Felbamate displays in vitro antiepileptic effects as a broad spectrum excitatory amino acid receptor antagonist

Effects of GYKI 52466 and some 2,3-benzodiazepine derivatives on hippocampal in vitro basal neuronal excitability and 4-aminopyridine epileptic activity

In order to determine whether the anticonvulsant effect of 2, 3-benzodiazepines is also displayed in a model of in vitro epilepsy, such as the "epileptiform" hippocampal slice, we studied the effects of 2,3-benzodiazepine 1-(4-aminophenyl)-4-methyl-7, 8-methylenedioxe-5H 2,3-benzodiazepine hydrochloride (GYKI 52466) and some new 2,3-benzodiazepine derivatives on CA1 basal neuronal excitability and on CA1 epileptiform burst activity produced by 4-aminopyridine in rat hippocampal slices. The results showed that GYKI 52466 affected basal neuronal excitability as evidenced by its influence on the magnitude of the CA1 orthodromic-evoked field potentials. 2,3-Benzodiazepines showed their antiepileptic effect also in an in vitro model of experimental epilepsy. The effects of the new 2,3-benzodiazepine derivatives suggest that the methylenedioxidation in positions 7 and 8 of the 2,3-benzodiazepine ring is the main structural modification for the antiepileptic effect of 2,3-benzodiazepines to take place.

Electrophysiological effects of felbamate

Felbamate is a broad spectrum antiepileptic drug recently introduced into clinical practice for controlling seizures in patients affected by Lennox-Gastaut epilepsy, complex partial seizures or otherwise intractable epilepsies. However, the cellular mechanisms by which the drug exerts its anticonvulsant actions are not fully understood. The aim of the present article is to outline the possible mechanisms of action of felbamate as suggested by findings obtained with electrophysiological approaches.

Characterization of the in vitro antiepileptic activity of new and old anticonvulsant drugs

1. The in vitro antiepileptiform effects of some old and new anticonvulsants in the experimental model of the "epileptiform" hippocampal slice have been reviewed. 2. On the basis of their influence on in vitro epileptogenesis and basal neuronal excitability, anticonvulsants can be classified into three main categories: (1) anticonvulsants (prototypical drug phenytoin) affecting basal neuronal excitability but not epileptogenesis; (2) anticonvulsants (prototypical drugs barbiturates) affecting basal neuronal excitability and epileptogenesis; (3) anticonvulsants (prototypical drug felbamate) affecting epileptogenesis but not basal neuronal excitability. 3. It is concluded that the model of the "epileptiform" hippocampal slices can be considered a previsional test for the study and the screening of new anticonvulsant drugs.

Felbamate inhibits cloned voltage-dependent Na+ channels from human and rat brain

The novel antiepileptic and neuroprotective drug felbamate (1 mM) caused a marked inhibition of voltage-dependent Na+ currents expressed in Xenopus oocytes upon injection of the cRNA encoding alpha-subunits from rat and human brain. This inhibition was present only if felbamate was perfused on the intracellular side of the membrane. In addition, felbamate seems to preferentially bind to and stabilize the inactivated state of the channel, resembling the action of local anesthetics. This study provides an additional mechanism by which felbamate might exert its wide-spectrum anticonvulsant and neuroprotective action.

Anticonvulsant activity of 5,7DCKA, NBQX, and felbamate against some chemoconvulsants in DBA/2 mice

The anticonvulsant effects of felbamate (10-300 mg/kg, intraperitoneally, IP), and those of two representative antagonists of the excitatory amino acid receptors, 5-7 dichlorokynurenic acid (5-7DCKA; 0.6-30 nmol/mouse, intracerebroventricularly, ICV), and 2, 3-dihydroxy-6 nitro-7-sulfamoylbenzo (F) quinoxoline (NBQX; 1.1-33.6 mg/kg, IP) were studied in the DBA/2 mice. All drugs protected the animals from sound-induced seizures. The drugs were also effective against seizures induced by stimulation of the excitatory amino acid receptor complex using the agonists N-methyl-D-aspartate (NMDA) or alpha-amino-3-hydroxy-5 methyl-4-isoxazolepropionic acid (AMPA). In separate studies, felbamate protected mice from seizures induced by ICV administration of the activator of dihydropyridine-sensitive calcium channels, methyl-1, 4-dihydro-2, 6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl) pyridine-5-carboxylate (Bay k 8644), with ED50 values of 26 and 46.9 mg/kg for tonus and clonus, respectively. Using Bay k 8644, NBQX (1-40 mg/kg IP) was uneffective, while 5,7DCKA (5-90 nmol/mouse, ICV) protected mice against tonus. Moreover, felbamate prevented seizures induced by blocking voltage-dependent K+ channels using alpha-dendrotoxin, with ED50 values of 22.6 mg/kg for tonus and of 34.8 mg/kg for clonus. Conversely, 5,7DCKA or NBQX did not significantly antagonize seizures induced by alpha-dendrotoxin. The present data indicate that felbamate is an effective anticonvulsant drug in DBA/2 mice with a broader anticonvulsant spectrum than 5,7DCKA and NBQX.

Effects of four antiepileptic drugs on sleep and waking in the rat under both light and dark phases

Sedation is a common side effect of anticonvulsant drug therapy. To find out whether the new antiepileptic drugs, felbamate and lamotrigine, are able to produce sedation, we carried out electroencephalographic (EEG) studies in the rat to measure drug effects on sleep-wake patterns, during both light and dark phases. For comparison, the reference drugs, carbamazepine and phenobarbital, were also studied. EEG activity was recorded for 6 h after oral (PO) administration of drugs or vehicle, and the stages of wakefulness, rapid eye movements (REM) sleep and non-REM sleep were classified thereafter. In the light phase, felbamate (30-300 mg/kg) did not produce sedative effects, while lamotrigine (3-30 mg/kg) increased wakefulness at each dose tested. Carbamazepine (10-100 mg/kg) did not produce sleep-wake alterations, and phenobarbital (100 mg/kg) markedly suppressed REM. In the dark phase, felbamate (300 mg/kg), lamotrigine (30 mg/kg), and carbamazepine (100 mg/kg) reduced REM but did not change the total amount of sleep. Phenobarbital, at 100 mg/kg, markedly increased total sleep and greatly reduced REM. This study shows that the anticonvulsant drugs examined have different effects on the states of sleep and wakefulness in the rat. The data are discussed on the basis of the mechanism of action that characterizes each individual drug.

7-chlorokynurenic acid prevents in vitro epileptiform and neurotoxic effects due to kainic acid

1. The effects of 7-chlorokynurenic acid were studied against the epileptiform and neurotoxic effects due to the non-NMDA excitatory amino acid, kainic acid, in rat hippocampal slices. 2. Slice perfusion with 7-chlorokynurenic acid (100 microM), significantly (p < 0.05) decreased the duration of the CA1 epileptiform bursting due to 1 microM kainic acid. 3. Slice perfusion with 7-chlorokynurenic acid (100 microM) significantly (p < 0.05) increased the probability of recovery of the CA1 population spike after a neurotoxic concentration (12 microM) of kainic acid. 4. The results indicate that 7-chlorokynurenic acid affects, with a similar potency, epileptiform and neurotoxic effects due to kainic acid.

Electrophysiological actions of felbamate on rat striatal neurones

1. We have investigated the effects of the anticonvulsant drug, felbamate (FBM), on striatal neurones, recorded in vitro by using both intracellular and extracellular conventional recordings in slices and whole-cell recordings in acutely isolated neurones. 2. FBM, at therapeutically relevant concentrations (30-300 microM) showed multiple mechanisms of action. Like other antiepileptic drugs, FBM (30-300 microM) showed a direct inhibitory action on current-evoked firing discharge of striatal neurones. A patch-clamp analysis of this effect revealed a dose-related reduction of voltage-dependent sodium (Na+) currents (10-100 microM), with a half inhibiton dose (IC50) value of 28 microM. 3. We also tested whether FBM affected corticostriatal glutamate transmission. In control medium (1.2 mM external magnesium), both extracellularly recorded field potentials and intracellularly recorded excitatory postsynaptic potentials (e.p.s.ps) evoked by cortical stimulation were no affected by bath application of 30-300 microM FBM. 4. When magnesium was removed from the perfusing solution, a procedure which reveals a N-methyl-D-aspartate (NMDA)-mediated component in the corticostriatal synaptic potential, FBM (30-300 microM) produced a dose-dependent reduction of the amplitude of both the field potential and the e.p.s.p. 5. FBM reduced the inward currents produced either by bath or by focal applications of 30 microM NMDA, finding consistent with the hypothesis that the observed reduction of the NMDA-mediated component of the synaptic potentials may be caused at postsynaptic level. 6. The reduction of the NMDA-mediated component of the synaptic transmission by FBM and its depressant effect on the voltage-dependent Na+ channels, may account for the antiepileptic action of this drug. Moreover, the pharmacological properties of FBM might render this drug interesting as a neuroprotectant agent.

NMDA antagonists: antiepileptic-neuroprotective drugs with diversified neuropharmacological profiles

In conclusion, NMDA antagonists as anticonvulsants are especially active in preventing the generalization of the behavioural and electrical seizures and display a typical spectrum of in vitro antiepileptiform activities. In addition, based on in vitro and in vivo limbic kindled studies, the drugs should be regarded more as an antiepileptiform than as an anticonvulsant drugs. As neuroprotective drugs, NMDA antagonists are effective against many types of neuronal injury and show a window of activity which does not exceed 1-2 h, thus suggesting an influence of NMDA receptors in the 'early' or 'acute' mechanisms of brain damage. Among NMDA antagonists, glycine antagonists or the morphinans dextromethorphan and dextrorphan showed a spectrum of antiepileptiform and neuroprotective activities broader than other NMDA antagonists. The primary pharmacological activities of NMDA antagonists are accompanied by some effects including perturbation of many sensory, psychological or motor processes. Typical behavioural and EEG changes were also induced by the drugs. In spite of the side-effects elicited by the drugs, differential effects detected among the various classes of NMDA antagonists (i.e. lack of induction of typical EEG-behavioural effects and of typical cortical neurotoxicity) might render some of these suitable for full clinical application as anticonvulsant-neuroprotective drugs.

Excitatory amino acid neurotransmission through both NMDA and non-NMDA receptors is involved in the anticonvulsant activity of felbamate in DBA/2 mice

The anticonvulsant activity of felbamate against sound-induced seizures was studied in the DBA/2 mouse model. Felbamate (10-300 mg/kg, i.p.) produced dose-dependent effects with ED50 values for the suppression of tonic, clonic and wild running phases of 23.1, 48.8 and 114.6 mg/kg, respectively. Felbamate also protected DBA/2 mice from N-methyl-D-aspartate (NMDA)-induced seizures with ED50 values of 12.1 and 29 mg/kg for tonus and clonus, respectively. Pretreatment with glycine, an agonist to the glycine/NMDA receptors, shifted the dose-response effect of felbamate to the right (ED50 = 56.8 against tonus and 94.8 mg/kg versus clonus). Similarly, D-serine, an agonist at the glycine site, shifted the ED50 of felbamate against the tonic component of audiogenic seizures from 23.1 to 78.1, and that against clonus from 48.8 to 90.3 mg/kg. Felbamate was also potent to prevent seizures induced by administration of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), an AMPA/kainate receptor agonist (ED50 = 11.8 and 20.9 mg/kg, against tonus and clonus, respectively). The data indicate that felbamate is an effective anticonvulsant drug in the genetic model of seizure-prone DBA/2 mice. Our findings suggest that the anticonvulsant properties of felbamate depend upon its interaction with neurotransmission mediated by both the glycine/NMDA and the AMPA/kainate receptor complex.