The acute administration of 1R,cis,αS-cypermethrin, deltamethrin fenvalerate and permethrin produced a dose-dependent lowering of the dose of pentylenetetrazol required to elicit a seizure in rats. The proconvulsant action of cypermethrin displayed stereospecificity in that the 1R,cis,αS isomer of cypermethrin was the most potent compound tested, while the non-insecticidal isomer, 1S,cis,αR-cypermethrin, was devoid of proconvulsant activity. Pretreatment of rats with PK 11195, an antagonist of the peripheral-type benzodiazepine binding site, elicited a complete reversal of the proconvulsant actions of both deltamethrin and permethrin. In contrast, pretreatment with phenytoin did not alter the pyrethroid-induced proconvulsant activity. These results suggest that the effect of pyrethroids on pentylenetetrazol seizure threshold are mediated via an interaction with peripheral-type benzodiazepine binding sites.
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