Anticonvulsant effect of flutamide on seizures induced by pentylenetetrazole: involvement of benzodiazepine receptors

PURPOSE: There is some structural similarity between the androgen receptor antagonist, flutamide (Flut) and benzodiazepines (BZDs). We evaluated the possible anticonvulsant effect and interaction of Flut with BZD receptors in common seizure models. METHODS: (a) Different groups of mice each were pretreated i.p. with Flut, and after 0.5 h, they received chemoconvulsants [pentylenetetrazole (PTZ), bicuculline, aminophylline, strychnine or kainic acid]. Latency and incidence of a clonic seizure were recorded. (b) Mice were pretreated i.p. with Flut, and after 0.5 h, transauricular electroshock was applied. Occurrence of a tonic seizure was observed. (c) Amygdala-kindled rats were pretreated i.p. with Flut, and 0.5, 1, or 2 h later, they were stimulated at afterdischarge threshold. Then the seizure parameters (afterdischarge duration, seizure severity, and stage 5 duration) were recorded. (d) The effect of Flut on clonic seizure threshold was determined by i.v. infusion of bicuculline or PTZ to different groups of Flut-receiving mice. To determine the possible interaction of Flut with BZD receptors, the flumazenil (FMZ)+Flut effect on clonic seizure threshold was compared with the effect of Flut. (e) Neurotoxicity of Flut was evaluated by rotarod test at 30 min after administration. RESULTS: Flut produced a dose-dependent anticonvulsant effect against PTZ-induced seizures [median effective dose (ED50), 67.0 mg/kg]. Moreover, Flut elevated the clonic seizure threshold induced by bicuculline or PTZ. FMZ reversed the effect of Flut on the threshold of PTZ seizures. A median toxic dose (TD50) value of 124.8 mg/kg was obtained for Flut. CONCLUSIONS: Flut both blocks PTZ-induced clonic seizures and elevates the threshold of PTZ or bicuculline-induced clonic seizures, through interaction with BZD receptors.     

The role of technical, biological and pharmacological factors in the laboratory evaluation of anticonvulsant drugs. III. Pentylenetetrazole seizure models

Although seizure models using systemic administration of the chemoconvulsant pentylenetetrazol (PTZ) for induction of generalized clonic seizures in rodents are widely employed to identify potential anticonvulsants, the important role of diverse technical, biological and pharmacological factors in interpretation of results obtained with these models is often not recognized. The aim of this study was to delineate factors other than sex, age, diet, climate, and circadian rhythms, which are generally known. For this purpose, experiments with 8 clinically established antiepileptic drugs were undertaken in the following PTZ models: (1) the threshold for different types of PTZ seizures, i.e., initial myoclonic twitch, generalized clonus with loss of righting reflexes, and tonic backward extension of forelimbs (forelimb tonus), in mice; (2) the traditional PTZ seizure test with s.c. injection of the CD97 for generalized clonic seizures in mice; and (3) the s.c. PTZ seizure test in rats. In rats, in addition to evaluating drug effects on generalized clonic seizures, a ranking system was used to determine drug effects on other seizure types. When drugs were dissolved in vehicles which themselves did not exert effects on seizure susceptibility, the most important factors which influenced drug potencies were: (1) bishaped dose-response curves, i.e., a decline in anticonvulsant dose-response at high doses of some drugs, leading to misinterpretations of drug efficacy if only a single high drug dosage is tested; (2) effects of route of PTZ administration (i.v. infusion vs. s.c. injection) on estimation of anticonvulsant potency; (3) species differences in drug metabolism; (4) differences in drug potencies calculated on the basis of administered doses compared to potency calculations based on 'active' drug concentrations in plasma; (5) qualitative and quantitative species differences in drug actions; (6) endpoints used for PTZ tests; (7) misleading predictions from PTZ seizure models. Analysis of anticonvulsant drug actions indicated that myoclonic or clonic seizures induced by i.v. or s.c. PTZ might be suitable for predicting efficacy against myoclonic petit mal seizures in humans, but certainly not to predict efficacy against absence seizures. Tonic seizures induced by PTZ were blocked by drugs, such as ethosuximide, which exert no effect on tonic seizures in humans. In order to reduce the variability among estimates of anticonvulsant activity in PTZ seizure models, the various factors delineated in this study should be rigidly controlled in experimental situations involving assay of anticonvulsant agents.     

Effect of clobenpropit, a centrally acting histamine H3-receptor antagonist, on electroshock- and pentylenetetrazol-induced seizures in mice

Summary. The anticonvulsant activity of clobenpropit, an isothiourea derivative of histamine and potent H₃-receptor antagonist, was investigated in two representative seizure models in mice. In the maximal electroshock seizure threshold test, clobenpropit dose-dependently raised the electroconvulsive threshold for tonic (hindlimb extension) seizures, but a significant increase of about 15% was determined only at the high dose of 40 mg/kg i.p. The protective action of this drug was reduced by immepip and (R)-α-methylhistamine, selective H₃-receptor agonists. In co-medication with two standard antiepileptics, clobenpropit (20 and 40 mg/kg) significantly increased the anticonvulsant effectiveness of carbamazepine and tended to increase the effectiveness of valproate. Additional studies indicated that the high dose of clobenpropit also significantly enhanced the plasma carbamazepine concentration. One the other hand, in the s.c. PTZ seizure threshold test clobenpropit revealed no protective effects. In the rotarod ataxia test, impaired motor function was observed at 80 mg/kg clobenpropit. In conclusion, the present findings indicated no pronounced anticonvulsant effects of clobenpropit against generalized tonic as well as clonic seizures. Accepted March 10, 1998; received December 22, 1997     

Parenteral magnesium sulfate fails to control electroshock and pentylenetetrazol seizures in mice

Magnesium sulfate has been used as an anticonvulsant in the treatment of eclampsia, but efficacy of magnesium in other types of seizure disorders is poorly documented. We examined the effects of magnesium sulfate (MgSO4) on seizures produced in mice by maximal electroshock (MES) and pentylenetetrazol (PTZ), MgSO4 injection (6.7 mEq/kg i.p.) caused weakness in all animals. With suprathreshold electroshock, 10/10 controls and 11/12 treated animals had seizures with tonic hind limb extension (P = NS). Electroshock threshold was unaltered by magnesium treatment (n = 48; P = 0.47). PTZ induced clonic seizures in 12/12 controls and 5/14 treated animals (P less than 0.05). This difference was likely due to muscular weakness because frequency of EEG spikes was the same in PTZ and PTZ + MgSO4 groups. Mean serum magnesium levels were 2.3 +/- 0.3 mEq/l in animals not given MgSO4; 10.9 +/- 1.4 mEq/l and 12.8 +/- 2.2 mEq/l in treated animals with and without seizures (P = NS). We conclude that magnesium sulfate had no significant anticonvulsant activity in mouse MES and PTZ models for epilepsy. The relevance of these findings to the possible efficacy of magnesium sulfate in eclamptic seizures and other types of epilepsy remains to be determined.     

Effects of piracetam alone and in combination with antiepileptic drugs in rodent seizure models

Summary. The nootropic drug piracetam was investigated in various experimental models of epilepsy. Generally, piracetam exhibits no or only moderate anticonvulsant properties against generalized tonic or clonic seizures. However, in many cases it did increase the anticonvulsant effectiveness of conventional antiepileptics, as shown in the maximal electroshock seizure (MES) threshold test, the traditional MES test or in DBA/2 mice. A pharmacokinetic interaction does not seem to be responsible for this effect. In lethargic mice, a model of absence seizures, piracetam significantly decreased the incidence and duration of spike-wave discharges. Furthermore, in the cobalt-induced focal epilepsy model piracetam reduced the number of spikes/min and in the hippocampal stimulation model it increased the anticonvulsant potency of phenobarbital and phenytoin after single and repeated administration. In conclusion, the well tolerated piracetam itself did not show marked anticonvulsant effects in most screening tests, however, its co-medication with antiepileptic drugs improved seizure protection in various models which may bear potential clinical significance.     

The anticonvulsant activity of acetone, the major ketone body in the ketogenic diet, is not dependent on its metabolites acetol, 1,2-propanediol, methylglyoxal, or pyruvic acid

BACKGROUND: Acetone, one of the principal ketone bodies elevated during treatment with the ketogenic diet, exhibits anticonvulsant properties that may contribute to the seizure protection conferred by the diet. The anticonvulsant mechanism of acetone is unknown, but it is metabolized to several bioactive substances that could play a role. METHODS: Acetone and its major metabolites-acetol, 1,2-propanediol, methylglyoxal, and pyruvic acid-were assessed for anticonvulsant activity in two mouse seizure models. Various doses of the substances administered intraperitoneally were characterized for their ability to elevate the threshold for clonic seizures induced by intravenous infusion of pentylenetetrazol (PTZ) and for protection against tonic seizures induced by subcutaneous bolus administration of 4-aminopyridine (4-AP). The inverted-screen test was used to assess acute neurological toxicity. RESULTS: Acetone (1-32 mmol/kg, i.p.), in a dose-dependent fashion, elevated the PTZ threshold and conferred protection against 4-AP seizures (ED(50), 26.3 mmol/kg). Effective doses of acetone (10-32 mmol/kg) did not cause motor impairment in the inverted-screen test (TD(50), 45.7 mmol/kg). In doses 10-fold greater than the minimally effective dose of acetone (3.2 mmol/kg), the metabolites acetol, 1,2-propanediol, and pyruvic acid were inactive in the PTZ model. At higher doses that produced motor impairment, acetol and 1,2-propanediol (but not pyruvic acid) did elevate the PTZ threshold. Methylglyoxal had both proconvulsant and anticonvulsant actions, and had substantial toxicity, producing respiratory distress, motor impairment, and death. None of the acetone metabolites protected against 4-AP seizures. CONCLUSIONS: This study confirms the broad-spectrum anticonvulsant properties of acetone and indicates that the seizure protection conferred is unlikely to result from its major metabolic products.     

Anti-epileptogenic effect of beta-carotene and vitamin A in pentylenetetrazole-kindling model of epilepsy in mice

Vitamin A (Vit A) and its derivatives have recently been reported to be implicated in synaptic plasticity. In this study, the possible effect of Vit A and its precursor, beta-carotene on acute seizure and kindling, induced by pentylenetetrazole (PTZ) was assessed. Vit A and beta-carotene were evaluated for their ability to: (1) elevate the threshold of clonic seizures induced by i.v. infusion of PTZ; (2) suppress the seizures (clonic and tonic) and lethality induced by i.p. PTZ in PTZ-kindled mice (anticonvulsant effect); (3) attenuate the development of sensitization to convulsive and lethal effects of i.p. PTZ in kindled mice (anti-epileptogenic effect). Diazepam was employed as positive control. All the drugs showed anti-epileptogenic effect against PTZ-induced tonic seizures and lethality. Vit A and beta-carotene had no effect on clonic seizures threshold and also on tonic seizures and lethality induced by PTZ in kindled mice. Non-genomic and genomic mechanisms could be involved in the anti-epileptogenic effect of Vit A and beta-carotene.     

Hydroalcoholic extract of Zizyphus jujuba ameliorates seizures, oxidative stress, and cognitive impairment in experimental models of epilepsy in rats

The anticonvulsant effect of the hydroalcoholic extract of Zizyphus jujuba (HEZJ) fruit (100, 250, 500, and 1000 mg/kg, orally) was evaluated in experimental seizure models in rats. The effect of HEZJ on seizure-induced cognitive impairment, oxidative stress, and cholinesterase activity was also investigated. HEZJ (1000 mg/kg) exhibited maximum protection (100%) against generalized tonic-clonic seizures in the pentylenetetrazole (PTZ) seizure model and and 66.7% protection against tonic hindlimb extension in the maximal electroshock (MES) seizure model. Significant impairment in cognitive functions was observed in both PTZ- and MES-challenged rats. Pretreatment with HEZJ resulted in significant improvement in learning and memory. HEZJ also reversed the oxidative stress induced by both PTZ and MES. The significant decrease in cholinesterase activity observed in the PTZ and MES models was significantly reversed by pretreatment with HEZJ. Thus, the present study demonstrates the anticonvulsant effect of HEZJ as well as amelioration of cognitive impairment induced by seizures in rats.     

Effect of Tadalafil on Seizure Threshold and Activity of Antiepileptic Drugs in Three Acute Seizure Tests in Mice

Tadalafil, a selective phosphodiesterase type 5 inhibitor, is a long-acting oral agent for the treatment of erectile dysfunction of multiple etiologies. Although generalized tonic-clonic seizures were reported in a healthy man after taking tadalafil, the influence of tadalafil on seizure susceptibility has not been studied so far. Therefore, the aim of the present study was to investigate the effect of tadalafil on seizure threshold as well as on the activity of some first- and second-generation antiepileptic drugs in three acute seizure tests in mice. The obtained results showed that tadalafil, at the highest dose tested (20 mg/kg), significantly decreased the threshold for the first myoclonic twitch in the intravenous pentylenetetrazole (i.v. PTZ) seizure test. It did not affect the threshold for generalized clonic seizure and forelimb tonus in the i.v. PTZ, for tonic hindlimb extension in the maximal electroshock seizure threshold test, and for psychomotor seizure in the 6-Hz-induced seizure threshold test. Tadalafil did not alter the anticonvulsant activity of any of the studied antiepileptic drugs in electrically induced seizure tests. Interestingly, tadalafil potentiated the anticonvulsant activity of clonazepam and decreased the anticonvulsant activity of oxcarbazepine in the i.v. PTZ test. These interactions were pharmacodynamic in nature, as tadalafil did not alter clonazepam and oxcarbazepine concentrations both in serum and brain tissue. Furthermore, neither tadalafil alone nor its combinations with the studied antiepileptic drugs produced any significant impairment of motor coordination (assessed in the chimney test), muscular strength (investigated in the grip-strength test), and long-term memory (assessed in the passive avoidance task). In conclusion, tadalafil may increase the risk of myoclonic seizure and decrease the anticonvulsant efficacy of oxcarbazepine. Further studies are warranted to evaluate the safety of tadalafil usage in patients with epilepsy.     

Sildenafil influences the anticonvulsant activity of vigabatrin and gabapentin in the timed pentylenetetrazole infusion test in mice

Sildenafil, a selective phosphodiesterase 5 (PDE5) inhibitor, has recently been reported to affect convulsant activity in some animal models of seizures and epilepsy. Moreover, its influence on the protective activity of some antiepileptic drugs (AEDs) was also noted. The aim of the present study was to investigate the effect of sildenafil on the anticonvulsant potential of gabapentin (GBP) and vigabatrin (VGB) in the timed intravenous (i.v.) pentylenetetrazole (PTZ) test in mice. The chimney test, the passive avoidance task and the grip strength test were used to estimate some possible side effects caused by the studied AEDs and their combinations with sildenafil. Total brain and free plasma concentrations of GBP and VGB were determined to evaluate the characteristics of interactions. Our studies revealed that GBP (25-100mg/kg) increases the threshold for the forelimb tonic extension, whereas VGB raises thresholds both, for myoclonic (200-600mg/kg) and generalized clonic (400-600mg/kg) seizures in the used model of seizures. GBP at sub-effective dose of 12.5mg/kg co-administered with sildenafil at doses of 10 and 20mg/kg significantly increases the threshold for tonic seizures in the i.v. PTZ test in mice. Combination of sub-effective dose of VGB (200mg/kg) with sildenafil at a dose of 5mg/kg also showed significant anticonvulsant activity against clonic seizures. The studied AEDs and their combinations with sildenafil did not produce any changes in the motor coordination, long-term memory and muscular strength in mice. Sildenafil did not influence total brain and free plasma concentrations of GBP and VGB. Interactions between the studied AEDs and sildenafil were pharmacodynamic in nature and for that reason they are worthy of consideration in the clinical practice.     

Timed pentylenetetrazol infusion test: a comparative analysis with s.c.PTZ and MES models of anticonvulsant screening in mice.

The intravenous pentylenetetrazol (i.v.PTZ) seizure test provides threshold dose for induction of seizures in individual animals. In the present study, the i.v. and s.c.PTZ seizure models in mice were compared for seizure pattern, intra- and interanimal variability. Anticonvulsant activities of several antiepileptic drugs (AEDs) at non-ataxic dose levels were evaluated in the PTZ and maximal electroshock (MES) seizure tests. In the i.v.PTZ test, at 0.5 ml/min rate of administration, the mean threshold PTZ doses for induction of clonus and tonic extensor were 44.17 and 99.59 mg/kg, respectively. The intra- and interanimal variabilities in the seizure response were low in the i.v.PTZ as compared to the s.c.PTZ model. Phenobarbital sodium, ethosuximide, sodium valproate, diazepam, tiagabine, oxcarbazepine and zonisamide enhanced threshold or onset latency for clonus in the i.v. and s.c.PTZ tests, respectively. Levetiracetam and pregabalin were active in the i.v.PTZ test, but had no effect in the s.c.PTZ test. Ability of AEDs to protect from tonic extensor was compared in the MES and i.v.PTZ tests. For this effect, phenobarbital sodium, phenytoin, carbamazepine, sodium valproate, gabapentin, oxcarbazepine, zonisamide and pregabalin were effective in the i.v.PTZ and MES tests. Ethosuximide, diazepam and levetiracetam were effective in the i.v.PTZ test, but not the MES test. On the contrary, lamotrigine and topiramate were active in the MES, but not the i.v.PTZ test. These results indicate that it is advantageous to use i.v.PTZ test as an acute seizure model for screening of antiepileptic drugs. This model can identify molecules with varied mechanism of action and broad clinical utility in the treatment of epilepsy.     

The synergistic anticonvulsant effect of agmatine and morphine: possible role of alpha 2-adrenoceptors

Recent demonstrations of the anticonvulsant properties of agmatine suggest it may be considered as a potential adjunct for protection against seizure. We investigated the possibility of an additive anticonvulsant effect between low doses of agmatine and morphine. The thresholds for the clonic seizures induced by the intravenous administration of gamma-aminobutyric acid (GABA)-antagonist, pentylenetetrazole (PTZ) were assessed in mice. Morphine at lower doses (1-3mg/kg) increased and at higher doses (30, 60 mg/kg) decreased the seizure threshold. Pretreatment with a per se non-effective dose of agmatine (1mg/kg) potentiated the anticonvulsant effect of morphine. The combination of subeffective doses of agmatine and morphine led to potent anticonvulsant effects. The pro-convulsant effect of morphine was attenuated by agmatine. Yohimbine with a dose (1mg/kg) incapable of affecting seizure threshold reversed the effect of agmatine on both anticonvulsant and pro-convulsant effects of morphine. These results suggest that agmatine potentiates the anticonvulsant effect of morphine and alpha 2-adrenoceptors may be involved in this effect.     

A Review of the Preclinical Pharmacology of Tiagabine: A Potent and Selective Anticonvulsant GABA Uptake Inhibitor

Summary: We review the neurochemical and behavioral profile of the selective γ-aminobutyric acid (GABA) up-take inhibitor, (R)-N-(4,4-di-(3-methylthien-2-yl)but-3-enyl) nipecotic acid hydrochloride [tiagabine (TGB), previously termed NNC 05-0328, NO 05-0328, and NO-328], which is currently in phase III clinical trials for epilepsy. TGB is a potent, and specific GABA uptake inhibitor. TGB lacks significant affinity for other neurotransmitter receptor binding sites and/or uptake sites. In electrophysiological experiments in hippocampal slices in culture, TGB prolonged the inhibitory postsynaptic potentials (IPSP) and inhibitory postsynaptic currents (IPSC) in the CA1 and CA3 produced by the addition of exogenous GABA. In vivo microdialysis shows that TGB also in-creases extracellular GABA overflow in a dose-dependent manner. Together these biochemical data suggest that the in vitro and in vivo mechanism of action of TGB is to inhibit GABA uptake specifically, resulting in an increase in GABAergic mediated inhibition in the brain. TGB is a potent anticonvulsant agent against methyl-6,7-dimethyox-4-ethyl-B-carboline-3-carboxylate (DMCM)-induced clonic convulsions (mice), subcutaneous pentylenetetrazol (PTZ)-induced tonic convulsions (mice and rats), sound-induced convulsions in DBA/2 mice and genetically epilepsy-prone rats (GEPR), and electrically induced convulsions in kindled rats. TGB is partially efficacious against subcutaneous PTZ-induced clonic convulsions, and photically induced myoclonus in Papio papio. TGB is weakly efficacious in the intravenous PTZ seizure threshold test and the maximal electroshock seizure (MES) test and produces only partial protection against bicuculline (BIC)-induced convulsions in rats. The overall biochemical and anticonvulsant profile of TGB suggests potential utility in the treatment of chronic seizure disorders such as generalized clonic-tonic epilepsy (GTCS), photomyoclonic seizures, myoclonic petit mal epilepsy, and complex partial epilepsy.     

Avian brainstem neurogenesis is stimulated during cochlear hair cell regeneration

Cyclosporin A (CsA) is known to decrease nitric oxide (NO) release in the nervous system. The present study was aimed at investigating the effects of acute administration of CsA on pentylenetetrazole (PTZ)-induced seizure threshold and latency and probable modulation of these effects by NO synthesis substrate L-arginine, and NO synthesis inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine. Moreover, the effect of CsA per se or concomitant with L-arginine on the development of PTZ-induced kindling was assessed. CsA (0.05, 1, 5, 10 and 20 mg/kg, s.c.) dose-dependently increased PTZ-induced clonic seizure threshold and the latency for onset of myoclonic jerks, clonic seizures and clonic-tonic generalized seizures following PTZ administration. L-NAME (10 and 30 mg/kg, i.p.) but not aminoguanidine (50 and 100 mg/kg, i.p.) potentiated the anticonvulsant effects of CsA (1 and 10 mg/kg). L-arginine (60, 100 and 200 mg/kg, i.p.) inhibited the anticonvulsant effects of CsA (20 mg/kg) in a dose-related manner. The inhibitory effect of L-arginine on CsA-induced alterations of seizure threshold and latency was blocked by L-NAME but not with aminoguanidine. CsA (20 mg/kg) significantly inhibited the development of PTZ kindling and decreased the seizure intensity as tested by a challenge dose of PTZ. Pretreatment with L-arginine (60 mg/kg) reversed the inhibitory effects of CsA on kindling development. It was concluded that CsA exerts some anticonvulsant properties that may be due to its inhibition of nitric oxide synthesis.     

Anticonvulsant and proconvulsant actions of 2‐deoxy‐d‐glucose

Purpose: 2‐Deoxy‐d ‐glucose (2‐DG), a glucose analog that accumulates in cells and interferes with carbohydrate metabolism by inhibiting glycolytic enzymes, has anticonvulsant actions. Recognizing that severe glucose deprivation can induce seizures, we sought to determine whether acute treatment with 2‐DG can promote seizure susceptibility by assessing its effects on seizure threshold. For comparison, we studied 3‐methyl‐glucose (3‐MG), which like 2‐DG accumulates in cells and reduces glucose uptake, but does not inhibit glycolysis. Methods: Mice were treated with 2‐DG or 3‐MG and the seizure threshold determined in the 6‐Hz test, the mouse electroshock seizure threshold (MEST) test, and the intravenous pentylenetetrazol (i.v. PTZ) or kainic acid (i.v. KA) seizure threshold tests. 2‐DG was also tested in fully amygdala‐kindled rats. Results: 2‐DG (125–500 mg/kg, i.p., 30 min before testing) significantly elevated the seizure threshold in the 6‐Hz seizure test. 2‐DG (250–500 mg/kg) decreased the threshold in the MEST and i.v. PTZ and i.v. KA tests. 3‐MG had no effect on seizure threshold in the 6‐Hz test but, like 2‐DG, decreased seizure threshold in the i.v. PTZ test. 2‐DG (250 and 500 mg/kg, i.p., 30 min before testing) had no effect on amygdala‐kindled seizures. Conclusions: Although 2‐DG protects against seizures in the 6‐Hz seizure test, it promotes seizures in some other models. The proconvulsant action may relate to reduced glucose uptake, whereas the anticonvulsant action may require inhibition of glycolysis and shunting of glucose metabolism through the pentose phosphate pathway.     

The role of technical, biological and pharmacological factors in the laboratory evaluation of anticonvulsant drugs. I. The influence of administration vehicles

Although animal models, such as electroshock seizures, pentylenetetrazol (PTZ)-induced seizures and the rotorod test, are widely employed in the search for and evaluation of new anticonvulsant drugs, the important role of diverse technical, biological and pharmacological factors in the interpretation of results obtained with these models is often not recognized. In order to delineate factors other than strain, sex, age, diet, climate, and circadian rhythms, which are generally known, a series of studies was undertaken. In the experiments described here, the influence of administration vehicles and drug formulations on bioavailability, potency and time course of anticonvulsant drugs was studied in mice. Two standard anticonvulsant drugs, primidone and carbamazepine, with poor aqueous solubility were used for these experiments, because water insolubility is a common problem in the laboratory evaluation of anticonvulsant agents. Since vehicles, especially organic solvents or detergents, may exert effects of their own, sensitive electroshock and PTZ seizure threshold tests were used for the assessment of vehicle-related actions. Of various aqueous or lipophilic vehicles tested, only glycofurol increased seizure thresholds, when concentrations exceeding 10% were administered. However, even at a concentration of 30%, the solubilizer did not exert measurable effects in the maximal electroshock seizure (MES) test in mice, but markedly potentiated the effect of primidone. In contrast, polyethylene glycol 400 (PEG 400) up to a concentration of 30% did not affect electrical or chemical seizure thresholds nor did it alter the pharmacological potency of primidone. When primidone or carbamazepine were administered as a suspension in a Tween/water vehicle, their anticonvulsant effects were considerably lower compared to injections of the same doses as a solution.(ABSTRACT TRUNCATED AT 250 WORDS)     

The interaction between morphine and propranolol in chemical and electrical seizure models of mice

Objectives: Morphine and propranolol have different effects on seizure. Several studies have shown interaction between adrenergic and opioid systems in different models. In this study, interaction between morphine and propranolol in different seizure models was examined in mice.

Methods: In this study, three seizure models, including intravenous pentylenetetrazole (PTZ), intraperitoneal PTZ and electroshock, were examined in mice. Animals were injected with different doses of morphine or propranolol in the 60th and 45th min, before seizure induction, respectively.

Results: Acute administration of propranolol or lower doses of morphine induced an anticonvulsant effect in intravenous PTZ, intraperitoneal PTZ and electroshock-induced seizure models; on the contrary, higher doses of morphine exert proconvulsant effects in all three models. Also additive anticonvulsant effect of propranolol and lower doses of morphine was observed in all examined models. The additive anti-seizure effect of propranolol and lower doses of morphine was blocked by naltrexone in intraperitoneal PTZ model. Moreover, the anticonvulsant effect of propranolol was inhibited by naltrexone in intraperitoneal PTZ seizure model of mice. Propranolol restrained the proconvulsant effects in higher doses of morphine in clonic seizures of intravenous and intraperitoneal PTZ models.

Discussion: In conclusion, we believe that this is the first study that has indicated the interaction of propranolol and lower doses of morphine in the anticonvulsant effects in three seizure models of intravenous PTZ, intraperitoneal PTZ and electroshock. The involvement of μ-opioid receptor in this interaction was also demonstrated. Simultaneously, we showed the interaction between propranolol and higher doses of morphine in proconvulsant effects.     

Striking differences in proconvulsant-induced alterations of seizure threshold in two rat models

During drug development, seizure threshold tests are widely used to identify potential proconvulsant activity of investigational drugs. The most commonly used tests in this respect are the timed intravenous pentylenetetrazole (PTZ) infusion seizure test and the maximal electroshock seizure threshold (MEST) test in mice or rats. To our knowledge, no study is available in which proconvulsant drug activities in these models are directly compared, which prompted us to perform such experiments in male Wistar rats. Five drugs with reported proconvulsant activity were tested in the two models: d-amphetamine, chlorpromazine, caffeine, theophylline, and tramadol. Furthermore, the anticonvulsant drug phenobarbital was included in the experiments. While phenobarbital exerted anticonvulsant activity in both models, the five proconvulsant drugs markedly differed in their effects. In the dose range tested, d-amphetamine significantly lowered the PTZ seizure threshold but increased the MEST, caffeine and theophylline did not alter the PTZ seizure threshold but decreased the MEST, and tramadol reduced the PTZ threshold but increased the MEST. These marked differences between seizure threshold tests are most likely a consequence of the mechanisms underlying seizure induction in these tests. Our data indicate that using only one seizure threshold model during preclinical drug development may pose the risk that potential proconvulsant activity of an investigational drug is overseen. However, the label "proconvulsant" may be misleading if such activity only occurs at doses high above the therapeutic range, but the drug is not proconvulsant or even exerts anticonvulsant effects at lower, therapeutically relevant doses.     

Pharmacodynamic interaction studies with topiramate in the pentylenetetrazol and maximal electroshock seizure models.

There is emerging evidence to support the efficacy of some antiepileptic drug (AED) combinations in refractory epilepsy. Definitive clinical studies are, however, difficult to perform. Experimental seizure models can be employed to identify potentially useful combinations for subsequent clinical evaluation. We have investigated the anticonvulsant effects of topiramate (TPM) in combination with 13 other AEDs in the pentylenetetrazol (PTZ) and maximal electroshock (MES) seizure models. Single drugs and combinations were administered by intraperitoneal injection and anticonvulsant effects determined at 1-hour post-dosing. TPM was without significant effect in the PTZ test. In contrast, phenobarbital, primidone, ethosuximide, sodium valproate, felbamate and tiagabine all increased the latency to the first generalised seizure. Combinations of TPM and active adjunctive drug were universally effective. Combinations of TPM with clobazam, lamotrigine and levetiracetam were also anticonvulsant, despite the inactivity of the constituent compounds when administered alone. TPM reduced the incidence of MES-induced seizures in a dose-dependent manner, as did phenobarbital, phenytoin, primidone, carbamazepine, sodium valproate, clobazam, lamotrigine, felbamate and tiagabine. All combination treatments were similarly effective. These findings suggest that combinations of TPM with lamotrigine and levetiracetam may demonstrate anticonvulsant synergism and merit further investigation in additional model systems and with recourse to more quantitative mathematical analysis.     

Trans-2-en-valproate: reevaluation of its anticonvulsant efficacy in standardized seizure models in mice, rats and dogs.

The anticonvulsant potency of the trans isomer of 2-en-valproate (trans-2-en-VPA) was determined in standardized models for different seizure types in rodents and dogs. In mice and rats, adverse effects were quantified by the rotarod and chimney tests. Clinically established antiepileptic drugs (valproate, ethosuximide, phenobarbital, carbamazepine, phenytoin, diazepam) were used for comparison. Based on time course studies, drug potencies were determined and compared at the individual time of peak anticonvulsant effect. Potency comparisons were based on administered dosages and, in the case of trans-2-en-VPA and valproate, also on plasma levels determined after administration of anticonvulsant doses. The data show that trans-2-en-VPA exerts anticonvulsant effects against different seizure types, i.e., myoclonic, clonic, and tonic seizures in rodents and (myo)clonic seizures in dogs. In most seizure models, trans-2-en-VPA was more potent than valproate, when both compounds were compared at their individual times of peak effect. Time course and pharmacokinetic studies showed that duration of action and pharmacokinetic characteristics of trans-2-en-VPA and valproate are similar. In the rotarod and chimney tests in mice and rats, trans-2-en-VPA was more potent than valproate. However, because of the higher anticonvulsant potency of trans-2-en-VPA, protective indices calculated from rodent models were similar to those of valproate. Similarly, in dogs trans-2-en-VPA exerted anticonvulsant effects at doses below those which induced sedation and ataxia. In view of the previously reported advantages of trans-2-en-VPA compared to valproate with respect to teratogenic and hepatotoxic effects, the present data substantiate that trans-2-en-VPA might be a valuable alternative to valproate in antiepileptic therapy.