N(G)-nitro-L-arginine impairs the anticonvulsive action of ethosuximide against pentylenetetrazol

N(G)-nitro-L-arginine (NNA; an inhibitor of nitric oxide synthase) in a dose of 40 mg/kg impaired the protective activity of ethosuximide against the clonic phase of pentylenetetrazol-induced seizures in mice. The ED50 value of ethosuximide was significantly increased from 108 to 158 mg/kg. NNA (40 mg/kg) was ineffective against the protective effects of diazepam, phenobarbital and valproate against pentylenetetrazol-induced seizures. NNA (40 mg/kg) did not influence the plasma levels of the antiepileptic drugs studied, so a pharmacokinetic interaction is not probable. L-Arginine (500 mg/kg) prevented the NNA-induced reduction of the anticonvulsive activity of ethosuximide. It can be concluded that nitric oxide participates in the expression of the anticonvulsive action of ethosuximide, but not that of diazepam, phenobarbital and valproate, against pentylenetetrazol-induced seizures.     

Interactions of MRZ 2/576 with felbamate, lamotrigine, oxcarbazepine and topiramate in the mouse maximal electroshock-induced seizure model

This study focused on the evaluation of interactions between MRZ 2/576 (8-chloro-4-hydroxy-1-oxo-1,2-dihydropyridazino(4,5-b)quinoline-5-oxide choline salt), an N-methyl-D-aspartate (NMDA) receptor antagonist acting at the NMDA receptor/glycine(B) site and four newer antiepileptic drugs (felbamate, lamotrigine, oxcarbazepine, and topiramate) in the mouse maximal electroshock seizure model. Results indicate that MRZ 2/576 administered intraperitoneally, 5 min before the test, exerted a clear-cut anticonvulsant effect in the maximal electroshock seizure test in mice and its ED(50) value was 13.71 (11.95-15.73) mg/kg. In the subthreshold method, MRZ 2/576 (administered intraperitoneally, at a subthreshold dose of 5 mg/kg) significantly enhanced the anticonvulsant action of felbamate, oxcarbazepine and topiramate, by reducing their ED(50) values from 73.0 to 53.8 mg/kg (p < 0.05) for felbamate, from 10.77 to 7.48 mg/kg (p < 0.05) for oxcarbazepine, and from 49.3 to 28.7 mg/kg (p < 0.01) for topiramate. In contrast, MRZ 2/576 (5 mg/kg, i.p.) did not significantly affect the antiseizure effects of lamotrigine in the maximal electroshock seizure test in mice. Isobolographic transformation of data revealed that MRZ 2/576 (5 mg/kg, i.p.) exerted barely additive interactions with all investigated antiepileptic drugs in the maximal electroshock seizure test. In conclusion, the isobolographic analysis revealed that MRZ 2/576 additively cooperates with newer antiepileptic drugs in terms of suppression of maximal electroshock-induced seizures in mice.     

Influence of lithium on the anticonvulsant activity of carbamazepine

The present study was undertaken to see whether the recently reported synergism between lithium and carbamazepine (CBZ) in mania also extends against convulsions. The anti-convulsant effect of various doses of CBZ was assessed in albino rats pretreated with vehicle or lithium salt (0.54 mEg/kg/day, p.o. for 9 days). The animals were subjected to 3 tests: maximum electro shock seizures (MES); minimum electro convulsive thresholds (MET) and pentylenetetrazol (PTZ)-induced convulsions: abolition of hind limb extension after electro shock, increases in the MET for appearance of neck jerk and absence of convulsions for one hr after PTZ were taken as parameters of the anticonvulsive effect respectively. In the MES and MET tests lithum did not alter the anticonvulsive effect of CBZ. Lithium, however, potentiated the anticonvulsant effect of CBZ against PTZ-induced convulsions.     

Aspirin modulates the anticonvulsant effect of diazepam and sodium valproate in pentylenetetrazole and maximal electroshock induced seizures in mice

Release of prostaglandins in brain after spontaneous and experimentally induced seizures, has been demonstrated. The possible role of prostaglandins in modulation of seizure activity is still inconclusive. In the present study, the effects of aspirin and its interaction with the anticonvulsants (diazepam and sodium valproate) were studied in pentylenetetrazole (PTZ) and maximal electroshock (MES) induced seizures in mice. Aspirin 50, 100, and 500 mg/kg, i.p. was administered 45 min before the pentylenetetrazole (60 mg/kg, i.p.) and MES (60 mA, 0.2 s duration via car clip electrodes) challenge. In MES seizures significant protection was seen with aspirin 100 mg/kg where as higher dose of aspirin 500 mg/kg was required to elicit maximum protection against PTZ seizures. Sub anticonvulsant dose of sodium valproate 150 mg/kg, i.p. and aspirin 50 mg/kg i.p. showed complete protection in MES seizures and the same dose of sodium valproate offered superior protection in PTZ seizures than either drug used alone. When mice were pretreated with combination of diazepam 0.5 mg/kg and aspirin 50 mg/kg protection was significantly enhanced in PTZ seizures. However, aspirin did not show any significant protection with subanticonvulsant dose of diazepam against MES seizures. The present study suggests that prostaglandins may have anticonvulsant potential and also may have modulatory effect on anticonvulsant effect of conventional antiepileptic drugs.     

An experimental evaluation of anticonvulsant activity of Vitex-negundo

Maximal electroshock seizures (MES) in albino rats and pentylenetetarazole (PTZ) induced seizures in albino mice were used to study anticonvulsant activity of Vitex-negundo leaf extract. The ethanolic leaf extract of Vitex-negundo was administered orally in graded doses (250, 500 and 1000 mg/kg p.o) in both the experimental models and the effects were compared with diphenylhydantoin in MES method and valporic acid in PTZ induced seizures method as standard control respectively. The Vitex-negundo in the doses (250, 500 and 1000 mg/kg, p.o) did not show protection against MES to any significant extent but significant post-ictal depression was observed in the dose of 1000 mg/kg body weight in comparison to control. However, sub-protective dose of test drug (100 mg/ kg, p.o) potentiated the anticonvulsant action of diphenylhydantoin. The test drug in the dose (1000 mg/kg, po) showed 50% protection in clonic seizures and 24-hour mortality against PTZ induced seizures. It also decreased number and duration of convulsions significantly. Vitex-negundo potentiated anticonvulsant activity of valporic acid. The anticonvulsant activity of Vitex-negundo has not been found equi-effective with standard drugs. These findings suggest that Vitex-negundo possesses anticonvulsant activity particularly against PTZ induced convulsions. Moreover, the potentiation of diphenylhydantoin and valporic acid by Vitex-negundo indicates that it may be useful as an adjuvant therapy along with standard anticonvulsants and can possibly lower the requirement of diphenylhydantoin and valporic acid.     

Effect of amlodipine upon the protective activity of antiepileptic drugs against maximal electroshock-induced seizures in mice.

Amlodipine, a calcium channel antagonist of the dihydropyridine class, up to 10 mg kg(-1)(i.p.) did not significantly affect the threshold for electroconvulsions. However, this calcium channel antagonist (10 mg kg(-1)) enhanced the anticonvulsive activity of carbamazepine, valproate and phenobarbital against maximal electroshock-induced seizures in mice. Furthermore, amlodipine (5 mg kg(-1)) intensified the protection offered by carbamazepine. This effect was associated with the increased free plasma level of carbamazepine in the presence of amlodipine. Amlodipine did not influence the free or total plasma level of phenobarbital and valproate, so a pharmacokinetic interaction is not probable for valproate and phenobarbital. The anticonvulsive action and free plasma level of diphenylhydantoin was not modified by amlodipine. The combined treatment of the calcium channel antagonist and antiepileptics caused motor impairment (evaluated in the chimney test). Long-term memory (assessed in the passive avoidance test) in case of combinations of amlodipine with carbamazepine or diphenylhydantoin was not affected. The combination of amlodipine with valproate or phenobarbital significantly influenced the retention in this test. A possible usefulness of amlodipine as add-on therapy in epileptic patients may be limited by its considerable adverse effect revealed by behavioural tests. The pharmacokinetic interaction between carbamazepine and amlodipine might have some clinical importance for patients treated with these drugs.     

Effect of magnesium oxide on the activity of standard anti-epileptic drugs against experimental seizures in rats

Objectives:

To study the effect of oral magnesium oxide supplementation alone and on the activity of standard anti-epileptic drugs in the animal models of maximal electroshock seizures (MES) and chemically (pentylenetetrazole [PTZ])-induced seizures.

Methods:

Healthy male albino rats were given magnesium oxide (MgO) supplementation orally in various doses (500, 750 and 1000 mg/kg /day) for 4 weeks (day 1 to day 28). On day 0 and day 29, response to MES (180 mA for 0.2 s) was tested 1 h after pre-administration of phenytoin or carbamazepine orally. Similarly, in the other groups, the response to PTZ 40 mg/kg i.p. was tested 1 h after pre-administration of oral sodium valproate.

Results:

Oral administration of MgO in a low dose (500 mg/kg) for 4 weeks in healthy rats appears to exert protective effect against MES. High oral doses of MgO (750 and 1000 mg/kg) appear to enhance the activity of phenytoin and carbamazepine in the MES model. MgO supplementation was seen to decrease the latency of PTZ-induced seizures.

Conclusion:

The dose of oral MgO appears to have an inverse relation with the protective effect in MES-induced seizure model. High doses of MgO supplementation given orally appear to enhance the activity of standard anti-epileptic drugs in the MES-induced seizure model.     

Acute exposure to caffeine decreases the anticonvulsant action of ethosuximide, but not that of clonazepam, phenobarbital and valproate against pentetrazole-induced seizures in mice

This study examines the effect of acute administration of caffeine sodium benzoate (CAF) on the anticonvulsant action of four conventional antiepileptic drugs (AEDs: clonazepam - CZP, ethosuximide - ETS, phenobarbital - PB and valproate - VPA) against pentetrazole (PTZ)-induced clonic seizures in mice. The results indicate that CAF at a dose of 92.4 mg/kg significantly reduced the threshold for PTZ-induced clonic seizures in mice from 69.5 to 51.7 mg/kg (p<0.05), being ineffective at lower doses of 69.3 and 46.2 mg/kg. Moreover, CAF at doses of and 92.4 mg/kg attenuated the protective action of ETS against PTZ-induced seizures, by increasing its median effective dose (ED50) from 127.7 to 182.3 (p<0.05), and 198.3 mg/kg (p<0.01), respectively. In this case, no pharmacokinetic changes in total brain ETS concentrations after systemic ip administration of CAF (at 92.4 mg/kg) were observed, indicating a pharmacodynamic nature of interaction between ETS and CAF in the PTZ-test in mice. In contrast, CAF (at a dose of 92.4 mg/kg reducing the threshold for PTZ-induced seizures) combined with other AEDs (CZP, PB and VPA) did not affect their anticonvulsant action in the PTZ test in mice. Moreover, CAF (92.4 mg/kg) did not alter significantly total brain concentrations of the remaining AEDs (CZP, PB and VPA). The evaluation of potential acute adverse effects produced by AEDs in combination with CAF revealed that neither CAF (up to 92.4 mg/kg) administered alone nor combined with the studied drugs (at doses corresponding to their ED(50) values in the PTZ-test) affected motor performance of animals in the chimney test. In conclusion, the acute exposure to CAF may diminish the antiseizure protection offered by ETS in epileptic patients. Therefore, patients treated with ETS should avoid CAF.     

Cytisine inhibits the anticonvulsant activity of phenytoin and lamotrigine in mice

BackgroundCytisine (CYT), the most commonly used drug for smoking cessation in Poland, was experimentally found to induce convulsions. There is a lack of studies on the influence of CYT on the anticonvulsant activity of antiepileptic drugs (AEDs).MethodsThe effects of CYT on the anticonvulsant activity of six AEDs were examined in maximal electroshock (MES)-induced seizures in mice.ResultsSingle intraperitoneal (ip) administration of CYTin a subthreshold dose of 2 mg/kg antagonized the protective activity of ip phenytoin and lamotrigine against MES-induced seizures in mice. Adose of 1 mg/kg did not reverse the protective activity of phenytoin and lamotrigine. CYT in a dose of 2 mg/kg had no effect on the anticonvulsive activity of carbamazepine, oxcarbazepine, phenobarbital, and valproate magnesium.ConclusionCYT ability to antagonize the anticonvulsive activity of phenytoin and lamotrigine can be of serious concern for epileptic smokers, who might demonstrate therapeutic failure to these drugs resulting in possible breakthrough seizure attacks.     

Antiepileptogenic effects of the novel synthetic neuroactive steroid,ganaxolone, against pentylenetetrazol-induced kindled seizures: Comparison with diazepam and valproate

Pharmacological treatment of epilepsy is often unsatisfactory due to side effects and the lack of drugs that control the progressive epileptogenic process. Modulation of inhibitory γ-aminobutyric acid (GABA)-ergic neurotransmission by synthetic agonists of the neuroactive steroid binding site on the GABA_A receptor complex is one approach toward the identification of improved antiepileptic agents. In this study, antiepileptogenic and anticonvulsive effects of the novel synthetic neuroactive steroid, ganaxolone (3α-hydroxy-3β-methyl-5α-pregnan-20-one), were evaluated in comparison with diazepam and valproate against pentylenetetrazol (PTZ)-induced kindled seizures in mice. Kindled seizures provide a model of the progressive epileptogenic process. Successive administration of 45 mg/kg PTZ on days 1, 3, 5, 8, and 10 resulted in the rapid development of kindled seizures and significant reductions in thresholds for clonic convulsions, tonic convulsions, and lethality induced by PTZ on day 10. Ganaxolone, diazepam, and valproate dose-dependently protected against clonic convulsions induced by acute submaximal dose of PTZ (70 mg/kg). The compounds also dose-dependently suppressed fully kindled seizures and blocked the expression of kindled seizures over successive treatments with PTZ (45 mg/kg). Relative to acute anticonvulsive potencies against 70 mg/kg PTZ, however, ganaxolone was more potent than valproate or diazepam against fully kindled seizures and in blocking the expression of kindled seizures over successive treatments with PTZ. Importantly, only ganaxolone demonstrated antiepileptogenic activity by blocking the development of kindling, as evidenced when PTZ was administered in the absence of anticonvulsant treatments. Both diazepam and valproate failed to prevent development of kindled seizures even at doses that fully suppressed motor expression of seizures during kindling acquisition. Unlike diazepam and valproate, ganaxolone did not impair ambulatory activity within the dose range used in this study. These data, taken in conjunction with other findings on the unique pharmacological actions of ganaxolone, predict an improvement in the pharmacological management of epilepsy with this synthetic neuroactive steroid. Drug Dev. Res. 44:21–33, 1998. © 1998 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.     

Effect of MPEP, a selective mGluR5 antagonist, on the antielectroshock activity of conventional antiepileptic drugs

MPEP, a selective non-competitive antagonist of group I metabotropic glutamate receptor subtype 5 (mGluR5), administered at doses ranging from 0.75 to 1 mg/kg, failed to influence the electroconvulsive threshold in mice. However, when administered at higher doses (1.25 and 1.5 mg/kg), it significantly increased the threshold. Moreover, MPEP (applied at its highest subprotective dose of 1 mg/kg) did not affect the protective action of valproate, carbamazepine, diphenylhydantoin and phenobarbital against maximal electroshock-induced seizures in mice. The presented results indicate that mGluR5 antagonists should not be considered as good candidates for add-on therapy of generalized seizures.     

Amlodipine enhances the activity of antiepileptic drugs against pentylenetetrazole-induced seizures

Amlodipine (AML), which belongs to the 1,4-dihydropyridine calcium channel antagonists, possesses pharmacological and pharmacokinetic profile that distinguishes it from other agents of this class. Pentylenetetrazole (PTZ)-induced clonic and tonic convulsions in mice were significantly reduced by administration of AML at 10 mg/kg. At this dose AML remained without influence upon the plasma level of PTZ. The ED50 value of AML against clonic seizures induced by PTZ was 5.4 mg/kg. This calcium channel antagonist (at 2.5 mg/kg) combined with ethosuximide (ETX), valproate magnesium (VPA) or phenobarbital (PB) significantly reduced their ED50 values against clonic phase of PTZ-induced seizures. AML administered alone or in combination with antiepileptic drugs (AEDs) worsened the motor performance of mice in the chimney test. However, these treatments remained without significant influence on the retention time in the passive avoidance test. Plasma levels of antiepileptics remained unchanged in the presence of AML. The results indicate that AML does not seem a good candidate for a combination therapy in epileptic patients because of its adverse potential.     

Interaction of astemizole,an H1 receptor antagonist,with conventional antiepileptic drugs in mice

Histamine is one of the aminergic neurotransmitters, playing an important role in the regulation of a number of physiological processes. There are several subtypes of histamine receptors-H(1), H(2), H(3) and the recently discovered H(4). H(1) receptors exist on mast cells, basophils, enterochromaffin cells and in the central nervous system, being located postsynaptically. H(1) receptor antagonists, including classical antiallergy drugs, occasionally have been expected to induce convulsions in children and epileptics. The aim of this study was to evaluate the effects of astemizole-given intraperitoneally, singly or for 7 days on the anticonvulsant activity of antiepileptic drugs (AEDs) against maximal electroshock (MES)-induced convulsions in mice. The following AEDs were administered intraperitoneally: valproate magnesium, carbamazepine, diphenylhydantoin and phenobarbital. Adverse effects were evaluated in the chimney test (motor performance) and passive avoidance task (long-term memory). Brain and plasma levels of AEDs were measured by immunofluorescence. Astemizole (a single dose and following a 7-day treatment at 2-6 mg/kg) reduced the threshold for electroconvulsions, being without effect upon this parameter at lower doses. Astemizole (1 mg/kg) did not significantly alter the protective effect of AEDs against MES (after acute and 7-day administration). Also, acute astemizole (2 mg/kg) remained ineffective in this respect. Astemizole (2 mg/kg), following chronic administration, significantly reduced the protective efficacy of phenobarbital and diphenylhydantoin, reflected by an increase in their ED(50) values (50% effective dose necessary to protect 50% of animals tested against MES) from 21.1 to 34.0 mg/kg and from 10.4 to 19.2 mg/kg, respectively. Astemizole (2 mg/kg) did not alter the protective activity of the remaining AEDs. Moreover, astemizole (2 mg/kg) did not influence the free plasma levels and brain concentration of the studied AEDs. Also, this H(1) receptor antagonist did not impair long-term memory or motor coordination when given acutely. However, 7-day treatment with astemizole (2 mg/kg) significantly decreased TD(50) (50% toxic dose required to induce motor impairment in 50% of animals) value of phenobarbital, being without effect on carbamazepine, valproate and diphenylhydantoin in this respect. Similarly, phenobarbital and diphenylhydantoin, administered alone at their ED(50)s against MES, or combined with astemizole, disturbed long-term memory in mice. The results of this study indicate that astemizole may need to be used with caution in epileptic patients.     

Histamine and selective H3-receptor ligands: a possible role in the mechanism and management of epilepsy.

The interaction of selective histamine H3-receptor agonist R(alpha)-methyl-histamine (RAMH) and antagonist thioperamide (THP) with some antiepileptic drugs [AED; phenytoin (PHT), carbamazepine (CBZ), sodium valproate (SVP), and gabapentin (GBP)] was studied on seizures induced by maximal electroshock (MES) and pentylenetetrazole (PTZ) in mice. It was found that subeffective dose of THP in combination with the subeffective doses of PHT and GBP provided protection against MES and/or PTZ-induced seizures. Further, RAMH reversed the protection afforded by either PHT or GBP on MES and/or PTZ seizures. In another set of experiments, the histamine content was measured in the whole brain and in different brain regions including cerebral cortex, hypothalamus, brain stem and cerebellum following convulsant (MES and PTZ) and AED treatment. It was seen that while MES exhibited a tendency to enhance brain histamine levels, PTZ showed the opposite effect. AEDs either increased (PHT and GBP) or decreased (SVP) brain histamine content in different regions to varying degrees. The results indicate a role for histamine in seizures and in the action of AEDs and suggest that selective H3-receptor antagonists may prove to be of value as adjuncts to conventional AEDs.     

Fluoxetine enhances the anticonvulsant effects of conventional antiepileptic drugs in maximal electroshock seizures in mice

The present study was designed to investigate the effects of fluoxetine (FXT), a selective serotonin reuptake inhibitor, on the effect of antiepileptic drugs (AEDs) in the maximal electroshock seizure (MES) model in mice. FXT at the doses of 25, 20 and 15 mg/kg significantly increased the electroconvulsive threshold. The antidepressant applied at the lower doses (10, 5 and 2.5 mg/kg) did not influence the threshold. Moreover, FXT (at the highest subprotective dose of 10 mg/kg) increased the anticonvulsive potential of carbamazepine (CBZ), diphenylhydantoin (DPH), valproate (VPA) and phenobarbital (PB), producing a dose-related decrease in their ED50 values against MES. Nevertheless, pharmacokinetic events may be involved in the interaction between FXT and PB or CBZ, since the antidepressant raised the total brain concentration of the two antiepileptics. FXT in combination with AEDs did not influence the motor performance in the chimney test and long-term memory. In conclusion, the data suggest that FXT modulates seizure processes in the brain and may be advantageous in the treatment of epilepsy in depressed patients, improving the seizure control in epilepsy.     

The role of different types of adrenergic receptors in phentylenetetrazol-induced seizures and the effect of di-n-propylacetate in the rat

Selective depletion of forebrain noradrenaline has been shown to potentiate various types of experimentally induced seizures. This study was aimed at exploring the role of different types of adrenergic receptors in pentylenetetrazol (PTZ)-induced seizures in rats and the anticonvulsive effect of di-n-propylacetate (DPA). Piperoxane (10 and 20 mg/kg, IP) significantly potentiated PTZ-induced tonic seizures and mortality. Similar effects were observed after 6-hydroxydopamine (6-OHDA)-induced depletion of forebrain noradrenaline, whereas no effects were found in animals with depletion of spinal noradrenaline. Neither phenoxybenzamine (20 mg/kg, IP) nor prazosin (1 and 10 mg/kg, IP) nor propranolol (2 and 5 mg/kg, IP) modified tonic seizures and mortality caused by PTZ. Combined treatment with propranolol (5 mg/kg, IP) and prazosin (10 mg/kg, IP) had no effect either. Various agents used to increase central serotonin transmission (d-fenfluramine, 5 mg/kg, IP; quipazine, 10 mg/kg, IP; m-chlorophenylpiperazine, 3 mg/kg, IP) did not alter the effect of piperoxane on PTZ-induced seizures. None of the conditions used to diminish central adrenergic function significantly affected the inhibitory effect of DPA on tonic seizures and mortality caused by PTZ. Combined treatment with subthreshold doses of clonidine (0.1 mg/kg, IP) and DPA (75 mg/kg, IP) significantly reduced tonic seizures and mortality caused by PTZ. The data suggest that alpha 2 type adrenoceptors are involved in the control of PTZ-induced seizures in rats. The peculiarity of the role of these receptors in the effect of PTZ is discussed.     

Influence of antazoline and ketotifen on the anticonvulsant activity of conventional antiepileptics against maximal electroshock in mice.

Experimental studies have indicated that the central histaminergic system plays an important role in the inhibition of seizures through the stimulation of histamine H1 receptors. H1 receptor antagonists, including classical antiallergic drugs, occasionally may induce convulsions in healthy children and patients with epilepsy. The purpose of this study was to investigate the effects of antazoline and ketotifen (two H1 receptor antagonists) on the anticonvulsant activity of antiepileptic drugs against maximal electroshock (MES)-induced convulsions in mice. The following antiepileptic drugs were used: valproate, carbamazepine, diphenylhydantoin and phenobarbital. In addition, the effects of antiepileptic drugs alone or in combination with antazoline or ketotifen were studied on long-term memory (tested in the passive avoidance task) and motor performance (evaluated in the chimney test), acutely and after 7-day treatment with these H1 receptor antagonists. The influence of antazoline and ketotifen on the free plasma and brain levels of the antiepileptics was also evaluated. Antazoline (at 0.5 mg/kg), given acutely and after 7-day treatment, significantly diminished the electroconvulsive threshold. Similarly, ketotifen, after acute and chronic doses of 8 mg/kg markedly reduced the threshold for electroconvulsions. In both cases, antazoline and ketotifen were without effect upon this parameter at lower doses. Antazoline (0.25 mg/kg) significantly raised the ED50 value of carbamazepine against MES (both, acutely and after 7-day treatment). Furthermore antazoline (0.25 mg/kg) also reduced the anticonvulsant activity of diphenylhydantoin, but only after repeated administration, without modifying the brain and free plasma level of this drug. Moreover, valproate and phenobarbital did not change their protective activity when combined with antazoline. Ketotifen (4 mg/kg) possessed a biphasic action, acutely it enhanced the anticonvulsant action of carbamazepine and phenobarbital while, following 7-day treatment, reduced the antiseizure activity of carbamazepine. Ketotifen did not affect the free plasma or brain levels of antiepileptics tested. Only acute antazoline (0.25 mg/kg) applied with valproate impaired the performance of mice evaluated in the chimney test. Ketotifen (4 mg/kg) co-administered with conventional antiepileptic drugs impaired motor coordination in mice treated with valproate, phenobarbital or diphenylhydantoin. Acute and chronic antazoline (0.25 mg/kg) alone or in combination with antiepileptic drugs did not disturb long-term memory, tested in the passive avoidance task. Similarly, ketotifen (4 mg/kg) did not impair long-term memory, acutely and after 7-day treatment. However, valproate alone or in combination with chronic ketotifen (4 mg/kg) worsened long-term memory. The results of this study indicate that H1 receptor antagonists, crossing the blood brain barrier, should be used with caution in epileptic patients. This is because antazoline reduced the protective potential of diphenylhydantoin and carbamazepine. Also, ketotifen reduced the protection offered by carbamazepine and elevated the adverse activity of diphenylhydantoin, phenobarbital and valproate.     

Influence of SIB 1893, a selective mGluR5 receptor antagonist, on the anticonvulsant activity of conventional antiepileptic drugs in two models of experimental epilepsy

SIB 1893, a non-competitive antagonist of group I metabotropic glutamate receptor subtype 5, administered at doses ranging from 0.25 to 10 mg/kg, failed to influence pentetrazole-induced convulsions in mice. Moreover, SIB 1893 (10 and 20 mg/kg) did not affect the protective action of valproate, ethosuximide, phenobarbital and clonazepam in this test. Similarly, the mGluR5 antagonist did not modulate the antiseizure activity of carbamazepine, diphenylhydantoin and phenobarbital against maximal electroshock in mice. The combined treatment of SIB 1893 with conventional antiepileptic drugs did not lead to motor impairment. Long-term memory disturbances were observed only in the case of the combination of SIB 1893 with phenobarbital.     

Acute and chronic effects of the synthetic neuroactive steroid, ganaxolone, against the convulsive and lethal effects of pentylenetetrazol in seizure-kindled mice: comparison with diazepam and valproate

A high-affinity positive modulator of the GABA(A) receptor complex, ganaxolone, is a 3beta-methylated analog of the naturally occurring neuroactive steroid allopregnanolone. In the present study, ganaxolone was tested for its ability to (1) suppress seizures (clonic and tonic) and lethality induced by pentylenetetrazol (PTZ) in PTZ-kindled mice (anticonvulsive effect) and (2) to attenuate the development of sensitization to the convulsive and lethal effects of PTZ in kindled mice (anti-epileptogenic effect) when given as a pretreatment prior to each PTZ injection during kindling acquisition. Two classical antiepileptic drugs, diazepam and valproate, were tested for comparison. All three drugs dose-dependently suppressed tonic seizures and lethality induced by PTZ in kindled mice; only ganaxolone was effective against clonic seizures. Ganaxolone showed anti-epileptogenic properties as it reduced the sensitivity of kindled mice to the convulsive (clonic and tonic seizures) and lethal effects of PTZ. Diazepam showed anti-epileptogenic effects against tonic seizures and lethality, but not clonic seizures; valproate was ineffective in preventing development of any of these effects. Sensitivity to PTZ-induced seizures and lethality was not affected in mice with a history of repeated treatment with ganaxolone, diazepam, or valproate. The drugs had effects on ambulatory activity that ranged from no effect (ganaxolone) through moderate impairment (diazepam) to marked disruption (valproate). Taken together, the results of the present study add to accumulating evidence of the unique anticonvulsive/behavioral profile of neuroactive steroids.     

Etifoxine: evaluation of its anticonvulsant profile in mice in comparison with sodium valproate, phenytoin and clobazam

The anticonvulsant potential of 6-chloro-2-(ethylamino)-4-methyl-4-phenyl-4H-3,1-benzoxazine (etifoxine), a non-benzodiazepine tranquilizer, was evaluated in mice in comparison to valproate, phenytoin and clobazam. Maximal seizures were induced by electroshock (MES) and the chemical convulsants pentetrazol (PTZ), picrotoxin (PTX), bicuculline (BIC), isoniazid (INH), nicotine (NIC) and strychnine (STR). Tonic extensor convulsions were prevented by etifoxine in the following rank order of potency (ED50 values with seizure tests): 39.5 (PTX), 101 (PTZ), 101 (MES), 154 (INH), 181 (NIC), 397 (BIC), and greater than 800 mg/kg p.o. (STR). Clonic seizures were induced by threshold doses of PTZ, PTX and pilocarpine (PIL) and antagonized by etifoxine at ED50 values of 181 (PIL), 221 (PTZ), and greater than 800 mg/kg p.o. (PTX). Hence, etifoxine blocked both tonic and clonic seizures but was more potent against the tonic component. The anticonvulsant profile of etifoxine appeared similar to that of valproate. However, in terms of potency, protective indices (ED50 rotarod/ED50 seizure test) and therapeutic indices (LD50/ED50 seizure test) etifoxine was on an average 3.7, 12 and 14 times superior to valproate, respectively. It is concluded that etifoxine has a marked anticonvulsive potential and may be beneficially used in epileptic disorders, especially of the grand mal type.