Strategies for identifying and developing new anticonvulsant drugs

Psychopharmacological effects and safety of styryl-2-pyrones and dihydrostyryl-2-pyrones-rich fraction from Polygala sabulosa: absence of withdrawal syndrome and tolerance to anxiolytic-like and anticonvulsant effects

Objectives

To investigate whether mice develop tolerance to the anxiolytic‐like and anticonvulsant effects of subchronic treatment with EA (the styryl‐2‐pyrones and dihydrostyryl‐2‐pyrones‐rich fraction of Polygala sabulosa), as well as any withdrawal symptoms after abrupt discontinuation; to compare the effects of EA with those of diazepam (DZP) on withdrawal‐induced anxiety; and to evaluate the toxicity of EA according to OECD guidelines.

Methods

Male or female mice were acutely or subchronically treated with EA or DZP, and their tolerance to anxiolytic (evaluated in the elevated plus maze, EPM) and anticonvulsant effects (measured against pentylenetetrazole (PTZ)‐induced convulsions) were investigated. Other groups received EA or DZP for 28 days followed by withdrawal, being the anxiety‐like behaviour evaluated in the EPM.

Key findings

Both acute and subchronic treatments with EA induced an anxiolytic effect in the EPM. The anticonvulsant activity of DZP, but not EA, was reduced by protracted treatment. EA withdrawal retained the anxiolytic profile, while DZP withdrawal induced anxiogenesis. EA counteracted the anxiogenic‐like actions of DZP withdrawal. EA has low toxicity as it did not cause any changes in the biochemical, haematological and histopathological markers.

Conclusions

EA avoids the development of tolerance to its anxiolytic‐like and anticonvulsant actions, and does not promote withdrawal syndrome. EA does not cause relevant toxic effects in rodents.

Anticonvulsant and anxiolytic-like effects of compounds isolated from Polygala sabulosa (Polygalaceae) in rodents: in vitro and in vivo interactions with benzodiazepine binding sites

RATIONALE

Polygala sabulosa, a folk medicine, presents dihydrostyryl-2-pyrones (DST) and styryl-2-pyrones (STY), compounds structurally similar to kavalactones. Our previous study showed that the ethyl acetate fraction (EA) and these constituents present anxiolytic-like, hypno-sedative, and anticonvulsant effects in mice.

OBJECTIVES

This study investigated the role of benzodiazepine binding site (BDZ-bs) in the central effects of either EA or three DST (1, 2, and 3) and three STY (4, 5, and 7), using in vivo and in vitro assays.

METHODS AND RESULTS

In the elevated plus-maze (EPM), flumazenil (FMZ), a BDZ antagonist, partially blocked the anxiolytic-like effect of DST-3 or STY-4 and STY-7, but not DST-1. Using electroencephalogram (EEG), EA protected against pentylenetetrazole (PTZ)-induced convulsion in rats, an effect partially blocked by FMZ, suggesting the participation of the BDZ-bs in this action. EA also protected against the maximal electroshock (MES)-induced convulsions in mice, a profile distinct from diazepam (DZP). DST and STY compounds inhibited the [(3)H]-flunitrazepam ([(3)H]-FNZ) binding to BDZ-bs in rat cortical synaptosomes with K (i) higher than 100 microM (DST-1), 41.7 microM (DST-2), 35.8 microM (DST-3), 90.3 microM (STY-4), 31.0 microM (STY-5) and 70.0 microM (STY-7). In the saturation assay, DST-3 and STY-7 competitively inhibited the binding of [(3)H]-FNZ to BDZ-bs with a significant decrease in apparent affinity (K (d)) and no change in maximal binding (B (max)).

CONCLUSIONS

The present data support a partial BDZ-bs mediation of the anxiolytic-like and anticonvulsant effects of EA of P. sabulosa and its main isolated constituents, DST and STY.

Study of anticonvulsant effect of citronellol, a monoterpene alcohol, in rodents

Citronellol is one monoterpene alcohol, which is present in the essential oils of various aromatic plant species. This study evaluated the neuroprotective activity of citronellol on pentylenetetrazol- and picrotoxin-induced convulsions and maximal electroshock-induced seizures in mice. Administration of citronellol significantly reduced the number of animals of convulsion induced by pentylenetetrazol and eliminated the extensor reflex of maximal electroshock-induced seizures test in about 80% of the experimental animals. In addition, administration of citronellol showed protection in the pentylenetetrazol and picrotoxin tests by increasing the latency of clonic seizures. We also investigated the effect of citronellol in the rat isolated nerve using the single sucrose-gap technique. We showed that the amplitude of the compound action potential decreased more than 90% when the monoterpene was incubated for 30 min at 6.4 mM and we did not verify any effect on the repolarization of the compound action potential. Taken together, our results demonstrated an anticonvulsant activity of the citronellol that could be, at least in part, explained by the diminution of the action potential amplitude.

Separation of Antiepileptogenic and Antiseizure Effects of Levetiracetam in the Spontaneously Epileptic Rat (SER)

PURPOSE

The long-lasting antiseizure effects of levetiracetam (LEV) have been observed in the spontaneously epileptic rat (SER) that expresses both tonic and absence-like seizures. Furthermore, the antiepileptogenic effects of LEV in addition to antiseizure effects have been reported in the amygdala-kindling model in rats. This suggests that the long-lasting seizure protection of LEV may be at least partly due to its antiepileptogenic effects. Therefore this study aimed to differentiate the antiseizure and potential antiepileptogenic effects of LEV by administering LEV continuously to SERs before the appearance of any seizure expression.

METHODS

LEV was administered to the SERs at 80 mg/kg/day (i.p.) from postnatal weeks 5 to 8. The period of observation for tonic convulsions was from postnatal week 5 to 13. Absence-like seizures were recorded by using conventional EEG in weeks 12 and 13.

RESULTS

After age 7-8 weeks, SERs exhibit spontaneous tonic convulsions. Development of tonic convulsions was significantly inhibited in the LEV group, compared with the control group, by the middle of week 9. A significant reduction of tonic convulsions also was observed in the LEV group until week 13 (5 weeks after termination of the administration). In week 12, the absence-like seizures were significantly lower in the LEV group, compared with the control group.

CONCLUSIONS

This study demonstrates a significant inhibition of seizures after prolonged treatment with LEV before the developmental expression of seizure activity in SERs. This effect is suggested to be due to an antiepileptogenic effect and not an antiseizure effect of LEV, because the half-life of the drug in plasma is short (2-3 h in rats) after single and long-term administration. Furthermore, the inhibition of seizure expression in SERs was still apparent 5 weeks after termination of LEV treatment. These results further suggest that LEV possesses not only antiseizure effects but also antiepileptogenic properties.

Anticonvulsant properties of N-salicyloyltryptamine in mice

A new tryptamine analogue, N-salicyloyltryptamine (STP), a potential central nervous system (CNS) depressant, was tested in the pentylenetetrazol (PTZ) and maximal electroshock (MES) models of epilepsy in mice. When administered concurrently, STP (100 mg/kg ip) significantly reduced the number of animals that exhibited PTZ-induced seizures and eliminated the extensor reflex of maximal electric-induced seizures test in 50% of the experimental animals. In addition, it showed protection in the PTZ test by diminishing the death rate.

Pharmacodynamic interaction between phenytoin and sodium valproate changes seizure thresholds and pattern

1. In this study we used cortical stimulation to assess the effects of phenytoin (PHT), sodium valproate (VPA), and their interaction on total motor seizure and on the constituent elements of the seizure. 2. PHT (40 mg kg(-1)) was administered as an intravenous bolus infusion to animals receiving either a continuous infusion of VPA or saline. VPA plasma concentration was maintained at levels that produced no detectable anticonvulsant effect. 3. Analysis of ictal components (eyes closure, jerk, gasp, forelimb, clonus, and hindlimb tonus) and their durations revealed both qualitative and quantitative differences in drug effects. 4. The anticonvulsant effect is represented by the increase in the duration of the stimulation required to reach a given seizure threshold. PHT significantly increased the duration of the stimulation and of the motor seizure. This increase was greatly enhanced by VPA. In addition, ictal component analysis revealed that the combination of PHT and VPA causes the reduction of a specific seizure component (JERK). 5. Neither the free fraction of PHT nor the biophase equilibration kinetics changes in the presence of VPA. It is concluded that the synergism may be due to a pharmacodynamic rather than a pharmacokinetic interaction.