Differential activity of drugs to induce emesis and pica behavior in Suncus murinus (house musk shrew) and rats

We have previously reported that emetic stimuli induce kaolin ingestion behavior (pica behavior) in rats and mice (i.e., species that do not have the emetic reflex) and that the behavior may be analogous to gastrointestinal discomfort, such as nausea and emesis. We hypothesized that pica behavior may also occur in species capable of vomiting and that it may serve as an additional index of discomfort relevant to antiemetic drug development. The present experiments were conduced using Suncus murinus and rats and kaolin consumption was measured at 24 h after the administration of nicotine (1.25-5 mg/kg, s.c.), copper sulfate (10-120 mg/kg, p.o.), lithium chloride (50-200 mg/kg, i.p.) and cisplatin (1-30 mg/kg, i.p.). In S. murinus, all treatments, excepting lithium chloride, were emetic but none induce kaolin consumption. Conversely, all treatments induced kaolin consumption in rats without inducing emesis. The results indicate that pica behavior is not likely to be useful to assess gastrointestinal discomfort in S. murinus.