injury induces the formation of a neuroma. Some neuromas cause excruciating pain. Overexpression of Na+ channels leads to hyperexcitability and painful phenomena. Ankyrin G, a multifunctional transmembrane protein of the axolemma, might be a key protein in neuroma formation because it binds Na+ channels in the initial segments of a regenerating axon and links with neuronal cell adhesion molecules. The authors wanted to determine if ankyrin G could be detected in neuroma, and if present, whether there would be differences in distribution between nonpainful neuromas, painful neuromas, and normal nerve.

METHODS

First, frozen sections of nine nerve specimens obtained from six patients (six nonpainful neuromas, one painful neuroma, and two normal nerves) were immunocytochemically screened for ankyrin G by using confocal laser scanning microscopy. Second, specimens from 29 patients (seven painful neuromas, 15 nonpainful neuromas, and seven normal nerves) were examined using immunoblot analysis for their ankyrin G content. Western blot analysis detected ankyrin G, which was visualized by applying the enhanced chemiluminescence technique. Computerized densitometry was used to quantitate ankyrin G expression by comparing band intensities. Normal nerve served as control. Neurofilament was used as a marker for nerve tissue content. Ankyrin G could be detected and was found to be increased in neuromas. The mean band intensity values were 1838 for painful neuromas, 1166 for nonpainful neuromas, and 411 for normal nerves. In two cases the authors were able to compare specimens of painful neuroma and normal nerve from the same patient. The painful neuromas exhibited considerably higher levels of ankyrin G. Painful neuroma and normal nerve densitometry values were 499 and 165, respectively, for one patient, and 4254 and 821, respectively, for the other patient. Painful neuromas were also found to have higher neurofilament values than nonpainful neuromas.

CONCLUSIONS

Altered regulation of ankyrin G after nerve injury may lead to hyperexcitability and painful phenomena via clustering of Na+ channels. A propensity to overexpress ankyrin G after peripheral nerve trauma may turn out to be a factor in the development of painful neuromas and neuropathic pain. The relevant literature regarding the importance of ankyrin G for nerve regeneration and nerve membrane remodeling is reviewed.

Changes in Na(+) channel currents of rat dorsal root ganglion neurons following axotomy and axotomy-induced autotomy

Section of rat sciatic nerve (axotomy) increases the excitability of neurons in the L(4)-L(5) dorsal root ganglia (DRG). These changes are more pronounced in animals that exhibit a self-mutilatory behavior known as autotomy. We used whole cell recording to examine changes in the tetrodotoxin-sensitive (TTX-S) and the tetrodotoxin-resistant (TTX-R) components of sodium channel currents (I(Na)) that may contribute to axotomy-induced increases in excitability. Cells were initially divided on the basis of size into "large," "medium," and "small" groups. TTX-S I(Na) predominated in "large" cells, whereas TTX-R I(Na) predominated in some, but not all "small cells." "Small" cells were therefore subdivided into "small-slow" cells, which predominantly exhibited TTX-R I(Na) and "small fast" cells that exhibited more TTX-S I(Na). In contrast to results obtained in other laboratories, where slightly different experimental procedures were used, we found that axotomy increased TTX-R and/or TTX-S I(Na) and slowed inactivation. The effects were greatest in "small-slow" cells and least in "large" cells. The changes promoted by axotomy were expressed more clearly in animals that exhibited autotomy. Also, the presence of autotomy correlated with a shift in the properties of I(Na) in "large" rather than "small-slow," putative nociceptive cells. These trends parallel previous observations on axotomy-induced increases in excitability, spike height, and spike width that are also greatest in "small" cells and least in "large" cells. In addition, the presence of autotomy correlates with an increase in excitability of "large" rather than "small" cells. Increases in TTX-R and TTX-S I(Na) thus coincide with axotomy-induced increases in excitability and alterations in spike shape across the whole population of sensory neurons. Injury-induced changes of this type are likely associated with the onset of chronic pain in humans.

Beyond neurons: evidence that immune and glial cells contribute to pathological pain states

Chronic pain can occur after peripheral nerve injury, infection, or inflammation. Under such neuropathic pain conditions, sensory processing in the affected body region becomes grossly abnormal. Despite decades of research, currently available drugs largely fail to control such pain. This review explores the possibility that the reason for this failure lies in the fact that such drugs were designed to target neurons rather than immune or glial cells. It describes how immune cells are a natural and inextricable part of skin, peripheral nerves, dorsal root ganglia, and spinal cord. It then examines how immune and glial activation may participate in the etiology and symptomatology of diverse pathological pain states in both humans and laboratory animals. Of the variety of substances released by activated immune and glial cells, proinflammatory cytokines (tumor necrosis factor, interleukin-1, interleukin-6) appear to be of special importance in the creation of peripheral nerve and neuronal hyperexcitability. Although this review focuses on immune modulation of pain, the implications are pervasive. Indeed, all nerves and neurons regardless of modality or function are likely affected by immune and glial activation in the ways described for pain.

Neuropeptide expression in the ferret trigeminal ganglion following ligation of the inferior alveolar nerve

Previous studies have found changes in neuropeptide expression in trigeminal ganglion cells after inferior alveolar nerve (IAN) section. These changes may play a part in the persistent sensory abnormalities that can be experienced after trigeminal nerve injuries. Here, neuropeptide expression after IAN ligation was studied, as this type of injury is thought to be more likely to result in sensory disturbances. The neuropeptides investigated were substance P, calcitonin gene-related peptide, enkephalin (ENK), galanin (GAL), neuropeptide Y (NPY) and vasoactive intestinal polypeptide. In anaesthetised adult female ferrets the left IAN was sectioned and the central stump tightly ligated. Recovery was allowed for 3 days, 3 or 12 weeks before perfusion-fixation. In a second procedure, 1 week before perfusion, the IAN was exposed and an injection made central to the injury site, using a mixture of 4% Fluorogold and 4% Isolectin B4 conjugated to horseradish peroxidase, to identify cell bodies with axons in the inferior alveolar nerve and cells with unmyelinated axons within this population, respectively. Control experiments involved tracer injection alone. After harvesting the tissue, sagittal sections were taken from both the right and left ganglia and immunohistochemical staining used to reveal the presence of peptides and Isolectin B4 tracer. The results showed a significant decrease in GAL expression after injury and an increase in ENK and NPY expression. No significant differences were seen in the expression of the other peptides or in the proportion of lectin-positive cells at any time after injury. When compared with previous data, significant differences were found between peptide expression following nerve ligation and nerve section. These results reveal that the changes in neuropeptide expression in the trigeminal ganglion that follow IAN injury are dependent upon the type of injury. The extent to which changes in the central neuropeptide levels contribute to the development of sensory disorders remains to be established.

Nerve injury-induced pain in the trigeminal system

This article reviews some recent findings on peripheral mechanisms related to the development of oro-facial pain after trigeminal nerve injury. Chronic injury-induced oro-facial pain is not in itself a life-threatening condition, but patients suffering from this disorder undoubtedly have a reduced quality of life. The vast majority of the work on pain mechanisms has been carried out in spinal nerve systems. Those studies have provided great insight into mechanisms of neuropathic spinal pain, and much of the data from them is obviously relevant to studies of trigeminal pain. However, it is now clear that the pathophysiology of the trigeminal nerve (a cranial nerve) is in many ways different to that found in spinal nerves. Whereas some of the changes seen in animal models of trigeminal nerve injury mimic those occurring after spinal nerve injury (e.g., the development of spontaneous activity from the damaged axons), others are different, such as the time-course of the spontaneous activity, some of the neuropeptide changes in the trigeminal ganglion, and the lack of sprouting of sympathetic terminals in the ganglion. Recent findings provide new insights that help our understanding of the etiology of chronic injury-induced oro-facial pain. Future investigations will hopefully explain how data gained from these studies relate to clinical pain experience in man and should enable the rapid development of new therapeutic regimes.