Evidence that serotonin receptors are involved in the anticonvulsant effect of yohimbine in mice.

The threshold of seizures induced by electroconvulsive shock (ECS) was determined in mice and the effects of alpha 2-adrenoceptor antagonists (yohimbine, rauwolscine, idazoxan), alpha 2-adrenoceptor agonists (clonidine, B-HT 920), serotonin antagonists (methysergide, metergoline) and a serotonin agonist (quipazine) were studied. The interaction of yohimbine with clonidine, methysergide, metergoline and quipazine was also examined. It was found that yohimbine and rauwolscine elevated the seizure threshold, while idazoxan was ineffective. Clonidine and B-HT 920 were also ineffective, but quipazine elevated the seizure threshold. Methysergide and metergoline did not change the seizure threshold alone, but both of them antagonized the anticonvulsant effect of yohimbine. Clonidine failed to antagonize yohimbine's effects. Quipazine potentiated yohimbine's action. These results suggest that, in mice, the protective effect of yohimbine against ECS-induced seizures may be mediated via serotonin receptors and not via alpha 2-adrenoceptors.