EFFECT OF THIOPERAMIDE, A HISTAMINE-H(3) RECEPTOR ANTAGONIST, ON ELECTRICALLY INDUCED CONVULSIONS IN MICE

The effect of thioperamide, a histamine H-3 receptor antagonist, on electrically induced convulsions was studied in mice. Thioperamide significantly and dose dependently decreased the duration of each phase of convulsion and raised the electroconvulsive threshold. Its anticonvulsant effects were prevented by pretreatment with (R)-alpha-methylhistamine, a histamine H-3 receptor agonist. These findings suggest that the effect of thioperamide on electrically induced convulsions is due to an increase in endogenous histamine release in the brain, an effect mediated by histamine H-3 receptors. The anticonvulsant effect of thioperamide was antagonized strongly by mepyramine (or pyrilamine), a centrally acting histamine H-1 receptor antagonist, but not by zolantidine, a centrally acting histamine H-2 receptor antagonist. Thus, the blockade by mepyramine of the thioperamide-induced decrease in seizure susceptibility indicates that histamine released by thioperamide from the histaminergic nerve terminals interacts with the histamine H-1 receptors of postsynaptic neurons. These findings support the hypothesis that the central histaminergic system is involved in the inhibition of seizures.