Neurological mechanisms of migraine: potential of the gap-junction modulator tonabersat in prevention of migraine

Zinc as An Emerging Therapy in the Management of Migraine: A Systematic Review

Migraine, a common neurological condition, is characterized by a chronic and recurring headache that affects numerous people globally. Several drugs are available for the treatment and prophylaxis of migraine with their shortfalls. Zinc could play a role in migraine management because of its anti-inflammatory and antioxidant properties. This study was planned to systematically review the scientific databases to gather evidence regarding the role of zinc in the management of migraine. The protocol was registered with the PROSPERO (CRD42023398478). Three databases PubMed, The Cochrane Central Register of Controlled Trials, and Clinicaltrials.gov were searched with the keywords "migraine", "migraine disorders" and "zinc". A literature search led to the retrieval of 35 studies; of these five studies (2 clinical trials and 3 observational studies) were comprised in a systematic review. Clinical trials' risk of bias assessment is low. The review suggested a positive role of zinc in managing migraine however, the evidence requires further strengthening. The available clinical literature on the effectiveness of zinc in migraines is limited; hence, more robust and large clinical trials are required to support the role of zinc in migraines.

A cross-sectional, multicenter survey of the prevalence and influencing factors for migraine in epilepsy

OBJECTIVES

Epilepsy and migraine are common chronic neurological disease. Epidemiologic studies and shared pathophysiology and treatment suggest that these two diseases overlap. However, migraine is often underestimated among patients with epilepsy. This study aimed to evaluate the prevalence of migraine and identify the related influencing factors among adult patients with epilepsy.

METHODS

Adult patients with epilepsy were recruited at the outpatient epilepsy clinic of 13 tertiary hospitals in China from February to September 2022. ID Migraine questionnaire was applied to evaluate for migraine. Both univariable and multivariable logistic regression models were used to explore the influencing factors of migraine.

RESULTS

A total of 1326 patients with epilepsy were enrolled in this study. The prevalence of migraine among patients with epilepsy was 19.2% (254/1326). In the multivariable analysis, being female (OR = 1.451, 95% CI: 1.068-1.975; p = 0.018), focal and focal to bilateral tonic-clonic seizures (OR = 1.583, 95% CI: 1.090-2.281; p = 0.015), and current seizure attack in the last 3 months (OR = 1.967, 95% CI: 1.282-3.063; p = 0.002) were the influencing factors for migraine. However, <10% of patients with epilepsy received analgesics for migraine.

SIGNIFICANCE

Approximately 20% of patients with epilepsy screened positive for migraine. Being female, focal and focal to bilateral tonic-clonic seizures, and current seizure attack in the last 3 months were the influencing factors for migraine. Neurologists should pay more attention to the screening and management of the migraine among patients with epilepsy in China.

PLAIN LANGUAGE SUMMARY

Epilepsy and migraine are common chronic neurological disease with shared pathophysiological mechanisms and therapeutic options. However, migraine is often underestimated among patients with epilepsy. This multicenter study aimed to evaluate the prevalence of migraine and current status of treatment. In this study, approximately 20% of patients with epilepsy screened positive for migraine. Female, focal and focal to bilateral tonic-clonic seizures, and current seizure attack in the last 3 months were identified as independent influencing factors for migraine. Despite the high prevalence, the treatment for migraine was not optimistic, neurologists should pay more attention to the screening and management of migraine.

The Vasodilatory Response to CGRP of the Anterior and Posterior Cerebral Circulation in Migraine

Introduction

Migraine aura can be associated with headache or it may occur without one, which suggests an independent mechanism for the aura and for migraine headache. The role of CGRP in migraine headache is well established, but the connection between CGRP and the aura is still lacking an explanation. Exogenous CGRP can induce CGRP headaches and migraine auras in patients with migraine. The results of our recent study suggest differences in the vascular response to CGRP stimulation between migraine without aura and migraine with aura. Therefore, we hypothesized that the magnitude of the posterior cerebral circulation response in migraine with aura is greater than in migraine without aura and that CGRP stimulation has different effects on the anterior and posterior circulation in migraine with aura and migraine without aura.

Methods

By using transcranial doppler, we studied the hemodynamic effects of CGRP intravenous infusion at a rate of 1.5 mcg/min in 20 min on the mean arterial velocity in the middle cerebral artery and in the posterior cerebral artery in twenty patients with migraine and in a control group of twenty healthy subjects. The same CGRP effects on cerebral hemodynamics were analyzed separately for the group of patients with migraine with aura and the group of patients with migraine without aura. Fifteen patients with migraine (75%) had migraine without aura and 5 patients (25%) had migraine with aura.

Results

We found that migraine has a significant impact on the vasodilatory response of the anterior (B = 4,249, SE = 1.023, r = 0.363, p < 0.001) and posterior cerebral circulation (B = 3.634, SE = 1.461, r = 0.227, p = 0.014). Migraine with aura was significantly associated with changes in the anterior (B = 2.558, SE = 0.880, r = 0.275, p = 0.005) and posterior cerebral circulation (B = 7.565, SE = 2,368, r = 0.359, p = 0.002), while migraine without aura was only significantly associated with changes in the anterior circulation. In addition, we established a significant impact of migraine with aura on VR PCA (B = 5.901, SE = 2,546, r = 0.291, p = 0.024).

Conclusion

We conclude that TVR in the posterior cerebral circulation might be enhanced in MA and that aura might be a consequence of TVR enhancement.

Cx43 hemichannels contribute to astrocyte-mediated toxicity in sporadic and familial ALS

Our results demonstrate that connexin 43 hemichannels are the conduits for amyotrophic lateral sclerosis (ALS) astrocyte-mediated motor neuron toxicity and disease spread, acting as a common mechanism that can target both familial ALS and sporadic ALS populations. Furthermore, our present work provides proof of principle that tonabersat, as a drug already studied in clinical trials for other indications, could serve as a potential ALS therapeutic.

Connexin 43 (Cx43) gap junctions and hemichannels mediate astrocyte intercellular communication in the central nervous system under normal conditions and contribute to astrocyte-mediated neurotoxicity in amyotrophic lateral sclerosis (ALS). Here, we show that astrocyte-specific knockout of Cx43 in a mouse model of ALS slows disease progression both spatially and temporally, provides motor neuron (MN) protection, and improves survival. In addition, Cx43 expression is up-regulated in human postmortem tissue and cerebrospinal fluid from ALS patients. Using human induced pluripotent stem cell–derived astrocytes (hiPSC-A) from both familial and sporadic ALS, we establish that Cx43 is up-regulated and that Cx43-hemichannels are enriched at the astrocyte membrane. We also demonstrate that the pharmacological blockade of Cx43-hemichannels in ALS astrocytes using GAP 19, a mimetic peptide blocker, and tonabersat, a clinically tested small molecule, provides neuroprotection of hiPSC-MN and reduces ALS astrocyte-mediated neuronal hyperexcitability. Extending the in vitro application of tonabersat with chronic administration to SOD1^G93A mice results in MN protection with a reduction in reactive astrocytosis and microgliosis. Taking these data together, our studies identify Cx43 hemichannels as conduits of astrocyte-mediated disease progression and a pharmacological target for disease-modifying ALS therapies.

Emerging importance of satellite glia in nervous system function and dysfunction

Satellite glial cells (SGCs) closely envelop cell bodies of neurons in sensory, sympathetic and parasympathetic ganglia. This unique organization is not found elsewhere in the nervous system. SGCs in sensory ganglia are activated by numerous types of nerve injury and inflammation. The activation includes upregulation of glial fibrillary acidic protein, stronger gap junction-mediated SGC-SGC and neuron-SGC coupling, increased sensitivity to ATP, downregulation of Kir4.1 potassium channels and increased cytokine synthesis and release. There is evidence that these changes in SGCs contribute to chronic pain by augmenting neuronal activity and that these changes are consistent in various rodent pain models and likely also in human pain. Therefore, understanding these changes and the resulting abnormal interactions of SGCs with sensory neurons could provide a mechanistic approach that might be exploited therapeutically in alleviation and prevention of pain. We describe how SGCs are altered in rodent models of four common types of pain: systemic inflammation (sickness behaviour), post-surgical pain, diabetic neuropathic pain and post-herpetic pain.

Inhibition of gap junctional intercellular communication by an anti-migraine agent, flunarizine

Gap junctions (GJs), which consist of proteins called connexins, are intercellular channels that allow the passage of ions, second messengers, and small molecules. GJs and connexins are considered as emerging therapeutic targets for various diseases. Previously, we screened numerous compounds using our recently developed iodide yellow fluorescent protein gap junctional intercellular communication (I-YFP GJIC) assay and found that flunarizine (FNZ), used for migraine prophylaxis and as an add-on therapy for epilepsy, inhibits GJIC in LN215 human glioma cells. In this study, we confirmed that FNZ inhibits GJIC using the I-YFP GJIC assay. We demonstrated that FNZ inhibits GJ activities via a mechanism that is independent of calcium channels and dopaminergic D2, histaminergic H1, or 5-HT receptors. In addition, we showed that FNZ significantly increases connexin 43 (Cx43) phosphorylation on the cell surface, but does not alter the total amount of Cx43. The beneficial effects of FNZ on migraines and epilepsy might be related to GJ inhibition.

Nitric oxide as a messenger between neurons and satellite glial cells in dorsal root ganglia

Abnormal neuronal activity in sensory ganglia contributes to chronic pain. There is evidence that signals can spread between cells in these ganglia, which may contribute to this activity. Satellite glial cells (SGCs) in sensory ganglia undergo activation following peripheral injury and participate in cellular communication via gap junctions and chemical signaling. Nitric oxide (NO) is released from neurons in dorsal root ganglia (DRG) and induces cyclic GMP (cGMP) production in SCGs, but its role in SGC activation and neuronal excitability has not been explored. It was previously reported that induction of intestinal inflammation with dinitrobenzoate sulfonate (DNBS) increased gap junctional communications among SGCs, which contributed to neuronal excitability and pain. Here we show that DNBS induced SGC activation in mouse DRG, as assayed by glial fibrillary acidic protein upregulation. DNBS also upregulated cGMP level in SGCs, consistent with NO production. In vitro studies on intact ganglia from DNBS-treated mice showed that blocking NO synthesis inhibited both SGCs activation and cGMP upregulation, indicating an ongoing NO production. Application of NO donor in vitro induced SGC activation, augmented gap junctional communications, and raised neuronal excitability, as assessed by electrical recordings. The cGMP analog 8-Br-cGMP mimicked these actions, confirming the role of the NO-cGMP pathway in intraganglionic communications. NO also augmented Ca²⁺ waves propagation in DRG cultures. It is proposed that NO synthesis in DRG neurons increases after peripheral inflammation and that NO induces SGC activation, which in turn contributes to neuronal hyperexcitability. Thus, NO plays a major role in neuron-SGC communication.

Understanding Spreading Depression from Headache to Sudden Unexpected Death

Spreading depression (SD) is a neurophysiological phenomenon characterized by abrupt changes in intracellular ion gradients and sustained depolarization of neurons. It leads to loss of electrical activity, changes in the synaptic architecture, and an altered vascular response. Although SD is often described as a unique phenomenon with homogeneous characteristics, it may be strongly affected by the particular triggering event and by genetic background. Furthermore, SD may contribute differently to the pathogenesis of widely heterogeneous clinical conditions. Indeed, clinical disorders related to SD vary in their presentation and severity, ranging from benign headache conditions (migraine syndromes) to severely disabling events, such as cerebral ischemia, or even death in people with epilepsy. Although the characteristics and mechanisms of SD have been dissected using a variety of approaches, ranging from cells to human models, this phenomenon remains only partially understood because of its complexity and the difficulty of obtaining direct experimental data. Currently, clinical monitoring of SD is limited to patients who require neurosurgical interventions and the placement of subdural electrode strips. Significantly, SD events recorded in humans display electrophysiological features that are essentially the same as those observed in animal models. Further research using existing and new experimental models of SD may allow a better understanding of its core mechanisms, and of their differences in different clinical conditions, fostering opportunities to identify and develop targeted therapies for SD-related disorders and their worst consequences.

Tonabersat Prevents Inflammatory Damage in the Central Nervous System by Blocking Connexin43 Hemichannels

The cis benzopyran compound tonabersat (SB-220453) has previously been reported to inhibit connexin26 expression in the brain by attenuating the p38-mitogen-activated protein kinase pathway. We show here that tonabersat directly inhibits connexin43 hemichannel opening. Connexin43 hemichannels have been called "pathological pores" based upon their role in secondary lesion spread, edema, inflammation, and neuronal loss following central nervous system injuries, as well as in chronic inflammatory disease. Both connexin43 hemichannels and pannexin channels released adenosine triphosphate (ATP) during ischemia in an in vitro ischemia model, but only connexin43 hemichannels contributed to ATP release during reperfusion. Tonabersat inhibited connexin43 hemichannel-mediated ATP release during both ischemia and reperfusion phases, with direct channel block confirmed using electrophysiology. Tonabersat also reduced connexin43 gap junction coupling in vitro, but only at higher concentrations, with junctional plaques internalized and degraded via the lysosomal pathway. Systemic delivery of tonabersat in a rat bright-light retinal damage model (a model for dry age-related macular degeneration) resulted in significantly improved functional outcomes assessed using electroretinography. Tonabersat also prevented thinning of the retina, especially the outer nuclear layer and choroid, assessed using optical coherence tomography. We conclude that tonabersat, already given orally to over 1000 humans in clinical trials (as a potential treatment for, and prophylactic treatment of, migraine because it was thought to inhibit cortical spreading depression), is a connexin hemichannel inhibitor and may have the potential to be a novel treatment of central nervous system injury and chronic neuroinflammatory disease.

Anchored PKA as a gatekeeper for gap junctions

Anchored protein kinase A (PKA) bound to A Kinase Anchoring Protein (AKAP) mediates effects of localized increases in cAMP in defined subcellular microdomains and retains the specificity in cAMP-PKA signaling to distinct extracellular stimuli. Gap junctions are pores between adjacent cells constituted by connexin proteins that provide means of communication and transfer of small molecules. While the PKA signaling is known to promote human trophoblast cell fusion, the gap junction communication through connexin 43 (Cx43) is a prerequisite for this process. We recently demonstrated that trophoblast fusion is regulated by ezrin, a known AKAP, which binds to Cx43 and delivers PKA in the vicinity gap junctions. We found that disruption of the ezrin-Cx43 interaction abolished PKA-dependent phosphorylation of Cx43 as well as gap junction communication and subsequently cell fusion. We propose that the PKA-ezrin-Cx43 macromolecular complex regulating gap junction communication constitutes a general mechanism to control opening of Cx43 gap junctions by phosphorylation in response to cAMP signaling in various cell types.

Typical aura without headache: a case report and review of the literature

Introduction

Typical aura without headache (TAWH), which has been rarely reported both at home and abroad, is a rare type of migraine with aura.

Case presentation

This is a report on a 64-year-old Chinese migraineur who has had recurrent typical visual aura without headache attacks for more than 30 years, and has been misdiagnosed as having had transient ischemic attacks (TIA) many times. He mainly experienced episodes of ‘homonymous blurred vision’ or photopsia, which presented as different shapes located at the side or above his visual field, for example, patchy, cord-like, zigzag, curtain-like or irregular shapes. The shape was inconsistent during each attack, however, the color was mainly gray or light blue. The visual symptoms gradually disappeared in about 30 minutes. Our patient has never suffered a headache attack during or after the visual aura. Normal results were observed in his neurological and eye examinations, complete blood test, electroencephalogram and neuroimaging examination.

Conclusions

TAWH is an uncommon phenomenon of migraine. Migraine with visual aura mainly presents positive and dynamic symptoms. It has a benign course and can be diagnosed after exclusion of other organic diseases such as TIA and epilepsy.

Gabapentin inhibits central sensitization during migraine

Peripheral and central sensitizations are phenomena that occur during migraine. The role of pentin, a migraine preventive drug, on central sensitization remains unclear. In this study, a rat model of migraine was established by electrical stimulation of the trigeminal ganglion, and the an-imals were given intragastric gabapentin. Changes in amino acid content in the cerebrospinal fluid and protein kinase C membrane translocation in the spinal trigeminal nucleus were examined to clarify the mechanisms underlying the efficacy of gabapentin in the treatment of central sensitization during migraine. Electrophysiology, liquid chromatography-mass spectrometry and western blot analysis results revealed that gabapentin reduces neuronal excitability in the spinal nucleus in the trigeminal nerve, decreases excitatory amino acid content and inhibits the activation of protein ki-nase C. This provides evidence that excitatory amino acids and protein kinase C are involved in the formation and maintenance of central sensitization during migraine. Gabapentin inhibits migraine by reducing excitatory amino acid content in the cerebrospinal fluid and inhibiting protein kinase C ac-tivation.

Cortical spreading depression: origins and paths as inferred from the sequence of events during migraine aura

Patients with migraine with aura often experience a variety of visual and somatosensory phenomena and disturbances of higher cortical functions. Analysis of these alterations may provide important information about the involvement of different cortical regions in cortical spreading depression (CSD). We report five cases of migraineurs who experience unusually abundant clinical phenomena during auras. These patients were selected from a cohort of migraine with aura patients who were interviewed, using a specially designed questionnaire, to evaluate the presence of higher cortical dysfunctions. On the basis of the aura symptoms they reported, we attempted to infer the origin and the possible paths of CSD in each patient. According to their reported symptoms, CSD could begin in the primary visual cortex, in the primary somatosensory cortex or simultaneously in both, and propagate to the posterior parietal cortex, the temporal lobe and Broca's area. We believe that clinical descriptions of aura could play an important role in further investigations of the pathophysiology of migraine.

Involvement of gap junction channels in the pathophysiology of migraine with aura

Migraine is a common, recurrent, and disabling primary headache disorder with a genetic component which affects up to 20% of the population. One third of all patients with migraine experiences aura, a focal neurological disturbance that manifests itself as visual, sensitive or motor symptoms preceding the headache. In the pathophysiology of migraine with aura, activation of the trigeminovascular system from the meningeal vessels mediates migraine pain via the brainstem and projections ascend to the thalamus and cortex. Cortical spreading depression (CSD) was proposed to trigger migraine aura and to activate perivascular trigeminal nerves in the cortex. Quinine, quinidine and the derivative mefloquine are able to inhibit CSD suggesting an involvement of neuronal connexin36 channels in CSD propagation. More recently, CSD was shown to induce headache by activating the trigeminovascular system through the opening of stressed neuronal Pannexin1 channels. A novel benzopyran compound, tonabersat, was selected for clinical trial on the basis of its inhibitory activity on CSD and neurogenic inflammation in animal models of migraine. Interestingly, in the time course of animal model trials, tonabersat was shown to inhibit trigeminal ganglion (TGG) neuronal-glial cell gap junctions, suggesting that this compound could prevent peripheral sensitization within the ganglion. Three clinical trials aimed at investigating the effectiveness of tonabersat as a preventive drug were negative, and conflicting results were obtained in other trials concerning its ability to relieve attacks. In contrast, in another clinical trial, tonabersat showed a preventive effect on attacks of migraine with aura but had no efficacy on non-aura attacks. Gap junction channels seem to be involved in several ways in the pathophysiology of migraine with aura and emerge as a new promising putative target in treatment of this disorder.

Cortical spreading depression as a target for anti-migraine agents

Spreading depression (SD) is a slowly propagating wave of neuronal and glial depolarization lasting a few minutes, that can develop within the cerebral cortex or other brain areas after electrical, mechanical or chemical depolarizing stimulations. Cortical SD (CSD) is considered the neurophysiological correlate of migraine aura. It is characterized by massive increases in both extracellular K⁺ and glutamate, as well as rises in intracellular Na⁺ and Ca²⁺. These ionic shifts produce slow direct current (DC) potential shifts that can be recorded extracellularly. Moreover, CSD is associated with changes in cortical parenchymal blood flow. CSD has been shown to be a common therapeutic target for currently prescribed migraine prophylactic drugs. Yet, no effects have been observed for the antiepileptic drugs carbamazepine and oxcarbazepine, consistent with their lack of efficacy on migraine. Some molecules of interest for migraine have been tested for their effect on CSD. Specifically, blocking CSD may play an enabling role for novel benzopyran derivative tonabersat in preventing migraine with aura. Additionally, calcitonin gene-related peptide (CGRP) antagonists have been recently reported to inhibit CSD, suggesting the contribution of CGRP receptor activation to the initiation and maintenance of CSD not only at the classic vascular sites, but also at a central neuronal level. Understanding what may be lying behind this contribution, would add further insights into the mechanisms of actions for "gepants", which may be pivotal for the effectiveness of these drugs as anti-migraine agents. CSD models are useful tools for testing current and novel prophylactic drugs, providing knowledge on mechanisms of action relevant for migraine.

Underestimated phenomena: higher cortical dysfunctions during migraine aura

INTRODUCTION

Aura occurs in 20-30% of patients with migraine. Some descriptions of aura go far beyond the most frequent visual and sensory symptoms, suggesting the involvement of different cortical areas. The aim of this prospective study was to evaluate the frequency and types of disorders of higher cortical functions (HCF) that occur during visual and/or sensory aura.

METHODS

We interviewed 60 patients with visual and/or sensory aura about HCF disorders of praxia, gnosia, memory, and speech, during aura. Patients were divided into two groups, with and without HCF disorders, and were compared in terms of demographic data and aura characteristics.

RESULTS

From all 60 patients, 65% reported at least one HCF disorder during aura. The patients with HCF disorders had longer-lasting auras (28.51 ± 16.39 vs. 19.76 ± 11.23, P  = 0.016). The most common HCF disorders were motor dysphasia (82.05%) and dysnomia (30.74%). Motor dysphasia was more often reported by patients with visual as well as sensory aura ( P  = 0.002). The number of HCF disorders correlated with the aura duration ( P  = 0.003).

CONCLUSION

According to our results, HCF disorders during aura occur more often than previously thought. The aura duration has some influence on the HCF disorders.

Intercellular communication in sensory ganglia by purinergic receptors and gap junctions: implications for chronic pain

Peripheral injury can cause abnormal activity in sensory neurons, which is a major factor in chronic pain. Recent work has shown that injury induces major changes not only in sensory neurons but also in the main type of glial cells in sensory ganglia-satellite glial cells (SGCs), and that interactions between sensory neurons and SGCs contribute to neuronal activity in pain models. The main functional changes observed in SGCs after injury are an increased gap junction-mediated coupling among these cells, and augmented sensitivity to ATP. There is evidence that the augmented gap junctions contribute to neuronal hyperexcitability in pain models, but the mechanism underlying this effect is not known. The changes in SGCs described above have been found following a wide range of injuries (both axotomy and inflammation) in somatic, orofacial and visceral regions, and therefore appear to be a general feature in chronic pain. We have found that in cultures of sensory ganglia calcium signals can spread from an SGC to neighboring cells by calcium waves, which are mediated by gap junctions and ATP acting on purinergic P2 receptors. A model is proposed to explain how augmented gap junctions and greater sensitivity to ATP can combine to produce enhanced calcium waves, which can lead to neuronal excitation. Thus this simple scheme can account for several major changes in sensory ganglia that are common to a great variety of pain models.

Dysfunction of astrocyte connexins 30 and 43 in dorsal lateral prefrontal cortex of suicide completers

BACKGROUND

Suicide is an important public health problem that results from the interaction of both psychosocial and biological factors. Although it is known that particular neurobiological processes underlie suicidal ideation and behavior, there still remains limited knowledge about the specific factors involved.

METHODS

To explore the neurobiology of suicide we generated microarray data from dorsal lateral prefrontal cortex (DLPFC) in each of 28 male French-Canadian subjects (20 suicide completers). These results were followed up in a larger French-Canadian sample (n = 47, 38 suicide completers) and in microarray data available from the Stanley Foundation (n = 100, 36 suicide completers). To investigate the molecular mechanisms of this finding, we performed RNA interference and electrophoretic mobility shift assays. Animal behavioral experiments were done to control for drug and alcohol effects.

RESULTS

We found reduced expression of Cx30 and Cx43 in DLPFC of suicide completers. We identified a previously unknown function for Sox9 as a transcription factor affecting expression of Cx30 in brain.

CONCLUSIONS

These results suggest that alterations of astrocyte connexins might be involved in the suicide process and provide further evidence implicating astrocytes in psychopathology.

The role of gap junctions in the brain in health and disease

Gap junctions connect the cytosolic compartments of adjacent cells for direct electrotonic and metabolic cell-to-cell communication. Gap junctions between glial cells or neurons are ubiquitously expressed in the brain and play a role in brain development including cell differentiation, cell migration and survival, tissue homeostasis, as well as in human diseases including hearing loss, skin disease, neuropathies, epilepsy, brain trauma, and cardiovascular disease. Furthermore, gap junctions are involved in the synchronization and rhythmic oscillation of hippocampal and neocotical neuronal ensembles which might be important for memory formation and consolidation. In this review the accumulated evidence from mouse mutant and pharmacological studies using gap junction blockers is summarized and the progress made in dissecting the physiological, pathophysiological and behavioral roles of gap junction mediated intercellular communication in the brain is discussed.

Dietary grape seed polyphenols repress neuron and glia activation in trigeminal ganglion and trigeminal nucleus caudalis

BACKGROUND

Inflammation and pain associated with temporomandibular joint disorder, a chronic disease that affects 15% of the adult population, involves activation of trigeminal ganglion nerves and development of peripheral and central sensitization. Natural products represent an underutilized resource in the pursuit of safe and effective ways to treat chronic inflammatory diseases. The goal of this study was to investigate effects of grape seed extract on neurons and glia in trigeminal ganglia and trigeminal nucleus caudalis in response to persistent temporomandibular joint inflammation. Sprague Dawley rats were pretreated with 200 mg/kg/d MegaNatural-BP grape seed extract for 14 days prior to bilateral injections of complete Freund's adjuvant into the temporomandibular joint capsule.

RESULTS

In response to grape seed extract, basal expression of mitogen-activated protein kinase phosphatase 1 was elevated in neurons and glia in trigeminal ganglia and trigeminal nucleus caudalis, and expression of the glutamate aspartate transporter was increased in spinal glia. Rats on a normal diet injected with adjuvant exhibited greater basal levels of phosphorylated-p38 in trigeminal ganglia neurons and spinal neurons and microglia. Similarly, immunoreactive levels of OX-42 in microglia and glial fibrillary acidic protein in astrocytes were greatly increased in response to adjuvant. However, adjuvant-stimulated levels of phosphorylated-p38, OX-42, and glial fibrillary acidic protein were significantly repressed in extract treated animals. Furthermore, grape seed extract suppressed basal expression of the neuropeptide calcitonin gene-related peptide in spinal neurons.

CONCLUSIONS

Results from our study provide evidence that grape seed extract may be beneficial as a natural therapeutic option for temporomandibular joint disorders by suppressing development of peripheral and central sensitization.

New drugs in migraine treatment and prophylaxis: telcagepant and topiramate

Although the triptan drugs provide effective relief from migraine for many patients, a substantial number of affected individuals are unresponsive to these compounds, and such therapy can also lead to a range of adverse effects. Telcagepant represents a new class of antimigraine drug-the calcitonin gene-related peptide receptor blockers. This compound exerts its effects by blocking receptors for the calcitonin-gene-related peptide at several sites in the trigeminal and central nervous systems, resulting in pain relief. Telcagepant does not cause vasoconstriction, a major limitation in the use of triptans. Comparisons with triptans in clinical trials for acute treatment of migraine attacks revealed clinical effects similar to those of triptans but better than those of placebo. Telcagepant might provide hope for those who have a poor response to, or are unable to use, older drugs. In patients who need prophylaxis because of frequent attacks of migraine, topiramate is a first-line drug for migraine prevention in many countries; it is generally safe and reasonably well tolerated. Data suggest that topiramate could aid reversion of chronic migraine to episodic migraine.

The relevance of preclinical research models for the development of antimigraine drugs: focus on 5-HT(1B/1D) and CGRP receptors

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology.

Gap junction-mediated spontaneous Ca(2+) waves in differentiated cholinergic SN56 cells

Neuronal gap junctions are receiving increasing attention as a physiological means of intercellular communication, yet our understanding of them is poorly developed when compared to synaptic communication. Using microfluorimetry, we demonstrate that differentiation of SN56 cells (hybridoma cells derived from murine septal neurones) leads to the spontaneous generation of Ca(2+) waves. These waves were unaffected by tetrodotoxin (1microM), but blocked by removal of extracellular Ca(2+), or addition of non-specific Ca(2+) channel inhibitors (Cd(2+) (0.1mM) or Ni(2+) (1mM)). Combined application of antagonists of NMDA receptors (AP5; 100microM), AMPA/kainate receptors (NBQX; 20microM), nicotinic AChR receptors (hexamethonium; 100microM) or inotropic purinoceptors (brilliant blue; 100nM) was also without effect. However, Ca(2+) waves were fully prevented by carbenoxolone (200microM), halothane (3mM) or niflumic acid (100microM), three structurally diverse inhibitors of gap junctions, and mRNA for connexin 36 was detected by PCR. Whole-cell patch-clamp recordings revealed spontaneous inward currents in voltage-clamped cells which we inhibited by Cd(2+), Ni(2+) or niflumic acid. Our data suggest that differentiated SN56 cells generated spontaneous Ca(2+) waves which are propagated by intercellular gap junctions. We propose that this system can be exploited conveniently for the development of neuronal gap junction modulators.