dizocilpine-maleate and Epilepsy

Phencyclidine (PCP), ketamine (Special K), and MK-801 are noncompetitive N-methyl-d-aspartate (NMDA) antagonists that produce acute psychosis in humans. The psychosis produced by these psychomimetic drugs is indistinguishable from schizophrenia and includes both positive and negative symptoms. This drug-induced psychosis occurs after puberty in humans. On the basis of the MK-801-induced spike-and-wave activity in rats and increased blood flow and metabolism in brain of patients with psychosis caused by these psychomimetics, this brief review argues that this psychosis is an atypical form of limbic epilepsy. Moreover, there is a specific limbic thalamcortical psychosis circuit that mediates cell injury in limbic cortex of rodents and may mediate this PCP-induced psychosis in humans. It is proposed that this thalamocortical psychosis circuit develops at puberty and can mediate PCP and ketamine-mediated psychosis and possibly the psychosis of schizophrenia, bipolar disease and other disorders that have their onset at puberty. Finally, based on this developmentally regulated psychosis/epilepsy-related thalamocortical circuitry, it is proposed that antiepileptic drugs that promote GABAergic mechanisms may decrease the probability of episodic psychosis from any cause.

Topics: Adolescent; Animals; Antipsychotic Agents; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Hallucinogens; Humans; Ketamine; Limbic System; Neurons; Phencyclidine; Psychoses, Substance-Induced; Psychotic Disorders; Puberty; Rats; Regional Blood Flow; Sexual Maturation

Topics: Animals; Brain; Cell Death; Cells, Cultured; Dizocilpine Maleate; Epilepsy; Gene Expression Regulation; Hippocampus; Humans; In Vitro Techniques; Ischemic Preconditioning; Mice; Microarray Analysis; Neuronal Plasticity; Phenotype

Epileptic activity leads to rapid insertion of calcium-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (CP-AMPARs) into the synapses of cortical and hippocampal glutamatergic neurons, which generally do not express them. The physiological significance of this process is not yet fully understood; however, it is usually assumed to be a pathological process that augments epileptic activity. Using whole-cell patch-clamp recordings in rat entorhinal cortex slices, we demonstrate that the timing of epileptiform discharges, induced by 4-aminopyridine and gabazine, is determined by the shunting effect of Ca

Topics: Adamantane; Animals; Calcium; Computer Simulation; Dizocilpine Maleate; Entorhinal Cortex; Epilepsy; GABA-B Receptor Antagonists; In Vitro Techniques; Male; Membranes; Models, Theoretical; Neurons; Patch-Clamp Techniques; Phosphinic Acids; Propanolamines; Rats, Wistar; Receptors, AMPA; Receptors, GABA-B; Receptors, N-Methyl-D-Aspartate

Glutamic acid decarboxylase (GAD), the enzyme responsible for GABA synthesis, requires pyridoxal phosphate (PLP) as a cofactor. Thiosemicarbazide (TSC) and γ-glutamyl-hydrazone (PLPGH) inhibit the free PLP-dependent isoform (GAD65) activity after systemic administration, leading to epilepsy in mice and in young, but not in adult rats. However, the competitive GAD inhibitor 3-mercaptopropionic acid (MPA) induces convulsions in both immature and adult rats. In the present study we tested comparatively the epileptogenic and neurotoxic effects of PLPGH, TSC and MPA, administered by microdialysis in the hippocampus of adult awake rats. Cortical EEG and motor behavior were analyzed during the next 2h, and aspartate, glutamate and GABA were measured by HPLC in the microdialysis-collected fractions. Twenty-four hours after drug administration rats were fixed for histological analysis of the hippocampus. PLPGH or TSC did not affect the motor behavior, EEG or cellular morphology, although the extracellular concentration of GABA was decreased. In contrast, MPA produced intense wet-dog shakes, EEG epileptiform discharges, a >75% reduction of extracellular GABA levels and remarkable neurodegeneration of the CA1 region, with >80% neuronal loss. The systemic administration of the NMDA glutamate receptor antagonist MK-801 30 min before MPA did not prevent the MPA-induced epilepsy but significantly protected against its neurotoxic effect, reducing neuronal loss to <30%. We conclude that in adult awake rats, drugs acting on PLP availability have only a weak effect on GABA neurotransmission, whereas direct GAD inhibition produced by MPA induces hyperexcitation leading to epilepsy and hippocampal neurodegeneration. Because this degeneration was prevented by the blockade of NMDA receptors, we conclude that it is due to glutamate-mediated excitotoxicity consequent to disinhibition of the hippocampal excitatory circuits.

Topics: Amino Acids; Animals; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Enzyme Inhibitors; Epilepsy; Hippocampus; Male; Microdialysis; Neurodegenerative Diseases; Neuroprotective Agents; Phenylacetates; Pyridoxal Phosphate; Rats; Rats, Wistar; Semicarbazides; Time Factors; Wakefulness

Cell apoptosis can cause hippocampal neuronal loss after epileptic seizures. Hypoxia inducible factor (HIF)-1α is an important factor mediating apoptosis after brain injuries, such as cerebral ischemia and traumatic brain injures, but little research has been done on its role in the lithium chloride-pilocarpine induced epileptic model. Here, we used a rat model of pilocarpine-induced status epilepticus (SE) to investigate HIF-1α expression and apoptosis in the hippocampus, and to explore their relationship during epileptogenesis. 120 male Sprague Dawley (SD) rats were treated with lithium chloride-pilocarpine injections and divided into an experimental group (administered by MK-801) and a positive control group (administered by saline). Then the HIF-1α expression and hippocampal apoptosis were investigated by histological confirmation and western blotting at 24h, 3d, 7d and 14d, respectively. The results showed that the administration of MK-801 significantly reduced (P<0.05) HIF-1α expression and hippocampal apoptosis during epileptogenesis in comparison with the positive control. Moreover, the expression of HIF-1α and hippocampal apoptosis presented significant time-dependent changes (P<0.01) within 2 weeks, and their positive correlation (P<0.05) analyzed by Pearson׳s correlation analysis. Meanwhile, the HIF-1α immunostained cells were distributed in accord with TUNEL immunostained cells and Caspase-3 immunopositive cells in the hippocampus. These results indicate that the HIF-1α expression is associated with hippocampal apoptosis, and suggest that HIF-1α is an important factor during epileptogenesis.

Topics: Animals; Apoptosis; Convulsants; Dizocilpine Maleate; Electroencephalography; Epilepsy; Excitatory Amino Acid Antagonists; Hippocampus; Hypoxia-Inducible Factor 1, alpha Subunit; Lithium Chloride; Male; Pilocarpine; Rats; Rats, Sprague-Dawley

Hypersynchronicity of neuronal brain circuits is a feature of Alzheimer's disease (AD). Mouse models of AD expressing mutated forms of the amyloid-β precursor protein (APP), a central protein involved in AD pathology, show cortical hypersynchronicity. We studied hippocampal circuitry in APP23 transgenic mice using telemetric electroencephalography (EEG), at the age of onset of memory deficits. APP23 mice display spontaneous hypersynchronicity in the hippocampus including epileptiform spike trains. Furthermore, spectral contributions of hippocampal theta and gamma oscillations are compromised in APP23 mice, compared to non-transgenic controls. Using cross-frequency coupling analysis, we show that hippocampal gamma amplitude modulation by theta phase is markedly impaired in APP23 mice. Hippocampal hypersynchronicity and waveforms are differentially modulated by injection of riluzole and the non-competitive N-methyl-D-aspartate (NMDA) receptor inhibitor MK801, suggesting specific involvement of voltage-gated sodium channels and NMDA receptors in hypersynchronicity thresholds in APP23 mice. Furthermore, APP23 mice show marked activation of p38 mitogen-activated protein (MAP) kinase in hippocampus, and injection of MK801 but not riluzole reduces activation of p38 in the hippocampus. A p38 inhibitor induces hypersynchronicity in APP23 mice to a similar extent as MK801, thus supporting suppression of hypersynchronicity involves NMDA receptors-mediated p38 activity. In summary, we characterize components of hippocampal hypersynchronicity, waveform patterns and cross-frequency coupling in the APP23 mouse model by pharmacological modulation, furthering the understanding of epileptiform brain activity in AD.

Topics: Alzheimer Disease; Animals; Disease Models, Animal; Dizocilpine Maleate; Electrodes, Implanted; Electroencephalography; Enzyme Inhibitors; Epilepsy; Excitatory Amino Acid Antagonists; Gamma Rhythm; Hippocampus; Imidazoles; Male; Mice, Inbred C57BL; Mice, Transgenic; p38 Mitogen-Activated Protein Kinases; Pyridines; Receptors, N-Methyl-D-Aspartate; Riluzole; Theta Rhythm

Perfusion of 4-aminopyridine (4-AP) by microdialysis in the hippocampus produces intense epileptiform behavioral and electrical activity and neurodegeneration, resulting from a stimulated release of glutamate from nerve endings. In contrast, accumulation of extracellular glutamate by blockade of its transport in vivo in anesthetized rats is innocuous, and studies in vitro in brain slices suggest that under these conditions glutamate may activate presynaptic group III metabotropic glutamate receptors (mGluRs) and inhibit its own release. Therefore, using microdialysis, EEG recording, and histological evaluation, we studied the effect of increased endogenous extracellular glutamate by blockade of its transport with pyrrolidine dicarboxylic acid (PDC) on the excitotoxic action of 4-AP in the hippocampus of awake rats. We found that up to a 20-fold increase in extracellular glutamate during >90 min with PDC does not induce any sign of excitotoxicity. On the contrary, this glutamate increase notably protected against the 4-AP-induced seizures and neurodegeneration, and, remarkably, this protection was dependent on the time of perfusion with PDC and thus on the duration of extracellular glutamate accumulation. To test whether this protective action was mediated by the activation of group III mGluRs, we used specific antagonists of these receptors and found that they clearly prevented the protective effect of PDC, without affecting the accumulation of extracellular glutamate. We conclude that the spillover of the excess extracellular glutamate activates presynaptic group III mGluRs and inhibits the stimulatory effect of 4-AP on its release, thus preventing the activation of postsynaptic N-methyl-D-aspartate receptors and its deleterious consequences.

Topics: 4-Aminopyridine; Amino Acids; Animals; Carboxylic Acids; Chromatography, High Pressure Liquid; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Electrochemistry; Electroencephalography; Epilepsy; Excitatory Amino Acid Antagonists; Extracellular Fluid; Glutamic Acid; Hippocampus; Male; Microdialysis; Phosphoserine; Potassium Channel Blockers; Pyridines; Rats; Rats, Wistar; Receptors, Metabotropic Glutamate; Time Factors

We report on a novel mouse in vitro brain slice preparation that contains intact callosal axons connecting anterior cingulate cortices (ACC). Callosal connections are demonstrated by the ability to regularly record epileptiform events between hemispheres (bilateral events). That the correlation of these events depends on the callosum is demonstrated by the bisection of the callosum in vitro. Epileptiform events are evoked with four different methods: (1) bath application of bicuculline (a GABA-A antagonist); (2) bicuculline+MK801 (an NMDA receptor antagonist), (3) a zero magnesium extracellular solution (0Mg); (4) focal application of bicuculline to a single cortical hemisphere. Significant increases in the number of epileptiform events, as well as increases in the ratio of bilateral events to unilateral events, are observed during bath applications of bicuculline, but not during applications of bicuculline+MK-801. Long ictal-like events (defined as events >20 seconds) are only observed in 0Mg. Whole cell patch clamp recordings of single neurons reveal strong feedforward inhibition during focal epileptiform events in the contralateral hemisphere. Within the ACC, we find differences between the rostral areas of ACC vs. caudal ACC in terms of connectivity between hemispheres, with the caudal regions demonstrating shorter interhemispheric latencies. The morphologies of many patch clamped neurons show callosally-spanning axons, again demonstrating intact callosal circuits in this in vitro preparation.

Topics: Animals; Axons; Bicuculline; Calcium; Corpus Callosum; Diagnostic Imaging; Dizocilpine Maleate; Epilepsy; Extracellular Space; Female; Gyrus Cinguli; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Magnesium; Male; Mice; Microinjections; Models, Neurological; Perfusion; Solutions

Epilepsy, a common neurological disorder, is characterized by the occurrence of spontaneous recurrent epileptiform discharges (SREDs). Acquired epilepsy is associated with long-term neuronal plasticity changes in the hippocampus resulting in the expression of spontaneous recurrent seizures. The purpose of this study is to evaluate and characterize endogenous epileptiform activity in hippocampal-entorhinal cortical (HEC) slices from epileptic animals. This study employed HEC slices isolated from a large series of control and epileptic animals to evaluate and compare the presence, degree and localization of endogenous SREDs using extracellular and whole cell current clamp recordings. Animals were made epileptic using the pilocarpine model of epilepsy. Extracellular field potentials were recorded simultaneously from areas CA1, CA3, dentate gyrus, and entorhinal cortex and whole cell current clamp recordings were obtained from CA3 neurons. All regions from epileptic HEC slices (n=53) expressed SREDs, with an average frequency of 1.3Hz. In contrast, control slices (n=24) did not manifest any SREDs. Epileptic HEC slices demonstrated slow and fast firing patterns of SREDs. Whole cell current clamp recordings from epileptic HEC slices showed that CA3 neurons exhibited paroxysmal depolarizing shifts associated with these SREDs. To our knowledge this is the first significant demonstration of endogenous SREDs in a large series of HEC slices from epileptic animals in comparison to controls. Epileptiform discharges were found to propagate around hippocampal circuits. HEC slices from epileptic animals that manifest SREDs provide a novel model to study in vitro seizure activity in tissue prepared from epileptic animals.

Topics: Action Potentials; Animals; Cerebral Cortex; Disease Models, Animal; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Excitatory Amino Acid Antagonists; Hippocampus; In Vitro Techniques; Lysine; Neural Pathways; Neurons; Patch-Clamp Techniques; Pilocarpine

Application of choline (5 and 10 mM) to electrically stimulated (1 Hz) rat hippocampal slices evoked epileptoid activity manifested by generation of extra population spikes. Application of methyllycaconitine (10 nM), a specific agonist for α7-subunit of nicotinic acetylcholine receptors, did not prevent generation of extra population spikes. In contrast, pretreatment of slices with Mg(2+) (5 mM) or blockade of NMDA-type glutamate receptors with MK-801 (100 μM) prevented generation of the extra population spikes. It was hypothesized that elevation of choline concentration during cerebral pathology can promote activation of NMDA-receptors and provoke epileptoid activity not related to activation of α7-subunit of nicotinic acetylcholine receptor.

Topics: Aconitine; Action Potentials; Animals; CA1 Region, Hippocampal; Choline; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; In Vitro Techniques; Nicotinic Antagonists; Pyramidal Tracts; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Receptors, Nicotinic

Status epilepticus is a clinical emergency that can lead to the development of acquired epilepsy following neuronal injury. Understanding the pathophysiological changes that occur between the injury itself and the expression of epilepsy is important in the development of new therapeutics to prevent epileptogenesis. Currently, no anti-epileptogenic agents exist; thus, the ability to treat an individual immediately after status epilepticus to prevent the ultimate development of epilepsy remains an important clinical challenge. In the Sprague-Dawley rat pilocarpine model of status epilepticus-induced acquired epilepsy, intracellular calcium has been shown to increase in hippocampal neurons during status epilepticus and remain elevated well past the duration of the injury in those animals that develop epilepsy. This study aimed to determine if such changes in calcium dynamics exist in the hippocampal culture model of status epilepticus-induced acquired epilepsy and, if so, to study whether manipulating the calcium plateau after status epilepticus would prevent epileptogenesis. The in vitro status epilepticus model resembled the in vivo model in terms of elevations in neuronal calcium concentrations that were maintained well past the duration of the injury. When used following in vitro status epilepticus, dantrolene, a ryanodine receptor inhibitor, but not the N-methyl-D-aspartic acid channel blocker MK-801 inhibited the elevations in intracellular calcium, decreased neuronal death and prevented the expression of spontaneous recurrent epileptiform discharges, the in vitro correlate of epilepsy. These findings offer potential for a novel treatment to prevent the development of epileptiform discharges following brain injuries.

Topics: Animals; Calcium; Cell Death; Cells, Cultured; Dantrolene; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Hippocampus; Muscarinic Agonists; Muscle Relaxants, Central; Neurons; Neuroprotective Agents; Patch-Clamp Techniques; Pilocarpine; Rats; Rats, Sprague-Dawley; Status Epilepticus

Stress induces changes in the endogenous tone of both GABA and NMDA receptor-mediated neurotransmission in the intact mouse. Because changes are observed 24 h after stress, epigenetically-regulated alterations in gene expression may mediate these effects. In earlier work, sodium butyrate, a centrally-active histone deacetylase inhibitor that promotes gene expression, was shown to modulate the stress-induced reduction of the ability of MK-801 (dizocilpine), a noncompetitive NMDA receptor antagonist, to antagonize electrically-precipitated seizures. In the current study, we extended this work to look at sodium butyrate's modulatory effect on stress-induced changes in the antiseizure efficacy of flurazepam, a benzodiazepine receptor agonist, in two strains of mice. Epigenetic mechanisms, genetic strain differences and a standard stress interacted to alter flurazepam's antiseizure efficacy. These data support examination and development of epigenetic treatment strategies.

Topics: Animals; Anti-Anxiety Agents; Behavior, Animal; Butyrates; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Electroshock; Epilepsy; Excitatory Amino Acid Antagonists; Flurazepam; Mice; Mice, Inbred BALB C; Species Specificity; Stress, Psychological

The present study was undertaken to clarify the participation of the GABA-ergic system in epileptogenic activity induced by teicoplanin.. Under pentobarbital anesthesia, mice were fixed to a stereotaxic apparatus, and stainless steel electrodes were implanted into the frontal cortex (FCOR), hippocampus (HPC) and amygdala (AMG). Behavioral and electroencephalographic (EEG) changes were observed for 60min following teicoplanin intracerebroventricular (i.c.v.) injection.. I.c.v. injection of teicoplanin caused dose-related behavioral and EEG seizures. MK-801 (N-methyl-d-aspartate receptors antagonist) had no significant influence on either behavioral or EEG seizures induced by teicoplanin (500microg, i.c.v.). On the other hand, NNC-711 (GABA transporters inhibitor) dose-dependently antagonized behavioral and EEG seizures induced by teicoplanin (500microg, i.c.v.). The inhibitory effect of NNC-711 (10mg/kg, i.p.) on teicoplanin-induced epileptogenic activity was antagonized by bicuculline (GABA(A) receptor antagonist) but not by TPMPA (GABA(C) receptor antagonist).. It is reasonable to presume that teicoplanin-induced epileptogenic seizures are closely related with GABA-ergic mechanisms through GABA(A) receptors rather than GABA(C) receptors.

Topics: Animals; Anti-Bacterial Agents; Bicuculline; Brain; Disease Models, Animal; Dizocilpine Maleate; Electric Stimulation; Electroencephalography; Epilepsy; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; Male; Mice; Mice, Inbred ICR; Nipecotic Acids; Oximes; Phosphinic Acids; Pyridines; Teicoplanin

Dark neurons have plagued the interpretation of brain tissue sections, experimentally and clinically. Seen only when perturbed but living tissue is fixed in aldehydes, their mechanism of production is unknown. Since dark neurons are seen in cortical biopsies, experimental ischemia, hypoglycemia, and epilepsy, we surmised that glutamate release and neuronal transmembrane ion fluxes could be the perturbation leading to dark neuron formation while the fixation process is underway. Accordingly, we excised biopsies of rat cortex to simulate neurosurgical production of dark neurons. To ascertain the role of glutamate, blockade of N-methyl-D-aspartate (NMDA) and non-NMDA receptors was done prior to formaldehyde fixation. To assess the role of transmembrane sodium ion (and implicitly, water) fluxes, tetraethylammonium (TEA) was used. Blockade of NMDA receptors with MK-801 and non-NMDA receptors with the quinoxalinediones (CNQX and NBQX) abolished dark neuron formation. More delayed exposure of the tissue to the antagonist, CNQX, by admixing it with the fixative directly, allowed for some production of dark neurons. Aminophosphonoheptanoate (APH), perhaps due to its polarity, and TEA, did not prevent dark neurons, which were abundant in control formaldehyde fixed material unexposed to either receptor or ion channel antagonists. The results demonstrate a role for the pharmacologic subtypes of glutamate receptors in the pathogenetic mechanism of dark neuron formation. Our results are consistent with the appearance of dark neurons in biopsy where the cerebral cortex has been undercut, and rendered locally ischemic and hypoglycemic, as well as in epilepsy, hypoglycemia, and ischemia, all of which lead to glutamate release. Rather than a pressure-derived mechanical origin, we suggest that depolarization, glutamate release or receptor activation are more likely mechanisms of dark neuron production.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Artifacts; Biopsy; Brain Ischemia; Cerebral Cortex; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Glutamic Acid; Hypoglycemia; Male; Neurons; Potassium Channel Blockers; Quinoxalines; Rats; Rats, Wistar; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Tetraethylammonium

Twenty-four hours after mice are exposed to a single session of forced swimming in cold water, the ability of MK-801 (dizocilpine), a noncompetitive NMDA receptor antagonist, to antagonize electrically precipitated seizures is reduced. Conceivably, this reduction in MK-801's antiseizure efficacy reflects a stress-induced alteration in NMDA receptor-mediated neurotransmission due to changes in gene expression 24 h after a single stress. Recently, epigenetic interventional strategies impacting expression of genes whose regulation is controlled by the acetylation status of histone proteins in the nucleosome, an octomeric complex of histone proteins and promoter regions of double-stranded DNA, have been tested in preclinical models of various neuropsychiatric disorders, including Huntington disease and major depression. These strategies have been studied extensively in cancer biology. In the current investigation, the severity of the stress-induced reduction of MK-801's ability to raise the threshold voltage for the elicitation of tonic hindlimb extension was reduced when sodium butyrate (1.5 g/kg, ip) was administered around the time of stress. Prior research showed that this dose of sodium butyrate reliably increased the acetylation status of H3 and H4 histone proteins in the hippocampus and cerebral cortex of mice. Thus, the attenuation of the stress-induced reduction of MK-801's antiseizure efficacy may be due to the increased acetylation of histone proteins in the nucleosomal core and promotion of gene expression. These data encourage development of epigenetic strategies to prevent some of the deleterious consequences of stress.

Topics: Analysis of Variance; Animals; Butyrates; Dizocilpine Maleate; Dose-Response Relationship, Drug; Electroshock; Epilepsy; Male; Mice; Neuroprotective Agents; Stress, Psychological

To observe the effect of dizocilpine (MK801), a noncompetitive antagonist of N-methyl-D-aspartic acid (NMDA) receptor, on P-glycoprotein (P-gp) expression after limbic seizure, and to explore whether NMDA receptor play a role in the regulation of P-gp expression during limbic seizure.. 120 Wistar rats were randomly divided into 2 equal sets. 50 rats in Set 1 underwent intraperitoneal injection of lithium chloride, scopolamine, and pilocarpine so as to cause status epilepticus (SE) for 90 min. Then diazepam was given to terminate the SE. The rats were killed 0, 3, 6, 14, and 72 h after the SE respectively. The hippocampus was isolated. Realtime fluorescent quantitative RT-PCR (qRT-PCR) was used to detect the expression of multidrug resistance gene 1a (mdr1a) and mdr1b. Immunohistochemistry was used to detect the P-gp. The rats were used as controls. Another 60 rats (Set 2) were randomly divided into 3 equal groups: control group, given with normal saline (NS) only, SE group, given with NS 20 min before administration of pilocarpine, and MK801 group, given with MK801 20 min before administration of pilocarpine. The 3 groups in Set 2 were further divided into 2 equal subgroups of 10 rats to be killed 6 or 24 h after SE.. The mdr1a expression in hippocampus within 72 h after seizure was much higher at each time point: the level of mdr1a expression instantly after the seizure was terminated was [5.6 (2.9) x 10(5) mRNA copies/40 ng total RNA], significantly higher than that of the controls [2.4 (1.1) x 10(5) mRNA copies/40 ng total RNA, P < 0.05], increased to the level of [7.6 (6.3) x 10(5), P < 0.01] 3 h after, and kept at such level till 72 h after. The msr1b expression transiently increased 2.2 and 2.4 times that of the controls respectively 3 h and 6 h after the seizure was terminated [(3.3 +/- 0.4) x 10(4), and (3.6 +/- 1.0) x 10(4), both P < 0.01)]. The expression level of mdr1a 6 h after the seizure was terminated of the MK801 group was (4.3 +/- 0.8) x 10(5) and the expression level of mdr1b 6 h after the seizure was terminated of the MK801 group was (2.0 +/- 0.7) x 10(4), both significantly lower than those of the SE group (both P < 0.01). The P-gp expression level 24 h after the seizure was terminated of the MK801 group was 26.6 +/- 5.0 pieces of microvessels/400 times field, significantly lower than that of the SE group (39.0 +/- 4.1, P < 0.01).. MK801 down-regulates the overexpression of P-gp after seizure, which indicates that NMDA receptor may be involved in the regulation of P-gp expression during seizure. Therefore, it is possible to prevent the overexpression of P-gp after seizure by inhibiting NMDA receptor's overactivation effectively.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Gene Expression; Hippocampus; Immunohistochemistry; Male; Random Allocation; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Excitatory amino acids play an important role in generation of epileptic seizures. To study the participation of different types of their receptors in cortical epileptic afterdischarges, a noncompetitive NMDA receptor antagonist dizocilpine and a competitive AMPA receptor antagonist NBQX were used. Adult rats with implanted epidural stimulation and registration electrodes were pretreated either with NBQX (30 or 60 mg/kg i.p.) or with dizocilpine (0.1 or 0.5 mg/kg i.p.) and low-frequency stimulation of sensorimotor cortical area was repeatedly applied with stepwise increased current intensities. Lower dose of NBQX unexpectedly decreased thresholds for elicitation of spike-and-wave afterdischarges (ADs), clonic seizures accompanying this type of ADs and for transition into the second, limbic type of ADs. Lower dose of dizocilpine increased these three thresholds. Higher doses of either drug did not significantly change threshold intensities. Duration of ADs was also influenced by the two antagonists in opposite directions: higher dose of NBQX resulted in prolongation of ADs mainly due to an increased duration of the spike-and-wave part of ADs whereas dizocilpine shortened ADs in a dose-dependent manner affecting both types of ADs. In addition, NBQX did not influence interhemispheric responses meanwhile dizocilpine moderately suppressed these evoked potentials. According to our results, NMDA receptors are important for generation of cortical epileptic afterdischarges meanwhile the role of AMPA receptors is not clear and has to be analyzed.

Topics: Animals; Cerebral Cortex; Dizocilpine Maleate; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Electric Stimulation; Electroencephalography; Epilepsy; Evoked Potentials; Excitatory Amino Acid Antagonists; Quinoxalines; Rats; Rats, Wistar

The aim of the study was to define sleep disturbances in pentylenetetrazole (PTZ)-kindled rats and to explore the effects of the nootropic drug piracetam (Pir; 100 mg/kg) and the noncompetitive N-methyl-D-aspartate (NMDA)-antagonist MK-801 (0.3 mg/kg), which normalized learning performance in PTZ-kindled rats, on altered sleep parameters.. This is the first report showing a significant reduction in paradoxical sleep (PS) as a consequence of PTZ kindling. A correlation analysis revealed a significant correlation between seizure severity and PS deficit.. Pir did not interfere with seizure severity, and the substance did not ameliorate the PS deficit. However, the substance disconnected the correlation between seizure severity and PS deficit. MK-801, which reduced the severity of kindled seizures, counteracted the PS deficit efficaciously.. The results suggest that seizure severity and alterations in sleep architecture are two factors in the comprehensive network underlying learning impairments associated with epilepsy. Considering the results obtained in the experiments with Pir, reduction of seizure severity does not guarantee the reduction of impairments in the domain of learning.

Topics: Animals; Behavior, Animal; Convulsants; Disease Models, Animal; Dizocilpine Maleate; Electromyography; Epilepsy; Kindling, Neurologic; Learning; Male; Neuroprotective Agents; Nootropic Agents; Pentylenetetrazole; Piracetam; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Severity of Illness Index; Sleep; Sleep, REM; Wakefulness

Epileptic afterdischarges elicited by stimulation of sensorimotor cortex were chosen to test anticonvulsant effects of NMDA receptor antagonists in developing rats (12, 18 and 25 days old) with implanted electrodes. Afterdischarges were elicited four times with 10-min intervals in the experiments with dizocilpine and 20 min with the other two drugs. Dizocilpine (0.5 or 1 mg/kg), CGP 40116 (0.1, 0.5 or 1 mg/kg) or 2-amino-7-phosphonoheptanoic acid (AP7, 30 or 60 mg/kg) was injected intraperitoneally between the first and second stimulation. Intensity of movements accompanying stimulation was diminished regularly only by CGP 40116. Duration of afterdischarges was reduced and intensity of clonic seizures was decreased by CGP 40116 in all age groups; dizocilpine exhibited similar action in 25- and 18-day-old rats, AP7 only in 25-day-old animals. Anticonvulsant action of the three NMDA antagonists exhibited different developmental profiles in our model; this difference might be due to developmental changes of NMDA receptors.

Topics: 2-Amino-5-phosphonovalerate; Animals; Anticonvulsants; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Excitatory Amino Acid Antagonists; Injections, Intraperitoneal; Motor Cortex; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Time Factors

The relationship between epilepsy, modeled here by pentylenetetrazol kindling, and learning deficits, modeled here by long-term potentiation (LTP), was studied. The field excitatory postsynaptic potentials and population spikes (PS) were recorded from strata radiatum and pyramidale, respectively, in urethane-anesthetized rat dorsal hippocampus CA1 area upon stimulation of Schaffer collaterals. To induce LTP, a 100 Hz primed-burst stimulation protocol was used. Experiments were carried out at approximately 30 days after the last pentylenetetrazol dose. The effects of voltage dependent calcium channel blocker verapamil and N-methyl-D-aspartate receptor antagonist MK-801 on LTP expression were examined. Tetanic stimulation elicited both field excitatory postsynaptic potential LTP and PS LTP in control animals, and LTP-induction of the PS in control animals was attenuated by MK-801, but not by verapamil. By contrast, kindled rats showed LTP of the PS only. MK-801 reduced the extent of potentiation of PS amplitude and verapamil inhibited the PS amplitude potentiation, completely. The results suggest that seizure induction modifies mechanisms underlying LTP induction and causes a shift in the form of LTP expression. The pentylenetetrazol-kindling-induced increase in PS LTP is sensitive to verapamil and not to MK-801 and therefore primarily dependent on activation of voltage dependent calcium channels rather N-methyl-D-aspartate receptors. Kindling may lead to a shift in synaptic plasticity thresholds much like the shift that occurs during aging, and such alterations may contribute to deficits in learning and memory.

Topics: Animals; Anticonvulsants; Calcium Channel Blockers; Calcium Channels; Convulsants; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Excitatory Amino Acid Antagonists; Hippocampus; Kindling, Neurologic; Long-Term Potentiation; Male; Pentylenetetrazole; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate

The regulatory mechanisms of neuropeptide-metabolizing enzymes often play a critical role in the pathogenesis of neuronal damage. A systemic administration of pentylenetetrazol (PTZ), an antagonist of GABA(A) receptor ion channel binding site, causes generalized epilepsy in an animal model. In the present study, we examined the involvement of prolyl oligopeptidase (POP), thimet oligopeptidase/neurolysin (EP 24.15/16) and glial proteins in PTZ-treated rat brain regions, and the suppressive effect of MK-801, a non-competitive NMDA receptor antagonist, pretreatment for their proteins. The activity of POP significantly decreased in the hippocampus at 30min and 3h, and in the frontal cortex at 3h after PTZ treatment, and pretreatment with MK-801 recovered the activity in the cortex at 3h. The activity of EP 24.15/16 significantly decreased in the hippocampus at 3h and 1 day, and in the cortex at 3h after the PTZ administration, whereas pretreatment with MK-801 recovered the change of the activity. The Western blot analysis of EP 24.15 showed significant decrease of the protein level in the hippocampus 3h after the PTZ treatment, whereas pretreatment with MK-801 recovered. The expression of GFAP and CD11b immunohistochemically increased in the hippocampus of the PTZ-treated rat as compared with controls. Pretreatment with MK-801 also recovered the GFAP and CD11b expression. These data suggest that PTZ-induced seizures of the rats cause indirect activation of glutamate NMDA receptors, then decrease POP and EP 24.15/16 enzyme activities and EP 24.15 immunoreactivity in the neuronal cells of the hippocampal formation. We speculate that changes of those peptidases in the brain may be related to the levels of the neuropeptides regulating PTZ-induced seizures.

Topics: Animals; Brain; CD11b Antigen; Cerebral Cortex; Convulsants; Disease Models, Animal; Dizocilpine Maleate; Down-Regulation; Epilepsy; Excitatory Amino Acid Antagonists; GABA Antagonists; Glial Fibrillary Acidic Protein; Hippocampus; Male; Metalloendopeptidases; Nerve Degeneration; Neuroglia; Neurons; Pentylenetetrazole; Prolyl Oligopeptidases; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Serine Endopeptidases

Changes in the membrane distribution of N-methyl-D-aspartate (NMDA) glutamate receptors seem to produce dramatic modifications in neuronal excitability and other properties of the neuron. In order to determine in vivo if these effects are due to the binding of extracellular glutamate and glycine to NMDA extrasynaptic receptors, we perfused the hippocampus of freely moving rats with the actin depolymerizant agent latrunculin A (4 microM) through microdialysis probes. One month later, continuous microperfusion of glutamate (1 mM) or glycine (1 mM) was used to induce epileptic seizures in the animals pretreated with latrunculin A. Glutamate microperfusion induced seizures in 50% of the animals studied, and glycine induced seizures in 75% of the rats. However, no effect was observed on control rats, or on those animals previously treated with picrotoxin. Simultaneous microperfusion of 100 microM MK-801 significantly reduced the number and duration of seizures induced by both glutamate and glycine. This study demonstrates that the application of latrunculin A results in long-term changes in susceptibility to the epileptogenic action of glutamate and glycine.

Topics: Animals; Bridged Bicyclo Compounds, Heterocyclic; Dizocilpine Maleate; Drug Interactions; Epilepsy; Excitatory Amino Acid Antagonists; Glutamic Acid; Glycine; Hippocampus; Male; Microdialysis; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Thiazoles; Thiazolidines

The intrahippocampal perfusion of 4-aminopyridine (4-AP) in the rat produces immediate seizures and delayed neuronal death, due to the overactivation of N-methyl-D-aspartate (NMDA) receptors by endogenous glutamate released from nerve endings. With the same time course, 4-AP also induces the expression of the cell stress marker heat shock protein 70 (HSP70) in the contralateral non-damaged hippocampus. We have used this experimental model to study the mechanisms of the delayed neuronal stress and death. The NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate (MK-801), administered intraperitoneally 30 or 60 but not 120 min after 4-AP perfusion, when animals show intense electroencephalography epileptiform activity, prevented the delayed neurodegeneration whereas the seizures continued for about 3 h as in the control animals. With an identical time window, MK-801 treatment also modified the pattern of HSP70 expression; the protein was expressed in the protected perfused hippocampus but no longer in the undamaged contralateral hippocampus. The possible role of Ca2+ in the delayed cell death and HSP70 expression was also studied by coperfusing the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis(acetoxymethyl ester) with 4-AP. This treatment resulted in protective and HSP70 effects very similar to those of MK-801. These results suggest that the seizures are not linked to neurodegeneration and that NMDA receptors need to be continuously overactivated by endogenous glutamate for at least 60 min in order to induce delayed neuronal stress and death, which are dependent on Ca2+ entry through the NMDA receptor channel.

Topics: 4-Aminopyridine; Animals; Cell Count; Cell Death; Chelating Agents; Disease Models, Animal; Dizocilpine Maleate; Drug Interactions; Egtazic Acid; Electroencephalography; Epilepsy; Excitatory Amino Acid Antagonists; Functional Laterality; Glutamic Acid; Hippocampus; Male; Microdialysis; Nerve Degeneration; Neurons; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Stress, Physiological; Time Factors

To investigate the antiepileptic effect of dizocilpine (MK-801) on amygdala kindling models in rats and the effects of its combination with general antiepileptic drugs.. To establish amygdala kindling models in rats and observe the effect of dizocilpine on kindling models and its combination with general antiepileptic drugs (phenobarbital, valproate and nicardipine) at ineffective dose. The influence of dizocilpine on convulsions induced by semicarbazide (SCZ) in mice were also observed.. Dizocilpine (0.1-0.25 mg.kg-1, i.p.) was shown to dose-dependently inhibit amygdala kindled seizure, shorten the after discharge duration (ADD) and reduce the Racine's stage (P < 0.01). The combination of dizocilpine with phenobarbital, valproate, nicardipine at ineffective dose shortened ADD or reduced Racine's stages (P < 0.01). Dizocilpine (0.1-0.25 mg.kg-1, i.p.) significantly prolonged the latency and reduced the rate of convulsions and death in mice.. Dizocilpine inhibits the seizure of the amygdala kindling and improve the antiepileptic activity of phenobarbital, valproate and nicardipine, indicating that these combination may provide a new approach for treating epilepsy.

Topics: Amygdala; Animals; Anticonvulsants; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Female; Kindling, Neurologic; Male; Mice; Nicardipine; Phenobarbital; Random Allocation; Rats; Rats, Wistar; Semicarbazides; Valproic Acid

Dendritic targeting of mRNA and local protein synthesis are mechanisms that enable neurons to deliver proteins to specific postsynaptic sites. Here, we demonstrate that epileptogenic stimuli induce a dramatic accumulation of BDNF mRNA and protein in the dendrites of hippocampal neurons in vivo. BDNF mRNA and protein accumulate in dendrites in all hippocampal subfields after pilocarpine seizures and in selected subfields after other epileptogenic stimuli (kainate and kindling). BDNF accumulates selectively in discrete dendritic laminas, suggesting targeting to synapses that are active during seizures. Dendritic targeting of BDNF mRNA occurs during the time when the cellular changes that underlie epilepsy are occurring and is not seen after intense stimuli that are non-epileptogenic, including electroconvulsive seizures and high-frequency stimulation. MK801, an NMDA receptor antagonist that can prevent epileptogenesis but not acute seizures, prevents the dendritic accumulation of BDNF mRNA, indicating that dendritic targeting is mediated via NMDA receptor activation. Together, these results suggest that dendritic accumulation of BDNF mRNA and protein plays a critical role in the cellular changes leading to epilepsy.

Topics: Animals; Biological Transport; Brain-Derived Neurotrophic Factor; Cell Compartmentation; Convulsants; Dendrites; Dizocilpine Maleate; Electroshock; Epilepsy; Hippocampus; Kainic Acid; Kindling, Neurologic; Male; Pilocarpine; Protein Transport; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; RNA, Messenger; Seizures; Status Epilepticus; Synapses

To study the protection of IL-1ra in cultured developing neuron injury following Mg(2+)-free-induced epileptiform discharges.. Rat embryo cortical neurons cultured for 6 d and 17 d were directly exposed to Mg(2+)-free media, or pretreated with IL-1 receptor antagonist or NMDA receptor antagonists before being exposed to Mg(2+)-free media, and then returned to regular media.MTT assay was used to study mitochondrial function injury, laser-scanning confocal microscope to measure [Ca(2+)]i, and real-time RT-PCR to detect gene mRNA expression.. (1) MTT conversion rates were higher in neurons pre and co treated with 10 mg/L IL-1ra than those of neurons with only Mg(2+)-free treatment in neurons cultured for 17 d, but not in neurons cultured for 6 d.(2) [Ca(2+)]i was lower in neurons pre and co-treated with 10 mg/L IL-1ra than those of neurons with only Mg(2+)-free treatment, either in neurons cultured for 6 d or in neurons cultured for 17 d, and the effects of IL-1ra on [Ca(2+)]i change were different between neurons cultured for 6 d and neurons cultured for 17 d.(3) Pre and co-treated with 10 mg/L IL-1ra NR1 mRNA expression increase induced by Mg(2+)-free treatment was decreased, either in neurons cultured for 6 d or neurons cultured for 17 d, and this effect showed no difference between neurons cultured for 6 d and 17 d; Pre and co-treated with 10 mg/L IL-1ra NR2A mRNA expression increase induced by Mg(2+)-free treatment in neurons cultured for 17 d was decreased, and NR2A mRNA expression showed no difference between IL-1ra group and age-matched control group, but have no effect on neurons cultured for 6 d; Pre and co-treated with 10 mg/L IL-1ra have NR2B mRNA expression increase induced by Mg(2+)-free treatment was not affected, either in neurons cultured for 6 d or neurons cultured for 17 d.. Neuroprotection of IL-1Ra in seizure-induced injury is age-dependent. The mech-anism of the neuroprotection of IL-1Ra includes down-regulation of [Ca(2+)]i and others.

Topics: Animals; Cells, Cultured; Cerebral Cortex; Culture Media; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Female; Gene Expression; Interleukin 1 Receptor Antagonist Protein; Magnesium; Neurons; Neuroprotective Agents; Pregnancy; Rats; Rats, Wistar; Receptors, Interleukin; Receptors, N-Methyl-D-Aspartate; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Alterations in hippocampal neuronal Ca(2+) and Ca(2+)-dependent systems have been implicated in mediating some of the long-term neuroplasticity changes associated with acquired epilepsy (AE). However, there are no studies in an animal model of AE that directly evaluate alterations in intracellular calcium concentration ([Ca(2+)](i)) and Ca(2+) homeostatic mechanisms (Ca(2+) dynamics) during the development of AE. In this study, Ca(2+) dynamics were evaluated in acutely isolated rat CA1 hippocampal, frontal, and occipital neurons in the pilocarpine model by using [Ca(2+)](i) imaging fluorescence microscopy during the injury (acute), epileptogenesis (latency), and chronic-epilepsy phases of the development of AE. Immediately after status epilepticus (SE), hippocampal neurons, but not frontal and occipital neurons, had significantly elevated [Ca(2+)](i) compared with saline-injected control animals. Hippocampal neuronal [Ca(2+)](i) remained markedly elevated during epileptogenesis and was still elevated indefinitely in the chronic-epilepsy phase but was not elevated in SE animals that did not develop AE. Inhibiting the increase in [Ca(2+)](i) during SE with the NMDA channel inhibitor MK801 was associated in all three phases of AE with inhibition of the changes in Ca(2+) dynamics and the development of AE. Ca(2+) homeostatic mechanisms in hippocampal neurons also were altered in the brain-injury, epileptogenesis, and chronic-epilepsy phases of AE. These results provide evidence that [Ca(2+)](i) and Ca(2+)-homeostatic mechanisms are significantly altered during the development of AE and suggest that altered Ca(2+) dynamics may play a role in the induction and maintenance of AE and underlie some of the neuroplasticity changes associated with the epileptic phenotype.

Topics: Animals; Apoptosis; Calcium; Dizocilpine Maleate; Epilepsy; Hippocampus; Homeostasis; Male; Neurons; Rats; Rats, Sprague-Dawley; Seizures; Time Factors

Hypoxia of the brain may alter further seizure susceptibility in a different way. In this study, we tried to answer the question how episode of convulsion induced by hypoxia (HS) changes further seizure susceptibility, and how N-methyl-D-aspartic acid (NMDA) and AMPA/KA receptor antagonists influence this process. Adult Albino Swiss mice exposed to hypoxia (5% O(2)) developed clonic/tonic convulsions after about 340 s. Mice which underwent 10 s but not 5 s seizures episode subsequently exhibited significantly increased seizure susceptibility to low doses (equal ED(16)) of bicuculline (BCC) and NMDA during a 3-week observation period. No morphological signs of brain tissue damage were seen in light microscope on the third day after a hypoxia-induced seizure (HS). Learning abilities assessed in passive avoidance test as well as spontaneous alternation were not disturbed after an HS episode. Pretreatment with AMPA/KA receptor antagonist NBQX effectively prolonged latency to HS and given immediately after seizure episode also attenuated subsequent convulsive susceptibility rise, however, NMDA receptor antagonist, MK-801, appeared to be ineffective. These results suggest that a seizure episode induced by hypoxia, depending on its duration, may play an epileptogenic role. The AMPA/KA receptor antagonist prolongs the latency to HS, and given after this episode, prevents the long-term epileptogenic effect.

Topics: Animals; Avoidance Learning; Bicuculline; Brain Chemistry; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; GABA Antagonists; gamma-Aminobutyric Acid; Hypoxia; Mice; N-Methylaspartate; Quinoxalines; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Seizures

We examined the effects of non-competitive NMDA glutamate receptor antagonists on seizures elicited by 4-aminopyridine (4-AP), and in particular, on the expression of the transcription factor c-fos induced by these seizures. Induction of c-fos mRNA due to 4-AP-elicited seizures was ascertained by reverse transcription polymerase chain reaction in samples of the neocortex. Adult rats were pretreated with the NMDA receptor antagonists amantadine (40 mg/kg), ketamine (3mg/kg), dizocilpine (MK-801; 1mg/kg) or dextrometorphan (40 mg/kg); 4-AP (5mg/kg) was then injected i.p. Controls were treated with either antagonist only or with 4-AP only. Pretreatment with the antagonists (with the exception of amantadine) increased the latency of behavioural seizures, but not all of the antagonists caused symptomatic seizure protection. In the brains which were processed for Fos immunohistochemistry, quantitative evaluation of immunostained cells was performed in the neocortex and hippocampus. Treatment with either antagonist did not induce by itself c-fos expression, with the exception of amantadine, which caused slight Fos induction in the neocortex. Pretreatment with all the antagonists resulted in decrease of seizure-induced Fos immunoreactivity with respect to non-pretreated animals. Decrease of immunostained cells was significant in the neocortex, in the granule cell layer and hilus of the dentate gyrus, in hippocampal areas CA1 and CA2. MK-801, ketamine and dextrometorphan decreased significantly Fos immunoreactivity also in area CA3. The decrease of Fos immunostaining was not directly correlated with a suppression of behavioural seizures. The results support an important role of NMDA receptors in c-fos gene induction in acute 4-AP seizures.

Topics: 4-Aminopyridine; Amantadine; Animals; Behavior, Animal; Cerebral Cortex; Dizocilpine Maleate; Dopamine Agents; Epilepsy; Excitatory Amino Acid Antagonists; Gene Expression; Hippocampus; Immunohistochemistry; Ketamine; Male; Potassium Channel Blockers; Proto-Oncogene Proteins c-fos; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; RNA, Messenger

The intrahippocampal administration of 4-aminopyridine (4-AP) induces epileptic seizures and neurodegeneration, due probably to stimulation of glutamate release from synaptic terminals. We have studied the time course of the neurodegenerative changes produced by 4-AP, perfused through microdialysis cannulas in rat hippocampus, and correlated them with the expression of the inducible heat shock protein 70 (HSP70), detected immunocytochemically. Electroencephalographic seizure activity appeared immediately after the beginning of 4-AP perfusion. The first signs of histological neuronal damage were observed in CA1 and CA3 subfields of the perfused hippocampus 3 h after treatment and progressed until reaching a maximal neuronal loss at 24 h. In 4-AP-treated rats HSP70 was expressed mainly in neurons of the contralateral hippocampus, with a time course and cellular distribution very similar to the neurodegeneration observed in the perfused hippocampus, but no neuronal damage was observed. The N-methyl-D-aspartate (NMDA) receptor antagonists MK-801 and (3-phosphonopropyl)-piperazine-2-carboxylic acid prevented the seizures, the neurodegeneration and the expression of HSP70. These data demonstrate that the 4-AP-induced release of endogenous glutamate overactivates NMDA receptors in the perfused hippocampus and that the resulting neuronal hyperexcitability propagates to the contralateral hippocampus, generating a glutamate-mediated neuronal stress sufficient to induce the expression of HSP70 but not to produce neurodegeneration. These findings provide a useful model for investigating the relationships between neuronal hyperexcitation, neurodegeneration and the role of HSP expression.

Topics: 4-Aminopyridine; Animals; Anticonvulsants; Cell Count; Chromatography, High Pressure Liquid; Dizocilpine Maleate; Drug Interactions; Electroencephalography; Epilepsy; Extracellular Space; Functional Laterality; Gene Expression; Glutamic Acid; Hippocampus; HSP70 Heat-Shock Proteins; Immunohistochemistry; Male; Microdialysis; Nerve Degeneration; Neuroprotective Agents; Piperazines; Potassium Channel Blockers; Quinoxalines; Rats; Rats, Wistar; Somatosensory Cortex; Stress, Physiological; Time Factors

To investigate the effect of intracellular-free Ca2+ concentration ([Ca2+]i) on injury following transient Mg(2+)-free treatment in vitro in developing cortical neurons.. Embryo cortical neurons of rats cultured for 6 d and 17 d were directly exposed to Mg(2+)-free media, or pretreated with NMDA receptor antagonists or calcium channel antagonist before being exposed to Mg(2+)-free media. MTT assay was used to study the injury of neurons. [Ca2+]i were measured using fluo-3, a fluorescent calcium-sensitive dye and laser-scanning confocal microscope, and calculated by the fluorescent intensity.. Compared with control, MTT conversion rates decreased after transient (3 h) Mg(2+)-free treatment in neurons cultured for 6 d and 17 d in vitro, (59.1 +/- 6.87)% and (51.2 +/- 5.90)%, respectively. In neurons pre- and co-treated with 10 mumol.L-1 MK-801, 50 mumol.L-1 AP-5 and 10 mumol.L-1 nifedipine, MTT conversion rates were higher than those of neurons with only Mg(2+)-free treatment. Peak values of [Ca2+]i in neurons cultured for 6 d and 17 d were 2.4 +/- 0.23 and 3.2 +/- 0.32, respectively. Peak value of neurons 17 d in vitro was significantly higher than that of neurons 6 d in vitro (P < 0.05). In neurons pre- and co-treated with MK-801, AP-5 and nifedipine, [Ca2+]i were lower than those of neurons with only Mg(2+)-free treatment.. Neuronal injury and [Ca2+]i changes following Mg(2+)-free-treatment-induced seizure were different between neurons 6 d and 17 d in vitro. It suggested that the age-dependent [Ca2+]i changes might play a role in an age-dependent manner of injury following Mg(2+)-free-treatment-induced seizure. NMDA receptor-Ca2+ pathway activation was crucial in the [Ca2+]i change and the cellular injury induced by Mg(2+)-free treatment.

Topics: Aniline Compounds; Animals; Calcium; Calcium Channel Blockers; Calcium Channels; Cells, Cultured; Culture Media; Dizocilpine Maleate; Epilepsy; Magnesium; Neurons; Rats; Receptors, N-Methyl-D-Aspartate; Xanthenes

Hippocampal sclerosis and massive neurodegeneration in other parts of the limbic system are considered hallmarks of temporal lobe epilepsy. Using the rat model of kainate-induced status epilepticus, we sought to determine if limbic sclerosis after an excitotoxic insult follows a delayed type of neurodegeneration and is thus accessible to neuroprotective intervention after the insult. Effective pharmacologic neuroprotection after status epilepticus also addresses the old question of whether degenerative morphologic changes after an epilepsy-inducing event like status epilepticus are the primary cause of epileptogenesis (i.e., the development of recurrent spontaneous seizures) during the following weeks.. Female Wistar rats after 90 min of generalized status epilepticus were used. Molecular biologic and histologic techniques were used to demonstrate markers of delayed cell death (apoptosis) 48 h after the status. The neuroprotective effects of i.c.v. injections of caspase inhibitors and systemic injections of the anticonvulsant drugs (AEDs) dizocilpine and retigabine after the status epilepticus were studied. The effect of neuroprotective intervention on the development of recurrent spontaneous seizures was investigated by behavioral observation of the rats.. After generalized status epilepticus in Wistar rats, massive sclerosis of the hippocampus and the piriform cortex occurred. TUNEL labeling and electron microscopy revealed that apoptosis is involved in the degenerative processes. Immunohistochemical analysis of the time course of the expression of the proapoptotic protein Bax suggested a maximal induction of apoptosis 24-48 h after the status. Application of caspase inhibitors before or after the status did not reduce lesions, although Bax labeling was reduced. Injection of dizocilpine and to a lower extent also of retigabine after the status prevented limbic neurodegeneration and expression of markers of apoptosis. However, the neuroprotection by dizocilpine did not prevent the development of recurrent spontaneous seizures.. Prolonged seizure activity can induce delayed sclerosis in the hippocampus and other parts of the limbic system. This delayed cell loss can be prevented by neuroprotective drugs after a status epilepticus. However, the damage in limbic brain regions is not the main reason for limbic epileptogenesis and the occurrence of recurrent spontaneous seizures.

Topics: Animals; Anticonvulsants; Apoptosis; Biomarkers; Carbamates; Caspase Inhibitors; Dizocilpine Maleate; Enzyme Inhibitors; Epilepsy; Female; Hippocampus; Limbic System; Neuroprotective Agents; Phenylenediamines; Rats; Rats, Wistar; Sclerosis; Status Epilepticus; Time Factors

Stroke is the most common cause of acquired epilepsy. The purpose of this investigation was to characterize the role of calcium in the in vitro, glutamate injury-induced epileptogenesis model of stoke-induced epilepsy.. Fura-2 calcium imaging and whole-cell current clamp electrophysiology techniques were used to measure short-term changes in neuronal free intracellular calcium concentration and long-term alterations in neuronal excitability in response to epileptogenic glutamate injury (20 microM, 10 min) under various extracellular calcium conditions and in the presence of different glutamate-receptor antagonists.. Glutamate injury-induced epileptogenesis was associated with prolonged, reversible elevations of free intracellular calcium concentration during and immediately after injury and chronic hyperexcitability manifested as spontaneous recurrent epileptiform discharges for the remaining life of the cultures. Epileptogenic glutamate exposure performed in solutions containing low extracellular calcium, barium substituted for calcium, or N-methyl-d-aspartate (NMDA)-receptor antagonists reduced the duration of intracellular calcium elevation and inhibited epileptogenesis. Antagonism of non-NMDA-receptor subtypes had no effect on glutamate injury-induced calcium changes or the induction epileptogenesis. The duration of the calcium elevation and the total calcium load statistically correlated with the development of epileptogenesis. Comparable elevations in neuronal calcium induced by non-glutamate receptor-mediated pathways did not cause epileptogenesis.. This investigation indicates that the glutamate injury-induced epileptogenesis model of stroke-induced epilepsy is calcium dependent and requires NMDA-receptor activation. Further, these experiments suggest that prolonged, reversible elevations in neuronal free intracellular calcium initiate the long-term plasticity changes that underlie the development of injury-induced epilepsy.

Topics: Animals; Calcium; Cells, Cultured; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Glutamic Acid; Hippocampus; Intracellular Membranes; Neurons; Osmolar Concentration; Rats; Rats, Sprague-Dawley; Receptors, Glutamate; Receptors, N-Methyl-D-Aspartate; Stroke; Time Factors

Phosphinothricin (PPT), the active component of a widely used herbicide, induces convulsions in rodents and humans. PPT shares structural analogy with glutamate, which could explain its powerful inhibitory effect on glutamine synthetase and its probable binding to glutamate receptors. To characterize the epileptogenic effect of PPT, electrographic and behavioural studies were carried out on PPT-treated adult mice. We investigated the role of N-methyl-D-aspartate (NMDA) receptor activation and nitric oxide (NO) production in induction of seizures triggered by PPT, by using specific NMDA antagonist and nitric oxide synthase (NOS) inhibitor. The inhibitory effect of PPT on glutamine synthetase of mouse brain was assessed after in vitro and in vivo treatments. The results obtained show that PPT induces tonic-clonic seizures and generalized convulsions in mice. They suggest that these seizures are mediated through an NMDA receptor activation and NO production, without involvement of inhibition of glutamine synthetase.

Topics: Aminobutyrates; Animals; Brain; Dizocilpine Maleate; Electroencephalography; Enzyme Inhibitors; Epilepsy; Excitatory Amino Acid Antagonists; Glutamate-Ammonia Ligase; Male; Mice; Mice, Inbred C57BL; Nitric Oxide; Receptors, N-Methyl-D-Aspartate; Seizures

Vigilance and parallel occurrence of epileptic activity after administration of the 5-HT(1A) agonist 8-OH-DPAT and the NMDA receptor antagonist MK-801 were studied in the genetic absence epilepsy model WAG/Rij rats. Spike-wave discharges (SWD) were present predominantly in passive awake and light slow wave sleep (SWS1) either in control animals or after treatments. Injection of 8-OH-DPAT (20.0 microg/rat i.c.v.) caused marked increase and MK-801 (10.0 microg/rat i.c.v.) decrease in SWD densities, thus the ratios of SWD in passive awake and in SWS1. SWD densities of MK-801 plus 8-OH-DPAT in combination were similar to those of CSF+CSF treated control rats. Both 8-OH-DPAT and MK-801 transiently increased the duration of active awake, increased latency and decreased duration of rapid eye movement (REM) sleep. 8-OH-DPAT increased the amount of SWD despite the decrease in the duration of SWS1. MK-801 decreased the amount of SWD despite the lack of significant change in duration of passive awake or SWS1. Pre-treatment with MK-801 reversed 8-OH-DPAT- induced increase in duration of SWD without any effect on 8-OH-DPAT-induced changes in sleep parameters. Our studies provide evidence that 8-OH-DPAT-induced epileptic activity is independent of its effect on sleep, and that interaction of serotonergic and glutamatergic systems plays a role in the generation of SWD, but not in the regulation of vigilance and sleep.

Topics: 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Attention; Behavior, Animal; Dizocilpine Maleate; Epilepsy; Injections, Intraventricular; Male; Rats; Sleep

CHF3381 [n-(2-indanyl)-glycinamide hydrochloride] has been selected on the basis of a screening program as the compound displaying the highest anticonvulsant activity in the maximal electroshock seizure (MES) test and the best therapeutic index with reference to the rotarod test in mice and rats. In this study, the antiepileptic activity and the behavioural toxicity of CHF3381 were characterised in multiple model systems. CHF3381 effectively prevented MES-induced convulsions when administered i.p. (ED50, 24 mg/kg and 7.5 mg/kg) or p.o. (ED50, 21 mg/kg and 21 mg/kg) in both mice and rats, respectively. The time course of oral anti-MES activity in the rat was related to the brain concentration profile of unchanged CHF3381. Interestingly, the brain drug levels were about 4-5 times higher than in plasma. CHF3381 was very effective in mice against picrotoxin-, and i.c.v. N-methyl-D-aspartate (NMDA)-induced hind limb tonic extension (ED50 Approximately/=10 mg/kg), but was a weaker antagonist of 4-amynopyridine- and bicuculline-induced tonic seizures (ED50 approximately/=100 mg/kg), and ineffective against pentylentetrazole- and picrotoxin-induced clonic seizures. CHF3381 antagonised the behavioural effects and lethality of i.p. administered NMDA (ED50 = 57 mg/kg p.o.), indicating that the compound may act as a functional NMDA antagonist. In keeping with this idea, CHF3381 weakly displaced [(3)H]-TCP from binding to NMDA receptor channels (Ki, 8.8 microM). In the rat amygdala kindling model, CHF3381 was more efficient against kindling development than against kindled seizures (minimally active dose = 80 vs. 120 mg/kg i.p). Furthermore, it significantly increased the seizure threshold in kindled rats at relatively low doses (40 mg/kg i.p.). In contrast with MK-801-induced hyperactivity, CHF3381 moderately reduced the spontaneous locomotor activity in mice at anticonvulsant doses. Toxic effects on motor performance (rotarod test) were found at high doses only (TD50 approximately/= 300 mg/kg p.o., congruent with 100 mg/kg i.p. in both mice and rats). Furthermore, CHF3381 did not impair passive avoidance and Morris water maze responding in the therapeutic range of doses. Finally, the development of tolerance after repeated doses was negligible. These data indicate that CHF3381 exerts anticonvulsant and antiepileptogenic effects in various seizure models and possesses good therapeutic window, with scarce propensity to cause neurological side-effects.

Topics: Animals; Anticonvulsants; Dizocilpine Maleate; Drug Evaluation, Preclinical; Epilepsy; Excitatory Amino Acid Antagonists; Glycine; Indans; Kindling, Neurologic; Lamotrigine; Male; Mice; Motor Activity; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Triazines

Intraperitoneal guanosine has been shown to prevent quinolinic acid-induced seizures in mice. In this study, we investigated the effect of orally administered guanosine on seizures induced by the glutamate agonists quinolinic acid and kainate, and the endogenous glutamate releaser alpha-dendrotoxin. Guanosine (7.5 mg/kg, per os), administered 75 min in advance, prevented 70% of seizures induced by i.c.v. quinolinic acid, being as efficient as the NMDA channel blocker MK-801 administered intraperitoneally. Guanosine was ineffective against kainate-induced seizures, but significantly reversed the potentiation of seizures and death caused by the concomitant injection of MK-801. Guanosine also significantly prevented seizures and death induced by i.c.v. alpha-dendrotoxin, whereas MK-801 and phenobarbital only prevented death. Altogether, our findings underscore the therapeutic potential of oral administration of guanosine for treating diseases involving glutamatergic excitotoxicity, including epilepsy.

Topics: Animals; Brain; Caffeine; Death; Dizocilpine Maleate; Dose-Response Relationship, Drug; Elapid Venoms; Epilepsy; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Glutamic Acid; Guanosine; Kainic Acid; Male; Mice; Neuroprotective Agents; Phenobarbital; Phosphodiesterase Inhibitors; Quinolinic Acid; Receptors, Purinergic P1

Various genes for transcription factors are induced in neurons involving long-lasting synaptic plasticity that is accompanied by de novo protein synthesis. In this study, we analyzed the gene expression of NeuroD-related factor (NDRF/neuroD2), a neural basic helix-loop-helix transcription factor, in the mouse hippocampus following pentylenetetrazol (PTZ)-induced seizures. Both the levels of mRNA and protein of NDRF were elevated by PTZ injection. In contrast to c-fos, a representative neuronal activation-related immediate-early gene that was induced within 1 h after PTZ administration, induction of the NDRF gene expression reached a maximum level at 7-8 h after PTZ injection and was inhibited by pretreatment with cycloheximide and MK801. In situ hybridization of the mouse hippocampus revealed that NDRF mRNA was significantly induced in the dentate gyrus. During hippocampal development, NDRF transcripts were found to be highly expressed in a juvenile period, when extensive synaptogenesis occurs. Our present results demonstrate that NDRF is a new member of the family of activation-induced transcription factors, whose expression is probably regulated by immediate-early transcription factors. NDRF is thought to be involved in long-lasting neuronal activation.

Topics: Age Factors; Animals; Basic Helix-Loop-Helix Transcription Factors; Convulsants; Cycloheximide; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Gene Expression; Hippocampus; Male; Mice; Mice, Inbred ICR; Nerve Tissue Proteins; Neuronal Plasticity; Neuropeptides; Pentylenetetrazole; Protein Synthesis Inhibitors; RNA, Messenger; Transcription Factors

Twenty cDNA differential fragments were isolated from the hippocampus of rats in epileptic state using mRNA differential display technique. Four fragments were sequenced and compared with the known sequences in the Genebank, which showed that ERG8, ERG11, ERG12 had no significant identity to any known sequences; ERG14 had 64%-69% identity to microtubulin-associated protein of the rat. Because the differential expression of these genes was caused by epilepsy inducer coriaria lactone (CL) and anti-epilepsy drug MK-801 and ERG8 might be a novel candidate epilepsy gene; ERG11 and ERG12 might be novel candidate anti-epilepsy genes. Since the microtubulin-associated protein is closely associated with the collateral sprouting of mossy fibers in the hippocampus of seizured rat, the high expression of ERG14 in the early stage of epilepsy might predict the growth of axon and formation of synapse.

Topics: Animals; Carrier Proteins; Cloning, Molecular; Dizocilpine Maleate; DNA, Complementary; Epilepsy; Gene Expression Profiling; Hippocampus; N-Ethylmaleimide-Sensitive Proteins; Oligonucleotide Array Sequence Analysis; Random Allocation; Rats; Rats, Sprague-Dawley; Vesicular Transport Proteins

Specific [3H]-MK801 binding to rat NMDA receptors following the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied in striatal membrane fractions. MP administration (150 mg/kg, i.p.) caused an increase of 53% and 82% in [3H]-MK801 binding during seizure and the postseizure period respectively. Administration of CPA (2 mg/kg, i.p.) raised [3H]-MK801 binding by 72%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 64%, was observed. Saturation results indicate that receptor sites increased their maximal binding capacity (Bmax) in all treatments while the apparent dissociation constant (Kd) remained unchanged. MP administration brought about an increase of 52% and 42% in [3H]-MK801 binding sites during seizure and postseizure respectively. Administration of CPA raised receptor density by 75%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 62%, was observed. These results show that striatal NMDA receptors have a selective role in seizure activity in the basal ganglia and that the adenosine analogue administration may modify [3H]-MK801 binding in a way similar to that of the convulsant drug.

Topics: 3-Mercaptopropionic Acid; Adenosine; Animals; Cell Membrane; Convulsants; Corpus Striatum; Dizocilpine Maleate; Epilepsy; Male; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Tritium; Up-Regulation

Bilateral intracerebroventricular infusion of dl-homocysteic acid (DL-HCA) (600 nmol on each side) to immature 12-day-old rats induced generalized clonic-tonic seizures, recurring frequently for at least 90 min, with a high rate of survival. Electrographic recordings from sensorimotor cortex, hippocampus, and striatum demonstrated isolated spikes in the hippocampus and/or striatum as the first sign of dl-HCA action. Generalization of epileptic activity occurred during generalized clonic-tonic seizures, but electroclinical correlation was very low; dissociation between EEG pattern and motor phenomena was common. Seizures were accompanied by large decreases of cortical glucose and glycogen and by approximately 7- to 10-fold accumulation of lactate. ATP and phosphocreatine (PCr) levels remained unchanged even during longlasting (3 h) convulsions. Metabolite levels became normalized during the recovery period (24 h). The examination of the effect of selected antagonists of NMDA [AP7 (18.5 and 37 mg/kg, respectively), MK-801 (0.5 mg/kg)] and non-NMDA [NBQX (10, 15 and 30 mg/kg, respectively)] receptors revealed that seizures could be attenuated or prevented (depending on the dose employed) by antagonists of both NMDA and non-NMDA receptors, as evaluated not only according to the suppression of behavioral manifestations of seizures, but also in terms of the protection of metabolite changes accompanying seizures. All antagonists employed, when given alone in the same doses as those used for seizure protection, did not influence metabolite levels, with the exception of increased glucose concentrations. Furthermore, the pronounced anticonvulsant effect could be achieved by the combined treatment with low subthreshold doses of NMDA (AP7) and non-NMDA (NBQX) receptor antagonists, which may be of potential significance for a new approach to the treatment of epilepsy.

Topics: 2-Amino-5-phosphonovalerate; Age Factors; Animals; Cerebral Cortex; Disease Models, Animal; Dizocilpine Maleate; Electroencephalography; Energy Metabolism; Epilepsy; Excitatory Amino Acid Antagonists; Glucose; Homocysteine; Injections, Intraventricular; Male; Neuroprotective Agents; Quinoxalines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Seizures

SGB-017 (ADCI) is a novel anticonvulsant that blocks both voltage-activated sodium channels and N-methyl-D-aspartate (NMDA)-receptor-gated channels. Results by Rogawski et al. suggested that SGB-017 produces its anticonvulsant action primarily by inhibition of NMDA-receptor channels. However, SGB-017 is effective in several animal models of epilepsy that are unresponsive to NMDA antagonists. These results indicate that block of NMDA-receptor channels is not the only mechanism contributing to its anticonvulsant activity. Thus the effects of SGB-017 on neuronal sodium channels were investigated.. Whole cell voltage-clamp techniques were used to record sodium currents in freshly dissociated rat superior cervical ganglion (SCG) and hippocampal neurons and cultured human NT2 neurons. The effects of SGB-017 on the amplitude of sodium currents, elicited by a depolarizing pulse to 0 mV from different holding potentials, were measured and compared with those of carbamazepine (CBZ).. SGB-017 inhibited sodium currents in rat SCG and hippocampal neurons with a similar potency to CBZ. Like CBZ, the inhibition of sodium channels by SGB-017 was voltage dependent. Its median inhibitory concentration (IC50) for inhibition of sodium channels at depolarized holding potentials is similar to that for its inhibition of NMDA receptor channels. In human hNT2 neurons, SGB-017 was more potent than CBZ at inhibiting sodium currents.. SGB-017 produces its anticonvulsant activity by blocking both sodium- and NMDA-receptor channels in a voltage- and use-dependent manner. The combination of these two mechanisms of action makes SGB-017 an effective AED in several different animal models of epilepsy.

Topics: Animals; Anticonvulsants; Carbamazepine; Cells, Cultured; Disease Models, Animal; Dizocilpine Maleate; Epilepsy; Hippocampus; Humans; Neurons; Patch-Clamp Techniques; Rats; Rats, Long-Evans; Receptors, N-Methyl-D-Aspartate; Sodium Channel Blockers; Sodium Channels; Superior Cervical Ganglion

The involvement of glutamatergic and GABAergic mechanisms in the behavioral effects induced by the intrastriatal injection of 5-aminolevulinic acid (ALA) (1-8 mgr;mol/2 mgr;l), a metabolite that accumulates in porphyrias, was evaluated. ALA administration to adult female rats increased locomotor activity, induced clonic convulsions and elicited dose-dependent body asymmetry assessed by the elevated body swing test. ALA-induced convulsions were prevented by intrastriatal preadministration of the glutamate antagonists, 6, 7-dinitroquinoxaline-2,3-dione (8 nmol/0.5 microl) or dizocilpine (2. 5 nmol/0.5 microl), but not by the GABA agonist, muscimol (46 pmol/0. 5 microl). Body asymmetry was prevented only by 6, 7-dinitroquinoxaline-2,3-dione pretreatment. A higher dose of muscimol (92 pmol/0.5 microl) prevented both ALA-induced convulsions and body asymmetry. However, this dose of muscimol induced motor biases, which make difficult to ascertain the involvement of GABA(A) receptors in ALA-induced behavioral effects. This study suggests that glutamatergic mechanisms underlie the ALA-induced convulsions and body asymmetry. The present results may be of value in understanding the physiopathology of the neurological dysfunction occurring in acute porphyrias.

Topics: Aminolevulinic Acid; Animals; Convulsants; Corpus Striatum; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Female; GABA Agonists; gamma-Aminobutyric Acid; Glutamic Acid; Microinjections; Muscimol; Quinoxalines; Rats; Rats, Wistar

Activation of cholinergic mechanisms in the pontine reticular formation by local microinjections of carbachol was shown to induce pontine electrographic seizures and clonic convulsions. In this study we found that glutamate microinjections into the pons induced similar electrographic seizures and clonic convulsions. Microinjections into the PRF of glutamate in subconvulsive doses prior to carbachol potentiated the epileptogenic effect of carbachol. The duration of the seizure activity increased and the convulsions became more severe. The NMDA receptor antagonist MK-801 and the non-NMDA receptor antagonists DNQX significantly reduced the potentiating effect of glutamate. These results indicate a possible role of EAA receptors in the generation of epilepsy in the pons. They also suggest the importance of studying the role of synergistic interactions between EAA mechanisms and cholinergic mechanisms in the various pontine functions.

Topics: Animals; Brain Stem; Carbachol; Cholinergic Agonists; Dizocilpine Maleate; Drug Synergism; Epilepsy; Excitatory Amino Acid Antagonists; Excitatory Amino Acids; Glutamic Acid; Male; Microinjections; Pons; Quinoxalines; Rats; Receptors, N-Methyl-D-Aspartate; Time Factors

Systemic administration of kainic acid (KA) to rodents results in limbic seizures and subsequent neurodegeneration similar to that observed in certain types of human epilepsy, and it is a commonly used animal model for this disease. Oxidative stress has been suggested to play a role in the neuronal injury associated with KA administration. Based on this observation, chronic treatment with antioxidants has been proposed as a possible protective therapy against neuronal damage associated with epileptic seizures. Here we demonstrate by histochemical, electrophysiological, and biochemical means that knockout mice with decreased activity of the protective antioxidant enzyme glutathione peroxidase, which display elevated basal brain oxidative stress levels, are resistant to KA-induced seizure activity and neurodegeneration. This appears to be a result of decreased NMDA receptor function due to oxidation of its NR1 subunit. This suggests that the chronic use of antioxidants as antiepileptic agents to modulate NMDA-dependent seizure-induced neurodegeneration may be detrimental rather than protective and calls into question their use as a therapeutic agent in the treatment of epilepsy.

Topics: Animals; Brain; Cell Death; Disease Models, Animal; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Glutathione Peroxidase; In Situ Nick-End Labeling; In Vitro Techniques; Kainic Acid; Mice; Mice, Inbred Strains; Mice, Knockout; Neurons; Oxidative Stress; Receptors, N-Methyl-D-Aspartate; Sulfhydryl Compounds

We examined the generation, propagation and pharmacology of 4-aminopyridine (4-AP)-induced epileptiform activity (EA) in the intact interconnected limbic structure of the newborn (P0-7) rat in vitro. Whole-cell recordings of CA3 pyramidal cells and multisite field potential recordings in CA3, CA1, dentate gyrus, and lateral and medial entorhinal cortex revealed 4-AP-induced EA as early as P0-1. At this age, EA was initiated in the CA3 region and propagated to CA1, but not to the entorhinal cortex. Starting from P3-4, EA propagated from CA3 to the entorhinal cortex. Along the CA3 septo-temporal axis, EA arose predominantly from the septal pole and spread towards the temporal site. Whereas the onset of 4-AP-induced EA decreased with age from 21.2 +/- 1.6 min at P0-1 to 4.7 +/- 0.63 min at P6-7, the seizure duration increased in the same age groups from 98 +/- 14 s to 269.4 +/- 85.9 s, respectively. The EA was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) but not by DL-2-amino-5-phosphonovaleric acid (APV), (+)-MK-801 hydrogen maleate (MK-801) or (+/-)-alpha-methyl-4-carboxyphenylglycine (MCPG), suggesting that they were mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptor activation. We conclude that: (i) the septal pole of the hippocampal CA3 region plays a central role in the generation of EA in the neonatal limbic system; and (ii) AMPA/kainate receptor-mediated EA can be generated in CA3 already at birth. Therefore, the recurrent collateral synapses and circuits required for the generation of EA are developed earlier than previously suggested on the basis of studies on hippocampal slices.

Topics: 2-Amino-5-phosphonovalerate; 4-Aminopyridine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Age Factors; Animals; Animals, Newborn; Benzoates; Dizocilpine Maleate; Entorhinal Cortex; Epilepsy; Excitatory Amino Acid Antagonists; Glycine; Hippocampus; In Vitro Techniques; Neurons; Patch-Clamp Techniques; Rats; Rats, Wistar; Receptors, Glutamate

The aim of the study was to examine the role of NMDA receptors in modulation of protective effect against bicuculline toxicity after transient brain ischemia in mice. Animals were exposed for 30 min to bilateral clamping of the common carotid arteries (BCCA) in anaesthesia. MK-801 was administered intraperitoneally in two paradigms: a) acute treatment: twice, 1.0 mg/kg; 1 hour before clamping and 6 hours after re-circulation and b) chronic treatment: 0.1 mg/kg; started 24 hours after re-circulation and continued once daily for 13 days, the last injection was administered 24 hours before seizure induction. 14 days after BCCA, the animals were injected with bicuculline (3.5 mg/kg s.c). A significant decrease in seizure susceptibility could be observed in BCCA treated mice compared with sham-operated controls. Acute treatment with MK-801 did not affect seizure activity both in sham and BCCA mice. Chronic treatment with the drug potentiated anticonvulsant effect of brain ischemia but had no influence on seizure activity in sham-operated mice. The analysis of GABA content in brain tissue performed 14 days after BCCA showed a moderate increase in vehicle-treated mice and significant elevation after chronic treatment with MK-801. It can be suggested that NMDA receptors are not involved in the induction of a protective effect against bicuculline toxicity after transient brain ischemia. The prolonged treatment with low doses of MK-801 may potentiate a developed process in a mechanism of chemical preconditioning.

Topics: Age Factors; Animals; Behavior, Animal; Bicuculline; Brain Chemistry; Convulsants; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; gamma-Aminobutyric Acid; Ischemic Attack, Transient; Ischemic Preconditioning; Male; Mice; Receptors, N-Methyl-D-Aspartate; Seizures; Survival Rate

The aim of this study was to evaluate the contribution of ionotropic glutamate receptors to kindled seizure-evoked somatostatin release in the hippocampus, using a microdialysis approach. Basal and amygdala stimulation-evoked somatostatin-like immunoreactivity (-LI) release was significantly greater in kindled compared to naive rats. In naive rats, neither hippocampal perfusion with the selective AMPA/kainate receptor antagonist GYKI 52466 nor with the selective NMDA receptor antagonist MK-801 affected behavior, EEG, or somatostatin-LI release. In kindled rats, GYKI 52466 was still devoid of any effect, while MK-801 significantly decreased stimulus-evoked (but not basal) somatostatin-LI efflux. MK-801 produced identical effects when injected i.p. This study provides the first direct evidence that kindled seizure-evoked somatostatin release in the hippocampus is partly NMDA receptor dependent.

Topics: Amygdala; Animals; Disease Models, Animal; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Excitatory Amino Acid Antagonists; Glutamic Acid; Hippocampus; Kindling, Neurologic; Male; Neurons; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Seizures; Somatostatin

The objective of this study was to determine if a change in brain tissue excitatory amino acid receptor binding occurs during pregnancy using in vitro quantitative autoradiography and to examine seizure potential during pregnancy via central injection of N-methyl-D-aspartate (NMDA). For the receptor autoradiography studies, eight pregnant rats (day 21) and eight non-pregnant rats were euthanized with carbon dioxide, perfused, their brains dissected and frozen. Cryostat sections were taken and labeled in vitro by one of the following ligands: [3H]-CGP 39653, [3H]-glycine, [3H]-MK-801, [3H]-2-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) or [3H]-kainate. Optical density measurements of binding in 11 brain regions were performed using image analysis. To test seizure susceptibility, 74 rats were surgically implanted with an electrode into the hippocampus and a cannula into the lateral ventricle. Rats were mated; others served as non-pregnant controls. On gestational day 20, rats were randomized to receive no drug or an injection of NMDA (34, 68 or 136 nmol) through their indwelling cannulae. Seizures were assessed for 20 min. During pregnancy, the density of the NMDA competitive antagonist site measured by [3H]-CGP 39653 was decreased in the hippocampus, thalamus and hypothalamus (P<0.01), while the glycine modulation site was decreased in the cortex, hippocampus, thalamus, caudate and cerebellum (P<0.01). Kainate binding was significantly decreased in the hippocampus (P<0. 05). Total seizure duration and total number of seizures were significantly reduced in pregnant vs. non-pregnant rats (P<0.05). Pregnancy is associated with a significant alteration of NMDA and non-NMDA receptor binding in rats. These findings suggest that pregnancy affords some protection against seizures induced by an activation of NMDA receptors in the brain.

Topics: 2-Amino-5-phosphonovalerate; alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Convulsants; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Glutamic Acid; Glycine; Hippocampus; Male; N-Methylaspartate; Pregnancy; Pregnancy, Animal; Radioligand Assay; Rats; Rats, Long-Evans; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Tritium

"Kindling" is a phenomenon of epileptogenesis, which has been widely used as an experimental model of temporal lobe epilepsy. At the present work we investigated the contribution of NMDA receptors in the Pentylenetetrazol-induced "kindling" model in the mouse brain, by using quantitative autoradiography and the radioactive ligands [3H]MK801 and [3H]L-glutamate (NMDA-sensitive component). One week after establishment of kindling, a small but significant increase in [3H]MK801 as well as NMDA-sensitive [3H]glutamate binding was seen, being restricted to the molecular layer (ML) of the dentate gyrus (DG) and the CA3 region of the hippocampus. These binding augmentations persisted one month after establishment of kindling. A significant increase of NMDA receptor binding was also observed in the cortex-somatosensory and temporal one week after acquisition of the kindled state. The upregulation of NMDA receptors seen in DG and CA3 region of the hippocampus could be associated with the kindling process of this model especially with its maintenance phase, since it persists at long term, is area-specific and consistent with electrophysiological data. The increase of NMDA receptors seen in the cortex of the kindled animals could underlie the hyperexcitability detected by electrophysiological studies in this area.

Topics: Animals; Autoradiography; Dentate Gyrus; Dizocilpine Maleate; Epilepsy; Glutamic Acid; Hippocampus; Kindling, Neurologic; Male; Mice; Mice, Inbred BALB C; Pentylenetetrazole; Pyramidal Cells; Receptors, N-Methyl-D-Aspartate; Reference Values; Tritium; Up-Regulation

Administration of the excitotoxin kainate produces seizure activity and selective neuronal death in various brain areas. We examined the degeneration pattern of hippocampal neurons following systemic injections of kainate in the hamster and the rat. As reported, treatment with kainate resulted in severe neuronal loss in the hilus and CA3 in the rat. While the hilar neurons were also highly vulnerable to kainate in the hamster, neurons in the CA1 area, but not CA3, were highly sensitive to kainate. In both animals, immunoreactivity to anti-p50 nuclear factor kappa B antibody was increased in nuclei of the hilar neurons within 4 h following administration of kainate. Kainate treatment also increased the nuclear factor kappa B immunoreactivity in hamster CA1 neurons and rat CA3 neurons 24 h later. Neurons showing intense nuclear factor kappa B signal were stained with acid fuchsin. Kainate also increased DNA binding activity of p50 and p65 nuclear factor kappa B in the nuclear extract of the hippocampal formation as analysed by electrophoretic mobility shift assay in the hamster, suggesting that activation of nuclear factor kappa B may contribute to kainate-induced hippocampal degeneration. Administration of 100 nmol dizocilpine maleate 3 h prior to kainate attenuated kainate-induced activation of nuclear factor kappa B and neuronal death in CA1 in the hamster. The present study provides evidence that the differential vulnerability of neurons in the rat and the hamster hippocampus to kainate is partly mediated by mechanisms involving N-methyl-D-aspartate-dependent activation of nuclear factor kappa B.

Topics: Animals; Cell Death; Cell Nucleus; Cricetinae; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Hippocampus; Kainic Acid; Mesocricetus; N-Methylaspartate; Nerve Degeneration; Neurons; Neurotoxins; NF-kappa B; Rats; Rats, Sprague-Dawley

Since a disturbed balance between excitatory and inhibitory amino acid receptors is suggested to be an important condition for epileptogenic cortical activity, the present study has focused on the analysis of the densities of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), N-methyl-D-aspartate, kainate and GABA subtype A receptors in neocortical tissue surgically removed from patients with focal epilepsy. The mean densities (collapsed over cortical layers I-VI) and the laminar distribution patterns of [3H]AMPA, [3H]MK-801, [3H]kainate and [3H]muscimol binding to AMPA, N-methyl-D-aspartate, kainate and GABAA receptors were determined with quantitative receptor autoradiography in the neocortex of patients with focal epilepsy and controls. The tissue probes used in the present study were functionally characterized by parallel electrophysiological investigations. From that, the different probes could be subdivided into a spontaneously spiking and a non-spontaneously spiking group. The mean density of [3H]AMPA binding sites was significantly increased (+37%) in the group of epileptic brains (n = 10) compared with controls (n = 10), but the mean densities of [3H]MK-801, [3H]kainate and [3H]muscimol binding sites were not significantly altered (-8%, +/-0% and -7%, respectively). The relation between the densities of all four binding sites were simultaneously displayed as polar plots in each single brain ("receptor fingerprints"). The consistent up-regulation of [3H]AMPA binding sites in all epileptic brains was found to be associated with a down-regulation of the N-methyl-D-aspartate receptor in four of the five non-spontaneously spiking cases, and an associated up-regulation of the N-methyl-D-aspartate receptor was seen in all spontaneously spiking cases. Finally, the laminar distribution of binding site densities was analysed, since the mean densities collapsed over all neocortical layers may obscure layer-specific alterations. Layer- and receptor- specific up- or down-regulations were found in epileptic tissue compared with controls. Moreover, the laminar distribution pattern of current sinks associated with epileptiform potentials in a spontaneously spiking cortical slice was found to be co-localized with local maxima of AMPA receptor densities. The present analysis of four ionotropic glutamate and GABA receptor subtypes demonstrates a consistent and significant up-regulation of [3H]AMPA binding sites in all cases of human focal epilep

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Autoradiography; Binding Sites; Dizocilpine Maleate; Epilepsy; Female; Humans; Kainic Acid; Male; Muscimol; Neocortex; Receptors, AMPA; Receptors, GABA-A; Receptors, Glutamate; Tissue Distribution

Effect of dizocilpine (0.5 mg/kg i.p.) on epileptic afterdischarges elicited by low-frequency electrical stimulation of the dorsal hippocampus was studied in rat pups aged 12 and 18 days. Repeated elicitation of afterdischarges (ADs) in control animals resulted in a progressive increase of the duration of ADs in both age groups. Dizocilpine (MK-801) injected after the first afterdischarge suppressed this prolongation in 12-day-old rats only. Hypobaric hypoxia (simulated altitude of 9000 m for one hour) led to a marked prolongation of the first afterdischarge in both age groups with a tendency to shorter ADs after repeated stimulations. Dizocilpine potentiated this tendency in 12-day-old rat pups so that it became statistically significant. Administration of dizocilpine before hypoxia prevented the increase in duration of the first afterdischarge in both age groups.

Topics: Animals; Dizocilpine Maleate; Electric Stimulation; Electroencephalography; Epilepsy; Hippocampus; Hypoxia; Male; Neuroprotective Agents; Rats; Rats, Wistar

NMDA receptor activation has been implicated in modulating seizure activity; however, its complete role in the development of epilepsy is unknown. The pilocarpine model of limbic epilepsy involves inducing status epilepticus (SE) with the subsequent development of spontaneous recurrent seizures (SRSs) and is widely accepted as a model of limbic epilepsy in humans. The pilocarpine model of epilepsy provides a tool for looking at the molecular signals triggered by SE that are responsible for the development of epilepsy. In this study, we wanted to examine the role of NMDA receptor activation on the development of epilepsy using the pilocarpine model. Pretreatment with the NMDA receptor antagonist MK-801 does not block the onset of SE in the pilocarpine model. Thus, we could compare animals that experience similar lengths of SE in the presence or absence of NMDA receptor activation. Animals treated with MK-801 (4 mg/kg) 20 min prior to pilocarpine (350 mg/kg) (MK-Pilo) were compared to the pilocarpine treated epileptic animals 3-8 weeks after the initial episode of SE. The pilocarpine-treated animals displayed both ictal activity and interictal spikes on EEG analysis, whereas MK-801-pilocarpine and control animals only exhibited normal background EEG patterns. In addition, MK-801-pilocarpine animals did not exhibit any SRSs, while pilocarpine-treated animals exhibited 4.8 +/- 1 seizures per 40 h. MK-801-pilocarpine animals did not demonstrate any decrease in pyramidal cell number in the CA1 subfield of the hippocampus, while pilocarpine animals averaged 15% decrease in cell number. In summary, the MK-801-pilocarpine animals exhibited a number of characteristics similar to control animals and were statistically significantly different from pilocarpine-treated animals. Thus, NMDA receptor inhibition by MK-801 prevented the development of epilepsy and interictal activity following SE. These results indicate that NMDA receptor activation is required for epileptogenesis following SE in this model of limbic epilepsy.

Topics: Animals; Cell Count; Dizocilpine Maleate; Electroencephalography; Epilepsy; Excitatory Amino Acid Antagonists; Hippocampus; Male; Neurons; Pilocarpine; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Recurrence; Status Epilepticus; Time Factors

Seizures are one of the most frequent complications after cerebral ischemia in patients. Up to now it is unknown which mechanisms are responsible for this. As shown previously photothrombotic infarction in rat neocortex leads to a sweeping suppression of GABAergic inhibition. In this study we investigated whether and to what extent epileptiform discharges can be observed in this ischemia model. In neocortical slices from lesioned animals we did not find spontaneous epileptic activity or paroxysmal depolarisation shifts. However, ipsi- and contralateral to a photothrombotic lesion the frequency of double and multiple discharges was markedly increased when compared to unlesioned controls. Surprisingly, neither the drug lubeluzole which was has been shown to prevent the GABAergic disinhibition observed after photothrombotic lesioning of rat neocortex, nor the prevention of spreading depressions by the NMDA-receptor antagonist MK-801 during lesion induction significantly affected the frequency of epileptiform discharges. This indicates that the epileptiform discharges are probably caused by functional alterations of glutamatergic receptors.

Topics: Animals; Cerebral Infarction; Dizocilpine Maleate; Electric Stimulation; Electrophysiology; Epilepsy; In Vitro Techniques; Intracranial Embolism and Thrombosis; Light; Male; Neocortex; Neuroprotective Agents; Piperidines; Rats; Rats, Wistar; Reaction Time; Thiazoles

In this study, the anticonvulsant and adverse effects of compounds that belong to four different categories of systemically available N-methyl-D-aspartate (NMDA) receptor ligands were compared, namely the competitive antagonist CGP 40116, the noncompetitive antagonist MK-801 (dizocilpine), the glycineB receptor antagonist L-701,324, and the glycineB receptor high-efficacy partial agonist D-cycloserine. The maximal electroshock seizures (MES), which are widely used to detect drug efficacy against generalized tonic-clonic seizures in humans, were produced by transcorneal electrical stimulation. Abolition of tonic hind-limb extension was taken as the end-point. The drug-induced motor and long-term memory deficits were quantified by using the inverted screen test and the step-through passive-avoidance test, respectively. All tested compounds exhibited significant anticonvulsant effect. The rank order of potency for the respective compounds was: MK-801 = CGP 40116 > L-701,324 >> D-cycloserine. All of these compounds induced motor impairment at doses close to those found to be anticonvulsant, however, hyperlocomotion and stereotyped behavior occurred only with MK-801. The highest protective indices [PI = TD50 (inverted screen)/ED50 (MES)] were calculated for CGP 40116 and D-cycloserine (2.4 and 2.2, respectively). When tested for memory impairment at one-half the MES ED50, again only MK-801 induced significant memory disruption in the passive avoidance test. In conclusion, these results suggest that glycineB receptor high-efficacy partial agonists and competitive NMDA receptor antagonists may be advantageous to noncompetitive NMDA antagonists and glycineB receptor antagonists as potential antiepileptic drugs.

Topics: 2-Amino-5-phosphonovalerate; Animals; Anticonvulsants; Antimetabolites; Avoidance Learning; Binding, Competitive; Brain Chemistry; Cycloserine; Dizocilpine Maleate; Electroshock; Epilepsy; Excitatory Amino Acid Antagonists; Ligands; Male; Mice; Neurotoxins; Quinolones; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate

Stimulation of afferent fibers with current pulse trains has been reported to induce long-term potentiation (LTP) in piriform cortex in vitro but not in vivo. LTP has been observed in vivo only when trains are paired with behavioral reinforcement and as a consequence of kindled epileptogenesis. This study was undertaken in the urethan-anesthetized rat to determine if the reported failures to observe pulse-train evoked LTP in vivo may be related to a lesser persistence rather than lack of occurrence, if disinhibition might facilitate induction, and to examine the nature of the relationship between seizure activity and LTP. Stimulation of afferent fibers in the lateral olfactory tract with theta-burst trains under control conditions potentiated the monosynaptic field excitatory postsynaptic potential (EPSP) by approximately the same extent (20.3 +/- 2%; n = 12) as reported for the slice. However, in contrast to the slice, potentiation in vivo decayed to a low level within 1-2 h after induction (70% loss in 1.5 h, on average). The N-methyl--aspartate (NMDA)-receptor antagonists -APV and MK-801 blocked the induction of this decremental potentiation. Pharmacological reduction of gamma-aminobutyric acid-mediated inhibition at the recording site did not increase the duration of potentiation. In contrast, theta-burst stimulation applied after recovery from a period of epileptiform bursting induced stable NMDA-dependent potentiation. Mean increase in the population EPSP was approximately the same as under control conditions (21 +/- 2%; n = 6), but in five of six experiments there was little or no decay in potentiation for the duration of the monitoring period (

Topics: 2-Amino-5-phosphonovalerate; Animals; Dizocilpine Maleate; Electric Stimulation; Electrophysiology; Epilepsy; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; GABA Antagonists; gamma-Aminobutyric Acid; Long-Term Potentiation; Male; N-Methylaspartate; Neural Inhibition; Olfactory Pathways; Rats; Rats, Sprague-Dawley; Reaction Time; Synapses; Theta Rhythm

The molecular basis for developing symptomatic epilepsy (epileptogenesis) remains ill defined. We show here in a well characterized hippocampal culture model of epilepsy that the induction of epileptogenesis is Ca2+-dependent. The concentration of intracellular free Ca2+ ([Ca2+]i) was monitored during the induction of epileptogenesis by prolonged electrographic seizure activity induced through low-Mg2+ treatment by confocal laser-scanning fluorescent microscopy to directly correlate changes in [Ca2+]i with alterations in membrane excitability measured by intracellular recording using whole-cell current-clamp techniques. The induction of long-lasting spontaneous recurrent epileptiform discharges, but not the Mg2+-induced spike discharges, was prevented in low-Ca2+ solutions and was dependent on activation of the N-methyl-D-aspartate (NMDA) receptor. The results provide direct evidence that prolonged activation of the NMDA-Ca2+ transduction pathway causes a long-lasting plasticity change in hippocampal neurons causing increased excitability leading to the occurrence of spontaneous, recurrent epileptiform discharges.

Topics: 2-Amino-5-phosphonovalerate; Animals; Animals, Newborn; Benzoates; Calcium; Cells, Cultured; Dizocilpine Maleate; Egtazic Acid; Epilepsy; Excitatory Amino Acid Antagonists; Glycine; Hippocampus; Magnesium; Membrane Potentials; Microscopy, Confocal; Neurons; Nifedipine; Patch-Clamp Techniques; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Signal Transduction

The aim of this study was to assess whether a drug which combines an antagonistic action at both NMDA and non-NMDA receptors offers advantages for treatment of epileptic seizures compared to drugs which antagonize only one of these ionotropic glutamate receptors. The novel glutamate receptor antagonist LU 73068 (4,5-dihydro-1-methyl-4-oxo-7-trifluoromethylimidazo[1,2a]quinoxal ine-2-carbonic acid) binds with high affinity to both the glycine site of the NMDA receptor (Ki 185 nM) and to the AMPA receptor (Ki 158 nM). Furthermore, binding experiments with recombinant kainate receptor subunits showed that LU 73068 binds to several of these subunits, particularly to rGluR7 (Ki 104 nM) and rGluR5 (Ki 271 nM). In comparison, the prototype non-NMDA receptor antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo[f]quinoxaline) binds with high affinity to AMPA receptors only. Both NBQX and LU 73068 were about equieffective after i.p. injection in mice to block lethal convulsions induced by AMPA or NMDA. In the rat amygdala kindling model of temporal lobe epilepsy, LU 73068 dose-dependently increased the focal seizure threshold (afterdischarge threshold, ADT). When rats were stimulated with a current 20% above the individual control ADT, LU 73068 completely blocked seizures with an ED50 of 4.9 mg kg(-1). Up to 20 mg kg(-1), only moderate adverse effects, e.g. slight ataxia, were observed. NBQX, 10 mg kg(-1), and the glycine/NMDA site antagonist L-701,324 (7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-quinoline-2(1H)one), 2.5 or 5 mg kg(-1), exerted no anticonvulsant effects in kindled rats when administered alone, but combined treatment with both drugs resulted in a significant ADT increase. The data indicate that combination of glycine/NMDA and non-NMDA receptor antagonism in a single drug is an effective means of developing a potent and effective anticonvulsant agent.

Topics: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; Animals; Anticonvulsants; Disease Models, Animal; Dizocilpine Maleate; Drug Synergism; Epilepsy; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Imidazoles; Kindling, Neurologic; Male; Mice; Mice, Inbred Strains; N-Methylaspartate; Quinolones; Quinoxalines; Receptors, AMPA; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Tritium

The time course of alteration in neuronal nitric oxide synthase (nNOS) and the influence of glutamate receptor antagonists on immunoreactivity of nNOS were investigated immunohistochemically in rat hippocampus during penicillin-induced epilepsy. It was found that nNOS-like immunoreactivity in hippocampus increased at 4 h after initiation of seizure and reached a peak at 24 h. When MK-801 (6 micrograms) and DNQX (4 micrograms) were injected respectively into hippocampus 20 min before administration of penicillin, seizure was reduced in strength. Meanwhile, the nNOS-like immunoreactivity in hippocampus was decreased, compared with the group which were administered penicillin alone. These results suggest that the increase of nitric oxide may be related to the injury of neurons during and after epilepsy; the changes' of nNOS may be related to the activity of NMDA and non-NMDA receptors. Neuron protective effect of MK-801 and DNQX may be in part mediated by nNOS.

Topics: Animals; Dizocilpine Maleate; Electroencephalography; Epilepsy; Excitatory Amino Acid Antagonists; Female; Hippocampus; Male; Penicillin G; Quinoxalines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

We have developed and characterized a novel model of epileptogenesis based on the convulsive actions of flurothyl in mice. The hallmark feature of this model is a reliable change in the type of seizure expressed in response to flurothyl from generalized clonic to generalized tonic seizures. The purpose of our study was to evaluate the effects of chronic administration of valproate (VPA), phenytoin (PHT), and MK-801 on the change in seizure phenotype observed in our model system.. Male C57BL/6J mice received flurothyl seizures on 8 consecutive days. Two hours after the last generalized seizure, chronic drug or vehicle was administered twice daily at 12-h intervals for 28 days. The drugs evaluated were VPA (250 mg/kg), PHT (30 mg/kg), and MK-801 (0.5 mg/kg). After a 7-day drug washout period, mice were retested with flurothyl.. Among uninjected or vehicle-injected control mice, there was a significant increase in the proportion of animals expressing tonic seizures after the 28-day stimulation-free interval. Chronic administration of VPA or MK-801, but not PHT, blocked the characteristic change in seizure type from clonic to tonic.. The change in seizure phenotype observed after exposure to our paradigm indicates a fundamental reorganization in the propagation of flurothyl-initiated seizures. As in electrical kindling, VPA and MK-801 are effective at blocking or retarding the reorganization, whereas PHT is not. The concordance in pharmacologic profiles between kindling and our model suggests that the processes underlying changes in seizure susceptibility in these two models share mechanisms in common.

Topics: Animals; Anticonvulsants; Behavior, Animal; Brain Stem; Disease Models, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Epilepsy; Epilepsy, Generalized; Epilepsy, Tonic-Clonic; Flurothyl; Kindling, Neurologic; Male; Mice; Mice, Inbred C57BL; Motor Activity; Neural Pathways; Phenytoin; Valproic Acid

Clinically, and in experimental models, perinatal hypoxic encephalopathy is commonly associated with seizures. We previously described a rat model in which hypoxia induces seizures and permanently increases in seizure susceptibility in immature rats [postnatal day (P) 10-12] but not in older rats. In the present study, we compared the effect of pretreatment with the excitatory amino acid antagonists MK-801 and NBQX versus lorazepam in our rat model of perinatal hypoxia. Animals exposed to hypoxia at P10 without treatment have frequent seizures during hypoxia and subsequently exhibit increased seizure susceptibility to flurothyl. Treatment with 6-nitro-7-sulfamoylbenzo(f)quinoxaline-2,3-dione (NBQX 20 mg/kg) effectively suppressed hypoxia-induced seizures in immature rats and also protected against permanent changes in flurothyl threshold in adulthood, whereas treatment with MK-801 (1 mg/kg) or lorazepam (LZP 1 mg/kg) did not prevent these hypoxia-related epileptogenic effects. These results suggest that activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazol propionic acid (AMPA) receptors may partly mediate the age-dependent epileptogenic effect of hypoxia in the perinatal period.

Topics: Age Factors; Animals; Dizocilpine Maleate; Epilepsy; Excitatory Amino Acid Antagonists; Flurothyl; Hypoxia, Brain; Lorazepam; Male; Quinoxalines; Rats; Receptors, AMPA

The anticonvulsant properties of memantine (Mem) were compared to those of MK-801. Extracellular field recordings were obtained from area CA1 of guinea pig hippocampal slices in a total submersion chamber at 32 degrees C in normal oxygenated artificial cerebrospinal fluid (ACSF). Evoked responses were elicited by 0.07 Hz stimulation of the Schaffer collateral and commissural fibers. Bath perfusion of slices with Mg(2+)-free ACSF and N-methyl-D-aspartate (NMDA)-containing ACSF induced epileptiform afterdischarges following evoked responses. Pretreatment of slices by bath application of 100 microM Mem for 18-20 min prevented epileptiform afterdischarges under both convulsant conditions. Perfusion with 100 microM Mem alone for up to 50 min had no discernible effect on evoked responses. MK-801 was as effective at < or = 10 microM and required application for over 15 min to suppress afterdischarges completely. Both Mem and MK-801 suppressed epileptiform activity when applied after such activity was induced by NMDA or MG(2+)-free ACSF. The EC50 of Mem was 16.6 microM and that of MK-801 was 0.19 microM for blocking NMDA-induced evoked response suppression. Thus, in the guinea pig hippocampal slice preparation, Mem appeared to have anticonvulsant properties qualitatively similar to those of MK-801, but was 10-100 fold less potent.

Topics: Animals; Anticonvulsants; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Guinea Pigs; Hippocampus; In Vitro Techniques; Male; Memantine; Membrane Potentials; N-Methylaspartate; Pyramidal Cells; Synapses; Synaptic Transmission

Topics: Animals; Brain; Dizocilpine Maleate; Electroencephalography; Electron Transport Complex IV; Epilepsy; Glutamates; Glutamic Acid; Hemoglobins; Kainic Acid; Male; N-Methylaspartate; Oxidation-Reduction; Oxygen; Rats; Rats, Wistar; Spectrophotometry, Infrared

Bath application of trypsin (0.05%, type I) gave rise to epileptiform activities in CA1 of the rat hippocampal slice. A non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptors, MK-801, blocked the induction of the epileptiform activity, whereas a competitive antagonist, D-APV, showed weak antagonism on the induction of the epileptiform activity. These results may lead us to the understanding of the role of NMDA receptors in the neurotoxic action of trypsin.

Topics: 2-Amino-5-phosphonovalerate; Animals; Dizocilpine Maleate; Electrophysiology; Epilepsy; Hippocampus; In Vitro Techniques; Male; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Trypsin

Some non-competitive antagonists of N-methyl-D-aspartate (NMDA) were evaluated for potency to antagonize audiogenic seizures in genetically epilepsy-prone rats, following intraperitoneal administration. Phencyclidine (PCP), dizocilpine (MK-801), ketamine, ifenprodil and dextromethorphan, displayed anticonvulsant activity at doses similar to those which impaired performance in the rotarod equilibrium procedure. The noncompetitive NMDA receptor antagonists, at doses which slightly overlapped with the doses required for a full anticonvulsant protection against audiogenic seizures in genetically epilepsy-prone rats, induced profound untoward behavioural effects. This behavioural syndrome was characterized by marked ataxia, hyperactivity, stereotypes and wet dog shakes. In contrast, the effective anticonvulsant dose of 3-(2-carboxypiperazin-4-yl)propenyl-1-phosphonic acid (CPPene) was less than that required to impair rotarod performance and did not produce the PCP-like syndrome. A potential use in antiepileptic therapy, of CPPene or other new selective NMDA antagonists, with fewer neurotoxic effects but not for non-competitive antagonists such as MK-801, is suggested.

Topics: Acoustic Stimulation; Adrenergic alpha-Antagonists; Animals; Anticonvulsants; Dextromethorphan; Dizocilpine Maleate; Epilepsy; Injections, Intraperitoneal; Ketamine; Male; Movement; Phencyclidine; Piperazines; Piperidines; Postural Balance; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate

Sound-induced seizures in genetically epilepsy-prone rats were used to compare the anticonvulsant effect of phenytoin and diazepam with compounds which decrease glutamatergic neurotransmission including excitatory amino acid antagonists acting at N-methyl-D-aspartate (NMDA) receptors: D(-)CPPene, CGP 37849 and MK 801 or at the glycine/NMDA site: ACPC (1-aminocyclopropane-dicarboxylic acid) (partial agonist) or non-NMDA receptors: NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzo[f]-quinoxaline.Li) and GYKI 52466 (1-(aminophenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazepin e.HCl) or acting at sodium channels to decrease glutamate release: lamotrigine and BW 1003C87 (5(2,3,5-trichlorophenyl)-2,4-diaminopyrimidine ethane sulphonate). ED50 values against clonic seizures (in mumol/kg at the time of peak anticonvulsant effect) were: phenytoin 30.5 (2 h), diazepam 0.5 (0.5 h), MK 801 0.01 (4 h), D(-)CPPene 1.9 (4 h), CGP 37849 2 (1 h), GYKI 52466 24 (0.25 h), NBQX 40 (0.5 h), ACPC 1053 (0.5 h), BW 1003C87 2.2 (1 h), lamotrigine 4.8 (4 h). BW 1003C87, lamotrigine, MK 801, phenytoin, diazepam and CGP 37849 had the most favourable therapeutic indices (rotarod locomotor deficit ED50/anticonvulsant ED50).

Topics: 2-Amino-5-phosphonovalerate; Acoustic Stimulation; Amino Acids; Amino Acids, Cyclic; Analysis of Variance; Animals; Anticonvulsants; Behavior, Animal; Diazepam; Disease Models, Animal; Dizocilpine Maleate; Epilepsy; Female; Lamotrigine; Male; Motor Activity; Phenytoin; Pyrimidines; Quinoxalines; Rats; Rats, Sprague-Dawley; Time Factors; Triazines

1. The effects of the non-opioid antitussives caramiphen and carbetapentane and of the anticonvulsants 5,5-diphenylhydantoin and MK 801 were tested towards hypoxia-induced electrical changes in rat hippocampal slices. 2. The incidence of appearance of hypoxia-induced epileptiform bursting was significantly decreased (P < 0.05) by carbetapentane (50-100 microM), caramiphen (50-100 microM), 5,5-diphenylhydantoin (25-50 microM), and the glutamate antagonist dizocilpine (MK 801, 25-50 microM). 3. The incidence of reappearance of the CA1 population spike after hypoxia was significantly increased (P < 0.05) by carbentapentane (50-100 microM), caramiphen (50-100 microM), 5,5-diphenylhydantoin (25-50 microM), and MK 801 (25-50 microM). 4. The results suggest a useful role for non-opioid antitussives and some anticonvulsants in the treatment of hypoxia-induced functional disturbances.

Topics: Animals; Anticonvulsants; Antitussive Agents; Cyclopentanes; Dizocilpine Maleate; Electrophysiology; Epilepsy; Hippocampus; Hypoxia, Brain; In Vitro Techniques; Male; Membrane Potentials; Phenytoin; Rats; Rats, Wistar

Using the low-frequency kindling procedure, we studied the effects of periodic 2-week stimulus-free intervals and chronic scopolamine administration on hippocampal kindling seizure development. In Experiment 1, rats were divided into two groups, interval group and no-interval group. In the interval group a 2-week stimulus interval was set after every five consecutive daily stimulations until the 21st stimulation. The number of stimulating pulses required for the triggering of epileptic afterdischarge, pulse-number threshold (PNT), was used as an indicator of the seizure threshold. PNT, afterdischarge duration (ADD) and behavioral seizure stage (BSS) of each induced seizure in the initial stage of kindling, kindling rate, seizure parameters at the completion of kindling were recorded and compared to the values of the no-interval, control group. Our result showed that PNT at the 6th stimulation, the first stimulation after the first 2-week stimulus interval increased significantly compared to control. Other seizure parameters did not differ significantly between the two groups. In Experiment 2 scopolamine hydrobromide, 0.5 and 1.0 mg/kg i.p., was administered 1 h before each electrical stimulation until each rat showed the stage-3 seizure. PNT, ADD and BSS in the initial stage of kindling, kindling rate for the stage-3 and -5 seizures, seizure parameters at the first stage-3 and -5 were recorded and compared to the values of saline-treated, control group. Although scopolamine 1.0 mg/kg increased PNT at the 5th stimulation compared to control, no other significant changes of the seizure parameters were found by scopolamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Dizocilpine Maleate; Electric Stimulation; Electrodes, Implanted; Electroencephalography; Epilepsy; Hippocampus; Kindling, Neurologic; Male; Neuronal Plasticity; Rats; Rats, Wistar; Scopolamine; Stereotaxic Techniques

Topics: Amino Acids; Animals; Anticonvulsants; Autoradiography; Binding, Competitive; Brain; Brain Mapping; Convulsants; Culture Techniques; Dizocilpine Maleate; Epilepsy; Glycine; N-Methylaspartate; Neurons; Rats; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Synaptic Membranes; Synaptic Transmission

Systemic administration of kainic acid results in the development of a characteristic convulsive syndrome, accompanied by neuropathological alterations and loss of transmitter markers in some forebrain regions. Since some of these effects appear to involve the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors, the protection given by a non-competitive (MK-801) and a competitive (CGP 39551) NMDA receptor antagonist against the loss of glutamatergic and gamma-amino butyric acid (GABAergic) neurochemical markers was compared. Appropriate doses of both compounds (1 mg/kg MK-801 and 25 mg/kg CGP 39551) completely reversed the decrease of high affinity uptake of glutamate and activity of glutamate decarboxylase in the olfactory cortex, amygdala, hippocampus and lateral septum. In addition, they also essentially counteracted the increase of a glial marker, the enzyme glutamine synthetase, consequent to neuronal degeneration. The results confirmed that involvement of NMDA receptors is essential for the full expression of neuropathological effects of kainic acid. They also support the use of a competitive antagonist of the NMDA receptor, such as CGP 39551, to afford substantial protection against the excitotoxic damage, whilst giving fewer side effects and motor disturbances than MK-801.

Topics: 2-Amino-5-phosphonovalerate; Animals; Dizocilpine Maleate; Epilepsy; Kainic Acid; Male; Neuroglia; Neurotransmitter Agents; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Syndrome

To determine the effect of suppression of epileptiform activity that develops after hypoxic-ischemic injury in the immature brain, chronically instrumented near-term fetal sheep (119-133 days) were subjected to 30 minutes of complete cerebral ischemia: 6 were given a 0.3-mg/kg bolus of MK-801 at 6 hours after the insult followed by continuous infusion of 1 mg/kg over the next 36 hours, and were compared to 6 control sheep. Electrocorticographic activity and edema within the parasagittal region of the cortex were quantified with real-time spectral analysis and impedance measurements, respectively. Histological outcome was assessed 72 hours later. The intense epileptiform activity seen from 9 +/- 2 to 30 +/- 3 hours in the control group was completely suppressed in the MK-801-treated group. The onset of secondary cortical edema was delayed from 9.4 +/- 1.1 hours to 14.8 +/- 0.7 hours (p < 0.01). Neuronal damage was reduced, particularly in the lateral cortex and hippocampus (p < 0.05). Infarction of the parasagittal cortex was not prevented. These results suggest that N-methyl-D-aspartate-mediated epileptiform activity that develops after a global hypoxic-ischemic insult worsens neuronal outcome in the immature brain.

Topics: Animals; Brain Ischemia; Cell Death; Cerebral Cortex; Dizocilpine Maleate; Electric Impedance; Electroencephalography; Epilepsy; Fetal Diseases; Hippocampus; Sheep

In rats made susceptible to audiogenic seizures by exposing them to an intense noise at a critical time during development, subsequent noise exposure elicited seizures and induced the proto-oncogene c-fos in auditory regions of the brain. Cells showing Fos-like immunoreactivity were especially dense in dorsal and external cortices of the inferior colliculus, and were nearly absent after pretreatment with the N-methyl-D-aspartate (NMDA) antagonist MK-801. Noise exposure alone (i.e. no seizure) produced a localized zone of c-fos induction within the inferior colliculus, but only when presented during the time period when susceptibility to audiogenic seizures can be most effectively induced.

Topics: Acoustic Stimulation; Aging; Animals; Brain; Disease Models, Animal; Dizocilpine Maleate; Epilepsy; Gene Expression; Genes, fos; Proto-Oncogene Proteins c-fos; Rats; Rats, Inbred Strains; Seizures

Conventional intracellular recording techniques were used to investigate the N-methyl-D-aspartate (NMDA) and non-NMDA mediated synaptic mechanisms underlying the stimulus-induced paroxysmal depolarization shift (PDS) generated by cells in rat neocortical slices treated with bicuculline methiodide (BMI). The NMDA receptor antagonists CPP or MK-801 were ineffective in abolishing the PDS. However, both drugs were able to attenuate the late phase of the PDS and delay its time of onset. In contrast, the non-NMDA receptor blocker CNQX demonstrated potent anticonvulsant property by reducing the PDS into a depolarizing potential that was graded in nature. This CNQX-resistant depolarizing potential was readily blocked by CPP. Voltage-response analysis of the PDS indicated that the entire response (including its NMDA-mediated phase) displayed conventional voltage characteristics reminiscent of an excitatory postsynaptic potential that is mediated by non-NMDA receptors. We conclude that the activation of non-NMDA receptors is necessary and sufficient to induce epileptiform activity in the neocortex when the GABAergic inhibitory mechanism is compromised. The NMDA receptors contribute to the process of PDS amplification by prolonging the duration and reducing the latency of each epileptiform discharge. However, the participation of NMDA receptors is not essential for BMI-induced epileptogenesis, and their partial involvement in the PDS is dependent upon the integrity of the non-NMDA mediated input. The lack of NMDA-like voltage dependency observed in the PDS's late phase might reflect an uneven distribution of NMDA receptors along the cell and/or an association of this excitatory amino acid receptor subtype in the polysynaptic pathways within the neocortex.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amino Acids; Animals; Bicuculline; Cerebral Cortex; Dizocilpine Maleate; Electric Stimulation; Epilepsy; In Vitro Techniques; Male; Membrane Potentials; N-Methylaspartate; Neurons; Piperazines; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, Amino Acid; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate

Kindling, induced by repeated subconvulsive electrical or chemical stimulations leads to progressive and permanent amplification of seizure activity, culminating in generalized seizures. We report that kindling induced by electrical stimulation in the ventral hippocampus leads to a marked and transient increase in mRNA for NGF and BDNF in the dentate gyrus, the parietal cortex, and the piriform cortex. BDNF mRNA increased also in the pyramidal layer of hippocampus and in the amygdaloid complex. No change was seen in the level of HDNF/NT-3 mRNA. The increased expression of NGF and BDNF mRNAs was not influenced by pretreatment with the NMDA receptor antagonist MK801, but was partially blocked by the quisqualate, AMPA receptor antagonist NBQX. The presumed subsequent increase of the trophic factors themselves may be important for kindling-associated plasticity in specific neuronal systems in the hippocampus, which could promote hyperexcitability and contribute to the development of epileptic syndromes.

Topics: Animals; Brain; Brain-Derived Neurotrophic Factor; Dizocilpine Maleate; Epilepsy; Kindling, Neurologic; Male; Nerve Growth Factors; Nerve Tissue Proteins; Quinoxalines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; RNA, Messenger

The El mouse is an animal model with genetically determined epilepsy. To elucidate the mechanism of convulsive seizures in El mice, the effects of L-glutamate and glycine on the binding of (+)[3H]MK-801 were studied in well-washed membranes from forebrains of ddY, BALB/c and El (stimulated and non-stimulated) mice. There were no significant differences in affinity (Kd) or density (Bmax) among the 4 groups of mice under basal conditions. Incubation in the presence of L-glutamate and/or glycine led to an increase in apparent density, but not in affinity. No significant change was observed in either Kd, Bmax, or the percentage increase in (+)[3H]MK-801 binding amount the 4 groups in the presence of L-glutamate and/or glycine. These results suggest that the seizure susceptibility of El mice cannot be explained by changes in affinity or density of the NMDA receptor/channel complex.

Topics: Animals; Brain; Dizocilpine Maleate; Epilepsy; Glutamates; Glycine; Kinetics; Mice; Radioligand Assay; Receptors, N-Methyl-D-Aspartate

Persistent effects of chronic neonatal administration of the N-methyl-D-aspartate (NMDA) antagonist MK-801 were investigated by measuring susceptibility to CA1 kindling epileptogenesis in adulthood. Rat pups were chronically treated with MK-801 from postnatal day 8 through day 19. Hippocampal kindling showed an increase in electrical seizure duration in the MK-801-treated group as compared with controls along with a more severe expression of behavioral seizures during the first few kindling stimulations. These results show that neonatal interference with NMDA receptor function leads to a long-lasting increase in hippocampal excitability.

Topics: Animals; Animals, Newborn; Disease Susceptibility; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Female; Hippocampus; Kindling, Neurologic; Male; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate

Tonic-clonic convulsions of mutant quaking mice were antagonized by the intracerebroventricular injection of N-methyl-D-aspartate receptor antagonists. The competitive antagonists, CPP (3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid) and CGS 19755 (cis-4-(phosphonomethyl)-2-piperidine carboxylic acid), exerted a partial anticonvulsant action, with ED50S of 0.115 and 0.076 nmol, respectively. The non-competitive antagonists, TCP (1-(1-(2-thienyl)cyclohexyl)piperidine) and MK-801 [+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine), provided full protection, with ED50s of 4.49 and 2.67 nmol, respectively. The competitive antagonists elicited a marked ataxia whereas the non-competitive antagonists did not have side-effects. These results might reflect the involvement of glutamatergic neurotransmission in the convulsions of the quaking mutants.

Topics: Animals; Anticonvulsants; Dibenzocycloheptenes; Dizocilpine Maleate; Epilepsy; Injections, Intravenous; Male; Mice; Mice, Quaking; Phencyclidine; Physical Stimulation; Piperazines; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter

The inhibitory influence of excitatory amino acid (E.A.A.) antagonists such as kynurenic acid, 2-amino-5-phosphonopentanoic acid (AP5), cis-2,3-piperidine dicarboxylic acid (cis-2,3 PDA) and (+)-5-methyl-10,11,-dihydro-5H-dibenzo(a,d)cyclo-hepten-5,10-imine maleate (MK 801), has been studied on the epileptiform activity elicited in rat hippocampal slices, bathed in penicillin (1 mM). The rank of the inhibitory potency was: MK 801 greater than kynurenic acid greater than cis 2,3 PDA greater than AP5. Moreover, only MK 801 was able to block the last population spike of the penicillin-induced epileptiform bursting in 100% of the experiments. The data indicate that the antiepileptic activity of E.A.A. antagonists on the penicillin epileptiform bursting in CA1 pyramidal cells is low and limited, indicating that the hippocampal area is not the primary site of the anticonvulsant activity of E.A.A. antagonists.

Topics: Amino Acids; Animals; Anticonvulsants; Dibenzocycloheptenes; Dizocilpine Maleate; Electric Stimulation; Electrophysiology; Epilepsy; Hippocampus; In Vitro Techniques; Kynurenic Acid; Male; Penicillins; Rats; Rats, Inbred Strains

A radioimmunoassay is described for MK-801, a potent anticonvulsant and neuroprotective agent. Two immunogens were prepared from N-glutaryl- and N-carboxyethyl-MK-801 by coupling through their carboxyl groups to bovine serum albumin. Radioligands were I-125-iodotyramine conjugates of the same derivatives. Both types of antisera displayed bridge recognition which could be circumvented. In the first case, specificity for N-acyl derivatives was satisfied by acetylating the analyte prior to measurement. Antisera to the N-alkyl derivative yielded a satisfactory assay for MK-801 when the heterologous radioligand was employed. The first of these strategies was adopted for the routine assay. Specificity relative to hydroxylated metabolites was a function both of antiserum selectivity and sample preparation. High plasma concentrations of drugs concomitantly administered to epileptics posed special analytical problems. Assay sensitivity is 40 pg/ml in plasma and the interassay CV is about 5%.

Topics: Cross Reactions; Dizocilpine Maleate; Epilepsy; Evaluation Studies as Topic; Humans; Radioimmunoassay; Sensitivity and Specificity

Intracellular recordings were obtained from neurons located in the superficial layers of rat neocortical slices maintained in vitro. In the presence of 50 microM of bicuculline methiodide, epileptiform discharges were evoked by extracellular local stimuli. Bath applications of the NMDA receptor antagonists CPP or MK-801 (3-5 microM) produced the following effects: (i) prolongation of the burst latency; (ii) attenuation of the burst duration, mainly its late phase; (iii) increase in the threshold of burst activation. These effects were not accompanied by any change in membrane potential, input resistance and repetitive firing evoked by intracellular pulses of depolarizing current. Our results indicate the involvement of conductances mediated through NMDA receptors in the genesis of epileptiform activities recorded in the neocortex upon blockade of GABA receptors.

Topics: Animals; Bicuculline; Cerebral Cortex; Dibenzocycloheptenes; Dizocilpine Maleate; Epilepsy; Male; Piperazines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter

Anticonvulsant action of MK-801, a novel noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptor, was examined in genetically epileptic E1 mice. Systemic injection of MK-801 (0.1-1.0 mg/kg) potently suppressed generalized tonic-clonic convulsions of in a dose-dependent manner (ED50, 0.17 mg/kg). This anticonvulsant effect of MK-801 appeared at a dose which did not induce any obvious behavioral changes. Following the administration of a fully anticonvulsant dose of MK-801 (1 mg/kg), amino acid analysis revealed a significantly elevated level of glycine in the hippocampus. Levels of other amino acids including glutamate, aspartate, taurine, glutamine, alanine, and gamma-aminobutyrate were not changed either in the hippocampus or in the cerebral cortex. This study suggests that NMDA system may play an essential role in seizure-triggering mechanisms in E1 mouse.

Topics: Amino Acids; Animals; Anticonvulsants; Brain; Cerebral Cortex; Dibenzocycloheptenes; Dizocilpine Maleate; Epilepsy; Hippocampus; Mice; Mice, Mutant Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter

Topics: Amygdala; Animals; Anticonvulsants; Dibenzocycloheptenes; Dizocilpine Maleate; Electroencephalography; Epilepsy; Evoked Potentials; gamma-Aminobutyric Acid; Kindling, Neurologic; Neural Inhibition; Rats; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter

In an electrographic model of seizures in the hippocampal slice, both of the N-methyl-D-aspartate (NMDA) antagonists 2-amino-5-phosphonovaleric acid and 5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate (MK-801) prevented the progressive development of seizures but did not block previously induced seizures. Thus, a process dependent on the NMDA receptor-ionophore complex establishes a long-lasting, seizure-prone state; thereafter the seizures depend on non-NMDA receptor-ionophore mechanisms. This suggests that there is an important distinction between epileptogenesis and seizure expression and between antiepileptogenic and anticonvulsant pharmacological agents.

Topics: 2-Amino-5-phosphonovalerate; Animals; Anticonvulsants; Aspartic Acid; Dibenzocycloheptenes; Disease Models, Animal; Dizocilpine Maleate; Electric Stimulation; Electrophysiology; Epilepsy; Evoked Potentials; Hippocampus; In Vitro Techniques; N-Methylaspartate; Rats; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Seizures; Valine

Our understanding of how new antiepileptic drugs work mirrors what we know about how currently marketed antiepileptic compounds exert their action--that information is scarce and elusive. The mechanism of action of antiepileptic drugs is nevertheless inextricably linked to epileptogenesis itself, and investigations of several promising new compounds are underway to establish the levels at which these drugs act. Compounds act on synapses and membranes as well as affecting receptors, neurotransmitters, and peptides. The most extensive data are available on drugs that inhibit the action of GABA or its receptors, including new benzodiazepine-like agents and barbituric-acid derivatives. The few drugs that act by inhibiting the effects of excitatory amino acids are reviewed. Finally, the maximal electroshock test is an empirical method to determine the antiepileptic properties of a drug; several agents under development have been effective in this screening technique.

Topics: Acetamides; Acetates; Amines; Aminocaproates; Aminopyridines; Anti-Anxiety Agents; Anticonvulsants; Aspartic Acid; Benzodiazepines; Benzodiazepinones; Clobazam; Cyclohexanecarboxylic Acids; Dibenzocycloheptenes; Dizocilpine Maleate; Epilepsy; Felbamate; Flumazenil; GABA Antagonists; Gabapentin; gamma-Aminobutyric Acid; Glutamates; Glutamic Acid; Imidazoles; Lamotrigine; Phenylcarbamates; Propylene Glycols; Receptors, GABA-A; Triazines; Vigabatrin

In rats under urethane anesthesia, iontophoresis of high amounts of glutamate (50-150 nA) in hippocampus caused repetitive field potentials. These synchronized discharges were best recorded in the proximal part of stratum radiatum as positive waves of 10-15 ms duration and of 0.5-5 mV amplitude. A tetrodotoxin-sensitive faster component of 2-5 ms duration was frequently superimposed on the peaks of the positive waves and was followed by a negative wave of 1-6 mV and 20-30 ms. Glutamate-evoked discharges were suppressed by iontophoresis of N-methyl-D-aspartate (NMDA) antagonists, MK-801, Mg2+ and ketamine and also by ketamine injection (i.v. 5-10 mg/kg). The population spikes evoked by fimbrial stimulation were not facilitated by glutamate and the synchronized discharges were suppressed for up to 300 ms following the stimulation, suggesting the presence of an efficient inhibition during glutamate-induced synchronized activity. Glutamate also had no effect on paired-pulse inhibition. No synchronized discharges were recorded with a second electrode separated more than 150 microns from the iontophoretic electrode, suggesting that the activity was local. These data demonstrate that high amounts of glutamate evoke synchronized discharges in hippocampus, possibly through activation of NMDA receptors. The model presented may be utilized to study the mechanisms of synchronization without disinhibition.

Topics: Action Potentials; Animals; Dibenzocycloheptenes; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Glutamates; Glutamic Acid; Hippocampus; Male; Rats; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter

CGP 31358, a novel triazole, inhibited the binding of L-[3H]glutamate and [3H]MK-801 to the N-methyl-D-aspartate (NMDA) receptor complex in rat brain synaptic membrane fractions, and showed anticonvulsant activity in mice. It had no effect on the strychnine-insensitive binding of [3H]glycine. Saturation and Hill analyses indicated that CGP 31358 binds to a site on the NMDA receptor which is separate from, but coupled to, both the transmitter recognition site and the channel domain. Available data indicate that this site is distinct from those with which tricyclic antidepressants and ifenprodil interact. CGP 31358 is a new chemical entity with a novel mechanism of action at the NMDA receptor, and as such may form a tool for understanding the molecular pharmacology of this receptor-channel complex.

Topics: Animals; Anticonvulsants; Binding, Competitive; Brain; Dibenzocycloheptenes; Dizocilpine Maleate; Epilepsy; Glutamates; Glutamic Acid; Mice; Rats; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Subcellular Fractions; Triazoles

Recent studies have demonstrated that (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), a use-dependent blocker of N-methyl-D-aspartate (NMDA)-activated membrane channels, attenuates the development of long-term potentiation in vitro and kindling in vivo. Both of these phenomena are manifestations of physiological plasticity related to behavioural states and the results of these studies add to the gathering evidence for the involvement of the NMDA receptor/channel system in such processes. In the present experiment, slices of hippocampus, prepared from rats, were electrically stimulated to produce either long-term potentiation of the CA1 population spike or stimulus train-induced epileptiform bursting in area CA3. At 10 microM, MK-801 attenuated the development of long-term potentiation, but had no attenuating effect upon the previously-potentiated population spike. Similarly, 10 microM MK-801 attenuated the development of epileptiform activity in area CA3, but had little or no effect on the previously-established bursting in area CA3. These data support the suggestion that MK-801 exerts an antiepileptogenic, but not an anticonvulsant effect, at concentrations which also inhibit long-term potentiation.

Topics: Animals; Anticonvulsants; Dibenzocycloheptenes; Dizocilpine Maleate; Electric Stimulation; Epilepsy; Hippocampus; In Vitro Techniques; Male; Rats; Rats, Inbred Strains; Tetany; Time Factors

The actions of MK-801, a noncompetitive antagonist at the N-methyl-d-aspartate subtype of excitatory amino acid receptor, were investigated on the development of kindling and on seizures in the electroshock and kindling models. The drug MK-801 potently and effectively suppressed the tonic hindlimb extension component of electroshock-induced seizures; it also suppressed both the electrophysiological and behavioral manifestations of the development of kindling. In contrast to its effects on electroshock-induced seizures and the development of kindling, MK-801 only partly reduced the duration of seizures in fully kindled animals and did not elevate the threshold for afterdischarge despite the use of a large dose, associated with profound untoward behavioral effects. Together with previous findings, these results support the idea that noncompetitive blockade of NMDA receptors markedly inhibits the development of kindling. The diminished effectiveness of MK-801 against kindled seizures suggests that MK-801 will not be a clinically-useful anticonvulsant against complex partial seizures.

Topics: Amygdala; Animals; Anticonvulsants; Dibenzocycloheptenes; Dizocilpine Maleate; Electroshock; Epilepsy; Kindling, Neurologic; Male; Models, Neurological; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter