Blockade Of Voltage-gated Sodium Channels Research Articles

Behavioral control through the direct, focal silencing of neuronal activity.

The ability to optically stimulate and inhibit neurons has revolutionized neuroscience research. Here, we present a direct, potent, user-friendly chemical approach for optically silencing neurons. We have rendered saxitoxin (STX), a naturally occurring paralytic agent, transiently inert through chemical protection with a previously undisclosed nitrobenzyl-derived photocleavable group. Exposing the caged toxin, STX-bpc, to a brief (5ms) pulse of light effects rapid release of a potent STX derivative and transient, spatially precise blockade of voltage-gated sodium channels (NaVs). We demonstrate the efficacy of STX-bpc for parametrically manipulating action potentials in mammalian neurons and brain slice. Additionally, we show the effectiveness of this reagent for silencing neural activity by dissecting sensory-evoked swimming in larval zebrafish. Photo-uncaging of STX-bpc is a straightforward method for non-invasive, reversible, spatiotemporally precise neural silencing without the need for genetic access, thus removing barriers for comparative research.

The enhancing effect of 5-HT on phasic contractions of human isolated distal ureter and the mechanisms mediating these effects

5-Hydroxytryptamine (5-HT) can enhance human ureteral contractions. However, the mediating receptors have not been clarified. This study sought to further characterize the mediating receptors using several selective antagonists and agonists. Human distal ureters were obtained from 96 patients undergoing cystectomy. The mRNA expression levels of 5-HT receptors were examined using RT-qPCR experiments. The phasic contractions of ureter strips, either spontaneous or evoked with neurokinin, were recorded in an organ bath. Among the 13 5-HT receptors, 5-HT2A and 5-HT2C receptors showed the highest mRNA expression levels. 5-HT (10-7–10-4 M) increased the frequency and baseline tension of phasic contractions in a concentration-dependent manner. However, a desensitization effect was observed. The 5-HT2C receptor selective antagonist, SB242084 (10,30,100 nM), shifted the 5-HT concentration-response curves (frequency and baseline tension) rightward with a pA2 value of 8.05 and 7.75, respectively. 5-HT2C receptor selective agonist, vabicaserin, increased contraction frequency with an Emax of 35% of 5-HT. 5-HT2A receptor selective antagonist, volinanserin (1,10,100 nM), only reduced baseline tension with a pA2 of 8.18. The selective antagonists of 5-HT1A, 1B, 1D, 2B, 3, 4, 5, 6, and 7 had no antagonism. Blockade of voltage-gated sodium channels, α1-adrenergic receptors, adrenergic neurotransmission, and neurokinin-2 receptors using tetrodotoxin, tamsulosin, guanethidine, and Men10376, respectively, and desensitization of sensory afferents using capsaicin (100 μM), significantly reduced 5-HT effects. We conclude that 5-HT enhanced ureteral phasic contractions mainly by activating 5-HT2C and 5-HT2A receptors. Sympathetic nerve and sensory afferents partly contributed to 5-HT effects. 5-HT2C and 5-HT2A receptors could be promising targets for ureteral stone expulsion.

New Insights Into the Anticonvulsant Effects of Essential Oil From Melissa officinalis L. (Lemon Balm).

Melissa officinalis L. is used in traditional European and Iranian folk medicines to treat a plethora of neurological diseases including epilepsy. We utilized the in vitro and in vivo models of epilepsy to probe the anticonvulsant potentials of essential oil from M. officinalis (MO) to gain insight into the scientific basis for its applications in traditional medicine for the management of convulsive disorders. MO was evaluated for effects on maximal electroshock (MES) and pentylenetetrazole (PTZ) -induced seizures in mice, on 4–aminopyridine (4-AP)-brain slice model of epilepsy and sustained repetitive firing of current clamped neurons; and its ameliorative effects were examined on seizure severity, anxiety, depression, cognitive dysfunction, oxidative stress and neuronal cell loss in PTZ-kindled rats. MO reversibly blocked spontaneous ictal-like discharges in the 4-AP-brain slice model of epilepsy and secondary spikes from sustained repetitive firing, suggesting anticonvulsant effects and voltage-gated sodium channel blockade. MO protected mice from PTZ– and MES–induced seizures and mortality, and ameliorated seizure severity, fear-avoidance, depressive-like behavior, cognitive deficits, oxidative stress and neuronal cell loss in PTZ–kindled rats. The findings warrant further study for the potential use of MO and/or its constituent(s) as adjunctive therapy for epileptic patients.

Long-term effect of safinamide on primary motor cortex excitability and plasticity in Parkinson's disease: A TMS study

In a recent Transcranial Magnetic Stimulation (TMS) study, we demonstrated abnormally enhanced Short-Interval Intracortical Facilitation (SICF) in patients with Parkinson's Disease (PD). These abnormalities reflect increased glutamatergic transmission in primary motor cortex (M1). A short-term treatment with safinamide at 100 mg/day can restore SICF in PD by reducing glutamatergic transmission via blockade of voltage-gated sodium channels. We here examined the long-term effect of chronic treatment with safinamide 100 mg/day on SICF and other measures of M1 excitability and plasticity in PD.

Identification of a novel distension-evoked motility pattern in the mouse uterus.

The dynamic changes in uterine contractility in response to distension are incompletely understood. Rhythmic, propagating contractions of nonpregnant uterine smooth muscle occur in the absence of nerve activity (i.e., myogenic), events that decline during pregnancy and reemerge at parturition. We therefore sought to determine how myogenic contractions of the nonpregnant uterus are affected by distension, which might provide mechanistic clues underlying distension-associated uterine conditions such as preterm birth. Uteri isolated from nulliparous adult female mice in proestrus were video imaged to generate spatiotemporal maps, and myoelectrical activity simultaneously recorded using extracellular suction electrodes. Motility patterns were examined under basal conditions and following ramped intraluminal distension with fluid to 5 and 10 cmH2O. Intraluminal distension caused pressure-dependent changes in the frequency, amplitude, propagation speed, and directionality of uterine contractions, which reversed upon pressure release. Altered burst durations of underlying smooth muscle myoelectric events were concurrently observed, although action potential spike intervals were unchanged. Voltage-gated sodium channel blockade [tetrodotoxin (TTX); 0.6 µM] attenuated both the amplitude of contractions and burst duration of action potentials, whereas all activity was abolished by L-type calcium channel blockade (nifedipine; 1 µM). These data suggest that myogenic motility patterns of the nonpregnant mouse uterus are sensitive to changes in intraluminal pressure and, at high pressures, may be modulated by voltage-gated sodium channel activity. Future studies may investigate whether similar distension-evoked changes occur in the pregnant uterus and the possible pathophysiological role of such activity in the development of preterm birth.

Potential induction of epileptic spasms by nonselective voltage-gated sodium channel blockade: Interaction with etiology

PurposeEpileptic spasms are often preceded by focal (or multifocal) seizures. Based on a series of case reports suggesting that carbamazepine and oxcarbazepine may induce epileptic spasms, we set out to rigorously evaluate the potential association between exposure to voltage-gated sodium channel blockade and latency to epileptic spasms. MethodsWe identified 50 cases (children with focal seizures and evolution to epileptic spasms) and 50 controls (children with focal seizures without evolution to epileptic spasms). For each patient, we reviewed all sequential neurology encounters between onset of epilepsy and emergence of epileptic spasms. For each encounter we recorded seizure-frequency and all anti-seizure therapy exposures. Using multivariable Cox proportional hazards regression, we evaluated the association between voltage-gated sodium channel exposure (carbamazepine, oxcarbazepine, lacosamide, or phenytoin) and latency to epileptic spasms onset, with adjustment for etiology and seizure-frequency. ResultsLatency to epileptic spasms onset was independently associated with exposure to sodium channel blockade (hazard ratio = 2.4; 95% CI 1.1–5.2; P = 0.03) and high-risk etiology (hazard ratio = 2.8; 95% CI 1.5–5.1; P = 0.001). With assessment for interaction between sodium channel blockade and etiology, we identified an estimated 7-fold increased risk of epileptic spasms with the combination of sodium channel blockade and high-risk etiology (hazard ratio = 7.0, 95% CI 2.5–19.8; P < 0.001). ConclusionThis study suggests that voltage-gated sodium channel blockade may induce epileptic spasms among children at risk on the basis of etiology. Further study is warranted to replicate these findings, ascertain possible drug- and dose-specific risks, and identify potential mechanisms of harm.

Co-Application of Eugenol and QX-314 Elicits the Prolonged Blockade of Voltage-Gated Sodium Channels in Nociceptive Trigeminal Ganglion Neurons.

Local anesthetics (LAs) can completely block nociception by inhibiting voltage-gated sodium channels (VGSCs), and thus, blocking action potentials (APs) within sensory neurons. As one of the several LAs, eugenol is used for dental pain treatment. It reportedly features multiple functions in regulating diverse ion channels. This study aimed to investigate the long-lasting analgesic effect of eugenol alone, as well as that of the combination of eugenol as a noxious-heat-sensitive transient receptor potential vanilloid 1 (TRPV1) channel agonist and a permanently charged sodium channel blocker (QX-314), on neuronal excitability in trigeminal ganglion (TG) neurons. Eugenol alone increased inward current in a dose-dependent manner in capsaicin-sensitive TG neurons. Eugenol also inhibited the VGSC current and AP. These effects were reversed through wash-out. The combination of eugenol and QX-314 was evaluated in the same manner. The combination completely inhibited the VGSC current and AP. However, these effects were not reversed and were continuously blocked even after wash-out. Taken together, our results suggest that, in contrast to the effect of eugenol alone, the combination of eugenol and QX-314 irreversibly and selectively blocked VGSCs in TG neurons expressing TRPV1.

Partial Blockade of Human Voltage-Dependent Sodium Channels by the Marine Toxins Azaspiracids.

Azaspiracid toxins were first identified at the end of the last century in Irish mussels, and during the last two decades considerable cytotoxic and neurotoxic effects caused by these toxins have been described. Azaspiracids are synthesized by dinoflagellates and accumulate in several species of filter-feeding bivalve mollusks, thereby incorporating into the food chain and causing human intoxications. Among the cellular effects of azaspiracids, inhibition of spikes in neurons and hyperpolarization of the neuronal membrane potential have been reported; however, the underlying processes leading to these effects were never elucidated. In this regard, initial studies reported no activity of the toxin in neuronal voltage-gated sodium channels, and a recent work described no effect of azaspiracid-1 on the inactivation kinetics of voltage-gated sodium channels; however, the relationship between the known alterations of the cytoskeleton caused by these toxins and their effects on ion channels has never been evaluated. In this work, the cytotoxic effect of azaspiracids was evaluated in human cells as well as their activity on voltage-gated sodium channels and in cell morphology in order to unravel the cellular targets involved in the mechanism of action of this group of marine toxins. The data reported here demonstrate, for the first time, that both azaspiracid-1 and azaspiracid-2 caused a rapid concentration-dependent inhibition of the amplitude of voltage-gated sodium currents without affecting their inactivation kinetics, an effect that was increased after long-term treatment of the cells with the toxin. Simultaneously, long-term exposure of the cells to azaspiracids caused a profound alteration of the cell cytoskeleton and decreased the metabolic activity of human cells. Altogether, the data presented here indicate that the partial blockade of voltage-gated sodium channels by these toxins is not related with their effect on the actin cytoskeleton. However, since azaspiracids are common toxins in European waters, their effect on voltage-gated sodium channels, first reported here, should be considered to avoid synergistic toxicity with other marine toxins that are known potent blockers of sodium channels such as the saxitoxins and tetrodotoxins, but further studies are needed in order to elucidate how these compounds alter ion homeostasis.

Neosaxitoxin Inhibits the Expression of Inflammation Markers of the M1 Phenotype in Macrophages.

(1) Background: Neosaxitoxin (NeoSTX) has been used as a local anesthetic, but its anti-inflammatory effects have not been well defined. In the present study, we investigate the effects of NeoSTX on lipopolysaccharide (LPS)-activated macrophages. (2) Methods: Raw 264.7 and equine PBMC cells were incubated with or without 100 ng/mL LPS in the presence or absence of NeoSTX (1µM). The expression of inflammatory mediators was assessed: nitric oxide (NO) content using the Griess assay, TNF-α content using the ELISA assay, and mRNA of inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) using a real-time polymerase chain reaction. (3) Results: NeoSTX (1 μM) significantly inhibited the release of NO, TNF-α, and expression of iNOS, IL-1β, and TNF-α in LPS-activated macrophages of both species studied. Furthermore, our study shows that the LPS-induced release of inflammatory mediators was suppressed by NeoSTX. Additionally, NeoSTX deactivated polarized macrophages to M1 by LPS without compromising its polarization towards M2. (4) Conclusions: NeoSTX inhibits LPS-induced release of inflammatory mediators from macrophages, and these effects may be mediated by the blockade of voltage-gated sodium channels (VGSC).

Voltage-gated sodium channel inhibitor reduces atherosclerosis by modulating monocyte/macrophage subsets and suppressing macrophage proliferation

Inflammatory monocyte and macrophage subset accumulation during the inflammatory response that drives atherosclerosis can exacerbate the extent of atherosclerosis. It has been demonstrated that voltage-gated sodium channels (VGSCs) can regulate cell bioactivities in monocytes/macrophages. We hypothesized that blockade of mononuclear phagocyte VGSCs was atheroprotective through monocyte/macrophage subset modulation and macrophage proliferation suppression in atherosclerotic lesions. In this experimental study, when VGSCs were knocked down with RNA interference plasmid transfection in mouse peripheral blood monocytes and monocyte-macrophage lineage RAW264.7 cells in vitro, the biological characteristics of proliferation, phagocytosis, and migration in RAW264.7 cells declined. In addition, suppression of LPS-induced M1 polarization and facilitation of IL-4-induced M2 polarization were also observed. In an in vivo study, ApoE knockout (ApoE−/−) mice were fed a standard chow diet (CD) or a western diet (WD). After feeding with phenytoin (PHT), no significant differences were detected in plasma lipids, and the anti-inflammatory phenotypes of both monocytes and macrophages were elevated and proinflammatory phenotypes declined. The local proliferation of macrophages was also distinctly suppressed, along with a significant reduction in atheromatous plaques. In conclusion, blockade of VGSCs in the mononuclear phagocyte system reduced atherosclerotic lesions, which may occur through altering monocyte/macrophage subsets and suppressing macrophage proliferation in atherosclerotic plaques. Blockage of VGSCs may play an important role in cardiovascular protection.

A review and new insights to antimicrobial action of local anesthetics.

Local anesthetics (LAs) are medications which can provide analgesia in distinct body regions through the blockade of voltage-gated sodium channels. Besides pain management, the supplemental role of LAs as antimicrobial agents has been documented in several studies. Different databases including PubMed, Scopus, and Web of Science with the name of different local anesthetics and related names for antimicrobial keywords were searched without time limitation. This review summarized different in vitro and in vivo studies regarding antimicrobial effects of different LAs with focuses on antimicrobial applications of most studied LAs, interaction with different agents which combined with LAs, and mechanisms of action and structural dependence of LAs antibacterial effects. Among different LAs, lidocaine is the most studied preparation. Reduction of the incidence of endophthalmitis after intravitreal injection, prophylaxis for surgical wound infections, prevention of the incidence of catheter-associated infections, oral biofilm reduction on the buccal mucosa, and prevention against bacteria that produced nosocomial infection are some examples of lidocaine antimicrobial application. Studies showed that different factors including structure, concentration, duration of exposure, type of microorganism tested, and temperature affect the degree of LA antimicrobial activity. In addition, various agents such as antibiotics, preservatives, opioids, epinephrine, and propofol can combine with LAs and affect their antimicrobial properties through synergistic or antagonistic action. Due to antibacterial activities, LAs could be applied in a clinic for prophylaxis of surgical site infection. In the application of LAs prior to diagnostic procedures caution should be needed; otherwise, when culturing the specimen, they could lead to false negative results.

Revealing oxidative damage to enzymes of carbohydrate metabolism in yeast: An integration of 2D DIGE, quantitative proteomics, and bioinformatics.

Clinical usage of lidocaine, a pro-oxidant has been linked with severe, mostly neurological complications. The mechanism(s) causing these complications is independent of the blockade of voltage-gated sodium channels. The budding yeast Saccharomyces cerevisiae lacks voltage-gated sodium channels, thus provides an ideal system to investigate lidocaine-induced protein and pathway alterations. Whole-proteome alterations leading to these complications have not been identified. To address this, S. cerevisiae was grown to stationary phase and exposed to an LC50 dose of lidocaine. The differential proteomes of lidocaine treatment and control were resolved 6 h post exposure using 2D DIGE. Amine reactive dyes and carbonyl reactive dyes were used to assess protein abundance and protein oxidation, respectively. Quantitative analysis of these dyes (⩾ 1.5-fold alteration, p ⩽ 0.05) revealed a total of 33 proteoforms identified by MS differing in abundance and/or oxidation upon lidocaine exposure. Network analysis showed enrichment of apoptotic proteins and cell wall maintenance proteins, while the abundance of proteins central to carbohydrate metabolism, such as triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase, and redox proteins superoxide dismutase and peroxiredoxin were significantly decreased. Enzymes of carbohydrate metabolism, such as phosphoglycerate kinase and enolase, the TCA cycle enzyme aconitase, and multiple ATP synthase subunits were found to be oxidatively modified. Also, the activity of aconitase was found to be decreased. Overall, these data suggest that toxic doses of lidocaine induce significant disruption of glycolytic pathways, energy production, and redox balance, potentially leading to cell malfunction and death.

Lidocaine Enhances Contractile Function of Ischemic Myocardial Regions in Mouse Model of Sustained Myocardial Ischemia.

RationalePerioperative myocardial ischemia is common in high-risk patients. The use of interventional revascularisation or even thrombolysis is limited in this patient subset due to exceedingly high bleeding risks. Blockade of voltage-gated sodium channels (VGSC) with lidocaine had been suggested to reduce infarct size and cardiomyocyte cell death in ischemia/reperfusion models. However, the impact of lidocaine on cardiac function during sustained ischemia still remains unclear.MethodsSustained myocardial ischemia was induced by ligation of the left anterior descending artery in 12–16 weeks old male BALB/c mice. Subcutaneous lidocaine (30 mg/kg) was used to block VGSC. Cardiac function was quantified at baseline and at 72h by conventional and speckle-tracking based echocardiography to allow high-sensitivity in vivo phenotyping. Infarct size and cardiomyocyte cell death were assessed post mortem histologically and indirectly using troponin measurements.ResultsIschemia strongly impaired both, global systolic and diastolic function, which were partially rescued in lidocaine treated in mice. No differences regarding infarct size and cardiomyocyte cell death were observed. Mechanistically, and as shown with speckle-tracking analysis, lidocaine specifically improves residual contractility in the ischemic but not in the remote, non-ischemic myocardium.ConclusionVGSC blockade with lidocaine rescues function of ischemic myocardium as a potential bridging to revascularisation in the setting of perioperative myocardial ischemia.

Antimanic-like effects of (R)-(−)-carvone and (S)-(+)-carvone in mice

Carvone is a monoterpene that is present in spearmint (Mentha spicata) and caraway (Carum carvi) essential oils and has been shown to have anticonvulsant effects, likely through the blockade of voltage-gated sodium channels, and anxiolytic-like effects. Considering that some anticonvulsants that blocked voltage-gated sodium channels (e.g., sodium valproate and carbamazepine) exert clinical antimanic effects, the aim of the present study was to evaluate (R)-(−)-carvone and (S)-(+)-carvone in animal models of mania (i.e., hyperlocomotion induced by methylphenidate and sleep deprivation).Mice that were treated with methylphenidate (5mg/kg) or sleep-deprived for 24h using a multiple-platform protocol exhibited an increase in locomotor activity in an automated activity box. This effect was blocked by pretreatment with acute (R)-(−)-carvone (50–100mg/kg), (S)-(+)-carvone (50–100mg/kg), and lithium (100mg/kg, positive control). These doses did not alter spontaneous locomotor activity in the methylphenidate-induced experiments while (S)-(+)-carvone decreased spontaneous locomotor activity in sleep deprivation experiment, indicating a sedative effect. Chronic 21-day treatment with (R)-(−)-carvone (100mg/kg), (S)-(+)-carvone (100mg/kg), and lithium also prevented methylphenidate-induced hyperactivity.The present results suggest that carvone may have an antimanic-like effect.

Blockade of voltage-gated sodium channels inhibits invasion of endocrine-resistant breast cancer cells.

Voltage-gated Na+ channels (VGSCs) are membrane proteins which are normally expressed in excitable cells but have also been detected in cancer cells, where they are thought to be involved in malignancy progression. In this study we examined the ion current and expression profile of VGSC (Nav1.5) in estrogen receptor (ER)-positive (MCF-7) and silenced (pII) breast cancer cells and its possible influence on their proliferation, motility and invasion. VGSC currents were analysed by whole cell patch clamp recording. Nav1.5 expression and localization, in response to EGF stimulation, was examined by western blotting and immunofluorescence respectively. Cell invasion (under-agarose and Matrigel assays), motility (wound healing assay) and proliferation (MTT assay) were assessed in pII cells in response to VGSC blockers, phenytoin (PHT) and tetrodotoxin (TTX), or by siRNA knockdown of Nav1.5. The effect of PHT and TTX on modulating EGF-induced phosphorylation of Akt and ERK1/2 was determined by western blotting. Total matrix metalloproteinase (MMP) was determined using a fluorometric-based activity assay. The level of various human proteases was detected by using proteome profiler array kit. VGSC currents were detected in pII cells, but were absent in MCF-7. Nav1.5 showed cytoplasmic and perinuclear expression in both MCF-7 and pII cells, with enhanced expression upon EGF stimulation. Treatment of pII cells with PHT, TTX or siRNA significantly reduced invasion towards serum components and EGF, in part through reduction of P-ERK1/2 and proteases such as cathepsin E, kallikrein-10 and MMP-7, as well as total MMP activity. At high concentrations, PHT inhibited motility while TTX reduced cell proliferation. Pharmacological or genetic blockade of Nav1.5 may serve as a potential anti-metastatic therapy for breast cancer.

Sodium channel blockers for neuroprotection in multiple sclerosis.

Multiple sclerosis (MS) is an autoimmune, inflammatory, demyelinating disease of the central nervous system (CNS), which can occur in many parts of the CNS and result in a wide range of symptoms including sensory impairment, fatigue, walking or balance problems, visual impairment, vertigo and cognitive disabilities. At present, the most commonly used MS treatments are immunomodulating agents, but they have little effect on the disability. Experimental studies show that sodium (Na(+)) accumulation leads to intracellular calcium (Ca(2+)) release, and the increased calcium levels can activate nitric oxide synthase and harmful proteases and lipases. These factors contribute to axonal injury in people with MS. If partial blockade of voltage-gated sodium channels could result in neuroprotection, this would be of benefit for preventing disability progression in these people. Neuroprotection is emerging as a potentially important strategy for preventing disability progression in people with MS. To assess the efficacy and safety of sodium channel blockers for neuroprotection in people with MS to prevent the occurrence of disability and alleviate the burden of the disease. We searched the Cochrane Multiple Sclerosis and Rare Diseases of the Central Nervous System Group Specialised Register (27 August 2015) which, among other sources, contains references from the Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Library 2015, Issue (8), MEDLINE (1966 to August 2015), EMBASE (1974 to August 2015), Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1981 to August 2015), Latin American and Caribbean Health Science Information Database (LILACS) (1982 to August 2015), ClinicalTrials.gov (http://clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Portal (ICTRP) search portal (http://apps.who.int/trialsearch). In addition, we searched four Chinese databases, ongoing trials registers and relevant reference lists. Randomised controlled trials (RCTs) that examined sodium channel blockers used alone or as an add-on to any approved treatments for MS. Two review authors independently selected trials, assessed trial quality and extracted the data. Only one study evaluating lamotrigine in secondary progressive MS was eligible. One hundred and twenty people were included, 61 randomly assigned to lamotrigine treatment and 59 to placebo treatment. The average age of participants in the two groups was 51.9 years and 50.1 years, respectively. The proportion of male participants was 27.5%. The period of follow-up was 2 years. No data were found on disability progression and people who experienced relapses. No significant differences were found for serious adverse events between the two groups. Treatment with lamotrigine was associated with more rashes (20% vs 5%, P value 0.03) and transient, dose-related deterioration of mobility (66% vs 34%, P value 0.001) than placebo. Furthermore, no significant difference between the two groups was found in the magnetic resonance imaging (MRI) measurements of cerebral atrophy, Expanded Disability Status Score changes, Multiple Sclerosis Functional Composite score changes. This study was judged to be at high risk of bias. This review will be updated when the three ongoing studies we identified are completed. The quality of evidence was judged to be very low due to the low number of available studies and included participants. There is a lack of evidence to address the review question on the efficacy of sodium channel blockers for people with MS. Assessment of the three ongoing trials might change this conclusion. Further high-quality large scale studies are needed.

Neuroprotection in Experimental Autoimmune Encephalomyelitis and Progressive Multiple Sclerosis by Cannabis-Based Cannabinoids.

Multiple sclerosis (MS) is the major immune-mediated, demyelinating, neurodegenerative disease of the central nervous system. Compounds within cannabis, notably Δ9-tetrahydrocannabinol (Δ9-THC) can limit the inappropriate neurotransmissions that cause MS-related problems and medicinal cannabis is now licenced for the treatment of MS symptoms. However, the biology indicates that the endocannabinoid system may offer thepotential to control other aspects of disease. Although there is limited evidence that the cannabinoids from cannabis are having significant immunosuppressive activities that will influence relapsing autoimmunity, we and others can experimentally demonstrate that they may limit neurodegeneration that drives progressive disability. Here we show that synthetic cannabidiol can slow down the accumulation of disability from the inflammatory penumbra during relapsing experimental autoimmune encephalomyelitis (EAE) in ABH mice, possibly via blockade of voltage-gated sodium channels. In addition, whilst non-sedating doses of Δ9-THC do not inhibit relapsing autoimmunity, they dose-dependently inhibit the accumulation of disability during EAE. They also appear to slow down clinical progression during MS in humans. Although a 3year, phase III clinical trial did not detect a beneficial effect of oral Δ9-THC in progressive MS, a planned subgroup analysis of people with less disability who progressed more rapidly, demonstrated a significant slowing of progression by oral Δ9-THC compared to placebo. Whilst this may support the experimental and biological evidence for a neuroprotective effect by the endocannabinoid system in MS, it remains to be established whether this will be formally demonstrated in further trials of Δ9-THC/cannabis in progressive MS.

Anaesthetic tricaine acts preferentially on neural voltage-gated sodium channels and fails to block directly evoked muscle contraction.

Movements in animals arise through concerted action of neurons and skeletal muscle. General anaesthetics prevent movement and cause loss of consciousness by blocking neural function. Anaesthetics of the amino amide-class are thought to act by blockade of voltage-gated sodium channels. In fish, the commonly used anaesthetic tricaine methanesulphonate, also known as 3-aminobenzoic acid ethyl ester, metacaine or MS-222, causes loss of consciousness. However, its role in blocking action potentials in distinct excitable cells is unclear, raising the possibility that tricaine could act as a neuromuscular blocking agent directly causing paralysis. Here we use evoked electrical stimulation to show that tricaine efficiently blocks neural action potentials, but does not prevent directly evoked muscle contraction. Nifedipine-sensitive L-type Cav channels affecting movement are also primarily neural, suggesting that muscle Nav channels are relatively insensitive to tricaine. These findings show that tricaine used at standard concentrations in zebrafish larvae does not paralyse muscle, thereby diminishing concern that a direct action on muscle could mask a lack of general anaesthesia.

Voltage-dependent blockade by bupivacaine of cardiac sodium channels expressed in Xenopus oocytes.

Bupivacaine ranks as the most potent and efficient drug among class I local anesthetics, but its high potential for toxic reactions severely limits its clinical use. Although bupivacaine-induced toxicity is mainly caused by substantial blockade of voltage-gated sodium channels (VGSCs), how these hydrophobic molecules interact with the receptor sites to which they bind remains unclear. Nav1.5 is the dominant isoform of VGSCs expressed in cardiac myocytes, and its dysfunction may be the cause of bupivacaine-triggered arrhythmia. Here, we investigated the effect of bupivacaine on Nav1.5 within the clinical concentration range. The electrophysiological measurements on Nav1.5 expressed in Xenopus oocytes showed that bupivacaine induced a voltage- and concentration-dependent blockade on the peak of I Na and the half-maximal inhibitory dose was 4.51 μmol/L. Consistent with other local anesthetics, bupivacaine also induced a use-dependent blockade on Nav1.5 currents. The underlying mechanisms of this blockade may contribute to the fact that bupivacaine not only dose-dependently affected the gating kinetics of Nav1.5 but also accelerated the development of its open-state slow inactivation. These results extend our knowledge of the action of bupivacaine on cardiac sodium channels, and therefore contribute to the safer and more efficient clinical use of bupivacaine.

Sodium Channels Contribute to Degeneration of Dorsal Root Ganglion Neurites Induced by Mitochondrial Dysfunction in anIn VitroModel of Axonal Injury

Axonal degeneration occurs in multiple neurodegenerative disorders of the central and peripheral nervous system. Although the underlying molecular pathways leading to axonal degeneration are incompletely understood, accumulating evidence suggests contributions of impaired mitochondrial function, disrupted axonal transport, and/or dysfunctional intracellular Ca(2+)-homeostasis in the injurious cascade associated with axonal degeneration. Utilizing an in vitro model of axonal degeneration, we studied a subset of mouse peripheral sensory neurons in which neurites were exposed selectively to conditions associated with the pathogenesis of axonal neuropathies in vivo. Rotenone-induced mitochondrial dysfunction resulted in neurite degeneration accompanied by reduced ATP levels and increased ROS levels in neurites. Blockade of voltage-gated sodium channels with TTX and reverse (Ca(2+)-importing) mode of the sodium-calcium exchanger (NCX) with KB-R7943 partially protected rotenone-treated neurites from degeneration, suggesting a contribution of sodium channels and reverse NCX activity to the degeneration of neurites resulting from impaired mitochondrial function. Pharmacological inhibition of the Na(+)/K(+)-ATPase with ouabain induced neurite degeneration, which was attenuated by TTX and KB-R7943, supporting a contribution of sodium channels in axonal degenerative pathways accompanying impaired Na(+)/K(+)-ATPase activity. Conversely, oxidant stress (H2O2)-induced neurite degeneration was not attenuated by TTX. Our results demonstrate that both energetic and oxidative stress targeted selectively to neurites induces neurite degeneration and that blockade of sodium channels and of reverse NCX activity blockade partially protects neurites from injury due to energetic stress, but not from oxidative stress induced by H2O2.