NEUROPHARMACOLOGICAL MECHANISMS OF EMESIS .1. EFFECTS OF ANTIEMETIC DRUGS ON MOTION-INDUCED AND APOMORPHINE-INDUCED PICA IN RATS

The effects of diphenhydramine, domperidone, ondansetron, and diphenid ol on motion- and apomorphine-induced pica (i.e., kaolin ingestion) in rats as the measure analogous to emesis in other species were examine d. Diphenhydramine (10 and 20 mg/kg) and diphenidol (30 mg/kg) inhibit ed kaolin intake induced by 60-min double rotation, while domperidone and ondansetron did nor. Kaolin intake induced by apomorphine (10 mg/k g) was inhibited by domperidone (2 mg/kg) and diphenidol (30 mg/kg), b ut not by diphenhydramine or ondansetron. These findings suggest that the emetic pathways through the inner ear (double rotation) and the ch emoreceptor trigger zone (apomorphine) are pharmacologically independe nt and are mediated by histamine H-1 receptors and dopamine D-2 recept ors, respectively. Diphenidol may inhibit a common locus of emesis.