Neuropharmacological mechanisms of emesis. I. Effects of antiemetic drugs on motion- and apomorphine-induced pica in rats.

The effects of diphenhydramine, domperidone, ondansetron, and diphenidol on motion- and apomorphine-induced pica (i.e., kaolin ingestion) in rats as the measure analogous to emesis in other species were examined. Diphenhydramine (10 and 20 mg/kg) and diphenidol (30 mg/kg) inhibited kaolin intake induced by 60-min double rotation, while domperidone and ondansetron did not. Kaolin intake induced by apomorphine (10 mg/kg) was inhibited by domperidone (2 mg/kg) and diphenidol (30 mg/kg), but not by diphenhydramine or ondansetron. These findings suggest that the emetic pathways through the inner ear (double rotation) and the chemoreceptor trigger zone (apomorphine) are pharmacologically independent and are mediated by histamine H1 receptors and dopamine D2 receptors, respectively. Diphenidol may inhibit a common locus of emesis.