The antiepileptic effects of sodium valproate and the calcium antagonist riodipine when used jointly in a model of generalized korazol-induced epileptic activity]

In experiments on male Wistar rats on the model of generalized pentylenetetrazol-induced epileptic activity the efficacy of the combination of the drugs influencing different mechanisms of epileptogenesis: sodium valproate enhancing GABA-ergic processes and calcium antagonist, ryodipine (1,4-dihydropyridine), have been studied. Sodium valproate and ryodipine when used in combination at relatively small doses (70 and 0.75 mg/kg, respectively) produced more marked antiepileptic effect than each of these drugs given alone. The results obtained suggest that complex pathogenetic therapy (CPT) as a combination of antiepileptic drugs acting on corresponding basic mechanisms of respective form of epilepsy is reasonable to be used. According to our previous results, CPT can reduce the risk of side effects of each drug due to decreased doses. CPT may be of great importance in case of long-term treatment.     

Effect of combined treatment of thioperamide with some antiepileptic drugs on methionine-sulfoximine induced convulsions in mice

Methionine-sulfoximine (MSO), a convulsant is known to increase the activity of histamine N-methyl transferase. The effect of a selective H3 receptor agonist R- (alpha) methylhistamine (RAMH) and antagonist (thioperamide, THP) and some antiepileptic drugs (gabapentin and sodium valproate) have been evaluated on MSO-induced convulsions in mice. The effect of THP was also evaluated in combination with these antiepileptic drugs. Sodium valproate (300 mg/kg, po) and gabapentin (400 mg/kg, po) offered protection against MSO-induced convulsions as evidenced by a significant prolongation of latency to abnormal dorsoflexion and complete protection against mortality within 6 h of administration. THP (15 mg/kg, ip) alone and in combination with sub-effective doses of gabapentin (75 mg/kg, po) and sodium valproate (75 mg/kg, po) revealed no significant differences from the control group or either drug alone. Hence, the convulsant action of MSO does not appear to be mediated via histaminergic mechanisms.     

Interaction of hydroalcoholic extract of Acorus calamus Linn. with sodium valproate and carbamazepine

Anticonvulsant property of Acorus calamus is known. Since combination therapy can lower the dose of individual drug and dose related toxicities, in this study, the effect of co-administration of hydroalcoholic extract of A. calamus (HAEAC) on conventional antiepileptic drugs (AEDs), sodium valproate and carbamazepine was determined using pentylenetetrazole-induced seizures model in rats. On combining the subanticonvulsant doses of HAEAC with sodium valproate and carbamazepine, greater protection as compared to either drug alone was observed. This was not related to change in levels of the AEDs. Thus, the results further substantiate anticonvulsant effect of HAEAC and suggest a potential for add on therapy with AEDs.     

Influence of Ivabradine on the Anticonvulsant Action of Four Classical Antiepileptic Drugs Against Maximal Electroshock-Induced Seizures in Mice

Although the role of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in neuronal excitability and synaptic transmission is still unclear, it is postulated that the HCN channels may be involved in seizure activity. The aim of this study was to assess the effects of ivabradine (an HCN channel inhibitor) on the protective action of four classical antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) against maximal electroshock-induced seizures in mice. Tonic seizures (maximal electroconvulsions) were evoked in adult male albino Swiss mice by an electric current (sine-wave, 25 mA, 0.2 s stimulus duration) delivered via auricular electrodes. Acute adverse-effect profiles of the combinations of ivabradine with classical antiepileptic drugs were measured in mice along with total brain antiepileptic drug concentrations. Results indicate that ivabradine (10 mg/kg, i.p.) significantly enhanced the anticonvulsant activity of valproate and considerably reduced that of phenytoin in the mouse maximal electroshock-induced seizure model. Ivabradine (10 mg/kg) had no impact on the anticonvulsant potency of carbamazepine and phenobarbital in the maximal electroshock-induced seizure test in mice. Ivabradine (10 mg/kg) significantly diminished total brain concentration of phenytoin and had no effect on total brain valproate concentration in mice. In conclusion, the enhanced anticonvulsant action of valproate by ivabradine in the mouse maximal electroshock-induced seizure model was pharmacodynamic in nature. A special attention is required when combining ivabradine with phenytoin due to a pharmacokinetic interaction and reduction of the anticonvulsant action of phenytoin in mice. The combinations of ivabradine with carbamazepine and phenobarbital were neutral from a preclinical viewpoint.     

Effect of verapamil on focal epileptic activity in the rat cerebral cortex

Experiments were carried out on 64 nonanesthetized male Wistar rats (200-220 g). Epileptic foci were induced by the application of a filter paper saturated with a solution of benzylpenicillin sodium salt (12,000 and 20,000 U/ml) to the sensorimotor cortex. It was shown that subsequent intraperitoneal administration of verapamil (5 mg/kg and 10 mg/kg) during steady focal epileptic activity (EpA) resulted in the suppression of EpA in most animals. The antiepileptic effect of verapamil was manifested in a reduced frequency and amplitude of spike discharges, decreased power of epileptic foci and less frequent appearance of seizure (ictal) discharges. The role of Ca canals of neuronal membranes in the pathogenesis of epilepsy is discussed.     

Interaction of Delta Sleep-inducing Peptide and Valproate on Metaphit Audiogenic Seizure Model in Rats

Effects of valproate (VPA), a conventional antiepileptic drug and natural delta sleep-inducing peptide (DSIP) on metaphit (1-[1-(3-isothiocyanatophenyl)-cyclohexyl]-piperidine)-induced audiogenic reflex epilepsy were studied. For the purpose of the study, valproate in the doses of 50 or 75 mg/kg and DSIP (1.0 mg/kg) was i.p. injected either alone or in combination to adult Wistar male rats with fully developed metaphit seizures after eight audiogenic testing. The animals were stimulated using an electric bell (100 ± 3 dB and 5–8 kHz, for 60 s) 60 min after metaphit injection and afterwards at hourly intervals during the experiment. For EEG recording and power spectra analysis, three gold-plated screws were implanted into the scull. In EEGs of metaphit-treated animals polyspikes, spike-wave complexes and sleep-like patterns were recorded, while the power spectra were increased. Combined treatment of metaphit-induced seizures with valproate and DSIP was more effective than drugs alone especially during 4 h after administration. None of the applied dose combinations eliminated the EEG signs of metaphit-provoked epileptiform activity. Taken together, the results of the present study suggest that the combinations of valproate and DSIP should be considered as beneficial polytherapy in metaphit model of epilepsy.     

Effects of the antiepileptic drug valproate on metabolism and function of inhibitory and excitatory amino acids in the brain

Valproate is currently one of the major antiepileptic drugs in clinical use. Because of its wide spectrum of anticonvulsant activity against different seizure types, it has repeatedly been suggested that valproate acts through a combination of several mechanisms. As shown in this review, there is substantial evidence that valproate increases GABA turnover and thereby potentiates GABAergic functions in some specific brain regions, such as substantia nigra, thought to be involved in the control of seizure generation and propagation. Furthermore, valproate seems to reduce the release of the epileptogenic amino acid gamma-hydroxybutyric acid and to block cell firing induced by NMDA-type glutamate receptors. In addition to effects on amino acidergic neurotransmission, valproate presumably exerts a direct action on ion channels, thereby limiting sustained repetitive neuronal firing. Recent microdialysis data suggest that valproate also alters dopaminergic and serotonergic functions. These diverse effects of valproate might explain why the drug not only exerts anticonvulsant activity but also other pharmacodynamic and pharmacotherapeutic actions, such as antipsychotic and antidystonic efficacy.Special issue dedicated to Dr. Claude Baxter.     

Mexiletine and its Interactions with Classical Antiepileptic Drugs: An Isobolographic Analysis

Using the mouse maximal electroshock test, the reference model of tonic–clonic seizures, the aim of the present study was to determine the type of interaction between mexiletine (a class IB antiarrhythmic drug) and classical antiepileptics: valproate, carbamazepine, phenytoin, and phenobarbital. Isobolographic analysis of obtained data indicated antagonistic interactions between mexiletine and valproate (for fixed ratio combinations of 1:1 and 3:1). Additivity was observed between mexiletine and valproate applied in proportion of 1:3 as well as between mexiletine and remaining antiepileptics for the fixed ratios of 1:3, 1:1, and 3:1. Neither motor performance nor long-term memory were impaired by mexiletine or antiepileptic drugs regardless of whether they were administered singly or in combination. Mexiletine did not significantly affected brain concentrations of carbamazepine, phenobarbital or phenytoin. In contrast, the antiarrhythmic drug decreased by 23 % the brain level of valproate. This could be, at least partially, the reason of antagonistic interaction between the two drugs. In conclusion, the observed additivity suggests that mexiletine can be safely applied in epileptic patients treated with carbamazepine, phenytoin or phenobarbital. Because of undesirable pharmacodynamics and pharmacokinetic interactions with valproate, mexiletine should not be used in such combinations.

     

Effect of diazepam, carbamazepine, sodium valproate and their combinations with vitamin preparations on epileptic activity

The anticonvulsive action of diazepam, carbamazepine, sodium valproate and their combinations with pyridoxal-5-phosphate, nicotinamide, and alpha-tocopherol were investigated in acute experiments on mice with corazole-induced seizures. Diazepam (0.5 mg/kg), carbamazepine (50 mg/kg) and sodium valproate (200 mg/kg) were shown to reduce convulsive intensity and lethality. Vitamins nicotinamide (250 mg/kg), pyridoxal-5-phosphate (10 mg/kg) and alpha-tocopherol (100 mg/kg) potentiated anticonvulsive action of the above antiepileptic drugs. The results of the investigation suggest the efficacy of pathogenetic therapy and give new evidence of the advisability of using vitamins in combination with synthetic anticonvulsive drugs.     

Effect of Inhibitors of GABA Aminotransferase on the Metabolism of GABA in Brain Tissue and Synaptosomal Fractions

Abstract: Five inhibitors of the GABA degrading enzyme GABA-aminotransferase (GABA-T), viz., gabaculine, γ-acetylenic GABA, γ-vinyl GABA, ethanolamine O -sulphate, and aminooxyacetic acid, as well as GABA itself and the antiepileptic sodium vdproate were administered to mice in doses equieffective to raise the electroconvulsive threshold by 30 V. The animals were killed at the time of maximal anticonvulsant effect of the respective drugs and GABA, GABA-T and glutamate decarboxylase (GAD) were determined in whole brain and synaptosomes, respectively. The synaptosomal fraction was prepared from brain by conventional ultracentrifugation procedures. All drugs studied brought about significant increases in both whole brain and synaptosomal GABA concentrations, and, except GABA itself, inhibited the activity of GABA-T. Furthermore, all drugs, except GABA and γ-acetylenic GABA, activated GAD in the synaptosomal fraction. This was most pronounced with ethanolamine O -sulphate, which induced a twofold activation of this enzyme but exerted only a weak inhibitory effect on GABA-T. The results suggest that activation of GAD is an important factor in the mechanism by which several inhibitors of GABA-T and also valproate increase GABA concentrations in nerve terminals, at least in the relatively non-toxic doses as used in this study.     

Anticonvulsant profile of nimodipine and nitrendipine against pentylenetetrazole induced seizures in rats

The activity of nimodipine and nitrendipine against pentylenetetrazole (PTZ) induced seizures in Albino rats was studied alone and in combination with valproate. The median effective dose [ED50] of valproate, nimodipine and nitrendipine were initially determined. All the 3 drugs were injected i.p. 30 min before the induction of seizures. Seizures were induced by PTZ 85 mg/kg i.p., and subsequently the effect of combining ED50 doses of nimodipine and nitrendipine with ED50 dose of valproate was evaluated. ED50 of valproate and nitrendipine were 129 and 2.5 mg/kg respectively. ED50 of nimodipine could not be established since a dose-response relationship was not obtained. Hence, for the purpose of combination studies, 4 mg/kg of nimodipine was used. Both nimodipine (4 mg/kg) and nitrendipine (2.5 mg/kg) decreased the ED50 of valproate from 129 to 40 mg/kg. Both nimodipine and nitrendipine potentiate the activity of valproate against PTZ induced seizures and can be considered as potential adjuvant anticonvulsants which merit further study.     

Anticonvulsive effect of superoxide dismutase

The influence of superoxide dismutase (SOD) on the development of focal epileptic activity (EpA) in the rat brain cortex has been investigated. Intraperitoneal administration of SOD to rats (1 mg/kg) 30 minutes before penicillin application to the sensorimotor cortex led to marked relaxation of EpA and a decrease in the concentration of lipid peroxidation (LPO) products in EpA focus. The results corroborate our earlier assumption on an important pathogenetic role of LPO disturbances in epileptogenesis and make reasonable the combination of the traditional anticonvulsive therapy with the agents activating the oxidative system.     

Antiepileptic Drugs Prevent Changes Induced by Pilocarpine Model of Epilepsy in Brain Ecto-Nucleotidases

Ecto-nucleotidases, one of the main mechanisms involved in the control of adenosine levels in the synaptic cleft, have shown increased activities after the pilocarpine model of epilepsy. Here we have investigated the effect of the antiepileptic drugs (AEDs) on ecto-nucleotidase activities from hippocampal and cerebral cortical synaptosomes of rats at seven days after the induction of the pilocarpine model. Expression of these enzymes were investigated as well. Our results have demonstrated that phenytoin (50 mg/kg) and carbamazepine (30 mg/kg) were able to prevent the increase in ecto-nucleotidase activities elicited by pilocarpine in brain synaptosomes. However, sodium valproate (at 100 mg/kg) was only able to avoid the increase on ATP and ADP hydrolysis in hippocampal synaptosomes. Increase on ATP hydrolysis in hippocampal synaptosomes was also prevented by sodium valproate at 286 mg/kg, which corresponds to ED50 for pilocarpine model. NTPDase1, NTPDase2, NTPDase3, and ecto-5′-nucleotidase expressions were not affected by pilocarpine in cerebral cortex. However, expressions of NTPDase2, NTPDase3, and ecto-5′-nucleotidase were increased by pilocarpine in hippocampus. Our results have indicated that previous treatment with AEDs was able to prevent the increase in hippocampal ecto-nucleotidases of pilocarpine-treated rats. These findings have shown that anticonvulsant drugs can modulate plastic events related to the increase of nucleotidase expression and activities in pilocarpine-treated rats.     

Effects of different classes of antiepileptic drugs on brain-stem pathways

Antiepileptic drugs probably act by preventing the spread of the abnormal paroxysmal activity from the epileptogenic focus to surrounding normal neurons. An investigation of the mechanism of action of established anticonvulsant drugs on normal neuronal systems may therefore offer useful insights into the pathogenesis of the seizure disorders that these drugs serve to control. Antiabsence drugs (ethosuximide, valproate) depress reticular inhibitory pathways. Drugs effective against generalized tonic-clonic seizures (phenytoin, carbamazepine, valproate) depress reticular excitatory pathways. Drugs that are also effective against trigeminal neuralgia (phenytoin, carbamazepine) also depress afferent excitation and facilitate segmental inhibition in the trigeminal complex. Drugs that depress afferent excitation and facilitate segmental inhibition but do not depress the reticular system (baclofen) are effective against trigeminal neuralgia but do not have clinical antiepileptic properties. These observations indicate that the ability to depress the reticular core is an important characteristic of antiepileptic drugs, and suggest that the reticular core is involved in the spread and generalization of clinical seizures.     

三种抗癫痫药对癫痫患者脑电图的背景影响比较研究

目的：研究对比三种抗癫痫药（苯妥因钠、丙戊酸钠、卡马西平）对癫痫患者脑电图的背景影响。方法：选取我院于2009年3月至2011年2月收治的60例癫痫患者,随机分为苯妥因钠（PHT）、卡马西平（CBZ）和丙戊酸钠（SVP）组各20例,动态观察各组患者于治疗期间痫样波放电的频度和EEG背景的变化。结果：EEG痫样波放电的抑制率以SVP最为明显,而CBZ在EEG背景活动影响方面均比其他两组显著。结论：三种药物对癫痫波放电的抑制顺序是SVP〉PHT〉CBZ,SVP组明显优于其他两组。     

Effects of Antiepileptic Agents on Homotypic Fusion of Synaptic Vesicles

We studied the effects of three antiepileptic drugs (AEDs) in a cell-free model system containing isolated synaptic vesicles (SVs) and cytosolic proteins, which allowed us to reproduce one of the stages of complex exocytosis. Ethosuximide, sodium valproate, and gabapentin intensified calcium- and Mg²⁺-ATP-induced fusion of SVs; the effect was indicative of the ability of these agents to influence the processes of simple and/or complex exocytosis in synaptic connections in the CNS structures. Antiepileptic drugs did not change the intensity of calcium-dependent fusion of liposomes and SVs treated by proteases. Therefore, the effect of AEDs can be realized via their interaction with proteins of SVs. After decrease in the level of cholesterol in the membranes of SVs using treatment by methyl-β- cyclodextrin, the ability of AEDs to activate fusion of SVs remained unchanged. Therefore, the studied AEDs act via proteins localized beyond the borders of cholesterol-enriched microdomains of the membrane. Drugs that induce convulsions (corazole and picrotoxin) did not change the characteristics of fusion of SVs under the in vitro action of AEDs. This is indicative of the absence of molecular targets for the above chemoconvulsants in the SV membranes, as compared with those in the plasma membranes of nerve terminals. According to our experiments, just proteins of SVs are functional targets for ethosuximide, sodium valproate, and gabapentin providing their anticonvulsant actions. The proposed model, which allows one to reproduce the membrane fusion, can be successfully used for the testing of drugs influencing a presynaptic link of synaptic contacts in the CNS.     

Effect of GABA-acting drugs diazepam and sodium valproate on thermoregulation in rats

Gamma-aminobutyric acid (GABA) is involved in the mechanism of action of many drugs affecting different functions in the central nervous system. The present study has investigated the effect of diazepam, a positive allosteric GABA_A receptor modulator, and sodium valproate, a GABA transaminase inhibitor, on thermoregulation in rats. The experiments were designed into two main parts: (1) in vivo experiments on body temperature of conscious rats; (2) in vitro experiments on temperature sensitivity (temperature coefficient, TC) of rat PO/AH neurons in slice preparations. Central (i.c.v.) or systemic (i.p.) administration of diazepam, as well as sodium valproate produced dose-dependent hypothermia in rats. Both GABAergic drugs diazepam and sodium valproate increased temperature sensitivity (TC) in warm-sensitive rat PO/AH neurons. These results are in agreement with the neuronal model of temperature regulation and confirm the involvement of GABAergic mechanisms in thermoregulation.     

Absence of effects of sodium valproate on the estrous cycle of the rat

Regarding interrelationships between epilepsy, antiepileptic drugs and neuroendocrinological events, sodium valproate effects on estrous cycle of the rat have been performed by daily vaginal smears for twenty one days with 200, 100, 20 and 10 mg per kg bodyweight. Our data showed that sodium valproate did not significantly modify the evolution of estrous cycle even if intracerebral GABA content increase has been reported to influence hormonal secretions.     

Antiepileptic Agents Affect Hypothalamic β-Endorphin Concentrations

beta-Endorphin, Met-enkephalin, substance P, and somatostatin concentrations were evaluated in the hypothalami of rats treated either acutely or chronically (15 days) with sodium valproate, diphenylhydantoin, phenobarbital, or ethosuximide. All of these drugs, with the exception of ethosuximide, induced significant decreases in beta-endorphin concentrations after acute treatment, while only sodium valproate induced a decrease after chronic treatment. The acute and chronic effects of sodium valproate were also produced by aminooxyacetic acid, an inhibitor of gamma-aminobutyric acid (GABA) transaminase, while another GABA transaminase inhibitor, ethanolamine-O-sulphate, and THIP, a GABA receptor agonist, were effective after acute administration. Metenkephalin, substance P, and somatostatin concentrations were never affected by the drugs used. The present results, indicating that antiepileptic agents specifically decrease beta-endorphin concentrations, seem to correlate well with the capacity of these agents to blunt the epileptic activity of the peptides tested. Moreover, our data suggest that GABA may be involved in the anticonvulsant-induced reduction of beta-endorphin concentrations.     

Use of spectral characteristics of ryodipine in the study of dihydropyridine receptor complex of neuronal membranes]

A fluorescent dihydropyridine (DHP) derivative, ryodipine, was used to study structural characteristics of the DHP-sensitive Ca-channels in nerve terminals (synaptosomes) isolated from the rat cerebral cortex. It was found that an inductive resonance energy transfer from membrane proteins to ryodipine occurred in synaptosomal membranes. Two groups of membrane proteins differentially accessible to ryodipine were found by quenching of their own fluorescence. The percentage of group I proteins (20%) whose fluorescence was quenched by up to 1 microM ryodipine, was increased by 50% upon K(+)-depolarization and remained unchanged upon the addition of 100 microM Ni2+, whereas the addition of 100 microM Cd2+ prevented the increase induced by K(+)-depolarization. Nifedipine and nicardipine competed with ryodipine for the DHP receptor as evidenced by the change in percentage of group I proteins. The percentage of group II proteins (50% at 10 microM ryodipine) remained unchanged during various functional alterations of the synaptosomal membranes. Model experiments on proteoliposomes demonstrated that binding of ryodipine to synaptosomal membranes was due mainly to the hydrophobicity of DHP but not the ligand-receptor interaction. Nonetheless we that the membrane proteins-ryodipine system could be a qualitative test for the functional state of DHP-sensitive Ca-channels.