6-methyl-2-(phenylethynyl)pyridine and Seizures

Microinjection of kainic acid into rat hippocampus causes excitotoxic neuronal damage predominantly in the CA3 and CA1 fields. These lesions can be significantly reduced by simultaneous administration of MPEP, a negative allosteric modulator of type 5 metabotropic glutamate receptors, and LY354740, an agonist of type 2 metabotropic glutamate receptors. The decrease in neuronal death in the hippocampus during pharmacological modulation was paralleled by adaptive changes in gene expression. In the hippocampus, gene expression of type 5 postsynaptic metabotropic glutamate receptor was close to the control level, and in the frontal cortex expression of the gene of α

Topics: Animals; Bridged Bicyclo Compounds; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Frontal Lobe; Gene Expression Regulation; Hippocampus; Kainic Acid; Male; Neurons; Organ Specificity; Pyridines; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, GABA-A; Receptors, Metabotropic Glutamate; Seizures; Stereotaxic Techniques

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Electroencephalography; Hippocampus; Kainic Acid; Male; Pyridines; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Receptors, AMPA; Receptors, Kainic Acid; Seizures

The aim of this study was to determine the effects of 2-methyl-6-(phenylethynyl)pyridine (MPEP - a selective antagonist for the glutamate metabotropic receptor subtype mGluR5) on the protective action of some novel antiepileptic drugs (lamotrigine, oxcarbazepine, pregabalin and topiramate) against maximal electroshock-induced seizures in mice. Brain concentrations of antiepileptic drugs were measured to determine whether MPEP altered pharmacokinetics of antiepileptic drugs. Intraperitoneal injection of 1.5 and 2mg/kg of MPEP significantly elevated the threshold for electroconvulsions in mice, whereas MPEP at a dose of 1mg/kg considerably enhanced the anticonvulsant activity of pregabalin and topiramate, but not that of lamotrigine or oxcarbazepine in the maximal electroshock-induced seizures in mice. Pharmacokinetic results revealed that MPEP (1mg/kg) did not alter total brain concentrations of pregabalin and topiramate, and the observed effect in the mouse maximal electroshock seizure model was pharmacodynamic in nature. Collectively, our preclinical data suggest that MPEP may be a safe and beneficial adjunct to the therapeutic effects of antiepileptic drugs in human patients.

Topics: Animals; Anticonvulsants; Brain; Carbamazepine; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Drug Therapy, Combination; Electroshock; Excitatory Amino Acid Antagonists; Fructose; Lamotrigine; Male; Mice; Oxcarbazepine; Pregabalin; Pyridines; Random Allocation; Receptor, Metabotropic Glutamate 5; Seizures; Topiramate; Triazines

Current treatment of nerve agent poisoning with ionotropic drugs proves inadequate, and alternative treatment strategies are searched for. Based on positive findings with metabotropic glutamate modulators in microinfusion studies, the present study was initiated to examine anticonvulsant effects of MPEP (2-Methyl-6-(phenylethynyl)pyridine hydrochloride), a metabotropic glutamate receptor 5 antagonist, and DCG-IV ((2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine), a metabotropic glutamate receptor 2/3 agonist, when administered systemically in combinations with HI-6 (1-[([4-(aminocarbonyl)pyridino]methoxy)methyl]-2-[(hydroxyimino)methyl]pyridinium) and procyclidine or HI-6 and levetiracetam relative to the combination of HI-6, procyclidine, and levetiracetam. The results showed that MPEP or DCG-IV combined with HI-6 and procyclidine resulted in substantial antidotal efficacy when administered 20 min after onset of seizures elicited by soman. MPEP or DCG-IV combined with HI-6 and levetiracetam did not terminate seizures and preserve lives. When given 20 min before challenge with soman, DCG-IV in combination with HI-6 and procyclidine provided protection, whereas MPEP combined with HI-6 and procyclidine did not. Combinations with metabotropic glutamate receptor modulators did not achieve the same high level of antidotal efficacy as the combination of HI-6, procyclidine, and levetiracetam. MPEP alone inhibited pseudocholinesterase activity in the brain markedly. A positive correlation was found between latency to seizure onset or full protection and level of pseudocholinesterase activity in brain. MPEP and DCG-IV can serve as effective anticonvulsants against nerve agent poisoning when combined with HI-6 and procyclidine. Metabotropic glutamate receptor modulators may represent an alternative or supplement to treatment with ionotropic drugs.

Topics: Acetylcholinesterase; Animals; Anticonvulsants; Butyrylcholinesterase; Cyclopropanes; Drug Interactions; Glycine; Levetiracetam; Male; Oximes; Piracetam; Procyclidine; Pyridines; Pyridinium Compounds; Rats; Rats, Wistar; Receptor, Metabotropic Glutamate 5; Seizures; Soman

Microinfusion of anticonvulsants into the perirhinal cortex through 1 guide cannula in each hemisphere only invades a small area of this seizure controlling site in rats exposed to soman. The purpose of the present study was to examine whether infusions made through 2 cannulas in each perirhinal cortex may produce more efficacious anticonvulsant action against soman intoxication than the use of 1 cannula only in rats infused with the ionotropic antagonists procyclidine and caramiphen or the metabotropic glutamate modulators DCG-IV and MPEP. The results showed that the mere presence of indwelling double cannulas caused proconvulsant effect in response to subsequent systemic administration of soman. Both the control and caramiphen groups with double cannulas had significantly shorter latencies to seizure onset than the corresponding groups with single cannula. Procyclidine resulted in anticonvulsant efficacy, even in rats with double cannulas. In rats that received twin infusions of DCG-IV or MPEP, the anticonvulsant impact was very high, inasmuch as a majority of the rats in each group was protected against seizure activity. Drugs possessing powerful anticonvulsant potency can apparently counteract the proconvulsant effect of double cannulas, and some can even gain enhanced anticonvulsant capacity when invading a larger area of the perirhinal cortex. Perirhinal EEG recordings (electrodes in indwelling cannulas) in a separate set of rats not exposed to soman or drugs showed no differences in basal electrical activity (total power 0.5-25Hz or the theta band 4-12Hz) between groups with single or double cannulas. The intrinsic excitability and synaptic connectivity of the perirhinal cortex may be associated with the proconvulsant impact observed in rats with double cannulas when exposed to soman.

Topics: Animals; Anticonvulsants; Brain Waves; Catheters, Indwelling; Cerebral Cortex; Cyclopentanes; Cyclopropanes; Disease Models, Animal; Drug Delivery Systems; Electroencephalography; Glycine; Infusions, Parenteral; Male; Micromanipulation; Procyclidine; Pyridines; Rats; Rats, Wistar; Reaction Time; Seizures; Soman; Time Factors

The ability of MK-801 (dizocilpine), a noncompetitive N-methyl D-aspartate (NMDA) antagonist, to antagonize electrical seizures is reduced in stressed mice. Stress-associated alterations in seizure susceptibility and diminished efficacy of antiseizure medications in humans have been reported [Joëls, 2009; Haut et al., 2007; Moshe et al., 2008]; thus, these experimental observations implicate altered endogenous tone of NMDA receptor-mediated neurotransmission in clinically adverse effects of stress on seizure proneness and treatment. The current exploratory experiment examined the effect of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), an antagonist of mGluR5, administered prior to stress on the stress-induced reduction of MK-801's antiseizure effect in Swiss-Webster and Balb/c mice; the Balb/c mouse is behaviorally hypersensitive to MK-801. Interestingly, the data suggest that MPEP can attenuate the severity of the stress-induced reduction of MK-801's antiseizure effect in the Balb/c strain. Thus, mGluR5 could serve as a target for strategies for adjuvant treatment of seizures exacerbated by stress.

Topics: Animals; Dizocilpine Maleate; Electroshock; Male; Mice; Mice, Inbred BALB C; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Seizures; Stress, Physiological; Stress, Psychological

Examination of critical subreceptors in the seizure controlling perirhinal cortex has revealed that microinfusion of ionotropic glutamatergic antagonists can exert anticonvulsant efficacy against soman-induced seizures. The purpose of the present study was to investigate whether modulators of metabotropic glutamate (mGlu) receptors may ensure anticonvulsant effects when microinfused into the perirhinal cortex. The results showed that the mGlu5 receptor antagonist MPEP hydrochloride (2-Methyl-6-(phenylethynyl)pyridine hydrochloride) and the mGlu2/3 receptor agonist DCG-IV ((2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine) caused full protection against seizures or increased latency to onset of seizures, whereas the mGlu1 receptor antagonist LY367385 ((S)-(+)-alpha-Amino-4-carboxy-2-methylbenzeneacetic acid) did not produce anticonvulsant efficacy in response to systemically administered soman (1.3 x LD(50)). Low doses of the above modulators had no anticonvulsant effects, whereas too high dose of MPEP resulted in proconvulsant effects. The results suggest that the perirhinal cortex is a likely site of cholinergic recruitment of glutamatergic hyperactivity after exposure to a convulsant dose of soman. Modulators of mGlu receptors may represent an alternative or supplement to ionotropic glutamate antagonists as anticonvulsants against nerve agent-evoked seizures.

Topics: Animals; Anticonvulsants; Benzoates; Cyclopropanes; Dose-Response Relationship, Drug; Glycine; Infusion Pumps; Male; Microinjections; Pyridines; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Seizures; Soman; Temporal Lobe; Time Factors

Significant advances have been made in understanding the underlying defects of and developing potential treatments for Fragile X syndrome (FXS), the most common heritable mental retardation. It has been shown that neuronal metabotropic glutamate receptor 5 (mGluR5)-mediated signaling is affected in FX animal models, with consequent alterations in activity-dependent protein translation and synaptic spine functionality. We demonstrate here that a central metabolic regulatory enzyme, glycogen synthase kinase-3 (GSK3) is present in a form indicating elevated activity in several regions of the FX mouse brain. Furthermore, we show that selective GSK3 inhibitors, as well as lithium, are able to revert mutant phenotypes of the FX mouse. Lithium, in particular, remained effective with chronic administration, although its effects were reversible even when given from birth. The combination of an mGluR5 antagonist and GSK3 inhibitors was not additive. Instead, it was discovered that mGluR5 signaling and GSK3 activation in the FX mouse are coordinately elevated, with inhibition of mGluR5 leading to inhibition of GSK3. These findings raise the possibility that GSK3 is a fundamental and central component of FXS pathology, with a substantial treatment potential.

Topics: Acoustic Stimulation; Analysis of Variance; Animals; Antimanic Agents; Brain; Citrates; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Exploratory Behavior; Fragile X Mental Retardation Protein; Gene Expression Regulation; Glycogen Synthase Kinase 3; Indoles; Lithium Chloride; Male; Maleimides; Mice; Mice, Knockout; Pyridines; Seizures; Serine; Thiazoles; Urea

Metabotropic glutamate receptor 5 (mGluR(5)) regulates the translation of amyloid precursor protein (APP) mRNA. Under resting conditions, mRNA is bound to and translationally repressed by the fragile X mental retardation protein (FMRP). Upon group 1 mGluR activation, FMRP dissociates from the mRNA and translation ensues. APP levels are elevated in the dendrites of primary neuronal cultures as well as in synaptoneurosomes (SN) prepared from embryonic and juvenile fmr-1 knockout (KO) mice, respectively. In order to study the effects of APP and its proteolytic product Abeta on Fragile X syndrome (FXS) phenotypes, we created a novel mouse model (FRAXAD) that over-expresses human APPSwe/Abeta in an fmr-1 KO background. Herein, we assess (1) human APP(Swe) and Abeta levels as a function of age in FRAXAD mice, and (2) seizure susceptibility to pentylenetetrazol (PTZ) after mGluR(5) blockade. PTZ-induced seizure severity is decreased in FRAXAD mice pre-treated with the mGluR(5) antagonist MPEP. These data suggest that Abeta contributes to seizure incidence and may be an appropriate therapeutic target to lessen seizure pathology in FXS, Alzheimer's disease (AD) and Down syndrome (DS) patients.

Topics: Age Factors; Amyloid beta-Protein Precursor; Animals; Anti-Anxiety Agents; Disease Models, Animal; Fragile X Mental Retardation Protein; Fragile X Syndrome; Gene Expression; Gene Silencing; Humans; Mice; Mice, Inbred C57BL; Mice, Knockout; Protease Nexins; Pyridines; Receptors, Cell Surface; RNA, Messenger; Seizures

Kindling induced by repeated application of the convulsant pentylenetetrazole (PTZ) is a validated model of epilepsy and epilepsy-related neuromorphological, neurophysiological and behavioural alterations. In this study, we examined whether kindling-induced long-term aberrations in hippocampal synaptic plasticity can be prevented by application of group I mGluR antagonists. Kindling resulted in a higher magnitude of long-term potentiation (LTP) induced by a strong high-frequency stimulation in the hippocampal CA1 region in vitro. When the specific mGluR1 antagonist LY 367385 (0.40 microMol) or the specific mGluR5 inhibitor MPEP (0.06 microMol) were given 30 min prior to PTZ, this kindling-induced enhancement of LTP was almost completely prevented. In addition, application of MPEP led to an impaired maintenance of population spike LTP in kindled animals. LY 367385 applied to unkindled control animals caused a reduction of the initial magnitude of population spike LTP. MPEP, in contrast, left the initial magnitude untouched but resulted in a faster decay of potentiation. A single administration of LY 367385 (200 microM) and MPEP (50 microM), respectively, directly into the bath had almost no effect. Our data suggest that the long-lasting aberrations of hippocampal synaptic plasticity induced by the repeated occurrence of generalized epileptic seizures ultimately require a concurrent operation of mGluR1 and mGluR5.

Topics: Analysis of Variance; Animals; Benzoates; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation; Excitatory Postsynaptic Potentials; Glycine; Hippocampus; Long-Term Potentiation; Male; Neuronal Plasticity; Pentylenetetrazole; Pyridines; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Seizures; Time Factors

Homer-1a/Vesl1S, a member of the scaffold protein family Homer/Vesl, is expressed during seizure and serves to reduce seizure susceptibility. Cellular mechanisms for this feedback regulation were studied in neocortex pyramidal cells by injecting Homer-1a protein intracellularly. The injection reduced membrane excitability as demonstrated in two ways. First, the resting potential was hyperpolarized by 5-10 mV. Second, the mean frequency of spikes evoked by depolarizing current injection was decreased. This reduction of excitability was prevented by applying each of the followings: the calcium chelator BAPTA, the calcium store depletor cyclopiazonic acid (CPA), the insitol-1,4,5-trisphosphate receptor (IP(3)R) blocker heparin, the phospholipase C (PLC) inhibitor U-73122, the metabotropic glutamate receptor (mGluR) antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP), and the large-conductance calcium activated potassium channel (BK channel) antagonist charybdotoxin. The small-conductance calcium activated potassium channel (SK channel) blocker dequalinium was ineffective. These findings suggest that activation of mGluR by Homer-1a produced IP(3), which caused inositol-induced calcium release and a consequent BK channel opening, thus hyperpolarizing the injected neurons. In slices from rats subjected to electroconvulsive shock (ECS), a comparable reduction of excitability was observed without Homer-1a injection. The ECS-induced reduction of excitability was abolished by MPEP, charybdotoxin, heparin or BAPTA. Intracellular injection of anti-Homer-1a antibody was suppressive as well, but anti-Homer-1b/c antibody was not. We propose that ECS-induced Homer-1a stimulated the same pathway as did the injected Homer-1a, thereby driving a feedback regulation of excitability.

Topics: Animals; Animals, Newborn; Carrier Proteins; Charybdotoxin; Chelating Agents; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Drug Interactions; Egtazic Acid; Electroshock; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Heparin; Homer Scaffolding Proteins; Membrane Potentials; Neocortex; Patch-Clamp Techniques; Potassium Channel Blockers; Pyramidal Cells; Pyridines; Rats; Rats, Wistar; Recombinant Proteins; Seizures; Time Factors

The effects of several metabotropic receptor (mGluR) ligands on baseline hippocampal glutamate and GABA overflow in conscious rats and the modulation of limbic seizure activity by these ligands were investigated. Intrahippocampal mGluR group I agonist perfusion via a microdialysis probe [1 mm (R,S)-3,5-dihydroxyphenylglycine] induced seizures and concomitant augmentations in amino acid dialysate levels. The mGlu1a receptor antagonist LY367385 (1 mm) decreased baseline glutamate but not GABA concentrations, suggesting that mGlu1a receptors, which regulate hippocampal glutamate levels, are tonically activated by endogenous glutamate. This decrease in glutamate may contribute to the reported LY367385-mediated anticonvulsant effect. The mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine (50 mg/kg) also clearly abolished pilocarpine-induced seizures. Agonist-mediated actions at mGlu2/3 receptors by LY379268 (100 microm, 10 mg/kg intraperitoneally) decreased basal hippocampal GABA but not glutamate levels. This may partly explain the increased excitation following systemic LY379268 administration and the lack of complete anticonvulsant protection within our epilepsy model with the mGlu2/3 receptor agonist. Group II selective mGluR receptor blockade with LY341495 (1-10 microm) did not alter the rats' behaviour or hippocampal amino acid levels. These data provide a neurochemical basis for the full anticonvulsant effects of mGlu1a and mGlu5 antagonists and the partial effects observed with mGlu2/3 agonists in vivo.

Topics: Amino Acids; Animals; Anticonvulsants; Benzoates; Bridged Bicyclo Compounds, Heterocyclic; Cyclopropanes; Disease Models, Animal; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Extracellular Fluid; gamma-Aminobutyric Acid; Glutamic Acid; Glycine; Hippocampus; Ligands; Limbic System; Male; Microdialysis; Pilocarpine; Pyridines; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Seizures

The selective mGlu5 antagonists, MPEP, 2-methyl-6-phenylethynyl-pyridine, and SIB1893, (E)-6-methyl-2-styryl-pyridine, have been evaluated as antiepileptic drugs in DBA/2 mice and lethargic mice. Clonic seizures induced by the selective mGlu5 agonist, (R,S)-2-chloro-5-hydroxyphenylglycine (CHPG), 3 micromol intracerebroventricularly (i.c.v.), are potently suppressed by both compounds (MPEP, ED(50)=0.42 [0.28-0.62] mg/kg intraperitoneally (i.p.); SIB 1893 ED(50)=0.19 [0.11-0.33] mg/kg i.p. ). Clonic seizures induced by the mGlu1,5 agonist, 3, 5-dihydroxyphenylglycine (DHPG), 1.5 micromol i.c.v., are less potently suppressed by both compounds (MPEP, ED(50)=22 [13-38] mg/kg i.p., 110 [67-180] nmol i.c.v.; SIB1893, ED(50)=31 [18-54] mg/kg i.p. , 95 [82-110] nmol i.c.v.). Sound-induced seizures in DBA/2 mice are suppressed at 15 min by MPEP and SIB 1893 (MPEP ED(50) clonic seizures=18 [10-32] mg/kg i.p., 93 [69-125] nmol i.c.v.; tonic seizures=6.1 [4.5-8.3] mg/kg i.p., 46 [26-80] nmol i.c.v.; SIB 1893 ED(50) clonic seizures=27 [17-44] mg/kg i.p., 825 [615-1108] nmol i. c.v., tonic seizures=5.4 [3.4-8.6] mg/kg i.p., 194 [113-332] nmol i. c.v.). The ED(50) for MPEP for impaired rotarod performance is 128 [83-193] mg/kg i.p., at 15 min, i.e. a therapeutic index for sound-induced seizures of 5-20. In lethargic mice (lh/lh), a genetic absence model, MPEP, 50 mg/kg i.p., caused a marked reduction in the incidence of spontaneous spike-and-wave discharges. These selective antagonists of mGlu5 block seizures due to activation of mGlu5 at very low systemic doses. At rather higher doses they block convulsive and non-convulsive primary generalised seizures.

Topics: Animals; Anticonvulsants; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Female; Glycine; Injections, Intraperitoneal; Injections, Intraventricular; Male; Mice; Mice, Inbred DBA; Pyridines; Receptor, Metabotropic Glutamate 5; Receptors, Metabotropic Glutamate; Resorcinols; Seizures; Sound; Time Factors