Riluzole delayed appearance of parkinsonian motor abnormalities in a chronic MPTP monkey model

D1 Agonist Improved Movement of Parkinsonian Nonhuman Primates with Limited Dyskinesia Side Effects

Parkinson's disease is a progressive neurodegenerative disease characterized by striatal dopaminergic loss. L-DOPA treatment replaces lost dopamine and enables motor function; however, eventually, fluctuating efficacy and side effects associated with its use become challenging for many patients. Here, we demonstrate, in a clinically translatable nonhuman primate model of parkinsonian motor symptoms, that treatment with the partial D1 receptor agonist CVL-751, formerly known as PF-06649751, is just as effective as L-DOPA in enabling movement and reducing disability. Importantly, CVL-751 efficacy is observed with less of the concomitant dyskinesia side effect associated with L-DOPA treatment. Data presented suggest that partial D1 agonists may be an effective and important treatment strategy for the management of Parkinson's patients.

NMDA antagonists as Parkinson’s disease therapy: disseminating the evidence

SUMMARY Oral levodopa is the current baseline therapy in the management of Parkinson’s disease, but nonmotor complications and therapy-related dyskinesias pose an important challenge for clinicians. Glutamate receptors have been implicated in the neurodegenerative process of Parkinson’s disease and also in the development of levodopa-induced dyskinesias. This article discusses the role of NMDA receptors in Parkinson’s disease and their modulation as a possible therapeutic approach.

Riluzole neuroprotection in a Parkinson's disease model involves suppression of reactive astrocytosis but not GLT-1 regulation

Background

Riluzole is a neuroprotective drug used in the treatment of motor neurone disease. Recent evidence suggests that riluzole can up-regulate the expression and activity of the astrocyte glutamate transporter, GLT-1. Given that regulation of glutamate transport is predicted to be neuroprotective in Parkinson's disease, we tested the effect of riluzole in parkinsonian rats which had received a unilateral 6-hydroxydopamine injection into the median forebrain bundle.

Results

Rats were treated with intraperitoneal riluzole (4 mg/kg or 8 mg/kg), 1 hour before the lesion then once daily for seven days. Riluzole produced a modest but significant attenuation of dopamine neurone degeneration, assessed by suppression of amphetamine-induced rotations, preservation of tyrosine hydroxylase positive neuronal cell bodies in the substantia nigra pars compacta and attenuation of striatal tyrosine hydroxylase protein loss. Seven days after 6-hydroxydopamine lesion, reactive astrocytosis was observed in the striatum, as determined by increases in expression of glial fibrillary acidic protein, however the glutamate transporter, GLT-1, which is also expressed in astrocytes was not regulated by the lesion.

Conclusions

The results confirm that riluzole is a neuroprotective agent in a rodent model of parkinson's disease. Riluzole administration did not regulate GLT-1 levels but significantly reduced GFAP levels, in the lesioned striatum. Riluzole suppression of reactive astrocytosis is an intriguing finding which might contribute to the neuroprotective effects of this drug.

Neuroprotective effect of naphtha[1,2-d]thiazol-2-amine in an animal model of Parkinson's disease

Increased oxidative stress has been implicated in the pathogenesis of dopaminergic neurodegeneration leading to the development of Parkinson's disease. In this study, we investigated whether naphtha[1,2-d]thiazol-2-amine (NTA) may ameliorate haloperidol-induced catalepsy and oxidative damage in mice brain. Haloperidol-induced catalepsy was measured with the standard bar test. The extent of oxidative stress has been evaluated by measuring levels of MDA, GSH and activities of antioxidant enzymes (SOD and GSH-Px) from brain homogenate. Haloperidol treatment significantly induced the catalepsy as observed from increased descent time measured in the bar test. Pretreatment with NTA significantly reduced the catalepsy induced by haloperidol in a dose-dependent manner. The elevated level of MDA in haloperidol-treated mice was significantly decreased by NTA pretreatment. The decreased level of GSH as well as SOD and GSH-Px activities in haloperidol-treated mice were significantly increased by NTA pretreatment. NTA reduces the oxidative stress allowing recovery of detoxifying enzyme activities and controlling free radical production, suggesting a potential role of the drug as an alternative/adjuvant drug in preventing and treating the neurodegenerative diseases, such as Parkinson's disease.

Functional models of Parkinson's disease: a valuable tool in the development of novel therapies

Functional models of Parkinson's disease (PD) have led to effective treatment for the motor symptoms. Toxin-based models, such as the 6-hydroxydopamine-lesioned rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primate, have resulted in novel dopaminergic therapies and new therapeutic strategies. They have also been used to study processes underlying motor complications, particularly dyskinesia, and for developing pharmacological approaches to dyskinesia avoidance and suppression. Symptomatic models of PD based on nigrostriatal degeneration have a high degree of predictability of clinical effect of dopaminergic drugs on motor symptoms in humans. However, the effects of nondopaminergic drugs in these models do not translate effectively into clinical efficacy. Newer experimental models of PD have attempted to reproduce the pathogenic process and to involve all areas of the brain pathologically affected in humans. In addition, models showing progressive neuronal death have been sought but so far unsuccessfully. Pathogenic modeling has been attempted using a range of toxins, as well as through the use of transgenic models of gene defects in familial PD and mutant rodent strains. However, there are still no accepted progressive models of PD that mimic the processes known to occur during cell death and that result in the motor deficits, pathology, biochemistry, and drug responsiveness as seen in humans. Nevertheless, functional models of PD have led to many advances in treating the motor symptoms of the disorder, and we have been fortunate to have them available. They are an important reason the treatment of PD is so much better compared with treatments for related illnesses.

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.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.

Glutamate release inhibition ineffective in levodopa-induced motor complications

Reported benefits of various glutamatergic receptor antagonists in Parkinson's disease (PD) prompted an evaluation of the antidyskinetic effect of a putative glutamate release inhibitor in 15 moderately advanced patients. In a 3-week, double-blind, proof-of-concept study, riluzole (200 mg/day) failed to alter parkinsonian or levodopa-induced motor complication severity. Opposing effects of a generalized inhibition of glutamate-mediated synaptic transmission may limit the usefulness of this approach to treat PD.

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.

Actions of the sodium channel inhibitor 202W92 on rat midbrain dopaminergic neurons

Excessive glutamatergic activity is implicated in Parkinson's disease (PD) and sodium channel blockade, resulting in inhibition of glutamate release, is a potential therapeutic approach to PD therapy. Beneficial effects of riluzole and lamotrigine have been reported in animal models of PD, but these compounds have relatively low potency as sodium channel inhibitors and also inhibit N and P/Q-type calcium channels. 202W92, a structural analog of lamotrigine, is a potent sodium channel inhibitor, with no effect on N, P/Q-type channels. Here we present the effects of 202W92 on single patch-clamped dopaminergic neurons. 202W92 (> or =10 microM) inhibited spontaneous action potential firing and reduced amplitude and frequency of evoked action potentials. It also inhibited the frequency of 4-aminopyridine (4-AP)- and electrically evoked excitatory postsynaptic currents (EPSCs) and GABAergic inhibitory postsynaptic currents (IPSCs), with >80% inhibition at 10 microM (IC(50) 1.5 microM). EPSC and IPSC amplitudes were partially inhibited. 202W92 did not affect postsynaptic responses to locally applied glutamate and GABA, nor spontaneously occurring mini-IPSCs. These actions of 202W92 are compatible with sodium channel inhibition and depression of transmitter release.

Effect of chronic treatment with riluzole on the nigrostriatal dopaminergic system in weaver mutant mice

The effects of a chronic treatment with the anti-glutamate and sodium channel modulating neuroprotective agent riluzole on the degeneration of dopamine-containing neurons were studied in the brain of weaver mutant mice. In these animals, as in Parkinson's disease, dopaminergic neurons of the nigro-striatal pathway undergo spontaneous and progressive cell death. Homozygous weaver mice were orally treated twice a day with either 8 mg/kg riluzole or placebo for 2 months. Quantification of tyrosine-hydroxylase and dopamine-transporter axonal immunostaining in the striatum revealed that riluzole significantly increased the density of striatal dopaminergic nerve terminals. These results suggest that riluzole protects dopaminergic processes in the weaver mice and/or promotes their neuroplasticity.

Neuroprotective potential of ionotropic glutamate receptor antagonists

From the therapeutic point of view, the real challenge is not only to improve the symptoms, but to interfere with the pathomechanism of the disease. That is why a considerable interest has recently been devoted to developing glutamate receptor antagonists (mainly of the NMDA type) for acute and chronic neurodegeneration. Developing such a treatment that slows down the progression of the disease is extremely time and cost consuming. At present there is consensus that competitive NMDA receptor antagonists will not find therapeutic applications, in contrast to agents acting at the glycine(B) site, or channel blockers. Recently, at least seven glycine(B) antagonists (e.g. ACEA 1021, GV-150526, GV-196771A, ZD-9379, MRZ 2/576) and over 10 NMDA channel blockers (e.g. Remacemide, ARL-15896AR, HU-211, ADCI, CNS-5161, Neramexane-MRZ 2/579) have been under development, most of them as neuroprotective agents for acute (stroke, trauma) or chronic insult (e.g. Huntington's or Alzheimer's disease). Several substances selective for NR2B NMDA receptor subtypes such as eliprodil, CP-101606 and Ro-25-6981 have been claimed to have a good neuroprotective profile. This presentation is an attempt to critically review preclinical and scarce clinical experience in the development of new NMDA receptor antagonists as neuroprotective agents according to the following scheme: rational, preclinical findings in animal models and finally clinical experience if available. The general impression is that NMDA receptor antagonists may find use in chronic type of neurodegeneration while AMPA antagonists seem to show better promise in acute insult.

A double-blind, placebo-controlled and longitudinal study of riluzole in early Parkinson's disease

BACKGROUND

To the extent that excitotoxicity may play a role in the pathogenesis of certain neurodegenerative disorders, antagonists of glutamate, an excitatory neurotransmitter, should exert neuroprotective effects in these disorders, including Parkinson's disease (PD).

METHODS

Patients in early stages of PD, not previously treated with levodopa, were randomized to receive riluzole 50mg capsules orally, taken twice daily or a matching placebo. All subjects were evaluated at baseline (pre-treatment), at 1, 3 and 6 months (post-treatment), and following a 6-week washout. After the washout, all subjects were offered an enrollment in an open label, 1-year, extension study. The principal investigator (JJ), however, remained blinded to the original assignment during the entire study. The patients were assessed by the Unified Parkinson's Disease Rating Scale (UPDRS), Activities of Daily Living (ADL), Hoehn & Yahr (HY) stage, and Schwab and England (SE) ADL scale. The quantitative assessments included Movement Time (MT) and Reaction Time (RT). Additionally, the time to initiate dopaminergic therapy was assessed. Safety was determined at each visit by clinical history and examination, a panel of blood safety laboratory tests including complete blood count, chemistry profile, and liver function studies.

RESULTS

Twenty patients with a mean age of 62+/-9.02 (range: 46-73) years and mean duration of symptoms of 18+/-9.53 (range: 6-36) months were enrolled. One patient withdrew from the study because he needed more aggressive treatment of his symptoms. Analysis of the efficacy variables showed no meaningful symptomatic effect of riluzole on UPDRS score. Likewise, there was no significant change in the median HY stage, SE ADL rating, or the MT/RT. Seventeen patients (mean age 62+/-9.26) elected to continue in the open label extension study. Although the observed deterioration in UPDRS scores seemed to be more pronounced in the placebo group than in the riluzole group, the difference did not reach statistical significance. There was no statistically significant difference in the latency between enrollment and start of symptomatic therapy when patients initially treated with riluzole were compared to those initially treated with placebo (8.3 vs 9 months).

CONCLUSIONS

This pilot and extension study showed that riluzole, 100mg/day, was well tolerated in patients with early PD. No evidence of symptomatic effect of riluzole was observed. Because of the exploratory nature of the design and small size of the study, it was not possible to determine whether riluzole affected the natural history of PD. The encouraging results from our study, however, suggest that larger, longitudinal studies are warranted.

Neuroprotective effect of riluzole in a primate model of Parkinson's disease: behavioral and histological evidence

Our study aimed to determine whether riluzole, which has shown efficacy as a disease-modifying agent in amyotrophic lateral sclerosis (ALS), is neuroprotective in a marmoset model of Parkinson's disease (PD). Reduction of energy demand by riluzole could be a rational neuroprotective strategy with good tolerability. The efficacy of riluzole was evaluated in marmosets by testing its ability to reduce MPTP-induced behavioral deficits and loss of dopaminergic nigral neurons. Marmosets were divided into two groups of four animals each: animals in Group 1 were injected twice with MPTP (2 mg/kg subcutaneous) and treated with riluzole (10 mg/kg per os b.i.d.), animals in Group 2 (controls) were injected with MPTP and with the vehicle of riluzole. A third group of marmosets which did not receive MPTP or riluzole drug was introduced for neurohistopathological studies (normal animals). Marmosets treated with riluzole preserved a better motor function and neurological performance through the 26 days of assessment when compared with the controls. Histologically, there was sparing of TH- and Nissl-stained nigral neurons and of TH-stained terminals in the striatum and the putamen in the group treated with riluzole compared to the controls. We conclude that riluzole protects dopaminergic neurons and reduces behavioral deficits in a marmoset model of PD.

Neuroprotective effect of riluzole in MPTP-treated mice

The neuroprotective effects of riluzole, a Na(+) channel blocker with antiglutamatergic activity, and MK-801, a blocker of N-methyl-D-aspartate (NMDA) receptors, were compared in the model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced depletion of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels in mice. The mice were injected intraperitoneally (i.p.) with four administrations of MPTP (10 mg/kg) at 1 h intervals and then the brains were analyzed 1, 3 and 7 days after the treatment. Dopamine and DOPAC levels were significantly decreased in the striatum from 1 day after MPTP treatment. A severe depletion in dopamine and DOPAC levels was found in the striatum 3 and 7 days after MPTP treatment. Riluzole antagonized the MPTP-induced decrease in dopamine, DOPAC and HVA levels in the striatum. On the other hand, MK-801 prevented the MPTP-induced decrease in DOPAC levels, but not in dopamine levels in the striatum. An immunohistochemical study indicated that riluzole can protect against MPTP-induced neuronal damage in the substantia nigra. These results suggest that riluzole is effective against MPTP-induced neurodegeneration of the nigrostriatal dopaminergic neuronal pathway.

Riluzole reduces hyperactivity of subthalamic neurons induced by unilateral 6-OHDA lesion in the rat brain

An abnormal increase in the activity of neurons of the subthalamic nucleus is a key pathophysiological feature of Parkinson's disease. We sought to determine whether riluzole, a sodium channel inhibitor that interferes with glutamatergic neurotransmission, affects neuronal activity in this brain region. Intravenous administration of riluzole reduced the discharge rate of subthalamic neurons in rats with 6-OHDA-induced lesions of the midbrain. By contrast, no effect was observed in nonlesioned control animals. This property may contribute to the neuroprotective effects of riluzole in animal models of PD through the modulation of the glutamatergic inputs these neurons feedback to nigral dopaminergic neurons.

Riluzole (2-amino-6-trifluoromethoxy benzothiazole) attenuates MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in mice

The protective effects of 2-amino-6-trifluoromethoxy benzothiazole (riluzole), a Na(+) channel blocker with antiglutamatergic activity were investigated in the model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced depletion of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels in mice. The mice were injected intraperitoneally (i.p.) with four administrations of MPTP (10 mg/kg) at 1 h intervals and then the brains were analyzed at 3 and 7 days after the treatments. Dopamine, DOPAC and HVA levels were significantly decreased in the striatum 3 days after MPTP treatments. Riluzole dose-dependently antagonized the MPTP-induced decrease in dopamine, DOPAC and HVA levels in the striatum. MPTP treatment also caused a severe decrease in the amount of nigral tyrosine hydroxylase protein (TH) and microtuble-associated protein 2 (MAP 2) and produced a marked increase in the striatal glial fibrillary acidic protein (GFAP). Our immunohistochemical study with TH and MAP 2 staining showed that riluzole can protect against MPTP-induced neuronal damage in the substantia nigra. Furthermore, riluzole markedly increased the striatal GFAP-positive astrocytes 3 days after MPTP treatments. These results suggest that riluzole is effective against MPTP-induced neurodegeneration of the nigrostriatal dopaminergic neuronal pathway. Our findings also may provide a rationale for the identification of astrocytes as a prominent target for the development of new therapies of Parkinson's disease.

Neuroprotective effects of (+/-)-kavain in the MPTP mouse model of Parkinson's disease

This is the first study to investigate the potential protective effects of the lipophilic kavapyrone (+/-)-kavain in the experimental MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease (PD). Male C57BL/6 mice were treated with (+/-)-kavain (50, 100, or 200 mg/kg i.p.) or vehicle 60 min before and 60 min after a single administration of MPTP (30 mg/kg s.c.) or saline, respectively. Mice were sacrificed after 7 days and the neostriatum was analyzed for dopamine and its metabolites using HPLC with electrochemical detection. Furthermore, nigral sections were processed for tyrosine hydroxylase (TH) immunocytochemistry. To determine the effects of (+/-)-kavain (200 mg/kg) on MPTP metabolism, HPLC analysis of striatal MPP(+) (1-methyl-4-phenylpyridinium) levels was performed. MPTP treatment alone led to a significant depletion of striatal dopamine levels to 12.61% of saline controls. The lower dosages of (+/-)-kavain (50 and 100 mg/kg) showed only a nonsignificant attenuation of MPTP-induced dopamine depletion, but a high dosage of (+/-)-kavain (200 mg/kg) significantly antagonized the dopamine depletion to 58.93% of saline control values. Remarkably, the MPTP-induced decrease of TH-immunoreactivity as well as the loss of nigral neurons was completely prevented by (+/-)-kavain (200 mg/kg). Striatal MPP(+) levels were not altered by (+/-)-kavain treatment. In conclusion, we found that MPTP metabolism was not influenced by (+/-)-kavain and postulate the antiglutamatergic effects of (+/-)-kavain for its protective effects against MPTP toxicity. (+/-)-Kavain may be a novel candidate for further preclinical studies in animal models of PD and other disorders with glutamatergic overactivity.

Protective effects of riluzole on dopamine neurons: involvement of oxidative stress and cellular energy metabolism

Riluzole is neuroprotective in patients with amyotrophic lateral sclerosis and may also protect dopamine (DA) neurons in Parkinson's disease. We examined the neuroprotective potential of riluzole on DA neurons using primary rat mesencephalic cultures and human dopaminergic neuroblastoma SH-SY5Y cells. Riluzole (up to 10 microM:) alone affected neither the survival of DA neurons in primary cultures nor the growth of SH-SY5Y cells after up to 72 h. Riluzole (1-10 microM:) dose-dependently reduced DA cell loss caused by exposure to MPP(+) in both types of cultures. These protective effects were accompanied by a dose-dependent decrease of intracellular ATP depletion caused by MPP(+) (30-300 microM:) in SH-SY5Y cells without affecting intracellular net NADH content, suggesting a reduction of cellular ATP consumption rather than normalization of mitochondrial ATP production. Riluzole (1-10 microM:) also attenuated oxidative injury in both cell types induced by exposure to L-DOPA and 6-hydroxydopamine, respectively. Consistent with its antioxidative effects, riluzole reduced lipid peroxidation induced by Fe(3+) and L-DOPA in primary mesencephalic cultures. Riluzole (10 microM) did not alter high-affinity uptake of either DA or MPP(+). However, in the same cell systems, riluzole induced neuronal and glial cell death with concentrations higher than those needed for maximal protective effects (> or =100 microM:). These data demonstrate that riluzole has protective effects on DA neurons in vitro against neuronal injuries induced by (a) impairment of cellular energy metabolism and/or (b) oxidative stress. These results provide further impetus to explore the neuroprotective potential of riluzole in Parkinson's disease.

Riluzole reduces brain swelling and contusion volume in rats following controlled cortical impact injury

Modulation of the glutamatergic and excitotoxic pathway may attenuate secondary damage following traumatic brain injury by reducing presynaptic glutamate release and blocking sodium channels in their inactivated state. The aim of the present study was to investigate the neuroprotective potential of riluzole in traumatic brain-injured rats. A left temporoparietal contusion was induced in 70 male Sprague-Dawley rats (controlled cortical impact injury). Riluzole (8 mg/kg body weight) was given 30 min, and 6, 24, and 30 h after trauma, while control rats received physiological saline. Experiments were performed at two different degrees of trauma severity as defined by penetration depth of the impactor rod (1 vs. 1.5 mm) with the aim of investigating impact of severity of tissue damage on the neuroprotective potential of riluzole. At 48 h after trauma, brains were removed to determine hemispheric swelling and water content and to assess cortical contusion volume. Before brain removal cisternal cerebrospinal fluid (CSF) was collected in all rats to determine the effects of riluzole on substances associated with edema formation. For this, the excitatory transmitter glutamate, the volume-regulatory amino acid taurine, and the ATP-degradation product hypoxanthine were analyzed by high-performance liquid chromatography. Overall, the degree of tissue damage seems to influence the neuroprotective potential of riluzole. In rats with a less severe trauma (1-mm penetration depth), hemispheric swelling, cerebral water content of the traumatized hemisphere and cortical contusion volume were significantly reduced under riluzole compared to controls (p < 0.05). In rats with a more severe trauma (1.5-mm penetration depth), the neuroprotective effect of riluzole failed to reach statistical significance. Following trauma, CSF glutamate, taurine, and hypoxanthine levels were significantly increased compared to nontraumatized rats (p < 0.001). However, these neurochemical parameters as measured in cisternal CSF failed to reflect trauma-dependent increases in severity of tissue damage and did not reveal riluzole-mediated neuroprotection. Under the present study design, riluzole significantly reduced brain edema formation and contusion volume in rats subjected to a mild focal cortical contusion.

Riluzole prolongs survival and delays muscle strength deterioration in mice with progressive motor neuronopathy (pmn)

The neuroprotective drug riluzole (Rilutek) is a sodium channel blocker and anti-excitotoxic drug which is marketed for the treatment of amyotrophic lateral sclerosis (ALS). Previous studies have shown that riluzole prolongs survival of transgenic mice harboring the mutated form of Cu,Zn-superoxide dismutase found in familial forms of the human disease. In this study we have examined the effect of treatment with riluzole in mice suffering from progressive motor neuronopathy (pmn), a hereditary autosomal recessive wasting disease which shares some symptoms of ALS. These mutants display hind limb weakness starting during the 3rd week of life and leading to paralysis and death during the 7th week of life. Daily treatment with 8 mg/kg of riluzole by oral route significantly retarded the appearance of paralysis, increased life span and improved motor performance on grip test and electromyographic results in the early stage of the disease. There was no effect of riluzole on weight gain. These data demonstrate that riluzole significantly prolongs life span, retards the onset of paralysis and slows the evolution of functional parameters connected with muscle strength in the pmn mouse model of motor neuron disease.

Dopamine-receptor stimulation: biobehavioral and biochemical consequences

The MPTP monkey is a well-characterized animal model of parkinsonism and provides an exceptional tool for the study of dyskinesias induced by dopamine-like agents. Several such agents have been tested during the past 15 years, and it has been found that the duration of action of these compounds is the most reliable variable with which to predict their dyskinesiogenic profile. It is proposed that L-dopa-induced dyskinesias represent a form of pathological learning caused by chronic pulsatile (nonphysiological) stimulation of dopamine receptors, which activates a cascade of molecular and biochemical events. These events include defective regulation of Fos proteins that belong to the deltaFosB family, increased expression of neuropeptides, and defective GABA- and glutamate-mediated neurotransmission in the output structures of the basal ganglia.

Protective effect of riluzole on MPTP-induced depletion of dopamine and its metabolite content in mice

The neuroprotective effects of riluzole (2-amino-6-trifluoromethoxy benzothiazole), a Na+ channel blocker with antiglutamatergic activity, MK-801, a blocker of N-methyl-D-aspartate (NMDA) receptors and monoamine oxidase (MAO) inhibitor pargyline were compared in the model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced depletion of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) levels in mice. The mice received four intraperitoneal injections of MPTP (10 mg/kg) at 1-hr intervals and then the brains were analyzed at 1, 3 and 7 days after the treatments. Dopamine and DOPAC levels were significantly decreased in the striatum from 1 day after MPTP treatments. A severe depletion in dopamine and DOPAC levels was found in the striatum 3 and 7 days after MPTP treatments. Riluzole dose-dependently antagonized the MPTP-induced decrease in dopamine and DOPAC levels in the striatum. Pargyline also protected against MPTP-induced decrease in dopamine levels in the striatum. However, this drug showed no significant change in the striatal DOPAC levels. On the other hand, MK-801 failed to protect against MPTP-induced decrease in dopamine levels in the striatum. However, MK-801 reversed the MPTP-induced decrease in DOPAC levels. These results suggest that riluzole can protect against MPTP-induced striatal dopamine and DOPAC depletion in mice. This protective effect may be caused by inactivation of voltage-dependent Na+ channels by riluzole. Furthermore, the present study suggests that the activation of NMDA receptors does not mainly contribute to MPTP-induced neurodegeneration, whereas MAO, especially MAO type B(MAO-B) plays a crucial role in MPTP-induced degeneration of the nigrostriatal dopaminergic neuronal pathway.

NMDA receptors in the basal ganglia

The basal ganglia consist of several interconnected nuclei located in the telecephalon, diencephalon and mesencephalon that are involved in a variety of motor and non-motor behavioural functions. Glutamate receptors play a major role in neurotransmission within the basal ganglia and are present in all nuclei of the basal ganglia. This review focuses on the contribution of the NMDA class of glutamatergic receptors to various movement disorders whose primary pathology lies within the basal ganglia and discusses how pharmacological manipulation of such receptors may be therapeutically useful.

Comparison of eight clinical rating scales used for the assessment of MPTP-induced parkinsonism in the Macaque monkey

The most valuable model of Parkinson's disease available at present is the primate model treated with 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP), frequently used to study response to new drugs or surgical treatments. The evaluation of such therapies requires clinical rating scales which measure precisely motor behaviour in both normal and parkinsonian monkeys. It is obvious that such evaluation can only be valid if parallel studies are carried out under similar experimental conditions with well-defined objective criteria. Hence the need to compare and assess the different rating scales in use if we want to be able to compare the results of clinical studies. In order to give rise to some fresh thinking on the necessity of a certain uniformity of assessment, this study compares eight clinical rating scales and considers their capacity to express in quantitative terms both the severity of MPTP intoxication in five cynomolgus monkeys and the alleviation afforded by levodopa. None of the eight scales reaches all the criteria despite the Kurlan scale would appear as an interesting working basis for a further consensual definition of a worldwide used parkinsonian monkey clinical rating scale

Strategies for the protection of dopaminergic neurons against neurotoxicity

Degenerative diseases of the central nervous system (CNS) frequently have a predilection for specific cell populations. An explanation for the selective vulnerability of particular neuronal populations and the mechanisms of cell death remains, as yet, elusive. Partial elucidation of the processes underlying the selective action of neurotoxic substances such as iron, 6-hydroxydopamine (6-OHDA), glutamate, kainic acid, quinolinic acid or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), has revealed possible molecular mechanisms for neurodegeneration. Hypotheses regarding the neurotoxic mechanisms of these substances have evolved based on our understanding of the pathogenesis of cell death in neurodegenerative disorders and have been the rationale for neuroprotective approaches. Various experimental models have demonstrated that monoamine oxidase type B (MAO-B) inhibitors and dopamine agonists exert a neuroprotective effect at the cellular, neurochemical and functional levels, however as yet it has not been possible to demonstrate an unequivocal neuroprotective effect of these substances in clinical studies. This does not suggest, however, that the pathogenetic processes underlying neurodegenerative disorders are not amenable to neuroprotective treatment. This chapter briefly reviews the mechanisms underlying dopaminergic cell death in Parkinson's disease (PD) as an example of a neurodegenerative disorder and discusses preclinical approaches which attempt to demonstrate the neuroprotective effects of representative drugs in experimental models of this disorder. The problems associated with carrying out clinical neuroprotective studies aimed to demonstrate neuroprotection in PD are also discussed.

Effect of the alpha 2 adrenoreceptor antagonist, idazoxan, on motor disabilities in MPTP-treated monkey

1. The motor effect of the alpha 2 adrenoreceptor antagonist, idazoxan, was compared to that of L-dopa in MPTP-treated monkeys. 2. Idazoxan 2.0 mg/kg improved parkinsonian motor abnormalities which was comparable to the effects of a minimal effective dose of L-dopa. 3. At 2.0 and 5.0 mg/kg, the parkinsonian rigidity was the item most frequently alleviated by idazoxan (respectively 63.6% and 68.2%). 4. These findings provide support for the therapeutic utility of alpha 2 antagonists in the treatment of Parkinson's disease.