Kainate-induced currents in rat cortical neurons in culture are modulated by riluzole

Ca2+-regulated expression of high affinity methylaminoisobutryic acid transport in hippocampal neurons inhibited by riluzole and novel neuroprotective aminothiazoles

High affinity methylaminoisobutyric acid(MeAIB)/glutamine(Gln) transport activity regulated by neuronal firing occurs at the plasma membrane in mature rat hippocampal neuron-enriched cultures. Spontaneous Ca2+-regulated transport activity was similarly inhibited by riluzole, a benzothiazole anticonvulsant agent, and by novel naphthalenyl substituted aminothiazole derivatives such as SKA-378. Here, we report that spontaneous transport activity is stimulated by 4-aminopyridine (4-AP) and that phorbol-myristate acetate (PMA) increases high K+ stimulated transport activity that is inhibited by staurosporine. 4-AP-stimulated spontaneous and PMA-stimulated high K+-induced transport is not present at 7 days in vitro (DIV) and is maximal by DIV∼21. The relative affinity for MeAIB is similar for spontaneous and high K+-stimulated transport (Km ∼ 50 μM) suggesting that a single transporter is involved. While riluzole and SKA-378 inhibit spontaneous transport with equal potency (IC50 ∼ 1 μM), they exhibit decreased (∼3-5 X) potency for 4-AP-stimulated spontaneous transport. Interestingly, high K+-stimulated MeAIB transport displays lower and differential sensitivity to the two compounds. SKA-378-related halogenated derivatives of SKA-75 (SKA-219, SKA-377 and SKA-375) preferentially inhibit high K+-induced expression of MeAIB transport activity at the plasma membrane (IC50 < 25 μM), compared to SKA-75 and riluzole (IC50 > 100 μM). Ca2+-dependent spontaneous and high K+-stimulated MeAIB transport activity is blocked by ω-conotoxin MVIIC, ω-agatoxin IVA, ω-agatoxin TK (IC50 ∼ 500 nM) or cadmium ion (IC50 ∼ 20 μM) demonstrating that P/Q-type CaV channels that are required for activity-regulated presynaptic vesicular glutamate (Glu) release are also required for high-affinity MeAIB transport expression at the plasma membrane. We suggest that neural activity driven and Ca2+ dependent trafficking of the high affinity MeAIB transporter to the plasma membrane is a unique target to understand mechanisms of Glu/Gln recycling in synapses and acute neuroprotection against excitotoxic presynaptic Glu induced neural injury.

An In Vivo Electroencephalographic Analysis of the Effect of Riluzole against Limbic and Absence Seizure and Comparison with Glutamate Antagonists

BACKGROUND

Riluzole (RLZ) has demonstrated neuroprotective effects in several neurological disorders. These neuroprotective effects seem to be mainly due to its ability to inhibit the excitatory glutamatergic neurotransmission, acting on different targets located both at the presynaptic and postsynaptic levels.

METHODS

In the present study, we evaluated the effects of Riluzole (RLZ) against limbic seizures, induced by AMPA, kainate, and NMDA receptor agonists in Sprague-Dawley rats, and in a well-validated genetic model of absence epilepsy, the WAG/Rij rat. Furthermore, in this latter model, we also studied the effect of RLZ in co-administration with the competitive NMDA receptor antagonist, CPP, or the non-competitive AMPA receptor antagonist, THIQ-10c, on spike-wave discharges (SWDs) in WAG/Rij rats, to understand the potential involvement of AMPA and NMDA receptors in the anti-absence effect of RLZ.

RESULTS

In Sprague-Dawley rats, RLZ pretreatment significantly reduced the limbic seizure severity induced by glutamatergic agonists, suggesting an antagonism of RLZ mainly on NMDA rather than non-NMDA receptors. RLZ also reduced SWD parameters in WAG/Rij rats. Interestingly, the co-administration of RLZ with CPP did not increase the anti-absence activity of RLZ in this model, advocating a competitive effect on the NMDA receptor. In contrast, the co-administration of RLZ with THIQ-10c induced an additive effect against absence seizure in WAG/Rij rats.

CONCLUSIONS

these results suggest that the antiepileptic effects of RLZ, in both seizure models, can be mainly due to the antagonism of the NMDA glutamatergic receptors.

Administration of the glutamate-modulating drug, riluzole, after stress prevents its delayed effects on the amygdala in male rats

Extracellular glutamate levels are elevated across brain regions immediately after stress. Despite sharing common features in their genesis, the patterns of stress-induced plasticity that eventually take shape are strikingly different between these brain areas. While stress causes structural and functional deficits in the hippocampus, it has the opposite effect on the amygdala. Riluzole, an FDA-approved drug known to modulate glutamate release and facilitate glutamate clearance, prevents stress-induced deficits in the hippocampus. But whether the same drug is also effective in countering the opposite effects of stress in the amygdala remains unexplored. We addressed this question by using a rat model wherein even a single 2-h acute immobilization stress causes a delayed expression of anxiety-like behavior, 10 days later, alongside stronger excitatory synaptic connectivity in the basolateral amygdala (BLA). This temporal profile-several days separating the acute stressor and its delayed impact-allowed us to test if these effects can be prevented by administering riluzole in drinking water after acute stress. Poststress riluzole not only prevented the delayed increase in anxiety-like behavior on the elevated plus maze but also blocked the increase in spine density on BLA neurons 10 days later. Further, stress-induced increase in the frequency of miniature excitatory postsynaptic currents recorded in BLA slices, 10 days later, was also blocked by the same poststress riluzole administration. Together, these findings underscore the importance of therapeutic strategies, aimed at glutamate uptake and modulation, in correcting the delayed behavioral, physiological, and morphological effects of stress on the amygdala.

Riluzole and novel naphthalenyl substituted aminothiazole derivatives prevent acute neural excitotoxic injury in a rat model of temporal lobe epilepsy

Epileptogenic seizures, or status epilepticus (SE), leads to excitotoxic injury in hippocampal and limbic neurons in the kainic acid (KA) animal model of temporal lobe epilepsy (TLE). Here, we have further characterized neural activity regulated methylaminoisobutryic acid (MeAIB)/glutamine transport activity in mature rat hippocampal neurons in vitro that is inhibited by riluzole (IC₅₀ = 1 μM), an anti-convulsant benzothiazole agent. We screened a library of riluzole derivatives and identified SKA-41 followed by a second screen and synthesized several novel chlorinated aminothiazoles (SKA-377, SKA-378, SKA-379) that are also potent MeAIB transport inhibitors in vitro, and brain penetrant following systemic administration. When administered before KA, SKA-378 did not prevent seizures but still protected the hippocampus and several other limbic areas against SE-induced neurodegeneration at 3d. When SKA-377 - 379, (30 mg/kg) were administered after KA-induced SE, acute neural injury in the CA3, CA1 and CA4/hilus was also largely attenuated. Riluzole (10 mg/kg) blocks acute neural injury. Kinetic analysis of SKA-378 and riluzoles' blockade of Ca²⁺-regulated MeAIB transport in neurons in vitro indicates that inhibition occurs via a non-competitive, indirect mechanism. Sodium channel Na_V1.6 antagonism blocks neural activity regulated MeAIB/Gln transport in vitro (IC₅₀ = 60 nM) and SKA-378 is the most potent inhibitor of Na_V1.6 (IC₅₀ = 28 μM) compared to Na_V1.2 (IC₅₀ = 118 μM) in heterologous cells. However, pharmacokinetic analysis suggests that sodium channel blockade may not be the predominant mechanism of neuroprotection here. Riluzole and our novel aminothiazoles are agents that attenuate acute neural hippocampal injury following KA-induced SE and may help to understand mechanisms involved in the progression of epileptic disease.

Riluzole prevents stress-induced spine plasticity in the hippocampus but mimics it in the amygdala

Stress elicits divergent patterns of structural plasticity in the amygdala and hippocampus. Despite these contrasting effects, at least one of the immediate consequences of stress – elevated levels of extracellular glutamate – is similar in both brain areas. This raises the possibility that the contrasting effects of stress on neuronal plasticity is shaped by differences in astrocytic glutamate clearance in these two brain areas. Although astrocytes play a key role in glutamate reuptake, past analyses of, and interventions against, stress-induced plasticity have focused largely on neurons. Hence, we tested the impact of riluzole, which potentiates glutamate clearance by astrocytic glutamate transporters, on principal neurons and astrocytes in the basal amygdala (BA) and hippocampal area CA1. Chronic immobilization stress reduced spine-density on CA1 pyramidal neurons of male rats. Riluzole, administered in the drinking water during chronic stress, prevented this decrease; but, the drug by itself had no effect. In contrast, the same chronic stress enhanced spine-density on BA principal neurons, and this effect, unlike area CA1, was not reversed by riluzole. Strikingly, riluzole treatment alone also caused spinogenesis in the BA. Thus, the same riluzole treatment that prevented the effect of stress on spines in the hippocampus, mimicked its effect in the amygdala. Further, chronic stress and riluzole alone decreased the neuropil volume occupied by astrocytes in both the BA and CA1 area. Riluzole treatment in stressed animals, however, did not reverse or further add to this reduction in either region. Thus, while the effects on astrocytes were similar, neuronal changes were distinct between the two areas following stress, riluzole and the two together. Therefore, similar to the impact of repeated stress, pharmacological potentiation of glutamate clearance, with or without stress, also leads to differential effects on dendritic spines in principal neurons of the amygdala and hippocampus. This highlights differences in the astrocytic glutamate reuptake machinery that are likely to have important functional consequences for stress-induced dysfunction, and its reversal, in two brain areas implicated in stress-related psychiatric disorders.

Decreased Mitochondrial Function, Biogenesis, and Degradation in Peripheral Blood Mononuclear Cells from Amyotrophic Lateral Sclerosis Patients as a Potential Tool for Biomarker Research

Amyotrophic lateral sclerosis (ALS) is a multifactorial and progressive neurodegenerative disease of unknown etiology. Due to ALS’s unpredictable onset and progression rate, the search for biomarkers that allow the detection and tracking of its development and therapeutic efficacy would be of significant medical value. Considering that alterations of energy supply are one of ALS’s main hallmarks and that a correlation has been established between gene expression in human brain tissue and peripheral blood mononuclear cells (PBMCs), the present work investigates whether changes in mitochondrial function could be used to monitor ALS. To achieve this goal, PBMCs from ALS patients and control subjects were used; blood sampling is a quite non-invasive method and is cost-effective. Different parameters were evaluated, namely cytosolic calcium levels, mitochondrial membrane potential, oxidative stress, and metabolic compounds levels, as well as mitochondrial dynamics and degradation. Altogether, we observed lower mitochondrial calcium uptake/retention, mitochondria depolarization, and redox homeostasis deregulation, in addition to a decrease in critical metabolic genes, a diminishment in mitochondrial biogenesis, and an augmentation in mitochondrial fission and autophagy-related gene expression. All of these changes can contribute to the decreased ATP and pyruvate levels observed in ALS PBMCs. Our data indicate that PBMCs from ALS patients show a significant mitochondrial dysfunction, resembling several findings from ALS’ neural cells/models, which could be exploited as a powerful tool in ALS research. Our findings can also guide future studies on new pharmacological interventions for ALS since assessments of brain samples are challenging and represent a relevant limited strategy.

Cortical Circuit Dysfunction as a Potential Driver of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that affects selected cortical and spinal neuronal populations, leading to progressive paralysis and death. A growing body of evidences suggests that the disease may originate in the cerebral cortex and propagate in a corticofugal manner. In particular, transcranial magnetic stimulation studies revealed that ALS patients present with early cortical hyperexcitability arising from a combination of increased excitability and decreased inhibition. Here, we discuss the possibility that initial cortical circuit dysfunction might act as the main driver of ALS onset and progression, and review recent functional, imaging and transcriptomic studies conducted on ALS patients, along with electrophysiological, pathological and transcriptomic studies on animal and cellular models of the disease, in order to evaluate the potential cellular and molecular origins of cortical hyperexcitability in ALS.

Metabolic Alteration and Amyotrophic Lateral Sclerosis Outcome: A Systematic Review

Background: The development of strategies that could not only efficiently detect the onset of Amyotrophic Lateral Sclerosis (ALS), a fatal neurodegenerative disorder with no cure but also predict its development and evaluate therapeutic intervention would be of great value. In this respect, the metabolic status of ALS patients has called attention. Hence, this study aimed to investigate the potential correlation between changes in ALS's metabolic parameters with the disease outcome in a systematic review.

Methods: The manuscripts were manually searched within different databases (PubMed, Web of Science and Cochrane). The inclusion criteria were original articles and reviews about individuals with ALS and its survival, disease prognosis and metabolism (weight, cholesterol, hypertension, BMI, and glycaemia). The authors also established three different exclusion criteria: studies including ALS and other degenerative disorders, works including animal models and published before the year 2000.

Results: In total, 29 papers were selected. From all manuscripts, only 82.8% ensured the participation of sALS patients. Also, 27.6% of selected studies described the presence of a genetic mutation. Regarding ALS prognosis, patient's age, the age of ALS onset, ALS duration and survival, <50% of the papers addressed these issues. Specifically, regarding metabolism, 65.5% of articles mentioned BMI, 20.7% mentioned any data concerning hypertension, 6.89% cardiovascular risk, 10.3% obesity, 13.78% diabetes and 10.3% glycaemia. Concerning lipid metabolism, more results were gathered, but still, they did not suffice to establish a correlation with ALS development.

Conclusions: Altogether, the authors concluded that available information is not enough to establish a link between ALS and metabolism. In reality, less than half of the manuscripts evaluated show an association between both factors. Nonetheless, it is worth mentioning that metabolism does influence ALS, but not in a unique manner. There is a debate about patients' hypo- and hypermetabolism. Thus, to provide a reliable record, a public policy in which all research and clinical centers might assess the parameters discussed herein is suggested. Accordingly, this systematic review attempts to provide a comprehensible database to facilitate multicentered collaboration, validation, and clinical translation.

Longer-term open-label study of adjunctive riluzole in treatment-resistant depression

BACKGROUND

While riluzole has been investigated for the treatment of depression, little is known about its longer-term efficacy and optimal treatment duration in treatment-resistant depression (TRD). The objective of this study is to characterize the longer-term outcome of adjunctive riluzole therapy for TRD in an open-label extension of an 8-week acute treatment trial.

METHODS

The data from 66 patients with TRD who received adjunctive riluzole in a 12-week open-label extension phase were analyzed. Response rates (⩾50% reduction in the Mongomery-Asberg Depression Rating Scale [MADRS] score), relapse rates (a MADRS score of ⩾22 in patients who had previously achieved response), and adverse events were examined in patients who had achieved response at the end of the acute phase and those who had not.

RESULTS

Among acute phase responders, the maintained response rate was 66.7% (8/12) and the relapse rate was 8.3% (1/12). In acute phase non-responders, the response rate was 24.1% (13/54). The most commonly reported adverse event was fatigue (9.1%). Three cases were considered serious adverse events; vomiting (n = 1), shortness of breath (n = 1), and aborted suicide attempt (n = 1).

LIMITATIONS

This longer-term study was open-label and uncontrolled. The sample size was relatively small.

CONCLUSIONS

Longer-term adjunctive riluzole appears relatively well tolerated and beneficial for maintaining previous response. Additionally, approximately one fourth of patients who did not respond to 8-week antidepressant treatment might respond if treated with riluzole for 12 weeks. Those findings warrant further investigation because adjunctive riluzole could represent an option for treatment of depression when standard antidepressants have failed.

Riluzole attenuates the efficacy of glutamatergic transmission by interfering with the size of the readily releasable neurotransmitter pool

Riluzole is a potent neuroprotective agent which primarily inhibits excitatory neurotransmission interfering with presynaptic release, uptake and postsynaptic actions of glutamate by mechanisms that are not well understood. Riluzole and related prodrugs with improved blood brain barrier penetrance, are shown to be effective for the treatment of amyotrophic lateral sclerosis, ataxias, epilepsy and mood disorders. Our study was undertaken to decipher molecular and subcellular mechanisms of riluzole's antiglutamatergic effect, particularly focusing on presynaptic active zone structure and function. Applying multifarious live cell imaging techniques and amperometric glutamate recordings, we measured the impact of riluzole on presynaptic activity, synaptic vesicle recycling and glutamate release. Our in vitro and in vivo data revealed a unique mechanism whereby riluzole reduces the efficacy of glutamatergic transmission by selectively lowering the size of the readily releasable pool. This effect was correlated with the inhibition of protein kinase C-dependent Munc18-1 phosphorylation which is known to interfere with neurotransmitter release.

Effect of fluoxetine on disease progression in a mouse model of ALS

Selective serotonin reuptake inhibitors (SSRIs) and other antidepressants are often prescribed to amyotrophic lateral sclerosis (ALS) patients; however, the impact of these prescriptions on ALS disease progression has not been systematically tested. To determine whether SSRIs impact disease progression, fluoxetine (Prozac, 5 or 10 mg/kg) was administered to mutant superoxide dismutase 1 (SOD1) mice during one of three age ranges: neonatal [postnatal day (P)5-11], adult presymptomatic (P30 to end stage), and adult symptomatic (P70 to end stage). Long-term adult fluoxetine treatment (started at either P30 or P70 and continuing until end stage) had no significant effect on disease progression. In contrast, neonatal fluoxetine treatment (P5-11) had two effects. First, all animals (mutant SOD1(G93A) and control: nontransgenic and SOD1(WT)) receiving the highest dose (10 mg/kg) had a sustained decrease in weight from P30 onward. Second, the high-dose SOD1(G93A) mice reached end stage ∼8 days (∼6% decrease in life span) sooner than vehicle and low-dose animals because of an increased rate of motor impairment. Fluoxetine increases synaptic serotonin (5-HT) levels, which is known to increase spinal motoneuron excitability. We confirmed that 5-HT increases spinal motoneuron excitability during this neonatal time period and therefore hypothesized that antagonizing 5-HT receptors during the same time period would improve disease outcome. However, cyproheptadine (1 or 5 mg/kg), a 5-HT receptor antagonist, had no effect on disease progression. These results show that a brief period of antidepressant treatment during a critical time window (the transition from neonatal to juvenile states) can be detrimental in ALS mouse models.

Pre- and postsynaptic mechanisms underlying inhibition of hypoglossal motor neuron excitability by riluzole

Riluzole is the sole treatment for amyotrophic lateral sclerosis (ALS), but its therapeutically relevant actions on motor neurons are not well defined. Whole cell patch-clamp recordings were made from hypoglossal motor neurons (HMs, n = 25) in brain stem slices from 10- to 23-day-old rats anesthetized with pentobarbital sodium to investigate the hypothesis that riluzole inhibits HMs by multiple mechanisms. Riluzole (20 μM) hyperpolarized HMs by decreasing an inward current, inhibited voltage-gated persistent Na(+) and Ca(2+) currents activated by slow voltage ramps, and negatively shifted activation of the hyperpolarization-activated cationic current (IH). Repetitive firing of HMs was strongly inhibited by riluzole, which also increased action potential threshold voltage and rheobase and decreased amplitude and maximum rise slope but did not alter the maximal afterhyperpolarization amplitude or decay time constant. HM rheobase was inversely correlated with persistent Na(+) current density. Glutamatergic synaptic transmission was inhibited by riluzole by both pre- and postsynaptic effects. Riluzole decreased activity-dependent glutamate release, as shown by decreased amplitude of evoked and spontaneous excitatory postsynaptic currents (EPSCs), decreased paired-pulse ratio, and decreased spontaneous, but not miniature, EPSC frequency. However, riluzole also decreased miniature EPSC amplitude and the inward current evoked by local application of glutamate onto HMs, suggesting a reduction of postsynaptic glutamate receptor sensitivity. Riluzole thus has a marked inhibitory effect on HM activity by membrane hyperpolarization, decreasing firing and inhibiting glutamatergic excitation by both pre- and postsynaptic mechanisms. These results broaden the range of mechanisms controlling motor neuron inhibition by riluzole and are relevant to researchers and clinicians interested in understanding ALS pathogenesis and treatment.

The Sur1-Trpm4 Channel in Spinal Cord Injury

Spinal cord injury (SCI) is a major unsolved challenge in medicine. Impact trauma to the spinal cord shears blood vessels, causing an immediate 'primary hemorrhage'. During the hours following trauma, the region of hemorrhage enlarges progressively, with delayed or 'secondary hemorrhage' adding to the primary hemorrhage, and effectively doubling its volume. The process responsible for the secondary hemorrhage that results in early expansion of the hemorrhagic lesion is termed 'progressive hemorrhagic necrosis' (PHN). PHN is a dynamic process of auto destruction whose molecular underpinnings are only now beginning to be elucidated. PHN results from the delayed, progressive, catastrophic failure of the structural integrity of capillaries. The resulting 'capillary fragmentation' is a unique, pathognomonic feature of PHN. Recent work has implicated the Sur1-Trpm4 channel that is newly upregulated in penumbral microvessels as being required for the development of PHN. Targeting the Sur1-Trpm4 channel by gene deletion, gene suppression, or pharmacological inhibition of either of the two channel subunits, Sur1 or Trpm4, yields exactly the same effects histologically and functionally, and exactly the same unique, pathognomonic phenotype - the prevention of capillary fragmentation. The potential advantage of inhibiting Sur1-Trpm4 channels using glibenclamide is a highly promising strategy for ameliorating the devastating sequelae of spinal cord trauma in humans.

Comparative effects of glibenclamide and riluzole in a rat model of severe cervical spinal cord injury

Both glibenclamide and riluzole reduce necrosis and improve outcome in rat models of spinal cord injury (SCI). In SCI, gene suppression experiments show that newly upregulated sulfonylurea receptor 1 (Sur1)-regulated NC(Ca-ATP) channels in microvascular endothelial cells are responsible for "persistent sodium currents" that cause capillary fragmentation and "progressive hemorrhagic necrosis". Glibenclamide is a potent blocker of Sur1-regulated NC(Ca-ATP) channels (IC(50), 6-48 nM). Riluzole is a pleotropic drug that blocks "persistent sodium currents" in neurons, but in SCI, its molecular mechanism of action is uncertain. We hypothesized that riluzole might block the putative pore-forming subunits of Sur1-regulated NC(Ca-ATP) channels, Trpm4. In patch clamp experiments, riluzole blocked Sur1-regulated NC(Ca-ATP) channels in endothelial cells and heterologously expressed Trpm4 (IC(50), 31 μM). Using a rat model of cervical SCI associated with high mortality, we compared the effects of glibenclamide and riluzole administered beginning at 3h and continuing for 7 days after impact. During the acute phase, both drugs reduced capillary fragmentation and progressive hemorrhagic necrosis, and both prevented death. At 6 weeks, modified (unilateral) Basso, Beattie, Bresnahan locomotor scores were similar, but measures of complex function (grip strength, rearing, accelerating rotarod) and tissue sparing were significantly better with glibenclamide than with riluzole. We conclude that both drugs act similarly, glibenclamide on the regulatory subunit, and riluzole on the putative pore-forming subunit of the Sur1-regulated NC(Ca-ATP) channel. Differences in specificity, dose-limiting potency, or in spectrum of action may account for the apparent superiority of glibenclamide over riluzole in this model of severe SCI.

A review of the neural mechanisms of action and clinical efficiency of riluzole in treating amyotrophic lateral sclerosis: what have we learned in the last decade?

Amyotrophic lateral sclerosis (ALS) is a devastating and fatal neurodegenerative disease of adults which preferentially attacks the neuromotor system. Riluzole has been used as the only approved treatment for amyotrophic lateral sclerosis since 1995, but its mechanism(s) of action in slowing the progression of this disease remain obscure. Searching PubMed for "riluzole" found 705 articles published between January 1996 and June 2009. A systematic review of this literature found that riluzole had a wide range of effects on factors influencing neural activity in general, and the neuromotor system in particular. These effects occurred over a large dose range (<1 μM to >1 mM). Reported neural effects of riluzole included (in approximate ascending order of dose range): inhibition of persistent Na(+) current = inhibition of repetitive firing < potentiation of calcium-dependent K(+) current < inhibition of neurotransmitter release < inhibition of fast Na(+) current < inhibition of voltage-gated Ca(2+) current = promotion of neuronal survival or growth factors < inhibition of voltage-gated K(+) current = modulation of two-pore K(+) current = modulation of ligand-gated neurotransmitter receptors = potentiation of glutamate transporters. Only the first four of these effects commonly occurred at clinically relevant concentrations of riluzole (plasma levels of 1-2 μM with three- to four-fold higher concentrations in brain tissue). Treatment of human ALS patients or transgenic rodent models of ALS with riluzole most commonly produced a modest but significant extension of lifespan. Riluzole treatment was well tolerated in humans and animals. In animals, despite in vitro evidence that riluzole may inhibit rhythmic motor behaviors, in vivo administration of riluzole produced relatively minor effects on normal respiration parameters, but inhibited hypoxia-induced gasping. This effect may have implications for the management of hypoventilation and sleep-disordered breathing during end-stage ALS in humans.

Orchestration of "presto" and "largo" synchrony in up-down activity of cortical networks

It has been demonstrated using single-cell and multiunit electrophysiology in layer III entorhinal cortex and disinhibited hippocampal CA3 slices that the balancing of the up-down activity is characterized by both GABA_A and GABA_B mechanisms. Here we report novel results obtained using multi-electrode array (60 electrodes) simultaneous recordings from reverberating postnatal neocortical networks containing 19.2 ± 1.4% GABAergic neurons, typical of intact tissue. We observed that in each spontaneous active-state the total number of spikes in identified clusters of excitatory and inhibitory neurons is almost equal, thus suggesting a balanced average activity. Interestingly, in the active-state, the early phase is sustained by only 10% of the total spikes and the firing rate follows a sigmoidal regenerative mode up to peak at 35 ms with the number of excitatory spikes greater than inhibitory, therefore indicating an early unbalance. Concentration-response pharmacology of up- and down-state lifetimes in clusters of excitatory (n = 1067) and inhibitory (n = 305) cells suggests that, besides the GABA_A and GABA_B mechanisms, others such as GAT-1-mediated uptake, I_h, I_NaP and I_M ion channel activity, robustly govern both up- and down-activity. Some drugs resulted to affect up- and/or down-states with different IC₅₀s, providing evidence that various mechanisms are involved. These results should reinforce not only the role of synchrony in CNS networks, but also the recognized analogies between the Hodgkin–Huxley action potential and the population bursts as basic mechanisms for originating membrane excitability and CNS network synchronization, respectively.

Targeting glial physiology and glutamate cycling in the treatment of depression

Accumulating evidence indicates that dysfunction in amino acid neurotransmission contributes to the pathophysiology of depression. Consequently, the modulation of amino acid neurotransmission represents a new strategy for antidepressant development. While glutamate receptor ligands are known to have antidepressant effects, mechanisms regulating glutamate cycling and metabolism may be viable drug targets as well. In particular, excitatory amino acid transporters (EAATs) that are embedded in glial processes constitute the primary means of clearing extrasynaptic glutamate. Therefore, the decreased glial number observed in preclinical stress models, and in postmortem tissue from depressed patients provides intriguing, yet indirect evidence for a role of disrupted glutamate homeostasis in the pathophysiology of depression. More direct evidence for this hypothesis comes from studies using magnetic resonance spectroscopy (MRS), a technique that non-invasively measures in vivo concentrations of glutamate and other amino acids under different experimental conditions. Furthermore, when combined with the infusion of (13)C-labeled metabolic precursors, MRS can measure flux through discrete metabolic pathways. This approach has recently shown that glial amino acid metabolism is reduced by chronic stress, an effect that provides a link between environmental stress and the decreased EAAT activity observed under conditions of increased oxidative stress in the brain. Furthermore, administration of riluzole, a drug that enhances glutamate uptake through EAATs, reversed this stress-induced change in glial metabolism. Because riluzole has antidepressant effects in both animal models and human subjects, it may represent the prototype for a novel class of antidepressants with the modulation of glial physiology as a primary mechanism of action.

Riluzole in the treatment of mood and anxiety disorders

Recent advances implicate amino acid neurotransmission in the pathophysiology and treatment of mood and anxiety disorders. Riluzole, which is approved and marketed for the treatment of amyotrophic lateral sclerosis, is thought to be neuroprotective through its modulation of glutamatergic neurotransmission. Riluzole has multiple molecular actions in vitro; the two that have been documented to occur at physiologically realistic drug concentrations and are therefore most likely to be clinically relevant are inhibition of certain voltage-gated sodium channels, which can lead to reduced neurotransmitter release, and enhanced astrocytic uptake of extracellular glutamate.Although double-blind, placebo-controlled trials are lacking, several open-label trials have suggested that riluzole, either as monotherapy or as augmentation of standard therapy, reduces symptoms of obsessive-compulsive disorder, unipolar and bipolar depression, and generalized anxiety disorder. In studies of psychiatrically ill patients conducted to date, the drug has been quite well tolerated; common adverse effects include nausea and sedation. Elevation of liver function tests is common and necessitates periodic monitoring, but has been without clinical consequence in studies conducted to date in psychiatric populations. Case reports suggest utility in other conditions, including trichotillomania and self-injurious behaviour associated with borderline personality disorder. Riluzole may hold promise for the treatment of several psychiatric conditions, possibly through its ability to modulate pathologically dysregulated glutamate levels, and merits further investigation.

Direct effects of riluzole on 5-hydroxytryptamine (5-HT)3 receptor-activated ion currents in NCB-20 neuroblastoma cells

The pharmacological action of riluzole, a drug that has been approved as a neuroprotective agent for the treatment of amyotrophic lateral sclerosis, has not yet been established. We examined the effects of riluzole on 5-hydroxytryptamine (5-HT)3) receptors in NCB-20 neuroblastoma cells using the whole-cell voltage clamp technique combined with a fast drug application method. Co-application of riluzole (1 - 300 microM, 5 s) produced a dose-dependent reduction in peak amplitudes and in the rise slope of the currents induced by 2 microM 5-HT. In addition, 5-HT3-mediated currents evoked by dopamine, a partial 5-HT3-receptor agonist, were inhibited by riluzole co-application. These inhibitory effects were clearly shown at low concentrations of 5-HT. The decay time constants of the receptor desensitization and deactivation were also significantly attenuated by riluzole. G-protein inhibitors (pertussis toxin and guanosine 5'-[beta-thio] diphosphate) did not completely block these inhibitory actions of riluzole. These results indicate that riluzole inhibits 5-HT3-induced ion currents directly by slowing channel activation in NCB-20 neuroblastoma cells.

Anti-glutamatergic effect of riluzole: comparison with valproic acid

Riluzole, an anti-amyotrophic lateral sclerosis drug, known to decrease presynaptic glutamate release, is viewed as a candidate supplementary medication for epilepsy. In the present study, we compared the effects of riluzole and valproate (VPA) in the pilocarpine-induced limbic seizure model and in the gamma-hydroxybutyrate lactone (GBL)-induced absence seizure model. We applied immunohistochemical study for vesicular transporter 1 (VGLUT1) and extracellular recording in the rat dentate gyrus of both pilocarpine- and GBL-induced seizure models to measure effects of riluzole and VPA. Both VPA and riluzole treatments reduced VGLUT1 immunoreactivity. Riluzole treatment completely inhibited pre-ictal spikes and spike-wave discharges in the pilocarpine- and GBL-induced epilepsy models, whereas VPA partially inhibited these phenomena. In both seizure models, the anti-epileptic effects of VPA and riluzole are basically related to anti-glutamatergic (reducing field excitatory postsynaptic potential slope and excitability ratio), not GABAergic (paired-pulse inhibition) effect. Riluzole was more effective at reducing seizure activity in both epilepsy models than VPA. These results suggest that riluzole is a potential antiepileptic drug with activity against limbic seizure and absence seizure.

Persistent sodium currents participate in fictive locomotion generation in neonatal mouse spinal cord

The persistent sodium current (I(Na(P))) has been implicated in the regulation of synaptic integration, intrinsic membrane properties, and rhythm generation in many types of neurons. We characterized I(Na(P)) in commissural interneurons (CINs) in the neonatal (postnatal days 0-3) mouse spinal cord; it is activated at subthreshold potentials, inactivates slowly, and can be blocked by low concentrations of riluzole. The role of I(Na(P)) in locomotor pattern generation was examined by applying riluzole during fictive locomotion induced by NMDA, serotonin, and dopamine or by stimulation of the cauda equina. Blockade of I(Na(P)) has marginal effects on the locomotion frequency but progressively weakens the rhythmic firing and locomotor-related membrane oscillation of CINs and motoneurons (MNs) and the locomotor-like bursts in ventral roots, until the motor pattern ceases. Riluzole directly affects the intrinsic firing properties of CINs and MNs, reducing their ability to fire repetitively during tonic depolarizations and raising their spike threshold. At the same time, riluzole has little effects on the strength of spike-evoked synaptic transmission onto CINs and MNs. Our results suggest that I(Na(P)) is essential for the generation of the locomotor pattern and acts in part by regulating the frequency of interneuron firing in the central pattern generator for locomotion.

Modulation of AMPA receptors in spinal motor neurons by the neuroprotective agent riluzole

We investigated the interaction of riluzole, a therapeutic agent used in amyotrophic lateral sclerosis (ALS), with alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor channels in mouse spinal motor neurons in culture using whole-cell patch-clamp recording techniques. Kainate elicited concentration-dependent (EC(50) = 35 microM) inward currents in all the patched cells. These responses were mediated primarily through the activation of AMPA receptors with a negligible contribution from kainate receptors, because bath application of 100 microM GYKI53655, a potent noncompetitive AMPA receptor antagonist, completely blocked the kainate-induced currents. Riluzole (0.5-100 microM) reduced in a dose-dependent manner the kainate-induced currents with an IC(50) of 1.54 microM in all tested neurons (n = 25) and this effect was found to be reversible. The response to kainate decreased in the presence of 1 microM riluzole in all spinal motor neurons tested, without changing its EC(50), indicating a noncompetitive mechanism of inhibition. The amplitude of the responses induced by kainate under control condition and during riluzole was a linear function of the membrane potential. The reversal potential of the current was not significantly different in the two experimental conditions, whereas the total conductance of the motor neurons for the currents induced by 100 microM kainate was reduced significantly in the presence of 1 microM riluzole (P < 0.05). These results reveal an interaction of riluzole with glutamatergic neurotransmission in spinal cord motor neurons and can contribute to explain its beneficial effect in the ALS treatment.

α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate receptors in spinal cord motor neurons are altered in transgenic mice overexpressing human Cu,Zn superoxide dismutase (Gly93→Ala) mutation

There are many evidences implicating glutamatergic toxicity as a contributory factor in the selective neuronal injury occurring in amyotrophic lateral sclerosis (ALS). This neurodegenerative disorder is characterized by the progressive loss of motor neurons, whose pathogenesis is thought to involve Ca(2+) influx mediated by alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate receptors (AMPARs). In the present study we report alterations in the AMPARs function in a transgenic mouse-model of the human SOD1(G93A) familial ALS. Compared with those expressed in motor neurons carrying the human wild type gene, AMPAR-gated channels expressed in motor neurons carrying the human mutant gene exhibited modified permeability, altered agonist cooperativity between the sites involved in the process of channel opening and were responsible for slower spontaneous synaptic events. These observations demonstrate that the SOD1(G93A) mutation induces changes in AMPAR functions which may underlie the increased vulnerability of motor neurons to glutamatergic excitotoxicity in ALS.

Riluzole suppresses experimental autoimmune encephalomyelitis: implications for the treatment of multiple sclerosis

Recent studies suggest that glutamate neurotoxicity is involved in the pathogenesis of multiple sclerosis (MS), and that treatment with glutamate receptor (AMPA/kainate) antagonists inhibits experimental autoimmune encephalomyelitis (EAE), the conventional model of MS. Therefore, we examined whether riluzole, an inhibitor of glutamate transmission, affects the pathogenesis and clinical features of MS-like disease in myelin oligodendrocyte glycoprotein (MOG)-induced EAE in mice. Here we report that riluzole (10 mg/kgx2/day, i.p.), administered before and even after the appearance of clinical symptoms, dramatically reduced the clinical severity of MOG-induced EAE, while all the MOG-immunized control mice developed significant clinical manifestations. Moreover, the riluzole-treated mice demonstrated only mild focal inflammation, and less demyelination, compared to MOG-treated mice, using histological methods. Furthermore, riluzole markedly reduced axonal disruption, as assessed by Bielshowesky's silver staining and by antibodies against non-phosphorylated neurofilaments (SMI-32). No difference was detected in the immune system potency, as T-cell proliferative responses to MOG were similar in both groups. In conclusion, our study demonstrates, for the first time, that riluzole can reduce inflammation, demyelination and axonal damage in the CNS and attenuate the clinical severity of MOG-induced EAE. These results suggest that riluzole, a drug used in amyotrophic lateral sclerosis (ALS), might be beneficial for the treatment of MS.