Histaminergic mechanisms in experimental convulsions.

Effect of some histamine (HA) agonists and antagonists were assessed on electroshock (MES) convulsions in mice and rats. In mice, pretreatment with the HA precursor, l-histidine (100, 500 and 1000 mg/kg) precipitated seizures after a subthreshold (30 mA) stimulus. Both incidence (%) and tonic hind limb extensor phase (THE) were more than that in vehicle treated controls. The H1 blockers, pheniramine (25 mg/kg) and promethazine (25 mg/kg) both protected against (60 mA) MES and both incidence of convulsions and THE were reduced. A similar protective effect was not seen with either the H2 blocker, cimetidine (up to 200 mg/kg), or atropine (1 mg/kg). In rats, both the classical antihistamines blocked MES seizures, whereas, the H2-blocker, cimetidine, and atropine were, ineffective. Further, both H1 blockers were ineffective in antagonizing seizures induced by pentylenetetrazole, INH, caffeine or strychnine. These results are discussed in light of a possible HA-ergic regulation of experimental convulsions.